Turkish Journal of Electrical Engineering and Computer Sciences




Aerial vehicles (AVs) have challenges in terms of realizing low complexity and wide coverage area wireless communications architectures, especially for crowded or high density groups of AVs with state-of-the-art free space optical (FSO) and radio frequency (RF) based system designs. FSO architectures generally target point-to-point high gain directional links while requiring strict acquisition and tracking due to the narrow beam width of laser transmitters with challenges of vibration, turbulence, misalignment, atmospheric absorption, scattering, and fading. In this article, a novel multiuser free space optical system design of modulation and coding denoted by space-track modulation and coding (STMC) is proposed for crowded downlink communications. STMC does not require high accuracy tracking and costly system components by utilizing large beam divergence angles, more transmitter units with smaller aperture sizes and weights, and large spatial regions to receive modulated data at AV tracks. In addition, the spatio-optical wireless caching problem is introduced for AV networks while defining STMC problem information theoretically. STMC combines track based multiuser modulation and coding, with geographical and positional data for low data rate broadcasting applications with wide area coverage. Numerical simulations provide tens of bit/s data rates for thousands of kilometers of coverage area while simultaneously serving a significantly larger number of AVs. Finally, future works and open issues are discussed. The novel modulation and coding mechanisms are promising future applications for both high altitude AVs and low altitude drone networks with low complexity hardware for multiuser low data rate communications.

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