The Noncoherent Rician Fading Channel -- Part II : Spectral Efficiency in the Low-Power Regime

TL;DR

This paper investigates the spectral efficiency and energy tradeoffs in noncoherent Rician fading channels at low power, revealing that peak constraints affect optimal energy use and proposing a new signaling scheme for efficiency.

Contribution

It introduces a new signaling scheme combining phase-shift keying with on-off keying that is optimal in low-power conditions under peak constraints.

Findings

Minimum bit energy is not always at zero spectral efficiency with peak constraints.

A new overlay signaling scheme is proposed and shown to be optimal in the low-power regime.

The low-power performance is characterized under fixed peak power limits.

Abstract

Transmission of information over a discrete-time memoryless Rician fading channel is considered where neither the receiver nor the transmitter knows the fading coefficients. The spectral-efficiency/bit-energy tradeoff in the low-power regime is examined when the input has limited peakedness. It is shown that if a fourth moment input constraint is imposed or the input peak-to-average power ratio is limited, then in contrast to the behavior observed in average power limited channels, the minimum bit energy is not always achieved at zero spectral efficiency. The low-power performance is also characterized when there is a fixed peak limit that does not vary with the average power. A new signaling scheme that overlays phase-shift keying on on-off keying is proposed and shown to be optimally efficient in the low-power regime.