ARJ 2008 Vol 99 No 1

Combined Spectral Shaping Codes and OFDM Modulation for Narrowband Interference Channels
by K. Ouahada, H.C. Ferreira, A.J. Han vinck, A.J. Snyders and T.G. Swart
Abstract: Abstract: Distance Preserving Mappings is a relatively new technique finding its way to a wide use in the coding field. New codes mapping convolutional code outputs onto spectral nulls codewords have the purpose of generating a code with a certain spectrum specification and error correction capabilities, which can be exploited by the Viterbi decoder. Combining this class of new codes with an Orthogonal Frequency Division Multiplexing modulation scheme is actually a tool to reduce Electromagnetic Compatibility Interference in selected subbands or to cancel the narrowband interference potentially caused by, amongst others, HF radio transmissions. Taking into consideration the fact that a narrowband noise source is almost similar to a modulated OFDM carrier, and also the periodicity of the nulls in our spectrum, we are able to cancel the narrowband signal and its sideband interferences without using traditional techniques of cancellation, which is based on filtering. Shaping our spectrum at the transmitter is a technique, which can be exploited at the receiver to suppress any narrowband signal interference, which is regarded as noise. We will present in this paper the technique of cancellation and the coding gain that can be obtained when comparing to the uncoded data.
Considerations in Design of Low Altitude Long Endurance Solar Powered Unmanned Aerial Vehicles
by J. Meyer, J.A.F. du Plessis, W. Clark and P. Ellis
Abstract: Abstract: This paper presents design considerations for a low altitude long endurance solar powered Unmanned Aerial Vehicle. The considerations addressed include the determination of the available solar power, the design of the Unmanned Aerial Vehicle wing for long endurance flights and the determination of the electrical power and energy balance of the Unmanned Aerial Vehicle. Using these considerations, a solar powered UAV was designed and a long endurance flight simulated. Based on the simulation results it is in principle possible to design and build a solar powered long endurance solar powered Unmanned Aerial Vehicle.
Negative Effects of Energy-Saving, Non-Linear Loads on LV Systems: Causes and Recommendations
by R. Herman, C.T. Gaunt and G.S. Raubenheimer
Abstract: Abstract: Pressure is being exerted on utilities and electrical energy customers to reduce energy consumption. There are two concerns: the effect that increasing greenhouse gasses have on global warming and the dwindling non-renewable resources currently used for the production of electrical power. The user of modern energy-efficient appliances such as Compact Fluorescent Lamps and micro-wave ovens is a widely promoted solution. These types of devices are recommended not only in affluent areas but also in developing countries (such as South Africa) where the use of computers and television sets are also being encouraged as devices for increasing the level of information and education. However, the use of these devices can introduce significant problems. This paper reviews a range of published material on the various aspects of this topic. It also includes the results from experimental measurements. Finally, the paper discusses some recommendations that are intended to bridge the gap between theoretical analyses and the practical implementation of mitigating steps, as they apply to low voltage distribution systems.
Software Aided Design of a CMOS Based Power Amplifier Deploying a Passive Inductor
by M. Božanic and S. Sinha
Abstract: Abstract: This paper presents the design methodology of an integrated power amplifier, and coins the methodology as a software routine: for a given set of power amplifier specifications and CMOS process parameters, the routine computes the passive component values for a Class-E based power amplifier. The routine includes the matching network for standard impedance loads. The program also provides its user with a spiral inductor calculator, which can be used to determine inductance and parasitic values for an integrated square planar spiral inductor. The same tool has the ability to extract a SPICE netlist of inductor geometry, which can be used in the post-layout simulations of the power amplifier. Operation of the program was demonstrated by simulations in AMS 0.35 µm single-supply process for a 10 dBm, 2.4 GHz power amplifier design.
Sparse Graph Codes on a Multi-dimensional CDMA Platform for Application in Mobile Wireless Communication Systems
by J.D. Vlok and L.P. Linde
Abstract: Abstract: This paper presents the uncoded and coded multiuser error performance results of a novel super-orthogonal 4D CDMA communication platform under AWGN and multipath fading channel conditions. The communication platform employs root-of-unity filtered constant envelope complex spreading sequences with zero cross-correlation properties. The uncoded communication platform employs multi-layered-modulation to improve spectral efficiency compared with existing multi-level modulation techniques, and the coded system uses the multiple dimensions to transmit redundancy to improve error performance. Three classes of sparse graph coding schemes are evaluated on the multi-dimensional communication platform. The channel codes include a 3D block-turbo-code with extended Reed-Muller constituent codes, low-density parity-check codes and repeat-accumulate codes.