A Four-State Trellis-Coded 8-PSK Modulation Computer Simulation

Abstract

The continuing growth of the telecommunications industry has created a steadily increasing need for higher performance communications systems - systems that can transfer data at faster rates while meeting stringent bit error rate requirements. In the case of satellite and mobile communications these same systems must also maintain minimum size and power consumption requirements. To help implement this industry demand computer simulations of communications systems can be a viable tool. Simulators can be used to demonstrate feasibility while maintaining minimum research and development costs during the design phase of these new and more complex communications systems. One type of system where simulation has proved helpful has been trellis-codedmodulation (TCM). This paper documents a simulation of a four-state trellis-coded eight- PSK modulation scheme currently being researched at New Mexico State University (NMSU). In the past simulations of convolutionally coded schemes have used binary symbols in the decoding process. In TCM the Euclidean space components of the modulation scheme are used in place of the binary symbols. The simulator under development incorporates these Euclidean signal components which are taken from an eight-PSK signal constellation. Soft-decision maximum likelihood decoding using trellis trace-back techniques are then applied to the Euclidean signal components to recover the simulated transmitted data. The simulator supplies the user with the number of undetected errors generated during a simulation as well as the bit error rate for a given signal to noise ratio. This simulator is intended to provide an environment for investigating improved communication system designs and it is hoped that the results that are obtained from such telecommunication simulators will help satisfy the ever increasing demands of the telecommunications industry. It should be noted that the research being conducted at NMSU on TCM is being directed by Dr. Frank Carden. The development of the simulator was conducted by the author to assist Dr. Carden in the continuing investigation of TCM.