基于突发OFDM系统的时域符号同步关键技术研究

The OFDM systems have the ability to overcome the channel frequency-selectivity, which have been widely adopted by many mobile telecommunication standards. The OFDM technique is also regarded as one of the most potential candidate techniques for 4G telecommunications. The symbol timing issue of the burst OFDM systems in the time-domain is crucial for reliable and stable reception, while the relatively fundamental research is very meaningful. Because of the limitation of the transmitting training symbols, the conventional symbol timing algorithms are highly influenced by severe multi-path fading channels in low SNR region. In our project, we plan to fully explore the correlation terms belonging to the preamble. By utilizing quantization for ranking the correlation characteristics, the "Optimum selecting for the correlation terms " technique can be solved. In order to generate the timing metric with one sharp peak in the presence of large carrier frequency offset (CFO), the "Stable and efficient coarse symbol timing algorithm" can be achieved by introducing geometry optimization and delayed correlation filtering. Further, we try to investigation the probabilistic modeling and parameter estimation jointly, and to work out "Probabilistic modeling based fine symbol timing algorithm" for performance improvement. After solving these basic techniques, a solid foundation is established for researching on the burst OFDM synchronization module.

正交频分复用（OFDM）由于具有很强的抗频率选择性衰落能力，已广泛被多种移动通信标准所采纳，它也是4G移动通信最具潜力的技术之一，其中关于突发OFDM系统的时域符号同步问题，是实现接收机可靠和稳定工作的关键，相关的基础性研究具有重要的科学和实际意义。由于传输训练符号数的限制，为应对现有同步算法在低信噪比严重多径衰落信道中，符号同步精度和稳定性受到较大影响的问题，本项目拟充分挖掘同步头内潜在的相关项，通过引入量化排序来解决"优选同步头相关项"关键技术，严格控制算法的实现复杂度；从产生单峰值和抵抗大频偏定时度量的角度出发，通过引入几何优化和延迟相关滤波等方法，来实现"稳定高效的符号粗同步算法"；拟通过联合优化概率建模和参数估计，突破"基于概率建模的符号精同步算法"，来进一步提高精同步算法性能。相应的关键基础问题的解决，将为突发OFDM系统的同步模块的研制打下坚实的基础。

在本项目中，我们研究了突发OFDM系统时域符号同步关键技术问题，主要完成的研究工作包括：1）通过对同步头相关性的挖掘，提出了一种量化同步头相关序列的方法。在离线阶段，根据定时度量峰值与平均值幅值比的大小来衡量定时度量的尖锐程度，从而可以通过选择合适的同步头相关序列来抵抗较强的多径衰落；2）借助几何优化的思想，提出了采用加权算术平均对传统定时度量函数后处理的符号粗同步方法，在只增加少许运算量的前提下，可以将原有的符号粗同步MSE性能提升约一个量级；3）提出了利用同步头之前噪声的统计特性来估计符号精同步阈值的方法，无需预先获得准确的信噪比值便可实现阈值随噪声功率变化的自适应调整；4）研究了脉冲干扰对突发OFDM系统整体接收性能的影响，提出了采用alpha稳定分布对干扰进行建模的方法，并通过建立与高斯噪声下Q函数的映射机制，获得强干扰下的SER性能解析解，为干扰抑制、信道编码提供了理论依据。项目按计划执行，至今在IEEE GLOBECOM、ICC、MILCOM、Wireless Personal Communications、通信学报等国内外高水平学术会议和期刊上发表录用相关成果12篇。项目组已获得授权专利8项，另有3项国家发明专利处于申请阶段。这些成果为进一步深化和拓展在相关领域的理论与应用奠定了坚实基础。