Handoff algorithms and co-channel interference analysis for microcellular systems.

摘要

In order to handle the expected growth in traffic, microcells have been proposed for future wireless communications due to their large capacity advantages. However, using present handoff techniques, microcells are likely to have many dropped calls, and inconsistent handoff performance for subscribers moving at different velocities. These problems are mainly a result of the harsh microcellular propagation environment and the link quality evaluations presently used for handoff algorithms. In this thesis, several methods are presented for better mobility management and cell planning in microcellular systems through the use of robust handoff algorithms and precise co-channel interference analysis.;For the handoff algorithm research, several methods are proposed for improving handoff performance in microcells. Velocity adaptive handoff algorithms are investigated for providing consistent handoff performance for users moving at a variety of speeds. Three in-service velocity estimation methods that use the fading statistics of a constant envelope modulated signal are proposed, which are robust to Rician fading, non-isotropic scattering, and additive white Gaussian noise. Alternatively, a velocity estimation technique using maximum Doppler detection in differentially detected CPM is presented. The moving direction of a mobile is also investigated for improving handoff performance. Using this information, a novel class of direction biased handoff algorithms are proposed which are shown to improve the cell membership properties and handoff performance in urban microcells. For improving link quality estimation, two in-service signal quality estimation techniques are presented for resource allocation (e.g. handoff) algorithms in TDMA cellular systems. These techniques, based on either the signal-to-interference ratio or the interference power, are representative of speech quality in an interference limited environment.;The co-channel interference research involves the analysis of shadowing and Rician fading on the co-channel interference probability, and the accurate modeling of the effect co-channel interference on signal strength based handoff algorithms. An analytic method for evaluating the probability of co-channel interference for composite Rician/log-normal interferers is presented and the effect of line-of-sight interferers is studied. By using a popular signal strength based handoff analysis model, the effects of co-channel interference are incorporated for improved handoff performance prediction in a co-channel interference environment.