Optimization Research And Application Of Pilot Sequence In OFDM System

The Orthogonal Frequency Division Multiplexing(OFDM) technology has the characteristics of high spectral efficiency and strong anti-multipath fading capability, thus researchers choose this technology as the research focus of next generation mobile communication. In OFDM system, the performance always influenced by two factors: the accuracy of channel estimation and the value of Peak to Average Power Ratio(PAPR). The transmitted signal will inevitably suffer from various fading through complex wireless channel, the received signal may generate distortion phenomenon, which need the channel estimation to ensure the accuracy of signal. In channel estimation, we have found the channel exhibits the sparsity, the better performance will be obtained by utilizing the fewer pilots when we make full use of the characteristic of channel. In addition, high PAPR value will lead to the high power amplifier(HPA) work in non-linear region and cause signal distortion, while the PAPR suppression method can effectively improve the system performance.Aiming at the problem of channel estimation accuracy and high PAPR, this dissertation mainly investigates the optimization of pilot sequence scheme under sparse channel and the application of the optimized pilot sequence, the specificresearch work as follows:(1) This dissertation first analyses the channel estimation problem and introduce the conventional channel estimation method, while these methods couldn’t make full use of the sparsity of channel to improve performance;(2) Based on the compressed sensing(CS) theory and the sparsity of channel, this dissertation proposes a feedback algorithm to optimize the pilot sequence, the proposed algorithm combines the coherence minimization criterion and the effective feedback of channel state information(CSI) at the receiver to jointly optimize the pilot sequence to ensure the performance.(3) Utilizing the optimized pilot sequence to perform the sparse channel estimation, and simulation results demonstrate that the better BER performance can be obtained using the proposed algorithm when the number of pilots unchanged.(4) Considering the high PAPR problem, this dissertation proposes a PAPR suppression method. Based on the generated optimized pilot sequence, this method adopts the four-phase factors of the partial transmit sequence(PTS)technology to reduce the PAPR value. The simulation results show that the proposed method have better PAPR performance compared to the uniform method of inserting pilots.