CN105721106A - Multiuser detection method based on serial strategy for SCMA (Sparse Code Multiple Access) uplink communication system - Google Patents

Abstract

The invention provides a multiuser detection method based on a serial strategy for an SCMA (Sparse Code Multiple Access) uplink communication system, and belongs to the field of signal detection of wireless communication systems. The method is characterized in that nodes in a conventional SCMA factor graph are divided into J groups (J is a quantity of user nodes); each group comprises one user node and all resource nodes connected with the user node; and all nodes (one user node and all the resource nodes which are connected with the user node) of each group are updated in sequence in each iteration process. According to the multiuser detection method, already-updated node messages are utilized in each iteration process, so that a utilization ratio of the already-updated node messages can be effectively increased. The BER (Bit Error Rate) performance of the method is far superior to the BER performance of a method in the prior art under the condition of less iteration times. The calculation complexity of the method is much lower than the calculation complexity of the method in the prior art under the condition of hardly any loss of the BER performance.

Description

SCMA ascending communication system multi-user test method based on serial strategy

Technical field

The invention belongs to the signal detection field of wireless communication system, relate to the low Sparse Code multiple access of a kind of fast convergence rate, complexity and access (SCMA) ascending communication system multi-user test method, it is specially a kind of MPA detection method based on serial strategy, is used for solving the Multiuser Detection problem of 5G (the 5th third-generation mobile communication) the alternative multiple access technique of mobile communication.

Background technology

Multiple access access is one of core technology of radio communication physical layer, and it makes base station can distinguish and service multiple terminal use simultaneously.In order to meet 5G (the 5th third-generation mobile communication) Large Copacity, magnanimity connects, the demands such as low delay access, the patent of invention " system and method that user's Sparse Code multiple access accesses " that application number is 201380059380.X proposes a kind of SCMA (Sparsecodemultipleaccess, Sparse Code multiple access accesses) technology, Fig. 1 is SCMA ascending communication system model, some neutral element in SCMA spread spectrum code word, the base band data of each user only carries out nonzero digit band spectrum modulation on a small amount of chip, and every spread-spectrum code chip is also only carried out nonzero digit band spectrum modulation by a small amount of user, SCMA encoder selects a code book for each data Layer or user in predefined codebook set, it is then based on selected code book to be mapped directly to by data bit in corresponding code word, finally the code word of multiple data Layers or user is carried out nonopiate superposition, receiving terminal carries out the multiuser detection based on belief propagation algorithm to received signal, i.e. parallel MPA detection method, accompanying drawing 2 is the SCMA factor graph of the method, parallel MPA detection method is in each iterative process, first all of resource node is updated, then all of user node is updated.

Patent of invention " system and method that user's Sparse Code multiple access accesses " proposes a kind of MPA detection method based on paralleling tactic, specifically includes following steps:

Step 1, initialization: when iteration starts, user does not have prior information, therefore user node u_jTo resource node c_kMessage be:J=1,2 ..., J, k=1,2 ..., K, u_jFor jth user node, c_kFor kth resource node, M is the number of codewords of code book,Family node u is started with for iteration_jTo resource node c_kMessage；

Step 2, set maximum iteration time as t_max；

Step 3, in the t time iterative process, the message of resource node and user node updates parallel, namely first updates all of resource node c_kTo user node u_jMessage $M_{c_k\→u_j}^t\left(x_j\right)=\underset{~x_j}{\mathrm{\Σ}}\left\{\exp \left(-\frac{1}{2{\mathrm{\σ}}^2}\left|\right|y_k-\underset{i\∈{\mathrm{\ϵ}}_k}{\mathrm{\Σ}}{h}_{k,i}{x}_{k,i}|{|}^2\×\underset{l\∈{\mathrm{\ϵ}}_k\backslash j}{\mathrm{\Π}}{M}_{u_l\→c_k}^{t-1}\left(x_l\right)\right)\right\},\∀j,\∀k;$ T=1,2 ..., t_maxBe t (t=1,2 ..., t_max) calculated resource node c in secondary iterative process_kTo user node u_jMessage, x_j=(x_1,j,...,x_K,j)^ΤFor the SCMA code word of jth user, x_l=(x_1,l,...,x_K,l)^ΤIt is the SCMA code word of l user, y_kFor receiving the signal that in signal y, kth Energy Resources Service receives,The sparse Spread Spectrum Matrix of transmitter SCMA encoder (F be) is for being connected to resource node c_kUser node collection；X_k,iRepresent the kth resource of the code word of i-th user, h_k,iFor h_i=(h_1,i,h_2,i,...,h_K,i)^ΤIn kth element, h_iChannel vector for i-th user；Then all of user node u is updated_jTo resource node c_kMessage:An iteration completes；For being connected to user node u_jSet of resource nodes；

Step 4, judge t > t_maxWhether setting up, if setting up, performing step 5；If being false, then making t=t+1, returning step 3, carrying out next iteration；

Step 5, through t_maxSecondary iteration backed off after random circulates, and calculates codeword message:

$Q\left(x_j\right)=\underset{q\∈{\mathrm{\ζ}}_j}{\mathrm{\Π}}{M}_{c_q\→u_j}\left(x_j\right);$

Step 6, calculating obtain the Soft Inform ation of data bit

${\mathrm{LLR}}_j=\log \frac{P\left(b_j=1\right)}{P\left(b_j=0\right)}=\log \frac{\underset{b_j=1}{\mathrm{\Σ}}Q\left(x_j\right)}{\underset{b_j=0}{\mathrm{\Σ}}Q\left(x_j\right)};$

b_jData bit for jth user；

Step 7, data bit judgement (hard decision) $\widehat{U_j}=\left\{\begin{array}{cc}1& {\mathrm{LLR}}_j>0\\ 0& {\mathrm{LLR}}_j\≤0\end{array}\right..$

Above-mentioned based on, in the MPA detection method of paralleling tactic, detecting accuracy and maximum iteration time t_maxAnd message circulation way is relevant.But, in practical engineering application, along with the increase of iterations, the hardware computation complexity of communication system is more and more higher, therefore that the requirement of hardware is also more and more higher；And in the method all resource nodes to the renewal of user node messageIt is based on the user node message to resource node of the t-1 time iteration acquisitionAll user nodes are to the renewal of resource node messageIt is based on when previous iteration updatesAlthoughCurrent iteration is well make use of to updateButIt is based on last grey iterative generationDo not utilize the message that in current iteration, user node updates to resource node, cause that its rate of convergence is relatively low.To sum up, although above-mentioned parallel MPA detection method can be effectively improved the probability of correct decoding, but owing to its computation complexity is higher and rate of convergence is relatively low, it is impossible to meet 5G to high speed, efficient demand.

Summary of the invention

The present invention is directed to the defect that background technology exists, it is proposed that a kind of SCMA ascending communication system multi-user test method based on serial strategy.Node in traditional SCMA factor graph is divided into J group (J is the number of user node) by the present invention, often group is a user node and all resource nodes being connected with this user node thereof, in each iterative process, successively all nodes (all resource nodes that a user node is coupled) of each group are updated；The present invention all make use of the node messages updated in each iterative process, can be effectively improved the utilization rate having updated node messages, and computation complexity is low, BER function admirable.

Technical scheme is as follows:

A kind of SCMA ascending communication system multi-user test method based on serial strategy, including initializing, resource node and the renewal of user node message, the calculating of data bit Soft Inform ation, data bit decision steps；It is characterized in that, the renewal of described resource node and user node message is that successive ignition completes, each time in iterative process, using a user node and all resource nodes of being connected with this user node thereof as one group, user node and resource node are divided into J group, and J is the number of user node；Then successively the message of the message of all of resource node in each group to user node and user node to resource node is updated, namely completes the process of an iteration.

A kind of SCMA ascending communication system multi-user test method based on serial strategy, specifically includes following steps:

Step 1, initialization: SCMA is when iteration starts, and user does not have prior information, therefore user node u_jTo resource node c_kMessage be:J=1,2 ..., J, k=1,2 ..., K, u_jFor jth user node, c_kFor kth resource node, M is the number of codewords of code book,Family node u is started with for iteration_jTo resource node c_kMessage；

Step 2, set maximum iteration time as t_max；

Step 3, in the t time iterative process, first using jth user node and all resource nodes of being connected with jth user node as one group, user node and resource node are divided into J group, j=1,2 ..., J, J group node is respectively labeled as γ₁,γ₂,...,γ_JGroup；Then, γ is calculated₁The all of resource node of group is to the message of user node $M_{c_k\&RightArrow;u_j}^t\left(x_j\right)=\underset{~x_j}{\mathrm{\&Sigma;}}\left\{\exp \left(-\frac{1}{2{\mathrm{\&sigma;}}^2}\left|\right|y_k-\underset{i\&Element;{\mathrm{\&epsiv;}}_k}{\mathrm{\&Sigma;}}{h}_{k,i}{x}_{k,i}|{|}^2\right)\&times;\underset{l<j}{\underset{l\&Element;{\mathrm{\&epsiv;}}_k\backslash j}{\mathrm{\&Pi;}}}{M}_{u_l\&RightArrow;c_k}^t\left(x_l\right)\underset{l>j}{\underset{l\&Element;{\mathrm{\&epsiv;}}_k\backslash j}{\mathrm{\&Pi;}}}{M}_{u_l\&RightArrow;c_k}^{t-1}\left(x_l\right)\right\}$ Message with user node to resource nodeThen γ is calculated successively₂,...,γ_JThe resource node of group is to the message of user node and user node to the message of resource node, and an iteration completes；X_j=(x_1,j,...,x_K,j)^ΤFor the SCMA code word of jth user, x_l=(x_1,l,...,x_K,l)^ΤIt is the SCMA code word of l user, y_kFor receiving the signal that in signal y, kth Energy Resources Service receives,The sparse Spread Spectrum Matrix of transmitter SCMA encoder (F be) is for being connected to resource node c_kUser node collection；X_k,iRepresent the kth resource of the code word of i-th user, h_k,i∈h_i=(h_1,i,h_2,i,...,h_K,i)^Τ, hi is the channel vector of user i,For being connected to user node u_jSet of resource nodes；

Step 4, judge t > t_maxWhether setting up, if setting up, performing step 5；If being false, then making t=t+1, returning step 3, carrying out next iteration；

Step 5, through t_maxSecondary iteration backed off after random circulates, and calculates codeword message:

$Q\left(x_j\right)=\underset{q\&Element;{\mathrm{\&zeta;}}_j}{\mathrm{\&Pi;}}{M}_{c_q\&RightArrow;u_j}\left(x_j\right);$

Step 6, calculate data bit Soft Inform ation

${\mathrm{LLR}}_j=\log \frac{P\left(b_j=1\right)}{P\left(b_j=0\right)}=\log \frac{\underset{b_j=1}{\mathrm{\&Sigma;}}Q\left(x_j\right)}{\underset{b_j=0}{\mathrm{\&Sigma;}}Q\left(x_j\right)};$

b_jData bit for jth user；

Step 7, data bit judgement (hard decision) $\widehat{U_j}=\left\{\begin{array}{cc}1& {\mathrm{LLR}}_j>0\\ 0& {\mathrm{LLR}}_j\&le;0\end{array}\right..$

The invention have the benefit that for resource node and user node message, the message updated is more uncorrelated, its reliability is more strong, a kind of SCMA ascending communication system multi-user test method based on serial strategy is proposed based on this thought present invention, in each iterative process, all nodes are grouped as the mode of a group according to each user node and all resource nodes of being connected with this user node, it is divided into J group, successively the message of the node in each group is updated.The present invention all make use of the node messages updated in each iterative process, can be effectively improved the utilization rate having updated node messages；In the less situation of iterations, BER performance of the present invention is much better than the BER performance of background technology method；In BER performance almost without when losing, the computation complexity of the present invention is far below the computation complexity of background technology method.

Accompanying drawing explanation

Fig. 1 is the SCMA ascending communication system model that background technology proposes；

Fig. 2 is the factor graph of SCMA up-link in background technology；

Fig. 3 is the factor graph of SCMA up-link in the present invention；

Fig. 4 is the BER performance comparison figure of the inventive method and background technology method；

Fig. 5 is the computation complexity comparison diagram of the inventive method and background technology method.

Detailed description of the invention

Below in conjunction with drawings and Examples in detail, technical scheme is described in detail.

Program according to transmission conditions and detection process, the following parameter of Initialize installation:

The number J=6 of user node, the code word number M=4 of code book, code word size K=4, system overload rateChannel model is AWGN (white Gaussian noise) channel, and sparse Spread Spectrum Matrix is $F=\left[\begin{array}{cccccc}0& 1& 1& 0& 1& 0\\ 1& 0& 1& 0& 0& 1\\ 0& 1& 0& 1& 0& 1\\ 1& 0& 0& 1& 1& 0\end{array}\right];$ User profile bit is mapped as corresponding code word x through SCMA encoder, is transmitted through channel, the reception signal of receiving terminal after all user's code word superpositionsx_j=(x_1,j,x_2,j,...,x_K,j)^ΤIt is the SCMA code word of user j, h_j=(h_1,j,h_2,j,...,h_K,j)^ΤFor the channel vector of user j, n～CN (0, σ²Ι) for Gaussian noise；Receive the signal y that the kth Energy Resources Service of signal y receives_kIt is expressed as:Wherein k=1,2 ..., K, j=1,2 ..., J.

The code book of each user of transmitting terminal is:

The code book of user 1 is $CB1=\left[\begin{array}{cccc}0& 0& 0& 0\\ -0.1815-0.1318i& -0.6351-0.4615i& 0.6351+0.4615i& 0.1815+0.1318i\\ 0& 0& 0& 0\\ 0.7851& -0.2243& 0.2243& -0.7851\end{array}\right],$ The code book of user 2 is $CB2=\left[\begin{array}{cccc}0.7851& -0.2243& 0.2243& -0.7851\\ 0& 0& 0& 0\\ -0.1815-0.1318i& -0.6351-0.4615i& 0.6351+0.4615i& 0.1815+0.1318i\\ 0& 0& 0& 0\end{array}\right]$ , the code book of user 3 is $CB3=\left[\begin{array}{cccc}-0.6351+0.4615i& 0.1815-0.1318i& -0.1815+0.1318i& 0.6351-0.4615i\\ 0.1392-0.1759i& 0.4873-0.6156i& -0.4873+0.6156i& -0.1392+0.1759i\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right]$ , the code book of user 4 is $CB4=\left[\begin{array}{cccc}0& 0& 0& 0\\ 0& 0& 0& 0\\ 0.7851& -0.2243& 0.2243& -0.7851\\ -0.0055-0.2242i& -0.0193-0.7848i& 0.0193+0.7848i& 0.0055+0.2242i\end{array}\right]$ , the code book of user 5 is $CB5=\left[\begin{array}{cccc}-0.0055-0.2242i& -0.0193-0.7848i& 0.0193+0.7848i& 0.0055+0.2242i\\ 0& 0& 0& 0\\ 0& 0& 0& 0\\ -0.6351+0.4615i& 0.1815-0.1318i& -0.1815+0.1318i& 0.6351-0.4615i\end{array}\right]$ , the code book of user 6 is $CB6=\left[\begin{array}{cccc}0& 0& 0& 0\\ 0.7851& -0.2243& 0.2243& -0.7851\\ 0.1392-0.1759i& 0.4873-0.6156i& -0.4873+0.6156i& -0.1392+0.1759i\\ 0& 0& 0& 0\end{array}\right]$

Fig. 3 is the present invention SCMA factor graph based on the SCMA ascending communication system multi-user test method of serial strategy, it is distinctive in that with background technology method factor graph: be divided into one group with each user node and all resource nodes of being connected with this user node, all resource nodes and user node can be divided into J group, be respectively labeled as γ₁,γ₂,...,γ_JGroup, in iterative process each time, updates γ successively₁,γ₂,...,γ_JAll nodes in group (i.e. each user node and all resource nodes of being connected with this user node).

Receiver place, based on the SCMA ascending communication system multi-user test method of serial strategy, comprises the following steps:

Step 1. iterative detection starts, it does not have the user message of priori, and therefore each user obtains the probability of arbitrary code word in corresponding code book is identical, then the information of user node is

Step 2. enters iterative cycles, referring to the Fig. 3 factor graph based on the MPA detection method of serial strategy, all of resource node and user node is divided into J group, and the sequence number that labelling is good each group is γ₁,γ₂,...,γ_J；

Step 3. updates first group of γ₁In all of resource node and user node；Then judging whether to have updated the node of all J groups, if having updated, performing step 4, otherwise, continue to update the node of next group；

Step 4. judges t > t_maxWhether setting up, if setting up, performing step 5；If being false, then making t=t+1, returning step 2, carrying out next iteration；

The resource node that step 5. exports according to iterationCalculate codeword message $Q\left(x_j\right)=\underset{q\&Element;{\mathrm{\&zeta;}}_j}{\mathrm{\&Pi;}}{M}_{c_q\&RightArrow;u_j}\left(x_j\right);$

The codeword message that step 6. obtains according to step 5, calculates the likelihood value of original data bits

${\mathrm{LLR}}_j=\log \frac{P\left(b_j=1\right)}{P\left(b_j=0\right)}=\log \frac{\underset{b_j=1}{\mathrm{\&Sigma;}}Q\left(x_j\right)}{\underset{b_j=0}{\mathrm{\&Sigma;}}Q\left(x_j\right)};$

The last hard decision original information bits of step 7., if LLR_j> 0, adjudicates data bitIf LLR_j≤ 0, adjudicate data bit

Utilizing Matlab that BER error performance in awgn channel of the parallel MPA method of background technology and the SCMA ascending communication system multi-user test method based on serial strategy of the embodiment of the present invention and computation complexity are carried out simulation comparison analysis, simulation result is as shown in Figure 4 and Figure 5.As shown in Figure 4, at E_b/N₀=12dB, the BER value of 2 iteration background technologies is 1.2 × 10^-3, and the BER value of the present invention is 2.5 × 10^-4, the BER performance of the present invention improves an order of magnitude；Secondly, in the inventive method the BER performance of 2 iteration close to the performance of 6 iteration of background technology method, it was shown that the inventive method can effectively reduce the complexity of decoding.Owing to the present invention is identical with the computation complexity of background technology an iteration, therefore analyze the computation complexity of 2 iteration of the present invention and the computation complexity of 6 iteration of background technology is significant.Fig. 5 is BER=1.2 × 10^-3When, namely when 2 iteration of the inventive method are identical with the detection performance of 6 iteration of background technology, the computation complexity of background technology method is 3 times of the inventive method, therefore, the present invention adopts 2 iterative process to achieve that the performance of 6 iteration of background technology, is substantially reduced the computation complexity of system.

Claims (2)

1. based on a SCMA ascending communication system multi-user test method for serial strategy, including initializing, resource node and the renewal of user node message, the calculating of data bit Soft Inform ation, data bit decision steps；It is characterized in that, the renewal of described resource node and user node message is that successive ignition completes, each time in iterative process, using a user node and all resource nodes of being connected with this user node thereof as one group, user node and resource node are divided into J group, J is the number of user node, then successively the message of the message of all of resource node in each group to user node and user node to resource node is updated, namely completes the process of an iteration.

2., based on a SCMA ascending communication system multi-user test method for serial strategy, comprise the following steps:

Step 1, initialization: when iteration starts, user does not have prior information, therefore user node u_jTo resource node c_kMessage be:J=1,2 ..., J, k=1,2 ..., K, u_jFor jth user node, c_kFor kth resource node, M is the number of codewords of code book；

Step 2, set maximum iteration time as t_max；

Step 3, in the t time iterative process, first using jth user node and all resource nodes of being connected with jth user node as one group, user node and resource node are divided into J group, j=1,2 ..., J, J group node is respectively labeled as γ₁,γ₂,...,γ_JGroup；Then, γ is calculated₁The all of resource node of group is to the message of user node $M_{c_k\&RightArrow;u_j}^t\left(x_j\right)=\underset{~x_j}{\mathrm{\&Sigma;}}\left\{\exp (-\frac{1}{2{\mathrm{\&sigma;}}^2}||y_k-\underset{i\&Element;{\mathrm{\&epsiv;}}_k}{\mathrm{\&Sigma;}}{h}_{k,i}{x}_{k,i}|{|}^2)\underset{l<j}{\underset{l\&Element;{\mathrm{\&epsiv;}}_k\backslash j}{\mathrm{\&Pi;}}}{M}_{u_l\&RightArrow;c_k}^t\left(x_l\right)\underset{l>j}{\underset{l\&Element;{\mathrm{\&epsiv;}}_k\backslash j}{\mathrm{\&Pi;}}}{M}_{u_l\&RightArrow;c_k}^{t-1}\left(x_l\right)\right\}$ Message with user node to resource nodeFinally calculate γ successively₂,...,γ_JThe resource node of group is to the message of user node and user node to the message of resource node, and an iteration completes；Wherein,For being connected to resource node c_kUser node collection, h_{K, i}∈h_i=(h_{1, i}, h_{2, i}..., h_{K, i})^T, h_iFor the channel vector of user i,For being connected to user node u_jSet of resource nodes；

Step 4, judge t > t_maxWhether setting up, if setting up, performing step 5；If being false, then making t=t+1, returning step 3, carrying out next iteration；

Step 5, through t_maxSecondary iteration backed off after random circulates, and calculates codeword message:

Step 6, calculate data bit Soft Inform ation:

${\mathrm{LLR}}_j=\log \frac{P(b_j=1)}{P(b_j=0)}=\log \frac{\underset{b_j=1}{\&Sigma;}Q\left(x_j\right)}{\underset{b_j=0}{\&Sigma;}Q\left(x_j\right)};$

b_jData bit for jth user；

Step 7, data bit judgement $\widehat{U_j}=\left\{\begin{array}{cc}1& {\mathrm{LLR}}_j>0\\ 0& {\mathrm{LLR}}_j\&le;0\end{array}\right..$