Adaptive modulation requires channel state information (CSI), which can be acquired at the receiver by inserting pilot symbols in the transmitted signal. In this paper, we first analyze the effect linear minimum mean square error (MMSE) channel estimation and prediction errors have on bit-error rate (BER). Based on this analysis, we develop adaptive pilot symbol assisted modulation (PSAM) schemes that account for both channel estimation and prediction errors to meet a target BER. While pilot symbols facilitate channel acquisition, they consume part of transmitted power and bandwidth, which in turn, reduces spectral efficiency. With imperfect (and thus, partial) CSI available at the transmitter and receiver, two questions arise naturally: how often should pilot symbols be transmitted, and how much power should be allocated to pilot symbols. We address these two questions by optimizing pilot parameters to maximize spectral efficiency.
Bibliographical noteFunding Information:
Manuscript received February 17, 2003; revised July 28, 2003, October 26, 2003; accepted October 29, 2003. The editor coordinating the review of this paper and approving it for publication is D. Gesbert. This work was prepared 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. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. This paper was presented in part at the 37th Conference on Information Science and Systems, Baltimore, MD, March 12–14, 2003.
- Adaptive modulation
- Channel estimation
- Channel prediction
- Rayleigh fading