Finite state channels with time-invariant deterministic feedback
IEEE Transactions on Information Theory
Feedback capacity of stationary Gaussian channels
IEEE Transactions on Information Theory
Capacity of fading channels with channel side information
IEEE Transactions on Information Theory
Capacity and mutual information of wideband multipath fading channels
IEEE Transactions on Information Theory
Spectral efficiency in the wideband regime
IEEE Transactions on Information Theory
What is the value of limited feedback for MIMO channels?
IEEE Communications Magazine
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The Rayleigh flat fading channel at low SNR is considered. With full channel state information (CSI) at the transmitter and receiver, its capacity is shown to be essentially SNRlog(1/SNR) nats/symbol, as SNR goes to zero. In fact, this rate can be achieved with a just one bit of CSI at the transmitter (per fading realization) and with no receiver CSI. The capacity for the case of noisy transmitter CSI is also found. Then a Rayleigh block fading channel of coherence interval T ≤ 1/SNR is considered which has causal feedback and no a priori CSI. A training based scheme is proposed for such channels, which achieves a rate of SNR T nats/symbol in the limit of small SNR and large T. Thus, when coherence interval T is of the order 1/SNR, without any a priori CSI at either end, the capacity with full CSI at both ends is achievable. For smaller values of T, a rate of SNR log T nats/symbol is shown to be achievable.