Wireless Communications Research Group
Limited Feedback MIMO
Channel state information (CSI) at the transmitter helps to improve the performance of MIMO systems by enabling the transmitter to exploit the channel conditions. In MIMO frequency division duplexing (FDD) systems, it is not possible for a transmitter to acquire a CSI without any feedback information from a receiver. For this purpose, a codebook with the same entries and size is maintained at both transmitter and receiver, containing quantized channel information. Due to bandwidth limitations, instead of feeding back the entire channel information to the transmitter, the receiver feeds back the index of the nearest codebook entry (or codeword) to the transmitter via a low-rate feedback link. The number of bits required to send the index of the selected codeword to the transmitter is considered as feedback overhead.
There is a lot of interest in the performance of limited feedback (or codebook) beamforming MIMO systems. Codebook beamforming is now part of the LTE and LTE advanced standards. However, there are other families of codebooks for i.i.d. channels e.g. Grassmaninan codebooks, and Vector Quantization codebooks. Recently, the research focus has shifted towards adaptive codebook precoding, where the codebook tracks the correlated channel and updates itself accordingly. This approach is driven by the fact that MIMO real-world channels are both spatially and temporally correlated and codebooks designed for i.i.d. channels do not perform well in correlated channels.
We are working towards effective differential codebook design for MU MISO and MU MIMO systems in spatially and temporally correlated channels. The performance of differential codebook design heavily depends upon the scaling and rotation operations. One of the main objectives of this project is to use adaptive scaling technique in order to make the differential codebook to effectively follow the slow changing channels.
D.J. Love, R.W. Heath, V. K N Lau, D. Gesbert, B.D. Rao, M. Andrews, "An overview of limited feedback in wireless communication systems," IEEE Journal on Selected Areas in Communications, vol.26, no.8, pp.1341-1365, October 2008.
Au-Yeung, Chun Kin, and David J. Love. "On the performance of random vector quantization limited feedback beamforming in a MISO system." IEEE Transactions on Wireless Communications, vol.6, no.2, pp. 458-462, 2007.
D. J. Love, Robert W. Heath Jr, and Thomas Strohmer. "Grassmannian beamforming for multiple-input multiple-output wireless systems." IEEE Transactions on Information Theory, vol 49, no.10 pp. 2735-2747, 2003.
J. Choi, B. Clerckx, Namyoon Lee, G. Kim, "A New Design of Polar-Cap Differential Codebook for Temporally/Spatially Correlated MISO Channels," IEEE Transactions on Wireless Communications, vol.11, no.2, pp.703,711, February 2012.
Kyeongyeon Kim, Taejoon Kim, D.J. Love, Han Kim, "Differential Feedback in Codebook-Based Multiuser MIMO Systems in Slowly Varying Channels," IEEE Transactions on Communications, vol.60, no.2, pp.578,588, February 2012.
Taejoon Kim, D.J Love, B. Clerckx, "MIMO Systems with Limited Rate Differential Feedback in Slowly Varying Channels," IEEE Transactions on Communications, vol.59, no.4, pp.1175,1189, April 2011.
J. Mirza, P.J. Smith, P. Dmochowski, M. Shafi, "Limited Feedback MU Massive MISO Systems with Differential TCQ in Temporally Correlated Channels", submitted to IEEE Transactions on Vehicular Technology,
J. Mirza, P.J. Smith, M. Shafi, P. Dmochowski, A. Firag, A. Papathanassiou, "Double-Cap Differential Codebook Structure for MU MISO Systems in Correlated Channels", IEEE Wireless Communications Letters,
J. Mirza, P. Dmochowski, P.J. Smith, M. Shafi, "A Differential Codebook with Adaptive Scaling for Limited Feedback MU MISO Systems", IEEE Wireless Communications Letters, 2014.
J. Mirza, P. Dmochowski, P.J. Smith, M. Shafi, "Limited Feedback Multiuser MISO Systems with Differential Codebooks in Correlated Channels", in _Proc. IEEE International Conference on Communications (ICC), June 2013, pp. 3979-3984.
J. Mirza, P. Dmochowski, P.J. Smith, M. Shafi, "Capacity Loss for Multilayer Codebook Precoding in MIMO Systems", in Proc. 23rd IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Sydney, 2012.
M. Zhang, P.J. Smith, M. Shafi, P. Dmochowski, J. Mirza, "MIMO Capacity Gain Analysis for General Channel Models", in Proc. IEEE International Conference on Communications (ICC)
, Ottawa, 2012.