Subrat Kar

• PhD
• Professor at Indian Institute of Technology Delhi

Optical networks are now evolving due to the high bit rate demands of multimedia applications and internet services. These applications demand high bandwidth and the current fixed grid network can no longer work for data rate of 400Gbps or higher. This paper focuses on Link Margin (LM) and its effect on the spectrum saving for the demand of 100Gbps...

A compact, wideband, completely reconfigurable, and digitally controlled embedded instrument has been designed to generate a sawtooth waveform in the radio frequency regime. This instrument drives an RF structure called a Multi-Harmonic Buncher in a particle accelerator. Its main application is to time-bunch a DC or continuous ion beam for nuclear...

Developing a novel category of 2-D sparse arrays to improve information resolution with a minimum of possible actual sensors has proven to be a notable and persistent demanding objective. This study introduces a new layout for planar sparse arrays to estimate signal arrival angles in both azimuth and elevation dimensions. By introducing this new ca...

The massive data demand requires content distribution networks (CDNs) to use evolving techniques for efficient content distribution with guaranteed quality of service (QoS). The distributed fog-based CDN model, with optimal fog node placements, is a suggested aproach by researchers to meet this demand. While many studies have focused on improving Q...

Contour tracing is a critical technique in image analysis and computer vision, with applications in medical imaging, big data analytics, machine learning, and robotics. We introduce a novel hardware accelerator based on the adapted and segmented (AnS) vertex following (VF) and run-data-based-following (RDBF) families of fast contour tracing algorit...

We introduce “GajGamini”, a novel method for detecting elephant movement by analyzing ground vibrations recorded using seismic sensors. This method is based on the principle that ground vibrations from elephants are distinct from those caused by humans and background noise. In this paper, we address two main challenges. Firstly, there was a lack of...

In correlation-based processing, sparse arrays offer the capacity to resolve a greater number of uncorrelated sources than physical sensors due to the considerable breadth of their difference coarrays, originating from variations in the locations of elements. Consequently, there is significant interest in devising sparse arrays with sizable differe...

Efficient content distribution to end-users poses a significant challenge in content distribution networks (CDNs). Traditional CDNs rely on cloud-based architectures, which may not be optimal for delivering content in densely populated areas due to increased network latency and bandwidth limitations. These problems can be mitigated by adopting fog/...

Cognitive Buildings are a nascent area of research which envisions a paradigm shift from of a static notion of the building as a container of human activities to that of dynamic cyber-physical system capable of integrating, analysing and learning from the vast amount of sensor data generated from within a building and its environment. This paper pr...

This paper presents a novel technique that uses the stereoscopic arrangement of multiple cameras to determine the trajectory of a high-speed projectile. It can be used to detect and track artillery shells moving at high speed in the air toward friendly territory. A system with the proposed concept can enhance retaliation success in battlefield coun...

The manufacturing and characterization of freeform optical surfaces are influenced by their high sensitivity to misalignments. In this work, the computational sampling moiré technique combined with phase extraction is developed for the precise alignment of freeform optics during fabrication and in metrology applications. This novel, to the best of...

Torus networks connect processing elements in network-on-chips for several high-performance computing applications. Though square torus networks are the most popular, Rectangular Torus (RT) net- works are also used where the number of multiprocessors is con- strained. A twist in the rectangular torus topology can be used to reduce the average inter...

In biometrics, footstep-based seismic signals for person identification have become increasingly popular. Person identification is a crucial aspect because it serves as the foundation for personalized services like elderly monitoring, tailored access control, etc. However, these systems may not have enough data for specific individuals, especially...

With the advancement of technology in the field of VLSI, it is possible to integrate several computing elements onto a single chip. The performance of these single bus-based models still suffers from scalability on large-scale platforms. Therefore, network-on-chip (NoC) architecture integrating multiple cores in a single chip has emerged as an alte...

The term fractal refers to the fractional dimensions that have recursive nature and exhibit better array factor properties. In this article, we present a new class of sparse array where the recursive nature of a fractal can be used in designing an antenna array called a sparse fractal array by combining sparsity properties of the various sparse arr...

EONs (Elastic Optical Networks) form the backbone of web-scale cloud infrastructure. These networks should deal with network faults and restoration in real-time with high accuracy and scalability. Thus, fault management functions to detect and localize such failures, play a critical role in modern day EONs. Network impairments are complex in nature...

Received signal strength (RSS)-based localization techniques have attracted a lot of interest as they are easy to implement and do not require any localization-specific hardware. However, maximum likelihood (ML) formulation of RSS-based localization problem is non-convex, non-linear, and discontinuous, and cannot be solved using standard optimizati...

Designing a new class of rectangular two-dimensional sparse array to enhance the signal resolving capabilities with a limited number of sensors has always been a challenge. We explore the non-uniformity of the sparse arrays to enhance the Degrees of Freedom (DOF) by considering the under-determined cases using the concept of the virtual array. In t...

The optical signal-to-noise ratio (OSNR) and received optical channel power are critical parameters in determining the quality of transmission. The OSNR and received optical channel power are influenced by network impairments such as fiber loss, amplified stimulated emission noise, and nonlinear impairments. Furthermore, environmental effects and r...

The ability to determine the location of a sensor node in a wireless sensor network is essential in many applications. We propose a received signal strength (RSS) based cooperative localization technique. The target nodes, whose locations are unknown during the deployment phase, communicate with the anchor nodes (whose locations are known) and the...

Modern day particle accelerators use resonating RF cavities to generate high electric field for enhancing the kinetic energy of particles for beam acceleration. These RF cavities are made using normal conducting or superconducting material. A closed loop control electronics is applied to maintain stability of the field gradient inside the cavity in...

Contour tracing is an important pre-processing step in many image processing applications such as feature recognition, biomedical imaging, security and surveillance. As single processor architectures reach their performance limits, parallel processing architectures offer energy efficient and high performance solutions for real time applications. Pa...

The ability of a sensor node to determine its location in a sensor network is important in many applications. We address the scenario where malicious anchor node(s) attempt to disrupt, in an uncoordinated or coordinated manner, the localization process of a target node. We propose four localization techniques: weighted least square (WLS), secure we...

The objective is to detect landslide and report it as soon as it is detected so that appropriate measures can be taken in time in order to reduce the loss of life and infrastructure and to issue advisories to the public. A camera surveillance system with an image processing algorithm for 24/7 monitoring of flow is proposed to detect landslides. The...

In this paper, we present a person identification system for Internet of Things (IoT) based smart home applications that utilizes footstep induced structural vibrations as biometric modality. Footfall events are generated by rhythmic contact of heel and toe on the floor while walking. In case of such biometric systems, there is no disturbance of th...

Social IoT (or SIoT) is an alternate architectural pattern for IoT, which involves IoT devices with social behavioural attributes. A SIoT-based service network makes use of social collaboration between IoT devices to enable low-latency collaborative services and applications. A key challenge in implementing a SIoT-based service network in a multi-v...

In this work, we propose a novel unconstrained biometric authentication system that utilizes footstep generated seismic waves. It has the following advantages over existing systems: i) it doesn't require any special orientation or positioning of the individual for authentication, and ii) seismic data do not interfere with the individual's privacy....

In a wireless sensor network (WSN), locations of a few sensor nodes are assumed to be known at the time of deployment (known as anchor nodes) and localization techniques are used to estimate the locations of the other sensor nodes (known as target nodes). We consider a received signal strength (RSS) based localization problem for which the maximum...

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...

The ability of a sensor node to determine its location in a sensor network is important in many applications. The infrastructure for the location-based services is an easy target for malicious attacks. We address scenarios where malicious node(s) attempt to disrupt, in an uncoordinated or coordinated manner, the localization process of a target nod...

The objective of the study was to establish the characteristics of pedometer activity in crossbred cows (20) and to determine the relationships between the pedometer activity and the serum concentrations of periestrual hormones. Animals in oestrus were detected by trained personnel based on oestrus behaviour by visual observation twice daily. Furth...

Routing protocols in wireless sensor networks are critical as they affect performance, lifetime and scaling. A novel approach to collect data in sensor networks is presented in this paper. The end-user can configure devices to operate for a desired lifetime and achieve reliable operation for that duration—this is the motivation behind the developme...

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...

In this paper, we have analysed the performance of a one-coincidence frequency hopping code/quadratic congruence code (OCFHC/QCC) and compared its performance with an existing code. The error probabilities of an eight user optical code division multiple access (OCDMA) system are $4.7934\times10^{-9}$ and $5.9497\times10^{-10}$ for the synchronous p...

The probability of error of a new two‐dimensional (2D) code, one‐coincidence frequency hopping code/quadratic congruence code, atmospheric optical code division multiple access (OCDMA) system is evaluated with single hard limiter and double hard limiter in presence of weak, moderate and strong turbulence. In the atmospheric channel, weak turbulence...

Atmospheric turbulence causes severe impairment of FSO communication link. By using the earlier model for the Gaussian beam, we analyze the beam wander effect for the flat-topped multi-Gaussian beam. The link availability decreases drastically in high turbulence regime for a Gaussian beam due to turbulence induced beam wander. In this paper, we mod...

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...

Geotagging of sensor data in a wireless sensor network is important in many applications. It may not always be possible to record locations of the sensor nodes during deployment. Localization techniques provide the node location information, however most of these techniques rely on the neighboring nodes for localization. Thus it is essential that t...

Social Internet of Things (SIoT), an amalgamation of Social Networking concepts to the Internet of Things (IoT), is a strong architectural alternative for IoT solutions. A lot of research work in SIoT has proposed the use of social networking data for community and trust management in SIoT networks. While it seems like an interesting choice, it is...

Footfall based biometric system is perhaps the only person identification technique which does not hinder the natural movement of an individual. This is a clear edge over all other biometric systems which require a formidable amount of human intervention and encroach upon an individual's privacy to some extent or the other. This paper presents a Fo...

Atmospheric turbulence causes severe impairment of FSO communication link. Existing model underestimates the beam wander effect in high turbulence regime. In this paper, we model each turbulent eddy as a thin dielectric lens with Gaussian shaped refractive index profile and assume there are several sheets of eddies throughout the propagation path....

Passive infrared (PIR) sensors are sensitive to infrared (IR) rays and are mostly used for motion detection. In this paper we propose a mathematical model that enables better understanding of the analog response of the PIR sensor, the Fresnel lens, and the associated electronic circuitry. The proposed model relates the sensor's analog output wavefo...

The model can be used by engineers to design features of the Fresnel Lens, amplifier circuit, and sensor properties during the development phase of a PIR-based solution. The simulator can be used to simulate the analog response of a PIR sensor with different properties and Fresnel lens. This software tool will be an aid to the PIR sensor and Fresne...

In this paper, the performance of one-coincidence frequency hopping code/quadratic congruence code (OCFHC/QCC) is analysed and compared with the existing codes. The impact of variation in code weight, code length and number of wavelengths on error probability is evaluated. It is observed that for the same code weight, code length and number of avai...

In this paper, a comparative analysis of various performance enhancement techniques in two-dimensional (2-D) atmospheric optical code division multiple access (OCDMA) system is studied in presence of beam divergence, multiple access interference (MAI), noise and atmospheric turbulence. Lognormal and gamma-gamma probability density functions (pdfs)...

In this paper, a comparative analysis of various performance enhancement techniques in two-dimensional (2-D) atmospheric optical code division multiple access (OCDMA) system is studied in presence of beam divergence, multiple access interference (MAI), noise and atmospheric turbulence. Lognormal and gamma-gamma probability density functions (pdfs)...

In this paper, performance enhancement of one- coincidence frequency hopping code/quadratic congruence code (OCFHC/QCC) based two-dimensional (2-D) optical code divi- sion multiple access (OCDMA) system is studied using Reed- Solomon (R-S) code in presence of multiple user interference (MUI) and turbulence. Atmospheric turbulence is presumed to be...

Footstep-based systems have myriad uses like activity monitoring, person identification, and fall detection, to name a few. These highly perceptive systems employ seismic signals generated from human footfall events. Extraction of such events from a time-varying signal is a vital aspect of signal analysis. The essential quality of such an event det...

In the scenario of first laser communication relay satellite being launched into geostationary earth orbit, we evaluate the reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links in presence of turbulence and various weather conditions using spatial diversity technique. In channel modeling,...

Detection of intruders and predicting their activities are the first and foremost needs of surveillance. An embedded system employing geophone, adaptive event extraction and robust machine learning algorithms have made it possible not only to detect the presence of a potentially harmful intruder but also to predict to a high degree of accuracy, his...

Subrat Kar, Bodhibrata Mukhopadhyay, Sahil Anchal, “Diagnosis of subclinical mastitis in dairy animals,” (Filed Provisional Indian Patent Application No.: 201711034211 dated November 3, 2017)

The atmospheric turbulence has severe impact on the performance of FSO link. The eddy created by the turbulence can be modelled as Gaussian shaped dielectric lens. We assume there are multiple sheets of eddies between the transmitter and the receiver. Assuming the eddy sizes to be Chi-Square distributed, outcomes of our simulation show good correla...

In this paper, the effect of transmitter beam size on the performance of free space optical (FSO) communication has been determined experimentally. Irradiance profile for varying turbulence strength is obtained using optical turbulence generating (OTG) chamber inside laboratory environment. Based on the results, an optimum beam size is investigated...

In this paper, the effect of transmitter beam size on the performance of free space optical (FSO) communication has been determined experimentally. Irradiance profile for varying turbulence strength is obtained using optical turbulence generating (OTG) chamber inside laboratory environment. Based on the results, an optimum beam size is investigated...

In this study, the authors compare the performance of one-dimensional (1D) and two-dimensional (2D) optical code division multiple access (OCDMA) systems in presence of turbulence and various weather conditions. Lognormal fading model is used for analysis of weak turbulence and gamma-gamma model for moderate and strong turbulence. It is observed th...

This book provides an in-depth understanding of free space optical (FSO) communication with a particular emphasis on optical beam propagation through atmospheric turbulence. The book is structured in such a way that it provides a basic framework for the beginners and also gives a concise description from a designer’s perspective. The book provides...

When an optical signal propagates from ground to satellite, various effects of atmosphere, viz., absorption, scattering, and turbulence, will degrade the link performance. The loss arising due to beam propagation in space and effects of atmospheric turbulence are considered in link feasibility study. In this chapter, the received optical signal pow...

The link design plays an important role in the implementation of any FSO system. Before designing a link, the requirements have to be specified very carefully and clearly understood to build up system modules in a cost-effective way to meet the given requirements. Once the requirements, e.g., data rate, range, bit error rate, acquisition time, etc....

For ground-to-satellite laser communication link, it is essential to establish line-of-sight (LOS) path between ground-based station and the onboard satellite to ensure reliability of the system. Since the optical beam is very narrow, it requires a very accurate acquisition, tracking, and pointing (ATP) subsystems especially for long-distance commu...

The turbulence in an FSO link causes fluctuations in the intensity and the phase of the received signal. These fluctuations ultimately lead to the degradation in the link error probability and limit the system performance. In this chapter, bit error rate (BER) performance of coherent subcarrier (SC-BPSK and SC-QPSK) and noncoherent (OOK and \(\math...

As seen in the previous chapter, turbulence in the atmosphere causes random fluctuations of the phase and amplitude of the received signal leading to deep signal fades or surges. These fluctuations of the received signal severely degrade the link performance, particularly over a link distance of 1 km or longer or if communication is taking place wi...

The last few decades have seen rapid advances in information and communication technology. We commonly use broadband technology with high-speed Internet connectivity at our homes, offices, and in our mobile devices. The bandwidth and high-capacity requirements due to the increased use of Internet and broadband services have exceeded our expectation...

This chapter focuses on statistical description, physical characteristics, and modeling of free-space optical channel. The primary factors characterizing an atmospheric communication channel include atmospheric attenuation (both due to scattering and absorption) and turbulence. This chapter will provide good understanding of various types of atmosp...

We show that the WSS passband shape needs to be optimized to the 3.6th and 3.2th Super-Gaussian orders in BT-UK and PAN-Europe networks, respectively, for realizing the 30% capacity increase promised by the flexible-spectrum standard.

We evaluate the error performance of a free space optical (FSO) downlink from a geostationary earth orbit satellite to an earth station in presence of turbulence and different weather conditions such as fog, clouds, etc. Combined channel state probability density function (pdf) is derived by using log-normal model for weak turbulence, gamma–gamma m...

In this paper, the performance analysis of a Free Space Optical (FSO) satellite link from Earth to Geostationary Earth Orbit (GEO) satellite is carried out by considering atmospheric turbulence effects. It is observed that spatial diversity is a feasible option at the transmitter side and not at the receiver side. Further, increasing aperture diame...

In elastic optical networks, the success of providing high network capacity depends on the optical signal-to-noise ratio (OSNR) values of network lightpaths. As each lightpath’s OSNR value defines the modulation format and capacity it can support, having high OSNR lightpaths is always beneficial. Hence, with a given set of modulation formats, servi...