摘要
本文主要针对OFDM的同步问题进行研究并对其进行了仿真和实现。论文的主要工作包括以下几个方面:
(一)介绍OFDM的相关技术
(二)探讨了系统同步要求,分析各种同步误差对系统性能的影响,给出各项同步指标。提出采用粗同步和细同步相结合的方法,实现系统同步范围与同步精度的统一,其中,采取短前导与最大似然同步算法相结合实现系统定时粗同步以及频偏粗估计,可以保证足够的同步范围;采取长前导与基于循环移位的最大相关定时同步新方法实现定时细同步,采取长前导与最大似然算法相结合实现载波频偏精估计,以保证足够的同步精度。提出了采用差分编码的新方法对传统子载波间干扰(ICI)自消除算法加以改进,消除了ICI带来的地板效应,提高了传统ICI自消除方案的频谱利用率。
(三)设计同步算法实现方案,从实现的角度优化同步算法,完成verilog代码编写,实现同步模块的硬件仿真验证,完成系统设计。
This paper proposes a physical layer scheme based on Orthogonal Frequency Division Multiplexing (OFDM), and studys the key techniques in the system design, synchronization and ICI cancellation of this scheme. The major work is as following:
1.The introduction of OFDM
2.Based on the study of synchronization demand and the influence of synchronization error, the synchronization target is presented. This paper adopts a method combining rough synchroniation and accurate synchronization to realize unification of synchronization scope and synchronization precision. To realize enough synchronization precision, long preamble combining a new timing synchronization method based on circular shifted maximum correlation algorithm is adopted to realize accurate timing synchronization; long preamble combining maximum likelihood synchronization algorithm is adopted to realize accurate frequency offset estimation. At the same time, differential coding is proposed to ameliorate the traditional Inter-Carriers Interference (ICI) self-cancellation method, thereby canceling the error floor resulted from ICI and improving the bandwidth efficiency.
3.Design system architecture of OFDM synchronization solution. Improved algorithm is provided to save hardware resource. Verilog code of synchronization is validated on FPGA。
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