With the advent of analog to digital transition in TV broadcasting, a substantial amount of spectrum has become available in TV bands. To take advantage of this, the idea for cognitive radios was introduced for two major reasons: better utilization of spectrum in urban areas and facilitation of wireless connectivity in rural areas. To achieve these two goals, however, many challenges have to be addressed first. Considering that these frequencies are commonly licensed, besides primary user detection, a serious challenge remains the detection and identification of other secondary devices and networks. The problems arising from this issue concern the coexistence problems happening from having several primary and secondary networks of different technologies cohabiting the same licensed spectrum simultaneously and from many secondary systems/users coexisting at the same place while using identical or different technologies. In this survey we provide a review of existing works and outline new challenges regarding coexistence and self-coexistence in heterogeneous wireless networks in TV White Spaces including a comparative analysis between selected coexistence mechanisms.

This is the accepted version of the paper.This version of the publication may differ from the final published version. Abstract-This paper focuses on coexistence and selfcoexistence challenges between secondary heterogeneous wireless networks/users sharing TV Whitespace spectrum. The coexistence problems arise from having several primary and secondary networks of different technologies cohabiting the same licensed spectrum simultaneously. The self-coexistence problems arise from many secondary systems /users coexisting at the same place while using identical or different technologies. In particular, fair distribution of available spectrum becomes a serious issue. In this work we use a game theoretic approach to model the self-coexistence problem as a competitive game between secondary networks. We show that our game belongs to the class of congestion-averse games which are known to posses pure Nash Equilibria. This leads us to a decentralized approach for spectrum sharing among systems with different PHY/MAC characteristics. We show that our proposal outperforms other centralized algorithms in terms of user fairness and per-user theoretical data rates. Permanent

In this study we conduct an assessment of usage and availability of frequency bands, traditionally assigned to TV broadcasters, in urban environments in Kosovo. The assessment was performed for VHF and UHF bands at 8 different urban locations. Localized measurements indicate that a major part of these frequencies is severely under-utilized even in highly urbanized areas where a higher utilization level would be expected. Preliminary results further show that spectrum utilization level varies significantly with altitude and is much lower in indoor environments. Our initial calculations show that current percentage of availability of TV bands in tested locations varies between 87.5% and 100%. These results indicate that spectrum utilization in these bands could be greatly improved by allowing the opportunistic use of spectrum by cognitive radios and other wireless communication technologies, such as future cellular networks.

Higher educational institutions in Western Balkan countries strive for continuous development of their teaching and learning processes. One of the priorities is employing state-of-the-art technology to facilitate experience-based learning, and virtual and augmented reality are two of the most effective solutions to providing the opportunity to practice the acquired theoretical knowledge. This report presents (apart from the theoretical introduction to the issue) an overall picture of the knowledge of AR and VR technology in education in Western Balkan universities. It is based on a semi-structured online questionnaire whose recipients were academic staff and students from universities in Albania, Kosovo, and North Macedonia. The questionnaire differed for each target group; the version for academics comprised 11 questions for 710 respondents, and the version for students comprised 10 questions for 2217 respondents. This paper presents and discusses the results for each question with the aim to illustrate Western Balkan countries’ current state of VR and AR application in education.

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