Large contests in dense networks : a mean-field type game approach

Abstract

With the development of wireless communication technologies, an increasing number of sensor nodes can be accommodated in a wireless sensor network (WSN). To evaluate the performance of a large-scale networked system and efficiently exploit the channel resources, it is necessary to employ an accurate and computationally efficient model for a dense network. This thesis investigates competition for channel resources in wireless communication with a mean-field type game model, which addresses large-scale interactions among a non-cooperative player population with low complexity. Both performance comparison between different generations of multiple access protocols and optimal design of a channel allocation mechanism for accommodating data sources have been investigated. We first consider a competition in transmission power control over a shared uplink channel. We propose a framework of a massive transmission power contest in a dense network with a mean-field limit model. The CDMA protocol, as a supporting technology of 3G networks accommodating signal from different sources over the code domain, represents the orthogonal multiple access (OMA) techniques. With the development of 5G wireless networks, non-orthogonal multiple access (NOMA) has been introduced to improve the efficiency of channel allocation. Our goal is to investigate whether the power-domain NOMA protocol can regulate the non-cooperative channel access behaviors, i.e., steering the competition among the non-cooperative users in a direction with improved efficiency and fairness. It is compared with the CDMA protocol, which drives each user to compete fiercely against the population, hence sacrificing the efficiency of channel usage. The existence and uniqueness of an equilibrium strategy under CDMA and NOMA is characterized. Subsequently, we adopt the social welfare of the population as the performance metric, which is defined as the expectation of utility over the distribution of users with different channel gains. It is shown that under equilibrium strategies, NOMA outperforms CDMA in the social welfare achieved, which is also illustrated through simulation. Moreover, it is observed from numerical results that NOMA can improve the fairness of the achieved data rates among different users. As efficiency is often sacrificed when resources are allocated through competition, another goal of this thesis is to consider, from the perspective of the base station, how to regulate the behaviors among channel users to achieve better social welfare when the equilibrium is reached in a large user population. We consider a mechanism design formulation of resource allocation, where the channel resources are allocated to the users by auction. The base station takes bids from all channel users and allocates channel capacity accordingly, which induces "payments" from the users to the base station in terms of transmission power. We identify the structure of the optimal mechanism for accommodating a large user population with the CDMA protocol. The optimal mechanism design for NOMA remains a direction of future work.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology