Issues in diversity and adaptive error control coding for wireless communications
Date
1995
Authors
Mueller, Arndt Joseph
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
One of the most challenging aspects of mobile cellular communications is the non-stationary nature of the channel. Due to user mobility, the channel conditions vary widely. Thus, to achieve efficient and reliable data transmission, techniques for combating these fluctuations are required. This thesis addresses two such techniques: diversity and adaptive error control coding.
Two channel models are considered: the land mobile satellite channel and the land mobile terrestrial channel. Following previous empirical studies, the terrestrial channel is modelled as a lognormally shadowed Rician distribution and the satellite channel is modelled as a weighted sum of Rice and Suzuki distributions. Where analysis is performed, the channel model parameters are obtained from actual channel measurements.
For systems employing diversity, an analytical technique well suited to numerical analysis is presented for computing the average bit error rate (BER) and outage probability for several common modulation schemes including both M-ary coherent PSK (M-PSK) and differential PSK (M-DPSK). Both micro- and macro-diversity reception are considered where either maximal ratio or selection diversity combining techniques are employed. A numerical example is provided illustrating the achievable performance of both M-PSK and M-DPSK with micro-diversity in the satellite channel.
Classically, adaptive error control coding has been used to compensate for time varying channel conditions. Therefore, the cellular channel - where the propagation channel is continuously changing and fades greater than 20 dB are not uncommon - is an ideal candidate. A more recent motivation for adaptive coding is presented by the need to transmit multi-media data, where each data source may possess unique bit error rate and delay requirements. In light of these motivations, a rate adaptive error control code using a hybrid type-II automatic repeat request I forward error correction (ARQ/FEC) scheme is proposed.
For forward error correction, a concatenated code composed of a punctured rate (N- 1) I N convolutional code and a punctured Reed-Solomon code is used. Type-II hybrid ARQ is then employed through the decomposition of the Reed-Solomon code into two or more smaller code words and by soft-decision combining of repeated unreliable packets. Examples of the BER performance are provided for the fading channel through simulation.