HIGH ALTITUDE PLATFORM STATIONS IN DESIGN WIRELESS COMMUNICATION SYSTEM FOR COVER THE SPECIFIC AREA

This paper explains how to design a wireless communication system via high altitude platform stations HAPS to cover the specific area (Using Diwaniyah city area as a model). High altitude platform station HAPS is unmanned airplane provides the wireless communication service to the wider area. It is designed to work at high altitude between (17-22 Km) and coverage area 400 Km. This study illustrated for calculating the cochannel interference between HAPS ground station with a terrestrial station and satellite station. Free space losses for a HAPS ground station has been applied to meet the geographic of Diwaniyah city. In addition, explaining the relationship between elevation angles with the radius of the coverage area. Interference mitigation techniques have been given, such as improving the antenna radiation pattern, then it proposed the elevation angle for the HAPS's ground stations to reduce an interference between HAPS network with Fixed Service (FS) and fixed satellite service (FSS). Finally, this study explains the relationship between elevation angles with the radius of the coverage area. For more reliability, the Scenario for covers the city of Diwaniya. Two ground stations have been proposed to connect with high-altitude platform station.


INTRODUCTION
High Altitude Platform Stations (HAPS) is one of the new technologies that provide the wireless communication service. This technology can be performing the service of the terrestrial station and satellite system. The service of high altitude platform station (HAPS) includes wireless communication, broadband communication, weather monitoring, security monitoring and data of city map collection. The High-Altitude Platform Station (HAPS) is situated between 17 and 22 Km above ground [2]. HAPS coverage area about 200 Km to 500 Km depend on the specific area which has been chosen to design these technologies [12]. One of the advantages of using high altitude platform station can provide a wide coverage area. Single HAPS can be covering an area equivalent to 258 ground terrestrial towers [1]. High altitude platform station technology has been several advantages compared with satellite and terrestrial services such as low propagation delay compares with satellite and wide area coverage compare with terrestrial services [9]. HAPS coverage area, depending on the altitude of HAPS and the elevation angle. (Figure 1) describes how HAPS can carry a large variety of wireless communications payload which provide a high capacity of endusers of broadband service.

DYNAMIC CHANNEL ASSIGNMENT (DCA)
It is to reduce the interference; this mitigation is to search un-use frequencies, not to give interference to another service and not so as to be received from another service. When wireless communication system operating base on demand assignment, DCA scheme is using self-control ineffective for sharing with another service. [4]

AUTOMATIC TRANSMISSION POWER CONTROL (ATPC)
In the wireless communication system use a high-bandwidth, and system design consider the attenuation of rain. To compensate for attenuation, is to increase the transfer of power from the rain value. ATPC has the potential to control the production of energy in monitoring the weather or receive power. Transmission power is increasing with rain condition and its decreasing with clear sky condition [5].

HAPS INTERFERENCE AND FREE SPACE LOSS EVALUATION
For the calculation interference from the HAPS ground stations to FWA stations used following equations.
"The interference from HAPS ground Station to an FWA station is obtained by the equation (1)" [13] (1) I is Interference, The free space path losses between HAPS ground stations and FWA stations is given by equation (2) (2) Where d is the distance between HAPS and FWA station in (Km), is a wavelength in (m) and the interference to noise ratio (I/N) was obtained by equation (3) [8].

LOCATION
Diwaniyah Coordinates longitude 31°59'15"N and latitude 44°55'42"E, according to the map of Diwaniyah city. The location of HAPS to the center of the coverage area after studying these area is shown in (Figure 3). According to the whole area of Diwanyiah city, the footprints of coverage area shown in (Google map), the area of Diwaniyah city center is (1212 Sq. Km).

SYSTEM PARAMETERS
The parameters of HAPS and FS systems are Summary in (Table 1) to covering a Diwaniyah city area. In (Table 1) shows the angle and corresponding ground coverage area have been measured from nadir.

HAPS COVERAGE AREA
The coverage area of the high altitude platform station (HAPS) is depending on altitude and elevation angle of the antenna. One HAPS airship can be offer remarkable coverage measurement 400 Km distance of the ground area instead of 258 ground terrestrial towers [2]. (Figure 5) have been plotted with Matlab program, it explains the relationship between the elevation angle and the radius of the coverage area. reducing elevation angle lead to increase the radius of the coverage area it is an inverse relationship.
From table1. the elevation angle of the HAPS ground station for Diwanyiah city using the UAC coverage area will be at 30°, 60° and 90° with altitude 20 Km, so the distance of the HAPS ground station will be: Copyright  2017 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.

INTERFERENCE TO NOISE RATIO I/N UNDER CLEAR SKY CONDITION
To calculate interference to noise ratio I/N must find the free space loss Ls by using equation (2) and calculate interference power (I) using equation (1). (Figure 6) show the antenna pattern for the HAPS ground station while the typical link budget for the HAPS system is given in (table 2) used 28/31.28GHz under clear sky conditions [13]. Both (table 2) and (Figure 6) are adopted the value of parameter regard the HAPS ground in equation (1). Copyright  2017 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved. Table 2: Link budget for HAPS system at 20Km altitude, clear sky conditions [13]. Both ( Table 3) and (Figure 7) are using to obtain the value of a parameter regarding FWA base station. after calculating interference, can be computed interference to noise ratio I/N using equation (3).

RESULT AND DISCUSSION
Using MATLAB to plot and analysis the graphs for showing the relationship between interference to noise ratio (I/N), separation distance(d) and the azimuth angles in clear sky condition shown in (Figure 8).
The main importance in this survey is to get minimum separation distance necessary to optimize interference to noise ratio, it will be -10dB. subsequently, the analysis is performed on this graph. (Figure 8) shown the graph of interference to noise ratio I/N versus distance between HAPS ground station and the ground station for various azimuths in clear-sky condition. It includes the azimuth angles are 30°, 60° and 90° from (Figure  8), can be seen that interference to noise ratio I/N is decreased when the separation distance d is increasing for various azimuth. A minimum separation distance has been required to obtain the optimum interference to noise ratio I/N for the azimuth of 30°, or any azimuth less than 40°, is 188 km. For azimuth of 60°, 119 km is needed. Finally, optimum interference to noise ratio I/N at an azimuth equal to 90°, the minimum separation distance is 53 km. The results obtained require to install tow ground stations with elevation angles 30° and 60° Assuming the location of fixed service (FS) and fixed service satellite (FSS) to avoid the interference between HAPS ground stations and (FS, FSS), location of the HAPS ground stations will be at (d1 and d2), the interference with FS and FSS stations decrease because user starts to go out of the HAPS coverage area and transmission power of terrestrial station is getting high there for quality of service to improve the chances of coexistence.