Subrat Kar

Effect of four-wave mixing on optimal placement of optical amplifier in WDM star networks

In this article, the effect of four-wave mixing (FWM) and amplified spontaneous emission (ASE) noise on WDM optical star networks has been investigated. Analysis for the evaluation of probability of error has been carried out (a) when only FWM is present and (b) when both FWM and ASE noise are present. Numerical results are presented in the graphical and tabular forms for the practical values of parameters. Finally, optimal location of the amplifier in the network has been identified as being before the star coupler preceding the receiver.

Novel Strategies for Reducing FWM Using Modified Repeated Unequally Spaced Channel Allocation

Four-wave mixing (FWM) is a dominant nonlinear effect present in optical wavelength division multiplexing (WDM) networks employing dispersion-shifted fiber. The method of placing the carrier at unequally spaced frequencies to reduce the FWM effect in these networks is known. A modification to this method with periodic unequally spaced channel allocation repeated base unit structures has been suggested that leads to a much better bandwidth utilization with lesser number of FWM components. A figure of merit, defined as the ratio of decrease in number of FWM components generated to increase in bandwidth, has been used as a metric of performance.

Adaptive Transmission Power Protocol for heterogeneous Wireless Sensor Networks

A novel communication protocol - Adaptive Transmission Power Protocol - for Wireless Sensor Networks with the facility of reconfiguring the transmission power of the hardware is presented. Specifications of the protocol including the packet format and the contention avoidance methods are described. The protocol is implemented on a hardware platform and the performance is considered for a fundamental operation. The results show that non-overlapping regions exist for different transmission power levels where the system performance is optimum. More importantly, these regions move farther from the node with increase in transmission power level. It is observed that reconfiguring transmission power levels is an effective way of saving energy in Wireless Sensor Networks, the operation of which is abstracted by the implementation of the Adaptive Transmission Power Protocol.

Analysis of UMTS radio channel access delay

We present an analysis of delay encountered in successfully accessing the Random Access Channel (RACH) of Universal Mobile Telecommunication System (UMTS) Radio Interface by User Equipments (UE) that want to initiate data transfer. The process of random channel access is described and the MS state modeled as a DTMC in order to derive the delay. We evaluate the variation of the channel access delay with the preamble power, preamble detection threshold, maximum attempts, inter-attempt time interval, number of mobile users, number of slots, persistence level, rate of incoming data and rate of retransmissions. We also derive the capture probability of preambles sent in the same slot by multiple UEs in the presence of Rayleigh fading.

A Simulated Annealing Based Routing Sub-Heuristic for the Indirect Star Based ATM Network

We propose a heuristic based on the Simulated Annealing method for efficient routing in the Indirect Star based Multistage Interconnection Networks of O [n]. We assert and demonstrate through simulation results, that this heuristic is more efficient than those previously proposed for this class of MINs since it offers a higher probability of acceptance.

Performance evaluation of region estimation with reactive routing in wireless sensor networks

Sensor networks with mobile nodes often employ reactive routing strategies to transfer events to the gateway of the network. Estimating the region of presence of a GPS-less mobile sensor node is non-trivial as infrastructural assumptions for the network are time-dependent. Our contribution has two parts. Firstly, we propose an anchor node placement algorithm, ANCHREG, which establishes the theoretical basis for maximising region estimation performance with reactive routing in sensor networks. Region of a mobile node is estimated by detection if the region is anchored and prediction if the region is unanchored. ANCHREG calculates the minimum number of anchor nodes required and generates their optimal deployment configuration to maximise region estimation accuracy. Secondly, we simulate reactive routing over optimal ANCHREG-generated deployment configurations and compare the performance of region prediction for mobile nodes with machine learning models, namely - artificial neural networks ANN and support vector machines SVM.

Performance improvement techniques for optical wireless link in presence of atmospheric turbulence

Atmospheric turbulence can cause significant performance degradation in free space optical (FSO) communication system. Major effects on the beam such as beam wander and beam scintillation degrades the performance at the receiver. We investigate the impact of diversity technique and aperture averaging technique on the performance of FSO system. Performance evaluation is made in terms of average bit error rate and scintillation index.

Effects of Turbulence on Beam Propagation in an OTG Chamber and Transmitted Beam Width Optimization

In spite of the technical development of the components, the major limitation of free-space laser communication performance is due to the effects of atmospheric turbulence. Major effects on the beam such as beam wander and beam scintillation degrade the performance at the receiver. In our analysis BER is determined at the receiver in different turbulence conditions for different transmitted laser beam widths. Aperture averaging technique is considered to improve the performance.

Analysis of GPRS Radio Channel Access Delay

We present an analysis of delay encountered in successfully accessing the random access channel (RACH) of general packet radio service (GPRS) Radio Interface by mobile stations that want to initiate data transfer. The process of RACH access is described and the MS state modeled as a discrete-time Markov chain (DTMC) in order to derive the delay. We evaluate the variation of the radio channel access delay with the maximum attempts, inter attempt time interval, number of mobile users, number of backlogged users, radio priority, rate of incoming data and rate of retransmissions. The blocking probability or the probability of complete channel access failure is also evaluated.

Review of physical layer related issues in WDM networks: Part-II

In order to increase the transmission capacity there has been a growing interest in WDM for optical networks. The factors affecting the physical layer of the optical network are the nonlinear effects, the necessity to have in-line optical amplification and the requirement of placing wavelength converters. This paper, which is the first part in a series of two, reviews the nonlinear effects present in optical fiber emphasizing those which result in degradation in WDM system. In-line amplifiers are used in WDM systems to overcome the losses incurred by the signal while propagating through the medium. This paper also reviews different types of amplifiers available, their limitations and those used in long haul WDM systems. The noise generated by the amplifiers limits the number of amplifiers used in WDM systems. The algorithms used for optimal placement of in-line amplifier has also been discussed. While designing the long haul WDM system, wavelength converters play a major role in reducing the blocking probability of optical network. The second part of this paper [1] reviews the effect of using wavelength converters, the benefits in term of decreased probability of blocking, the routing and wavelength assignment schemes and the various algorithms for their optimal placement.