A Hierarchical Spectrum Access Scheme for TV White Space Coexistence in Hetergeneous Networks

Among current techniques for dynamic access to television (TV) white space (TVWS), geolocation database-based access provides a promising performance in protecting the TV-band incumbents from interference that cannot be efficiently achieved in other license-exempt models. However, in heterogeneous wireless networks, most portable devices do not have such access and may cause interference to TV incumbents. We propose a hierarchical model for spectrum sharing in TVWS that includes a wide range of fixed and portable devices. In the first tier, the TV broadcaster can lease the spectrum bands to local fixed users based on a soft license agreement. The fixed users are allowed to share access to this spectrum with some mobile users in their proximity in exchange for cooperative relaying. We consider a practical scenario, where only partial channel state information (CSI) is available at the users\u27 transmitters, and we propose a robust algorithm against such uncertainties in CSI values. We also propose a reputation-based relay selection mechanism to identify selfish portable users. The proposed spectrum sharing framework can provide a practical model for TVWS-coexistence that prevents undesired interference to the incumbents while restricting interference among the unlicensed devices. The simulation results show the enhancement of fixed users\u27 rate compared with alternative relay selection methods

Security-aware Cooperation in Dynamic Spectrum Access

We have witnessed a massive growth in wireless data, which almost doubles every year. The wireless data is expected to skyrocket further in the future due to the proliferation of devices and the emerging data-hungry applications. To accommodate the explosive growth in mobile traffic, a large amount of wireless spectrum is needed. With the limited spectrum resource, the current static spectrum allocation policy cannot serve well for future wireless systems. Moreover, it exacerbates the spectrum scarcity by resulting in severe spectrum underutilization. As a promising solution, dynamic spectrum access (DSA) is envisaged to increase spectrum efficiency by dynamic sharing all the spectrum. DSA can be enabled by cognitive radio technologies, which allow the unlicensed users (the secondary users, i.e., SUs) to dynamically access the unused spectrum (i.e., spectrum holes) owned by the licensed users (the primary users i.e., PUs). In order to identify the unused spectrum (spectrum holes), unlicensed users need to conduct spectrum sensing. While spectrum sensing might be inaccurate due to multipath fading and shadowing. To address this problem, user cooperation can be leveraged, with two main forms: cooperative spectrum sensing and cooperative cognitive radio networking (CCRN). For the former, SUs cooperate with each other in spectrum sensing to better detect the spectrum holes. For the latter, SUs cooperate with the PUs to gain access opportunities from the PUs by improving the transmission performance of the PUs. Whereas cooperation can also incur security issues, e.g., malicious users might participate into cooperation, corrupting or disrupting the communication of legitimate users, selfish users might refuse to contribute to cooperation for self-interests, etc. Those security issues are of great importance and need to be considered for cooperation in DSA. In this thesis, we study security-aware cooperation in DSA. First, we investigate cooperative spectrum sensing in multi-channel scenario such that a user can be scheduled for spectrum sensing and spectrum sharing. The cooperative framework can achieve a higher average throughput per user, which provides the incentive for selfish users to participate in cooperative spectrum sensing. Second, secure communication in CCRN is studied, where the SUs cooperate with the PU to enhance the latter’s communication security and then gain transmission opportunities. Partner selection, spectrum access time allocation, and power allocation are investigated. Third, we study risk aware cooperation based DSA for the multiple channel scenario, where multiple SUs cooperate with multiple PUs for spectrum access opportunities, considering the trustworthiness of SUs. Lastly, we propose an incentive mechanism to stimulate SUs to cooperate with PUs when they have no traffic. The cooperating SUs are motivated to cooperate with PUs to enhance the security of the PUs by accumulating credits and then consume the earned credits for spectrum trading when they have traffic in the future

Radio Resource Management for Unmanned Aerial Vehicle Assisted Wireless Communications and Networking

In recent years, employing unmanned aerial vehicles (UAVs) as aerial communication platforms or users is envisioned as a promising solution to enhance the performance of the existing wireless communication systems. However, applying UAVs for information technology applications also introduces many new challenges. This thesis focuses on the UAV-assisted wireless communication and networking, and aims to address the challenges through exploiting and designing efficient radio resource management methods. Specifically, four research topics are studied in this thesis. Firstly, to address the constraint of network heterogeneity and leverage the benefits of diversity of UAVs, a hierarchical air-ground heterogeneous network architecture enabled by software defined networking is proposed, which integrates both high and low altitude platforms into conventional terrestrial networks to provide additional capacity enhancement and expand the coverage of current network systems. Secondly, to address the constraint of link disconnection and guarantee the reliable communications among UAVs as aerial user equipment to perform sensing tasks, a robust resource allocation scheme is designed while taking into account the dynamic features and different requirements for different UAV transmission connections. Thirdly, to address the constraint of privacy and security threat and motivate the spectrum sharing between cellular and UAV operators, a blockchain-based secure spectrum trading framework is constructed where mobile network operators and UAV operators can share spectrum in a distributed and trusted environment based on blockchain technology to protect users' privacy and data security. Fourthly, to address the constraint of low endurance of UAV and prolong its flight time as an aerial base station for delivering communication coverage in a disaster area, an energy efficiency maximization problem jointly optimizing user association, UAV's transmission power and trajectory is studied in which laser charging is exploited to supply sustainable energy to enable the UAV to operate in the sky for a long time