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Waveform clipping in FSK modulated signal to combat impulse noise

- Shongwe, Thokozani, Han Vinck, A. J.

Analysis of the probability of sync-words in Reed-Solomon codes

- Shongwe, Thokozani

Closed-form BER expressions for HSV based MPSK-CSK systems

- Ndjiongue, Alain Richard, Ferreira, Hendrik C., Shongwe, Thokozani

BPSK-OFDM versus QFSK-OFDM in combating the effects of narrowband interference and impulsive noise in power line communication

- Bolaji, Abiola G., Shongwe, Thokozani

PSK to CSK mapping for hybrid systems involving the radio frequency and the visible spectrum

- Ndjiongue, Alain Richard, Shongwe, Thokozani, Ferreira, Hendrik C., Ngatched, Telex, Han Vinck, A. J.

Distance-preserving mapping with euclidean distance for 4-ary PAM

- Shongwe, Thokozani, Swart, Theo G., Ferreira, Hendrik C.

Cascaded PLC-VLC channel using OFDM and CSK techniques

- Ndjiongue. A. R., Shongwe, Thokozani, Ferreira, Hendrik C., Ngatched, T. M. Nkouatchah, Han Vinck, A. J.

Impedance analysis of a power line distribution network using short-time Fourier transform

- Sanya, Timothy O., Shongwe, Thokozani, Han Vinck, A. J., Ferreira, Hendrik C.

A study on impulse noise and its models

- Shongwe, Thokozani, Han Vinck, A. J., Ferreira, Hendrik C.

Trellis coded 4-ary PAM using distance preserving mapping

- Shongwe, Thokozani

  • Authors: Shongwe, Thokozani
  • Date: 2018
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/279715 , uj:30043 , Citation: Shongwe, T. 2018. Trellis coded 4-ary PAM using distance preserving mapping.
  • Description: Abstract: A trellis coded 4-ary Pulse Amplitude Modulation (4-PAM) is presented, where the encoding algorithm 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. Index Terms—Distance-preserving mappings, Hamming distance, Euclidean distance, Pulse Amplitude Modulation.
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Applications of artificial intelligence in powerline communications in terms of noise detection and reduction : a review

- Shekoni, Olamide M., Hasan, Ali N., Shongwe, Thokozani

Interleaving and nulling to combat narrow-band interference in PLC standard technologies PLC G3 and PRIME

- Shongwe, Thokozani, Han Vinck, A. J.

Reducing the probability of sync-word false acquisition with Reed-Solomon codes

- Shongwe, Thokozani, Han Vinck, A. J., Ferreira, Hendrik C.

  • Authors: Shongwe, Thokozani , Han Vinck, A. J. , Ferreira, Hendrik C.
  • Date: 2013
  • Subjects: Reed-Solomon codes , Sync-words , Sync-word based synchronization
  • Type: Article
  • Identifier: uj:4754 , ISSN 1555-5798 , http://hdl.handle.net/10210/11740
  • Description: In our previous work we introduced a method for avoiding/excluding some symbols in Reed-Solomon (RS) codes, called symbol avoidance. In this paper, we apply the symbol avoidance method in sync-word based synchronization of RS encoded data. With the symbol avoidance method we reduce the probability of the RS encoded data being mistaken for the sync-word used to delimit the start/end of the data. The symbols in the RS code are avoided according to the sync-word used, such that the sync-word has very low probability of being found in the RS codewords, where it was not inserted. Therefore, for different sync-words, different symbols need to be avoided in the RS code. The goal here is to reduce the probability of false acquisition of the sync-word in the RS encoded framed data.
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On impulse noise and its models

- Shongwe, Thokozani, Han Vinck, A. J., Ferreira, Hendrik C.

  • Authors: Shongwe, Thokozani , Han Vinck, A. J. , Ferreira, Hendrik C.
  • Date: 2014
  • Subjects: Impulse noise models , Multi-carrier modulation , Single-carrier modulation , Bernoulli-Gaussian model , Middleton Class A model
  • Type: Article
  • Identifier: uj:4728 , ISSN 978-1-4799-4961-8 , http://hdl.handle.net/10210/11553
  • Description: This article gives a discussion on impulse noise, its models and how it affects communications systems. We discuss the different impulse noise models in the literature, looking at their similarities and differences in communications systems. The impulse noise models discussed are memoryless (Middleton Class A and Bernoulli-Gaussian), and with memory (Markov- Middleton and Markov-Gaussian). We then go further to give performance comparisons in terms of bit error rates for some of the variants of impulse noise models. We also compare the bit error rate performance of single-carrier (SC) and multicarrier (MC) communications systems operating under impulse noise. It can be seen that MC is not always better than SC under impulse noise. Lastly, the known impulse noise mitigation schemes (clipping/nulling using thresholds, iterative based and error control coding methods) are discussed.
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Effects of fulgurites on the earthing system

- Tshubwana, Rembuluwani Phillip, Shongwe, Thokozani, Hove, Miidzo

  • Authors: Tshubwana, Rembuluwani Phillip , Shongwe, Thokozani , Hove, Miidzo
  • Date: 2017
  • Subjects: Earthing , Fulgurites , Impulse tests
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/249218 , uj:25924
  • Description: Abstract: This paper presents results that demonstrate the effects of fulgurites on the earthing system of a power system. The importance of grounding in power systems cannot be over emphasized. Although studies of fulgurites have been done in the past, no research work has reported on the impact of fulgurites on electrical grounding. The backfill materials used to enhance an earthing system play a pivotal role in controlling ground impedance of the soil by lowering the impedance of the earth. The impedance of the grounding is the sum of the static and dynamic impedance. The results of this work show that the static impedance of the backfill material increased in the event of fulgurite formation. Regarding the soil sample studied from a Swaziland 11 kV feeder, this occurred for lightning impulse currents equal to or greater than 30 kA. Swaziland is a country that experiences frequent power failures due to lightning, especially during the rainy season. It is thus essential to have a sound grounding system that is able to withstand all types of fault conditions and hence, the need for this study. The long-term aim of this research is to characterize a backfill material that will address the performance requirements of the network earthing system.
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The effect of Hamming distances on permutation codes for multiuser communication in the power line communications channel

- Shongwe, Thokozani, Speidel, Ulrich, Swart, Theo G., Ferreira, Hendrik C.

  • Authors: Shongwe, Thokozani , Speidel, Ulrich , Swart, Theo G. , Ferreira, Hendrik C.
  • Date: 2011
  • Subjects: Multiuser communication system , Permutation codes , Permutation sequences , Hamming distances , Power line communications
  • Type: Article
  • Identifier: uj:4742 , ISSN 978-1-61284-992-8 , http://hdl.handle.net/10210/11728
  • Description: We partition permutation sequences into groups to form permutation codes for multiuser communication. Each group becomes a codebook for each user in a multiuser communication system. We present simulation results for the performance of different partitions of permutation codes for multiuser communication, where the codes are to be used in channels with background noise and jamming, such as the Power Line Communications (PLC) channel. With the help of the simulation results, we show that by partitioning codebooks according to distance properties we can affect the performance of the codes. The permutation codes have codewords of length M with symbols taken from an alphabet whose cardinality is M, where M is any integer. Each symbol may be seen as representing one out of the M frequencies in an M-ary Frequency Shift keying modulation scheme, for example. Each user has a codebook of cardinality greater or equal to M and there can be a maximum of M - 1 users communicating at the same time through a multiple access OR channel.
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Narrow-band interference model for OFDM systems for powerline communications

- Shongwe, Thokozani, Papilaya, Victor N., Han Vinck, A. J.

Multiple access with distance preserving mappings for permutation codes

- Shongwe, Thokozani, Swart, Theo G., Ferreira, Hendrik C.

  • Authors: Shongwe, Thokozani , Swart, Theo G. , Ferreira, Hendrik C.
  • Date: 2013
  • Subjects: Convolutional codes , Encoding , Modulation , Noise , Power line communications , Time division multiple access
  • Type: Article
  • Identifier: uj:4725 , ISSN 978-1-4673-5940-5 , http://hdl.handle.net/10210/11550
  • Description: We present results for Distance Preserving Mappings (DPMs) for permutation codes that can be used for multiple access communication even under frequency jamming. We give examples of multiple codebooks that are DPMs such that each DPM can be assigned to a user for communication over a multiple access channel. We only consider one type of DPM called Distance Increasing Mappings (DIMs). The multiple access channel of interest is Time Division Multiple Access (TDMA). We show that it is possible to give a construction for DIMs that can be uniquely decoded even in the presence of frequency jamming. The DPMs are permutation codes found by mapping binary sequences to permutation sequences. The permutation codes have codewords of length M with symbols taken from an alphabet whose cardinality is M, where M is any integer. Each symbol may be seen as representing one out of the M frequencies in an M-ary Frequency Shift keying modulation scheme, for example.
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Selected subcarriers QPSK-OFDM transmission schemes to combat frequency disturbances

- Shongwe, Thokozani, Han Vinck, A. J., Ferreira, Hendrik C., Papilaya, Victor N.

  • Authors: Shongwe, Thokozani , Han Vinck, A. J. , Ferreira, Hendrik C. , Papilaya, Victor N.
  • Date: 2012
  • Subjects: Reed-Solomon codes , Carrier transmission on power lines , Data communication , Frequency selective surfaces , Impulse noise , Quadrature phase shift keying , Power line communications
  • Type: Article
  • Identifier: uj:4738 , ISBN 978-1-4673-0360-6 , http://hdl.handle.net/10210/11724
  • Description: To combat the impairments caused by frequency disturbances in the power line communications (PLC), a modified conventional QPSK-OFDM transmission scheme is presented. The idea of this scheme is to first group the N OFDM subcarriers into groups of M and then transmit data by selecting a subset of the subcarriers in the group. Real and imaginary parts of QPSK symbols are independently assigned to the selected subcarriers in a group, such that the minimum squared Euclidean distance is maximised. With this kind of symbol assignment to subcarriers our scheme has no net loss in terms of SNR requirements, in AWGN, in comparison to the conventional QPSK-OFDM, even though it has half the data rate of the conventional QPSK-OFDM. We refer to the conventional QPSK-OFDM as Scheme A. Our scheme displays a superior performance over Scheme A and another scheme (Scheme B), in the presence of frequency disturbances and also frequency selective fading noise. We further modify Scheme B and come up with additional two new QPSK-OFDM schemes that have better performance than Scheme B in AWGN and impulse noise. To encode, we apply a (n, k) RS code and a simple permutation code on the conventional QPSK-OFDM scheme, which significantly improves the decoder's performance in the presence of frequency disturbances. A simple narrow band noise model is developed and presented.
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Reed-Solomon code symbol avoidance

- Shongwe, Thokozani, Han Vinck, A. J.

  • Authors: Shongwe, Thokozani , Han Vinck, A. J.
  • Date: 2014
  • Subjects: Reed-Solomon codes , Subcodes
  • Type: Article
  • Identifier: uj:4722 , ISSN 1991-1696 , http://hdl.handle.net/10210/11444
  • Description: A Reed-Solomon code construction that avoids or excludes particular symbols in a linear Reed-Solomon code is presented. The resulting code, from our symbol avoidance construction, has the same or better error-correcting capabilities compared to the original Reed-Solomon code, but with reduced efficiency in terms of rate. The codebook of the new code is a subset of the original Reed-Solomon code and the code may no longer be linear. We also present computer search results for the bound on the number of symbols that can be avoided, and we make an attempt to find an expression for the bound. Such a code, by symbol avoidance, can be well suited to a number of applications, some of which include markers for synchronization, frequency hopping signatures, and pulse position modulation.
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