Energy-efficient communications in MIMO systems based on adaptive packets and congestion control with delay constraints

In this paper, we propose adaptive techniques for multiple input and multiple output (MIMO) systems, to solve the problem of energy efficient communications with delay constraint, where the energy efficiency is defined as the number of bits per second correctly received per power consumed. We first investigate the optimal multiple quadrature amplitude modulation (MQAM) constellation size for each transmission stream and the optimal packet size. By exploiting the intrinsic relationship among the constellation size, the packet size, the symbol error rate (SER) and delay, we propose an adaptive transmission mode for different delay demands. For the case of user's buffer overflow, we use the congestion control algorithm to schedule the average queue length, and maintain the optimal delay performance for energy efficiency. Simulations show that to maximize the energy efficiency and offer different Quality of Service (QoS) of delay simultaneously, the transmitter should adaptively choose the constellation size and the packet size as well as the transmission mode. In this framework, the tradeoff between energy efficiency and delay demand are well demonstrated.