Adaptive modulation has the potential to increase the system throughput significantly by matching transmitter parameters to time-varying channel conditions. However, adaptive modulation schemes that rely on perfect channel state information (CSI) are sensitive to CSI imperfections induced by estimation errors and feedback delays. In this paper, we design adaptive modulation schemes for multiantenna transmissions based on partial CSI, that models the spatial fading channels as Gaussian random variables with nonzero mean and white covariance, conditioned on feedback information. Based on a two-dimensional beamformer. our proposed transmitter optimally adapts the basis beams, the power allocation between two beams, and the signal constellation, to maximize the transmission rate, while maintaining a target bit-error rate. Adaptive trellis-coded multiantenna modulation is also investigated. Numerical results demonstrate the rate improvement, and illustrate an interesting tradeoff that emerges between feedback quality and hardware complexity.
Bibliographical noteFunding Information:
Manuscript received July 27, 2002; revised May 18, 2003. The editor co-ordinating the review of this paper and approving it for publication was J. K. Cavers. This work was supported by the National Science Foundation under Grant 0105612, and by the Army Research Laboratory under the Collaborative Technology Allliance Program, Cooperative Agreement DAAD19-01-2-011. The material in this paper was presented in part at the International Conference on Communications, Anchorage, AK, May 11–14, 2003.
- Adaptive modulation
- Channel feedback
- Multiantenna transmissions
- Space-time block coding
- Trellis-coded modulation