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Efficient Transmission and Reception in Wireless Communication Systems based on NOMA

Mokhtari, Fatemeh | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57370 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Nasiri Kenari, Masoumeh
  7. Abstract:
  8. Multiple access technologies are one of the key features of different generations of wireless communication. From the first generation to the fourth generation, orthogonal multiple access (OMA) schemes have been utilized to serve multiple users in different orthogonal resource blocks in time, frequency or code domain. However, the new application scenarios for the fifth generation impose the requirements of higher system throughput, massive connectivity, and low latency, which can not be fulfilled with OMA schemes. Therefore, non-orthogonal multiple access (NOMA) schemes have attracted increasing attention in both industry and academia. In NOMA, multiple users may occupy the same resource block to realize overloading at the expense of more sophisticated receiver. When the NOMA principle is applied to a single carrier, multiple access is realized in the power domain by allocating different power levels to different users. There are different power allocation policies with different objectives such as fairness or QoS requirement. NOMA is also applicable to the multi-carrier system, where users are divided into multiple groups to implement NOMA with fewer users on different orthogonal resource blocks. Then, the resource allocation consisting of user grouping, subcarrier assignment, and power allocation is of crucial importance for multi-carrier NOMA (MC-NOMA) system. In this thesis, we study the resource allocation in different scenarios for MC-NOMA system in downlink transmission. In all considered scenarios, we encounter two sets of users with different rate requirements. We study NOMA transmission in a multi-cell network with two traffic models, a cognitive radio network, and a cooperative network with simultaneous wireless information and power transfer. For each scenario, the resource allocation is characterized by an optimization problem which is a mixed-integer non-linear program. We propose different iterative algorithms to solve the developed optimization problems by decoupling the subchannel assignment and power allocation. The convergence of the proposed algorithms is proved in all scenarios and the superiority of the NOMA scheme compared to OMA is investigated through numerical results. There is another application for power-domain NOMA in random access for uplink transmission when there is no central coordination. When multiple transmitters simultaneously send a packet to a central receiving station, the difference in the received powers from different transmitters can be utilized for multi-user detection. Thus, the randomization of transmit power level might increase the throughput. Here, we study a random access scenario with two classes of users which have different throughput requirement and optimize the power distribution for each class. Our main objective is to maximize the throughput of one class, subject to a minimum required throughput for the other class. The non-convex optimization problem is solved through a numerical method and the results show how increasing the number of power levels improves the throughput
  9. Keywords:
  10. Non-Orthogonal Multiple Access ; Fifth Generation of Mobile Networks ; Resources Allocation ; Nonconvex Optimization ; Random Access ; Power Distribution

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