Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Faeze Heydaryanfroshani
Ph.D. Final
Aug 28, 2020, 10:00 am - 12:30 pm
Distributed Medium Access Control for an Enhanced Physical-Link Layer Interface
Abstract: Current wireless network architecture equips data link layer with binary transmission/idling options and gives the control of choosing other communication parameters to the physical layer. Such a network architecture is inefficient in distributed wireless networks where user coordination can be infeasible or expensive in terms of overhead. To address this issue, an enhancement to the physical-link layer interface is proposed. At the physical layer, the enhanced interface is supported by a distributed channel coding theory, which equips each physical layer user with an ensemble of channel codes. The coding theory allows each transmitter to choose an arbitrary code to encode its message without sharing such a decision with the receiver. The receiver, on the other hand, should decode the messages of interest or report collision depending on whether or not a predetermined reliability threshold can be met. Fundamental limits of the system is characterized asymptotically using a ``distributed channel capacity'' when the codeword length can be taken to infinity, and non-asymptotically using an achievable performance bound when the codeword length is finite.

The focus of this dissertation is to support the enhanced interface at the data link layer. We assume that each link layer user can be equipped with multiple transmission options each corresponds to a coding option at the physical layer. Each user maintains a transmission probability vector whose entries specify the probability at which the user chooses the corresponding transmission options to transmit its packets. We propose a distributed medium access control (MAC) algorithm for a time-slotted multiple access system with/without enhanced physical-link layer interface to adapt the transmission probability vector of each user to a desired equilibrium that maximizes a chosen network utility. The MAC algorithm is applicable to a general channel model and to a wide range of utility functions. The MAC algorithm falls into the stochastic approximation framework with guaranteed convergence under mild conditions. We developed design procedures to satisfy these conditions and to ensure that the system should converge to a unique equilibrium. Simulation results are provided to demonstrate fast and adaptive convergence behavior of the the MAC algorithm as well as the near optimal performance of the designed equilibrium.

We then extend the distributed MAC algorithm to support hierarchical primary-secondary user structure in a random multiple access system. The hierarchical user structure is established in the following senses. First, when the number of primary users is small, channel availability is kept above a pre-determined threshold regardless of the number of secondary users that are competing for the channel. Second, when the number of primary users is large, transmission probabilities of the secondary users are automatically driven down to zero. Such a hierarchical structure is achieved without the knowledge of the numbers of primary and secondary users and without direct information exchange among the users.

Furthermore, we also investigate distributed MAC for a multiple access system with multiple non-interfering channels. We assume that users are homogeneous but the multiple channels can be heterogeneous. In this case, forcing all users to converge to a homogeneous transmission scheme becomes suboptimal. We extend the distributed MAC algorithm to adaptively assign each user to only one channel and to ensure a balanced load across different channels. While theoretical analysis of the extended MAC algorithm is still incomplete, simulation results show that the algorithm can help users to converge to a near optimal channel assignment solution that maximizes a given network utility.
Adviser: Dr. Jie Rockey Luo
Co-Adviser: Not Applicable
Non-ECE Member: Dr. Haonan Wang
Member 3: Dr. Ali Pezeshki
Addional Members: Dr. Liuqing Yang
Faeze Heydaryan, Jie Luo, "Random Multiple Access with Hierarchical Users" submitte to IEEE Transaction on Communications.
Faeze Heydaryan, Jie Luo, "Distributed Multiple Access with Multiple Transmission Options at The Link Layer" submitted to Ad Hoc Networks.
Yanru Tang, Faeze Heydaryan, Jie Luo, "Distributed coding in a multiple access environment”,Foundations and Trends inNetworking, vol. 12, pp. 260–412, 2018.
Y. Tang, F. Heydaryan, and J. Luo, “Distributed multiple access with a general link layerchannel”,Ad Hoc Networks, vol. 85, pp. 120–130, Mar. 2019.
Program of Study: