Development of accurate physical layer models is very important for generating realistic network simulation results. Significant effort has been put into setting up physical layer models for wireless channels that emulate the impact of the channel on the higher layers of the network. Setting up the models is especially difficult for a frequency selective channel. In this thesis the use of non-linear functions to convert the frequency selective channel to an equivalent flat fading channel is examined. The analytical expressions for the statistics of the equivalent flat fading process that are needed to set up the physical layer models are derived. These results are used to set up the physical layer model for the frequency selective channel. Extensive simulations are performed to verify the accuracy of the model against a detailed physical layer implementation. The statistics of the model and the actual channel are seen to match, validating the method of setting up the models.

No description available.

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.

A Rayleigh/Rician fading channel based on Jakes¡¦ model is implemented by FPGA hardware in this thesis. Parameters, including vehicular speed, carrier frequency, quantization bits and internal clock rate, are carefully chosen according to the fading statistics. Verification of this fading channel hardware is carried out on Altera FPGA board with functional and time sequential test. Finally, performance of a differential PSK modem via fading and noisy channel is simulated and emulated in both software and hardware methods.

Aphasia can severely impact an individual’s ability to communicate. However, existing research on interventions is limited. The current study compared different stimulus fading procedures with an older adult diagnosed with aphasia. A multielement within a multiple baseline design across behaviors was used to measure the efficacy of each approach. Results showed that the time delay procedure was more efficient at fading prompts when teaching intraverbals.

A diversity combining scheme is examined that utilizes a demodulator's hard decisions in conjunction with knowledge of each decision's reliability. A maximum-likelihood bit decision is made, based on these partial decisions from the demodulator and on measurements of the state of the fading channel. The technique is sub-optimal since hard decisions are processed, but it may find application in low cost receiver design. The technique is optimal in the sense that a minimum probability of bit error is achieved, given a set of partial decisions and knowledge of their reliability. Performance analysis for the case of non-coherent frequency shift keying on a slow Rayleigh fading channel with additive white Gaussian noise includes the derivation of a tight upper bound on the probability of bit error, and estimates of the asymptotic performance relative to standard diversity schemes such as majority-voting, selection diversity, square-law, and maximal ratio combining. These results are supported by simulation results for bit and packet error rates in an example system. With five independent bit repeats and a BER of 10⁻³, the receiver is about 3 dB more efficient than majority-voting, and about 1 dB more efficient than selection diversity. The gain in efficiency, relative to the standard partial decision combination schemes, increases with the number of repeats. The degradation in performance in a practical receiver implementation is addressed, and it is demonstrated that near ideal performance may be obtained with only a few reliability weights quantized to a small number of levels. Furthermore, this performance is maintained over a wide range of average signal to noise ratio without having to adapt the reliability weights. When the reliability estimate is corrupted by additive white Gaussian noise, it is demonstrated that simple low- pass filtering of the signal strength estimate is sufficient to obtain near ideal performance. The performance is degraded in the presence of cochannel interference, but for a moderate level of interference the performance is demonstrated to be superior to majority-voting or selection diversity. Other results include a method to estimate the optimal quantization thresholds, and a method to obtain the probability of error of selection diversity receivers employing signal to noise ratio measurement quantization. The selection diversity analysis is applicable to the more general case of Rician fading. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / While investigating methods for more efficiently allocating the available spectrum researchers noticed that in many geographical locations, there are broad bands of frequencies that are lightly utilized. Such inefficiencies are inevitable with fixed spectral allocation rules. Cognitive Radios actively measure the spectral utilization and adapt their modulation, frequencies, bandwidths, power, etc. to take advantage of these lightly used “spectral holes” or “white spaces”. Much of the research work in cognitive radios has not taken into account some of the challenges faced in the telemetry community-including multipaths and a guaranteed quality of service. This paper highlights how some mathematical models of adaptive modulation discussed extensively in many research papers and textbooks can be used in Cognitive Radios as well.

No description available.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / This paper investigates the application of iterative equalization techniques to overcome multipath fading for shaped offset QPSK (SOQPSK) in aeronautical telemetry. Two iterative equalization techniques for turbo encoded SOQPSK are presented. The first is the optimal-MAP turbo equalizer for OQPSK. The second equalizer is the adaptive decision feedback equalizer. Simulation shows that in the presence of frequency selective multipath typically encountered in aeronautical telemetry, both of these equalizers exhibit impressive performance.

Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Downgrading of fruit due to insufficient red colour has limited the profitability of lucrative blushed pear cultivars (Pyrus communis L.). In 'Rosemarie', poor fruit colour has been ascribed to pre-harvest red colour loss during periods of high temperature. The regulation of colour development in pears has not been studied and, in addition, little is known about anthocyanin degradation in attached fruit. Changes in colour were recorded and phenylalanine ammonia-lyase (PAL) and UDPGalactose: flavonoid-3-0-glycosyltransferase (UFGT) activities assessed in response to cold fronts and during fruit development in order to establish the regulation of colour development in red and blushed pear cultivars. Best red colour was generally attained a month or more before harvest whereafter red colour faded towards harvest. Unlike in some other fruits, UFGT activity apparently did not limit colour development whereas fading of red colour towards harvest might relate to decreasing PAL activity. 'Rosemarie' colour fluctuated considerably, increasing with cold fronts and decreasing during intermittent warmer periods, while red colour was more stable in other cultivars. PAL and UFGT activities in 'Rosemarie' increased in response to low temperatures, but were unaffected in 'Bon Rouge'. We concluded that anthocyanin synthesis in 'Rosemarie' requires low temperatures while colour development in 'Bon Rouge' and probably also other cultivars is primarily regulated by endogenous factors. Detached pome fruit were used to study temperature and light effects on anthocyanin degradation and fruit colour and to assess the modifying effect of anthocyanin concentration on colour loss. Anthocyanin degradation and red colour loss increased linearly between 10°C and 30°C. Irradiation further increased the rate of degradation and colour loss. The rate of colour loss depended on anthocyanin concentration, being much faster in fruit with high compared to fruit with low pigment levels. This was ascribed to the exponential relationship between anthocyanin concentration and hue at high pigment levels and the linear relationship at lower pigment levels. Anthocyanin degradation and pre-harvest red colour loss in 'Rosemarie' was quantitatively confirmed and corresponded with a warm period during fruit development. Based on these data, we attributed the susceptibility of 'Rosemarie' to pre-harvest colour loss to low anthocyanin concentrations in its peel that allow the visualisation of net anthocyanin degradation at high temperatures. Overhead evaporative cooling (EG) as measure to improve red colour in blushed pears was evaluated. 'Rosemarie' fruit that received pulsed EG applications from two weeks before harvest at air temperatures exceeding 28°G were redder than control fruit at harvest. EG had no effect on 'Forelle' colour. Though EG could be used to improve 'Rosemarie' fruit colour in warm production areas, its effect was relatively small compared to colour change in response to temperature. Lastly, we assessed the photoprotective function of anthocyanin in pear peel. Photoinhibition was evident in exposed faces of pears under natural conditions. The extent of photoinhibition increased with decreasing redness of peel and was maintained after photoinhibitory treatment. Although anthocyanin was apparently able to afford photoprotection at 40oG, we argued against this as a general function. There were indications that photoprotection was associated, but not necessarily due to light attenuation by anthocyanin. / AFRIKAANSE OPSOMMING: Afgradering van vrugte vanweë onvoldoende rooi kleur beperk die winsgewendheid van blospeercultivars (Pyrus communis L.). In die geval van 'Rosemarie' word swak kleur toegeskryf aan vooroes rooikleurverlies gedurende warm periodes. Die regulering van kleurontwikkelling in pere is nog nie ondersoek nie terwyl min bekend is oor antosianiendegradasie aan die boom. Om die regulering van kleurontwikkelling in rooi- en blospeercultivars vas te stel, is veranderinge in kleur en in die aktiwiteit van fenielalanien ammonia-liase (FAL) en UDPGalaktose: flavonoied-3-o-glikosieltransferase (UFGT) gemeet gedurende vrugontwikkelling en in reaksie op koue fronte. Pere was op hul rooiste 'n maand of langer voor oes. Hierna het rooi kleur afgeneem tot met oes. Anders as in sommige ander vrugsoorte het UFGT aktiwiteit nie kleurontwikkeling beperk nie. Die afname in rooi kleur tot met oes mag egter verband hou met 'n gelyktydige afname in FAL aktiwiteit. 'Rosemarie' kleur het aansienlik gefluktueer in reaksie op temperatuur. Rooi kleur het toegeneem met koue fronte en afgeneem in die warmer periodes tussen fronte. Rooi kleur was meer stabiel en klaarblyklik minder afhanlik van lae temperature in ander peercultivars. Die noodsaaklikheid van lae temperature vir kleurontwikkelling in 'Rosemarie' is bevestig deur 'n toename in ensiemaktiwiteit in reaksie op koue fronte. Lae temperature het geen effek gehad op ensiemaktiwiteit in 'Bon Rouge' nie. Appels en pere is gebruik om die effek van temperatuur en lig op antosianiendegradasie en vrugkleur te ondersoek. Die modifiserende effek van antosianienkonsentrasie op kleurverlies is ook ondersoek. Antosianiendegradasie en rooi kleurverlies het lineêr toegeneem tussen 10° en 30°C. Beligting het degradasie en kleurverlies verder versnel. Die tempo van kleurverlies was afhanklik van antosianienkonsentrasie. Kleurverlies was aansienlik vinniger in vrugte met hoë pigmentvlakke, in vergelyking met vrugte met lae pigmentvlakke vanweë die eksponensiële verwantskap tussen antosianienkonsentrasie en kleurskakeringswaardes (hue values) by hoë pigmentvlakke en die lineêre verwantskap by lae pigmentvlakke. Antosianiendegradasie en vooroes rooikleurverlies in 'Rosemarie' is kwantitatief bevestig en het saamgeval met 'n warm periode tydens vrugontwikkelling. Gebaseer op hierdie data is die gevoeligheid van 'Rosemarie' vir vooroes rooikleurverlies toegeskryf aan lae antosianienkonsentrasies wat die sigbaarheid van netto antosianiendegradasie by hoë temperature verhoog. Die gebruik van oorhoofse evaporatiewe verkoeling (EG) om rooi kleur van blospere te verbeter is ge-evalueer. 'Rosemarie' vrugte wat evaporatief verkoel is bo 28°G vanaf twee weke voor oes, was rooier as kontrole vrugte by oes. 'Forelle' kleur het nie gereageer op EG nie. Die effek van EG op vrugkleur was relatief klein in vergelyking met die effek van temperatuur. AI kan EG 'Rosemarie' kleur verbeter in warm produksiestreke sou dit meer effektief wees om 'Rosemarie' se verbouing te beperk tot koeler klimaatstreke. Laastens is die vermoë van antosianien om peerskil teen fotoinhibisie te beskerm ondersoek. Fotoinhibisie was aanwesig in vrugskil wat direk blootgestel was aan sonlig in die boord. Die omvang van fotoinhibisie het toegeneem met 'n afname in rooi pigmentasie van vrugskil. Die verband tussen skilkleur en fotoinhibisie was steeds aanwesig na blootstelling aan ligstres by 10° en 400G. Ons het egter geredeneer teen 'n algemene funksie vir antosianien in fotobeskerming by hoë temperature. Verder was daar aanduidings dat, alhoewel geassossieer met rooi skilkleur, beskerming teen ligstres nie noodwendig te wyte was aan antosianien nie.