Keynote Talk #1: Power efficiency in wireless communications — A historical review

In this talk, we focus on power efficiency and give a historical review of some major advances in transmission and multiple access, which shaped the development of the wireless communications standards developed over the past two decades. The review includes the development of OFDM and single-carrier transmission with frequency-domain equalization (SCFDE) as well as the birth of OFDMA and of single-carrier FDMA (SC-FDMA), which were adopted by the Mobile WiMAX and the 3GPP LTE standards. Next, we address the nonlinear distortion problems caused by the high-power amplifier (HPA) at the transmitter in wireless communications systems and describe the various techniques devised to compensate for this phenomenon in single-carrier and multicarrier transmission. We emphasize the fact that the optimum operating point of the power amplifier cannot be always achieved in practice due to the stringent spectral masks imposed. We describe ideal signal predistortion that is applicable to both single-carrier and multicarrier systems and then we discuss peak-to-average power ratio (PAPR) reduction for multicarrier systems. We point out the fact that the gain achieved in terms of PAPR does not directly translate in terms of transmitted signal power for a given power amplifier. The issues highlighted in this talk are of significant interest to current 4G as well as future 5G systems.