Communications Research

The communication system performance depends heavily on each involved component: coding, modulation, LED source, beam energy distribution, light propagation, detection, and post-processing. We develop a theoretical framework for optimizing LED lamp placement, beam energy distribution and concentration, and design components incorporating nonimaging optics. First, we characterize white LEDs, photodiodes and channel properties (impulse response, path loss, and frequency response) using an integrated analytical and experimental approaches. Exemplified approaches include wave propagation analysis, Monte Carlo simulation, and parametric fitting. Various developed models are compared against channel measurements in time and frequency. Effects of link geometries and source/detector angles are analyzed.

With attainable measurements and models, we then develop and analyze capacity-maximization communication techniques, performance limits and system optimization. Applying advanced signal processing and communication theory, we particularly pursue advanced data modulation formats beyond traditional on-off-keying, coding and demodulation techniques that help to increase the data rate. Bandwidth and power efficiencies are better comprised. Additional signal processing capabilities such as channel estimation and equalization are explored to improve detection performance under imperfect device and channel conditions. We further enhance and optimize communication performance by various diversities. We investigate duplexing options to achieve bi-directional communication as well. Guided by analytical studies, we also study maximal system achievable rate.