Research Of Radio Resource Allocation Strategies In Future Wireless Communication Systems

With the popularization of Internet and the rapid development of mobile communications, a variety of high data-rate applications such as multimedia services have become the dominant part for future wireless communication systems. The next generation commincation networks are envisioned to provide QoS guarantees for with high spetral efficiency. Thus the design of effiective and flexible radio resource management and packet scheduling become crucial for network operators.This dissertation focuses on studying the radio resource allocation (RRA) and packet scheduling algorithms for future wireless communication systems, which are supposed to adopt new physical layer transmission techonologies (such as OFDM, MIMO, MIMO/OFDM) and novel network achitectures (such as DWCS).Chapter 1 reviews the history of wireless systems in brief and lists the opportunities and chanllenges in radio resource allocation. Finally we give the concept of cross-layer designs which are of great interests in recent literate.Chapter 2 gives an overview of existing RRA schemes in OFDMA systems. Subcarrier assignment and power allocation for both single user OFDM system and multiuser scenarios are investigated under different optimization criterias. Then RRA algorithms using rate-based utility function and delay-utility functions are formulated. Finally the RRA problem for multicell OFDMA systems is discussed and some existing strategies are given.Chapter 3 investigates packet scheduling for multiuser MIMO systems and proposes a unified cross-layer optimization framework for the downlink of mutiuser MIMO systems. The concept of utility function is adopted to transform the complicated constrained optimization RRA problem into utility maximization. In addition, we develop a novel user grouping method and a group based opportunistic fair scheduling algorithm base on the proposed framework.Chapter 4 investigates the resource allocation problem for Orthogonal Frequency Division Multiple Access-Spatial Division Multiple Access systems (OFDMA-SDMA). We propose a cross-layer design, which jointly takes the constraints posed by the physical layer (in terms of BER performance and spatial orthogonality) and the constraints posed by the media access control layer (in terms of quality of service requirements and user fairness). At each scheduling interval, the scheduling procedure is divided into two steps: user selection, bit and power allocation. The two-step algorithm is shown to enjoy a low implementation complexity. It improves the spectral efficiency significantly while maintaining QoS guarantees and certain fairness.Chapter 5 discusses the radio resource allocation problem for OFDMA based distributed wireless communication systems (OFDMA-DWCS). We propose a fair and simple resource allocation scheme, which hierarchically decouple the subcarrier and power allocation problem into two subproblems. A distributed scheduling is employed on two levels: access-point-level (AP-level) and user-level. In AP-level scheduling, the subcarriers are roughly allocated by the central unit (CU) to different APs. In user-level scheduling, a further subcarrier and power allocation is performed by each AP for its underlying users. We adopt Nash bargain solution fairness criterion in our scheme, which ensures a good tradeoff between fairness and efficiency on both the AP-level and the user-level. Simulation results demonstrate that the distributed scheme can achieve comparable overall system rate to that of centralized algorithms with much reduced complexity.Finally, the dissertation is summarized, and some ideas about future research on RRA are put forward.