Resource Allocation in OFDMA Wireless Networks with Time-Varying Arrivals

This paper considers the issue of optimal subcarrier allocation in OFDMA wireless networks when the arrivals and channels are stochastic and time-varying. Our objective is to minimize the long-term average packet delay over multiple time epochs. We show by an example that water-filling-based subcarrier allocation policy which maximizes throughput at each time epoch is not optimal in this case. This is because such policy ignores the time-varying queue state information, while in fact such information is necessary to minimize the long-term average delay. We present an optimal policy for a special case of On-Off channel and two homogeneous users. For general channel, the optimal policy is complicated and unknown. However, based on the insights learned from the On-Off case, we provide heuristic policies that use different degrees of knowledge about the channel and queue state information. Through simulation, we show that the value of queue vs. channel information varies with the traffic load. For instance, at low-to-moderate traffic regime, a policy which ignores much of channel state information outperforms a water-filling policy which ignores much of the queue state information. The opposite is true when considering heavy traffic regime. Index Terms OFDMA, subcarrier allocation, water-filling, load-balancing, queue state information