Showing papers by "Bhaskaran Raman published in 2012"

Wolverine: Traffic and road condition estimation using smartphone sensors

Abstract: Monitoring road and traffic conditions in a city is a problem widely studied. Several methods have been proposed towards addressing this problem. Several proposed techniques require dedicated hardware such as GPS devices and accelerometers in vehicles [7][15][8] or cameras on roadside and near traffic signals [13]. All such methods are expensive in terms of monetary cost and human effort required. We propose Wolverine1 - a non-intrusive method that uses sensors present on smartphones. We extend a prior study [12] to improve the algorithm based on using accelerometer, GPS and magnetometer sensor readings for traffic and road conditions detection. We are specifically interested in identifying braking events - frequent braking indicates congested traffic conditions - and bumps on the roads to characterize the type of road. We evaluate the effectiveness of the proposed method based on experiments conducted on the roads in Mumbai, with promising results.

Kyun queue: a sensor network system to monitor road traffic queues

Abstract: Unprecedented rate of growth in the number of vehicles has resulted in acute road congestion problems worldwide. Better traffic flow management, based on enhanced traffic monitoring, is being tried by city authorities. In many developing countries, the situation is worse because of greater skew in growth of traffic vs the road infrastructure. Further, the existing traffic monitoring techniques perform poorly in the chaotic non-lane based traffic here.In this paper, we present Kyun Queue, a sensor network system for real time traffic queue monitoring. Compared to existing systems, it has several advantages: it (a) works in chaotic traffic, (b) does not interrupt traffic flow during its installation and maintenance and (c) incurs low cost. Our contributions in this paper are four-fold. (1) We propose a new mechanism to sense road occupancy based on variation in RF link characteristics, when line of sight between a transmitter-receiver pair is obstructed. (2) We design algorithms to classify traffic states into congested or free-flowing at time scales of 20 seconds with above 90% accuracy. (3) We design and implement the embedded platforms needed to do the sensing, computation and communication to form a network of sensors. This network can correlate the traffic state classification decisions of individual sensors, to detect multiple levels of traffic congestion or traffic queue length on a given stretch of road, in real time. (4) Deployment of our system on a Mumbai road, after careful consideration of issues like localization and interference, gives correct estimates of traffic queue lengths, validated against 9 hours of image-based ground truth. Our system can provide input to several traffic management applications like traffic light control, incident detection, and congestion monitoring.

Intelligent Transport Systems for Indian Cities.

Abstract: Road traffic congestion is a recurring problem worldwide. In India, a fast growing economy, the problem is acutely felt in almost all major cities. This is primarily because infrastructure growth is slow compared to growth in number of vehicles, due to space and cost constraints. Secondly, Indian traffic being non-lane based and chaotic, is largely different from the western traffic. The difference can be understood fully only through experience, but some example scenarios can be seen at [1]. Thus, Intelligent Transport Systems (ITS), used for efficient traffic management in developed countries, cannot be used as it is in India. ITS techniques have to undergo adaptation and innovation to suit the contrasting traffic characteristics of Indian roads. In this position paper, we present a comprehensive study of all available ITS systems,including both research prototypes and deployed systems. We next pose a set of interesting open research problems in the context of Indian ITS. Finally, we list a set of public and private organizations, that play a role in Indian traffic management and research, as meaningful collaboration between field practitioners and researchers is needed for efficient transfer of relevant technology. Though our paper focuses on the Indian traffic scenario because of our hands-on experience of working with it [2, 3, 4], many of the problems and solutions outlined in this paper, are relevant for other developing countries as

SIR based interference modeling for wireless mesh networks: A detailed measurement study

Abstract: Spatial reuse is a central aspect in the efficiency of wireless mesh networks. Accurate inter-link interference measurement and estimation is necessary for such spatial reuse. In this work, we explore in depth Signal to Interference Ratio (SIR) based interference modeling. We take a measurement centric approach, characterizing the SIR versus PDR (Packet Delivery Ratio) relationship in outdoor mesh network settings. Our significant findings are the following. (1) In outdoor environment there is a range of SIR values (intermediate SIR region), wherein it is difficult to predict the PDR accurately. (2) Fortunately, the width of this intermediate SIR region is small: about 4–5dB for most data rates. (3) The SIR vs PDR relationship depends significantly on the modulations used by transmitter as well as the interferer: we characterize this dependence. The use of an outdoor 802.11g-based testbed is a significant aspect of our measurements. The above findings have important implications for the design of interference measurement and prediction schemes. We quantify the accuracy of our SIR-based technique by applying an offline prediction model in our outdoor mesh testbed and observe that of the 44 pairs of links the SIR technique predicts performance with less than 10% error for over 85% of the links for which the SIR values lie outside the intermediate SIR region. An evaluation of existing interference modeling techniques reveals that these make certain incorrect assumptions which make them perform significantly worse than our proposed technique.

PIP: A multichannel, TDMA-based MAC for efficient and scalable bulk transfer in sensor networks

Abstract: In this article, we consider the goal of achieving high throughput in a wireless sensor network. Our work is set in the context of those wireless sensor network applications which collect and transfer bulk data. We present PIP (Packets in Pipe), a MAC primitive for use by the transport module to achieve high throughput. PIP has a unique set of features: (a) it is a multihop connection-oriented primitive, (b) it is TDMA based, (c) it uses multiple radio channels, and (d) it is centrally controlled. This represents a significant shift from prior MAC protocols for bulk data transfer. PIP has several desirable properties: (a) its throughput degrades only slightly with increasing number of hops, (b) it is robust to variable wireless error rates, (c) it performs well even without any flow control, and (d) requires only small queue sizes to operate well. We substantiate these properties with a prototype implementation of PIP on the Tmote-Sky CC2420-based platform. PIP achieves about eleven times better throughput than the state-of-the-art prior work, over a network depth of 24 hops. We also show that PIP can be interagted with duty cycling, and that PIP can support streaming data from/to flash at little overhead.

Building a low cost low power wireless network to enable voice communication in developing regions

Abstract: In this work, we describe our experiences in building a low cost and low power wireless mesh network using IEEE 802.15.4 technology to provide telephony services in rural regions of the developing world. 802.15.4 was originally designed for a completely different application space of non-real-time, low data rate embedded wireless sensing. We use it to design and prototype a telephony system, which we term as Lo3 (Low cost, Low power, Local voice). Lo3 primarily provides two use cases; (1) local and broadcast voice within the wireless mesh network, and (2) remote voice to a phone in the outside world. A Lo3 network can cost as less as $2K, and can last for several days without power "off the grid", thus making it an ideal choice to meet cost and power constraints of rural regions. We test deployed a full-fledged Lo3 system in a village near Mumbai, India for 18 hours over 3 days. We established voice calls with an end-to-end latency of less than 120ms, with an average packet loss of less than 2%, and a MOS of 3.6 which is considered as good in practice. The users too gave a positive response to our system. We also tested Lo3 within our department where it can be used as a wireless intercom service. To our knowledge, Lo3 is the first system to enable such a voice communication system using 802.15.4 technology, and show its effectiveness in operational settings.

A Dvaar to LokVaani: extending cellular coverage inside villages of developing world

Abstract: In India, the rural teledensity is just 37% and there are a large number of villages which do not have cellular coverage to this day but many such villages are only a few km away from the cellular coverage Exploiting these cellular points near villages, we present a low cost and low power gateway system to extend the cellular coverage into the rural areas Specifically, we develop and demonstrate a low cost, low power 802154 gateway which can connect a number of villages in its vicinity to the cellular backhaul In prior work, we designed a low cost, low power, local voice (called as Lo3) system using 802154 technology Lo3 system enabled villagers inside a village to communicate with each other In this demo, we show that, using the gateway node, the 802154 handsets of Lo3 system enable villagers to establish real-time voice calls from/to the village to/from the outside world We test deployed our system in Ahupe village near Mumbai, India for 18 hours over 3 days, and received positive response from the villagers