Showing papers by "Nitin H. Vaidya published in 2004"

Multi-channel mac for ad hoc networks: handling multi-channel hidden terminals using a single transceiver

Abstract: This paper proposes a medium access control (MAC) protocol for ad hoc wireless networks that utilizes multiple channels dynamically to improve performance. The IEEE 802.11 standard allows for the use of multiple channels available at the physical layer, but its MAC protocol is designed only for a single channel. A single-channel MAC protocol does not work well in a multi-channel environment, because of the multi-channel hidden terminal problem . Our proposed protocol enables hosts to utilize multiple channels by switching hannels dynamically, thus increasing network throughput. The protocol requires only one transceiver per host, but solves the multi-channel hidden terminal problem using temporal synchronization. Our scheme improves network throughput signifiantly, especially when the network is highly congested. The simulation results show that our protocol successfully exploits multiple hannels to achieve higher throughput than IEEE 802.11. Also, the performance of our protocol is comparable to another multi-hannel MAC protocol that requires multiple transceivers per host. Since our protocol requires only one transceiver per host, it an be implemented with a hardware complexity comparable to IEEE 802.11.

A vehicle-to-vehicle communication protocol for cooperative collision warning

Abstract: This paper proposes a vehicle-to-vehicle communication protocol for cooperative collision warning Emerging wireless technologies for vehicle-to-vehicle (V2V) and vehicle-to-roadside (V2R) communications such as DSRC are promising to dramatically reduce the number of fatal roadway accidents by providing early warnings One major technical challenge addressed in this paper is to achieve low-latency in delivering emergency warnings in various road situations Based on a careful analysis of application requirements, we design an effective protocol, comprising congestion control policies, service differentiation mechanisms and methods for emergency warning dissemination Simulation results demonstrate that the proposed protocol achieves low latency in delivering emergency warnings and efficient bandwidth usage in stressful road scenarios

Deafness: a MAC problem in ad hoc networks when using directional antennas

Abstract: This work addresses deafness - a problem that appears when MAC protocols are designed using directional antennas. Briefly, deafness is caused when a transmitter fails to communicate to its intended receiver, because the receiver is beamformed towards a direction away from the transmitter. Existing CSMA/CA protocols rely on the assumption that congestion is the predominant cause of communication failure, and adopt backoff schemes to handle congestion. While this may be appropriate for omnidirectional antennas, for directional antennas, both deafness and congestion can be the reason for communication failures. An appropriate directional MAC protocol needs to classify the actual cause of failure, and react accordingly. This paper quantifies the impact of deafness on directional medium access control, and proposes a tone-based mechanism as one way of addressing deafness. The tone-based mechanism, ToneDMAC, assumes congestion as the default reason for communication failures, and applies a corrective measure whenever the cause is deafness. Simulation results indicate that ToneDMAC can alleviate deafness, and perform better than existing directional MAC protocols.

A wakeup scheme for sensor networks: achieving balance between energy saving and end-to-end delay

Abstract: Energy saving is a critical task for sensor networks with limited energy supply. Wakeup schemes that turn off sensors' radio when communication is not necessary have great potential in energy saving. However, existing wakeup schemes encounter critical tradeoffs between energy saving and wakeup latency, and little attention has been paid to reducing the packet end-to-end delay while preserving the energy saving capability. We argue that a long delay can be detrimental for large sensor networks. We propose a wakeup scheme that helps to achieve the balance between energy saving and end-to-end delay. The conditions under which the proposed scheme can show improvement are identified.

The utility of explicit rate-based flow control in mobile ad hoc networks

Abstract: Flow control in a mobile ad hoc network (MANET) must face many new challenges such as frequent rerouting and bandwidth variation of the wireless links. TCP's implicit AIMD flow control performs poorly in this environment, because it often cannot keep up with the dynamics of the network. This paper explores the potential utility of explicit flow control in the MANET domain. To this end, we propose an end-to-end rate-based flow control scheme (called EXACT), where a flow's allowed rate is explicitly conveyed from intermediate routers to the end-hosts in each data packet's special control header. As a result, EXACT reacts quickly and precisely to re-routing and bandwidth variation, which makes it especially suitable for a dynamic MANET network and also discusses several supporting mechanisms required for such a scheme at the MAC and the transport layers. By ns-2 simulations, we show that EXACT outperforms TCP in terms of fairness and efficiency, especially in a highly dynamic MANET environment.

Efficient content location in wireless ad hoc networks

Abstract: The advances in wireless networking have enabled new paradigms in computing. An abundance of information and services provided by remote servers is expected to become available to wireless users. A fundamental issue in this environment is efficiently locating needed content. Such content may be in the form of files, services, or any other kind of data. In this paper, we describe an algorithm for efficient content location in location-aware ad hoc networks. The Geography-based Content Location Protocol (GCLP) makes use of physical location information to lower proactive traffic while reducing query cost. The results of our analysis show that GCLP performs favorably in terms of overhead and scalability.

MAC-layer anycasting in ad hoc networks

Abstract: A wireless ad hoc network is formed by a group of wireless hosts, without the use of any infrastructure. To enable communication, hosts cooperate among themselves to forward packets on behalf of each other. A key challenge in ad hoc networks lies in designing efficient routing strategies. While several routing protocols have been proposed, most of them aim to select one optimal route between the source and destination. The MAC layer at each intermediate node is then required to forward packets to the next downstream node on that route. We argue that choosing a single optimal route at the network layer may not be sufficient. Knowledge of short-term channel conditions at the MAC layer can play an important role in improving end-to-end performance. Instantaneous interference, channel contention, power constraints and other considerations may be taken into account along with the network layer's long-term view. This paper proposes MAC layer anycasting- a forwarding strategy that combines the guidelines from the network layer, with MAC layer knowledge of the local channel. We describe some applications of MAC-layer anycasting, and discuss the performance related tradeoffs.

Minimizing energy consumption in sensor networks using a wakeup radio

Abstract: For increasing the life of sensor networks, each node must conserve energy as much as possible. In this paper, we propose a protocol in which energy is conserved by amortizing the energy cost of communication over multiple packets. In addition, we allow sensors to control the amount of buffered packets since storage space is limited. To achieve this, a two-radio architecture is used which allows a sensor to "wakeup" a neighbor with a busy tone and send its packets for that destination. However, this process is expensive because all neighbors must awake and listen to the primary channel to determine who is the intended destination. Therefore, triggered wakeups on the primary channel are proposed to avoid using the more costly wakeup procedure. We present a protocol for efficiently determining how large the period for these wakeups should be such that energy consumption is minimized.

Routing and Channel Assignment in Multi-Channel Multi-Hop Wireless Networks with Single-NIC Devices

Abstract: In this paper, we present a routing and channel assignment protocol for multi-channel multi-hop wireless networks We consider a multi-hop network, where a mobile host may connect to an access point using multi-hop wireless routes, via other mobile hosts or wireless routers Also, we consider a multi-channel network where multiple non-overlapping (orthogonal) channels are available, and each host or router can dynamically select a channel to improve performance In this environment, we propose a multi-channel routing protocol that works with nodes (mobile hosts or wireless routers) equipped with a single NIC (network interface card) Supporting single NIC devices is beneficial because having multiple network interface can be costly for small and cheap devices Using the proposed protocol, nodes discover multiple routes to multiple access points possibly operating on different channels Based on the traffic load information, each node selects the “best” route to an access point, and stays on the channel where the access point is on With this behavior, the protocol balances load across the channels, thus removing hot spots and improving channel utilization The channel assignment does not cause network partitions, assuring that if a path exists from a node to an access point, the node finds a route to an access point, where all the intermediate nodes and the destination are operating on the same channel Our simulation results that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a protocol with random channel assignment

Power save mechanisms for multi-hop wireless networks

Abstract: In this paper, we discuss power save mechanisms that allow hosts to go to sleep to conserve energy When sleeping hosts need to receive packets from other hosts, these hosts must somehow wake up the sleeping hosts The paper discusses a busy-tone mechanism for this purpose, and an approach to improve the mechanism by using multiple busy tones We generalize this protocol to develop the notion of multi-level power save mechanisms, and present some examples to illustrate this notion

Method and apparatus for channel assignment within ad-hoc communication system

Abstract: A method and apparatus for channel assignment within an ad-hoc communication system utilizing multiple channels is provided herein. Individual nodes receive and send route-request (RREQ) packets on all channels rather than a single channel. Each route-request packet comprises a first and a second table. The first table comprises a channel state for the link and the second table comprises a channel quality metric for the link. Each node updates the channel state and channel quality tables and forwards them in the RREQ packet as part of the route-discovery process. When channel selection is made, the channel selection is based on the channel state and the channel quality tables.

MTSF: A Timing Synchronization Protocol to Support Synchronous Operations in Multihop Wireless Networks

Abstract: In this paper, we propose a protocol for synchro- nizing time in multihop wireless networks. Protocols for power management or dynamic channel assignment often require syn- chronous operations, such as waking up at the same time or listen- ing to a common channel. Having the nodes synchronized in time is often crucial for these protocols to work. However, the exist- ing synchronization mechanisms do not work well with these pro- tocols because either they may fail to synchronize the time even without transient failures or packet loss, or they may require a large overhead. The proposed synchronization protocol, called MTSF (Multihop Timing Synchronization Function), successfully synchronizes time in a multihop network, at a low cost. In the absence of packet loss, MTSF guarantees an upper bound on the clock error between any two pair of nodes in the network. More- over, MTSF can tolerate packet losses to some extent and its per- formance degrades gracefully when the loss rate becomes high. The cost of MTSF increases very slowly as the number of nodes increase, which makes the protocol highly scalable. MTSF is fully distributed, and operates without a central coordinator. Finally, MTSF is self-stabilizing, which means that starting from an arbi- trary state, the protocol converges to a steady state. Due to these features, MTSF can support protocols that require synchronous operations at a low cost.

A mix route algorithm for mix-net in wireless mobile ad hoc networks

Abstract: Providing anonymous connection service in mobile ad hoc networks is a challenging task. In addition to security concerns, performance concerns must be addressed properly as well. Chaum's mix method (Comms. of the ACM, vol.24(2), p.84-88, 1981) can effectively thwart an adversary's attempt at tracing packet routes and can hide the source and/or destination of packets. However, applying the mix method in ad hoc networks may cause significant performance degradation due to its non-adaptive mix route selection algorithm. We propose a dynamic mix routing algorithm to find topology-dependent mix routes for anonymous connections. Its effectiveness in improving network performance is validated by simulation results. We also address the potential degradation of anonymity due to dynamic mix routing.

A routing protocol for k-hop networks

Abstract: Recent years have witnessed the widespread deployment of IEEE 802.11 LANs in areas such as airports, campuses, and enterprises. These networks allow users to access network services and the Internet in remote locations and without the need Tor wires. The data rates for 802.11a, b and g far surpass that of wide-area cellular networks, however, the range of transmission of 802.11 is much less than that of cellular (250m versus 20km). Employing ad-hoc mode in 802.11 can extend traditional WLANs to multiple hops, thus increasing coverage and reducing the need for additional infrastructure. The amount of network extension (in terms of wireless hops) is limited by the density of the network (i.e., the availability of wireless devices that can serve as relays for other devices), and the scalability of stand-alone wireless ad-hoc networks. In this paper, we introduce a k-hop architecture and routing protocol utilizing a "beaconing" approach for route discovery and maintenance. We demonstrate through simulations the efficiency and reliability of our routing protocol in the presence of mobility and high node density.

DIWANS: workshop on dependability issues in wireless ad hoc networks and sensor networks

Abstract: Summary form only given. Widespread proliferation of wireless RF technology has brought the possibility of infrastructureless networking to the forefront. Infrastructureless networks are often referred to as wireless ad hoc networks and they include sensor networks as an important subclass. Dependability issues such as security, reliability, availability, and quality of service are complicated by the wireless and infrastructureless environment. Reliability and availability solutions must account for the varying characteristics of a wireless channel, which is subject to interference, fading, and multipath effects, among other problems. The presence of mobile nodes in many of these settings complicates even further the dependability issues. To date, no conference or workshop has specifically addressed dependability-related issues for ad hoc and sensor networks. One of the goals of this workshop is to bring together researchers to focus exclusively on this important topic, to outline its specific and unique research challenges, and to identify some of the most promising candidate solution methods and techniques to address those challenges. A second, and equally important, goal is to promote synergy between the networking and dependability communities on this topic of mutual concern. DIWANS includes invited talks from several prominent researchers in the field, and peer-reviewed papers on a variety of relevant topics. Most important, however, are the interactions among a diverse set of researchers, working at all network layers and interested in a wide range of problems, from the most fundamental to the most applied.

Adaptive protocols for mobile ad hoc networks

Abstract: Recent advances in low-power technologies have resulted in the proliferation of inexpensive handheld mobile computing devices. Soon, just like the Internet empowered a whole new world of applications for personal computers, the development and deployment of robust ubiquitous wireless networks will enable many new and exciting futuristic applications. Certain to be an important part of this future is a class of networks known as “mobile ad hoc networks.” Mobile ad hoc networks (or simply “ad hoc networks”) are local-area networks formed “on the spot” between collocated wireless devices. These devices self-organize by sharing information with their neighbors to establish communication pathways whenever and wherever they are. For ad hoc networks to succeed, however, new protocols must be developed that are capable of adapting to their dynamic nature. In this dissertation, we present a number of adaptive protocols that are designed for this purpose. We investigate new link layer mechanisms that dynamically monitor and adapt to changes in link quality, including a protocol that uses common control messages to form a tight feedback control loop for adaptation of the link data rate to best match the channel conditions perceived by the receiver. We also investigate routing protocols that adapt route selection according to network characteristics. In particular, we present two on-demand routing protocols that are designed to take advantage of the presence of multirate links. We then investigate the performance of TCP, showing how communication outages caused by link failures and routing delays can be very detrimental to its performance. In response, we present a solution to this problem that uses explicit feedback messages from the link layer about link failures to adapt TCP's behavior. Finally, we show how link failures in heterogeneous networks containing links with widely varying bandwidth and delay can cause repeated “modal” changes in capacity that TCP is slow to detect. We then present a modified version of TCP that is capable of more rapidly detecting and adapting to these changes.