滤波多音调制系统中降低码间干扰（ISI）的方法与技术研究

【作者】 李晨；

【导师】 高振明；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 为了实现未来移动通信的高速宽带传输,以正交频分复用(OFDM)为代表的多载波调制(MC)技术因其良好的抗多径能力和克服ISI的能力而正在获得深入研究和广泛应用,其中OFDM技术已经被多个标准采用。但是OFDM也存在一些缺点,如它的正交性在传输中易受破坏,从而需要大量的开销(CP和虚载波等)、较为严格的定时同步等来保证系统性能。为了克服OFDM存在的这些缺点,本文提出了一种新的正交多载波滤波器组调制技术——滤波多音调制(FMT)在无线通信中的应用,并就其中的一些问题进行了研究。 论文首先对移动无线信道的传输特性、无线通信中的研究现状和多载波传输中可能存在的问题进行了介绍和分析,简述了FMT技术的研究背景和意义;通过简述FMT技术的基本原理、基本系统模型,详细介绍了FMT技术的基本轮廓,着重研究了FMT系统的有效实现问题,针对FMT系统内的ISI问题,提出了高效的MMSE-DFE均衡方法,并提出了用预编码(THP)代替MMSE-DFE来消除ISI,通过仿真研究比较了DFE和THP在FMT系统中的性能;最后在THP的基础上研究了带限情况下的信道编码在FMT系统中的性能。传统差错控制编码的最大缺陷就是可靠性和有效性的矛盾,因为其纠错能力的提高是靠增加冗余位获得的,因而不可避免牺牲一定的带宽,编码与波形成形的结合可以有效地解决这一矛盾。本文将网格码与预编码结合,考虑网格预编码带来的编码增益和成形增益,计算机仿真得到了其在多径衰落信道中的性能。以PSK和QAM为调制方式,通过计算机仿真,比较了FMT中MMSE-DFE、无编码THP及Trellis Precoding在AWGN和多径衰落信道环境中的性能,在保证不扩展带宽和传输速率不变的情况下,提高了FMT系统的性能,所得结论对系统的实用化会有所帮助。更多还原

【Abstract】 To ensure prospective reliable high-speed and wideband wireless mobile communications, multicarrier modulation technique has recently evoked considerable interests and widespread applications for its attractive qualities in resisting multi-path effects and mitigating ISI. Taken as an example, the OFDM technique has been adopted for some formed standards. However, OFDM has some intrinsic shortcomings: its orthogonality is susceptible to be destroyed by frequency offset in practical transmission, thus considerable overheads (CP and virtual carriers), strict synchronization and etc. are needed to guarantee it. In order to avoid these disadvantages of OFDM, a new orthogonal multicarrier modulation technique, named Filtered Multitone Modulation (FMT) is studied for its applications in wireless communication in this thesis, with some related aspects being investigated intensively.In this paper, to introduce the background and purpose of research efforts on FMT’s application, the transmission character of mobile wireless channel, latest research developments in wireless communications and potential problems in OFDM are firstly discussed. Second, the principle of FMT and its efficient implementation is particular studied from its basic idea and system model. Then, Based on the analysis of ISI caused by FMT system, MMSE-DFE in FMT system and its efficient implementation are brought forward; and THP, improvement of DFE, is introduced to take the place of DFE in FMT to cancel ISI. The performance of DFE and THP in FMT is compared by simulation. Finally, the performance of channel coding and trellis shaping in FMT system based on THP is studied in the circumstance of band limitation. The traditional error-control coding technique’s great disadvantage is confliction between reliability and efficiency. Since the ability of error-correction is obtained at the expense of adding redundance, the loss of bandwidth is inevitable. Combination of trellis shaping and channel coding can solve the problem. In this paper, we combine trellis shaping with THP in FMT system and study the gain caused by trellis precoding. The performance of FMT using MMSE-DFE, THP and Trellisprecoding are given by simulation in AWGN and Raileigh channel. Compared with uncoded QPSK scheme, trellis shaping achieves a coding gain and a shaping gain, increases FMT system’s performance without reducing information transmitting speed or expanding bandwidth. This will help to FMT scheme practical.更多还原