ADAPTIVE RADIO RESOURCE ALLOCATION FOR DOWNLINK OFDMA/SDMA SYSTEMS WITH MULTIMEDIA TRAFFIC

This project proposes an adaptive radio resource allocation (ARRA) algorithm for downlink OFDMA/SDMA systems with multimedia traffic. Considering multiple service classes and diverse QoS requirements of multimedia traffic, the ARRA algorithm is designed with the goal to maximize spectrum efficiency and to fulfill quality of service (QoS) requirements. It is composed of two parts, a dynamic priority adjustment (DPA) scheme and a priority-based greedy (PBG) scheme. The DPA adopts a type of time-to-expiration to indicate the degree of user’s urgency, and dynamically gives high priorities to urgent users. The PBG allocates the radio resource iteratively, based on a cost value, to maximize the system throughput while allocating enough resource to high-priority users. Simulation results show that the ARRA algorithm outperforms conventional algorithms in terms of system throughput and satisfaction extent of QoS requirements; it can sustain users’ QoS requirements up till a traffic load of 0.8, while the conventional algorithms cannot guarantee QoS requirements after a traffic load of 0.3

INTRODUCTION

ORTHOGONAL frequency division multiple access combined with space division multiple access (OFDM A/SDMA) can be an effective approach to support high-speed wireless communications. The OFDMA is based on OFDM (orthogonal frequency division multiplexing) and inherits its superiority of mitigating multipath fading and maximizing spectral efficiency (Nyquist rate). The SDMA uses a beam forming technique in a multiple-antenna system and multiplexes multiple users on the same subchannel to increase the system throughput.

For a multiuser OFDMA system, Jang and Lee proposed a linkgain-based resource allocation (LBRA) scheme and proved that the data rate of the system was maximized when each subcarrier was assigned to the user with the best channel gain. However, this statement is not always true when SDMA is enabled in an OFDMA system. Instead, the system data rate is the largest when an optimal set of cochannel users, which depends on the spacial signature of each user, is selected for each subcarrier. But the algorithm for finding the optimal set of cochannel users is of a high computational complexity. Hence, when the channel state information (CSI) is available at the base station, a sophisticated and low complexity radio resource allocation (RRA) scheme is needed for OFDMA/SDMA systems to properly exploit system diversity so that spectrum efficiency is maximized.

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