Pratap Kumar Sahu

Congestion-Controlled-Coordinator-Based MAC for Safety-Critical Message Transmission in VANETs

Vehicular ad hoc networks (VANETs) provide the communication framework for the dissemination of safety-critical messages such as beacons and emergency messages. The communication channel witnesses significant network load generated by frequently exchanged beacons. Under high-density situations, it leads to a serious scalability problem in VANETs. Moreover, contention-based medium access control (MAC) protocols suffer from a great number of packet collisions, and as a result, the reliability and latency of safety messages are severely affected. Because of the periodic nature of beacons, time-division multiple access (TDMA) can be a good choice over contention-based MAC. In this paper, we propose congestion-controlled-coordinator-based MAC (CCC-MAC), which is a time-slot-based medium access protocol that addresses beacons and emergency messages. Basically, the network is virtually partitioned into a number of segments. Within a segment, medium access is accomplished by using a time-slot-scheduling mechanism supervised by a local coordinator vehicle. A significant number of vehicles can be supported under the proposed configuration. In fact, the proposed scheduling mitigates channel congestion by reducing the transmission time of beacons through the use of multiple data rates. Bandwidth utilization is also improved by reusing the unoccupied time slots. Finally, CCC-MAC ensures fast and reliable propagation of emergency messages by employing a pulse-based reservation mechanism. In the simulations, we demonstrate the ability of CCC-MAC to scale well in different vehicular density scenarios. Moreover, it outperforms existing MAC-layer protocols with respect to packet reception probability and latency of safety messages.

Energy Efficient Cooperative Computing in Mobile Wireless Sensor Networks

Advances in future computing to support emerging sensor applications are becoming more important as the need to better utilize computation and communication resources and make them energy efficient. As a result, it is predicted that intelligent devices and networks, including mobile wireless sensor networks (MWSN), will become the new interfaces to support future applications. In this paper, we propose a novel approach to minimize energy consumption of processing an application in MWSN while satisfying a certain completion time requirement. Specifically, by introducing the concept of cooperation, the logics and related computation tasks can be optimally partitioned, offloaded and executed with the help of peer sensor nodes, thus the proposed solution can be treated as a joint optimization of computing and networking resources. Moreover, for a network with multiple mobile wireless sensor nodes, we propose energy efficient cooperation node selection strategies to offer a tradeoff between fairness and energy consumption. Our performance analysis is supplemented by simulation results to show the significant energy saving of the proposed solution.

Dynamic spatial partition density-based emergency message dissemination in VANETs

Location and density based emergency message broadcasting has attracted researchers attention in vehicular ad-hoc networks. However, most of current approaches do not provide good performance, in terms of delay in both light and dense traffic scenarios. Reliability in message delivery is another significant performance metric, especially in dense traffic scenarios. In this paper, we have analyzed and implemented a reliable time-efficient and multi-hop broadcasting scheme, called Dynamic Partitioning Scheme (DPS), which works well in both dense and light traffic scenarios. Our solid analytical evaluation and simulation results indicate that our proposed scheme outperforms five efficient broadcasting protocols in VANETs in terms of delay and reliability in emergency message broadcasting.

Multi-hop reliability for broadcast-based VANET in city environments

We propose a multi-hop reliable broadcasting (M-HRB) scheme suitable for a wide range of vehicular ad-hoc network (VANET) applications in urban setting. Multi-hop reliability is performed using local state information. Basically, a street is divided into multiple cells to form grid-like zones. We apply a proactive local state processing scheme exploiting features of periodic beacons to estimate wireless link quality of the neighbours. With availability of local state information, adequate numbers of forwarders are selected to achieve desired reliability in each hop for a multi-hop broadcast. Furthermore, M-HRB saves bandwidth consumption by enabling cooperation among forwarders. Simulation results show the superior performance of M-HRB in city environment in terms of reliability and bandwidth consumption. M-HRB also satisfies transmission latency requirements for time-sensitive vehicular applications.

A stable minimum velocity CDS-based virtual backbone for VANET in city environment

For safety applications, fast delivery is the key requirement that broadcasting protocols in VANET must fulfill. To achieve this goal, most of the existing schemes try to select the optimal next forwarder through a distributed contention phase. This latter adds few units of delay at each hop which is substantial in case of multihop transmission. A more pragmatic approach is to build a stable virtual infrastructure, ahead of time, which will be in charge of relaying messages. In this regard, this paper presents the Minimum Stable CDS-based Virtual Backbone, labeled CDS-SVB, which guarantees fast and efficient broadcasting. It selects vehicles with identical velocities to assure stability as well as low dissemination delay, and it deploys acknowledgments to ensure reliability. Simulation results show that CDS-SVB outperforms DBA-MAC in terms of dissemination delay, backbones lifetime, and packets delivery ratio.

A collision-based beacon rate adaptation scheme(CBA) for VANETs

Safety applications in VANET use two types of messages (a)periodical messages/beacons: they are broadcast several times per second to exchange information with neighbors; and (b) warning (event driven) messages: they are generated when an event occurs (e.g., a car accident) and are disseminated in the network to notify nodes of interest. Although warning messages have higher priority, beacons are equally as important since a good dissemination strategy usually relies on information provided by beacons to choose forwarding nodes. However, in dense networks, beacons may cause network congestion leading to performance degradation of safety applications. In this paper, we propose CBA: a congestion control approach that uses the number of detected collisions as a metric to control the beacon generation frequency and therefore reduce the effect of congestion. Simulation results show that our proposed scheme achieves a balanced trade-off between beacon information accuracy and beacon related overhead.

Congestion control in vehicular networks using network coding

Beacon messages are periodic 1-hop broadcast messages which are sent by each vehicle to let neighboring vehicles/infrastructures be aware of its position, speed, and change of direction. Beacon information plays a crucial role for many applications including active safety applications through which vehicles can predict the position of neighboring vehicles and be able to take instant decisions to avoid any emergency situation. However, such influx of broadcast messages may lead to beacon overhead and congestion. These result in low message reception as well as excessive delay. Beacon overhead and congestion may affect emergency messages, channel arbitration messages and other control messages which share a common channel as specified by DRSC/WAVE. This paper proposes a mechanism for controlling beacon overhead by adopting packet level network coding. The simulations prove that our scheme has higher packet delivery ratio and higher successful channel utilization compared to CSMA/CA protocol.

A Novel Architecture and Mechanism for On-Demand Services in Vehicular Networks with Minimum Overhead in Target Vehicle Tracking

Vehicular Ad hoc Networks (VANETs) are one of the building blocks for future Intelligent Transportation Systems (ITS). They will support applications for safety and entertainments on the streets. VANETs also provide an excellent potential for on-demand services. Such services in VANETs require real-time request-reply routing between vehicle client and service provider, and also tracking of client location. The vehicle requesting for a service acts as a client. The service provider communicates with clients through fixed base stations. Due to frequent link break- ups in VANET communications, maintaining a one-to- one communication path between service provider and client is an open issue. We refer to such one- to-one communication as the unicast service. In this paper, we propose a novel architecture to solve the unicast service provisioning and vehicle tracking in an integrated manner. Simulation results show that our proposed model reduces network overhead dramatically, and provides an on- demand unicast service with acceptable delivery delay and delivery ratio.

DMAP: Density Map Service in City Environments

Vehicle density information is crucial for efficient functioning of many vehicular applications, including emergency notification, driver assistance, and infotainment applications. This information is used for evacuation planning in accident scenarios, finding alternate routes in the case of road congestion, and providing stable routing paths for uninterrupted internet connections. In a city scenario, it is a tedious task to continuously collect and share large volumes of data containing density information. In this paper, we propose a mechanism to create a density map for city environments. A hierarchy (i.e., tree) is established, where a node represents a road segment and the density is used to determine the height of the node; the root node represents the road segment having highest density. The purpose of this tree is to collect and aggregate density information starting from the leaves until the root node is reached. Then, the aggregated density information (i.e., density map) is forwarded down the hierarchy. For efficient aggregation of density information, we adopt an effective curve-fitting method where data are represented in an equation. Simulation results show that the proposed mechanism allows highly accurate computing of density map while generating low network overhead.

Inter street interference cancelation in urban vehicular networks using network coding

An urban scenario is the center stage for vehicles to roam around the concrete jungle. Any sorts of wireless communication would be affected by hidden terminal problems, fading and interferences. Unintended nodes are unnecessarily bothered by such huge volume of microwave communications. The most common forms of communication are beaconing messages, which let the vehicles know about its neighboring vehicles and possibly choose an appropriate forwarder for safety and non-safety messages. However, such influx of broadcast messages may lead to beacon overhead and congestion resulting in low message reception as well as excessive delay. Interferences due to inter-street beacon messages may affect emergency messages, channel arbitration messages and other control messages which share a common channel as specified by DRSC/WAVE. This paper proposes a scheme to cancel interferences due to inter-street beacon communications by adaptive transmission control, while maintaining application layer transmission range, through multi-hop beacon forwarding and network coding. The simulations show that our scheme has higher packet delivery ratio and higher successful channel utilization compared to CSMA/CA protocols.