Variable redundancy coding for mobile channels

Mobile data channels carry different communication services with different data formats and rates. In modern CDMA systems as in UMTS, such different data rates and services are carried in a fixed frame. This results with some free data gaps in the frame. A novel coding concept called variable redundancy coding (VRC) to replace the currently used bit repetition for filling such gaps is presented. The key idea behind the proposed VRC is simple: instead of repeating bits to match the channel rate, block code redundancy bits are stuffed in the free gaps. Such VRC bits particularly improve the frame error rate (FER) and at the same time fill the free gaps. This results in a more efficient overall channel throughput, as the data throughput depends mainly on the frame error rate and on the ARQ strategy employed. A particular VRC technique based on the burst error correcting Fire code is presented and is shown to be effective to optimize the overall system performance