Optimal Resource Allocation in Wireless Communications Subject to Several Power and Eneregy Constraints

It is known that adaptive power and rate allocation is a useful technique for combating channel variations induced by multipath fading in wireless systems. We consider several fading channel models for which we aim to optimize a performance metric subject to various power and energy constraints. First, we find the general structure of optimal or suboptimal power policies in order to maximize the ergodic capacity subject to various combination of short-term, long-term, and per-antenna power constraints in multiple-input multiple-output (MIMO) wireless systems. The power policies depend upon the ratio of the power constraints. Furthermore, we characterize the conditions for which one or more power constraints dominates and the others can be ignored. Next, we specialize the results to Rayleigh fading. An important observations in this case is that the short-term power constraint is more relevant in the low SNR regime. Therefore, a system designer can ignore a short-term power constraint that is larger than a long-term power constraint for large values of average SNR's. Finally, we consider an energy harvesting wireless system, and study rate allocation policies to minimize a delay criterion, e.g., average delay in the data buffer or probability of overflow, subject to the hard power constraints imposed by the available energy.