CN102098263A - Low-detection complexity full-rate wireless cooperative relay transmission scheme - Google Patents

Abstract

The invention discloses a low-detection complexity full-rate wireless cooperative relay transmission scheme and is applied to a distributed wireless communication system employing an orthogonal frequency division multiplexing (OFDM) technology. The scheme is that: data to be transmitted of a source node is subjected to reasonable complex domain encoding in a frequency domain so as to obtain a full-diversity gain of the distributed wireless system and enhance channel fading resistance of signals in the cooperative relay transmission process; the encoded data is divided into two parts, is subjected to OFDM modulation and is transmitted by the source node in two adjacent time slots in turn; a relay node receives a first part of data from the source node in a first time slot and transmits the first part of data to a destination node in a second time slot by employing a cycle delay amplifying and forwarding mode; and a receiving end can finish decoding by only performing joint detection on two symbols through comprehensive processing of the received signals in the two time slots. The provided relay transmission scheme is simple in encoding structure, is applied to scenes with free number of relay antennae, can achieve full-diversity gain performance and obviously reduce the detection complexity, and has higher practical value compared with a relay scheme pursuing the transmission rate or error code performance only.

Description

The full rate wireless cooperation relay transmission scheme of low detection complexity

Technical field

The present invention relates to a kind of full rate wireless cooperation relay transmission scheme of low detection complexity, belonged to moving communicating field, be applicable to the DWCS that adopts orthogonal frequency division multiplexi.

Background technology

Wireless cooperation communication (CC:Cooperative Communication) technology utilization is distributed in one of a plurality of portable terminals antenna configuration separately " empty multiple-input and multiple-output (MIMO:Multiple-Input-Multiple-Output) " system that capacity is bigger, reliability is higher of different physical locations, overcome the deficiency that single antenna mobile terminal can't obtain space diversity gain, can realize high bit error properties data transmission, become one of hot spot technology of current tool researching value and application potential.

In the many technology that realize remote-wireless communication, the cooperating relay mode has been proved to be one of low-power consumption transmission plan that is applicable to distributed wireless networks and tool advantage.But the existing cooperating relay scheme availability of frequency spectrum and transmission rate are generally lower, and especially in multihop network, this deficiency is particularly evident.In order to improve the availability of frequency spectrum of cooperating relay technology, the article " the distributed Space Time Coding of full rate that is used for collaboration communication " (Full-Rate Distributed Space-Time Codes forCooperative Communications) that Zhang Wei and Letaief deliver in U.S.'s " Institute of Electrical and Electronics Engineers radio communication transactions " (IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS) the 7th in July, 2008 the 7th phase of volume has proposed to realize the cooperating relay scheme of full rate transmission in conjunction with the advantage of linear complex field coding techniques.This scheme is carried out linear complex field combined coding with source node and via node information transmitted, maximally utilised the frequency spectrum resource of wireless network, but this scheme must be carried out joint-detection to all symbols that participate in precoding at receiving terminal and could be obtained full-diversity and gain.When the relaying interstitial content was big, pre-coding matrix was very complicated, and coding and detection complexity are all very high, are difficult to obtain practical application.The article " random rotation that is used for cooperation communication system postpones coding " (Randomized Cyclic Delay Code for CooperativeCommunication Systems) that Choi equals to deliver the 12nd the 4th phase of volume in U.S.'s " Institute of Electrical and Electronics Engineers communication wall bulletin " (IEEE COMMUNICATIONS LETTERS) in April, 2008 is based on the cyclic delay diversity technology, proposed to have the distributed collaborative encoding scheme of unified receiver structure, for the design of hanging down detection complexity wireless cooperation communication network provides a kind of new approaches, but Choi etc. are also not nearly enough deep in the research work aspect this, the space-frequency coding process of its scheme correspondence is also only finished between via node and destination node, and the transmission rate of system is still not high.

To sum up, in the wireless cooperation communication network, the contradiction between error performance, detection complexity and the transmission rate is the difficult problem that up to the present still can not satisfactorily resolve, and is worth further investigation and discussion.

Summary of the invention

The present invention utilizes the advantage of cyclic delay diversity technology aspect many antennas of reduction code detection complexity, characteristics in conjunction with linear complex field coding techniques, invented a kind of cooperating relay scheme that has low detection complexity and can realize full rate, highly-reliable transmission, the existing trunking plan of only pursuing transmission rate or error performance more has practical value.

Concrete technical scheme of the present invention is as follows:

1, the full rate wireless cooperation relay transmission scheme of low detection complexity, overall model is as follows:

1a) distributed wireless system is made of a source node, a plurality of via node and a destination node, each node assembling single transmit antenna, communicate with semiduplex mode, internodal message transmission adopts OFDM (OFDM:Orthogonal Frequency DivisionMultiplexing) mode to finish;

1b) cooperating relay transmission is finished in two time slots, and the frequency domain symbol that source node transmits in adjacent two time slots is respectively S ₁, S ₂, be respectively X through the symbol that obtains behind the linear complex field coding ₁, X ₂, data length is N _F, N _FCarrier number for OFDM; In first time slot, source node S is to all node broadcasts signals, and in second time slot, source node S continues to send new data to destination node D, thereby can realize the relay transmission of full rate; All via nodes carry out sending to destination node D at second time slot to amplify pass-through mode behind the circulation delay to the signal that receives in first time slot;

1c) on p subcarrier of first time slot, the received signal of i via node and destination node can be described as respectively:

$R_i\left(p\right)=\sqrt{P_1}{H}_i^{\mathrm{SR}}\left(p\right)X_1\left(p\right)+N_i\left(p\right),$ p∈[1，N _F]，i∈[1，M]

$D_1\left(p\right)=\sqrt{P_1}{H}^{\mathrm{SD}}\left(p\right)X_1\left(p\right)+W_1\left(p\right)$

In the formula, P ₁Be the source node transmitted power, M is the via node number, H ^SD(p) and

Be respectively the frequency domain complex channel fading coefficients of source node, X to destination node, an i via node ₁(p) for to upload defeated X at p subcarrier ₁In symbol, N _i(p) and W ₁(p) represent that respectively average is zero, covariance is N ₀Multiple Gaussian noise;

1d) on p subcarrier of second time slot, the received signal matrix of destination node is:

$D_2\left(p\right)=\sqrt{P_3}{H}^{\mathrm{SD}}\left(p\right)X_2\left(p\right)+\mathrm{\α}\sqrt{P_1}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\left(H_i^{\mathrm{RD}}\left(p\right)H_i^{\mathrm{SR}}\left(p\right){\mathrm{\ψ}}_1^p\left(X_1\right)\right)+\mathrm{\α}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{H}_i^{\mathrm{RD}}\left(p\right)N_i\left(p\right)+W_2\left(p\right)$

In the formula,

Be power amplification coefficient power amplification ratio, P ₂Be the transmitted power of each via node, P ₃Be the transmitted power of second Timeslot source node, X ₂(p) for to upload defeated X at p subcarrier ₂In symbol,

Be the equivalent modulation symbol that behind the process circulation delay that transmits on i the via node, obtains,

Be the frequency domain complex channel fading coefficients of i via node to destination node, W ₂(p) be that average is zero, covariance is N ₀Multiple Gaussian noise.

2, in the transmission course of data, the data to be transmitted in the source node frequency domain is carried out combined coding, at via node the received signal on each antenna is carried out circulation delay;

2a) in the wireless cooperation communication system that adopts the OFDM technology, because i via node transmission is the modulation symbol that obtains after passing through circulation delay, then the equivalent modulation symbol on p subcarrier becomes:

${\mathrm{\ψ}}_i^p\left(X_1\right)=e^{-j\frac{2\mathrm{\π}}{N_F}p{\mathrm{\Δ}}_i}{X}_1\left(p\right),$ p∈[1，N _F]，i∈[1，M]

In the formula, Δ _iBe that i root relay antenna is adopting the circulation delay mode to finish the circulation delay amount of using when amplification is transmitted, can determine in the following way:

${\mathrm{\Δ}}_i={\mathrm{\Δ}}_{i-1}+\frac{N_F}{M},$ Δ ₁＝0，i∈[2，M]

2b) via node adopts circulation delay to amplify after the pass-through mode, and the received signal matrix of destination node becomes:

$D_2\left(p\right)=\sqrt{P_3}{H}^{\mathrm{SD}}\left(p\right)X_2\left(p\right)+\mathrm{\α}\sqrt{P_1}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\left(H_i^{\mathrm{RD}}\left(p\right)H_i^{\mathrm{SR}}\left(p\right)e^{-j\frac{2\mathrm{\π}}{N_F}p{\mathrm{\Δ}}_i}\right)X_1\left(p\right)+\mathrm{\α}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{H}_i^{\mathrm{RD}}\left(p\right)N_i\left(p\right)+W_2\left(p\right)$

Equivalent channel in the following formula is an one dimension, and does not increase with the increase of via node number, and detection complexity is reduced significantly;

Be further to excavate potential diversity gain between source node and via node 2c), the data that source node sends in adjacent two time slots are the symbols that obtain through after the linear complex field coding:

[X ₁(p)?X ₂(p)] ^T＝Θ·[S ₁(p)?S ₂(p)] ^T，p∈[1，N _F]

In the formula, S ₁(p) and S ₂(p) be respectively S ₁And S ₂In p element, Θ is 2 * 2 pre-coding matrix, can adopt in the following method and design:

$\mathrm{\Θ}=F_2^H\mathrm{diag}(1,\mathrm{\θ})$

In the formula,

Be 2 * 2 discrete Fourier transform matrix, θ=e ^{J π/4}Because the combined coding in the such scheme only carries out at two intersymbols, the detection of carrying out for the acquisition optimum performance also only needs unite estimation to two symbols, and therefore the detection complexity of whole relay transmission scheme is very low.

3, the relay transmission scheme of the present invention's proposition is characterised in that: at first the data to be transmitted of source node is carried out rational linear complex field coding, then in two continuous time slot, transmit successively, via node amplifies pass-through mode with the The data circulation delay that receives and sends destination node to, not only can obtain the full-diversity gain of distributed wireless system, the anti-channel fading ability in the enhancing cooperating relay transmission process like this, can obviously reduce detection complexity simultaneously, simplify coding structure.

Description of drawings

The structure chart of the wireless cooperation communication network that Fig. 1 is suitable for for the present invention.

Fig. 2 is the overall transfer block diagram of the full rate wireless cooperation relay transmission scheme of the low detection complexity of the present invention's proposition.

Fig. 3 is the comparison of full rate wireless cooperation relay transmission scheme performance of BER under different via node numbers of the low detection complexity of the present invention's proposition.

The comparison of the performance of BER of coding transmission scheme during the full rate distributed space that proposes in the full rate wireless cooperation relay transmission scheme of the low detection complexity that Fig. 4 proposes for the present invention and the Zhang Wei literary composition.

Embodiment

Below in conjunction with accompanying drawing specific embodiments of the present invention is described further.

Wireless cooperative network structure as shown in Figure 1, system is made of a source node, a plurality of via node and a destination node, each node constitutes by a single aerial system, and carry out collaboration communication with semiduplex mode, internodal message transmission adopts OFDM (OFDM:Orthogonal Frequency Division Multiplexing) mode to finish.The data to be transmitted of source node sends in two adjacent time slots successively.Source node frequency domain signal transmitted in former and later two time slots is respectively S ₁, S ₂, be designated as X through the symbol behind the linear complex field coding ₁, X ₂, each data length that sends is N _F(i.e. the length of an OFDM modulation symbol).In first time slot, source node S is to other all node broadcasts signals, in second time slot, source node S continues to send new data to destination node D, and all via nodes carry out sending to destination node D to amplify pass-through mode behind the circulation delay to the signal that receives at first time slot.

Transmission block diagram as shown in Figure 2 at first carries out rational linear complex field coding to the data to be transmitted of source node in frequency domain, to obtain the full-diversity gain of distributed wireless system, the anti-channel fading ability of enhancing signal in the cooperating relay transmission process.This example is selected following pre-coding matrix:

$\mathrm{\Θ}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& e^{\mathrm{\π}\·j/4}\\ 1& -e^{\mathrm{\π}\·j/4}\end{array}\right]$

Data behind the coding are divided into two parts, are sent successively by source node in two adjacent time slots after the OFDM modulation.Via node receives first's data from source node at first time slot, and adopts the circulation delay mode to transmit this partial data to destination node at second time slot.The circulation delay mode makes that the variation of the equivalent channel amplitude of fading in frequency domain is more violent, present stronger frequency selectivity, thereby make whole system can obtain higher frequency diversity, but the frequency diversity of this enhancing must adopt error correction coding to obtain, therefore before carrying out the OFDM modulation, must carry out Bit Interleave and error correction coding to the data to be transmitted of source node earlier.Adopt QPSK modulation symbol, sub-carrier number N in the example _F=1024, channel is a frequency-selective channel, and the footpath number is 2, and carrier frequency is 3.5GHZ, and noise is an additive white Gaussian noise, and application rate is (133,171) convolution code of 0.5, adopts normalized E _b/ N ₀As signal to noise ratio standard, wherein E _bThe average energy that adopts when being whole wireless cooperation communication system transmits 1 bit information.

Be illustrated in figure 3 as the comparative result of full rate wireless cooperation relay transmission scheme performance of BER under different via node numbers of low detection complexity.Along with the increase of via node number, the coding transmission scheme of proposition can obtain bigger diversity gain, and the error rate is able to continuous reduction.When signal to noise ratio was 25dB, the error performance of four relay node obviously was better than two relay node.

Simulation result as shown in Figure 4, compare with Zhang Wei " the distributed Space Time Coding of full rate that is used for collaboration communication " (Full-Rate DistributedSpace-Time Codes for Cooperative Communications) paper coding method, though the whole error performance of scheme that the present invention proposes is poor slightly, to increase the decrease speed that presents with signal to noise ratio be consistent (the full-diversity gain that all obtains) to bit error rate under two kinds of schemes.In addition, in two relay node of Zhang Wei, the receiving terminal desire obtains the optimal bit error performance, needs carry out joint-detection to 4 symbols, and along with the increase of via node number, and the joint-detection symbolic number will be square and time increase, and complexity is too high.And the relay transmission scheme that the present invention proposes only needs 2 symbols are carried out joint-detection at receiving terminal, and the joint-detection symbolic number does not change with the increase of via node number, and detection complexity is very low, more has practical value.

Claims (3)

1. hang down the full rate wireless cooperation relay transmission scheme of detection complexity, overall model is as follows:

1a) distributed wireless system is made of a source node, a plurality of via node and a destination node, each node assembling single transmit antenna, communicate with semiduplex mode, internodal message transmission adopts OFDM (OFDM:Orthogonal Frequency DivisionMultiplexing) mode to finish;

1b) cooperating relay transmission is finished in two time slots, and the frequency domain symbol that source node transmits in adjacent two time slots is respectively S ₁, S ₂, be respectively X through the symbol that obtains behind the linear complex field coding ₁, X ₂, data length is N _F, N _FCarrier number for OFDM; In first time slot, source node S is to all node broadcasts signals, and in second time slot, source node S continues to send new data to destination node D, thereby can realize the relay transmission of full rate; All via nodes carry out sending to destination node D at second time slot to amplify pass-through mode behind the circulation delay to the signal that receives in first time slot;

1c) on p subcarrier of first time slot, the received signal of i via node and destination node can be described as respectively:

$R_i\left(p\right)=\sqrt{P_1}{H}_i^{\mathrm{SR}}\left(p\right)X_1\left(p\right)+N_i\left(p\right),$ p∈[1，N _F]，i∈[1，M]

$D_1\left(p\right)=\sqrt{P_1}{H}^{\mathrm{SD}}\left(p\right)X_1\left(p\right)+W_1\left(p\right)$

In the formula, P ₁Be the source node transmitted power, M is the via node number, H ^SD(p) and Be respectively the frequency domain complex channel fading coefficients of source node, X to destination node, an i via node ₁(p) for to upload defeated X at p subcarrier ₁In symbol, N _i(p) and W ₁(p) represent that respectively average is zero, covariance is N ₀Multiple Gaussian noise;

1d) on p subcarrier of second time slot, the received signal matrix of destination node is:

$D_2\left(p\right)=\sqrt{P_3}{H}^{\mathrm{SD}}\left(p\right)X_2\left(p\right)+\mathrm{\α}\sqrt{P_1}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\left(H_i^{\mathrm{RD}}\left(p\right)H_i^{\mathrm{SR}}\left(p\right){\mathrm{\ψ}}_1^p\left(X_1\right)\right)+\mathrm{\α}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{H}_i^{\mathrm{RD}}\left(p\right)N_i\left(p\right)+W_2\left(p\right)$

In the formula,

Be power amplification coefficient power amplification ratio, P ₂Be the transmitted power of each via node, P ₃Be the transmitted power of second Timeslot source node, X ₂(p) for to upload defeated X at p subcarrier ₂In symbol,

Be the equivalent modulation symbol that behind the process circulation delay that transmits on i the via node, obtains,

Be the frequency domain complex channel fading coefficients of i via node to destination node, W ₂(p) be that average is zero, covariance is N ₀Multiple Gaussian noise.

2. one kind is used for described many relayings cyclic delay diversity of claim 1 and combined coding scheme, and this scheme is carried out circulation delay to the received signal on each via node antenna, in frequency domain data to be transmitted is encoded;

2a) in the wireless cooperation communication system that adopts the OFDM technology, because i via node transmission is the modulation symbol that obtains after passing through circulation delay, then the equivalent modulation symbol on p subcarrier becomes:

${\mathrm{\ψ}}_i^p\left(X_1\right)=e^{-j\frac{2\mathrm{\π}}{N_F}p{\mathrm{\Δ}}_i}{X}_1\left(p\right),$ p∈[1，N _F]，i∈[1，M]

In the formula, Δ _iBe that i root relay antenna is adopting the circulation delay mode to finish the circulation delay amount of using when amplification is transmitted, can determine in the following way:

${\mathrm{\Δ}}_i={\mathrm{\Δ}}_{i-1}+\frac{N_F}{M},$ Δ ₁＝0，i∈[2，M]

2b) via node adopts circulation delay to amplify after the pass-through mode, and the received signal matrix of destination node becomes:

$D_2\left(p\right)=\sqrt{P_3}{H}^{\mathrm{SD}}\left(p\right)X_2\left(p\right)+\mathrm{\α}\sqrt{P_1}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\left(H_i^{\mathrm{RD}}\left(p\right)H_i^{\mathrm{SR}}\left(p\right)e^{-j\frac{2\mathrm{\π}}{N_F}p{\mathrm{\Δ}}_i}\right)X_1\left(p\right)+\mathrm{\α}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{H}_i^{\mathrm{RD}}\left(p\right)N_i\left(p\right)+W_2\left(p\right)$

Equivalent channel in the following formula is an one dimension, and does not increase with the increase of via node number, and detection complexity is reduced significantly;

Be further to excavate potential diversity gain between source node and via node 2c), the data that source node sends in adjacent two time slots are the symbols that obtain through after the linear complex field coding:

[X ₁(p)?X ₂(p)] ^T＝Θ·[S ₁(p)?S ₂(p)] ^T，p∈[1，N _F]

In the formula, S ₁(p) and S ₂(p) be respectively S ₁And S ₂In p element, Θ is 2 * 2 pre-coding matrix, can adopt in the following method and design:

$\mathrm{\Θ}=F_2^H\mathrm{diag}(1,\mathrm{\θ})$

In the formula, Be 2 * 2 discrete Fourier transform matrix, θ=e ^{J π/4}, because the combined coding in the such scheme only carries out at two intersymbols, the detection of carrying out for the acquisition optimum performance also only needs unite estimation to two symbols, therefore the detection complexity of whole relay transmission scheme is very low.

3. wireless cooperation relay transmission scheme as claimed in claim 1, it is characterized in that: at first the data to be transmitted of source node is carried out rational linear complex field coding, then in two continuous time slot, transmit successively, via node amplifies pass-through mode with the The data circulation delay that receives and sends destination node to, not only can obtain the full-diversity gain of distributed wireless system, the anti-channel fading ability in the enhancing cooperating relay transmission process like this, can obviously reduce detection complexity simultaneously, simplify coding structure.

Images