Multiuser MIMO for Broadband Wireless Communication Systems
Multiple-input multiple-output (MIMO) is a promising technology for future wireless communication systems. By exploiting the multi-dimensional wireless channel created by multiple transmit and receive antennas, MIMO systems significantly increase the channel capacity and link robustness of wireless communication, and have been widely adopted in many future wireless communication standards (e.g., WiMAX, 3GPP LTE, etc).
In a multiuser MIMO (MU-MIMO) system, a single base station transmits to multiple mobile stations simultaneously over the same frequency band, thereby substantially increasing the sum data-rate and reducing the latency of mobile users compared to other multi-access (MAC) schemes such as conventional TDMA. The gains achievable by the introduction of the MU-MIMO broadcast channel in wireless systems are yet to be demonstrated in practice, and are forecast to play a major role in the increase of spectral efficiency of future wireless networks. Non-linear dirty-paper-coding process required to achieve the sum-capacity of the MU-MIMO channel is very difficult to implement in practical systems. In addition, interuser interference needs to be properly cancelled at the transmitter to enable low-complexity and energy-efficient mobile terminals. What do we do? Our research is focused on the design and analysis of various downlink transmit precoding techniques for MU-MIMO broadcast transmission. We are interested in theoretical analysis and practical algorithm design for MU-MIMO, which include:- Transmit precoding with transmit selection diversity : use transmit antenna arrays to support multiple users, and optimize the capacity / error performance with transmit selection diversity. We have investigated various transmit selection precoding techniques with different RF/antenna configures and low-complexity selection algorithms for commercial implementation.
- Adaptive user scheduling and link adaptation : Select the optimum set of users and dynamically optimize the number of data substreams to each user to exploit the multiuser diversity and maximize channel capacity.
- Multiuser precoding with limited feedback : In the case where channel information is not perfectly available at the transmitter, design a methodology to inform the transmitter about the wireless channel with a low-rate feedback channel, and optimize the transmit precoder with limited channel side information for capacity /error optimization.
- Codebook design : inform the receiver of their desired filters with Grassmanian codebook.
- Adaptive codebook allocation : select the best codeword length based on each user's received SINR with constraint on sum feed-forward overhead to increase cell throughput.
- Optimality analysis : show the optimality of the coordinated MIMO communications and compare it with dirty-paper-coding.
- Applications to wideband systems : use interpolation techniques to apply the coordinated concept to multi-user OFDM (OFDMA) systems.
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R. Chen, R.W. Heath, Jr., and J. G. Andrews, ``Transmit Selection Diversity for Unitary Precoded Multiuser Spatial Multiplexing Systems with Linear Receivers,'' accepted to IEEE Transactions. on Signal Processing, January 2005.
Z. Shen, R. Chen, J. G. Andrews, R.W. Heath, Jr., and B. L. Evans,, ``Sum Capacity of Multiuser MIMO Broadcast Channels with Block Diagonalization,'', accepted to IEEE Transactions on Wireless Communcations , accepted for publication.
Z. Shen, R. Chen, J.G. Andrews, R.W. Heath, Jr., and B.L. Evans, ``Low Complexity User Selection Algorithms for Multiuser MIMO Systems with Block Diagonalization,'' IEEE Transactions on Signal , vol. 54, no. 9, pp. 3658-3663, Sep. 2006.
C.B. Chae, D.Mazzarese, and R.W. Heath, Jr., ``Coordinated Beamforming for Multi-user MIMO Systems with Grassmanian Codebook,' IEEE Communication Theory Workshop, Mar. 2006.
C.B. Chae, D.Mazzarese, and R.W. Heath, Jr., ``Coordinated Precoding for Multi-user MIMO Communication with Limited Feedfoward,'' (invited) to appear in Proc. IEEE Asilomar Conference , Pacific Grove, CA, Oct. 29 - Nov. 1, 2006.
C.B. Chae, R.W. Heath, Jr, and D. Mazzarese, ``Achievable Sum Rate Bounds of Zero-forcing based Multi-user MIMO Systems,'' to appear in Proc. Allerton Conf. on Comm. Control and Comp., Sep. 2006.
K.B. Huang, R.W. Heath, Jr., and J.G. Andrews, ``Space Division Multiple Access with a Sum Feedback Rate Constraint,'' submitted to IEEE Trans. on Signal Processing, Aug. 2006.
K.B. Huang, R.W. Heath, Jr., and J.G. Andrews, ``Joint Beamforming and Scheduling for SDMA Systems with Limited Feedback,'' submitted to IEEE Trans. on Communications, June 2006. Also available at ArXiv.
S. Shim, C.B. Chae, and R.W. Heath, Jr., ``A Lattice-Based MIMO Broadcast Precoder with Block Diagonalization for Multi-Stream Transmission,'' to appear in Proc. of IEEE Global Telecommunications Conference, San Francisco, CA, USA, 27 Nov.-1 Dec. 2006.
