Electrical and Electronic Engineering - Theses
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ItemCommunication Receivers with Low-Resolution Quantization: Fundamental Limits and Task-based Designs( 2023-08)The use of low-resolution analog-to-digital converters (ADCs) in communication receivers has gained significant interest in the research community since it addresses practical issues in 5G/6G deployment such as massive data processing, high power consumption, and high manufacturing cost. An ADC equipped in communication receivers is often designed such that its quantization thresholds are equally-spaced or the distortion between its input and output is minimized. These design approaches, however, may yield suboptimal performance as they neglect the underlying system task that the ADCs are intended to be used for. This presents an opportunity for us to explore receiver quantization designs that cater to specific communication tasks (e.g. symbol detection, channel estimation) and to understand how quantization impacts various aspects of receiver performance such as error rate, channel capacity, estimation error. In this thesis, we consider five independent research problems related to the communication receivers with low-resolution quantizers. Three of these research problems deal with capacity analysis of certain communication channels with quantized outputs. More precisely, we derive the capacity-achieving input distributions for four different channels with phase-quantized observations and the Gaussian channel with polar-quantized observations. For the channels with b-bit phase quantizer at the output, 2^b-phase shift keying modulation scheme can attain the channel capacity. Meanwhile, the capacity can be achieved in the Gaussian channel with polar quantization by an input distribution with amplitude phase shift keying structure. Capacity bounds for MIMO Gaussian channel with analog combiner and 1-bit sign quantizers are also established in this thesis. The remaining two research problems fall under the category of task-based quantizer design. The idea is to design the quantizer in accordance to the underlying system task rather than simply minimize its input-output distortion. Focusing on M-ary pulse amplitude modulation (PAM) receiver with symmetric scalar quantizer, the closed-form expression of the symbol error rate is derived as a function of quantizer structure and position of equiprobable PAM symbols. The derived expression is used to design the quantizer according to the symbol detection task. The high signal-to-noise ratio (SNR) behavior of the error rate of the quantized communication system is characterized. Our final work is a development of a new design and analysis framework for task-based quantizers with hybrid analog-to-digital architecture. In contrast to existing task-based quantization frameworks, the theoretical predictions of our proposed framework perfectly coincides with the simulated results. Moreover, the proposed frameworks can be used in data acquisition systems with non-uniform quantizers and observations with unbounded support.