【作者】 赵越；

【导师】 方旭明；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2012， 博士

【摘要】 由于具有吞吐率高和覆盖性强的特点,OFDMA多跳中继蜂窝网络(MRCN)受到广泛关注。但其仍有三个重要问题亟待解决：首先,中继站(RS)的引入改变了传统蜂窝网络的频率规划策略,因此如何在策略设计中对中继链路进行高效的频率资源分配成为极具挑战的问题；其次,小区频率复用越紧密,同频干扰(CCI)越严重,进而对系统的整体性能产生影响；最后,在真实网络环境中,小区内用户呈非均衡分布状态。大量用户接入同一站点将导致MRCN的负载失衡,影响热点区域的系统性能,从而无法满足用户的服务质量(QoS)要求。本文基于IEEE802.16j/m标准,以下行链路的无线资源管理为基本手段,结合时分复用、空间复用、频率复用等技术,对MRCN网络中的路径选择、本地转发、资源调度、干扰协调、负载均衡、功率控制等问题的设计与优化进行深入研究。首先,提出OFDMA多跳中继蜂窝网络的高效资源复用策略。从路径选择和频率规划两个方面对比分析不同算法对系统性能的影响。该策略提出的高效资源复用方案以部分频率复用技术作为研究主线,分别从理论分析和性能仿真两个方面进行深入研究；并以路径选择与同频干扰的空间相关性为基础,设计合理的资源复用策略及其对应的多跳中继下行子帧结构,在保证网络的资源利用率的同时,降低干扰给相邻小区边缘用户带来的影响,有利于全局频率复用策略的实施。与常规MRCN相比,采用该策略的MRCN能够充分利用频谱资源,系统吞吐率增益达13.8%,小区覆盖率增益达5.4%。其次,提出OFDMA多跳中继蜂窝网络的本地转发方案。针对中继用户数据链路的优化问题,该方案允许移动台(MS)间的数据通信只需通过中继站进行本地转发传输,而无需再将数据传送给基站(BS),这样即可降低BS的空口负载,提高系统的资源利用率,同时还减少了MS之间的数据传输跳数。接着提出联合考虑本地转发模式特性和资源分配方案的路径选择算法。该算法所选出的最佳路径更有利于系统性能的优化。此外,在IEEE802.16j/m网络架构和信令机制的基础上,分析MRCN系统中实现本地转发功能的控制信令交互机制。与常规MRCN相比,本地转发技术与部分频率复用技术相结合的MRCN可获得36.2%的系统吞吐率增益。再次,提出OFDMA多跳中继蜂窝网络的空间复用及干扰协调策略。根据多跳蜂窝网络的特点,对空间复用方案、时分复用方案、频率复用方案进行联合设计与优化。基于部分频率复用技术提出两种策略,分别是在同扇区内BS采用部分频率复用而RS采用正交频率分配(BFRO)策略和BS与RS都采用部分频率复用(BFRF)策略。BFRO策略和BFRF策略既确保高效的资源利用率,同时也能有效降低因资源复用产生的同频干扰。此外,详细分析策略涉及的频率规划、功率控制、路径选择和区域选择、时隙资源分配等一系列关键技术问题。提出的两种策略可有效解决扇区内因空间复用产生严重干扰的问题；与正交资源分配技术和NT-RS(非透明中继站)集中分配技术相比,虽然覆盖率些微下降,但依然能满足覆盖率95%的要求,同时扇区吞吐率性能增益达16%以上。然后,提出OFDMA多跳中继蜂窝网络基于负载均衡的资源分配策略。考虑难以得到联合分配的最优解,在减少计算复杂度的前提下,采用分步式次优化分配。首先采用比例公平算法对子载波进行分配,并对功率分配进行数学建模。接着根据凸规划和注水算法,确定满足功率分配最优解的条件,在逼近最优解的目标下,求得基站和中继站的发射功率。提出的基于负载均衡的资源分配策略兼顾了效率与公平性,在满足系统发射功率和子载波数量的限制条件下,可适应单个小区内不同的用户分布,解决负载失衡问题。在四种典型用户分布场景中,与静态资源分配策略相比,该策略的系统吞吐率提升幅度分别为7.8%、22.6%、31.1%和46.7%。最后,提出OFDMA多跳中继蜂窝网络的干扰协调与负载均衡联合策略。首先,提出可降低小区边缘区域干扰并保持较高频谱效率的频率复用方式;再结合干扰协调技术,将高效的比例公平调度算法扩展到多跳中继蜂窝网络,旨在提升系统性能；其次,设计出基于负载均衡的切换机制,该机制可对业务负载进行均匀分配并满足用户的QoS要求。干扰协调与负载均衡联合策略可以根据信道质量和业务负载进行自适应的资源管理,充分利用MRCN系统的频率复用和功率控制技术,对系统性能参数进行联合优化,其目的为最大程度地提升频谱效率,改善用户传输速率的公平性,降低传输中断率,克服因干扰功率约束改变而导致的系统吞吐率和覆盖率降低。更多还原

【Abstract】 OFDMA-based multi-hop relay cellular networks (MRCNs) have drawn tremendous attention due to its high throughput and extensive converage. However, there are still three issues not well addressed:1) with the introduction of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue;2) for mobile stations (MSs) near the cell edge, co-channel interference (CCI) becomes severe, which significantly affects the network performance;3) in real network environment, users are not evenly distributed in cells/sectors, so too many users accessing one station (BS or RS) probably yields load imbalance, which makes the station congested and violates the quality of service (QoS) requirements of the users. Based on the downlink of radio resource management, with technologies such as time division duplex (TDD), spatial reuse and frequency reuse, this paper studies the design and optimization of path selection, local forwarding, resource scheduling, interference coordination (IC), load balancing (LB), and power control according to IEEE802.16j/m specification, which can be elaborated as follows:Firstly, an efficient frequency reuse scheme for OFDMA-based MRCNs is proposed. The effect of different algorithms on system performance is analyzed in terms of both path selection and frequency planning. The author also puts forward an efficient resource reuse scheme focuses on FFR in both theoretical analysis and performance simulation. Furthermore, a proper resource reuse scheme and multi-hop relay downlink sub-frame are designed to deal with the inter-cell interference for the implementation of overall frequency reuse scheme. It not only guarantees the efficient utilization of resource in networks but also protect the users in the edge of adjacent cell from interference, which is conducive to the implement of full frequency reuse scheme. Compared with the traditional MRCN, the MRCN adopting the proposed scheme is able to make full use of spectrum resource. Its throughput gain and cell coverage probability gain is13.8%and5.4%, respectively.Secondly, a local forwarding transmission scheme for OFDMA-based MRCN is imtroduced. For the optimization of the data transmission link of the users associated with RSs. the scheme allows the data transmission between MSs via RSs instead of the re-delivery of data to Base Station (BS). It not only mitigates the air-interface at BS. promotes the system resource utilization level, but also reduces the number of hops in the data transmission between MSs. A path selection algorithm for local forwarding mode is also proposed with jointly considering the characteristics of local forwarding mode and the resource allocation scheme, and the optimum path selected whereby can enhance the optimization of the system performance. Additionally, according to the networks structure and signaling mechanism of IEEE802.16j/m, the author analyzes the mechanism of control signaling interaction supporting administrable local forwarding. Compared with the traditional MRCN, the MRCN jointly considering local forwarding transmission and FFR can increase the system throughput by36.2%.Thirdly, a spatial reuse with interference coordination scheme for OFDMA-based MRCN is put forward. The scheme is designed and optimized with spatial reuse, time division multiplexing and frequency reuse considered jointly according to the characteristics of MRCNs. Based on FFR. two schemes are proposed, namely BS Adopts FFR and RS Adopts FFR (BFRF) scheme and BS Adopts FFR and RS Adopts Orthogonal Allocation (BFRO) scheme. The two proposed schemes can both mitigate the CCI and maintain high resource utilization. Moreover, the key issues on frequency planning, power control, path selection and zone selection, and slot allocation that are involved in the two proposed schemes are specifically analyzed. The two proposed schemes can give an effective resolution to the serious interference caused by intra-sector spatial reuse. Compared with the orthogonal allocation scheme and NT-RS with centralized allocation mode, the schemes, although causing a bit decrease in the coverage probability, can not only satisfy the requirement of95%, but also highly improve the sector throughput by16%.Fourthly, a resource allocation based on load balancing for OFDMA-based MRCNs is raised. Since it is difficult to solve a joint optimization problem, the author provides a step-by-step sub-optimal allocation scheme on the premise of reducing the computational complexity. With advance sub-channel allocation by proportional fair algorithm, the paper introduces the math modeling for power allocation algorithm. According to convex optimization and water-filling algorithm, the paper determines the certain conditions to satisfy the optimal power allocation solution, and also calculates the results of transmission power among BS and RSs for approaching the optimal solution. The proposed resource allocation scheme based on load balancing (RALB) takes efficiency and fairness into consideration. Under conditions of transmission power and number of subcarrier, the scheme is adaptable to different user distributions and can solve load unbalancing. In four different typical use distribution scenes, compared to traditional static resource allocation (SRA), the schemes can improve throughput by7.8%,22.6%,31.1%and46.7%, respectively.At last, a scheme jointly considering interference coordination and load balancing for OFDMA-based MRCNs is given. Firstly, present a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency; secondly, apply the efficient PF algorithm to MRCN, combined with IC; thirdly, design practical LB-based handover mechanisms which can evenly distribute the traffic load and guarantee QoS of users. The proposed scheme can do adaptive resource management according to channel quality and service load, make the best of frequency reuse and power control, and realize joint optimization of parameters of system performance, in order to promote spectrum efficiency to the most extent, improve the fairness of use transmission rate, reduce transmission outage probability, and overcome low throughput and coverage probability caused by changing interference power constraint.更多还原