A Cooperative Diversity-Based Robust Mac Protocol in Wireless Ad Hoc Networks

In interference-rich and noisy environment, wireless communication is often hampered by unreliable communication links. Recently, there has been active research on cooperative communication that improves the communication reliability by having a collection of radio terminals transmit signals in a cooperative way. This paper proposes a medium access control (MAC) algorithm, called Cooperative Diversity MAC (CD-MAC), which exploits the cooperative communication capability of the physical (PHY) layer to improve robustness in wireless ad hoc networks. In CD-MAC, each terminal proactively selects a partner for cooperation and lets it transmit simultaneously so that this mitigates interference from nearby terminals, and thus, improves the network performance. For practicability, CD-MAC is designed based on the widely adopted IEEE 802.11 MAC. For accurate evaluation, this study presents and uses a realistic reception model by taking bit error rate (BER), derived from Intersil HFA3861B radio hardware, and the corresponding frame error rate (FER) into consideration. System-level simulation study shows that CD-MAC significantly outperforms the original IEEE 802.11 MAC in terms of packet delivery ratio and end-to-end delay

Distributed opportunistic scheduling in multihop wireless ad hoc networks

In this paper, we introduce a framework for distributed opportunistic scheduling in multihop wireless ad hoc networks. With the proposed framework, one can take a scheduling algorithm originally designed for infrastructure-based wireless networks and adapt it to multihop ad hoc networks. The framework includes a wireless link state estimation mechanism, a medium access control (MAC) protocols and a MAC load control mechanism. The proposed link state estimation mechanism accounts for the latest results of packet transmissions on each wireless link. To improve robustness and provide service isolation during channel errors, the MAC protocol should not make any packet retransmissions but only report the transmission result to the scheduler. We modify IEEE 802.11 to fulfill these requirements. The MAC load control mechanism improves the system robustness. With link state information and the modified IEEE 802.11 MAC, we use BGFS-EBA, an opportunistic scheduling algorithm for infrastructured wireless networks, as an example to demonstrate how such an algorithm is converted into its distributed version within the proposed framework. The simulation results show that our proposed method can provide robust outcome fairness in the presence of channel errors. ©2008 IEEE.published_or_final_versio

Energy efficiency and capacity modeling for cooperative cognitive networks

Cooperative relaying has recently appeared as one of the widely recognized features for future wireless communication systems. The great potential of cooperative communication in increasing system capacity and enhancing power efficiency has attracted large efforts over the last few years. In this paper, we propose a Cooperation Loop as a reference model for all algorithms in relay based cooperative wireless networks. Using this model, we discuss cooperative relay based protocols in IEEE 802.11 standards and limits posed to cognitive approaches. We show the potential location area of relay nodes as well as the performance bounds of capacity gain, delay and power efficiency achieved in relay based scenarios for any cooperative cognitive algorithms

Mobile Ad-Hoc Networks

Ad-hoc networks are a key in the evolution of wireless networks. Ad-hoc networks are typically composed of equal nodes, which communicate over wireless links without any central control. Ad-hoc wireless networks inherit the traditional problems of wireless and mobile communications, such as bandwidth optimisation, power control and transmission quality enhancement. In addition, the multi-hop nature and the lack of fixed infrastructure brings new research problems such as configuration advertising, discovery and maintenance, as well as ad-hoc addressing and self-routing. Many different approaches and protocols have been proposed and there are even multiple standardization efforts within the Internet Engineering Task Force, as well as academic and industrial projects. This chapter focuses on the state of the art in mobile ad-hoc networks. It highlights some of the emerging technologies, protocols, and approaches (at different layers) for realizing network services for users on the move in areas with possibly no pre-existing communications infrastructure