CN111082842A - Uplink SCMA transmitting method and receiving method based on codebook multiplexing - Google Patents

Abstract

The invention discloses an uplink SCMA transmitting method and an uplink SCMA receiving method based on codebook multiplexing. The uplink SCMA transmission method includes the steps of: a base station distributes codebooks for a plurality of users in a scheduling period, wherein the same codebook is distributed to a specific number of users; the user carries out SCMA codebook mapping according to the distributed codebook to obtain a code word; and the user sends the code words to the base station by using a sparse spread spectrum method. The invention can improve the system capacity on the premise of not designing a complex power distribution mode and not changing a resource distribution mode.

Description

Uplink SCMA transmission method and reception method based on codebook multiplexing

technical field

The invention relates to an uplink SCMA transmitting method based on codebook multiplexing, and also relates to a codebook multiplexing-based uplink SCMA receiving method, belonging to the technical field of wireless communication.

Background technique

The International Telecommunication Union (ITU) defines three scenarios for 5G: Enhanced Mobile Broadband (eMBB), Massive Machine Type Communication (mMTC), and Low Latency High Reliability Communication (URLLC), where eMBB can be regarded as a 4G mobile broadband technology evolution. In 5G, non-orthogonal multiple access technologies such as SCMA share resources by multiple users, thereby improving resource utilization.

SCMA (Sparse Code Multiple Access, multiple access) directly maps different bit streams to different sparse codewords. The SCMA system is mainly composed of four parts: SCMA coding, MPA (Message Passing Algorithm) detection, Turbo coding and decoding. Among them, the SCMA coding and MPA detection modules respectively realize the functions of non-orthogonal mapping of user information to time-frequency access physical resources and the functions of separating user information from time-frequency access resources, and are the core modules of the SCMA system. The turbo coding and decoding module is an auxiliary module to improve the separation performance of the core modules of the SCMA system, and it plays an important role in the realization of the performance of the overall system.

The multi-dimensional constellation diagram of SCMA is designed as a codebook, which brings about a "shaping gain" that cannot be achieved by LDS-CDMA. SCMA codebook design is a complex problem because different layers are multiplexed with different codebooks, and since suitable design criteria and specific solutions for multidimensional problems are still unknown, various solutions have been proposed in the prior art. However, these existing design methods do not allow multiple users to multiplex the same codebook in the uplink, so the number of access users depends on the number of codebooks. In the paper "Codebook Allocation Optimization in Sparse Code Multiple Access Systems" (published in "Signal Processing", Vol. 34, No. 2), Ma Xinying et al. introduced the following technical methods: One user commonly used in SCMA technology allocates one code This codebook can be dynamically allocated, but a codebook that is always saved can only be allocated to one user, and multiple users cannot share a codebook at the same time.

SUMMARY OF THE INVENTION

The primary technical problem to be solved by the present invention is to provide an uplink SCMA transmission method based on codebook multiplexing.

Another technical problem to be solved by the present invention is to provide an uplink SCMA receiving method based on codebook multiplexing.

In order to achieve the above object, the present invention adopts the following technical method:

According to a first aspect of the embodiments of the present invention, a method for transmitting uplink SCMA based on codebook multiplexing is provided, including the following steps:

The base station allocates codebooks to multiple users in one scheduling period, and a certain number of users allocate the same codebook;

The user performs SCMA codebook mapping according to the allocated codebook to obtain a codeword;

The user transmits the codeword to the base station using a sparse spread spectrum method.

Preferably, the codewords of the specific number of users using the same codebook are mapped to different resource units.

Preferably, in one scheduling period, the number of user codewords superimposed on a single resource unit is β×d _f , where d _f represents that when one codebook is only allocated to one user in one scheduling period, one resource The number of codewords of users using different codebooks that the unit is superimposed on.

According to a second aspect of the embodiments of the present invention, a method for receiving uplink SCMA based on codebook multiplexing is provided, including the following steps:

Calculate the initial prior probability of each codeword;

Calculate the conditional probability of the codeword of the user on each resource unit;

Based on the initial prior probability and the conditional probability, iterative message passing is performed between the resource node (FN) and the user node (VN) to obtain the codeword probability;

Based on the codeword probability, LLR calculation and bit estimation are performed to obtain a user bit stream,

Wherein, the codewords of the users on the respective resource units are the superposition of the codeword information of multiple users who use the same codebook.

Preferably, in one scheduling period, the number of user codewords superimposed on a single resource unit is β×d _f , where d _f represents that when one codebook is only allocated to one user in one scheduling period, one resource The number of codewords of users using different codebooks that the unit is superimposed on.

Preferably, the codewords of the specific number of users using the same codebook are mapped to different resource units according to the same mapping relationship.

Preferably, a double summation operation is used to sum the codewords of all users multiplexing the same codebook, and the sum of all codewords on a resource unit is obtained, and at the same time, the codewords using the same codebook are calculated. Codeword conditional probabilities for multiple users.

Preferably, the calculation of the codeword probability includes:

Update the codeword probability from resource node (FN) to user node (VN) for the first time;

The codeword probability updated in the previous step is input, and the codeword probability from the user node (VN) to the resource node (FN) is updated.

Preferably, the first update of the codeword probability from the resource node (FN) to the user node (VN) includes the following steps:

Calculate the possibility probability that the codeword of one user in the specific number of users using the same codebook is matched with the possible codewords of other users who use the same codebook on the resource unit;

The maximum value is selected from the probabilities of the possibilities as the codeword probability finally passed from the resource node (FN) to the user node (VN).

Preferably, the codeword probability of each user in the specific number of users using the same codebook is updated respectively.

Compared with the prior art, the present invention can improve the system capacity effect on the premise of not designing a complex power allocation mode and changing the resource allocation mode, allowing β users to reuse the same codebook, thereby increasing the number of users accessing the system. increased to the original beta times.

Description of drawings

1A is a schematic diagram of an uplink CB-reuse-SCMA system model when two users multiplex a codebook;

1B is a schematic diagram of an uplink CB-reuse-SCMA system model when three users multiplex one codebook;

Fig. 2 is a system factor diagram when 12 users share 4 subcarriers;

3 is a schematic diagram of the relationship between codebook multiplexing and resource mapping in the present invention;

4 is a logical block diagram of an uplink SCMA receiving method based on codebook multiplexing in the present invention;

Fig. 5 is the BER performance simulation effect comparison diagram of conventional SCMA and the present invention;

FIG. 6 is a comparison diagram of the throughput simulation effect of conventional SCMA and the present invention.

Detailed ways

The technical content of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

In order to solve the access problem of a large number of users in the 5G Internet of Things, the present invention proposes an uplink codebook multiplexing method without involving a complex power allocation mode and without changing the resource allocation mode, so that β Each user reuses the same codebook, so that the number of users accessing the system is increased by β times of the original. In this way, the number of simultaneous access users can be greatly increased.

Specifically, the present invention first provides a SCMA method (CB-reuse-SCMA) based on codebook multiplexing. Wherein, a base station (BS) allocates the same codebook to multiple users, and then the users perform uplink transmission according to the allocated codebook. Finally, the BS side decodes the uplink data based on the improved log-domain message passing algorithm (Log-MPA) algorithm to obtain the uplink data of all users.

In the embodiment of the present invention, the above-mentioned SCMA method can be divided into an uplink SCMA transmission method and an uplink SCMA reception method. Wherein, the uplink SCMA transmission method includes the following steps:

Step 1: The base station allocates codebooks to multiple users in one scheduling period, and a specific number of users allocate the same codebook

In this embodiment, it is assumed that there are J users, wherein β (β, J, both are natural numbers) users share (multiplex) a codebook.

As shown in FIG. 1A , when the number of subcarriers used is K=4, the codebook size is L=6 codebooks of M×K, and the codebook modulation order M=4. When the codebook multiplexing number β=2, two users multiplex one codebook, and the user UE1 and the user UE2 multiplex codebook 1 in the figure. After passing through the SCMA encoder, the codewords S ¹ ₁ and S ² ₁ are output. The upper index refers to the users who reuse the same codebook, and the lower index refers to the codebook.

As shown in Fig. 1B, when β=3, it means that three users multiplex one codebook. The base station assigns the same codebook to the β users that need to send data, that is, assigns codebook 1 to user 1, user 2, and user 3 in the figure, so that β=3 users multiplex codebook 1, and these 3 users After passing through the SCMA encoder, the data stream will output the code words S ¹ ₁ , S ² ₁ , S ³ ₁ .

In SCMA, every four subcarriers and each subframe in the time domain form a subcarrier group, and the length of each subframe is denoted as a scheduling period. In a scheduling period, when the base station allocates codebooks, it may allocate L (number of codebooks) users J ₁ , J ₂ ...... J _L to different codebooks 1, 2 ...... Users J _L+1 , J _L+2 ,...J _2L are allocated to codebook 1, codebook 2...codebook L, and so on, until codebooks are allocated to all users. For example, user 1 assigns codebook 1; user 2 assigns codebook 2...User 6 assigns codebook 6; user 7 assigns codebook 1; user 8 assigns codebook 2...user 12 assigns codebook 6.

In a scheduling period, when the base station allocates codebooks, it can also allocate codebook 1 to the first β (number of codebook multiplexing) users, and then allocate codebook 2 to β+1 to 2β users, so as to And so on until the codebook is assigned to all users. As shown in Fig. 1A, user 1 and user 2 are assigned codebook 1; user 3 and user 4 are assigned codebook 2... User 11 and user 12 are assigned codebook 6; as shown in Fig. 1B, user 1, user 2, and user 3 are assigned Codebook 1; User 4, User 5, User 6 allocate Codebook 2... User 16, User 17, User 18 allocate Codebook 6.

Step 2: The user terminal UE performs SCMA codebook mapping according to the allocated codebook to obtain a codeword

The UE uses the SCMA encoder to map the user's data to the M*K*L-dimensional codebook and outputs the codeword S _l , where M is the modulation order of the user data, that is, a codebook has M kinds of codewords; K refers to the number of resources (Resource, in this embodiment, the number of subcarriers is used as an example, but it is not limited to this, and can be any time-frequency resource unit RE); L is the number of codebooks, and S1 is the codeword output after mapping using the _lth codebook , the size is K × 1. 1A and 2, both user 1 and user 2 of multiplexing codebook 1 should be spread to subcarrier 1 and subcarrier 3 (the first column of the mapping matrix in A specific number of β users are all mapped to sub-carrier 1 and sub-carrier 3, that is, the sub-carrier corresponding to the value 1 in the first column).

1B and FIG. 3, the data of user 1, user 2 and user 3 of the multiplexing codebook 1 are spread to the subcarriers corresponding to the lth column in the resource mapping matrix (that is, the resource mapping in FIG. 2). cell with a 1 in the lth column of the matrix). The data of these three users have completed high-dimensional modulation and sparse spread spectrum after passing through the SCMA encoder. It can be seen that β users in the present invention (β=3 in FIG. 1B and FIG. 3 ) multiplex the same codebook (in the prior art transmitter, one user uses one codebook; in the present invention, β of the transmitter The user multiplexes a codebook), in fact, the β users multiplex the resource mapping relationship corresponding to the codebook, that is, the codebook corresponds to the lth column in the resource mapping matrix, so the data of the β users is spread to the same resource.

这β个码字维度一致，调制符号可能不同，但是资源映射关系相同。比如，图1B和图2所示β＝3时，假如用户1、2、3复用码本1，则这三个用户复用了资源映射矩阵中的第一列，也就是这三个用户的数据都被扩频到了第1个和第3个子载波上。而现有的SCMA方法中一个码本上的单个子载波上只扩频了一个用户的数据流。The β users select different codewords according to the transmitted data, and output the codewords respectively

The dimensions of the β codewords are the same, and the modulation symbols may be different, but the resource mapping relationship is the same. For example, when β=3 as shown in Figure 1B and Figure 2, if users 1, 2, and 3 multiplex codebook 1, then these three users multiplex the first column in the resource mapping matrix, that is, the three users The data are spread to the 1st and 3rd subcarriers. However, in the existing SCMA method, only the data stream of one user is spread on a single subcarrier on a codebook.

Step 3: The user sends the codeword to the base station using the orthogonal subcarriers

发送给基站,τ＝1,…,β。The τth UE using the lth codebook uses K orthogonal subcarriers to convert the codeword

Sent to the base station, τ=1,...,β.

Assume that in the uplink multi-user SCMA communication system, a base station serves J users with the same priority, and the J users share K orthogonal time-frequency resources (OFDM subcarriers). The SCMA communication system has L codebooks, each A user is allocated a codebook of size M, one codebook is allocated to β users, and J user data streams are mapped to the same base station after being mapped by the codebook, and the overload factor is defined as λ=J/K.

When K=4 subcarriers are used, the existing SCMA method is β=1, J0 ₌ 6, K=4, L=6, λ=150%. In the present invention, J=β×J ₀ , K=4, L=6, λ=J/K=β×150%. When β=2, J=12, K=4, L=6, λ=300% uplink CB-reuse-SCMA system model is shown in Figure 1A; when β=3, J=18, K=4 , L=6, λ=450% uplink CB-reuse-SCMA system model is shown in Figure 1B.

和

分别表示的是使用第6个码本的第2个用户的码字和信道相关系数，其他含义类似。在用户终端UE发送侧，SCMA编码器将用户log₂(M)bit的数据映射到一个大小为M的K维码本并输出码字

其中，K维码字是具有N(N<K)个非零单元的稀疏向量，即N个特定的子载波，N的选择取决于码本的资源映射矩阵。同时，如图3所示，单个子载波上叠加β×d_f个用户的码字(现有技术中，单个子载波上叠加1×d_f个码字，d_f表示一个码本在一个调度周期内只分配给一个用户时，一个资源单元(正交子载波)上叠加的使用不同码本的用户的码字数量)。本发明采用在一个调度周期内给特定数量(例如图1A中特定数量β＝2，图1B中特定数量β＝3)的用户分配同一个码本，使得单个资源单元上叠加的用户码字数量变为β×d_f，是现有技术的β倍，即图3中资源单元1上承载的使用同一个码本1的UE1、UE2、UE3的码字数量，使用同一个码本3的UE7、UE8、UE9的码字数量以及使用同一个码本5的UE13、UE14、UE15的码字数量的叠加。The following takes the uplink CB-reuse-SCMA system with β=2 (indicating that every two users use the same codebook) as an example for introduction. As shown in FIG. 1A , a plurality of user terminals UE (12 in FIG. 1A ) pass through codebook 1 , codebook 2 . . . codebook 6 . In Figure 1,

and

Respectively represent the codeword and channel correlation coefficient of the second user using the sixth codebook, and other meanings are similar. On the sending side of the user terminal UE, the SCMA encoder maps the user log ₂ (M)bit data to a K-dimensional codebook of size M and outputs the codeword

The K-dimensional codeword is a sparse vector with N (N<K) non-zero units, that is, N specific subcarriers, and the selection of N depends on the resource mapping matrix of the codebook. At the same time, as shown in Fig. 3 , codewords of β×d _f users are superimposed on a single subcarrier (in the prior art, 1×d _f codewords are superimposed on a single subcarrier, and d _f indicates that one codebook is used in a scheduler When only one user is allocated in a period, the number of codewords of users using different codebooks superimposed on one resource element (orthogonal subcarriers). The present invention allocates the same codebook to a specific number of users (for example, a specific number β=2 in FIG. 1A and a specific number β=3 in FIG. 1B ) in one scheduling period, so that the number of user codewords superimposed on a single resource unit is It becomes β×d _f , which is β times of the prior art, that is, the number of codewords of UE1, UE2, and UE3 using the same codebook 1 carried on resource unit 1 in FIG. 3, and the number of UE7 using the same codebook 3 , the number of codewords of UE8 and UE9, and the number of codewords of UE13, UE14, and UE15 using the same codebook 5.

When β=1, it means that in the prior art, there is only one user who uses the same codebook in one scheduling period, and then there are only 1 users who use codebook 1, codebook 3, and codebook 5 carried on resource unit 1. For example, UE1, UE7, and UE13 (for the convenience of understanding, the users carried on resource 1 in Figure 3 do not have UE2, UE3, UE8, UE9, UE14, and UE15, and only UE1, UE7, and UE13 are left. At this time, a single subcarrier The superimposed 1×d _f codewords is the sum of the codewords of UE1, UE7, and UE13).

The codebook itself adopted in the present invention adopts conventional design, for example, M.Taherzadeh, H.Nikopour, A.Bayesteh and H.Baligh, "SCMA Codebook Design," 2014IEEE 80th VehicularTechnology Conferenc (VTC2014-Fall), Vancouver, BC, 2014 , the codebook mentioned in pp.1-5. Based on the SCMA method, the codebook composed of subcarriers is the basic resource unit of the network.

为用户的码字信息，

为用户的信道信息。In Figure 1A,

is the codeword information of the user,

is the channel information of the user.

和用户2的码字

均被映射到第1个和第3个子载波上(如图2，SCMA中每个用户的码字需要被映射到不同的两个子载波上)。图2中K＝4，J＝12，即12个用户被扩频到4个子载波。即，复用同一码本的多个用户的码字按照相同的映射关系被映射到不同资源单元。Assuming that all users are time-synchronized, each user modulates the user data according to the assigned codebook and uses the SCMA encoder to perform sparse spreading according to the resource mapping matrix, and then the codewords of the J users are spread to K orthogonal subsections. On the carrier, the resource mapping matrix and the resource mapping relationship of the present invention when β=2 is shown in Fig. 2 . The resource mapping relationship in the figure includes two different types of nodes: K resource nodes FN; J user nodes VN, the connection line represents the bearing relationship between user data and resources, where VN1 ¹ and VN1 ² , VN2 ¹ and VN2 ² .. .VN6 ¹ and VN6 ² are user pairs that multiplex the same codebook, and they multiplex the same column of the resource mapping matrix, that is, multiplex the resource mapping relationship of the same codebook. For example, VN1 ¹ and VN1 ² are user 1 and user 2 that multiplex the first codebook, and the codeword of user 1

and the codeword of user 2

Both are mapped to the first and third subcarriers (as shown in Figure 2, the codeword of each user in SCMA needs to be mapped to two different subcarriers). In Fig. 2, K=4, J=12, that is, 12 users are spread to 4 subcarriers. That is, codewords of multiple users multiplexing the same codebook are mapped to different resource elements according to the same mapping relationship.

The following describes the uplink SCMA receiving method provided by the present invention with reference to FIG. 4 .

The signal sent by the uplink SCMA transmission method provided by the present invention is received at the base station, and the received signal can be expressed as:

和

分别表示复用第l个码本的两个用户在K个子载波上的码字信息，

和

分别表示复用第l个码本的两个用户的K个子载波的信道相关系数。n是均值为0，方差为σ²的高斯白噪声，即：n～CN(0，σ²I)。in

and

respectively represent the codeword information of the two users multiplexing the lth codebook on K subcarriers,

and

respectively represent the channel correlation coefficients of the K subcarriers of the two users multiplexing the lth codebook. n is Gaussian white noise with a mean value of 0 and a variance of σ ² , namely: n～CN(0,σ ² I).

The received signal on the kth carrier is:

为有效承载，即与子载波k连接的码本l的集合，且连接总数为β×d_f，n_k表示第k个子载波上的噪声，

表示第k个子载波上所有的码字的叠加运算。式2表明，基站在第k个载波上接收到了复用(共用)码本的多个用户的码字信息

和

的叠加，需要采用本发明所提供的上行链路SCMA接收方法进行译码。in,

is an effective bearer, that is, a set of codebooks l connected to subcarrier k, and the total number of connections is β×d _f , n _k represents the noise on the kth subcarrier,

Represents the superposition operation of all codewords on the kth subcarrier. Equation 2 shows that the base station receives the codeword information of multiple users of the multiplexed (shared) codebook on the kth carrier

and

The superposition needs to be decoded using the uplink SCMA receiving method provided by the present invention.

In the uplink SCMA system, MPA (Message Passing Algorithm) is usually used for multi-user decoding. MPA is a near-optimal iterative detection algorithm that models the receiver based on a bipartite factor graph. Different from the traditional decoding algorithm, MPA determines the user codeword by iteratively detecting the probability of the user codeword. The process of MPA detection can be explained with Figure 4.

As shown in Figure 4, the MPA decoder first calculates the conditional probability according to the received signal and the estimated correlation channel coefficient and noise power value; then the conditional probability and the codeword prior probability are input as external information for internal iterative message transmission; By iteratively transferring the codeword probability information between the FN node and the VN node, after reaching the maximum number of iterations, the maximum probability information of the codeword is output as soft information; finally, the LLR hard decision is performed to obtain the user codeword information.

The base station receives the signal sent by the user terminal and passes through the SCMA encoder, and uses the decoder to decode using the improved Log-MPA algorithm, including:

Step 21: Calculate the initial prior probability for each codeword

表示使用第l个码本的第τ个用户的码字

在第t次迭代从FN节点k到VN节点l∈N(k)的外部信息，用

表示使用第l个码本的第τ个用户的码字

在第t次迭代从VN节点l到FN节点k∈R(l)的外部信息。其中，τ＝{1,2,...,β}，

是与子载波k连接的VN节点l的集合，连接总数为β×d_f，

表示VN节点l有效承载的子载波，且子载波数为N＝2。因为各码字有M种可能性，所以

Assuming that the BS has perfect channel state information, here VN node 1 is used to represent the lth codebook, that is, VN node 1 contains β users of multiplexing codebook 1, as shown in the resource mapping relationship in Figure 2, VN node 1 includes VN1 ¹ and VN1 ² . use

represents the codeword of the τth user using the lth codebook

Extrinsic information from FN node k to VN node l∈N(k) at iteration t, with

represents the codeword of the τth user using the lth codebook

Extrinsic information from VN node l to FN node k ∈ R(l) at iteration t. where τ={1,2,...,β},

is the set of VN nodes l connected to subcarrier k, and the total number of connections is β×d _f ,

Indicates the subcarriers effectively carried by the VN node 1, and the number of subcarriers is N=2. Because each codeword has M possibilities, so

码字的概率一样，所以每个用户的每个码字的先验概率为：because send

The probability of the codeword is the same, so the prior probability of each codeword for each user is:

Step 22: Calculate the conditional probability of the codeword of the user on each resource element (subcarrier)

The conditional probability of the codeword of the user on the FN node k is:

运算，而本系统β个用户复用码本所以同一子载波上叠加了β×d_f个用户的码字，因此在现有Log-MPA算法的基础上要同时计算复用的用户码字条件概率，即

运算，先对复用同一码本的所有用户的码字求和，再求得有效承载中第k个子载波上所有码字求和。现有技术没有求和

这一步，因为现有技术中一个码本只是分配给一个用户使用，所以不需要。但是，本发明中因为同一个码本复用了β个用户，所以需要累加运算，把这β个用户的码字的概率也计算进去。The meaning of conditional probability is to estimate the probability of M possibilities of each codeword by judging the difference between each codeword and the received signal. The codewords of d _f users are superimposed on the same subcarrier of the exclusive codebook in the existing SCMA, that is,

However, in this system, the codebooks of β users are multiplexed, so the codewords of β×d _f users are superimposed on the same subcarrier. Therefore, on the basis of the existing Log-MPA algorithm, the conditions of the multiplexed user codewords should be calculated at the same time. probability, that is

Operation, first sum up the codewords of all users who multiplex the same codebook, and then obtain the summation of all the codewords on the kth subcarrier in the effective bearer. Existing technology does not sum up

This step is not required because a codebook is only allocated to one user in the prior art. However, in the present invention, since β users are multiplexed in the same codebook, an accumulation operation is required, and the probability of the codewords of these β users is also calculated.

Step 23: Iterative message passing between FN and VN

作为外部信息在FN和VN之间进行迭代消息传递，包括以下步骤：put f _k and

Iterative message passing between FN and VN as external information consists of the following steps:

Step a: Update the codeword probability from FN to VN for the first time.

为码字概率，第二次之后用步骤b中更新的概率为码字概率。When updating the codeword probability from FN to VN for the first time, iteratively uses the initialized

is the codeword probability, and the probability updated in step b after the second time is the codeword probability.

in,

和

两部分。The difference between formula (5) and the existing calculation formula is that the codeword probability of the multiplexed codebook user is introduced, that is: in formula (6)

and

two parts.

表示的是和τ用户一起复用码本l的另外β-1个用户上一次迭代最终计算出的码字概率的累加。Formula (6) is to calculate the probability of (β×d _f -1)×M×1 possibilities generated after the codeword of user τ is matched with the possible codewords of other users on the subcarrier.

It represents the accumulation of the codeword probabilities finally calculated by the last iteration of the other β-1 users who multiplex the codebook l together with the τ user.

The formula (7) is used to select the maximum value from the probabilities of (β×d _f -1)×M×1 possibilities as the codeword probability message finally transmitted from FN to VN.

Step b: The codeword probability updated in the previous step is input, and the codeword probability from VN to FN is updated.

Here, the prior art only updates the codeword probability of one user 1 for one VN node 1. The codebook of the present invention multiplexes β users, and all the codeword probabilities of β users need to be updated at the same time, that is, τ is 1 and 2 respectively. The codeword probability of the user when ... β.

Step 24: Perform LLR calculation and bit estimation:

的后验概率为：numbers

The posterior probability of is:

Then, the binary log-likelihood ratio (LLR) of log ₂ (M)bit is determined as:

为：Then, the bit value for each user is estimated by comparing the LLR with 0, estimating

for:

in,

To verify the performance of the proposed algorithm, this section compares the bit error rate and throughput performance of SCMA and CB-reuse-SCMA systems in AWGN channel uplink scenarios through simulation results.

In the SCMA system, 6 users share 4 subcarriers, that is, J=6, K=4; in the CB-reuse-SCMA system, J=12, K=4, that is, the number of users is doubled. In addition, the two systems use the same codebook, and the simulation parameters are set as shown in the table below.

parameter Numerical value Number of symbols N 500000 Number of users J 12 MPA Iterations Nit 10 Codebook number L 6

Figure 5 is a comparison chart of the BER performance of SCMA and CB-reuse-SCMA, which verifies the BER performance of the two algorithms under different SNR conditions. It can be seen from the figure that the BER performance of CB-reuse-SCMA is about 3dB lower than that of SCMA. This is because the multiplexing of the same codebook by CB-reuse-SCMA results in interference between users of multiplexed codebooks, but with With the increase of SNR, the BER performance of CB-reuse-SCMA gradually approaches SCMA.

Figure 6 is a comparison chart of the throughput of SCMA and CB-reuse-SCMA systems, which verifies the system throughput of SCMA and CB-reuse-SCMA under different SNR conditions. It can be seen from the figure that with the improvement of SNR, the throughput of the two algorithms gradually converges. SCMA converges after 6dB, while CB-reuse-SCMA converges after 10dB. The throughput of CB-reuse-SCMA is twice that of SCMA, that is, the system throughput is doubled, and the number of user connections is doubled. It can be seen that the use of the codebook multiplexing SCMA technical method provided by the present invention achieves a significant increase in system capacity, and can even be increased by 2 times.

Compared with the prior art, the present invention can improve the system capacity effect on the premise of not designing a complex power allocation mode and changing the resource allocation mode, allowing β users to reuse the same codebook, thereby increasing the number of users accessing the system. increased to the original beta times.

The codebook multiplexing-based uplink SCMA transmitting method and receiving method provided by the present invention have been described in detail above. For those skilled in the art, any obvious changes made to it without departing from the essential content of the present invention will fall within the protection scope of the patent right of the present invention.

Claims (10)

1. an uplink SCMA transmission method based on codebook multiplexing is characterized in that comprising the following steps: The base station allocates codebooks to multiple users in one scheduling period, and a certain number of users allocate the same codebook; The user performs SCMA codebook mapping according to the allocated codebook to obtain a codeword; The user transmits the codeword to the base station using a sparse spread spectrum method. 2. uplink SCMA transmission method as claimed in claim 1, is characterized in that: For the specific number of users using the same codebook, their codewords are mapped to different resource units according to the same mapping relationship. 3. uplink SCMA transmission method as claimed in claim 2, is characterized in that: In one scheduling period, the number of user codewords superimposed on a single resource unit is β×d _f , where d _f indicates that when one codebook is only allocated to one user in one scheduling period, the superimposed use of one resource unit is different The number of codewords for the user of the codebook. 4. An uplink SCMA receiving method based on codebook multiplexing is characterized in that comprising the following steps: Calculate the initial prior probability of each codeword; Calculate the conditional probability of the codeword of the user on each resource unit; Based on the initial prior probability and the conditional probability, iterative message transmission is performed between the resource node and the user node to obtain the codeword probability; Based on the codeword probability, LLR calculation and bit estimation are performed to obtain a user bit stream, Wherein, the codewords of the users on the respective resource units are the superposition of the codeword information of multiple users who use the same codebook. 5. The uplink SCMA receiving method as claimed in claim 4, wherein: In one scheduling period, the number of user codewords superimposed on a single resource unit is β×d _f , where d _f indicates that when one codebook is only allocated to one user in one scheduling period, the superimposed use of one resource unit is different The number of codewords for the user of the codebook. 6. The uplink SCMA receiving method as claimed in claim 5, wherein: For the specific number of users using the same codebook, their codewords are mapped to different resource units according to the same mapping relationship. 7. The uplink SCMA receiving method as claimed in claim 5, wherein: Using a double summation operation, sum the codewords of all users who multiplex the same codebook, and obtain the sum of all codewords on a resource unit, and simultaneously calculate the codewords of the multiple users who use the same codebook Word conditional probability. 8. The uplink SCMA receiving method according to claim 7, wherein the calculation of the codeword probability comprises: Update the codeword probability from resource node to user node for the first time; The codeword probability updated in the previous step is input, and the codeword probability from the user node to the resource node is updated. 9. The uplink SCMA receiving method as claimed in claim 8, wherein: The first update of the codeword probability from the resource node to the user node includes the following steps: Calculate the possibility probability that the codeword of one user in the specific number of users using the same codebook is matched with the possible codewords of other users who use the same codebook on the resource unit; The maximum value is selected from the probabilities of the possibilities as the codeword probability finally passed from the resource node to the user node. 10. The uplink SCMA receiving method as claimed in claim 8, wherein: The codeword probability for each of the specified number of users using the same codebook is updated separately.

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