CN107852198B - Apparatus and method for receiver driven precoding - Google Patents
Apparatus and method for receiver driven precoding Download PDFInfo
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- CN107852198B CN107852198B CN201580081554.1A CN201580081554A CN107852198B CN 107852198 B CN107852198 B CN 107852198B CN 201580081554 A CN201580081554 A CN 201580081554A CN 107852198 B CN107852198 B CN 107852198B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
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Abstract
The invention proposes a receiver (311) served by a multi-antenna transmitter (301) on a downlink (321). The receiver comprises at least one antenna (311a) adapted to receive data from the transmitter on a downlink, an estimation unit adapted to estimate channel state information on the downlink (321), a connection unit adapted to establish a connection with at least one cooperating receiver (312) on a respective communication link (331, 332) and to receive from each cooperating receiver (312) channel state information of a channel (322) between the transmitter (301) and the cooperating receiver (312), a calculation unit adapted to calculate a precoder for the downlink (321) between the transmitter (301) and the receiver (311) based on the estimated channel state information and the received channel state information, and a feedback unit adapted to transmit information derived from the calculated precoder to the transmitter (301).
Description
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 solutions are known for reducing or avoiding the interference level due to lack of cooperation. A first type of solution, which may be labeled as Resource Allocation (RA) solution, aims at designing algorithms for orthogonalizing communications by intelligently allocated resource radio blocks so 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. Such as TDMA and CSMA follow this approach. The disadvantage of these methods is their inefficiency for two reasons. First, they waste radio resources in the time and/or frequency domain. Second, they require a degree of synchronization between transmitters. The second type of solution assumes the presence of a noise-free high throughput backhaul connecting the transmitter and/or 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 the existence of a noise-free high-throughput backhaul between SC or WiFi access points is unlikely.
In terms of precoding, two strategies can be distinguished. The first strategy is based on a codebook based 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 pre-computed non-optimized precoding matrices, where these matrices are known at both the transmitter and the receiver. In practice, when the receiver receives the 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, the first strategy does not take full advantage of the potential of 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 this CSI to design a particular precoder. An example of a possible precoder is maximum ratio combining (maximum ratio co)mbining, MRC) precoding, wherein,
zero-forcing (ZF) precoder, wherein
And Minimum Mean Square Error (MMSE) transmitter, wherein
Wherein WnIs the pre-coder employed by the transmitter n,
is the total CSI feedback from all receivers served by transmitter n. This strategy is effective for reducing the negative impact of intra-cell interference, but is not responsible for the negative impact 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 context, mutually interfering Base Stations (BSs) or transmitters handling full CSI, which is information about the channel to an unserviceable 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 employing a ZF precoder. More effectively, the base station may use MMSE transmit filtering to maximize the signal to interference plus noise ratio (SINR) at all receivers.
However, there is currently no existing solution for wireless communication networks, where there is neither cooperation nor coordination between transmitters. 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 and the receivers 111, 112, 113 are for example handheld devices such as tablet computers, handheld computers or smart phones.
The first receiver 111 is served by the first transmitter 101 on a first downlink 121. Similarly, the second receiver 112 is served by the second transmitter 102 on a second downlink 124, and the third receiver 113 is served by the third transmitter 103 on 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 and the first receiver 111, respectively. Similarly, 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 via the downlink 121, the channels 126, 129 received by the first receiver 111 from the other 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 cells). On the one hand, known multi-antenna transmitters have the ability to null or mitigate the negative impact of interference on network performance, but at the cost of centralization. On the other hand, interference in a decentralized wireless communication network is difficult to cope with, and even more difficult to cope with 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 invention to provide an improved wireless communication with reduced interference.
The invention is particularly intended to improve wireless communication in non-centralized networks and does not require cooperation between transmitters. The present invention aims to mitigate the interference caused at the receiver.
The above object of the present invention is achieved by the solution provided in the appended independent claims. Advantageous implementations of the invention are further defined in the respective dependent claims.
A first aspect of the invention provides a receiver served by a multi-antenna transmitter on a downlink. The receiver includes at least one antenna adapted to receive data from the transmitter on the downlink. The receiver comprises an estimation unit adapted to estimate channel state information on the downlink. The receiver comprises a connection unit adapted to establish a connection with at least one cooperating receiver over the respective communication link and to receive from each cooperating receiver channel state information of a channel between the sender and the cooperating receiver. The receiver comprises a calculation unit adapted to calculate a precoder for a downlink between the transmitter and the receiver from said estimated channel state information and said received channel state information. The receiver comprises a feedback unit adapted to send information derived from said calculated precoder to said transmitter.
Thus, the present invention can compensate for lack of cooperation between transmitters, particularly in the context of MIMO non-cooperative networks, and can reduce interference and increase SINR at the receiver. The receiver may advantageously utilize knowledge of the interfering channel from the transmitter to the cooperating receiver in order to feed information back to the transmitter to reduce inter-cell interference at the cooperating receiver.
In an implementation form of the receiver according to the first aspect, the information derived from the calculated precoder is adapted to be used by the transmitter for precoding the downlink. Thus, the interference reduction may be performed in a way that is completely invisible to the transmitter.
In another implementation form of the receiver according to the first aspect, the computed precoder is a maximal ratio combining precoder or a zero-forcing precoder, or a combination of a maximal ratio combining precoder and a zero-forcing precoder. Thereby interference can be further reduced.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to establish a connection with the at least one cooperating receiver using a radio access technology different from a radio access technology used for the downlink between the sender and the receiver. Thus, cooperation at the sender level is not necessary.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to establish an ad hoc network with the at least one cooperating receiver.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to establish a Wi-Fi direct, bluetooth or device-to-device connection with the at least one cooperating receiver.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to broadcast a cooperation request, to receive a response to the cooperation request from the at least one cooperation receiver, and to establish the connection with the at least one cooperation receiver based on the response.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to establish a connection with at least one cooperating receiver over the respective communication link in that the connection unit is adapted to establish a connection with a plurality of other receivers and to select the at least one cooperating receiver from the plurality of other receivers.
In another implementation form of the receiver according to the first aspect, the connection unit is adapted to select the at least one cooperating receiver such that
Wherein on each downlink one or more other multi-antenna transmitters are via RiEach selected cooperative receiver is served by a single antenna,
wherein
-R0Is the number of the at least one antenna of the receiver for the downlink from the transmitter to the receiver,
-
is said number R of antennas on all selected cooperative receiversjThe sum of the values,
-T0is the number of antennas of the transmitter for the downlink from the transmitter to the receiver, an
-{TiI ≠ 0 is a set including the number of antennas of the other transmitters for all of the other transmitters serving the selected cooperative receiver.
In another implementation form of the receiver according to the first aspect, the receiver is adapted to negotiate a policy for calculating the precoder with the at least one cooperating receiver.
In another implementation form of the receiver according to the first aspect, the computed precoder is a combination of a maximum ratio combining precoder and a zero-forcing precoder. The receiver is adapted to negotiate a policy with the at least one cooperating receiver for calculating the precoder to define a level of selfishness defining the combination of the maximum ratio combining precoder and the zero forcing precoder.
In another implementation form of the receiver according to the first aspect, 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.
In another implementation form of the receiver according to the first aspect, the calculation unit is adapted to construct the extended channel matrix by stacking together the 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 calculate the precoder based on the extended channel matrix.
In another implementation form of the receiver according to the first aspect, the calculation unit is adapted to generate
According to the equation pMRC＝hn，rA maximum ratio combining precoder corresponding to the channel matrix of the downlink,
according to the equation
The zero-forcing precoder of (1),
wherein
Is dimension NrA unit matrix of, and
is a dimension consisting of only zeros of (M-N)r)×NrAnd is adapted to calculate the precoder according to the following equation:
P＝αρMRC+(1-α)ρZF
where α is the level of selfishness between 0 and 1.
In another implementation form of the receiver according to the first aspect, the feedback unit is adapted to calculate an inverse of the precoder and to send the inverse to the transmitter as information derived from the calculated precoder.
In another implementation form of the receiver according to the first aspect, the receiver comprises an estimating unit adapted to estimate channel state information on a channel from the other transmitter to said receiver, the receiver comprising a connecting unit adapted to establish a connection with a cooperating receiver over the respective communication link. The receiver is not served by the other transmitters, and the cooperative receiver is served by the other transmitters on respective downlinks. The receiver is adapted to send the estimated channel state information to the cooperating receiver.
Thus, the cooperating receiver may utilize knowledge of the interfering channel from the other transmitter to the receiver to feed back precoder information to the other transmitter that may reduce inter-cell interference at the receiver.
A second aspect of the invention provides a receiver comprising: an estimating unit adapted to estimate channel state information on a channel from a sender to the receiver, the receiver comprising a connecting unit adapted to establish a connection with a cooperating receiver over respective communication links. The receiver is not served by the sender, and the cooperative receiver is served by the sender on each downlink. The receiver is adapted to send the estimated channel state information to the cooperating receiver.
Thus, the cooperating receiver may utilize knowledge of the interfering channel from the transmitter to the receiver to feed back precoder information to the transmitter that may reduce inter-cell interference at the receiver.
In an implementation form of the receiver according to the first or second aspect, 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 invention provides a communication network comprising a plurality of receivers and a multi-antenna transmitter according to the first or second aspect.
A fourth aspect of the present invention provides a method of serving a receiver on a downlink by a multi-antenna transmitter and reducing interference caused at a cooperative receiver through a channel from the transmitter to the cooperative receiver. The receiver and the cooperating receiver establish a connection over a communication link. The receiver estimates channel state information regarding the downlink. The cooperative receiver estimates channel state information regarding the channel from the sender to the cooperative receiver. The receiver receives the channel state information from the cooperating receiver on the communication link regarding the channel estimated by the cooperating receiver. The receiver calculates a precoder for the downlink between the transmitter and the receiver according to the estimated channel state information for the downlink and the received channel state information for the channel. The receiver sends information derived from the calculated precoder to the transmitter. Thus, the method proposes a receiver cooperation protocol that can perform cooperation on the sender to achieve the target performance.
Other features or implementations of the method according to the fourth aspect of the invention may perform the function of the receiver according to the previous aspect of the invention and its different implementations.
A fifth aspect of the invention provides a computer program having a program code for performing the method according to the fourth aspect of the invention, when the computer program runs on a computing device.
The present invention is directed to a system in which a set of MIMO transmitters communicate with their intended receivers without requiring any necessary cooperation or coordination between the transmitters. Receivers implementing the invention establish a communication channel in which some side information about the CSI is exchanged, allowing each receiver to establish feedback that, upon receipt by the respective serving transmitter, may affect the precoder implemented in the serving transmitter. The precoder is adapted to increase the achievable rates of all cooperating receiving devices.
This happens in a completely invisible or transparent way for the transmitter, making the invention particularly attractive in many scenarios. For example, in one embodiment thereof, the present invention may be employed in a multi-vendor/operator system in which 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 employed 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, in particular in networks that are not centralized and do not require cooperation between transmitters. The invention proposes in particular to transmit the load of an efficient method of calculating the avoidance of interference, i.e. to transmit the load of calculating the effective precoder from the transmitter to the receiver. In other words, the present invention proposes a receiver-centric decision making process.
The present invention has the advantage of increasing overall network throughput while being transparent to the transmitter, without requiring expensive network/transceiver modifications to achieve the same goal. In other words, by the present invention, each transmitter contributes to the improvement of the overall performance while employing a conventional precoding scheme without requiring explicit or implicit cooperation or coordination between the transmitters.
The idea of the invention is to utilize knowledge about the interfering channel of the cooperating receiver in order to feed back a precoder that mitigates the negative effects of the cooperating receiver. This mitigation is advantageous because it occurs in a completely invisible manner for the transmitter. Since all receivers of the network may apply the inventive strategy, all receivers cooperating by the invention may experience significant performance gains, thereby increasing overall network throughput. The present invention creates a receiver-centric scenario in which the network limitations of the prior art are overcome without requiring further cost to the operator or manufacturer.
It has to 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 performed by the various entities described in the present application, as well as the functions described as being performed by the various entities, are intended to mean that the various 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 the entity implementing the specific step or function, it is clear to a person skilled in the art that these methods and functions can be implemented in respective software or hardware elements or any kind of combination thereof.
Drawings
The above aspects and implementations of the invention will be explained in the following description of specific embodiments with reference to the drawings, in which
Figure 1 shows a non-centralized wireless communication network according to the prior art,
figure 2 shows a wireless communication network according to an embodiment of the invention,
figure 3 shows a wireless communication network according to another embodiment of the invention,
figure 4 shows a wireless communication network according to another embodiment of the invention,
figure 5 shows a method according to an embodiment of the invention,
figure 6 shows a method according to another embodiment of the invention,
figure 7 shows an application scenario according to an embodiment of the invention,
FIG. 8 shows an application scenario according to another embodiment of the present invention, an
Fig. 9 illustrates performance gains 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 a specific embodiment of a general wireless communication network according to the present invention and consists of N autonomous transmitters, indexed by N e { 1...., N }, the transmitter N being connected to KnA receiver. Here, the characteristic autonomy refers to the fact that the transmitters do not exchange or, in particular, cannot exchange any information between them, and therefore it appears that no other transmitter is present in the same radio resource block.
Embodiments of such networks are shown in fig. 2 and include WiFi networks and SC networks, among others. Each transmitter in the network is equipped with Mn> 1 antenna and the receiver is equipped with NrMore than or equal to 1 antenna. MIMO downlink channel routing matrix between transmitter n and receiver r
And (4) showing. As for frequency-division duplex (FDD) communications, it is assumed that the matrix is estimated at each receiver by a downlink pilot/training sequence
By stacking the channel matrices of all intended receivers of the transmitter n, i.e. for all receivers served by the transmitter n, a channel matrix according to the following equation (1) is obtained:
the signal received by the receiver r can therefore be expressed according to the following equation (2):
wherein
-xnA vector of transmit symbols representing a transmitter n, an
-wrRepresenting the additive noise vector.
In equation (2), three terms can be identified:
-a first term representing a useful signal
-a second term representing intra-cell interference
And
-a third term representing inter-cell interference
In this case, the downlink operates in the same frequency band. Therefore, mutual interference occurs, and the performance of communication is degraded. MIMO techniques can be utilized to mitigate intra-cell interference even if the transmitters are not cooperating. In particular, assume that each transmitter employs its selected precoder based on CSI feedback from its receiver. That is, each transmitter implements the following general precoding strategy:
wherein
-WnIs the precoder used by the transmitter n,
-fnis some kind of reversible precoding function, e.g. any standard linear precoding strategy such as reversible Maximum Ratio Combining (MRC), ZF or MMSE transmission, and
-
is the CSI feedback of all receivers connected to the transmitter n, i.e.
Is the overall CSI feedback for all receivers served by 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, even if the second set of receivers 214, 215 is not served by the first transmitter 201, there is a respective channel 224, 225 between the first transmitter 201 and the second set of receivers 214, 215.
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 alternatively comprise more than one antenna 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 on a downlink 321 according to an embodiment of the present invention. The receiver 311 comprises at least one antenna 311a adapted to receive data from the transmitter 301 on a downlink 321. The receiver 311 comprises an estimation unit adapted to estimate channel state information on the downlink 321. The receiver 311 comprises a connection unit adapted to establish a connection with at least one cooperative receiver 321 over respective communication links 331, 332 and to receive channel state information of a channel 322 between said sender 301 and said cooperative receiver 312 from each cooperative receiver 312. The receiver 311 comprises a calculation unit adapted to calculate a precoder for the downlink 321 between the transmitter 301 and the receiver 311 from said estimated channel state information and said received channel state information. The receiver 311 comprises a feedback unit adapted to send information derived from said calculated precoder to said transmitter 301.
Accordingly, when the receiver 311 is served by the transmitter 301 on the downlink 321, the cooperative receiver 312 is not served by the transmitter 301. The channel 322 defined between the transmitter 301 and the cooperating receiver 312 represents an interference channel, which is used for reception at the cooperating receiver 312.
Thus, the receiver 311 is adapted to utilize knowledge about the interfering channel 322 to feed back to the transmitter 301a precoder that mitigates the negative effects of the cooperating receiver 312, i.e. reduces inter-cell interference at the cooperating receiver 312.
According to an embodiment of the invention, the receiver 311 comprises an estimating unit adapted to estimate channel state information on a channel 324 from the other transmitter 302 to said receiver 311, said receiver 311 comprising a connection unit adapted to establish a connection with a cooperating receiver 321 over 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 on each downlink 323. The connection unit is adapted to send the estimated channel state information to the cooperative receiver 312.
Accordingly, the cooperative receiver 312, but not the receiver 311, is served by the other transmitter 302 on 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 cooperating receiver 312 may utilize knowledge of the interfering channel 324 to feed back a precoder to the other transmitter 302 that mitigates the negative effects of the receiver 311, i.e., reduces inter-cell interference at the receiver 311.
Similar to the embodiment shown in fig. 2, the transmitters 301, 302 are multi-antenna transmitters and each transmitter comprises in particular 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 alternatively comprise more than one antenna and may thus be a multi-antenna receiver. The transmitters 301, 302 of fig. 3 and more generally the transmitters according to the invention are for example base stations or WiFi access points. The receiver 311, 312 of fig. 3, more generally a receiver according to the present invention, is for example a handheld device, such as a tablet, a laptop or a smartphone.
In FIG. 3, h2，1A channel matrix representing a unidirectional communication link 331 from the receiver 311 to the cooperating receiver 312, and h1，2A channel matrix representing a unidirectional communication link 332 from the cooperative receiver 312 to the receiver 311. The receiver 311 and the cooperative receiver 312 are equipped with the capability of exchanging data therebetween. The exchange of data may occur wirelessly, at least when the receiver 311 and the cooperating receiver 312 are in proximity. This may be achieved, 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 on a downlink 421, which corresponds to the receiver 311 served by the transmitter 301 on a downlink 321. The wireless communication network 400 includes a cooperative receiver 412 served by other transmitters 402 on a downlink 423 that corresponds to the cooperative receiver 312 served by other transmitters 302 on other downlinks 323. Further, the wireless communication network 400 comprises a channel 422 from the transmitter 401 to the cooperative receiver 412 and a channel 424 from the other transmitter 402 to the receiver 411, which correspond to the channel 322 from the transmitter 301 to the cooperative receiver 312 and the channel 324 from the other transmitter 302 to the receiver 311, respectively.
The difference between the embodiments of fig. 3 and fig. 4 is the data exchange between the receiver 411 and the cooperative receiver 412. Data exchange of channel state information is performed via the other network 430. The exchange of data from the receiver 411 to the cooperative receiver 412 is performed over a unidirectional communication link 432 to the other network 430, and a unidirectional communication link 433 from the other network 430 to the cooperative receiver 412. The exchange of data from the cooperative receiver 412 to the receiver 411 is performed over a unidirectional communication link 434 to the other network 430, and a unidirectional communication link 431 from the other network 430 to the cooperative receiver 411. Other networks 430 may be based on cloud computing, or relays or repeaters, for example.
Fig. 5 shows a method 500 for serving a receiver 311 by a multi-antenna transmitter 301 on a downlink 321 and reducing interference caused by a channel 322 from the transmitter 301 to a cooperating receiver 312 at the cooperating receiver 312, according to an embodiment of the invention.
According to the method, the receiver 311 and the cooperating receiver 312 establish 501 a connection over the communication links 331, 332. The receiver 311 estimates 502 channel state information for the downlink 321. The cooperative receiver 312 estimates channel state information about the channel 322 from the sender 301 to the cooperative receiver 312. The receiver 311 receives 504 the channel state information regarding the channel 322 estimated by the cooperative receiver 312 from the cooperative receiver 312 over the communication links 331, 332. The receiver 311 calculates 505 a precoder for the downlink 321 between the transmitter 301 and the receiver 311 from the estimated channel state information for the downlink 321 and the received channel state information for the channel 322. The receiver 311 sends 506 information derived from the calculated precoder to the transmitter 301.
Advantageously, the receiver 311 is adapted to utilize knowledge about the interfering channel 322 to feed back a precoder to the transmitter 301, which reduces the negative effects of the cooperative receiver 312, i.e. reduces inter-cell interference at the cooperative receiver 312.
Advantageously, inter-cell interference at the receiver 311 caused by the interfering channel 324 may also be reduced. Thus, the receiver 311 estimates channel state information regarding the channel 324 from the other transmitter 302 to the receiver 311. The cooperative receiver 312 estimates channel state information about the downlink 323 from the other transmitters 302 to the cooperative receiver 312. The cooperative receiver 312 receives the channel state information for the channel 324 estimated by the receiver 311 from the receiver 311 over the communication links 331, 332. The cooperative receiver 312 calculates a precoder for the downlink 323 between the other transmitter 302 and the cooperative receiver 312 based on the estimated channel state information for the downlink 323 and the received channel state information relative to the channel 324. The cooperative receiver 312 transmits information derived from the calculated precoder to the other transmitter 302.
Fig. 6 shows a method 600 according to another embodiment of the invention. The receiver 311 is served by a multi-antenna transmitter 301 on a downlink 321, the method being adapted to reduce interference caused at the cooperative receiver 312 by a channel 322 from the transmitter 301 to the cooperative receiver 312. The method 600 may be implemented by respective baseband functional blocks of the receiver 311 and the cooperating receiver 312.
The method 600 includes a step 601 of discovering and answering the findings. The purpose of this step is to establish a connection between receivers within the scope of implementing the invention, i.e. for example between the receiver 311 and a plurality of other receivers. This connection may also be referred to as a handshake. For establishing the connection, the receiver 311 broadcasts a request for cooperation over a suitable Radio Access Technology (RAT), such as WiFi direct or bluetooth. The baseband modules of a plurality of other receivers acknowledge. A connection is then established between the receiver 311 and each of a plurality of other receivers. The plurality of other receivers is a set of potential cooperating receivers.
The method 600 further comprises a step 602 of collaborative receiver selection. After the receiver 311 has established a connection with a plurality of other receivers, the receiver 311 is adapted to select at least one cooperating receiver 312 from the plurality of other receivers. The set of cooperating receivers 312 is selected from the potential cooperating receivers, i.e., from a plurality of other receivers connected.
The selection is based on different criteria. In one embodiment of the invention, the selection criterion for selecting one of the other receivers as the cooperating receiver may be the distance between the receiver 311 and the other receivers and/or the number of antennas of the other receivers.
The advantage of this selection phase is that it makes the total number of antennas of the receiver 311 and the cooperative receiver 312 smaller than the minimum number of transmit antennas of the transmitter 301 and the other transmitters 302 serving the receiver 311 and the cooperative receiver 312. Thus, the receiver 311 is adapted to select the at least one cooperative receiver 312 such that the following equation is verified:
wherein on each downlink 323 one or more other multi-antenna transmitters 302 via RiAn antenna 312a serves each selected cooperative receiver 312, an
Wherein
-R0Is the number of the at least one antenna 311a of the receiver 311, which receiver 311 is used for the downlink 321 from the transmitter 301 to the receiver 311,
-
is the sum of said number Rj of antennas 312a over all selected cooperative receivers 312,
-T0is the number of antennas 301a, 301b, 301c of the transmitter 301 for the downlink 321 from the transmitter 301 to the receiver 311, and
-{Tii ≠ 0 is the set comprising the number of antennas 302a, 302b, 302c of the other transmitters 302 for all the other transmitters 302 serving the selected cooperative receiver 312.
In the embodiment of FIG. 3, R01, because the receiver 311 has one antenna 311a,
since the only cooperating receiver 312 has one antenna 312a, T 03 because the transmitter 301 serving the receiver 311 has three antennas 301a, 301b, 301c and TiI ≠ 0 ≠ 3, since it serves the cooperative receiver 312The other transmitter 302 has three antennas 302a, 302b, 302 c. For the embodiment of FIG. 3, equation (4) is verified because 1+1 ≦ min (3, 3).
This cooperative receiver selection 602 may also be used to exclude other receivers with very high mobility, as the receiver 311 and other receivers with very high mobility may not cooperate well. The minimum output of this step is a group comprising receiver 311 and cooperative receiver 312, where the total number of antennas K of the cooperative device must be less than the minimum number of antennas of the involved transmitters.
The method 600 comprises a further collaboration level bargaining and establishing step 603. The receiver 311 selected in step 602 and the at least one cooperating receiver 312 negotiate or negotiate what kind of precoding strategy should be employed based on the amount of information available. The minimum output of this step is the precoding strategy to be employed, e.g. ZF or MRC. Optional outputs of this step are the selfishness level and/or the transmit SNR level. The level of selfishness can be defined as a parameter α that defines the computed precoder as a combination of a maximum ratio combining precoder and a zero-forcing precoder.
The method 600 also comprises a further information gathering step 604. The necessary information, e.g. information about 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 on the downlink 321, and the cooperative receiver 312 may estimate channel state information on the interfering channel 322 from the transmitter 301 to the cooperative receiver 312.
The method 600 also comprises a further information exchange step 605. The receiver 311 selected in step 602 and the at least one cooperative receiver 312 exchange information required for creating feedback, in particular information about interfering channels. In particular, the reception (504) from the cooperative receiver 312 may send its estimate of the channel state information about the interfering channel 322 from the transmitter 301 to the cooperative receiver 312 to the receiver 311. The transmission is over communication link 332. In one embodiment, the necessary information is exchanged over a RAT (e.g., bluetooth or WiFi direct) or over other networks 430, e.g., based on cloud computing or relays or repeaters.
The method 600 includes a further precoder calculation step 606.
The precoder calculation step 606 may be designed according to several criteria. In one embodiment of the invention, criteria may be determined to arrive at a pareto optimal solution as described below.
In a first sub-step, the receiver 311, labeled "r", stacks its own channel matrix and the channel matrix of the cooperative receiver 312 together to form an extended channel matrix according to the following equation
Wherein
-
A channel matrix representing the receiver 311, an
-
Representing the channel matrix of the i cooperating receivers 312 labeled from "1" to "i".
k is the total number of antennas of the receiver 311 and cooperating receiver 312 devices, wherein preferably
And
-Mnis the number of antennas of the transmitter n.
Notably, the necessity is always satisfied in the precoder computation 606 stepRequirement Mn≤K。
In a second sub-step, the ZF precoder is evaluated according to the following equation:
wherein
-
Is dimension NrA unit matrix of, and
-
is a dimension consisting of only zeros of (M-N)r)×NrOf the matrix of (a).
In a third sub-step, the MRC precoder is evaluated according to the following equation:
ρMRC＝hn，r. (7)
in a fourth substep, the desired precoder is calculated according to the following equation:
P＝αρMRC+(1-α)ρZF (8)
where α is the level of selfishness.
The value α ═ 1 will basically apply MRC precoding to the transmitter 301 and may be referred to as selfish selection, while the value α ═ 0 will apply ZF precoding and may be referred to as lyhis selection.
The method 600 further comprises a further feedback signal transmission step 607. In this step, the baseband block of the receiver 311 finally creates a feedback signal and transmits to the transmitter 301 serving the receiver 311. Based on the precoder P calculated in step 606, the receiver 311 calculates and sends this vector as feedback to the transmitter:
f-1(P). (9)
it is assumed that the precoding function f is invertible. In this regard, it is noted that standard and generalized precoding functions such as MRC, ZF, and MMSE are reversible. In particular, MMSE is a widely used near-optimal linear solution.
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 711 served by the transmitter 701 on a downlink 721 corresponding to the receiver 311 served by the transmitter 301 on a downlink 321. The wireless communication network 700 includes a cooperative receiver 712 served by the other transmitter 702 on a downlink 723, which corresponds to the cooperative receiver 312 served by the other transmitter 302 on the other downlink 323. Further, the wireless communication network 700 comprises a channel 722 from the transmitter 701 to the cooperative receiver 712 and a channel 724 from the other transmitter 702 to the receiver 711, which correspond to the channel 322 from the transmitter 301 to the cooperative receiver 312 and the channel 324 from the other transmitter 302 to the receiver 311, respectively.
The transmitter 701 and the other transmitters 702 may be small cells belonging to different network operators or alternative pico cells or femto cells. Alternatively, the transmitter 701 and the other transmitter 702 may be constructed by different vendors. Preferably, the transmitter 701 and the other transmitter 702 may be equipped with multiple antennas.
The transmitter 701 and the other transmitters 702 may be WiFi access points belonging to different operators or built by different vendors and are preferably equipped with multiple antennas.
The wireless communication network 700 may involve device-to-device communication, wherein preferably at least the transmitter 301 and the other transmitters 702 are equipped with multiple antennas.
Fig. 8 shows an application scenario according to another embodiment of the present invention. The application scenario is based on a wireless communication network 800, which may be similar to the wireless communication network in fig. 3. The wireless communication network 800 comprises a receiver 811 served by a transmitter 801 on a downlink 821 corresponding to the receiver 311 served by the transmitter 301 on a downlink 321. The wireless communication network 800 includes a cooperative receiver 812 served by other transmitters 802 on the downlink 823 that corresponds to the cooperative receiver 312 served by other transmitters 302 on the other downlink 323. Further, the wireless communication network 800 comprises a channel 822 from the transmitter 801 to the cooperative receiver 812 and a channel 824 from the other transmitters 802 to the receiver 811, which correspond to the channel 322 from the transmitter 301 to the cooperative receiver 312 and the channel 324 from the other transmitters 302 to the receiver 311, respectively.
In fig. 8, an example of macro cell communication is shown. 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 a cellular communication network, while similarly the other transmitters 802 are also in the form of base stations of a cellular communication network. The receiver 811 and the cooperative receiver 812 are near the edge of the cell and experience interference from the other transmitter 802 and the transmitter 801, respectively.
Fig. 9 illustrates performance gains according to an embodiment of the invention.
For evaluating the performance, a network according to the embodiment of fig. 3 is considered, i.e. a network comprising a transmitter and other transmitters, each equipped with three antennas, and a receiver and a cooperating receiver, each equipped with one antenna. Performance is measured in SINR. In particular, in the case of the pareto optimal feedback creation procedure, values of different selfishness levels α are also measured.
The performance gain of the proposed idea over the prior art approach is shown in fig. 9. In particular, the performance of prior art schemes involving single cell precoders is labeled MRT and shows low spectral efficiency. The receiver-driven precoding according to the invention, labeled RDP, shows better spectral efficiency.
The performance of different RDPs shows a significant SNR gap with respect to the prior art. RDP as a regularized inverse precoder outperforms other less complex methods at the cost of higher computational complexity. It can be noted that making the value α equal to 0, i.e. always applying the ZF precoder to the transmitter, becomes close to optimal in case of high SNR values, i.e. when the performance of the network is strongly limited by intra-cell and inter-cell interference.
The invention has been described in connection with various embodiments and implementations as examples. However, other variations can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure and the independent claims. In the claims as well as in the description, 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 (17)
1. A receiver served by a multi-antenna transmitter on a downlink,
comprises that
-at least one antenna adapted to receive data from the transmitter on the downlink,
an estimation unit adapted to estimate channel state information on the downlink,
a connection unit adapted to establish a connection with at least one cooperating receiver over each communication link,
and receiving channel state information of a channel between the transmitter and the cooperative receiver from each of the cooperative receivers,
-a calculation unit adapted to calculate a precoder for the downlink between the transmitter and the receiver from the estimated channel state information and the received channel state information,
-a feedback unit adapted to transmit information derived from the calculated precoder to the transmitter;
wherein the calculation unit is adapted to construct an extended channel matrix by stacking together the 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 arrive at a pareto optimal solution based on the extended channel matrix to calculate the precoder;
wherein the calculation unit is adapted to generate:
according to the equation ρMRC=hn,rA maximum ratio combining precoder corresponding to the channel matrix of the downlink, where pMRCIs the maximal ratio combining precoder, hn,rIs a matrix of the channels and is,
according to the equation
Wherein the zero forcing precoder
Is dimension NrUnit matrix of [ rho ]ZFIs a zero-forcing precoder that is,
is an extended channel matrix, and
is a dimension consisting of only zeros of (M-N)r)×NrAnd a matrix of
Is adapted to calculate the precoder according to the following equation:
P＝αρMRC+(1-α)ρZF
where P is a combination of a maximum ratio combining precoder and a zero forcing precoder, α is a level of selfishness comprised between 0 and 1;
wherein the connection unit is further adapted to select the at least one cooperating receiver from a plurality of other receivers, wherein the criteria of the selection are the distances between the receiver and the plurality of other receivers and the number of antennas of the plurality of other receivers and to exclude the plurality of other receivers having a high mobility;
wherein the feedback unit is adapted to calculate an inverse of the precoder and to transmit the inverse to the transmitter as information derived from the calculated precoder.
2. The receiver in accordance with claim 1, wherein,
wherein the information derived from the calculated precoder is suitable for use by the transmitter for precoding the downlink.
3. Receiver according to one of the preceding claims,
wherein the calculated precoder is a combination of the maximum ratio combining precoder and the zero-forcing precoder.
4. The receiver according to claim 1 or 2,
wherein the connection unit is adapted to establish a connection with the at least one cooperating receiver using a radio access technology different from a radio access technology used for the downlink between the sender and the receiver.
5. The receiver according to claim 1 or 2,
wherein the connection unit is adapted to establish an ad hoc network with the at least one cooperating receiver.
6. The receiver according to claim 1 or 2,
wherein the connection unit is adapted to establish a Wi-Fi direct, Bluetooth, or device-to-device connection with the at least one cooperative receiver.
7. The receiver according to claim 1 or 2,
wherein the connection unit is adapted to broadcast a cooperation request, to receive a response to the cooperation request from the at least one cooperation receiver, and to establish the connection with the at least one cooperation receiver based on the response.
8. The receiver according to claim 1 or 2,
wherein
The connection unit is further adapted to establish a connection with a plurality of other receivers.
9. The receiver in accordance with claim 8, wherein,
wherein the connection unit is adapted to select the at least one cooperating receiver such that
Wherein on each downlink one or more other multi-antenna transmitters are via RiEach selected cooperative receiver is served by a single antenna,
wherein
-R0Is the number of the at least one antenna of the receiver for the downlink from the transmitter to the receiver,
-
is the number of antennas R on all selected cooperative receiversiThe sum of the values,
-T0is the number of antennas of the transmitter for the downlink from the transmitter to the receiver, an
-{TiI ≠ 0 is a set including the number of antennas of the other transmitters for all of the other transmitters serving the selected cooperative receiver.
10. Receiver according to one of claims 1, 2, 9,
wherein the receiver is adapted to negotiate a policy for calculating the precoder with the at least one cooperating receiver.
11. The receiver in accordance with claim 10, wherein,
wherein the precoder calculated is a combination of a maximum ratio combining precoder and a zero-forcing precoder,
and wherein the receiver is adapted to negotiate a policy for calculating the precoder with the at least one cooperating receiver to define a level of selfishness defining the combination of the maximum ratio combining precoder and the zero forcing precoder.
12. Receiver according to one of claims 1, 2, 9, 11,
wherein 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.
13. Receiver according to one of claims 1, 2, 9, 11,
comprises that
An estimation unit adapted to estimate channel state information on a channel from a transmitter to the receiver,
a connection unit adapted to establish a connection with a cooperating receiver over each communication link,
wherein the receiver is not served by the sender and the cooperative receiver is served by the sender on each downlink,
wherein the receiver is adapted to send the estimated channel state information to the cooperating receiver.
14. The receiver in accordance with claim 13, wherein,
wherein 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.
15. A communication network comprising a plurality of receivers according to any of the preceding claims and the multi-antenna transmitter.
16. A method for serving a receiver on a downlink by a multi-antenna transmitter and reducing interference caused by a channel from the transmitter to a cooperating receiver at the cooperating receiver,
wherein
-the receiver and the cooperating receiver establishing a connection over a communication link,
-the receiver estimating channel state information on the downlink,
-the cooperative receiver estimating channel state information on the channel from the sender to the cooperative receiver,
-the receiver receiving the channel state information on the channel estimated by the cooperating receiver from the cooperating receiver over the communication link,
-the receiver calculating a precoder for the downlink between the transmitter and the receiver from the estimated channel state information on the downlink and the received channel state information on the channel, and
-the receiver sends to the transmitter information derived from the calculated precoder;
wherein the receiver constructs 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 channels between the transmitter and each cooperating receiver to arrive at a pareto optimal solution based on the extended channel matrix to compute the precoder;
the calculating the precoder based on the extended channel matrix reaching a pareto optimal solution comprises:
generated according to equation ρMRC=hn,rA maximum ratio combining precoder corresponding to the channel matrix of the downlink, where pMRCIs the maximal ratio combining precoder, hn,rIs a matrix of the channels and is,
according to the equation
Wherein the zero forcing precoder
Is dimension NrUnit matrix of [ rho ]ZFIs a zero-forcing precoder that is,
is an extended channel matrix, and
is a dimension consisting of only zeros of (M-N)r)×NrAnd a matrix of
Calculating the precoder according to the equation:
P=αρMRC+(1-α)ρZF
where P is a combination of a maximum ratio combining precoder and a zero forcing precoder, α is a level of selfishness comprised between 0 and 1;
wherein the receiver selects at least one cooperative receiver from a plurality of other receivers, wherein criteria of the selection are distances between the receiver and the plurality of other receivers and the number of antennas of the plurality of other receivers and excludes the plurality of other receivers having high mobility;
wherein the receiver calculates an inverse of the precoder and transmits the inverse to the transmitter as information derived from the calculated precoder.
17. A computer-readable storage medium storing a computer program for performing the method of claim 16.
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