A Channel Model of Atmospheric Impairment for the Design of Adaptive Coding and Modulation in Stratospheric Communication

Wireless communication in the millimetre frequency bands is subject to severe atmospheric impairment caused by rain and scintillation, which may occasionally cause deep fades and thus needs to be mitigated by an efficient countermeasure such as adaptive coding and modulation (ACM). In this paper we focus on stratospheric communication and propose appropriate rain and scintillation fading channel models, which we use to describe the conceptual design of adaptive coding and modulation on four reference theoretical ACM schemes. Rain fading is modelled according to the modified DLR segment approach for generating channel attenuation time series, taking into consideration the specifics of stratospheric communication systems, namely the variable elevation angle and different carrier frequency. Additional fading due to scintillation, which may be harmful in deep fades caused by the rain, is modelled by adjusting the satellite scintillation channel model so that the amount of scintillation fading is correlated to the attenuation caused by the rain. We describe two extreme approaches to the ACM design process, one for maximizing the system reliability and the other for maximizing the system throughput. We present simulation results for four representative theoretical ACM schemes with different SNR ranges as the variation of bandwidth efficiency in time, and as system outage probability. Finally we show that, for a given SNR range, increasing system complexity by increasing the number of different coding-modulation (CM) modes beyond a certain optimum value does not yield a notable increase in bandwidth efficiency. In other words, there is a trade off between the system complexity and bandwidth efficiency that needs to be taken into account when designing the ACM scheme. Finally, two standards with ACM schemes applicable for stratospheric communications are proposed and analyzed, namely IEEE standard 802.16 for single carrier transmission and ETSI standard for digital video broadcasting over satellites DVB-S2. Key-Words: rain fading, scintillation fading, millimetre frequency band, stratospheric communication system, propagation channel model, adaptive coding and modulation