Dharmaraja Selvamuthu

• PhD
• Professor (Full) at Indian Institute of Technology Delhi

Due to the increasing demand of the tethered high altitude platform (HAP) systems, it is imperative to assess their power consumption along with their deployment. This study considers the power management of lithium-ion batteries based tethered HAP systems for wireless communications service provisioning. This article discusses a novel model based...

An analytical model for tethered high altitude platform (HAP) systems, that handle voice, video, and data traffic, is presented in this work. The Markovian arrival process (MAP) is used to depict the arrival of traffic due to the burstiness and self-similar properties of the incoming traffic. Guard channel policy has been employed for the prioritiz...

An M/M/1/DV queueing system with a dual-threshold policy, vacation interruption and a waiting server are analysed in this paper. Power-saving mechanisms (PSM) of WiMAX could be modelled using this model. In the investigated model, after transmitting all the data frames in the awake state, the server switches to the sleep state for some random durat...

In India, the number of infections is rapidly increased with a mounting death toll during the second wave of Coronavirus disease (COVID-19). To measure the severity of the said disease, the mortality rate plays an important role. In this research work, the mortality rate of COVID-19 is estimated by using the Susceptible-Exposed-Infected-Recovered-D...

This article deals with single server queue with modified vacation policy. The modified vacation policy captures the operation of a close down period, type 1 vacation period, type 2 vacation period, a start-up period and a dormant period. Here, type 1 vacations takes a short period of random duration and type 2 vacation take a long period of random...

Recent development in communications have increased the demand of internet protocol (IP)-based multimedia conferencing services. Session initiation protocol (SIP) is a signaling protocol used for providing group communication in IP-based next generation network. The conferencing frameworks proposed by Internet Engineering Task Force working groups...

Over the years, the authors have witnessed tremendous growth in mobile data traffic. To address the capacity requirements, the mobile network operators (MNOs) are adding more radio nodes and spectrum layers. The spectrum layers vary in quality of service (QoS), utilisation and usage fee. To save operational costs, the MNOs could share their radio n...

Self-exciting point processes are applied to various fields such as seismology, finance, neurophysiology, criminology, biology etc to model the clustering/contagion phenomenon and extreme risk events. This article proposes an analytically tractable point process, a generalization of the classical Hawkes process, with the intensity process following...

In LTE-A, Carrier Aggregation allows the user to simultaneously transmit and receive data on multiple carriers resulting in increased throughputs. The Radio Resource Management (RRM) framework of Long Term Evolution (LTE) is thus modified, as not one but more Component Carriers (CCs) are assigned to the user. The CC selection mechanism has to be ca...

To address the capacity requirements resulting from huge growth in mobile data traffic, the mobile network operators (MNOs) are densifying their networks with more base stations, and with more spectrum layers. The addition of base stations and spectrum layers increases the energy consumption of the access network. Hence the network needs to be opti...

During the Discontinuous Reception (DRX) mechanism, a User Equipment (UE) turns off most of its components for a prolonged period. The battery charge of a UE, which is a continuous quantity, arises as a fluid model. In this scenario, we represent the system as the reservoir where battery charge gets accumulated or is depleted gradually over the tim...

During the Discontinuous Reception (DRX) mechanism, a User Equipment (UE) turns off most of its components for a prolonged period. The battery charge of a UE, which is a continuous quantity, arises as a fluid model. In this scenario, we represent the system as the reservoir where battery charge gets accumulated or is depleted gradually over the tim...

Power saving and Quality of Service (QoS) are the two significant aspects of Long Term Evolution-Advanced (LTE-A) networks. DRX (“Discontinuous Reception”) is a mechanism, commonly exercised to enhance the power saving competency of a User Equipment (UE) in LTE-A networks. In this paper, based on the kind of traffic running at the UE, a new applian...

Power saving and Quality of Service (QoS) are the two significant aspects of Long Term Evolution-Advanced (LTE-A)networks. DRX (“Discontinuous Reception”) is a mechanism, commonly exercised to enhance the power saving competencyof a User Equipment (UE) in LTE-A networks. In this paper, based on the kind of traffic running at the UE, a new appliance...

In the next generation wireless networks, various radio access technologies will coexist through multinode receivers and antennas, in which Quality of Service (QoS) and user experience are the utmost priorities. A scheme called Joint Call Admission Control (JCAC) plays an important role in making a decision that, whether a coming call request shoul...

Power saving is a leading issue in the User Equipment (UE) for limited source of power in Long Term Evolution-Advanced (LTE-A) networks. Battery power of an UE gets exhaust quickly due to the heavy use of many service applications and large data transmission. Discontinuous reception (DRX) is a mechanism used for power saving in UE in the LTE-A netw...

Vehicular ad hoc network (VANET) is a technology that facilitates communication between vehicles by creating a 'mobile Internet'. The system aims at ensuring road safety and achieving secured commutation. For this reason, reliability and survivability of the network become matters of prime concern. Reliability and survivability of the network is im...

Voice over Internet Protocol (VoIP) or Internet telephony has become an evolutionary and promising technology in the area of telecommunications. Lower costs and simpler maintenance are the major reasons of its increasing popularity. However, the network is inherently unreliable and highly challenged when it comes to quality of service (QoS). The Vo...

In this paper, we propose to study the performance of a multi-server queuing system in which a customer requires simultaneous service from a random number of servers with the queuing disciplines retrial and preemptive priority. The infinitesimal generator matrix is presented for the proposed model and steady state measures are discussed. In particu...

Nowadays Voice over IP (VoIP) has become an evolutionary technology in telecommunications. Because of the increasing dependencies of people on VoIP for voice communication, it is important to design a reliable and performance oriented VoIP system. In this paper a hierarchical model combining reliability and performance is proposed for a server base...

Vehicular ad hoc network (VANET) is a technology that enables communication amongst the vehicles by creating mobile Internet. The primary purpose of VANET is road safety and security, besides private communication. Hence reliability and survivability of the network become matters of prime concern. Reliability and survivability of the network is imm...

An easily accessible, real-world approach to probability and stochastic processes Introduction to Probability and Stochastic Processes with Applications presents a clear, easy-to-understand treatment of probability and stochastic processes, providing readers with a solid foundation they can build upon throughout their careers. With an emphasis on a...

In wireless networks, the system capacity can vary unpre-dictably with time, due to mobility of users and dynamic channel assignment protocols. This variation in capacity with time, known as 'stochastic capacity', can have a major impact on the performance measures such as call blocking probabil-ity and queueing delay, of the wireless networks. The...

Wireless cellular networks experience the handoff phe-nomenon, in which a call already in progress in a cell due to user mobility is "handed-over" (switched) to another cell. A common assumption in most of these dimensioning models is that call cell arrival processes (both for new and handoff) are Poisson. Call service time distributions and cell r...

Nowadays VoIP has become an evolutionary technology in telecommunications. Hence it is very important to study and enhance its dependability attributes. In this paper, an analytical dependability model for VoIP is proposed. The study is focused on analyzing the combined effects of resource degradation and security breaches on the Quality of Service...

Volatility has a significant role to play in the determination of risk and in the valuation of options and other financial derivatives. The well-known Black-Scholes model for the financial derivatives deals with constant volatility. This paper presents a new model based on shot noise behaviour, in which the volatility jump occurs in random instant...

The lack of centralised infrastructure in adhoc network makes it vulnerable to various attacks. MANET routing disrupts if the participating node start performing malicious activity instead of the intended function. One such specific attack is a blackhole attack in which malicious node falsely claiming itself as having the fresh and shortest path to...

Survivability is the capability of a system to fulfill its mission in a timely manner in the presence of failures, attacks and accidents. In this paper, quantitative assessment of survivability of cellular networks is conducted by developing an analytical model using Markov chains. A stochastic reward net model is then developed for the automated g...

The lack of centralised infrastructure in ad hoc network makes it vulnerable to various attacks. MANET routing disrupts if participating node do not perform its intended function and start performing malicious activity. A specific attack called Wormmhole attack enables an attacker to record packets at one location in the network, tunnels them to an...

This paper presents an analytical approach to model the bi-directional multi-channel IEEE 802.11 MAC protocols (Bi-MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The obj...

TCP (Transmission Control Protocol) is one of the protocols which are widely used in Internet environments. This paper presents an analytical model developed using the stochastic reward net (SRN) modeling technique for the TCP flow behavior in WLANs. The purpose of developing an analytical model is the evaluation of stationary TCP flow behavior. In...

We present a fluid queue model driven by two independent finite state birth–death processes with the objective to study the buffer occupancy distribution in any intermediate node in a communication network. In a communication network, at any node, the arrival and service of the packets are with variable rates. To model this scenario we develop a fl...

The increase in multimedia usage places stringent requirements on wireless network performance in terms of lesser handoff delays. A VOIP client, for example, cannot tolerate a delay larger than 150 ms between the incoming voice packets to ensure a satisfactory interactive service to the user. Of the 150ms, only 50ms is allowed for handoff and the r...

Mobile devices generates a call request message while initiating a call, which is then sent to a base station (BS). A BS processes a call request message and then takes a decision of acceptance or rejection for the call. It is important to analyze the total time, which includes the waiting time and the processing time, spent by a call request messa...

Nowadays Voice over Internet Protocol (VoIP) has become an evolutionary technology in telecommunications, and hence it is very important to study and enhance its survivability measures. In this paper, an analytical framework of survivabil- ity model for VoIP is proposed. The study is mainly focused on analyzing the combined effects of resource degr...

Reliability and survivability are the two important attributes of cellular networks. In the existing literature, these measures were studied through the simulation. In this paper, we construct an analytical model to determine reliability and survivability attributes of third generation and beyond Universal Mobile Telecommunication Systems (UMTS) ne...

We present an overview of evaluating the reliability of the complex systems with Markov modeling. In this article, the definition of reliability and the description of basic reliability models are given. Markov models are discussed in detail and illustrations are provided to explain the technique of Markov modeling.

This paper presents energy aware greedy routing (EAGR) scheme for wireless ad hoc networks. In this scheme, the cost metric of a node depends on the following parameters of a neighboring node: (1) Distance from the destination, (2) fraction of energy consumed, and (3) rate of energy consumption. When a node has the least cost metric, the packet is...

This paper presents an analytical model for cellular networks supporting voice, video and data traffic. Self-similar and bursty nature of the incoming traffic causes correlation in inter-arrival times of the incoming traffic. Therefore, arrival of calls is modeled with Markovian arrival process as it allows for the correlation. Call holding times,...

For cellular communication systems, mobility and limited radio coverage of a cell require calls to be handed over from one base station system (BSS) to another. Due to the limited bandwidth available in various cells, there is a finite probability that an ongoing call, while being handed off, may get dropped. Minimizing the dropping of ongoing call...

SUMMARY In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11-based wireless local area networks (WLANs). We consider the distributed co- ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily cap...

In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11 based wireless local area networks (WLANs). We consider the distributed co-ordination function (DCF) mode of medium access control (MAC). The current literature provides very few models to analyze the DCF performance. Existing a...

Handoff is an important issue in cellular mobile telephone systems. Recently, studies that question the validity of the assumption of handoff arrivals being Poissonian have appeared in the literature. The reasoning behind this claim can be summarized as follows: even if the new call arrival process is assumed to be Poisson, the handoff process due...

The high expectations of performance and availability for wireless mobile systems has presented great challenges in the modelling and design of fault tolerant wireless systems. The proper modelling methodology to study the degradation of such systems is so-called performability modelling. In this paper, we give overview of approaches for the constr...

In this paper, we report our recent work on closed form solutions to the blocking and dropping probability in wireless cellular networks with handoff. First, we develop a performance model of a cell in a wireless network where the effect of handoff arrival and the use of guard channels are included. Fast recursive formulas for the loss probabilitie...

The NASA Remote Exploration and Experimentation (REE) Project, managed by the Jet Propulsion Laboratory, has the vision of bringing commercial supercomputing technology into space, in a form which meets the demanding environmental requirements, to enable a new class of science investigation and discovery. Dependability goals of the REE system are 9...

Recently, the phenomenon of "software aging", one in which the state of a software system gradually degrades with time and eventually leads to performance degradation or crash/hang failure, has been reported. Preventive maintenance of operational software systems is used specifically to counteract this phenomenon. However preventive maintenance inc...

In this paper, we report our recent work on closed form solutions to the blocking and dropping probability in wireless cellular networks with handoff. First, we develop a performance model of a cell in a wireless network where the effect of handoff arrival and the use of guard channels are included. Fast recursive formulas for the loss probabilitie...

Most of the real-time applications involve connection establishment in point-to-point (unicast) communication in computer networks that can be modelled as a problem of resource allocation and resource sharing. These applications have different streams, such as video, voice, graphics, etc., each having different arrival rates. A stream (call) will b...

A two-processor system heterogeneous with Poisson arrival of jobs having exponentially distributed execution times is considered. Here, the service rates of these processors are not identical. Each job requires exactly one processors for its execution and the scheduling policy is FCFS. When both the processors are idle, the faster processor is sche...

The transient solution is obtained for a multiprocessor system with multiple Poisson streams of task and exponential execution times. Each task requires exactly one processor for its execution and the scheduling policy is FCFS. The scheduler schedules a newly arriving task into any one of the idle processors, and the task is rejected if there is no...

The finite set of rate equations C m,n ' (t)=α n,n-1 C m,n-1 (t)+α n,n C m,n (t)+α n,n+1 C m,n+1 (t),0≤m≤N,0≤n≤N, where α i,j are α j,j-1 =A, α j,j =-(A+B), α j,j+1 =B, with α 0,0 =-α 1,0 =-a and α N,N =-α N-1,N =-b, α 0,-1 =α N,N+1 =0, subject to the initial condition C m,n (0)=δ n,m (Kronecker delta) for some m, arises in a number of applications...

A stochastic model for the rate of conformational change in freely-jointed chain of two regularly alternating kinds of beads joined by bonds with end effects is considered. Using explicit transformations the exact time-dependent average length of bond vectors are derived as a sum of exponentials involving roots of an underlying polynomial. These ro...

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Survivability analysis measure the degree of function-ality remaining in a system after failures. It consists of evaluating metrics which quantify the system perfor-mance during failure scenarios as well as in normal oper-ation. Existing research work in this area discusses fault tolerant architecture of cellular networks and analyze impact of fail...