Wireless broadband systems operating in the millimeter wave (mmWave) spectrum are thought to be a prime candidate to provide the system throughput enhancements needed for fifth generation (5G) wireless networks. The wide bandwidths available at mmWave frequencies can be an attractive alternative to the sub-6GHz frequencies employed in most of today's cellular networks. The small wavelengths of mmWave frequencies enable a large number of antennas to be implemented in a small form factor, which makes it possible to generate pencil-beams to mitigate pathloss and reduce inter-user interference.
MmWave systems having a large number of antennas, however, may not be able to use fully digital beamforming techniques requiring one radio frequency (RF) chain per antenna due to the high cost and power consumption. Therefore, hybrid beamforming techniques using a few RF chains wired to sets of phase shifters have been of much interest in both academia and industry.
The following topics are my main research interest in mmWave communication systems.
- Hybrid beamforming-comparable limited feedback designs [1-2]
- MmWave channel estimation techniques [3-6]
 J. Song, J. Choi, and D. J. Love, "Common Codebook Millimeter Wave Beam Design: Designing Beams for Both Sounding and Communication with Uniform Planar Arrays," submitted to IEEE Transactions on Communications, Jun. 2016. [Online]. Available: http://arxiv.org/abs/1606.05634.
 J. Song, J. Choi, and D. J. Love, "Codebook Design for Hybrid Beamforming in Millimeter Wave Systems," in Proc. of IEEE International Conference on Communications, Jun. 2015.
 J. Song, J. Choi, S. G. Larew, D. J. Love, T. A. Thomas, and A. Ghosh, "Adaptive Millimeter Wave Beam Alignment for Dual-Polarized MIMO Systems," IEEE Transactions on Wireless Communications, vol. 14, no. 11, pp. 6283-6296, Nov. 2015.
 D. Zhu, J. Choi, and R. W. Heath Jr., "Auxiliary Beam Pair Enabled AoD and AoA Estimation in Closed-Loop Large-Scale mmWave MIMO System," submitted to IEEE Transactions on Wireless Communications, Jul. 2016.
 D. Zhu, J. Choi, and R. W. Heath Jr., "Auxiliary Beam Pair Design in mmWave Cellular Systems with Hybrid Precoding and Limited Feedback," in Proc. of IEEE International Conference on Acoustics, Speech and Signal Processing, Mar. 2016.
 D. Zhu, J. Choi, and R. W. Heath Jr., "Auxiliary Beam Pair Enabled AoD and AoA Estimation in mmWave FD-MIMO Systems," to appear in Proc. of IEEE Global Communications Conference, Dec. 2016.