Performance Study of Hybrid Spread Spectrum Techniques

This thesis focuses on the performance analysis of hybrid direct sequence/slow frequency hopping (DS/SFH) and hybrid direct sequence/fast frequency hopping (DS/FFH) systems under multi-user interference and Rayleigh fading. First, we analyze the performance of direct sequence spread spectrum (DSSS), slow frequency hopping (SFH) and fast frequency hopping (FFH) systems for varying processing gains under interference environment assuming equal bandwidth constraint with Binary Phase Shift Keying (BPSK) modulation and synchronous system. After thorough literature survey, we show that hybrid DS/FFH systems outperform both SFH and hybrid DS/SFH systems under Rayleigh fading and multi-user interference. Also, both hybrid DS/SFH and hybrid DS/FFH show performance improvement with increasing spreading factor and decreasing number of hopping frequencies

Indoor Radio Propagation Measurements in Different Environments Using Two Types of Transmitting Antenna

The tremendous growth in Wireless Communications System has greatly increased the need to improve the accuracy of predicting signal propagation. It is important to have a tool that can be used to predict the signal coverage area, a method to determine the path loss in microcells, the attenuation due to different partitions and the effect of the environments. To understand radio propagation characteristics in buildings for Personal Communication Systems (PCSs), a comprehensive measurement was carried out in a shopping and business complex, The Mall, in Kuala Lumpur. Two types of Base Station (BS) antennas, Omni-directional and Panel antenna, were mounted on the ceiling and wall respectively. The Mobile Station (MS) uses an antenna with 3dB gain, height 0.5 m and 1.2 m respectively, at 935 MHz carrier frequency. Many test settings were chosen in the office, on the floor sharing with the atrium, lower ground floor and car park, with Line-of-Sight (LOS) and without LOS. The results show some variations of signal strengths with distance that have distinct near and far field regions. The buildings where the measurements were carried out typically have walls and columns constructed from concrete blocks. Within the building the time spread of arriving radio signals depends on reflections and scattering from the structure of the buildings. The results of these measurements are presented and discussed in order to investigate penetration losses in walls, soft boards and floors. The results showed that shadowing due to the objects has a greater influence on the signal strength than the distance between the transmitting and receiving antenna. The path loss within a building is linearly dependent on the logarithm of the distance, on the number of obstacles blocking the signal, on the number of walls between transmitter and receiver antenna, and on the number of floors vertically between the transmitter and receiver antennas. Another important factor is the type of the environment it is operating in, which is given as the factor n. Comparisons between predicted and measured results have shown that the model is capable of predicting the attenuation within the building for different environment

Transcriptional Silencing and Anti-Silencing of Virulence Genes in the Bacterial Pathogen Shigella Flexneri: VIRB, DNA Supercoiling, and the Histone-Like Nucleoid Structuring Protein

Transcriptional silencing and anti-silencing affect many aspects of bacterial physiology, including virulence in bacterial pathogens. In Shigella species, a group of gram-negative pathogens that cause bacillary dysentery in humans, the histone-like nucleoid structuring protein (H-NS) transcriptionally silences virulence genes found on the large virulence plasmid while VirB anti-silences these genes. However, the mechanistic details of their interplay are not fully understood. To elucidate their regulatory mechanisms, I use the icsP virulence locus, which shares a long intergenic region with the divergently transcribed ospZ gene (1535 bp from TSS to TSS). Prior to this work, two discrete H-NS binding regions had been identified, suggesting H-NS-mediated bridging of these two regions as the mechanism of silencing. However, I show that changes to the spacing and helical phasing designed to disrupt the potential bridging were tolerated, suggesting an alternate mechanism of silencing is at play. In addition to H-NS, two other H-NS homologs found in S. flexneri, StpA and Sfh, can also silence the icsP promoter. Interestingly, VirB counters transcriptional silencing mediated by these other H-NS homologs. The site required for VirB-dependent anti-silencing of the icsP promoter is located over 1 kb upstream of the TSS, and nearly 500 bp upstream of the ospZ promoter, but exactly how VirB accomplishes this long-range regulation is not known. I show that VirB docks to this recognition site in vitro and has a high specificity for this site in vivo. Using a combination of 1D and 2D chloroquine-based agarose gel electrophoresis, I demonstrate that, upon docking to its recognition site, VirB triggers a loss of negative supercoiling of our VirB-dependent PicsP-lacZ reporter; importantly, this phenomenon occurs with native VirB levels in S. flexneri. Because H-NS is sensitive to DNA topology at some promoters, it is tantalizing to envision that VirBmediated changes in supercoiling alleviate H-NS-mediated silencing of virulence genes in Shigella. Although anti-silencing proteins in other bacteria, including related pathogens, bear little sequence homology to VirB, the possibility that changes to DNA supercoiling mechanistically unite this group of proteins requires further consideration when studying transcriptional silencing and anti-silencing processes in bacteria

A comparison between coherent and noncoherent mobile systems in large Doppler shift, delay spread, and C/I environment

The performance and implementation complexity of coherent and of noncoherent QPSK and GMSK modulation/demodulation techniques in a complex mobile satellite systems environment, including large Doppler shift, delay spread, and low C/I, are compared. We demonstrate that for large f(sub d)T(sub b) products, where f(sub d) is the Doppler shift and T(sub b) is the bit duration, noncoherent (discriminator detector or differential demodulation) systems have a lower BER floor than their coherent counterparts. For significant delay spreads, e.g., tau(sub rms) greater than 0.4 T(sub b), and low C/I, coherent systems outperform noncoherent systems. However, the synchronization time of coherent systems is longer than that of noncoherent systems. Spectral efficiency, overall capacity, and related hardware complexity issues of these systems are also analyzed. We demonstrate that coherent systems have a simpler overall architecture (IF filter implementation-cost versus carrier recovery) and are more robust in an RF frequency drift environment. Additionally, the prediction tools, computer simulations, and analysis of coherent systems is simpler. The threshold or capture effect in low C/I interference environment is critical for noncoherent discriminator based systems. We conclude with a comparison of hardware architectures of coherent and of noncoherent systems, including recent trends in commercial VLSI technology and direct baseband to RF transmit, RF to baseband (0-IF) receiver implementation strategies

Improvement of mobile trilateration accuracy with modified geo-location techniques.

Masters Degree. University of KwaZulu-Natal, Durban.Abstract available in pdf

Event program

UNLV Undergraduates from all departments, programs and colleges participated in a campus-wide symposium on April 16, 2011. Undergraduate posters from all disciplines and also oral presentations of research activities, readings and other creative endeavors were exhibited throughout the festival