Random Access Game and Medium Access Control Design

Motivated partially by a control-theoretic viewpoint, we propose a game-theoretic model, called random access game, for contention control. We characterize Nash equilibria of random access games, study their dynamics, and propose distributed algorithms (strategy evolutions) to achieve Nash equilibria. This provides a general analytical framework that is capable of modeling a large class of system-wide quality-of-service (QoS) models via the specification of per-node utility functions, in which system-wide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus propose a novel medium access method derived from carrier sense multiple access/collision avoidance (CSMA/CA) according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. We present a concrete medium access method that adapts to a continuous contention measure called conditional collision probability, stabilizes the network into a steady state that achieves optimal throughput with targeted fairness (or service differentiation), and can decouple contention control from handling failed transmissions. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols

Dynamic channel allocation in satellite and wireless networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 161-165).The objective of this thesis is to understand how to utilize wireless channels in a fair and efficient manner within a multi-users communication environment. We start by exploring the allocation of a single wireless downlink fading channel among competing users. The allocation of a single uplink multiacccess fading channel is studied as well. With multiple parallel fading channels, a MAC protocol based on pricing is proposed to allocate network resource according to users' demand. We also investigate the use of parallel transmissions and redundant packets to reduce the file transmission delay. Specifically, we develop a novel auction-based algorithm to allow users to fairly compete for a downlink wireless fading channel. We first use the second-price auction mechanism whereby user bids for the channel, during each time-slot, based on the fade state of the channel, and the user that makes the highest bid wins use of the channel by paying the second highest bid. Under the assumption that each user has a limited budget for bidding, we show the existence of a Nash equilibrium strategy. And the Nash equilibrium leads to a unique allocation for certain channel state distribution. We also show that the Nash equilibrium strategy leads to an allocation that is pareto optimal. We also investigate the use of another auction mechanism, the all-pay auction, in allocating a single downlink channel. A unique Nash equilibrium is shown to exist. We also show that the Nash equilibrium strategy achieves a throughput allocation for each user that is proportional to the user's budget For the uplink of a wireless channel, we present a game-theoretical model of a wireless communication system with multiple competing users sharing a multiaccess fading channel.(cont.) With a specified capture rule and a limited amount of energy available, a user opportunistically adjusts its transmission power based on its own channel state to maximize the user's own individual throughput. We derive an explicit form of the Nash equilibrium power allocation strategy. Furthermore, as the number of users in the system increases, the total system throughput obtained by using a Nash equilibrium strategy approaches the maximum attainable throughput. In a communication scenario where multiple users sharing a set of multiple parallel channels to communicate with multiple satellites, we propose a novel MAC protocol based on pricing that allocates network resources efficiently according to users' demand. We first characterize the Pareto efficient throughput region (i.e., the achievable throughput region). The equilibrium price, where satellite achieve its objective and users maximize their payoffs, is shown to exist and is unique. The resulting throughput at the equilibrium is shown to be Pareto efficient. Finally, we explore how a user can best utilize the available parallel channels to reduce the delay in sending a file to the base-station or satellite. We study the reduction of the file delay by adding redundant packets (i.e., coding). Our objective here is to characterize the delay and coding tradeoff in a single flow case. We also want to address the question whether coding will help to reduce delay if every user in the system decides to add redundancy for its file transmission.by Jun Sun.Ph.D

Optimal Random Access in Networks with Two-Way Traffic

We consider a random access network in which the nodes need to optimize their channel access rates. The nodes are assumed to be rational and interested in their performance seen as a transmitter as well as a receiver. By casting this problem as a non-cooperative game, we derive conditions for the Nash equilibrium. We also show the existence of a Nash equilibrium when the nodes are constrained by their battery power (for this case, the constraints on the access rates of the nodes become coupled). For the special case where all nodes are each other's neighbors, we find that the equilibrium is given by the solution of a system of linear equations. An adaptive distributed scheme is then proposed for learning this equilibrium and its convergence is studied numerically