Frequency hopping SCMA codebook joint construction method and system

Abstract

The invention discloses a frequency hopping SCMA codebook joint construction method and system, and relates to the technical field of frequency hopping control, and the method comprises the steps: S1, generating a p-element sequence based on a two-stage nonlinear chaos sequence function, and taking the p-element sequence as a shift sequence; and S2, based on the step S1, controlling an SCMA codebook factor graph matrix to perform cyclic shift, and constructing a frequency hopping SCMA codebook by generating a hopping factor graph matrix. According to the method, the two-stage nonlinear chaotic sequence is used, the frequency hopping period can be infinitely long, the randomness of the sequence is better, and the nonlinearity, unpredictability and safety of the sequence are improved.

Description

Technical Field

[0001] The present invention relates to the field of frequency hopping control technology, and in particular to a frequency hopping SCMA codebook joint construction method and system. Background Technology

[0002] Non-orthogonal multiple access (NOMA) is one of the key technologies for realizing large-scale node access in civil cellular B5G / 6G communications. SCMA (Sparse Code Multiple Access) is one of the code domain non-orthogonal multiple access technologies. It realizes non-orthogonal multiplexing of multiple user data on the same time-frequency resource block (subcarrier) by multi-dimensional spread spectrum coding of user data. Based on non-orthogonal multiplexing transmission, the SCMA system can significantly increase the number of user node accesses, and its system overload rate mainly depends on the SCMA codebook design scheme. The SCMA system can better adapt to the large-scale multi-node access scenario of future wireless communications. In the multi-user detection at the receiving end of the SCMA system, with the help of the sparsity of SCMA codewords, the low-complexity message passing algorithm MPA is used to separate and determine the transmission codewords of each user. In the SCMA system, the codebooks of each user are prefabricated and fixed on specific subcarriers for transmission. The SCMA factor graph matrix determines on which subcarriers the codebook transmits data. Therefore, with the help of the factor graph matrix, MPA decoding can achieve the decoding performance of the MAP algorithm. However, the original intention of SCMA was to provide multiple access to massive machine-type communications in the civilian licensed frequency band, and to continuously send information on several fixed subcarriers. If it is in the unlicensed IoT frequency band, this fixed subcarrier method of sending data is susceptible to interference from external jammers. Therefore, in the future unlicensed IoT frequency band, the SCMA system lacks signal processing and system solutions to ensure its highly reliable and secure transmission.

[0003] Frequency-hopping (FH) is a typical physical layer signal security transmission technology, which is widely used in various civil and tactical communications (for example, Bluetooth communication, Data-Link 11 / 16 / 22, PUSCH in 5G / 6G, etc.). FH technology controls the random hopping of frequency points through the frequency hopping sequence (frequency hopping code), flexibly obtains idle or high-quality frequency bands, and effectively avoids interference attacks and fading effects. The frequency hopping sequence is the key component to control the frequency hopping law of the FH system, which determines many performances of the FH system. The integration of 5G / B5G SCMA and secure FH technology (FH-SCMA) provides a new idea for solving the challenges of ubiquitous connectivity and secure data transmission in wireless IoT communications.

[0004] If Figure 1As shown in the figure, a frequency hopping and SCMA fusion method is used. This scheme uses SCMA to multiplex multiple user data on a resource block group, but the subcarrier (time-frequency resource block) used by each user is not fixed, and it jumps under the control of the FH strategy (that is, the subcarrier actually used by the SCMA codebook jumps within the RB group), thereby achieving the purpose of avoiding interference. SUMMARY OF THE INVENTION

[0005] The purpose of the present invention is to provide a method and system for jointly constructing a frequency hopping SCMA codebook, which uses a frequency hopping strategy to control the change of the SCMA factor matrix diagram to achieve the purpose of avoiding interference.

[0006] To achieve the above purpose, the present invention provides a frequency hopping SCMA codebook joint construction method, in order to obtain a uniform p Meta sequence, using two-level nonlinear chaotic mapping to obtain pseudo-random simulation sequence, and then using uniform mapping method to obtain p Meta sequence, thereby improving p Security and unpredictability of metasequences. The following steps are included: Step S1, generate a based on the two-level nonlinear chaotic sequence function p meta sequence, and p Meta sequence as a shift sequence; Step S2: Based on step S1, an existing SCMA codebook factor graph matrix is ​​controlled to perform cyclic shift to generate a hopping factor graph matrix to construct a frequency hopping SCMA codebook.

[0007] Optionally, step S1 includes the following steps: Using nonlinear chaos Bernoulli The function generates random initial values ​​and obtains the simulation sequence B ; Use Tent Map to get a sequence of simulated values X ; Send a sequence of simulated values X Maps to p Meta sequence.

[0008] Optionally, the nonlinear chaos Bernoulli The function is: ; In the formula, in the formula, n is the time scale; λ is Bernoulli Function parameters; given a lambda and initial value , get the simulation sequence , indicates a sequence B Middle nelements.

[0009] Optional, the Tent The calculation expression of the mapping is: ; Among them, , For X cycle; β Yes Tent Mapped parameters, parameters β After a period of time, from the simulation sequence B This can further increase the unpredictability of the generated sequence by replacing it once with a fixed parameter and initial value , get a sequence of simulated values X : ; Where, is the number in the simulation value sequence n elements, .

[0010] Optional, the step will simulate a sequence of values X Maps to p The meta-sequence method comprises the following steps: Continuous interval Divided into p Non-overlapping partitions: ; Among them, , ; Define the mapping relationship, if Simulated value of , then , the length is Pseudo-random p Meta-sequences S : ; Where, is the defined non-overlapping partitions; is a sequence S Middle n elements; k For the first k non-overlapping partitions; p is a positive integer.

[0011] Due to the obtained sequence S The length can be long enough, with better randomness and greater unpredictability. It can be used as an extension of the SCMA codebook for better results. ​​

[0012] Optionally, step S2 includes the following steps: With the given SCMA codebook factor graph matrix Column vector of is the basic unit, and After the cyclic shift operation of the bit, the new factor graph matrix is ​​obtained; among them, is from p Meta Sequence S Elements, j and J is a positive integer, j<J.

[0013] For different moments l , using the pseudo-random in step S1 p Meta Sequence S Combined with the new factor graph matrix, the hopping SCMA codebook factor graph matrix is ​​generated, and the original fixed SCMA codebook is constructed into a frequency-hopping SCMA codebook.

[0014] Optionally, the obtained new factor graph matrix is: ; Where, For those from p Meta Sequence S Elements, ; is the moment, ; is the first in the SCMA codebook V Column vector.

[0015] Optionally, the SCMA codebook factor graph matrix of the jump is: ; Where, For the first The frequency-hopping SCMA codebook factor graph matrix at time

[0016] On the other hand, the present invention provides a frequency hopping SCMA codebook joint construction system, which is applied to the frequency hopping SCMA codebook joint construction method, including: Generation module: Based on the two-level nonlinear chaotic sequence function, it is used to generate a meta sequence, and Meta sequence as a shift sequence; Shift construction module: Based on the output of the generation module, it is used to control an existing SCMA codebook factor graph matrix to perform cyclic shift, generate a hopping factor graph matrix, and thus construct a frequency-hopping SCMA codebook.

[0017] Compared with the prior art, the present invention has the following beneficial effects:​ The present invention uses a two-level nonlinear chaotic sequence, the frequency hopping period can be infinitely long, the sequence has better randomness, and its nonlinearity, unpredictability and security are improved; the frequency hopping is used to control the cyclic shift of the SCMA codebook factor graph matrix to achieve subcarrier frequency hopping. At the same time, the sparsity of the hopping SCMA codebook is guaranteed, and no additional performance damage is caused to the MPA decoding of SCMA. Brief Description of the Figures

[0018] Figure 1 Design block diagram for frequency hopping and SCMA fusion system.

[0019] Figure 2 is a flow chart of the method for jointly constructing the frequency-hopping SCMA codebook.

[0020] Figure 3 is the mapping matrix used by SCMA user #j in the interference case in the prior art Schematic diagram of data transmission.

[0021] Figure 4 This is a schematic diagram of the actual subcarrier hopping of user #1 in the FH-SCMA system in Example 1 of the present invention (the shaded part is the subcarrier actually used).

[0022] Figure 5 This is a schematic diagram of the actual subcarrier hopping of user #3 in the FH-SCMA system in Example 1 of the present invention (the shaded part is the subcarrier actually used).

[0023] Figure 6 It is a schematic diagram of the bit error rate comparison of the traditional SCMA system, random FH-SCMA and the FH-SCMA system proposed in the present invention under the condition of an external jammer in Example 1 of the present invention.

[0024] Figure 7 is a schematic diagram of the structure of Example 2 of the present invention. Specific implementation method

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Each SCMA user selects from the set {01,2,... m ..., M}Send a MMetasymbol. This code element symbol is mapped to SCMA codeword. Assume that a SCMA system has J Users and K orthogonal subcarriers, then a matrix with J The SCMA codebook set of codebooks, each codebook is ( M * K ) dimension. This J The SCMA codebook set used by a user is expressed as: ; ; ; Where, For User j The codebook used contains M column vectors (codewords); For User j Sent m A SCMA codeword mapped to a meta-symbol, generally, is a sparse column vector (that is, some elements are 0), and the position of 0 represents the subcarrier k No data is transmitted on; x is the SCMA codebook set; is the code word In subcarrier k The element sent on .

[0027] In a given SCMA codebook, and The sparsity of (i.e. which subcarriers transmit data and which subcarriers do not transmit data) can be represented by its factor graph matrix V: ; ; Among them The element value in is "1" or "0". "1" means that the subcarrier transmits data, and "0" means that the subcarrier does not transmit data. Therefore, Characterizes the user j Here K The usage of orthogonal subcarriers also represents On which subcarriers are the elements in transmitted. Constraints on the sparsity of the factor graph matrix V by MPA multi-user detection at the SCMA receiver: Assume that the number of "1" in each row of the factor graph matrix V is expressed as , the number of "1"s in each column is expressed as , then the SCMA codebook factor graph sparsity must satisfy the following expression: ; Traditional SCMA systems, J SCMA users use the same factor graph matrix V, so each user transmits on a fixed subcarrier. In this fixed transmission mode, when a subcarrier is interfered, the performance of some users in the SCMA system is easily broken. Therefore, the traditional SCMA system cannot effectively resist / avoid interference. For example Figure 3 As shown, this is the mapping matrix of a SCMA user In the case of sending data, the user only transmits data on fixed subcarriers #1 and #2, which is easily interfered by the jammer.

[0028] In order to solve the problem that the traditional SCMA system is easily interfered, the existing technology solves it by adding the SCMA codebook (codeword) used by each SCMA user to the frequency hopping technology. In other words: at different times, SCMA users use different subcarriers to form a frequency hopping SCMA codebook solution. This can effectively avoid the interference of jammers on subcarriers. However, the technical problems that need to be solved are: 1) In order to achieve efficient MPA multi-user detection at the SCMA receiver, the factor graph of the frequency-hopping SCMA codebook must still meet the sparsity requirement; 2) The frequency hopping sequence period is long enough and the randomness is good enough to achieve the security and unpredictability of the factor graph jump; 3) The frequency hopping strategy cannot bring about additional subcarrier collisions, which will deteriorate the MPA decoding of the SCMA system. Therefore, the traditional pseudo-random frequency hopping method is not applicable.

[0029] In summary, it is very challenging to achieve all of the above goals at the same time. The frequency hopping strategy design must be jointly designed with the SCMA codebook (factor graph matrix) features.

[0030] Based on the above reasons, the present invention provides the following implementation.

[0031] Example 1: Please refer to Figure 2-Figure 6 As shown, this embodiment provides a frequency hopping SCMA codebook joint construction method, including the following steps: Step S1, generate a based on the two-level nonlinear chaotic sequence function meta sequence, and Meta sequence as a shift sequence. In order to get a uniform Meta sequence, this embodiment uses two-level nonlinear chaotic mapping to obtain a pseudo-random simulation sequence, and then uses a uniform mapping method to obtain Meta sequence, thereby improving The security and unpredictability of the meta sequence. Specifically includes the following steps: First, using nonlinear chaos Bernoulli The function generates a random initial value, the Bernoulli The function is: ; Where, n is the time scale; λ is Bernoulli Function parameters; given a lambda and initial value , get the simulation sequence , indicates a sequence B Middle n elements.

[0032] Secondly, use Tent Map to get a sequence of simulated values X .

[0033] Said Tent The calculation expression of the mapping is: ; Among them, , For X Cycle Among them, , β Yes Bernoulli Mapped parameters, parameters β After a period of time (for example, every L =1000 intervals) from the simulated sequence B is replaced once, which can further improve the unpredictability of the generated sequence. By obtaining the current And the initial value of the next step , get a sequence of simulated values X : ; Where, is the number in the simulation value sequence n elements.

[0034] Finally, based on the uniform partitioning method, the simulated value sequence X Maps to p Meta sequence. The specific steps are as follows: Continuous interval Divided into p Non-overlapping partitions: ; Among them, ; Define the mapping relationship, if Simulated value of ​​, then . According to the mapping relationship, the simulation value sequence X Each element in is mapped to an integer, resulting in a length of Pseudo-random p Meta-sequences S : ; Where, is the defined non-overlapping partitions; is a sequence S Middle n elements; k For the first k non-overlapping partitions; p is a positive integer.

[0035] This embodiment uses a two-level chaotic nonlinear mapping and adopts a uniform Tent and Figure 4-Figure 5 Function, therefore, the obtained S The sequence length can be long enough, with better randomness and greater unpredictability. Using it as an SCMA codebook extension will have a better effect.

[0036] Step S2: Based on step S1, an existing SCMA codebook factor graph matrix is ​​controlled to perform cyclic shift to generate a hopping factor graph matrix to construct a frequency hopping SCMA codebook.

[0037] Exemplarily, step S2 includes the following steps: Step S21: Given a SCMA codebook, that is, given a factor graph matrix , with the column vector is the basic unit, and bit circular shift operation, where is from p Meta Sequence S Elements, j and J is a positive integer, j<J. When constructing S , it is necessary to meet . After the circular shift operation, the new factor graph matrix is ​​obtained: ; Where, For those from p Meta Sequence S Elements, ; is the moment, ; is the first in the SCMA codebook V Column vector.

[0038] Step S22: for different time periods , using the pseudo-random in step S1 p Meta Sequence S and the corresponding p Meta-sequence element , and obtain a series of new jump SCMA codebook factor graph matrices: ; Based on the above steps, using pseudo-random p Meta Sequence S Combined with the factor graph matrix V, the hopping factor graph matrix is ​​constructed; and the factor graph matrix corresponds to the SCMA codebook one by one, controlling which subcarriers the codebook is transmitted on, thereby converting the original fixed SCMA codebook into a frequency-hopping SCMA codebook.

[0039] In a specific embodiment, using a ( K * J ) = (4*6) SCMA codebook, its factor graph matrix is: ; Setting Parameters p =6, =2000, =6, =0.09, =0.02, L =100 generated 6-element chaotic random frequency hopping sequence S , intercept it A paragraph, expressed as: ; According to the sequence S element value, perform a circular shift operation on V, and you can get J =6 users each in The mapping matrix of moment jump: ; According to the frequency-hopping SCMA codebook set generated by the above steps, the mapping matrix (factor graph matrix) used by each user is hopping, so the subcarrier used by each user is also changing.

[0040] Test 1: If Figure 6 shows the frequency hopping SCMA codeword subcarrier hopping situation, taking user 1 and user 3 as examples. It can be seen from the figure that the subcarrier used by the user changes according to the "hopping mapping matrix", and the hopping mapping matrix is ​​generated by ​​​​​​​​​​​Therefore, the randomness, long periodicity and unpredictability of sequence S also determine the various security features of the user frequency hopping SCMA codebook. This can flexibly avoid the influence of external jammers.

[0041] Test 2: In the generated frequency-hopping SCMA codebook, the sparsity of the frequency-hopping SCMA codebook is verified from the characteristics of each column and each row element. l , each column of the frequency-hopping SCMA codebook consists of arranged and combined, and There is no change in the elements in the code, so the sparsity of the jump SCMA codebook and the cause subgraph matrix Consistent, that is: ; It shows that the frequency hopping SCMA codebook joint construction method proposed in this embodiment does not change the sparsity of the frequency hopping SCMA codebook, which is conducive to the FH-SCMA system receiving end to use the multi-user MPA detection algorithm for decoding, and will not cause additional decoding errors.

[0042] The test results of the usage (uniformity) of each subcarrier combination in the constructed frequency-hopping SCMA codebook are shown in Table 1; Table 1: Subcarrier combination usage (uniformity) test table

[0043] Taking the subcarrier usage of users #1, #3, and #6 as an example, the subcarrier combinations used by the users are: #1SC+#2SC, #1SC+#3SC, #2SC+#3SC, #1SC+#4SC, #2SC+#4SC, #3SC+#4SC, and the usage of each combination is basically uniform (the number of times used is distributed between 314 and 349 times). In addition, in the above 6 subcarrier combinations, the number of times each subcarrier appears is the same (each subcarrier appears 3 times).

[0044] Test 3: Comparison of bit error rates of traditional SCMA system, random FH-SCMA and FH-SCMA system proposed in this invention under external jammer conditions.

[0045] If Figure 7 ​The figure shows the bit error rate performance comparison between the FH-SCMA system proposed by the present invention and the traditional SCMA system when the external interference SJR=0dB. It can be seen that the present invention can effectively resist external interference, and the bit error rate is lower than that of the traditional SCMA system, and is also better than the performance of the FH-SCMA system using random frequency hopping. Among them, the reason why the random frequency hopping FH-SCMA system is not good is that random frequency hopping and SCMA codebook design will cause additional subcarrier collisions, and subcarrier collisions indicate that the sparsity of the SCMA codebook has changed, so that the use of the MPA algorithm at the SCMA receiving end will cause additional decoding errors. Therefore, the performance gain brought by the random frequency hopping SCMA codebook design is not large (or even no gain), and the present invention improves the anti-interference ability of the SCMA system.

[0046] Example 2: Corresponding to the above-mentioned frequency-hopping SCMA codebook joint construction method, the present invention also proposes a frequency-hopping SCMA codebook joint construction system. Since the embodiments of the system of the present invention correspond to the above-mentioned method embodiments, the details not disclosed in the system embodiments can be referred to the above-mentioned method embodiments, and will not be repeated in the present invention.

[0047] If ​ As shown, a frequency hopping SCMA codebook joint construction system includes: Generation module: Based on the two-level nonlinear chaotic sequence function, it is used to generate a meta sequence, and Meta sequence as a shift sequence; Shift construction module: Based on the output of the generation module, it is used to control an existing SCMA codebook factor graph matrix to perform cyclic shift, generate a hopping factor graph matrix, and thus construct a frequency-hopping SCMA codebook.

[0048] The frequency-hopping SCMA codebook joint construction system of the present invention can be installed in a computer device. The computer device includes a processor, a memory, and a computer program stored in the memory and executable on the processor, such as a frequency-hopping SCMA codebook joint construction program. The memory includes at least one type of readable storage medium, and the readable storage medium includes a flash memory, a mobile hard disk, a multimedia card, a card-type memory (e.g., SD or DX memory, etc.), a magnetic memory, a disk, an optical disk, etc. The processor is the control core of the electronic device, and uses various interfaces and lines to connect the various components of the entire computer device, and executes various functions of the computer device and processes data by running or executing programs or modules stored in the memory, and calling data stored in the memory.

[0049] The module described in the present invention refers to a series of computer program segments that can be executed by a processor of a computer device and can complete fixed functions, and is stored in the memory of the computer device.

[0050] The above description is only a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A frequency hopping SCMA codebook joint construction method, characterized in that: The following steps are involved: Step S1: Generate a two-level nonlinear chaotic sequence function p meta sequence, and p Metasequence as a shift sequence; Step S2: Based on step S1, a SCMA codebook factor graph matrix is ​​controlled to perform cyclic shift, and a frequency hopping SCMA codebook is constructed by generating a hopping factor graph matrix.

2. A frequency hopping SCMA codebook joint construction method according to claim 1, characterized in that: Step S1 includes the following steps: Using nonlinear chaos Bernoulli The function generates random initial values ​​and obtains the simulation sequence B ; use Tent Mapping gets a sequence of simulated values X ; The simulated value sequence X Map to p meta sequence.

3. A frequency hopping SCMA codebook joint construction method according to claim 2, characterized in that: The nonlinear chaos Bernoulli The function is: ； In the formula, n is the time scale; λ is Bernoulli Function parameters; Given a λ and an initial value , and obtain the simulation sequence , Representation sequence B Middle n elements.

4. A frequency hopping SCMA codebook joint construction method according to claim 2, characterized in that: Said Tent The calculation expression of the mapping is: ； in, , for X cycle; β yes Tent Mapping parameters, parameters β Every time the set time passes, the simulation sequence B Replace once and obtain a simulation value sequence through parameters and initial values X : ； In the formula, is the first n elements, .

5. A frequency hopping SCMA codebook joint construction method according to claim 4, characterized in that: The simulated value sequence X Map to p The meta-sequence method includes the following steps: The continuous interval Divided into p non-overlapping partitions: ； in, , ; Define the mapping relationship, if The simulated value of ,but , and the length is Pseudo-random p Metasequence S : ； In the formula, for non-overlapping partitions defined; For sequence S Middle n elements; k For the k non-overlapping partitions; p is a positive integer.

6. A frequency hopping SCMA codebook joint construction method according to claim 1, characterized in that: Step S2 includes the following steps: Step S21: Given the SCMA codebook factor graph matrix Column vector of As the basic unit, After the cyclic shift operation of bits, a new factor graph matrix is ​​obtained, where Is from p metasequence S Elements of j and J is a positive integer, j<J; Using the pseudo-random p metasequence S The new factor graph matrix is ​​combined with the hopping SCMA codebook factor graph matrix to construct the original fixed SCMA codebook into a frequency-hopping SCMA codebook.

7. A frequency hopping SCMA codebook joint construction method according to claim 6, characterized in that: The new factor graph matrix obtained is: ； In the formula, For p metasequence S Elements of ; For the moment, ; is the first Column vector.

8. A frequency hopping SCMA codebook joint construction method according to claim 6, characterized in that: The SCMA codebook factor graph matrix of the jump is: ； In the formula, For the The frequency hopping SCMA codebook factor graph matrix at time .

9. A frequency hopping SCMA codebook joint construction system, applied to a frequency hopping SCMA codebook joint construction method according to any one of claims 1 to 8, characterized in that: include: Generation module: Based on the two-level nonlinear chaotic sequence function, it is used to generate a meta sequence, and Metasequence as a shift sequence; Shift construction module: Based on the output of the generation module, it is used to control an existing SCMA codebook factor graph matrix to perform cyclic shift, generate a hopping factor graph matrix, and thus construct a frequency-hopping SCMA codebook.

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