Multiuser SM-MIMO versus Massive MIMO: Uplink Performance Comparison

摘要

In this paper, we propose algorithms for signal detection in large-scalemultiuser {\em spatial modulation multiple-input multiple-output (SM-MIMO)}systems. In large-scale SM-MIMO, each user is equipped with multiple transmitantennas (e.g., 2 or 4 antennas) but only one transmit RF chain, and the basestation (BS) is equipped with tens to hundreds of (e.g., 128) receive antennas.In SM-MIMO, in a given channel use, each user activates any one of its multipletransmit antennas and the index of the activated antenna conveys informationbits in addition to the information bits conveyed through conventionalmodulation symbols (e.g., QAM). We propose two different algorithms fordetection of large-scale SM-MIMO signals at the BS; one is based on {\emmessage passing} and the other is based on {\em local search}. The proposedalgorithms are shown to achieve very good performance and scale well. Also, forthe same spectral efficiency, multiuser SM-MIMO outperforms conventionalmultiuser MIMO (recently being referred to as massive MIMO) by several dBs; fore.g., with 16 users, 128 antennas at the BS and 4 bpcu per user, SM-MIMO with 4transmit antennas per user and 4-QAM outperforms massive MIMO with 1 transmitantenna per user and 16-QAM by about 4 to 5 dB at $10^{-3}$ uncoded BER. TheSNR advantage of SM-MIMO over massive MIMO can be attributed to the followingreasons: (i) because of the spatial index bits, SM-MIMO can use a lower-orderQAM alphabet compared to that in massive MIMO to achieve the same spectralefficiency, and (ii) for the same spectral efficiency and QAM size, massiveMIMO will need more spatial streams per user which leads to increased spatialinterference.