Energy and Bandwidth-Efficient Modulation

Abstract

In addition to the requirement of high spectral efficiency, power (or energy) efficiency—equivalent to battery life—is another important requirement for modulation techniques. In some applications, such as mobile handset devices, portable devices, and even satellite communication equipment, energy efficiency is crucial to achieve longer battery life or longer communication time. In these applications, to maintain minimum DC power consumption by power amplifiers, the power amplifier must operate in or close to the saturation region to maximize energy efficiency or minimize DC power consumption because the minimum DC current consumption occurs in a saturation region. However, a saturated amplifier introduces amplitude modulation to amplitude modulation (AM/AM) and amplitude modulation to phase modulation (AM/PM) conversions into the amplified signal, which is usually the amplitude- and phase-modulated signal. If such an input signal to a power amplifier that operates in or close to a saturated condition is a non-constant envelope modulation signal, its output will be affected by the AM/AM and AM/PM conversions. As a result, a nonlinearly amplified signal at the output of the power amplifier is affected by spectrum regrowth such that its output signal cannot meet the required spectrum mask or adjacent channel power ratio (ACPR) imposed by different standards and its error vector magnitude (EVM) is degraded as well. Thus, requirements of both energy efficiency and ACPR or spectrum efficiency impose constant or nearly constant envelope characteristics on the modulated signal to the power amplifier.