A random multiple access transmission method without user tags

Abstract

The present invention discloses a user-tag-free random multiple access transmission method. Compared with the transmission of all source bits, the present invention can restore the entire bit sequence by transmitting only a partial bit sequence. At the same time, the improvement of the active detection performance of the spread spectrum sequence codewords at the receiving end of the present invention can be achieved with only extremely low computational complexity. Due to the interference resistance performance of the spread spectrum code sequence codewords, the present invention can achieve better performance than similar technologies under the condition of limited random multiple access channel usage, and is close to the theoretical capacity limit under random multiple access in this scenario.

Description

Technical Field

[0001] The present invention belongs to the field of wireless / digital communications, and in particular relates to a user-tag-free random multiple access transmission method. Background Art

[0002] Vertical industry applications represented by the Internet of Things have become one of the main factors driving the development of post-5G and 6G mobile communication systems. Compared with 5G, 6G is expected to achieve an order of magnitude improvement in performance indicators such as data transmission rate, number of device access, and communication latency to better support diverse application needs. Among them, ultra-large-scale connections (also known as giant connections, giant address access, etc.) support low-power and wide-coverage Internet of Things, smart agriculture, integrated transportation and other industry applications. The closely related connection density indicator will reach 107-108 / Km 2 .

[0003] Massive Machine-Type Communication (mMTC) aims to ensure that next-generation wireless communication systems can support dense interactions between machine-type communication devices. Unlike traditional communication systems designed for human-to-human interaction, mMTC systems are characterized by sporadic traffic, short packet transmissions, and low energy reserves. As the number of active communicating devices increases, traditional random access schemes such as ALOHA and TIN have proven ineffective. In this context, uncoordinated / unsourced random access (URA) is considered a future enabling technology for mMTC scenarios. Information theory has proven (Yury Polyanskiy) that a URA multiple access transmission scheme exists in additive white Gaussian noise (AWGN) channels that can support a large number of potential users with low energy consumption. However, the current technology in this field is immature and diverse, resulting in limited theoretical analysis and limited results.

[0004] Based on this situation, the present invention designs a user-tag-free random multiple access transmission scheme that is flexible and adaptable to existing technologies, has low complexity and low power consumption, and is closer to the theoretical capacity than other works. Summary of the Invention

[0005] The present invention aims to improve the user capacity of the useless label random multiple access system of mMTC for short code sporadic services. A cascade coding method, a sending method, and a decoding method are designed that are unique to this transmission scheme. The source bit data generated by each user terminal is divided into a leading bit sequence and a sending bit sequence part according to the coding method. The corresponding spreading sequence codeword is selected from the pre-stored common spreading sequence codebook according to the leading bit sequence. The spreading sequence codeword will be used in the sending method. The sending bit sequence is first subjected to FEC channel error correction coding to form an FEC bit sequence. After modulation, the FEC bit sequence is spread by the spreading sequence to complete channel transmission according to the sending method. The sending method divides a certain amount of used channel into a number of sub-channels, and stipulates that each sub-channel carries spread spectrum signals from multiple users. The decoding method first uses a common spreading sequence codebook. The receiver detects active spreading sequence codewords for each subchannel's received signal. This detection corresponds to the recovery of the user's preamble bit sequence. Simultaneously, the activity information of each subchannel's signal is combined to improve activity detection performance. This improved spreading sequence codeword activity detection ensures that the modulation information of the FEC bit sequence carried by the spreading sequence codeword can be recovered based on linear or nonlinear error criteria. The demodulated bit information is then input into the FEC decoder to complete full bit recovery. Under short-code transmission with limited channel usage, this scheme increases the user capacity of multiple access, approaching the theoretical capacity of random multiple access without users.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a user tag-free random multiple access transmission scheme, comprising the following steps:

[0007] The cascade coding method comprises:

[0008] Source bit data sent by the user source;

[0009] Common spreading sequence codebook pre-stored at the user end and the receiving end;

[0010] Encoding the source data into a leading bit sequence and a transmission bit sequence, and performing corresponding encoding on each of the leading bit sequence and the transmission bit sequence; selecting a spreading sequence codeword from a common spreading sequence codebook using the leading bit sequence, performing FEC channel error correction encoding on the transmission bit sequence, and obtaining an FEC bit sequence;

[0011] Modulating the FEC bit sequence to obtain a modulation sequence to be transmitted, spreading the modulation sequence based on the spreading sequence codeword to obtain a spread spectrum signal, and completing channel transmission of the spread spectrum signal according to a preset transmission method;

[0012] The sending method includes:

[0013] The fixed usage channel is divided into several consecutive sub-channels;

[0014] The spread spectrum signals from multiple users are superimposed on each sub-channel;

[0015] The receiving end receives (separately or simultaneously) the signals superimposed on each sub-channel and recovers the source data based on the set decoding method;

[0016] The decoding method for recovering the source data includes:

[0017] Given that the active spreading sequence codewords carried by each subchannel have the same state, the receiver uses activity detection to recover (in parallel or serially) the activity probabilities of the spreading sequence codewords of each subchannel. This is then combined with the detection probabilities of each subchannel to improve the overall activity detection performance of the system. Furthermore, since the active spreading sequence codewords of each user correspond to the preamble bit sequence, the preamble bit sequences transmitted by each user are simultaneously recovered after the combined activity detection.

[0018] Specifically, the number of optional spreading codeword sequences in the public spreading sequence codebook is much larger than the number of active spreading codewords. The sub-channel receiving signal model can be equivalent to the compressed sensing model y = Ax + z, where is the subchannel signal model, is a common spreading sequence codebook, containing K tot codewords, L is the length of the spread spectrum sequence codeword, x is the sparse signal to be estimated, the number of its non-zero elements is equal to the number of users transmitting the signal, z is the received Gaussian white noise, and the noise variance is σ 2 The prior distribution of the signal to be estimated can be assumed to be the following Gauss-Bernoulli mixture distribution:

[0019]

[0020] In this mixed distribution, λ k That is, the activity probability of the kth spreading sequence codeword and its spread spectrum signal. This activity probability can be obtained by repeated iteration of the approximate message passing algorithm. The calculation process is briefly described below. The posterior probability distribution of the signal to be estimated can be written as:

[0021]

[0022] in p l,k is a codebook element of the common spreading series, is the noise variance of the qth cycle, the normalization constant Remaining intermediate variables The calculation is as follows:

[0023]

[0024] In view of the above, the posterior support probability of the parameter element to be estimated can be obtained as follows:

[0025]

[0026] At the same time, the active probability is updated to By iterating the estimated signal elements and performing the above calculations, the active probability of each spreading sequence codeword under the subchannel signal can be obtained. The joint active probability can be obtained by expectation The spreading sequence codewords that meet the active probability threshold or correspond to the first several maximum active probabilities are taken as active spreading sequence codewords, and all the spreading sequence codewords determined to be active are recorded as a matrix P.

[0027] Along with the active state information of the spreading sequence codeword, the modulation sequence information of the FEC bit sequence carried by the active spreading sequence codeword can be obtained by using a linear or nonlinear error criterion (such as MMSE, The active spreading sequence codeword corresponding signal can be restored.

[0028] The demodulated information formed after the recovered modulation sequence is demodulated is input into the FEC decoder. After verification and detection, the corresponding signal of the bit sequence that passes the verification can be eliminated from the received signal. The receiver decoding operation is further repeated until no bit sequence that passes the verification can be generated. In this way, the sending bit sequence transmitted by each user is recovered.

[0029] Compared with the existing technology, the main feature of the present invention is its higher transmission efficiency. Compared with the transmission of all source bits, the present invention can restore the entire bit sequence by transmitting only part of the bit sequence. At the same time, the improvement of the active detection performance of the spread spectrum sequence codewords at the receiving end of the present invention can be achieved with only extremely low computational complexity. Due to the anti-interference performance of the spread spectrum code sequence codewords, the present invention can achieve better performance than similar technologies under the condition of limited usage of random multiple access channels, and is close to the theoretical capacity limit under random multiple access in this scenario.

[0030] The present invention has the beneficial effects:

[0031] (1) The transmission method of the present invention has the characteristics of low complexity. Only the system architecture needs to be adjusted. The main functional parts of the system, such as activity detection and the generation of spread spectrum sequence codewords, can be flexibly adapted to existing technologies. The system activity detection performance can be improved with extremely low additional complexity.

[0032] (2) The transmission method of the present invention has energy-saving characteristics. When the number of active users is 300, it is only about 2 dB away from the theoretical limit, which can adapt to the needs of energy-constrained systems;

[0033] (3) The transmission method of the present invention has high information transmission efficiency. All bit information can be restored by sending only part of the bit information. In scenarios where channel usage is limited, the information transmission resource occupation is saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the encoding method and sending method of the user tag-free multiple access transmission scheme of the present invention;

[0035] Figure 2 A schematic diagram of decoding of a receiver in a decoding method for a user-tag-free multiple access transmission scheme according to the present invention, including sub-channel joint activity detection and data recovery;

[0036] Figure 3 This is a comparison chart of sub-channel joint activity detection performance of the user tag-free multiple access transmission scheme of the present invention;

[0037] Figure 4 This is a comparison chart of the user capacity of the system of the non-user tag multiple access transmission scheme of the present invention and similar non-user tag multiple access schemes. DETAILED DESCRIPTION

[0038] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to the present invention.

[0039] Example 1

[0040] A single user source sends 95 bits of data;

[0041] The common spread spectrum sequence codebook pre-stored by the user end and the receiving end contains 2 11 Spread spectrum sequence codewords, each spreading sequence occupies 300 unit channel usage;

[0042] The source data is encoded and divided into a leading 11-bit sequence and a sending 84-bit sequence, and the corresponding encoding is completed respectively; a spreading sequence codeword is selected from a common spreading sequence codebook through the leading bit sequence, and the sending bit sequence is encoded at a code rate of Low Density Parity Check Code (LDPC) channel error correction coding is used to obtain the FEC bit sequence;

[0043] Performing BPSK modulation on the FEC bit sequence to obtain a modulation sequence to be transmitted, performing spectrum spreading on the modulation sequence based on the spreading sequence codeword to obtain a spread spectrum signal, and completing channel transmission of the spread spectrum signal according to a preset transmission method;

[0044] The sending method includes:

[0045] The fixed usage channel is divided into 96 consecutive sub-channels;

[0046] The spread spectrum signals from 50 to 300 users are superimposed on each sub-channel, and the user's bit signal-to-noise ratio is

[0047] The receiving end receives (respectively and simultaneously) the signals superimposed on each sub-channel and recovers the source data based on the set decoding method;

[0048] The decoding method for recovering the source data includes:

[0049] Given that the states of the active spreading sequence codewords carried by each subchannel are the same, the receiver recovers (in parallel or serially) the active state probabilities of the spreading sequence codewords of each subchannel through the Approximate Message Passing (AMP) algorithm, and then recovers the active information by combining the detection probabilities of each subchannel.

[0050] Figure 3 This is a comparison chart of the sub-channel joint activity detection performance of the user tag-free multiple access transmission scheme of the present invention. It can be seen that compared with single sub-channel activity estimation, the performance of sub-channel joint activity estimation has a performance gain of 10 to 1000 times. This is due to the transmission structure of the present invention's ability to create multiple observation samples of activity information. These observation samples lay the foundation for the excellent performance of joint estimation.

[0051] Example 2

[0052] 95 bits of data sent by a single user source;

[0053] The common spread spectrum sequence codebook pre-stored by the user end and the receiving end contains 2 11 Spread spectrum sequence codewords, each spreading sequence occupies 300 unit channel usage;

[0054] The source data is encoded and divided into a leading 11-bit sequence and a sending 84-bit sequence, and the corresponding encoding is completed respectively; a spreading sequence codeword is selected from a common spreading sequence codebook through the leading bit sequence, and the sending bit sequence is encoded at a code rate of Low Density Parity Check Code (LDPC) channel error correction coding is used to obtain the FEC bit sequence;

[0055] Performing BPSK modulation on the FEC bit sequence to obtain a modulation sequence to be transmitted, performing spectrum spreading on the modulation sequence based on the spreading sequence codeword to obtain a spread spectrum signal, and completing channel transmission of the spread spectrum signal according to a preset transmission method;

[0056] The sending method includes:

[0057] The fixed usage channel is divided into 96 consecutive sub-channels;

[0058] The spread spectrum signals from 50 to 300 users are superimposed on each sub-channel;

[0059] The receiving end receives (respectively and simultaneously) the signals superimposed on each sub-channel and recovers the source data based on the set decoding method;

[0060] The decoding method for recovering the source data includes:

[0061] Given that the states of the active spreading sequence codewords carried by each subchannel are the same, the receiver recovers (in parallel or serially) the active state probabilities of the spreading sequence codewords of each subchannel through the Approximate Message Passing (AMP) algorithm, and then recovers the active information by combining the detection probabilities of each subchannel.

[0062] Carrying the active state information of the spreading sequence codeword, the modulation sequence information of the FEC bit sequence carried by the active spreading sequence codeword is recovered through a linear MMSE estimator;

[0063] The soft demodulation information formed after the recovered modulation sequence is demodulated by BPSK is input into the LDPC soft decoder. After verification and detection, the corresponding signal of the bit sequence that passes the verification can be eliminated from the received signal, and the receiver decoding operation is further repeated until no bit sequence that passes the verification can be generated.

[0064] Figure 4 This is a comparison chart of the user capacity of the system of the non-user tag multiple access transmission scheme of the present invention and similar non-user tag multiple access schemes. Figure 4 The minimum signal-to-noise ratio required for each system to achieve the target single-user error probability (PUPE) when the number of users is fixed is shown. When the number of active users is less than 175, the performance of the solution of the present invention exceeds that of most reference solutions. When the number of users exceeds 175, the solution of the present invention is the best among the reference solutions. At the same time, the bit signal-to-noise ratio growth trend of the solution of the present invention is closest to the theoretical limit, with a slower growth rate, and has the characteristics of low energy consumption and high user capacity. When the number of active users is 300, it is about 2.5dB away from the theoretical limit.

[0065] Figure 4 Corresponding literature:

[0066] [1]Y.Polyanskiy,“Aperspective on massive random-access,”inProc.ofIEEEInternational Symposium on Information Theory(ISIT),Aachen,Germany,Jun.25-30,2017,pp.2523–2527.

[0067] [2]V.K.Amalladinne,J.F.Chamberland,and K.R.Narayanan,“An enhanceddecoding algorithm for coded compressed sensing,”in Proc.of IEEEInternational Conference on Acoustics,Speech and SignalProcessing-Proceedings(ICASSP),Barcelona,Spain,May.4-8,2020,pp.5270–5274.

[0068] [3]E.Paolini,G.Liva,and M.Chiani,“Coded slotted ALOHA:A graphbasedmethod for uncoordinated multiple access,”IEEE Trans.Inf.,vol.61,no.12,pp.6815–6832,Dec.2015.

[0069] [4]A.Vem,K.R.Narayanan,J.F.Chamberland and J.Cheng,“A userindependentsuccessive interference cancellation based coding scheme for the unsourcedrandom access gaussian channel,”IEEE Trans.Commun.,vol.67,no.12,pp.8258–8272,Dec.2019.

[0070] [5]V.K.Amalladinne,A.Department,C.Rush,J.F.Chamberland andK.R.Narayanan,“On approximate message passing for unsourced access with codedcompressed censing,”in Proc.of IEEE International Symposium on InformationTheory(ISIT),Los Angeles,CA,USA,June.21-26,2020,pp.2995-3000.

[0071] [6]A.Glebov,N.Matveev,K.Andreev,A.Frolov and A.Turlikov,“Achievability bounds for T-Fold irregular repetition slotted ALOHA scheme inthe gaussian MAC,”in Proc.of IEEE Wireless Communications and NetworkingConference(WCNC),Marrakesh,Morocco,Apr.15-18,2019,pp.1-6.

[0072] [7]M.Zheng,Y.Wu,and W.Zhang,“Polar coding and sparse spreading formassive unsourced random access,”in Proc.of IEEE Vehicular TechnologyConference(VTC),Victoria,BC,Canada,Nov.18-Dec.16,2020,pp.1-5.

[0073] [8] AKPradhan, VKAmalladinne, A.Vem, KRNarayanan and J.F.Chamberland, "Sparse IDMA: A joint graph-based coding scheme for unsourced random access," IEEE Trans.Commun., vol.70, no.11, pp.7124-7133, Nov.2022.

[0074] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by ordinary technicians in this field based on the contents disclosed in the present invention should be included in the protection scope recorded in the claims.

Claims

1. A method for multiple access transmission without user tag, characterized in that: The steps include: The user source sends source bit data; Encoding the source data, and dividing the sequence obtained after encoding into a leading bit sequence and a transmission bit sequence; Selecting a spreading sequence codeword from a common spreading sequence codebook pre-stored at the user end and the receiving end using the preamble bit sequence, performing FEC channel error correction coding on the sending bit sequence to obtain an FEC bit sequence; Modulating the FEC bit sequence to obtain a modulation sequence to be transmitted, and spreading the modulation sequence based on the spreading sequence codeword to obtain a spread spectrum signal; The user sends the spread spectrum signal; Dividing a fixed usage channel into a plurality of continuous sub-channels; superimposing the spread spectrum signals from multiple users on each sub-channel; The receiving end receives the signals superimposed on each subchannel and completes the following steps: recovering the activity state probability of each subchannel's spreading sequence codeword through activity detection, and recovering the spreading sequence codeword by combining the detection probabilities of each subchannel; recovering the preamble bit sequence based on the correspondence between the spreading sequence codeword and the preamble bit sequence; and recovering the modulation sequence of the FEC bit sequence carried by the spreading sequence codeword. The demodulated information formed after demodulating the recovered modulation sequence is input into the FEC decoder. After verification and detection, the corresponding signals of the bit sequences that pass the verification are eliminated from the received signal. The receiver decoding operation is further repeated until no bit sequence that passes the verification can be generated. In this way, the transmitted bit sequence transmitted by each user is recovered.

2. The method for transmitting user-tag-free multiple access according to claim 1, wherein: The preamble bit sequence is only responsible for selecting the spreading sequence codeword from the public spreading sequence codebook, and does not perform subsequent channel error correction coding, modulation and transmission; The transmitted bit sequence undergoes channel error correction coding, modulation and spread spectrum operations before being sent into the channel for transmission. The spread spectrum sequence codeword used for spread spectrum transmission will not change.

3. The method for transmitting user-tag-free multiple access according to claim 1, wherein: The total transmission channel usage is divided into multiple sub-channels, and the spread signal is transmitted on each sub-channel. The number of sub-channels can be determined by the number of symbols carried by a single spreading code.

4. The method for transmitting multiple access without user tag according to claim 1, wherein: The modulation sequence of the FEC bit sequence carried by the spread spectrum sequence codeword is restored based on a linear or nonlinear error criterion.

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