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 propagation channels and hardware constraints will be much different from sub-6 GHz and millimeter wave (mmWave) band.
To compare the performance of massive MIMO in the UHF and mmWave bands, our group have proposed a stochastic geometry framework to analyze the signal-to-interference-plus-noise ratio (SINR) and the rate of massive MIMO in both sub-6 GHz and mmWave bands. The proposed models incorporate key features of different frequency bands, such as different large-scale path loss and small-scale fading correlations. Based on the proposed models, analytical expressions for the SINR and rate distribution derived for both sub-6 GHz and mmWave systems.
In , the asymptotic SINR coverage and rate was analyzed in a sub-6 GHz large-scale massive MIMO networks, when the number of base station antennas goes to infinity; the results showed that the asymptotic SINR is limited by pilot contamination, and the SINR coverage increases with a larger path loss exponent.
In our recent work in [2,3], we extended the framework in  to the case of finite base station antennas, where we expressed the SINR distribution as a functions of the number of a function of the numbers of base stations and simultaneously served users per cell, in sub-6 GHz uplink networks. Our analyses show that to maintain the same spatial-average SINR distribution at a typical user, the number of base station antennas should scale superlinearly with the number of served users in a cell, which is different from the linear scaling law examined in most prior work.
The performance of mmWave massive MIMO was examined in , where we showed that the SINR coverage performance is much sensitive to the base station density. In certain dense base station case, the SINR coverage approaches the asymptotic limit with around 200 antennas, while in the sparse networks, the SINR coverage is poor and limited by noise and coverage holes due to blockages.
The performance comparison between sub-6 GHz and mmWave massive MIMO was present in : 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 sub-6 GHz systems, which translates into a magnitude order higher cell throughput due to the larger bandwidth.
1. T. Bai and R. W. Heath, Jr., “Asymptotic coverage and rate in massive MIMO networks”, in Proc. of GlobeSIP, June, 2014. (Presentation video)
2. T. Bai and R. W. Heath, Jr., “Analyzing uplink SIR and rate in massive MIMO networks”, submitted to IEEE Trans. Commun., Oct 2015. (Arxiv)
3. T. Bai and R. W. Heath Jr., “Uplink massive MIMO SIR analysis: how do antennas scale with users?”, to appear in Proc. of IEEE Globalcom, Dec. 2015. (Presentation video)
4. T. Bai and R. W. Heath Jr., “Asymptotic SINR for millimeter wave massive MIMO cellular networks”, in Proc. of IEEE SPAWC, June 2015.
5. T. Bai and R. W. Heath, Jr., “Comparing massive MIMO and mmWave massive MIMO”, Preprint, coming soon, 2016 (slides)