【作者】 周朝荣；

【导师】 李乐民；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2009， 博士

【摘要】 CDMA蜂窝系统是干扰受限的，降低多址干扰是提高系统容量的有效途径。基站接收机可采用多用户检测算法降低多址干扰、提高系统容量，其中，串行干扰消除(Successive Interference Cancellation，SIC)由于具有低实现复杂度、高系统性能而受到了广泛的关注。尽管采用诸如SIC之类的多用户检测算法有助于降低CDMA蜂窝系统中的多址干扰、提高系统容量，但随着移动用户数目的快速增长以及用户对于通信业务要求的提高，系统对于无线资源将有更高的需求，有限的系统资源与无限的用户需求之间的矛盾依然存在。因此，即使在基于SIC的CDMA系统中，同样需要研究无线资源管理，即在保证服务质量(Quality of Service，QoS)的前提下，研究如何充分有效地利用无线资源的问题。在基于SIC的CDMA系统中，不同的译码顺序导致不同的系统性能，其无线资源管理与基于单用户检测(Single user detection，SUD)接收机的无线资源管理有所区别，此时，需要结合译码顺序的调整联合考虑。本文从系统设计出发，研究基于SIC的CDMA系统中的无线资源管理关键问题，包括功率控制、速率分配、呼叫接纳控制以及多径衰落分集信道下的容量分析等几个方面。本论文的主要工作总结如下：首先研究结合SIC的CDMA蜂窝系统中的功率控制及相关问题。推导出多小区情况下最佳功率分配的表达式；针对用户发射(接收)功率存在限制的情况，提出了如何检验系统可行与否的有效方法；针对用户发射(接收)功率存在限制的情况，推导出能够最小化系统中断概率的最优译码顺序；推导出能够最小化总发射功率的最优译码顺序。在基于SIC的CDMA蜂窝系统中，可能的速率模式与译码顺序随着用户数的增长而指数增长，如何有效地分配用户速率是一NP问题，需要考虑速率分配与译码顺序调整的联合优化。本文首先提出了两种贪婪算法求解此问题，算法具有较低的计算复杂度与较好的性能。进一步地，又提出了结合遗传算法的速率分配算法求解该问题，理论上证明了该算法能够完全收敛到全局最优解。仿真结果表明，较之贪婪算法而言，有着更高计算复杂性的结合遗传算法的速率分配算法能够获取更好的解。呼叫接纳控制也是无线资源管理的一个重要功能模块，本文接着研究采用SIC的CDMA系统中的呼叫接纳控制，提出两种呼叫接纳控制算法。一种是在用户发射(接收)功率限制下基于业务升降级的呼叫接纳控制算法，另外一种是在用户发射(接收)功率与基站接收机处总接收功率的共同限制下基于服务等级(Gradeof Service，GoS)设置接纳门限的呼叫接纳控制算法。前者在尽可能多地接纳新用户的同时有助于最大化系统吞吐量，后者有利于优化系统服务等级。SIC技术对于CDMA系统的容量也有重要影响，本文最后分析了多径衰落分集信道下基于SIC的多业务CDMA蜂窝系统容量，综合考虑了功率控制误差、阴影效应、多径衰落以及Rake接收机最大比合并多条分集信道等因素。分别用对数正态分布与高斯分布近似基站接收机处的总接收功率，得到了在这样的情况下系统容量的计算方法。在分析中，避免了当前文献中一些过于简单或理想的假设条件，相应得到的解析结果有助于为系统容量的规划与设计提供参考。更多还原

【Abstract】 CDMA cellular systems are interference-limited and one effective way to increase the system capacity is to reduce the multiple access interference (MAI). The receiver in the base station can use multi-user detection (MUD) algorithms to reduce MAI and increase system capacity. Among these algorithms, successive interference cancellation (SIC) is widely employed due to its low implementation complexity and satisfying performance. Although MUD algorithms like SIC can help to reduce MAI and increase system capacity, CDMA cellular system desires more radio resources in response to the rapid increment of mobile users and the high requirements of communication services. This pose a challenge to satisfy the increasing users’ requirements based on limited system resources. Hence, in CDMA systems based on SIC, it is also imperative to address the issue of radio resource management (RRM), i.e., subject to Quality of Service (QoS) guarantee, the issue how to fully and efficiently utilize radio resources needs to be carefully studied. In CDMA systems based on SIC, different decoding orders result in different system performance. Consequently, the issue of RRM in this kind of systems is different from those of RRM in systems based on the single user detection (SUD) receiver. In this case, the research of RRM needs to be studied by taking into account the adjustment of decoding orders. This dissertation, from a system design point of view, is devoted to the essential problems of RRM in CDMA systems based on SIC, such as power control, rate allocation, call admission control (CAC) and system capacity analysis under multi-path diversity fading channels. The main contributions of this dissertation can be summarized as follows:We first study power control and related problems in CDMA cellular systems with SIC. The optimal power allocation formula under the multi-cell model is derived. An efficient method for examining the feasibility of systems is proposed, where the transmission (received) powers of users are constrained. The optimal decoding order of minimizing the system outage probability is derived for the case where powers of users are constrained. Finally, the optimal decoding order of minimizing the total transmission power is proposed.In the CDMA cellular system based on SIC, the numbers of possible rate modes and decoding orders grow exponentially with the number of users. How to efficiently allocate rates is an NP problem, which involves the joint optimization of rate allocation and decoding order adjustment. We propose two greedy algorithms for this problem. As a result, both algorithms have a low computation of complexity while achieving good performance. Furthermore, another rate allocation algorithm based on the genetic algorithm is proposed to solve this kind of rate allocation problems. We theoretically prove that the algorithm can completely converge to the global optimum. The simulation results show that the latter algorithm with higher computational complexity can obtain the better solution than the greedy algorithms.CAC is also an important functional module of RRM, next, we turn to study CAC in CDMA cellular systems with SIC and propose two CAC algorithms. One is the CAC algorithm based on upgrading and degrading service levels under the limit of users’ transmission (received) power, and the other is the CAC algorithm based on Grade of Service (GoS) to set the admission threshold under both limits of users’ transmission (received) power and total received power in base stations. The former helps to maximize the throughput while allowing more users accepted, and the latter benefits to optimize the GoS of system.SIC has heavy impacts on the capacity of CDMA systems, finally, we analyze the capacity of multi-services CDMA cellular systems based on SIC under multi-path fading diversity channels. We take into account the aspects of power control error, shadowing effects, multi-path fading, and multiple diversity channels which are maximal ratio combined by the Rake receiver, etc. The log-normal distributed random variable and Gaussian distributed random variable are used to approximate the total received power in base stations, respectively. The method calculating system capacity in this situation is obtained. Unlike the methods in existing literatures, we avoid the simplified or unrealistic assumptions during analysis such that the corresponding results can be used as a reference for system capacity planning and design.更多还原