Reolyn Heymann

Using tree structures to resynchronize permutation codes

Permutation codes are used in powerline communications (PLC), together with M-FSK modulation, to combat errors introduced by the channel. Synchronization errors are rare but can be catastrophic if not detected and corrected. In this paper, we propose a fast and simple decoding algorithm that uses a tree structure, called a permutation code tree, to detect and correct errors. The decoder is able to detect and correct substitution, insertion or deletion errors. The decoder has an error correction capability of one error per codeword.

Adapting HomePlug C&C PLC for use in a low voltage smart grid

The paper presents the adaptations that were required to HomePlug Command and Control (C&C) V1.0 to meet the requirements, and deal with the issues, that arose out of a field trial of a low voltage smart grid deployed in a blanket fashion in Johannesburg, South Africa for Eskom by Util Labs and EON consulting. The field trial spanned 3 years and 27 000 supply points. HomePlug C&C based PLC was used as the primary communications mechanism inside the LV distribution islands. During the trial the LV distribution networks where mapped and instrumented extensively. The paper looks at a number of physical network parameters that influenced the deployment architecture and the development of the network protocol. The HomePlug implementation was modified to allow for transmission based on node and packet priority. This removed packet collisions. Fairness and bandwidth guarantees were implemented using a super frame co-ordinated by a network master. This allowed the PLC implementation to reach 95% channel utilization under very heavy loads of 30+ simultaneously transmitting nodes. During the trial it was discovered that there was significant PLC leakage between LV distribution islands. PLC leakage introduces multiple masters and hidden nodes into the network. The protocol implementation was adapted to mitigate the impact of this.

Concatenated permutation block codes based on set partitioning for substitution and deletion error-control

A new class of permutation codes is presented where, instead of considering one permutation as a codeword, codewords consist of a sequence of permutations. The advantage of using permutations, i.e. their favourable symbol diversity properties, is preserved. Additionally, using sequences of permutations as codewords, code rates close to the optimum rate can be achieved. Firstly, the complete set of permutations is divided into subsets by using set partitioning. Binary data is then mapped to permutations from these subsets. These permutations, together with a parity permutation, will form the codeword. Two constructions will be presented: one capable of detecting and correcting substitution errors and the other capable of detecting and correcting either substitution or deletion errors.

Markov modelling of in-vehicle power line communication

This paper presents three different Markov models of a vehicles power line as a communication medium. Two based on previous literature, and one proposed by this paper. An experimental setup to gather bit error data to create bit error distribution graphs is presented and the experimental results from the experiments are shown. The methods for creating the Markov models is then described and, using the data from the experiments as well as the described method for modelling, the respective models were created. Simulations based on these models were run and the output was compared with the original data.

Correcting adjacent errors using permutation code trees

Permutation codes are M-ary codes which can be used, in combination with M-ary FSK, to correct errors in Power Line Communications (PLC). It has been shown in [1] that permutation code trees can be used to correct a single substitution or synchronization error per codeword, without the use of markers. In this paper, we show that, due to the structure of the permutation code tree, adjacent errors can also be corrected if the codebook is adapted.

Regaining synchronization using neural networks to detect watermark codes

A binary neural network configuration is presented which is capable of correcting synchronization errors in a received bit sequence. The neural network uses the bit positions of a watermark sequence, which is inserted into the sequence before transmission, to determine whether an insertion or a deletion has occurred.

Location based games as the bridge between capstone students, junior students and the public

This paper reviews recent attempts by researchers at the University of Johannesburg (UJ) to increase the level of interaction between students, faculty and industry stakeholders by creating an alternate reality game (ARG) which is run during student presentations of Electrical Engineering capstone project work. The paper introduces the context, followed by a justification from current literature, the approach followed and finally a summary of the outcomes obtained by the project. Inspiration is taken from the work done by McGonigal and the MAGELLAN consortium on creating ARGs within an educational context. The Jen ratio is used as a measure of the social well-being of the space the game is played in and interactions between different players are used as the main gauge of success. Results from the first successful implementation of the game are presented and discussed. It is hoped that this study will inspire other educators in similar situations to consider playful design when interacting with large numbers of people inside and outside of the classroom.

Codebreakers: Designing and Developing a Serious Game for the Teaching of Information Theory

This paper reports the conceptualization, design, and development of the first and second prototype of a serious game for the teaching of the basics of Information Theory. Using the steps for a needs and context analysis, the researchers, lecturer and game developers participated in a focused group discussion to conceptualize the context and content for the game. Based on the design concepts found through the literature review, the team chose to follow a design research approach to create the academic intervention. The team used known game attributes and design principles, as well as feedback from guided evaluations, to create the first two prototypes of the game Codebreakers which is currently being used at the University of Johannesburg. As described in the design research approach, the team used an iterative process to develop the prototypes, with the final goal being to reach a point where the academic intervention can be generalized to other contexts.

Investigating a visible light communication channel with an LED transmitter and a smartphone receiver

Visible light communication (VLC) has become an option for data communication due to its unregulated bandwidth, being cost effective and not posing any health threats to people and the environment. Several studies on the performance of VLC systems have been conducted, where the systems were used for both solid-state illumination and data transmission. In this paper, an application using a single LED as a transmitter and a smartphone camera as a receiver, is considered. The purpose of this project is to investigate this specific VLC channel in terms of the bit error rate as a function of the distance between the transmitter and receiver.

Concatenated permutation block codes for correcting single transposition errors

Permutation codes are advantageous due to their favourable symbol diversity properties and are applied in flash memories combined with rank modulation. Codebooks traditionally consist of permutations with specific distance properties. A class of permutation codes was presented where a codeword consists of a sequence or concatenation of permutations, rather than a single permutation. These codebooks were constructed to correct substitution or deletion errors. In this paper, permutations are concatenated to form codewords with the goal of detecting and correcting adjacent transposition errors. An outer code is used to detect erroneous permutations in the codeword, using additional parity permutations. The symbol diversity of permutation codes is preserved and codebooks with higher cardinalities are constructed which result in better code rates.