Capacity of the Discrete-Time AWGN Channel Under Output Quantization

We investigate the limits of communication over the discrete-time Additive White Gaussian Noise (AWGN) channel, when the channel output is quantized using a small number of bits. We first provide a proof of our recent conjecture on the optimality of a discrete input distribution in this scenario. Specifically, we show that for any given output quantizer choice with K quantization bins (i.e., a precision of log2 K bits), the input distribution, under an average power constraint, need not have any more than K + 1 mass points to achieve the channel capacity. The cutting-plane algorithm is employed to compute this capacity and to generate optimum input distributions. Numerical optimization over the choice of the quantizer is then performed (for 2-bit and 3-bit symmetric quantization), and the results we obtain show that the loss due to low-precision output quantization, which is small at low signal-to-noise ratio (SNR) as expected, can be quite acceptable even for moderate to high SNR valu...

• Type: Journal
• Year: 2008
• Where: CORR
• Authors: Jaspreet Singh, Onkar Dabeer, Upamanyu Madhow
• Keywords: Additive White Gaussian Noise, CORR 2008, Education, Input Distributions, Output Quantizer Choice