High Altitude Platform System (HAPS) is an exceptional technology in aerial communications systems. Some inimitable facets of HAPS compose it as a spectacular service provider. However, interference with other aerial or terrestrial communications systems is a significant issue. With regards to system interference as of other commercial products or systems which perform partially at the same frequency range as HAPS, escalating HAPS performance by bringing about in conjunction with these systems seems unavoidable. One of the most significant systems which operating at the same frequency of HAPS is Fixed Satellite Service (FSS). This article concentrates on tropical and subtropical areas' coexisting systems specifications Functioning in C-band. Foremost emphasis would be given to interference amount gauge churned out by FSS uplink (5925-6725 MHz) towards HAPS gateway links in commission at 5850-7075 MHz frequency range. The criteria are compatible to and derived out from the International Telecommunication Union (ITU) and World Radio-Communication Conferences (WRCs) publications.

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<p>In this work, a new rain attenuation time series synthesizer based on the stochastic approach is presented. The model combines a well-known interest-rate prediction model in finance namely the Cox-Ingersoll-Ross (CIR) model, and a stochastic differential equation approach to generate a long-term gamma distributed rain attenuation time series, particularly appropriate for heavy rain regions. The model parameters were derived from maximum-likelihood estimation (MLE) and Ordinary Least Square (OLS) methods. The predicted statistics from the CIR model with the OLS method are in good agreement with the measurement data collected in equatorial Malaysia while the MLE method overestimated the result. The proposed stochastic model could provide radio engineers an alternative solution for the design of propagation impairment mitigation techniques (PIMTs) to improve the Quality of Service (QoS) of wireless communication systems such as 5G propagation channel, in particular in heavy rain regions.</p>

The uniqueness of HAPS technology has led to evaluation of several issues concerning this new technology. Interference issue is one such issue. Several types of the systems, either terrestrial or aerial, interfere with HAPS based on the frequency range. FSS links are one of the most significant interferer with HAPS gateway links. At this juncture, adjacent channel interference between these two systems is evaluated. Interference computation has been done only for the 1st and 2nd adjacent channels. Evaluation has been performed for both urban and suburban area elevation angles. The results help to determine the HAPS gateway links enhancement possibilities to coexist with FSS links.keywords-Antenna Radiation Pattern, Adjacent Channel Interference Ratio (ACIR), Interference to Noise Ratio (I/N).