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Over the past few decades, the size and scope of the Internet has grown exponentially. In order to maintain support for legacy clients, new applications and services have been limited by dependence on traditional sockets and TCP, which provide no support for modifying endpoints after connection setup. This forces applications to implement their own logic to reroute communications to take advantage of composable services or handle failover. Some solutions have added socket operations that allow for endpoints to be redirected on the fly, but these have been limited in scope to handling failover and load balancing. We present two new sets of socket operations. The first set allows servers to dynamically insert and remove intermediaries into communication streams. This allows applications to decide in real time whether to use services provided by 3rd parties such as encryption, filtering, and compression. In this way, applications can employ dynamic service composition to customize communication between clients and servers. The second set of operations allows sockets to be split such that all frames written to the socket are sent to multiple recipients. This is useful for implementing fast failover and passive communication monitoring. All of these operations are implemented in user space and gracefully handle legacy TCP clients, making quick deployment of distributed Internet applications a real possibility. Performance tests of the new operations on remote hosts show that the overhead introduced is not prohibitive.

Microprocessor techniques are always developed with the purpose of achieving greater data capacity per unit time. There are many different types of cables on the market which can be used in connecting the digital processing system. No matter what kind of material the cable is made of, the characteristic impedance mismatch and crosstalk from the neighboring lines could generate the noise to the line itself. Therefore, it is necessary to reduce the noise, especially for the high frequency data transmission bus. This report presents a simulation of two long distance transmission buses and reducing the noise by diode terminators.

The aim of this paper is to develop a series of designs which allow evaluation of several digital communication system design concepts. Circuits were developed and tested which deal with three central areas of concern in digital communication networks. They include random signal generation and detection, signal conditioning, and digital timing extraction. A pseudorandom sequence generator and correlator design form the basic digital channel. Bi-phase transmission coding and digital timing regeneration were later added to the initial channel. System performance was confirmed by inserting errors and measuring error rate.

The focus of this dissertation is the performance analyses of two classes of frequency-hopped spread-spectrum multiple access (FH-SSMA) systems in various fading environments. The capacity of Viterbi’s FH-SSMA system is evaluated under three types of fading, namely Rician, shadowed Rician, and Nakagami fading. The results of recent experiments have indicated that these fading phenomena occur in various environments where the FH-SSMA system may be implemented. In this dissertation, the deletion probability for each fading scenario is derived. Subsequently, the system capacity is analyzed in terms of maximum number of users versus average bit error rate. The effect of a change in the signal-to-noise ratio level on the system capacity is also demonstrated. For Rician fading, it is found that the capacity of the system with a Rician factor of 2 dB is reduced by 13 percent as compared to the capacity of the non-fading case. For shadowed Rician fading, three shadowing scenarios are considered: light, average, and heavy. It is shown that the light and the average shadowing scenarios provide only a slight decrease in the capacity, while the heavy shadowing scenario renders a capacity identical to that for the Rayleigh fading case. Finally, for Nakagami fading the capacity is found to decrease by 50 percent as the fading parameter is reduced to 0.5. The performance of a cellular frequency-hopped spread-spectrum multiple access system is studied under an indoor environment. It is demonstrated how the system capacity, given in terms of the number of users per cell, is affected by the number of cells in the system. Also, the influence of the delay spread, which is the result of multipath propagation, is investigated. The analysis focuses on a worst-case scenario where a user receives both the desired and interfering signals with equal power levels. This scenario applies to both the downlink and the uplink. It is shown that the system capacity is reduced drastically as the number of adjacent interfering cells increases from one to three. Previous work concerning the indoor multipath propagation assumed that the number of paths is fixed, the path delays are uniformly distributed, and the path gains are equal. In this dissertation, a more realistic channel model derived from actual impulse response measurements by Saleh and Valenzuela is employed. The model consists of clusters of rays with constant cluster and ray arrival rates and power-delay time constants. The system performance is shown to be affected strongly by the change in the power-delay time constants, yet only slightly influenced by the variation in the arrival rates of the rays and clusters. In addition, the degradation in the system performance due to the delay spread becomes more severe as the transmission rate increases. / Graduate

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / A repeater is being designed to provide a telemetry and compressed video link from a remote robot located in the Dry Valleys Region of Antarctica, over a mountain range to California via McMurdo Antarctica. In return a command link is provided for control. A simple task normally, but a bit more difficult when considerations include the unforgiving elements of Antarctica itself. Even with a design using the most robust equipment, tradeoffs must always be made for the effects of the isolation and the weather. This paper describes one approach to the design of equipment capable of insuring the proper bandwidth, power output, and receive sensitivity that can use the energy provided by Mother Nature to continually charge the primary power source, and the engineering struggle to use electronic equipment in the severe and harsh environment of Antarctica.

In this thesis, the physical layer of the Single Channel Ground and Airborne Radio System (SINCGARS) was analyzed in order to gain insight into the bit-error-rate (BER) performance in various channel conditions. The BER performance of the radio was examined using theoretical, simulation, and experimental techniques. These results are presented in graphical form as the probability of bit error as a function of the energy per bit to noise power spectral density ratio. The results of the simulation show excellent agreement with the theory, while the experimental results deviate from theory at higher signal-to-noise levels. This suggests sub-optimal SINCGARS performance, most notably in the signal power to noise power range where reliable data transmission should take place.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis (M.Eng.)(Electronic)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references.

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