Effect of Different Locations of Millimeter Wave HAPS on the Downlink Sum Rate

Telecommunication services globally use two communication systems: terrestrial and satellite, but they still have weaknesses that must be addressed immediately. An alternative is High Altitude Platform Station (HAPS), which was studied extensively in the 1990s and 2000s, and is now returning to public attention. In this study, we firstly determine the optimal HAPS position assuming equal power allocation to each User Equipment (UE) in order to maximize the downlink Sum Rate given a backhaul link constraint and minimum data rate of each UE. HAPS operates at the 28 GHz millimeter-wave band with an altitude of 20 km. The antenna configuration is Uniform Planar Array (UPA) with varying number of elements. The number of UE is fixed but randomly distributed in an area of 100x100 km
²
. The area is divided into 100 equal-sized grids, from which the HAPS location will be varied for optimization purpose. The simulation results indicate that the optimal location is grid number 29 when the antenna element is 16x16. Increasing the antenna element to 128x128 results in higher data rate for each UE. After determining the optimal HAPS location, power allocation for each UE is carried out to fulfill the backhaul link constraint. From several power combinations for each UE, the combination that has the minimum total power is taken. Thus, as the array elements increase, the total minimum power will decrease.