WO2012010048A1

WO2012010048A1 - Transmission method and system for cooperative relay based on limited feedback precoding

Info

Publication number: WO2012010048A1
Application number: PCT/CN2011/076710
Authority: WO
Inventors: 梁枫; 毕峰; 袁明; 吴栓栓; 杨瑾; 姜静
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-07-23
Filing date: 2011-06-30
Publication date: 2012-01-26
Also published as: CN102340380A

Abstract

The present invention discloses a transmission method and system for cooperative relay based on limited feedback precoding. The method includes: a base station and a relay station receive signals from multiple users (401); the relay station judges whether the received signals are correct or not, forwards the correctly received signals to the base station in a precoding manner or in a non-precoding manner, and does not forward the incorrectly received signals (402); the base station estimates the signals of a user by performing combination decision for the received signals directly transmitted from the user and the signals forwarded by the relay station for the same user, and estimates the signals of the user by performing direct decision for the signals which are directly transmitted from the user and are not forwarded by the relay station (403). The present invention can improve the forwarding efficiency and the bit error performance for a relay system.

Description

Cooperative relay transmission method and system based on limited feedback precoding

The present invention relates to a relay technology in the field of wireless communications, and in particular, to a cooperative relay transmission method and system based on limited feedback precoding. Background technique

In order to meet the development needs of mobile communications, the International Telecommunication Union (ITU) defined a new generation of mobile communication systems, the IMT-Advanced (International Mobile Telecommunication) system, in 2005, to explore the next generation of mobile communications. The new architecture of the network will be the core issue for further research. Under low-cost conditions, wireless relay technology has become a kind of realization of broad application prospects in the framework of next-generation wireless communication systems because relay can effectively enhance the transmission efficiency of the system, expand cell coverage, and suppress inter-cell interference. The solution has been identified as one of the key enhancement technologies of IMT-Advanced; currently the Institute of Electrical and Electronics Engineers (IEEE, 802.16m, 3rd Generation Partnership Project) The LTE-Advanced (Long Term Evolution-Advanced) standards organization is conducting research on relay technology. Introducing trunking in LTE-Advanced systems can improve high data rate coverage, group mobility, temporary network configuration and cell edge throughput, and provide coverage in new areas.

In the uplink of the cellular system based on the wireless relay, the relay needs to receive information of multiple users, and processes the data to the base station in a certain manner; the base station recovers the data sent by the user end by combining the data from the user end and the relay end. Data and give users a collaborative gain. Existing research shows that when all terminals are equipped with a single antenna, network coding techniques such as network coding based on bit-level XOR (XOR) and network coding based on symbol-level overlapping modulation can be used in the relay. Users gain collaboration gain while saving forwarding resources. However, in the actual scenario, the relay and the base station can usually configure multiple antennas, and how to perform multi-user signal processing on the relay and the base station to obtain the cooperation gain. There is no related solution in the prior art.

In addition, in the cooperative relay system, how to optimize the design of the transmitting end by using the limited feedback channel is also a research hotspot in recent years. Aiming at the single-source multi-relay scenario, aiming at maximizing the receiving signal-to-noise ratio, a joint optimization mechanism of relay-side precoding and base-end decoding using partial channel state information (CSI) has been proposed. For the single-source single/multi-relay scenario, a pre-coding mechanism using a partial CSI is proposed, which can improve the pairwise error probability performance of the system. However, how to optimize the transmitter using a limited feedback channel for a specific cooperative relay scenario remains to be studied.

The existing relay network model is shown in Fig. 1, in which the user and ^, as well as the relay station R and the base station D are included. The relay station and the base station are each configured with multiple antennas, and the relay stations are distributed in a certain area to assist communication between the wireless terminal and the base station.

In order to make full use of the extra channel freedom brought by multi-antenna relay, the cooperative transmission process occupies three time slots. As shown in FIG. 2, time slot 1 and time slot 2 are broadcast phases, and respectively broadcast respective data S^o S ₂ , the relay station and the base station are in the receiving mode; in the time slot 3, the relay station uses the precoding matrix P fed back by the base station to preprocess and forward the data estimates of the two users, and the destination end performs data signals from the user end and the relay station. Merge to get the cooperative diversity gain. Among them, (·) indicates a signal preprocessing method used by the relay station.

In the data broadcasting phase, it is assumed that the relay station R can learn a certain way to judge whether the signal can be correctly received. Then there are four kinds of relay scenarios as follows: 1. The relay station R can correctly receive the signal of ^ ₂ ; 2. The relay station R The signal can only be correctly received; 3. The signal that the relay station R can only receive correctly; 4. The relay station R cannot correctly receive the signal. Specify the scene = (/ _3⁄4 ) _2Χ2 , in the rest of the scene Ρ = / _2Χ2 , / _2Χ2 represents the 2x2 unit matrix.

Only data that the user sends within a single symbol interval is considered. Assume a single character in time slot 1 The A, t/ ₂ is transmitted in the interval of the interval, and the coordinated transmission is performed at the corresponding interval of the time slot 2. The signals received by the base station in the time slots are respectively:

(1) (2)

In equations (1)~(3), the superscript indicates the time slot, P is the 2x2 precoding matrix, and ( _e {l,2}) represents the channel vector of user i to the base station, h _id ( e{l, 2} ) indicates the channel vector of the ith antenna of the relay station R to the base station, and ^ is the detected value of the relay station R in the broadcast phase and the transmitted data, respectively. Therefore, there are four kinds of relay scenarios as follows: 1. The relay station R can correctly receive the signal of the ^; 2. The relay station R can only correctly receive the signal; 3. The relay station R can only correctly receive the signal; 4. The relay station R cannot be correctly Receive and signal. In each scenario, the base station combines the signals received in the two phases and uses the maximum likelihood decision to obtain the cooperative diversity gain.

In the scene, the relay station R can correctly receive the signal of ^ and s ₂ = s ₂ , and equation (3) can be expressed as:

Where = (A,) _2X2 and the total transmit power is limited to 2, ie

Equation (4) shows that the received signal of the cooperative system in the third time slot is the same as the multiple-input multiple-output (MIMO) spatial division multiplexing system, using traditional linear zero-forcing (ZF) equalization. G = left multiply, you can get the decision statistics of the 3rd time slot

S = + G«〗. Since the user uplink channel and /^ are independent of each other, the equivalent subchannels ^ and ^ are generally not orthogonal, resulting in the noise component of G«] being independent, so the conventional ZF receiver will be used. Bring performance loss. Summary of the invention

In view of this, the main object of the present invention is to provide a cooperative relay transmission method and system based on limited feedback precoding to solve the performance loss of the existing ZF receiver due to the non-orthogonality of the equivalent subchannels ^ and ^ The problem.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

The present invention provides a cooperative relay transmission method based on limited feedback precoding, the method comprising:

The base station and the relay station receive signals from a plurality of users;

The relay station determines whether the received signal is correct. When it is determined that the signals from the plurality of users are correctly received, the signal is pre-coded and then forwarded to the base station; if the received signal is received correctly, the receiving is also incorrect. When the signal is received, the correct signal is forwarded to the base station in a non-precoded manner, and the incorrectly received signal is not forwarded; when all the signals are received incorrectly, no forwarding is performed;

The base station combines the received signal directly sent by the user with a signal forwarded from the relay station for the same user, and estimates the signal of the user; the terminal directly sent by the user and the relay station does not perform The forwarded signal is directly judged to estimate the signal of the user.

The relay station determines whether the received signal is correct, specifically:

The relay station performs a cyclic redundancy (CRC) check on the received signal from the user to determine whether the received signal is correct;

Or the relay station compares the received signal to noise ratio of the signal from the user with a preset threshold, and if the signal to noise ratio of the signal is not lower than the preset threshold, determining that the signal is received correctly; otherwise, It is judged that the signal is received incorrectly.

The precoding matrix of the precoding process is sent by the base station to a codebook finger sent to a relay station The code information indication information includes: an index of a precoding matrix generation parameter or a precoding matrix generation parameter in a precoding matrix generation parameter set;

Correspondingly, the relay station generates a precoding matrix P according to the precoding matrix generation parameter according to the following formula:

The precoding matrix generation parameter is obtained by the base station by measuring a channel transmission matrix H = [ h _2d ] between the relay stations, and is obtained according to the following formula:

Where a = - 1 , (.wide represents the conjugate of the channel vector

Transpose, |Bu| represents the modulus of the channel vector, and Bu| represents the modulus of the complex number.

The present invention also provides a cooperative relay transmission system based on limited feedback precoding, the system comprising: a base station and a relay station, wherein

The relay station is configured to receive signals from a plurality of users, determine whether the received signal is correct, and when determining that signals from a plurality of users are correctly received, perform precoding processing on the signals and forward the signals to the base station; When receiving the correct signal or receiving the incorrect signal, the correct signal is forwarded to the base station by non-precoding, and the incorrect signal is not forwarded; the signal is not received correctly. When not, forwarding is not performed;

The base station is configured to receive signals from a plurality of users, perform a combined decision on the received signal directly sent by the user, and a signal forwarded from the relay station for the same user, to estimate the signal of the user; The signal sent directly by the user and not forwarded by the relay station is directly determined, and the signal of the user is estimated.

The relay station is further configured to perform a CRC check on the received signal from the user to determine whether the received signal is correct. The relay station is further configured to compare the received signal to noise ratio of the signal from the user with a preset threshold, and determine that the signal is received correctly when the signal to noise ratio of the signal is not lower than the preset threshold; When the signal to noise ratio of the signal is lower than the preset threshold, it is determined that the signal is received incorrectly.

The base station is further configured to: specify a precoding matrix of the precoding process by using codebook indication information that is sent to the relay station, where the codebook indication information includes: a precoding matrix generation parameter corresponding, and the relay station further uses The precoding matrix generation parameter generates a precoding matrix P by:

Ah

Among them, 2d

A― W + U ² -l , (^ denotes the conjugate h '2d of the channel vector

The invention provides a cooperative relay transmission method and system based on limited feedback precoding, which receives signals from a plurality of users by a base station and a relay station; the relay station determines whether the received signal is correct, and passes the correct signal through precoding. Or non-pre-coded mode forwarded to the base station, does not forward and receive the incorrect signal; the base station combines the received signal directly sent by the user with the signal forwarded from the relay station for the same user, and estimates the user's signal; The signal sent directly from the user and not relayed by the relay station is directly judged, and the signal of the user is estimated. Through the present invention, it is possible to make full use of limited system resources and make the relay system The overall error performance improves network transmission reliability. DRAWINGS

1 is a schematic diagram of an existing relay network model;

2 is a schematic diagram of time slots occupied by a cooperative transmission process in the prior art;

3 is a flowchart of a method for cooperative relay transmission based on limited feedback precoding according to the present invention; FIG. 4 is a schematic diagram of orthogonal decomposition of a channel at a base station according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of cooperative relay transmission based on CRC check according to an embodiment of the present invention; FIG. 6 is a schematic diagram of cooperative relay transmission based on received signal to noise ratio judgment according to an embodiment of the present invention. detailed description

The technical solutions of the present invention are further elaborated below in conjunction with the accompanying drawings and specific embodiments.

In order to solve the problem that the traditional ZF receiver suffers performance loss due to the non-orthogonality of the equivalent subchannels, the present invention decomposes the channel H into two orthogonal subchannels in the vector space, and the channel orthogonal decomposition diagram at the base station side is as follows. Figure 3 shows. For scenario one, let = ^ , h ₂ =h _ld , and decompose H into two directions, parallel and orthogonal, that is, H is:

H = h _v Λ ₂ ] = ah _l ] + [0 h ₂ - ah _v ] ( 6 ) In the above formula, and /i ₂ - are parallel and orthogonal components and

Substituting equation (6) into (4) and letting ³ = ί", η] = η, you can get:

^{r = h l [(Pll +} a Pll) S l + (Pl2 + a Pl2) ¾] + (^ 2 ~ β / ί 1) (^ 21 * 1 + ^ 22 * 2) + "^,) due to /i ₂ - mutually orthogonal, a simplified ZF equalizer and its output is:

_3⁄4 =^^ = 11^11 ( _Ρι , +αρ ₂₁ )s, + I (p _l2 + ap ₂₂ )s ₂ +

a(h ₇ -ak) ^H \\h ₂ -al^ a(h ₇ -ak) ^H n

^Z 2 = Tl\, 7J ^r = ~ Π ~ 2 A + ap ₂₂ S ₂ ) + -rr - ~~ '-r-

\ \\\n ₂ -an^ \a\ |α|||« ₂ -alt^

It can be seen from equation (8) that the noise components of 3⁄4 are independent of each other, so the receiver does not carry To performance loss.

The present invention utilizes a two-dimensional signal detection technique to separate the sums of the signals in equation (8), i.e., the hypotheses and the in-phase components and the quadrature components, respectively. In order to maximize the signal-to-noise ratio of the received signal, _Al and p _l2 should be divided into ¹ J and ap _2l and ap ₂₂ . Further, if p ≥ 0, -jp _n ≥ 0, then ap _2l ≥ 0, -jap ₂₂ > . For the signal in equation (8) and the maximum ratio combining (MRC, Maximal Ratio Combining)

The real part of the sum of 5 ₂ is taken separately, and the noise is normalized, and the sum of the decision statistics in the time slot 3 is:

In formula (10), Re(.) represents the real part of the signal,

= (||Oi2 +"1⁄2| ² +H— ΊΙ ^Λ 2— " || ² |" 3⁄4| ² ) ^1/2 , "' and "; both obey the mean o, the variance is

N. Gaussian distribution of /2. Let the symbol SNR ^= , then the system average bit error rate is:

No

Substituting and substituting (11), can be further expressed as

Under the condition that the total transmission power is constant, in order to optimize the precoding matrix Ρ, the system error rate is minimized.

Using the Lagrangian multiplier method, combined with the aforementioned assumptions >0, ap _2l ≥ 0

-jap ₂₂ ≥0, the optimal precoding matrix P is satisfied.

P21 = kp , P ₂ 2 = kp, 2 ( 14 ) h ₂ - ah,

Where P = -+ a -1

Substituting equation ( 14 ) into ( 5 )

Substituting equation (14) into (11), the equivalent received signal-to-noise ratio of the signal sum is obtained) ² ^r _s (h ₂ ') ² respectively

In the above formula, I Bu "= | Bu _{^{2 || = || ^ | 2 |}} ΐ + ^ α | 2 + || Λ 2 -a ^!

The nature of the function is known

When | _Ai | ² =| _A2 | ² = . / _2, the equation (17) with equality, then the minimum BER achieved. Combining conditions to limit _Al > 0 and -j _Pu > 0, we can get _Al = (l + \k\Y' ² , p _l2

Therefore, the precoding matrix under the minimum error rate of the system is

As can be seen from equation (18), the precoding matrix P is determined only by parameters, the amount of feedback required is small, and the implementation complexity is low. Substituting equation (18) into (10), the decision statistics and ³ in slot 3 are obtained.

According to equations (1) and (2), and in the time slots 1 and 2, the decision statistics and ² are

In order to obtain the cooperative diversity gain, the base station performs a joint maximum likelihood decision on the two-stage decision statistical signal, and the estimated value of the sum is obtained.

Sy = arg min ( <i ² (^ ¹ , ^ ) + <i ² (i , ^ ) )

(20) s ₂ = arg min (< ² (3⁄4 ² , 5 ₂ ) + d ² ( ^{3⁄4 3} , ^3⁄4 ))

Where S is the set of signals on the constellation diagram.

For scenes 2, 3, and 4, no precoding is performed, that is, the precoding matrix P 2x2 is for scene 2, and the relay station R corrects decoding, but the decoding error for ί/ _{2 is} s ₂ =0, and formula (3) can be Expressed as

The base station performs maximum ratio combining on the signals received in the two stages, and the available decision variable is

ί/ _{2 is} in non-cooperative mode, the available decision variable is

= Α Μ, + Α (23) For scenario 3, the relay station R has a decoding error, but the ί/ ₂ decoding is correct. At this time, 4=0, s ₂ = s ₂ , in the non-cooperative mode, the decision variable of A can be obtained as

^ ~= =\ΚΧ^ ⁺ ^ (24) Formula (3) can be expressed as

^1 = A + = (l 『 + \K f ) , + ( ^3⁄4 + h _d n _d ³ ) (26) For scenario 4, the relay station R decodes both U and U ₂ errors. At this time, 4=0, s ₂ =0, U ί/ ₂ are in non-cooperative mode, the decision variable is the same as equation (24), and the decision variable is the same as equation (23).

The decision variables obtained in each scene are sent to the Maximum Likelihood (ML) decoder to obtain the signal estimates of the sum.

Therefore, the cooperative relay transmission method based on the limited feedback precoding provided by the present invention can be summarized. The scenario of configuring two or more antennas for the relay station and the base station, as shown in FIG. 4, mainly includes the following steps:

Step 401: The base station and the relay station receive signals from a plurality of users.

Step 402: The relay station determines whether the received signal is correct, and forwards the received correct signal to the base station in a pre-coded or non-pre-coded manner, and does not forward the received incorrect signal.

Step 403: The base station combines the received signal directly sent by the user with the signal forwarded by the relay station for the same user, and estimates the signal of the user. The signal directly sent by the user and not forwarded by the relay station is directly determined. , estimate the user's signal.

In step 402, the relay station may perform a Cyclic Redundancy Check (CRC) check on the received signal from the user to determine whether the received signal is correct, and perform cooperative relay transmission based on the CRC check of the relay station. The schematic diagram is shown in Figure 5. Alternatively, the relay station may compare the received signal-to-noise ratio of the signal from the user with a preset threshold, and if the signal-to-noise ratio of the signal is not lower than the preset threshold, determine that the signal is received correctly; otherwise, determine that the signal is not received. correct. A schematic diagram of cooperative relay transmission implemented based on the received signal to noise ratio of the relay station is shown in FIG. 6. When the relay station judges that the signals from multiple users are correctly received, the signal is precoded and forwarded to the base station; when both the correct signal is received and the incorrect signal is received, the correct signal is received through the non-precoding. The method is forwarded to the base station, and the signal that is not received correctly is not forwarded; when all the signals are received incorrectly, no forwarding is performed. Taking the signal from two users simultaneously received by the base station and the relay station, if the relay station judges that the signals from the two users are correctly received, the signal is pre-coded and then forwarded to the base station; if the relay station judges the signals from the two users If one of the receivers receives correctly and the other receives incorrectly, only the correct received signal is forwarded to the base station in a non-precoded manner, and the incorrectly received signal is not forwarded; if the relay station judges that the signals from both users are received incorrectly , then it will not be forwarded.

In addition, the precoding matrix of the precoding process is specified by the base station by using codebook indication information that is sent to the relay station, where the codebook indication information includes: a precoding matrix generation parameter or a precoding matrix generation parameter k in the precoding matrix generation parameter set. Index in

Correspondingly, the relay station generates parameters according to the precoding matrix fed back by the base station.

(18) generating a precoding matrix P; or, the relay station generates an index in a precoding matrix generation parameter set according to a precoding matrix fed back by the base station, and obtains a precoding matrix generation parameter in the precoding matrix generation parameter set, and then passes the foregoing formula. (18) Generate a precoding matrix.

The precoding matrix generation parameter is obtained by the base station by measuring the channel transmission matrix H = [ h _2d ] between the relay stations, and is obtained according to the following formula:

Where a = - 1 , (.wide represents the conjugate of the channel vector

Corresponding to the above-described cooperative relay transmission method based on limited feedback precoding, the present invention also provides a cooperative relay transmission system based on limited feedback precoding, which is composed of a base station and a relay station. The relay station is configured to receive signals from multiple users, and determine whether the received signal is correct. The received signal is forwarded to the base station in a pre-coded or non-pre-coded manner, and the incorrectly received signal is not forwarded. a base station, configured to receive signals from a plurality of users, and combine the received signals directly sent by the user with the signals forwarded by the relay station for the same user, and estimate the signal of the user; The relay station does not perform a direct decision on the forwarded signal to estimate the user's signal.

Preferably, the relay station is further configured to perform a CRC check on the received signal from the user to determine whether the received signal is correct. Or comparing the received signal-to-noise ratio of the signal from the user with a preset threshold, and when the signal-to-noise ratio of the signal is not lower than a preset threshold, determining that the signal is received correctly; the signal-to-noise ratio of the signal is lower than When the threshold is preset, it is judged that the signal is not received correctly.

The relay station is further configured to: when it is determined that the signals from the plurality of users are correctly received, the signal is pre-coded and then forwarded to the base station; when both the correct signal is received and the incorrect signal is received, the receiving is correct. The signal is forwarded to the base station in a non-precoded manner, and the signal that is not received correctly is not forwarded; when all signals are received incorrectly, no signal is forwarded.

In summary, according to the present invention, the limited system resources can be fully utilized to maximize the coding gain and diversity gain of the relay system, thereby improving the forwarding efficiency of the system, improving the error performance of the relay system, and improving network transmission reliability. Sex.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

Claim

A cooperative relay transmission method based on limited feedback precoding, characterized in that: the method comprises:

The cooperative relay transmission method based on the limited feedback precoding according to claim 1, wherein the relay station determines whether the received signal is correct, specifically:

The cooperative relay transmission method based on the finite feedback precoding according to claim 1, wherein the precoding matrix of the precoding process is specified by the base station by using codebook indication information sent to the relay station, where The codebook indication information includes: an index of a precoding matrix generation parameter or a precoding matrix generation parameter in a precoding matrix generation parameter set; Correspondingly, the relay station generates a precoding matrix P according to the precoding matrix generation parameter according to the following formula:

Where (. broadly indicates the conjugate of the channel vector

A cooperative relay transmission system based on limited feedback precoding, characterized in that the system comprises: a base station and a relay station, wherein

The cooperative relay transmission system based on the limited feedback precoding according to claim 4, wherein the relay station is further configured to perform a CRC check on the received signal from the user, and determine whether the received signal is correct. .

6. The cooperative relay transmission system based on limited feedback precoding according to claim 4, The relay station is further configured to: compare the received signal to noise ratio of the signal from the user with a preset threshold, and determine the signal when the signal to noise ratio of the signal is not lower than the preset threshold. Receiving correctly; when the signal to noise ratio of the signal is lower than the preset threshold, it is judged that the signal is received incorrectly.

The cooperative relay transmission system based on limited feedback precoding according to claim 4, 5 or 6, wherein the base station is further configured to specify the precoding by codebook indication information sent to the relay station. a precoding matrix that is processed, where the codebook indication information includes: an index in the pre-combination;

Correspondingly, the relay station is further configured to: generate, by using the following formula, a precoding matrix P by using the precoding matrix:

The precoding matrix generation parameter is obtained by the base station by measuring a channel transmission matrix H=[h _2d ] between the relay stations, and is obtained according to the following formula:

Where - I represents the conjugate of the channel vector

Transpose, |·| represents the modulus of the channel vector, and || represents the modulus of the complex number ₍