BITS Faculty Publications
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Item RD-TDMA: A Randomized Distributed TDMA Scheduling for Correlated Contention in WSNs(IEEE, 2014) Bhatia, AshutoshIn wireless sensor networks (WSNs), contention occurs when two or more nodes in a proximity simultaneously try to access the channel. The contention causes collisions, which are very likely to occur when traffic is correlated. The excessive collision not only affects the reliability and the QoS of the application, but also the lifetime of the network. It is well known that random access mechanisms do not efficiently handle correlated-contention, and therefore, suffer from high collision rate. Most of the existing TDMA scheduling techniques try to find an optimal or a sub-optimal schedule. Usually, the situation of correlated-contention persists only for a short duration, and therefore, it is not worthwhile to take a long time to generate an optimal or a sub-optimal schedule. We propose a randomized distributed TDMA scheduling (RD-TDMA) algorithm to quickly generate a feasible schedule (not necessarily optimal) to handle correlated-contention in WSNs. In RD-TDMA, a node in the network negotiates a slot with its neighbors using the message exchange mechanism. The proposed protocol has been simulated using the Castalia simulator to evaluate its runtime performance. Simulation results show that the RD-TDMA algorithm considerably reduces the time required to schedule.Item A Design for Performance Improvement of Clock Synchronization in WSNs Using a TDMA-Based MAC Protocol(IEEE, 2014) Bhatia, AshutoshClock synchronization in a wireless sensor network (WSN) is quite essential as it provides a consistent and a coherent time frame for all the nodes across the network. Typically, clock synchronization is achieved by message passing using a contention-based scheme for media access, like carrier sense multiple access (CSMA). The nodes try to synchronize with each other, by sending synchronization request messages. If many nodes try to send messages simultaneously, contention-based schemes cannot efficiently avoid collisions. In such a situation, there are chances of collisions, and hence, message losses, which, in turn, affects the convergence of the synchronization algorithms. However, the number of collisions can be reduced with a frame based approach like time division multiple access (TDMA) for message passing. In this paper, we propose a design to utilize TDMA-based media access and control (MAC) protocol for the performance improvement of clock synchronization protocols. The basic idea is to use TDMA-based transmissions when the degree of synchronization improves among the sensor nodes during the execution of the clock synchronization algorithm. The design significantly reduces the collisions among the synchronization protocol messages. We have simulated the proposed protocol in Castalia network simulator. The simulation results show that the proposed protocol significantly reduces the time required for synchronization and also improves the accuracy of the synchronization algorithm.Item A TDMA-Based Energy Aware MAC (TEA-MAC) Protocol for Reliable Multicast in WSNs(IEEE, 2014) Bhatia, AshutoshMulticast in wireless sensor networks (WSNs) is an efficient way to spread the same data to multiple sensor nodes. It becomes more effective due to the broadcast nature of wireless link, where a message transmitted from one source is inherently received by all one-hop receivers, and therefore, there is no need to transmit the message one by one. Reliable multicast in WSNs is desirable for critical tasks like code updation and query based data collection. The erroneous nature of wireless medium coupled with limited resource of sensor nodes, makes the design of reliable multicast protocol a challenging task. In this work, we propose a time division multiple access (TDMA) based energy aware media access and control (TEA-MAC) protocol for reliable multicast in WSNs. The TDMA eliminates collisions, overhearing and idle listening, which are the main sources of reliability degradation and energy consumption. Furthermore, the proposed protocol is parametric in the sense that it can be used to trade-off reliability with energy and delay as per the requirement of the underlying applications. The performance of TEA-MAC has been evaluated by simulating it using Castalia network simulator. Simulation results show that TEA-MAC is able to considerably improve the performance of multicast communication in WSNs.Item A Fast and Fault-Tolerant Distributed Algorithm for Near-Optimal TDMA Scheduling in WSNs(IEEE, 2014) Bhatia, AshutoshThe time division multiple access (TDMA) based channel access mechanisms perform better than the contention based channel access mechanisms, in terms of channel utilization, reliability and power consumption, specially for high data rate applications in wireless sensor networks (WSNs). Most of the existing distributed TDMA scheduling techniques can be classified as either static or dynamic. The primary purpose of static TDMA scheduling algorithms is to improve the channel utilization by generating a schedule of smaller length. But, they usually take longer time to schedule, and hence, are not suitable for WSNs, in which the network topology changes dynamically. On the other hand, dynamic TDMA scheduling algorithms generate a schedule quickly, but they are not efficient in terms of generated schedule length. In this paper, we propose a novel scheme for TDMA scheduling in WSNs, which can generate a compact schedule similar to static scheduling algorithms, while its runtime performance can be matched with those of dynamic scheduling algorithms. Furthermore, the proposed distributed TDMA scheduling algorithm has the capability to trade-off schedule length with the time required to generate the schedule. This would allow the developers of WSNs, to tune the performance, as per the requirement of prevalent WSN applications, and the requirement to perform re-scheduling. Finally, the proposed TDMA scheduling is fault-tolerant to packet loss due to erroneous wireless channel. The algorithm has been simulated using the Castalia simulator to compare its performance with those of others in terms of generated schedule length and the time required to generate the TDMA schedule. Simulation results show that the proposed algorithm generates a compact schedule in a very less time.Item UMAC: A Universal MAC protocol for Wireless Networks(ACM Digital Library, 2014-10) Bhatia, AshutoshThere are a number of wireless networks such as MANETs, WSNs, WLANs, BAN etc. which have come into prominence during the past several decades because of various kinds of requirements. From the very beginning, the design of various MAC protocols for these networks has been considered independently, targeting a few specific issues of the networks. Additionally, due to lack of compatibility with older protocols, various MAC protocols designed for wireless networks and available in the literature are not widely used in practice. We strongly believe that there is a requirement for a universal MAC (UMAC) protocol for mobile devices with multiple type of sensors, which can be used for a large spectrum of applications with different parametric requirements, deployment scenarios and device capabilities. In this paper, we first propose the design guidelines for such a UMAC, and then give an implementation of the same as an extension of IEEE 802.11 MAC, and the performance analysis of the proposed UMAC.Item A Distributed TDMA Slot Scheduling Algorithm for Spatially Correlated Contention in WSNs(Wiley, 2015-02) Bhatia, AshutoshIn WSNs the communication traffic is often time and space correlated, where multiple nodes in a proximity start transmitting simultaneously. Such a situation is known as spatially correlated contention. The random access method to resolve such contention suffers from high collision rate, whereas the traditional distributed TDMA scheduling techniques primarily try to improve the network capacity by reducing the schedule length. Usually, the situation of spatially correlated contention persists only for a short duration, and therefore generating an optimal or suboptimal schedule is not very useful. Additionally, if an algorithm takes very long time to schedule, it will not only introduce additional delay in the data transfer but also consume more energy. In this paper, we present a distributed TDMA slot scheduling (DTSS) algorithm, which considerably reduces the time required to perform scheduling, while restricting the schedule length to the maximum degree of interference graph. The DTSS algorithm supports unicast, multicast, and broadcast scheduling, simultaneously without any modification in the protocol. We have analyzed the protocol for average case performance and also simulated it using Castalia simulator to evaluate its runtime performance. Both analytical and simulation results show that our protocol is able to considerably reduce the time required for scheduling.Item DSLR: A Distributed Schedule Length Reduction Algorithm for WSNs(IEEE, 2015) Bhatia, AshutoshWireless sensor networks (WSNs) benefit from theMAC protocols that reduce power consumption by avoiding frame collisions. Time Division Multiple Access (TDMA) method provides collision free channel access by employing a pre-defined schedule so that the nodes can transmit at their allotted time slots. Most of the existing distributed TDMA-scheduling techniques for WSNs either try to improve the channel utilization by generating compact schedule which usually takes longer time, or generate schedule quickly, that may not be very efficient in terms of the schedule length. In this paper, we present a new approach to TDMA-scheduling for WSNs, that bridges the gap between these two extreme types of TDMA-scheduling techniques, by providing the flexibility to trade-off the schedule length with the time required to generate the schedule, as per the requirements of the underlying applications and channel conditions. The idea into generate a TDMA-schedule quickly using any of the existing algorithms, and then progressively reduce the TDMA-schedule length. In this context, we provide a distributed schedule length reduction (DSLR) algorithm which can be terminated after the execution of arbitrary number of iterations, and still bereft with a valid schedule. Additionally, unlike other TDMA-scheduling algorithms which use contention-based channel access, the DSLR algorithm uses TDMA-based channel access to perform the schedule reduction. The algorithm has been simulated using the Castalia simulator to compare its performance with those of others in terms of generated schedule length and the time required to generate the TDMA-schedule. Simulation results confirm the effectiveness of the approach, and show that the proposed algorithm generates a compact schedule in much less time in comparison to existing approaches.Item TRM-MAC: A TDMA-based reliable multicast MAC protocol for WSNs with flexibility to trade-off between latency and reliability(Elsevier, 2016-07) Bhatia, AshutoshMulticast in wireless sensor networks (WSNs) is an efficient way to deliver the same data to multiple sensor nodes. Reliable multicast in WSNs is desirable for critical tasks like code updation and query based data collection. The erroneous nature of the wireless medium coupled with limited resources of sensor nodes, makes the design of reliable multicast protocol a challenging task. In this paper, we propose a framework for reliable multicast transmission in WSNs using TDMA-based channel access which works on top of a Multicast Spanning Tree (MST) rooted at the base station. The existing TDMA-based MAC protocols do not provide any mechanism to handle the collision and explosion of feedback messages, and therefore, they cannot be used in the proposed framework to support reliable multicast. To handle this issue, we propose a TDMA-based reliable multicast MAC (TRM-MAC) protocol for WSNs. The TRM-MAC protocol is parametric in the sense that it can be used to trade-off between reliability and delay performance, as per the requirement of the underlying applications. We have analyzed the TRM-MAC protocol to evaluate its delay and reliability performance at different packet loss rates, and have also compared its performance with those of others using simulation study. Both simulation and analytical results show that the TRM-MAC protocol considerably improves the performance of multicast communication in WSNs.Item A Two-Phase Scheme for Distributed TDMA Scheduling in WSNs with Flexibility to Trade-off between Schedule Length and Scheduling Time(2019) Bhatia, AshutoshThe existing distributed TDMA-scheduling techniques can be classified as either static or dynamic. The primary purpose of static TDMA-scheduling algorithms is to improve the channel utilization by generating a schedule of shorter length. But, they usually take a longer time to schedule, and hence, are not suitable for WSNs, in which the network topology changes dynamically. On the other hand, dynamic TDMA-scheduling algorithms generate a schedule quickly, but they are not efficient in terms of generated schedule length. In this paper, we propose a new approach to TDMA scheduling for WSNs, that bridges the gap between the above two extreme types of TDMA-scheduling techniques, by providing the flexibility to trade-off between the schedule length and the time required to generate the schedule (scheduling time). The proposed TDMA scheduling works in two phases. In the first phase, we generate a TDMA schedule quickly, which need not have to be very efficient in terms of schedule length. In the second phase, we iteratively reduce the schedule length in a manner, such that the process of schedule length reduction can be terminated after the execution of an arbitrary number of iterations, and still be left with a valid schedule. This step provides the capability to trade-off between schedule length and scheduling time. We have used Castalia network simulator to evaluate the performance of proposed TDMA-scheduling scheme. The simulation result together with theoretical analysis shows that in addition to the advantage of trading-off the schedule length with scheduling time, the proposed TDMA scheduling approach achieves better performance than existing algorithms in terms of schedule length and scheduling time.Item Exploiting Multiple Paths in Multi-hop Co-operative Ad-Hoc Networks for Providing Security without Trusted Third Party(Springer, 2019-03) Bhatia, AshutoshEnsuring secure communication in large scale wireless networks is a challenging issue, especially when the nodes participating in the network itself cannot be trusted fully. This situation is very much pertinent in the case of multi-hop wireless cooperative networks, where the nodes co-operate with each other to support multi-hop communication in the network. In such networks, assuming the presence of a trusted third party to provide key exchange and authentication services in the network is not viable. Additionally, the classical Diffie-Hellman based key establishment mechanism as such cannot be used because of Man-In-The-Middle and impersonation attacks, as the nodes participating in a multi-hop path from source to destination cannot be trusted. In this paper, we investigate the use of the multi-paths and secret sharing in multi-hop cooperative adhoc networks to provide practical secure communication between the nodes in the network. We propose a couple of routing algorithms that give multiple-paths to send different segments of information required to be communicated securely, under various behavioral models of the participating nodes. The simulation results show that the majority of times, we are able to find the multiple paths in the network through which the different segments of a piece of information can be sent to achieve desirable security.