Adaptive Modulation with Adaptive Pilot Symbol Assisted Estimation and Prediction of Rapidly Fading Channels

Adaptive modulation requires channel state information (CSI) at both transmitter and receiver. In practice, CSI can be acquired at the receiver by inserting pilot symbols in the transmitted signal. In this paper, we first analyze the effect 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 the 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.