Transmission Experiments Using Delay Generator Actualizing Fixed Communication System for HAPS

High-altitude platform stations (HAPSs) are promising to actualize extreme coverage extension from the stratosphere whereby mobile communications can be made available in various locations including mountainous areas, air, and sea. In particular, a fixed communications system for HAPS that uses the broadband millimeter-wave band will enable the provision of high-capacity communications infrastructure for many types of use cases such as high-capacity backhaul and industrial communications. However, the propagation delay is longer than that for ground systems, and processing delays caused by the HAPS stations and other devices are cumulative. Therefore, the system design must take these delays into account when implementing a network using HAPS. In this paper, to investigate the delay requirements in a fixed communications system for HAPS, we verify the transmission characteristics between a core network and a set of user equipment according to the insertion delay using a delay generator to emulate the delay caused by the HAPS and other system configurations. Up to now no transmission experiments have been reported that evaluate the impact of network latency on the communications quality in a fixed communications system for HAPS. Experimental results show that in the non-standalone 5th generation device environment used in this experiment, one-way delays of up to approximately 90 ms are acceptable, and that the observed communications performance is sufficient for the length of delay expected in a real-world environment.