Phase-Quantized Block Noncoherent Communication

Abstract

Analog-to-digital conversion (ADC) is a key bottleneck in scaling DSP-centric receiver architectures to multiGigabit/s speeds. Recent information-theoretic results, obtained under ideal channel conditions (perfect synchronization, no dispersion), indicate that low-precision ADC (1-4 bits) could be a suitable choice for designing such high speed systems. In this work, we study the impact of employing low-precision ADC in a carrier asynchronous system. Specifically, we consider transmission over the block noncoherent additive white Gaussian noise channel, and investigate the achievable performance under low-precision output quantization. We focus attention on an architecture in which the receiver quantizes only the phase of the received signal: this has the advantage of being implementable without automatic gain control, using multiple 1-bit ADCs preceded by analog multipliers. For standard uniform Phase Shift Keying (PSK) modulation, we study the structure of the transition density of the phase-quantized block noncoherent channel. Several results, based on the symmetry inherent in the channel model, are provided to characterize this transition density. Low-complexity procedures for computing the channel information rate, and for block demodulation, are obtained using these results. Numerical computations are performed to compare the performance of quantized and unquantized systems, for different quantization precisions, and different block lengths. With QPSK modulation, it is observed, for example, that for SNR larger than 2-3 dB, 8-bin phase quantization of the received signal recovers about 80-85% of the mutual information attained with unquantized observations, while 12-bin phase quantization recovers more than 90% of the unquantized mutual information. Dithering the constellation is shown to improve the performance in the face of drastic quantization.