ES2215166T3

Demodulation element assignment in a system capable of receiving multiple signals

Abstract

Method for assigning, in a receiver having a plurality of demodulation elements, said plurality of demodulation elements to a group of available signals, comprising the following steps: conducting a survey of said available signals and creating a list of paths probing that includes the arrival time, signal strength and transmission rate of each of said available signals; comparison of a list of demodulation paths, comprising the arrival time, signal strength and transmission rate corresponding to the signals that are demodulated by said receiver, with said list of polling paths, and assignment of an element of unassigned demodulation, if such unassigned demodulation element exists, to a particular survey path having a corresponding transmission rate that is different from the transmission rates of said demodulation path list.

ES2215166T3, drawing sheet 1 — Sheet 1 of 16

Term

Term ended

Projected expiry passed 28 October 2014, 11.9 years ago.

53 claims: 2 independent, 51 dependent

1
ES 2 215 166 T3 REIVINDICACIONES 1. Procedimiento para asignar, en un receptor que tiene una pluralidad de elementos de demodulación, dicha pluralidad de elementos de demodulación a un grupo de señales disponibles, que comprende las etapas siguientes:realización de un sondeo de dichas señales disponibles y creación de una lista de trayectorias de sondeo que comprende el tiempo de llegada, la intensidad de señal y el índice de transmisión de cada una de dichas señales disponibles;comparación de una lista de trayectorias de demodulación, que comprende el tiempo de llegada, la intensidad de señal y el índice de transmisión correspondiente a las señales que son demoduladas por dicho receptor, con dicha lista de trayectorias de sondeo, y asignación de un elemento de demodulación no asignado, si dicho elemento de demodulación no asignado existe, a una trayectoria de sondeo particular que tiene un correspondiente índice de transmisión que es distinto a los índices de transmisión de dicha lista de trayectorias de demodulación.
2
Procedimiento según la reivindicación 1, en el que en dicha etapa de asignación de dicho elemento de demodulación no asignado, dicha trayectoria de sondeo particular corresponde a la trayectoria de sondeo que tiene la intensidad de señal más elevada de todas las trayectorias de sondeo que tienen dicho correspondiente índice de transmisión.
3
Procedimiento según la reivindicación 1, que además comprende la etapa siguiente:reasignación de un elemento de demodulación particular a dicha trayectoria de sondeo particular si no existe ningún elemento de demodulación no asignado, comprendiendo esta etapa las etapas siguientes: anulación de la asignación de dicho elemento de demodulación particular, y asignación de dicho elemento de demodulación particular a dicha trayectoria de sondeo particular.
4
Procedimiento según la reivindicación 3, en el que dicho elemento de demodulación particular corresponde a la trayectoria de demodulación que tiene una intensidad de señal que es inferior a la intensidad de señal de cualquier elemento de demodulación.
5
Procedimiento según la reivindicación 3, en el que dicho elemento de demodulación particular corresponde a una trayectoria de demodulación que tiene una intensidad de señal que es inferior a la intensidad de señal de dicha trayectoria de sondeo particular.
6
Procedimiento según la reivindicación 3, en el que dicho elemento de demodulación particular se asigna a una trayectoria de demodulación que tiene una intensidad de señal que es por lo menos una cierta proporción inferior a la intensidad de señal de dicha trayectoria de sondeo particular.
7
Procedimiento según la reivindicación 3, en el que dicho elemento de demodulación se asigna a una trayectoria de demodulación que tiene una intensidad de señal que es 3 dB inferior a la intensidad de señal de dicha trayectoria de sondeo particular.
8
Procedimiento según la reivindicación 3, en el que dicho elemento de demodulación particular se asigna a una trayectoria de demodulación particular que tiene un índice de transmisión que es igual al índice de transmisión de por lo menos otra trayectoria de demodulación.
9
Procedimiento según la reivindicación 8, en el que dicha trayectoria de demodulación particular tiene la intensidad de señal más débil de cualquiera de las trayectorias de dicha lista de trayectorias de demodulación.
10
Procedimiento según la reivindicación 1, en el que dicho índice de transmisión representa una estación base.
11
Procedimiento según la reivindicación 1, en el que dicho índice de transmisión representa un sector de una estación base.
12
Procedimiento según la reivindicación 1, en el que cada transmisor transmite una señal de espectro ensanchado utilizando modulación por pseudorruido y en el que dicho índice de transmisión representa el desplazamiento de código de la señal de espectro ensanchado transmitida.
13
Procedimiento según la reivindicación 1, en el que dicha etapa de comparación de dicha lista de trayectorias de demodulación con dicha lista de trayectorias de sondeo establece la correspondencia entre cada una de las entradas de dicha lista de trayectorias de demodulación y una entrada de dicha lista de trayectorias de sondeo. ES 2 215 166 T3
14
Procedimiento según la reivindicación 1, en el que dicha etapa de comparación de dicha lista de trayectorias de demodulación con dicha lista de trayectorias de sondeo comprende las etapas siguientes:comparación de una primera trayectoria de demodulación que tiene una primera intensidad de señal con una primera trayectoria de sondeo;comparación de una segunda trayectoria de demodulación que tiene una segunda intensidad de señal con dicha primera trayectoria de sondeo, siendo dicha segunda intensidad de señal superior a dicha primera intensidad de señal, y anulación de asignación de un primer elemento de demodulación correspondiente a dicha primera trayectoria de demodulación.
15
Procedimiento según la reivindicación 1, en el que cada elemento de demodulación de dicha pluralidad de elementos de demodulación que se asigna a una trayectoria de demodulación indica un estado de demodulación satisfactoria o insatisfactoria, que además comprende la etapa de anulación de la asignación de un elemento de demodulación particular si dicho elemento de demodulación particular indica una demodulación insatisfactoria.
16
Procedimiento según la reivindicación 1, en el que dicho receptor tiene por lo menos un elemento de búsqueda y en el que dicha etapa de realización de un sondeo de las señales disponibles y de creación de una lista de trayectorias de sondeo comprende las etapas siguientes:recepción, desde dicho por lo menos un elemento de búsqueda, de un punto de datos de máximo local que incluye un tiempo de llegada, una intensidad de señal y un índice de transmisión;inclusión de dicho punto de datos de máximo local en dicha lista de trayectorias de sondeo si dicha intensidad de señal de dicho punto de datos de máximo local sobrepasa un nivel predeterminado.
17
Procedimiento según la reivindicación 1, en el que dicho receptor tiene por lo menos un elemento de búsqueda, y en el que dicha etapa de realización de un sondeo de las señales disponibles y de creación de una lista de trayectorias de sondeo comprende las etapas siguientes:recepción, desde dicho elemento de búsqueda por lo menos, de un grupo de puntos de datos de máximo local cada uno de los cuales tiene un tiempo de llegada, una intensidad de señal y un índice de transmisión común, e inclusión de un número limitado de dichos puntos de datos de máximo local en dicha lista de trayectorias de sondeo si la intensidad de señal de cada uno de los puntos de datos de máximo local de dicho número limitado incluido sobrepasa un nivel predeterminado.
18
Procedimiento según la reivindicación 17, en el que dicho número limitado de dichos puntos de datos de máximo local es igual al número de elementos de demodulación de dicha pluralidad de elementos de demodulación.
19
Procedimiento según la reivindicación 1, en el que dicha etapa de comparación de dicha lista de trayectorias de demodulación con dicha lista de trayectorias de sondeo comprende además las etapas siguientes:búsqueda de una trayectoria de demodulación que no coincida con ninguna trayectoria de sondeo de dicha lista de trayectorias de sondeo, e inclusión de una entrada en dicha lista de trayectorias de sondeo correspondiente a dicha trayectoria de demodulación no coincidente.
20
Procedimiento según la reivindicación 1, en el que cada índice de transmisión de dicha lista de trayectorias de sondeo es igual al índice de transmisión de dicha lista de trayectorias de demodulación, que comprende además la etapa de asignación de un elemento de demodulación no asignado, si dicho elemento de demodulación no asignado existe, a una segunda trayectoria de sondeo particular.
21
Procedimiento según la reivindicación 20, en el que, en dicha etapa de asignación de dicho elemento de demodulación no asignado, dicha segunda trayectoria de sondeo particular no tiene el mismo tiempo de llegada e índice de transmisión que ninguna de las trayectorias de demodulación de dicha lista de trayectorias de demodulación.
22
Procedimiento según la reivindicación 21, en el que la intensidad de señal de dicha segunda trayectoria de sondeo particular es más elevada que la de cualquiera de dichas trayectorias.
23
Procedimiento según la reivindicación 1, que además comprende la etapa siguiente:reasignación de un elemento de demodulación particular, comprendiendo esta etapa las etapas siguientes: ES 2 215 166 T3 anulación de la asignación de dicho elemento de demodulación particular asignado a una trayectoria de demodulación particular, y asignación de dicho elemento de demodulación particular a una segunda trayectoria de sondeo particular.
24
Procedimiento según la reivindicación 23, en el que dicha trayectoria de demodulación particular tiene el mismo índice de transmisión que dicha segunda trayectoria de sondeo particular.
25
Procedimiento según la reivindicación 24, en el que dicha trayectoria de demodulación particular tiene una intensidad de señal que es inferior a la intensidad de señal de dicha segunda trayectoria de sondeo particular.
26
Procedimiento según la reivindicación 24, en el que dicha trayectoria de demodulación particular tiene una intensidad de señal que es por lo menos cierta proporción inferior a la intensidad de señal de dicha segunda trayectoria de sondeo particular.
27
Procedimiento según la reivindicación 24, en el que dicha trayectoria de demodulación particular tiene una intensidad de señal que es 3 dB inferior a la intensidad de señal de dicha segunda trayectoria de sondeo particular.
28
Procedimiento según la reivindicación 23, en el que dicha trayectoria de demodulación particular tiene el mismo índice de transmisión que por lo menos otra entrada de dicha lista de trayectorias de demodulación.
29
Procedimiento según la reivindicación 23, en el que dicha trayectoria de demodulación particular tiene una intensidad de señal que es la menor de todas las trayectorias de demodulación que tienen el mismo índice de transmisión que dicha trayectoria de demodulación particular.
30
Procedimiento según la reivindicación 1, en el que dicha etapa de comparación de dicha lista de trayectorias de demodulación con dicha lista de trayectorias de sondeo comprende además la etapa de comparación de dicho tiempo de llegada de cada trayectoria de demodulación de dicha lista de trayectorias de demodulación con el tiempo de llegada de una entrada correspondiente de dichas trayectorias de sondeo.
31
Procedimiento según la reivindicación 1, en el que dicha etapa de comparación de dicha lista de trayectorias de demodulación con dicha lista de trayectorias de sondeo comprende además la etapa de comparación, en un desplazamiento de tiempo predeterminado, de dicho tiempo de llegada de cada trayectoria de demodulación de dicha lista de trayectorias de demodulación con el tiempo de llegada de una correspondiente entrada de dichas trayectorias de sondeo.
32
Procedimiento según la reivindicación 1, en el que cada transmisor transmite una señal modulada mediante pseudorruido utilizando un código de pseudorruido que consiste en una secuencia de valores de código, y en el que dicho tiempo de llegada corresponde a un desplazamiento de valor de código de dicho código de pseudorruido.
33
Procedimiento según la reivindicación 1, en el que cada transmisor transmite una señal modulada mediante pseudorruido utilizando un código de pseudorruido que consiste en una secuencia de valores de código, y en el que dicho tiempo de llegada corresponde a un intervalo de tiempo en torno a un desplazamiento de valor de código de dicho código de pseudorruido.
34
Procedimiento según la reivindicación 33, en el que cada valor de código de dicha secuencia de valores de código tiene una duración determinada y en el que dicho intervalo de tiempo es la mitad de dicha duración.
35
Procedimiento según la reivindicación 1, en el que cada transmisor transmite una señal modulada mediante pseudorruido común utilizando un código de pseudorruido común que consiste en una secuencia de valores de código, y cada transmisor transmite con un desplazamiento de tiempo diferente al de dichos demás transmisores, y en el que dicho índice de transmisión corresponde a dicho desplazamiento de tiempo diferente.
36
Procedimiento según la reivindicación 1, en el que dicha etapa de realización de un sondeo de dichas señales disponibles se repite de forma sistemática a lo largo del tiempo.
37
Procedimiento para asignar, en un sistema de recepción que consiste en un grupo de receptores, dichos receptores a un grupo de señales existentes procedentes de por lo menos una fuente, que comprende las etapas siguientes:creación de una lista de dichas señales existentes, teniendo cada señal existente de dicha lista de señales existentes una indicación de la intensidad de señal, una indicación del tiempo y una correspondiente indicación de fuente;comparación de dicha lista de dichas señales existentes con una lista de señales asignadas actualmente a dichos receptores, teniendo cada señal de dicha lista de señales asignadas actualmente a dichos receptores una indicación de la intensidad de señal, una indicación del tiempo y una correspondiente indicación de fuente, y asignación a dichos receptores de dichas señales existentes, de tal forma que se dispone de un número máximo de correspondientes indicaciones de fuente diferentes en dicha lista de señales asignadas actualmente a dichos receptores. ES 2 215 166 T3
38
Procedimiento según la reivindicación 37, que además comprende la etapa de reasignación de un receptor, de tal forma que se dispone de dicho número máximo de correspondientes indicaciones de fuente diferentes en dicha lista de señales asignadas actualmente a dichos receptores, que comprende las etapas siguientes:anulación de la asignación de un receptor particular, y asignación de dicho receptor particular a una de dichas señales existentes de dicha lista de señales existentes.
39
Procedimiento según la reivindicación 37, en el que la frecuencia de aparición de dichas etapas de reasignación está limitada en el tiempo.
40
Procedimiento según la reivindicación 37, en el que se lleva a cabo un número predeterminado de dichas etapas de reasignación en cada una de dichas etapas de creación de dicha lista de dichas señales existentes.
41
Procedimiento según la reivindicación 37, en el que dicha etapa de creación de dicha lista de dichas señales existentes se repite de forma sistemática a lo largo del tiempo.
42
Procedimiento según la reivindicación 38, en el que dicha etapa de creación de dicha lista de dichas señales existentes se repite de forma sistemática a lo largo del tiempo.
43
Procedimiento según la reivindicación 37, que comprende además la etapa de provisión de un primer receptor asignado a una primera señal, siendo la indicación de intensidad de señal de dicha primera señal inferior a un nivel predeterminado.
44
Procedimiento según la reivindicación 43, en el que dicho receptor disponible pasa al estado de reposo.
45
Procedimiento según la reivindicación 43, en el que dicho receptor disponible continúa recibiendo dicha primera señal.
46
Procedimiento según la reivindicación 43, en el que, en dicha etapa de asignación de dichos receptores a las señales existentes, puede asignarse una señal existente particular a dicho receptor disponible.
47
Procedimiento según la reivindicación 37, que además comprende la etapa de provisión de un primer receptor asignado a una primera señal, siendo la correspondiente indicación de intensidad de señal de dicha primera señal inferior a un nivel predeterminado durante un período de tiempo predeterminado.
48
Procedimiento según la reivindicación 47, en el que dicho receptor disponible está en estado de reposo.
49
Procedimiento según la reivindicación 47, en el que dicho receptor disponible continúa recibiendo dicha primera señal.
50
Procedimiento según la reivindicación 47, en el que, en dicha etapa de asignar dichos receptores a las señales existentes, puede asignarse una señal existente particular a dicho receptor disponible.
51
Procedimiento según la reivindicación 37, en el que dicha indicación de intensidad de dichas señales asignadas a dichos receptores se genera a partir de una salida RSSI en dichos receptores.
52
Procedimiento según la reivindicación 51, en el que dicha salida RSSI de dichos receptores se mide de forma repetitiva.
53
Procedimiento según la reivindicación 37, que además comprende la etapa de provisión de un primer receptor asignado a una primera señal, siendo la correspondiente indicación de intensidad de señal de dicha primera señal inferior a un nivel predeterminado para un número predeterminado de dichas mediciones.

Independent claims53

217 paragraphs in 8 sections, as filed

IS 2 215 166 T3

DESCRIPTION

Assignment of demodulation elements in a system capable of receiving multiple signals. Background of the invention

I. Field of the invention

The present invention relates to communication systems and, in particular, to a method of assigning demodulation elements for a communication system capable of receiving multiple signals.

II. Description of Related Art

In a code division multiple access (CDMA) cellular telephone system, a common frequency band is used for communication with all base stations in the system. The common frequency band allows simultaneous communication between a mobile station and more than one base station. The signals occupying the common frequency band are discriminated at the receiving station through the spread spectrum CDMA waveform properties, based on the use of a high speed pseudo noise (PN) code. The high speed PN code is used to modulate the signals transmitted from base stations and mobile stations. Transmitting stations using different PN codes or PN codes shifted in time generate signals that can be received separately at the receiving station. High-speed PN modulation also allows the receiving station to receive, from a single transmitting station, a signal that has traveled through differentiated propagation paths.

It is the multipath characteristics of the cell channel that determine the generation of the signal that travels through several differentiated propagation paths. One of the characteristics of multipath channels is the time spread introduced in the signals that are transmitted on these channels. For example, if an ideal pulse is transmitted through a multipath channel, the received signal appears as a train of pulses. Another characteristic of multipath channels is that each path of a channel can cause a different attenuation factor. For example, if an ideal pulse is transmitted through a multipath channel, each pulse in the received pulse train will generally have a different signal strength than the other received pulses. Finally, another characteristic of multipath channels is that each path of a channel can cause a different phase in the signal. For example, if an ideal pulse is transmitted through a multipath channel, each pulse in the received pulse train will generally have a different phase than the other received pulses.

In the mobile radio channel, multipaths are created by reflecting the signal off surrounding obstacles (buildings, trees, vehicles, and people). In general, the mobile radio channel is a time-varying multipath channel, due to the relative movement of the structures that create the multipath. For example, if an ideal pulse is transmitted through the time-varying multipath channel, the received pulse train will change location, attenuation, and phase over time, based on the time it was transmitted.

The multipath characteristic of a channel can cause the signal to fade. The fading is caused by the phasing characteristics of the multipath channel. Fading occurs when the vectors of the various trajectories are added destructively, receiving a signal that is less than any of the individual vectors. For example, if a sine wave is transmitted through a multipath channel that has two paths, one of which has an attenuation factor of X dB, a propagation time δ, and a phase shift of Θ radians, and the other, an attenuation factor of X dB, a propagation time δ and a phase shift of Θ + π radians, no signal will be received through the channel output.

In narrowband modulation systems, such as FM analog modulation systems used in conventional radiotelephony systems, the existence of multipath in the radio channel causes considerable multipath fading. However, as noted above in connection with a wideband CDMA system, the various paths can be discriminated in the demodulation procedure. This discrimination not only greatly reduces the severity of multipath fading, but provides advantages to the CDMA system.

The detrimental effects of fading in a CDMA system can be mitigated by controlling the transmit power. A system for controlling the power of the base station and mobile station is disclosed in US Patent No. 5,056,109 entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM", published on October 8, 1991 and granted to the assignee of the present invention. Furthermore, the effect of multipath fading can be reduced in communicating with various base stations, using a call handoff procedure. U.S. Patent No. 5,101,501 entitled "SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM" issued October 8, 1991 and issued to the assignee of the present invention, a call transfer procedure is disclosed.

IS 2 215 166 T3

In a cellular phone system, it is of utmost importance to maximize the capacity of the system in terms of the number of simultaneous phone calls that can be processed. The capacity of a spread spectrum system can be maximized by controlling the transmit power of each mobile station such that each transmitted signal reaches the base station receiver at the same level. In a real system, each mobile station can transmit the minimum signal level that generates a signal-to-noise ratio that allows acceptable data retrieval. If the signal transmitted by a mobile station reaches the base station receiver at too low a power level, the bit error rate may be too high to allow high quality communications, due to interference from other mobile stations. On the other hand, if the signal transmitted by the mobile station reaches too high a power level to the base station, communication with this particular mobile station is acceptable, but its high signal power acts as an interference for the other mobile stations. . This interference can adversely affect communications with other mobile stations.

Accordingly, to maximize the capacity of an exemplary spread spectrum CDMA system, the transmit power of each mobile station in a base station's coverage area is controlled by the base station to generate the same nominal signal power received at the base station. In the ideal case, the total signal power received by the base station is equal to the nominal power received from each mobile station, multiplied by the number of mobile stations transmitting within the coverage area of the base station, plus the power it receives from mobile stations in the coverage area of nearby base stations.

Path loss on the mobile radio channel can be characterized by two different phenomena: mean path loss and fading. The downlink (ie, from the base station to the mobile station) operates at a different frequency than the uplink (ie, from the mobile station to the base station). However, because the downlink and uplink frequencies are in the same frequency band, there is a significant correlation between the mean path loss of the two links. On the other hand, fading is an independent phenomenon for downlink and uplink and varies as a function of time.

In an exemplary CDMA system, each mobile station calculates the downlink path loss, based on the total power at the input to the mobile station. Total power is the sum of the power of all base stations operating with the same frequency assignment detected by the mobile station. From the time-averaged downlink path loss calculation, the mobile station establishes the transmission level of the uplink signal. In case the uplink channel of a mobile station experiences a sudden improvement relative to the downlink channel of the same mobile station due to independent fading of the two channels, the signal received at the base station from this mobile station will increase in power. This increase in power causes more interference with all signals that share the same frequency assignment. Therefore, if this sudden improvement in the channel has a rapid response in the transmission power of the mobile station, the performance of the system will also experience an improvement.

The transmission power of the mobile station is also controlled by one or more base stations. Each base station with which the mobile unit communicates measures the strength of the signal received from the mobile unit. The measured signal strength is compared to the desired signal strength level for that particular mobile station. Each base station generates and sends a downlink power adjustment command to the mobile unit. In response to the base station power adjustment command, the mobile unit increases or decreases the transmit power of the mobile unit by a predetermined amount. This procedure provides a rapid response to channel changes, which determines an improvement in the average performance of the system.

When a mobile station communicates with more than one base station, it receives power adjustment commands from each base station. The mobile station takes the necessary actions according to the various power control commands of the base stations, to prevent transmitting power levels that could negatively interfere with the communications of other mobile stations and, at the same time, provide enough power to establish communication between the mobile station and at least one of the base stations. This power control mechanism is implemented by allowing the mobile station to increase the signal transmission level only when all base stations with which it communicates request a power level increase. The mobile station decreases the transmission level of the signal when one of the base stations with which it communicates requests a decrease in power.

The existence of multiple paths can provide path diversity to a wideband spread spectrum system. Spread spectrum systems generate a spread information signal by modulating an information signal with a pseudo-noise (PN) code. Typically, PN code runs much higher than the information signal. The frequency at which the PN code is generated is called the segment frequency and the duration of the data bits of the PN code is called the segment duration. If there are two or more paths with a differential propagation time greater than the segment duration, two or more processing elements, called demodulation elements, can be used to separately demodulate these signals. The multipath fading of these signals is typically independent, that is, the signals do not typically fade together. Therefore, the output of the two or more elements

ES 2 215 166 T3 demodulation can be combined to obtain path diversity. Signal loss will only occur when signals from all demodulation elements experience fading at the same time. In an ideal system, both the base station and the mobile station employ various demodulation elements.

As a mobile station moves through the physical environment, the number of signal paths and the intensity of the signals that are transmitted on these paths, received at both the mobile station and the base station, vary constantly. Consequently, a receiver embodying the present invention will use a special processing element, called a search element, that continuously scans the channel, in the time domain, to determine the existence, time shift and intensity of the signals. of the multipath environment. The search element output provides information to ensure that the demodulation elements are tracking the most favorable trajectories. The present invention provides a method of assigning the various demodulation elements to the multiple received signals, based on the information from the search element.

In an exemplary CDMA cellular telephone system, each base station transmits a spread spectrum "pilot" reference signal. Mobile stations use the pilot signal to obtain initial system synchronization and provide reliable tracking of the time, frequency and phase of the signals transmitted by the base station. The pilot signal transmitted by each base station in a system can use the same PN code with a different code phase shift, which determines that the PN codes transmitted by nearby base stations are identical, albeit shifted from each other in time. . The phase shift makes it possible to differentiate some pilot signals from others, depending on their base station of origin. The mobile station paging element continues to scan the received signal with the code offsets corresponding to the pilot signals transmitted by nearby base stations, while in idle call mode. Once a call is initiated, a PN code address is determined to use during the call. The address of the code can be assigned by the base station or it can be determined in advance based on the identity of the mobile station. After the call is initiated, the mobile station's paging element continues to scan for pilot signals transmitted by nearby base stations. When the pilot signal transmitted by a nearby base station becomes strong enough to establish communication, the mobile station generates and transmits a control message to the base station currently answering the call. The current base station provides the control message to the cellular system controller.

The cellular system controller begins the base station diversity procedure called the "call handoff" procedure. First, the cellular system controller assigns a modem located in the new base station to the call. The modem receives the PN address associated with the call between the mobile station and the current base station modem. The modem of the new base station in charge of answering the call searches and finds the signal transmitted by the mobile station. Also, the modem of the new base station begins transmitting a downlink signal to the mobile station. The search element of the mobile station searches for the downlink signal according to the signal information provided by the previous base station. When the mobile station acquires the signal transmitted by the modem of the new base station, the mobile station can continue to communicate through the two base stations. To this first new base station, another base station can also be added. In this case the mobile station can continue to communicate through three base stations. This procedure can continue until the mobile station communicates with the base station of each demodulation element it contains, or it can take even longer.

The combination of diversity in the mobile station provides significant benefits to the communication quality and reliability of a cellular telephone system. A form of maximum ratio blending can be used to aid in the determination of the signal-to-noise ratio for each path. Each path can then be combined with the contributions of other weighted signal-to-noise paths. The combination can be coherent, since the demodulation of the pilot signal allows the phase of each path to be determined.

On the path from the mobile station to the base station, path diversity reception occurs in a similar manner. A base station can contain a set of processing elements analogous to that of the mobile station, insofar as the search element can provide data to assign a plurality of demodulation elements. The present invention defines a method for assigning demodulation elements to multipath signals at the base station.

During communication with an end user, demodulated data signals from a base station are sent to the cellular system controller along with an indication of the signal quality. The cellular system controller transmits the signals to the end user. When a mobile station is in base station diversity mode with two independent base stations, the demodulated data signals from both base stations are transmitted to the cellular system controller along with an indication of the signal quality. The cellular system controller then combines the two signal versions from the mobile station or selects the signal with the best quality indication. In an alternative system configuration, it is possible to transmit the uncoded or even unmodulated signals to the cellular system controller to allow the use of a better diversity combining procedure.

A common base station configuration can contain multiple sectors. A multi-sector base station comprises several independent transmit and receive antennas. When a mobile station is in modali4

ES 2 215 166 T3 diversity of base stations and communicates with two sectors of the same base station, the demodulated data signals from both sectors are available for combination at the base station before passing the signals to the cellular system controller . In reality, in a base station with several sectors, it is possible to configure a system in which each demodulation element can be assigned to any received signal, regardless of the sector from which it comes. This system configuration allows a procedure called "call smoother transfer procedure" to be carried out, and the present invention defines a procedure for allocating demodulation elements for this configuration.

Accordingly, one of the objectives of the present invention is to provide a method for assigning several demodulation elements in a mobile station.

Another objective of the present invention is to provide a method for assigning several demodulation elements in a base station.

Summary of the invention

The present invention defines a method for assigning various demodulation elements in a spread spectrum system. In the present invention, a search element of the mobile station polls in which it scans a range of time offsets around the nominal arrival time of each signal from each base station with which active communication has been established. Each probe provides a list of probe paths comprising pilot signal strengths, time offsets, and the corresponding base station pilot offset. The search element passes the information to a controller. The controller tries to match the time offset of each probe path and the time offset of the paths that are currently being demodulated by the demodulation elements. If there are multiple demodulation paths coincident with a sounding path, all demodulation elements assigned to that path, except for the demodulation element with the highest signal strength indication, are designated as "free". If there is any demodulation path that does not match any survey path, a survey path entry is added to the list of survey paths based on the demodulation path information.

The controller then considers the probe paths in order of signal strength, placing the probe path with the highest signal strength first. If no demodulation element has been assigned to any path of the corresponding sector of the considered sounding path, the controller attempts to assign a demodulation element to the sounding path in the order indicated below. If there is any demodulation element not assigned or designated as "free", the demodulation element is assigned to the sounding path. If there is no free demodulation element, the demodulation element that has the weakest path and that is not the only demodulation path of its base station sector, if any, is reassigned to the probe path. Finally, if in the first two cases no demodulation element can be assigned to the sounding path, the demodulation element assigned to the weakest path is reassigned to the sounding path if the signal strength of the sounding path probing is greater than the signal strength of the weakest demodulation path. This procedure continues until a reassignment occurs or until the last criterion fails to reassign any demodulation element to the considered sounding path.

If none of the above rules allows a demodulation element to be reassigned for the present probe, the controller reconsiders the probe paths in order of signal strength, placing the probe path with the highest signal strength first. If the sounding path is not currently assigned to a demodulation element, the controller can assign any demodulation element not assigned or designated as "free" to the considered sounding path. If there is no unassigned or designated "free" demodulation element, the controller can also reassign a demodulation element that is assigned to the same base station sector as a probe path if the probe path is stronger than the probe path. demodulation. Also, the controller can reassign the weakest demodulation element assigned to any base station sector that has two or more demodulation elements assigned if the probing path is stronger than the demodulation path. When either of the two previous rules allows reassignment or when both of the previous reassignment rules are unsuccessful for the polling path under consideration, the procedure starts over.

The present invention uses these steps to ensure diversity of base stations and sectors. Each time a demodulation element is reassigned, data modulation does not resume until a finite time interval elapses. Accordingly, the present invention limits the number of reassignments of demodulation elements per sounding. Comparison indices are used to create hysteresis in the assignments and thereby reduce excessive remapping of demodulation elements.

The base station uses a similar but less complicated procedure to assign the demodulation elements. Because each base station sector receives the same information from a single mobile station, it is not necessary to sacrifice peak signal level paths to favor diversity. Therefore, the base station procedure relies more strictly on the signal level, while limiting the number of reassignments per poll similar to the mobile station procedure. The base station also uses rates similar to those of the mobile station to create hysteresis and reduce excessive reallocation of demodulation elements.

IS 2 215 166 T3

Brief description of the drawings

The characteristics, objectives and advantages of the present invention will become more apparent from the detailed description provided below, in relation to the drawings in which equivalent reference characters are used for the corresponding indications, and in which:

Figure 1 is an illustration of an exemplary mobile station comprising several independent demodulation elements;

Figure 2 is a detailed block diagram of an exemplary demodulation element of the mobile station of Figure 1;

Figures 3A to 3C illustrate pilot signal strength versus time for three different base stations or base station sectors;

Figure 4 is a summary of the demodulation element assignment procedure for a mobile station according to the present invention;

Figures 5A to 5D are a detailed example of the demodulation element assignment procedure for a mobile station according to the present invention;

Figure 6 is an illustration of an exemplary base station comprising several independent demodulation elements;

Figure 7 is a detailed block diagram of an exemplary demodulation element of the base station of Figure 6;

Figure 8 is a summary of the demodulation element assignment procedure for a base station according to the present invention;

Figures 9A to 9D are a detailed example of the demodulation element assignment procedure for a base station according to the present invention and Figures 10A and 10B illustrate the signal strength of a single mobile station in relation to time for two sectors of different base stations.

Detailed description of the preferred embodiments

The present invention defines a method for assigning various demodulation elements in a spread spectrum system. In the following, two procedures are disclosed: one directed to the operation of the base station and the other directed to the operation of the mobile station. Both algorithms are disclosed by specific executions that illustrate the general principles of the present invention.

The method used by the mobile station assumes that the mobile station comprises several independent demodulation elements. Figure 1 illustrates an exemplary embodiment of such a mobile station. The elements are controlled by controller 200 through interface 212. Input signal 210 provides the signal received by the mobile station, which has undergone RF / analog processing, to search element 202 and demodulation elements 204A to 204N. Search element 202 continuously scans the time domain for pilot signals from nearby base stations. Search element 202 also scans a group of time offsets around the nominal signal arrival time from each base station to find the generated multipath signals.

Search element 202 passes the generated data to controller 200. Search element 202 can pass data through interface 212. Alternatively, search element 202 can pass data to controller 200 through direct access to the memory. Direct memory access allows search element 202 to pass information to controller memory 218 directly, without interrupting controller functions. The direct memory access operation is illustrated by a dashed line 216 that directly connects the search element 202 with the memory 218 of the controller 200. The controller 200 uses the data stored in the memory 218 to assign demodulation elements 204A to 204N to one of the plurality information signals that the input signal 210 may contain.

Demodulation elements 204A through 204N process input signal 210 to generate soft decision data bits 220A through 220N that are combined in symbol combiner 208. The output of symbol combiner 208 (not shown) is soft decision data. combinations suitable for Viterbi decoding. Demodulation elements 204A through 204N further provide multiple output control signals to controller 200, via interface 212, which are used in the allocation procedure.

IS 2 215 166 T3

Each of the demodulation elements 204A to 204N is very similar in structure to the others. The

Figure 2 illustrates in more detail an exemplary demodulation element 204 of Figure 1. In Figure

2, the input signal 210 is assumed to be a quadrature phase shift keying (QPSK) signal having in-phase (I) signal samples and quadrature-phase (Q) signal samples. The I and Q signal samples, each of which is made up of a multi-bit value, are input to QPSK de-spreaders 230 and 250.

The QPSK spreader 230 also receives the PNI pilot PNI and PNQ sequences from the pilot PN 232 sequence generator. The pilot PN 232 sequence generator generates the PNI and PNQ sequences that are identical to those used in the base station based on the timing of the base station. sequence and status (not shown) provided by controller 200 of Figure 1. The QPSK expander 230 removes PN spreading from the unprocessed I and Q signal samples to extract the I and Q component samples found.

The I and Q component samples found are transmitted respectively from QPSK decoder 230 to digital filters 234 and 236. Filters 234 and 326 are typically configured as simple first order low pass digital filters. The filtered I and Q samples obtained from filters 234 and 236 are samples of the I and Q components of the pilot signal and are indicated as pilot samples I and pilot samples Q. Pilot samples I and Q are provided to phase rotation and data scaling unit 238, latch indicator 258, and vector product unit 256.

In the modulation system considered for this example, the pilot signal uses the Walsh code only zeros. When using the zeros-only Walsh code, the spread pilot PN signal equals the I and Q PN spreading sequences themselves. Therefore, by removing the PN spreading from the I and Q signal samples and filtering the result, the result is recovered the pilot signal.

To retrieve the data, the I and Q component samples found from the QPSK de-spreader 230 are also obtained and transmitted respectively to the digital mixers 240 and 242. The digital mixers 240 and 242 receive a Walsh sequence from the Walsh sequence generator 244 . This Walsh sequence is identical to the Walsh sequence assigned to this channel at the base station and is selected based on a sequence assignment provided by controller 200 (not shown).

The found and decoded I and Q component samples are passed from digital mixers 240 and 242 to accumulators 246 and 248, respectively. Accumulators 246 and 248, respectively, accumulate the I and Q component samples found and decoded over the time of a symbol. The output from accumulators 246 and 248 is the I and Q symbol data, called I data samples and Q data samples. The I data samples and Q data samples are provided to the data scale and phase rotation unit 238. Accumulators 246 and 248 are zeroed or reset after data output to accumulate the next group of samples. .

The phase rotation and data scaling unit 238 performs a dot product operation on the I pilot samples and Q pilot samples from filters 234 and 236 and the I data and Q data from accumulators 246 and 248. To find the magnitude of the component of the data vector that is in phase with the pilot signal, the dot product DP of the data samples I and the data samples Q, and the vector of pilot samples I and pilot samples Q, are calculated. Finally, the data obtained is provided to the "first in, first out" storage register (FIFO) 260.

The "first in, first out" (FIFO) storage register 260 performs a realignment function. The realignment function delays the output of data 220 from a particular demodulation element so that the data can be aligned with data from other demodulation elements. For example, referring again to Figure 1, it is assumed that demodulation element 204A demodulates data that has taken a direct path from a first base station to the mobile station. Furthermore, the demodulation element 204B is assumed to demodulate a multipath signal that also originates from the first base station. The multipath signal has taken an indirect path to the mobile station and therefore arrives later than that of the direct path. To combine the two data paths in symbol combiner 208, the output of demodulation element 204A must be delayed and aligned with the output of demodulation element 204B. FIFO storage register 260A will delay the data output from demodulation element 204A to match the output from demodulation element 204B. Also, the demodulation element 240C (not shown) is assumed to demodulate a signal from a second base station that is far removed from the mobile station and therefore experiences a delay greater than even the indirect path signal from the mobile station. first base station. The FIFO 260A and FIFO 260B storage registers must delay the output of demodulation elements 204A and 204B, respectively, so that the signals received by the symbol combiner 208 are time aligned.

The demodulation element 204 provides the received signal strength indicator (RSSI) of the demodulation path 262 and the on / off signal 264 to the controller. The energy accumulator and latch detector 258 calculate the mean signal intensity of the pilot samples I and Q. The demodulation path RSSI 262 indicates the calculated pilot signal intensity value. Latch indicator 258 compares the calculated pilot signal intensity value to a threshold. If the value exceeds the threshold, the demodulation element is phase locked. If the calculated pilot signal intensity value is below the threshold, the demodulation element is phase disengaged. When the demodulation element is disengaged

ES 2 215 166 T3 in phase, the data output 220 may be disturbed by noise due to low signal levels. The controller may use a trip indication to designate data output 220 as invalid and, prevent, from being used to calculate the combined result. The latch function can support hysteresis and thus if the latch threshold has already been exceeded once, the demodulation element does not indicate a latch condition until the signal strength is less than a second lower threshold . The controller can unassign the demodulation element that is not phase locked and the demodulation element is then in the idle state. Alternatively, the controller can designate the demodulation element as "free" to indicate that the demodulation element is a candidate for reassignment, leaving the demodulation element in the active state so that it tries to demodulate a signal and can recover the latch state. phase.

Each demodulation element calculates the carrier frequency error. Vector product unit 256 generates an estimate of frequency error 268 by measuring the pilot phase shift between symbols. The vector product unit 256 calculates the vector product of the present pilot vector consisting of the pilot samples I and Q for a previous pilot vector. The frequency error estimate is used in a carrier tracking loop (not shown).

The demodulation element 204 tracks the time offset of the signal it is demodulating. The input signal 210 having the I and Q signal samples is input to the QPSK decoder 250. The QPSK decoder 250 also receives the PNI and PNQ pilot PN sequences from the pilot PN sequence generator 232, through the control unit. time misalignment 252. Time misalignment unit 252 advances and lags the PNI and PNQ pilot PN sequences. The QPSK spreader 250 removes PN spreading of the I and Q signal samples to extract the leading or lagging samples found from the I and Q components. The I & Q summation unit (Σ) 252 sums the results relative to a group of samples PN and provides the result to time tracking unit 254. The time tracking unit 254 compares the summed leading and lagging I and Q component samples and provides the demodulation path time 270 that reflects the current estimate of the time location of the input signal.

Each time a demodulation element is assigned to a new signal, it takes the demodulation element some time to output the old data that is still in the demodulation path and latch onto the new signal. This procedure provides a finite time in which the demodulation element does not generate any valid output data. The present invention limits the number of reassignments per poll (as will be described later), thereby preventing large blocks of data from being lost. The procedure also includes a hysterical comparison operation that limits excessive reallocation between two similarly favorable signals.

The input signal 210 provides signals to the search element and demodulation elements. The input signal 210 can contain pilot signals from many base stations and can also contain information signals from a variety of base stations destined for other mobile stations, apart from the present mobile station. Figures 3A through 3C illustrate an exemplary format showing the components of input signal 210 necessary to design the method of the present invention. The specific procedure described below assumes that there are three demodulation elements available for allocation. Figure 3A illustrates the intensity of the pilot signal in relation to time for a first base station or sector. Figures 3B to 3C illustrate the intensity of the pilot signal in relation to time for a second and third base station or sector, respectively. In Figures 3A to 3C, the horizontal axis contains time divisions and the vertical axis, energy divisions in dB. In Figure 3A, there are four paths above the noise floor and are designated as paths 300, 302, 304, and 306. Path 300 is the one that arrives first and can be assumed to be the most direct directory between the base station and the mobile station. Paths 302, 304 and 306 then arrive one after another and are the multipath signals of the same signal as path 300. Line 320 represents a threshold below which the signal-to-noise level does not provide any data. reliable.

Figure 3B and Figure 3C represent input signals from two other base stations or base station sectors. The time offset between the three base stations is not explicitly shown. Figures 3B and 3C can be considered normalized with respect to the delay of Figure 3A for illustrative purposes. In Figure 3B, there are two paths above the noise floor and are designated as paths 308 and 310. Path 308 is the first to arrive and is followed by path 310. Again, line 320 represents a threshold below which the signal-to-noise level does not provide any reliable data. In Figure 3C, there are two paths above the noise floor and are designated as paths 312 and 314. Path 312, which is the first to arrive, is followed by path 314 which takes a certain time to arrive. Again, line 320 represents a threshold below which the signal-to-noise level does not provide any reliable data.

As described above, mobile station power control is crucial to overall system performance. Each mobile station must transmit the minimum possible signal to allow reliable communication and achieve high system capacity. Because each base station through which the mobile station communicates independently controls the transmit power of the mobile station, the method favors a high degree of base station or base station sector diversity. To obtain maximum system capacity, the mobile station must reduce its transmit power, if requested by any base station. The mobile station will only increase the transmission power when all the base stations through which

ES 2 215 166 T3 communicates requesting an increase in the transmission power. Since the method favors base station diversity, the power control information from a particular base station will reach the mobile station without problems.

In the system example described here, only one active base station is needed for a mobile station when the mobile station is in the idle state (e.g. when the mobile station is active but not busy in continuous two-way communication with a mobile station). Base station). As noted above, when the mobile station switches to an extended communication mode (for example, during a telephone call), it can establish communication with a plurality of base stations. The allocation procedure described below applies to idle mode operation and extended communication. The method of the present invention is simplified when there is only one active base station (for example, when the mobile station is in idle mode). The present invention is not limited to systems that operate in the manner described.

Figure 4 is a summary of an exemplary demodulation element assignment procedure for a mobile station in accordance with the present invention. The procedure runs cyclically. In the first stage of each cycle, the search element polls pilot signal strengths versus time for each active base station, as indicated in block 350 of Figure 4. An active base station is a base station through which communication has been established. These base stations are globally called a group of active base stations. The search element scans a time interval around the expected arrival time of the signal from each base station to find multipath signals. The search element creates a group of sounding path data comprising time offset and signal strength.

The controller compares the probing paths and the demodulation paths, as indicated in block 352. The demodulation paths are paths that are currently assigned to demodulation elements. The controller collects the corresponding path information (time offset and signal strength) from each demodulation element.

As noted above, the main consideration in assigning a demodulation element to a path is the number of different paths that the same base station or sector currently has assigned to demodulation elements. If the poll path belongs to a base station that has a signal that is not currently being demodulated by any demodulation elements, the poll path becomes a candidate for demodulation element assignment. If there is any demodulation element whose assignment to a path needs to be unassigned and which needs to be reassigned to a probing path in block 354, the procedure returns to block 350 to avoid reassigning more than one demodulation element per cycle, as indicated at block 356. If no demodulation elements have been reassigned, demodulation elements can be assigned according to signal strength as indicated in block 358. The procedure then returns to block 350 and the next cycle begins.

Figures 5A to 5D are a detailed example of the summary of the demodulation element allocation procedure of Figure 4. In Figures 5A to 5D, it is assumed that there are three demodulation elements available for allocation. However, from the execution of Figures 5A to 5D, many different embodiments of the present invention will be readily apparent. For example, the number of demodulation elements may be greater or less than three. Accordingly, Figures 5A to 5D are not intended to limit the present invention, but to show a preferred embodiment.

Figure 5A begins the cycle and is roughly equivalent to block 350 of Figure 4. Block 10 indicates the initial function of the procedure. Block 12 deletes the list of probe paths found in the last cycle. Block 14 establishes a first base station sector with which communication has been established as the first sector considered in the search procedure. Block 16 instructs the search element to search in a time interval around the expected arrival time of the signals of the sector under consideration. Block 18 finds at most the three most intense local maxima in the search for the sector under consideration. In this example, it is not efficient to find more than three maxima, because there are only three demodulation elements available for allocation and in no case will a demodulation element be assigned to the fourth strongest probe path in a single base station sector.

In the exemplary embodiment, a local maximum is found in the search interval, based on the use of probe samples having a mutual time spacing of 0.5 segments. If a lower sounding sample resolution is used, it is highly likely that a single signal path will generate more than one distinct peak. In such a system, the discrete peaks can be used to create a single local maximum for demodulation element assignment purposes.

Block 20 adds the information for each of the three maxima that exceed a minimum signal level threshold to the list of sounding paths. If there is any sector of the active group that has not been scanned, block 22 routes the procedure to block 26. Block 26 selects the next considered sector and then blocks 16 to 22 are repeated for the next considered sector. If the sector considered is the last sector to be scanned, the polling list is complete. Block 22 routes the flow to the next part of the procedure, through connection block 24.

IS 2 215 166 T3

Once the group of sounding paths is completed, the procedure continues through Figure 5B, which is roughly equivalent to block 352 of Figure 4. Connection block 24 routes the flow to block 32. Block 32 establishes as demodulation path considered one of the paths that is currently being demodulated by a demodulation element. Block 34 checks the latch / unhook status of the demodulation element corresponding to the demodulation path considered. If the demodulation element is disengaged, the controller can unassign the demodulation element or it can designate the demodulation element as "free", as indicated in block 50. In that case, there is no valid data that matches the sounding paths. The action corresponding to the demodulation path considered will have ended and block 50 routes the flow to block 46.

If the demodulation element under consideration is currently phase locked, block 36 attempts to compare the time offset of the demodulation path and the analogous information from the list of sounding paths. In general, each demodulation path coincides with at least one sounding path. In other words, if a path from a base station is strong enough to be demodulated, it should be detectable by the search element. On certain occasions, the search element may omit some trajectory and therefore not include the trajectory corresponding to a demodulation trajectory in the list of probing trajectories. The demodulation element estimates the signal level and the time offset of a path more accurately than the search element. Therefore, the procedure considers that the demodulation element is accurate and that such a path does not exist. Then, if there is no probe path input for a demodulation path, block 52 creates a probe path entry corresponding to the demodulation path. The action corresponding to the demodulation path considered will have ended and block 52 routes the flow to block 46.

If there is any probing path that corresponds to the considered demodulation path, block 38 finds out if the considered demodulation path is the first demodulation path that matches the particular probing path. If the demodulation path considered is the first coincident, the action corresponding to the demodulation path considered will have ended and block 38 routes the flow to block 46.

If the demodulation path considered is not the first demodulation path that matches the particular probing path, it means that there are two demodulation elements that are demodulating substantially the same path. This situation can occur on a regular basis. Each demodulation element tracks the signal to which it was originally assigned. Commonly, two multipath signals meet over time on the same or nearly the same path. Block 38 determines said situation. If the demodulation path considered is not the first demodulation path that matches a particular probe path, block 40 determines which demodulation path has the highest signal level. If the demodulation element under consideration has the highest signal level, block 42 unassigns the previous demodulation element that has a path coinciding with the same probing path, or designates it as free. If the demodulation element considered is weaker than the previous path, block 44 unassigns the demodulation element corresponding to the demodulation path considered, or designates it as free. The action corresponding to the demodulation path considered will have been completed.

If there is any demodulation path still to be considered, block 46 routes the procedure to block 48. Block 48 selects the next considered demodulation path and block 34 begins repeating the procedure for that demodulation path. If the demodulation path considered is the last demodulation path to be considered, block 46 routes the flow to the next part of the procedure, through connection block 54.

Once the group of probing paths is completed and the demodulation paths have been compared with the probing paths, the procedure continues through Figure 5C, which is roughly equivalent to blocks 354 and 356 of Figure 4. The connection block 54 routes the flow to block 60. Block 60 designates as the polling path considered the sounding path that has the strongest signal level. Also, block 60 records the base station sector to which the polling path corresponds. The procedure in Figure 5 highlights the advantages of the diversity of sectors for the power control of a specific system execution. A method according to the present invention can highlight the diversity of base stations. In other systems, emphasizing base station diversity over sector diversity can be an advantage.

To maximize the diversity of sectors, block 62 finds out if any demodulation element has been assigned to demodulate any sector path of the survey path under consideration. If so, the action corresponding to the polling path considered is complete. If no demodulation element has been assigned to any path in the sector of the polling path under consideration, the flow continues through block 64. Block 64 asks if there is any free or unassigned demodulation element. If there is any unassigned or free demodulation element, block 72 assigns the unassigned or free demodulation element to the considered demodulation path and the action corresponding to the considered sounding path is complete.

The procedure in Figure 5C can continue for the next probe path. Consequently, the pro10

The yield continues from block 62 and from block 72 to block 74. Block 74 finds out if any probing paths remain. If indeed there is any probe path remaining, block 70 chooses the next strongest probe path as the considered probe path and flow continues through block 62. If no more probe path remains, flow continues at through connection block 78 to Figure 5D.

Starting from block 64, if there is no unassigned or free demodulation element, block 66 finds out if there is any sector that has several assigned demodulation elements. If there is any sector that has more than one demodulation path, block 76 reassigns the demodulation element that has the weakest demodulation path. This reassignment is the only reassignment of this cycle and the flow continues, through connection block 80, towards the start of a new cycle in Figure 5A.

Starting from block 66, if there is no sector that has more than one demodulation path, block 68 finds out if there is any demodulation path that has a signal intensity that is at least 3 dB lower than the signal intensity of the considered sounding path. The 3 dB offset is the hysteresis interval necessary to prevent excessive reallocation between two similarly favorable paths. Higher or lower hysteresis ranges can be used, depending on the system application. If such a 3 dB lower intensity path exists, block 76 reassigns the demodulation element corresponding to the weakest demodulation path to the probing path. This reassignment is the only reassignment in this cycle, and flow continues through connection block 80 toward the start of a new cycle in Figure 5A. If there is no such path of 3 dB lower intensity, the rest of the sounding paths will continue through Figure 5C in the same way as the demodulation path considered. Therefore, if no such path exists, meaning that no reallocation has occurred during this cycle, the flow continues from block 68 to Figure 5D, through block 78.

After the group of probing paths is completed and the demodulation paths compared to the probing paths, the procedure continues through Figure 5D if no reallocation has yet occurred at that point in the cycle. Figure 5D is roughly equivalent to block 358 of Figure 4. Connection block 78 directs flow to block 84. Block 84 designates the sounding path considered as the sounding path with the highest signal level. Also, block 84 records the base station sector to which the polling path under consideration corresponds. The procedure of Figure 5D highlights the diversity of sectors as the most advantageous for power control. However, as noted above, an alternative embodiment of the present invention can enhance the diversity of base stations regardless of sectors.

Block 86 finds out if any demodulation elements have been assigned to the survey path under consideration. If any demodulation element has a demodulation path corresponding to the survey path under consideration, block 104 asks if there are any more survey paths. If there is any other survey path, block 100 sets the survey path with the next highest signal level as the survey path under consideration and records the sector corresponding to the new survey path under consideration. The procedure starts over at block 86. If the probe path considered is the last probe path to be considered, the flow continues through the connection block 80 until the beginning of a new cycle in Figure 5A.

If there is no demodulation element that has a demodulation path corresponding to the survey path under consideration, block 88 asks if there is any unassigned or free demodulation element. If there is any unassigned or free demodulation element, block 102 assigns the unassigned or free demodulation element to the survey path under consideration. Flow continues through block 104 in the manner described. If there is no unassigned or free demodulation element, block 90 selects the weakest demodulation path to compare with the survey path under consideration.

Block 92 finds out if the demodulation path to compare corresponds to the sector of the probing path considered. If the demodulation path to compare belongs to the same sector as the considered sounding path, block 106 asks if the signal level of the demodulation path to compare is more than 3 dB lower than the signal level of the considered sounding path . The 3 dB delta value is the hysteresis interval to prevent excessive reallocation between two similarly favorable paths. Longer or shorter hysteresis ranges can be used, depending on the system application. If the level of the sounding path signal is not at least 3 dB higher than that of the demodulation path for comparison, the cycle starts over as indicated in connection block 80. If the level of the probing path signal is at least 3 dB higher than the signal level of the demodulation path for comparison, the demodulation element corresponding to the demodulation path for comparison is reassigned to the path Polling time considered as indicated in block 108. This reassignment is the only reassignment of this cycle and the cycle begins again at Figure 5A, as indicated in connection block 80.

Starting from block 92, if the demodulation path for the comparison does not belong to the same sector as the probing path considered, block 94 determines if the demodulation path for the comparison is the only demodulation path of the sector corresponding to the path of demodulation for comparison. If the demodulation path for comparison is not the only demodulation path in this sector, the flow continues through block 106 as indicated.

If the demodulation path for comparison is the only demodulation path in this sector, the

ES 2 215 166 T3 block 96 finds out if there is any more demodulation path left. If there is no more demodulation path remaining, the cycle starts over with Figure 5A, as indicated in connection block 80. If there is any more demodulation path remaining, block 98 designates as the demodulation path for comparison the path demodulation having the next weakest signal strength. Flow continues through block 92.

By way of example, it is assumed that the procedure of Figures 5A to 5D is performed based on the signals shown in Figures 3A to 3C. It is assumed that there is no other base station sector available to the mobile station. The three demodulation elements are assumed to be assigned as follows:

<td>Demodulation element</td><td>Time shift</td><td>signal level</td><td>Hitch</td><td>Sector</td>

the sector corresponding to the numbers in Figures 3A to 3C. The flow begins with Figure 5A. The poll list is cleared and the sector in Figure 3A is set as the first sector considered (blocks 10 to 14). The search element begins a search for multipath signals as shown in Figure 3A with the following prompts:

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td>

Path 304 is the one with the lowest level of the four and is below the threshold level indicated by threshold line 320. The search element finds three maxima (blocks 16-20). Therefore, the final data added to the list of probing paths for this cycle is as follows:

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td>

Sector 3B is established as the next sector considered (blocks 22 and 26). Two more entries are added to the polling path list as follows (blocks 16-20):

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td>

Sector 3C is established as the next sector considered (blocks 22 and 26). Two more entries are added to the polling path list as follows (blocks 16-20):

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td>

Thus, the list of probe paths is complete and the flow continues through Figure 5B.

IS 2 215 166 T3

Figure 5B begins by designating the path of demodulation element 1 as the first path considered. Because demodulation path 1 is locked, the demodulation path is compared to a probing path (blocks 34 to 36). In this example, t1 is assumed to be roughly equal to t10, and therefore demodulation path 1 matches probing path 300. Because demodulation path 1 is the first demodulation path to match probing path 300, the procedure continues with the next demodulation path (blocks 38 and 46).

The demodulation path 2 is set as the demodulation path considered (block 48). Because demodulation path 2 is disengaged, the demodulation path is designated as free (blocks 34 and 50). The procedure continues with the next demodulation path (block 46).

The demodulation path 3 is set as the demodulation path considered (block 48). Because demodulation path 3 is locked, the demodulation path is compared to a probing path (blocks 34 to 36). In this example it is assumed that t3 is also approximately equal to t10 and therefore demodulation path 3 coincides with probing path 300 the same as demodulation path 1. Because demodulation path 3 is the second demodulation path that coincides with probing path 300, the method compares the amplitudes of the two paths (blocks 38 and 40). In this example, it is assumed that A 3 <A 1 and therefore demodulation element 3 is designated as free (block 44). Because demodulation path 3 is the last demodulation path, the functions in Figure 5B will have ended and the flow continues through Figure 5C, with the following list of demodulation paths:

Displacement Element Signal level Latch Time demodulation sector ti ^ tio Al S 3A

FREE 2 FREE 3 and the following list of probe paths:

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td><td>I agree. with</td>

<td> 300</td><td>tio</td><td>TOio</td><td>3A</td><td>path.demod.1</td>

Assuming that AI4 is the highest signal level, Figure 5C begins by setting probe path 308 as the survey path under consideration and setting sector 3B as the sector containing that path (block 60). In this case, no demodulation element is assigned to sector 3B and demodulation element 2 is free (blocks 62 and 64). Consequently, demodulation element 2 is assigned to probe path 308 and the new list of demodulation paths is as follows:

<td>Demodulation element</td><td>Time shift</td><td>signal level</td><td>Hitch</td><td>Sector</td>

FREE 3

Assuming that Aii is the next highest signal level, probe path 302 is the next survey path considered and 3A is the sector containing that path (blocks 74 and 70). Since a demodulation element has already been assigned to sector 3A, probe path 310 is set as the next survey path considered and sector 3B as the sector containing said path (blocks 62, 74, and 70), assuming that Ai5 is the following signal level higher. This procedure continues through sounding paths 300 and 306, assuming Aio and Ai3 are the next signal levels. When the probing path 314 is the path under consideration and 3C the sector that contains said path, the demodulation element 3 that

ES 2 215 166 T3 was previously free is assigned to probe path 314 (blocks 62, 64 and 72). Probing path 312 is set as the probing path considered (blocks 74 and 70) and, because the demodulation path is assigned to sector 3C, the functions of Figure 5C are complete (blocks 62 and 74) and the list of demodulation trajectories is as follows:

<td>Demodulation element</td><td>Time shift</td><td>signal level</td><td>Hitch</td><td>Sector</td>

In this situation, no demodulation elements have yet been reassigned up to this point and therefore the flow continues through Figure 5D. Probe path 308 is reestablished as the considered probe path (block 84). Because probe path 308 is assigned to demodulation element 2, the procedure continues with probe path 302 as the considered probe path (blocks 86, 104, and 100). Probing path 302 is not currently demodulated by any demodulation element, and consequently demodulation path 3 is set as the demodulation path considered, because it is the weakest demodulation path (blocks 86, 88 and 90). Because demodulation path 3 does not belong to the same sector as probing path 302 and because no other demodulation element has been assigned to sector 3C, demodulation path 1 is set as the demodulation path considered, because it is the next weakest demodulation path (blocks 92, 94, 96 and 98). The demodulation path 1 is contained in the same sector as the probing path 3A (block 92). Assuming that A11 is more than 3 dB higher than A1, demodulation element 1 is reassigned to probe path 302. This reassignment ends the procedure for this cycle. The probing path (block 12) is suppressed for the next cycle and the list of demodulation paths is as follows:

<td>Demodulation element</td><td>Time shift</td><td>signal level</td><td>Hitch</td><td>Sector</td>

The base station procedure is less complicated than the mobile station procedure. Unlike the mobile station, the base station having several sectors is not affected by the diversity of sectors, because no analogous power control information is sent from the mobile station. The base station procedure focuses on assigning all available demodulation elements to the strongest paths, while avoiding excessive reallocations.

The procedure used by the base station assumes that the base station comprises several independent demodulation elements. Figure 6 illustrates an embodiment of such a base station. Figure 6 depicts a three sector base station, where each of the antennas 422A to 422C is the one sector antenna. Each of the antennas 422A 'to 422C' corresponds to one of the antennas 422A to 422C, this being the diversity of antennas for the sector corresponding to the antennas with equivalent numbering. Each of the antennas 422A to 422C comprises the same coverage area as the corresponding antenna of the antennas 422A 'to 422C'. In a typical base station, antennas 422A to 422C have coverage areas that overlap and subdivide the base station into three sectors, with each antenna covering more than one-third of the total combined coverage area of the base station. Consequently, a signal from a single mobile station can be present on more than one antenna at a time. The number of sectors and the number of antennas assigned to each sector can vary. Variations of this type do not affect the general principles of the present invention.

The antennas 422A, 422B, 422C, 422A ', 422B' and 422C 'provide the received signal to the RF processing unit and digital conversions 424A, 424B, 424C, 424A', 424B 'and 424C', respectively. The RF processing unit and digital conversions 424A, 424B, 424C, 424A ', 424B' and 424C 'process the RF signal and convert the signal into digital bits. RF processing unit and digital conversions 424A, 424B, 424C, 424A ', 424B', and 424C 'filter the digital bits and provide the resulting digital bits to interface gate 426. Interface gate 426 can connect any of the six input signal paths to any of the search elements or demodulation elements controlled by controller 400, through interface 412.

Search and demodulation elements are also controlled by controller 400 through interface 412. Search elements 402A through 402N continuously scan a time domain interval to find the information signal of a particular controlled mobile station. by the system controller 400. Search elements 402A through 402N also scan a group of time offsets in

ES 2 215 166 T3 around the nominal signal arrival time to find the multipath signals that have been generated.

Search elements 402A to 402N pass the generated data to controller 400 for storage in memory 418. Search elements 402A to 402N can pass data through a standard bus or can pass data to memory 418 through of a direct memory access (not shown) in the manner indicated in relation to Figure 1. Controller 400 uses the data stored in memory 418 to assign demodulation elements 404A through 404N to one of the plurality of information signals from a single mobile station.

In this exemplary embodiment, to maintain high system capacity, each mobile station in the system does not transmit a pilot signal continuously. The absence of a pilot signal on the uplink increases the time required to carry out, with a single search element, a poll of all possible time offsets in which a mobile station signal can be received. Therefore, to provide a quick search procedure, more than one search item is used to carry out a complete search. The controller assigns each of the search elements 402A to 402N to search in a group of time offsets. Each of the search items 402A through 402N returns the results of the search it performs to controller 400. Controller 400 arranges the results in a table for use in the allocation procedure.

Demodulation elements 404A through 404N generate data bits 420A through 420N that are combined in symbol combiner 408. The output of symbol combiner 408 (not shown) is combined soft decision data suitable for Viterbi decoding. It should be noted that the symbol combiner 408 may combine signals from only one sector to generate an output or it may combine symbols from multiple sectors selected by the interface gate 426. When symbol combiner 408 combines signals from a mobile station that is communicating through more than one sector, this state is called smoother call handoff. The base station can send the output of symbol combiner 408 to a cellular system controller, in which symbols from a common mobile station are also combined with signals from other base stations to generate a single output. This procedure is called call transfer. The demodulation elements 404A through 404N also provide the controller 400 with multiple output control signals that are used in the allocation procedure, via interface 412.

Each of the demodulation elements 404A to 404N is very similar in structure to the others. Figure 7 illustrates in greater detail the demodulation element 404 of Figure 6. In Figure 7, the digitized input signal is assumed to be a quadrature shift keying (QPSK) signal having in-phase signal samples. (I) and in quadrature phase (Q). The I and Q signal samples, each of which is made up of a multi-bit value, are input to the decimator and the 430 decoder. Typically the I and Q signal samples are oversampled to the extent that the input it is received at a data transmission rate higher than the segment rate. At the decimator and de-spreader 430, the decimated data passes from the subsampling data transmission rate to the PN segment rate. The decimator and de-spreader 430 then de-spread the data using the same PN sequence used to modulate this signal at the mobile station.

Decimator and de-spreader 430 provide the I and Q signal components to accumulator 438. Accumulator 438 accumulates the de-spread I and Q signal components for a period equivalent to one Walsh segment to generate accumulated I and Q segment data. Next, the fast Hadamard transform (FHT) and select unit 440 processes the accumulated I and Q segment data. The FHT portion of the FHT and selection unit 440 correlates the accumulated I and Q segment data to all possible Walsh sequences. Each I and Q correlation result is then used to estimate the magnitude of the corresponding Walsh symbol. The magnitude estimates for each of the I and Q correlation results are compared to each other. The Walsh symbol corresponding to the I and Q correlation result having the highest magnitude is selected by the selection part of the FHT unit and selection 440 as the demodulated Walsh symbol. The demodulated Walsh symbol is provided together with the corresponding estimated magnitude of said Walsh symbol.

As in the case of the mobile station, due to the different arrival times of the signal paths assigned to the different demodulation elements, the demodulation element 404 also performs the realignment of the symbols. The time realignment unit 442 delays the output such that each demodulation element provides data in sync with the other demodulation elements.

The energy accumulator and latch detector 444 sums a series of consecutive Walsh symbol magnitudes. The resulting sum is provided as signal strength 464 to the controller for use in the allocation procedure. The resulting sum is also compared to a threshold to indicate latched or unlatched status.

The arrival time of the signal path assigned to demodulation element 404 may change over time, due to movement of the mobile station or the change in the environment of the mobile station. Therefore, in the same way as the demodulation element of the mobile station, the demodulation element of the base station includes time tracking circuits. The 430 Decimator and Stretcher provides a

ES 2 215 166 T3 early and late version of the I and Q signal components de-spread for use in the time tracking procedure. Accumulator 432 accumulates early and late de-spread I and Q signal components over a period of a Walsh segment to generate accumulated early and late I and Q segment data. The leading and lagging metric generating unit 434 multiplies the accumulated leading and lagging I and Q segment data by the Walsh sequence corresponding to the demodulated Walsh symbol and accumulating the result to generate leading and lagging I and Q Walsh symbols. The magnitude of the leading Walsh symbol is found based on the leading Walsh symbol I and Q, and the magnitude of the leading Walsh symbol is found based on the leading I and Q Walsh symbol. The magnitude of the leading symbol is subtracted from the magnitude of the leading symbol to generate an error metric. The error metric is provided to the time tracking unit 436. The time tracking unit 436 uses the error metric to determine whether the de-spreading operation at the decimator and de-spreader 430 is early or late or on time. The time tracking unit 436 also tracks the time of the absolute demodulation path 470 of the demodulation element to provide it to the controller.

The search elements are similar to the demodulation element, except that the search elements do not include time tracking or hook detection. Time tracking is not necessary for search items, because the search procedure is done quickly in relation to the consistency of the channel. In other words, the time offsets during the time taken for a single search are negligible.

Figure 8 is a summary of an exemplary demodulation element assignment procedure for a sectored base station in accordance with the present invention. The procedure runs cyclically. In the first stage of each cycle, the paging elements poll the mobile station's signal strength versus time for a single mobile station with which communication has been established, as indicated in block 450 of Figure 8. Each search element scans a time interval around the expected time of arrival of the signal from the mobile station to find multipath signals. The controller creates a group of sounding path data based on the search element data, comprising time offsets and signal strengths.

The controller compares the probing paths to the demodulation paths, as indicated in block 452. The demodulation paths are paths currently assigned to the demodulation elements. The corresponding path information (time offset and signal strength) of each demodulation element is collected by the controller.

As stated above, one of the main considerations for allocating demodulation elements at the base station is obtaining the highest possible combined signal level. All free and unhooked demodulation elements are assigned to the highest signal intensity probe paths that do not correspond to the demodulation paths, at block 454. Also, in each cycle, at most a fixed number of demodulation elements can be reassigned to sounding paths that have a higher signal intensity than the original demodulation path, at block 456. After block 456 is completed, the cycle it starts over at block 450.

Figures 9A to 9D show the procedure of Figure 8 in greater detail. In this exemplary flow chart, the system is assumed to have four demodulation elements and eight search elements. In accordance with the present invention, the method shown is considered to be a preferred embodiment. In this run, the number of reassignments is limited to two per cycle. Other maximum numbers may be chosen without departing from the scope of the present invention. Furthermore, many different embodiments of the present invention will be readily apparent after considering the execution of Figures 9A to 9D. Accordingly, Figures 9A to 9D are not intended to limit the present invention, but to illustrate the preferred embodiment.

The cycle begins in Figure 9A, which is roughly equivalent to block 450 of Figure 8. Block 510 indicates the initial function of the procedure. Block 512 clears the list of poll paths found in the last cycle. Block 516 instructs the search elements to search in a time interval around the expected arrival time of the signals from the mobile station with which they have established communication. Block 518 receives at most the four strongest local maxima. In this example, receiving more than four stronger local maxima is ineffective, because only four demodulation elements are available to assign and in no case will a demodulation element be assigned to a fifth stronger sounding path. Block 520 adds the information for each of the local maxima that exceeds a minimum signal level threshold to the list of poll paths. Block 520 routes the flow to the next part of the procedure, through block 524.

Once the group of probe paths is complete, the procedure continues through Figure 9B, which is roughly equivalent to block 452 of Figure 8. Connection block 524 routes flow to block 532. Block 532 designates as a demodulation path considered one of the paths that is currently being demodulated by a demodulation element. Block 534 checks the on / off status of the demodulation element corresponding to the demodulation path considered. If the demodulation element is disengaged, the controller can unassign the demodulation element or it can designate the demodulation element as "free", as indicated in block 550. In such case, there will be no

ES 2 215 166 T3 valid data that matches the sounding paths. The action corresponding to the demodulation path considered will have been completed.

If the demodulation element corresponding to the demodulation path under consideration is currently locked, block 536 tries to compare the time offset of the demodulation path with the analogous information from the polling path list. If there is any probing path that corresponds to the considered demodulation path, block 538 finds out if the considered demodulation path is the first demodulation path that matches the particular probing path. If the demodulation path considered is the first matching path, the action corresponding to the demodulation path considered is complete.

If the demodulation path considered is not the first demodulation path that matches the particular probing path, then it means that there are two demodulation elements that are demodulating substantially the same path. This situation can occur frequently. Each demodulation element tracks the signal to which it was originally assigned. Two multipath signals can meet over time on the same or nearly the same path. Block 538 identifies said situation. If the demodulation path considered is not the first demodulation path that matches a particular probe path, block 540 determines which demodulation path has the highest signal level. If the demodulation element under consideration has the highest signal level, block 542 unassigns the previous demodulation element that matches the same probe path, or designates it as free. If the demodulation element considered is weaker than the previous path, block 544 unassigns the demodulation element corresponding to the demodulation path considered, or designates it as free. The action corresponding to the demodulation path considered will have been completed.

If there is any demodulation path left to be considered, block 546 routes the procedure to block 548. Block 548 selects the next considered demodulation path and block 534 begins repeating the procedure for the next considered demodulation path. If the demodulation path considered is the last demodulation path to compare, block 546 routes the flow to the next part of the procedure, through connection block 554.

Once the group of probing paths has been completed and the demodulation paths have been compared with the probing paths, the procedure continues through Figure 9C, which is roughly equivalent to block 454 of Figure 8. Connection block 554 routes the flow to block 560. Block 560 designates as the sounding path considered the sounding path with the highest signal level.

Block 562 finds out if any demodulation elements have been assigned to demodulate the survey path under consideration. If so, the action corresponding to the polling path considered is complete. If no demodulation elements have been assigned to the survey path under consideration, the flow continues through block 564. Block 564 asks if there are any unassigned or free demodulation elements. If there is any unassigned or free demodulation element, block 572 designates the unassigned or free demodulation element as the considered sounding path and the action corresponding to the considered sounding path is complete.

The procedure of Figure 9C continues from block 562 and from block 572 to block 574. Block 574 finds out if any more probe paths remain. If any probe paths remain, block 570 chooses the next strongest probe path as the considered probe path and flow continues through block 562. If there are no more probe paths remaining, meaning that the number of demodulation elements is greater than or equal to the number of probe paths found, the flow continues through block 580 through Figure 9A and the cycle starts over. On the other hand, if there are more probing paths than demodulation elements, the stream continues to scan the probing paths until it finds some unassigned or free demodulation element. Starting from block 564, flow continues through connecting block 578 in Figure 9D.

The procedure continues through Figure 9D which is roughly equivalent to block 456 of Figure 8. Connection block 578 routes flow to block 590 of Figure 9C. When block 578 is reached and Figure 9D is started, the probing path considered remains the probing path considered in Figure 9C.

Block 590 selects the weakest demodulation path to compare with the survey path under consideration. Block 592 finds out whether the signal level of the demodulation path for comparison is more than 3 dB lower than the signal level of the considered sounding path. The 3 dB difference is a hysteresis interval to prevent excessive reallocation between two similarly favorable paths. Larger or shorter hysteresis ranges can be used depending on the system application. If the signal level of the probing path is not at least 3 dB higher than the demodulation path for comparison, the cycle starts over again as indicated in connection block 580. If the signal level of the sounding path is at least 3 dB higher than the demodulation path for comparison, the demodulation element corresponding to the demodulation path for comparison is reassigned to the considered sounding path, as follows indicates at block 594. Because this reassignment is the first reassignment of this cycle, the flow continues through block 576. If block 596 is reached for the second time, the maximum number of

ES 2 215 166 T3 reassignments for this cycle and the cycle begins again with Figure 9A, as indicated in the connection block

580.

Block 576 asks if there are any more probe paths left. If another probe path remains, block 564 sets the probe path with the next highest signal level as the survey path under consideration. Block 586 finds out if any demodulation elements have been assigned to the survey path under consideration. The procedure continues according to block 590 or block 576. If the probe path under consideration is the last probe path to consider, the flow continues through the connection block 580 and begins a new cycle through Figure 9A.

Figures 10A and 10B illustrate an exemplary format showing the components of the input signal from a single mobile station. In general, there are a plurality of signals at each antenna, belonging to a plurality of mobile stations in or near the system. Figures 10A and 10B show only the signal from a mobile station with which communication has been established. Figure 10A illustrates the signal strength versus time for the mobile station, received in a first base station sector. Figure 10B illustrates signal strength versus time for the same mobile station, received in a second base station sector. In Figures 10A and 10B, the horizontal axis shows the time units and the vertical axis the energy units in dB. In Figure 10A, there are four paths that exceed the noise floor indicated by 462, 464, 466, and 468. Path 462 is the first to arrive and can be assumed to be the most direct path available between the mobile station and the station. base. Next, paths 464, 466, and 468 arrive in sequence, representing the multipath signals of the same signal from path 462. Line 460 represents a threshold below which signal strength does not generate reliable data.

The time offset between the sector of Figure 10A and the sector of Figure 10B is not explicitly shown. Figure 10B can be considered normalized to the delay of Figure 10A for illustrative purposes. In Figure 10B, there are six paths that exceed the noise floor, designated by 470, 472, 474, 476, 478, and 480. Again, line 460 represents a threshold below which signal strength does not generate data. reliable.

By way of example, it will be assumed that the procedure of Figures 9A to 9D is performed based on the signals shown in Figures 10A and 10B. The four demodulation elements are assumed to be assigned as follows:

<td>Demodulation element</td><td>Time shift</td><td>signal level</td><td>Hitch</td><td>Sector</td>

the sector corresponding to the numbers in Figures 10A and 10B. The flow begins with Figure 9A. The poll list is cleared and search items are assigned to the appropriate sector and ordered to search within a time interval (blocks 510 to 516). Search data for each search element is received and the four strongest local maxima are recorded in descending order of signal strength, as follows (blocks 520 and 524):

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td>

Figure 9B begins by establishing the trajectory of demodulation element 1 as the first trajectory considered. Since demodulation element 1 is latched, an attempt is made to compare the demodulation path with a probing path (blocks 534 to 536). In this example, t1 is assumed to be approximately equal to the arrival time of path 466 of Figure 10A, which has a relatively low signal intensity and therefore does not have a corresponding entry in the probe path list. . The procedure continues for the next demodulation path (block 546).

The demodulation path 2 is set as the demodulation path considered (block 548). Because demodulation path 2 is locked, it is a matter of comparing demodulation path with

ES 2 215 166 T3 a probing path (blocks 534 to 536). In this example, t2 is assumed to be approximately equal to the arrival time of path 468 of Figure 10A, which has a relatively low signal strength and therefore does not have a corresponding entry in the probe path list. . The procedure continues for the next demodulation path (block 546).

The demodulation path 3 is set as the demodulation path considered (block 548). Since demodulation path 3 is locked, an attempt is made to compare the demodulation path with a probing path (blocks 534 to 536). In this example, t3 is assumed to correspond to t10 of path 470. Because demodulation path 3 is the first demodulation path to match probing path 470, the procedure continues for the next demodulation path (blocks 538 to 546).

The demodulation path 4 is set as the demodulation path considered (block 548). Since demodulation path 4 is locked, an attempt is made to compare the demodulation path with a probing path (blocks 534 to 536). In this example, t4 is assumed to be approximately equal to the arrival time of path 480 of Figure 10A, which has a relatively low signal strength and therefore does not have a corresponding entry in the probe path list. . Because demodulation path 4 is the last demodulation path, the functions in Figure 5B will be complete and the procedure continues through Figure 5C with the following list of probing paths:

<td>Trajectory indicator</td><td>Time shift</td><td>signal level</td><td>Sector</td><td>I agree. with</td>

<td> 470</td><td>t10</td><td>TO10</td><td>10B</td><td>path.demod.3</td>

Assuming that the signal level A10 is the highest, Figure 9C begins by setting the probe path 470 as the probe path under consideration (block 560). In this case, demodulation element 3 is assigned to probe path 470 (block 562). Accordingly, probe path 476 is set as the next considered path (blocks 574 and 570). Because no demodulation elements have been assigned to probe path 476 and no unassigned or free demodulation elements exist, the flow continues through Figure 5D (blocks 562, 564, and 578).

Demodulation path 1 (corresponding to path 466 of Figure 10A) is set as the demodulation path considered, because it is the lowest demodulation path (block 590). Assuming that A11 is more than 3 dB higher than A1, demodulation element 1 is reassigned to probe path 476 (blocks 592 and 594). This reassignment is the first reassignment of this search cycle and consequently poll path 472, to which no demodulation element has been assigned, is set as the next considered poll path (blocks 596, 576, 564 and 586).

The demodulation path 2 (corresponding to path 468 of Figure 10A) is set as the demodulation path considered because it is now the weakest demodulation path (block 590). Assuming that A12 is more than 3 dB higher than A2, demodulation element 2 is reassigned to probe path 472 (blocks 592 and 594). This reassignment is the second reassignment of this search cycle, therefore the flow continues through Figure 9A to start another cycle. The list of demodulation element assignments is as follows:

<td>Demodulation element</td><td>Trajectory correspondent</td><td>Hitch</td><td>Sector</td>

An interesting point to note from the results of the previous example of assigning the base station is that all demodulation elements are assigned to the same sector, even if communication is established through more than one sector. This result contrasts with the result that would be obtained from the mobile station assignment procedure that highlights the diversity of sectors. Also, it is interesting to note that the four demodulation elements are not assigned to the four strongest paths, as indicated in Figure 10B. The demodulation element 4 is assigned to path 480 which is the sixth strongest path in sector 10B. However, in the example above, the maximum number of reassignments per cycle is reached before this demodulation element

ES 2 215 166 T3 is compared to a probe path for possible reassignment. It should be noted that the above procedure is equally applicable to a base station having only one sector.

There are numerous obvious variants of embodiments of the present invention. The previous description of the preferred embodiments is provided to enable those skilled in the art to create or use the present invention. The various modifications of these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments, without using inventiveness. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but to encompass the broadest scope consistent with the principles and novel features disclosed herein.

It should be noted that the objects and advantages of the present invention may be achieved by any compatible combination noted in particular in the points of the following summary of the present invention and the appended claims.

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Document	Office	Kind	Date
14490293	United States of America	A	1993-10-28
19930144902	United States of America	–	1993-10-28

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Family members, oldest first
Document	Office	Kind
IL111432D0	Israel	D0	1994-12-29
CA2150932A1	Canada	A1	1995-05-04
WO9512262A1	World Intellectual Property Organization (WIPO)	A1	1995-05-04
ZA947841B	South Africa	B	1995-05-18
AU8096394A	Australia	A	1995-05-22
TW252244B	Taiwan Province of China	B	1995-07-21
FI953210A	Finland	A	1995-08-28
FI953210A7	Finland	A7	1995-08-28
EP0676107A1	European Patent Office (EPO)	A1	1995-10-11
BR9405888A	Brazil	A	1995-12-26
KR960700594A	Republic of Korea	A	1996-01-20
US5490165A	United States of America	A	1996-02-06
JPH08508152A	Japan	A	1996-08-27
AU685869B2	Australia	B2	1998-01-29
IL111432A	Israel	A	1998-03-10
JP2938573B2	Japan	B2	1999-08-23
RU2138918C1	Russian Federation	C1	1999-09-27
HK1015210A1	Hong Kong, China	A1	1999-10-08
CA2150932C	Canada	C	2002-09-24
MY114370A	Malaysia	A	2002-10-31
KR100347655B1	Republic of Korea	B1	2002-11-22
FI110295B	Finland	B	2002-12-31
EP0676107B1	European Patent Office (EPO)	B1	2004-01-02
AT257298T	Austria	T	2004-01-15
ATE257298T1	Austria	T1	2004-01-15
DE69433459D1	Germany	D1	2004-02-05
DK0676107T3	Denmark	T3	2004-02-16
PT676107E	Portugal	E	2004-05-31
SI0676107T1	Slovenia	T1	2004-08-31
ES2215166T3This record	Spain	T3	2004-10-01
DE69433459T2	Germany	T2	2004-11-04

Demodulation element assignment in a system capable of receiving multiple signals

Abstract

Term

IS 2 215 166 T3

DESCRIPTION

IS 2 215 166 T3

IS 2 215 166 T3

IS 2 215 166 T3

IS 2 215 166 T3

IS 2 215 166 T3

FREE 3

Priority claims2

Members31

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Classification