Cellular telephone systems

In the present computer age, cellular technology and portable computers are becoming an integral part of the life. Each computer user wants to access the computing resources, irrespective of the location. Because of this need the computing paradigm "Mobile Computing" has assumed a primary role in modern computer communication technology. While dimensioning the network resources, it is very important to know how the users move around the geographical area covered by the cellular network. This knowledge allows us to plan the system resources in order to achieve the QoS required. The major factors that affect the performance, along with the mobility pattern of the mobile user, are the speed at which the user is moving and the load on the network. In this research, we study different types of mobility patterns the user can follow and it's impact on the network services. We have proposed and evaluated a reservation scheme to improve the QoS in the cellular network. The reservation scheme reserves some part of the bandwidth for handoff connections. We have developed simulation programs and have studied three mobility patterns namely leading movement type, random motion, and square-street mobility pattern for measuring the QoS for cellular network. It has been observed from the results that at an average speed of 50 miles per hour with the average loading of the network, a significant improvement in QoS has been achieved for all the mobility patterns by using the reservation scheme.

This dissertation is concerned with studies on the performance aspects of digital cellular radio systems operating in non-Gaussian multipath fading environments. The multipath fading channel, modeled as a superposition of sinusoidal random vectors, is the main focus of this work. Elementary phase distributions, which cause quadrature components of the composite received vector to be correlated, are studied and relevant envelope distribution for the resulting non-Gaussian quadrature components is investigated. The Student-t distributed random process is chosen to model the quadrature components in an indoor multipath fading channel when the number of sinusoidal random vectors is small. For the correlated bivariate non-Gaussian quadrature components, the exact probability distribution function, corresponding to those elementary phase distributions as well as the Gaussian approximation for resultant envelope are evaluated. The scenario where the elementary envelope is beta distributed is also considered. Spherically invariant random process (SIRP) is also used to model the multipath fading channel. The performance analysis based on the spherically invariant multipath fading channel, is then evaluated. The system performance, specified in terms of outage probability and average error probability, significantly depends on the choice of characteristic probability distribution function of the random process that describes the RF ambient. It is shown that the optimality of the optimum combining and maximal ratio combining schemes in interference-limited environments is still retained under the spherically invariant multipath fading channel model.