高速率无线OFDM移动通信系统中的干扰抵消技术研究

【作者】 刘召伟；

【导师】 王宗欣；

【作者基本信息】 复旦大学 ， 电路与系统， 2006， 博士

【摘要】 受到B3G(Beyond 3G)中对移动多媒体和无线Internet等业务的高涨需求驱使，无线通信数据传输速率不断提高；而无线频谱资源却由于自然界的客观唯一性和不可再生性而日益紧张。不断提高的数据传输速率会由于无线信道的多径扩展而产生更加严重的符号间干扰(ISI)。OFDM技术由于较高的频率利用率、有效对抗无线信道多径扩展和易于数字实现等优点成为B3G技术研究的热点。但OFDM系统预留较长保护间隔(GI)的设计要求会降低无线频谱资源的利用率，尤其在高速率无线OFDM系统中，当GI不足时，会引起严重的子载波间干扰(ICI)和符号间干扰(ISI)，故高速率OFDM通信系统中需要设计更为有效的干扰抵消(IC)方法。本文在以前工作的基础上，从时域、频域、时域频域结合等不同角度进一步改进并设计了高速率无线OFDM系统中的IC算法，使之具有较高的系统性能和系统适用性。 首先，论文在时域分析了当数据传输速率提高后无线OFDM系统GI相对不足时，可能产生的各种干扰、各种干扰的不同贡献和相应解析表达式，给出了时域信道压缩的高速率无线OFDM通信系统的干扰抵消方法，分析了高速率OFDM系统中采用MMSE准则进行时域信道压缩存在的问题和容量最大化的信道压缩问题，提出了一种可以进一步提升系统性能的改进的MMSE-TEQ算法，然后给出了一种利用信道传输矩阵特性的、采用DFT计算的快速时域信道压缩算法。 接着，论文在频域从无保护间隔OFDM系统频域均衡出发，给出了高速率无线OFDM系统中采用部分频域均衡实现干扰抵消的方法，同时给出了相应的OFDM系统频域干扰抵消的快速实现，论文使用该快速实现结构提出了一种新的高速率无线OFDM系统中采用Turbo迭代的频域干扰抵消算法。 然后，论文从时频结合角度，指出了时域或频域单独处理时存在误码率平台的原因，提出了两种新的时频结合的高速率OFDM系统中干扰抵消方法，一种是信道压缩结合双重自适应配置的干扰抵消方法；另一种是具有频域制约的时域信道压缩的干扰抵消方法，进一步改善了高速率无线OFDM系统传输质量性能，并同时提高了系统容量。 最后，论文借鉴最近在多用户检测技术中提出的多级迭代干扰抵消技术，在高速率无线OFDM系统中引入并改进了多级迭代干扰抵消的实现方法。给出了在高速率无线OFDM通信系统中容易工程实现的多级干扰抵消方法(MSIC)，包括可以克服误差传播的加权MSIC算法和自适应补偿的MSIC算法。 论文还对上述几种算法进行了相应的仿真和比较。更多还原

【Abstract】 With the rising requirement of the mobile multimedia and wireless Internet accessing in the B3G communications system, the wireless transmitting symbol rate becomes much higher. However, the wireless spectrum is unique and cannot be regenerated in the nature. At the same time, the ISI becomes more and more serious especially after higher speed symbol passed through the multi-path wireless channel. Wireless OFDM system is widely studied because of its higher spectrum efficiency, multi-path overcoming and easy digital realization. However, long guard intervals in OFDM system decrease the spectrum usage. So it is necessary to design an efficient interference canceller (IC) to overcome the interference introduced by non-enough GI in high speed wireless OFDM system.Firstly, the IC design in time domain is presented. By analyzing the various ISI and ICI introduced by non-enough GI in high speed wireless OFDM system, the channel shortening IC method and the maximum capacity method by using MMSE criterion are given. Then, a new modified MMSE-TEQ IC algorithm and a fast algorithm based on the FFT structure, which is benefited from the advantages of the special transmit channel matrix.Secondly, the IC processing method in frequency domain is given. By analyzing the frequency equalization proceeding, when the GI is removed thoroughly in high rate wireless OFDM system, the block equalizer IC method in frequency domain in wireless OFDM system is given. Also, a fast algorithm for frequency IC method and its iterative realization based on Turbo equalization are given.Thirdly, time domain and frequency domain method are combined, two new IC methods are proposed. These are a new doubly adaptive loading with channel shorten IC method and a new frequency constraint channel shorten IC method in high speed wireless OFDM system. These two proposed methods may not only improve the BER performance but also enhance the OFDM system capacity.Then, a multistage IC (MSIC) iterative method is included into high rate wireless OFDM system, which refers to the iterative algorithm in multi-user detection. The new MSIC method, including an error-diffusion-combated MSIC method and a adaptive filter MSIC method, can be easily realized in real OFDM communications system.The simulations and comparison of the proposed algorithms are also given.更多还原