Katzis, Konstantinos

Cognitive radio-based TV White Space (TVWS) is a promising idea which seeks to increase spectrum utilization by opportunistically accessing spectrum initially licensed to TV transmitters or incumbents. Orthogonal frequency multiple access (OFDM) is thought to be a promising technology for TVWS systems. In this paper, we consider an OFDM based cognitive High-Altitude Platform (HAP) exploiting the TVWS spectrum. We employ dynamic resource allocation for providing wireless access from a HAP at an altitude of 20km, while utilizing the TVWS spectrum. This paper focuses on the resource allocation algorithms, which are designed to increase the system transmission rate of secondary users while keeping the disturbance applied to the incumbent band below a threshold level and the overall power within a range using the Artificial Immune System Algorithm. As per the simulation demonstrated so far, the proposed algorithm outperforms the water-filling algorithm, implying that the system transmission rate is greatly optimized. Moreover, the proposed resource allocation algorithm allocates resources to users in a fair manner, without favoring any particular user, and has good convergence performance.

Many rural and low-income areas around the globe have poor quality (or no) internet service with limited telephone coverage due to a lack of infrastructure, insufficient power supply, and a limited core telecommunications network. Because of limited mobile device propagation capabilities, sparse population density and poor purchasing power, it is not economically feasible for mobile operators to deploy traditional communication networks in these regions. Researchers recently discovered that a portion of the underutilized TV spectrum known as TV white space (TVWS) could be suitable for those areas in terms of bandwidth, improved reception features, good penetration of buildings, and broad reach. This paper presents a comprehensive evaluation of available TVWS channels in Ethiopia using a Geolocation Database front-end (GLSD) aided by the CSIR Calculation Engine hosted by the CSIR Meraka Institute. GLSD and the CSIR calculation engine together are able to quantify the amount of TVWSs through dynamically allocating the TVWS network radio services according to the geographic position of WSDs. The GLSD was developed using the ITU-R P.1546-5 propagation model. Using the GLSD and the CSIR calculation engine, the quantification of TVWS free channels are calculated. The results show that among the 58 VHF and UHF TV channels, 52 of the channels are free (underutilized) in Ethiopia. These free channels can be employed to provide wireless broadband solutions for connecting the rural areas as well as offloading the urban traffic.

The beginning of TV white space (TVWS) for cognitive system is amongst the perceptible move towards solving the spectrum scarcity as well as rural connectivity problems. For the reason that this section of the spectrum band has higher bandwidth, good transmission characteristics and wide coverage. In this paper, we proposed a realistic implementation of the TVWS assignment simulation method focused on geo-location that solves the issue of spectrum under-utilization. The model is aided by the Calculation Engine of CSIR which is used in the radio frequency band of interest in Ethiopia to Intelligently quantify white spaces. More broadly, we aimed at the necessary input parameters, like radio propagation models suitable for the Ethiopian terrain environment, and calculation procedures to determine underutilized TVWSs. The models used by the Engine will approximate the contour coverage span of the incumbent TV station, separation distances for neighboring and co-channel locations, co-channel lists, as well as adjacent channels. In addition, using the planned implementation for the Ethiopia usage case; substantial amounts (87.9–98.23%) of geographically unoccupied broadcast TV channels are identified, such channels can be used for secondary provisioning of inexpensive broadband wireless networks.

Aiming at the problem of downlink power allocation in cognitive high-altitude platform wireless networks exploiting TV white space spectrum, it is mathematically formulated as a constrained optimization problem, and then an improved immune clonal optimization algorithm is proposed. The mathematical optimization model, algorithm realization process, and key technologies for power allocation are given, and coding, cloning, and mutation suitable operator for algorithm solving are designed. The findings of the simulation experiment indicate that, under the constraints of total transmit power, bit error rate, and interference tolerable to the main user, the algorithm can obtain a greater total data throughput, faster convergence speed, and better power allocation can be obtained. Finally, the proposed algorithm outperforms the Particle Swarm Optimization algorithm.

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.

The issue of spectrum allocation in cognitive high altitude platform wireless networks using TV White Space (TVWS) spectrum is presented in this paper. The mathematical model of spectrum allocation is given, and this model is converted into a constrained optimization problem with the goal of maximizing network benefits. Then, a spectrum allocation optimization approach is proposed that is based on improved immune clonal selection algorithm. According to the characteristics of the problem, the design, coding, cloning, mutation, hypermutation and selection operators suitable for the algorithm's solution are presented. Finally, a simulation experiment was carried out on this algorithm. The proposed algorithm was validated and proved that it converges better than Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). Moreover, experiments demonstrate that the suggested approach maximizes network benefits or rewards more effectively when compared with GA and PSO algorithms and results proved the effectiveness of the algorithm.