ES2287282T3

Method and apparatus for allocating resources in a multiple-input multiple-output (MIMO) communication system

Abstract

A method for planning the transmission of downlink data to a plurality of terminals (106) for a wireless communication system (100), the system comprising: forming one or more sets of terminals for possible data transmission, in which each game includes a combination of one or more terminals (106) and correspond to a hypothesis to evaluate; assign a plurality of transmitting antennas (524) to one or more terminals (106) in each set; evaluate the performance of each hypothesis based on part of the antenna assignments for the hypothesis, in which each hypothesis is evaluated based on the information of the channel status, hereinafter CSI, for each terminal (106) in the hypothesis, in which the CSI is indicative of the characteristics of the channel between the transmitting antennas (524) and the terminal (106) to select one of the one or more hypotheses evaluated based on performance; and plan data transmission to the terminal (106) in the selected hypothesis; and the procedure characterized by: prioritizing terminal planning (106).

ES2287282T3, drawing sheet 1 — Sheet 1 of 18

Term

Term ended

Projected expiry passed 15 May 2022, 4.4 years ago.

47 claims: 3 independent, 44 dependent

1
ES 2 287 282 T3 REIVINDICACIONES 1. Un procedimiento para planificar la transmisión de datos de enlace descendente hacia una pluralidad de terminales (106) para un sistema (100) de comunicación inalámbrica, comprendiendo el sistema:formar uno o más juegos de terminales para posible transmisión de datos, en el cual cada juego incluye una combinación de uno o más terminales (106) y se corresponden con una hipótesis a evaluar;asignar una pluralidad de antenas (524) de transmisión a uno o más terminales (106) en cada juego;evaluar el rendimiento de cada hipótesis en función de parte de las asignaciones de antena para la hipótesis, en el cual cada hipótesis se evalúa en función de la información del estado del canal, en adelante CSI, para cada terminal (106) en la hipótesis, en el cual la CSI es indicadora de las características del canal entre las antenas (524) de transmisión y el terminal (106) seleccionar una de entre las una o más hipótesis evaluadas en función del rendimiento;y planificar transmisión de datos hasta el o los terminales (106) en la hipótesis seleccionada;y el procedimiento caracterizado por: priorizar la planificación de terminales (106).
2
El procedimiento de la reivindicación 1, que comprende, además:formar una pluralidad de sub-hipótesis para cada hipótesis, en el cual cada sub-hipótesis se corresponde con asignaciones específicas de las antenas (524) de transmisión hacia la o las terminales (106) en las hipótesis, y en el cual el rendimiento de cada sub-hipótesis se evalúa y una de las sub-hipótesis evaluadas de selecciona en función del rendimiento.
3
El procedimiento de la reivindicación 1, en el cual la asignación incluye identificar una antena (524) de transmisión y par de terminales con un mejor rendimiento entre todas las antenas (524) de transmisión sin asignar, asignando la antena de transmisión en el par al terminal en el par, y retirando la antena de transmisión y el terminal asignados de la consideración.
4
El procedimiento de la reivindicación 3, en el cual la CSI para cada terminal (106) comprende unas estimaciones de la relación señal-a-ruido-más-interferencia, en adelante SNR, obtenidas en el terminal (106) en función de señales transmitidas desde las antenas (524) de transmisión.
5
El procedimiento de la reivindicación 4, en el cual cada juego de uno o más terminales (106) a evaluar está asociado a una matriz correspondiente de las SNR conseguidas por el o los terminales (106) en el juego.
6
El procedimiento de la reivindicación 4, que comprende, además:Determinar un esquema de codificación y modulación para cada antena (524) de transmisión en función de la CSI asociada a la antena (524) de transmisión.
7
El procedimiento de la reivindicación 1, en el cual el o los terminales (106) en cada juego se seleccionan de entre un grupo de terminales.
8
El procedimiento de la reivindicación 7, en el grupo de terminales incluyen uno o más terminales SIMO, cada uno diseñado para recibir una sola corriente de datos.
9
El procedimiento de la reivindicación 8, en el cual las hipótesis seleccionadas incluyen una pluralidad de terminales SIMO.
10
El procedimiento de la reivindicación 7, en el cual el grupo de terminales incluyen uno o más terminales SIMO, cada uno diseñado para recibir múltiples corrientes de datos de múltiples antenas de transmisión.
11
El procedimiento de la reivindicación 10, en el cual las hipótesis seleccionadas incluyen un solo terminal MIMO.
12
El procedimiento de la reivindicación 10, en el cual cada terminal MIMO realiza procesado de receptor de cancelación sucesiva para recuperar datos transmitidos al terminal MIMO. ES 2 287 282 T3
13
El procedimiento de la reivindicación 4, en el cual uno o más juegos de haces de antena son evaluadas por cada terminal (106) para ser consideradas para la planificación para proporcionar uno o más vectores de SNR, un vector por cada juego de haces de antena.
14
El procedimiento de la reivindicación 1, en el cual cada juego incluye terminales que tienen márgenes de enlace similares.
15
El procedimiento de la reivindicación 1, en el cual la evaluación incluye calcular una métrica de rendimiento para cada hipótesis.
16
El procedimiento de la reivindicación 15, en el cual la métrica de rendimiento es una función de la capacidad de salida conseguible por cada terminal (106) en la hipótesis.
17
El procedimiento de la reivindicación 15, en el cual la hipótesis que tiene la mejor métrica de rendimiento es seleccionada para la planificación.
18
El procedimiento de la reivindicación 1, en el cual la pluralidad de antenas (524) de transmisión se asignan al o a los terminales (106) en cada juego en función de la prioridad de los terminales en el juego.
19
El procedimiento de la reivindicación 18, en el cual un terminal de la más alta prioridad en el juego es asignado a una antena (524) de transmisión asociada a una capacidad de salida más alta, y un terminal de la más baja prioridad en el juego es asignado a una antena de transmisión asociada a la más baja capacidad de salida.
20
El procedimiento de la reivindicación 1, que comprende, además:terminales de limitación que habrá que considerar en la planificación del un grupo de N terminales de la más alta prioridad, donde N es uno o el mayor.
21
El procedimiento de la reivindicación 1, que comprende, además:mantener una o más métricas para cada terminal (106) que se considerará en la planificación, y en el cual la prioridad de cada terminal se determina, en parte, en función de la o las métricas mantenida para el terminal (106).
22
El procedimiento de la reivindicación 21, en el cual una métrica mantenida para cada terminal (106) se refiere a una tasa de transmisión media de la capacidad de salida conseguida por el terminal.
23
El procedimiento de la reivindicación 1, en el cual la prioridad de cada terminal (106) se determina, además, en función de uno o más factores mantenidos para el terminal y asociados con la calidad del servicio, en adelante QoS.
24
El procedimiento de la reivindicación 1, en el cual uno o más terminales (106) en las hipótesis seleccionadas se planifican para transmitir datos en un canal que incluye una pluralidad de subcanales espaciales.
25
El procedimiento de la reivindicación 1, en el cual uno o más terminales (106) en las hipótesis seleccionadas se planifican para transmitir datos en un canal que incluye una pluralidad de subcanales de frecuencia.
26
El procedimiento de la reivindicación 1, en el cual uno o más juegos de terminales incluyen una combinación exclusiva de uno o más terminales (106) y en el cual el procedimiento comprende las etapas adicionales de formar una o más sub-hipótesis para cada hipótesis, en el cual cada sub-hipótesis se corresponde con asignaciones específicas de una pluralidad de antenas (524) de transmisión hacia el o los terminales (106) en la hipótesis;y en el cual la etapa de evaluar el rendimiento comprende la etapa de evaluar el rendimiento de cada sub-hipótesis;y en el cual la etapa de seleccionar comprende la etapa de seleccionar una de entre una pluralidad de sub-hipótesis evaluadas en función de su rendimiento;y en el cual la etapa de planificar comprende la etapa de planificar la transmisión de datos hacia el o los terminales (106) en la sub-hipótesis seleccionada;y transmitir datos a cada terminal (106) planificado en la sub-hipótesis seleccionada desde una o más antenas de transmisión asignadas al terminal (106).
27
El procedimiento de la reivindicación 26, en el cual la evaluación incluye determinar una capacidad de salida para el o los terminales (106) en las sub-hipótesis en función de las asignaciones específicas de antena, y en el cual se selecciona la sub-hipótesis con mayor capacidad de salida.
28
El procedimiento de la reivindicación 26, en el cual se forma un juego de terminales, y en el cual los terminales en el juego se seleccionan en función de la prioridad de terminales que desean transmisión de datos. ES 2 287 282 T3
29
El procedimiento de la reivindicación 1, en el cual la etapa de formar uno o más juegos, comprende identificar a uno o más juegos de terminales (106), incluyendo cada juego uno o más terminales y correspondiéndose con las mencionadas hipótesis a ser evaluadas en función de uno o más criterios;en el cual la etapa de evaluar el rendimiento comprende evaluar el rendimiento de cada hipótesis en función de la CSI asociada con cada terminal, siendo la CSI indicadora de las características del canal entre el terminal correspondiente y las correspondientes antenas (524) de transmisión;y en el cual la etapa de seleccionar comprende seleccionar al menos un juego de terminales para recibir transmisión de datos en función, al menos en parte, del rendimiento de cada hipótesis.
30
El procedimiento de la reivindicación 29, en el cual cada hipótesis comprende una pluralidad de sub-hipótesis cada una de las cuales se corresponde con una o más asignaciones específicas de las antenas (524) de transmisión hacia el o los terminales (106) en el juego correspondiente, y en el cual el rendimiento de cada hipótesis se evalúa en función del rendimiento de la correspondiente sub-hipótesis.
31
El procedimiento de la reivindicación 29, en el cual la CSI para cada terminal comprende estimaciones de relación seña-a-ruido-más-interferencia, en adelante SNR, obtenidas en el terminal (106) correspondiente en función de señales transmitidas desde las antenas de transmisión.
32
El procedimiento de la reivindicación 29, en el cual la evaluación incluye:calcular una métrica de rendimiento para cada hipótesis como una función de la capacidad de salida conseguible por cada terminal (106) en el juego correspondiente.
33
El procedimiento de la reivindicación 29, en el cual la pluralidad de antenas (524) de transmisión se asignan al o a los terminales en cada juego, en función de la prioridad de terminales (106) en el juego.
34
El procedimiento de la reivindicación 33, en el cual la prioridad de cada terminal (106) se determina en función de uno o más factores incluyendo la calidad del Servicio, en adelante QoS, asociada al terminal correspondiente.
35
Una estación (104) base para un sistema (100) de comunicación con entrada múltiple y salida múltiple, en adelante MIMO, comprendiendo la estación base:una pluralidad de antenas (524) de transmisión configuradas para recibir y transmitir señales de datos;y un planificador (534) configurado para recibir información del estado del canal, en adelante CSI, asociado a una pluralidad de terminales en el sistema de comunicación, dividir una pluralidad de terminales (106) en uno o más juegos de terminales, incluyendo cada juego uno o más terminales (106) y correspondiéndose con una hipótesis, seleccionar un juego de uno o más terminales para transmitir datos en función del rendimiento de cada hipótesis, al menos en parte, de la CSI recibida, y asignar la pluralidad de antenas (524) de transmisión a uno o más terminales seleccionados;en el cual el rendimiento de cada hipótesis se evalúa en función, al menos en parte, de la información del estado del canal (CSI) para cada terminal (106) en la hipótesis, en el cual la CSI es indicadora de las características del canal entre las antenas (524) de transmisión y el terminal (106);y la estación base caracterizada en la cual los terminales (106) planificados son priorizados.
36
La estación (104) base de la reivindicación 35, que comprende, además:Un procesador (514) de datos de transmisión configurado para recibir y procesar datos para proporcionar una pluralidad de corrientes de datos para su transmisión a uno o más terminales (106) planificados para transmitir datos, en el cual los datos se procesan en función de la mencionada CSI indicadora de estimaciones de canal para el o los terminales planificados;una pluralidad de moduladores (522) configurados para procesar la pluralidad de corrientes de datos para proporcionar una pluralidad de señales moduladas;la mencionada pluralidad de antenas (524) de transmisión configuradas para recibir y transmitir la pluralidad de señales moduladas hasta el o los terminales planificados. ES 2 287 282 T3
37
La estación base de la reivindicación 36, en la cual la corriente de datos para cada antena (524) de transmisión se procesa en función de un esquema de codificación y modulación seleccionado para la antena (524) de transmisión en función de la CSI asociada a la antena de transmisión.
38
La estación base de la reivindicación 37, que comprende, además:una pluralidad de demoduladores (522) configurados para procesar una pluralidad de señales recibidas vía la pluralidad de antenas (524) de transmisión para proporcionar una pluralidad de señales recibidas, y un procesador (532) de datos de recepción configurado para procesar, además, la pluralidad de señales recibidas para obtener CSI para la pluralidad de terminales en el sistema (100) de comunicación.
39
Un sistema (100) de comunicación de entrada múltiple y salida múltiple, en adelante MIMO, que comprende la estación base de la reivindicación 35, y uno o más terminales, comprendiendo cada terminal:una pluralidad de antenas (552) de recepción, configurada cada antena (552) de recepción para recibir señales transmitidas desde una estación (104) base;y un procesador (556, 562) configurado para procesar las señales recibidas, obtener información del estado del canal, en adelante CSI, asociada a las señales recibidas, y para enviar la CSI de nuevo a la estación (104) base, en el cual el terminal (106) está en un juego de terminales planificados para recibir transmisión de datos desde la estación (104) base en un intervalo de tiempo particular, incluyendo cada juego uno o más terminales (106) y correspondiéndose con una hipótesis, y en el cual el juego de terminales planificados para recibir transmisión de datos se selecciona de entre uno o más juegos de terminales (106), incluyendo cada juego uno o más terminales (106) y correspondiéndose con una hipótesis, en el cual el juego de terminales se selecciona en función del rendimiento de cada hipótesis y en el cual cada hipótesis se evalúa en función, al menos en parte, de la CSI recibida desde los terminales (106) en cada juego, en el cual la CSI es indicadora de características de canal entre antenas (524) de transmisión y el terminal (106) y el sistema caracterizado en el cual los terminales (106) planificados están priorizados.
40
Un sistema (100) de comunicación de entrada múltiple y salida múltiple, en adelante MIMO, que comprende la estación base de la reivindicación 36 y uno o más terminales, comprendiendo cada terminal:una pluralidad de antenas (552) de recepción, estando configurada cada antena (552) de recepción para recibir señales transmitidas desde una estación (104) base;y un procesador (556, 562) configurado para procesar las señales recibidas, obtener información del estado del canal, en adelante CSI, asociada a las señales recibidas, y para enviar la CSI de nuevo a la estación (104) base, en el cual el terminal (106) está en un juego de terminales planificados para recibir transmisión de datos desde la estación (104) base en un intervalo de tiempo particular, incluyendo cada juego uno o más terminales (106) y correspondiéndose con una hipótesis, y en el cual el juego de terminales planificado para recibir transmisión de datos se selecciona de entre uno o más juegos de terminales (106), incluyendo cada juego uno o más terminales (106) y correspondiéndose con una hipótesis, en el cual el juego de terminales se selecciona en función del rendimiento de cada hipótesis y en el cual cada hipótesis se evalúa en función, al menos en parte, de la CSI recibida desde los terminales (106) en cada juego, en el cual la CSI es indicadora de características de canal entre antenas (524) de transmisión y el terminal (106) y el terminal (106) comprende, además, una pluralidad de unidades (554) de extremo frontal, configurada cada unidad (554) de extremo frontal para procesar una señal procedente de una antena (552) de recepción asociada para proporcionar una señal recibida correspondiente;en el cual el mencionado procesador (556) comprende un procesador (556) de recepción configurado para procesar una pluralidad de señales recibidas de la pluralidad de unidades de extremo frontal para proporcionar una o más corrientes de datos decodificados, y para obtener, además, la CSI de cada corriente de datos decodificada;y en el cual el mencionado procesador (556) comprende un procesador (562) de datos de transmisión configurado para procesar la CSI para transmitir de nuevo a la estación (104) base, el sistema, caracterizado porque en él los terminales planificados son priorizados.
41
Un aparato para gestionar la transmisión de datos para un sistema (100) de comunicación inalámbrica, comprendiendo el aparato:ES 2 287 282 T3 medios para identificar uno o más juegos de terminales (106), incluyendo cada juego uno o más terminales y correspondiéndose con una hipótesis para ser evaluada en función de uno o más criterios;medios para asignar una pluralidad de antenas (524) de transmisión al o a los terminales (106) en cada juego;medios para evaluar el rendimiento de cada hipótesis en función de la información del estado de canal, en adelante CSI, asociada a cada terminal (106), siendo la cSi indicadora de las características del canal entre la terminal (106) correspondiente y las antenas (524) de transmisión correspondientes;y medios para seleccionar al menos unjuego de terminales (106) para recibir transmisión de datos en función, al menos en parte, en el rendimiento de cada hipótesis;el aparato caracterizado por medios para priorizar los terminales (106) planificados.
42
El aparato de la reivindicación 41, que comprende, además:medios para planificar transmisión de datos hacia el o los terminales (106) en el juego seleccionado.
43
El aparato de la reivindicación 41, en el cual cada hipótesis comprende una pluralidad de sub-hipótesis cada una de las cuales se corresponde con una o más asignaciones específicas de las antenas de transmisión con el o los terminales en el juego correspondiente, y en el cual el rendimiento de cada hipótesis se evalúa en función del rendimiento de las sub-hipótesis correspondientes.
44
El aparato de la reivindicación 41, en el cual la CSI para cada terminal (106) comprende estimaciones de relación de señal-a-ruido-más-interferencia, en adelante SNR, obtenidas en la correspondiente terminal en función de terminales transmitidas desde las antenas (524) de transmisión.
45
El aparato de la reivindicación 41, en el cual medios para evaluar incluyen:medios para calcular una métrica de rendimiento para cada hipótesis como una función de la capacidad de salida conseguible por cada terminal (106) en el juego correspondiente.
46
El aparato de la reivindicación 41, en el cual la pluralidad de antenas (524) de transmisión se asigna al o a los terminales (106) en cada juego en función de la prioridad de los terminales en el juego.
47
El aparato de la reivindicación 43, en el cual la prioridad de cada terminal (106) se determina en función de uno o más factores, incluyendo la calidad de servicio, en adelante QoS, asociada con el terminal (106) correspondiente.

Independent claims47

235 paragraphs in 13 sections, as filed

IS 2 287 282 T3

DESCRIPTION

Procedure and apparatus for allocating resources in a multiple input / output communication system.

Background

Field

The present invention relates generally to data communication, and more specifically, to techniques for allocating downlink resources in a multiple input / output (MIMO) communication system.

Background

Wireless communication systems are widely used to provide various types of communication such as voice, data, and others, for a number of users. These systems can be based on code division multiple access (CMDA), time division multiple access (TDMA), frequency division multiple access (FDMA) or by some other multiple access techniques.

A multiple input / output (MIMO) communication system employs multiple (NT) transmit antennas and multiple (NR) receiving antennas for transmitting multiple independent data streams. In another common MIMO system implementation, all of the data streams are transmitted to a single terminal at any one time. However, a multiple access communication system having a base station with multiple antennas can also concurrently communicate with a number of terminals. In this case, the base station employs a number of antennas and each terminal employs NR antennas to receive one or more of the streams of multiple data streams.

The connection between a multi-antenna base station and a single multi-antenna terminal is called a MIMO channel. A MIMO channel formed by these transmitting NT and receiving NR antennas can be decomposed into NC independent channels, with NC <min {NT, NR}. Each of the independent Nc channels is also referred to as a spatial subchannel of the MIMO channel and corresponds to a dimension. The MIMO system can provide improved performance (eg, improved transmission capacity), if the additional dimensionalities of these subchannels created by the multiple transmit and receive antennas are used.

Each MIMO channel between the base station and a terminal typically experiences different link characteristics and is associated with different transmission capacity, such that the spatial subchannels available at each terminal have different effective capacities. Efficient use of available (and higher powered) downlink resources can be achieved if the available spatial NC subchannels are efficiently allocated such that data is transmitted on these subchannels to a "suitable" set of terminals in the MIMO system.

However, there is a need in the art for techniques to allocate downlink resources in a MIMO system for the system to provide improved performance.

Attention is also drawn to document EP-A-0 884 862, which describes a radio communication apparatus with a diversity transmission function, in which the apparatus comprises an auxiliary transmitter, in addition to the transmitters peculiar to the channels. CDMA system signals received by antennas are modulated by corresponding channels, a maximum reception power level of each channel is detected, and an antenna with a maximum level is found. In a diversity transmission control, it is determined whether the maximum reception levels of all channels are equal or not, or if they are greater than a predetermined level. If the maximum reception levels of all channels are equal to or greater than the predetermined level, a regular diversity check is performed. The transmission signals of the corresponding channels are transmitted from antennas with maximum reception power levels via the transmitters, which are peculiar to the channels. If the maximum reception level of any one of the channels is the predetermined level or lower, the transmission signal of the associated channel is transmitted from the antenna with a second higher level of channel power level via the auxiliary transmitter, in addition to the regular diversity check.

In accordance with the method of the present invention, a method is provided for scheduling a downlink data transmission, as set forth in claim 1, a base station in a multiple input / output (MIMO) communication system, as set forth in claim 35, a terminal in a multiple input / output communication system, as set forth in claim 39, and an apparatus for managing data transmission, as set forth in claim 44.

Summary

Aspects of the invention provide techniques for increasing the downlink performance of a wireless communication system. In one aspect, data can be transmitted from a base station to one or more terminals using one or more of a number of different modes of operation. In a MIMO mode, all available downlink data streams are assigned to a single terminal employing multiple antennas (ie, one MIMO terminal). In an N-SIMO mode, a single data stream is assigned to each terminal out of a

ES 2 287 282 T3 a number of different terminals, each terminal employing multiple antennas (ie SIMO terminals). And in a mixed mode, the downlink resources can be assigned to a combination of SIMO and MIMO terminals, both types of terminals being supported simultaneously. By simultaneously transmitting data to multiple SIMO terminals, one or more SIMO terminals, or a combination thereof, the transmission capacity of the system is increased.

In another aspect, scheduling schemes are provided for scheduling data transmissions to active terminals. A planner selects the best operating mode to use, based on various factors such as, for example, the services that are being requested through the terminals. Furthermore, the scheduler can perform an additional level of optimization by selecting a particular set of terminals for simultaneous data transmission and assigning the available transmitting antennas to the selected terminals such that high system performance and other requirements are achieved. Some planning schemes and antenna assignment schemes are given and described in the following.

A specific embodiment of the invention provides a method for scheduling downlink data transmission to a number of terminals in a wireless communication system. According to the method, one or more sets of terminals are formed for the possible transmission of data, each set including a unique combination of one or more terminals and corresponding to a hypothesis to be evaluated. One or more sub-hypotheses can also be formed for each hypothesis, each sub-hypothesis corresponding to the specific assignments of a certain number of transmitting antennas to the terminal (s) in the hypothesis. The fulfillment of each sub-hypothesis is then evaluated, and one of the evaluated sub-hypotheses is selected based on its fulfillment. The terminal (s) in the selected sub-hypotheses are then scheduled to transmit data, and the data is then transmitted to each scheduled terminal from one or more transmitting antennas assigned to the terminal.

Each transmitting antenna can be used to transmit a separate data stream. To achieve high performance, each data stream can be encoded and modulated based on a selected scheme, for example based on a signal-to-noise-plus-interference (SNR) estimate for the antenna used to transmit the signal. data stream.

Terminals wishing to transmit data (ie "hot" terminals) can be prioritized, based on various metrics and factors. The priority of the active terminals can then be used to select which terminal (s) will be considered for planning and / or assigning the available transmit antennas to the selected terminals.

The invention further provides methods, systems, and apparatus that implement various aspects, embodiments, and features of the invention, as described in more detail below.

Brief description of the drawings

The characteristics, nature, and advantages of the present invention will become more apparent from the detailed description set forth below, when considered in conjunction with the drawings in which reference characters are identified correspondingly throughout the document, and in which:

Figure 1 is a diagram of a multiple input / output (MIMO) communication system that may be designed and operated to implement various aspects and embodiments of the invention;

Figure 2 is a flow chart of a process for scheduling terminals to transmit data, according to an embodiment of the invention;

Figure 3 is a flow chart of a process for assigning transmit antennas to receive antennas using a "max-max" criterion, according to one embodiment of the invention;

Figure 4 is a flow chart for a priority-based scheduling scheme, whereby a set of the high priority terminal (s) is considered for scheduling, in accordance with one embodiment of the invention;

Figure 5 is a block diagram of a base station and a number of terminals in the MIMO communication system;

Figure 6 is a block diagram of an embodiment of the transmitting portion of a base station capable of processing data for transmission to terminals based on available CSI;

Figure 7 is a block diagram of an embodiment of the receiving part of a terminal;

Figures 8A and 8B are block diagrams of an embodiment of a MIMO / channel data processor and an interface canceller, respectively, of a MIMO / receive data processor (Rx) in the terminal; Y

ES 2 287 282 T3 Figure 9 shows the average output capacity for a MIMO communication system with four transmitting antennas (i.e. NT= 4) and four receive antennas at each terminal (i.e., NR= 4) for two different modes of operation.

Detailed description

FIG. 1 is a diagram of a multiple input / output (MIMO) communication system 100 that may be designed and operated to implement various aspects and embodiments of the invention. The MIMO system 100 employs multiple (NT) transmit antennas and multiple (NR) receive antennas to transmit data. The MIMO system 100 is effectively comprised of a multiple access communication system having a base station (BS) 104 that can communicate concurrently with a number of terminals (T) 106. In this case, the base station 106 employs multiple antennas. y represents the multiple input (MI) for downlink transmissions from the base station to the terminals.

A set of one or more "communicating" terminals 106 collectively represents multiple output (MO) for downlink transmissions. As used herein, a communication terminal is one that receives user-specific data from the base station, and an "active" terminal is one that desires data transmission in an immediate or future transmission interval. Active terminals can include terminals that are currently communicating.

The MIMO system 100 can be designed to implement any number of standards and designs for CDMA, TDMA, FDMA, and other multiple access techniques. The CDMA standards include the IS-95, cdma2000, and W-CDMA standards, and the TDMA standards include the Global System for Mobile Communications (GSM) standard. These standards are known in the art and are incorporated herein by reference.

The MIMO system 100 can be operated to transmit data via a number of transmission channels. Each terminal 106 communicates with base station 104 via a MIMO channel. A MIMO channel can be decomposed into NC independent channels, with NC <min {NT, NR}. Reference is also made to each of the NC independent channels as well as a spatial subchannel of the MIMO channel. For a MIMO system that does not use orthogonal frequency division modulation (OFDM), there is typically only one frequency subchannel and each spatial subchannel can be referred to as a "transmission channel". And for a MIMO system using OFDM, each spatial subchannel of each frequency subchannel can be referred to as a transmission channel.

For the example shown in FIG. 1, base station 104 concurrently communicates with terminals 106a to 106d (as indicated by solid lines) via multiple antennas available at the base station and multiple antennas available at each terminal. Terminals 106e to 106h may receive pilot references and other signaling information from base station 104 (as indicated by dashed lines), but are not receiving these user specifics from the base station.

Each terminal 106 in the MIMO system 100 employs NR antennas to receive one or more data streams. Generally, the number of antennas of each terminal is equal to or greater than the number of data streams transmitted by the base station. However, the terminals in the system do not need to be equipped with an equal number of receiving antennas at all.

For the 100 MIMO system, the number of antennas at each of the terminals (NR) is typically greater than or equal to the number of antennas at the base station (NT). In this case, for the downlink, the number of spatial subchannels is limited by the number of transmitting antennas at the base station. Each transmitting antenna can be used to send an independent stream of data that can be encoded and modulated according to a scheme supported by the spatial subchannel associated with the MIMO channel between the base station and the selected terminal.

Aspects of the invention provide techniques for increasing the performance of a wireless communication system. These techniques can be used to advantage to increase the downlink capacity of a multiple access communication system. These techniques can also be used in combination with other multiple access techniques.

In one aspect, data can be transmitted from a base station to one or more terminals using one of a number of different modes of operation. In a MIMO mode, the available downlink resources are allocated to a single terminal (ie, a MIMO terminal). In an N-SIMO mode, the downlink resources are allocated to a number of different terminals, each terminal demodulating a single stream of data (ie, SIMO terminals). In a mixed mode, the downlink resources can be assigned to a combination of SIMO and MIMO terminals, both types of terminals being simultaneously supported on the same channel, which can be a time slot, a code channel, a subchannel. of frequency and successively. By transmitting data simultaneously, to multiple SIMO terminals, one or more MIMO terminals, or a combination thereof, the transmission capacity of the system is increased.

In another aspect, scheduling schemes are provided for scheduling data transmissions to activate terminals. A scheduler selects the best operating mode to use based on various aspects such as, for example, the services that are being requested by the terminals. In addition, the planner can perform a level

Additional optimization by selecting a particular set of terminals to transmit simultaneous data and assigning the available transmitting antennas to the selected terminals such that high performance and other system requirements are recorded. Some planning schemes and antenna assignment schemes are described in more detail below.

With MIMO, multiple independent data streams can be transmitted from the base station via multiple transmitting antennas to one or more planned terminals. If the propagation environment has sufficient dispersion, MIMO receiver processing techniques can be used at the terminals to effectively exploit the spatial dimensionalities of the MIMO channel to increase transmission capacity. MIMO receiver processing techniques can be used when the base station is simultaneously communicating with multiple terminals. From a processing point of view, the same receiver processing techniques can be used to process different N signals.T intended for this terminal (for example, a single MIMO terminal) or only one of the N signalsT (i.e. SIMO terminals).

As shown in Figure 1, the terminals can be randomly distributed in the covered area of the base station (or "cell") or can be co-located. For a wireless communication system, the link characteristics typically vary over time due to a number of factors such as fading and multi-path. At a particular instant in time, the channel responds between the ordered set of transmitting antenna base station NT of the NR Receiving antennas for a single terminal can be characterized by a matrix H whose elements are composed of independent Gaussian random variables, as follows:

1 * 2.1 Λ ^ 2.2 Λ / ^, 2 Μ Μ fl2.NR /'Nt.Nr

Eq (l) where H is the channel response matrix for the terminal, and h, j is the coupling between the ith transmitting antenna of the base station and the jth receiving antenna of the terminal.

As shown in equation (1), the channel estimates for each terminal can be represented by a matrix that has NT x NR elements corresponding to the number of transmit antennas at the base station and the number of receive antennas at the terminal. . Each element of the matrix H describes the response of a pair of respective transmit-receive antennas between the base station and a terminal. For simplicity, equation (1) describes a channel characterization based on a flat fading channel model (ie, a complex value for the entire system bandwidth). In a current working environment, the channel can be frequency selective (i.e., the channel response varies across the entire bandwidth of the system) and more detailed channel characterization can be used (for example, each element of the matrix H may include a set of values for different frequency subchannels or time delays).

The active terminals in the MIMO system periodically estimate the channel response for each pair of transmit-receive antennas. Channel estimates can be provided in a number of ways, such as, with the use of pilot and / or data driven decision techniques known in the art. The channel estimates may comprise the estimate in response of the channel complex value for each pair of transmit-receive antennas, as described above in equation (1). The channel estimates give information about the transmission characteristics of each of the spatial subchannels, that is, what data transmission rate is supportable in each subchannel with a given set of transmission parameters. The information given by the channel estimates can be distilled into a post-processed estimate of the signal-to-noise-plus radio interference (SNR) for each spatial subchannel (described below), or some other statistics that allow the transmitter to select the appropriate transmission parameters for each spatial subchannel. Typically, this process of obtaining essential statistics reduces the amount of data required to characterize a channel. In either case, this information represents a form of channel status information (CSI) that can be reported to the base station. Information about other forms of CSI can also be given and described below.

The aggregate CSI received from the terminal collection can be used to (1) select a "best" set from one or more terminals for data transmission, (2) assign the available transmit antennas to select terminals in the game, and (3) selecting the appropriate code and modulation scheme for each transmitting antenna. With the CSI available, various planning schemes can be designed to maximize downlink performance by evaluating which specific combination of terminals and antenna assignments provide the best performance to the system (e.g. highest output capacity) subject to any restriction and requirements in the system. By exploiting the spatial "signatures" (and possibly the frequency) of individual active terminals (ie, their channel estimates), the average downlink output capacity can be increased.

IS 2 287 282 T3

Terminals can be planned for data transmission based on various factors. One set of factors can refer to system constraints and requirements such as desired quality of service (QoS), maximum latency, average data rate, and so on. Some or all of these factors may have to be satisfied depending on the terminal (ie, for each terminal) in a multiple access communication system. Another set of factors may be related to the performance of the system, which may be qualified by an average transmission rate of the output capacity of the system or by some other performance indications. These various factors are described in more detail below.

Planning schemes can be designed to select the best set of terminals for simultaneous transmission of data from available transmission channels, such that system performance is maximized while conforming to system constraints and requirements. For simplicity, various aspects of the invention are described below for a non-OFDM MIMO system, in which the base station can transmit a separate data stream from each transmitting antenna. In this case, (up to) NT independent data streams can be simultaneously transmitted by the base station from NT transmitting antennas and target one or more terminals, each equipped with NR receiving antennas (i.e. NT x NR MIMO), where NR > NT.

For simplicity, the number of receiving antennas is assumed to be equal to the number of transmitting antennas (ie, NR = NT) for much of the description that follows. This is not a necessary condition, since everything in the analysis applies to the case in which NR> NT.

Downlink data transmission planning comprises two parts: (1) selecting one or more sets of terminals for evaluation, and (2) evaluating the transmitting antennas available to the terminals in each set. All or only a subset of the active terminals can be considered for planning, and these terminals can be combined to form one or more sets (ie, hypotheses) to be evaluated. For each hypothesis, the available transmitting antennas can be assigned to the terminals in the hypothesis based on any scheme among a number of antenna assignment schemes. The terminals in the best case can then be scheduled to transmit data in a close interval. Flexibility both in selecting the best set of terminals for data transmission and in exploiting the diversity of the multi-user environment.

In order to determine the "optimal" transmission for a set of terminals, SNRs or some other sufficient statistics are provided for each terminal and each spatial subchannel. If there are statistics in the SNR, then for each terminal set to be evaluated to transmit data in an incoming transmission interval, a matrix Γ "processed" SNR hypotheses (defined below) for this terminal set, can be expressed as:

Eq (2) where γ ^ is the post-processed SNR for a data stream (hypothetically) transmitted from the i-th terminal to the j-th term.

In the N-th mode, the NT rows in the matrix Γ hypothesis corresponds to NT SNR vectors from different N terminalsT. In this mode, each row in the Γ hypothesis matrix gives the SNR. In this mode, each row in the Γ hypothesis matrix gives the SNR of each data transmission stream antenna and a terminal. And in mixed mode, for a particular MIMO terminal designated to receive two or more data streams, this SNR terminal vector can be replicated such that the vector appears in many other rows as the number of data streams to be transmitted by the terminal (that is, one row per data stream). Alternatively, a row in the Γ hypothesis matrix can be used for each SIMO and MIMO terminal, and the scheduler can be designed to mark and evaluate these different types of terminals accordingly.

In each terminal, in the game to be evaluated, the (hypothetically) NT Transmitted data streams are received by the NR receive antennas, and the NR receive antennas can be processed using spatial or space-time equalization to separate the NT transmitted data streams, as described below. the SNR of a post-processed data stream (ie, after equalization) can be estimated, and comprises the post-processed SNR for that data stream. For each terminal, a set of post-processed SNR NTs can be provided for the NT data streams that can be received by that terminal.

If an interference cancellation and successive equalization receiver processing technique (or "rolling cancellation") is used in a terminal to process the received signals, then the post-processed SNR achieved in the terminal for each transmitted data stream depends on the order in which the transmitted data streams were detected (ie, demodulated and decoded) to recover the transmitted data, as described below. Multiple hypothesis matrices can then be formed and evaluated to determine which specific combination of terminals and order of detection provides the best system performance.

IS 2 287 282 T3

In any case, each Γ hypothesis matrix includes the post-processed SNRs for a specific set of terminals (ie, hypotheses) to be evaluated. These post-processed SNRs represent the SNRs achievable by the terminals that are used to test the hypotheses.

FIG. 2 is a flow diagram of a process 200 for scheduling terminals to transmit data, in accordance with one embodiment of the invention. For clarity, the process as a whole is first described and details for some of the stages in the process are described subsequently.

Initially, in step 212 the metrics that will be used to select the best set of terminals to transmit data are initialized. Various performance metrics can be used to evaluate terminal set and some of these are described in more detail below. For example, you can use a performance metric that maximizes the system everywhere.

Next, a (new) set is selected from one or more active terminals, from among all active terminals considered for planning, in step 214. This set of terminals forms a hypothesis to be evaluated. Various techniques can be used to limit the number of active terminals to consider in planning, which reduces the number of hypotheses to be evaluated, as described below. For each terminal in the hypothesis, in step 216 the SNR vector is recovered (for example, Yj = Dy1, j, Y2, j, ..., YNT, j]. The SNR vectors for all terminals in the hypothesis form the matrix Γ hypothesis shown in equation (2).

For each matrix Γ hypothesis of NT transmitting antennas and NT terminals, there are NT factorial possible combinations of assigning transmit antennas to terminals (i.e., NT! sub-hypothesis). Thus, a particular (new) combination of antenna / terminal assignments is selected for evaluation, in step 218. This particular combination of antenna / terminal assignments forms a sub-hypothesis to be evaluated.

In step 220 these sub-hypotheses and the performance metric (eg, the output capacity of the system) that corresponds to this sub-hypothesis (eg, based on the SNRs for the sub-hypothesis) are determined. This performance metric is then used in step 222 to update the performance metric for the current best sub-hypothesis. Specifically, if the performance metric for this sub-hypothesis is better than that of the current best sub-hypothesis, then this sub-hypothesis becomes the new best sub-hypothesis, and the performance metric and the other terminal metrics corresponding to this sub-hypothesis are saved. The performance and endpoint metrics are described below.

A determination is then made as to whether or not all the sub-hypotheses for the current hypothesis have been tested at step 224. If not all the hypotheses have been tested, the process returns to step 218 and a different combination still Non-evaluated antenna / terminal assignments is selected for evaluation. Steps 218 to 224 are repeated for each sub-hypothesis to be tested.

If all the sub-hypotheses for a particular hypothesis have been evaluated, at step 224, a determination is then made as to whether or not all the hypotheses have been considered. If all the hypotheses have not been considered, then the process returns to step 214 and a different, not yet considered set of terminals is selected for evaluation. Steps 214 to 226 are repeated for each hypothesis to be considered.

If all the hypotheses have been considered in step 226, then the specific set of terminals planned for data transmission in the upcoming data interval and their assigned transmit antennas are well known. The post-processed SNRs that correspond to this set of terminals and antenna assignments can be used to select the correct code and modulation schemes for the data streams to be transmitted to the terminals. The planned transmission interval, antenna assignments, coding and modulation schemes, other information, or any combination thereof, can be carried to the planned terminals (eg, via a control channel), in step 228. Alternatively , the terminals may perform "blind" detection and attempt to detect all transmitted data streams to determine which, if any, of the data streams are intended for them.

If the planning scheme requires other terminal systems and metrics to be maintained (for example, average data rate over transmission intervals K past, latency for data transmission, and so on), then these metrics are updated in step 230. Terminal metrics can be used to evaluate the performance of individual terminals, and are described below. Scheduling is typically done for each transmission interval.

For a given hypothesis Γ matrix, the planner evaluates various combinations of antenna pairs and transmission terminals (ie, sub-hypotheses) to determine the best assignments for the hypothesis. Various assignment schemes can be used to assign antennas to terminals to achieve various successes in the system, such as fairness, maximized performance, and others.

In an antenna mapping scheme, all possible sub-hypotheses are evaluated based on a particular performance metric and the sub-hypothesis with the best performance metric is selected. For each matrix Γ hypothesis, there are NT factorial (that is, NT!) possible sub-hypotheses that can be evaluated. Each sub-hypothesis corresponds

ES 2 287 282 T3 with a specific assignment of each transmitting antenna to a corresponding terminal. Each sub-hypothesis can be represented, in this way, with a vector of post-processed SNRs, which can be expressed as:

where γ ^ is the post-processed SNR for the jth transmitting antenna relative to the jth terminal, and the subscripts {a, b ... and r} identify the specific terminals in the transmitting antenna / terminal pairs for the sub-hypotheses.

Each sub-hypothesis is also associated with a performance metric, Rsub_hyp, which can be a function of various factors. For example, a performance metric based on post-processed SNRs can be expressed as:

z-mb-kyp

Where f (·) is a particular positive function realizing the argument (s) in parentheses.

Various functions can be used to formulate the performance metric. In one embodiment a function of the achievable output capacity for the NT transmit antennas for the sub-hypotheses can be used, which can be expressed as:

Eq (3)

Where r, is the output capacity associated with the ith transmitting antenna in the sub-hypothesis, and can be expressed as:

r¡ = cF-log, (l + y ,.)

Eq (4)

Where CI is a positive constant that reflects the fraction of the theoretical capacity reached by the coding and modulation scheme selected for the data stream transmitted by the i-th transmitting antenna, and γ is the post-processed SNR for the i- th data stream.

The first antenna assignment scheme shown in Figure 2 and described above, represents a specific scheme that evaluates all possible combinations of assignments of transmitting antennas to the terminals. The total number of potential sub-hypotheses that the evaluator has to evaluate for each hypothesis is NT !, which can be large considering that a large number of hypotheses may have to be evaluated. The first planning scheme performs an exhaustive search to determine the sub-hypotheses that provide the “optimal” system performance, as they are quantified by the performance metric used to select the best sub-hypotheses.

A number of techniques can be used to reduce the complexity of the processing for assigning transmit antennas. One of these techniques is described below, and others can also be implemented and are within the scope of the invention. These techniques can also provide high system performance while reducing the amount of processing required to assign transmit antennas to terminals.

In a second antenna assignment scheme, a maximum-maximum criterion (“max-max”) is used to assign transmitting antennas to terminals in the hypotheses being evaluated. Using max-max criterion ester each transmitting antenna is assigned to a particular terminal that achieves the best SNR for the transmitting antenna. Antenna assignment will be done for a transmitting antenna one at a time.

Figure 3 is a flow chart of a process 300 for assigning transmit antennas to terminals using the max-max criterion in accordance with one embodiment of the invention. The processing shown in figure 3 is carried out for a particular hypothesis, which corresponds to a specific set of one or more terminals. Initially, the maximum post-processed SNR in the Γ hypothesis matrix is determined, in step 312. This maximum SNR corresponds to a specific transmit antenna / terminal pair, and the transmit antenna is assigned to this terminal, in step 314. This antenna and transmit terminal are then removed from the matrix Γ, and the matrix Γ is reduced to dimension (NT-1) x (NT-1) removing both the column corresponding to the transmitting antenna and the row corresponding to the terminal that has just been assigned, in step 316.

In step 318, a determination is made as to whether all the transmitting antennas in the assumptions have been assigned or not. If all transmitting antennas have been assigned, then the antenna assignments are provided in the

ES 2 287 282 T3 step 320, and the process ends. Otherwise, the process returns to step 312 and another transmit antenna is assigned similarly.

Once the antenna assignments have been made for a given hypothesis Γ matrix, the performance metric (for example, system output capacity) that corresponds to this hypothesis can be determined (for example, based on the SNRs corresponding to the antenna) as shown in equations (3) and (4). This performance metric is updated for each scenario. When all the hypotheses have been evaluated, the best set of terminal and antenna assignments is selected to transmit data in the next data interval.

Table 1 shows an example matrix Γ of post-processed SNRs obtained by terminals in a 4 x 4 MIMO system in which the base station includes four transmit antennas and each terminal includes four receive antennas. For the antenna assignment scheme based on the max-max criterion, the best sNr (16 dB) in the original matrix is achieved by transmitting antenna 3 and is assigned to terminal 1, as indicated by the shaded box in the third row of the fourth column of the table. The transmitting antenna 3 and terminal 1 are then removed from the array. The best SNR (14 dB) in the reduced 3 x 3 matrix is achieved by the two transmitting antennas 1 and 4, which are assigned respectively to terminals 3 and 2. The remaining transmitting antenna 2 is then assigned , to terminal 4.

Table 2 shows the antenna assignments that use the max-max criterion for the matrix Γ example shown in Table 1. For terminal 1, the best SNR (16 dB) is achieved by processing the signal transmitted from antenna 3 of transmission. The improved transmission antennas for the rest of the terminals are also indicated in Table 2. The planner can use this information to select the appropriate coding and modulation scheme to use in the data transmission.

TABLE 2

The planning scheme described in Figures 2 and 3 represents a specific scheme that evaluates various hypotheses that correspond to the various possible sets of active terminals that want data transmission in the next data interval. The total number of hypotheses to be evaluated by the planner can be quite large, even for a small number of active terminals. In fact, the total number of hypotheses, Nhyp, can be expressed as:

Whereor is the number of active terminals that must be considered for planning: for example, if Nor = 8 and NT = 4, then Nhyp= 70. An exclusive search can be used to determine the particular assumptions (and particular antenna assignments) that provide optimal system performance, as quantified by the performance metric used to select the best assumptions and antenna assignments.

IS 2 287 282 T3

Other planning schemes that have reduced complexity can also be implemented and are within the scope of the invention. One such planning scheme is described below. These schemes can also provide high system performance while reducing the amount of processing required to the processing terminals to transmit data.

In another scheduling scheme, active terminals are scheduled to transmit data based on their priority. The priority of each terminal can be obtained based on one or more metrics (for example, average output capacity), constraints and demands of the system (for example, maximum latency), other factors, or a combination thereof, as shown describes in what follows. A list can be maintained for all active terminals that want data transmission in a nearby data interval (also referred to as a "frame"). When a terminal wants data transmission, it is added to the list and its metrics are initialized (eg, to zero). The metrics for each terminal in the list are then updated on each frame. Once a terminal does not want data transmission, it is removed from the list.

For each frame, all terminals of a subset of terminals in the list can be considered for planning. The specific number of terminals to consider can be based on a number of factors. In one embodiment, only the NT Higher priority terminals are selected to transmit data. In another embodiment, the Nx Terminals with the highest priorities in the list are considered for planning where, Nx > NT.

FIG. 4 is a flow chart for a priority-based scheduling scheme 400, whereby a set of higher priority terminal NTs is considered for scheduling. According to an embodiment of the invention. At each interval of the frame, the scheduler examines the priority of all active terminals in the list and selects the set of NT Higher priority terminals, in step 412. The remaining terminals in the list are not considered for planning. The channel estimates for each selected terminal are then retrieved, in step 414. For example, the post-processed SNRs for the selected terminals can be retrieved and used to form the Γ hypothesis matrix.

The NT transmit antennas are then assigned to selected terminals based on channel estimates and using only one of a number of antenna assignment schemes, in step 416. For example, the antenna assignments they can be based on extensive research or the max-max criteria described above. In another antenna assignment scheme, the transmitting antennas are assigned to terminals such that their priorities are normalized as strictly as possible, once the terminal metrics are updated.

The data rates and the modulation and coding schemes for the terminals are determined based on the antenna assignments, in step 418. The planned transmission interval and data rates can be reported to the tanks. storage. The planned (and unplanned) terminal metrics in the lists are updated to reflect the planned data transmission (and no transmission), and system metrics are also used in step 420.

Various metrics and factors can be used to determine the priority of active terminals. In one embodiment, a "score" can be maintained for each terminal in the list and for each metric that will be used for planning. In one embodiment a score indicative of an average output capacity over an average time interval is maintained for each active terminal. In one implementation, the On (k) score for terminal n in frame k is calculated as an average linear output capacity achieved over some time interval, and can be expressed as:

Eq (6)

Where rneither) is the realized data transmission rate (in units of bits / frame) for terminal n in frame i and can be computed as shown in equation (4). Typically, rneither) is limited by a particular achievable maximum data rate, rmax, and a particular minimum data rate (eg zero). In another implementation, the score On (k) for terminal n in frame k is an average exponential output capacity achieved over some time interval, and can be expressed as:

Φ ,, (¿) = O “or) · Φ„ “1) + to · r„(O / ς

Eq (7)

Where α is a time constant to obtain the exponential mean, with a larger value for α corresponding to a larger mean time interval.

When a terminal wants data transmission, it is added to the list and its score is initialized to zero. The score for each terminal in the list is subsequently updated in each frame. Whenever a terminal is not scheduled for transmission in a frame, its data rate for the frame is set to zero (ie, rn (k) = 0) and its score is updated accordingly. If a frame is received by mistake by a terminal, the

ES 2 287 282 T3 terminal effective data rate for that frame can be set to zero. The frame error can be known immediately (for example, due to round trip delay of the negative acknowledgment / acknowledgment scheme (Ack / Nak) used for data transmission) but the score can be adjusted accordingly a once this information is available.

The priority for active terminals can also be determined based on part of the constraints and demands of the system. For example, if the maximum latency for a particular terminal exceeds a threshold value, then the terminal can be raised to high priority.

Other factors can also be considered when determining the priority of active terminals. One such factor can be related to the type of data to be transmitted to the terminals. Lag-sensitive data may be associated with higher priority, and insensitive lag may be associated with lower priority. Data retransmitted due to decoding errors for a priority transmission may also be associated with higher priority since other processes may be waiting for the retransmitted data. Another factor may be related to the type of data service that is being provided for the terminals. Other factors can also be considered when determining priority and are within the scope of the invention.

The priority of a terminal can then be a function of any combination of (1) the score held for the terminal for each metric to be considered, (2) other parameter values held for system constraints and demands, and (3) other factors. In one embodiment, the system constraints and demands represent "hard" values (ie, high or low priority, depending on whether the constraints and demands have been violated) and the scores represent "soft" values. For this embodiment, terminals for which the system constraints and demands have not yet been met are considered immediately, along with other terminals based on their scores.

A priority-based scheduling scheme can be designed to achieve average output capacity (ie equal QoS) for all terminals on the list. In this case, active terminals are prioritized based on their achieved average output capacity, which can be determined as shown in equation (6) or (7). In this priority-based planning scheme, the scheduler uses the scores to prioritize terminals to assign available transmit antennas. The terminal scores are updated based on their assignments or lack of assignment to the transmitting antennas. The active terminals in the list may have priorities such that the terminal with the lowest score is given the highest priority, and the terminal with the highest score receives, in turn, the lowest priority. Other procedures for ordering terminals can also be used. Prioritization can also assign non-uniform weighting factors to endpoints.

For a scheduling scheme in which terminals are selected and scheduled to transmit data based on their priority, it is possible that poor terminal groups will occasionally occur. A "poor" terminal game is one that results in matrices Hk channel response rates that cause similar and poor SNRs for all terminations on all transmitted data streams, as given in the matrix Γ hypothesis. This then translates to a low overall output capacity for each terminal in the game. When this happens, the priorities of the terminals may not vary substantially across multiple frames. Thus, the planner may be shocked by this particular terminal game until priorities change sufficiently to cause a change in game members.

To avoid the "clumping" effect described above, the scheduler can be designed to recognize this condition before assigning terminals to available transmit antennas and / or detect the condition once it has occurred. A number of different techniques can be used to determine the degree of linear dependence in the channel response matrices Hk. A simple detection procedure is to apply a particular threshold in the Γ hypothesis matrix. If all SNRs are below this threshold, then the clustering condition is present. In the event that the clustering condition is detected, the scheduler may reorder the terminals (eg, in a random fashion) in an attempt to reduce the line dependency in the hypothesis matrix. A free space reclamation scheme can also be tested to force the planner to select sets of terminals that result in "good" hypothesis matrices (that is, those with minimal linear dependence).

Some of the planning schemes described above describe techniques for reducing the amount of processing required to select terminals and assign transmitting antennas to selected terminals. These and other techniques can also be combined to obtain other planning schemes, and this is within the scope of the invention. For example, the Nx Higher priority terminals can be considered for planning using any one of the schemes described above.

More complex planning schemes can also be tested that may be able to achieve through a closer to optimal output capacity. These schemes may be required to evaluate a larger number of assumptions and antenna assignments in order to determine the best set of terminals and the best antenna assignments. Other planning schemes can also be designed to take advantage of the statistical distribution of data rates achieved by each terminal. This information can be useful in reducing the number of hypotheses to be tested. Also, for some applications, it may be possible to learn which grouping

ES 2 287 282 T3 terminal (ie hypothesis) works well analyzing performance over time. This information can be stored, updated, and used by the planner at future planning intervals.

The techniques described above can use scheduling terminals to transmit data using MIMO mode, N-SIMO mode, and mixed mode. Other considerations also apply to each of these modes of operation, as described below.

MIMO mode

In MIMO mode (up to) NT Independent data streams can be transmitted simultaneously by the base station from NT transmit antennas and target a single MIMO terminal with NR receiving antennas (i.e. NT x NR MIMO), where NR > NT. The terminal can use spatial equalization (for a non-dispersive MIMO channel with a flat channel frequency response) to process and separate the transmitted NT data streams. The SNR of each data stream post-processed (i.e., after equalization) can be estimated and sent back to the base station as CSI, which then uses the information to select the appropriate modulation and coding scheme for Use on each transmitting antenna such that the target terminal is capable of detecting each transmitted data stream at the desired level of performance.

If all data streams are transmitted to one terminal as is the case in MIMO mode, then the successive cancellation receiver processing technique can be used at the terminal to process NR received signals to recover NT transmitted data streams. This technique successively processes the NR signals received a certain number of times (or iterations), to recover the signals transmitted from the terminals, a signal transmitted for each iteration being recovered. For each iteration, the technique performs linear and non-linear processing (i.e. space-time equalization) on the received NR signals to recover one of the transmitted signals, and cancels the interference due to the recovered signal from the received signals to obtain "modified" signals that have the interference component removed.

The modified signals are then processed by the next iteration to recover another transmitted signal. By removing the interference due to each recovered signal from the received signals, the SNR is improved by the transmitted signals included in the modified but not yet removed signals. Enhanced SNR translates to improved performance for the terminal as well as the system. In fact, under certain service conditions, the performance obtainable with the use of successive cancellation receiver processing combined with a minimum mean square error (MMSE) equalization is comparable to that of CSI processing. The successive cancellation receptor processing technique is described in more detail in US patent application Ser. US 2005 002 468 entitled "METHOD AND APPARATUS FOR PROCESSING DATA IN A MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) COMMUNICATION SYSTEM UTILIZING CHANNEL STATE INFORMATION", filed on May 11, 2001, transferred to the assignee of this application.

In one embodiment, each MIMO terminal in the system estimates and returns NT post-processed SNR values for the NT transmit antennas. The SNRs from active terminals can be evaluated by the scheduler to determine which terminal to transmit to and when, and the appropriate coding and modulation scheme to use based on a transmitting antenna for each selected terminal.

MIMO terminals can be selected to transmit data based on a particular performance metric formulated to achieve desired system goals. The performance metric can be based on one or more functions and on any number of parameters. Various functions can be used to formulate the performance metric, such as the obtainable output capacity function for the MIMO terminals, shown above in equations (3) and (4).

S-SIMO mode

In the N-SIMO (up to) NT mode independent data streams can be transmitted simultaneously by the base station from the NT transmitting antennas and target (up to) NT different SIMO terminals. To maximize performance, the scheduler can consider a large number of possible terminal sets for transmitting data. The planner then determines the best game in NT terminals for simultaneously transmitting on a given channel (ie, timeslot, code channel, frequency subchannel, and so on). In a multiple access communication system, there are generally restrictions to satisfy certain requirements depending on the terminal, such as maximum latency or average data transmission rate. In this case, the scheduler may be designed to select the best set of terminals subject to these restrictions.

In an implementation for the N-SIMO mode, the terminals use spatial linear spatial equalization to process the received signals, and the post-processed SNR corresponding to each transmitting antenna is provided to the base station. The scheduler then uses the information to select the terminals to transmit data and to assign the transmit antennas to the selected terminals.

In another implementation for the N-SIMO mode, the terminals use successive cancellation receiver processing to process the received signal to achieve higher post-processed SNRs. With successive cancellation receiver processing, the post-processed SNRs for the transmitted data streams depend on the order in which

ES 2 287 282 T3 the data streams are detected (ie demodulated and decoded). In some cases, a particular SIMO terminal may not be able to cancel out interference from a given transmitted data stream for another terminal, since the coding and modulation scheme used for this data stream was selected based on the other. Post-processed SNR of the terminal. For example, the transmitted data stream can be taken as a target for the ux terminal and coded and modulated for adequate detection in a post-processed (e.g. 10 dB) SNR on the target ux terminal, but another terminal and can receive the same data stream transmitted in a worse post-processed SNR and thus is not able to adequately detect the data stream. If the data stream intended for another terminal cannot be detected without errors, then cancellation of the interference due to this data stream is not possible. Successive cancellation receiver processing is feasible when post-processed SNR corresponding to a transmitted data stream enables reliable detection.

In order for the planner to take advantage of the improvement in the post-processed SNRs allowed by the SIMO terminals using successive cancellation receiver processing, each of such terminals can obtain the post-processed SNRs corresponding to the different possible orders of detection for the transmitted data streams. The NT transmitted data streams can be detected as a function of NT factorial (ie NT!) Possible orders in a SIMO terminal, and each order is associated with NT post-processed SNR values. In this way, [can report / can account for] NT-NT! SNR values for each active terminal to the base station (for example, if NT = 4, then 96 SNR values can be reported for each SIMO terminal). The scheduler can then use the information to select terminals for transmitting data and to further assign transmitting antennas to the selected terminals.

If successive cancellation receiver processing is used at the terminals, the scheduler can also consider the possible detection orders for each terminal. However, a large number of these commands are typically invalid as a particular terminal may not be able to adequately detect data streams transmitted to the other terminals due to the lower post-processed SNRs achieved at this terminal for the data streams. undetectable.

As noted above, transmitting antennas can be assigned to selected terminals based on various schemes. In an antenna assignment scheme, transmitting antennas are assigned for high throughput in the system and based on the priority of the terminals.

Table 3 shows an example of the post-processed SNRs obtained by each terminal in a hypothesis being considered. For terminal 1, the best SNR is achieved by detecting the transmitted data stream from transmitting antenna 3, as indicated by the shaded box in row 3, column 4 of the table. The best transmitting antennas for the other terminals in the hypothesis are also indicated by the shading in the boxes.

TABLE 3

SNR (dB)

Transmitting antenna

If each terminal identifies a different transmitting antenna from which the best post-processed SNR is detected, then the transmitting antennas can be assigned to the terminals based on their best post-processed SNRs. For the example shown in Table 3, terminal 1 can be assigned to transmit antenna 3, and terminal 2 can be assigned to transmit antenna 2.

If more than one terminal prefers the same transmitting antenna, then the planner can determine antenna assignments based on various criteria (eg, fairness, performance metrics, and others). For example, Table 3 indicates that the best post-processed SNRs for terminals 3 and 4 occur for the data stream transmitted from the same transmitting antenna 1. If the goal is to maximize output capacity, then the planner can assign transmit antenna 1 to terminal 3 and transmit antenna 2 to terminal 4. However, if the antennas were assigned for fairness, then transmit antenna 1 will be assigned. You can assign to terminal 4, if terminal 4 has higher priority than terminal 3.

IS 2 287 282 T3

Mixed mode

The techniques described above can be generalized to handle mixed SIMO and MIMO terminals. For example, if four transmitting antennas are available at the base station, then four independent data streams can be transmitted to a single 4 x 4 MIMO terminal, two 2 x 4 MIMO terminals, four 1 x 4 SIMO terminals, one MIMO terminal 2 x 4 plus two 1 x 4 SIMO terminals, or any other combination of terminals designated to receive a total of four data streams. The scheduler can be designed to select the best combination of terminals based on the post-processed SNRs for the various sets of terminal hypotheses, where each hypothesis set may include a mix of both MIMO and SIMO terminals.

As long as mixed-mode traffic is supported, the use of successive cancellation receiver processing by the terminals (eg, MIMO) places additional restrictions on the scheduler due to the dependencies introduced. These restrictions can translate into more sets of hypotheses being evaluated, since, in addition to considering different sets of terminals, the planner must also consider demodulation of data streams in various orders by each terminal. The assignment of the transmitting antennas and the selection of the coding and modulation schemes would take these dependencies into account in order to achieve improved performance.

Transmission antennas

The set of transmitting antennas at a base station can be a physically different set of "apertures", each of which can be used to directly transmit a corresponding stream of data. Each aperture can be formed by a collection of one or more antenna elements that are distributed in space (eg, physically located in a single location or distributed in multiple locations). Alternatively, the antenna apertures may be preceded by one or more (fixed) beamforming arrays, each array being used to synthesize a different set of antenna beams from the aperture set. In this case, the above description for transmitting antennas applies analogously to transformed antenna beams.

A number of fixed beamforming matrices can be predefined, and the terminals can evaluate the post-processed SNRs for each of the possible matrices (or sets of antenna beams) and send SNR vectors to the base station. Different performance (ie post-processed SNRs) is typically achieved from different sets of transformed antenna beams, and this is reflected in the reported SNR vectors. The base station can then perform antenna planning and assignment for each of the possible beamforming matrices (using the reported SNR vectors), and select a particular beamforming matrix, as well as a set of terminals and their antenna assignments that make the best use of available resources.

The use of beamforming arrays allows additional flexibility in terminal planning and can also provide improved performance. As examples, the following situations are well suited for beamforming transformations:

• Correlation on the MIMO channel is high so that the best performance can be achieved with a small number of data streams. However, transmitting with only a subset of the transmitting antennas available (and when only their associated transmitting amplifiers) results in a lower total transmitting power. A terminal can be selected to use most or all of the transmitting antennas (and their amplifiers) for the data streams to be sent. In this case, higher power is achieved for the transmitted data streams.

• Physically dispersed terminals can be somewhat isolated by their locations. In this case, the terminals can be served by a standard FFT-type transformation of horizontally spaced apertures into a set of beams pointing to different azimuths.

Performance

The techniques described herein can be viewed as a particular form of spatial division multiple access (SDMA) access, in which a given transmitting antenna in the array of base station antennas is used to transmit a stream of data. different that uses information of the state of the channel (for example, SNR or some other sufficient parameter that determines the bearable data rate) obtained by the terminals in the coverage area. High performance is achieved based on CSI, which is used in planning terminals and processing data.

The techniques described in this document can provide improved system performance (eg, higher output capacity). Simulations have been carried out to quantify the possible output capacity of the system with any of these techniques. In the simulations the matrices Hk of channel response coupling the ordered set of transmitting antennas and the receiving antennas of the k-th terminal are assumed to be composed of complex Gaussian random variables of zero mean and equal variance. The simulations were carried out for the MIMO and N-SIMO modes.

IS 2 287 282 T3

In MIMO mode, four MIMO terminals (each with four receive antennas) are considered for each embodiment (eg, each transmission interval) and the best terminal is selected and scheduled to transmit data. The scheduled terminal transmits four independent data streams and uses successive cancellation receiver processing (with MMSE equalization) to process the received signals and recover the transmitted data streams. The average output capacity for the planned MIMO terminals is recorded.

In the N-SIMO mode, four SIMO terminals, each with four receiving antennas, are considered for each embodiment. Post-processed SNRs for each SIMO terminal are determined using MMSE linear spatial equalization (no successive cancellation receiver processing). In the stage they are assigned to the selected terminals based on the max-max criterion. The four planned terminals transmit four independent data streams and each terminal uses MMSE equalization to process the received signal and recover its data stream. The output capacities for each planned SIMO terminal are recorded separately, and the average output capacity for all planned terminals is also recorded.

Figure 9 shows the average output capacity for a MIMO communication system with four transmit antennas (that is, NT = 4) and four receive antennas per terminal (that is, NR = 4) for MIMO and N- modes. SIMO. The simulated output capacity associated with each mode of operation is provided as a function of the mean post-processed SNR. Average output capacity for SIMO mode is shown as graph 910, and average output capacity for N-SIMO mode is shown as graph 912.

As shown in Figure 9, the simulated output capacity associated with the N-SIMO mode using the antenna allocation by the max-max criterion shows a better performance than that achieved by the SIMO mode. In SIMO mode, MIMO terminals benefit from using successive cancellation receiver processing to achieve higher post-processed SNRs. In SIMO mode, scheduling schemes are able to exploit multi-user selection diversity to achieve improved performance (ie, higher output capacity) even though each SIMO terminal uses linear spatial equalization. In fact, the multi-user diversity provided in the NSIMO mode translates into an average downlink output capacity that exceeds the output capacity achieved by dividing a transmission interval into four sub-slots of equal length, and assigning each terminal. MIMO to a corresponding sub-slot.

The planning schemes used in the simulations for both modes of service were not designed to provide proportionate fairness, and some terminals will observe higher average output capacity than others. When a fairness criterion is imposed, the differences in output capacity for the two modes of service can be reduced. However, the ability to accommodate both MIMO and N-SIMO terminals provides added flexibility in providing wireless data service.

For simplicity, various aspects and embodiments of the invention have been described for a communication system in which (1) the number of receiving antennas equals the number of transmitting antennas (i.e., NR = NT), and (2 ) a stream of data is transmitted from each antenna in the base station. In this case, the number of transmission channels is equal to the number of available spatial subchannels of the MIMO channel. For a MIMO system using OFDM, multiple frequency subchannels can be associated with each spatial subchannel, and these frequency subchannels can be assigned to terminals based on the techniques described above. For a dispersive channel, a matrix H would represent a three-dimensional cube of channel response estimates for each terminal.

Each planned terminal may also be equipped with more receiving antennas than the total number of data streams. Furthermore, multiple terminals can share a given transmitting antenna, and the comparison can be achieved via time division multiplexing (for example, assigning different fractions of a transmission interval to different terminals), frequency division multiplexing (for example, assigning different frequency subchannels to different terminals), code division multiplexing (for example, assigning different orthogonal codes to different terminals), some other multiplexing schemes, or any combination of these schemes.

The scheduling schemes described herein select terminals and assign antennas to transmit data based on channel status information (eg, post-processed SNRs). The post-processed SNRs for the terminals depend on the particular transmit power level used by the data streams transmitted from the base station. For simplicity, the same transmit power level is assumed for all data streams (ie, there is no power control of the transmit power). However, by controlling the transmit power for each antenna, the available SNRs can be adjusted. For example, as the transmit power for a particular transmitting antenna decreases via power control, the SNR associated with a data stream transmitted from this antenna is reduced, the interference caused by this data stream on other data streams it would also be reduced, and other data streams may be able to achieve better SNRs. Thus, power control can also be used in conjunction with planning schemes described herein, and this is within the scope of the invention.

Terminal planning based on priority is also described in US Patent Application Serial No. 09 / 675,706, entitled "METHOD AND APPARATUS FOR DETERMINING AVAILABLE TRANSMIT POWER IN A WIRELESS COMMUNICATION SYSTEM," filed on September 29, 2000. He plans it15

ES 2 287 282 T3 data transmission for the downlink is also described in US Patent Application Serial No. 08 / 798,951, entitled "METHOD AND APPARATUS FOR FORWARD LINKRATE SCHEDULING", filed on September 17, 1999. These applications are assigned to the assignee of the present invention.

The planning schemes described herein incorporate a number of features and provide numerous advantages. Some of these features and benefits are described below.

First, the scheduling schemes support various modes of service, including mixed mode whereby any combination of SIMO and MIMO terminals can be scheduled to transmit data on the downlink. Each SIMO or MIMO terminal is associated with an SNR vector (that is, a row in equation (2)). Planning schemes can evaluate any number of possible combinations of terminals to transmit data.

Second, scheduling schemes provide a plan for each transmission interval that includes a set of "mutually compatible" terminals (optimal or near optimal) based on their spatial signatures. Mutual compatibility can be considered to mean transmission coexistence on the same channel at the same time given specific restrictions in terms of terminal data rate requirements, transmission power, link margin, capacity between SIMO or MIMO terminals, and possibly other factors.

Third, the scheduling schemes support adaptation of the variable data rate as a function of post-processed SNRs achieved at the terminals. Each scheduled terminal can be informed when data transmission is expected, the assigned transmission antenna (s), and the data transmission rate (s) for data transmission (for example, depending on an antenna of transmission).

Fourth, planning schemes can be designed to consider sets of terminals that have similar link margins. Terminals can be grouped accordingly to their bonding properties. The planner can then consider combinations of terminals in the same group "bridging margin" when investigating mutually compatible spatial signatures. This grouping according to the link margin can improve the spectral performance of the set of planning schemes compared to that achieved by ignoring the link margins. Furthermore, by scheduling terminals with similar link margins, downlink power control can be more easily exercised (eg, over the entire set of terminals) to improve spectral reuse of the set. This can be viewed as a combination of downlink adaptive scheduling combined with SDMA for SIMO / MIMO. Planning based on tie margins is described in more detail in US Patent Application Serial No. 09 / 539,157, entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMSISSIONS OF A COMMUNICATIONS SYSTEM," filed on 30 March 2000, and US Patent Application Serial No. US 2003 013 451, entitled "METHOD AND APPARATUS FOR CONTROLLING UPLINK TRANSMSISSIONS OF A WIRELESS COMMUNICATION SYSTEM", filed May 3, 2001, both transferred to the assignee of the present invention.

MIMO communication system

Figure 5 is a block diagram of a base station 104 and terminals 106 within the MIMO communication system 100. At base station 104, a data source 512 provides data (ie, bits of information) to a transmit (TX) data processor 514. For each transmitting antenna, the TX data processor 514 (1) encodes the data according to a particular encoding scheme, (2) interleaves (i.e., reorders) the encoded data based on a particular interleaving scheme, and (3 ) raises a map of the interleaved bits into modulation symbols for one or more transmission channels selected for transmitting data. Encryption increases the reliability of data transmission. Interleaving provides temporal diversity for the encoded bits, allows data to be transferred based on an average SNR for the transmitting antenna, combats fading, and removes any additional correlation between the encoded bits to form each modulation symbol. Interleaving can further provide frequency diversity if the coded bits are transmitted over multiple frequency subchannels. In one aspect, symbol mapping and coding can be performed based on control signals provided by a scheduler 534.

Coding, interleaving, and signal mapping can be accomplished based on various schemes. Some of such schemes are described in the aforementioned US patent application US 002 468; US Patent Application Serial No. 09 / 826,481, entitled "METHOD AND APPARATUS FOR UTILIZING CHANNEL STATE INFORMATION IN A WIRELESS COMMUNICATION SYSTEM," filed March 23, 2001; and US patent application. Serial No. 09 / 776,075, entitled "CODE SCHEME FOR A WIRELESS COMMUNICATION," filed February 1, 2001, all assigned to the assignee of the present invention.

Modulation symbols from TX data processor 514 are received and demultiplexed in TX MIMO processor 520, and provides a stream of demodulation symbols for each transmit channel (e.g., each transmit antenna), one modulation symbol per slot temporary. The 520x MIMO TX processor may further precondition the modulation symbols for each selected transmission channel if the entire CSI is available (eg, the H channel response matrix). MIMO processing and the entire CSI is described in more detail in US Patent Application Serial No. 09 / 532,492, entitled "HIGH EFFICIENCY HIGH

IS 2 287 282 T3

PERFORMANCE COMMUNICATIONS SYSTEM EMPLOYING MULTI-CARRIER MODULATION ”, filed March 22, 2000, transferred to the assignee of the present invention.

If OFDM is not used, the MIMO TX processor 520 provides a stream of modulation symbols for each antenna used to transmit data. If OFDM is used, the TX MIMO processor 520 provides a stream of modulation symbol vectors for each antenna used to transmit data. And if full CSI processing is performed, the MIMO TX processor 520 provides a stream of preconditioned modulation symbols or preconditioned modulation vectors for each antenna used to transmit data. Each stream is then received and modulated by a corresponding modulator (MOD) 522 and transmitted via an associated antenna 524.

At each planned terminal 106, a number of receive antennas 552 receive the transmitted signals and each receive antenna provides a received signal up to a corresponding demodulator (DEMOD) 554. Each demodulator (or front end unit) 554 performs complementary processing to the performed on the 522 modulator. Modulation symbols from all 554 demodulators are then provided up to a receive data / MIMO processor 556 (RX) and processed to receive one or more transmitted data streams for the terminal. The MIMO / RX data processor 556 performs complementary processing to that performed by the TX data processor 514 and the TX MIMO processor 520 and provides decoded data up to a data sink 560. Processing by terminal 106 is described in more detail in US patent applications US 2005 002 468 and 09 / 775,075.

At active terminal 106 poop, RX data / MIMO processor 556 further estimates link conditions and provides CSIs (eg, post-processed SNRs or channel gain estimates). The TX data processor 562 then receives and processes the CSI, and provides processed data indicating the CSI up to one or more modulators 554. The modulator (s) 554 further conditions the processed data and transmits the CSI. back to base station 104 via a reverse channel. CSI can be reported by the terminal using various signaling techniques (eg, in total, differentially, or a combination thereof), as described in US Patent Application Serial No. 09 / 826,481.

At base station 104, the transmitted feedback signal is received by antennas 524, demodulated by demodulators 522, and provided to a data / MIMO RX processor 532. The RX data / MIMO processor 532 performs supplemental processing as performed by the TX data processor 562 and retrieves the reported CSI, which is then provided to the scheduler 534.

The scheduler 534 uses the reported CSI to perform a number of functions such as (1) selecting the set of the best terminals to transmit data, (2) assigning the available transmit antennas to the selected terminals, and ( 3) determine the coding and modulation scheme to be used by each assigned transmitting antenna. Scheduler 534 may schedule terminals to achieve high throughput capacity or based on some other performance criteria or metrics, as described above. In FIG. 5, the scheduler 534 is shown as being implanted within the base station 104. In another implementation, the scheduler 534 may be implanted within some other element of the communication system 100 (eg, a base station controller that couples and interacts with a number of base stations).

Figure 6 is a block diagram of an embodiment of a base station 104x capable of processing data for transmission to the terminals as a function of CSI available at the base station (eg, as reported by the terminals). Base station 104x is an embodiment of the transmitter portion of base station 104 in FIG. 5. Base station 104x includes (1) a TX data processor 514x that receives and processes bits of information to provide modulation symbols and (2) a 520x MIMO TX processor that demultiplexes modulation symbols for NT transmitting antennas.

In the specified embodiment shown in Figure 6, the TX data processor 514x includes a demultiplexer 608 coupled to a number of channel data processors 610, one processor for each of the NC transmission channels. The demultiplexer 608 receives and demultiplexes the aggregated information bits into a number of (up to NC) data streams, one data stream for each of the transmission channels that will be used to transmit data. Each data stream is provided up to a corresponding channel data processor 610.

In the embodiment shown in FIG. 6, each channel data processor 610 includes an encoder 612, a channel interleaver 614, and an element 616 for raising a symbol map. Encoder 612 receives and encodes the information bits in the received data stream in accordance with a particular encoding scheme to provide encoded bits. Channel interleaver 614 interleaves the coded bits based on a particular interleaving scheme to provide time diversity. And the element 616 to raise a symbol map, raises the map of the interleaved bits in the modulation symbols for the transmission channel used to transmit the data stream.

Pilot data (eg data of a known pattern) can also be encoded and multiplexed with the processed information bits. The processed pilot data may be transmitted (eg, in a time division multiplexed (TDM) fashion) on all or a subset of the transmission channels used to transmit the information bits. The pilot data can be used at the terminals to perform the channel estimation.

IS 2 287 282 T3

As shown in Figure 6, data encoding, interleaving, and modulation (or a combination thereof) can be adjusted based on available CSI (eg, as reported by terminals). In an encoding and modulation scheme, adaptive encoding is achieved using a fixed base code (for example, a 1/3 Turbo code rate) and adjusting the punch to achieve the desired encoding rate, as supported by the SNR of the transmission channel used to transmit the data. For this scheme, drilling can be done after interleaving the channel. In another coding and modulation scheme. Different encoding schemes can be used depending on the reported CSI. For example, each of the data streams can be encoded with a separate code. With this scheme, a successive cancel receiver processing scheme can be used at the terminals to detect and decode the data streams to obtain a more reliable estimate of the transmitted data streams, as described in more detail below. .

The element 616 for raising a symbol map can be designed to group interleaved bit sets to form non-binary symbols, and to map each non-binary symbol at a point in a signal constellation corresponding to a particular modulation scheme ( eg, QPSK, M-PSK, M-QAM, or some other scheme) selected by the transmission channel. Each signal point represented on the map corresponds to a modulation symbol. The number of bits of information that can be transmitted for each modulation symbol for a particular level of performance (eg, a one percent packet error rate (PER)), depends on the SNR of the transmission channel. In this way, the coding and modulation scheme for each transmission channel can be selected based on the available CSI. Channel interleaving can also be adjusted based on the available CSI.

The modulation symbols for the 514x TX data processor are provided to the 520x MIMO TX processor, which is an embodiment of the 520 MIMO TX processor in Figure 5. Within the 520x MIMO TX processor, a 622 demultiplexer receives (up to) NC symbol modulation currents of the NC channel data processors 610 and demultiplexes the received modulation symbols into a number of (NT) symbol modulation streams, one stream for each antenna used to transmit the modulation symbols. Each symbol modulation stream is provided to a corresponding modulator 522. Each modulator 522 converts the modulation symbols to an analog signal, and further amplifies, filters, modulates quadrature, and up-converts the signal to generate a modulated signal, suitable for transmitting over a wireless link.

A transmission design that implements OFDM is described in the aforementioned US patent applications US 200 500 2468 09 / 826,481, 09 / 776,075 and 09 / 532,492.

Figure 7 is a block diagram of a 106x terminal embodiment capable of implementing various aspects and embodiments of the invention. Terminal 106x is an embodiment of the receive portion of terminals 106a to 106n in FIG. 5, and implements the successive cancel receiver processing technique to receive and recover transmitted signals. The signals transmitted from (to) NT transmit antennas are received by each of the NR antennas 552a to 552r and routed to a corresponding demodulator (DEMOD) 554 (also referred to as a front end processor). Each 554 demodulator conditions (eg, filters and amplifiers) a corresponding received signal, downconverts the conditioned signal to an intermediate frequency or baseband, and digitizes the downconverted signal into samples to provide. Each 554 demodulator may further demodulate the samples with a received pilot to generate a stream of received modulation symbols, which are provided to a 556x MIMO / Rx data processor.

In the embodiment shown in Figure 7, the 556x MIMO / Rx data processor (which is an embodiment of the 556 MIMO / Rx data processor of Figure 5), includes a number of successive receiver processor stages 710 (i.e., in cascade), one stage for each of the transmitted data streams to be retrieved by terminal 106x. In a transmission processing scheme, a stream of data is transmitted on each transmission channel assigned to terminal 106x, and each stream of data is processed independently (for example, with its own coding and modulation scheme) and transmitted from a corresponding transmitting antenna. For this transmission processing scheme, the number of data streams equals the number of assigned transmission channels, which is also equal to the transmission antennas assigned to transmit data to terminal 106x (which may be a subset of the transmission antennas). transmission available). For clarity, 556x MIMO / RX data processor is described for this transmission processing scheme.

Each receiver processing stage 710 (except for the last stage 710n) includes a data / MIMO channel processor 720 coupled to an interference canceller 730, and the last stage 710n includes only a data / MIMO channel processor 720n. For the first receiver processing stage 710a, the MIMO channel / data processor 720a receives and processes the NR symbol modulation streams for demodulators 554a through 554r to provide a decoded data stream for the first transmission channel (or the first transmission channel). transmitted signal). And for each of the last stages 710b to 710h, the MIMO channel / data processor 720 for this stage receives and processes the NR modified symbol streams for the interference canceller 720 in the preceding stage to obtain a decoded data stream for the transmission channel that is being processed by this stage. Each MIMO channel / data processor 720 further provides CSI (eg, SNR) for the associated transmission channel.

For the first stage 710a of receiver processing, the interference canceller 730 receives the NR symbol modulation currents from all the Nr demodulators 554. And for each of the second to third to last stages, the interference canceller 730 receives the NR currents modulation of symbols from the canceller

ES 2 287 282 T3 of interferences in the preceding stage. Each interference canceller 730 also receives the decoded data stream from the MIMO channel / data processor 720 within the same stage, and performs the processing (e.g., encoding, interleaving, modulation, channel response, and so on) to obtain NR remodulated symbol streams that are estimates of the interference components of the received symbol modulation streams due to this decoded data stream. The remodulated symbol streams are then subtracted from the received symbol modulation streams to obtain NR symbol modulation streams that include all but the subtracted (ie, canceled) interference components. The NR symbol modulation currents are provided below for the next step.

In Figure 7, a controller 740 is shown coupled to a 556x MIMO / RX data processor and can be used to drive various stages in the successive cancel receiver processing performed by the 556x processor.

Figure 7 shows a receiver structure that can be used in a straight way when each data stream is transmitted over a corresponding transmitting antenna (ie, a data stream corresponding to each transmitted signal). In this case, each receiver processing stage 710 may be operated to recover one of the transmitted signals and provide the decoded data stream corresponding to the recovered transmitted signal. For some transmission processing schemes, a data stream can be transmitted over multiple transmitting antennas, frequency subchannels, and / or time slots to provide spatial, frequency, and temporal diversity, respectively. For these schemes, the initially processing receiver obtains a received modulation symbol stream for the transmitted signal on each transmitting antenna of each frequency subchannel. The modulation symbols for multiple transmitting antennas, frequency subchannels, and / or time slots can then be combined in a complementary manner such as demultiplexing performed at the base station. The combined modulation symbol stream is then processed to set the corresponding decoded data stream.

Figure 8A is a block diagram of a 720x data / channel MIMO processor embodiment, which is a 720x data / channel MIMO processor embodiment in Figure 7. In this embodiment, the 720x data / channel MIMO processor includes a spatial / spatio-temporal processor 810, a CSI processor 812, a selector 814, a demodulation element 818, a deinterleaver 818, and a decoder 820.

The 810 spatial / spatio-temporal processor performs linear spatial processing on the NR signals received for a non-dispersive MIMO channel (for example, with flat fade), or spatio-temporal processing on the NR signals received for a dispersive MIMO channel (for example, with frequency selective). Spatial processing can be achieved using linear spatial processing techniques such as a channel correlation matrix inversion (CCMI) technique, a least root mean square error (MMSE) technique, and others. These techniques can be used to cancel out unwanted signals or to maximize the received SNR of each of the constituent signals in the presence of noise and interference from the other signals. Spatio-temporal processing can be achieved using spatio-temporal processing techniques such as MMSE linear equalizer (MMSE-LE), a decision feedback equalizer (DFE), a maximum probability sequence estimator (MLSE), and others. The CCMI, MMSE, MMSE-LE and DFE techniques are described in more detail in US Patent Application US 2005 002 468. The DFE and MLSE techniques are also described in more detail by SL Ariyavistakul et al. a document entitled "Optimum Space-Time Processors with Dispersive Interference: Unified Analysis and Required Filter Span", IEEE Communications Transactions, vol. 7, No. 7, July 1999.

Processor 812 CSI determines the CSI for each of the channels used to transmit data. For example, the CSI processor 812 can estimate a noise covariance matrix based on received pilot signals and then calculate the SNR of the k-th transmission channel used for the data stream to be decoded. SNR can be estimated similar to conventional single and multiple pilot assisted systems, as is known in the art. the SNR for all transmission channels used to transmit data may comprise the CSI that is reported back to the base station for this transmission channel. CSI processor 812 further provides selector 814 with a control signal that identifies the particular data stream to be retrieved by this receiver processing step.

The selector 814 receives a certain number of symbol streams from the spatial / spatio-temporal processor 810 and extracts the symbol stream corresponding to the data stream to be decoded, as indicated by the communication system from the CSI processor 812 . The drawn stream of modulation symbols is then provided up to a demodulation element 814.

For the embodiment shown in Figure 6, in which the data stream for each transmission channel is independently encoded and modulated as a function of the SNR of the channel, the recovered modulation symbols for the selected transmission channel are demodulated according to a demodulation scheme (eg M-PSK, M-QAM) that is complementary to the modulation scheme used for the transmission channel. The demodulated data from demodulation element 816 is deinterleaved by a deinterleaver 818 in a manner complementary to that performed by channel interleaver 614, and the deinterleaved data is then decoded by a deinterleaver 820. a form complementary to that performed by encoder 612. For example, a Turbo decoder or a Viterbi decoder can be used for the 820 decoder if Turbo or convoluted encoding, respectively, is performed at the base station. The decoded data stream from decoder 820 represents an estimate of the transmitted data stream that is being recovered.

IS 2 287 282 T3

Figure 8B is a block diagram of an interference canceller 730x which is one embodiment of an interference canceller 730 of Figure 7. Within the 730x interference canceller, the decoded data stream from the MIMO channel / data processor 720 within the same stage is re-encoded, interleaved, and re-modulated by a channel data processor 610x to provide re-modulated symbols. which are estimates of the modulation symbols in the base station before MIMO processing and channel distortion. Channel data processor 610x performs the same data processing (eg, encoded, interleaved, and modulation) as performed at the base station for the data stream. The remodulated symbols are then provided to a channel simulator 830, which processes the symbols with the estimated channel response to provide I estimates.k, from interference due to the decoded data stream. The estimation of the channel response can be obtained based on the pilot data and / or transmitted by the base station and according to the techniques described in the US patent application US 2005 002 468 described in what precedes.

The Nr elements in vector Ik interference correspond to the component of the signal received in each of the NR receiving antennas due to the symbol stream transmitted by the kth transmitting antenna. Each element of the vector represents an estimated component due to the decoded data stream in the corresponding modulation received symbol stream. These components interface the remaining transmitted (i.e. canceled) signals from the received signal vector rk by means of an adder 832 to provide a vector rk + 1 modified having components from the withdrawn decoded data stream. The vector rk+1 Modified is provided as the input vector for the next phase of receptor processing, as shown in Figure 7.

Various aspects of successive cancellation receptor processing are described in more detail in US patent application US 2005 002 468 described above.

Receiver designs that do not employ the successive cancellation receiver processing technique can also be used to receive, process, and recover transmitted data streams. Some of such receiver designs are described in US Patent Application No.you Serial Nos. 09 / 776,075 and 09 / 826,481 mentioned above, and in US Patent Application Serial No. 09 / 532,492, entitled "HIGH EFFICIENCY HIGH PERFORMANCE COMMUNICATIONS SYSTEM EMPLOYING MULTI-CARRIER MODULATION" filed March 30, 2000, assigned to the assignee of the present invention, and incorporated herein by reference.

For simplicity, various aspects and embodiments of the invention have been described in which the CSI comprises SNR. In general, the CSI can comprise any type of information that is indicative of the characteristics of the communications link. Various types of information can be provided as CSIs, some examples of which are described below.

In one embodiment, the CSI comprises a signal-to-noise-plus-interference (SNR) ratio, which is obtained as the ratio of signal power over noise power plus interference. The SNR is typically estimated and provided for each transmission channel used to transmit data (eg, each transmitted data stream), although an aggregated SNR can also be provided for a number of transmission channels. The SNR estimate may be quantized respectively of a value having a particular number of bits. In one embodiment, the SNR estimate is mapped as an SNR index, eg, using a look-up table.

In another embodiment, the CSI comprises signal power and interference plus noise power. These two components can be obtained separately and are provided for each transmission channel used to transmit data.

In still another embodiment, the CSI comprises signal power, cyan power, and noise power. These three components can be obtained and provided for each transmission channel used to transmit data.

In yet another embodiment, the CSI comprises a signal-to-noise ratio plus a list of interference powers for each observable interference term. This information can be obtained and provided for each transmission channel used to transmit data.

In yet another embodiment, the CSI comprises matrix-shaped signal components (e.g., NT x NT complex inputs for all transition-receive antenna pairs) and matrix-shaped noise plus interference components (e.g., NT x NT complex inputs). The base station can then suitably combine the signal components and the noise plus interference components for the appropriate transmit-receive antenna pairs to obtain the quality for each transmit channel used to transmit data. (eg post-processed SNR for each transmitted data stream, as received at terminals).

In yet another embodiment, the CSI comprises a data rate indicator for each transmitted data stream. The quality of a transmission channel to be used to transmit data can be determined initially (for example, based on the estimated SNR for the transmission channel) and a data transmission rate corresponding to the quality of the determined channel can be identified. , then, (for example, based on a lookup table). The identified data transmission rate is indicative of the maximum data transmission rate

ES 2 287 282 T3 that can be transmitted on the transmission channel for the required level of performance. The data rate is then mapped and represented by a data rate indicator (DRI), which can be efficiently coded. For example, if (up to) seven possible data rates are supported by the base station for each transmitting antenna, then a 3-bit value can be used to represent the DRI, where, for example, a zero can indicate a Data rate of zero (that is, it does not use the transmitting antenna) and 1 to 7 can be used to indicate seven different data rates. In a typical deployment, quality measures (eg, SNR estimates) are directly mapped according to the DRI, based on, for example, a look-up table.

In another embodiment, the CSI comprises power control information for each transmission channel. The power control information may include a single bit for each transmission channel to indicate a request for both more and less power, or it may include multiple bits to indicate the magnitude of the required power level change. In this embodiment, the base station can make use of the feedback power control information from the terminals to adjust the data processing and / or transmit power.

In yet another embodiment, the CSI comprises an indication of the particular processing scheme that will be used at the base station for each transmitted data stream. In this embodiment, the indicator can identify the particular coding scheme and the particular modulation scheme that will be used for the transmitted data stream such that the desired level of performance is achieved.

In yet another embodiment, the CSI comprises a differential indicator for a particular quality measure for a transmission channel. Initially, the SNR or DRI or some other quality measure for the transmission channel is determined and reported as a reference measure value. Hereinafter, the transmission channel quality monitoring continues, and the difference between the last reported measurement and the current measurement is determined. The difference can then be quantized to one or more bits, and the quantized difference is mapped and represented by a differential indicator, reported below. The differential indicator can indicate raising or lowering the last reported measure using a particular stage size (or keeping the last reported measure). For example, the differential indicator may indicate that (1) the SNR for a particular transmission channel has increased or decreased by a particular stage size, or (2) the data rate would be adjusted by a particular amount, or some another change. The reference measure can be transmitted periodically to ensure that errors in differential indicators and / or erroneous reception of these indicators do not accumulate.

Other forms of CSI are also used within the scope of the invention. In general, the CSI includes enough information in any form that can be used to fine-tune the process at the base station such that the desired level of performance is achieved for the transmitted data streams.

The CSI can be obtained based on the signals transmitted from the base station and received at the terminals. In one embodiment, the CSI is derived based on a pilot reference included in the transmitted signals. Alternatively or additionally, the CSI can be obtained based on the data included in the transmitted signals.

In yet another embodiment, the CSI comprises one or more signals transmitted in the uplink form from the terminals to the base station. In some planning schemes, a degree of correlation may exist between uplink and downlink systems (for example, Time Division Duplexed (TDD) where the uplink and downlink share the same bandwidth. a time division multiplexed form). In these systems, the quality of the downlink can be estimated (to a required degree of precision) based on the quality of the uplink, which can be estimated based on signals (e.g. pilot signals), transmitted from the terminals. . The pilot signals would then represent a means by which the base station could estimate the CSI when viewed from the terminals.

Signal quality can be estimated at terminals based on various techniques. Some of these techniques are described in the following patents, which are assigned to the assignees of the present application, are cited here, in the following:

• US Patent No. 5,799,005, entitled "SYSTEM AND METHOD FOR DETERMINING RECEIVED PILOT POWER AND PATH LOSS IN A CDMA COMMUNICATION SYSTEM," issued August 25, 1998 • US Patent No. No. 5,903,554, entitled “METHOD AND APPARATUS FOR MEASURING LINK QUALITY INA SPREAD SPRECTRUM COMMUNICATION SYSTEM,” published May 11, 1999.

• US patents no.you 5,056,109 and 5,265,119, both entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER INA CDMA CELLULAR MOBILE TELEPHONE SYSTEM", published respectively on October 8, 1991 and November 23, 1993, and • US Patent US No. 6,097,972, entitled “METHOD AND APPARATUS FOR PROCESSING POWER CONTROL SIGNALS IN CDMA MOBILE TELEPHONE SYSTEM,” published August 1, 2000.

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Procedures for estimating a single transmission channel based on a pilot signal or data transmission can also be found in a number of documents available in the art. One such channel estimation procedure is described by F. Ling in a paper entitled "Optimal Reception, Performance Bound, and Cutoff-Rate Analysis of References-Assisted Coherent CDMA Communications with Applications," IEEE Communications Transactions, October 1999.

Various types of CSI information and various CSI reporting mechanisms are also described in US Patent Application Serial No. 08 / 963,386, entitled "METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION", filed November 3, 1997, transferred to the present application and in "TIE / BIA / INSTRUMENTOS-856 cdma2000 High Rate Packet Data Air Interface Specification".

The CSI can report back to the base station using various CSI transmission schemes. For example, the CSI can be sent in total, differentially, or a combination of both. In one embodiment, the CSI is reported periodically, and differential updates are sent based on the previous CSI transmitted. In another embodiment, the CSI is sent only when there is a change (eg, if the change exceeds a particular threshold), which may be less than the effective transmission rate of the feedback channel. As an example, SNRs can be sent backward (eg differentially) only when it changes. For an OFDM system (with or without MIMO), the frequency domain correlation can be exploited to allow reduction in the amount of CSI to be fed back. As an example of an OFDM system, if the SNR corresponding to a particular spatial subchannel for NM subchannels frequency is the same, the SNR and the first and last frequency subchannels for which this condition is true can be reported. Other compression and feedback channel error recovery techniques to reduce the amount of data fed back by the CSI can also be used and are within the scope of this invention.

Base station elements and terminals can be implanted with one or more digital signal processors (DSP), single application specific integrated circuits (ASIC), processors, microprocessors, controllers, microcontrollers, in-situ programmable gate array ( FPGA), programmable logic devices, other electronic units, or any combination thereof. Some of the functions and processes described herein can also be implemented with a computer application executed by a processor.

Certain aspects of the invention can be implemented with a combination of information software and information hardware. For example, the processing for scheduling (ie, selecting terminals and assigning transmit antennas) can be performed based on program codes executed by a processor (scheduler 534 in FIG. 5).

Headings have been included herein by reference and to aid in locating certain sections. These headings are not intended to limit the scope of the concepts described in them, and these concepts may have applicability in other sections throughout the specification.

The previous description of the described embodiments is provided to enable any person skilled in the art to make use of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein will apply to other embodiments without departing from the scope of the invention as defined in the appended set of claims.

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Priority claims
Document	Office	Kind	Date
20010859345	United States of America	–	2001-05-16
85934501	United States of America	A	2001-05-16
85934501	United States of America	A	2001-05-16
85934502737005	–	–	–
US20010859345	–	–	–

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CA2446877A1	Canada	A1	2002-11-21
WO02093819A1	World Intellectual Property Organization (WIPO)	A1	2002-11-21
US2003087673A1	United States of America	A1	2003-05-08
TW545074B	Taiwan Province of China	B	2003-08-01
NO20035072D0	Norway	D0	2003-11-14
US6662024B2	United States of America	B2	2003-12-09
KR20030096405A	Republic of Korea	A	2003-12-24
EP1388231A1	European Patent Office (EPO)	A1	2004-02-11
MXPA03010414A	Mexico	A	2004-04-02
IL158760A0	Israel	A0	2004-05-12
IL158760D0	Israel	D0	2004-05-12
CN1522512A	China	A	2004-08-18
BR0209636A	Brazil	A	2004-08-31
JP2004535106A	Japan	A	2004-11-18
HK1065665A	Hong Kong, China	A	2005-02-25
HK1065665A1	Hong Kong, China	A1	2005-02-25
RU2003136165A	Russian Federation	A	2005-05-27
UA74882C2	Ukraine	C2	2006-02-15
RU2294599C2	Russian Federation	C2	2007-02-27
AU2002309974B2	Australia	B2	2007-03-01
EP1388231B1	European Patent Office (EPO)	B1	2007-06-20
AT365405T	Austria	T	2007-07-15
ATE365405T1	Austria	T1	2007-07-15
US7248879B1	United States of America	B1	2007-07-24
DE60220783D1	Germany	D1	2007-08-02
EP1830509A2	European Patent Office (EPO)	A2	2007-09-05
ES2287282T3This record	Spain	T3	2007-12-16
US2008013638A1	United States of America	A1	2008-01-17
DE60220783T2	Germany	T2	2008-03-06
IL158760A	Israel	A	2008-08-07
EP1830509A3	European Patent Office (EPO)	A3	2009-04-08
CN100505607C	China	C	2009-06-24
KR100938302B1	Republic of Korea	B1	2010-01-22
JP4537004B2	Japan	B2	2010-09-01
US7907972B2	United States of America	B2	2011-03-15
US2011261899A1	United States of America	A1	2011-10-27
CA2446877C	Canada	C	2013-01-29
US8489107B2	United States of America	B2	2013-07-16
EP1830509B1	European Patent Office (EPO)	B1	2013-10-09
ES2436766T3	Spain	T3	2014-01-07
BRPI0209636B1	Brazil	B1	2015-12-01

Method and apparatus for allocating resources in a multiple-input multiple-output (MIMO) communication system

Abstract

Term

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DESCRIPTION

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TABLE 3

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Priority claims5

Members41

Numbers

Titles2

Classification