| Over the past decades, the world has become increasingly mobile and wireless. As a result, traditional ways of networking will be inadequate to meet the challenges posed by the emerging multimedia applications. A primary challenge for future generation broadband wireless networks is the support of integrated multimedia type traffic over a unified network platform. Given the stringent constraints on bandwidth, power and cost relative to increasing end-user expectations, design optimization approaches for the air interface (involving multiple access/modem designs) that most efficiently exploit spectrum resources in a dynamic time-varying environment is a critical imperative.; Orthogonal frequency-division multiplexing (OFDM) is a form of modulation that presents excellent performance over frequency selective channel and the type of parallelism most suitable for DSP implementation. Built upon OFDM modem, orthogonal frequency division multiple access (OFDMA) has emerged as one of the prime multiple-access schemes for wireless broadband networks (e.g., IEEE 802.16a-e, IEEE 802.20 and 4G protocol candidates). The intrinsic structure of OFDMA allows one to efficiently exploit the network/multiuser diversity in wireless networks. In a large scale wireless system, users' channel characteristics, mutual interference patterns, as well as traffic requirements are largely diverse. Each radio resource unit in the time-frequency-space dimensions is likely to bear high utility value to certain users. Consequently, the total channel capacity or spectral efficiency of the network can be significantly increased through judicious resource allocation. Clearly, radio resource allocation strategies an important role in optimizing the performance of OFDM/OFDMA systems. In this work, we first establish the optimality of OFDMA SISO and MIMO systems in the generic multiuser multicarrier communication frameworks. Optimal and suboptimal subcarrier and power loading schemes are proposed for OFDMA MIMO systems. Following that, we develop resource allocation strategies for OFDM/OFDMA based broadband networks. Protocols and algorithms for single-cell, multi-cell and relay network are introduced. Significant throughput gains can be obtained with low computation complexity and signaling overhead. |
