An adaptive radio link protocol with enhanced data rates for GSM evolution

In this article we address the problem of link adaptation in a wireless dat a system. Link adaptation is necessary in order to match the data rate to t ime-varying channel and interference conditions. We present a robust radio link protocol based on the concept of incremental redundancy (IR). Here, re dundant data, for the purpose of error correction, is transmitted only when previously transmitted packets of information are received and acknowledge d to be in error. The redundant packet is combined with the previously rece ived (errored) information packets in order to facilitate error correction decoding. If there is a decoding failure, more redundancy is transmitted. I t is shown here that an RLP built using the IR concept is more robust and h as better throughput than link adaptation schemes using explicit channel me asurements such as instantaneous or average signal-to-noise or signal-to-in terference ratio. We study the performance of an implementation of a IR-bas ed RLP for EDGE data for and demonstrate its superior throughput and robust ness properties. The penalty paid for increased robustness and higher throu ghput is additional receiver memory and higher delay. IR based RLP has alre ady been standardized for IS-136+ packet data and is being actively conside red for EDGE standardization.