摘要
在移动通信系统中,小区间干扰(ICI)是一个固有的问题,由于受到相邻小区的干扰,小区边缘用户的吞吐量受到极大的干扰。为了提高小区边缘用户的性能,就必须采用小区间干扰消除技术。传统的干扰消除方法包括交织多址(IDMA)的迭代干扰消除技术、干扰随机化、干扰重构。随着协作通信的发展,在LTE-Advance中首次提出了使用协作通信的方式对干扰进行消除,协作多点传输CoMP技术作为协作通信的一种,通过多个基站之间的协作处理,将小区干扰消除。CoMP技术可以根据上下行链路的不同分为上行CoMP和下行CoMP。本文将分别对两种技术进行研究,但主要工作集中于上行CoMP。
首先,在本文的前期工作中,建立了一个2X2的OFDM-MIMO系统模型。对几种经典的MIMO检测算法进行了仿真和性能分析。并对下行CoMP基站协作干扰消除预编码技术进行了研究与仿真分析,其中,预编码算法包括ZF算法,BD算法,BD-SVD算法等。
接着,本文重点研究CoMP技术在上行协作干扰消除中的应用。通过对上行干扰的分析,本文将上行干扰场景分为强对称干扰、弱对称干扰和非对称干扰。同时,研究了上行干扰消除的信号合并方式。根据上行干扰消除信号合并处理的方式,可以分为分布式干扰消除(DIS)、压缩信号重传(CIF)、分布式天线-分布式检测(DAS-D)和分布式天线-中心检测(DAS-C)。针对非对称干扰,可以使用基于信号强度分组的上行协作干扰消除方案。该方案可以在一个协作簇内按各个用户信号的强度进行分组,确定基站协作干扰消除的先后顺序；然后根据干扰消除的顺序,将主基站解出的信号作为干扰信号消除信号的估计值,在下一个协作基站中消除,从而获得增益。通过在典型的非对称干扰场景下的仿真结果说明该方案能具有较好的干扰消除性能。
最后,论文搭建了3小区的LTE系统仿真模型,仿真对比了几种MIMO检测算法(ZF、MMSE、ZF-SIC、MMSE-SIC、ZF-OSIC、MMSE-OSIC)在DAS-C处理中的性能；同时也对比了几种不用协作方式(DIS、CIF、DAS-D)在不同干扰场景下的性能。仿真结果表明,在上行干扰消除的处理中,动态的选择不同的协作方案,能够在小区边缘频率复用因子为1的条件下,保证系统用户较好的性能的同时降低系统负载。
In mobile communication systems, Inter-Cell Interference (ICI) is an inherent problem which is critical to system capacity. Cell-edge users in cellular systems suffer from the interferences of adjacent cells and their throughputs are typically very low. In order to improve the performance of cell-edge users, it is necessary to use the inter-cell interference cancellation technology. Traditional interference cancellation techniques include interleaved multiple access (IDMA) iterative interference cancellation technology, interference randomization, interference reconstruction. With the development of cooperation communication, in the LTE-Advance the cooperation communication has been put forward to eliminate the interference. As a kind of cooperation communication,CoMP(Coordinated Multi-Point transmission/reception) can eliminate inter-cell interference effectively by processing jointly among multiple base stations. CoMP can be divided into uplink and downlink CoMP. This thesis discusses both but the main research work focus on the uplink CoMP.
Firstly, in the preliminary work of the thesis, a2X2OFDM-MIMO system model is established and several classical MIMO equalization algorithms are simulated and analyzed. Then the thesis discusses how the CoMP isused in the downlink to eliminate the interference with pre-coding techniques.The pre-coding algorithms used in CoMP are simulated and analyzed, including ZF, BD and BD-SVD algorithm.
Secondly, the thesis focuses on the uplink interference cancellation with CoMP. Uplink interference can be divided into strong symmetric interference,weak symmetry interference and asymmetric interference.The subtraction of signal in uplink interference cancellation with CoMP can be divided into Distributed Interference Subtraction (DIS), CoMPressed Interference Forwarding (CIF),(Distributed Antenna System-Decentralized Decoding (DAS-D) and (Distributed Antenna System-Centralized Decoding (DAS-C).For the asymmetric interference scenario, the thesis discusses that the base stations can eliminate interference by grouping the strength of users'signals, The simulation results in a typical asymmetric interference scenario,shows that this scheme has good performance in interference cancellation.
Finally, the thesis bulids a LTE system simulation model of3cells, simulates several different interference cancellation algorithms (ZF, MMSE, ZF-SIC, MMSE-SIC, ZF-OSIC, MMSE-OSIC) in DAS-C method. Also several uplink interference cancellation schemes (DIS, CIF, DAS-D) in the different interference scenarios are simulated and compared. The simulation results show that the dynamic program can guarantee better performance under the conditions of frequency reuse factor is1and balance load.
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