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A differential approach is proposed for tomographic rain field reconstruction using the estimated signal-to-noise ratio of microwave signals from low earth orbit satellites at the ground receivers, with the unknown baseline values eliminated before using least squares to reconstruct the attenuation field. Simulations are done when the baseline is modelled by an autoregressive process and when the baseline is assumed fixed. Comparisons between the reconstruction results for the differential and non-differential approaches suggest that the differential approach performs better in both scenarios. For high correlation coefficient and low model noise in the autoregressive process, the differential approach surpasses the non-differential approach significantly.

A contention-based opportunistic feedback protocol has been proposed in the literature, to achieve multiuser diversity for the downlink transmission of a multiuser wireless system, with the assumption that the incoming data for the active users are infinitely backlogged. However, this assumption is not valid if the authors consider the finite-length queuing effect in practical systems. By taking not only the channel states, but also the queuing states into account, the authors propose an improved opportunistic feedback protocol with multiuser diversity, and analyse its performance with adaptive modulation and coding. Additionally, instead of solving a system of equations directly, a simple iterative method is proposed to obtain the stationary distribution of the system, where the system behaviour is modelled by a two-dimensional finite-state Markov chain. Numerical results demonstrate that the authors proposed protocol is superior to the protocol in the literature in terms of the average throughput, the average spectral efficiency and the average packet delay, when considering the queuing dynamics. © The Institution of Engineering and Technology 2014.

A contention-based opportunistic feedback protocol has been proposed in the literature, to achieve multiuser diversity for the downlink transmission of a multiuser wireless system, with the assumption that the incoming data for the active users are infinitely backlogged. However, this assumption is not valid if the authors consider the finite-length queuing effect in practical systems. By taking not only the channel states, but also the queuing states into account, the authors propose an improved opportunistic feedback protocol with multiuser diversity, and analyse its performance with adaptive modulation and coding. Additionally, instead of solving a system of equations directly, a simple iterative method is proposed to obtain the stationary distribution of the system, where the system behaviour is modelled by a two-dimensional finite-state Markov chain. Numerical results demonstrate that the authors proposed protocol is superior to the protocol in the literature in terms of the average throughput, the average spectral efficiency and the average packet delay, when considering the queuing dynamics. © The Institution of Engineering and Technology 2014.

Multiuser diversity can be employed in wireless communications to significantly improve system performance by scheduling the channel to the user with the best instantaneous channel-state information (CSI). Conventionally, all users' CSI must be available at the base station (BS) to achieve the benefit of multiuser diversity, thereby inducing enormous system overhead. To solve the overhead issue, we propose a user identification approach (UIDA) in a generic wireless network and demonstrate its application in the orthogonal frequency-division multiplexing (OFDM) system and the multiple-input multiple-output OFDM (MIMO-OFDM) system. In the UIDA, to find the user with the best CSI, all active users simultaneously send response messages to the BS following a broadcast probing message from the BS, and only the selected user's CSI needs to be available at the BS, thus reducing the system overhead. We present a theoretical upper bound of the throughput of the system with the UIDA over general channels, and its tightness over Rayleigh fading channels is verified by simulations. In addition, a modified UIDA is proposed to effectively trade off throughput and fairness performances, where only the active users whose signal-to-noise ratios (SNRs) are above their predetermined thresholds will send response messages. Compared with medium access diversity and multiuser diversity with capture (two alternative approaches in the literature for exploiting multiuser diversity) and with a similar system setup, simulation results show that the UIDA achieves better throughput performance when there are a reasonably large number of users. © 2012 IEEE.

Multiuser diversity can be employed in wireless communications to significantly improve system performance by scheduling the channel to the user with the best instantaneous channel-state information (CSI). Conventionally, all users' CSI must be available at the base station (BS) to achieve the benefit of multiuser diversity, thereby inducing enormous system overhead. To solve the overhead issue, we propose a user identification approach (UIDA) in a generic wireless network and demonstrate its application in the orthogonal frequency-division multiplexing (OFDM) system and the multiple-input multiple-output OFDM (MIMO-OFDM) system. In the UIDA, to find the user with the best CSI, all active users simultaneously send response messages to the BS following a broadcast probing message from the BS, and only the selected user's CSI needs to be available at the BS, thus reducing the system overhead. We present a theoretical upper bound of the throughput of the system with the UIDA over general channels, and its tightness over Rayleigh fading channels is verified by simulations. In addition, a modified UIDA is proposed to effectively trade off throughput and fairness performances, where only the active users whose signal-to-noise ratios (SNRs) are above their predetermined thresholds will send response messages. Compared with medium access diversity and multiuser diversity with capture (two alternative approaches in the literature for exploiting multiuser diversity) and with a similar system setup, simulation results show that the UIDA achieves better throughput performance when there are a reasonably large number of users. © 2012 IEEE.

We present optical modeling of small pixels in reflective liquid crystal display (LCD). The optical analysis is divided into two parts. In the first part, the two-dimensional (2D) director configuration of the LCD in rectangular mesh was calculated by simultaneously solving the 2D Poisson equation and a 2D continuum theory equation. In the second part, the generalized Jones matrix was used to simulate for the optical reflectance through the LCD with the 2D director configuration obtained from the first part. This optical modeling was applied to analyze optical reflectance of small pixels in reflective mixed-mode twisted nematic (MTN) cells on silicon substrate. Both the simulated and experimental data of the MTN cells with a pixel pitch of 10 to 25 mu m under frame and column inversion of polarities are presented.

We present optical modeling of small pixels in reflective liquid crystal display (LCD). The optical analysis is divided into two parts. In the first part, the two-dimensional (2D) director configuration of the LCD in rectangular mesh was calculated by simultaneously solving the 2D Poisson equation and a 2D continuum theory equation. In the second part, the generalized Jones matrix was used to simulate for the optical reflectance through the LCD with the 2D director configuration obtained from the first part. This optical modeling was applied to analyze optical reflectance of small pixels in reflective mixed-mode twisted nematic (MTN) cells on silicon substrate. Both the simulated and experimental data of the MTN cells with a pixel pitch of 10 to 25 mu m under frame and column inversion of polarities are presented.