Thokozani Shongwe - Academia.edu (original) (raw)

Papers by Thokozani Shongwe

African Journal of Social Work, Apr 23, 2021

Licensed under a Creative Commons Attribution-Non-commercial 4.0 International License Indexed & ... more Licensed under a Creative Commons Attribution-Non-commercial 4.0 International License Indexed & Accredited with: African Journals Online (AJOL)|University of Zimbabwe Accredited Journals (UZAJ)|SCOPUS (Elsevier's abstract and citation database)|Directory of Open Access Journals (DOAJ)|Society of African Journal Editors (SAJE)|Asian Digital Library (ADL)|African Social Work Network (ASWNet)|Department of Higher Education and Training (DHET)-South Africa|SJR

Proceedings of 2011 IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 2011

ABSTRACT This paper considers a multicarrier communication system with n subchannels, each of whi... more ABSTRACT This paper considers a multicarrier communication system with n subchannels, each of which may be subject to insertion, deletion or inversion errors. A (variable-length) T-code is employed on each subchannel with two constraints: transmission of codewords starts simultaneously on all subchannels, and the codeword length ℓ is the same for all subchannels, i.e., codewords of different lengths may be used for each transmission in the time domain, but not in the frequency domain. This allows for the construction of an (n, K, d) error-correcting code over FQ, where Q ≤ mℓ, and mℓ is the number of codewords of length ℓ in the T-code.

2020 12th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP)

The presence of noise in PLC can eventually lead to information corruption. In this design, we pr... more The presence of noise in PLC can eventually lead to information corruption. In this design, we present the usage of several classification learners in detection of noise that might found in received PLC signals at the receiving end of the OFDM channel. A database of 5,000 PLC signals with their corresponding categories was used for training and evaluation. Four neural networks were studied through experiments: radial basis function (RBF) neural network, supervised Kohonen network, counter propagation neural network, and X-Y fused neural network. The results of the experiments indicate that the RBF model achieves the best performance among the proposed methods, overall classification accuracy of 98.2%. Furthermore, the remaining proposed algorithms: CPNN and XYF networks are considerably robust classification learners, resulting in true classification percentages of 87.9%, 95.3% and 92.1% respectively.

Journal of Energy in Southern Africa, 2021

The Integrated Energy Plan (IEP) was designed to consider South Africa’s energy needs from 2015 t... more The Integrated Energy Plan (IEP) was designed to consider South Africa’s energy needs from 2015 to 2050, as a guide for energy structural savings and the development of energy policy. The main aim of the Department of Energy is to ensure the security of energy supply. The current energy situation in the country has its gains and challenges. With the growing population and infrastructural development, the country requires prudent measures to meet the country’s energy needs for 2020–2050. The country’s energy is currently dominated by coal-fired plants, which represent about 70% of the total installed capacity, crude oil contributes about 21%, with only 9% from all other energy sources, including renewables. This paper examines the scope of the IEP framework, key objectives of the IEP, the methodology applied to achieve those objectives, and the projections made for attaining the framework target. The paper further reviews the energy requirements for the key sectors of the economy and...

2020 61st International Scientific Conference on Information Technology and Management Science of Riga Technical University (ITMS), 2020

Classification algorithms suffer from imbalanced training sets. In the area of detecting fraudule... more Classification algorithms suffer from imbalanced training sets. In the area of detecting fraudulent claims in the insurance industry, fraud cases are rare as compared to the genuine ones. Therefore, algorithms of detecting fraud have fewer training samples of positive cases, leading to lower performance metrics compared to when there are equal cases. In this paper, we propose a machine learning method of detecting fraudulent claims. The proposed method uses the adaptive synthetic sampling method (ADASYN) to remove imbalances in the dataset. We then used Support Vector Machines (SVM) to classify the claim cases. The outcome of the algorithm is compared to the imbalanced datasets and other existing methods.

2018 IEEE PES/IAS PowerAfrica, 2018

Power Line Communications (PLC) is positioning itself as the most natural communication technolog... more Power Line Communications (PLC) is positioning itself as the most natural communication technology for smart grid since it uses the existing power cables. However, the PLC channel still suffers from the devastating effects of impulsive noise. This paper investigates the effect of random impulsive noise on PSK, QAM and OFDM. The performance analyses results of M-PSK, 8-QAM and BPSK-OFDM are presented, showing the devastating effect of impulsive noise. We then go further by comparing the performance of BPSK to that of BPSK-OFDM and QPSK, 8-PSK to that of 8-QAM, showing that depending on the impulsive noise probability, 8-QAM outperforms 8-PSK and BPSK, BPSK-OFDM and QPSK have similar performance when the impulsive noise probability equal to 1 and subjected to the same impulse noise power.

2017 IEEE International Symposium on Power Line Communications and its Applications (ISPLC), 2017

The impedance of a low voltage distribution network is analyzed and presented. Data collected fro... more The impedance of a low voltage distribution network is analyzed and presented. Data collected from field measurement which was done over one week is used in this analysis. Basically, a chirp is injected into the electric grid, and the voltage and current signals (corrupted by various noises, including the 50 Hz mains signal) are time-sampled and stored for processing. The voltage and current are processed to obtain the impedance of the electric grid. Simulations are performed to establish the efficacy of the method of analysis used to obtain the impedance. The sliding window method of the Discrete Fourier Transform (DFT) is used in analyzing these impedance values. An eventual channel model describing the network is also presented.

International Journal of Electronics and Telecommunications, 2018

A trellis coded 4-ary Pulse Amplitude Modulation (4-PAM) is presented, where the encoding algorit... more A trellis coded 4-ary Pulse Amplitude Modulation (4-PAM) is presented, where the encoding algorith is derived from Distance Preserving Mapping (DPM) algorithm. In this work, we modify the DPM algorithm for 4-PAM and obtain a new construction for mapping binary sequences to permutation sequences, where the permutation sequences are obtained by permuting symbols of a 4-PAM constellation. The resulting codebook of permutation sequences formed this way are termed mappings. We also present several metrics for assessing the performance of the mappings from our construction, and we show that a metric called the Sum of Product of Distances (SOPD) is the best metric to use when judging the performance of the mappings. Finally, performance results are presented, where the mappings from our construction are compared against each other and also against the conventional mappings in the literature

Energies, 2020

Recently, the awareness of the severe consequences of greenhouse gases on the environment has esc... more Recently, the awareness of the severe consequences of greenhouse gases on the environment has escalated. This has encouraged the world to reduce the usage of fossil fuels for power generation and increase the use of cleaner sources, such as solar energy and wind energy. However, the conventional power system itself was designed as a passive power system, in which power generation is centralised, and power flows from substations towards the loads. Decentralised renewable energy sources, also called distributed generators, were introduced to create an active power system in which power generation can occur anywhere in the power system. Decentralised power generation creates challenges for the conventional power system, such as voltage fluctuations, high voltage magnitudes, reverse power flow, and low power factor. In this paper, an adaptive control system that coordinates different distributed generators for voltage regulation and power factor correction is introduced and designed. Th...

2020 12th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP), 2020

This paper presents a discussion and results of clipped digital modulated waveform signal that is... more This paper presents a discussion and results of clipped digital modulated waveform signal that is affected by Additive White Gaussian Noise (AWGN) and Impulse Noise (IN). It is shown that clipping the digital modulated waveform affected by AWGN results in the tails of the distribution being approximated by Gaussian distribution tails. Antipodal and non-coherent FSK modulation schemes are used to demonstrate the effect of clipping a digital modulated waveform signal, and in both schemes, the Bit Error Rate (BER) performance is signficantly improved by clipping, when both AWGN and IN are present.

This work serves to demonstrate the use of hybrid QFSK-OFDM (QFSK) and modified BPSK-OFDM (MBPSK)... more This work serves to demonstrate the use of hybrid QFSK-OFDM (QFSK) and modified BPSK-OFDM (MBPSK) in combating the effects of Narrowband Interference (NBI) and Impulsive noise (IN) as a mixture in Power Line Communication channel. Therefore, in this paper we demonstrate the superiority of modified BPSK-OFDM over QFSK-OFDM and over conventional BPSK-OFDM. The performance analysis of the system is carried out by Matlab simulations whereby the noise models used are the Middleton Class A for IN and NBI models as found in literature. The simulations show modified BPSK-OFDM to have better performance of 5 dB in terms of SNR as compared to QFSK-OFDM and 3 dB better than the conventional BPSK-OFDM.

We discuss the influence of random- and periodic impulse noise on narrowband (< 500 kHz freque... more We discuss the influence of random- and periodic impulse noise on narrowband (< 500 kHz frequency band) Power Line Communications. We start with random impulse noise and compare the properties of the measured impulse noise with the common theoretical models like Middleton Class-A and Mixed Gaussian. The main difference is the fact that the measured impulse noise is noise with memory for the narrowband communication, whereas the theoretical models are memoryless. Since the FFT can be seen as a randomizing, operation, the impulse noise is assumed to appear as Gaussian noise after the FFT operation with a variance that is determined by the energy of the impulses. We investigate the problem of capacity loss due to this FFT operation. Another topic is that of periodical noise. Since periodic in the time domain means periodic in the frequency domain, this type of noise directly influences the output of the FFT for an OFDM based transmission. Randomization is necessary to avoid bursty- ...

Journal of Communications

With a view to adapting information signals to suit the frequency characteristics of digital tran... more With a view to adapting information signals to suit the frequency characteristics of digital transmission channels, it is pertinent to design channel coding schemes that can exhibit spectral shaping capabilities after being processed with a suitable modulation technique. This involves concentrating the frequency energy of the coded and modulated information signal towards a predetermined range of the frequency spectrum, or making it have low power content at such frequencies. One modulation scheme that is suitable for achieving this is pulse amplitude modulation (PAM). We thus present a permutation coding (PC) system with injections that can exhibit spectral nulls at rational sub-multiples of the symbol frequency. Such injections are achieved by strategically removing δ columns from the source PC. We also present a mathematical expression that allows for the prediction of zero energy positions in the codebook’s spectrum. Due to the way the injections are introduced, it gives the sch...

International Journal of Electronics and Telecommunications, 2020

The article describes and compares two OFDM based communications schemes for reducing the effects... more The article describes and compares two OFDM based communications schemes for reducing the effects of the combination of Narrowband Interference (NBI) and Impulsive Noise (IN), which are noise types typical in Power Line Communication (PLC). The two schemes are Modified BPSK-OFDM (called MBPSK, for brevity) and QFSK-OFDM (called QFSK, for brevity), which are non-conventional OFDM schemes. We give a description of the two schemes, showing how they are derived and also show their similarities and eventually compare their performances. Performance simulation results, in terms of bit error rate, are given to compare the systems under the effect of IN and NBI. The popular Middleton Class A model is used for modelling IN. The results show that MBPSK scheme outperforms the QFSK scheme in terms of minimum distance, and hence in terms of bit error probability when no preprocessing is performed. However, under clipping/nulling, both schemes eventually reach the bit error rate floor.

2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP)

Power line communications (PLC) and visible light communications (VLC) are two emerging communica... more Power line communications (PLC) and visible light communications (VLC) are two emerging communication technologies which have several similarities. Among them, the advantage related to cost effectiveness is considered as strong research motivation. These two technologies are also characterized by the fact that each one of them barely form a complete communication system without the need of other supporting technologies. In this paper, based on the positive aspect of VLC technology, we exploit the Hermitian symmetry to design an hybrid system combining PLC and VLC technologies using orthogonal frequency division multiplexing (OFDM). A DC biased optical OFDM (DCO-OFDM), employed in VLC, is investigated when combined with PSK-OFDM (used in PLC). In the hybrid PLC-VLC system proposed in this paper, we exploit the inherent clipping feature of DCO-OFDM to combat impulsive noise found in the PLC channel, where the optimal combination of the DC bias level for optical communication, DC and impulse noise clipping threshold, Tc are investigated through simulations. We also exploit the fact that both DCO-OFDM and PSK-OFDM employ the FFT, to simplify the system.

2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP)

In this article we give: (a) a new construction for mapping binary sequences to permutation seque... more In this article we give: (a) a new construction for mapping binary sequences to permutation sequences formed from a 4-PAM constellation, and call the resulting codebooks mappings; (b) a metric for assessing the performance of mappings from our construction; (c) performance results comparing mappings from our construction against the conventional mappings in the literature. The results show that our mappings outperform the conventional mappings. Against conventional soft-decision decoded 4-PAM, our mapping showed 2.5 dB and 3.2 dB improvement over (R = 1/3, K = 4, dfree = 10) and (R = 1/3, K = 3, dfree = 6) convolutional codes, respectively.

2020 30th International Conference Radioelektronika (RADIOELEKTRONIKA)

This paper compares the performance of the FFT and DHT hybrid PLC-VLC systems based on Asymmetric... more This paper compares the performance of the FFT and DHT hybrid PLC-VLC systems based on Asymmetrically Clipped Optical - Orthogonal Frequency Division Multiplexing (ACO-OFDM) in impulsive noise. We will analyze and compare the Bit Error Rate (BER) performance of the two systems under the influence of Added White Gaussian Noise (AWGN) and Impulsive Noise (IN). Simulation results show that the Discrete Hartley Transform (DHT) based ACO-OFDM outperforms the Fast Fourier Transform (FFT) based ACO-OFDM cascaded PLC-VLC system.

Journal of Communications

In this paper, we investigate the performance of the discrete Hartley transform (DHT) hybrid Powe... more In this paper, we investigate the performance of the discrete Hartley transform (DHT) hybrid Power Line Communication - Visible Light Communication (PLC-VLC) system based on asymmetrically clipped optical - orthogonal frequency division multiplexing (ACO-OFDM) in impulsive noise, when the Perfect Nulling technique is utilized to analyze the combating of impulsive noise in the system. ACO-OFDM is a multicarrier modulation technique used in communications systems to allow for high data rates while adding robustness to the system. In this work, we derive the theoretical bit error rate (BER) error floor expression which enables us to calculate the error floor introduced into the system due to the nulling of data samples affected by impulsive noise, which we then compare to the simulated BER error floor. Results from this work show that the simulated BER error floor values are approximately the same as the theoretical BER error floor values with insignificant differences. The simulated B...

IEEE Access

The South African power distribution network is characterized by long power distribution lines wi... more The South African power distribution network is characterized by long power distribution lines with low short circuit capacity, and when distributed generation is introduced to these lines, voltage magnitudes are severely impacted. The existing voltage regulation methods of the on-load tap changer and step voltage regulator cannot successfully regulate voltage in long distribution lines with distributed generation since their control philosophy was designed for networks without distributed generation. Therefore, a dynamic system is proposed in this paper that coordinates the on-load tap changer, step voltage regulator, distributed generators, and the battery energy storage system to control voltage in long distribution lines with distributed generation. Their coordination will be based on response time and robustness. Unlike the conventional method, the proposed novel system will calculate a reference voltage that the on-load tap changer and the step voltage regulator must follow, based on the real time average voltage of the section of the network they each regulate. The system will also control the charging and discharging of a battery energy storage system based on the point of connection voltage and the average voltage of the feeder which it is connected to. Reactive power from distributed generators will also be used to enhance voltage regulation and refine the network power factor. When voltage magnitudes cannot be successfully brought within acceptable range, the proposed scheme will decrease the active power produced by distributed generators. The proposed system is examined on a South African 22kV network built in Matlab/Simulink.

African Journal of Social Work, Apr 23, 2021

Licensed under a Creative Commons Attribution-Non-commercial 4.0 International License Indexed & ... more Licensed under a Creative Commons Attribution-Non-commercial 4.0 International License Indexed & Accredited with: African Journals Online (AJOL)|University of Zimbabwe Accredited Journals (UZAJ)|SCOPUS (Elsevier's abstract and citation database)|Directory of Open Access Journals (DOAJ)|Society of African Journal Editors (SAJE)|Asian Digital Library (ADL)|African Social Work Network (ASWNet)|Department of Higher Education and Training (DHET)-South Africa|SJR

Proceedings of 2011 IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 2011

ABSTRACT This paper considers a multicarrier communication system with n subchannels, each of whi... more ABSTRACT This paper considers a multicarrier communication system with n subchannels, each of which may be subject to insertion, deletion or inversion errors. A (variable-length) T-code is employed on each subchannel with two constraints: transmission of codewords starts simultaneously on all subchannels, and the codeword length ℓ is the same for all subchannels, i.e., codewords of different lengths may be used for each transmission in the time domain, but not in the frequency domain. This allows for the construction of an (n, K, d) error-correcting code over FQ, where Q ≤ mℓ, and mℓ is the number of codewords of length ℓ in the T-code.

2020 12th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP)

The presence of noise in PLC can eventually lead to information corruption. In this design, we pr... more The presence of noise in PLC can eventually lead to information corruption. In this design, we present the usage of several classification learners in detection of noise that might found in received PLC signals at the receiving end of the OFDM channel. A database of 5,000 PLC signals with their corresponding categories was used for training and evaluation. Four neural networks were studied through experiments: radial basis function (RBF) neural network, supervised Kohonen network, counter propagation neural network, and X-Y fused neural network. The results of the experiments indicate that the RBF model achieves the best performance among the proposed methods, overall classification accuracy of 98.2%. Furthermore, the remaining proposed algorithms: CPNN and XYF networks are considerably robust classification learners, resulting in true classification percentages of 87.9%, 95.3% and 92.1% respectively.

Journal of Energy in Southern Africa, 2021

The Integrated Energy Plan (IEP) was designed to consider South Africa’s energy needs from 2015 t... more The Integrated Energy Plan (IEP) was designed to consider South Africa’s energy needs from 2015 to 2050, as a guide for energy structural savings and the development of energy policy. The main aim of the Department of Energy is to ensure the security of energy supply. The current energy situation in the country has its gains and challenges. With the growing population and infrastructural development, the country requires prudent measures to meet the country’s energy needs for 2020–2050. The country’s energy is currently dominated by coal-fired plants, which represent about 70% of the total installed capacity, crude oil contributes about 21%, with only 9% from all other energy sources, including renewables. This paper examines the scope of the IEP framework, key objectives of the IEP, the methodology applied to achieve those objectives, and the projections made for attaining the framework target. The paper further reviews the energy requirements for the key sectors of the economy and...

2020 61st International Scientific Conference on Information Technology and Management Science of Riga Technical University (ITMS), 2020

Classification algorithms suffer from imbalanced training sets. In the area of detecting fraudule... more Classification algorithms suffer from imbalanced training sets. In the area of detecting fraudulent claims in the insurance industry, fraud cases are rare as compared to the genuine ones. Therefore, algorithms of detecting fraud have fewer training samples of positive cases, leading to lower performance metrics compared to when there are equal cases. In this paper, we propose a machine learning method of detecting fraudulent claims. The proposed method uses the adaptive synthetic sampling method (ADASYN) to remove imbalances in the dataset. We then used Support Vector Machines (SVM) to classify the claim cases. The outcome of the algorithm is compared to the imbalanced datasets and other existing methods.

2018 IEEE PES/IAS PowerAfrica, 2018

Power Line Communications (PLC) is positioning itself as the most natural communication technolog... more Power Line Communications (PLC) is positioning itself as the most natural communication technology for smart grid since it uses the existing power cables. However, the PLC channel still suffers from the devastating effects of impulsive noise. This paper investigates the effect of random impulsive noise on PSK, QAM and OFDM. The performance analyses results of M-PSK, 8-QAM and BPSK-OFDM are presented, showing the devastating effect of impulsive noise. We then go further by comparing the performance of BPSK to that of BPSK-OFDM and QPSK, 8-PSK to that of 8-QAM, showing that depending on the impulsive noise probability, 8-QAM outperforms 8-PSK and BPSK, BPSK-OFDM and QPSK have similar performance when the impulsive noise probability equal to 1 and subjected to the same impulse noise power.

2017 IEEE International Symposium on Power Line Communications and its Applications (ISPLC), 2017

The impedance of a low voltage distribution network is analyzed and presented. Data collected fro... more The impedance of a low voltage distribution network is analyzed and presented. Data collected from field measurement which was done over one week is used in this analysis. Basically, a chirp is injected into the electric grid, and the voltage and current signals (corrupted by various noises, including the 50 Hz mains signal) are time-sampled and stored for processing. The voltage and current are processed to obtain the impedance of the electric grid. Simulations are performed to establish the efficacy of the method of analysis used to obtain the impedance. The sliding window method of the Discrete Fourier Transform (DFT) is used in analyzing these impedance values. An eventual channel model describing the network is also presented.

International Journal of Electronics and Telecommunications, 2018

A trellis coded 4-ary Pulse Amplitude Modulation (4-PAM) is presented, where the encoding algorit... more A trellis coded 4-ary Pulse Amplitude Modulation (4-PAM) is presented, where the encoding algorith is derived from Distance Preserving Mapping (DPM) algorithm. In this work, we modify the DPM algorithm for 4-PAM and obtain a new construction for mapping binary sequences to permutation sequences, where the permutation sequences are obtained by permuting symbols of a 4-PAM constellation. The resulting codebook of permutation sequences formed this way are termed mappings. We also present several metrics for assessing the performance of the mappings from our construction, and we show that a metric called the Sum of Product of Distances (SOPD) is the best metric to use when judging the performance of the mappings. Finally, performance results are presented, where the mappings from our construction are compared against each other and also against the conventional mappings in the literature

Energies, 2020

Recently, the awareness of the severe consequences of greenhouse gases on the environment has esc... more Recently, the awareness of the severe consequences of greenhouse gases on the environment has escalated. This has encouraged the world to reduce the usage of fossil fuels for power generation and increase the use of cleaner sources, such as solar energy and wind energy. However, the conventional power system itself was designed as a passive power system, in which power generation is centralised, and power flows from substations towards the loads. Decentralised renewable energy sources, also called distributed generators, were introduced to create an active power system in which power generation can occur anywhere in the power system. Decentralised power generation creates challenges for the conventional power system, such as voltage fluctuations, high voltage magnitudes, reverse power flow, and low power factor. In this paper, an adaptive control system that coordinates different distributed generators for voltage regulation and power factor correction is introduced and designed. Th...

2020 12th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP), 2020

This paper presents a discussion and results of clipped digital modulated waveform signal that is... more This paper presents a discussion and results of clipped digital modulated waveform signal that is affected by Additive White Gaussian Noise (AWGN) and Impulse Noise (IN). It is shown that clipping the digital modulated waveform affected by AWGN results in the tails of the distribution being approximated by Gaussian distribution tails. Antipodal and non-coherent FSK modulation schemes are used to demonstrate the effect of clipping a digital modulated waveform signal, and in both schemes, the Bit Error Rate (BER) performance is signficantly improved by clipping, when both AWGN and IN are present.

This work serves to demonstrate the use of hybrid QFSK-OFDM (QFSK) and modified BPSK-OFDM (MBPSK)... more This work serves to demonstrate the use of hybrid QFSK-OFDM (QFSK) and modified BPSK-OFDM (MBPSK) in combating the effects of Narrowband Interference (NBI) and Impulsive noise (IN) as a mixture in Power Line Communication channel. Therefore, in this paper we demonstrate the superiority of modified BPSK-OFDM over QFSK-OFDM and over conventional BPSK-OFDM. The performance analysis of the system is carried out by Matlab simulations whereby the noise models used are the Middleton Class A for IN and NBI models as found in literature. The simulations show modified BPSK-OFDM to have better performance of 5 dB in terms of SNR as compared to QFSK-OFDM and 3 dB better than the conventional BPSK-OFDM.

We discuss the influence of random- and periodic impulse noise on narrowband (< 500 kHz freque... more We discuss the influence of random- and periodic impulse noise on narrowband (< 500 kHz frequency band) Power Line Communications. We start with random impulse noise and compare the properties of the measured impulse noise with the common theoretical models like Middleton Class-A and Mixed Gaussian. The main difference is the fact that the measured impulse noise is noise with memory for the narrowband communication, whereas the theoretical models are memoryless. Since the FFT can be seen as a randomizing, operation, the impulse noise is assumed to appear as Gaussian noise after the FFT operation with a variance that is determined by the energy of the impulses. We investigate the problem of capacity loss due to this FFT operation. Another topic is that of periodical noise. Since periodic in the time domain means periodic in the frequency domain, this type of noise directly influences the output of the FFT for an OFDM based transmission. Randomization is necessary to avoid bursty- ...

Journal of Communications

With a view to adapting information signals to suit the frequency characteristics of digital tran... more With a view to adapting information signals to suit the frequency characteristics of digital transmission channels, it is pertinent to design channel coding schemes that can exhibit spectral shaping capabilities after being processed with a suitable modulation technique. This involves concentrating the frequency energy of the coded and modulated information signal towards a predetermined range of the frequency spectrum, or making it have low power content at such frequencies. One modulation scheme that is suitable for achieving this is pulse amplitude modulation (PAM). We thus present a permutation coding (PC) system with injections that can exhibit spectral nulls at rational sub-multiples of the symbol frequency. Such injections are achieved by strategically removing δ columns from the source PC. We also present a mathematical expression that allows for the prediction of zero energy positions in the codebook’s spectrum. Due to the way the injections are introduced, it gives the sch...

International Journal of Electronics and Telecommunications, 2020

The article describes and compares two OFDM based communications schemes for reducing the effects... more The article describes and compares two OFDM based communications schemes for reducing the effects of the combination of Narrowband Interference (NBI) and Impulsive Noise (IN), which are noise types typical in Power Line Communication (PLC). The two schemes are Modified BPSK-OFDM (called MBPSK, for brevity) and QFSK-OFDM (called QFSK, for brevity), which are non-conventional OFDM schemes. We give a description of the two schemes, showing how they are derived and also show their similarities and eventually compare their performances. Performance simulation results, in terms of bit error rate, are given to compare the systems under the effect of IN and NBI. The popular Middleton Class A model is used for modelling IN. The results show that MBPSK scheme outperforms the QFSK scheme in terms of minimum distance, and hence in terms of bit error probability when no preprocessing is performed. However, under clipping/nulling, both schemes eventually reach the bit error rate floor.

2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP)

Power line communications (PLC) and visible light communications (VLC) are two emerging communica... more Power line communications (PLC) and visible light communications (VLC) are two emerging communication technologies which have several similarities. Among them, the advantage related to cost effectiveness is considered as strong research motivation. These two technologies are also characterized by the fact that each one of them barely form a complete communication system without the need of other supporting technologies. In this paper, based on the positive aspect of VLC technology, we exploit the Hermitian symmetry to design an hybrid system combining PLC and VLC technologies using orthogonal frequency division multiplexing (OFDM). A DC biased optical OFDM (DCO-OFDM), employed in VLC, is investigated when combined with PSK-OFDM (used in PLC). In the hybrid PLC-VLC system proposed in this paper, we exploit the inherent clipping feature of DCO-OFDM to combat impulsive noise found in the PLC channel, where the optimal combination of the DC bias level for optical communication, DC and impulse noise clipping threshold, Tc are investigated through simulations. We also exploit the fact that both DCO-OFDM and PSK-OFDM employ the FFT, to simplify the system.

2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP)

In this article we give: (a) a new construction for mapping binary sequences to permutation seque... more In this article we give: (a) a new construction for mapping binary sequences to permutation sequences formed from a 4-PAM constellation, and call the resulting codebooks mappings; (b) a metric for assessing the performance of mappings from our construction; (c) performance results comparing mappings from our construction against the conventional mappings in the literature. The results show that our mappings outperform the conventional mappings. Against conventional soft-decision decoded 4-PAM, our mapping showed 2.5 dB and 3.2 dB improvement over (R = 1/3, K = 4, dfree = 10) and (R = 1/3, K = 3, dfree = 6) convolutional codes, respectively.

2020 30th International Conference Radioelektronika (RADIOELEKTRONIKA)

This paper compares the performance of the FFT and DHT hybrid PLC-VLC systems based on Asymmetric... more This paper compares the performance of the FFT and DHT hybrid PLC-VLC systems based on Asymmetrically Clipped Optical - Orthogonal Frequency Division Multiplexing (ACO-OFDM) in impulsive noise. We will analyze and compare the Bit Error Rate (BER) performance of the two systems under the influence of Added White Gaussian Noise (AWGN) and Impulsive Noise (IN). Simulation results show that the Discrete Hartley Transform (DHT) based ACO-OFDM outperforms the Fast Fourier Transform (FFT) based ACO-OFDM cascaded PLC-VLC system.

Journal of Communications

In this paper, we investigate the performance of the discrete Hartley transform (DHT) hybrid Powe... more In this paper, we investigate the performance of the discrete Hartley transform (DHT) hybrid Power Line Communication - Visible Light Communication (PLC-VLC) system based on asymmetrically clipped optical - orthogonal frequency division multiplexing (ACO-OFDM) in impulsive noise, when the Perfect Nulling technique is utilized to analyze the combating of impulsive noise in the system. ACO-OFDM is a multicarrier modulation technique used in communications systems to allow for high data rates while adding robustness to the system. In this work, we derive the theoretical bit error rate (BER) error floor expression which enables us to calculate the error floor introduced into the system due to the nulling of data samples affected by impulsive noise, which we then compare to the simulated BER error floor. Results from this work show that the simulated BER error floor values are approximately the same as the theoretical BER error floor values with insignificant differences. The simulated B...

IEEE Access

The South African power distribution network is characterized by long power distribution lines wi... more The South African power distribution network is characterized by long power distribution lines with low short circuit capacity, and when distributed generation is introduced to these lines, voltage magnitudes are severely impacted. The existing voltage regulation methods of the on-load tap changer and step voltage regulator cannot successfully regulate voltage in long distribution lines with distributed generation since their control philosophy was designed for networks without distributed generation. Therefore, a dynamic system is proposed in this paper that coordinates the on-load tap changer, step voltage regulator, distributed generators, and the battery energy storage system to control voltage in long distribution lines with distributed generation. Their coordination will be based on response time and robustness. Unlike the conventional method, the proposed novel system will calculate a reference voltage that the on-load tap changer and the step voltage regulator must follow, based on the real time average voltage of the section of the network they each regulate. The system will also control the charging and discharging of a battery energy storage system based on the point of connection voltage and the average voltage of the feeder which it is connected to. Reactive power from distributed generators will also be used to enhance voltage regulation and refine the network power factor. When voltage magnitudes cannot be successfully brought within acceptable range, the proposed scheme will decrease the active power produced by distributed generators. The proposed system is examined on a South African 22kV network built in Matlab/Simulink.