Wireless Communications with Low-Resolution Quantization

Abstract

Wireless communication systems with low-resolution quantization are envisioned to be a major part in future wireless communication networks because of their potential to improve the energy efficiency of the network. In this thesis, we present a comprehensive and rigorous analytical investigation on the performance impact of using low-resolution phase quantization at the receiver of a wireless communication system, when compared to traditional high-resolution systems. To that end, we consider three different system setups; a point-to-point wireless communication system with coherent detection, a point-to-point wireless communication system with non-coherent detection and a multi-antenna system with coherent detection. We study the optimum detectors and draw fundamental insights on the error probability performance of low-resolution quantization systems in the presence of fading and noise.

Firstly, we focus on coherent detection with M-ary phase shift keying (M-PSK) modulation and, derive the optimum maximum likelihood (ML) detector for a single-input single-output (SISO) system. Utilizing the structure of the derived detector, a general average symbol error probability (SEP) expression for M-PSK modulation with n-bit quantization is obtained when the wireless channel is subject to Nakagami-m fading. We show that a transceiver architecture with n-bit quantization is asymptotically optimum in terms of communication reliability if n is greater than or equal to log_2(M +1).

The coherent detection techniques discussed above require channel state information (CSI) to be available at the receiver. Due to the non-linear nature of quantization, channel estimation has been one of the major challenges associated with low-resolution quantization based systems. Taking these into account, next we focus on non-coherent detection by adopting the differential quadrature phase shift keying (DQPSK) modulation scheme to differentially encode the transmit data. At the receiver side, we employ non-coherent detection that does not require instantaneous CSI. With DQPSK modulation, the ML detector is derived using which, a general average SEP expression with n-bit quantization is obtained when the wireless channel is subject to Rayleigh fading. It is shown that a transceiver architecture with n-bit quantization is asymptotically optimum in terms of communication reliability if n is greater than or equal to 4. That is, the decay exponent for the average SEP is the same and equal to 1 with infinite-bit and n-bit quantizers for n is greater than or equal to 4. Therefore, when the channel knowledge is not available at the receiver, the quantizer has to use one additional bit to achieve optimum communication robustness.

Finally, we extend our investigation to low-resolution quantization based multi-antenna wireless communication systems equipped with one transmit antenna and N receive antennas. We derive the ML detector and then propose three sub-optimum detection rules based on selection combining which have less computational complexity compared to the ML detector. We also note that the simple sub-optimum detector that selects the path with the channel that locates the rotated constellation point furthest away from the decision boundary is asymptotically optimum in terms of communication reliability if n is greater than or equal to 3. An extensive simulation study is performed to illustrate the accuracy of the derived results.