Inaug.-diss.--Rostock.

Thesis (MScEng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Interference among neighbouring plants, often due to competition for limited resources, is central to subjects such as yield-density relationships, intercropping, self-thinning in dense plant stands and low reproductive yield in certain crops. An experiment was conducted to investigate plant interference in associated populations of beans {Phaseolus vulgaris L.) and beets [Beta vulgaris L.). Plants of the two species were grown at different total densities and at different mixture proportions in a randomized complete block design. Several analytical procedures were used to interpret and define treatment effects. The analysis of variance indicated that yield was significantly reduced with either increasing total population density or increasing bean proportions in mixtures. The interactions of total population density and mixture proportions were only occasionally significant. Parameters of non-linear models used to define yield-density relationships indicated that beans were the superior competitor, both against themselves and against beets. The model parameters were also used to determine differential yield responses on total dry weight, leaf dry weight, leaf number and leaf area in the bean-beet mixtures. Yield advantage was observed in leaf dry weight and leaf number when model parameters were used in calculating land equivalent ratios whereas total dry weight and leaf area showed yield disadvantage. Using observed values to calculate land equivalent ratios indicated yield advantage in all four variables. Plant size inequalities, as determined by the Gini coefficient tended to decrease in beet monocultures with increasing population density. In monocultures of beans and in the bean-beet mixtures, plant size distribution was not systematically changed by density and mixture treatments. Yield component analysis indicated that the variation in total yield due, to either population density or mixture treatments increased with age; the variation due to the population density by mixture proportions Interaction remained relatively constant throughout the growing season. Leaf number per plant was the yield component which was most frequently a significant source of yield variation both in the forward and backward yield component analysis. Plant growth analysis indicated that leaf area ratio and specific leaf weight were higher at higher population densities and at higher bean proportions. Harvest index decreased with increasing population density and with increasing proportions of the competing species in beets. Absolute growth, relative growth and unit leaf rates increased with time and declined after reaching a peak at about 68 days after planting. Both the lowest population density of 16 plants m ̄² and the mixture treatment with the least proportion of beans had the greatest increase in absolute growth, relative growth and unit leaf rates. Allometric relationships between total plant dry weight and any secondary measure per plant were influenced in different ways by density and mixture treatments and by time of harvest. The composition of models also varied considerably. The interpretation of plant interference, therefore is strongly influenced by the choice of plant characteristics which are measured, and by the time of measurement. / Land and Food Systems, Faculty of / Graduate

This thesis describes the design, construction, and testing of a radio-frequency interference monitoring system for use with the synthesis array telescope at the Dominion Radio Astrophysical Observatory near Penticton, B.C. The system is designed to provide continuous, automated surveillance of the radiospectrum around 408 MHz. Interfering signals are characterized and catalogued according to strength, duration, frequency, and direction. Although the monitor is presently a very useful tool for detecting and finding sources of interference, it is ultimately intended to communicate directly with the telescope's control computer, so that sporadic bursts of interference can be removed automatically. The system can detect a weak interfering signal that is within 5 dB of the smallest signal that can contaminate the astronomical observations. The smallest signal was calculated based on the following conditions, considered to be the case for which a synthesis telescope is most sensitive to interference, i.e., the worst case: a) observing at high declination (towards the North Pole), so that the fringes of the synthesis telescope are too slow to reduce the effects of the interference, and b) with the interference present continuously during the observation. These weak signals can be detected in the presence of other signals, nearby in frequency, which are up to 40 dB stronger, i.e., the dynamic range of the monitor is 40 dB. The monitor consists of an antenna system, a computer-tunable radio receiver, a fast Fourier transform (FFT) spectrum analyzer, and a microcomputer for control and data analysis. Everything except the microcomputer hardware was built as part of the project. A thorough survey of the literature on the design of dedicated FFT machines was required. It was discovered that there had been no investigation of the design details for fixed-point FFT machines which are required to do long integrations. In such situations, fixed-point errors limit the performance of the machine. A computer simulation of the Welch process was developed to analyze the effects of these errors and to optimize the design. Some new results concerning the detectability of small signals are presented. The FFT spectrum analyzer is used to estimate the power spectrum of 500 kHz-wide sub-bands using Welch's method of modified periodograms. It computes 256-point transforms in real-time with a resolution of 3.91 kHz (corresponding to one FFT every 512 μsec). This is comparable to the speed of a large array processor but at a fraction of the cost. Since the FFT is equivalent to a bank of contiguous filters, it can analyze the spectrum in much less time than the single swept filter found in most commercial spectrum analyzers, i.e., it is much more sensitive. The analyzer was specially designed and built using recently-available digital integrated circuits. The design draws upon several high-speed architectural concepts including pipelining, parallel arithmetic, and hard-wired control. Except for expensive array processors, the analyzer is much faster than any commercial FFT processors or FFT-based spectrum analyzers. As part of the antenna system, an array of helical antennas was designed and constructed, its characteristics were investigated and found to be suitable for the present application, and a method of remotely switching them on and off was devised. One more note - the radio spectrum is becoming more and more cluttered with man-made signals. Unprotected radio astronomy bands are being adversely affected and radio astronomers are turning to FFT spectrometers to cope with the relatively large interfering signals. The work herein on FFT-based design is applicable in such cases. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper describes and interference cancellation technique appropriate for ARTM Tier-1 waveforms. The technique requires the estimators for the bit sequences for the adjacent channels as well as the power levels of the adjacent channels. Simulation results show that the interference canceller allows a more dense “channel packing” thereby creating a channel utilization 67% ~ 100% greater than the current IRIG 106 recommendations.

Today and future wireless networks are facing one of their greatest limiting factors:interference. This is due to the unprecedented increase in the number of connecteddevices. Therefore, in order to meet the ever increasing demand for data rate andquality of services, more advanced techniques than what we have today are requiredto deal with interference. This thesis takes a step towards interference managementin multiuser wireless systems by means of relaying and cooperation. We study fourfundamental building blocks in network information theory, propose new codingschemes, and derive limits on the capacity regions. The first problem we consider is the one-sided interference channel with bidirectional and rate-limited receiver cooperation. We propose a coding scheme that tailors two versions of superposition coding with classical relaying protocols. Theproposed scheme unifies and recovers previous results for the unidirectional coop-eration, yet in simpler forms. Analytical and numerical results confirm the benefitsof cooperation and illuminate the ideas behind the coding strategy. The second problem generalizes the first one by allowing the existence of bothcrossover links in the channel. We propose a coding scheme for this channel byextending noisy network coding to encompass rate-splitting at the encoders. Theachievable rate region is shown to be the same as a region achieved by explicitbinning. As a corollary, we prove that noisy network coding achieves the capacityregion of the Gaussian channel within 1 bit, under strong interference. Our resultis among the first to show constant-gap optimality of noisy network coding for amultiple-unicast problem, and to demonstrate equivalence in terms of achievablerates of two different coding approaches for a noisy interference network. We follow up by introducing a dedicated relay into the interference channelwhich simultaneously helps both receivers. For this third problem, the interferencechannel with a relay, we propose new coding schemes based on layered codes for long- and short-message quantize-forward techniques. The short-message schemesshow improvements in the achievable rates compared to other known coding tech-niques, especially when the channel is asymmetric, while relaxing the excessive delayissue of the long-message scheme. The analysis also reveals the trade-off betweenachievable rates, encoding and decoding delays, and complexity. In the fourth problem, we propose a new model for cooperative communication,the interfering relay channels, which consists of two neighboring relay channelsinducing interference to each other. Each relay, by utilizing a finite-capacity andnoise-free link to its own receiver, helps the receiver decode the desired message.We characterize the exact and approximate capacity region and sum-capacity forvarious classes of channels. The established results generalize and unify severalknown results for the relay and interference channels.The methods and results shown in this thesis aim at providing insight intopotential techniques for cooperative interference management in real-world systems. / <p>QC 20131001</p>

The problem of electromagnetic field penetration in the finite-resistivity conductors of a uniform, multiple, coupled transmission line system (MTL) is considered. Under the assumption of quasi-transverse electric and magnetic (quasi-TEM) mode of propagation, the problem of determining the per-unit-length resistance and inductance matrices for such MTL systems reduces to solving a quasi-magnetostatic problem. An integral equation for the current density distribution inside the conductors is formulated and solved numerically using the method of moments. From straightforward energy considerations and the current density distribution, the per-unit-length resistance and inductance matrices are calculated. Several microstrip configurations are then analysed and the effects of the geometrical characteristics of the structures on the per-unit-length inductance and resistance matrices, as well as their frequency dependence are investigated.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / To achieve good efficiency in a space-based radio transmitter, its final amplifier must be operated near the saturation point, in its nonlinear region. Because of strict band limitations, this nonlinear operation is combined with the problem of intersymbol interference. Normally, these problems are addressed using a combination of equalization and power back-off, resulting in reduced power efficiency. Many proposed receiver-based methods, such as Volterra equalization, attempt to compensate for the nonlinearity and ISI in a single block before the detector, allowing higher efficiency operation, but introducing a great deal of complexity. We propose a receiver-based method in which the two effects are dealt with in separate blocks, an equalizer and a linearizer, resulting in considerable simplification. We go further and place the detector before the linearizer, achieving improved performance by eliminating the errors introduced by the linearizer. Simulation results compare favorably with the performance of a linear AWGN channel.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / The National Radio Astronomy Observatory (NRAO) operates the Very Large Array (VLA) Radio Observatory in New Mexico, and the Very Long Baseline Array (VLBA) with 10 radio antenna in locations from Hawaii to St. Croix, as well as other radio telescopes at Green Bank, West Virginia, and the 12 meter radio antenna near Tucson, AZ. Although radio frequency (RF) bands have been set aside for passive use by these radio telescopes, harmful interference from increased demands on the radio spectrum is a growing problem for earth-based radio astronomy. For example, locating a radio observatory in a remote area is little defense from satellite downlink telemetry. This paper describes why the operation of the radio telescopes is susceptible to RF telemetry interference, what bands are particularly vulnerable and at what power levels, and how data collection and centralized control of the arrays are accomplished without RF telemetry.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / The aeronautical channel model is a good candidate for modeling the effects of multipath interference of telemetry signals on test ranges. The aeronautical fading channel model is parameterized by the signal to noise ratio, the Doppler shift and time delay between the specular and direct components, the specular to direct power ratio, the direct to diffuse power ratio, and the bandwidth of the multipath fading process. Segments of weighting signal data measured during a test at Tyndall AFB provide data which can be used to determine typical values of the above parameters in a variety of telemetering environments. In this paper, the set of parameters which most closely model the actual telemetry channel using the Tyndall data is determined.