Multi-level Power Loading Using Limited Feedback

In this letter, we propose multi-level power loading (MPL) as a discrete version of mercury/waterfilling power allocation. In MPL, one among several discrete power levels is allocated to each subchannel. Firstly, we find an MPL solution with perfect channel state information at the transmitter. Lloyd´s algorithm is used for the joint optimization of grouping and power levels. Then, we propose stepwise mercury/waterfilling for practical implementation of the MPL under limited feedback. With a fixed feedback budget, we also show that the optimal power level size should be determined according to delay spread of given channel and operating SNR of a target system.