Geethika Wijeratne - Academia.edu (original) (raw)

Papers by Geethika Wijeratne

2018 IEEE International Conference on Communications (ICC), 2018

Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to s... more Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to save power and cost in communication systems using high bandwidth and/or multiple RF chains. The goal of this work is to address the design of optimal signaling schemes and establish the capacity limit of Rician fading channels with 1- bit output quantization. This fading channel can be used to accurately model a wide range of wireless channels with LOS components, including emerging mmWave communications. The focus is on non-coherent fast fading channels where neither the transmitter nor the receiver knows the channel state information (CSI). By first examining the continuity of the input-output mutual information, the existence of the optimal input signal is validated. Moreover, the optimal input is shown to be pi/2\pi/2pi/2 circularly symmetric. A necessary and sufficient condition for an input signal to be optimal, which is referred to as the Kuhn-Tucker condition (KTC), and Lagrangian optimization problem are then established. By exploiting novel log-quadratic bounds on the Gaussian QQQ-function, it is then demonstrated that for a given mass point's amplitude, the corresponding rotated mass points through the phase of LOS component must form a square grid centered at zero. Furthermore, by establishing an upper bound on the KTC coefficient, we show that there are exact four mass points in the optimal distribution. As a result, the capacity-achieving input is a rotated QPSK constellation, and the rotation angle is the phase of the LOS coefficient. By using this input, the channel capacity is finally established in closed-form.

IEEE Transactions on Wireless Communications, 2019

Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to s... more Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to save power and cost in communication systems using high bandwidth and/or multiple RF chains. The goal of this work is to address the design of optimal signaling schemes and establish the capacity limit of Rician fading channels with low-resolution output quantization. This fading channel can be used to accurately model a wide range of wireless channels with line-of-sight (LOS) components, including emerging mmWave communications. The focus is on non-coherent fast fading channels where neither the transmitter nor the receiver knows the channel state information (CSI). By examining the continuity of the input-output mutual information, the existence of the optimal input signal is first validated. Then considering the case of 1-bit ADC, we show that the optimal input is π/2 circularly symmetric. A necessary and sufficient condition for an input signal to be optimal, which is referred to as the Kuhn-Tucker condition (KTC), and Lagrangian optimization problem are then established. By exploiting novel log-quadratic bounds on the Gaussian Q-function, it is then demonstrated that for a given mass point's amplitude, the corresponding rotated mass points through the phase of LOS component must form a square grid centered at zero. Furthermore, the amplitude of the mass points in the optimal distribution can take on only one value. As a result, the capacity-achieving input with 1-bit ADC is a rotated quadrature phase-shift keying (QPSK) constellation, and the rotation angle depends on the Rician factor. The characterization of the optimal input has also been extended to the case of multibit ADCs. Specifically, it is shown that for a K-bit ADC, the optimal input is discrete having at most 2 2K mass points. In both cases of 1-bit and K-bit ADCs, the channel capacities are established in closed-form.

2018 IEEE International Conference on Communications (ICC), 2018

Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to s... more Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to save power and cost in communication systems using high bandwidth and/or multiple RF chains. The goal of this work is to address the design of optimal signaling schemes and establish the capacity limit of Rician fading channels with 1- bit output quantization. This fading channel can be used to accurately model a wide range of wireless channels with LOS components, including emerging mmWave communications. The focus is on non-coherent fast fading channels where neither the transmitter nor the receiver knows the channel state information (CSI). By first examining the continuity of the input-output mutual information, the existence of the optimal input signal is validated. Moreover, the optimal input is shown to be pi/2\pi/2pi/2 circularly symmetric. A necessary and sufficient condition for an input signal to be optimal, which is referred to as the Kuhn-Tucker condition (KTC), and Lagrangian optimization problem are then established. By exploiting novel log-quadratic bounds on the Gaussian QQQ-function, it is then demonstrated that for a given mass point's amplitude, the corresponding rotated mass points through the phase of LOS component must form a square grid centered at zero. Furthermore, by establishing an upper bound on the KTC coefficient, we show that there are exact four mass points in the optimal distribution. As a result, the capacity-achieving input is a rotated QPSK constellation, and the rotation angle is the phase of the LOS coefficient. By using this input, the channel capacity is finally established in closed-form.

IEEE Transactions on Wireless Communications, 2019

Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to s... more Low resolution analog-to-digital converter (ADC) has been considered as a promising solution to save power and cost in communication systems using high bandwidth and/or multiple RF chains. The goal of this work is to address the design of optimal signaling schemes and establish the capacity limit of Rician fading channels with low-resolution output quantization. This fading channel can be used to accurately model a wide range of wireless channels with line-of-sight (LOS) components, including emerging mmWave communications. The focus is on non-coherent fast fading channels where neither the transmitter nor the receiver knows the channel state information (CSI). By examining the continuity of the input-output mutual information, the existence of the optimal input signal is first validated. Then considering the case of 1-bit ADC, we show that the optimal input is π/2 circularly symmetric. A necessary and sufficient condition for an input signal to be optimal, which is referred to as the Kuhn-Tucker condition (KTC), and Lagrangian optimization problem are then established. By exploiting novel log-quadratic bounds on the Gaussian Q-function, it is then demonstrated that for a given mass point's amplitude, the corresponding rotated mass points through the phase of LOS component must form a square grid centered at zero. Furthermore, the amplitude of the mass points in the optimal distribution can take on only one value. As a result, the capacity-achieving input with 1-bit ADC is a rotated quadrature phase-shift keying (QPSK) constellation, and the rotation angle depends on the Rician factor. The characterization of the optimal input has also been extended to the case of multibit ADCs. Specifically, it is shown that for a K-bit ADC, the optimal input is discrete having at most 2 2K mass points. In both cases of 1-bit and K-bit ADCs, the channel capacities are established in closed-form.