Energy Efficiency of Spread Spectrum Single-Carrier Transmission

Abstract Energy efficiency (EE), which is defined as a ratio of spectrum efficiency (SE) to power consumption, is a key performance metric in mobile communication system. The signal waveform has little influence on energy consumption of analog circuit and baseband unit. On the other hand, the energy consumption of power amplifier (PA) highly depends on signal waveform. The power amplifier efficiency (PAE) generally depends on the signal power (equivalently signal amplitude) and decreases as the signal amplitude becomes smaller. If the signal exhibits large peak-to-average power ratio (PAPR), the transmit power needs to be backed off so that the peak signal amplitude is linearly amplified. This results in a poor PAE as the operation point of PA is far below its maximum. The authors previously proposed a single-carrier with frequency domain spread spectrum (SC-FDSS). In this paper, the EE and SE of SC-FDSS are compared to those of SC with conventional time-domain spread spectrum (SC-TDSS). We also observe an optimum spreading factor (SF) for each spreading scheme which gives good SE-EE tradeoff at particular received signal-to-noise power ratio (SNR). Keyword Spectral efficiency, energy efficiency, power amplifier, single-carrier transmission, spread spectrum