Ad hoc communication is gaining popularity in recent times, not only for pure ad hoc communication networks but also as a viable solution for coverage extension in wireless networks. Especially for upcoming WLAN hotspots this is an interesting option to decrease installation costs. In this paper we introduce a new MAC protocol that needs only marginal changes to the standard and enables e#cient multi--hop networking. We advocate the use of multiple IEEE802.11 channels, where one channel is reserved as a common signaling channel for the task of assigning the others ("data channels") among wireless terminals. The proposed MAC protocol is based on a four way handshake over the common signaling channel, while data transmission occurs on a dedicated channel. We propose a further optimization applying multiple wireless network interface cards. This improvement in performance comes at the price of a slightly more complex hardware. Two di#erent simulation models are implemented to investigate our approach. The first model investigates the MAC protocol and its improvements while the second model analyzes the multi--hop performance in terms of delivery ratio and transmission delay. By means of numerous simulations we present the performance of our MAC approach in comparison with two standard approaches in terms of bandwidth, packet delivery, and transmission delay. For our performance evaluation we apply the IEEE802.11a technology, but we note that our approach can also be used for IEEE802.11b.

Wireless video sensor networks (WVSN) have been envisioned for a wide range of important applications, including battlefield intelligence, security monitoring, emergency response, and environmental tracking. Compared to the traditional communication system, the WVSN operates under a set of unique resource constraints, including including limitations with respect to energy supply, on-board computational capability, and transmission bandwidth. The objective of this work is to study the resource utilization behavior of a wireless video sensor and analyze its performance under the resource constraints. More specifically, we develop an analytic power-rate-distortion (P-R-D) model to characterize the inherent relationship between the power consumption of a video encoder and its rate-distortion performance. Based on the P-R-D analysis and a simplified model for wireless transmission power, we study the optimum power allocation between video encoding and wireless transmission, and introduce a measure called achievable minimum distortion (AMD) to quantify the distortion under a total power constraint. We consider two scenarios in wireless video sensing: small-delay wireless video monitoring and largedelay wireless video surveillance, and analyze the performance limit of the wireless video sensor in each scenario. The analysis and results obtained in this paper provide an important guideline for practical wireless video sensor design.

Abstract — While packet capture has been observed in real implementations of 802.11 devices, there is a lack of accurate models that describe the phenomenon. We present a general analytical model and an iterative method that predicts error probabilities and throughputs of packet transmissions with multiple senderreceiver pairs. Our model offers a more accurate prediction than previous work by taking into account the cumulative strength of interference signals and using the BER model to convert a signal to interference and noise ratio value to a bit error probability. This permits the analysis of packet reception at any transmission rate with interference from neighbors at any set of locations. We also prove that our iterative method converges, and we verify the accuracy of our model through simulations in Qualnet. Last, we present a rate assignment algorithm to reduce the average delay as an application of our analysis. I.

Opportunistic dissemination protocols have potentially applications in the domain of vehicular networking, ranging from advertising to emergency/traffic/parking information spreading: one of the characteristics of vehicular networks is that they are often partitioned due to lack of continuity in connectivity among cars or limited coverage of infostations in remote areas. Most available opportunistic, or delay tolerant, networking protocols, however, fail to take into account the peculiarities of vehicular networks. This paper introduces a novel opportunistic event dissemination protocol for vehicular networks. The protocol takes into account the characteristics of these networks in order to dispatch the publications to the subscribers. Furthermore, it uses opportunistic cache and replay mechanisms to deliver the notifications to new subscribers in the area throughout the publication interval. We evaluate our approach through simulation using realistic vehicular traces. We compare our algorithm with a standard epidemic protocol, which offer the best alternative in terms of message delivery, by measuring overhead and delivery over a number of scenarios.

Mobile ad hoc network (MANET) is a new emerging field with its potential applications in extremely unpredictable and dynamic environments. These characteristics require the networks to have much harder security requirements than the contemporary networks. While current routing protocols do seem to adjust well to dynamically changing conditions, they offer either no security mechanisms at all or have only partial solutions for ensuring the correct routing. It is hard to simultaneously achieve both security and robustness in the routing protocols. In this paper, we analyze various possible threats to the routing protocols and introduce strategies to address the same. On one hand, routing protocol can be disrupted due to attacks from intruder nodes that do not belong to the network. On the other hand, routing is severely affected by the presence of compromised nodes that inflict unpredictable and undetectable Byzantine failure. We have addressed the issue of attacks from intruders by means of authentication techniques that rely on mutual trust between nodes. We also study the behavioral patterns of the nodes and isolate compromised nodes using a distributed approach. The effectiveness of our schemes is illustrated by means of extensive simulations using ns-2 simulator. The routing protocol chosen for the study is AODV. We have observed the performance of the network with and without our secured routing scheme.

Abstract—Wireless mesh networking is an exciting new technology that has applications in defence, metro-area Internet access, and transient networks (e.g: disaster recovery, conventions). In this paper, we describe the design and implementation of a self-configuring, secure infrastructure mesh network architecture, called MeshCluster, composed using multi-radio network nodes. A subset of radio interfaces on these nodes are used for providing network access to end-devices whereas other radio interface are used for relaying packets to nearest Internet gateway. We identify four key design problems: (1) auto-configuration of MeshCluster nodes and relay infrastructure, (2) single and multipath routing in the relay infrastructure using routing metrics, (3) load balancing in the relay infrastructure, and (4) support for end-device mobility across access interfaces of mesh network. For each of these problems, we describe in detail our design, prototype implementation, and performance results. I.

We present a new medium-access control protocol for ad hoc networks that does not require carrier sensing or the preassignment of unique codes to nodes to ensure that intended receivers receive unicast, or multicast, or broadcast data packets without interference from hidden sources. We call this new protocol channel hopping access with trains (CHAT). CHAT combines the notion of packet trains with synchronous channel hopping to improve channel utilization. We compare CHAT against two of the most efficient protocols proposed to date based on the preassignment of codes (MACA-CT), or channel hopping with no predefined code assignment (CHMA) via simulations. The results show that CHAT provides considerable improvement in the throughput of an ad hoc network for unicast traffic, broadcast traffic and mixed traffic consisting of both unicast and broadcast transmissions. CHAT is applicable to ad hoc networks based on commercial offthe -shelf spread spectrum radios operating in unlicensed frequency bands. Keywords--- Medium Access Protocols, ad-hoc networks, packet train, multichannel radio, frequency hopping spread spectrum I.

Abstract — With the emergence of high data rate sensor network applications, there is an increasing demand for highperformance query services in such networks. To meet this challenge, we propose Dynamic Conflict-free Query Scheduling (DCQS), a novel scheduling technique for queries in wireless sensor networks. In contrast to earlier TDMA protocols designed for general-purpose networks and workloads, DCQS is specifically designed for query services supporting in-network data aggregation. DCQS has several important features. First, it optimizes the query performance and energy efficiency by exploiting the temporal properties and precedence constraints introduced by data aggregation. Second, it can efficiently adapt to dynamic workloads and rate changes without explicitly reconstructing the transmission schedule. In addition, we provide an analytical capacity bound for DCQS in terms of query completion rate. This bound enables DCQS to handle overload through rate control. NS2 simulation results demonstrate that DCQS significantly outperforms a representative TDMA protocol (DRAND) and the 802.11 protocol in terms of query latency, throughput, and energy efficiency. I.

This paper proposes Efficient Sleep Scheduling based on Application Timing (ESSAT), a novel power management scheme that aggressively exploits the timing semantics of wireless sensor network applications. We present three ESSAT protocols each of which integrates (1) a lightweight traffic shaper that actively shapes the workload inside the network to achieve predictable timing properties over multiple hops, and (2) a local scheduling algorithm that wakes up nodes just-in-time based on the timing properties of shaped workloads. Our ESSAT protocols have several distinguishing features. First, they can save significant energy with minimal delay penalties. Second, they do not maintain TDMA schedules or communication backbones; as such, they are highly efficient and suitable for resource constrained sensor platforms. Moreover, the protocols are robust in highly dynamic network environments, i.e., they can handle variable multi-hop communication delays and aggregate workloads involving multiple queries, and can adapt to varying workload and network topologies. Our simulations showed that DTS-SS, an ES-SAT protocol, achieved an average node duty cycle 38-87 % lower than SPAN, and query latencies 36-98 % lower than PSM and SYNC. 1

In an ad hoc network each host (node) participates in routing packets. Ad hoc networks based on 802.11 WLAN technology have been the focus of several prior studies. These investigations were mainly based on simulations of scenarios involving up to 100 nodes (usually 50 nodes) and relaxed (too unrealistic) data traffic conditions. Many routing protocols in such setting offer the same performance, and many potential problems stay undetected. At the same time, an ad hoc network may not want (or be able) to limit the number of hosts involved in the network. As more nodes join an ad hoc network or the data traffic grows, the potential for collisions and contention increases, and protocols face the challenging task to route data packets without creating high administrative load. The investigation of protocol behavior in large scenarios exposes many hidden problems. The understanding of these problems helps not only in improving protocol scalability to large scenarios but also in increasing the throughput and other QoS metrics in small ones. This paper studies on the example of AODV and DSR protocols the influence of the network size (up to 550 nodes), nodes mobility, nodes density, suggested data traffic on protocols performance. In this paper we identify and analyze the reasons for poor absolute performance that both protocols demonstrate in the majority of studied scenarios. We also propose and evaluate restructured protocol stack that helps to improve the performance and scalability of any routing protocol in wireless ad hoc networks.