The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

Timing jitter, frequency offset, carrier phase jitter and sampling clock frequency offset are the main synchronization errors encountered by OFDM systems. As many literatures have proved, OFDM systems are very sensitive to frequency errors. In this paper, three new methods to estimate the integer part of frequency offset are proposed, simulation results show its robustness to mitigate the multi-path effect and its enlarged estimation range for frequency offset. The correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability. The proposed method is also suitable for burst mode transmission systems such as Wireless Local Area Network (WLAN) and Fixed-Broadband Wireless Access (F-BWA).

Orthogonal frequency division multiplexing (OFDM) systems are highly sensitive to carrier frequency errors. In this paper, a new method utilizing pilots to do frequency synchronization in frequency domain is proposed with large estimation range. It needs no such prerequisite assumption that a perfect symbol timing synchronization [IEEE Transactions on Communications 42 (1994) 2908; 45 (1997) 1613] has been done before performing integer carrier frequency synchronization. Also, a new adjusting model for fine carrier frequency is proposed. Simulation and performance analysis show that our overall frequency estimator has high accuracy. The corresponding FPGA circuit through test in high definition TV (HDTV) prototype in Team of Expert Engineering Group (TEEG) in China proves its availability and feasibility.

Most existing methods for HPA predistortion with memory effects are based on polynomial or indirect learning structures. Few papers concern about the memory predistortion with LUT based techniques. Based on the previously presented method, we propose an improved two-dimensional LUT indexing method for HPA predistortion with memory. Computer simulations and corresponding analysis demonstrate that the proposed method has more effective predistortion capabilities but lower computational complexity.

There have been many papers concerning about the Peak to Average Power Ratio (PAPR) reduction and High Power Amplifier (HPA) linearization techniques for wireless OFDM communication systems. Few papers, however, make deep analysis on the relation between these two techniques. Based on Saleh’s memoryless Traveling Wave Tube Amplifier (TWTA) model, computer simulations and analysis in this paper demonstrates that, especially when the HPA is working near or in the saturation region, a predistorter will cease to be in effect. In such cases, PAPR reduction techniques may be resorted to help to improve the Adjacent Channel Interference (ACI), BER performances and HPA efficiency 1.

In this paper we focus our research on the symbol timing synchronization technique in COFDM systems. A new method utilizing pilots to do coarse symbol timing is proposed. It overcomes the problem of fluctuation of the estimated symbol start position with cyclic prefix correlation method. The symbol timing error with the proposed method is within only 10 samples. Different from the algorithms in [1]–[3], we utilize the known pilot information to estimate the residual symbol timing offset with low system complexity. This paper also proposes a new control model for the sampling clock adjustment, different from the phase-locked loop (PLL) [4], [5] or delay-locked loop (DLL) [2] method. The simulation and correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability. The proposed method is also suitable for burst mode transmission systems such as Wireless Local Area Network (WLAN) and Fixed-Broadband Wireless Access (F-BWA).

In this paper, we focus on the Look-up Table (LUT) technique for the compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8 dB gain in out-of-band spectrum re-growth suppression and about 0.3 dB BER performance gain than conventional LUT technique with the same iteration times. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitter.

目前关于高功率放大器的研究中很少有文献详细分析关于相位失真对系统性能的影响尤其是在对SSPA功放的分析中许多文献认为其相位失真为0 基于典型的TWTA和SSPA模型从星座图弥散误码率BER功率谱密度PSD系统总性能损失TD 等几方面进行仿真深入分析了相位失真对OFDM 无线通信系统性能的影响根据仿真分析得出了重要结论。

Timing jitter, frequency offset, carrier phase jitter and sampling clock frequency offset are the main synchronization errors encountered by OFDM systems. As many literatures have proved, OFDM systems are very sensitive to frequency errors. In this paper, an improved method to do decimal frequency offset estimation in time domain is proposed. In addition, lots of simulations have proved that when the decimal frequency offset in data streams approaches to 0.5 of the subcarrier spacing, a wrong estimated frequency offset with inverse polarity will be presented, therefore, a novel adjusting model to deal with this problem is also proposed in this paper. Simulation results show that the mean square error (MSE) can be significantly improved by over three order of magnitude at high SNR with the proposed method compared with the conventional method [1], [2]. The correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability.

研究了高清晰度数字电视（HDTV）中的频率同步及采样钟同步技术对其中的小数倍频偏和采样钟偏移估计做了算法仿真分析，结合实际工程应用提出一种适用于数字视频地面广播（DVB-T）编码的正交频分复用（COFDM）调制系统的小数倍细频偏和采样钟偏移联合估计算法并提出了相应的现场可编程门阵列（FPGA）实现方案，设计出的硬件电路经国家高清电视总体组（TEEG）的HDTV功能样机调试证明了该算法的易实现性和优良性能。