Adaptive modulation and coding for WiMAX systems with vague channel state information using cognitive radio

Adaptive modulation and coding (AMC) schemes are used in WiMAX. Higher system throughput using higher order modulation is traded for higher output. In WiMAX higher modulation tends to be used close to the base station whereas lower order modulations tends to be used at longer range. The dependency of distance might sometimes be deceiving, as channel conditions can vary considerably especially in a mobile environment. In this paper we present a cognitive approach to alter the modulation and code rate using a cognitive engine that is based on linguistic and uncertainty reasoning as well as estimating the channel type. The cognitive engine controls the type of modulation and code rate in order to maintain a good system throughput without wasting available bandwidth. Fuzzy logic reasoning in the cognitive engine was chosen because it is well suited for situations of uncertainty, incompleteness and heterogeneity information, in the case of fast changing radio environments. The results showed that new combinations of modulation type and code rate should be considered in WiMAX since it outperforms the standard in spectral efficiency, especially in a fast changing radio environment.