UC Riverside

This thesis mainly focuses on the higher layer protocol design for optical wireless communication (OWC) networks in two different optical bands: (1) medium access control (MAC) protocol design and neighbor discovery methods for deep ultraviolet (UV) outdoor communications (UVOC), and (2) configuration of indoor visible light communication (VLC) networks.

For UVOC, solar blind and non-line-of-sight (NLOS) operations are attractive. Light beams from UV light-emitting diode (LED) arrays propagate through scattering media, creating spatially different communication links. This unique physical (PHY) layer characteristic was first captured experimentally based on a UV testbed, from which mathematical signal propagation models were developed and their impact on MAC design was realized, i.e., full duplexing and multi-rate transmission. Then we propose a novel contention-based MAC protocol (UVOC-MAC) that inherently accounts for the UV PHY layer and fully exploits multi-fold spatial reuse opportunities. Evaluations via simulation and analysis show that UVOC-MAC effectively mitigates collisions and achieves high throughput. We further develop efficient neighbor discovery protocols by accounting for the varying channel qualities along different scattering directions. Besides a list of neighbor nodes' identities, a ranked list of node pointing directions in terms of channel qualities was also included in the constructed table to facilitate the process. Utilizing neighbor feedback or alternating a leader node were proved to be able to alleviate the negative effects of random access based collisions and thus expedite neighbor discovery.

VLC by lighting LEDs is gaining popularity, but there is very limited research on the higher layer protocol design. Our extensive channel measurements using a physical layer testbed suggest two effective means to increase data rates, shrinking the beam width and tuning the transmission beam to point towards a target receiver. We design a configuration framework called VICO, by leveraging above PHY features towards achieving the highest throughput while maintaining fairness. VICO tries to schedule transmissions while minimizing conflicts of links. It also opportunistically tunes the idle LEDs to reinforce existing transmissions to increase throughput to the extent possible. Under these proposed treatments, VICO can provide as much as 5-fold increase in throughput as compared to a simple scheduler that does not exploit the possible variations in beamwidth or beam-angle.