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High-Altitude Platform (HAP) is a promising technique for providing wireless communications services with improved performance compared to terrestrial and satellite systems. A critical issue in this emerging system is the difficulty of providing user location information through two-dimensional direction-of-arrival (2D-DOA) estimation due to the high computational complexity and the large covered area. Therefore, in this paper, an efficient technique has been proposed to determine user location through 2D-DOA with a reduced processing time. The proposed technique estimates the 2D-DOA in two stages. In the first stage, a low-resolution 2D-DOA estimation technique will be utilized, such as Bartlett algorithm performed on a low-resolution distance grid, then a suitable threshold is applied on the normalized Bartlett 2D-DOA spectrum to define ground windows for the next high-resolution 2D-DOA stage. The second stage is carried out by a high-resolution technique such as MUSIC algorithm and will be performed on a high-resolution distance grid. Two scenarios are examined for the proposed technique to investigate the reduction in processing time compared with the conventional 2D-DOA MUSIC algorithm without windowing. Simulation results show that at 40 meters resolution, the required processing time is only 20% of the conventional MUSIC algorithm and can be further reduced to 4% at resolution of 100 meters at the same array size. In addition, the proposed technique can be applied to any other efficient low-complexity 2D-DOA algorithms.

AN APPROACH FOR EFFICIENT TWO-STAGE 2D-DOA ESTIMATION IN HIGH-ALTITUDE PLATFORMS MOBILE COMMUNICATIONS