Willem A. Clarke

Insertion/deletion correction with spectral nulls

Levenshtein (1966) proposed a class of single insertion/deletion correcting codes, based on the number-theoretic construction due to Varshamov and Tenengolts (1965). We present several interesting results on the binary structure of these codes, and their relation to constrained codes with nulls in the power spectral density function. One surprising result is that the higher order spectral null codes of Immink and Beenker (1987) are sub-codes of balanced Levenshtein codes. Other spectral null sub-codes with similar coding rates, may also be constructed. We furthermore present some coding schemes and spectral shaping markers which alleviate the fundamental restriction on Levenshteins codes that the boundaries of each codeword should be known before insertion/deletion correction can be effected.

On Helberg's Generalization of the Levenshtein Code for Multiple Deletion/Insertion Error Correction

A proof that the Helberg code is capable of correcting multiple deletion/insertion errors is presented. This code is a generalization of the number-theoretic Levenshtein code which is capable of correcting a single deletion/insertion. However, apart from exhaustive testing of short codes, no proof was hitherto given to verify that the Helberg code is indeed capable of correcting multiple deletions and insertions.

A Multiple Insertion/Deletion Correcting Code for Run-Length Limited Sequences

A code construction is proposed to add a multiple insertion/deletion error correcting capability to a run-length limited sequence. The codewords of this code are themselves run-length limited. The insertion/deletion correcting capability is achieved by requiring several weighted sums of run-lengths in the codewords to satisfy certain congruences modulo primes. The construction is similar to the number-theoretic code proposed by Dolecek and Anantharam, which can correct multiple repetition errors or, equivalently, multiple insertions of zeros. It is shown that if the codewords in this code are run-length limited, then the code is capable of correcting both insertions and deletions of zeros and ones. An algorithm is proposed for decoding over a multiple insertion/deletion channel. Following the work of Dolecek and Anantharam, a systematic encoding method is also proposed for the codes. Furthermore, it is shown that the proposed construction has a higher rate asymptotically than the Helberg code, which is unconstrained in terms of run-lengths, even though our construction has the additional run-length constraints. The need for run-length limited codes that can correct insertion/deletion errors is motivated by bit-patterned media for magnetic recording.

Beam steering for circular switched parasitic arrays using a combinational approach

In this paper we present a method of electronic beam steering for circular switched parasitic array (SPA) antennas. In circular SPA antennas, one achieves azimuth beam steering by open-circuiting and short-circuiting different parasitic elements, usually with only one parasitic element open-circuited at a time. For the SPA antenna with few parasitic elements, this results in low azimuth beam steering resolution. In the proposed method, we iterate through different combinations of parasitic elements and the possible switch states of the lumped impedance loads connected to the parasitic elements. Our method aims to increase the azimuth beam steering resolution of the circular SPA antennas. The method is verified using a combination of simulation (using both MATLAB and WIPL-D) and a SPA antenna prototype implementation. The MATLAB code uses the induced EMF method, while the WIPL-D uses the Methods of Moment (MoM) for solving the antenna impedances. The three sets of results (simulations and measurement) match very well at 2.4 GHz. The results indicate the availability of more options (different loading configurations) for electronic beam switching that can be adopted to improve the beam steering resolution of circular SPA antennas.

Watermarking for JPEG image using error correction coding

Compression is the most common process that limits the robustness of watermarking. We propose a watermarking method for JPEG compressed color images in the semi-decompression domain, using Reed-Solomon (RS) codes. The watermark embedding and recovery processes can be applied without decompressing the compressed file completely. There is no perceptible degradation between the watermarked image and the original image. Experimental results show that the scheme is robust against some distortion attacks and JPEG lossy compression with different compression rates

Structured guidelines for novice researchers to produce their first peer reviewed academic paper

The aim of this paper is to document the process of developing a usable publication guide to support students to publish their first academic paper. Academic publishing is obviously a wide and complex field, taking many years to master. The intention was therefore not to develop students to “expert” level in a single event, but rather to get students to “novice” level with a first success behind them - enough to ensure that they will try a second time. We are here reminded of a quote from Henry Boettinger: “Training teaches us the rules, experience teaches us the exceptions” - we will focus on teaching the rules, by the second paper a student will be a bit more experienced and can start to experiment with the exceptions.

A Structural Parameter Based Modification of Energy Conscious ESPAR Antenna System through Optimization for WLAN’s Dual-Band Operability

Phased array antenna’s radiation pattern can be electronically controlled, making them a relevant solution for multipath interference. Electronically Steerable Parasitic Array Radiator (ESPAR) antenna systems are part of the family of phased array antennas under the umbrella of aerial beam-forming antennas. Generally ESPAR antenna system design considers the quarter wavelength approach. In practice there are a significant number of multiband systems with many applications integrated in a single device. This paper looks at the design of a dual-band ESPAR antenna. The design is limited to the ESPAR antenna’s structural parameter modification through the loading of its element with inductance load (circuitry). This results in an antenna system which operates in both 2.4GHz and 5.8 GHz bands of the IEEE 802.11 WLAN (Wireless Local Area Network) suitable for rural areas. The approach employed in this work consists of different stages of structural modification with careful optimization processes. The two adopted process are the quarter wavelength design and the optimization process, conducted through the genetic optimization algorithm.

A Variable Length Approach to Moment Balancing

Moment balancing templates have been proposed for channels with a small probability of an insertion/deletion (several orders smaller than additive errors) that add a minimal amount of redundancy. These templates are essentially a systematic way of encoding number-theoretic codes (primarily Levenshteins s = 1 insertion/deletion code). Moment balancing templates proposed up to this point have been of fixed length. In this paper, it is shown that by using variable length templates, it is possible to obtain better performance than the optimal fixed length moment balancing template. Here, performance is defined as the amount of redundancy, which includes the moment balancing bits and the marker, that needs to be added.

Partitioned moment balancing template and the influence of partition distribution thereon

A partitioned moment balancing template (systematic encoding of some number theoretic codes) is presented that can correct a single insertion/deletion. Instead of dispersing the moment balancing bits across the template, they are grouped together. Moment balancing templates are used to add insertion/deletion correcting capability to an additive-error-correcting code. The effect of using a particular additive-error-correcting code on the minimum number of moment balancing bits is investigated.

Producing an Engineering Reality TV Show at a University: Key Learning Points

In this paper we present the key learning points from a publicly broadcasted reality TV show produced by the Faculty of Engineering and the Built Environment at the University of Johannesburg. This reality TV show was based on a preliminary development for the universitys entry in the 2012 South African leg of the Solar Challenge. It featured undergraduate and postgraduate engineering students working on the project. We describe the factors that gave rise to this unusual project, the process involved in setting up the project and the key learning points.