Channel Decoder Assisted Adaptive Coding and Modulation for HAP Communications

Provision of mobile broadband wireless access, for instance via high altitude platforms (HAPs) to the passengers on a high-speed train, requires the development of efficient and reliable radio interface, which has to adapt to the variation of propagation channel conditions in order to optimise the utilisation of radio resources. In this paper we focus on the implementation aspects and performance analysis of adaptive coding and modulation scheme based on the IEEE 802.16 standard. In order to maximize the link reliability in a fading environment we propose switching between the transmission schemes assisted by the information on the corrected bytes of the previous frames obtained from the Reed-Solomon decoder, thus increasing the throughput while retaining the targeted bit-error-rate (BER). To adequately take into account the real implementation aspects, the selected procedures were implemented on a digital signal processing (DSP) board and tested on a HAP propagation channel model. The performance evaluation results, given in terms of spectral efficiency and the Reed-Solomon decoder state, confirm the adaptability of the implemented switching scenarios to the variation of the HAP propagation channel attenuation.