Research On Timing And Frequency Synchronization And Implementation In OQAM/FBMC Systems

Rencently,Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation(OQAM/FBMC)systems have been a promising research area in future broadband mobile communication system.Benefiting from the low spectral sidelobe,high spectral efficiency,good flexibility,strong ability to anti-multipath interference etc.,it can be able to support the demand of the future mobile communication system such as asynchronous transmission,low latency transmission,massive connections,diverse communication scenarios.However,different from the conventional Orthogonal Frequency Division Multiplexing(OFDM)systems,due to the fact that OQAM/FBMC systems adopt well-designed pulse shaping non-rectangular filter,the adjacent symbols are overlapped.When designing training sequence,we should consider the interference to pilot symbols,caused by data symbols.Previous synchronization schemes usually consider constructing a training sequence with repetitive property by transmitting a group of continuous same pilot symbols.However,in these schemes,we usually jointly consider time and frequency synchronization.Thus,it may cause high implementation complexity and large pilot overhead.Therefore,proposing a new synchronization scheme,that can not only achieve timing offset and frequency offset estimation independently but also reduce pilot overhead,seems especially important.In this paper,we propose a new synchronization scheme based on a training sequence with conjugate-symmetry property.Firstly,we give the method of training sequence design.Then,according to the above training sequence,we propose the corresponding timing offset and carrier frequency offset estimation algorithm and the implementation process in detail.In multipath fading channels,the sliding window algorithm is applied to the proposed scheme to further improve synchronization performance.This scheme can reach almost the same performance with WBS scheme,achieve timing and frequency synchronization well.We can separate timing and frequency synchronization,complete them independently in steps.Thus,the implementation complexity could be reduced while keeping the synchronization performance.Meanwhile,we can choose the appropriate number of zero-valued symbols inserted between pilot symbols and data symbols to reduce pilot overhead anyway.Furthermore,we simulate actual communication scenario,i.e.,applying the proposed synchronization scheme to the USRP platform to evaluatethe performance.In the test,we subtlety use the constant envelope Gauss Minimum Shift Keying as reference signal,to test the performance of timing offset and carrier frequency offset estimation.We conduct single and multi frame trials,test the main performance indicators.The test results show that,the proposed scheme applied to USRP platform is almost accurate for timing offset and carrier frequency offset estimation.Then,after channel estimation and equlization according to the pilot symbols,we conduct demodulation to recover the transmitted data symbols.The output SNR can reaches the allowable value.All results reveal that the proposed scheme can obtain expected excellent performance.