Performance of handoff algorithms in various cellular system environments.

摘要

This thesis focuses on the optimization of the mobile assisted hard and soft handoff algorithm parameters, with the mean number of handoffs and the handoff delay for the hard handoff, and the mean number of BS's and active set updates, and the outage probability for the soft handoff as the objects of minimization. The propagation parameters such as the shadow fading standard deviation and the cross-correlation property are shown to influence the performance of handoff algorithms most. The sensitivity analysis of the performance metrics to the variation of the propagation environment is performed in macrocellular as well as in microcellular environments to provide a set of guidelines for selecting appropriate handoff algorithm parameters in various cellular system environments. The result is further used as a means of finding the algorithm parameters that are robust to the variation of the propagation environment.; Practical cellular system engineering issues are emphasized. The soft handoff percentage, a commonly used parameter in the design of CDMA systems, is related to the diversity gain, and it is shown that the diversity gain is determined not only by the soft handoff percentage but is also influenced by the handoff algorithm parameter settings. The tradeoff between the diversity gain and the network overhead is investigated to show such an effect and also other tradeoffs among the various soft handoff performance metrics. In the hard handoff case, a procedure for selecting the most robust algorithm parameters is illustrated, providing a method of quantifying the reduced fluctuation in the cost function.; Hard and soft handoff performances in microcellular environments are analyzed using two different approaches; first using the deterministic signal which is generated by a ray-tracing tool developed at Polytechnic University and Site Ware Technology, and second using the random signal composed of the numerically generated shadow fading signal having desired statistical properties. The deterministic signal approach, in the hard handoff case, exhibits a sharp knee on the tradeoff curves clearly identifying the optimum set of handoff algorithm parameters. In the soft handoff case, the deterministic and random signal approaches yield different spatial distributions of soft handoff area suggesting the use of the deterministic approach to identify problematic areas in a CDMA microcellular system.