Motivated by the poor experimental scaling reported in a study of the performance of ad hoc networks in [15], we propose a new protocol for media access control in ad hoc networks. Our protocol seeks to avoid collisions without making explicit reservations for each and every packet. The key idea is to employ a random schedule which is driven by a pseudo-random number generator. By exchanging the seeds of their pseudo-random number generators within a two-hop neighborhood, the nodes effectively publish their schedules to all hidden as well as exposed nodes. This allows each node to opportunistically choose transmission slots. This scheme can also be employed during the reservation phase of a protocol such as IEEE 802.11. Throughput calculations and simulation results are presented.

We explore the use of directional antennas to improve the performance of broadcasting in ad hoc networks. We investigate both the performance of unicast traffic in the presence of broadcast traffic and the performance of broadcast traffic when mixed with unicast traffic, which is different from previous investigations reported in the literature in which broadcast traffic is investigated in isolation. Through extensive simulation experiments with three MAC schemes, we show that throughput and delay can vary widely even in networks in which nodes are uniformly distributed. We also show that the use of a MAC protocol that utilizes directional antennas can help to improve the performance of broadcast traffic in ad hoc networks, in terms of both throughput and delay, through a more aggressive channel access scheme that maximizes spatial reuse.

Reliable broadcast is an important operation in mobile ad hoc networks (MANETs) (e.g., giving orders, searching routes, and notifying important signals). However, using a naive flooding to achieve reliable broadcasting may be very costly, causing a lot of contention, collision, and congestion, to which we refer as the broadcast storm problem [1]. This paper proposes an efficient reliable broadcasting protocol by taking care of the potential broadcast storm problem that could occur in the medium-access level. Existing protocols are either unreliable [1, 2, 3, 4, 5, 6], or reliable [7, 8] but based on a too costly approach. Our protocol differs from existing protocols by ensuring reliability but adopting a low-cost unreliable broadcast as a basic operation. Simulation results do justify the efficiency of the proposed protocol.

Abstract—With the rapid growth of WLAN capability for mobile devices such as laptops, handhelds, mobile phones and vehicles, we will witness WLANs with very large numbers of active nodes for which very efficient medium access control techniques will be needed to cope with high loads and mobility. We propose a high performance solution based on an innovative node elimination algorithm that uses short and unmodulated bursts of energy during contention – no data is exchanged. We also present a modified OFDM PHY layer, based on IEEE 802.11a, which allows sensing and bursting on individual subcarriers. We show that the protocol maintains a very low overhead and collision probability which lead to high and virtually constant network throughput at all analyzed network loads, even beyond 500 nodes. The protocol is validated by extensive simulation, comparing it against the IEEE 802.11a and SYN-MAC protocols. I.

This chapter deals with the problem of designing and effectively utilizing wireless communication channels. Since the wireless medium is inherently a shared resource, controlling channel access becomes a central theme that determines the fundamental capacity of the wireless network and has a dramatic impact on system complexity and cost. Therefore, our primary focus will be the design and implementation of Media Access Control (MAC) protocols for mobile wireless networks.

viii Acknowledgements x Dedication xii Chapter 1

2.1 Carrier Sense Multiple Access and IEEE 802.11.......... 4

for her love, care, and support during the study of this degree. I would not Medium Access Control (MAC) plays a vital role in wireless networks. With the increasing popularity of multimedia services, MAC protocols of wireless networks are required to satisfy a variety of Quality of Service (QoS) requirements, including short delays. One of techniques for satisfying such requirements is based on assignment of transmission rights on demand. Following such a protocol, bandwidth is assigned to mobile terminals when they have something to transmit. The base station has absolute control of the bandwidth, including assignment of different priorities to different classes of users. In this thesis, we survey recently proposed MAC protocols for wireless networks. The survey includes MAC protocols designed for different network generations and topologies. Next, we focus on the demand part of demand assignment MAC protocols. We propose a new strategy based on probabilistic assignment that allows mobile terminals to pick the best time for transmitting their demands. Building

The IEEE 802.11 standard uses channel reservation schemes and acknowledgements (ACKs) to provide reliable Medium Access Control (MAC) layer unicast services. In contrast, 802.11 does not guarantee the reliability of MAC layer broadcast and multicast transmissions. This lack of reliability extends to ad hoc routing protocols, such as DSR and AODV, which depend on broadcast packets to exchange routing information among nodes. In this