基于WiMAX的OFDMA上行干扰消除和下行多天线技术研究

【作者】 乔焕爽；

【导师】 刘镰斧；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2007， 硕士

【摘要】 随着多媒体通信的迅速发展，人们不再局限于传统的语音通信，而更多地需要进行大容量数据的通信，同时也要求无线通信具有更高的速率、更大的覆盖范围和更好的移动性，而WiMAX(World Interoperability for Microwave Access)技术的出现恰好能满足这些需求。WiMAX技术是基于无线城域网IEEE 802.16标准的宽带无线技术，可以在固定和移动的环境提供高速的数据、语音和视频等业务，具有广阔的应用前景。作为IEEE802.16标准的主流技术，OFDM和OFDMA技术被广泛地应用到WiMAX系统的物理层中，特别是后者，它支持移动性的IEEE802.16e标准，因此对于OFDMA技术的研究有很重要的现实意义。本文首先系统的介绍了OFDMA技术原理及WiMAX技术中的OFDMA技术。由于OFDMA技术采用正交的子载波来传输数据，因此对载波的正交性提出了很高的要求。在上行链路中每个用户由于载波频率偏差而存在潜在的不同步，这样使子载波之间失去正交性，从而在基站接收端产生多用户间干扰。本文针对上行链路任意分配子载波重点研究了载波频偏估计和多用户间干扰消除的方法。在载波频偏估计中，本文研究了一种载波频偏的最大似然(ML)算法，由于此算法要进行大量的多维运算，因此我们借助于交替迭代投影(AP)算法使最大似然估计从多维参数估计简化成一系列一维参数估计，降低了运算量；针对多用户间干扰消除，本文研究了一种能够实现载波频偏补偿的低复杂度迭代信号处理算法，通过对估计出的每个用户的载波频偏在接收端进行圆周卷积运算，对载波频偏进行补偿，最后通过迭代干扰消除的方法对多用户干扰进行消除。通过Matlab进行仿真的结果表明，本文的算法具有很好的性能，改善了上行链路的传输性能。此外，宽带无线技术能够提供较大的下行链路系统容量，而MIMO技术能在不增加带宽的情况下成倍地提高通信系统的容量和频谱利用率，因而本文也研究了基于OFDMA技术的下行多天线技术。本文重点研究了一种能最大增加系统容量和频谱利用率的基于D-STTD的多天线技术，详细介绍了OFDMA技术和D-STTD技术在下行链路中结合的模型。在接收端提出了一种矩阵求逆的算法降低了接收的复杂度，最后通过仿真分析了该系统在频率选择性信道及其相关信道下的性能。更多还原

【Abstract】 With the fast development of multimedia communication, large capacity data communication is much required than traditional voice communication. Wireless communication is developing with higher data rate, wider range and better mobility. And the appearance of WiMAX (World Interoperability for Microwave Access) meets the trend of development. WiMAX is a broadband wireless communication technology based on IEEE802.16 standard, supporting higher data rate, voice and video communication in fixed and mobile environment. OFDM and OFDMA technology are widely applied in WiMAX physical layer as the main technology in IEEE802.16 standard. Especially OFDMA supports mobile IEEE802.16e standard. So researches on OFDMA are important.OFDMA technology theories and OFDMA in WiMAX technology are introduced firstly. Transmitting data is achieved by exploiting the orthogonality of the sub-carriers in OFDMA. However in uplink channel, each user has its own frequency offset which leads to a loss of orthogonality among the sub-carriers and multiuser interference at the base station receiver. This paper focuses on carrier frequency offset estimation (CFO) and multiuser interference elimination in uplink OFDMA system based on generalized carrier assignment schemes. Maximum likelihood estimation algorithm is investigated in CFO estimation. The exact solution to this problem turns out to be too complex for practical purposes as it involves a search over a multi-dimensional domain. However, to make use of the alternating-projection technique, we replace the above search with a sequence of mono-dimensional searches. Then, we present a low-complexity algorithm using iterative signal processing to compensate for the CFO in OFDMA systems. Matlab simulation shows that the proposed algorithm could eliminate multiuser interference and improve the uplink performance of OFDMA.Furthermore, broadband wireless technology provides large capacity in downlink, and MIMO technology can enhance capacity and spectrum efficiency without increasing bandwidth. So this dissertation also researches multi-antenna technology in downlink based on OFDMA. To support high speed communication and largest system capacity, a downlink model based OFDMA and D-STTD is proposed. An algorithm about inverse matrix is proposed at the base station receiver, so that the complexity of receiver computation has been reduced. At last, through simulation, we analyses the downlink performance in frequency selective channels and correlative channels.更多还原