On Design of TDD for Joint Uplink and Downlink Resource Allocation in OFDMA-Based WiMax

In this paper, we study the joint design of uplink and downlink resources in OFDMA-based systems. We first analyze the interactions between uplink and downlink, due essentially to the usage of time division duplexing (TDD) and the TCP ACKs. This analysis is based on analytical models for interference and throughputs that we develop for both directions. We next study the capacity of the system using a Markovian analysis and matrix geometric solutions. Our performance analysis study allows us to determine the optimal proportion of resources that has to be allocated to the uplink so as to minimize blocking. In addition to that, we show that an admission control policy reserving some uplink resources to TCP ACKs may improve the overall capacity of the system.