Faculty Publications
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Item Long haul, repeaterless, coherent optical multichannel communication systems employing hybrid multiplexing schemes wherein Wavelength Division Multiplexing (WDM) and Optical Code Division Multiplexing (OCDM) are combined is analyzed in the presence of performance limiting factors such as Inter Channel Interference (ICI), Stimulated Raman Scattering (SRS) and detector shot noise. Error control coding techniques in the form of rate 1/2 convolutional codes are employed in the system to counter these performance limiting factors. It is seen that the use of error control coding technique can enhance the system performance to such an extent that a Bit Error Rate (BER) performance of less than 10-8 is achievable without crossing the SRS power threshold for as many as 1000 to 1200 channels. Advantages of the hybrid multiplexed system over systems relying solely on WDM or OCDM are also discussed along with the advantages of using error control coding compared to optical amplification in countering the performance degrading factors.(Fachverlag Schiele und Sohn GmbH, Coding to enhance performance of hybrid multiplexed coherent optical communication systems in the presence of ICI and SRS) Kumar, M.S.; Bhat, K.N.H.; Umesh, G.2003Item A multichannel reservation-based channel-access protocol is investigated in this paper. The available system bandwidth is divided into distinct frequency channels. Under the protocol, one channel (the control channel) is used to exchange reservation messages and the remaining channels (the traffic channels) are used for information-bearing traffic. The performance of this scheme is compared to that of a single-channel reservation-based protocol. A simple contention-based slotted-Aloha protocol is also considered. Performance results take into account the effects of multiple-access interference on acquisition and packet errors. Results show that the reservation-based approach is advantageous under conditions of high traffic. In addition, a pacing mechanism that mitigates multiple-access interference and promotes fairness is described, and results are presented that demonstrate its effectiveness.(Baltzer Sci Publ, Unslotted multichannel channel-access protocol for distributed direct-sequence networks) Raghavan, A.R.; Baum, C.W.2004Item A new approach for channel blind identification based on second order cyclostationary statistics and the group delay has been proposed. In this, two methods are proposed. In both the methods, the correction is applied to the basic phase estimate for both the poles and zeros, in the group delay domain. The basic phase estimate is derived from the spectral correlation density (SCD) of the system output. In the first method, the phase correction is based on magnitude group delay. In the second method, not only the phase correction but also an improved system magnitude estimate of better variance and frequency resolution is derived based on modified magnitude group delay. The results indicate a significant improvement in performance for both the methods. For the first method in the absence of noise, the percentage normalized mean square error is reduced by about 85% over that of the existing non-parametric method. The second method in the presence of noise (SNR=5 dB), provides a reduction of 74% over the existing non-parametric method and 57% over the existing combined parametric and non-parametric methods. © 2005 Elsevier B.V. All rights reserved.(Channel blind identification based on cyclostationarity and group delay) Narasimhan, S.V.; Hazarathaiah, M.; Giridhar, P.V.S.2005Item BER performance enhancement for secure wireless optical communication systems based on chaotic MIMO techniques(2014) Abdulameer, L.F.; Jignesh, J.D.; Sripati, U.; Kulkarni, M.There has been a growing interest in the use of chaotic techniques for enabling secure communication in recent years. This need has been motivated by the emergence of a number of wireless services which require the channel to provide low bit error rates (BER) along with information security. The aim of such activity is to steal or distort the information being conveyed. Optical Wireless Systems (basically Free Space Optic Systems, FSO) are no exception to this trend. Thus, there is an urgent necessity to design techniques that can secure privileged information against unauthorized eavesdroppers while simultaneously protecting information against channel-induced perturbations and errors. Conventional cryptographic techniques are not designed for protecting information integrity when data is being transferred over a harsh communication medium. Hence, a separate channel coding protocol is often necessary to achieve this goal. Our work indicates that the use of a suitable Chaotic Shift Keying (CSK) map combined with an appropriate Space-Time Code (STC) can allow both requirements to be met. In this paper, we have concentrated on investigating the error rate performance of chaotic-wireless optical communication links operating over atmospheric channel, where the turbulence-induced fading is described by the Gamma-Gamma and log-normal distributions. The main aim of the paper is to assess the feasibility of employing Space-Time Coded chaotic communications over Multiple Input Multiple Output (MIMO) communication channels. Our simulations indicate that the combination of the STC and tent map provides the best BER performance in addition to security when compared to the choice of other maps. © 2013 Springer Science+Business Media Dordrecht.Item A comprehensive framework for Double Spatial Modulation under imperfect channel state information(Elsevier B.V., 2017) G.D., G.S.; Koila, K.; Raghavendra, R.; Shripathi Acharya, U.The essential requirement for a 5G wireless communication system is the realization of energy efficient as well as spectrally efficient modulation schemes. Double Spatial Modulation (DSM) is a recently proposed high rate Index Modulation (IM) scheme, designed for use in Multiple Input Multiple Output (MIMO) wireless systems. The aim of this scheme is to increase the spectral efficiency of conventional Spatial Modulation (SM) systems while keeping the energy efficiency intact. In this paper, the impact of imperfect channel knowledge on the performance of DSM system under Rayleigh, Rician and Nakagami-m fading channels has been quantified. Later, a modified low complexity decoder for the DSM scheme has been designed using ordered block minimum mean square error (OB-MMSE) criterion. Its performance under varied fading environments have been quantified via Monte Carlo simulations. Finally, a closed form expression for the pairwise error probability (PEP) for a DSM scheme under conditions of perfect and imperfect channel state information has been derived. This is employed to calculate the upper bound on the average bit error probability (ABEP) over aforementioned fading channels. It is observed that, under perfect and imperfect channel conditions DSM outperforms all the other variants of SM by at least 2dB at an average bit error ratio (ABER) of 10?5. Tightness of the derived upper bound is illustrated by Monte Carlo simulation results. © 2017 Elsevier B.V.Item Non-orthogonal space–frequency block codes from cyclic codes for wireless systems employing MIMO-OFDM with index modulation(Elsevier B.V., 2019) Raghavendra, R.; Shripathi Acharya, U.S.Space–frequency codes (SFC) having error correcting structure can be used to enhance the bit error rate (BER) performance of modern wireless systems (5G and beyond) employing multiple-input multiple-output (MIMO) and multi-carrier communication. In this work, the construction of non-orthogonal space–frequency block codes (NSFBC) from (n,k) cyclic codes has been proposed. In which, n represents the number of symbols in the codeword and k represents the number of symbols in the information sequence. The performance of proposed codes has been evaluated in MIMO systems employing orthogonal frequency division multiplexing and index modulation (MIMO-OFDM-IM). We initially obtained (n,k) full rank cyclic codes for any 1 q m . Further, NSFBCs are obtained from full rank codes using Rank preserving maps. In a 2 × 2 system and a 10-path MIMO channel, the proposed full rank NSFBC with rank-preserving IM mapping (FR-NSFBC-IM), over F 5 2 , provides he similar BER performance when compared to MIMO-OFDM-IM system with Rate-1 Alamouti code and QPSK. Moreover, it provides an improvement in spectral efficiency of about 0.9 b/s/Hz. When compared to the MIMO-OFDM-IM with BPSK, FR-NSFBC-IM codes over F 5 2 provide an asymptotic SNR gain of about 1 dB and also the spectral efficiency has been improved by about 0.6 b/s/Hz. In the 4 × 4 scenario, full rank NSFBCs over F 5 4 with rank deficient IM mapping (RD-NSFBC-IM) provide an improvement in spectral efficiency of about 1.3 b/s/Hz. However, BER performance is similar to that of MIMO-OFDM-IM with BPSK. © 2019Item Maximal Connectivity Test with Channel-Open Faults in On-Chip Communication Networks(Springer, 2020) Bhowmik, B.The networks-on-chip (NoCs) as the prevalent interconnection infrastructure have been continuously replacing the contemporary chip microprocessors (CMPs) while high performance computing is the dominant consideration. Aggressive technology scaling progressively reduces the feature size of the chips resulting in increasing susceptibility to failures and breakdowns due to open faults on communication channels. The reliability and performance issues are then becoming more critical requirement in both current and future NoC-based CMPs. This paper first presents an on-line, distributed built-in-self-test (BIST) oriented test mechanism that particularly detects open faults on communication channels and identifies faulty wires from the channels in NoCs. Next, a suitable test scheduling scheme is presented in order to reduce the overall test time and related performance overhead due the fault. Such scheduling scheme makes the present test solution scalable with large scale NoC architectures in general. Implementation of the test mechanism takes little hardware area and few clocks to detect the fault in channels. The on-line evaluation of the proposed test solution demonstrates the effect of the channel-open faults on the NoC performance characteristics at large real like synthetic traffic. In comparison to wide range of prior works on 16-bit networks, the present scheme provides many advantages, e.g., it improves hardware area overhead by 35.36–67.73% and saves the test time by 96.43%. packet latency and energy consumption by 5.83–42.79% and 6.24–46.38%, respectively on the networks, the proposed scheme becomes competitive with the existing works. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Generalized designs for precoded receive spatial modulation derived from non-orthogonal space time block codes(Springer, 2022) Shashikant, S.G.; G.D., G.D.G.; Shripathi Acharya, U.S.In this paper, a new MIMO scheme termed as precoded Spatially Modulated Non-orthogonal Space Time Block Code (precoded SM-NSTBC) is proposed. The primary concept of precoded SM-NSTBC is to activate a subset of receive antennas in a pre-defined manner and choose specific activated patterns to represent information symbols. We have synthesized schemes derived from full rank Cyclic codes defined over Galois field Rank preserving transformations are used to map the full rank codewords over a finite field to full rank Space Time Block Codes. Due to the characteristics of full rank Cyclic codes employed, a performance improvement of approximately 2 dB to 7 dB is observed. This advantage is realized when the performance of these schemes is compared with precoded SM-OSTBC and precoded STBC-SM. The improvement due to the coding gain is observed in both uncorrelated as well as correlated Rayleigh fading environments. An upper bound on the average bit error rate (ABER) is derived. Close correspondence between Monte-Carlo simulations and analytic values are observed. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Improved Harmony Search Algorithm for Multihop Routing in Wireless Sensor Networks(Pleiades Publishing, 2022) Sowmya, G.V.; Manjappa, M.Abstract: Energy efficiency is critical for prolonging the network lifetime of Wireless Sensor Network (WSN), and is the most important objective for any routing algorithm for WSN. In this article authors have proposed a Multihop harmony search algorithm for WSN with two objectives, first being increasing the throughput of the network and second being optimizing the energy consumption of the sensor nodes and thereby prolonging the lifetime of network. Finding the goodness of the communication channel/path is quite important. Sometimes, though the channel capacity is more, fewer amounts of data may be transmitted in the channel resulting in under utilization of the resources; and other times, though the channel capacity is less, more data may be dumped into the channel resulting in channel congestion and less output. Thus, if the goodness of the communication channel is known in advance, then it is easy for the algorithms to decide the upper bound of the channel and can have a congestion free and error free information transmission. Thus, the proposed algorithm employ Shannon channel capacity ‘C’ (baud rate) for finding the best next hop and the same is used for initialization of Harmony Memory. An effective local search strategy is also proposed to strengthen the local harmony search ability so that the convergence speed and the accuracy of routing algorithm is improved. Finally, an objective function model is developed by taking path length, energy consumption, and residual energy in to consideration. The proposed algorithm is compared with existing Multihop LEACH, BRM (Baud rate based Multihop routing protocol) and EEHSBR (Energy Efficient Harmony Search Based Routing) algorithm for the quantitative and qualitative analysis. The simulation results reveal that the proposed algorithm performs better than the considered algorithms in terms of network lifetime, throughput and energy consumption. © 2022, Pleiades Publishing, Ltd.