Showing papers by "Samir R. Das published in 2006"

Ad hoc on-demand multipath distance vector routing

Abstract: We develop an on-demand, multipath distance vector routing protocol for mobile ad hoc networks. Specifically, we propose multipath extensions to a well-studied single path routing protocol known as ad hoc on-demand distance vector (AODV). The resulting protocol is referred to as ad hoc on-demand multipath distance vector (AOMDV). The protocol guarantees loop freedom and disjointness of alternate paths. Performance comparison of AOMDV with AODV using ns-2 simulations shows that AOMDV is able to effectively cope with mobility-induced route failures. In particular, it reduces the packet loss by up to 40% and achieves a remarkable improvement in the end-to-end delay (often more than a factor of two). AOMDV also reduces routing overhead by about 30% by reducing the frequency of route discovery operations. Copyright © 2006 John Wiley & Sons, Ltd.

Connected sensor cover: self-organization of sensor networks for efficient query execution

Abstract: Spatial query execution is an essential functionality of a sensor network, where a query gathers sensor data within a specific geographic region. Redundancy within a sensor network can be exploited to reduce the communication cost incurred in execution of such queries. Any reduction in communication cost would result in an efficient use of the battery energy, which is very limited in sensors. One approach to reduce the communication cost of a query is to self-organize the network, in response to a query, into a topology that involves only a small subset of the sensors sufficient to process the query. The query is then executed using only the sensors in the constructed topology. The self-organization technique is beneficial for queries that run sufficiently long to amortize the communication cost incurred in self-organization. In this paper, we design and analyze algorithms for suchself-organization of a sensor network to reduce energy consumption. In particular, we develop the notion of a connected sensor cover and design a centralized approximation algorithm that constructs a topology involving a near-optimal connected sensor cover. We prove that the size of the constructed topology is within an O(logn) factor of the optimal size, where n is the network size. We develop a distributed self-organization version of the approximation algorithm, and propose several optimizations to reduce the communication overhead of the algorithm. We also design another distributed algorithm based on node priorities that has a further lower communication overhead, but does not provide any guarantee on the size of the connected sensor cover constructed. Finally, we evaluate the distributed algorithms using simulations and show that our approaches results in significant communication cost reductions.

Multichannel MAC Protocols for Wireless Networks

Abstract: In this paper, we propose two new MAC protocols for multichannel operation in wireless ad hoc and mesh networks. The first protocol, extended receiver directed transmission protocol (xRDT) is based on a previously known multichannel solution called receiver directed transmission (RDT) that uses a notion of quiescent channel. xRDT solves the problems faced by RDT, such as multichannel hidden terminal and deafness, by using an additional busy tone interface and few additional protocol operations. We also develop a novel single interface solution, called local coordination-based multichannel MAC (LCM MAC). LCM MAC performs coordinated channel negotiations and channel switching to provide multichannel support. We demonstrate the effectiveness of these two protocols over two other well-known multichannel protocols - MMAC and DCA - via extensive ns2 simulations

Performance Optimizations for Deploying VoIP Services in Mesh Networks

Abstract: In the recent past, there has been a tremendous increase in the popularity of VoIP services as a result of huge growth in broadband access. The same voice-over-Internet protocol (VoIP) service poses new challenges when deployed over a wireless mesh network, while enabling users to make voice calls using WiFi phones. Packet losses and delay due to interference in a multiple-hop mesh network with limited capacity can significantly degrade the end-to-end VoIP call quality. In this work, we discuss the basic requirements for efficient deployment of VoIP services over a mesh network. We present and evaluate practical optimizing techniques that can enhance the network capacity, maintain the VoIP quality and handle user mobility efficiently. Extensive experiments conducted on a real testbed and ns-2 provide insights into the performance issues and demonstrate the level of improvement that can be obtained by the proposed techniques. Specifically, we find that packet aggregation along with header compression can increase the number of supported VoIP calls in a multihop network by 2-3 times. The proposed fast path switching is highly effective in maintaining the VoIP quality. Our fast handoff scheme achieves almost negligible disruption during calls to roaming clients

Benefit-based Data Caching in Ad Hoc Networks

Abstract: Data caching can significantly improve the efficiency of information access in a wireless ad hoc network by reducing the access latency and bandwidth usage. However, designing efficient distributed caching algorithms is non-trivial when network nodes have limited memory. In this article, we consider the cache placement problem of minimizing total data access cost in ad hoc networks with multiple data items and nodes with limited memory capacity. The above optimization problem is known to be NP-hard. Defining benefit as the reduction in total access cost, we present a polynomial-time centralized approximation algorithm that provably delivers a solution whose benefit is at least one-fourth (one-half for uniform-size data items) of the optimal benefit. The approximation algorithm is amenable to localized distributed implementation, which is shown via simulations to perform close to the approximation algorithm. Our distributed algorithm naturally extends to networks with mobile nodes. We simulate our distributed algorithm using a network simulator (ns2), and demonstrate that it significantly outperforms another existing caching technique (by Yin and Cao [30]) in all important performance metrics. The performance differential is particularly large in more challenging scenarios, such as higher access frequency and smaller memory.

A Topology Control Approach to Using Directional Antennas in Wireless Mesh Networks

Abstract: Directional antennas in wireless mesh networks can improve spatial reuse. However, using them effectively needs specialized protocol support at the MAC layer, which is always not practical. In this work, we present a topology control approach to effectively using directional antennas with legacy MAC layer protocols such as IEEE 802.11. The idea is to use multiple directional antennas on each node and orient them appropriately to create low interference topologies while maintatining network connectivity. Our approach is based on a well-known approximation algorithm to compute minimum degree spanning trees. We show via empirical studies that this approach can reduce interference significantly without increasing stretch factors to any appreciable extent. Detailed wireless network simulations also show that this approach improves end-to-end throughput of multihop flows relative to using omni-directional antennas. Three or four directional antennas per network node with only moderate beamwidths are sufficient to improve the saturation throughput of multihop flows by a factor of 3?4.

Collision avoidance in a dense RFID network

Abstract: In this work, we develop a CSMA-based MAC protocol to avoid reader-reader and reader-tag collisions in a dense RFID network. The network is implemented using mote-based RFID readers. To implement the MAC protocol,we develop an appropriate carrier sensing circuit using an RFID tag as an antenna and the mote as an apparatus to sample received signal strength. We have augmented a commercially available OEM RFID module with such carrier sensing capability and interfaced it with motes. Performance evaluation shows much superior performance relative to a naive and a randomized protocol in dense deployment environments both in regards to accuracy and time per tag read.

MAC Layer Multicast in Wireless Multihop Networks

Abstract: Many applications in wireless ad-hoc networks require multicast communication. In order to provide efficient multicast, various multicast routing protocols have been designed in recent years to facilitate formation of routes between multicast senders and receivers. There has also been some work to develop a suitable MAC protocol to improve efficiency of multicast communication. In this work we explore some approaches for reliable multicast at the MAC layer. We develop a multicast extension of IEEE 802.11 protocol and evaluate its performance. We have implemented our protocol in the popular ns-2 simulator and have performed experiments with multicast routing protocol.1. Our approach demonstrates superior performance in terms of packet deliveryfraction as well as delay compared to the IEEE 802.11 protocol.

Ad hoc on-demand multipath distance vector routing: Research Articles

Abstract: We develop an on-demand, multipath distance vector routing protocol for mobile ad hoc networks. Specifically, we propose multipath extensions to a well-studied single path routing protocol known as ad hoc on-demand distance vector (AODV). The resulting protocol is referred to as ad hoc on-demand multipath distance vector (AOMDV). The protocol guarantees loop freedom and disjointness of alternate paths. Performance comparison of AOMDV with AODV using ns-2 simulations shows that AOMDV is able to effectively cope with mobility-induced route failures. In particular, it reduces the packet loss by up to 40p and achieves a remarkable improvement in the end-to-end delay (often more than a factor of two). AOMDV also reduces routing overhead by about 30p by reducing the frequency of route discovery operations. Copyright © 2006 John Wiley & Sons, Ltd.

Performance of multichannel wireless ad hoc networks

Abstract: This paper addresses the design of Medium Access Control (MAC) protocols for wireless ad hoc networks that derive benefits from using multiple orthogonal channels for data transmission. Each node is assumed to have a single half-duplex transceiver that can dynamically select the best channel for transmitting data. We show that even with the same total bandwidth, multichannel MAC protocols can improve the throughput due to two factors reduction of the number of backoffs during channel access, and increase of the probability of success of transmitted data packets by selecting channels to minimise co-channel interference. We propose multichannel MAC protocols with signal-power based channel selection for achieving these goals and present performance results that show that the proposed protocols can provide significantly higher throughput than that obtained by using the IEEE 802.11 MAC.

Detecting wormhole attacks in wireless networks

Abstract: We study and propose a novel algorithm for detecting Wormhole Attacks in wireless ad hoc and sensor networks. The algorithm uses only local connectivity information and utilizes disk packing argument to detect such attacks. The success of the detection algorithm depends on the density of nodes in the network. Preliminary simulation results indicate that for uniformly distributed UDG networks, wormholes can be detected with very high probabilities for average degrees as low as 8.

A measurement-based model for estimating transmission capacity in a wireless mesh network

Abstract: In the past decade, wireless multihop networks have caught the fancy of wireless networking researchers and practitioners alike. However, wireless being a broadcast medium, links in close neighborhood interfere causing a capacity degradation. Network modeling community has investigated this issue of interference and how it limits the capacity of wireless multihop networks [3]. Much of these works use a somewhat abstract and idealized model of interference, initially proposed in the seminal work of Gupta and Kumar [2]. These models describe how two communicating links interfere based on physical distances between the transmitters and receivers, oversimplified radio propagation model, idealized transmitter and receiver characteristics, and so on. Such models have so far been sufficient for getting a highlevel understanding of the behavior of wireless networks and even for designing protocol support, but it has remained unclear how these models could be useful in practice for an operational network. Research in Wireless Networks needs to consider the phenomenon of interference between transmissions. A model for interference is an essential input to the design of any routing protocol. Design of a fairness model, or a capacity model for a wireless network also requires an interference model. Transport protocols and channel assignment protocols also need an understanding of wireless interference. So, its imperative to have a realistic and accurate interference model to assist research in various areas in wireless networking. Our work follows on the lines of previous works done on developing a measurement based model for quantifying the interference limited link capacity [4, 5]. In this work, we estimate the impact of interference on the transmission capacity of a node. When a node transmits a packet, all the other nodes who can either receive the packet, or can detect the transmission’s signal become silent. Thus, a transmitter