Research Of Time Synchronization And PAPR Reduction In TD-LTE Radio Remote Systems

In order to enhance the bit error rate (BER) performance, this paper studied the clock synchronization and peak-to-average power ratio (PAPR) reduction technology to deal with the clock drift and high PAPR problem in the TD-LTE radio remote systems respectively. The requirement of high accuracy and high performance is satisfied by hardware implementation of clock synchronization module and simulation of PAPR reduction algrithm.A clock synchronization technology based on phase-locked loop (PLL) was proposed to deal with the clock drift problem that occurs between the radio server and the remote radio unit in TD-LTE remote radio systems. It takes use of the phase-locked loop and achieves the goal of cancelling out the clock drift by tracking the clock drift and pre-compensating the clock signal. Starting with the research of the foundation of phase-locked loop, this paper analysed the conventional frequency stabilizing methods for mode-locked laser and proposed a method based on PLL chip to guarantee high frequency stability of the local clock.The research of the generation and impact of the clock drift was followed by the analysis of advantages and disadvantages of traditional clock synchronization technologies. And then a method based on PLL for clock drift compensating was proposed. After theoretical analysis of the feasibility, the clock synchronization module integrated in a four-layer printed circuit board was fabricated, consisting of local frequency stabilizing module, clock drift measuring and compensating module, evaluating module and controlling module. And the experiment results show that the clock frequency stability could reach10"12, achieving improvement of4orders of magnitude with the synchronization module. And the result was about the same for10Km and100Km one-way fiber link. This technology is able to eliminate the clock drift in a large dynamic range, and enhance the clock frequency stability, and therefore improve the BER performance.Taking into account of the characteristic of high PAPR of orthogonal frequency division multiplexing (OFDM) signal, this paper analysed the impact on power amplifier due to high PAPR. It leads to efficiency reduction of power amplifier and deterioration of BER performance. In order to suppress high PAPR and alleviate the influence on BER performance by non-lenearity of power amplifier, this paper proposed a modified tone reservation (TR) method and a joint method of modified interleaved partitioning partial transmit sequence (IP-PTS) method and TR method. The modified TR method makes use of null carriers of baseband signal and takes advantage of no side information. Part of the null carriers are used as reserved carriers to generate superposition signal for peak clipping. This method could obtain better performance improvement with a small number of null carriers. The joint method lowers the computational complexity of conventional IP-PTS method without performance degradation and improves performance further by combining modified TR with modified IP-PTS. The effectiveness of this two methods is proved by simulation results. The modified TR method and the proposed joint method can achieve1.8dB and2.9dB performance improvement respectively compared with the conventional IP-PTS method.