OFDMA-MIMO无线多跳中继系统下行链路自适应资源分配研究
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摘要
支持高速率多业务信息传输是下一代移动通信系统最突出的特点,考虑采用先进的正交频分多址接入(Orthogonal Frequency Division Multiple Access, OFDMA)、多输入多输出(Multiple Input Multiple Output, MIMO)和中继技术,结合适当的自适应资源分配机制,能够改善系统频谱利用率、扩大网络覆盖范围等性能,它们成为未来无线宽带接入系统／蜂窝移动通信系统研究的关键技术。
由于无线信道的频率选择性衰落特性,在OFDMA系统中可以根据信道状态信息(Channel State Information, CSI),为用户自适应地分配子载波资源,能够避开处于深衰落的信道,实现系统资源优化利用。MIMO和中继技术的引入,为自适应资源分配带来了新的问题,如空域资源与频域、时域资源的联合优化,中继链路需要占用额外的资源,多跳链路容量存在瓶颈效应等。因此,针对上述问题,改进设计适用于OFDMA-MIMO多跳中继系统下行链路的自适应资源分配机制是本文的研究重点。
论文首先介绍了OFDMA-MIMO多跳中继系统相关技术理论基础,包括OFDM系统多址接入方式基本原理、MIMO信道容量分析以及引入中继所带来的无线资源分配新问题。然后就OFDMA-MIMO多跳中继系统典型自适应资源分配算法进行详细地研究,并搭建仿真平台,根据算法仿真结果分析了现有典型算法的优缺点。考虑子载波信道差异的现有相关自适应资源分配算法频率资源最小分配单位为一个子载波,由于分配过程中循环迭代次数较多,算法运算量很大,因此,为了降低分配方案运算量,提出一种资源单位(Resource Unit, RU)组建模式,一个RU包含多个子载波信道,使频率资源最小分配单位为一个RU。基于该RU组建模式,提出适用于OFDMA-MIMO多跳中继系统下行链路的资源分配方案,包括基于RU组建的基站(Base Station, BS)集中式分配和基于RU组建的中继站(Relay Station, RS)辅助式分配,方案在保证非实时用户速率成比例公平性和BS/RS站点发射总功率受限的条件下,尽量提升系统吞吐量系能。通过分析和仿真验证,基于RU组建的分配算法粗化了资源分配的最小单位,与以单子载波为单位的分配算法相比,减少了分配算法的运算量,但是系统吞吐量性能有所降低；所提出的资源分配方案能够在保证用户数据速率比例公平、系统吞吐量性能和算法运算量之间取得良好的折中。
Next generation mobile communication systems are envisaged to be able to provide high rate multi-service information transmission. Deploying orthogonal frequency division multiple access (OFDMA), multiple input multilple output (MIMO) and relay technologies into the future wireless broadband access systems or cellular networks can help improve the system spectral efficiency and expand network coverage.
Due to the frequency-selective fading of wireless channel, the adaptive resource allocation algorithms are used in OFDMA systems for avoiding that the subcarriers assigned to a specific user experience deep fading. It assigns subcarriers to multi-user flexiblely according to the channel state information (CSI), thus the resource utilization is optimized. The introduction of MIMO and relay technologies has brought new problems for adaptive resource allocation, such as the joint optimization of the spatial, time and frequency domain resources, the extra resource allocation for relay link, the capacity balance between relay link and access link for relay users. It is therefore the objective of this thesis to investigate the adaptive resource allocation algorithms for application in OFDMA-MIMO multi-hop relay downlink systems.
In this thesis, the theory of related technologies for OFDMA-MIMO multi-hop relay system is introduced firstly, including the principle of the multiple access methods, the analysis of the MIMO channel capacity and the new features of resource allocation arising for relay enhanced networks. Then the typical existing adaptive resource allocation algorithms are investigated in details. A system-level simulation model is built up for OFDMA-MIMO multi-hop relay systems. Based on the analysis of simulation results, the advantages and disadvantages of the typical algorithms are studied. The minimum frequency resource allocation unit in existing algorithms is mainly a subcarrier. Therefore a large amount of computation work would be done due to the large loop iteration number of subcarrier allocation. In order to reduce the computation complexity, a novel mode of building a resource unit (RU) composed of a set of subcarries is introduced. Based on the novel mode, adaptive resource allocation schemes are proposed for the OFDMA-MIMO multi-hop relay downlink system. The former is a base station (BS) centralized algorithm, and the latter is a relay station (RS) assisted method. The target of the proposed schemes is to maximize the average system capacity under the limited total power constraint. Meanwhile, the proportional fairness of the user data rate should be achieved. According to the analysis of the simulation results, the novel RU building mode reduces the computation complexity at the expenses of the system capacity by enlarging the granularity of the minimum resource allocation unit. And the results also show that the proposed resource allocation schemes can achieve an efficient tradeoff among proportional fairness, system capacity and computation complexity.
由于无线信道的频率选择性衰落特性,在OFDMA系统中可以根据信道状态信息(Channel State Information, CSI),为用户自适应地分配子载波资源,能够避开处于深衰落的信道,实现系统资源优化利用。MIMO和中继技术的引入,为自适应资源分配带来了新的问题,如空域资源与频域、时域资源的联合优化,中继链路需要占用额外的资源,多跳链路容量存在瓶颈效应等。因此,针对上述问题,改进设计适用于OFDMA-MIMO多跳中继系统下行链路的自适应资源分配机制是本文的研究重点。
论文首先介绍了OFDMA-MIMO多跳中继系统相关技术理论基础,包括OFDM系统多址接入方式基本原理、MIMO信道容量分析以及引入中继所带来的无线资源分配新问题。然后就OFDMA-MIMO多跳中继系统典型自适应资源分配算法进行详细地研究,并搭建仿真平台,根据算法仿真结果分析了现有典型算法的优缺点。考虑子载波信道差异的现有相关自适应资源分配算法频率资源最小分配单位为一个子载波,由于分配过程中循环迭代次数较多,算法运算量很大,因此,为了降低分配方案运算量,提出一种资源单位(Resource Unit, RU)组建模式,一个RU包含多个子载波信道,使频率资源最小分配单位为一个RU。基于该RU组建模式,提出适用于OFDMA-MIMO多跳中继系统下行链路的资源分配方案,包括基于RU组建的基站(Base Station, BS)集中式分配和基于RU组建的中继站(Relay Station, RS)辅助式分配,方案在保证非实时用户速率成比例公平性和BS/RS站点发射总功率受限的条件下,尽量提升系统吞吐量系能。通过分析和仿真验证,基于RU组建的分配算法粗化了资源分配的最小单位,与以单子载波为单位的分配算法相比,减少了分配算法的运算量,但是系统吞吐量性能有所降低；所提出的资源分配方案能够在保证用户数据速率比例公平、系统吞吐量性能和算法运算量之间取得良好的折中。
Next generation mobile communication systems are envisaged to be able to provide high rate multi-service information transmission. Deploying orthogonal frequency division multiple access (OFDMA), multiple input multilple output (MIMO) and relay technologies into the future wireless broadband access systems or cellular networks can help improve the system spectral efficiency and expand network coverage.
Due to the frequency-selective fading of wireless channel, the adaptive resource allocation algorithms are used in OFDMA systems for avoiding that the subcarriers assigned to a specific user experience deep fading. It assigns subcarriers to multi-user flexiblely according to the channel state information (CSI), thus the resource utilization is optimized. The introduction of MIMO and relay technologies has brought new problems for adaptive resource allocation, such as the joint optimization of the spatial, time and frequency domain resources, the extra resource allocation for relay link, the capacity balance between relay link and access link for relay users. It is therefore the objective of this thesis to investigate the adaptive resource allocation algorithms for application in OFDMA-MIMO multi-hop relay downlink systems.
In this thesis, the theory of related technologies for OFDMA-MIMO multi-hop relay system is introduced firstly, including the principle of the multiple access methods, the analysis of the MIMO channel capacity and the new features of resource allocation arising for relay enhanced networks. Then the typical existing adaptive resource allocation algorithms are investigated in details. A system-level simulation model is built up for OFDMA-MIMO multi-hop relay systems. Based on the analysis of simulation results, the advantages and disadvantages of the typical algorithms are studied. The minimum frequency resource allocation unit in existing algorithms is mainly a subcarrier. Therefore a large amount of computation work would be done due to the large loop iteration number of subcarrier allocation. In order to reduce the computation complexity, a novel mode of building a resource unit (RU) composed of a set of subcarries is introduced. Based on the novel mode, adaptive resource allocation schemes are proposed for the OFDMA-MIMO multi-hop relay downlink system. The former is a base station (BS) centralized algorithm, and the latter is a relay station (RS) assisted method. The target of the proposed schemes is to maximize the average system capacity under the limited total power constraint. Meanwhile, the proportional fairness of the user data rate should be achieved. According to the analysis of the simulation results, the novel RU building mode reduces the computation complexity at the expenses of the system capacity by enlarging the granularity of the minimum resource allocation unit. And the results also show that the proposed resource allocation schemes can achieve an efficient tradeoff among proportional fairness, system capacity and computation complexity.
引文
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[3]徐国鑫,张平,“下一代移动通信系统中的无线资源管理”,移动通信,2004年11期,pp.93-95.
[4]田韬,张新程,周晓津,关山,“WiMAX 16e无线网络技术与应用”,人民邮电出版社,2009年1月,pp.24-54.
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[20]Zukang Shen, Andrews J.G, Evans B.L., "Adaptive Resource Allocation in Multiuser OFDM Systems with Proportional Rate Constraints", IEEE Transactions on Wireless Communications, Volume:4, Issue:6, November 2005, pp.2726-2737.
[21]Wong I.C., Zukang Shen, Evans B.L., Andrews J.G, "A Low Complexity Algorithm for Proportional Resource Allocation in OFDMA Systems", IEEE Workshop on Signal Processing Systems,2004. SIPS 2004.13-15 October 2004, pp.1-6.
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