| As communication systems scale up in speed and bandwidth, the cost and power consumption of high-precision (e.g., 10-12 bits) analog-to-digital converter (ADC) becomes the limiting factor in modern receiver architectures based on digital signal processing. One possible approach to relieve this ADC bottleneck is to employ a low-precision (e.g., 1-4 bits) ADC. This may be suitable for applications requiring limited dynamic range, such as line-of-sight communication using small constellations. However, the drastic reduction of ADC precision raises fundamental questions, at both information-theoretic and algorithmic levels, regarding whether it is even possible to engineer a communication link with such a significant nonlinearity so early in the receiver processing. In this thesis, we present results from our efforts towards answering some of these questions.;We first investigate the Shannon-theoretic limits of communication imposed by the choice of low-precision ADC, for transmission over the ideal real additive white Gaussian noise channel. For an ADC employing K quantization bins (i.e., a precision of log2 K bits), we prove that the channel capacity can be achieved using a discrete input distribution with at most K+1 support points. A joint optimization over the choice of the input and the quantizer is performed, and the obtained numerical results reveal that at SNR up to 20 dB, the use of 2-3 bit ADC incurs a loss of only about 10-15% in capacity compared to unquantized observations. Furthermore, we observe that a sensible choice of uniform pulse amplitude modulated input, with quantizer thresholds set to perform maximum likelihood hard decisions, achieves performance close to that attained by an optimal input and quantizer pair.;We then turn our attention to the problem of carrier synchronization using low-precision ADC. We focus on a block noncoherent channel model, wherein the phase rotation caused by a small frequency offset, although a priori unknown, can be approximated as constant over a block of symbols. For M-ary phase shift keyed (M-PSK) inputs, the performance of phase-only quantization, which is attractive due to its ease of implementation, is investigated. The symmetry inherent in the resulting phase-quantized channel model is exploited to obtain low-complexity algorithms for channel capacity computation and block noncoherent demodulation. Numerical results, quantifying the channel capacity, and the uncoded error rates, are obtained for QPSK input with different number of phase quantization sectors and different block lengths. Dithering the constellation is shown to improve the performance in the face of drastic quantization. |
