A study of constant envelope CDMA system for multimedia satellite communication

A variable data rate CDMA system with constant envelope modulation is studied for multimedia random access satellite communications. This system utilizes a constant occupied bandwidth and has variable data rates and processing gains to mitigate communication link impairments such as fading, rain attenuation and interference as well as to handle variable data rate on demand. A proof of concept hardware system for a 6 MHz bandwidth transponder is developed for hardware simulation, which uses MSK and OQPSK-type constant envelope direct sequence spread spectrum modulation and handles data rates of 4 to 64 kbps. The receiver is designed with coherent matched filter technique to achieve fast code acquisition, AFC and coherent detection in a single matched filter circuit. This receiver structure facilitates variable data rate on demand during a call without the aid of system control earth stations. The CDMA performance of the prototype equipment is evaluated with hardware simulation of nonlinear solid state power amplifier (SSPA) transponder. Both the IF loop back hardware simulation and nonlinear SSPA test performances of the prototype equipment prove it has the potential for personal multimedia satellite applications.