  In this paper, we propose a novel Adaptive Transmission Strategy to improve
energy efficiency~(EE) in a wireless point-to-point transmission system with
Quality of Service~(QoS) requirement, i.e., delay-outage probability
considered. The transmitter is scheduled to use the channel that has better
coefficients, and is forced into silent state when the channel suffers deep
fading. The proposed strategy can be easily implemented by applying two-mode
circuitry and is suitable for massive machine type communications (MTC)
scenarios. In order to enhance EE, we formulate an EE maximization problem,
which has a single optimum under a loose QoS constraint. We also show that the
maximization problem can be solved efficiently by a binary search algorithm.
Simulations demonstrate that our proposed strategy can obtain significant EE
gains, hence confirming our theoretical analysis.
