Research On Processing Technique For Wideband Multi-channel GMSK Burst Signal

The various independent combat platforms are linked in the data link network,to achieve resource sharing and improve operational performance of the combat system.In order to obtain the real-time situation of the battlefield more accurately,there are many types and a large number of tactical platforms,and the types and quantities of sensors they carry are also increasing,the amount of data generated by these sensors is increasing.Hence the data link network is required not only to have the ability of anti-jamming and anti-interception,but also to have the ability of high capacity,high performance and wideband transmission.The frequency hopping and time hopping technology is an effective anti-interference technology in the data link network.By implementing burst transmission in the wide frequency range,the anti-interference and anti-interception ability is effectively improved,and the frequency hopping time signal can be regarded as a burst wideband signal.In addition,Gaussian filter minimum frequency shift keying(GMSK)has good spectral efficiency and power efficiency,and the envelope is constant,which one of the effective modulation methods to improve the capacity and performance of the data link network.This dissertation studies the receiver of the wideband frequency-hopping and time-hopping signals,which mainly focuses on the processing techniques of wideband multi-channel GMSK signals in the burst mode.The specific contents are as follows:(1)A frequency hopping system for a conventional radio frequency has a problem of missing signals and difficulty in capturing multiple hopping time hopping signals simultaneously in a multi-user random access network,a wideband multi-channel reception processing scheme suitable for baseband frequency-hopping is designed,combining with characteristics of the burst frame structure and wideband hopping signal.The scheme utilizes a multi-channel baseband receive channel to simultaneously receive multiple frequency hopping time-hopping signals.(2)In order to reduce the sampling rate of input wideband signals and realize the operation of transforming broadband multi-channel frequency hopping signals into baseband,a frequency conversion scheme of combining coarse channelization and digital downconversion(DDC)is proposed,where the signals of each sub-channel are transformed to the baseband.A high-efficiency channelization module based on a multi-phase filter group structure is utilized to realize coarse channelization,which has many advantages including the sampling rate reduction,save computing resources and reduce hardware costs,and avoid sampling blind areas.Multiple digital down-conversion modules are used to achieve more accurate channelization and complete final baseband transformation for each subchannel.The simulation results show that the high efficiency channelization module based on the structure of the polyphase filter bank can accurately perform spectrum shifting on the signal,and suppress out-of-band noise to improve the signal-to-noise ratio.(3)Aiming at the resource consumption pressure caused by multi-channel parallel demodulation processing,the low complexity and high efficiency GMSK demodulation algorithm is studied.Four demodulation algorithms,that is,1-bit differential,2-bit differential demodulation and 1-bit and 2-bit differential demodulation with decision feedback are analyzed and compared.The analysis results show that compared with the other three algorithms,the 1-bit difference demodulation algorithm has a poor bit error rate but low complexity,and the signal-to-noise ratio loss at the bit error rate is about 2 dB.Therefore,considering the demodulation performance and complexity,the 1-bit differential demodulation algorithm with lower complexity is selected as the implementation scheme when the hardware resources are tight and the demodulation performance loss is not large.(4)The FPGA implementation scheme of the receiver for the wideband multi-channel system is designed.The implementation schemes are given in detail,including GMSK modulation module,digital channelization filter module,DDC group module,differential demodulation module and sequence correlation module.The functional simulation of each module is carried out to further verify the feasibility of the designed wideband multi-channel receiver.