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CN-122027418-A - Viterbi incoherent demodulation method and system

CN122027418ACN 122027418 ACN122027418 ACN 122027418ACN-122027418-A

Abstract

The invention relates to a Viterbi incoherent demodulation method and system, which comprises the steps of obtaining a received symbol sequence, calculating an incoherent branch metric of each candidate path based on a preset forgetting factor, a correlation accumulation amount of a previous moment state of each candidate path and an instantaneous correlation value between the received symbol of the current moment and a reference symbol of each candidate path, calculating a path metric of each candidate path at the current moment based on a path metric of the previous moment, selecting a candidate path with the largest path metric from a plurality of candidate paths in the current moment state as a surviving path in the current moment state, updating the correlation accumulation amount of the current moment state reached by the surviving path based on the forgetting factor, the correlation accumulation amount of the previous moment state corresponding to the selected surviving path and an instantaneous correlation value of the surviving path, processing the received symbol time by time, and finally selecting a state corresponding to the maximum value from the path metrics of all the states as a backtracking start point, and backtracking step by step to obtain a demodulated data sequence.

Inventors

  • SHEN YINXIAO
  • ZHANG JIANFENG

Assignees

  • 中国电子科技集团公司第三十六研究所

Dates

Publication Date
20260512
Application Date
20260227

Claims (10)

  1. 1. A Viterbi non-coherent demodulation method, comprising the steps of: step S1, acquiring a received symbol sequence, initializing path metrics and related accumulated quantities for each state in a state grid at the initial moment of a Viterbi algorithm; step S2, calculating the uncorrelated branch measurement of each candidate path at the current moment based on a preset forgetting factor, the correlated accumulated quantity of the previous moment state corresponding to each candidate path and the instantaneous correlation value between the received symbol at the current moment and the reference symbol corresponding to each candidate path; Step S3, calculating the path metric of each candidate path at the current moment based on the uncorrelated branch metrics of each candidate path and the path metric corresponding to the previous moment, and selecting the candidate path with the maximum path metric from a plurality of candidate paths in the current moment state as a surviving path in the current moment state; step S4, based on the forgetting factor, the relevant accumulated quantity of the state of the previous moment corresponding to the selected surviving path and the instantaneous relevant value corresponding to the surviving path, updating the relevant accumulated quantity of the state of the current moment reached by the surviving path; And S5, repeating the steps S2 to S4, processing the received symbol sequence time by time until all received symbol processing is completed, selecting a state corresponding to the maximum value from path metrics of all states at the last moment as a backtracking starting point, and carrying out step-by-step backtracking based on surviving paths of all states at each moment to obtain a demodulated data sequence.
  2. 2. The Viterbi non-coherent demodulation method according to claim 1, wherein the Viterbi non-coherent demodulation method is used for demodulating a QPSK-CPM modulated signal, and the received symbol is a QPSK-CPM modulated signal.
  3. 3. The Viterbi non-coherent demodulation method according to claim 1, wherein for each candidate path, the instantaneous correlation value between the received symbol at the current time and the reference symbol corresponding to the candidate path is calculated according to formula (1), as follows: Formula (1) Wherein, the Representing the received symbol at the current time and from the previous time state To the current time state Instantaneous correlation values between reference symbols corresponding to candidate paths; 、 the current time and the previous time are respectively; in order for the symbol interval time to be, The received symbol is the current moment; Is in the state of the previous moment Conjugate of the corresponding reference symbols.
  4. 4. A Viterbi non-coherent demodulation method according to claim 3, characterized in that for each candidate path, a non-coherent branch metric of the candidate path at the current time is calculated according to formula (2), as follows: Formula (2) Wherein, the Indicating the state from the previous time To the current time state Non-coherent branch metrics of candidate paths of (a); is a forgetting factor; representing the state of the previous time Is a function of the relative cumulative amounts of the (a).
  5. 5. The Viterbi non-coherent demodulation method according to claim 4, wherein for each current time state Calculating path metrics of candidate paths according to a formula (3), and selecting surviving paths from the candidate paths reaching the current moment state, wherein the path metrics are as follows: Formula (3) Wherein, the Representing the state of the current moment Is a path metric of (a); representing the state of the previous time Is a path metric of (a).
  6. 6. The Viterbi non-coherent demodulation method according to claim 5, wherein for each current time state Updating the relevant cumulative amount of the current time state reached by the surviving path according to the formula (4), as follows: Formula (4) Wherein, the Representing the state of the current moment The updated relevant cumulative amounts; To the current time state A previous time state corresponding to the survivor path of (a); representing the state of the previous time Is a related cumulative amount of (a); Representing slave states To state Instantaneous correlation value corresponding to the survivor path of (c).
  7. 7. The Viterbi non-coherent demodulation method according to claim 1, wherein selecting a state corresponding to a maximum value from path metrics of all states at a final moment as a backtracking start point, performing stepwise backtracking based on surviving paths of the states at each moment, and obtaining a demodulated data sequence, comprising: Comparing path metrics of all states at the last moment after all received symbols are processed, and taking the state corresponding to the maximum value in the path metrics at the last moment as a backtracking starting point; starting from the backtracking starting point, sequentially searching the surviving paths of all states at each moment according to the sequence of time from back to front, determining the state at the previous moment corresponding to each moment, and backtracking step by step to obtain a complete backtracking path; Based on the state pairs of adjacent moments in the backtracking path, the mapping relation between the Viterbi state transition and the input bits is searched to obtain the input bits corresponding to each moment, and the input bits of all moments are spliced according to the time sequence to obtain the complete demodulation data sequence.
  8. 8. The Viterbi non-coherent demodulation method according to any one of claims 1-7, wherein the state trellis of the Viterbi algorithm has a state number of 16 per time instant, each state corresponds to 4 forward branch paths, there are 64 candidate paths, and each time instant calculates 64 path metrics.
  9. 9. The Viterbi non-coherent demodulation method according to any one of claims 1-7, wherein the forgetting factor is a positive number less than 1.
  10. 10. The Viterbi incoherent demodulation system is characterized by comprising a symbol sequence receiving module M1, a branch metric calculating module M2, a surviving path selecting module M3, a related accumulated quantity updating module M4 and a backtracking demodulation module M5; The symbol sequence receiving module M1 is used for acquiring a received symbol sequence, initializing path metrics and related accumulated quantities for each state in a state grid at the initial moment of the Viterbi algorithm; The branch metric calculating module M2 is configured to calculate an uncorrelated branch metric of each candidate path at the current moment based on a preset forgetting factor, the correlated accumulation amount of the previous time state corresponding to each candidate path, and an instantaneous correlation value between a received symbol at the current moment and a reference symbol corresponding to each candidate path; the surviving path selection module M3 is configured to calculate a path metric of each candidate path at the current time based on the uncorrelated branch metrics of each candidate path and the path metric corresponding to the previous time, and select, from the multiple candidate paths in the current time state, a candidate path with the largest path metric as the surviving path in the current time state; The related accumulated amount updating module M4 is configured to update the related accumulated amount of the current time state reached by the surviving path based on the forgetting factor, the related accumulated amount of the previous time state corresponding to the selected surviving path, and the instantaneous related value corresponding to the surviving path; The backtracking demodulation module M5 is used for processing the received symbol sequence time by time until all received symbols are processed, selecting a state corresponding to the maximum value from path metrics of all states at the last moment as a backtracking starting point, and backtracking step by step based on surviving paths of all states at each moment to obtain a demodulated data sequence.

Description

Viterbi incoherent demodulation method and system Technical Field The present invention relates to the field of wireless communications technologies, and in particular, to a Viterbi (Viterbi algorithm) incoherent demodulation method and system. Background Quadrature phase shift keying-continuous phase modulation QPSK-CPM (QPSK, quadrature PHASE SHIFT KEYING; CPM, continuous Phase Modulation, continuous phase modulation) spread spectrum is an efficient modulation technique, has the characteristic of continuous phase, so that it does not need to have high requirements on transmission spectrum bandwidth like conventional PSK (PHASE SHIFT KEYING ) modulation, and has the other characteristic of constant envelope, which can effectively reduce the influence of fading channels on its modulation signal, and the use of a nonlinear amplifier, which can reduce the power of the system, has wide application in modern communication. Although the coherent demodulation of the CPM has optimal performance, in the condition of encountering an emergency, for example, under the condition of rapid change of certain channels, the demodulation time is greatly limited, and the coherent demodulation cannot accurately position the carrier phase in the corresponding demodulation time, so that the implementation of the optimal coherent demodulation algorithm of the CPM is very difficult. Disclosure of Invention In view of the above analysis, the present invention aims to provide a Viterbi non-coherent demodulation method and system, which are used to solve the technical problems of reduced demodulation performance and high implementation complexity caused by difficult carrier synchronization in the fast-varying channel in the conventional coherent demodulation method. The invention provides a Viterbi incoherent demodulation method, which comprises the following steps: step S1, acquiring a received symbol sequence, initializing path metrics and related accumulated quantities for each state in a state grid at the initial moment of a Viterbi algorithm; step S2, calculating the uncorrelated branch measurement of each candidate path at the current moment based on a preset forgetting factor, the correlated accumulated quantity of the previous moment state corresponding to each candidate path and the instantaneous correlation value between the received symbol at the current moment and the reference symbol corresponding to each candidate path; Step S3, calculating the path metric of each candidate path at the current moment based on the uncorrelated branch metrics of each candidate path and the path metric corresponding to the previous moment, and selecting the candidate path with the maximum path metric from a plurality of candidate paths in the current moment state as a surviving path in the current moment state; step S4, based on the forgetting factor, the relevant accumulated quantity of the state of the previous moment corresponding to the selected surviving path and the instantaneous relevant value corresponding to the surviving path, updating the relevant accumulated quantity of the state of the current moment reached by the surviving path; And S5, repeating the steps S2 to S4, processing the received symbol sequence time by time until all received symbol processing is completed, selecting a state corresponding to the maximum value from path metrics of all states at the last moment as a backtracking starting point, and carrying out step-by-step backtracking based on surviving paths of all states at each moment to obtain a demodulated data sequence. Further, the Viterbi incoherent demodulation method is used for demodulating QPSK-CPM modulation signals, and the received symbols are QPSK-CPM modulation signals. Further, for each candidate path, calculating an instantaneous correlation value between the received symbol at the current time and the reference symbol corresponding to the candidate path according to formula (1), as follows: Formula (1) Wherein, the Representing the received symbol at the current time and from the previous time stateTo the current time stateInstantaneous correlation values between reference symbols corresponding to candidate paths;、 the current time and the previous time are respectively; in order for the symbol interval time to be, The received symbol is the current moment; Is in the state of the previous moment Conjugate of the corresponding reference symbols. Further, for each candidate path, calculating an incoherent branch metric of the candidate path at the current moment according to the formula (2), as follows: Formula (2) Wherein, the Indicating the state from the previous timeTo the current time stateNon-coherent branch metrics of candidate paths of (a); is a forgetting factor; representing the state of the previous time Is a function of the relative cumulative amounts of the (a). Further, for each current time stateCalculating path metrics of candidate paths according to a formula (3), and selecting