Debarshi Kumar Sanyal

Improved performance with novel utility functions in a game-theoretic model of medium access control in wireless networks

This paper presents a novel game-theoretic design to optimize the performance of medium access control (MAC) in wireless networks. The nodes of the network are modeled as selfish and rational players of a non-cooperative game. We define novel utility functions to capture their gain from channel access. We characterize the Nash equilibrium of the game and show that it is unique and non-trivial. This ensures a stable operating point from which no player has an incentive to deviate unilaterally and where every player has an equal non-trivial share of the transmission channel. Thus the selfish behavior of the nodes is used to ensure desirable properties of the network as a whole. The nodes follow a distributed update mechanism to reach the equilibrium. They need no message passing or network-wide information. We implement its asynchronous version in NS-2 and study the dynamics of the game. We compare, via simulations, our game model with the distributed coordination function (DCF) in IEEE 802.11 and a comparable game model in the literature. We observe that our design outperforms both these designs and provides much higher throughput and lower collision overhead over a very wide range of network sizes.

Game-Theoretic Modeling and Optimization of Contention-Prone Medium Access Phase in IEEE 802.16/WiMAX Networks

IEEE 802.16/WiMAX is an emerging standard for broadband wireless networks. It operates in both point-to-multipoint (PMP) and mesh modes. In the former, a number of subscriber stations communicate directly with a central base station. Although it supports different traffic classes characterized by distinct QoS requirements, the simplest is the best effort traffic. In this class, the subscriber stations first send bandwidth requests to the base station in a contention prone manner. Once the desired bandwidth is granted, scheduled transmissions take place. With increasing number of subscriber stations, due to media contention, collisions increase causing high loss to request packets and hence fall in data throughput. In this paper we address the issue by designing a new medium access control protocol GTMA for this random access phase, using ideas from non-cooperative game theory. We show that the resulting game converges to a unique non-trivial Nash equilibrium. NS-2 simulations confirm the reduction in packet collisions and consequent increase in system-wide data throughput and improvement in short-term fairness. To the best of our knowledge, this is one of the first applications of game-theoretic ideas in the explicit setting of contention control in IEEE 802.16/WiMAX networks.

Recovering a game model from an optimal channel access scheme for WLANs

Idle Sense is an optimal channel access scheme to achieve high throughput with high short-term fairness in IEEE 802.11 style wireless LANs. This paper recovers a non-cooperative game model from the protocol. We show that the control algorithm used by Idle Sense can be reverse-engineered so that each node implicitly maximizes a selfish local utility function. We prove the game has a Nash equilibrium which, under certain conditions, is unique with all nodes sharing the wireless channel equally. We perform extensive numerical simulations to get the equilibrium point for various network sizes and compare the performance of the model with IEEE 802.11 DCF. The achieved throughput at equilibrium is close to optimal.

A DiffServ Architecture for QoS-Aware Routing for Delay-Sensitive and Best-Effort Services in IEEE 802.16 Mesh Networks

In todays networks, the widespread use of real-time traffic such as video and audio applications demand special service guarantee in terms of throughput, delay, and jitter, thus making quality of service (QoS) a key problem. IEEE 802.16 mesh networks are likely to be the basis of next-generation last mile network connectivity. So, providing QoS is one of the major designing goals in IEEE 802.16 mesh network. While the standard defines five service classes for PMP mode, no standard defined service classes exist for mesh mode. In this paper, we describe a differentiated service (DiffServ) architecture for QoS support in IEEE 802.16 mesh network by considering a basic requirement for QoS guarantee—delay. A new cross-layer routing metric is proposed, namely, expected scheduler delay (ESD). An efficient distributed scheme is proposed to calculate ESD and route the packets using source routing mechanism. This scheme is capable of differentiating between delay sensitive and best-effort traffic and route packets accordingly. Finally, the results of the proposed scheme are compared with the standard schemes that take hop count as a routing metric.

Tuning holdoff exponents for performance optimization in IEEE 802.16 Mesh Distributed Coordinated Scheduler

The IEEE 802.16/WiMAX mesh standard is a promising technology to support next generation wireless broadband metropolitan area networks. The medium access control (MAC) layer of IEEE 802.16 mesh supports both centralized and distributed scheduling mechanisms. The coordinated distributed scheduling mechanism uses a pseudo-random election algorithm to determine the transmission times of the nodes. The holdoff exponent is an important parameter of scheduling and determines the channel contention time of a node. In this paper, we propose a novel distributed search protocol that each node uses to select the holdoff exponent that minimizes the expected delay between its two successive transmissions in the control channel. We analyze the scheduler performance in NS-2 for various kinds of traffic including TCP, UDP and VoIP. Simulation results show that our scheme performs better than the standard algorithm and other comparable schemes in terms of throughput and delay.

Addressing Forwarder's Dilemma: A Game-Theoretic Approach to Induce Cooperation in a Multi-hop Wireless Network

Nodes in a multi-hop wireless network often have limited or constrained resources. Therefore, to increase their lifetime, intermediate nodes are often unwilling to forward packets for other nodes, thereby decreasing network throughput. Thus, some mechanism has to be designed which prevents the nodes from adopting such selfish behavior. In this paper, we suggest a scheme using game theory to induce such cooperation. The nodes are the players and their strategies are their packet forwarding probabilities. We design novel utility functions to capture the characteristics of packet forwarding dilemma. We then set up simulations to analyze the Nash equilibrium points of the game. We show that cooperation in multi-hop communication is feasible at the operating point if the costs of packet forwarding are not too high.

Congestion Games in Wireless Channels with Multipacket Reception Capability

A wireless transmission channel with multipacket reception capability is expected to be a common feature of next generation telecommunication systems. Probability of correctly receiving simultaneously transmitted packets at the base station in a given time slot depends on the number of transmitted packets as well as the geographical proximity of the transmitter to the base station. This paper formulates a congestion game with player-specific costs to model the situation, characterizes its Nash equilibrium and analyses the slot allocation at the operating point.

A Novel Incentive Based Scheme to Contain Selective Forwarding in Wireless Sensor Network

Selective forwarding or dropping of packets is a serious threat to multi hop communication in a Wireless Sensor Network (WSN). There are various schemes to induce cooperation in a WSN to overcome this problem. In this paper, we have introduced a novel adversary model and have proposed an incentive based scheme to inspire cooperation among nodes in a WSN. The scheme has been formally analyzed. The efficacy of the scheme is also established through various simulation experiments.

A Novel QoS Differentiation Framework for IEEE 802.11 WLANs: A Game-Theoretic Approach Using an Optimal Channel Access Scheme

The ubiquity of multimedia applications and its sustenance with more traditional data services demand a Quality of Service (QoS) differentiation mechanism in telecommunications networks. This paper takes up a novel access method called Idle Sense developed to provide short-term fair high aggregate throughput to wireless stations in an IEEE 802.11 WLAN. We use a game-theoretic interpretation of the algorithm to determine how to incorporate QoS in the game. We show how the parameters in the algorithm may be tuned in order to achieve proportional throughput differentiation at the Nash equilibrium point of the game. Extensive numerical simulations performed for both IEEE 802.11b and 802.11g indicate that the traffic classes are indeed differentiated in terms of throughput.