Zuyuan Fang

Fair bandwidth sharing algorithms based on game theory frameworks for wireless ad-hoc networks

This paper examines the theoretical aspects of bandwidth sharing in wireless, possibly mobile, ad-hoc networks (MANETs) through a game theoretic framework. It presents some applications to show how such a framework can be invoked to design efficient media access control protocols in a noncooperative, self-organized, topology-blind environment as well as in environments where the competing nodes share some basic information to guide their choice of channel access policies. For this purpose, contentions between concurrent links in a MANET are represented by a conflict graph, and each maximal clique in the graph defines a contention context which in turn imposes a constraint on the share of bandwidth that the links in the clique can obtain. Using this approach the fair bandwidth allocation problem is modeled as a general utility based constrained maximization problem, called the system problem, which is shown to admit a unique solution that can only be obtained when global coordination between all links is possible. By using Lagrange relaxation and duality theory, both a non-cooperative and a cooperative game formulation of the problem are derived. The corresponding mathematical algorithms to solve the two games are also provided where there is no need for global information. Implementation issues of the algorithms are also considered. Finally, simulation results are presented to illustrate the effectiveness of the algorithms.

A Fair MAC Protocol for IEEE 802.11-Based Ad Hoc Networks: Design and Implementation

In this paper, we model the problem of bandwidth sharing in wireless multi-hop networks as a general utility maximization problem with link bandwidth constraints. Lagrangean relaxation and duality are invoked to derive a gradient-based iterative algorithm to solve the problem. We then investigate the practical aspects of the problem and discuss how such theoretical framework can be used to design practical fair media access control frameworks that can be implemented in real systems based on the IEEE 802.11 distributed coordination function.

Adaptive power control for single channel ad hoc networks

Power control for mobile ad hoc networks has received increasing interest from the research community. Power control can be invoked to achieve different objectives, including the most popular goals of either increasing the network throughput by mitigating the effects of interference on a node or ensuring minimal power consumption. We propose a power control algorithm for ad hoc networks to improve network throughput. As such, we study and exploit the correlation that exists between the appropriate transmit power of successive RTS, CTS, DATA and ACK frames and propose an adaptive power control algorithm in the framework of the IEEE 802.11 MAC protocol. In contrast to some alternative approaches, our algorithm operates in a single channel and does not require additional hardware support, which makes it very appropriate for existing IEEE 802.11 based networks.

A novel topology-blind fair medium access control for wireless LAN and ad hoc networks

This paper introduces a new backoff mechanism for IEEE802.11, which aims to achieve fair channel access without knowledge of the network topology. By adjusting a time interval and the contention window dramatically, the algorithm aims to approach the optimal equilibrium where the time interval is the minimum possible such that every node that faces the same contention successfully sends only one packet per such interval. We show how this algorithm can be modeled as a game and use game theoretic arguments to prove the existence and uniqueness of the equilibrium as well as convergence of the algorithm to this equilibrium.

Design and implementation of a MAC scheme for wireless ad-hoc networks based on a cooperative game framework

Due to their dynamic topologies, providing quality of service (QoS) in wireless/mobile ad-hoc networks introduces major new challenges to the research community. Today, the only commercially available ad-hoc network products are those based on the widely deployed IEEE 802.11 distributed coordination function (DCF). However DCF is a random access scheme, which not only cannot provide any guarantees, is also well known to suffer from a problem of fairness. In this paper, the bandwidth allocation problem in the medium access control (MAC) layer of ad-hoc networks is modelled as a constrained maximization problem. Based on duality, the problem is further modelled as a cooperative game and an algorithm to solve this problem is provided, and the discussion is centered on the design and implementation issues of the algorithm.

Collision-free MAC scheduling algorithms for wireless ad hoc networks

Providing quality of service (QoS) in wireless ad hoc networks introduces a major challenge due to their dynamic topologies. In general, a QoS scheme requires close collaboration between all layers in the protocol stack. At the base of the scheme is a QoS capable MAC protocol. In ad hoc networks nowadays, the widely deployed distributed coordination function (DCF) proposed by the IEEE 802.11 standard is a random access scheme and suffers from a fairness problem. In order to provide a guarantee of minimal throughput and improve the fairness of bandwidth sharing, a class of collision-free MAC scheduling algorithms is proposed. When implementing these algorithms, the set of node identifiers (IDs) that can connect to the network should be known in advance. In addition, neighborhood information sharing is required. Compared with their counterparts proposed in the literature, these algorithms can guarantee a minimal throughput and do not rely on per-packet information exchange. Simulation results show that these algorithms can provide better long term fairness when compared with IEEE 802.11 DCF, even when they are implemented in coarse time granularity.

Adaptive power control algorithm for ad hoc networks with short and long term packet correlations

Power control is often invoked in mobile ad hoc networks to achieve one of two popular goals: i) increasing network throughput by mitigating the effects of mutual interference of nodes or; ii) ensuring minimal power consumption. This paper proposes a new adaptive power control algorithm for ad hoc networks to save energy while maintaining a similar throughput as that achieved by the IEEE 802.11 MAC protocol. The contributions of this proposed scheme are two fold. First, we define and invoke the concept of MAC packet delivery curve to guide the power control algorithm in the adaptation decision under different possible scenarios. In particular when choosing among different service profiles the packet curve can tell which is better in the long term. Then, the power control algorithm takes into consideration the short term correlations between transmit powers of RTS/CTS frames and those of DATA/ACKs frames, to ensure robustness

Correlative power control for single channel ad hoc networks

Power control for mobile ad hoc networks has received an increasing research interests in recent years. Power control can he invoked to achieve different objectives, among which the most popular goals of either increasing the network throughput by mitigating the effects of interference on a node or ensuring minimal power consumption. In this paper, we propose a correlative power control algorithm for ad hoc networks target for low energy consumption. As such, we study and exploit the correlation that exists between the appropriate transmit power of successive RTS, CTS, DATA and ACK frames and propose a power control algorithm in the framework of the IEEE802.11 MAC protocol. At the opposite of some alternative approaches our algorithm operates in a single channel and does not require additional hardware support, which makes it very appropriate for the existing IEEE 802.11 based networks. Simulation results show that our algorithm outperforms the IEEE 802.11 protocol in throughput and reduces energy consumption.