An OTFS signal detection method based on hybrid message passing

Abstract

The present invention relates to an OTFS signal detection method based on hybrid message passing, and belongs to the technical field of wireless communications. In this method, after receiving a signal, a receiving end first performs block LMMSE pre-detection in the time domain. The pre-detection result is converted to the delay-Doppler domain via OTFS inverse transform and demodulated via QAM to serve as the initial value for a HMP signal detector. The delay-Doppler domain pre-detection result is then matched filtered and fed into the HMP signal detector to complete signal detection. The present invention provides an initial value for the HMP signal detector through time-domain block LMMSE pre-detection, thereby improving the signal detection success rate. Furthermore, the complexity of the algorithm is further reduced by reducing the number of iterations of the HMP algorithm through matched filtering.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communication technology, and mainly relates to a signal detection technology for an OTFS communication system receiving end, and specifically relates to an OTFS signal detection method based on hybrid message transmission. Background Art

[0002] In 2017, Cohere, a US company, proposed Orthogonal Time-Frequency-Space (OTFS) modulation and demodulation technology. Unlike OFDM, OTFS models the time-varying physical channel from the perspective of delay and Doppler shift. It modulates the data to be transmitted in the Delay-Doppler (DD) domain and then transforms it into the Time-Frequency (TF) domain using a specific method. Once converted to the TF domain, the DD domain data symbols occupy the entire TF domain plane, fully utilizing the system's time and frequency diversity. Under the same conditions, it can achieve better performance than OFDM.

[0003] Due to the inherent characteristics of OTFS, which transmits two-dimensional modulation symbols and performs two-dimensional transformations between the delay-Doppler and time-frequency domains, traditional detection algorithms such as MMSE and ZF suffer from high complexity and low detection accuracy. Signal detection based on the high sparsity of the channel matrix can further reduce computational complexity. Message-passing-based detection algorithms, which establish a factor graph and only iterate information between message nodes and variable nodes corresponding to nonzero elements, suffer from slow convergence and excessive iterations. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention proposes an OTFS signal detection method based on hybrid message passing. This method can be used in the channel detection process at the receiving end of an OTFS communication system. By performing block LMMSE detection in the time domain to provide initial values ​​for the subsequent hybrid message passing algorithm, and by incorporating a matched filtering algorithm before the hybrid message passing detection algorithm in the delay-Doppler domain, the method further reduces the number of detection algorithm iterations while ensuring no performance loss.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] An OTFS signal detection method based on hybrid message passing comprises the following steps:

[0007] Step 1: At the transmitter, the information bits are modulated by QAM in the delay-Doppler domain and converted to the time domain after OTFS transformation for transmission.

[0008] Step 2: The transmitted signal s reaches the receiving end after passing through the time and frequency dual selective channel G, and the received signal r is obtained;

[0009] Step 3: After receiving the signal, the receiving end performs block LMMSE pre-detection in the time domain;

[0010] Step 4: Pre-detection signal Perform OTFS inverse transform and transform the signal Converting from the time domain to the delay-Doppler domain, we get

[0011] Step 5: In the time-frequency domain Perform QAM demodulation to obtain QAM demodulation results

[0012] Step 6, Perform matched filtering to obtain

[0013] Step 7, QAM demodulation result As the initial value, Perform hybrid message passing detection to obtain the final OTFS signal detection result

[0014] Furthermore, in step 1, the number of symbols of the OTFS transformation is M×N, where M and N represent the number of delay axis and Doppler axis grid points in the delay-Doppler domain, respectively, and M and N also represent the number of subcarriers and symbols in the time-frequency domain.

[0015] Furthermore, in step 2, the relationship between the received signal r and the transmitted signal s is:

[0016] r=G×s+w

[0017] Where G is the time domain channel matrix and w is the noise.

[0018] Furthermore, in step 3, the transmitted signal s and the received signal r are divided into N blocks s of size M. n and r n , the time domain channel matrix G is a block diagonal matrix, which is decomposed into N parallel linear matrix equations G0, G1, ... G N-1 As the corresponding channel matrix G n , the relationship between the received signal and the transmitted signal after block processing is:

[0019] r n =G n ×s n +w n

[0020] Among them, w nFor noise.

[0021] Furthermore, in step 3, the received signal r after block n Perform LMMSE pre-detection by:

[0022]

[0023] in,(·) H represents the conjugate transpose operation of the matrix, is the noise variance, I M Represents the unit matrix of dimension M×M;

[0024] Signal after pre-detection for:

[0025]

[0026] The beneficial effects of the present invention are:

[0027] 1. Reduce the number of iterations of OTFS system signal detection. The present invention adds a matched filtering algorithm before the hybrid message passing algorithm, making the amplitude of the diagonal elements of the channel matrix larger than the amplitude of the off-diagonal elements, thereby reducing the number of iterations of the detection algorithm.

[0028] 2. Improved detection performance of the OTFS system. The present invention performs block LMMSE detection in the time domain and QAM demodulates the result, which is used as the initial value input for the hybrid message passing algorithm. This accelerates the convergence speed of the hybrid message passing algorithm and improves the detection performance of the OTFS system.

[0029] 3. Reduced computational complexity of the OTFS detection algorithm. The present invention reduces complexity while ensuring performance by adopting hybrid message passing.

[0030] In summary, the present invention improves the message passing algorithm and improves the detection accuracy of the message passing algorithm through methods such as approximate message passing and iterative combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of an OTFS signal detection method based on hybrid message passing.

[0032] Figure 2 It is a schematic diagram of the implementation principle of the present invention. DETAILED DESCRIPTION

[0033] An OTFS signal detection method based on hybrid message passing comprises the following steps:

[0034] Step 1: At the transmitting end, the information bits are QAM modulated in the delay-Doppler domain and converted to the time domain after OTFS transformation for transmission.

[0035] Step 2: The transmitted signal s reaches the receiving end after passing through the time and frequency dual selective channel G, and the received signal r is obtained.

[0036] Step 3: After receiving the signal, the receiving end performs block LMMSE pre-detection in the time domain.

[0037] Step 4: Pre-detection signal Perform OTFS inverse transform and transform the signal Converting from the time domain to the delay-Doppler domain, we get

[0038] Step 5: In the time-frequency domain Perform QAM demodulation to obtain QAM demodulation results

[0039] Step 6, Perform matched filtering to obtain

[0040] Step 7, QAM demodulation result As the initial value, the signal Perform hybrid message passing detection to obtain the final OTFS signal detection result

[0041] The following takes 16QAM modulation, 16 symbols and 64 subcarriers as an example to explain the method in more detail. Figure 1 , including the following steps:

[0042] (1) At the transmitter, the information bits are modulated with 16QAM in the delay-Doppler domain and converted to the time domain after OTFS for transmission. The number of OTFS symbols is 64×16, which means that the number of delay axis and Doppler axis grid points in the delay-Doppler domain is 64 and 16 respectively. The number of subcarriers and symbols in the time-frequency domain is also 64 and 16.

[0043] (2) The transmitted signal s reaches the receiving end after passing through the time and frequency dual selective channel G, and the received signal r is obtained. The relationship between the received signal r and the transmitted signal s can be expressed as:

[0044] r=G×s+w

[0045] Where G is the time domain channel matrix and w is the noise.

[0046] (3) After receiving the signal, the receiving end performs block LMMSE pre-detection in the time domain. The specific method is:

[0047] Divide the transmitted signal s and the received signal r into 16 blocks of size 64 n and r n , the time domain channel matrix G is a block diagonal matrix, which is decomposed into 16 parallel smaller linear matrix equations G0, G1, ... G N-1 As the corresponding channel matrix G n , after block processing, the received signal and the transmitted signal can be expressed by the following formula:

[0048] r n =G n ×s n +w n

[0049] The received signal after block n Perform LMMSE pre-detection, the formula is as follows:

[0050]

[0051] in,(·) H represents the conjugate transpose operation of the matrix, is the noise variance, I M Represents the identity matrix of dimension M×M.

[0052] Finally, the output of the time domain block LMMSE detection algorithm is

[0053] (4) Signal after pre-detection Perform OTFS inverse transform and transform the signal Converting from the time domain to the delay-Doppler domain, we get

[0054] (5) In the time-frequency domain Perform QAM demodulation to obtain QAM demodulation results

[0055] (6) Yes Perform matched filtering to obtain

[0056] (7) QAM demodulation results As the initial value, the signal Perform hybrid message passing detection to obtain the final OTFS signal detection result

[0057] The hybrid message passing algorithm is a combination of the message passing algorithm and the Gaussian approximate message passing algorithm. The algorithm divides the channel path into a primary path and an auxiliary path, executes the message passing algorithm (non-approximate algorithm) on the primary path, and executes the Gaussian approximate message passing algorithm on the auxiliary path, thereby reducing complexity while ensuring performance.

[0058] Figure 2 This is a schematic diagram of the implementation principle of the present invention, which includes a time-domain block LMMSE pre-detector, a delay-Doppler domain matched filter (MF), and a hybrid message passing (HMP) signal detector. After receiving the signal, the receiving end first performs block LMMSE pre-detection in the time domain. The pre-detection result is converted to the delay-Doppler domain via an inverse OTFS transform and demodulated via QAM to serve as the initial value for the HMP signal detector. The delay-Doppler domain pre-detection result is then matched filtered and fed into the HMP signal detector to complete signal detection.

[0059] In summary, the present invention provides an initial value for the HMP signal detector through time-domain block LMMSE pre-detection, thereby improving the signal detection success rate, and further reduces the complexity of the algorithm by reducing the number of iterations of the HMP algorithm through matched filtering.

Claims

1. An OTFS signal detection method based on hybrid message passing, characterized in that: Hybrid message passing is a combination of the message passing algorithm and the Gaussian approximation message passing algorithm. It divides the channel path into a primary path and an auxiliary path. The message passing algorithm is executed on the primary path, and the Gaussian approximation message passing algorithm is executed on the auxiliary path. It includes the following steps: Step 1: At the transmitter, the information bits are modulated by QAM in the delay-Doppler domain and converted to the time domain after OTFS transformation for transmission. The number of symbols in OTFS transformation is , and denote the number of delay axis and Doppler axis grid points in the delay-Doppler domain, respectively. and It also indicates the number of subcarriers and symbols in the time-frequency domain; Step 2: Send a signal Dual selective channels via time and frequency After reaching the receiving end, the received signal is obtained ; Receive signal Sending a signal The relationship between them is: in, is the time domain channel matrix, For noise; Step 3: After receiving the signal, the receiving end performs block LMMSE pre-detection in the time domain; wherein, the signal is sent and receive signals Divided into The size is Block and , the time domain channel matrix is a block diagonal matrix, decomposed into Parallel linear matrix equations As the corresponding channel matrix , the relationship between the received signal and the transmitted signal after block processing is: in, For noise; The received signal after block Perform LMMSE pre-detection by: in, represents the conjugate transpose operation of the matrix, is the noise variance, The representative dimension size is The unit array; Signal after pre-detection for: ； Step 4: Pre-detection signal Perform OTFS inverse transform and transform the signal Converting from the time domain to the delay-Doppler domain, we get ; Step 5: In the time-frequency domain Perform QAM demodulation to obtain QAM demodulation results ; Step 6, Perform matched filtering to obtain ; Step 7, QAM demodulation result As the initial value, Perform hybrid message passing detection to obtain the final OTFS signal detection result .

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