Spectrum Efficiency Enhancement in Wireless Communication Networks

• Author / Creator

  Wei, Ziling

• With the fast growth of mobile data traffic, spectrum scarcity has become a serious problem to the development of wireless networks. Due to the limited available spectrum resources, it is critical to improve the spectrum efficiency. Cognitive radio, opportunistic scheduling, and non-orthogonal multiple access (NOMA) are promising techniques which can largely improve the spectrum efficiency in wireless communication networks. However, some challenges exist in deploying them in practical wireless networks. In this thesis, we aim at quality-of-service provisioning of networks by solving these challenges, with four research components.The first research component focuses on the optimal slot length configuration in cognitive radio networks. A slot length configuration scheme with imperfect spectrum sensing is proposed in this research. In the proposed scheme, the spectrum sensing result is considered when configuring the slot length. Then, an optimization problem to find out the optimal slot length configuration is formulated and analyzed. And an algorithm is proposed to solve the problem.Then, the opportunistic scheduling in wireless networks is considered in the next two research components. First, considering the limitations of existing centralized opportunistic scheduling schemes, the opportunistic scheduling problem is modeled as a semi-Markov decision process (SMDP) which reduces the implementation complexity. Then, a model-based scheduling method and a model-free scheduling method are proposed to derive the optimal scheduling policy for fully explored networks and partially explored networks, respectively. Second, the problem of distributed opportunistic channel access with energy-harvesting relays is investigated. A distributed opportunistic scheduling (DOS) scheme is proposed. To maximize the average throughput of the network, an optimal stopping strategy with threshold-based structure is derived in this scheme. To obtain the threshold, a low complexity algorithm is proposed to derive the stationary probability distribution of the energy level of each relay, and then, the threshold can be calculated off-line by a proposed iterative algorithm.Last but not least, NOMA power allocation is investigated for an Internet of Things (IoT) device to offload its computation tasks to a fog computing system. An optimization problem to maximize the long-term average system utility is formulated by optimizing the IoT device's power allocation and task allocation. An algorithm with polynomial time complexity is proposed to solve the problem.

• Subjects / Keywords

  • quality of service
  • opportunistic scheduling
  • spectrum efficiency
  • cognitive radio
  • non-orthogonal multiple access

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-40ha-ej59

• License

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