Superiority of Superposition Multiaccess With Single-User Decoding Over TDMA in the Low SNR Regime

This paper studies the Gaussian multiaccess channel with multiantenna basestation in the low signal to noise ratio (SNR) regime. We compare the spectral efficiencies of the optimal superposition channel sharing scheme and two simple alternatives: the time division multiaccess (TDMA) scheme and superposition multiaccess with single-user decoding (SSD). Due to the fact that SSD, but not TDMA, exploits the multiuser multiplexing gain, the relative spectral efficiency of SSD over TDMA grows drastically as the number of antennas at the basestation increases. The results suggest that, in the low SNR regime with multiple antenna basestation, TDMA´s suboptimality can no longer be offset by its simplicity since SSD can achieve much higher spectral efficiency while the simplicities of the two channel sharing schemes are similar.