CN108292937B

CN108292937B - Information provision and processing for receiver driven precoding

Info

Publication number: CN108292937B
Application number: CN201580084942.5A
Authority: CN
Inventors: 卢卡·罗斯; 马可·马索; 阿波斯特劳斯·德斯托尼斯
Original assignee: Huawei Technologies Co Ltd
Current assignee: XFusion Digital Technologies Co Ltd
Priority date: 2015-12-14
Filing date: 2015-12-14
Publication date: 2020-12-18
Anticipated expiration: 2035-12-14
Also published as: WO2017101973A1; CN108292937A

Abstract

The invention proposes a receiver comprising: r₀A receiving antenna for T from the transmitter₀More than or equal to 2 transmitting antennasReceiving data over a downlink; a connection unit for connecting with a first list of potential cooperating receivers, wherein the potential cooperating receivers respectively comprise a T for a slave sender_PCDL(i)R for receiving data by more than or equal to 2 transmitting antennas_PCDL(i)-a number of receive antennas, i being an index of said first list; and a calculation unit for selecting a second list of cooperating receivers by: recursively selecting a potential cooperating receiver at index I-c, adding it to the second list if formula (I) holds, and incrementing c, j being the index of the second list, R_CDL(j)Is the number of receive antennas of the cooperative receiver at index j, T_CDL(j)Is the number of transmit antennas of its transmitter. A calculation unit calculates a precoder for a downlink based on the second list.

Description

Information provision and processing for receiver driven precoding

Technical Field

The present invention relates generally to the field of wireless communications, and more particularly to wireless communications supporting precoding functionality.

Background

In autonomous networks, two types of solutions are known for reducing or avoiding the interference level due to the lack of cooperation. A first category of solutions, which may be denoted as Resource Allocation (RA) solutions, aims at designing algorithms for orthogonalizing the communication by means of intelligently allocated resource radio blocks, such that if one transmitter transmits data on a particular radio resource (e.g. frequency, time slot, code), the other transmitters do not transmit data on the same radio resource. TDMA and CSMA, for example, follow this approach. The disadvantage of these methods is that they are not efficient for two reasons. First, it wastes radio resources, whether in time and/or frequency domain. Second, it requires some degree of synchronization between the transmitters. The second category of solutions assumes the presence of a noise-free high-throughput backhaul connecting the transmitters and/or between all receivers. With this solution, the network can employ a theoretically optimal precoding and decoding scheme that maximizes the overall throughput. However, practical limitations of such systems are apparent, as it is unlikely that there is a noise-free high-throughput backhaul between SC or WiFi access points.

Both strategies may be significant in terms of precoding. The first strategy is based on codebook precoding. In this method, the precoder and, if necessary, the corresponding decoder at the receiver are selected by each transmitter of a finite number of precomputed non-optimized precoding matrices, where these matrices are known at both the transmitter and the receiver. In practice, when the receiver receives pilot/training symbols from the transmitter, it estimates the channel matrix and calculates the index corresponding to the best precoder based on some metric. However, this first strategy does not take full advantage of the potential for using multiple antennas. The second strategy requires the receiver to estimate the channel and then feed it back to the transmitter as Channel State Information (CSI). The transmitter then uses the CSI to design a specific precoder. An example of a possible precoder is Maximum Ratio Combining (MRC) precoding, wherein,

zero-forcing (ZF) precoder

And Minimum Mean Square Error (MMSE) transmitter

Wherein, W_nIs a precoder used by the transmitter n, and

is the overall CSI feedback from all receivers served by transmitter n. This strategy is effective for reducing the negative effects of intra-cell interference, but does not address the negative effects of inter-cell interference.

In view of the above, many wireless communication networks are based on two paradigms: multiple antenna devices, also known as multiple-input and multiple-output (MIMO) methods, and full frequency reuse. Examples of these paradigms may be found in WiFi or LTE wireless communication networks. MIMO has the potential to greatly improve the performance of wireless communication networks by mitigating the negative effects of interference and fading, while full frequency reuse maximizes spectrum occupancy at the expense of increased interference levels. Centralized networks provide many ways to achieve this goal.

In this case, a Base Station (BS) or transmitter that perfectly handles CSI for channels that are not served by a receiver or user may manage multi-user interference through precoding/beamforming. Indeed, by utilizing the special structure of MIMO precoding, the base station or transmitter can mitigate multi-user interference by using a ZF precoder. More effectively, the base station may employ MMSE transmit filtering to maximize the signal to interference plus noise ratio (SINR) at all receivers.

However, there is no existing solution for wireless communication networks, where neither cooperation nor coordination between transmitters is possible. Examples of such wireless communication networks are, for example, WiFi, small-cell (SC), femto-cell (FC).

Fig. 1 shows an example of a decentralized wireless communication system 100 with MIMO devices. The system 100 comprises three base stations in the form of three

multi-antenna transmitters

101, 102, 103 and

receivers

111, 112, 113. The

transmitters

101, 102, 103 are, for example, WiFi access points; the

receivers

111, 112, 113 are, for example, handheld devices such as tablet computers, laptops or smart phones.

The first receiver 111 is served by the first transmitter 101 over a first downlink 121. Similarly, the second receiver 112 is served by the second transmitter 102 over a second downlink 124, and the third receiver 113 is served by the third transmitter 103 over a third downlink 128. Furthermore, even if the first receiver 111 is not served by the second and

third transmitters

102, 103, there are respective channels 126, 129 between the second and

third transmitters

102, 103, respectively, and the first receiver 111. Likewise, the second receiver 112 is not served by the first and

third senders

101, 103, and the third receiver 113 is not served by the first and

second senders

101, 102. However, there are

respective channels

123, 127 from the first and

third transmitters

101, 103 to the second receiver 112 and

respective channels

122, 125 from the first and

second transmitters

101, 102 to the third receiver 113.

When the first receiver 111 is served by the first transmitter 101 over the downlink 121, the channels 126, 129 received by the first receiver 111 from the further second and

third transmitters

102, 103 cause interference at the first receiver 111. In fig. 1, these channels 126, 129 are therefore identified as interfering channels.

Interference strongly limits the performance of autonomous multi-user/multi-cell networks such as WiFi and small cell networks. On the one hand, known multi-antenna transmitters have the ability to eliminate or mitigate the negative impact of interference on network performance, but at the cost of concentration. On the other hand, interference is problematic in a decentralized wireless communication network, especially if the transmitters do not cooperate.

Disclosure of Invention

Recognizing the above disadvantages and problems, the present invention is directed to improving the prior art. In particular, it is an object of the present invention to provide improved wireless communication with reduced interference.

The invention is particularly intended to improve wireless communication in a network that is not centralised and in which it is envisaged that there is no cooperation between transmitters. The present invention aims to mitigate the interference caused at the receiver.

A first aspect of the invention provides a receiver served by a multi-antenna transmitter. The receiver includes: the number of R₀Adapted to receive at least one receiving antenna of number T from said transmitter₀Receive data through a downlink, wherein T₀Not less than 2. The receiver includes: a connection unit adapted to establish a connection with the first list of potential cooperating receivers over the respective communication link. One potential cooperative receiver is served by a corresponding multi-antenna transmitter and comprises a number R_PCDL(i)Is adapted to transmit a number T from the respective transmitter_PCDL(i)Receive data through a corresponding downlink, wherein T_PCDL(i)≧ 2 and i is the index of the first list. The receiver includes: a calculation unit adapted to select a second list of cooperating receivers from said first list by an initialization phase and a recursion phase. The initialization phase comprises: initializing the second list to an empty list and initializing a counter c. The recursion stage comprises: selecting a potential cooperative receiver located at index i-c if

Adding said selected potential cooperating receiver to said second list and incrementing said counter c, where j is the index of said second list, R_CDL(j)Is the number of receive antennas of the cooperative receiver at index j, T_CDL(j)Is the number of transmit antennas of the transmitter serving the cooperative receiver at index j. The calculation unit is adapted to calculate a precoder for the downlink from the transmitter to the receiver from channel state information for the downlink and for respective channels from the transmitter to each cooperative receiver of the second list.

In other words, the inequality includes

Term and { T_CDL(j)The term, | j }, where the former is the sum of the receive antennas of all cooperative receivers of the second list and the latter is the set comprising, for each cooperative receiver of the second list, the number of transmit antennas of the transmitter serving the cooperative receiver.

Thus, the invention can compensate for the lack of cooperation between transmitters, especially in the context of MIMO non-cooperative networks, and can reduce interference and increase SINR at the receiver. The receiver may advantageously utilize knowledge about the interfering channel from the transmitter to the cooperating receiver in order to calculate the precoder that may be used by the transmitter. For example, the receiver may comprise a feedback unit adapted to send to the transmitter the calculated parameters of the precoder or information derived from the calculated precoder.

Furthermore, the present invention advantageously provides a second list of cooperating receivers, based on which the precoders for the downlink can be calculated. In particular, the precoder of the downlink from the transmitter to the receiver may depend on the channel from the transmitter to each cooperating receiver.

In a first implementation form of the receiver according to the first aspect, the calculation unit is adapted to calculate the number R of receive antennas for each potential cooperating receiver according to the first list_PCDL(i)Sorting the first list such that the calculation unit is adapted to select the second list from the sorted first list.

Thus, the first list may be sorted accordingly before the second list is selected. Correspondingly, the selection of the selection list may be optimized according to desired criteria.

In a second implementation form of the receiver according to the first aspect, the calculation unit is adapted to calculate the number R of receive antennas for each potential cooperating receiver of the first list_PCDL(i)Sorting the first list in descending order.

Thus, it can be ensured that the maximum possible number of receive antennas is selected, which in turn can maximize throughput.

In a third implementation form of the receiver according to the first aspect, the calculation unit is adapted to calculate the number R of receive antennas for each potential cooperating receiver in the first list_PCDL(i)The first list is arranged in ascending order.

An advantage of this ordering arrangement is therefore that the inter-cell interference can be reduced for the maximum number of cooperating receivers. Accordingly, an increased number of cooperating receivers may benefit from interference reduction. This also correspondingly increases fairness among the receivers.

In a fourth implementation form of the receiver according to the first aspect, the calculation unit is adapted to serve the respective number T of transmit antennas of the transmitter of the potential cooperating receiver_PCDL(i)Sorting the potential cooperative receivers in the first list in descending order.

This therefore ensures that the potential cooperating receiver served by the transmitter with the largest number of transmit antennas is selected first during the recursion phase. The theoretical maximum number of receiver antennas is given by min (T) in view of the inequality that should be satisfied in order to add the potential cooperative receivers to the second list₀，{T_CDL(j)|j｝，T_PCDL(i)) It is given. By T_PCDL(i)The first list is sorted in descending order, again ensuring that this theoretical maximum number is maximized.

In a fifth implementation form of the receiver according to the first aspect, the recursion phase is performed until all potential cooperating receivers of the first list are selected.

Thus, it is guaranteed that all potential cooperating receivers have been verified. This is particularly advantageous, for example, in case the first list is randomly ordered, i.e. the first list is not ordered according to a particular criterion, such as the number of receive antennas RP of a potential cooperative receiver_CDL(i)。

Optionally, in a fifth implementation form of the receiver according to the first aspect, the recursion stage is performed until

Thus, by performing the recursion phase until the equation is verified, the recursion phase may not be stopped in advance without having to select each potential cooperating receiver of the first list.

In a sixth implementation form of the receiver according to the first aspect, the receiver comprises: a broadcasting unit adapted to broadcast a cooperation request to the potential cooperation receivers. The receiver includes: a receiving unit adapted to receive respective response messages from the potential collaboration receivers in response to the collaboration requests. The first list corresponds to potential cooperating receivers for which the receiving unit received a response message.

Thus, an advantage of this configuration is that the receiver can easily establish a connection with a potentially cooperating receiver.

In a seventh implementation form of the receiver according to the first aspect, the response message received from a given potential cooperative receiver comprises the number R of its receiving antennas_PCDL(i)And the number T of the transmitting antennas serving it_PCDL(i)The information of (1).

Thus, the receiver can easily collect information required for selecting the second list and performing the recursion stage.

In an eighth implementation form of the receiver according to the first aspect, the cooperation request broadcast by the receiver comprises information about the number T of transmit antennas of the transmitter₀And/or information about the number of receiving antennas R₀The information of (1).

This is therefore advantageous, as the potential collaboration receiver may actively decide not to send a response message after receiving the collaboration request. For example, if the number of its receiving antennas is higher than the number T included in the cooperation request₀Then no potential cooperating receivers may be added to the second list during the recursion phase. By not sending a responseThe recursion stage can be simplified.

Likewise, a potential cooperative receiver receiving a cooperation request may have served it the number of transmit antennas and the number of receive antennas R of the transmitter₀A comparison is made. If R is₀Above the number of transmit antennas, no potential cooperating receivers may be added to the second list during the recursion phase. Thus, the recursion phase can be simplified by not sending a response message.

In a ninth implementation form of the receiver according to the first aspect, the cooperation request broadcast by the receiver comprises information about the location of the receiver.

Thus, a potential collaboration receiver receiving a collaboration request may now compare the location of the receiver with its own location and decide whether to send a response message based on the distance between the two locations. If the distance is large enough, e.g. above a threshold, it can be assumed that the interference between the receiver and the potential cooperating receiver is low enough and the potential cooperating receiver need not be part of the second list. In this case, the potential cooperative receiver may decide not to send a response message, so that the selection of the second list may be simplified and accelerated.

In a tenth implementation form of the receiver according to the first aspect, the response message received from a given potential cooperating receiver comprises information about the location and/or speed and/or battery level of the given potential cooperating receiver.

Thus, the receiver may correspondingly optimize the first list based on the received information.

In a further eleventh implementation form of the receiver according to the first aspect, the calculation unit is adapted to order the first list according to information about the location and/or speed and/or battery level comprised in a response message received from the potentially cooperating receiver.

Thus, for example, if the distance between the location of the receiver and the location of the potential cooperating receiver increases, the potential cooperating receiver may move towards the end of the first list, as the potential interference between the receiver and the potential cooperating receiver is now reduced. Similarly, if the speed of the potential cooperating receiver increases, the latter may move towards the end of the first list, since in this case the potential interference between the receiver and the potential cooperating receiver is also reduced. Also, if the battery level decreases, the corresponding potential cooperating receiver may move towards the beginning of the first list to avoid interference with the potential cooperating receiver: at this point it can be avoided that a potential cooperating receiver with a low battery level has to retransmit the data.

In a twelfth implementation form of the receiver according to the first aspect, the calculation unit is adapted to remove a potential cooperating receiver from the first list in dependence of a position and/or a speed and/or a battery level of the one potential cooperating receiver.

Thus, the selection of the second list of cooperating receivers from the first list and in particular the recursion stage can be simplified and accelerated.

A second aspect of the invention provides a method for a receiver served by a multi-antenna transmitter. The receiver includes: the number of R₀Adapted to receive at least one receiving antenna of number T from said transmitter₀Receive data through a downlink, wherein T₀Not less than 2. The receiver establishes a connection with a first list of potential cooperating receivers over respective communication links. One potential cooperative receiver is served by a corresponding multi-antenna transmitter and comprises a number R_PCDL(i)Is adapted to transmit a number T from the respective transmitter_PCDL(i)Receive data through a corresponding downlink, wherein T_PCDL(i)≧ 2 and i is the index of the first list. The receiver selects a second list of cooperating receivers from the first list through an initialization stage and a recursion stage. The initialization phase comprises: initializing the second list to an empty list and initializing a counter c. The recursion stage comprises: selecting the potential cooperating receiver located at index i-c if

Adding the selected potential cooperating receiver to the second list and incrementing the counter c, j being the index of the second list, R_CDL(j)Is the number of receive antennas of the cooperative receiver at index j, T_CDL(j)Is the number of transmit antennas of the transmitter serving the cooperative receiver at index j. The receiver calculates a precoder for the downlink from the transmitter to the receiver according to channel state information for the downlink and for respective channels from the transmitter to each cooperating receiver of the second list.

Further implementations of the method according to the second aspect of the invention correspond to different implementations of the receiver according to the first aspect. In other words, further features or implementations of the method according to the second aspect of the invention may perform the functions of the receiver according to the first aspect of the invention and its different implementations.

A third aspect of the invention provides a computer program having a program code for performing the method according to the second aspect of the invention, when the computer program runs on a computing device.

It is noted that the receiver proposed by the present invention may advantageously comprise a transmitting unit adapted to transmit the second list to each cooperating receiver belonging to said second list. This is advantageous because each cooperative receiver can then also calculate the precoder for the respective downlink from its respective transmitter (i.e. from the respective transmitter serving the cooperative receiver) to the cooperative receiver. In particular, each cooperative receiver may comprise a calculation unit adapted to calculate the precoder in dependence on channel state information about the respective downlink from the respective transmitter to the cooperative receiver, about the channel from the respective transmitter to the receiver for which the second list has been calculated, and about the channels from the respective transmitter to the remaining cooperative receivers of the second list. Thus, interference occurring at the receiver and the remaining cooperating receivers may be reduced.

Furthermore, it should be noted that the receiver proposed by the present invention may advantageously comprise a receiving unit adapted to receive a cooperation request broadcast by another receiver and a receiving unit adapted to send a response message to said another receiver. All of the above aspects regarding collaboration request and response information may also be applicable in this case. Thus, the further receiver may comprise a similar calculation unit for selecting a second list, wherein the receiver may be part of such a second list and may comprise a receiving unit adapted to receive the second list.

The idea of the present invention is to provide a receiver driven precoding RDP for reducing interference and increasing SINR at the receiver and compensating for the situation where there is no cooperation between the transmitters. The inventive concept further consists in selecting cooperative receivers to ensure that the maximum possible number of cooperative receivers is selected. This may be important for the performance of the overall precoding system comprising the receiver, the transmitter, the cooperative receiver and the respective transmitter serving the cooperative receiver, since the amount of interference suppressed may be increased.

The rationale behind the invention is that the "cost" of the cooperative receiver added to the second list is determined by the degree of freedom it consumes for the whole system and the number of transmit antennas its transmitter is equipped with. The first aspect can be taken care of by counting the total number of degrees of freedom and reducing it when adding a new cooperative receiver to the second list. Conversely, the second aspect may be taken care of by ordering the potential cooperating receivers in the first list based on the number of antennas that their transmitters have. The information providing and processing protocol proposed by the present invention is advantageous in providing an ideal scenario for RDP to achieve its best performance.

Furthermore, the present invention is directed to RDP systems in which a group of MIMO transmitters communicate with their intended receivers without any required cooperation or coordination between the transmitters. The receivers implementing the invention establish a communication channel in which some side information about the CSI is exchanged, so that each receiver constructs a feedback that, once received by the respective serving transmitter, can affect the precoder implemented in the serving transmitter. Such a precoder is suitable to increase the achievable rates of all cooperating receiving devices.

This occurs in a completely invisible or transparent manner for the transmitter, which makes the invention particularly attractive in many cases. For example, in one of its embodiments, the invention may be used in a multi-vendor/operator system where a vendor/operator cannot control the behavior of a transmitter made by another vendor or owned by another operator. In another embodiment, the invention may be used in systems where the already deployed infrastructure/standards do not allow any reciprocal precoding/beamforming to be performed at the transmitter side.

The present invention proposes a solution to the interference problem, especially in decentralized networks and in networks where no cooperation between transmitters is required. The invention proposes in particular an efficient method for calculating load transmission to avoid interference from the transmitter to the receiver, i.e. a precoder that is efficient for calculating load transmission. In other words, the present invention proposes a receiver-centric decision process.

The present invention has the advantage of increasing overall network throughput while being apparent to the transmitter without requiring costly network/transceiver modifications to achieve the same goal. In other words, with the present invention, each transmitter contributes to overall performance improvement when employing a conventional precoding scheme without having to explicitly or implicitly coordinate or coordinate between transmitters.

The idea of the invention is that the negative impact of feeding back the cooperating receiver to the precoder with knowledge about the interfering channel of the cooperating receiver is mitigated. This mitigation is advantageous because the transmitter is completely invisible. Since all receivers of the network can apply the inventive strategy, all receivers cooperating by the invention can experience significant performance gains, thereby increasing overall network throughput. The present invention creates a receiver-centric scenario in which the latest network limitations are overcome without further cost to the operator or manufacturer.

It should be noted that all devices, elements, units and means described in the present application may be implemented as software or hardware elements or any kind of combination thereof. All steps described as being performed by various entities and the functions described as being performed by the various entities in this application are intended to mean that the respective entities are adapted or configured to perform the respective steps and functions. Even if in the following description of specific embodiments a specific function or step fully formed by an external entity is not reflected in the description of specific detailed elements of that entity performing that specific step or function, it is obvious to a person skilled in the art that these methods and functions may be implemented in corresponding software or hardware elements or any kind of combination thereof.

Drawings

The above aspects and implementations of the invention are explained in the following description of specific embodiments with reference to the drawings, in which:

fig. 1 illustrates a decentralized wireless communication network according to the prior art;

FIG. 2 illustrates a wireless communication network according to an embodiment of the present invention;

fig. 3 shows a wireless communication network according to another embodiment of the invention;

fig. 4 shows a wireless communication network according to another embodiment of the invention;

FIG. 5 illustrates a method according to an embodiment of the invention;

FIG. 6 illustrates a method according to another embodiment of the invention;

fig. 7 shows an algorithm for selecting a second list of cooperating receivers according to an embodiment of the invention.

Detailed Description

Fig. 2 illustrates a wireless communication network 200 according to an embodiment of the present invention.

The embodiment of fig. 2 is in accordance with the invention and consists of N autonomous transmitters with an index N e 1In which transmitters n and K_nAnd a receiver is connected. Here, the autonomous feature means that the transmitters do not exchange or, in particular, cannot exchange any information between each other, and thus behave as if there were no other transmitters in the same radio resource block.

One embodiment of such a network is depicted in fig. 2, which includes a WiFi network and an SC network. Each transmitter in the network is equipped with M_n> 1 antenna, while the receiver is equipped with N_rMore than or equal to 1 antenna. MIMO downlink channel routing matrix between transmitter n and receiver r

And (4) showing. Hypothesis matrix

The estimation is performed at each receiver through a downlink pilot/training sequence, e.g., as in frequency-division duplexing (FDD) communication. By stacking the channel matrices for all intended receivers of the transmitter n, i.e. all receivers served by the transmitter n, a channel matrix as described in the following equation (1) is obtained:

therefore, the signal received by the receiver r can be expressed according to the following equation (2):

wherein:

-x_nrepresents a transmission symbol vector of a transmitter n, and

-w_rrepresenting an additive noise vector.

In equation (2), three terms can be identified:

-a first item

Which is representative of the useful signal or signals,

-second term

Indicates intra-cell interference, and

-the third item

Indicating inter-cell interference.

In this case, the downlink operates in the same frequency band. Therefore, mutual interference is generated, and communication performance is degraded. MIMO techniques may be utilized to mitigate intra-cell interference even if the transmitters are not cooperative. Specifically, assume that each transmitter uses its selected precoder based on CSI feedback from its receiver. That is, each transmitter implements the following general precoding strategy:

wherein:

-W_nis the precoder used by the transmitter n,

-f_nis some reversible precoding function, e.g. any standard linear precoding strategy such as Maximal Ratio Combining (MRC), ZF or reversible MMSE transmission, and

-

is the CSI fed back by all receivers connected to transmitter n, i.e.,

is the overall CSI fed back by all receivers served by the transmitter n.

According to known techniques, the second term of the above equation (2) representing the intra-cell interference can be minimized or, even more efficiently, the SINR of all receivers can be maximized.

Returning to fig. 2, the wireless communication network 200 comprises two

transmitters

201, 202. The

transmitters

201, 202 are multi-antenna transmitters and each transmitter comprises in particular three antennas. The wireless communication network 200 comprises a first set of

receivers

211, 212, 213 served by a first transmitter 201 and

respective downlinks

221, 222, 223 from the first transmitter 201 to the first set of

receivers

211, 212, 213. The wireless communication network 200 also includes a second set of

receivers

214, 215 served by the second transmitter 202 and

respective downlinks

234, 235 from the second transmitter 202 to the second set of

receivers

214, 215.

Furthermore, even if the first group of

receivers

211, 212, 213 is not served by the second transmitter 202, there are

respective channels

231, 232, 233 between the second transmitter 202 and the first group of

receivers

211, 212, 213. Similarly, there is a

respective channel

224, 225 between the first transmitter 201 and the second set of

receivers

214, 215 even though the second set of

receivers

214, 215 is not served by the first transmitter 201.

The wireless communication network 200 of fig. 2 actually comprises two autonomous networks comprising a first transmitter 201 and a second transmitter 202, respectively. The transmission of the first transmitter 201 causes interference at the

receivers

214, 215 served by the second transmitter 202 and vice versa.

Channels

224, 225 cause inter-cell interference at

receivers

214, 215, respectively, while

channels

231, 232, 233 cause inter-cell interference at

receivers

211, 212, 213.

The

receivers

211, 212, 213, 214, 215 of the embodiment of fig. 2 each comprise an antenna. The receiver according to the invention may optionally comprise a plurality of antennas and may thus be a multi-antenna receiver. The

transmitters

201, 202 are, for example, base stations or WiFi access points. The

receivers

211, 212, 213, 214, 215 are, for example, handheld devices such as tablet computers, laptops or smart phones.

Fig. 3 shows a wireless communication network 300 according to another embodiment of the invention.

Fig. 3 shows a receiver 311 served by a multi-antenna transmitter 301, according to an embodiment of the present invention.

Receiver with a plurality of receivers311 includes: the number of R₀Is adapted to transmit a number T from said transmitter 301₀Receive data via downlink 321, wherein T₀≥2。

The receiver 311 includes: a connection unit adapted to establish a connection with the first list of potential cooperating receivers 312 via

respective communication links

331, 332. The first list may be referred to as PCDL and the potential cooperating receivers 312 of the first list PCDL may be referred to as PCDL (i), where i is an index of the first list PCDL.

One potential cooperative receiver 312, pcdl (i) served by a respective multi-antenna transmitter 302, and comprising a number R_PCDL(i)Is adapted to transmit a number T from the respective transmitter 302, said receiving antenna 312a being adapted to receive at least one receiving antenna 312a_PCDL(i)Receive data via a corresponding downlink 323, where T_PCDL(i)≥2。

The receiver 311 includes: a calculation unit adapted to select a second list of cooperating receivers from said first list of PCDLs. The second list may be referred to as CDL, the cooperating receivers of the second list CDL may be referred to as CDL (j), j being an index of the second list CDL. The calculation unit is adapted to select the second list by:

-an initialization phase comprising the initialization of said second list CDL as an empty list and of a counter c; and

a recursive phase comprising selecting a potential cooperative receiver 312, pcdl (i), located at index i ═ c, if

If so, the selected potential cooperative receiver 312, pcdl (i), is added to the second list CDL and the counter c is incremented. R_CDL(j)Is the number of receive antennas, T, of the cooperative receiver CDL (j) at index j_CDL(j)Is the number of transmit antennas 302a, 302b, 302c of the transmitter 302 serving the cooperative receiver cdl (j) at index j.

The calculation unit is adapted to calculate the precoder of the downlink 321 from the transmitter 301 to the receiver 311 from the channel state information on the downlink 321 and on the respective channel 322 from the transmitter 301 to each cooperating receiver CDL (j) of the second list CDL.

In particular, the receiver 311 may comprise an estimating unit adapted to estimate said channel state information on the downlink 321. The connection unit may be adapted to receive from each potential cooperative receiver 312 said channel state information on the respective channel 322 from the sender 301 to each cooperative receiver of the second list. The receiver 311 may include: a feedback unit adapted to send information characterizing or derived from the calculated precoder to the transmitter 301.

Correspondingly, when the receiver 311 is served by the sender 301 over the downlink 321, the potentially cooperating receiver 312 is not served by the sender 301. The channel 322 defined between the transmitter 301 and the potential cooperating receiver 312 represents a received interference channel at the potential cooperating receiver 312.

Thus, the receiver 311 is adapted to utilize knowledge of the interfering channel 322 with respect to the cooperating receivers in the second list in order to calculate a precoder that has a reduced negative impact on the cooperating receivers, i.e. a precoder that reduces inter-cell interference at the cooperating receivers.

According to an embodiment of the invention, the receiver 311 comprises an estimation unit adapted to estimate channel state information on a channel 324 from the further transmitter 302 to the receiver 311. The receiver 311 comprises a connection unit adapted to establish a connection with the cooperating receiver 312 via

respective communication links

331, 332. The receiver 311 is not served by the sender 302 and the cooperative receiver 312 is served by the sender 302 over the downlink 323. The connection unit is adapted to send the estimated channel state information to the cooperative receiver 312.

Correspondingly, the other transmitter 302 serves the cooperative receiver 312 instead of the serving receiver 311 through the downlink 323. The channel 324 defined between the other transmitter 301 and the receiver 312 represents the received interfering channel at the receiver 312.

Thus, the receiver 311 is adapted to estimate channel state information of the interfering channel 324 and to transmit the estimated channel state information to the cooperative receiver 312. In turn, the cooperative receiver 312 may now utilize knowledge of the interfering channel 324 in order to feed back to the other transmitter 302a precoder that mitigates the negative effects of the receiver 311, i.e., reduces inter-cell interference at the receiver 311.

Similar to the embodiment of fig. 2, the

transmitters

301, 302 are multi-antenna transmitters, and each transmitter specifically comprises three

antennas

301a, 301b, 301c and 302a, 302b, 302c, respectively. The

receivers

311, 312 of fig. 2 each comprise an antenna. The receiver according to the invention may optionally comprise a plurality of antennas and may thus be a multi-antenna receiver. The

transmitters

301, 302 of fig. 3, and more generally the transmitters according to the present invention, are e.g. base stations or WiFi access points. The

receivers

311, 312 of fig. 3, and more generally the receiver according to the invention, are handheld devices such as tablet computers, laptops or smart phones.

In FIG. 3, h_2，1A channel matrix representing a unidirectional communication link 331 from the receiver 311 to the potentially cooperating receiver 312, and h_1，2A channel matrix representing a unidirectional communication link 332 from the potential cooperative receiver 312 to the receiver 311. The receiver 311 and the potential collaboration receiver 312 are equipped with some capability to exchange data between them. The data exchange may be performed wirelessly, at least when both the receiver 311 and the potential cooperating receiver 312 are in proximity. This may be done, for example, by WiFi direct, bluetooth, or any device-to-device (D2D) Radio Access Technology (RAT).

Fig. 4 shows a wireless communication network 400 according to another embodiment of the invention. The wireless communication network 400 corresponds to the wireless communication network 300 of fig. 3. The wireless communication network 400 comprises a receiver 411 served by the transmitter 401 over a downlink 421, which corresponds to the receiver 311 served by the transmitter 301 over a downlink 321. The wireless communication network 400 includes potential cooperating receivers 412 served by respective transmitters 402 over respective downlinks 423 that correspond to the potential cooperating receivers 312 served by respective transmitters 302 over respective downlinks 323. Further, the wireless communication network 400 comprises a channel 422 from the transmitter 401 to the potential cooperative receiver 412 and a channel 424 from the further transmitter 402 to the receiver 411, which correspond to the channel 322 from the transmitter 301 to the potential cooperative receiver 312 and the channel 324 from the further transmitter 302 to the receiver 311, respectively.

The difference between the embodiments of fig. 3 and fig. 4 is the exchange of data between the receiver 411 and the potential cooperative receiver 412. Data exchange of channel state information is performed through another network 430. The exchange of data from receiver 411 to potential cooperative receiver 412 is performed over unidirectional communication link 432 to another network 430, over another network 430, and over unidirectional communication link 433 from another network 430 to potential cooperative receiver 412. The exchange of data from potential cooperative receiver 412 to receiver 411 is performed over unidirectional communication link 434 to another network 430, over another network 430, and over unidirectional communication link 431 from another network 430 to receiver 411. The other network 430 may be, for example, based on cloud computing or a relay or repeater.

Fig. 5 shows a method 500 for a receiver 311 served by a multi-antenna transmitter 301, the receiver 311 comprising a number R of receivers according to an embodiment of the invention₀Is adapted to transmit a number T from said transmitter 301₀Receive data via downlink 321, wherein T₀≥2。

According to the method 500, the receiver 311 establishes 501 a connection with a first list of PCDL of a potential cooperating receiver 312, PCDL (i), over

respective communication links

331, 332. One potential cooperative receiver 312, pcdl (i) served by a respective multi-antenna transmitter 302, and comprising a number R_PCDL(i)Is adapted to transmit a number T from the respective transmitter 302, said receiving antenna 312a being adapted to receive at least one receiving antenna 312a_PCDL(i)Are received via respective downlinks 323Receive data, wherein T_PCDL(i)≧ 2 and i is an index of the first list PCDL.

According to the method 500, the receiver 311 selects 502 a second list of cooperating receivers CDL (j) CDL from the first list PCDL by:

an initialization phase 503 comprising: initializing 504 said second list CDL to an empty list and initializing 505 a counter c; and

a recursion stage 506 comprising: selecting 507 the potential cooperative receiver 312, pcdl (i), located at index i ═ c, if

If so, the selected potential cooperative receiver 312, PCDL (i), is added 508 to the second list CDL, and the counter c is incremented 509, where j is the index of the second list CDL, R_CDL(j)Is the number of receive antennas, T, of the cooperative receiver CDL (j) at index j_CDL(j)Is the number of transmit antennas 302a, 302b, 302c of the transmitter 302 serving the cooperative receiver cdl (j) at index i.

According to the method 500, the receiver 311 calculates 510 a precoder for the downlink 321 from the transmitter 301 to the receiver 311 from the channel state information for the downlink 321 and for the respective channel 322 from the transmitter 301 to each cooperating receiver CDL (j) of the second list CDL.

Fig. 6 shows a method 600 according to another embodiment of the invention.

According to the present embodiment, the step of establishing 501 a connection between the receiver 311 and the first list PCDL of the potential cooperative receiver 312 comprises: a step 601 of broadcasting a cooperation request; a step of listening 602 to answer discovery; and, if any device answers 603, a step of creating 606 a first list PCDL.

The purpose of this setup 501 step is that the receiver 311 establishes a first connection or handshake with a device implementing the invention and within its vicinity. This step is performed, for example, by discovering and responding to the discovery. The receiver 311 broadcasts 401 a collaboration request over an appropriate RAT (bluetooth or Wi-Fi as described with respect to fig. 3). Each potential collaboration receiver 312 implementing the present invention replies via a response message. A connection is established 501 between the receiver 311 and the responding potential cooperative receiver 312. This phase of establishing 501 a connection comprises creating 606 a first list PCDL of potential cooperating devices.

Advantageously, the response message sent by the potential cooperative receiver 312 and received by the receiver 311 comprises a number R of receiving antennas 312a relating to the potential cooperative receiver 312_PCDL(i)And the number T of transmit antennas 302a, 302b, 302c of the transmitter 302 serving the potential cooperative receiver 312_PCDL(i)The information of (1).

The step of creating 606 a first list of PCDLs may further comprise the sub-step of ordering the first list of PCDLs. For example, the first list PCDL may be based on the number R of receive antennas 312a of the potential cooperating receivers 312_PCDL(i)Sorted in descending order.

In one embodiment of the invention, potential collaboration receivers 312 that have participated in the collaboration do not reply. In other words, if the potential collaboration receiver 312 receives a collaboration request from the receiver 311 for the first time and then receives a collaboration request from the same receiver 311, then preferably the potential collaboration receiver 312 does not send a response message.

In one embodiment of the invention, the cooperation request broadcast by the receiver 311 comprises information about the number T of transmitting antennas 301a, 301b, 301c of the transmitter 301₀And/or information about the number R of receiving antennas 311a₀The information of (1). Thus, the potential collaboration receiver 312 may advantageously decide not to send a response message. For example, if the number of its receiving antennas is higher than the number T contained in the cooperation request₀It is not possible to add potential cooperating receivers to the second list during the recursion phase. The recursion phase can be simplified by not sending a response message.

In one embodiment of the invention, the cooperation request may comprise information about the number T of transmit antennas 301a, 301b, 301c of the transmitter 301₀And information of the identity of the sender 301. This hasIt is advantageous that the potential cooperative receiver 312 knows the identity of the sender 301 and can easily identify the pilot received from the sender 301 when estimating channel state information about the channel 322 from the sender 301 to the potential cooperative receiver 312.

In one embodiment of the invention, the cooperation request may comprise information about the number T of transmit antennas 301a, 301b, 301c of the transmitter 301₀Information of the transmitter 301, information of the identification of the transmitter 301, and the number R of receiving antennas 311a₀The information of (1).

In the embodiment of fig. 6, the step of the receiver 311 selecting 502 a second list CDL of cooperating receivers CDL (j) from the first list PCDL corresponds to the step of identifying 607 a set of cooperating devices CDL (j), i.e. identifying 607 the second list CDL of cooperating receivers CDL (j).

In one embodiment of the invention the

selection

502, 607 of the second list of cooperating receivers is performed according to the algorithm shown in fig. 7.

In an initialization phase, the second list CDL is initialized to an empty list. Further, the variable K is a counter that counts the total number of receiving antennas, and is initialized to the number R of receiving antennas 311a of the receiver 311₀. The variable i represents the index of the first list PCDL and is initialized to a value corresponding to the counter c being 1. The variable i is used to scroll the first list PCDL. The variable M represents the minimum number of antennas in the

transmitter

301, 302 and is initialized to the number T of transmit antennas 301a, 301b, 301c of the transmitter 301₀。

In the recursive phase of the algorithm, a potential cooperative receiver 312, pcdl (i), located at index i is selected (507). The variable K for counting the total number of receive antennas is the number R of receive antennas 312a of the selected potential cooperative receiver 312, pcdl (i)_PCDL(i)An increase is made. The variable M represents the minimum number of antennas in the transmitter 301 of the receiver 311 and the transmitter 302 of the cooperative receiver 312 of the second list, and by considering the number T of transmit antennas 302a, 302b, 302c of the transmitter 302 serving the potential cooperative receiver 312, pcdl (i), identified by the index i_PCDL(i)And (6) updating.

If K ≦ M, i.e., if equation (4) above is verified, then the selected potential cooperative receiver 312, PCDL (i), is added to the second list. Otherwise, the selected potential cooperative receiver 312, pcdl (i), is not added to the second list, and the variables K and M are updated. Each time the recursion phase is performed, the index i is incremented, i.e. the counter c is incremented.

The second list of cooperating devices CDL is identified by the receiver 311 establishing a connection with a potential cooperating device.

Advantageously, the receiver 311 may sort the first list, or even remove some potential cooperating receivers from the first list. This ordering or removal may be based on different criteria. In one embodiment, this may be the number of antennas of the potentially cooperating receiver. This phase is advantageous, for example, to keep the number of antennas of the cooperative receiver smaller than the number of transmit antennas and, for example, to exclude very high mobility devices. The minimum output of this stage is a second list of cooperating receivers, where the total number of antennas of the receiver 311 and the cooperating receiver 312 is less than the minimum number of antennas of the transmitter involved.

In one embodiment of the invention, the parameter used to sort the first list or remove the potential cooperating receivers from the first list may be the location of the potential cooperating receivers, e.g. the GPS location. In fact, if a potential cooperating receiver is far enough from the receiver 311, the interference level between the two devices will be low enough that the corresponding potential cooperating receiver can be removed from the first list or reordered at the end of the first list. A threshold method may be used therein, and the removal or reordering may be performed if the distance between the receiver 311 and the potential cooperative receiver 312 is above a threshold.

In another embodiment of the invention, the parameter used to sort the first list or remove the potential cooperating receivers from the first list may be the speed of the latter or its speed relative to the receiver 311. For example, a potentially cooperative receiver moving at a speed above a given threshold may have a coherence time that is too short to actually take advantage of the benefits of the present invention, such that removal or reordering may be performed.

In another embodiment of the invention, the parameter used to sort the first list or remove the potential cooperating receivers from the first list may be a battery level of the potential cooperating receivers. A potentially cooperative receiver may be more desirable than other receivers using the present invention because its battery level is low and cannot afford to retransmit multiple times: a potential cooperating receiver with a low battery level may correspondingly move at the beginning of the first list. Alternatively, in case it appears that the invention is not energy efficient, this parameter may be considered in reverse, i.e. the potential cooperating receivers with low level batteries are removed from the first list.

Each of these parameters may be communicated during establishment of the cooperation, at the latest during creation 606 of the first list PCDL, and should be included in the exchange of messages.

These parameters may also be combined according to the following equation:

maximize_{r}f({X}，{S}，{B}) (5)

where X, S, B denote the set of all locations, the set of all velocity values and the set of all battery levels of the potential cooperating device 312, respectively. In view of this, equation (4) will also be verified when maximizing equation (5).

One possible implementation of the function f is a weighted sum according to the following equation:

f({X}，{S}，{B})＝w₁{X}+w₂{S}+w₃{B} (6)

the method 600 comprises the further step of negotiating a pre-coding strategy 608, i.e. a cooperation level anticipation and establishment. The receiver 311 and the cooperating receiver cdl (j) selected in step 607 agree or negotiate what precoding strategy should be employed based on the amount of available information. The minimum output of this step is the precoding strategy to be employed, e.g., ZF or MRC. Optional outputs of this step are selfishness and/or transmit SNR level. The selfishness can be defined as a parameter α, which defines the calculated precoder as a combination of a maximum ratio combining precoder and a zero-forcing precoder.

The method 600 includes the further step of information collection 609 included in the estimation of the state of the direct and interfering channels. The necessary information, e.g. information of the interfering channel, is estimated based on the pilot/training signal transmitted by the interfering transmitter, i.e. transmitted by the transmitter 301. Thus, the receiver 311 may estimate channel state information CSI on the downlink 321, and the cooperating receiver 312, cdl (i) may estimate channel state information on the interfering channel 322 from the transmitter 301 to the cooperating receiver 312, cdl (j).

In one embodiment of the invention, the CSI for non-sparse interfering channels is estimated by a linear estimator. In one embodiment of the invention, the CSI for non-sparse interfering channels is estimated by a non-linear estimator. In one embodiment of the invention, CSI on a sparse interfering channel is estimated by compressed sensing.

The method 600 includes the further step of information exchange 610. The receiver 311 selected in step 607 and the cooperative receiver 312 exchange information required to calculate the precoder, particularly information of the interfering channel. In particular, the cooperative receiver 312 may transmit its estimate of channel state information about the interfering channel 322 from the transmitter 301 to the cooperative receiver 312 to the receiver 311. The transmission is performed over communication link 332. In one embodiment, the necessary information is passed through a RAT (e.g., bluetooth or WiFi direct) or through another network 430, e.g., based on cloud computing or relays or repeaters.

In one embodiment of the invention, the transmitted CSI is a quantized version of the CSI estimated at the corresponding cooperating receiver. In one embodiment of the invention, the transmitted CSI is an actual analog realization of the CSI estimated at the corresponding cooperating receiver. In one embodiment of the invention, the transmitted CSI is a compressed version of the CSI estimated at the corresponding cooperating receiver.

The method 600 includes another step of precoder computation 611. This step can be designed according to several criteria.

In one embodiment of the invention, criteria may be determined to arrive at a pareto optimal solution, such asThe following is described. In a first sub-step, the receiver 311, labeled "r", establishes an extended channel matrix by stacking its own channel matrix and the channel matrix of the cooperative receiver 312 together according to the following equation

Wherein

-h_n，rA channel matrix representing the receiver 311, an

-h_n，1，...，h_n，iRepresenting the channel matrix of the i cooperating receivers 312 labeled from "1" to "i".

Is of dimension M_nX K, wherein:

k is the total number of antennas of the receiver 311 and the cooperating receiver 312,

-M_nis the number of antennas of the transmitter n.

In a second sub-step, the ZF precoder is evaluated according to the following equation:

wherein the content of the first and second substances,

-

is dimension N_rA unit matrix of, and

-

is a dimension consisting of only zeros of (M-N)_r)×N_rOf the matrix of (a).

In a third substep, the MRC precoder is evaluated according to the following equation:

ρ_MRC＝h_n，r. (9)

in a fourth substep, the desired precoder is calculated according to the following formula:

P＝αρ_MRC+(1-α)ρ_ZF (10)

where α is selfishness.

The value α ═ 1 would basically apply MRC precoding to the transmitter 301 and may be referred to as selfish selection, while the value α ═ 0 would apply ZF precoding and may be referred to as lyhis selection.

The method 600 comprises the further step of feeding back the signal transmission 605, i.e. the step of feeding back the precoder/CSI. In this step, the receiver 311 finally creates a feedback signal and sends it to the transmitter 301 serving the receiver 311. Based on the precoder P calculated in step 611, the receiver 311, for example, calculates and transmits as feedback to the transmitter a vector:

f^-1(P). (11)

the precoding function f is assumed to be invertible. In view of this, it should be noted that standard and generic precoding functions such as MRC, ZF, and MMSE are invertible. In particular, MMSE is a widely used near-optimal linear solution.

If the receiver does not receive any response message after broadcasting the cooperation request, the receiver estimates 604 its own downlink 321. The feedback 605 of the signal transmission at this time depends only on the CSI of the downlink 321, since there is no cooperating receiver 312 with the receiver.

The invention is described in connection with various embodiments and implementations. However, other variations will become apparent to those skilled in the art upon a study of the drawings, the specification and the appended claims, and may be made by practicing the claimed invention. In the claims as well as in the specification, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A receiver served by a first multi-antenna transmitter, comprising:

a number of R₀Adapted to transmit a number T of signals from said first multi-antenna transmitter₀Receive data through a downlink, wherein T₀≥2；

-a connection unit adapted to establish a connection with a first list of potential cooperating receivers over respective communication links;

wherein one potential cooperative receiver is served by a corresponding second multi-antenna transmitter and comprises a number R_PCDL(i)The receive antennas of the one potentially cooperating receiver are adapted to transmit from the second multi-antenna transmitter a number T_PCDL(i)Receive data through a corresponding downlink, wherein T_PCDL(i)≧ 2 and i is an index of the first list;

-a calculation unit adapted to select a second list of cooperating receivers from said first list by:

-an initialization phase comprising: initializing the second list to an empty list and initializing a counter c; and

-a recursive stage comprising: selecting a potential cooperative receiver located at index i-c if

Adding the selected potential cooperating receiver to the second list and incrementing the counter c;

where j is the index of the second list, R_CDL(j)Is the number of receive antennas of the cooperative receiver at index j, T_CDL(j)Is the number of transmit antennas of the transmitter serving the cooperative receiver at index j;

wherein the calculation unit is adapted to calculate a precoder for the downlink from the first multi-antenna transmitter to the receiver according to channel state information for the downlink and for respective channels from the first multi-antenna transmitter to each cooperative receiver of the second list.

2. The receiver in accordance with claim 1, wherein,

wherein the calculation unit is adapted to determine the number R of receiving antennas of each potential cooperative receiver according to the first list_PCDL(i)Sorting the first list such that the calculation unit is adapted to select the second list from the sorted first list.

3. The receiver in accordance with claim 2, wherein,

wherein the calculation unit is adapted to calculate the number R of receive antennas for each potential cooperative receiver of the first list_PCDL(i)Sorting the first list in descending order.

4. The receiver in accordance with claim 2, wherein,

wherein the calculation unit is adapted to calculate the number R of receive antennas for each potential cooperative receiver of the first list_PCDL(i)Sorting the first list in ascending order.

5. The receiver in accordance with claim 2, wherein,

wherein the computing unit is adapted to serve the respective number T of transmit antennas of the transmitter of the potential cooperating receiver_PCDL(i)Sorting the potential cooperative receivers in the first list in descending order.

6. Receiver according to one of the preceding claims,

wherein the recursion phase is performed until all potential cooperating receivers of the first list are selected, orUp to

7. The receiver according to any of claims 1-5, comprising:

-a broadcasting unit adapted to broadcast a collaboration request to the potential collaboration receivers;

-a receiving unit adapted to receive respective response messages from the potential collaboration receivers in response to the collaboration requests;

wherein the first list corresponds to potential cooperating receivers for which the receiving unit received a response message.

8. The receiver in accordance with claim 7, wherein,

wherein a response message received from a given potential cooperative receiver includes a number R of receive antennas for the given potential cooperative receiver_PCDL(i)And the number T of the transmit antennas serving the given potential cooperative receiver_PCDL(i)The information of (1).

9. The receiver in accordance with claim 8, wherein,

wherein the cooperation request broadcast by the receiver includes a number T of transmission antennas with respect to the transmitter₀And/or information about the number of receiving antennas R₀The information of (1).

10. The receiver according to claim 8 or 9,

wherein the cooperation request broadcast by the receiver includes information about a location of the receiver.

11. The receiver according to claim 8 or 9,

wherein the response message received from a given potential cooperating receiver comprises information about the location and/or speed and/or battery level of the given potential cooperating receiver.

12. The receiver in accordance with claim 11, wherein,

wherein the computing unit is adapted to order the first list according to the information on the position and/or the speed and/or the battery level comprised in the response message received from the potential cooperative receiver.

13. The receiver in accordance with claim 12, wherein,

wherein the calculation unit is adapted to remove one potential cooperating receiver from the first list in dependence of the position and/or the speed and/or the battery level of said one potential cooperating receiver.

14. A method for a receiver served by a first multi-antenna transmitter, the receiver comprising: the number of R₀Adapted to transmit a number T of signals from said first multi-antenna transmitter₀Receive data through a downlink, wherein T₀≥2；

-the receiver establishing a connection with a first list of potential cooperating receivers over respective communication links;

-the receiver selecting a second list of cooperating receivers from the first list by:

-a recursive stage comprising: the selection is located at the index i ═ cIf the potential cooperative receiver is

Adding the selected potential cooperating receiver to the second list, and incrementing the counter c,

where j is the index of the second list, R_CDL(j)Is the number of receive antennas of the cooperative receiver at index j, and T_CDL(j)Is the number of transmit antennas of the transmitter serving the cooperative receiver at index j;

-the receiver calculating a precoder for the downlink from the first multi-antenna transmitter to the receiver according to channel state information for the downlink and for the respective channel from the first multi-antenna transmitter to each cooperative receiver of the second list.

15. A computer-readable storage medium, having stored thereon a computer program for performing the method according to claim 14, when the computer program runs on a computing device.