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Massive MIMO

MIMO has been incorporated into emerging wireless broadband standards such as LTE and soon WiMAX. In general, in time division duplexing (TDD) systems, increasing the number of antennas at the base station, results in increased data rate, reliability, energy efficiency and reduced interference. Consequently, massive MIMO is being investigated as an emerging technology, where the number of antennas is scaled up by 1-2 orders of magnitude relative to systems today.

Massive MIMO uncovers a large number of new research problems, including; pilot contamination (the reusing of limited pilot sequences from one cell to another), reciprocity calibration (a TDD operation requirement which relies on the downlink channel to be a reciprocal of the uplink) and reliance on favourable propagation (where the propagation channel responses from the base station to different termianls are sufficiently different).

Our research, thus far, focuses on the perfromance analysis of precoding techniques in both colocated and distributed base station scenarios. We propose a system model for massive MU-MIMO which accounts for distributed base stations, unequal link gains between users and base stations, CSI imperfections and spatial correlation. Using this model, we analytically derive limiting expressions.

Key Publications:

[1] T. L. Mazetta, "Noncooperative cellular wireless with unlimited numbers of base station antennas," IEEE Transactions on Wireless Communications, vol. 9, no. 11, pp. 3590-3600, November 2010.

[2] H. Q. Ngo, E. G. Larsson, and T. L. Marzetta, "Energy and spectral efficiency of very large multiuser MIMO systems," IEEE Transactions on Communications, vol. 61, no. 4, pp. 1436-1149, April 2013.

[3] J. Hoydis, S. ten Brink, and M. Debbah, "Massive MIMO in the UL/DL of cellular networks: How many antennas do we need?" IEEE Journal on Selected Areas in Communications, vol. 31, no. 2, pp. 160-171, February 2013.

[4] H. Huh, G. Claire, H. C. Papadopoulos, and S. A. Ramprashad, "Achieving "massive MIMO" spectral efficiency with a not-so-large number of antennas," IEEE Transactions on Wireless Communications, vol. 11, no. 9, pp. 3226-3239, September 2012

[5] H. Yang and T. L. Marzetta, "Performance of conjugate and zero-focring beamforming in large-scale antenna systems," IEEE Journal on Selected Areas in Communications, vol. 31, no. 2, pp. 202-214, February 2013.

Our Publications:

[1] P. J. Smith, C. Neil, M. Shafi and P. A. Dmochowski, "On the convergence of massive MIMO systems," in Proc. IEEE International Conference on Communications (ICC) , June 2014.

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