Cross-layer Optimizations In Wireless Communica-tion Systems

The layered architecture in current mobile communication systems implies that every sublayer in the system can only guarantee a local optimal system performance. Cross-layer design can break the traditional layered architecture, and jointly optimize multiple layers to achieve better performance that is unattainable by single layer optimization technology. In the next generation wireless communication systems, the development of cross-layer de-sign technologies plays an important role in the fusion of different networks/technologies, and may motivate completely-new wireless system architectures. In this dissertation, we consider the problems of cross-layer power allocation policy, of cross-layer modeling of multiple antenna systems and of cross-layer designs in wireless sensor networks. Fol-lowing the standardization work of the fourth generation mobile communication system, the technologies of multiple antenna detector and coordinated multiple point transmis-sion/reception have also been studied.For the cross-layer power allocation problem, we obtain the optimal and suboptimal queuing-aware power allocation policies using Markov decision process theory and ap-proximated two-parameter polices respectively. Here, the goal is to identify the optimal queuing-aware power allocation policy to minimize the overall system packet error rate under constraint of long-term transmit power. One crucial step which we call 'inner'prob-lem is to find the optimal power vector at a given target packet error rate at physical layer. Rather than attacking the multi-dimensional optimization problem directly using conven-tional methods, we first observe that the 'inner'problem is closely related to an average reward Markov decision process problem, and relax the former to the latter so as to take advantage of its equivalence with linear program which allows efficient solution. Since the randomness in the associated Markov decision process is only slight, we propose two approximately deterministic policies as suboptimal solutions to the 'inner'problem with negligible insignificant performance degradation. We also propose two-parameter power allocation methods to achieve suboptimal results with low complexity. When the average queuing delay constraint is added to the cross-layer model, we also analysis its effect on the performance of above policies.Second we analyze the performance of adaptive modulation-based Bell-labs layered space-time (BLAST) systems with finite-length queuing model. Since the thresholds values for the adaptive modulation scheme should be optimized when the queuing model is taken into account in the system, cross-layer performance analysis on the queuing behavior is necessary. Based on the joint probability distribution function of the post-detection signal-to-noise ratios of BLAST, we express the service rate distribution of adaptive modulation-based BLAST system in closed form, and provide an accurate interface of physical layer for upper layer Markov chain analysis. We also discuss three applications of the accurate numerical results in cross-layer designs.Then we propose a sphere decoder-based complexity-reduced multistage detection algorithm in multiple antenna iterative detection and decoding system. According to con-stellation decomposition algorithm, high order multilevel quadrature amplitude modula-tion (QAM) system can be decomposed into several parallel quadrature phase shift keying sub-systems. We apply the efficient soft sphere decoder in every sub-system to calculate log-likelihood ratio of every bit.Next we propose an improved energy consumption cross-layer model in wireless sen-sor network. We propose a much improved approximation of the bound on the probability of bit error for uncoded multilevel quadrature amplitude modulation, with the desirable convexity of the optimization problem preserved. Simulation results show that our method can better improve energy efficiency with slight increased complexity.Finally a slot type-based frequency reuse plan is proposed in the mobile system using coordinated multiple point (CoMP) technology. CoMP cluster overlapping with real cell topology makes the resource allocation problem of CoMP system more complicated. The proposed frequency reuse plan can guarantee that cell edge-users who need cooperation service can be served by the best three neighboring cells, and improves the quality of the link effectively.VII...