Adaptive modulation has the potential to increase system throughput considerably by adapting transmission parameters to the time-varying channel characteristics. Crucial to adaptive systems is the requirement of a feedback channel, that is often capable of carrying only a limited number of bits. Under such a bandwidth-constrained feedback link, we aim to optimize a multiantenna system based on transmit beamforming and adaptive modulation, where the transmit power, the signal constellation, the beamforming direction, and the feedback strategy, are designed jointly. Our proposed nested iterative approach leads to an approximate, yet practical, solution. Simulation results demonstrate considerable improvement in transmission rate, as the number of feedback bits increases.
Bibliographical noteFunding Information:
Paper approved by M. Skoglund, the Editor for Source/Channel Coding of the IEEE Communications Society. Manuscript received September 29, 2003; revised November 4, 2004. This work was supported in part through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011, and in part by the National Science Foundation under Grant 01-0516. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. This paper was presented in part at the 37th Annual Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, November 9–12, 2003.
- Adaptive modulation
- Vector quantization