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Cooperative Networks from the MAC Layer Viewpoint

Vaezi, Kaveh | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52506 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ashtiani, Farid
  7. Abstract:
  8. Cooperative networks have attracted much attention in the last decade. Being introduced to mitigate the inefficiencies in the physical layer, cooperation can also be beneficial in upper layers, such as MAC layer. Using cooperative communications is specifically more challenging in the random access networks, where collision is a main concern. Delay, as one of the main performance metrics in random access networks, can decrease significantly by using cooperative communications. Transmission delay, i.e., the required time for delivering one packet form its source to destination, is an important metric in many communication networks, such as the networks in which each node generates and transmits a packet right after the departure of the previous one, e.g., body area networks, device-to-device networks or sensor networks. In this dissertation, we study two saturated cooperative networks based on slotted Aloha, and obtain the optimal cooperation policy in closed form such that the average transmission delay is minimized. In the first network, a relay node, beside transmitting its own data, cooperates with the other node in sending its packets. To this end, a separate queue is considered for the relay node to accommodate the unsuccessfully transmitted packets of the other node and send them in the next time slots. The cooperation policy determines whether to accept or reject the unsuccessfully transmitted packet of the other node and also on how to prioritize the transmission of these packets and the packets of the relay node itself. The aim of this cooperation is to minimize the average transmission delay of the packets of the other node. We show that based on the optimal policy, the relay node should always transmit the packets of the other node first. Moreover, cooperation is useful only if the successful transmission rate of the relay node is higher compared to the other node. In the second cooperative network scenario, both nodes in the network cooperate with each other. Also, full-duplex transmission capability with different self-interference cancelation efficiencies is considered for the nodes. In this network, if each node aims to minimize the average transmission delay of the other node, we face a multi-objective optimization problem. Since no priority is considered for the packets of one node over the packets of the other node, the optimal cooperation policy is attained such that the summation of average transmission delays of nodes is minimized. Both static and dynamic policies are studied in the dissertation and as we show, based on the optimal policy, only the node whose successful transmission rate to destination is at least Φ (the golden ratio) times the successful transmission rate of the other node, is allowed to cooperate, which is known as the relay node. Moreover, we will prove that based on the optimal dynamic policy, the relay node is allowed to accommodate at most a certain number of packets of the other node, which is attained in closed form. In this dissertation, closed form optimal cooperation policies are attained for a vast variety of half-duplex and full-duplex network scenarios and compared for their ability in minimizing the summation of average transmission delays. Moreover, the energy consumption of these policies are studied, and as shown, the delay minimizing policies may actually increase the energy consumption in the network
  9. Keywords:
  10. Random Access ; Cooperative Network ; Full Duplex Communication ; Transmission Delay ; Dynamic Policy ; Static Policy

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