Suitability-Based Subcarrier Allocation for Multicast Services Employing Layered Video Coding in Wireless OFDM Systems

In this paper, we discuss how to achieve optimal subcarrier allocation for multicast services in wireless OFDM systems. The multicast capacity is limited by the user with the worst channel condition. To overcome this limitation, we exploit the fine granularity scalability (FGS) video coding which divides multicast data into base layer and enhancement layer data. Then we develop an optimal subcarrier allocation that maximizes the enhancement layer throughput while satisfying the requirement for the base layer by employing linear programming (LP). For a simple subcarrier allocation we present the suitability-based subcarrier allocation (SSA) algorithm which allocates the subcarriers having a higher metric value to the base layer. The SSA algorithm turns out to be equivalent to the optimal solution of LP problem and is easily modifiable for application to practical OFDM systems. In addition, we present the channel condition-based user selection (CCUS) algorithm which selects a proper set of users to serve when the requirement cannot be met. Numerical results reveal that the SSA algorithm achieves the optimal performance in terms of average spectral efficiency and the CCUS algorithm combined with the SSA algorithm significantly improves the performance over the original SSA algorithm.