Method and apparatus for antenna selection in a mimo system
Abstract
An antenna selection apparatus in a MIMO system, comprising: means for selecting M virtual transmission antennas among V virtual transmission antennas, in which M is one or more and V is equal to or greater than M; in which an orthonormal matrix of dimensions TxV is used to form the V virtual transmission antennas, in which the orthonormal matrix is defined so that a sum of a squared magnitude of the V inputs in each row is equal to a value constant, and in which a permutation matrix is used to select the virtual M transmission antennas; means for correlating output symbols with the virtual M antennas; and means for providing the correlated output symbols for transmission from T transmission antennas, in which T is equal to or greater than V and T represents a certain number of physical transmission antennas.

Term
Term ended
Projected expiry passed 22 August 2026, 0.1 years ago.
- Priority
- Filed
- Published
- Projected expiry
- Today
33 claims: 2 independent, 31 dependent
- 1ES 2 525 474 T3 REIVINDICACIONES 1. Un aparato de selección de antenas en un sistema de MIMO, que comprende:medios para seleccionar M antenas de transmisión virtuales entre V antenas de transmisión virtuales, en el que M es uno o más y V es igual o mayor que M;en el que una matriz ortonormal de dimensiones TxV es usada para formar las V antenas de transmisión virtuales, en el que la matriz ortonormal está definida de modo que una suma de una magnitud al cuadrado de las V entradas en cada fila sea igual a un valor constante, y en el que una matriz de permutación es usada para seleccionar las M antenas de transmisión virtuales;medios para correlacionar símbolos de salida con las M antenas virtuales;y medios para proporcionar los símbolos de salida correlacionados para su transmisión desde T antenas de transmisión, en el que T es igual o mayor que V y T representa un cierto número de antenas de transmisión físicas.
- 2El aparato de la reivindicación 1, que comprende adicionalmente:medios para seleccionar distintos conjuntos de M antenas virtuales entre las V antenas virtuales para distintas sub-portadoras.
- 3El aparato de la reivindicación 1, que comprende adicionalmente:medios para aplicar T distintos retardos cíclicos para las T antenas de transmisión.
- 4El aparato de la reivindicación 1, que comprende adicionalmente:medios para transmitir una señal piloto por las M antenas de transmisión virtuales.
- 5El aparato de la reivindicación 1, en el cual los medios para seleccionar, los medios para correlacionar y los medios para proporcionar los símbolos de salida correlacionados para su transmisión comprenden:al menos un procesador;y el aparato comprende además: una memoria acoplada con dicho al menos un procesador.
- 6El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar un conjunto de M antenas de transmisión virtuales para cada una entre una pluralidad de sub-portadoras de frecuencia, recorriendo las V antenas de transmisión virtuales.
- 7El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para formar una matriz de permutación, indicativa de las M antenas de transmisión virtuales seleccionadas entre las V antenas de transmisión virtuales, para aplicar la matriz de permutación a los símbolos de salida, y para aplicar una matriz ortonormal usada para formar las V antenas de transmisión virtuales.
- 8El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar una antena de transmisión virtual entre V antenas de transmisión virtuales para un primer receptor asignado con un primer conjunto de sub-portadoras, para seleccionar más de una antena de transmisión virtual entre las V antenas de transmisión virtuales para un segundo receptor asignado con un segundo conjunto de sub-portadoras, para correlacionar símbolos de salida para el primer receptor con el primer conjunto de sub-portadoras de dicha antena de transmisión virtual, y para correlacionar símbolos de salida para el segundo receptor con el segundo conjunto de sub-portadoras de dichas más de una antenas de transmisión virtuales.
- 9El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para ajustar a escala símbolos de salida para las M antenas de transmisión virtuales con M ganancias.
- 10El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para transmitir una primera señal piloto por una primera antena de transmisión virtual entre las V antenas de transmisión virtuales, y para transmitir una segunda señal piloto por las restantes antenas de las V antenas de transmisión virtuales.
- 11El aparato de la reivindicación 10, en el cual dicho al menos un procesador está configurado para transmitir la primera señal piloto por un primer conjunto de sub-portadoras de la primera antena de transmisión virtual, y para transmitir la segunda señal piloto por un segundo conjunto de sub-portadoras, recorriendo las restantes antenas de las V antenas de transmisión virtuales.
- 12El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para transmitir símbolos piloto por al menos una sub-portadora en al menos un periodo de símbolos, seleccionado en base a un patrón de señales piloto.
- 13El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar una ES 2 525 474 T3 matriz ortonormal entre una pluralidad de matrices ortonormales disponibles para formar las V antenas de transmisión virtuales.
- 14El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para recibir retroalimentación que selecciona una matriz ortonormal entre una pluralidad de matrices ortonormales disponibles para formar las V antenas de transmisión virtuales.
- 15El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para generar símbolos de multiplexado por división ortogonal de frecuencia, OFDM, para las T antenas de transmisión, en base a los símbolos de salida correlacionados.
- 16El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para generar símbolos de acceso múltiple por división de frecuencia de portadora única, SC-FDMA, para las T antenas de transmisión, en base a los símbolos de salida correlacionados.
- 17El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar dinámicamente M, en base a las condiciones de canal.
- 18El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar dinámicamente V, en base a las condiciones de canal.
- 19El aparato de la reivindicación 5, en el cual una matriz ortonormal, usada para formar las V antenas de transmisión virtuales, es definida de modo que se use igual potencia de transmisión para las T antenas de transmisión.
- 20El aparato de la reivindicación 5, en el cual una matriz ortonormal, usada para formar las V antenas de transmisión virtuales, está basada en una matriz de Fourier o una matriz de Walsh.
- 21El aparato de la reivindicación 5, en el cual una matriz ortonormal, usada para formar las V antenas de transmisión virtuales, está basada en el ajuste a escala de una matriz de Fourier o una matriz de Walsh, con distintas fases aleatorias.
- 22El aparato de la reivindicación 5, en el cual dicho al menos un procesador está configurado para seleccionar M1 antenas de transmisión virtuales, a usar para la transmisión a un primer receptor, entre las V antenas de transmisión virtuales, para seleccionar M2 antenas de transmisión virtuales, a usar para la transmisión a un segundo receptor, entre las V antenas de transmisión virtuales, para correlacionar símbolos de salida para el primer receptor con las M1 antenas de transmisión virtuales, para correlacionar símbolos de salida para el segundo receptor con las M2 antenas de transmisión virtuales, para proporcionar los símbolos de salida correlacionados para el primer receptor, para su transmisión por una primera sub-portadora de las T antenas de transmisión, y para proporcionar los símbolos de salida correlacionados para el segundo receptor, para su transmisión por una segunda sub-portadora de las T antenas de transmisión, en el que tanto M1 como M2 son iguales a uno, o mayores, y V es igual o mayor que el mayor entre M1 y M2.
- 23El aparato de la reivindicación 22, en el cual M1 no es igual a M2.
- 24El aparato de la reivindicación 22, en el cual las sub-portadoras primera y segunda son una sub-portadora, y en el cual las transmisiones son enviadas a los receptores primero y segundo usando el acceso múltiple por división espacial, SDMA.
- 25El aparato de la reivindicación 5, en el cual:dicho al menos un procesador está configurado para correlacionar símbolos de salida con la pluralidad de antenas, en base a al menos un patrón de correlación seleccionado entre una pluralidad de patrones de correlación, en el que cada patrón de correlación indica una correlación específica de un símbolo de salida con la pluralidad de antenas.
- 26El aparato de la reivindicación 25, en el cual dicho al menos un procesador está configurado para seleccionar distintos patrones de correlación para distintas sub-portadoras en un periodo de símbolos.
- 27El aparato de la reivindicación 25, en el cual dicho al menos un procesador está configurado para seleccionar distintos patrones de correlación para periodos de símbolos.
- 28El aparato de la reivindicación 25, en el cual dicho al menos un procesador está configurado para seleccionar distintos patrones de correlación entre la pluralidad de patrones de correlación para distintas sub-portadoras o distintos periodos de símbolos, en base a un patrón predeterminado.
- 29El aparato de la reivindicación 25, en el cual dicho al menos un procesador está configurado para aplicar una columna distinta de una matriz ortonormal para cada una entre una pluralidad de sub-portadoras, de acuerdo a un patrón predeterminado, en el cual la matriz ortonormal incluye una pluralidad de columnas para la pluralidad de patrones de ES 2 525 474 T3 correlación.
- 30Un procedimiento de selección de antenas en un sistema de MIMO que comprende:seleccionar M antenas de transmisión virtuales, a usar para la transmisión, entre V antenas de transmisión virtuales, en el que M es uno o más y V es igual o mayor que M, 5 en el que una matriz ortonormal de dimensiones TxV es usada para formar las V antenas de transmisión virtuales, en el que la matriz ortonormal está definida de modo que una suma de una magnitud al cuadrado de las V entradas en cada fila sea igual a un valor constante, y en el que una matriz de permutación es usada para seleccionar las M antenas de transmisión virtuales;correlacionar símbolos de salida con las M antenas virtuales;y 10 proporcionar los símbolos de salida correlacionados para su transmisión desde T antenas de transmisión, en el que T es igual o mayor que V y T representa un número total de antenas de transmisión físicas.
- 31El procedimiento de la reivindicación 30, que comprende adicionalmente:seleccionar distintos conjuntos de M antenas virtuales entre las V antenas virtuales para distintas sub-portadoras.
- 32El procedimiento de la reivindicación 30, que comprende adicionalmente:15 aplicar T distintos retardos cíclicos para las T antenas de transmisión.
- 33El procedimiento de la reivindicación 30, que comprende adicionalmente:transmitir una señal piloto por las M antenas de transmisión virtuales.
Independent claims33
167 paragraphs in 9 sections, as filed
ES 2 525 474 T3
DESCRIPTION
Procedure and apparatus for selection of antennas in a MIMO system
This application claims priority over US Provisional Application Serial No. 60 / 710,408, entitled "Procedure and Apparatus for Antenna Diversity in Multiple Input and Multiple Output Communication Systems", filed on August 22, 2005 and the United States Provisional Application Serial No. 60 / 711,144, entitled "Procedure and apparatus for the diversity of antennas in communication systems of multiple inputs and multiple outputs", filed on August 24, 2005, both assigned to the assignee of this application. The present application is additionally related to the United States Patent Application, legally transferred, with Serial Number to be determined, entitled "Adaptive Sectorization in Cellular Systems", filed on the same day as the present application.
Background
I. Field
The present disclosure relates generally to communication and more specifically to transmission schemes for wireless communication.
II. Background
In a wireless communication system, a transmitter (e.g. base station or terminal) can use multiple (T) transmit antennas for data transmission to a receiver equipped with one or more (R) receive antennas. . Multiple transmit antennas can be used to increase the throughput of the system by transmitting different data from these antennas and / or to improve reliability by transmitting data redundantly. For example, the transmitter can transmit a given symbol from all the T transmitting antennas, and the receiver can receive multiple versions of this symbol via the R receiving antennas. These multiple versions of the transmitted symbol generally improve the receiver's ability to retrieve the symbol.
Transmission performance can be improved by exploiting the spatial dimension obtained with multiple transmitting antennas and, if present, multiple receiving antennas. There is a propagation path between each pair of transmitting and receiving antennas. TR distinct propagation paths are formed between the T transmitting antennas and the R receiving antennas. These propagation paths can experience different channel conditions (e.g. g., different fading, multipath, and interference effects) and can achieve different signal-to-noise ratios (SNR). Channel responses for TR propagation paths may vary from path to path and may further vary between frequencies for a spreader wireless channel and / or over time for a time-varying wireless channel.
A serious drawback to using multiple transmitting antennas for data transmission is that the channel response between each pair of transmitting and receiving antennas (or each propagation path) usually needs to be estimated in order to properly receive the data transmission. . Estimating the full channel response for all TR transmit and receive antenna pairs may be undesirable for several reasons. First, a large amount of link resources can be consumed in order to transmit a pilot signal used for channel estimation, which, in turn, reduces the link resources available to transmit data. Second, channel estimation for all TR transmit and receive antenna pairs increases the processing overhead at the receiver.
US Patent Publication No. US2004 / 0203347 discloses the selection of a set of antennas for use in a wireless communication system.
There is, therefore, a need in the art for transmission schemes that can alleviate the need to estimate the complete channel response for all pairs of transmitting and receiving antennas.
Summary
This need is satisfied by the invention as defined in the independent claims. Further developments of the invention are the subject of the dependent claims.
Transmission schemes that can flexibly achieve the desired spatial multiplexing order, spatial diversity order, and channel estimation overhead order are described herein. The order of spatial multiplexing determines the number of symbols to be sent simultaneously by a sub-carrier in a symbol period, the order of spatial diversity determines the magnitude of spatial diversity observed by the transmitted symbols and the order of channel estimation overhead determines the magnitude of pilot signal overload.
ES 2 525 474 T3
In one embodiment, as defined in the appended claims for a data transmission from a transmitter to a receiver, the sub-carriers assigned to the receiver and the spatial multiplexing order (M) for the receiver are determined, where M> 1. For each assigned sub-carrier, M virtual antennas are selected among V virtual antennas, formed with V columns of an orthonormal matrix, where V> M. V can be selected to achieve the desired order of spatial diversity and order of channel estimation overhead. The M virtual antennas for each assigned subcarrier can be selected in various ways, as described below. The output symbols for the receiver are correlated with the M virtual antennas selected for each assigned sub-carrier, applying the orthonormal matrix. The pilot symbols are also correlated with the V virtual antennas. The output symbols and the correlated pilot symbols (or transmit symbols) are provided for transmission from T physical transmitting antennas, where T> V. The transmitting symbols (e.g. OFDM symbols or SC- symbols) FDMA) are generated for each transmitting antenna based on the transmitting symbols for that transmitting antenna. Different cyclic delays can be applied to the transmit symbols for the T transmit antennas.
Various aspects and embodiments of the invention are described in greater detail below.
Brief description of the drawings
The characteristics and nature of the present invention will become more apparent from the detailed description set forth below, when considered in conjunction with the drawings, in which like reference characters identify correspondingly in their entirety.
FIG. 1 shows a wireless communication system.
FIGs. 2A and 2B show, respectively, MISO and MIMO channels.
FIG. 3 shows a transmission scheme with virtual antennas.
FIG. 4 shows a transmission scheme with virtual antennas and cyclic delay diversity.
FIG. 5 shows a MIMO transmission going through the virtual antennas.
FIGs. 6A, 6B and 6C show three exemplary subcarrier structures.
FIG. 7 shows an exemplary frequency hopping scheme.
FIG. 8 shows an exemplary pilot scheme for symbol rate hopping.
FIGs. 9A through 9D show four exemplary pilot schemes for block hopping.
FIG. 10 shows a process for transmitting data and pilot signals to one or more receivers.
FIG. 11 shows an apparatus for transmitting data and pilot signals to one or more receivers.
FIG. 12 shows a block diagram of a base station and two terminals.
Detailed description
The word "exemplary" is used herein to mean "serving as an example, case, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
FIG. 1 shows a wireless communication system 100 with multiple base stations 110 and multiple terminals 120. A base station is a station that communicates with terminals. A base station may also be called, and may contain some of, or all, the functionality of, an access point, a Node B, and / or some other network entity. Each base station 110 provides communication coverage for a specific geographic area 102. The term "cell" may refer to a base station and / or its coverage area, depending on the context in which the term is used. To improve system capacity, a coverage area of a base station can be divided into multiple smaller areas, e.g. eg, three smaller areas 104a, 104b, and 104c. Each smaller area is served by a respective base transceiver subsystem (BTS). The term "sector" may refer to a BTS and / or its coverage area, depending on the context in which the term is used. For a sectorized cell, the BTSs for all sectors of that cell are usually co-located within the base station for the cell. The transmission techniques described herein can be used for the system described in the aforementioned US Patent Application Serial No. [Agent File No. 05091]. For simplicity, in the following description, the term "base station" is used generically for a BTS serving a sector, as well as for a base station serving a cell.
ES 2 525 474 T3
Terminals 120 are typically dispersed throughout the system, and each terminal can be fixed or mobile. A terminal can also be called, and can contain some of, or all, the functionality of, a mobile station, user equipment, and / or some other device. A terminal can be a wireless device, a cell phone, a personal digital assistant (PDA), a wireless modem card, and so on. Each terminal can communicate with zero, one, or multiple base stations on the downlink and uplink at any given time. The downlink (or forward link) refers to the communication link from the base stations to the terminals, and the uplink (or reverse link) refers to the communication link from the terminals to the base stations.
For a centralized architecture, a system controller 130 couples with base stations 110 and provides coordination and control for these base stations. For a distributed architecture, the base stations can communicate with each other as needed.
The transmission techniques described herein can be used for various wireless communication systems, such as an orthogonal frequency division multiple access system (OFDM), a single carrier frequency division multiple access system (SC- FDMA), a frequency division multiple access (FDMA) system, a code division multiple access (CDMA) system, a time division multiple access (TDMA) system, a spatial division multiple access (SDMA) system, etc. An OFDMA system uses orthogonal frequency division multiplexing (OFDM), which is a multi-carrier modulation technique that divides the overall system bandwidth into multiple (K) orthogonal subcarriers. These sub-carriers can also be called tones, containers, etc. With OFDM, each sub-carrier is associated with a respective sub-carrier that can be modulated with data. An SC-FDMA system can use interleaved FDMA (IFDMA) to transmit on sub-carriers that are distributed over the system bandwidth, localized FDMA (LFDMA) to transmit on a block of adjacent sub-carriers, or the Enhanced FDMA (EFDMA) for transmitting on multiple adjacent subcarrier blocks. In general, modulation symbols are sent in the frequency domain with OFDM and, in the time domain, with SC-FDMA.
An OFDM symbol can be generated for a transmitting antenna in a symbol period, according to the following. N modulation symbols are correlated with N sub-carriers used for transmission (or N assigned sub-carriers) and zero symbols with signal value equal to zero are correlated with the remaining K - N sub-carriers. An inverse fast Fourier transform (IFFT), or an inverse discrete Fourier transform (IDFT), of K points is performed on the K modulation symbols and the zero symbols, to obtain a sequence of K time domain samples. The last Q samples of the sequence are copied to the beginning of the sequence to form an OFDM symbol containing K + Q samples. The Q copied samples are often called a cyclic prefix or guard interval, and Q is the length of the cyclic prefix. The cyclic prefix is used to combat inter-symbol interference (ISI) caused by selective frequency fading, which is a frequency response that varies across the system bandwidth.
An SC-FDMA symbol can be generated for a transmitting antenna in a symbol period, according to the following. N modulation symbols to be sent by N assigned subcarriers are transformed to the frequency domain with a fast Fourier transform (FFT), or a discrete Fourier transform (DFT) of N points, to obtain N symbols of the domain of the frequency. These N frequency domain symbols are mapped to the assigned N subcarriers, and the zero symbols are mapped to the remaining KN subcarriers. A K point IFFT or IDFT is then performed on the K frequency domain symbols and zero symbols to obtain a sequence of K time domain samples. The last Q samples of the sequence are copied to the beginning of the sequence to form an SC-FDMA symbol containing K + Q samples.
A transmit symbol can be an OFDM symbol or an SC-FDMA symbol. The K + Q samples of a transmit symbol are transmitted in K + Q sample / segment periods. A symbol period is the duration of a transmit symbol and is equal to K + Q sample / segment periods.
The transmission techniques described herein can be used for the downlink as well as the uplink. For clarity, much of the following description is for downlink transmission from a base station (a transmitter) to one or more terminals (receivers). For each sub-carrier, the base station can transmit to one terminal without SDMA or to multiple terminals with SDMA.
FIG. 2A shows a multi-input, single-output (MISO) channel made up of multiple (T) transmit antennas 112a to 112t at base station 110 and a single receive antenna 122x at terminal 120x. The MISO channel can be characterized by a channel response row vector h (k) of dimensions 1 x T, for each sub-carrier k, which can be expressed as:
h (k) = [hi (k) h2 (k) ... hT (k)], Eq. (1) where h (k), for i = 1, ..., T, indicates the coupling or gain Channel complex between the transmitting antenna i and the only receiving antenna for sub-carrier k.
ES 2 525 474 T3
FIG. 2B shows a multiple input multiple output (MIMO) channel formed by T transmit antennas 112a to 112t at base station 110 and multiple (R) receive antennas 122a to 122r at terminal 120y. The MIMO channel can be characterized by a channel response matrix H (/ i) of dimensions RxT for each sub-carrier k, which can be expressed as:
<img file="ES2525474T3_D0001.tif" />
where hj¡ (k), for j = 1, R ei = 1, T, indicates the complex channel gain between transmitting antenna i and receiving antenna j for sub-carrier k, and h¡ (/ <) is a channel response vector of dimensions Rx1 for transmitting antenna i, which is the Nth column of H (/ i).
The transmitter can transmit one or more output symbols from the T transmit antennas for each sub-carrier in each symbol period. Each output symbol can be a modulation symbol for OFDM, a frequency domain symbol for SC-FDMA, or some other complex value. Data transmission can be quantified by the following metrics:
* Spatial multiplexing order (M) - the number of output symbols transmitted by the T transmitting antennas by a sub-carrier in a symbol period;
* Order of spatial diversity (D) - the magnitude of spatial diversity observed by the transmitted output symbols; and * Channel estimation overload order (C) - the number of virtual antennas to be estimated by a receiver for each receiving antenna.
In general, M <min {T, R}, D <T, and C <T. Spatial diversity refers to transmit diversity resulting from the use of multiple transmit antennas and does not include receive diversity resulting from use of multiple transmitting antennas. receiving antennas.
If the transmitter transmits output symbols directly from the T transmit antennas, then a receiver typically needs to estimate the full channel response for all the T transmit antennas in order to recover the data transmission. The channel estimation overhead order is then C = T. In certain scenarios, it may be desirable to transmit less than T output symbols simultaneously, eg. eg, if channel conditions are bad. A subset of the T transmit antennas can be used to transmit less than T output symbols. However, this is undesirable, since the transmit powers available to the unused transmit antennas are not judiciously employed for the transmission.
The transmission schemes described herein allow a flexible selection of the three metrics M, D and C in order to achieve good performance for data transmission under different conditions. For example, a higher order M of spatial multiplexing may be selected for good channel conditions with high SNRs, and a lower order of spatial multiplexing may be selected for poor channel conditions with low SNRs. A lower channel estimation overhead order C can be selected, e.g. For example, in scenarios where low flow, due to low SNRs, does not justify a large channel estimation overhead.
The transmission schemes described herein can use all T transmit antennas for transmission, regardless of the number of output symbols sent and regardless of which subcarriers are used for transmission. This capability allows the transmitter to use all the transmit power available for the T transmit antennas, eg. eg, using the power amplifiers coupled with each of the antennas, for transmission, which generally improves performance. Using less than T transmit antennas for transmission usually results in less than all available transmit power being used for transmission, which would affect performance.
The transmission schemes described herein can immediately support MIMO, single input multiple output (SIMO) and single input single output (SISO) transmissions. A MIMO stream is a transmission of multiple output symbols from multiple virtual antennas to multiple
ES 2 525 474 T3 receiving antennas by a sub-carrier in a symbol period. A SIMO transmission is a transmission of a single output symbol from a virtual antenna to multiple receiving antennas by a sub-carrier in a symbol period. An SISO transmission is a transmission of a single output symbol from a virtual antenna to a receiving antenna by a sub-carrier in one symbol period. The transmitter can also send a combination of MIMO, SIMO and / or SISO transmissions to one or more receivers in a symbol period.
The transmitter can transmit M output symbols simultaneously from the T transmit antennas on a subcarrier in a symbol period, using various transmission schemes. In one embodiment, the transmitter processes the output symbols for transmission, as follows:
x (k) = U · P (k) · s (k), Eq. (3) where s (k) is a vector of dimensions Mx1 that contains M output symbols to be sent by sub-carrier k in a period of symbols;
P (k) is a permutation matrix of dimensions VxM for subcarrier k;
U = [U1 U2 ... Uv] is an orthonormal matrix of dimensions TxV; Y
X (k) is a vector of dimensions Tx1 containing T transmission symbols to be sent from the T transmission antennas on sub-carrier k in a symbol period.
V is the number of virtual antennas formed with the orthonormal matrix U. In general, 1 <M <V <T. V can be a fixed value or a configurable value.
The orthonormal matrix U is characterized by the property U<sup>H</sup> · U =], where “<sup>H</sup>"Indicates a conjugate transpose and J is the identity matrix. The V columns of U are orthogonal to each other, and each column has unit power. In one embodiment, U is defined so that the sum of the squared magnitude of the V entries in each row equals a constant value. This property results in the same transmit power being used for all T transmit antennas. U can also be a unitary matrix that is characterized by the property U<sup>H</sup> U = U U<sup>H</sup> = l · Orthonormal and unit matrices can be formed as described below. The V columns of U are used to form V virtual antennas that can be used to send up to V output symbols on a sub-carrier in one symbol period. Virtual antennas can also be called effective antennas or with some other terminology.
In one embodiment, a single orthonormal matrix U is used for all K total subcarriers in all symbol periods, so that U is not a function of subcarrier index k or symbol index n. In another embodiment, different orthonormal matrices are used for different sets of subcarriers that can be assigned to different receivers. In yet another embodiment, different orthonormal matrices are used for different subcarriers. In yet another embodiment, different orthonormal matrices are used for different time intervals, where each time interval may span one or more periods of multiple symbols. In yet another embodiment, one or more orthonormal matrices are selected for use from multiple orthonormal matrices, as described below. In general, data and pilot symbols can be transmitted using one or more orthonormal matrices, so that a receiver is able to estimate the channel response based on the pilot signal and use the channel response estimate to retrieve the data. sent to the receiver.
The permutation matrix P (k) selects which M virtual antennas to use for the sub-carrier k among the V virtual antennas available for use, or which M among the V columns of U. The permutation matrix P (k) can be defined in various ways, and different permutation matrices can be used for different subcarriers, as described below.
FIG. 3 shows a model 300 for the transmission scheme given by equation (3). The transmitter receives the data vector S (k) for each sub-carrier and symbol period used for transmission. A virtual antenna correlator 310 processes the data vector s (k) and generates the transmission vector x (k). Within the virtual antenna correlator 310, a virtual antenna-symbol correlation unit 312 multiplies the data vector s (k) by the permutation matrix P (k) and generates an intermediate vector of dimensions Vx1. A spatial spreading unit 314 multiplies the intermediate vector by the orthonormal matrix U and generates the transmission vector x (k). The transmission vector x (k) is transmitted from the T transmitting antennas, and via a MIMO channel 350, to R receiving antennas in a receiver.
The symbols received at the receiver can be expressed as:
r (k) = H (k) x (k) + n (k), = H (k) U P (k) s (k) + n (k), Eq. (4)
ES 2 525 474 T3 = H<sub>to</sub>/ (k) P (k) s (k) + n (k), = H<sub>used</sub>(k) · s (k) + n (k), where r (k) is a vector of dimensions Rx1 containing R symbols received from R receiving antennas by sub-carrier k in a symbol period;
He (k) is an effective channel response matrix of dimensions RxV for subcarrier k;
Husada (k) is a used response matrix of channel of dimensions RxM for sub-carrier k; and n (k) is a noise vector of dimensions Rx1 for subcarrier k.
The channel response matrices, effective and used, can be expressed as:
He / (k) = H (k) · U, = [H (k) · U1 H (k) · U2 ... H (k) · Uv], and Eq. (5)
H., sada (k) = Hef (k) · P (k), = [H (k) · U (1) H (k) · U (2) ... H (k) · U (M) ], Eq. (6) where {U (1) U (2) ... U (M)} c {U1, U2 ... Uv}.
As shown in equation (3) and illustrated in FIG. 3, an effective MIMO channel with V virtual antennas is formed by using the orthonormal matrix U. Data is sent by all, or a subset of, the V virtual antennas. A used MIMO channel is made up of the M virtual antennas used for transmission.
For the transmission scheme described above, a MIMO system of dimensions RxT is effectively reduced to a MIMO system of dimensions RxV. The transmitter appears as if it had V virtual antennas instead of T transmit antennas, where V <T. This transmission scheme reduces the channel estimate overload command to C = V. However, the order of spatial multiplexing is limited to V, or to M <V, and the order of spatial diversity is also limited to V, or to D <V.
The description above is for a sub-carrier k. The transmitter can perform the same processing for each subcarrier used for transmission. The frequency diversity of each virtual antenna between the subcarriers is the same as the frequency diversity of the physical transmitting antennas. However, the spatial diversity is reduced from T to V.
In another embodiment, the transmitter processes the output symbols for transmission, as follows:
Eq. (7) where D (k) is a diagonal matrix of dimensions TxT for subcarrier k. D (k) is used to achieve cyclic delay diversity, which improves the frequency selectivity of virtual antennas and can improve the order of spatial diversity to some value between V and T. Cyclic delay diversity can be achieved in the time domain or frequency domain.
Cyclic delay diversity can be achieved in the time domain by cyclically shifting (or cyclically retarding) the sequence of K time domain samples (obtained from the K-point IDFT or IFFT) for each transmitting antenna i, by a delay of T ,, for i = 1, ..., T. For example, T, can be defined as T, = (/ -1) J, where J can be equal to a period of samples, a fraction of a period of samples or more than one sample period. J can be selected so that the channel impulse response for each virtual antenna is expected to be shorter than the length of the cyclic prefix. A cyclic delay of X samples can be achieved by shifting the last X samples in the sequence of K samples from the time domain to the front of the sequence. The time domain samples for the T transmit antennas are cyclically delayed by different magnitudes. A cyclic prefix can be attached after applying the cyclic delay, in order to ensure orthogonality between the total K subcarriers.
Cyclic delay diversity can also be achieved in the frequency domain by applying a phase shift (or progressive phase shift) between the total K subcarriers for each transmitting antenna. T different phase drops are used for the T transmit antennas, to achieve K different cyclic delays for these antennas. The diagonal matrix D (k) for each subcarrier k can be defined as follows:
<img file="ES2525474T3_D0002.tif" />
ES 2 525 474 T3
D (*) = for k = 1, K.
Eq. (8)
As equation (8) indicates, the transmitting antenna 1 has a phase slope of 0 between the total K subcarriers, the transmitting antenna 2 has a phase slope of 2πύ / Τ between the total K subcarriers, and so on, and the transmitting antenna T has a phase slope of 2π (Τ-1) · ύ / Τ between the total K subcarriers. The diagonal matrix D (k) and the orthonormal matrix U can also be combined to obtain a new orthonormal matrix U (/ í) = D (/ í) U, where U (/ í) can be applied to the vector s (k ) of data.
Symbols received with a diversity of cyclic delays can be expressed as:
f (¿) = H (jt) -x (fc) + n (fc), = H (^ - D (fc) -UP (7c) -sa-) + nW, <sub>Ec (9)</sub> = W-PW-s (*) + n (¿), = H ^ ada (fc) -S (^) + n (Aí), where is a received vector of dimensions Rx1 with a diversity of cyclic delays
Ir (*) is an effective channel response matrix of dimensions RxV with cyclic delay diversity; Y
H used (k) is a used response matrix of RxM dimension channel with cyclic delay diversity.
The channel response matrices, effective and used, can be expressed as:
<td rowspan="2"></td><td></td><td></td>
<td></td><td>Eq. (10)</td>
<td>= [H (fc) · D (fc) · Ui H (fc) · D (fc) · u, ... H (fc) · D (At) · u<sub>v</sub> ]</td><td>, Y</td><td></td>
<td>H_ (?) = H<sub>éf</sub>W-PW,</td><td></td><td>□ λ / 4 4</td>
== [H (fc) -D (fc) u<sub>(1)</sub> HW-DW-üp, · ... H (t) -D (t) ·! ^]
FIG. 4 shows a model 400 for the transmission scheme given by equation (7). Within a correlator
410 of virtual antennas, a correlation unit 412 between symbols and virtual antennas multiplies the data vector s (/ i) by the permutation matrix P (/ i) and generates a vector of dimensions Vx1. A spatial spreading unit 414 multiplies the vector of dimensions Vx1 by the orthonormal matrix U and generates a vector of dimensions Tx1. A cyclic delay diversity unit 416 multiplies the vector of dimensions Tx1 by the diagonal matrix D (k) and generates the transmission vector x (/ i) of dimensions Tx1. The transmission vector x (/ i) is transmitted from the T transmitting antennas, and via a MIMO channel 450, to R receiving antennas in a receiver.
As shown in equation (7) and illustrated in FIG. 4, one channel - effective MIMO with V virtual antennas
ES 2 525 474 T3 is formed by the use of the orthonormal matrix U and the diversity of cyclic delays. A channel ~ used (k) used is made up of the M virtual antennas used for transmission.
Equations (3) and (7) assume that equal transmit power is used for the M output symbols sent simultaneously by a sub-carrier in a symbol period. In general, the transmit power available for each transmitting antenna can be distributed evenly, or non-uniformly, among the sub-carriers used for transmission. The transmit powers available to the T transmit antennas for each subcarrier can be distributed evenly, or non-uniformly, to the M output symbols sent by that subcarrier. Different transmit powers can be used for the M output symbols, scaling the data vector s (/ i) with a diagonal gain matrix G, as follows: ~ or x (^) - D (k) UP (k) G s (k), j,<sub>to</sub>g {G} = {g<sub>1</sub> g<sub>2</sub>... g<sub>M</sub>} yg, is the gain for the output symbol s.
Various types of matrices can be used to form the orthonormal matrix U. For example, U can be formed based on a Fourier matrix, a Walsh matrix, or some other matrix. An Ft matrix<sub>x</sub>Fourier t of dimensions TxT has the element f<sub>n</sub>,<sub>m</sub> in the nth row of the mth column, which can be expressed as:
<img file="ES2525474T3_D0003.tif" />
-jíx, for n = 1, ..., T and m = 1, ..., T.
Eq. (12)
Fourier matrices of any square dimension can be formed (eg, 2, 3, 4, 5, 6, and so on). A matrix W2 <<sub>2</sub> Walsh of dimensions 2x2 and a matrix W<sub>2</sub>Larger Walsh nx2n can be expressed as:
<img file="ES2525474T3_D0004.tif" />
<img file="ES2525474T3_D0005.tif" />
W<sub>2</sub>Nx2N ~
3ΥνχΝ
ÍYnxN
Eq. (13)
In one embodiment, the orthonormal matrix U is equal to a matrix containing V columns of a Fourier matrix of dimensions TxT or a Walsh matrix of dimensions TxT. In another embodiment, U is formed as follows:
U = AF, Eq. (14) where F is a matrix of dimensions TxV containing the first V columns of the Fourier matrix of dimensions TxT; and Λ is a diagonal matrix of dimensions TxT containing T scaling values for the T rows of F. For example, the diagonal matrix A can be defined as Λ = diag {1 e '<sup>e1</sup>...and'<sup>eT</sup>}, where Θ ,, for i = 1, ..., T, can be random phases. Equation (14) multiplies the rows of F by random phases, which changes the spatial directions illustrated by the columns of F. In yet another embodiment, U is an orthonormal matrix with pseudo-random elements, e.g. eg, with unit magnitude and pseudo-random phases.
The transmitter can send a MIMO, SIMO or SISO transmission to a receiver on a set of sub-carriers, which are called the assigned sub-carriers. The total K subcarriers can be divided into multiple non-overlapping subcarrier sets. In this case, the transmitter can transmit to multiple receivers simultaneously over multiple sets of sub-carriers. The transmitter can send the same or different types of transmission to these multiple receivers. For example, the transmitter may send a MIMO transmission over a first set of sub-carriers to a first receiver, a SIMO transmission over a second set of sub-carriers to a second receiver, an SISO transmission over a third set of sub-carriers. carriers to a third receiver, and so on.
A SIMO or SISO transmission can be sent from a single virtual antenna formed with a single column of the orthonormal matrix U. In this case, Μ = V = 1, and the effective MIMO channel becomes a SISO or SIMO channel from hefW = H (k) U! ñ<sub>ef</sub>(7í) = H (/ C) D (k) · Ut dimensions Rx1 with a channel response vector of o. The data vector s (/ í) is converted into a vector of dimensions 1x1 containing a single symbol of Output, the permutation matrix P (/ i) becomes a matrix of dimensions 1x1 containing a single '1' and the orthonormal matrix U becomes a matrix of dimensions Tx1 containing a single column.
A MIMO transmission can be sent from multiple virtual antennas formed with multiple columns of the orthonormal matrix U. If the number of output symbols is less than the number of virtual antennas (or M <S), then M virtual antennas can be selected. for use in various ways.
FIG. 5 shows an embodiment for transmitting output symbols cyclically from the V virtual antennas. For this embodiment, the first M output symbols are sent from virtual antennas 1 to M by the first assigned subcarrier, the next M output symbols are sent from virtual antennas 2 to M + 1 by the
ES 2 525 474 T3 next assigned sub-carrier, and so on. The assigned subcarriers can receive the indices of k = 1, 2, .... For the embodiment shown in FIG. 5, the M virtual antennas used for sub-carrier k + 1 are offset by one unit from the M virtual antennas used for sub-carrier k. The selected virtual antennas circularly revert to virtual antenna 1 upon reaching the last virtual antenna. Therefore, the virtual antennas ((k-1) mod V) + 1 to ((k + M - 2) mod V) + 1 are used for the assigned subcarrier k, where "mod S" indicates an operation on modulo S and the “-1” and “+1” are due to the fact that the index for the assigned subcarriers and the index for the virtual antennas start at 1 instead of 0. The M columns of the matrix P (k ) of permutation for each sub-
<img file="ES2525474T3_D0006.tif" />
In another embodiment, the first M output symbols are sent from the virtual antennas 1 to M by the first assigned subcarrier, the next M output symbols are sent from the virtual antennas M + 1 to ((2M - 1) mod V) +1 for the next assigned subcarriers, and so on. For this embodiment, the M virtual antennas used for subcarriers k + 1 start after the last virtual antenna used for subcarrier k. In yet another embodiment, the M virtual antennas for each sub-carrier are selected in a pseudo-random manner, e.g. eg, based on a generator or a sequence of pseudo-random numbers (PN), which is also known to the receiver.
In yet another embodiment, the virtual antennas are selected based on feedback from a receiver. For example, the feedback may indicate the specific virtual antennas to use for all assigned subcarriers, the specific virtual antennas to use for each assigned subcarrier, and so on. In yet another embodiment, the transmitter may select the virtual antennas based on a pilot signal or some other transmission received from the receiver. For example, the transmitter can estimate the uplink channel response based on the received pilot signal, estimate the downlink channel response based on the uplink channel response estimate, and select the virtual antennas based on to the downlink channel response estimate. The downlink and uplink channel responses can be similar, e.g. For example, in a time division duplexing (TDD) system in which the downlink and uplink transmissions are sent on the same frequency channel, but at different time slots.
In general, virtual antennas can be selected (1) by the transmitter deterministically (e.g. cyclically) or pseudo-randomly, with no feedback from the receiver, (2) by the transmitter based on feedback from the receiver or (3) by the receiver and sent to the transmitter.
The orthonormal matrix U can be fixed, and the V virtual antennas formed with U can be selected for use, as described above. In another embodiment, one or more orthonormal matrices are selected for use from a set of orthonormal matrices available for use. The set of orthonormal matrices forms a codebook, and one or more codebook entries can be used for transmission. The orthonormal matrices in the set are different (and can be pseudo-random) with respect to each other. For example, orthonormal matrices can be defined to provide good performance for different channel conditions, e.g. eg, conditions of low and high SNR, low and high mobility, etc. An orthonormal matrix can be selected for all assigned subcarriers, for each assigned subcarrier, etc. Matrix selection can be made (1) by the transmitter, with or without feedback from a receiver, or (2) by the receiver, and returned to the transmitter. Matrix selection can be made based on various factors, such as, e.g. eg, channel conditions, mobility, uplink resources, etc. In general, the specific codebook entry (s) to be used for transmission can be selected either autonomously by the transmitter or based on feedback from the receiver.
The transmission schemes described herein have the following desirable characteristics:
* Flexibility to easily select the number of virtual antennas;
* Flexibility to send any number of output symbols, up to the number of virtual antennas available; and * Use of all T transmitting antennas for transmission, regardless of the number of output symbols sent and the number of virtual antennas available.
ES 2 525 474 T3
The number of virtual antennas (V) can be selected to support the desired order (M) of spatial multiplexing, to achieve the desired order (D) of spatial diversity, and to obtain the desired order (C) of channel estimation overhead. . The number of virtual antennas can be selected autonomously by the transmitter, or based on a feedback from the receiver. The desired number of virtual antennas can be immediately obtained by defining the orthonormal matrix U with the appropriate number of columns.
The order of spatial multiplexing is limited by the number of transmitting antennas and the number of receiving antennas, or M <min {T, R}. A higher spatial multiplexing order may be desirable in certain scenarios (eg, high SNR conditions) and if supported by the receiver. A lower order of spatial multiplexing (e.g. M = 1) may be desirable in other scenarios (e.g. g., low SNR conditions) or if a higher spatial multiplexing order is not supported by the receiver. The order of spatial multiplexing can be dynamically selected based on channel conditions and / or other factors. For example, the spatial multiplexing order can be set to one if the SNR is less than a first threshold, set to two if the SNR is between the first threshold and a second threshold, set to three if the SNR is between the second threshold. and a third threshold, and so on. The number of virtual antennas is selected to be equal to or greater than the order of spatial multiplexing, that is V> M.
In general, a higher order of spatial diversity is desirable in order to improve performance, and a lower order of channel estimation overhead is desirable in order to reduce the amount of link resources used to transmit a pilot signal for channel estimation. channel. The channel estimation overhead order is closely related to the spatial diversity order, and both are determined by the number of virtual antennas. Thus, the number of virtual antennas can be dynamically selected based on the desired spatial diversity order, the desired channel estimation overhead order, channel conditions, and / or other factors.
The number of virtual antennas can be selected in various ways. In one embodiment, the number of virtual antennas is set equal to the spatial multiplexing order, that is V = M. In another embodiment, the number of virtual antennas is set to the highest possible value so that the link resources used for the transmission of pilot signals are kept within a certain percentage of the total link resources. In yet another embodiment, the number of virtual antennas is set based on channel conditions. For example, one virtual antenna can be defined if the SNR is less than a first value, two virtual antennas can be defined if the SNR is between the first value and a second value, and so on.
The transmission schemes described herein can be used with various subcarrier structures, some of which are described below. The following description assumes that the total K subcarriers are usable for transmission and receive indices between 1 and K.
FIG. 6A shows an interlacing subcarrier structure 600. For this subcarrier structure, the total K subcarriers are arranged in non-overlapping interleaved S, each interleaved contains N subcarriers that are evenly distributed among the total K subcarriers and the consecutive subcarriers in each interleaved are separated from each other by S subcarriers, where K = S · N. The interleaved u contains the sub-carrier u as the first sub-carrier, where ue {1, ..., S}.
FIG. 6B shows a block subcarrier structure 610. For this sub-carrier structure, the total K sub-carriers are arranged in S non-overlapping blocks, each block containing N adjacent sub-carriers, where K = S · N. The v block contains the sub-carriers v · N + 1 a (v + 1) · N, where you see {1, ..., S}.
FIG. 6C shows a group subcarrier structure 620. For this sub-carrier structure, the K total sub-carriers are arranged in S non-overlapping groups, each group contains G sub-groups that are distributed over the system bandwidth, and each sub-group contains L adjacent sub-carriers, where K = S · N and N = G · L. The total K subcarriers can be divided into G frequency ranges, each frequency range containing S · L consecutive sub-carriers. Each frequency range is further divided into S subgroups, each subgroup containing L consecutive subcarriers. For each frequency range, the first L sub-carriers are assigned to group 1, the next L sub-carriers are assigned to group 2 and so on, and the last L sub-carriers are assigned to group S. Each group contains G subgroups of L consecutive sub-carriers, that is, a total of N = G · L sub-carriers.
In general, the transmission techniques described herein can be used for any subcarrier structure with any number of subcarrier sets. Each set of sub-carriers can include any number of sub-carriers that can be arranged in any way. For example, a set of subcarriers can be equal to an interleaved, a block of sub-carriers, a group of sub-carriers, and so on. For each set of sub-carriers, (1) the sub-carriers in the set can be evenly, or non-uniformly, distributed over the system bandwidth, (2) the sub-carriers in the set can be adjacent to each other in a group or (3) the sub-carriers in the set can be distributed in multiple groups, where each group can be located anywhere within the bandwidth of the system and
ES 2 525 474 T3 may contain one or more subcarriers.
For all the sub-carrier structures described above, different receivers can be assigned different sets of sub-carriers, and the transmitter can transmit data to each receiver over its set of assigned sub-carriers. The transmitter may use the same orthonormal matrix U for all receivers, a different orthonormal matrix for each receiver, a different orthonormal matrix for each set of sub-carriers, a different orthonormal matrix for each sub-carrier, etc.
The transmission techniques described herein can be used with or without frequency hopping. With frequency hopping, the data transmission jumps between one sub-carrier and another in a pseudo-random or deterministic manner over time, which allows the data transmission to better withstand dire channel conditions, such as interference from narrow band, jam, fading, etc. Frequency hopping can provide frequency diversity and interference scrambling. A receiver may be assigned a traffic channel that is associated with a hopping pattern that indicates which set (s) of subcarriers, if any, to use in each time slot. A hopping pattern is also called a frequency hopping pattern or sequence. A timeslot is the amount of time spent on a given set of subcarriers and is also called a hopping period. The hopping pattern can select different sets of subcarriers in different time slots, in a pseudo-random or deterministic way.
FIG. 7 shows an exemplary frequency hopping scheme 700. In FIG. 7, traffic channel 1 is mapped to a specific sequence of time-frequency blocks. Each time-frequency block is a specific set of subcarriers in a specific time slot. In the example shown in FIG. 7, traffic channel 1 is mapped to subcarrier set 1 in time slot 1, subcarrier set 4 in time slot 2, and so on. Traffic channels 2 through S can be correlated with vertically and circularly shifted versions of the time-frequency block sequence for traffic channel 1. For example, traffic channel 2 can be mapped to set 2 of sub-carriers in time slot 1, with set 5 of sub-carriers in time slot 2, and so on.
Frequency hopping can be used with any of the subcarrier structures shown in FIGs. 6A to 6C. For example, a symbol rate hopping scheme may be defined in which each time-frequency block is a specific interleaving in a symbol period. For this hopping scheme, the assigned subcarriers span the entire bandwidth of the system and change from one symbol period to another. As another example, a block hopping scheme may be defined in which each time-frequency block is a specific block of subcarriers in a time slot of multiple symbol periods. For this hopping scheme, the assigned subcarriers are contiguous and fixed for an entire timeslot, but they change from one timeslot to another. For the block hopping scheme, the spatial multiplexing order can be set equal to the number of virtual antennas, so that a constant interference can be observed in any given block of time-frequency in any sector for a system with synchronous sectors. Another jump scheme can also be defined.
Pilot signals can be transmitted in various ways with the sub-carrier structures described above. Some exemplary pilot signal schemes for symbol rate hopping and block hopping are described below.
FIG. 8 shows an exemplary pilot signal scheme 800 for symbol rate hopping. For the pilot signal scheme 800, the transmitter transmits a common pilot signal over interleaving from the virtual antenna 1 at each symbol period. The transmitter can transmit the common pilot signal in different interleaves at different symbol periods, as shown in FIG. 8. Such a stepped pilot signal allows a receiver to sample the frequency spectrum on more sub-carriers and obtain a longer estimate of the channel impulse response. The transmitter can also transmit an auxiliary pilot signal on one or more interleaves from the remaining virtual antennas, to allow MIMO receivers to estimate the channel response for all virtual antennas used for transmission. For the embodiment shown in FIG. 8, the transmitter transmits the auxiliary pilot signal in an interleaving in each symbol period and travels the virtual antennas 2 to V in V-1 different symbol periods. For the case with V = 4, as shown in FIG. 8, the transmitter transmits the auxiliary pilot signal from the virtual antenna 2 in the n + 1 symbol period, then from the virtual antenna 3 in the n + 2 symbol period, then from the virtual antenna 4 in the n symbol period + 3, then from virtual antenna 2 in symbol period n + 4, and so on.
The transmitter can transmit the common and auxiliary pilot signals in other ways. In another embodiment, the auxiliary pilot signal is staggered and is sent by different sets of sub-carriers. In yet another embodiment, the common pilot signal is sent by one or more sets of sub-carriers that are pseudo-random (or have random offsets) with respect to said one or more sets of sub-carriers used for the auxiliary pilot signal.
ES 2 525 474 T3
The transmitter can transmit the common pilot signal for MIMO, SIMO and SISO receivers, and it can transmit the auxiliary pilot signal only when MIMO receivers are present. MIMO, SIMO and SISO receivers can use the common pilot signal to obtain a channel estimate for the total K subcarriers of virtual antenna 1. A MIMO receiver can use the auxiliary pilot signal to obtain channel estimates for the virtual antennas 2 a
V.
FIG. 9A shows an exemplary scheme 910 of pilot signals for block hopping. For the embodiment shown in FIG. 9A, a time-frequency block is composed of 16 adjacent subcarriers k + 1 to k + 16, and also encompasses 8 symbol periods n + 1 to n + 8. For the 910 pilot signal scheme, the transmitter transmits a dedicated pilot signal on subcarriers k + 3, k + 9 and k + 15 in each of the symbol periods n + 1 to n + 3 and n + 6 a n + 8, or six strips of three pilot symbols. Each pilot symbol can be sent from any virtual antenna. For example, if V = 3, then the transmitter can transmit the pilot signal from virtual antenna 1 in symbol periods n + 1 and n + 6, from virtual antenna 2 in symbol periods n + 2 and n + 7, and from the virtual antenna 3 in the symbol periods n + 3 and n + 8.
FIG. 9B shows an exemplary pilot signal scheme 920 for block hopping. For the 920 pilot signal scheme, the transmitter transmits a dedicated pilot signal on subcarriers k + 3, k + 9 and k + 15 in each of the symbol periods n + 1 to n + 8, or three strips of eight pilot symbols. Each pilot symbol can be sent from any virtual antenna. For example, if V = 4, then the transmitter can transmit the pilot signal from virtual antenna 1 in symbol periods n + 1 and n + 5, from virtual antenna 2 in symbol periods n + 2 and n + 6, from the virtual antenna 3 in the symbol periods n + 3 and n + 7, and from the virtual antenna 4 in the symbol periods n + 4 and n + 8.
FIG. 9C shows an exemplary pilot signal scheme 930 for block hopping. For the 930 pilot signal scheme, the transmitter transmits a dedicated pilot signal on the subcarriers k + 1, k + 4, k + 7, k + 10, k + 13 and k + 16 in each of the periods of symbols n + 1, n + 2, n + 7 and n + 8. Each pilot symbol can be sent from any virtual antenna. For example, the transmitter can transmit the pilot signal from the virtual antenna 1 in the period of symbols n + 1, from the virtual antenna 2 in the period of symbols n + 2, from the virtual antenna 1 or 3 in the period of symbols n + 7 and from virtual antenna 2 or 4 in the symbol period n + 8.
FIG. 9D shows an exemplary pilot signal scheme 940 for block hopping. For the pilot signal scheme 940, the transmitter transmits a pilot signal staggered by three subcarriers in each symbol period and by different pilot subcarriers at different symbol periods. Each pilot symbol can be sent from any virtual antenna. For example, the transmitter can transmit the pilot signal from a different virtual antenna in each symbol period and can traverse the V virtual antennas in V symbol periods.
In general, for the block hopping scheme, the transmitter can transmit a pilot signal in each time-frequency block, so that a receiver is able to obtain a channel estimate for each virtual antenna used for transmission. FIGs. 9A through 9D show four exemplary pilot signal patterns that can be used. Other pilot signal patterns can also be defined, and used for the transmission of pilot signals.
For both symbol rate hopping and block hopping, the transmitter can transmit the pilot signal from any number of virtual antennas, can use any number of pilot subcarriers for each virtual antenna, and can use any magnitude of transmit power for each virtual antenna. If the pilot signal is sent from multiple virtual antennas, then the transmitter can use the same or different subcarrier numbers for these virtual antennas and can transmit the pilot signal at the same or different power levels for the virtual antennas. The transmitter may or may not stagger the pilot signal for each virtual antenna. The transmitter can transmit the pilot signal on more sub-carriers to allow a receiver to get more "view" of the wireless channel in the frequency domain and to obtain a longer estimate of the channel impulse response. The transmitter can transmit the pilot signal on all pilot subcarriers from a virtual antenna in each symbol period, as described above. Alternatively, the transmitter may transmit the pilot signal from multiple virtual antennas over multiple subsets of subcarriers in a given symbol period.
In one embodiment, the transmitter transmits the pilot signal from the virtual antennas, as described above for FIGs. 8 to 9D. In another embodiment, the transmitter transmits the pilot signal from the physical antennas, without applying the orthonormal matrix U or the permutation matrix P (k). For this embodiment, a receiver can estimate the actual channel response based on the pilot signal and can then obtain an effective estimate of the channel response based on the actual estimate of the channel response and the orthonormal and permutation matrices.
FIG. 10 shows a process 1000 for transmitting data and pilot signals to one or more receivers. Processing for each receiver can be done as follows. Determine the set of subcarriers assigned to the receiver and the spatial multiplexing order (M) for the receiver, where M> 1 (block 1012). For each assigned subcarrier, M virtual antennas are selected for use among V virtual antennas formed with V columns of the orthonormal matrix U, where V> M (block 1014). The M virtual antennas for each assigned sub-carrier can be
ES 2 525 474 T3 selected in various ways, as described above. The output symbols for the receiver are mapped to the M selected virtual antennas for each assigned sub-carrier, applying the orthonormal matrix (block 1016). The correlated output symbols (or transmit symbols) are provided for transmission from T transmitting antennas, where T> V (block 1018).
The pilot symbols are also mapped to the virtual antennas used for transmission (block 1020). For example, the pilot symbols for a common pilot signal can be correlated to the first virtual antenna by a first set of pilot subcarriers, and the pilot symbols for an auxiliary pilot signal can be correlated to the remaining virtual antennas by a second set of pilot signal subcarriers.
If there are multiple receivers, then the same, or different, spatial multiplexing orders can be used for these receivers. Furthermore, data can be sent simultaneously on different sets of subcarriers to multiple receivers. For example, data can be sent from one virtual antenna over a first set of subcarriers to a SIMO or SISO receiver, from multiple virtual antennas over a second set of subcarriers to a MIMO receiver, and so on. In any case, the transmit symbols for all receivers are demultiplexed to the T transmit antennas (block 1022). For each transmitting antenna, the transmitting symbols for each receiver are mapped to the subcarriers assigned to that receiver (also block 1022). The transmitting symbols are then generated for each transmitting antenna, based on the transmitting symbols for that transmitting antenna, and using, e.g. eg OFDM or SC-FDMA (block 1024). Different cyclic delays can be applied for the T transmit antennas, e.g. eg, circularly delaying the transmit symbols for each transmit antenna by a different amount (block 1026).
For block 1016 in FIG. 10, the output symbol (s) for each sub-carrier assigned to each receiver are correlated to the T transmitting antennas based on M correlation patterns selected from V correlation patterns available for use. Each correlation pattern indicates a specific correlation of an output symbol with the T transmit antennas. The V correlation patterns can be formed by V columns of an orthonormal matrix, or in other ways. Different correlation patterns can be selected for different subcarriers in a given symbol period and / or in different symbol periods, e.g. eg, based on a predetermined pattern. The default pattern can be defined by a permutation matrix, or in some other way. The predetermined pattern can cycle through the V correlation patterns available on different subcarriers and / or symbol periods.
FIG. 11 shows an embodiment of an apparatus 1100 for transmitting data and pilot symbols to one or more receivers. Apparatus 1100 includes means for determining the set of subcarriers assigned to each receiver and the order of spatial multiplexing (M) for each receiver (block 1112), means for selecting M virtual antennas for use among V virtual antennas for each sub -carrier assigned to each receiver (block 1114), means for correlating the output symbols for each receiver with the virtual antennas selected for each sub-carrier assigned to the receiver (p. e.g., applying selected columns of an orthonormal matrix or selected correlation patterns) (block 1116), means for providing the correlated output symbols (or transmit symbols), for transmission from T transmitting antennas (block 1118), means to map pilot symbols to the virtual antennas used for transmission (block 1120), means for demultiplexing the transmission symbols for each receiver to the assigned sub-carriers of the T transmitting antennas (block 1122), means for generating transmitting symbols for each transmitting antenna, e.g. eg, using OFDM or SC-FDMA (block 1124) and means to apply different cyclic delays for the T transmit antennas (block 1126).
FIG. 12 shows a block diagram of one embodiment of base station 110, single antenna terminal 120x, and multiple antenna terminal 120y. At base station 110, a transmit (TX) data processor 1210 receives data for one or more terminals, processes (eg, encodes, interleaves, and symbol maps) the data based on one or more encoding schemes. and modulation, and provides modulation symbols. The TX data processor 1210 typically processes the data for each terminal separately, based on a coding and modulation scheme selected for that terminal. If the system 100 uses SC-FDMA, then the TX data processor 1210 can perform an FFT / DFT on the modulation symbols for each terminal to obtain frequency domain symbols for that terminal. The TX data processor 1210 obtains output symbols for each terminal (which may be modulation symbols for OFDM or frequency domain symbols for SC-FDMA) and multiplexes the output symbols for the terminal onto the sub-carriers and virtual antennas used for that terminal. The TX data processor 1210 further multiplexes pilot symbols onto the subcarrier and virtual antennas used for the transmission of pilot signals.
A TX spatial processor 1220 receives the multiplexed output symbols and pilot symbols, performs spatial processing for each sub-carrier, e.g. eg, as shown in equation (3) or (7), and provides transmit symbols for the T transmit antennas. A modulator (Mod) 1222 processes the transmit symbols for each transmit antenna, e.g. g., for OFDM, SC-FDMA or some other modulation technique, and generates an output sample stream for that transmitting antenna. Since TX's 1220 spatial processor
ES 2 525 474 T3 performs the spatial processing for each sub-carrier, the SC-FDMA modulation is divided into two parts that are performed by the TX data processor 1210 and the modulator 1222 The modulator 1222 provides T streams of samples of output to T transmitter units (TMTR) 1224a to 1224t. Each transmitter unit 1224 processes (eg, converts to analog, amplifies, filters, and increases frequency) its output sample stream and generates a modulated signal. T modulated signals, from transmitter units 1224a to 1224t, are transmitted from T antennas 112a to 112t, respectively.
At each terminal 120, one or more antennas 122 receive the modulated signals transmitted by base station 110, and each antenna provides a received signal to a respective receiver unit (RCVR) 1254. Each receiver unit 1254 processes (eg, amplifies , filters, downsamples, and digitizes) your receive signal and provides the received samples to a demodulator (Demod) 1256. The demodulator 1256 processes the received samples for each receive antenna 122 (eg. g., based on OFDM, SC-FDMA or some other modulation technique), obtains received symbols from the frequency domain for the total K sub-carriers, provides the received symbols for the assigned sub-carriers and provides the pilot symbols received for the sub-carriers used for the transmission of pilot signals.
For the single antenna terminal 120x, a data detector 1260x obtains received symbols from the 1256x demodulator, obtains channel estimates for the assigned subcarrier, based on the received pilot symbols, and performs data detection (e.g. ., the equalization) on the received symbols, based on the channel estimates, to obtain detected symbols, which are estimates of the output symbols transmitted to the terminal 120x. For the multi-antenna terminal 120y, a receive (RX) 1260y spatial processor obtains received symbols from the 1256y demodulator, obtains channel estimates for assigned subcarriers based on received pilot symbols, and performs receiver spatial processing on the received symbols, based on the channel estimates, to obtain detected symbols. The RX 1260y spatial processor can implement a least mean square error (MMSE) technique, a zero forcing technique (ZF), a maximum ratio combination technique (MRC), a successive interference cancellation technique, or some other technique. receiver processing technique. For each terminal, an RX data processor 1262 processes (p. (eg, de-relates symbols, deinterleaves, and decodes) the detected symbols and provides decoded data for the terminal. In general, the processing by each terminal 120 is complementary to the processing by the base station 110.
Each terminal 120 can generate feedback information for data transmission to that terminal. For example, each terminal 120 can estimate the SNRs for the virtual antennas, e.g. eg, based on received pilot symbols. Each terminal 120 can select one or more coding and modulation schemes, one or more packet formats, one or more virtual antennas to use for data transmission, one or more orthonormal matrices, etc., based on the SNR estimates. and / or other information. Each terminal 120 can also generate acknowledgments (ACKs) for correctly received data packets. The feedback information may include the SNR estimates, the selected modulation and coding schemes, the selected virtual antenna (s), the selected orthonormal matrix (s). (s), the selected sub-carrier (s), the ACKs, the information used for power control, some other information, or any combination of the above. The feedback information is processed by a TX data processor 1280, further processed by a TX spatial processor 1282 if multiple antennas are present, modulated by a modulator 1284, conditioned by one or more transmitter units 1254, and transmitted via the antenna (s) 122 to base station 110. At base station 110, modulated signals transmitted by terminals 120x and 120y are received by antennas 112, conditioned by receiver units 1224, and processed by demodulator 1240, RX spatial processor 1242, and RX data processor 1244. to retrieve the feedback information sent by the terminals. A controller / processor 1230 uses the feedback information to determine the data rates and the coding and modulation schemes to use for data transmission to each terminal, as well as to generate various controls for the TX data processor 1210. and TX's 1220 spatial processor.
Controllers / processors 1230, 1270x, and 1270y control the operation of various processing units at base station 110 and terminals 120x and 120y, respectively. Memory units 1232, 1272x, and 1272y store data and program codes used by base station 110 and terminals 120x and 120y, respectively. Controller / processor 1230 may implement parts of FIGs. 10 and 11 and can (1) assign sub-carriers and select the spatial multiplexing order for each terminal (block 1012 in FIG. 10) and (2) select the virtual antennas for each sub-carrier assigned to each terminal (block 1214 in FIG. 10). TX data processor 1220 may implement portions of FIGs. 10 and 11 and perform the processing shown in blocks 1116 to 1126 in FIG. 10.
For clarity, much of the description above is for a system with total K subcarriers. The transmission techniques described herein can also be used for a single subcarrier system. For such a system, k in the above description can be an index for the symbol period, rather than the sub-carrier.
ES 2 525 474 T3
The transmission techniques described herein can be implemented by various means. For example, these techniques can be implemented in hardware, firmware, software, or a combination thereof. For a hardware implementation, the processing units in a transmitter can be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSP), 5 digital signal processing devices (DSPD), programmable logic devices (PLD), field programmable gate arrays (FPGA), processors, controllers, micro-controllers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof. The processing units in a receiver can also be implemented within one or more ASICs, DSPs, processors, etc.
For a software implementation, the transmission techniques can be implemented with modules (eg, procedures, functions, etc.) that perform the functions described herein. The software codes can be stored in a memory (eg, 1230, 1272x, or 1272y memory in FIG. 12) and executed by a processor (eg, 1232, 1270x, or 1270y processor). Memory can be implemented within the processor or external to the processor.
The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention.
Contents9
20 sheets
Sheet 1 Sheet 2 Sheet 3 Sheet 4 Sheet 5 Sheet 6 Sheet 7 Sheet 8 Sheet 9 Sheet 10 Sheet 11 Sheet 12 Sheet 13 Sheet 14 Sheet 15 Sheet 16 Sheet 17 Sheet 18 Sheet 19 Sheet 20
67 members in 18 offices
Priority claims19
| Document | Office | Kind | Date |
|---|---|---|---|
| 710408P | United States of America | – | |
| 71040805 | United States of America | P | |
| 71040805 | United States of America | P | |
| 711144P | United States of America | – | |
| 71114405 | United States of America | P | |
| 71114405 | United States of America | P | |
| 261823 | United States of America | – | |
| 26182305 | United States of America | A | |
| 26182305 | United States of America | A | |
| 2006032900 | United States of America | W | |
| 2006032900 | United States of America | W | |
| 261823 | – | – | – |
| 710408P | – | – | – |
| 711144P | – | – | – |
| PCTUS2006032900 | – | – | – |
| US20050261823 | – | – | – |
| US20050710408P | – | – | – |
| US20050711144P | – | – | – |
| WO2006US32900 | – | – | – |
Members67
| Document | Office | Kind | |
|---|---|---|---|
| US2007041457A1 | United States of America | A1 | |
| US2007041464A1 | United States of America | A1 | |
| AU2006283166A1 | Australia | A1 | |
| CA2620067A1 | Canada | A1 | |
| WO2007024913A1 | World Intellectual Property Organization (WIPO) | A1 | |
| WO2007024935A2 | World Intellectual Property Organization (WIPO) | A2 | |
| TW200718060A | Taiwan Province of China | A | |
| TW200718065A | Taiwan Province of China | A | |
| WO2007024935A3 | World Intellectual Property Organization (WIPO) | A3 | |
| AR055382A1 | Argentina | A1 | |
| KR20080032655A | Republic of Korea | A | |
| KR20080037736A | Republic of Korea | A | |
| EP1917736A2 | European Patent Office (EPO) | A2 | |
| EP1917737A1 | European Patent Office (EPO) | A1 | |
| NO20081228L | Norway | L | |
| CN101288245A | China | A | |
| CN101292442A | China | A | |
| JP2009506653A | Japan | A | |
| JP2009506656A | Japan | A | |
| CL2009000739A1 | Chile | A1 | |
| RU2008110953A | Russian Federation | A | |
| CL2009000738A1 | Chile | A1 | |
| KR100954485B1 | Republic of Korea | B1 | |
| KR100962453B1 | Republic of Korea | B1 | |
| RU2395903C2 | Russian Federation | C2 | |
| NZ566171A | New Zealand | A | |
| UA92361C2 | Ukraine | C2 | |
| TWI337475B | Taiwan Province of China | B | |
| BRPI0614854A2 | Brazil | A2 | |
| JP4819897B2 | Japan | B2 | |
| US8073068B2 | United States of America | B2 | |
| JP2011259457A | Japan | A | |
| TWI358216B | Taiwan Province of China | B | |
| US2012120925A1 | United States of America | A1 | |
| JP2012100288A | Japan | A | |
| US2012140798A1 | United States of America | A1 | |
| US2012140838A1 | United States of America | A1 | |
| CA2620067C | Canada | C | |
| JP2014003625A | Japan | A | |
| JP5389894B2 | Japan | B2 | |
| JP5405108B2 | Japan | B2 | |
| JP5479411B2 | Japan | B2 | |
| EP1917736B1 | European Patent Office (EPO) | B1 | |
| ES2525474T3This record | Spain | T3 | |
| CN101288245B | China | B | |
| JP2015053704A | Japan | A | |
| CN104601212A | China | A | |
| CN104618004A | China | A | |
| CN104660316A | China | A | |
| CN104660317A | China | A | |
| JP2015222947A | Japan | A | |
| CN101292442B | China | B | |
| CN105450278A | China | A | |
| JP2016129337A | Japan | A | |
| JP6022641B2 | Japan | B2 | |
| US9660776B2 | United States of America | B2 | |
| JP6195944B2 | Japan | B2 | |
| US9860033B2 | United States of America | B2 | |
| CN104660317B | China | B | |
| CN104601212B | China | B | |
| EP1917737B1 | European Patent Office (EPO) | B1 | |
| ES2688275T3 | Spain | T3 | |
| CN104660316B | China | B | |
| HUE040634T2 | Hungary | T2 | |
| CN105450278B | China | B | |
| BRPI0614854B1 | Brazil | B1 | |
| CN104618004B | China | B |
Numbers
- Publication
- 2525474
- Publication, DOCDB
- 2525474
- Publication, EPODOC
- ES2525474T
- Application
- 6789944
- Application, DOCDB
- 06789944
- Application, EPODOC
- ES20060789944T
Titles2
- Spanish
- Procedimiento y aparato de selección de antenas en un sistema de MIMO
- English
- Procedure and apparatus for selecting antennas in a MIMO system
Classification
- CPC, 13
- H04B7/0671
- H04L5/0023
- H04L1/0026
- H04B7/02
- H04B7/0691
- H04B7/0697
- H04L1/06
- H04L1/20
- H04W52/42
- H04B7/061
- Y02D30/70
- H04L27/26035
- H04B7/0456
- IPC, 3
- H04L5 00
- H04B7 06
- H04L27 26