Performance Analysis Of Prototype Filter In OFDM-OQAM System

In recent years,the increase of mobile applications and data flow makes it necessary for the development of adaptive,flexible and efficient wireless access technology.As a result,multicarrier transmission is regarded as an attractive scheme for broadband wireless system and is widely used.Among many other multicarrier techniques,Orthogonal Frequency Divison Multiplex is dominant.On the other hand,OFDM has some shortcomings such as high spectrum leakage,strict synchronicity requirment and sensitivity to carrier frequency offset.The next generation of wireless transmission technology not only makes a demand for higher data rate,but also appears some new application scenarios,like tactile internet,internet of things,fragmented spectrum etc.Massive user access,efficient spectrum usage and real-time connection requirement make OFDM difficult to maintain orthogonality.Therefore,many researchers conduct in-depth study of next generation communication waveform.FBMC,which is named as Offset Quadrature Amplitude Modulation based Orthogonal Frequency Division Multiplex,OFDM-OQAM,is analyzed in terms of time frequency localization,computional complexity and spectrum usage.The aim of this thesis is to analyze charateristics of prototype filter,and thus improve the performance under doubly selective channel.The study mainly conclues three aspects listed as follows:First of all,the mathematical modeling of OFDM-OQAM system is established under multicarrier communication frame,which mainly conclues the continuous and discrete time system model.After that,the orthogonal condition that prototype filter should meet is proposed after mathematical deduction,which is also the basis of Chapter 4.Secondly,the implementation scheme of OFDM-OQAM is studied,including the implementation of filterbanks and OQAM modulation.When it comes to the implementation of filterbanks,the polyphase network method in time domain and frequency spread method in frequency domain are both introduced.While the implementation of OQAM modulation is researched and implemented on the basis of analysis of system's intrinsic interference.Then,the analysis and Matlab simulation of signal characteristics,system complexity and bit-error-rate performance under certain channel environment between OFDM and OFDM-OQAM system is proposed.In the last is the discussion of filter characristics based on the fact that prototype filter determines the connection between symbols and the robustness against doubly selective channels.Several common filters used in OFDM-OQAM system are reviewed and discussed in this paper,which is rectangular,gaussian,half cosine,extended Gaussian function,hermite and PHYDYAS function.In terms of connection between symbols,several evaluation parameter of filter's TFL property is introduced and ambiguity function is the key research content,because it can visualize the ISI and ICI of the system.In terms of robustness against doubly selective channel,the signal to interference ratio and bit error rate is selected.The SIR of various filters under different timing offset and carrier frequency offset is studied,and the bit errer probability of different prototype filters under ITU channel model is simulated and analyzed.