CN111082842A

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

Info

Publication number: CN111082842A
Application number: CN201911369012.0A
Authority: CN
Inventors: 杜军均; 易辉跃; 许晖; 张武雄; 裴俊
Original assignee: Shanghai Research Center for Wireless Communications
Current assignee: Shanghai Research Center for Wireless Communications
Priority date: 2019-12-26
Filing date: 2019-12-26
Publication date: 2020-04-28

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 transmitting method and receiving method based on codebook multiplexing

Technical Field

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

Background

The International Telecommunications Union (ITU) defines three 5G scenarios: enhanced mobile broadband (eMBB), which may be considered an evolution of 4G mobile broadband technology, large-scale machine type communication (mtc), and low-latency high-reliability communication (URLLC). In 5G, non-orthogonal multiple access techniques such as SCMA share resources across multiple users, thereby increasing resource utilization.

SCMA (Sparse Code Multiple Access) directly maps different bit streams to different Sparse codewords. The SCMA system is mainly composed of four parts of SCMA coding, MPA (message passing algorithm) detection, Turbo coding and decoding. The SCMA coding and MPA detection modules respectively realize the non-orthogonal mapping of user information to time-frequency access physical resources and the function of separating the user information from the time-frequency access resources, and are core modules of an SCMA system. The Turbo coding and decoding module is an auxiliary module for improving the separation performance of the SCMA system core module, and plays an important role in realizing the performance of the overall system.

The SCMA multidimensional constellation is designed as a codebook, resulting in a "shaping gain" that LDS-CDMA cannot achieve. SCMA codebook design is a complex problem because different layers are multiplexed with different codebooks and various solutions have been proposed in the prior art since the appropriate design criteria and specific solutions to the multidimensional problem remain unknown. However, in none of these conventional design methods, the same codebook is multiplexed by a plurality of users in the uplink, and therefore the number of users to access depends on the number of codebooks. In the paper "codebook allocation optimization in sparse code multiple access system" (published in "signal processing" vol 34, 2), the maxingyang et al introduced the following technical approaches: one user commonly used in the SCMA technology is allocated with one codebook, and the codebook can be dynamically allocated, but one codebook is always stored and can only be allocated to one user for use, and a plurality of users cannot share one codebook at the same time.

Disclosure of Invention

The invention provides an uplink SCMA transmitting 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 purpose, the invention adopts the following technical method:

according to a first aspect of embodiments of the present invention, there is provided an uplink SCMA transmission method based on codebook multiplexing, including 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 word to the base station by using a sparse spread spectrum method.

Wherein preferably, the specific number of users using the same codebook have codewords mapped to different resource units.

Preferably, the number of user code words superimposed on a single resource unit in one scheduling period is β × d_fWherein d is_fThe number of code words of users using different codebooks superimposed by one resource unit is shown when one codebook is only allocated to one user in one scheduling period.

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

calculating an initial prior probability of each codeword;

calculating the conditional probability of the code words of the users on each resource unit;

performing iterative message transfer between a resource node (FN) and a user node (VN) based on the initial prior probability and the conditional probability to obtain a codeword probability;

performing LLR calculation and bit estimation based on the codeword probability to obtain a user bit stream,

and the code word of the user on each resource unit is the superposition of the code word information of a plurality of users using the same codebook.

Preferably, the number of user code words superimposed on a single resource unit in one scheduling period is β × d_fWherein d is_fIndicating the use of a superposition of resource units using different codebooks when one codebook is allocated to only one user in one scheduling periodThe number of codewords for a user.

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

Preferably, the code words of all users multiplexing the same codebook are summed by using a dual summation operation, the sum of all code words on one resource unit is obtained, and the code word conditional probability of a plurality of users using the same codebook is calculated at the same time.

Preferably, the calculating of the codeword probability comprises:

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

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

Wherein preferably said first updating of the codeword probability from the resource node (FN) to the user node (VN) comprises the steps of:

calculating probability generated after the code word of one user in the specific number of users using the same codebook is matched with the possible code words of other users using the same codebook on the resource unit;

selecting the maximum value from the probabilities of the possibilities as the probability of the codeword ultimately delivered by the resource node (FN) to the user node (VN).

Wherein preferably the codeword probability for each of said certain number of users using the same codebook is updated separately.

Compared with the prior art, the invention can improve the system capacity effect on the premise of not designing a complex power distribution mode and not changing a resource distribution mode, so that β users multiplex the same codebook, and the user access quantity of the system is increased to β times of the original quantity.

Drawings

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

FIG. 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 graph when 4 subcarriers are shared by 12 users;

FIG. 3 is a diagram illustrating the codebook multiplexing and resource mapping relationship in the present invention;

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

FIG. 5 is a graph comparing the results of BER performance simulations of a conventional SCMA and the present invention;

figure 6 is a graph comparing the throughput simulation effect of a conventional SCMA and the present invention.

Detailed Description

The technical contents of the present invention will be further described in detail 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 invention provides an uplink codebook multiplexing method on the premise of not relating to a complex power distribution mode and not changing a resource distribution mode, so that β users multiplex the same codebook, and the user access quantity of the system is increased to β times of the original quantity.

Specifically, the present invention first provides a codebook multiplexing-based SCMA method (CB-reuse-SCMA). A Base Station (BS) allocates the same codebook to a plurality of users, and then the users perform uplink transmission according to the allocated codebook. And finally, the BS side decodes the uplink data based on a Log-MPA algorithm to obtain the uplink data of all the users.

In an embodiment of the present invention, the SCMA method described above may be divided into an uplink SCMA transmission method and an uplink SCMA reception method. The uplink SCMA transmitting method comprises the following steps:

step 1: the 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

In this embodiment, J users are assumed, and β (β, J, both natural numbers) share (multiplex) one codebook.

As shown in fig. 1A, when the number of adopted subcarriers K is 4, L of codebook size M × K is 6 codebooks, and the codebook modulation order M is 4, when the number of codebook multiplexes β is 2, two users multiplex one codebook, in the figure, user UE1 and user UE2 multiplex codebook 1, and output codeword S after passing through the SCMA encoder¹ ₁And S² ₁. The upper corner indicates users multiplexing the same codebook, and the lower corner indicates the codebook.

As shown in fig. 1B, when β is 3, it indicates that three users multiplex one codebook, the base station allocates β users that need to transmit data to the same codebook, i.e., allocates codebook 1 to user 1, user 2, and user 3 in the figure, so that β is 3 users multiplex codebook 1, and the data stream of the 3 users passes through the SCMA encoder and then outputs codeword S¹ ₁、S² ₁、S³ ₁。

In the SCMA, every four subcarriers and every subframe in the time domain form a subcarrier group, and the length of each subframe is recorded as a scheduling period. In one scheduling period, when the base station allocates the codebook, L (number of codebooks) of users J may be used₁，J₂……J_LSequentially allocated to

different codebooks

1,2 … …, codebook L, and then user J_L+1,J_L+2,……J_2LCodebook 1, codebook 2 … …, codebook L, and so on, until all users are assigned codebooks. For example, user 1 allocates codebook 1; user 2 allocation codebook 2 … … user 6 allocation codebook 6; user 7 allocates codebook 1; user 8 allocation codebook 2 … … user 12 allocates codebook 6.

In a scheduling period, when a base station allocates codebooks, the codebook 1 may be allocated to the first β (number of codebook multiplexes) users, then the codebook 2 is allocated to β +1 to 2 β users, and so on, until all users are allocated codebooks, for example, in fig. 1A, the codebook 1 is allocated to the user 1 and the user 2, the codebook 2 is allocated to the user 3 and the user 4 2 … …, the codebook 6 is allocated to the user 12, for example, in fig. 1B, the codebook 1 is allocated to the user 1, the user 2 and the user 3, and the codebook 2 … … is allocated to the user 4, the user 5 and the user 6, the codebook 16, the user 17 and the user 18 are allocated to the codebook 6.

Step 2: user terminal UE carries out SCMA codebook mapping according to the distributed codebook to obtain a codeword

UE utilizes SCMA encoder to map user data to M K L dimension codebook and output code word S_lM is the modulation order of user data, namely, one codebook has M kinds of code words; k refers to the number of resources (resources, in this embodiment, the number of subcarriers is taken as an example, but not limited thereto, and may be any time-frequency resource unit RE); l is the number of codebooks, S_lIs the codeword output after mapping using the ith codebook, and has a size K × 1. in conjunction with fig. 1A and 2, user 1 and user 2, both multiplexing codebook 1, should be spread onto subcarrier 1 and subcarrier 3 (the mapping matrix 1 in fig. 2 indicates that a specific number β of users using codebook 1 are mapped onto subcarrier 1 and subcarrier 3, i.e. the subcarrier corresponding to the value 1 in column 1).

Referring to fig. 1B and 3, the data of user 1, user 2 and user 3 multiplexing codebook 1 is spread to the subcarrier corresponding to the l-th column in the resource mapping matrix (i.e. the unit of 1 in the l-th column of the resource mapping matrix in fig. 2), the data of these 3 users has already completed high-dimensional modulation and sparse spreading after passing through the SCMA encoder, it can be seen that β users (β ═ 3 in fig. 1B and 3) of the present invention multiplex the same codebook (in the transmitting end of the prior art, one user uses one codebook; in the present invention, β users of the transmitting end multiplex one codebook), actually, these β users multiplex the resource mapping relationship corresponding to the codebook, that is, the codebook corresponds to the l-th column in the resource mapping matrix, so the data of these β users is spread to the same resource.

The β users select different code words according to the transmitted data, and output the code words respectively

For example, when β ═ 3 shown in fig. 1B and fig. 2, suppose that

users

1,2, and 3 multiplex codesIn this embodiment 1, the three users multiplex the first column in the resource mapping matrix, that is, the data of the three users are spread to the 1 st and 3 rd subcarriers. In the existing SCMA method, only one user's data stream is spread on a single subcarrier on one codebook.

And step 3: user sends code word to base station by using orthogonal sub-carrier

Tth UE using the l codebook uses K orthogonal subcarriers to encode a codeword

And transmitting the signals to a base station, wherein tau is 1, … and β.

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

When K-4 subcarriers are used, the existing SCMA method is β -1, J ₀6, K-4, L-6, λ -150%, J- β × J in the present invention₀The uplink CB-reuse-SCMA system model with K4, L6, λ J/K β × 150%, when β is 2, J12, K4, L6, λ 300% is shown in fig. 1A, and when β is 3, J18, K4, L6, λ 450% is shown in fig. 1B.

An uplink CB-reuse-SCMA system with β ═ 2 (indicating that the same codebook is used for every two users) will be described as an example, as shown in fig. 1A, a plurality of user terminals UE (12 in fig. 1A) are codebook 6 through codebook 1 and codebook 2 … …, in fig. 1,

and

respectively representing the code word and the channel correlation coefficient of the 2 nd user using the 6 th codebook, and othersThe meaning is similar. At the sending side of the user terminal UE, the SCMA encoder sends the user log₂Mapping (M) bit data to a K-dimensional codebook of size M and outputting a codeword

Wherein the K-dimensional codeword is of N (N)<K) The choice of the sparse vectors of non-zero elements, i.e. N specific subcarriers, depends on the resource mapping matrix of the codebook, while, as shown in fig. 3, β × d are superimposed on a single subcarrier_fCodewords for individual users (in the prior art, 1 × d is superimposed on a single subcarrier)_fIndividual code word, d_fIndicating the number of codewords of users using different codebooks superimposed on one resource unit (orthogonal subcarriers) when one codebook is allocated to only one user in one scheduling period), the present invention allocates the same codebook to a specific number of users (e.g. specific number β ═ 2 in fig. 1A, and specific number β ═ 3 in fig. 1B) in one scheduling period, so that the number of codewords of users superimposed on a single resource unit becomes β × d_fβ times of the prior art, that is, the number of codewords of UE1, UE2 and UE3 using the same codebook 1, the number of codewords of UE7, UE8 and UE9 using the same codebook 3 and the number of codewords of UE13, UE14 and UE15 using the same codebook 5, which are carried on the resource unit 1 in fig. 3, are superimposed.

β is 1, that is, it means the prior art, only one user using the same codebook in one scheduling period, then there are only 1

users using codebooks

1, 3 and 5, such as UE1, UE7 and UE13 (for easy understanding, the user using codebook 1 in fig. 3 has no UE2, UE3, UE8, UE9, UE14 and UE 35 15, and only UE1, UE7 and UE13 remain, and at this time, 1 xd is superimposed on a single subcarrier_fThe number of codewords is the sum of the numbers of codewords for UE1, UE7, and UE 13).

The codebooks employed in the present invention are themselves of conventional Design, such as those mentioned in m.taherzadeh, h.nikopour, a.bayeseh and h.baligh, "SCMA Codebook Design,"2014IEEE 80th temporal technology conference (VTC2014-Fall), Vancouver, BC,2014, pp.1-5. Based on the SCMA method, a codebook consisting of subcarriers is a basic resource unit of a network.

In the context of figure 1A of the drawings,

is the code word information of the user,

is the channel information of the user.

Assuming that all users are time-synchronized, each user utilizes an SCMA encoder to modulate user data according to an allocated codebook and then sparsely spreads the user data according to a resource mapping matrix, and then codewords of J users are spread to K orthogonal subcarriers, the resource mapping matrix and the resource mapping relation of the invention are shown in figure 2 when β is 2¹And VN1²,VN2¹And VN2²...VN6¹And VN6²The user pairs multiplexing the same codebook multiplex the same column of the resource mapping matrix, that is, multiplex the resource mapping relation of the same codebook. Such as VN1¹And VN1²For multiplexing user 1 and user 2 of the first codebook, the codeword of user 1

And user 2 code word

Are both mapped to the 1 st and 3 rd sub-carriers (as in figure 2, the code word for each user in the SCMA needs to be mapped to two different sub-carriers). In fig. 2, K is 4 and J is 12, i.e., 12 users are spread to 4 subcarriers. That is, the codewords of multiple users multiplexing the same codebook are mapped to different resource units according to the same mapping relationship.

The uplink SCMA reception method provided by the present invention is described below with reference to fig. 4.

The signal transmitted by the uplink SCMA transmission method provided by the present invention is received at the base station, and the received signal may be represented as:

wherein

And

respectively representing the code word information of two users multiplexing the ith codebook on K subcarriers,

and

respectively representing the channel correlation coefficients of K subcarriers of two users multiplexing the ith codebook. n is the mean 0 and the variance σ²White gaussian noise, i.e.: n to CN (0, sigma)²I)。

The received signal on the kth carrier is:

wherein,

is an effective bearer, i.e. the set of codebooks l connected to the subcarriers k, and the total number of connections is β × d_f，n_kRepresenting the noise on the k-th sub-carrier,

indicating the superposition operation of all the code words on the k-th subcarrier. Equation 2 shows that the base station receives codeword information of a plurality of users multiplexing (sharing) a codebook on the kth carrier

And

the uplink SCMA receiving method provided by the present invention needs to be used for decoding.

In the uplink SCMA system, mpa (message paging algorithm) is usually used for multi-user decoding. MPA is an approximately optimal iterative detection algorithm, and a receiver is modeled based on a two-factor graph. Unlike conventional decoding algorithms, MPA decides on user codewords by iteratively detecting user codeword probabilities. The process of MPA detection can be explained with fig. 4.

As shown in fig. 4, the MPA decoder first calculates a conditional probability based on the received signal and the estimated associated channel coefficients and noise power values; then inputting the conditional probability and the code word prior probability as external information into the interior for iterative message transmission; transmitting the code word probability information between the FN node and the VN node in an iterative manner, and outputting the maximum probability information of the code words as soft information after the maximum iteration times are reached; and finally, carrying out LLR hard decision to obtain user code word information.

The base station receives a signal which is sent by a user terminal and passes through an SCMA encoder, and utilizes a decoder to decode the signal by adopting an improved Log-MPA algorithm, wherein the decoding method comprises the following steps:

step 21: calculating an initial prior probability for each codeword

Assuming that the BS has perfect channel state information, the ith codebook is represented by VN node l, i.e. VN node l contains β users multiplexing codebook l, as in the resource mapping relationship of fig. 2, VN node 1 contains VN1¹And VN1². By using

Codeword representing the Tth user using the l-th codebook

Extrinsic information from FN node k to VN node l ∈ N (k) at the t-th iteration

Show to makeCodeword for the Tth user using the l-th codebook

Extrinsic information from VN node l to FN node k e r (l) at the tth iteration, where τ ═ 1, 2.

Is the set of VN nodes l connected to sub-carrier k, the total number of connections is β × d_f，

Indicating the subcarriers effectively carried by VN node l, and the number of subcarriers is N ═ 2. Since there are M possibilities for each codeword, so

Because of, sending

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

step 22: calculating conditional probability of a codeword for a user on each resource unit (subcarrier)

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

the meaning of the conditional probability is to estimate the probability of M possibilities for each codeword by judging the difference between each codeword and the received signal, and when the complete match (all estimates for each codeword are correct), the probability is the highest. D is superposed on the same subcarrier of exclusive codebook in the existing SCMA_fCode words of individual users, i.e.

Operation, the present system has β users multiplexing codebooks so that β × d are superimposed on the same subcarrier_fThe code words of individual users, therefore, the conditional probability of the multiplexed user code words is calculated simultaneously on the basis of the existing Log-MPA algorithm, i.e. the probability of the multiplexed user code words is calculated

And operation, summing the code words of all users multiplexing the same codebook, and then summing all the code words on the kth subcarrier in the effective load. None of the prior art sums

However, in the invention, since β users are multiplexed by the same codebook, an accumulation operation is needed, and the probability of the code word of β users is also calculated.

Step 23: iterative messaging between FN and VN

Will f is_kAnd

iterative messaging between the FN and the VN as external information, comprising the steps of:

step a: the codeword probabilities from FN to VN are updated for the first time.

The iteration being initialized when the probability of a codeword from FN to VN is first updated

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

Wherein,

here, the difference between equation (5) and the existing calculation equation is that the codeword probability of the user of the multiplexing codebook is introduced, that is: in formula (6)

And

two parts.

Equation (6) is the result of matching the codeword for user τ with possible codewords for other users on the subcarrier (β × d)_f-1) × M × 1 probabilities of the possibilities.

Represented is the accumulation of the codeword probabilities that were ultimately calculated for the last iteration of another β -1 users of the multiplexed codebook l along with the tau user.

Equation (7) for the slave (β × d)_f-1) x M x 1 probabilities the largest of the probabilities is chosen as the codeword probability message that is finally delivered by the FN to the VN.

And b, updating the probability of the code word from VN to FN by taking the probability of the code word updated in the previous step as input.

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

Step 24: LLR calculation and bit estimation:

code word

The posterior probability of (a) is:

then, log is determined₂The binary log-likelihood ratio (LLR) of (M) bits is:

the bit values for each user are then estimated by comparing the LLR to 0, estimating

Comprises the following steps:

wherein,

in order to verify the performance of the proposed algorithm, the section compares the error rate and throughput performance of the SCMA and CB-reuse-SCMA systems in an AWGN channel uplink scene through simulation results.

In the SCMA system, 6 users share 4 subcarriers, i.e., J is 6 and K is 4; j is 12 and K is 4 in the CB-reuse-SCMA system, i.e. the number of users is increased by 1 time. In addition, both systems use the same codebook and the simulation parameter settings are shown in the table below.

Parameter(s)	Numerical value
		Number of symbols N	500000
Number of users J	12
		Number of MPA iterations Nit	10
Number of codebook L	6

Fig. 5 is a graph comparing the BER performance of SCMA and CB-reuse-SCMA, verifying the BER performance of the two algorithms at different SNRs. It can be seen from the figure that the BER performance of the CB-reuse-SCMA is reduced by about 3dB with respect to the SCMA because the CB-reuse-SCMA multiplexes the same codebook resulting in interference between users of the multiplexed codebook, but the BER performance of the CB-reuse-SCMA gradually approaches the SCMA as the SNR increases.

FIG. 6 is a graph comparing the throughput of SCMA and CB-reuse-SCMA systems, verifying the system throughput for SCMA and CB-reuse-SCMA at different SNRs. It can be seen from the figure that as the SNR increases, the throughput of both algorithms converges gradually. The SCMA converges after 6dB, while the CB-reuse-SCMA converges after 10dB, with a throughput of 2 times that of SCMA, i.e.: the system throughput is improved by 1 time, and the user connection number is improved by 1 time. Therefore, the codebook multiplexing SCMA technical method provided by the invention realizes obvious system capacity improvement, and can even improve the system capacity by 2 times.

The uplink SCMA transmitting method and receiving method based on codebook multiplexing provided by the present invention are described in detail above. It will be apparent to those skilled in the art that various modifications can be made without departing from the spirit of the invention.

Claims

1. An uplink SCMA transmitting method based on codebook multiplexing, characterized by comprising the steps of:

2. The uplink SCMA transmission method of claim 1, wherein:

and the code words of the specific number of users using the same codebook are mapped to different resource units according to the same mapping relation.

3. The uplink SCMA transmission method of claim 2, wherein:

the number of user code words superposed on a single resource unit in one scheduling period is β × d_fWherein d is_fThe number of code words of users using different codebooks superimposed by one resource unit is shown when one codebook is only allocated to one user in one scheduling period.

4. An uplink SCMA receiving method based on codebook multiplexing is characterized by comprising the following steps:

calculating an initial prior probability of each codeword;

iterative message transmission is carried out between the resource node and the user node based on the initial prior probability and the conditional probability to obtain a codeword probability;

5. The uplink SCMA receiving method of claim 4, wherein:

6. The uplink SCMA receiving method of claim 5, wherein:

7. The uplink SCMA receiving method of claim 5, wherein:

and using double summation operation to sum the code words of all users multiplexing the same codebook, obtaining the sum of all code words on one resource unit, and simultaneously calculating the code word conditional probability of a plurality of users using the same codebook.

8. The uplink SCMA receiving method according to claim 7, characterized in that the calculation of the codeword probability comprises:

firstly updating the probability of the code words from the resource nodes to the user nodes;

and updating the code word probability from the user node to the resource node by taking the code word probability updated in the previous step as input.

9. The uplink SCMA receiving method of claim 8, wherein:

the first updating of the codeword probability from the resource node to the user node comprises the steps of:

the maximum value is selected from the probabilities of the possibilities as the probability of the code word ultimately passed on from the resource node to the user node.

10. The uplink SCMA receiving method of claim 8, wherein:

updating the codeword probability for each of the particular number of users using the same codebook separately.