C Siva Ram Murthy

A major issue in the energy-constrained ad hoc wireless networks is to find ways that increase their lifetime. The communication protocols need to be designed such that they are aware of the battery state. They should also consider the presence of varying sizes and models of the nodes' batteries. Traditional MAC protocols of these networks are designed considering neither the state nor the characteristics of the batteries of the nodes. Major contributions of this paper are: (a) a novel distributed heterogeneous Battery Aware MAC (HBAMAC) protocol, that takes benefit of the chemical properties of the batteries and their characteristics, to provide fair node scheduling and increased network and node lifetime through uniform discharge of batteries, (b) theoretical analysis, using discrete time Markov chains, for batteries of the nodes, and (c) a thorough comparative study of our protocol with IEEE 802.11 and DWOP (Distributed Wireless Ordering Protocol) MAC protocols. © Springer-Verlag 2004.

In this paper, the problem of optimal distribution of measurement data to be processed in minimal time on a hypercube network of sensor driven processors is considered. An analytical model is developed for solving the problem efficiently. Unlike the previous models, this model considers 1) explicitly the setup time which constrains exploiting all the available processors; 2) simultaneous use of links to expedite the communication; 3) partial solution combining time to encompass wider class of related problems. By deriving a lower bound on the amount of data to be received by a processor for efficient distribution, a new technique called fractal hypercube is introduced here to get the optimal solution with fewer processors. An optimal iterative method for hypercubes and a near-optimal recursive method with a refinement are presented for the same with the analysis. The effect of varying the originating processor and the choice of fractal hypercube are discussed with an effective technique called processor isomorphism. This study reveals that always the fractal hypercubes outperform the other two methods, the optimal iterative method for hypercubes and the near-optimal method. © 1998 IEEE.

In Heterogeneous cellular networks (HetNets), co-channel interference is a major concern due to the co-existence of multiple base stations with overlaid regions. Edge users are typically the victims because of high interference exposure. To counter this high interference, picocells communicate with the edge users in protected subframes (PSF). The severity of the problem intensifies in case of hotspot deployment, where picocells cannot provide coverage to the entire hotspot, thus forming a dense ring of macrocell users around picocells. We argue that these macrocell users are also victims, constituting a significant victim user population in hotspot deployment. We propose that, along with the macrocell muting during PSF, picocells should also be operated in cooperative manner with macrocell, and be barred from transmission during some of the subframes for protection of these macrocell victim users. We define a utility function to find the optimal values of PSF density for both macrocell and picocells, which would increase victim user throughput thereby enhancing system fairness. Exhaustive simulations illustrate that the proposed scheme improves victim user throughput significantly, while maintaining the overall system capacity. © 2014 IFIP.

The rapid growth of multicast applications initiated the need to realise multicasting in Wavelength Division Multiplexing (WDM) networks in an efficient and cost-effective way. However, most of the applications need to support dynamic multicast sessions wherein the membership of the multicast group changes with time as nodes join or leave the session dynamically. In addition, with the advancements in the multimedia and other real-time group applications, the construction of multicast trees satisfying Quality of Service (QoS) requirements of the member nodes is becoming a problem of prime importance. In this paper, we deal with on-line QoS multicast routing in WDM networks. As members leave the sessions, it will be mandatory to rearrange the trees in order to save costs, at the same time accounting for the disruption caused to the ongoing transmissions because of the rearrangement. We try to effectively decrease the disruption by considering only certain portions of the multicast tree and limiting the rearrangement to only those portions. A region's usefulness to the overall tree is judged by a novel concept of Cost-to-Service Ratio (CSR) and a region is selected for rearrangement based on its CSR value. Extensive simulation results reveal that rearrangements based on CSR can reduce the disruption to the member nodes by 20-85% compared to rearrangements based on the best known metric (Quality Factor) in the literature, for the same cost performance. We also demonstrate the cost-effectiveness of the trees generated by our on-line algorithm compared to that of static algorithm. © 2006 Elsevier B.V. All rights reserved.

In this paper, we consider the problem of solving a sparse system of linear equations using a new LU factorization based algorithm. The algorithm employs a new technique called two-sided factorization to produce the complete solution by solving only one triangular system after the factorization phase against the solution of two triangular systems in the existing LU factorization based methods. The effectiveness of the new algorithm in solving sparse linear systems on hypercubes is demonstrated using IEEE standard power system networks as benchmarks.

Vehicular Ad-hoc NETworks (VANETs) have lately gained the interest of researchers due to their unique properties of high mobility and constantly changing network topology. As mentioned in IEEE 802.11p which is the standard for VANETs, CSMA is used as the channel access mechanism. However, CSMA causes high contention and leads to lower network performance in terms of packet delivery ratio and average end-to-end delay. Many-to-Many (M2M) communication is a technique which makes use of simultaneous transmission of packets by using Code Division Multiple Access (CDMA). Although M2M communication helps to improve the performance of VANETs, further improvements can be done to fully reap the benefits of M2M communication. In this paper, we suggest piggybacking of information along with M2M communication in a vehicular network scenario. This leads to dissemination of more information from a vehicle at a time, thereby increasing the average packet delivery ratio and average end-to-end delay. Our simulation results confirm that piggybacking along with M2M communication helps to improve network performance in terms of packet delivery ratio and end-to-end delay. We mathematically analyse average packet delivery ratio and average end-to-end delay of such a system by modelling the buffers at vehicles and RSUs as M/M/1 and M/D/1 queues, respectively. Our analytical results are verified by extensive simulations. In M2M communication, vehicles are chosen randomly to enter in a communication session. In this paper, we formulate an optimization problem for selection of vehicles which can enter in a communication session and also propose an efficient vehicle selection algorithm for the same. Our proposed algorithm not only improves the average packet delivery ratio and average end-to-end delay of the network but also significantly reduces the number of packets dropped in the network.

The issue of providing fault-tolerance in real-time communication has been a problem of growing importance. There are two basic approaches for satisfying fault-tolerant requirements in real-time communication: (i) forward error recovery approach and (ii) detect and recovery approach. The first approach is well-suited for hard real-time communication, whereas the second approach is well-suited for soft real-time communication. Neither of these basic approaches is well-suited for supporting both hard and soft real-time communication. In this paper, we propose an integrated scheme that not only supports such a mixed communication requirements, but also improves the call acceptance rate significantly due to its efficient resource allocation mechanisms such as traffic dispersion and backup multiplexing. The effectiveness of the proposed scheme has been evaluated through extensive simulation studies. © 2002 Elsevier Science B.V. All rights reserved.

Several real-time applications require communication services with guaranteed timeliness and fault tolerance at an acceptable level of overhead. Different applications need different levels of fault tolerance and differ in how much they are willing to pay for the service they get. So, there is a need for a way of providing the requested level of reliability to different connections. We propose a new scheme based on the Primary-Backup approach for providing such service differentiation in a resource efficient manner. In our scheme, we provide partial backups for varying lengths of the primary path to enhance the reliability of the connection. We demonstrate the effectiveness of our scheme using simulation studies.

The problem of solving a linear system of equations is widely encountered in many fields of science and engineering. In this paper, we present a parallel algorithm to solve the above problem on a star graph. The proposed solution (i) is based on a variant of the Gaussian elimination algorithm (GE) called the successive Gaussian elimination algorithm (SGE) (IEE Proc. Comput. Digit. Tech. 143 (4) (1996)) and (ii) supports partial pivoting to provide numerical stability. We present efficient matrix distribution techniques on the star graph. Our proposed parallel algorithm employs these techniques to reduce communication overhead during matrix operations on the star graph. We estimate the performance of our parallel algorithm and demonstrate its effectiveness by comparing it with a recent algorithm for the same problem on star graphs (IEEE Trans. Parallel Distrib. Systems 8 (8) (1997) 803) © 2003 Elsevier Science (USA). All rights reserved.

In this paper, we present MuSeQoR: a new multi-path routing protocol that tackles the twin issues of reliability (protection against failures of multiple paths) and security, while ensuring minimum data redundancy. Unlike in all the previous studies, reliability is addressed in the context of both erasure and corruption channels. The reliability and security requirements of a session are specified by a user and are related to the parameters of the protocol adaptively. In addition, by using optimal coding schemes and by dispersing the original data, we minimize the redundancy. Finally, extensive simulations were performed to assess the performance of the protocol under varying network conditions. The simulation studies clearly indicate the gains in using such a protocol and also highlight the enormous flexibility of the protocol.