A Method and System for Joint Construction of Frequency Hopping SCMA Codebooks

Abstract

The present invention discloses a method and system for jointly constructing a frequency-hopping SCMA codebook, which relates to the technical field of frequency-hopping control. The method includes step S1: generating a p -element sequence based on a two-stage non-linear chaotic sequence function, and using the p -element sequence as a shift sequence; step S2: based on step S1, controlling a SCMA codebook factor graph matrix to perform cyclic shifts, and constructing a frequency-hopping SCMA codebook by generating a hopping factor graph matrix. The present invention uses a two-stage non-linear chaotic sequence, and the frequency-hopping period can be made infinitely long, the randomness of the sequence is better, and its non-linearity, unpredictability and security are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency hopping control, and in particular, to a method and system for jointly constructing a frequency hopping SCMA codebook. Background Art

[0002] Non-orthogonal multiple access (NOMA) is one of the key technologies for realizing large-scale node access in civilian cellular B5G / 6G communications. As a type of code-domain non-orthogonal multiple access technology, SCMA (Sparse Code Multiple Access) realizes non-orthogonal multiplexing of multiple user data on the same time-frequency resource block (subcarrier) through multi-dimensional spreading coding of user data. Based on non-orthogonal multiplexing transmission, the SCMA system can significantly increase the number of user nodes accessing, 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 multi-user detection at the receiving end of the SCMA system, by virtue of the sparsity of SCMA codewords, a low-complexity message passing algorithm MPA is used to separately judge and decode the transmitted codewords of each user. In the SCMA system, the codebook of each user is prefabricated and fixed on a specific subcarrier for transmission, and 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 design of SCMA is for multi-access of a large number of machine-type communications in civilian licensed frequency bands, and information is continuously transmitted on several fixed subcarriers. If in the unlicensed Internet of Things frequency band, this way of transmitting data on fixed subcarriers is vulnerable to external jammers. Therefore, in the future unlicensed Internet of Things frequency band, the SCMA system lacks signal processing and system solutions to ensure its highly reliable and secure transmission.

[0003] Frequency-hopping technology (FH) is a typical physical layer signal secure transmission technology, which is widely used in various civilian communications and tactical communications (for example, Bluetooth communication, Data-Link 11 / 16 / 22, PUSCH in 5G / 6G, etc.). The FH technology controls the random hopping of frequency points through a frequency hopping sequence (frequency hopping code), flexibly obtains idle or high-quality frequency bands, and effectively avoids interference attacks and fading effects. Among them, the frequency hopping sequence is the key component that controls the frequency hopping law of the FH system, and it 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 challenges such as ubiquitous connectivity and secure data transmission in wireless Internet of Things communications.

[0004] Such as Figure 1As shown in the figure, a frequency hopping and SCMA fusion method is adopted. In this scheme, multiple user data are multiplexed on a resource block group by using the SCMA method. However, the subcarriers (time-frequency resource blocks) used by each user are not fixed and jump under the control of the FH strategy (that is, the subcarriers actually used by the SCMA codebook jump within the RB group), so as to achieve 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, on the one hand, the present invention provides a method for jointly constructing a frequency hopping SCMA codebook. In order to obtain a uniform p m-sequence, a two-stage non-linear chaotic mapping is used to obtain a pseudo-random analog sequence, and then a uniform mapping method is used to obtain p the m-sequence, thereby improving p the security and unpredictability of the m-sequence. The method includes the following steps:

[0007] Step S1: Generate an p m-sequence based on a two-stage non-linear chaotic sequence function, and use the p m-sequence as a shift sequence;

[0008] Step S2: Based on Step S1, control a pre-existing SCMA codebook factor graph matrix to perform circular shifting to generate a hopping factor graph matrix, thereby constructing a frequency hopping SCMA codebook.

[0009] Optionally, Step S1 includes the following steps:

[0010] Use a non-linear chaotic Bernoulli function to generate a random initial value to obtain an analog sequence B ;

[0011] Use Tent mapping to obtain an analog value sequence X ;

[0012] Map the analog value sequence X to p the m-sequence.

[0013] Optionally, the non-linear chaotic Bernoulli function is:

[0014] ;

[0015] In the formula, in the formula, n is the time scale; λ is BernoulliFunction parameters; given a lambda and initial value , and obtain the simulation sequence , Representation sequence B Middle n elements.

[0016] Optionally, the Tent The calculation expression of the mapping is:

[0017] ;

[0018] in, , for X cycle;

[0019] β yes Tent Mapping parameters, parameters β After a period of time, 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. , to obtain a sequence of simulated values X :

[0020] ;

[0021] In the formula, is the first n elements, .

[0022] Optionally, the step will simulate a sequence of values X Map to p The meta-sequence method includes the following steps:

[0023] The continuous interval Divided into p non-overlapping partitions:

[0024] ;

[0025] in, , ;

[0026] Define the mapping relationship, if The simulated value of ,but , and the length is Pseudo-random p Metasequence S :

[0027] ;

[0028] Wherein, is a defined non-overlapping partition; is a sequence S the n th element; k is the k th non-overlapping partition; p is a positive integer.

[0029] Since the obtained sequence S can be long enough, with better randomness and stronger unpredictability. Using it as an extended SCMA codebook has better effects.

[0030] Optionally, step S2 includes the following steps:

[0031] Using the column vectors of the given SCMA codebook factor graph matrix as basic units, performing a -bit cyclic shift operation to obtain a new factor graph matrix; where is from p the S element of the sequence j and J are positive integers, j < J.

[0032] For different times l , using the pseudo-random p sequence S in step S1 and the new factor graph matrix to jointly generate a hopping SCMA codebook factor graph matrix, constructing the original fixed SCMA codebook into a frequency-hopping SCMA codebook.

[0033] Optionally, the obtained new factor graph matrix is:

[0034] ;

[0035] Wherein, is from p the S element of the sequence ; is the time, ; is the th column vector in the SCMA codebook V.

[0036] Optionally, the hopping SCMA codebook factor graph matrix is:

[0037] ;

[0038] Wherein, is the hopping SCMA codebook factor graph matrix at the th time.

[0039] On the other hand, the present invention provides a system for jointly constructing a frequency-hopping SCMA codebook, which is applied to the method for jointly constructing a frequency-hopping SCMA codebook, and includes:

[0040] A generation module: Based on a two-stage non-linear chaotic sequence function, it is used to generate a -ary sequence, and use the -ary sequence as a shift sequence;

[0041] A 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 shifts, generate a hopping factor graph matrix, and thus construct a frequency-hopping SCMA codebook.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention uses a two-stage non-linear chaotic sequence, and the frequency-hopping period can be made infinitely long. The randomness of the sequence is better, which improves its non-linearity, unpredictability and security; by using frequency hopping to control the cyclic shift of the SCMA codebook factor graph matrix, subcarrier frequency hopping is realized. At the same time, the sparsity of the hopping SCMA codebook is ensured, and no additional performance damage will be brought to the MPA decoding of SCMA. Description of the Drawings

[0044] Figure 1 It is a design block diagram of a frequency-hopping and SCMA fusion system.

[0045] Figure 2 It is a schematic flowchart of the method for jointly constructing a frequency-hopping SCMA codebook.

[0046] Figure 3 It is a schematic diagram of the data transmission situation of SCMA user #j using the mapping matrix in the case of interference in the prior art.

[0047] Figure 4 It is a schematic diagram of the actual subcarrier hopping situation of user #1 in the FH-SCMA system in Embodiment 1 of the present invention (the shaded part is the actually used subcarriers).

[0048] Figure 5 It is a schematic diagram of the actual subcarrier hopping situation of user #3 in the FH-SCMA system in Embodiment 1 of the present invention (the shaded part is the actually used subcarriers).

[0049] Figure 6 It is a schematic diagram of the comparison of the bit error rates of a traditional SCMA system, a random FH-SCMA, and the FH-SCMA system proposed by the present invention under the condition of an external jammer in Embodiment 1 of the present invention.

[0050] Figure 7 This is the structural schematic diagram of Embodiment 2 of the present invention. Detailed implementation manners

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments; based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] Each SCMA user sends a m ..., M from the set {0, 1, 2,... M} symbol. This symbol is mapped to an SCMA codeword. Assume that an SCMA system has J users and K orthogonal subcarriers, then an SCMA codebook set with J codebooks is formed, and each codebook is of dimension ( M * K ). The SCMA codebook set used by these J users is represented as:

[0053] ;

[0054] ;

[0055] ;

[0056] wherein, is the codebook used by user j and contains M column vectors (codewords); is a certain SCMA codeword mapped from the j symbol sent by user m . Generally, is a sparse column vector (i.e., some elements are 0), and the positions of 0 indicate that no data is transmitted on the subcarrier k ; x is the SCMA codebook set; is the element sent on the subcarrier in the codeword k .

[0057] In a given SCMA codebook, the sparsity of and (i.e., which subcarriers transmit data and which subcarriers do not transmit data) can be represented by its factor graph matrix V:

[0058] ;

[0059] ;

[0060] Among them The elements in take values of "1" or "0", where "1" indicates that data is transmitted on the subcarrier and "0" indicates that no data is transmitted on the subcarrier. Therefore, characterizes the user j in this K usage of these orthogonal subcarriers, and also characterizes on which subcarriers the elements in are transmitted. Constraints on the sparsity of the factor graph matrix V in the MPA multi-user detection at the SCMA receiver:

[0061] Assume that the number of "1"s in each row of the factor graph matrix V is denoted as , and the number of "1"s in each column is denoted as , then the sparsity of the SCMA codebook factor graph must satisfy the following expression:

[0062] ;

[0063] In a traditional SCMA system, J SCMA users use the same factor graph matrix V, so each user transmits on fixed subcarriers. With this fixed transmission method, when a certain subcarrier is interfered with, the performance of some users in the SCMA system is likely to collapse. Therefore, the traditional SCMA system cannot effectively resist / avoid the influence of interference. As Figure 3 shown, it is the mapping matrix for a SCMA user

[0064] showing the situation of transmitting data. This user only transmits data on fixed subcarriers #1 and #2 and is easily interfered with by a jammer.

[0065] 1) To achieve efficient MPA multi-user detection at the SCMA receiver, the factor graph of the frequency-hopping SCMA codebook still needs to satisfy sparsity;

[0066] 2) The frequency-hopping sequence has a long enough period and good enough randomness to achieve the security and unpredictability of the factor graph hopping;

[0067] 3) The frequency hopping strategy cannot bring additional subcarrier collisions, which will deteriorate the MPA decoding of the SCMA system. Therefore, the traditional pseudo-random frequency hopping method is not applicable.

[0068] In summary, it is very challenging to achieve all these goals simultaneously. The frequency hopping strategy design must be jointly designed with the characteristics of the SCMA codebook (factor graph matrix).

[0069] For the above reasons, the present invention provides the following embodiments.

[0070] Embodiment 1:

[0071] Please refer to Figures 2 - 6 As shown, this embodiment provides a method for jointly constructing a frequency hopping SCMA codebook, including the following steps:

[0072] Step S1: Generate a -element sequence based on a two-stage non-linear chaotic sequence function, and use the -element sequence as the shift sequence. In order to obtain a uniform -element sequence, this embodiment uses a two-stage non-linear chaotic mapping to obtain a pseudo-random analog sequence, and then uses a uniform mapping method to obtain the -element sequence, thereby improving the security and unpredictability of the -element sequence. Specifically, it includes the following steps:

[0073] First, use the non-linear chaotic Bernoulli function to generate a random initial value. The Bernoulli function is:

[0074] ;

[0075] In the formula, n is the time scale; λ is the Bernoulli function parameter; given a λ and an initial value , obtain the analog sequence , represents the B th element in the sequence n .

[0076] Secondly, use the Tent mapping to obtain an analog value sequence X .

[0077] The calculation expression of the Tent mapping is:

[0078] ;

[0079] Among them, , isX Period

[0080] Wherein, , β is Tent The parameter of the mapping. The parameter β Changes from the simulation sequence every period (e.g., every L = 1000 intervals), which can further improve the unpredictability of the generated sequence. By using the current B Obtained in the current step and the initial value of the next step , a sequence of simulation values is obtained: X :

[0081] ;

[0082] In the formula, Is the n th element in the sequence of simulation values.

[0083] Finally, based on the method of uniform partitioning, the sequence of simulation values X Is mapped to p -ary sequence. The specific steps are as follows:

[0084] Divide the continuous interval Into p Non-overlapping partitions:

[0085] ;

[0086] Wherein,

[0087] ;

[0088] Define the mapping relationship. If the simulation value of is , then . According to the mapping relationship, each element in the sequence of simulation values X Is mapped to an integer, thus obtaining a pseudo-random -ary sequence p : S :

[0089] ;

[0090] In the formula, Is the defined non-overlapping partition; Is the S th element in the sequence n ; k Is the k th non-overlapping partition; p Is a positive integer.

[0091] This embodiment uses two - stage chaotic non - linear mapping and adopts Bernoulli and Tent functions with better uniformity. Therefore, the obtained S sequence length can be long enough, with better randomness and stronger unpredictability. Using it as an extension of the SCMA codebook has a better effect.

[0092] Step S2: Based on Step S1, control an existing SCMA codebook factor graph matrix to perform cyclic shift to generate a jumping factor graph matrix, thereby constructing a frequency - hopping SCMA codebook.

[0093] Exemplarily, Step S2 includes the following steps:

[0094] Step S21: Given an SCMA codebook, that is, given a factor graph matrix , taking the column vector as the basic unit, perform -bit cyclic shift operation, where is an element from the p -ary sequence S , j and J are positive integers, and j < J. When constructing S , it is necessary to satisfy . After the cyclic shift operation, a new factor graph matrix is obtained:

[0095] ;

[0096] In the formula, is an element from the p -ary sequence S , ; is the time, ; is the -th column vector in the SCMA codebook V.

[0097] Step S22: For different times , using the pseudo - random p -ary sequence S and the corresponding p -ary sequence element , a series of new jumping SCMA codebook factor graph matrices are obtained:

[0098] ;

[0099] Based on the above steps, using the pseudo - random p -ary sequence SConstruct a factor graph matrix that generates jumps in combination with the factor graph matrix V; the factor graph matrix corresponds one-to-one with the SCMA codebook, controlling on which subcarriers the codebook is transmitted, thereby generating a frequency-hopping SCMA codebook from the originally fixed SCMA codebook.

[0100] In a specific embodiment, use a ( K * J ) = (4 * 6) SCMA codebook, and its factor graph matrix is:

[0101] ;

[0102] Set the parameters p = 6, = 2000, = 6, = 0.09, = 0.02, L = 100 to generate a 6 - element chaotic random frequency - hopping sequence S , intercept a segment of it, denoted as: :

[0103] ;

[0104] According to the element values of the sequence S , perform a cyclic shift operation on V, then we can obtain J = 6 mapping matrices that each user jumps at moment:

[0105] ;

[0106] In the frequency - hopping SCMA codebook set generated according to the above steps, the mapping matrix (factor graph matrix) used by each user is hopping, so the subcarriers used by each user are also changing.

[0107] Test 1:

[0108] As Figures 4 - 5 shows, taking User 1 and User 3 as examples, illustrate the subcarrier hopping situation of the frequency - hopping SCMA codeword. It can be seen from this figure that the subcarriers used by the user change according to the "hopping mapping matrix", and the hopping mapping matrix is controlled by the generated - element random sequence. Therefore, the randomness, long - periodicity, and unpredictability of the sequence S also determine various security characteristics of the user's frequency - hopping SCMA codebook. This can flexibly avoid the influence of external jammers.

[0109] Test 2:

[0110] In the generated frequency - hopping SCMA codebook, the sparsity of the frequency - hopping SCMA codebook is verified from the characteristics of the elements in each column and each row. At different timesl Under this condition, each column of the frequency-hopping SCMA codebook is composed of permutations and combinations, and each element within does not change at all. Therefore, the sparsity of the formed frequency-hopping SCMA codebook is the same as that of the factor graph matrix That is:

[0111] ;

[0112] It shows that the method for jointly constructing the frequency-hopping SCMA codebook proposed in this embodiment does not change the sparsity of the frequency-hopping SCMA codebook, which is beneficial for the receiving end of the FH-SCMA system to decode using the multi-user MPA detection algorithm and will not bring additional decoding errors.

[0113] In the constructed frequency-hopping SCMA codebook, the test results of the usage (uniformity) of each subcarrier combination are shown in Table 1;

[0114] Table 1: Test table of the usage (uniformity) of subcarrier combinations

[0115]

[0116] 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. The usage of each combination is basically uniform (the usage times are distributed between 314 times and 349 times). In addition, among the above 6 subcarrier combination usage methods, the number of times each subcarrier appears is the same (each subcarrier appears 3 times).

[0117] Test 3:

[0118] Under the condition of an external jammer, compare the bit error rates of the traditional SCMA system, random FH-SCMA, and the FH-SCMA system proposed in the present invention.

[0119] As Figure 6The figure shows the comparison of the bit error rate performance between the FH-SCMA system proposed by the present invention and the traditional SCMA system when the external interference SJR = 0 dB. 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 also better than that of the FH-SCMA system with random frequency hopping. Among them, the reason for the poor performance of the FH-SCMA system with random frequency hopping is that random frequency hopping and SCMA codebook design will bring additional subcarrier collisions, and subcarrier collisions indicate that the sparsity of the SCMA codebook has changed, so using the MPA algorithm at the SCMA receiver will bring additional decoding errors. Therefore, the performance gain brought by the random frequency hopping SCMA codebook design is not large (even no gain), and the present invention improves the anti-interference ability of the SCMA system.

[0120] Embodiment 2:

[0121] Corresponding to the above method for jointly constructing the frequency-hopping SCMA codebook, the present invention also proposes a system for jointly constructing the frequency-hopping SCMA codebook. Since the embodiments of the system of the present invention correspond to the above method embodiments, for the details not disclosed in the system embodiments, reference may be made to the above method embodiments, and no further description will be given in the present invention.

[0122] As Figure 7 shown, a system for jointly constructing the frequency-hopping SCMA codebook includes:

[0123] Generation module: Based on a two-stage non-linear chaotic sequence function, it is used to generate a -element sequence and use the -element sequence as the shift sequence;

[0124] Shift construction module: Based on the output of the generation module, it is used to control a pre-existing SCMA codebook factor graph matrix to perform cyclic shifts to generate a hopping factor graph matrix, thereby constructing the frequency-hopping SCMA codebook.

[0125] The system for jointly constructing the frequency-hopping SCMA codebook 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 program for jointly constructing the frequency-hopping SCMA codebook. Among them, the memory includes at least one type of readable storage medium, and the readable storage medium includes flash memory, mobile hard disk, multimedia card, card-type memory (such as: SD or DX memory, etc.), magnetic memory, magnetic disk, optical disk, etc. The processor is the control core of the electronic device, connecting various components of the entire computer device through various interfaces and lines, and by running or executing the programs or modules stored in the memory, and calling the data stored in the memory, to perform various functions of the computer device and process data.

[0126] 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 are stored in the memory of the computer device.

[0127] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can 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 these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for jointly constructing a frequency-hopping SCMA codebook, characterized in that Including the following steps: Step S1: Generate a p -element sequence based on a two-stage non-linear chaotic sequence function, and use the p -element sequence as the shift sequence. Step S2: Based on Step S1, control a SCMA codebook factor graph matrix to perform cyclic shift, and construct a frequency-hopping SCMA codebook by generating a factor graph matrix with jumps. The said Step S1 includes the following steps: Using non-linear chaos Bernoulli to generate random initial values and obtain a simulation sequence B ; Utilize Tent to map and obtain a sequence of analog values X ; Map a sequence of analog values X to p a sequence of elements; The said Step S2 includes the following steps: Using the column vectors of the given SCMA codebook factor graph matrix as the basic units, perform bit cyclic shift operations to obtain a new factor graph matrix, where is an element from the p m-sequence S , j and J are positive integers, and j < J; Using the pseudo-random p meta-sequence S and the new factor graph matrix to jointly generate a hopping SCMA codebook factor graph matrix, constructing the original fixed SCMA codebook into a frequency-hopping SCMA codebook.

2. The method for jointly constructing a frequency-hopping SCMA codebook according to claim 1, wherein The non-linear chaos Bernoulli function is as follows: ； In the formula, n is the time scale; λ is Bernoulli the function parameter; Given a λ and an initial value , a simulated sequence is obtained represents the sequence B and n represents the -th element in the sequence.

3. A method for jointly constructing a frequency-hopping SCMA codebook according to claim 1, characterized in that The said Tent The calculation expression of the mapping is as follows: ； Among them, , is X period of; β is Tent the parameter of the mapping, and the parameter β is changed from the simulation sequence every set time B and a simulation value sequence is obtained through the parameter and the initial value X : ； In the formula, is the n -th element in the simulated value sequence, .

4. A method for jointly constructing a frequency-hopping SCMA codebook according to claim 3, characterized in that A method for mapping a sequence of analog values X to p a sequence of elements includes the following steps: Divide the continuous interval into p non-overlapping partitions: ； Among them, , ; Define the mapping relationship. If the analog value of , then , obtaining a pseudo-random sequence of length p with S elements: ； In the formula, is a defined non-overlapping partition; is the sequence S the n th element; k is the k th non-overlapping partition; p is a positive integer.

5. A method for jointly constructing a frequency-hopping SCMA codebook according to claim 1, characterized in that The obtained new factor graph matrix is: ； wherein, is from p the m-th sequence S element; ; is the time instant, ; is the th column vector in the SCMA codebook V.

6. A method for jointly constructing a frequency-hopping SCMA codebook according to claim 1, characterized in that, The factor graph matrix of the frequency-hopping SCMA codebook with jumps is: ； In the formula, is the frequency-hopping SCMA codebook factor graph matrix at the 7. A frequency-hopping SCMA codebook joint construction system, applied to a frequency-hopping SCMA codebook joint construction method according to any one of claims 1-6, characterized in that Including: Generation module: Based on a two-stage non-linear chaotic sequence function, it is used to generate a primary sequence and use the primary sequence as the 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 factor graph matrix with jumps, and thus construct a frequency-hopping SCMA codebook.

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