大规模MIMO-OFDM系统导频污染消除技术研究

发布时间：2018-06-21 12:51

本文选题：正交频分复用 + 大规模多输入多输出　；参考：《郑州大学》2017年博士论文

【摘要】：超密集组网利用小基站密集部署改善网络覆盖,成为未来5G网络提高数据流量的有效解决方案之一。然而,超密集网络部署带来小区间干扰问题,成为制约系统容量的主要因素。由于多小区频率复用以及信道相干时间有限,导致超密集网络中相邻小区只能通过复用正交导频训练序列进行信道估计,由此引起的导频污染(Pilot Contamination,PC)问题成为小区间的主要干扰问题。多小区大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统配置的大规模天线所蕴含的高增益,可以显著提升通信系统的能效和谱效,被视为未来5G无线通信重要的备选技术。然而,增加基站天线的数目并不能消除导频污染的影响,导频污染问题已经成为限制多小区大规模MIMO系统性能的瓶颈问题。目前已有大量关于多小区大规模MIMO系统中导频污染消除技术的研究成果,其中基于导频分配方案的导频污染消除技术是研究的热点。由于不同的通信机制对应不同的正交导频设计,本论文将有机结合正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术和大规模MIMO技术构建多小区大规模MIMO-OFDM通信机制,基于此通信机制设计最优导频符号并结合导频污染消除方案,逐步开展导频污染消除技术的研究。主要工作和创新点如下:1.针对多小区大规模MIMO-OFDM系统由于多小区频率复用以及信道相干时间有限造成的导频污染问题,本论文利用OFDM技术所具有的频域(Frequency Domain,FD)多载波资源进行多载波上的导频信号建模,在此基础上为频率复用小区内用户设计最优导频符号集合。当系统子载波资源充足使得基站收发最优导频符号方程具备完备时域(Time Domain,TD)信道冲激响应(Channel Impulse Response,CIR)解时,理论证明最优导频符号集合与快速傅里叶变换(Fast Fourier Transform,FFT)矩阵相乘构成的乘积符号集合满足完全正交性。此时,时间同步最优导频符号发送可估计出准确的TD CIRs,完全消除导频污染。2.针对系统子载波资源不充足导致乘积符号集合不满足完全正交性,时间同步最优导频符号发送方案产生导频污染的问题,本论文设计了一种上行链路和下行链路相结合的TWO-STAGE导频发送方案,通过下行链路传输最优导频符号估计“纯净”的TD CIRs,并将其封装在上行最优导频符号中,使基站可以在上行链路信道估计阶段提取出“纯净”的TD CIRs。仿真结果表明,该方案的导频训练开销、信道估计精度以及系统和速率等性能较已有导频污染消除方案具有明显优势。此外,该方案可以使基站避免协作,也可避免已知信道二阶统计信息等复杂度过高的问题。3.为了进一步减小导频训练开销,提高系统谱效,本论文在系统子载波资源不充足的情况下基于最优导频符号集合提出了一种用户分组方案。乘积符号集合在子载波资源不充足时虽然不满足完全正交性,但其中某些元素构成的子集满足部分正交性。本论文利用此特性,理论证明频率复用小区内用户存在最优用户分组,使得每组内用户的乘积符号相互正交。用户分组方案则取决于系统有效信道相干间隔(Channel’s Coherence Interval,COHI),如果有效COHI不小于最优用户分组数,用户分组方案即为最优用户分组,否则用户分组方案由有效COHI的值确定,不同组的用户通过时间交错最优导频符号发送消除导频污染。仿真结果表明,该方案能获得较理想的导频训练开销、信道估计精度以及系统和速率。此外,该方案简单实用,具有实际应用价值。4.针对在给定上行总功率的前提下,上行导频和数据之间功率分配对多小区大规模MIMO-OFDM系统有效聚合速率(Aggregate Rate,AR)性能影响问题,本论文基于导频污染消除方案给出了上行导频功率优化评估函数,并基于此评估函数分别优化了传统时间同步导频训练序列发送方案和用户分组方案。仿真结果表明,系统有效AR为上行导频功率分配因子的凸函数。此外,为了获取系统最大有效AR,本论文建立了一个基于上行导频功率分配因子和系统有效AR的单变量最优函数,并采用黄金分割法求解最优上行导频功率分配因子,从而得到系统最大有效AR。仿真结果还表明用户分组方案由于较小的导频训练开销不仅能够提高系统谱效,而且能通过上行导频功率优化进一步提高系统能效。
[Abstract]:It is one of the most effective solutions to improve the data flow in the future 5G network. However, the inter cell interference problem is caused by the ultra dense network deployment, which has become the main factor restricting the capacity of the system. The overintensive network is caused by the multiple cell frequency reuse and the limited channel coherence time. The adjacent cells in the collaterals can only be estimated through the multiplexed orthogonal pilot training sequences. The resulting Pilot Contamination (PC) problem becomes the main interference problem between the cells. The high gain contained in the large scale multi cell multi input multiple output (Multiple-Input Multiple-Output, MIMO) system configuration of a large-scale antenna. It can significantly improve the energy efficiency and spectral efficiency of the communication system. It is considered as an important alternative for 5G wireless communication in the future. However, increasing the number of base station antennas does not eliminate the influence of pilot pollution. Pilot pollution has become a bottle neck problem that restrict the performance of a multi cell large-scale MIMO system. The research results of pilot pollution elimination technology in MIMO system, of which pilot pollution elimination technology based on pilot distribution scheme is the focus of research. Due to the different communication mechanisms corresponding to different orthogonal pilot design, this paper will combine orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology and large-scale MIMO technology constructs a multi cell and large-scale MIMO-OFDM communication mechanism. Based on this communication mechanism, the optimal pilot symbol is designed and the pilot pollution elimination scheme is combined with the pilot pollution elimination scheme. The main work and innovation points are as follows: 1. for the multi cell large-scale MIMO-OFDM system, the multiple cell frequency reuse and channel coherence are due to the multi cell large-scale system. The problem of pilot pollution caused by time is limited. This paper uses the frequency domain (Frequency Domain, FD) multi carrier resource of OFDM technology to model the pilot signal on multi carrier, and then designs the optimal pilot symbol set for the users in the frequency multiplexed cell. When the system subcarrier resources are sufficient, the base station receives and receives the optimal pilot When the number equation has the full time domain (Time Domain, TD) channel impulse response (Channel Impulse Response, CIR) solution, the theory proves that the product symbol set composed of the optimal pilot symbol set and the fast Fourier transform (Fast Fourier Transform, FFT) matrix satisfies complete orthogonality. At this time, the time synchronization optimal pilot symbol can be estimated. The accurate TD CIRs completely eliminates the pilot pollution.2. to solve the problem that the product symbol set does not satisfy the complete orthogonality because the system subcarrier resources are insufficient, and the time synchronization optimal pilot symbol sends the pilot pollution. This paper designs a TWO-STAGE pilot transmission scheme which combines the uplink and downlink links, and the scheme has been designed in this paper. The downlink transmission optimal pilot symbol estimates the "pure" TD CIRs, and encapsulates it in the upstream optimal pilot symbol, enabling the base station to extract "pure" TD CIRs. simulation results in the uplink channel estimation stage, indicating that the pilot training overhead, channel estimation accuracy, and system and rate performance of the scheme are relatively existing. In addition, the scheme can make the base station avoid cooperation and avoid the problem of high complexity such as the two order statistical information of the known channel. In order to further reduce the pilot training overhead and improve the spectral efficiency of the system, this paper is based on the optimal pilot symbol set in the case of insufficient subcarrier resources of the system. A user grouping scheme is proposed. The product symbol set is not satisfied with complete orthogonality when the subcarrier resource is inadequate, but the subset of some elements satisfies partial orthogonality. This paper uses this characteristic to prove that the users in the frequency reuse community have the optimal user grouping, which makes the product symbols of the users in each group. The user grouping scheme is orthogonal. The user grouping scheme depends on the system effective channel coherence interval (Channel 's Coherence Interval, COHI). If the effective COHI is not less than the optimal user packet number, the user packet scheme is the optimal user packet, otherwise the user grouping scheme is determined by the value of the effective COHI, and the users of the different groups interlace the optimal pilot through the time. The simulation results show that the scheme can obtain ideal pilot training overhead, channel estimation precision and system and rate. In addition, the scheme is simple and practical, and the practical application value.4. is based on the given upper total power, the uplink pilot and the power distribution between the data and the multi cell large-scale M The effective aggregation rate (Aggregate Rate, AR) performance of the IMO-OFDM system is affected. Based on the pilot pollution elimination scheme, the optimal evaluation function of the upstream pilot power is given. Based on this evaluation function, the transmission scheme and the user grouping scheme of the traditional time synchronous pilot training sequence are optimized. The simulation results show that the system is effective AR In addition, in order to obtain the maximum effective AR of the system, in order to obtain the maximum effective AR of the system, a single variable optimal function based on the power distribution factor of the upstream pilot and the effective AR of the system is established, and the optimal upper pilot power distribution factor is solved by the golden section method, thus the maximum effective AR. simulation node of the system is obtained. The result also shows that the user packet scheme can not only improve the spectral efficiency of the system, but also improve the energy efficiency of the system by optimizing the uplink pilot power.
【学位授予单位】：郑州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TN919.3

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