Research On Adjustment Of Frequency Offset And Realization In The Digital Relay System Of TD-LTE

TD-LTE (Time-Division Duplex Long Term Evolution) is one of key technology ofthe fourth-generation wireless communication system. Orthogonal frequency divisionmultiplexing (OFDM) is as the core technology, which is the multiplexing scenario formulti-users in TD-LTE system. The advantage of OFDM is the high spectrum efficiency.But at the same time, it also requires the orthogonality among each subcarrier, so the sendsignals and receive signals must assure the precise frequency synchronization. The Relaycame to the standardized specification agreement in Release10of LTE in2011. In order toagainst the bad influence of noise existed in the actual channel of mobile wireless system,the interference between cells, and the limited bandwidth, the relay was put forward toreduce the power consumption of the base station, to improve the link budget, and at thesame time expanding the coverage of the signals. In the paper the frequency offset is thefirst problem needed to study.Based on the understanding of the research status of the frequency synchronization,firstly we analyzes the basic principle of the existed algorithm of the frequency offsetestimation, and also present the advantages and disadvantages, which combined with thecharacteristic of TD-LTE relay system, a algorithm mixed the PSS and SSS is put forward.The integer frequency offset existed among the subcarriers was estimated by using theautocorrelation in frequency domain of PSS and the circulating shift characteristics of SSS.Secondly, according to the phase characteristic of the fractional frequency offset in the timedomain, utilizing PSS and SSS to get the fractional frequency offset estimate. To gain theultimate frequency offset, the smooth operation was needed by averaging the two estimates.Then we should adjust frequency offset of the received signals to ensure the consistencyfrequency of the signals in the sending ends and receiving ends. Finally, according to theprinciple of the frequency offset estimation algorithm, the theory simulation of MATLABand the hardware implementation of FPGA are carried on in this paper. Through analyzingthe algorithm, we set up the system model and give to the principle diagram of hardware.Simulation results show that the designed algorithm can keep the estimation range of thesome existed algorithms, and also has the high estimation precision, and keep the lowercomputation complexity.