Performance Analysis And Optimizition Of Doppler Resilient Orthogonal Time Frequency Space Ststems

One of the most challenging requirements of the 5th generation(5G)mobile communication system is the ability to be applied to high mobile scenes such as 500 km/h.Since the Orthogonal Time Frequency Space(OTFS)system has important features that are relatively insensitive to time variation in the delay-Doppler domain,the OTFS system can be well applied to high-mobility scenarios.The OTFS system can utilize channel diversity when combined with a suitable equalizer.The thesis studies the optimization of signal detection algorithm and the improvement of modulation scheme in OTFS system,which can obtain a reasonable compromise between algorithm complexity and system performance.Firstly,the thesis introduces the basic principle of fast time-varying channel and OTFS system.The interference of OTFS system in delay-Doppler domain and the theoretical error rate based on maximum likelihood detection is analyzed.The bit error rate and orthogonal precoding modulation error rate performance of OTFS system under fast time-varying channel conditions is simulated.It is verified that the OTFS system is better than the orthogonal frequency division multiplexing multi-carrier system in high-mobility scenarios.Then,in order to reduce the complexity of signal detection at the receiver.The algorithm based on graph theory message transmission is researched.And the signal detection performance of OTFS system is analyzed.On this basis,the thesis proposes doppler compensation or change the modulation matrix structure at the transmitter,which can enhance the sparsity of the channel.Then,the algorithms modifies the stopping criterion of the message passing algorithm at the receiver.In order to further reduce the complexity,the thesis applies Approximation Message Passing(AMP)to OTFS system detection,and introduces the principle of covariance processing in Principal Component Analysis(PCA)principle,which can compensate information loss caused by non-zero mean.The results show that compared with the traditional message passing algorithm,the AMP-based algorithm has a low complexity.The improved approximation message passing algorithm has a lower bit error rate than the traditional approximation message passing algorithm.Finally,the thesis combines the index modulation and OTFS system and proposes an OTFS system based on index modulation technology.Next,an implementation framework based on the performance of index-modulated OTFS system is given.The simulation is performed under the LTE standard channel.The final result shows that the index modulation based OTFS system has a lower bit error rate than the index modulation OFDM system.