Delay limited optimal and suboptimal power and bit loading algorithms for OFDM systems over correlated fading channels

This paper explores optimal and suboptimal power and bit loading algorithms for a multicarrier system. Specifically, we study the trade-offs between the total transmit power of an orthogonal frequency division multiplexing (OFDM) system and the buffering delay of the packets in a transmission buffer. The loading framework is formulated as a Markov decision process (MDP) and an optimal loading policy which minimizes the transmit power while meeting a target delay constraint is obtained via equivalent linear programming (LP) methodology. The complexity of finding the optimal loading policy and its' implementation issues are described. Since finding the optimal policies becomes complex and practically un-realizable for large number of carriers in the system, we offer a sub-optimal power and bit loading algorithm using the results of the single carrier system's power and rate adaptation policy and a greedy approach. Selected numerical examples show that the sub-optimal algorithm, which has reduced complexity, has performance close to the optimal one.