A low-complexity coherent demodulation method for gmsk signals

Abstract

The invention provides a GMSK signal low-complexity coherent demodulation method and aims at providing a coherent demodulation method achieving low complexity. The method is implemented by a following technical scheme: performing carrier phase synchronization on a GMSK signal s(kT) by means of a carrier phase-locked loop and outputting a same-phase baseband signal I1(kT) and a orthogonal baseband signal Q1(kT); performing accumulation and extraction on the orthogonal baseband signal under the control of a symbol synchronization pulse with a same-phase and orthogonal branch quadruple symbol rate by means of an integration clearing filter and outputting a same-phase baseband signal and a orthogonal baseband signal with a sampling rate equal to the quadruple symbol rate; filtering I3(mTs / 4) and Q3(mTs / 4) by means of a matching filter and outputting a same-phase baseband signal I4(mTs / 4) subjected to matching filtering and a orthogonal baseband signal Q4(mTs / 4) subjected to matching filtering; performing symbol equalization on the I4(mTs / 4) and the Q4(mTs / 4) by means of a symbol equalization filter, outputting a symbol same-phase baseband I5(nTs / ) with inter-symbol interference eliminated and a orthogonal baseband symbol Q5(nTs / ) with inter-symbol interference eliminated; and performing differential decoding on the orthogonal baseband symbol by means of a differential decoder and outputting demodulated bit information bn.

Description

Technical field [0001] The present invention relates to a signal demodulation technology in a communication system, especially a spacecraft measurement and control system with a high data rate in the future, and a satellite communication system. In particular, it relates to a low-complexity coherent demodulation method for GMSK signals. Background technique [0002] In recent years, aerospace measurement and control systems and satellite communication systems have increasingly higher requirements for data transmission rates, resulting in a corresponding increase in the occupied spectrum bandwidth. At the same time, with the increasing number of space measurement and control tasks and the number of satellites in orbit, the available radio frequency The frequency band is becoming more and more crowded. At present, the signal modulation method used in China's aerospace measurement and control and satellite communication systems has the disadvantages of large occupied bandwidth, slow...

AI Technical Summary

Problems solved by technology

Some systems using GMSK modulation (such as digital trunking systems, GSM systems) assist the receiving end in carrier phase synchronization by inserting fixed training sequences or pilots into the transmitted data, thereby reducing the complexity of coherent demodulation But this is at the cost of sacrificing a certain data bandwidth and transmission power. For aerospace measurement and control and satellite communication systems, the data bandwidth and transmission power used by satellites are strictly limited, so this method is not suitable for demodulation

Maximum Likelihood Sequence Detection (MLSE) is usually implemented using the Viterbi algorithm. After matching and filtering the received symbol sequence and all possible transmitted symbol sequences, they are sent to the Viterbi decoder to search for the best transmitted symbol sequence. However, this The algorithm has the following problems: the number of all possible transmitted symbol sequences is large, resulting in the need for a large number of matched filters, and also makes the input state of the Viterbi decoder too large, which greatly increases the search complexity of the Viterbi decoder. Therefore, maximum likelihood sequence detection (MLSE) is almost impossible to achieve in engineering practice.

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