Katzis, Konstantinos

The Uniform hexagonal array (UHA) sidelobe level (SLL) reduction is a crucial consideration for avoiding co-channel interference and improving Carrier-to-interference Ratio (CIR) performance in HAP wireless networks using the TVWS spectrum. The SLL reduction in UHA has been researched by applying evolutionary algorithms such as genetic algorithm (GA) and Particle Swarm Optimization (PSO). However, such algorithms have the drawbacks such as early convergence and the inability to reach globally. The beam pointing approaches for UHA antennas using Modified PSO (MPSO), for reducing the SLL on finding the optimal current weights is presented in this article. The UHA antenna array with 19 cells fitted with 169 elements in the HAPs cellular structure is considered to simulate the proposed approach. Then, the MPSO approach is employed and compared with the standard PSO algorithm and Uniform Weighting (UW) scheme. As per the simulation findings, the proposed approach drastically decreased sidelobes, with a reduction of up to -6.84dB and -13.3dB when compared to PSO and UW respectively. In other words, the proposed approach outperforms the UW and the PSO algorithms. Moreover, the CIR performance of the proposed approach has been demonstrated in terms of average outage probability and the proposed approach provides a better result.

Like with the past generations of mobile cellular networks, deployment of 5G services in rural areas are expected to be financially and technically challenging. Currently, researchers around the globe explore the possibility of employing the underutilized/unused portion of TV spectrum referred to as TV White Spaces (TVWS) as a low-cost alternative to traditional licensed type of wired/wireless broadband networks and possibly as a way to bridge the gap of broadband service availability between rural and urban areas. Delivering TVWS services from High Altitude Platforms (HAPs) is an option that many developed/developing countries can use to provide broadband services over many of their rural and low-income population. This work presents the advantages of employing TVWS spectrum from HAPs as well as the challenges of this type of communication architecture. More specifically, this work proposes a novel communication type of architecture where HAPs are delivering broadband services using the TVWS spectrum. Taking advantage of their position in the sky and the centralized nature of the communication system, they deliver communications over a wide area while monitoring and optimizing radio resource allocation. The paper evaluates the performance of such a system based on the IEEE 802.22 standard and the free space path-loss model ITV-R P.452.

The coverage and capacity of exploiting TV White Spaces (TVWS) from High Altitude Platforms (HAPs) with multiple antenna payloads using uniform rectangular phased array (URA) antennas are explored in this article. A scenario is suggested in which a HAP and TVWS base station are installed on the HAP within a HAP coverage area with a radius of 100 km and a cell radius of 10.5 km. The formation of HAP cells with various reuse patterns has been established. An analysis of coverage, capacity and power profile function for TVWS link from 25 × 25 URA HAP arrays is presented. To minimize the sidelobe levels in the antenna array synthesis, window function has been assumed. Power profile within a cell using URA is highlighted. Channel to Interference (CIR) performance contour, coverage probability and channel capacity have been determined. The channel capacity for the theoretical Shannon bound and practical truncated Shannon bound are determined and compared. Results show that a maximum channel capacity of 53 Mbps can be attained from the proposed model.

Due to the favorable propagation characteristics of the spectrum allocated for broadcast Television in the Very High Frequency (VHF) and Ultra High Frequency (UHF) spectrum bands; new innovative wireless technologies have emerged capable to operate on a secondary basis in the unused spectrum portions assigned to incumbent Television broadcasters. Television White Spaces (TVWS) is an umbrella term used to describe the unused portions of spectrum in the broadcast Television bands. Regulatory authorities require that White Space Devices (WSDs) must protect receivers of the incumbent services at the edge of the incumbent broadcast Television coverage contours from possible harmful interference. In this paper, we present a detailed mathematical framework for calculating the sufficient keep-out-distance (dk) between Digital TV (DTV) services and WSDs to allow the use of TVWS spectrum without causing interference to the receivers of the incumbent services in the Ethiopian context. The framework includes the calculation of co-channel and adjacent distance dk from the DTV contour using the ITU-R P. 1546-5 and ITU-R P.1411-9 propagation models respectively. The paper elaborates on how to compute the desired distance (ddesired) of DTV services using the interpolation approach. In addition, we simulate the adjacent and co-channel distance dk with respect to antenna Height Above Average Terrain (HAAT) values.