Browsing by Author "Morton, John M."

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    Adaptive Equalization for Indoor Channels
    Morton, John M. (Virginia Tech, 1998-08-03)
    This thesis describes the use of adaptive equalization techniques to compensate for the intersymbol interference (ISI) that results when digital data is transmitted over a multipath radio channel. The equalization structures covered in this work are the linear transversal equalizer (LTE), the fractionally spaced equalizer (FSE), the decision-feedback equalizer (DFE), and the maximum-likelihood sequence estimation (MLSE) equalizer. This work also covers adaptive algorithms for equalization including both the least mean squares (LMS) and the recursive least squares (RLS) algorithm. All these equalizer structures and algorithms will be modeled using various simulation modules. Equalization for both stationary and mobile radio channels is considered. Stationary channels are modeled with a simple exponentially decaying profile. The mobile radio channel is represented using a two-ray Rayleigh fading model for an outdoor environment. The SIRCIM channel modeling tool is used to create channel profiles for an indoor mobile radio channel. Adaptive arrays and their similarities to linear equalizers are also studied in this thesis. The properties and performance of simple adaptive array systems using the LMS and RLS algorithms are examined through simulation. This thesis concludes with an in-depth study of the use of adaptive equalization for high-speed data systems operating in an indoor environment. Both stationary and slowly varying radio channels are examined. Simulations of DFE and MLSE equalizers operating in such a system show that both equalizer structures provide better BER performance over a system with no equalization. These simulation results also show that the MLSE equalizer provides better performance than the DFE in almost all cases, but requires a great deal more computations.
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    Effects of human disturbance on the behavior and energetics of nonbreeding sanderlings
    Morton, John M. (Virginia Tech, 1996)
    Human disturbance of avifauna and other wildlife is defined as any intentional or unintentional anthropogenic action that elicits a metabolic or behavioral response. I proposed that the energetic response to disturbance should be reflected as increased existence metabolism (EM). If so, then there must be three behavioral responses to increased EM: increased energy intake compensates for increased EM, habituation reduces increased EM, and dispersal avoids increasing EM altogether. I applied this model to captive and free-ranging nonbreeding sanderlings (Calidris alba). I exposed 24 captive sanderlings to a 5-min disturbance event during each of 10 diurnal hours over two 4-d trials. The metabolizable energy of food ingested was determined for each bird daily. Total body electrical conductivity and body mass were measured during trials to account for energy derived from metabolized body tissues. These combined values suggest that EM was elevated by 7% in response to disturbance during 8% of daylight hours. Caged sanderlings responded to disturbance with alert and attempted escape behaviors; i.e., dispersal. Sanderlings spent more time attempting to escape on the first day of each trial and during the first of 10 disturbance events in a day, suggesting some behavioral habituation. There was evidence of compensatory feeding after the trials, but not during them. Abundance, behavior, and distribution of free-ranging sanderlings were studied at Assateague Island National Seashore, Maryland, during two winters in 1991-93. Increasing pedestrian traffic decreased the probability of sanderling occurrence on 200-m plots by as much as 45%. Average sanderlings ambulated or flushed when pedestrians and vehicles approached within 20 m and 10 m, respectively, and flushed more frequently in response to pedestrians than vehicles. Mean densities were nearly 60% less on disturbed than undisturbed 200-m plots. Sanderling densities were highest on plots with invertebrate prey and no disturbance, and lowest on those with disturbance and no prey. Apparently, higher food availability can partially compensate for the costs of disturbance. Disturbed sanderlings spent 177% more time in maintenance behaviors, 151% more time in flight, and 42% less time roosting than undisturbed sanderlings. On average, undisturbed sanderlings expended 6 kJ-h⁻¹ whereas disturbed sanderlings expended 9 kJ-h⁻¹. More than 90% of the variation in energy expenditure was attributable to time in flight. Although chronic human disturbance can elevate EM in the caged environment, the flush response largely determines the energetic cost of disturbance in free-ranging sanderlings.
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    Habitat Relationships and Life History of the Rota Bridled White-eye (Zosterops rotensis)
    Amidon, Frederick A. (Virginia Tech, 2000-09-01)
    The Rota bridled white-eye (Zosterops rotensis)(Aves, Passeriformes) has experienced a severe population decline and range restriction over the last four decades. Little is known about this species and factors involved in the decline and range restriction are unclear. This study examined the potential roles of habitat alteration, introduced black drongos (Dicrurus macrocercus), and introduced rats in the decline and gathered more information on the behavior and breeding biology of this species. New life history data were collected and Rota and Saipan bridled white-eyes were found to differ in nest site characteristics and some behaviors. The importance of habitat alteration was assessed by examining Rota bridled white-eye habitat relationships at the microhabitat, within-range, Sabana-wide, and island-wide levels. Rota bridled white-eyes show a preference for high elevation wet forest but what drives their distribution within their current range was unclear. However, the alteration of this forest type by supertyphoon Roy in 1988 was probably the major factor in the decline of Rota BWEs between 1982 and 1996. Black drongo and Rota bridled white-eye relationships were addressed using current and historical survey data. Black drongos were found to prey on Rota bridled white-eyes but they probably only played at most a partial role in the decline of the Rota bridled white-eye. Introduced rats densities were assessed in Rota bridled white-eye areas and on other areas of the island and no evidence for rat numbers limiting Rota bridled white-eyes to their current range was found.