Joint Adaptation of Code Length and Modulation Formats in OFDM Systems

Abstract

In order to reduce the signaling overhead in adaptive OFDM transmission systems being designed for B3G and 4G wireless communications, the basic resource unit, referred to as chunk, comprises a number of adjacent sub-carriers and OFDM symbol periods. A consequent open issue is the mapping of long codewords onto limited size chunks, especially when link adaptation per chunk is carried out. This paper proposes a new method for joint coding and modulation. A data packet, independently of its length, is encoded without any segmentation into a single codeword spanning different chunks employing different signal constellations. The parameters of the underlying error correction code are chosen independently of the signal constellation and no puncturing is required. Moreover, a joint adaptation of the code length and the modulation format is proposed to optimise the number of chunks allocated for transmission