Open Access
Kotobi, Khashayar
Graduate Program:
Electrical Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
November 17, 2017
Committee Members:
  • Sven Bilen, Dissertation Advisor
  • Sven Bilen, Committee Chair
  • Kenneth Jenkins, Committee Member
  • Jeffrey Mayer, Committee Member
  • Conrad Tucker , Outside Member
  • Cognitive Radio
  • Wireless Communication
  • Machine Learning
  • Data Science
  • Data Mining
  • Blockchain
  • Security
  • Spectrum Sharing
We introduce an ``informed cognitive radio" that data mines new information to improve the understanding of its environment and novel mathematical algorithms to react to that environment. We propose the data mining--informed cognitive radio, which uses non-traditional data sources and data-mining techniques for decision making and improving the performance of a wireless network. We consider a cognitive wireless network in which users adopt a spectrum-sharing strategy based on cooperation constraints. The majority of cognitive radio schemes bifurcate the role of players as either cooperative or non-cooperative. In this work, however, we modify this strategy to one in which players are hybrid, i.e., both cooperative and non-cooperative. Using a Stackelberg game strategy, we evaluate the improvement in performance of a cognitive radio network with these hybrid cognitive players using an M/D/1 queuing model. We use a novel game strategy (which we call altruism) to ``police'' a wireless network by monitoring the network and finding the non-cooperative players. Upon introduction of this new player, we present and test a series of predictive algorithms that show improvements in wireless channel utilization over traditional collision--detection algorithms. Our results demonstrate the viability of using this strategy to inform and create more efficient cognitive radio networks. Next, we study a Stackelberg competition with the primary license holder as the leader, and investigate the impact of multiple leaders by modeling the wireless channel as an M/D/1 queue. We find that, in the Stackelberg game, the leader can improve its utility by influencing the followers' decisions using its advertised cost function and the number of followers accepted in the network. The gain in utility monotonically increases until the network is saturated. The Stackelberg game formulation shows the existence of a unique Nash equilibrium using an appropriate cost function. The equilibrium maximizes the total utility of the network and allows spectrum sharing between primary and secondary cognitive users. We propose a novel medium access protocol. We investigate an auction mechanism for sharing available wireless bandwidth among competing cognitive radios. The bandwidth under consideration may be either in an unlicensed spectrum or in an unused licensed band. Spectrum sharing is achieved via a mechanism in which a cognitive radio acting as the auctioneer advertises spectrum availability to bidding cognitive radios and defines a puzzle to solve as a method to access it. The cognitive radios act as bidders by computing the solution to the problem (i.e., the ``puzzle''). The winner is the bidder who submits the first correct bid and thus gains access to the spectrum for the next time interval. We consider two different variations of our scheme based on parallelizable and non-parallelizable problems and demonstrate that the latter provides a fair auction in contrast to the former. We propose a verification database to counter malicious ``greedy'' players. Our algorithm provides a centralized, easy-to-implement, and computationally fast multiple-access scheme that is verifiable by all participating cognitive radios. To ensure a secure cognitive radio network, we propose a blockchain verification protocol as a method for enabling and securing spectrum sharing in cognitive radio networks. The spectrum-sharing mechanism is used as a medium access protocol for accessing wireless bandwidth among competing cognitive radios. We introduce a virtual currency, called ``Specoins'', for payment to access the spectrum. An auction mechanism based on a first-come-first-served queue is used, with the price for the spectrum advertised by each primary user in a decentralized fashion. The blockchain protocol facilitates the transactions between primary and secondary users and is used to validate and save each user's virtual wallet. Also important for mobile networks, the blockchain serves as a distributed database that is visible by all participating parties, and any node can volunteer to update the blockchain. The volunteer nodes are called miners and are awarded with Specoins. We propose diverse methods to exchange the Specoins in order to make leasing possible even by cognitive radios that are not miners. We show the improvement of the proposed algorithm compared to the conventional ALOHA medium access protocol in terms of spectrum usage. This difference is investigated using small-scale fading variation in the wireless channel to compare the performance of our secure method with the conventional medium access used in communications. The blockchain verification protocol is not only secure but also outperforms conventional systems in moderate cases of small-scale fading. In the case of severe small-scale fading the blockchain protocol will outperform the conventional system if multipath diversity is not used.