ADAPTIVE CODING AND TRANSMISSION PARADIGMS FOR WIRELESS CHANNELS A Light-Hearted Overview

Following a brief historical perspective on channel coding the concept of near-instantaneously adaptive wireless transceivers is introduced as a counter-measure of mitigating the channelquality fluctuations experienced in wireless communications. It is argued that channel coded adaptive modulation schemes can be viewed as a lower complexity alternative of mitigating the channel quality fluctuations of wideband wireless channels in comparison to multiple-transmitter and multiple-receiver based space-time codes. However, provided that the complexity of the latter schemes employing multiple transmitters and receivers is affordable, the performance advantages of adaptive modulation and adaptive channel coding schemes erode, since the channel quality fluctuations of the wireless channel are effectively mitigated. 1. BRIEF HISTORY OF CHANNEL CODING Following Shannon’s ground-breaking predictions outlining the mathematical foundations of information theory [1], during the 1950s coding theory researchers embarked on contriving coding schemes that are capable of approaching Shannon’s predictions. Fulfiling this ambition required about 45 years of intensive research by the entire channel coding community, which culminated in the invention of turbo codes by Claude Berrou and his colleagues [2, 3]. The history of channel coding research spanning over half a century is summarised in Figure 1 [4], showing particularly intensive activities during the 1990s, although the individual contributors are too numerous to name here. In parallel with the impressive developments in the processing capabilities of the chips dedicated to channel encoding and decoding, over the years more and more complex solutions have been invented for various commercial and professional applications in both storage and transmission. In this light it became clear that the conception of channel coding and transmission schemes dedicated to a particular application is based on a complex set of contradictory design factors, which are summarised in Figure 2 [4]. Convolutional FEC codes date back to 1955 [5], which were discovered by Elias, while Wozencraft and Reiffen [6, 7], as well as Fano [8] and Massey [9] proposed various algorithms for their decoding. A major milestone in the history of convolutional error correction coding was the invention of a maximum likelihood sequence estimation algorithm by Viterbi [10] in 1967. A classic This overview is based on L. Hanzo, T.H. Liew, B.L. Yeap: Trubo coding, turbo equalisation and space-time coding, John Wiley IEEE Press, 2002 199