A study of low-cost, robust Assistive Listening System (ALS) based on digital wireless technology

Abstract

Purpose. We have developed a simple, low-cost digital wireless broadcasting system prototype, intended for a classroom of hearing impaired students. The system is designed to be a low-cost alternative to an existing FM system.Method. The system implemented is for short-range communication, with a one-transmitter, multiple-receiver configuration, which is typical for these classrooms. The data is source-coded for voice-band quality, FSK modulated, and broadcasted via a 915 MHz radio frequency. A DES encryption can optionally be added for better information security.Results. Test results show that the system operating range is approximately ten metres, and the sound quality is close to telephone quality as intended. We also discuss performance issues such as sound, power and size, as well as transmission protocols.Conclusions. The test results are the proof of concept that the prototype is a viable alternative to an existing FM system. Improvements can be made to the system's sound quality via techniques such as channel coding, which is also discussed.