摘要
OFDM (Orthogonal Frequency-Division Multiplexing,正交频分复用)/OFDMA (Orthogonal Frequency-Division Multiple Access,正交频分多址)作为一种先进的调制/多址技术,能够提供高频谱效率的性能表现。在第四代移动通信系统中,OFDM作为基本技术之一决定了系统设计的基础架构。得益于OFDM本身的多载波特性以及子载波间正交性,OFDM系统的资源分配更为灵活、高效。鉴于已有资源分配研究成果在实际系统应用下的局限性,以及近年来对系统能源效率提升的迫切需求,本文重点关注实际OFDM系统资源分配的实现细节以及能源效率优化,结合用户业务需求进行动态无线资源分配研究。本文主要工作如下：
1.满足离散数据速率约束的低复杂度资源分配方案
针对调制、编码对子载波承载数据的影响,并且结合实际系统中依据SINR (Signal to Interference plus Noise Ratio,信干噪比)测量信息进行MCS (Modulation and Coding Schemes,调制编码方式)选择的反馈-决策方式,在离散数据速率约束下提出了一种具有低复杂度的资源分配算法,提高系统吞吐量/频谱效率性能并且满足用户最低速率请求。所提算法在最佳速率选择的基础上进行两轮子载波/子信道分配,相比现有基于迭代的资源分配方案具有更低的复杂度以及更好的适用性,并且通过进一步MCS拟合,易于在实际系统中实现。
2.满足子载波分组约束的频谱效率提升资源分配方案
针对实际系统MCS使用方式的限制,也即,为分配给同一用户的所有子载波/子信道资源使用同一种MCS进行数据的调制编码,提出了基于子载波分组约束的次优低复杂度资源分配方案,包括：一种满足用户速率区间的下行资源分配算法、一种满足用户速率比例约束的下行资源分配算法、以及一种联合子载波与功率分配进行频谱效率/吞吐量优化的上行资源分配算法。所提算法契合实际系统上行/下行资源分配要求,降低了实际系统中资源分配算法实现的复杂度,有效减少信令消耗并且简化基站/终端设备实现,能够满足系统公平性需求以及用户量化的速率请求,同时提升系统频谱效率/吞吐量。
3.满足系统公平性的能源效率提升资源分配方案
针对系统对best effort业务支持的公平性需求,提出了一种以能源效率为优化目标的资源分配算法,严格保证用户间比例速率约束,同时提升系统能源效率。所提算法将能效优化资源分配分为三个步骤：基于平衰落以及子载波共享假设的能效发射功率估算、基于max-min策略的频谱效率次优子载波分配、以及基于二分法的能效最优功率分配,将最优方案随子载波/子信道数目呈指数增长的复杂度降低为具有多项式时间级别、随用户数以及子载波/信道数目呈线性增长的复杂度。
本文从上述3个方面对OFDM系统动态无线资源分配进行了深入研究,针对实际系统的设计细节提出资源分配算法,解决了降低算法复杂度、提升算法适用度的问题；并且针对OFDM系统的能源效率提升进行了考虑系统公平性的算法研究,解决了能效资源分配算法建模合理性的问题。
OFDM (orthogonal frequency-division multiplexing)/OFDMA (orthogonal frequency-division multiple access),recognized as one of the most advantage modulation/multiplex techniques, can provide a high performance physical layer. In the well known4G wireless systems, OFDM is regarded as the fundamental technique affecting the network deployment. Benefiting from the multi-carrier transmission scheme and the orthogonality among subcarriers, the wireless resource allocation in OFDM systems is more flexible and efficient compared to the traditional solutions. Due to the limitation happened when employing the existing resource allocation algorithms in a real OFDM wireless system, practical resource allocation in OFDM wireless systems considering implementation issue and user requirement is investigated in this thesis. Furthermore, as a result of ever-increasing demand for green radio design, energy efficiency enhancement in OFDM systems is also investigated. Overall, three main aspects are covered:
1) A low-complexity suboptimal resource allocation algorithm with discrete rate sets constraint.
According to the effect of MCS (Modulation and Coding Schemes) on data loading in a real OFDM wireless system, a low-complexity suboptimal resource allocation algorithm with discrete rate sets constraint is developed assuming that MCS determination policy is executed based on SINR (Signal to Interference plus Noise Ratio) measurement. The proposed algorithm can not only reach a high system throughput/spectral efficiency, but also fulfill user minimum rate requirements. Comparing to the iterative-based algorithm in literature, the proposed algorithm is less complex via two-step subcarrier/subchannel allocation. Furthermore, the proposed algorithm is more flexible to be implemented in a real system via MCS related consideration.
2) Spectral-efficient resource allocation in OFDM wireless systems with subcarrier grouping constraint.
According to the implementation issue of MCS in a real OFDM wireless system, i.e., the subcarriers assigned to one user always use the same MCS, low-complexity suboptimal resource allocation schemes are proposed with subcarrier grouping constraint, including:a downlink resource allocation algorithm considering user rate allowed region, a downlink resource allocation algorithm considering proportional rate constraints, and a low-complexity resource allocation algorithm which carry out subcarrier assignment and power allocation jointly. The proposed algorithms fulfill the requirements of a real OFDM wireless system, reduce the complexity of resource allocation algorithms implementation, and also simplify related device implementation of both the base station and user side. Furthermore, system faireness and various user rate requirements are satisfied, and the system throughput/spectral efficiency is enhanced as well.
3) Energy-efficient resource allocation in OFDM wireless systems with system faireness consideration
According to system fairness requirement in a best-effort-service-based scenario, an energy-efficient resource allocation algorithm in OFDM wireless system with proportional rates constraint is proposed. Users are ensured achieving rate levels which equal to a predetermined proportion of the overall system throughput, and meanwhile the system energy efficiency is enhanced. The proposed algorithm includes three steps:energy-efficient transmit power estimation under assumption of flat fading and subcarrier sharing, max-min-based suboptimal spectral-efficient subcarrier assignment, and bisection-based optimal energy-efficient power allocation. Through the above steps, the complexity of the proposed algorithm is linearly increasing with respect to the number of users and that of subcarriers, compared to exponentially increasing with the number of subcarriers for optimal solution.
In this thesis, adaptive resource allocation in OFDM systems is investigated based on the above3aspects. According to the requirement of resource allocation in a real OFDM system, the algorithms are proposed to reduce computational complexity and inhance implementation flexibility. Furthermore, according to system fairness requirement in an energy-efficient OFDM system, the algorithm is proposed to make energy-efficient resource allocation more reasonable.
引文
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