WO2017028922A1 - Appareil et procédé de précodage entraîné par récepteur - Google Patents

Appareil et procédé de précodage entraîné par récepteur Download PDF

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Publication number
WO2017028922A1
WO2017028922A1 PCT/EP2015/069113 EP2015069113W WO2017028922A1 WO 2017028922 A1 WO2017028922 A1 WO 2017028922A1 EP 2015069113 W EP2015069113 W EP 2015069113W WO 2017028922 A1 WO2017028922 A1 WO 2017028922A1
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WIPO (PCT)
Prior art keywords
receiver
transmitter
cooperating
precoder
downlink
Prior art date
Application number
PCT/EP2015/069113
Other languages
English (en)
Inventor
Luca Rose
Apostolos Destounis
Marco MASO
Original Assignee
Huawei Technologies Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to CN201580081554.1A priority Critical patent/CN107852198B/zh
Priority to PCT/EP2015/069113 priority patent/WO2017028922A1/fr
Publication of WO2017028922A1 publication Critical patent/WO2017028922A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0014—Three-dimensional division
    • H04L5/0023—Time-frequency-space
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
    • H04L5/0033—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation each allocating device acting autonomously, i.e. without negotiation with other allocating devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/20—Control channels or signalling for resource management

Definitions

  • the present invention generally relates to the field of wireless communication, and specifically relates to a wireless communication supporting precoding functionality.
  • a first type of solutions which may be labeled resource allocation (RA) solutions aim at designing algorithms that orthogonalize the communications by smartly allocated resource radio blocks, so that if one transmitter transmits data over a particular radio resource (e.g., frequency, time slot, code) the other transmitters do not transmit data on the same radio resource. For instance TDMA and CSMA follow this approach.
  • RA resource allocation
  • TDMA and CSMA follow this approach.
  • a drawback of these approaches is that they are not efficient for two reasons. First, they waste radio resource, either in time and/or frequency domain. Second, they require some level of synchronization between the transmitters.
  • a second type of solution assumes the existence of a noiseless high throughput backhaul connecting the transmitters and/or among all the receivers.
  • the network can employ a theoretically optimal precoding and decoding scheme that maximizes the overall throughput.
  • the practical limits of such a system are evident, since the existence of a noiseless high throughput backhaul among SCs or WiFi access points is very unlikely.
  • the first strategy is based on a codebook-based precoding.
  • the precoder as well as if necessary the corresponding decoder at the receiver, is chosen by each transmitter among a finite number of pre-computed non-optimized precoding matrices, wherein these matrices are known at both the transmitter and the receiver.
  • a receiver receives the pilots/training symbols from a transmitter, it estimates the channel matrix and computes the index corresponding to the best precoder based on some metric.
  • This first strategy however does not fully exploit the potential of using multiple antennas.
  • the second strategy requires the receiver to estimate the channel and then feed it back as channel state information (CSI) to the transmitter.
  • CSI channel state information
  • the transmitter uses this CSI to design a specific precoder.
  • MRC maximum ratio combining
  • ZF zero-forcing
  • MIMO multiple-input and multiple-output
  • full frequency reuse Instances of these paradigms can be found in WiFi or LTE wireless communication networks.
  • MIMO has the potential of largely improving the performance of a wireless communication network by mitigating the negative effect of interference and fading, whereas full frequency reuse maximizes spectral occupation at the price of an increased interference level.
  • Centralized networks offer many ways of achieving this goal.
  • BSs base stations
  • transmitters that dispose of perfect CSI with respect to the channels towards the non-served receivers or users can manage the multi-user interferences by means of precoding/beamforming.
  • base stations or transmitters can mitigate the multiuser interferences by employing ZF precoders.
  • the base stations can employ MMSE transmit filtering to maximize the signal to interference plus noise ratio (SINR) at all receivers.
  • SINR signal to interference plus noise ratio
  • wireless communication networks in which neither cooperation nor coordination is possible between the transmitters. Examples of such wireless communication networks are e.g., WiFi, small-cells (SCs), femto-cells (FCs).
  • Fig. 1 shows an example of a non-centralized 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 as well as receivers 1 11, 1 12, 1 13.
  • the transmitters 101, 102, 103 are for example WiFi access points and the receivers 11 1, 112, 113 are for example handheld devices like tablets, laptops or smartphones.
  • a first receiver 1 11 is served by a first transmitter 101 over a first downlink 121.
  • a second receiver 1 12 is served by a second transmitter 102 over a second downlink 124 and a third receiver 113 is served by a third transmitter 103 over a third downlink 128.
  • the first receiver 1 11 is not served by the second and third transmitters 102, 103, there is a respective channel 126, 129 between respectively the second and third transmitters 102, 103 and the first receiver 11 1.
  • the second receiver 1 12 is not served by the first and third transmitters 101, 103, and the third receiver 1 13 is not served by the first and second transmitters 101, 102.
  • a respective channel 123, 127 exists from the first and third transmitters 101, 103 to the second receiver 112
  • a respective channel 122, 125 exists from the first and second transmitters 101, 102 to the third receiver 1 13.
  • these channels 126, 129 are therefore identified as being interfering channels.
  • known multi antenna transmitters have the capability of zeroing or mitigating the negative effect of interference on the performance of the network, but at the cost of centralization.
  • interference is problematic in non-centralized wireless communication networks, even more if the transmitters do not cooperate.
  • the present invention aims at improving the state of the art.
  • the object of the present invention is to provide an improved wireless communication with reduced interferences.
  • the present invention particularly intends to improve the wireless communication in a network that is not centralized and in which cooperation between the transmitters is not required.
  • the invention intends to mitigate the interferences caused at the receivers.
  • the above-mentioned object of the present invention is achieved by the solution provided in the enclosed independent claims.
  • Advantageous implementations of the present invention are further defined in the respective dependent claims.
  • a first aspect of the present invention provides a receiver for being served by a multi antenna transmitter over a downlink.
  • the receiver comprises at least one antenna adapted to receive data from the transmitter over the downlink.
  • the receiver comprises an estimation unit adapted to estimate channel state information with respect to the downlink.
  • the receiver comprises a connection unit adapted to establish a connection with at least one cooperating receiver over a respective communication link, and to receive from each cooperating receiver channel state information of a channel between the transmitter and said cooperating receiver.
  • the receiver comprises a computing unit adapted to compute, from the estimated channel state information and from the received channel state information, a precoder for the downlink between the transmitter and the receiver.
  • the receiver comprises a feedback unit adapted to transmit to the transmitter information derived from the computed precoder.
  • the invention may compensate for the absence of cooperation between transmitters, particularly in the context of MIMO non-cooperative networks, and may reduce interference and increase the STNR at the receivers.
  • the receiver may advantageously exploit the knowledge about the interfering channel from the transmitter to the cooperating receiver in order to feed back to the transmitter information for reducing inter-cell interferences at the cooperating receiver.
  • the information derived from the computed precoder is adapted to be used by the transmitter for precoding the downlink.
  • the interference reduction may be performed in a complete blind way for the transmitter.
  • the computed precoder is a maximum ratio combining precoder or a zero-forcing precoder or a combination of the maximum ratio combining precoder and the zero-forcing precoder.
  • the connection unit is adapted to establish a connection with the at least one cooperating receiver using a radio access technology that is different from a radio access technology used for the downlink between the transmitter and the receiver. Thereby, cooperation at the transmitter-level is not necessary.
  • connection unit is adapted to establish an ad hoc network with the at least one cooperating receiver.
  • connection unit is adapted to establish a Wi-Fi Direct, a Bluetooth, or a device-to-device connection with the at least one cooperating receiver.
  • connection unit is adapted to broadcast a request for cooperation, to receive from the at least one cooperating receiver a response to the request for cooperation, and to establish the connection with the at least one cooperating receiver based on the response.
  • connection unit is adapted to establish a connection with at least one cooperating receiver over a respective communication link in that the connection unit is adapted to establish a connection with a plurality of other receivers, and to select said at least one cooperating receiver from the plurality of other receivers.
  • connection unit is adapted to select said at least one cooperating receiver such that
  • each selected cooperating receiver is served, via a number 3 ⁇ 4 of antennas, by one or more further multi antenna transmitters over a respective downlink,
  • - Ro is the number of the at least one antenna of the receiver used for the downlink from the transmitter to the receiver, R; is the sum, over all selected cooperating receivers, of said number 3 ⁇ 4 of antennas, i ⁇ 0
  • - ⁇ 0 ⁇ is a set comprising, for all said further transmitters serving said selected cooperating receivers, the number of antennas of said further transmitter.
  • the receiver is adapted to negotiate with the at least one cooperating receiver a strategy for computing the precoder.
  • the computed precoder is a combination of a maximum ratio combining precoder and a zero-forcing precoder.
  • the receiver is adapted to negotiate with the at least one cooperating receiver a strategy for computing the precoder so as to define a level of selfishness defining said combination of the maximum ratio combining precoder and the zero-forcing precoder.
  • the estimation unit is adapted to estimate the channel state information based on pilot and/or training signals received from the transmitter over the downlink.
  • the computing unit is adapted to build an extended channel matrix by stacking together a channel matrix of the downlink between the transmitter and the receiver, and each channel matrix of the respective channel between the transmitter and each cooperating receiver, to compute the precoder based on the extended channel matrix.
  • the computing unit is adapted to generate
  • I Nr is an identity matrix of dimension N r
  • M _ Nr is a matrix of dimension
  • a is a level of selfishness comprised between 0 and 1.
  • the feedback unit is adapted to compute an inverse of the precoder, and to transmit to the transmitter said inverse as information derived from the computed precoder.
  • the receiver comprises an estimation unit adapted to estimate channel state information with respect to a channel from a further transmitter to the receiver.
  • the receiver comprises a connection unit adapted to establish a connection with a cooperating receiver over a respective
  • the receiver is not served by the further transmitter, and the cooperating receiver is served by the further transmitter over a respective downlink.
  • the receiver is adapted to transmit to the cooperating receiver the estimated channel state information.
  • the cooperating receiver to exploit the knowledge about the interfering channel from the further transmitter to the receiver in order to feed back to the further transmitter precoder information that may reduce inter-cell interferences at the receiver.
  • a second aspect of the present invention provides a receiver comprising an estimation unit adapted to estimate channel state information with respect to a channel from a transmitter to the receiver.
  • the receiver comprises a connection unit adapted to establish a connection with cooperating receiver over a respective communication link.
  • the receiver is not served by the transmitter, and the cooperating receiver is served by the transmitter over a respective downlink.
  • the receiver is adapted to transmit to the cooperating receiver the estimated channel state information.
  • the estimation unit is adapted to estimate the channel state information based on pilot and/or training signals received from the transmitter over the channel.
  • a third aspect of the present invention provides a communication network comprising a plurality of receivers according to the first aspect or to the second aspect and the multi antenna transmitter.
  • a fourth aspect of the present invention provides a method for serving a receiver by a multi antenna transmitter over a downlink and reducing interference caused at a cooperating receiver by a channel from the transmitter to the cooperating receiver.
  • the receiver and the cooperating receiver establish a connection over a communication link.
  • the receiver estimates channel state information with respect to the downlink.
  • the cooperating receiver estimates channel state information with respect to the channel from the transmitter to the cooperating receiver.
  • the receiver receives from the cooperating receiver, over the communication link, the channel state information with respect to the channel estimated by the cooperating receiver.
  • the receiver computes, from the estimated channel state information with respect to the downlink and from the received channel state information with respect to the channel, a precoder for the downlink between the transmitter and the receiver.
  • the receiver transmits to the transmitter information derived from the computed precoder.
  • the method proposes a receiver cooperation protocol that may enforce cooperation upon the transmitters to achieve a target performance.
  • a fifth aspect of the present invention provides a computer program having a program code for performing the method according to the fourth aspect of the present invention when the computer program runs on a computing device.
  • This invention targets 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 are exchanged, allowing each receiver to build a feedback that, once received by the respective serving transmitter, can influence the precoder implemented in the serving transmitter.
  • This precoder is adapted to improve the achievable rate for all the cooperating receiving devices. This happens in a complete blind or transparent way for the transmitters, making the invention particularly attractive in many scenarios.
  • this invention could be adopted in a multi-vendor/operator systems in which a vendor/operator cannot control the behavior of transmitters manufactured by another vendor or owned by another operator.
  • this invention could be adopted in systems in which already the deployed infrastructure/standard does not allow to perform any mutually beneficial precoding/beamforming at the transmitter side.
  • This invention proposes a solution to the problem of interferences particularly in a network that is not centralized and in which cooperation between the transmitters is not required.
  • the invention particularly proposes to transfer the load of computing an efficient method to avoid interference, i.e. to transfer the load of computing an efficient precoder, from the transmitter to the receiver.
  • the invention proposes to frame a receiver-centric decision process.
  • This invention has the advantage of increasing the overall network throughput while being transparent for the transmitters, without requiring expensive network/transceiver
  • each transmitter contributes to the overall performance increase while adopting the legacy precoding schemes, without however the necessity for an explicit or implicit cooperation or coordination between the transmitters.
  • An idea of the invention is to exploit knowledge about the interfering channels of cooperating receivers in order to feedback a precoder that mitigate the negative effects for the cooperating receivers. This mitigation is advantageous in that is occurs in a complete blind way for the transmitters. Since all receivers of a network may apply the strategy of the invention, all the receivers that cooperate through the invention may experience a significant performance gain, in turn increasing the overall network throughput. This invention yields a receiver-centric scenario, in which state-of-the-art network limitations are overcome without further costs for the operators or manufacturers.
  • Fig. 1 shows a non-centralized wireless communication network according to the state of the art
  • Fig. 2 shows a wireless communication network according to an embodiment of the present invention
  • Fig. 3 shows a wireless communication network according to a further embodiment of the present invention
  • Fig. 4 shows a wireless communication network according to a further embodiment of the present invention
  • Fig. 5 shows a method according to an embodiment of the present invention
  • Fig. 6 shows a method according to a further embodiment of the present invention
  • Fig. 7 shows an application scenario according to an embodiment of the present invention
  • Fig. 8 shows an application scenario according to a further embodiment of the present invention.
  • Fig. 9 shows performance gain according to an embodiment of the present invention.
  • FIG. 2 shows a wireless communication network 200 according to an embodiment of the present invention.
  • the embodiment of Fig. 2 is a specific embodiment of a general wireless communication network according to the present invention and being composed of N autonomous transmitters indexed as n ⁇ ⁇ 1, ... , N], with transmitter n being connected to K n receivers.
  • the feature autonomous refers to the fact that the transmitters do not exchange, or particularly cannot exchange, any information between them, and therefore behave as if no other transmitter is present in the same radio resource block.
  • An embodiment of such a network is depicted in Fig. 2 and encompasses among the others WiFi networks and SC networks.
  • Each transmitter in the network is equipped with M n > 1 antennas, while the receivers are equipped with N r ⁇ 1 antennas.
  • the MIMO downlink channel between a transmitter n and a receiver r is indicated by the matrix h r . It is assumed that the matrix h r is estimated at each receiver through downlink pilot/training sequences, e.g. as done for frequency-division duplexing (FDD) communications.
  • FDD frequency-division duplexing
  • each transmitter employs a precoder of its choice based on the CSI feedback from its receivers. That is, each transmitter implements the following general precoding strategy:
  • - / admirably is a certain invertible precoding function, for example any of the standard linear precoding strategies such as maximum ratio combining (MRC), ZF or MMSE transmission that are invertible, and
  • the wireless communication network 200 comprises two transmitters 201, 202.
  • the transmitters 201, 202 are multi antenna transmitters and each transmitter particularly comprises three antennas.
  • the wireless communication network 200 comprises a first set of receivers 21 1, 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 21 1, 212, 213.
  • the wireless communication network 200 also comprises a second set of receivers 214, 215 served by a second transmitter 202, and respective downlinks 234, 235 from the second transmitter 202 to the second set of receivers 214, 215.
  • the wireless communication network 200 of Fig. 2 in fact comprises two autonomous networks that respectively comprise the first transmitter 201 and the second transmitter 202.
  • the transmission of the first transmitter 201 causes interferences at the receivers 214, 215 served by the second transmitter 202 and vice versa.
  • the channel 224, 225 correspondingly cause inter-cell interference at the receivers 214, 215, while the channel 231, 232, 233 cause inter-cell interference at the receivers 211, 212, 213.
  • the receivers 211, 212, 213, 214, 215 of the embodiment of Fig. 2 respectively comprise one antenna.
  • a receiver according to the present invention may alternatively comprise more than one antenna and may consequently 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 like tablets, laptops or smartphones.
  • Fig. 3 shows a wireless communication network 300 according to a further embodiment of the present invention.
  • Fig. 3 shows a receiver 311 for being served by a multi antenna transmitter 301 over a downlink 321.
  • the receiver 311 comprises at least one antenna 31 la adapted to receive data from the transmitter 301 over the downlink 321.
  • the receiver 31 1 comprises an estimation unit adapted to estimate channel state information with respect to the downlink 321.
  • the receiver 311 comprises a connection unit adapted to establish a connection with at least one cooperating receiver 312 over a respective
  • the receiver 31 1 comprises a computing unit adapted to compute, from the estimated channel state information and from the received channel state information, a precoder for the downlink
  • the receiver 311 comprises a feedback unit adapted to transmit to the transmitter 301 information derived from the computed precoder.
  • the cooperating receiver 312 is not served by the transmitter 301.
  • the channel 322 that is defined between the transmitter 301 and the cooperating receiver 312 represents an interfering channel for the reception at the cooperating receiver 312.
  • the receiver 311 is adapted to exploit the knowledge about the interfering channel
  • the receiver 311 comprises an estimation unit adapted to estimate channel state information with respect to a channel 324 from a further transmitter 302 to the receiver 311.
  • the receiver 31 1 comprises a connection unit adapted to establish a connection with a cooperating receiver 312 over the respective communication link 331, 332.
  • the receiver 31 1 is not served by the transmitter 302, and the cooperating receiver 312 is served by the transmitter 302 over a respective downlink 323.
  • the connection unit is adapted to transmit to the cooperating receiver 312 the estimated channel state information.
  • the cooperating receiver 312 is served by the further transmitter 302 over the downlink 323.
  • the channel 324 that is defined between the further transmitter 301 and the receiver 312 represents an interfering channel for the reception at the receiver 312.
  • the receiver 311 is adapted to estimate the channel state information of this interfering channel 324, and to transmit the estimated channel state information to the cooperating receiver 312.
  • the cooperating receiver 312 it is then possible for the cooperating receiver 312 to exploit the knowledge about the interfering channel 324 in order to feed back to the further transmitter 302 a precoder that mitigates negative effects for the receiver 311, i.e. that reduces inter-cell interferences at the receiver 31 1.
  • the transmitters 301, 302 are multi antenna transmitters and each transmitter particularly comprises three antennas 301a, 301b, 301c and 302a, 302b, 302c respectively.
  • the receivers 311, 312 of Fig. 2 respectively comprise one antenna.
  • a receiver according to the present invention may alternatively comprise more than one antenna and may consequently be a multi antenna receiver.
  • the transmitters 301, 302 of Fig. 3, and more generally the transmitters according to the present invention are for example base stations or WiFi access points.
  • the receivers 31 1, 312 of Fig. 3, and more generally the receivers according to the present invention are for example handheld devices like tablets, laptops or smartphones.
  • Fig. 3 /3 ⁇ 4; represents the channel matrix of the unidirectional communication link 331 from the receiver 311 to the cooperating receiver 312, while h 1,2 represents the channel matrix of the unidirectional communication link 332 from the cooperating receiver 312 to the receiver 311.
  • the receiver 311 and the cooperating receiver 312 are equipped with some capabilities of exchanging data among them.
  • the exchange of data may be carried out wirelessly at least when both the receiver 311 and the cooperating receiver 312 are in proximity. This may be accomplished, for instance, by WiFi Direct, Bluetooth or any device-to-device (D2D) radio access technology (RAT).
  • RAT device-to-device
  • Fig. 4 shows a wireless communication network 400 according to a further embodiment of the present 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 being served by a transmitter 401 over a downlink 421, which corresponds to the receiver 311 being served by the transmitter 301 over the downlink 321.
  • the wireless communication network 400 comprises a cooperating receiver 412 being served by a further transmitter 402 over a downlink 423, which corresponds to the cooperating receiver 312 being served by the further transmitter 302 over the further downlink 323.
  • the wireless communication network 400 comprises a channel 422 from the transmitter 401 to the cooperating receiver 412 and a channel 424 from the further transmitter 402 to the receiver 411, which respectively correspond to the channel 322 from the transmitter 301 to the cooperating receiver 312 and to the channel 324 from the further transmitter 302 to the receiver 311.
  • the difference between the embodiments of Fig. 3 and Fig. 4 consists in the data exchange between the receiver 411 and the cooperating receiver 412.
  • the data exchange of channel state information is performed via a further network 430.
  • a data exchange from the receiver 411 to the cooperating receiver 412 is carried out by means of a unidirectional communication link 432 to the further network 430, by means of the further network 430 and by means of a unidirectional communication link 433 from the further network 430 to the cooperating receiver 412.
  • a data exchange from the cooperating receiver 412 to the receiver 411 is carried out by means of a unidirectional communication link 434 to the further network 430, by means of the further network 430 and by means of a unidirectional communication link 431 from the further network 430 to the receiver 41 1.
  • the further network 430 may be for example based on cloud computing, or on a relay or repeater.
  • Fig. 5 shows a method 500 according to an embodiment of the present invention for serving the receiver 31 1 by the multi antenna transmitter 301 over the downlink 321 and reducing interference caused at the cooperating receiver 312 by the channel 322 from the transmitter 301 to the cooperating receiver 312.
  • the receiver 311 and the cooperating receiver 312 establish 501 a connection over a communication link 331, 332.
  • the receiver 31 1 estimates 502 channel state information with respect to the downlink 321.
  • the cooperating receiver 312 estimates 503 channel state information with respect to the channel 322 from the transmitter 301 to the cooperating receiver 312.
  • the receiver 31 1 receives 504 from the cooperating receiver 312, over the communication link 331, 332, the channel state information with respect to the channel 322 estimated by the cooperating receiver 312.
  • the receiver 311 computes 505, from the estimated channel state information with respect to the downlink 321 and from the received channel state information with respect to the channel 322, a precoder for the downlink 321 between the transmitter 301 and the receiver 31 1.
  • the receiver 311 transmits 506 to the transmitter 301 information derived from the computed precoder.
  • the receiver 31 1 is adapted to exploit the knowledge about the interfering channel 322 in order to feed back to the transmitter 301 a precoder that mitigates negative effects for the cooperating receiver 312, i.e. that reduces inter-cell interferences at the cooperating receiver 312.
  • the receiver 311 estimates channel state information with respect to the channel 324 from the further transmitter 302 to the receiver 311.
  • the cooperating receiver 312 estimates channel state information with respect to the downlink 323 from the further transmitter 302 to the cooperating receiver 312.
  • the cooperating receiver 312 receives from the receiver 31 1, over the communication link 331, 332, the channel state information with respect to the channel 324 estimated by the receiver 311.
  • the cooperating receiver 312 computes, from the estimated channel state information with respect to the downlink 323 and from the received channel state information with respect to the channel 324, a precoder for the downlink 323 between the further transmitter 302 and the cooperating receiver 312.
  • the cooperating receiver 312 transmits to the further transmitter 302 information derived from the computed precoder.
  • Fig. 6 shows a method 600 according to a further embodiment of the present invention.
  • the receiver 31 1 being served by the multi antenna transmitter 301 over the downlink 321, the method is adapted to reduce interference caused at the cooperating receiver 312 by the channel 322 from the transmitter 301 to the cooperating receiver 312.
  • the method 600 may be implemented by a respective baseband functional block of the receiver 31 1 and of the cooperating receiver 312.
  • the method 600 comprises a step of discovery and answer to discovery 601.
  • the purpose of this step is to establish a connection among receivers in range that implement the invention, i.e. for example among the receiver 311 and a plurality of other receivers.
  • This connection may also be referred to as a handshake.
  • the receiver 31 1 broadcasts, through an appropriate radio access technology (RAT) like for example WiFi Direct or Bluetooth, a request for cooperation.
  • RAT radio access technology
  • the baseband module of the plurality of other receivers answers.
  • a connection is then established between the receiver 311 and each of the plurality of other receivers.
  • Said plurality of other receivers is a set of potential cooperating receivers.
  • the method 600 comprises a further step of cooperating receiver selection 602.
  • the receiver 311 is adapted to select the at least one cooperating receiver 312 from the plurality of other receivers.
  • the set of cooperating receivers 312 is selected from among the potential cooperating receivers, i.e. from among the connected plurality of other receivers.
  • the selection is based on different criteria.
  • the selection criteria for selection one of the plurality of other receivers as being a cooperating receiver may be the distance between the receiver 311 and the other receivers and/or the number of antennas of the other receiver.
  • This selection phase is advantageous in that it keeps the total number of antennas of the receiver 311 and of the cooperating receivers 312 smaller than the minimum number of transmitting antennas of the transmitter 301 and further transmitters 302 serving the receiver 31 1 and cooperating receivers 312. Accordingly, the receiver 311 is adapted to select said at least one cooperating receiver 312 such that the following equation is verified: wherein each selected cooperating receiver 312 is served, via a number 3 ⁇ 4 of antennas 312a, by one or more further multi antenna transmitters 302 over a respective downlink 323, and wherein
  • - Ro is the number of the at least one antenna 311a of the receiver 31 1 used for the downlink 321 from the transmitter 301 to the receiver 311, ⁇ i is me sum > over a ll selected cooperating receivers 312, of said number 3 ⁇ 4 of antennas 312a,
  • - 0 ⁇ is a set comprising, for all said further transmitters 302 serving said selected cooperating receivers 312, the number of antennas 302a, 302b, 302c of said further transmitter
  • the method 600 comprises a further step of cooperation level bargaining and establishment 603.
  • the receiver 311 and the at least one cooperating receivers 312 selected in step 602 bargain or negotiate what kind of precoding strategy should be adopted based on the amount of information available.
  • the minimum output of this step is the precoding strategy to be adopted, like for example ZF or MRC.
  • An optional output of this step is the level of selfishness and/or the transmit SNR level.
  • the level of selfishness may be defined as a parameter defining the computed precoder as a combination of a maximum ratio combining precoder and a zero-forcing precoder.
  • the method 600 comprises a further step of information gathering 604.
  • the necessary information e.g. information regarding the interfering channels, is estimated based on the pilot/training signals sent by the interfering transmitters, i.e. sent by the transmitter 301.
  • the receiver 31 1 may estimate channel state information with respect to the downlink 321
  • the cooperating receiver 312 may estimate channel state information with respect to the interfering channel 322 from the transmitter 301 to the cooperating receiver 312.
  • the method 600 comprises a further step of information exchange 605.
  • the receiver 3 1 1 and the at least one cooperating receiver 3 12 selected in step 602 exchange the information needed for creating the feedback, and particularly the information regarding the interfering channels.
  • the receives (504) from the cooperating receiver 3 12 may transmit to the receiver
  • the 31 1 its estimation of the channel state information with respect to the interfering channel 322 from the transmitter 301 to the cooperating receiver 312. This transmission is carried out over the communication link 332.
  • the necessary information is exchanged through RAT, like for example Bluetooth or WiFi Direct, or through a further network 430 for example based on cloud computing or on a relay or repeater.
  • the method 600 comprises a further step of precoder computation 606.
  • the precoder computation 606 step may be designed according to several criteria. In one embodiment of the invention, the criteria could be determined in order to reach a Pareto optimal solution, as described in the followings.
  • the receiver 3 1 1 labeled "r" builds a extended channel matrix H r by stacking together its own channel matrix and the channel matrices of the cooperating receivers
  • H r [hnr, hn,i, ⁇ , ⁇ , ⁇ ] represent the channel matrices of the i cooperating receivers 3 12 labeled from “1 " to "f .
  • the dimension of H r is M n x K, wherein:
  • - K is the total amount of antennas of the receiver 31 1 and of the cooperating receivers 312devices, wherein preferably K— R 0 5 and
  • - M n is the number of antennas of transmitter n.
  • a ZF precoder is evaluated according to the following equation:
  • M _ Nr is a matrix of dimension (M— N r ) x N r composed only of zeros.
  • an MRC precoder is evaluated according to the following equation:
  • the wished precoder is computed according to the following equation:
  • the method 600 comprises a further step of feedback signal transmission 607.
  • the baseband block of the receiver 3 1 1 finally creates a feedback signal and transmits to the transmitter 301 serving the receiver 311.
  • the receiver 31 1 computes and transmits to the transmitter as feedback the vector: rn ( )
  • Fig. 7 shows an application scenario according to an embodiment of the present invention.
  • the application scenario is based on a wireless communication network 700.
  • the wireless communication network 700 corresponds to the wireless communication network 300 of Fig. 3.
  • the wireless communication network 700 comprises a receiver 71 1 being served by a transmitter 701 over a downlink 721, which corresponds to the receiver 31 1 being served by the transmitter 301 over the downlink 321.
  • the wireless communication network 700 comprises a cooperating receiver 712 being served by a further transmitter 702 over a downlink 723, which corresponds to the cooperating receiver 312 being served by the further transmitter 302 over the further downlink 323. Further on, the wireless communication network 700 comprises a channel 722 from the transmitter 701 to the cooperating receiver 712 and a channel 724 from the further transmitter 702 to the receiver 711, which respectively correspond to the channel 322 from the transmitter 301 to the cooperating receiver 312 and to the channel 324 from the further transmitter 302 to the receiver 31 1.
  • the transmitter 701 and the further transmitter 702 may be small-cells, or alternatively pico- or femto-cells, belonging to different network operators. Alternatively, the transmitter 701 and the further transmitter 702 may be built by different vendors. Preferably the transmitter 701 and the further transmitter 702 may be equipped with multiple antennas.
  • the transmitter 701 and the further transmitter 702 may be WiFi access points either belonging to different operators, or built by different vendors, and preferably equipped with multiple antennas.
  • the wireless communication network 700 may relate to device-to-device communiations, in which preferably at least the transmitter 301 and the further transmitter 702 are equipped with multiple antennas.
  • Fig. 8 shows an application scenario according to a further embodiment of the present invention.
  • the application scenario is based on a wireless communication network 800 that may be similar to that of Fig. 3.
  • the wireless communication network 800 comprises a receiver 811 being served by a transmitter 801 over a downlink 821, which corresponds to the receiver 311 being served by the transmitter 301 over the downlink 321.
  • the wireless communication network 800 comprises a cooperating receiver 812 being served by a further transmitter 802 over a downlink 823, which corresponds to the cooperating receiver 312 being served by the further transmitter 302 over the further downlink 323. Further on, the wireless communication network 800 comprises a channel 822 from the transmitter 801 to the cooperating receiver 812 and a channel 824 from the further transmitter 802 to the receiver 811, which respectively correspond to the channel 322 from the transmitter 301 to the cooperating receiver 312 and to the channel 324 from the further transmitter 302 to the receiver 311.
  • the wireless communication network 800 is in the form of a cellular communication network.
  • the transmitter 801 is in the form of a base station defining a cell 803 of the cellular communication network, while similarly the further transmitter 802 is also in the form of a base station of the cellular communication network.
  • the receiver 811 and the cooperating receiver 812 are close to the edge of the cells and suffer from interference respectively from the further transmitter 802 and from the transmitter 801.
  • Fig. 9 shows performance gain according to an embodiment of the present invention.
  • a network according to the embodiment of Fig. 3 is considered, i.e. a network comprising a transmitter and a further transmitter each equipped with three antennas as well as a receiver and a cooperating receiver each equipped with one antenna.
  • the performance is measured in terms of SI R. Particularly, the performance is also measured for different values of the level of selfishness a in case of Pareto optimal feedback creation procedure.
  • the performance gain brought by the proposed idea over the state-of-the-art approach is shown is Fig. 9.
  • the performance of the state of the art solution involving a single-cell precoder is labeled as MRT and shows a low spectral efficiency.
  • the receiver driven precoding according to the present invention labeled as RDP, shows a better spectral efficiency.
  • the performance for different RDPs shows a significant SNR gap with respect to the state of the art.
  • the present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un récepteur (311) devant être desservi par un émetteur à plusieurs antennes (301) sur une liaison descendante (321). Le récepteur comprend : au moins une antenne (311a) adaptée pour recevoir des données de l'émetteur sur la liaison descendante ; une unité d'estimation adaptée pour estimer des informations d'état de canal par rapport à la liaison descendante (321) ; une unité de connexion adaptée pour établir une connexion avec au moins un récepteur coopérant (312) sur une liaison de communication respective (331,332) ; et recevoir, de chaque récepteur coopérant (312), des informations d'état de canal d'un canal (322) entre l'émetteur (301) et ledit récepteur coopérant (312) ; une unité de calcul adaptée pour calculer, d'après les informations d'état de canal estimées et les informations d'état de canal reçues, un précodeur pour la liaison descendante (321) entre l'émetteur (301) et le récepteur (311) ; et une unité de rétroaction adaptée pour transmettre à l'émetteur (301) des informations dérivées du précodeur calculé.
PCT/EP2015/069113 2015-08-20 2015-08-20 Appareil et procédé de précodage entraîné par récepteur WO2017028922A1 (fr)

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