Binary Adaptive Coded Pilot Symbol Assisted Modulation Over Rayleigh Fading Channels Without Feedback

Abstract

Abstract-Pilot symbol assisted modulation (PSAM) is a standard approach for transceiver design for time-varying channels, with channel estimates obtained from pilot symbols being employed for coherent demodulation of the data symbols. In this paper, we show that PSAM schemes can be improved by adapting the coded modulation strategy at the sender to the quality of the channel measurement at the receiver, without requiring any channel feedback from the receiver. We consider performance in terms of achievable rate for binary signaling schemes. The transmitter employs interleaved codes, with data symbols coded according to their distance from the nearest pilot symbols. Symbols far away from pilot symbols encounter poorer channel measurements at the receiver and are therefore coded with lower rate codes, while symbols close to pilot symbols benefit from recent channel measurements and are coded with higher rate codes. The performance benefits from this approach are quantified in the context of binary signaling over time-varying Rayleigh fading channels described by a Gauss-Markov model. The spacing of the pilot symbols is optimized to maximize the mutual information between input and output in this setting. Causal and noncausal channel estimators of varying complexity and delay are considered. It is shown that, by appropriate optimization for the spacing between consecutive pilot symbols, the adaptive coding techniques proposed can improve achievable rate, without any feedback from the receiver to the sender. Moreover, channel estimation based on the two closest pilot symbols is generally close to optimal.

On Achievable Data Rates and Optimal Power Allocation in Fading Channels with Imperfect Channel State Information

“…Otherwise, a residual estimation error is unavoidable and it increases with bandwidth due to the signal/noise overlap. Since working with long frames is unrealistic [8], it is safe to assume that the normalized covariance function is evaluated only for small lags and, therefore, can be approximated by a few terms of its Taylor series with respect to a small parameter f D T S :…”

“…the block fading assumption is often invalid. The authors of [8] treat such channels as an array of N − 1 partial channels, obtained by sampling the original channel at the rate 1/N T s and shifted by one symbol with respect to each other with each partial channel having a fixed effective SNR. The optimal communication strategy over such channels involves optimizations over each partial channel.…”

“…Most of the authors have focussed on optimizing pilot placement based on the desired bit error rate for fixed rate transmission [4] or block adaptive modulation [5] and assume that the same quality of estimates are available at all signal-to-noise ratio (SNR) values and all data symbol positions [5,6]. A new approach to solve this problem is proposed in [7,8] by finding a lower bound on the capacity of the channel with imperfect CSI. However, only the case of CSI at the receiver and a first-order Markov channel model was considered.…”

Cutoff rate optimal binary inputs with imperfect CSI

“…In [1], this methodology is proposed and used to characterize PSAM-based achievable rates for the Gauss-Markov correlation model. An adaptive binary modulation scheme was proposed in which the transmitter selects the achievable rate optimal binary input in each data slot.…”

On Achievable Data Rates and Optimal Power Allocation in Fading Channels with Imperfect CSI

“…Most of the authors have focused on optimizing pilot placing based on the desired bit error rate for fixed rate transmission or block adaptive modulation [4] and assume that the same quality of estimates are available at all SNR and all data symbol positions [4]- [6]. A new approach to this problem has been in [7], [8] by finding a lower bound on capacity of the channel with imperfect CSI. However, only the case of CSI at the receiver and a first-order Markov channel was considered.…”