Vinod Namboodiri

Prediction-Based Routing for Vehicular Ad Hoc Networks

Development in short-range wireless LAN (WLAN) and long-range wireless WAN (WWAN) technologies have motivated recent efforts to integrate the two. This creates new application scenarios that were not possible before. Vehicles with only WLAN radios can use other vehicles that have both WLAN and WWAN radios as mobile gateways and connect to the Internet while on the road. The most difficult challenge in the scenario is to deal with frequent route breakages due to dynamic mobility of vehicles on the road. Existing routing protocols that are widely used for mobile ad hoc networks are reactive in nature and wait until existing routes break before constructing new routes. The frequent route failures result in a significant amount of time needed for repairing existing routes or reconstructing new routes. In spite of the dynamic mobility, the motion of vehicles on highways is quite predictable compared to other mobility patterns for wireless ad hoc networks, with location and velocity information readily available. This can be exploited to predict how long a route will last between a vehicle requiring Internet connectivity and the gateway that provides a route to the Internet. Successful prediction of route lifetimes can significantly reduce the number of route failures. In this paper, we introduce a prediction-based routing (PBR) protocol that is specifically tailored to the mobile gateway scenario and takes advantage of the predictable mobility pattern of vehicles on highways. The protocol uses predicted route lifetimes to preemptively create new routes before existing ones fail. We study the performance of this protocol through simulation and demonstrate significant reductions in route failures compared to protocols that do not use preemptive routing. Moreover, we find that the overhead of preemptive routing is kept in check due to the ability of PBR to predict route lifetimes.

A study on the feasibility of mobile gateways for vehicular ad-hoc networks

Development in Wireless LAN and Cellular technologies has motivated recent efforts to integrate the two. This creates new application scenarios that were not possible before. Vehicles with Wireless LAN radios can use other vehicles with both Wireless LAN and Cellular radios as mobile gateways and connect to the outside world. We aim to study the feasibility of such global connectivity from the road through simulation of the underlying connectivity characteristics for varying traffic and gateway densities. The connectivity results suggest that each vehicle should be able to connect to at least one gateway for a majority of time. The average path lifetimes are found to be good enough many traditional Internet applications like FTP and HTTP. The effectiveness of the AODV wireless ad-hoc routing protocol over this scenario is evaluated and shown to perform well for the densities considered. However, the routes created by AODV can break very frequently due to the dynamic nature of mobility involved. We introduce a couple of prediction based routing protocols to minimize these route breakages and thus improve performance. These protocols take advantage of some deterministic characteristics of the mobility model to better predict route breakages and take preemptive action.

Energy-Aware Tag Anti-Collision Protocols for RFID Systems

Energy consumption of mobile readers is becoming an important issue as applications of RFID systems pervade different aspects of our lives. Surprisingly, however, these systems are not energy-aware with the focus till date being on reducing the time to read all tags by the reader. The problem of tag arbitration in RFID systems is considered with the aim of trading off time for energy savings at the reader. The approach of using multiple time slots per node of a binary search tree is explored through three anti-collision protocols that aim to reduce the number of colliding responses from tags. This results in fewer reader queries and tag responses and, hence, energy savings at both the reader and tags (if they are active tags). An analytical framework is developed to predict the performance of our protocols, with the numerical evaluation of this framework validated through simulation. It is shown that all three protocols provide significant energy savings when compared to the existing query tree protocol while sharing the deterministic and memoryless properties of the latter

Energy-Aware Tag Anticollision Protocols for RFID Systems

Energy consumption of portable RFID readers is becoming an important issue as applications of RFID systems pervade many aspects of our lives. Surprisingly, however, these systems are not energy-aware with the focus till date being on reducing the time to read all tags by the reader. In this work, we consider the problem of tag arbitration in RFID systems with the aim of designing energy-aware anticollision protocols. We explore the effectiveness of using multiple time slots per node of a binary search tree through three anticollision protocols. We further develop an analytical framework to predict the performance of our protocols and enable protocol parameter selection. We demonstrate that all three protocols provide significant energy savings both at the reader and tags (if they are active tags) compared to the existing Query Tree protocol, while sharing the deterministic property of the latter. Further, we show that our protocols provide similar benefits even with correlated tag IDs.

Energy-Efficient VoIP over Wireless LANs

Emerging dual-mode phones incorporate a wireless LAN (WLAN) interface along with the traditional cellular interface. The additional benefits of the WLAN interface are, however, likely to be outweighed by its greater rate of energy consumption. This is especially of concern when real-time applications, that result in continuous traffic, are involved. WLAN radios typically conserve energy by staying in sleep mode. With real-time applications like voice over Internet Protocol (VoIP), this can be challenging since packets delayed above a threshold are lost. Moreover, the continuous nature of traffic makes it difficult for the radio to stay in the lower power sleep mode enough to reduce energy consumption significantly. In this work, we propose the GreenCall algorithm to derive sleep/wake-up schedules for the WLAN radio to save energy during VoIP calls while ensuring that application quality is preserved within acceptable levels of users. We evaluate GreenCall on commodity hardware and study its performance over diverse network paths and describe our experiences in the process. We further extensively investigate the effect of different application parameters on possible energy savings through trace-based simulations. We show that, in spite of the interactive, real-time nature of voice, energy consumption during calls can be reduced by close to 80 percent in most instances.

To cloud or not to cloud: A mobile device perspective on energy consumption of applications

The cloud computing paradigm enables the work anywhere anytime paradigm by allowing application execution and data storage on remote servers. This is especially useful for mobile computing and communication devices that are constrained in terms of computation power and storage. It is however not clear how preferable cloud-based applications would be for mobile device users. For users of such battery life constrained devices, the most important criteria might be the energy consumed by the applications they run. The goal of this work is to characterize under what scenarios cloud-based applications would be relatively more energy-efficient for users of mobile devices. This work first empirically studies the energy consumption for various types of applications and for multiple classes of devices to make this determination. Subsequently, it presents an analytical model that helps characterize energy consumption of mobile devices under both the cloud and non-cloud application scenarios. Finally, an algorithm GreenSpot is presented that considers application features and energy-performance tradeoffs to determine whether cloud or local execution will be more preferable.

Wireless AMI application and security for controlled home area networks

Compared to the conventional grid, the smart grid requires active participation of consumers to improve the quality and reliability of power delivery. Advanced metering infrastructure (AMI), commonly known as the smart meter, which has the capability of supporting various functions beyond that of recording energy usage, will facilitate this expected increase in consumer participation. Another primary benefit of AMI is load and cost management for the utility. AMI requires a reliable communication system between the smart meter and consumer equipment. This paper identifies wireless networking solutions such as ZigBee as the best mode for such communication. Due to the shared nature of the wireless medium, however, these deployments face security challenges and interference issues. These must be addressed, taking into account the interests of both the utility and the consumer. This paper takes a comprehensive look at wireless security in the AMI based home-area network by identifying a wide range of possible vulnerabilities. Countermeasures that can be used by both the utility company as well as the customer are developed.

Wireless communication for smart grid applications at distribution level — Feasibility and requirements

Smart grid technology places greater demands for reliability on communications infrastructure. This work focuses on identifying requirements for distribution feeder level communications. Due to the large number of distribution components connected to the distribution level feeders, a massively deployed wireless communication network is identified as the potential technology for this application. This network would allow prioritized communication: high priority for abnormal events and system control operations, and low priority communication for asset management tasks. A three-layer wireless communication architecture is proposed in this work to increase the reliability and reduce the latency of event notification. Fault location is considered as an example application to illustrate the proposed architecture.

An extensive study of slotted Aloha-based RFID anti-collision protocols

Radio frequency identification (RFID) is used to identify, track, and manage tagged animate or inanimate objects automatically using wireless communication technology. A serious concern faced by RFID technology is the collisions that occur among tag responses when queried by a reader that limits system performance significantly. Collisions bring extra delay, a waste of bandwidth, and extra energy consumption to the interrogation process of RFID. This work extensively evaluates the performance of slotted Aloha based anti-collision protocols (that includes the current standard EPCGlobal Class 1 Generation 2) for passive tags through mathematical analysis, simulations, and practical experiments on a testbed. This comprehensive approach allows a better understanding of the theoretical and practical performance of RFID systems and the challenges that exist in improving practical performance in industrial settings. In particular, it is found that protocol mechanisms for the current standard theoretically add 10% overhead to the basic frame slotted Aloha in ideal conditions. Further, results indicate that factors like interference, antenna gain, and protocol implementation can add 50% additional delay in practical settings. This work also performs a low-level investigation of protocol behavior through power measurements and characterizes energy consumption in RFID readers.

Toward a Secure Wireless-Based Home Area Network for Metering in Smart Grids

Compared to the conventional grid, the smart grid requires active participation of consumers to improve the quality and reliability of power delivery. The increase in consumer participation is expected from the advanced metering infrastructure (AMI), commonly known as the smart meter, which has the capability of supporting various functions beyond that of recording energy usage. One of the primary objectives of the AMI is to allow load and cost management for the utility. This is envisioned partly through a communication system implemented between the smart meter and consumer equipment, currently deployed using wireless networking solutions such as ZigBee. Due to the shared nature of the wireless medium, however, these deployments face security challenges and interference issues, which must be addressed, taking into account the interests of both the utility company and the consumer. This work takes a comprehensive look at wireless security in the smart-meter-based home area network scenario and identifies possible vulnerabilities. Subsequently, some countermeasures are developed that can be used by both the utility company and the customer and are integrated into a common framework called SecureHAN that can be agreed to by both. In addition, the experiences from implementing the SecureHAN framework using commercial off-the-shelf hardware are described, including possible challenges.