Abstract not found

In this paper, we present a new medium access control (MAC) protocol for ad-hoc networks with multiple input multiple output (MIMO) links. MIMO links provide extremely high spectral efficiencies in multipath channels by simultaneously transmitting multiple independent data streams in the same channel. MAC protocols have been proposed in related work for ad-hoc networks with other classes of smart antennas such as switched beam antennas. However, as we substantiate in the paper, the unique characteristics of MIMO links coupled with several key optimization considerations, necessitate an entirely new MAC protocol. We identify several advantages of MIMO links, present a problem formulation for fair channel allocation when using such links, and discuss key optimization considerations that can help in realizing an effective MAC protocol for such an environment. We present a centralized algorithm called stream-controlled medium access (SCMA) that has the key optimization considerations incorporated in its design. Finally, we present a distributed SCMA protocol that approximates the centralized algorithm, and compare its performance against that of baseline protocols that are CSMA/CA variants.

This report addresses the problem of using directional antennas in ad hoc routing. Although the problems with utilizing directional antennas have been visited in the past, the research has been confined mostly to issues related to medium access control. To determine whether directional antennas are beneficial to ad hoc networks, it is necessary to evaluate the impact of directional antennas on the performance of routing protocols as well. In this report, we evaluate the performance of a reactive routing protocol for different scenarios using directional antennas. Using insights gained from simulations, we propose routing strategies that adapt the routing protocol to directional communication. Our analysis shows that by using directional antennas, ad hoc networks may achieve better performance. However, scenarios exist in which using omnidirectional antennas may be more appropriate.

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This paper evaluates the tradeoffs involved in using directional antennas in ad hoc routing. Although problems with utilizing directional antennas have been visited in the past, the research has been confined mostly to medium access control. To determine whether directional antennas are beneficial to ad hoc networks, it is necessary to evaluate the impact of directional antennas on the performance of routing protocols as well. In this paper, we evaluate the performance of DSR (Dynamic Source Routing) using directional antennas. We identify several issues that emerge from executing DSR (originally designed for omnidirectional antennas) over directional antennas. Using insights gained from simulations, we propose routing strategies that adapt the routing protocol to directional communication. Our analysis shows that by using directional antennas, ad hoc networks may achieve better performance. However, scenarios exist in which using omnidirectional antennas may be more appropriate.

In this paper, we introduce a novel CSMA/CA-based reservation scheme that improves the multiple access throughput of wireless ad-hoc networks using switched beam antennas. First, we show the performance limitations of the omni-directional and directional reservation paradigms investigated in the literature. This is done via emphasizing the trade-off between minimizing the number of control/data packet collisions and minimizing the number of neighbors that back-off unnecessarily. Next, we propose a novel concept that balances this trade-off via sending reservation messages, that carry information about the intended direction of transmission, on all unblocked beams. The innovation in this approach is to send directional information to as many neighbors as possible in order to better assist them in deciding whether to transmit or refrain from transmission on a specific beam. Finally, the algorithm is examined via simulations and compared to the omni-directional and directional reservation approaches.

Energy drainage from a node is mainly caused by the power consumption of the node's communication device. A MAC protocol is the main mechanism to provide efficient access to the shared wireless channel. Directional antennas provide several benefits over omnidirectional ones including the reduced energy consumption in frame transmissions. In this paper, we study and compare different generic directional virtual carrier sensing schemes (i.e., directional-RTS/CTS) in terms of their energy efficiency and performance. Both analytical and simulation results show that the schemes using directional-RTS and/or directional-CTS are more energy efficient than other schemes.

Contents 1 Ad hoc Networks: Brief Overview 3 1.1 Network Architecture . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Routing Protocols . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Routing Protocols: Overview 7 2.1 Ad hoc On-demand Distance Vector Routing (AODV) . . . . 7 2.1.1 Route Discovery . . . . . . . . . . . . . . . . . . . . . . 7 2.1.2 Local Connectivity Management . . . . . . . . . . . . . 11 2.1.3 Route Maintenance . . . . . . . . . . . . . . . . . . . . 11 2.2 Dynamic Source Routing (DSR) . . . . . . . . . . . . . . . . . 12 2.2.1 Route Discovery . . . . . . . . . . . . . . . . . . . . . . 12 2.2.2 Route Maintenance . . . . . . . . . . . . . . . . . . . . 14 2.2.3 Additional Features . . . . . . . . . . . . . . . . . . . . 16 2.3 Zone Routing Protocol (ZRP) . . . . . . . . . . . . . . . . . . 17 2.3.1 Neighbor Discovery Protocol . . . . . . . . . . . . . . . 17 2.3.2 Local routing (IARP) . . . . . . . . . . . . . . . . . . . 18 2.3.3 Route Discovery . . . . .

Traditionally medium access control protocols for ad hoc networks have been designed for nodes using omni directional antennas. Through the use of directional antennas, it is possible to obtain higher efficiency. In this thesis we investigate the impact of these antennas on aggregate throughput and end-to-end delay. The use of omni-directional antennas not only results in lower power efficiency, but also decreases network efficiency due to interference caused by the transmission of packets in undesired directions. This thesis explores the effect of using smart antennas and proposes a signaling mechanism for forming the extended links using the network layer. For the performance assessment of the wireless networks using directional antennas, baseline models of phased array antenna and channel have been developed using the discrete event simulator OPNET Modeler 8.0. Simulation scenarios have been created for single hop as well as multihop networks. From the results of the simulation we observe that although the nodes forming the extended link experience decrease in end-to-end delay, the data successfully transmitted using extended link is correlated to the spatial distribution of nodes. III Acknowledgements I would like to thank Dr Luiz DaSilva, my academic and research advisor for his guidance and assistance throughout the project, without which this work wouldn't have been possible. I am highly indebted to him for his infinite patience and understanding. I would also like to thank my committee members, Dr. Scott Midkiff and Dr. Annamalai Annamalai for serving on my committees and for their assistance and support for this thesis.

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented. I.