When accumulative information is beneficial for maximizing energy efficiency?

Energy efficiency (EE) has become an important design goal for wireless systems. Since the EE of a system is evaluated in a duration where the channel may vary, designing a transmission strategy to maximize instantaneous EE may lead to a loss in achievable EE of the system. To exploit the accumulative information of throughput and energy, accumulative EE (ACEE) can be used as the objective function, which is the ratio of the accumulated throughput divided by the overall energy consumed over the past time slots. By analyzing the solutions of three EE maximal problems to optimize rate allocation among multiple subcarriers in multiple time slots, we show when and why the ACEE can achieve high system EE. Simulation results verify our theoretical analysis. Our analysis show that the ACEE is beneficial for the systems with low circuit power consumption under time-varying channels when either the data rate requirement or signal to noise ratio is low, and either the number of antennas or subcarriers is small.