Designing an audio channel for low-bandwidth mobile optical networks

Free-space optical communication links are well established as high bandwidth data transfer facilities. They also provide secure communication in hostile environments where Radio Frequency-based communication can be easily tapped into or jammed by a hostile agent. Mobile optical communication will thus provide a highly desirable system in such an environment, e.g., a battlefield. This paper presents the design and performance of a system for providing mobile voice communication that is based on optical links. The voice channel is created over two Field Programmable Gate Array (FPGA) development boards which allow parameters to be changed as needed. These parameters are chosen so that the voice channel emulates the G.711 ITU-T standard. Several configurations with different data rates can be obtained by varying the sampling rate and the number of bits representing each sample so as to optimize the transmission parameters from both fidelity and dynamic range perspectives. The Quality of the audio channel for each configuration is determined by measuring the Mean Opinion Score (MOS) using an Agilent Voice Quality Tester (VQT). Other parameters such as echo and delay are also measured.