Optimal Resource Allocation in the OFDMA Downlink with Feedback of Buffer State Information

With the advent of new applications, one of the primary applications supported in downlink cellular systems is streaming video. QoS for streaming video entails data transmission to the mobile stations with limited latency and limited jitter. This requirement on latency and jitter can be mapped to the number of yet-to-be-played packets in a mobile station´s buffer, to always be above a certain minimum. Additionally, there should be no overflow of finite-size user buffers. This paper solves the problem of optimal resource allocation in a downlink OFDMA system with buffer constraints for all downlink users. The optimal strategy is shown to be a generalized version of water-filling and channel-inversion. Specifically, with infinite buffer size and no minimum constraint on buffer, it reduces to water-filling; and to channel-inversion in the absence of a buffer. It is shown that scheduling gains from the derived optimal strategy, in terms of number of users that the system can support, can be an order-of-magnitude higher than that of heuristic scheduling schemes.