Alvin S. Lim

ACAR: Adaptive Connectivity Aware Routing for Vehicular Ad Hoc Networks in City Scenarios

Multi-hop vehicle-to-vehicle communication is useful for supporting many vehicular applications that provide drivers with safety and convenience. Developing multi-hop communication in vehicular ad hoc networks (VANET) is a challenging problem due to the rapidly changing topology and frequent network disconnections, which cause failure or inefficiency in traditional ad hoc routing protocols. We propose an adaptive connectivity aware routing (ACAR) protocol that addresses these problems by adaptively selecting an optimal route with the best network transmission quality based on statistical and real-time density data that are gathered through an on-the-fly density collection process. The protocol consists of two parts: 1) select an optimal route, consisting of road segments, with the best estimated transmission quality, and 2) in each road segment of the chosen route, select the most efficient multi-hop path that will improve the delivery ratio and throughput. The optimal route is selected using our transmission quality model that takes into account vehicle densities and traffic light periods to estimate the probability of network connectivity and data delivery ratio for transmitting packets. Our simulation results show that the proposed ACAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, throughput and data packet delay. Since the proposed model is not constrained by network densities, the ACAR protocol is suitable for both daytime and nighttime city VANET scenarios.

Distributed services for information dissemination in self-organizing sensor networks

Abstract Dynamic enterprise systems, such as the battlefield, use self-organizing sensor network infrastructure to gather and disseminate real-time information for controlling the enterprise. Very large number of highly mobile sensor data sources and users may be scattered over a wide area with little or no fixed network support. These large surveillance sensor networks must adapt rapidly to dynamic changes in sensor nodes configuration. Dynamic query processing and target tracking through this unstructured sensor network of surveillance information sources and users must use the appropriate distributed services and network protocols to solve the problems of mobility, dispersion, weak and intermittent disconnection, dynamic reconfiguration and limited power availability. We provide three main distributed services: lookup service, composition service and dynamic adaptation service. Through a distributed implementation of these services, other application-specific network and system services can be defined spontaneously in the sensor network. They also enable dynamic adaptation of these services to incremental addition and removal of sensor nodes, device failure and degradation, migration of sensor nodes, and changing requirements in tasks and networks. When placed together impromptu, sensor nodes should immediately know about the capabilities and functions of other smart nodes and work together as a community system to perform coordinated tasks and networking functionalities.

ACAR: Adaptive Connectivity Aware Routing Protocol for Vehicular Ad Hoc Networks

Developing routing protocol for vehicular ad hoc networks (VANET) is a challenging task due to potentially large network sizes, rapidly changing topology and frequent network disconnections, which can cause failure or inefficiency in traditional ad hoc routing protocols. We propose an adaptive connectivity aware routing (ACAR) protocol that addresses these problems by adaptively selecting an optimal route with the best network transmission quality based on the statistical and realtime density data that are gathered through an on-the-fly density collection process. The protocol consists of two parts: (1) select an optimal route, consisting of road segments, with the best estimated transmission quality (2) in each road segment in the selected route, select the most efficient multi-hop path that will improve delivery ratio and throughput. The optimal route can be selected using our new connectivity model that takes into account vehicles densities and traffic light periods to estimate transmission quality at road segments, which considers the probability of connectivity and data delivery ratio for transmitting packets. In each road segment along the optimal path, each hop is selected to minimize the packet error rate of the entire path. Our simulation results show that the proposed ACAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, throughput and data packet delay. In addition, ACAR works very well even if accurate statistical data is not available.

Connectivity Aware Routing in Vehicular Networks

Multi-hop car to car communications are useful for supporting many vehicular applications that provide drivers with safety and convenience ranging from office on the wheel to real traffic query, vehicle safety, parking space searching and on-road advertisement. Developing multi-hop communication in vehicular ad hoc networks (VANET) is a challenging problem due to the rapidly changing topology and frequent network disconnections, which cause failure or inefficiency in traditional ad hoc routing protocols. The problem of frequent network disconnections can be partially addressed using a carry-and- forward mechanism which may incur higher delay. However, our connectivity aware routing (CAR) protocol addresses this problem by selecting an optimal route with the least probability of network disconnection and avoids carry-and-forward delay. This can be achieved using our new probabilistic model of network connectivity which takes into account a more realistic clustering phenomenon of vehicle traffic in city scenarios that is caused by traffic lights. Our simulation results show that the proposed CAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, data packet delay and network throughput. In addition, CAR improves performance for both sparse and dense networks.

Requirements and design principles for multisimulation with multiresolution, multistage multimodels

The significance of simulation modeling at multiple levels, scales, and perspectives is well recognized. However, existing proposals for developing such models are often application specific. The position advocated in this paper is that generic design principles for specifying and realizing multiresolution, multistage models are still lacking. Requirements for simulation environments that facilitate multiresolution multistage model specification are introduced. A multimodel specification formalism based on graph of models is suggested along with design precepts to enable flexible dynamic model updating. The notion of multisimulation is introduced to enable exploratory simulation using various types of multimodels.

Jamming and anti-jamming techniques in wireless networks: a survey

Because of the proliferation of wireless technologies, jamming in wireless networks has become a major research problem due to the ease in blocking communication in wireless networks. Jamming attacks are a subset of denial of service (DoS) attacks in which malicious nodes block legitimate communication by causing intentional interference in networks. To better understand jamming and anti-jamming, we surveyed and analysed their various techniques. For evaluating jamming, we categorised the types of jammers implemented in the literature and investigated the placement strategies for supporting effective jamming. For anti-jamming approaches, we start by discussing the protocols for localising jammers before presenting the mechanisms for detection and jamming countermeasure. We present comparison tables for each of the jammer types, jammer placements, jammer localisation, jamming detection schemes and jamming countermeasures. Our analyses are helpful for selecting an existing strategy for a particular system setup. Finally, we discuss open issues in this field.

A Sensor Network Architecture for Tsunami Detection and Response

In this paper, we propose a sense and response system for tsunami detection and mitigation. We use the directed diffusion routing protocol as a baseline network protocol and develop several communication mechanisms to improve its performance. These include an efficient flooding technique, a route repair algorithm, and distributed services framework. We summarize the analysis mechanism used to predict tsunami propagation and briefly discuss the results of this algorithm. Finally, we describe potential barrier mechanisms and the real-time communication protocol that supports time-critical response of the system.

Delay-constrained high throughput protocol for multi-path transmission over wireless multimedia sensor networks

Real-time multimedia transport has stringent QoS requirements, such as bandwidth, delay, jitter, and loss ratio. Wireless sensor networks are useful for streaming multimedia data in infrastructure-free and hazardous environments. However, these networks are composed of nodes with constrained bandwidth and energy. In QoS routing for wired networks, multipath routing is widely used. Some existing ad hoc routing algorithms also provide multipath routing. Directed diffusion has been commonly used for wireless sensor networks because of its energy efficiency and scalability. However, the basic protocol only routes packets through a single path, which barely meets the throughput requirement of multimedia data. Instead, we propose a multipath algorithm based on directed diffusion that reinforces multiple routes with high link quality and low latency. We use the NS-2 simulation tool with video trace generated by multiple description coding (MDC) to evaluate the performance. The results show that our algorithm gives better throughput and delay performance than standard directed diffusion.

A survey of broadcast authentication schemes for wireless networks

With the increase in the usage of wireless networks and their applications where broadcast transmission is widely used, it has become critical to authenticate broadcast messages. Several broadcast authentication techniques are currently available. However, no scheme is ideal for all broadcast transmission applications. Our goal is to classify, compare and analyze existing broadcast authentication techniques to enable designers to select an appropriate technique that suits their system, computation, communication and application requirements. Furthermore, this study provides better understanding of the research challenges that are still not addressed or only partially addressed.

Improving performance of adaptive media access control protocols for high-density wireless networks

The problems of intermittent disconnection, high error rate and collision in high-density wireless networks cause degradation in the performance of wireless media access control protocols, such as slotted ALOHA Time Division Multiple Access (slotted ALOHA/TDMA) and Direct Sequence Code Division Multiple Access (DS/CDMA). We propose adaptive techniques for improving performance of media access protocols through awareness of the mobile communication environment. These techniques involve detection of intermittent disconnection, high error rates, and collisions. Upon detection and notification of these conditions by snooping devices, the media access control layer adapts its operation and synchronization accordingly to reduce delay and loss of bandwidth. Results from our simulation studies show that adaptive TDMA improves performance by as much as 12 times over basic TDMA and adaptive CDMA improves by as much as 4 times over basic CDMA in wireless network with high population cells. Overall, adaptive CDIMA still performs better than adaptive TDMA by about 4 times.