Tham khảo tài liệu 'mobile and wireless communications physical layer development and implementation part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Space-Time Diversity Techniques for WCDMA High Altitude Platform Systems 111 Fig. 4. A plot illustrating the change of HAP position dm to create different elevation angles m- 4. Simulation Results In this simulation we assume M HAPs uniformly located along a circular boundary with the centre of the circular boundary acting as the pointing direction of the HAPs base station antennas which simulate several overlapping cells see figure 1. The beamwidth of these base station antennas are determined by the radius of the cell coverage area see figures 1 and 3 . These results are acquired through running Monte Carlo simulations of the multiple HAP system. The aim of the simulation is to assess the effect of adding more HAPs on the system s capacity and of the impact of using space-time diversity techniques. The distance dm between the cell centre and the vertical projection of the HAP on the earth s surface is denoted as distance on the ground and is varied from 0 to 70 km with a fixed cell position as shown in figure 4. The distance to the cell centre is also changing the elevation angle 9m towards the HAP base station m as seen from the user. The cell radius has been set to 10 km and 30 km and the HAP altitude is 20 km. Each HAP base station serves 100 users within each corresponding cell. From figure 5 it is clear that with the smaller cell radius 10 km the worst case scenario will occur when all the HAPs are stacked on top of each other at 90 degrees elevation angle from the cell centre . at a distance dm on the ground of 0 km . In the larger cell radius case 30 km the worst case scenario happens approximately at 30 km which is at the edge of the cell. Comparing the bottom diagram in figure 5 with the two diagrams in figure 6 we can see that if we utilize a maximum allowed other-to-own interference ratio equal to one then as the service data rate decreases the number of possible HAP base stations covering the same area can increase from 2-4 HAPs depending on the .
