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Theethayi, Nelson
Publications (10 of 61) Show all publications
Anatory, J., Theethayi, N., Thottappillil, R. & Mvungi, N. H. (2009). A broadband power-line communication system design scheme for typical Tanzanian low-voltage network. IEEE Transactions on Power Delivery, 24(3), 1218-1224
Open this publication in new window or tab >>A broadband power-line communication system design scheme for typical Tanzanian low-voltage network
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 3, p. 1218-1224Article in journal (Refereed) Published
Abstract [en]

Information and communications technologies (ICTs) are gaining importance in developing countries. Power-line network is a potential infrastructure for ICT services provision. Power-lines are highly interconnected network with stochastic variation in number of branches. Under such distributed network conditions the design of a broadband power-line communication (BPLC) system is a challenge. In this paper a case study of an actual power-line network, representative of a low-voltage BPLC channel in Dar es Salaam, Tanzania is considered. We shall investigate the performance of such a low-voltage channel that uses orthogonal frequency division multiplexing (OFDM) technique with binary phase shift keying (BPSK) modulation scheme for communication. For sensitivity analysis, three different transmitter locations were chosen and receiver points were varied to identify the possible degraded performance scenarios. Analysis show that in the frequency bands of 100 MHz, the channel delay spread for such networks is about 4 s, giving a maximum number of subchannels 4096 with 512 cyclic prefix. To improve the degraded performance scenarios, the concatenated Reed Solomon outer code with punctured convolution inner code was applied to the network. It was found that when the branches were terminated by its corresponding characteristic impedances the performance is improved by 10-20 dB compared to a corresponding uncoded system. On the contrary for a coded system when the branches were terminated either in low or higher impedances compared to branch characteristic impedances the improvement was greater than 2-15 dB. This study demonstrates that the specification proposed by IEEE-802.16 broadband wireless access working groups can be used for performance improvement of distributed low-voltage systems.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
broadband networks, carrier transmission on power lines, channel coding, concatenated codes, convolutional codes, modulation coding, OFDM modulation, phase shift keying, radio access networks, Reed-Solomon codes, wireless channels
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113132 (URN)10.1109/TPWRD.2009.2014478 (DOI)000267765100029 ()0885-8977 (ISBN)
Note

10731611 broadband power-line communication system design Tanzanian low-voltage network orthogonal frequency division multiplexing OFDM technique binary phase shift keying BPSK modulation scheme sensitivity analysis channel delay spread concatenated Reed Solomon outer code punctured convolution inner code characteristic impedance IEEE-802.16 broadband wireless access network

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N. & Thottappillil, R. (2009). Channel characterization for indoor power-line networks. IEEE Transactions on Power Delivery, 24(4), 1883-1888
Open this publication in new window or tab >>Channel characterization for indoor power-line networks
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 4, p. 1883-1888Article in journal (Refereed) Published
Abstract [en]

Power-line networks are promising mediums by which broadband services can be offered, such as Internet services, voice over Internet protocol, digital entertainment, etc. In this paper, an analysis of delay spread, coherence bandwidth, channel capacity, and averaged delay in the frequency bands up to 100 MHz for typical indoor power-line networks are studied. Earlier studies for indoor power-line networks considered frequencies up to 30 MHz only and earlier works have shown that at these frequency bands, the data rates are generally low and are inefficient for digital entertainment in comparison with wireless local-area networks standards, such as IEEE 802.11 n. In this paper, it is shown that at 100 MHz, the average channel capacity for typical indoor power-line networks can be up to 2 Gb/s and it is found that by increasing the number of branches in the link between transmitting and receiving ends, the average channel capacity decreases from 2 Gb/s to 1 Gb/s (when the number of branches was increased by four times for a power spectral density of -60 dBm/Hz). At the same time, the coherence bandwidth decreased from 209.45 kHz to 137.41 kHz, which is much better than the coherence bandwidths corresponding to 30-MHz systems. It is therefore recommended to operate the indoor power-line networks at 100-MHz bandwidths for a wide variety of broadband services.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Branched network, communication channel model, multipath, power-line communication, transfer function
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113129 (URN)10.1109/TPWRD.2009.2021044 (DOI)000270139900017 ()0885-8977 (ISBN)
Note

10880672 channel characterization indoor power-line networks channel capacity averaged delay frequency bands wireless local-area networks transfer function power-line communication

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N. & Thottappillil, R. (2009). Effects of multipath on OFDM systems for indoor broadband power-line communication networks. IEEE Transactions on Power Delivery, 24(3), 1190-1197
Open this publication in new window or tab >>Effects of multipath on OFDM systems for indoor broadband power-line communication networks
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 3, p. 1190-1197Article in journal (Refereed) Published
Abstract [en]

Power-line networks are an excellent infrastructure for broadband data transmission. However, various multipaths within a broadband power-line communication (BPLC) system exist due to stochastic changes in the network load impedances, branches, etc. This further affects network performance. This paper attempts to investigate the performance of indoor channels of a BPLC system that uses orthogonal frequency-division multiplexing (OFDM) techniques. It is observed that when a branch is added in the link between the sending and receiving end of an indoor channel, an average of 4-dB power loss is found. Additionally, when the terminal impedances of the branch change from the line characteristic impedance to impedance of lower values, the power loss (signal-to-noise ratio) is about 0.67 dB/. On the contrary, for every increase in the terminal impedances by 100 , above the line characteristic impedance, the power loss is 0.1 dB/. When the line terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. In this paper, it is shown that to overcome such performance degradation, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used. The observations presented in the paper could be useful for an efficient design of a BPLC system that uses OFDM techniques.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Branched network, broadband power-line communication (BPLC), communication channel model, concatenated coding, convolutional codes, impulsive noise, interleaving, orthogonal frequency-division multiplexing (OFDM), Reed-Solomon codes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113130 (URN)10.1109/TPWRD.2009.2014281 (DOI)000267765100026 ()0885-8977 (ISBN)
Note

10731635 OFDM systems indoor broadband power line communication networks broadband data transmission indoor channels orthogonal frequency division multiplexing techniques signal-to-noise ratio power loss concatenated Reed-Solomon codes interleaved Viterbi methods

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N. & Thottappillil, R. (2009). Performance of underground cables that use OFDM systems for broadband power-line communications. IEEE Transactions on Power Delivery, 24(4), 1889-1897
Open this publication in new window or tab >>Performance of underground cables that use OFDM systems for broadband power-line communications
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 4, p. 1889-1897Article in journal (Refereed) Published
Abstract [en]

Power-line networks are proposed for broadband data transmission. The presence of multipaths within the broadband power-line communication (BPLC) system, due to stochastic changes in the network load impedances, branches, etc. pose a real challenge as it affects network performance. This paper attempts to investigate the performance of an orthogonal frequency-division multiplexing (OFDM)-based BPLC system that uses underground cables. It is found that when a branch is added in the link between the sending and receiving end, there is an average of 4-dB power loss. In addition, when the terminal impedances of the branches that are connected to the link between the transmitting and receiving end vary from line characteristic impedance to low-impedance values, the power loss (signal-to-noise ratio) is about 0.35 dB/ . On the contrary, for an increase in the terminal impedances by 100 above line characteristic impedance, the power loss is 0.23 dB//. When the branch terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. It is shown that to overcome degraded network performance, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used, which could be used for an efficient design of the BPLC system that uses OFDM techniques.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Branched network, broadband communication, concatenated coding, convolution codes, impulse noise, interleaved coding, multipath channels, orthogonal frequency-division multiplexing (OFDM), power-line communication, Reed-Solomon codes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113126 (URN)10.1109/TPWRD.2009.2031674 (DOI)000270139900018 ()0885-8977 (ISBN)
Note

10880673 OFDM broadband power-line communications broadband data transmission network load impedances orthogonal frequency-division multiplexing concatenated coding convolution codes impulse noise interleaved coding multipath channels Reed-Solomon codes

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N. & Thottappillil, R. (2009). Power-line communication channel model for interconnected networks. Part I: two-conductor system. IEEE Transactions on Power Delivery, 24(1), 118-123
Open this publication in new window or tab >>Power-line communication channel model for interconnected networks. Part I: two-conductor system
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 1, p. 118-123Article in journal (Refereed) Published
Abstract [en]

This paper presents a generalized transmission-line approach to determine the transfer function of a power-line network of a two-conductor system (two parallel conductors) with distributed branches. The channel frequency responses are derived considering different terminal loads and branches. The model's time-domain behavior is validated using commercial power system simulation software called Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP). The simulation results from the model for three different topologies considered have excellent agreement with corresponding ATP-EMTP results. Hence, the model can be considered as a tool to characterize any given power-line channel topology that involves the two-conductor system. In the companion paper (Part II), the proposed method is extended for a multiconductor power-line system.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Branched network, communication channel model, multipath, power-line communication (PLC), transfer function
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113127 (URN)10.1109/TPWRD.2008.2005679 (DOI)000262260800015 ()0885-8977 (ISBN)
Note

10370589 power-line communication channel interconnected networks two-conductor system transfer function channel frequency responses alternative transients program-electromagnetic transients program

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N. & Thottappillil, R. (2009). Power-line communication channel model for interconnected networks: Part II: multiconductor system. IEEE Transactions on Power Delivery, 24(1), 124-128
Open this publication in new window or tab >>Power-line communication channel model for interconnected networks: Part II: multiconductor system
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 1, p. 124-128Article in journal (Refereed) Published
Abstract [en]

In this paper, we present an approach to determine the transfer function for multiconductor power-line networks with distributed branches and load terminations for broadband power-line communication (BPLC) applications. The applicability of the proposed channel model is verified numerically in time domain using the finite-difference-time domain (FDTD) method for the solution of transmission lines. The channel model simulation results are in excellent agreement with the corresponding FDTD results. The model therefore could be useful in the analysis and design of BPLC systems involving multiconductor power-line topology.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Broadband power-line communication (BPLC), communication channel model, multiconductor, multipath branched network, transfer function
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113128 (URN)10.1109/TPWRD.2008.2005681 (DOI)000262260800016 ()0885-8977 (ISBN)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N., Thottappillil, R., Kissaka, M. & Mvungi, N. (2009). The effects of load impedance, line length, and branches in typical low-voltage channels of the BPLC systems of developing countries: transmission-line analyses. IEEE Transactions on Power Delivery, 24(2), 621-629
Open this publication in new window or tab >>The effects of load impedance, line length, and branches in typical low-voltage channels of the BPLC systems of developing countries: transmission-line analyses
Show others...
2009 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 2, p. 621-629Article in journal (Refereed) Published
Abstract [en]

This paper presents the influence of line length, number of branches (distributed and concentrated), and terminal impedances on the performance of a low-voltage broadband power-line communication channel. For analyses, the systems chosen are typical low-voltage power-line networks found in Tanzania. The parameters varied were the network's load impedances, direct line length (from transmitter to receiver), branched line lengths, and number of branches. From the frequency responses of the transfer functions (ratio of the received and transmitted signal), it is seen that the position of notches and peaks in the amplitude responses are affected by the aforementioned network parameters and topology. As a result, the time-domain responses are attenuated and distorted. Time-domain responses of power-line channels under various conditions are also investigated for a given pulse input at the transmitter. The observations presented in this paper could be useful for suitable power-line communication system design.

Keyword
Branched network, broadband power line, impulse response, interconnections, load impedance, low-voltage channel, multipath, transfer function
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113131 (URN)10.1109/TPWRD.2008.923395 (DOI)000265093000016 ()0885-8977 (ISBN)
Note

10557484 transmission-line analyses low-voltage broadband power-line communication channel low-voltage power-line networks Tanzania network load impedance frequency response transfer function time-domain response transmitter power-line communication system design load impedance effect line length effect developing countries

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
Anatory, J., Theethayi, N., Thottappillil, R., Mwase, C. & Mvungi, N. (2009). The Effects of Multipath on OFDM Systems for Broadband Power-Line Communications a Case of Medium Voltage Channel. World Academy of Science, Engineering and Technology, 54, 205-208
Open this publication in new window or tab >>The Effects of Multipath on OFDM Systems for Broadband Power-Line Communications a Case of Medium Voltage Channel
Show others...
2009 (English)In: World Academy of Science, Engineering and Technology, ISSN 2070-3724, Vol. 54, p. 205-208Article in journal (Refereed) Published
Abstract [en]

Power-line networks are widely used today for broadband data transmission. However, due to multipaths within the broadband power line communication (BPLC) systems owing to stochastic changes in the network load impedances, branches, etc., network or channel capacity performances are affected. This paper attempts to investigate the performance of typical medium voltage channels that uses Orthogonal Frequency Division Multiplexing (OFDM) techniques with Quadrature Amplitude Modulation (QAM) sub carriers. It has been observed that when the load impedances are different from line characteristic impedance channel performance decreases. Also as the number of branches in the link between the transmitter and receiver increases a loss of 4dB/branch is found in the signal to noise ratio (SNR). The information presented in the paper

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-122180 (URN)
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2016-04-14Bibliographically approved
De Conti, A., Visacro, S., Theethayi, N. & Cooray, V. (2008). A comparison of different approaches to simulate a nonlinear channel resistance in lightning return stroke models. Journal of Geophysical Research, 113(D14), D14129
Open this publication in new window or tab >>A comparison of different approaches to simulate a nonlinear channel resistance in lightning return stroke models
2008 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no D14, p. D14129-Article in journal (Refereed) Published
Abstract [en]

Different physical models that describe the time variation of the channel resistance are investigated in a lightning return stroke model. Such models consider one of the three following hypotheses: (1) the channel resistance decays exponentially with time, (2) the channel resistance decays with the radial expansion of the channel core, which is assumed to be described by the strong-shock approximation, or (3) the channel resistance varies with time according to three different arc resistance models (defined by Toepler, Barannik and Kushner et al.). Analyses illustrate the effect of a time-varying channel resistance on channel currents and corresponding electromagnetic fields. It is shown that the strong-shock approximation is able to predict typical features of experimentally observed lightning electromagnetic fields and return stroke speed profiles. It is also shown that results predicted by the strong-shock approximation can be qualitatively reproduced by either using simplified arc resistance equations (such as Toepler's and Barannik's ones) or considering an exponential decay of the channel resistance with attenuation constants linearly increasing with height.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-109162 (URN)10.1029/2007JD009395 (DOI)000258151000001 ()
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13Bibliographically approved
Montano, R., Theethayi, N. & Cooray, V. (2008). An Efficient Implementation of the Agrawal et al. Model for Lightning-Induced Voltage Calculations Using Circuit Simulation Software. IEEE Transactions on Circuits and Systems Part I: Regular Papers, 55(9), 2959-2965
Open this publication in new window or tab >>An Efficient Implementation of the Agrawal et al. Model for Lightning-Induced Voltage Calculations Using Circuit Simulation Software
2008 (English)In: IEEE Transactions on Circuits and Systems Part I: Regular Papers, ISSN 1549-8328, Vol. 55, no 9, p. 2959-2965Article in journal (Refereed) Published
Abstract [en]

One of the popular, simple, and accurate field-to-wire coupling models for studying transmission-line lightning interaction is the Agrawal et al model [1]. In this model, the coupling mechanisms are represented by distributed sources along the line, wherein each distributed source is due to the horizontal component of the illuminating electric field at that point on the line. These sources give rise to the propagating scattered voltage along the line, while the total voltage at any instant at a given point along the line is the sum of scattered voltage and the voltage at that point due to the illuminating vertical component of the electric field. There is a difficulty in applying the Agrawal et al. model with the built-in transmission-line models of various circuit simulation software such as the Alternate Transients Program-Electromagnetic Transients Program [2]-[5], PSpice [6], Simpow [7], PSS/E [71, etc., as the voltage source due to the horizontal component of the electric field in the Agrawal el al. model is in series with the line impedance [1], [8] and not in between two transmission-line segments. In this paper, a simple circuit approach for efficient implementation of the Agrawal et al. model using any circuit simulation software that has built-in transmission-line models is proposed.

Keyword
Electric impedance, interference, lossy circuits, power systems, transient response, transmission line
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-107096 (URN)10.1109/TCSI.2008.920072 (DOI)000260863700048 ()
Available from: 2009-07-16 Created: 2009-07-16 Last updated: 2016-04-13Bibliographically approved
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