Widespread application of multimedia wireless services and requirement of ubiquitous access have triggered rapidly booming energy consumption at both transmitter and the receiver sides. Hence, energy-efficient design in wireless networks is very important and is becoming an inevitable trend. In this paper, we take decoding power into consideration when studying joint transmitter and receiver design for achieving high energy efficiency (EE). Based on a new function between transmit power and data rate that is derived by minimizing a lower bound on the overall transmit and receiver power, we investigate when and how should the decoding power be considered for optimizing EE. We find that the decoding power cannot be ignored for short-range wireless communications with a large bandwidth where the transmit power is usually low and give an analytical expression for quantifying the impact of decoding power on EE.