Browsing by Issue Date, starting with "1998-09"
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- Capacity trade-offs in mobile broadband systems using guard channels for high mobility handoverPublication . Velez, Fernando J.; Correia, Luis M.Models allowing the study of the influence of coverage distance and mobile velocity on the supported traffic and on the new calls traffic linear density are examined, and results are obtained for typical scenarios in a mobile broadband system (MBS) with a linear coverage geometry. In order to cope with handover failure probability requirements, the use of guard channels for handover is assumed, mainly for high mobility scenarios. For these scenarios one concludes that there is a degradation in system capacity because, for the typical coverage distances foreseen for MBS, the new calls traffic linear density is one order of magnitude bellow the values obtained for the pedestrian scenario (where it is approximately 15 Erlang/km), decreasing from 2.47 Erlang/km, in the urban scenario, down to 0.84 Erlang/km, in the highway scenario, when two guard channels are used.
- Validation of models for traffic resulting from mobility in microcellular mobile broadband systemsPublication . Velez, Fernando J.Approximate models for traffic resulting from mobility are presented and their validity is examined for a system without guard channels for handover. The blocking probability for both new and handover calls is assessed via a Markov chain, which can be approximated by a model that allows the use of the theory from Jackson networks. Some examples are given where the blocking and handover failure probabilities are computed; their approximation error being negligible in a wide range of coverage distances foreseen for mobile broadband system environments, mainly for the blocking probability. Although it is usual to consider the handover traffic as Poisson distributed, one can show that for homogeneous traffic in the whole coverage area this is not strictly necessary. The independence among the number of calls being served in each cell is also presented as a conclusion in the range of validity of the approximation.
- Modelos de Tráfego de Mobilidade em Sistemas de Comunicações Móveis MicrocelularesPublication . Velez, Fernando J.; Correia, Luis M.Approximate models for traffic resulting from mobility are presented and their validity is examined for a system without guard channels for handover. The system can be modelled by a Markov chain whose exact solution for the steady-state probabilities is obtained by solving a system of equations with a dimension that considerably increases with the number of cells and the number of channels, which strongly limits its use. However, the blocking probability for both new and handover calls is assessed via this Markov chain, which can be approximated by a model that allows the use of the theory from Jackson networks. Some examples are given where the blocking and handover failure probabilities are computed; their approximation error being negligible in a wide range of coverage distances foreseen for MBS (Mobile Broadband System), environments, mainly for the blocking probability. Although it is usual to consider the handover traffic as Poisson distributed, one can show that for homogeneous traffic in the whole coverage area this is not strictly necessary. The independence among the number of calls being served in each cell is also presented as a conclusion in the range of validity of the approximation.