Development and Implementation of an Adaptive Error Correction Coding Scheme for a Full Duplex Communications Channel

摘要

This research investigates, via simulation, the bit error probability (BEP) associated with a variable redundancy coding scheme operating in a wireless communications environment. Within a slowly varying (flat fading) Rayleigh channel, adaptive algorithms provide increased throughput over fixed coding implementations. From a family of BCH codes of the same block length (n=63), a code with appropriate redundancy is chosen depending on the receiver's estimation of the current conditions experienced in this channel. Two different decision techniques are compared. The first method statistically evaluates the receiver's input and calculates the signal to noise ratio (Eb/No), while the second method observes the number of corrected errors in recently decoded blocks. With this information, the adaptive system decides to modify the correction ability of the code, and then transmits this decision to the encoder over a low bandwidth feedback channel. The correction ability can be changed on a block by block basis. This algorithm is implemented in software and, therefore, can be optimized for many real world communications systems. The low cost of high speed microprocessors and DSPs allows for the development of a robust adaptive coding system in hardware. The results are compared against fixed coding implementations and show that the adaptive process maintains a better efficiency (eta=k/n) of information rate while keeping the bit error probability near the level obtained by maximum encoding.