Massive MIMO: At Ultra-High Frequency or Millimeter Wave?

29 Jan 2015
Massive multiple-input multiple-out (MIMO) is a promising technique for 5G cellular networks. Prior work showed that high throughput can be achieved with a large number of base station antennas through simple signal processing in massive MIMO networks. The carrier frequencies for massive MIMO systems, however, are not clear yet; as the ultra-high frequency (UHF) band, where the conventional systems are operated, has favorable propagation conditions but limited bandwidth, and the millimeter wave (mmWave) frequency has a large potential spectrum but different propagation conditions than the UHF band.
To compare the performance of massive MIMO in the UHF and mmWave bands, WNCG graduate student Tianyang Bai and WNCG Professor Robert Heath have proposed a stochastic geometry framework to analyze the signal-to-interference-plus-noise ratio (SINR) and the rate of massive MIMO in both the uplink and downlink. Their proposed model incorporates key features of both frequency bands, such as different large-scale path loss and small-scale fading correlations. Based on the proposed model, closed form expressions for the SINR distribution, as a function of the numbers of base stations and simultaneously served users per cell, are derived for both UHF and mmWave systems. Their results indicate that in low BS density, mmWave massive MIMO networks suffer from severe outage due to building blockages. In the case of dense BS networks, mmWave networks are shown to provide comparable SINR (to UHF systems), which translates into a magnitude order higher cell throughput due to the larger bandwidth. 
The research was funded by the National Science Foundation under Grant No. 1218338 and 1319556.