This thesis proposes a multistage RAKE receiver for use at the base station of a Code Division Multiple Access (CDMA) cellular communications system. This receiver combines the interference rejection capability of multiuser receivers with the robust performance of a RAKE receiver in the presence of multipath interference. Unlike previous multiuser receiver designs, this multistage RAKE receiver requires no a priori information about the time-vary multipath radio channel. The thesis presents a mathematical description of the multistage receiver, and a software simulation of the receiver performance. A wide range of channel models are considered which include the effects of Gaussian noise, multipath propagation, imperfect power control and multiple access interference for the reverse link CDMA channel. Under a wide range of conditions, the multistage RAKE receiver is able to support two to three times as many users as a conventional single stage RAKE receiver. The receiver is also shown to be robust to the near-far problem. / Master of Science

This research aims at solving an engineering design problem encountered in the field of wireless communication systems using mathematical programming techniques. The problem addressed is an indispensable part of micro-cellular radio system design. It involves an optimal location of radio transmitters, given a distribution of receivers and desired signal characteristics. The study has been conducted with the intent of making this problem an integral part of a CAD system for designing radio communication systems. The tool that has been developed for locating a transmitter in such a context is sensitive to different needs of coverage at different locations in the design space. The physical nature of this problem enables it to be conceptualized as a traditional facility location problem. The transmitter is a service facility responsible for serving all the receivers in the design space. A cost is incurred in terms of path-loss, delay spread, and other separation-based measures, whenever service is extended to a receiver. The objective is to place this transmitter in such a way that it optimally serves all the receivers, as measured according to some merit function. However, the nature of the latter merit or objective function, and the nature of the acceptable region for transmitter placement, imparts a special structure to the problem that distinguishes it from traditional facility location problems. The aim of this research effort is to construct a suitable representative mathematical model for this problem, and to design and compare various solution methodologies that are computationally competitive, numerically stable, and accurate. / Master of Science

The design of cellular wireless communication systems is influenced by the propagation characteristics of the channel and their effect on transmitted signals. The multipath propagation characteristics of a channel, except under simple transmission conditions, limits the design of emerging cellular systems. Once the propagation conditions are understood, systems can be designed more efficiently in terms of site layout and frequency planning, to reduce deployment costs and improve performance. A software tool for site specific radio propagation prediction is being developed at the Mobile and Portable Radio Group, Virginia Tech. The objective of this research is to develop re-usable program modules that can be utilized to implement several functional features of the software. This thesis describes the raster and vector programming libraries that have been developed during this research. These libraries are utilized in the database module, user interface and graphics module and propagation prediction module of the software. Significant among the capabilities that these libraries provide are the ability to store and retrieve raster and vector data from the database, import measured and predicted data available in standard data formats into the database, obtain user inputs through an interactive mechanism, display images of site specific information at various resolutions, and enable the user to view and analyze measured and predicted data. This thesis also presents the data format, that has been defined during this research, to acquire and import contour and elevation information of buildings. The SISP General Data Format (GDF), that has been developed, to facilitate import of measured and predicted data has also been described. The Hierarchical Data Format (HDF), developed by the National Center for Supercomputing Applications (NCSA), has been adopted to store measured and predicted data in the database. The programming techniques used to retrieve and display data stored in this format are also outlined in this thesis. SISP has been developed on Sun Sparc workstations. Details of the function libraries that have been developed, programming methodologies employed, and data formats that have been defined for site specific and measured and predicted RF data are included in this thesis. / Master of Science

Our society is undergoing a wireless revolution in which there is a rapidly increasing demand for personal communication services (PCS). Several alternate technologies have been proposed to meet this demand, including a 1.25 MHz CDMA system. It is important to provide system designers with tools to accurately predict system performance. Analytical techniques are useful for providing general information on system performance, but may not fully capture the complexities of the mobile radio channel needed to accurately predict the performance of complex system designs. This thesis presents a novel simulation technique in which a CDMA system is modeled by software, but the channel impulse response model is derived from actual measurements. This thesis describes a bit error simulation tool for a 1.25 MHz bandwidth CDMA system. The simulator incorporates measurement-based channel impulse response data with the simulated CDMA system. Bit error rate for COMA is simulated under a variety of actual channel conditions, including heavy urban, urban, suburban and rural environments. Simulation results for both 915 MHz and 1920 MHz are presented. Vertical and circular antenna polarization are compared. In the simulation, a RAKE receiver is implemented, the advantage of this RAKE receiver implementation is demonstrated by comparison to a single correlation receiver. Results for outage probability are also presented. / Master of Science

The objective of this research is to compare radio channel impulse response measurements with site-specific radio wave propagation prediction techniques. A wide band spread spectrum measurement system was developed, and desirable measurement locations were selected on the Virginia Tech campus. These measurements are designed togo beyond statistical characterizations of the channel and will aid in determining how the propagation environment is influencing the multi path propagation. The objective is to not only measure the delays and relative powers of multi path components, but to carefully document their angles of arrival and resolve the overall paths that these multipaths had to take to reach the receiver. This information will be used to compare with propagation prediction simulations using the modeled environment, and therefore, provide new insight into the nature of reflection and scattering of radio propagation in typical microcellular environments. As a first step in this endeavor, building surface characterizations are made in order to determine empirical reflection coefficients of common building materials. Propagation experiments have been designed to determine applicability of Fresnel reflection formulas to non-ideal conditions, such as waves that are not perfect plane waves, rough surfaces, etc. This information allows propagation prediction techniques to further quantify the site-specific mobile radio environment and yield more accurate propagation estimates. For this endeavor, Whittemore Hall and Squires Student Center were Chosen to provide reflection measurements from rough stone, glass, and brick surfaces. Detailed descriptions of measurement techniques, analysis and results are included. / Master of Science

No description available.

Rural communities have been disconnected from the global world in the past due to lack of infrastructure that rendered connectivity a challenge for them. Recent developments in information and communication technology (ICT) have led to improved connectivity in these areas. As a result, mobile phones have become ubiquitous in these rural communities. A matrix was proposed in this study in order to evaluate and assess the impact of mobile devices on development of the rural communities. Existing measurement tools have not yet explored how the usages of mobile phones and other ICTs are impacting the lives of people in rural communities of South Africa. The aim of this study was to understand the existing criteria used to measure the impact of ICTs in rural communities. This was be achieved by focusing on the use of mobile phones in the community of Phake Rebone, taking into account different users. Once this was established, the study had a primary objective to design a matrix that would assist in evaluating and assessing the impact of a mobile phone in social activities such as learning, business and governance. This was achieved by using a case study method, employing qualitative and quantitative research methods. Cases within a case study were used to uncover how the core groups within the community used the mobile phone. A mixed method approach was used in data gathering and analysis to enable the researcher to identify usages and challenges related to the mobile phones. Data was collected from 401 participants and was analysed through the computer-aided tools such GoogleDocs and Microsoft Excel. The findings of the study showed a greater usage of the mobile phone. The literature findings of the use of the mobile phone for basic communication as well as growing adoption of applications such as social media and Internet were confirmed. The use in community related activities and work purposes that impacted the community members were minimal. The need of training to gain knowledge on how to use the device more effectively was established. The proposed matrix therefore seemed v relevant not only to measure impact but also to highlight the areas in which the community members can be trained on. The noted usage trends and needs by the community were then used to formulate indicators that could be used for the matrix. The indicators were then used to develop a matrix that could be used by community members and other interested parties to measure the impact of mobile phone on development of the users. The results of the matrix were also proved to be efficient in assisting individual users in recording the skills acquired through the use of the mobile phone. The matrix can be used in consultation with the guidelines that were formulated to ensure that each user, particularly from rural communities, benefits from such an evaluation tool / Development Studies / D. Litt. et Phil. (Development Studies)

Mobile phone usage involves the mobile phone, the telecommunications system, mobile phone users, and the adoption and use of the system. Mobile communications is a complex and rapidly changing industry consisting of the hardware, software, network and business aspects. Mobile phone users are influenced by demographic, social, cultural and contextual factors that complicate the understanding of mobile phone usage. Advances in technology and market competition drive the addition of new services and features. In contrast, human cognition and attention are more constrained and many users find it difficult to cope with the cognitive demands of mobile phone technology. The aim of this study is to develop a model for representing the influence of motivational needs and cultural factors on mobile phone usage variety. The link between motivational needs and mobile phone usage variety, the cultural factors that influence mobile phone usage variety, as well as usage spaces as an approach to representing usage variety, are researched. The research encompasses a literature study, structured interviews, a pilot study and a survey. The pilot study and survey yielded data about mobile phone usage of university students under the age of 30 in South Africa. The results from the statistical analysis were triangulated with the findings of the literature study and the observations made about mobile phone usage during this two-year period. A final survey was conducted to verify the model. The contribution of this study is a mobile phone technology usage model (MOPTUM) for representing the motivational and cultural factors that influence mobile phone usage variety in such a way that users can use the model to express their mobile phone usage needs in non-technical terms while marketers and designers can use the model to convert the expressed user needs into the features required. MOPTUM draws on concepts and models from sociology, computer-supported cooperative work, human-computer interaction and technology adoption models from the field of marketing. MOPTUM verifies some existing findings on mobile phone usage and then integrates and extends these existing models to provide a new model for understanding the motivational and cultural factors that influence mobile phone usage variety. / Computing / Ph. D. (Computer Science)

Thesis (MBA (Business Management))--University of Stellenbosch, 2009.

This thesis takes a deeper look into customer behaviours when it comes to buying new mobile phones. We take a look at four main types of planned obsolescence we’ve found, which include: economic obsolescence, obsolescence of function, obsolescence of desirability and obsolescence of quality. With a questionnaire and focus group study we try to find out the underlying reasons why users buy new phones while their old ones are still functional. Since this is not a new subject, we try to map the problems we encounter in our study to the four already defined forms described above, and we try to see if there are other forms that are not yet defined. What we found out was that these four categories hold up very well, but are not as separate as one would have thought when reading. While we find out many reasons why people change their phones we do not offer a solution. But we do offer a better understanding of the problem and hope the consumer will take part of the knowledge.