Anti-Fading Performance Improvement Of Ultra Narrow Band Communication System

The Internet of Things can interconnect everything through the basic network,but some devices cannot access the Internet of Things due to issues such as power consumption and signal coverage.The emergence of Low-Power Wide-Area Network solves the access problem of these devices.As the key technology of the physical layer of the Low-Power Wide-Area Network,ultra narrow band modulation has strong anti-interference performance because of its very narrow bandwidth and high frequency band utilization,which is of great significance to the high reliability and high coverage of the Low-Power Wide-Area Network.This paper mainly takes the Extended Binary Phase Shift Keying(EBPSK)and M-ary Position Phase Shift Keying(MPPSK)in ultra narrow band modulation as the research objects.This paper studies the system performance in different fading channels and proposes solutions that can improve the system's anti-fading performance for different fading channels.The main research results are as follows:Aiming at the problem of continuous error codes caused by the inverted impact envelope of the EBPSK system caused by deep fading in the fading channel,this paper proposes an improved interpolation estimation decision threshold algorithm.By inserting the training sequence into the transmitted symbols,the linear interpolation is used to estimate the value of each transmitted symbol as symbol "0" or symbol "1" after sampling the received signal.If the value of symbol "1" is detected to be less than the value of symbol "0",then the estimated value of symbol "1" and the value of received symbol are updated to the difference between two values and two times of the estimated value of symbol "0",so as to eliminate the influence of inversion of impact envelope.Finally,the demodulated signal can be obtained by threshold decision.Simulation results show that the improved interpolation estimation decision threshold algorithm can further reduce the bit error rate of the EBPSK system compared with the existing anti-fading algorithm.Aiming at the problems of inaccurate delay estimation and high bit error rate of EBPSK system in multipath time-varying channels,this paper proposes a multipath time-varying channel EBPSK system multipath delay estimation scheme and an improved interpolation estimation decision threshold algorithm for multipath time-varying channel.First,the multipath delay estimation scheme is used to estimate each path delay according to the peak value of the envelope.Then the multipath time-varying channel improved interpolation estimation decision threshold algorithm is used to estimate the real-time decision threshold of each symbol in each path.Finally,the sum of the decision thresholds of each path corresponding to each symbol is used to determine the sum of the received signals of each path corresponding to each symbol to demodulate the signal.Simulation results show that the algorithm reduces the bit error rate of the system in time-varying multipath channels.Aiming at the problem that multipath signals are prone to inter-symbol interference,this paper proposes a multipath separation scheme for MPPSK systems.By setting the mppsk modulation parameters to meet the multipath separation expression,the phase hopping part of the sub-path signal will fall into the phase non hopping part of the main path signal,so the envelope impact generated by the signal passing through the impact filter will not be overlapped with each other.Then the receiver can use the delay of each path to sample the signals of each path to jointly decide the signal.Simulation results show that the scheme avoids inter-symbol interference without sacrificing the symbol transmission rate.After the receiver realizes the multipath separation,it demodulates the signal using the multipath joint decision scheme to improve the demodulation performance of the system.The above work provides a certain reference for the application of EBPSK system and MPPSK system in the actual fading channel,and provides a certain basis for the study of EBPSK system and MPPSK system in more complex scenarios.