Research On FTN Signal Reception Techniques

With the continuous expansion of wireless mobile communication application fileds and the sharp increase of user requirements,demands for wireless communication transmission will be growing exponentially in the coming decade.However,the current situation is that spectrum resources are becoming increasingly short,so the future 5G mobile communication networks need to introduce new technologies to improve the spectrum efficiency.Under the reality of the shortage of spectrum resources,Non-orthogonal transmission technology(access,modulation)is regarded as the breakthrough direction after 4G orthogonal transmission.As a candidate technology for 5G,faster than Nyquist(FTN)technique that allows the signal to be transmitted at a rate faster than the Nyquist rate can provide higher system capacity and spectrum efficiency than traditional transmission technology,but the infinite intersymbol interference(ISI)is introduced artificially.How to eliminate the interference and reduce the complexity of the receiver is the main bottleneck of the FTN technology development,therefor the reception techniques of FTN signal in both single-carrier and multi-carrier FTN system are studied in this paper.For single-carrier FTN transmission system,the transmission model,the modulation and demodulation method,and the equivalent model of single-carrier FTN system are introduced firstly.Based on the equivalent model,the common detection technologies are introduced and theirs performance are simulated.From the simulation results,as the packing factor becomes smaller,the system performance after equalization becomes worse and worse than orthogonal transmission.Therefore,in order to improve the bit error rate(BER)performance of single-carrier FTN transmission system,the reception techniques of FTN signal based on iterative equalization are studied.The iterative receiver based on MMSE equalization can effectively eliminate the introduced interference through multiple iterations,but there are a lot of matrix multiplication and inverse operations.For this reason,an iterative receive scheme based on successive interference cancellation(SIC)is designed and the simulation results show that the proposed scheme can reduce the computational complexity of the receiver and achieve better performance.At the same time,the reception techniques of FTN signal under multipath channel are studied.The iterative receive scheme under Gauss channel is applied to multipath channel and it can acquire the BER performance approximate to the orthogonal transmission situation.For multi-carrier FTN transmission system,OFDM/OQAM system is adopted.According to the fast implementation method of OFDM/OQAM system,the modulation and demodulation of multi carrier FTN signals can be realized on the basis of the original orthogonal transmission signal modulator and demodulator,without the need to map at the transmitter and store large amounts of data.The iterative receive scheme based on SIC is also adopted at the receiver,and multi-carrier FTN signal detection is completed through multiple iterative equalization.For multipath channels,due to the frequency selectivity of the channel,the fading factors of subchannel are different.Therefore,soft demapping module and SIC module of receiver are modified in order to realize multi-carrier FTN signal receiving under multipath channel,based on the channel parameters and the time frequency characteristics of OFDM/OQAM system pulse shaping filter.The simulation results show that the iterative receiver based on SIC can effectively eliminate the ISI/ICI introduced by FTN technique.