IT-UBI - Instituto de Telecomunicações
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The IT – Covilhã is a research unit of the IT (Instituto de Telecomunicações, Pole of Coimbra). It is hosted by Faculty of Engineering, University of Beira Interior, and where about 20 faculty members and 40 researchers develop their research activities in seven major topics: Computer Graphics and Multimedia; Mobile; Technologies and Telecommunications; Network and Multimedia Computing; Soft Computing and Image Analysis; Next Generation Networks and Applications; Applied Mathematics; Power Systems.
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- Traffic from Mobility in Mobile Broadband SystemsPublication . Velez, Fernando J.; Correia, Luis M.Models allowing the study of the influence of coveragedistance and velocity on the supported traffic and on thenew calls traffic linear density are examined, and resultsare obtained for typical scenarios in a Mobile BroadbandSystem (MBS) with a linear coverage geometry. For systemswithout guard channels for handover, for a fixed boundingvalue for the blocking probability, the new calls traffic lin-ear density was analyzed, increasing with the decrease of themaximum coverage distance, R, being upper limited by avalue which depends on the characteristics of the mobilityscenario. However, call-dropping probability requirementsalso need to be fulfilled, leading to a new calls traffic densitythat only increases with the decrease of R down to an opti-mum value of R, and being lower for scenarios with highermobility. These optimum values of R are higher for scenar-ios with higher and higher mobility, leading to limitations insystem capacity, mainly for high mobility scenarios. Inorder to resolve these limitations, the use of guard channelsfor handover is studied, particularly for high mobilityscenarios. For these scenarios one concludes that there is adegradation in system capacity because, for the typicalcoverage distances foreseen for MBS, the new calls trafficlinear density is one order of magnitude below the valuesobtained for the pedestrian scenario (where it is approxi-mately 15 Erlang/km), decreasing from 2.47 Erlang/km, inthe urban scenario, down to 0.84 Erlang/km, in the highwayscenario, when two guard channels are used.
- Influence of Traffic from Mobility on the Microcellular Coverage Distance in Mobile Broadband SystemsPublication . Velez, Fernando J.; Correia, Luis M.Models allowing the study of the influence of coverage distance and 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. For situations without using guard channels for handover, for a fixed bounding value for the blocking probability, the new calls traffic linear density has been analyzed, increasing with the decrease of the coverage distance R, and being upper limited by a value which depends on the characteristics of the mobility scenario. However, call-dropping probability requirements also need to be fulfilled, leading to a new calls traffic linear density that only increases with the decrease of R down to an optimum value of R, and being lower for scenarios with higher mobility. This situation leads to limitations in system capacity for lower values of the coverage distance, mainly for high mobility scenarios.
- Microcellular Design and System capacity determination for Outdoors Urban Mobile Broadband Communication Systems in the Millimetrewave BandsPublication . Velez, Fernando José; Brazio, José M.This paper addresses lhe cellular design of mobile microcellular communications systems operating in lhe millimetrewave bands in outdoor urban environments. ln such systems and environments lhe shape of cells and lhe interference among them are highly dependent on lhe geomctry of lhe surrounding obstacles (c.g., buildings) and lhe classical regular geametry based approaches to frequency reuse and capacity evaluation eannat be used. In lhe paper is described an approach to frequency reuse and system capacity evaluation where canclusions are drawn frem cellular layouts obtained, via an interactive computer graphical tool, for specific urban environments. Numerical examples are presented for coverage in lhe 40 and 60 GHz bands showing that, depending on lhe celI size, reuse factors in lhe range 5-11 are achievable. It is also concluded that, in interference límited scenarios, if cells with similar coverage length are used, equal values are obtained for lhe reuse factor and system eapacity in both bands.
- 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.
- 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.
- New Calls Traffic Performance in Microcellular Mobile Broadband Systems with High Mobility HandoverPublication . Velez, Fernando J.; Correia, Luis M.The maximisation of system capacity in Mobile Broadband Systems (MBSs) is addressed via an approach for traffic analysis that considers different scenarios for the mobility of terminals and two different types of services: short and long duration ones. For short duration services, the maximum of the new calls traffic linear density occurs for the typical coverage distances, R, of MBS, i.e., 100-350 m, except for the highways scenario, where it occurs for R = 500 m. However, for long duration services, these maxima are obtained for Rs approximately four times the previous values, new calls traffic linear density being 16% lower; feasible values, lower than the optimum ones, are obtained for lower coverage distances in high mobility scenarios. The use of guard channels for handover improves system performance only for short duration services, 2 being the recommended value for the number of guard channels in the considered cases.
- Multi-service Traffic Analysis in Mobile Broadband SystemsPublication . Velez, Fernando J.A model for multi-service traffic analysis in Mobile Broadband Systems is proposed, which takes into account the way in which mobility of terminals affects the occupancy of service components for a typical set of applications. The Bernoulli-Poisson-Pascal theory is used to model the traffic. For scenarios where HDV based applications are mostly used the system performance is affected. When a high mobility of terminals is considered, at least 72 channels of 8 Mbit/s are needed to obtain a fraction of active users of the order of 10 %.
- Deployment scenarios for mobile broadband communicationsPublication . Velez, Fernando J.; Correia, Luis M.The multi-service traffic analysis of a mobile broadband system (MBS), with a given mixture of applications, requires the definition of their main operation environments, corresponding to the residential, the mixed (half business/half residential), the business and the industrial markets. In this work, the respective deployment scenarios are defined by the values for the usage of a set of 26 applications. The usage of broadband applications (>2 Mb/s) increases from the residential market (17%) to the business one (25%), corresponding to a decrease in the usage of wideband (<2 Mb/s) ones (from 50 down to 42%), and to a constant value for the usage of low-MBS ([128, 384] kb/s) ones (33%); slight differences exist from the business to the industrial market. The actual number of users also depends on the density factor, varying from 0.004 users/m/sup 2/ in the industrial scenario to 0.150 users/m/sup 2/ in hotspots, e.g., offices.
- Classification and characterisation of mobile broadband servicesPublication . Velez, Fernando J.; Correia, Luis M.The available data about mobile broadband services / applications is put together, and their characterisation parameters are identified, enabling some insight into new approaches for multi-service traffic analysis in MBS. On one hand, a classification of services and applications is proposed based on the 1.21 1 ITU-T Recommendation. It distinguishes between interactive and distribution services, and also identifies the types of information supporting each one. On the other hand, a taxonomy is proposed for applications’ characterisation parameters, which are divided into five different types: main ones, traffic and communications parameters, service components and operation environments as well. Examples are given for the range of variation of each type of parameters.
- Capacity Analysis in a Multi-service Mobile Broadband SystemPublication . Velez, Fernando J.; Correia, Luis M.Multi-service traffic engineering will be a key aspect in cellular planning for Mobile Broadband Systems, the feasibility of the aggregate traffic model being crucial. An MMPP model is proposed for the modelling of the superimposition of data and video IPP sources. Given the correspondence between applications and their bearer service components, an algorithm for the Bernoulli case of the Bernoulli-Poisson-Pascal model is used to compute the blocking probability. The supported number of users is higher in scenarios with a lower maximum load per user. In a cell with 384 channels of 384 kb/s, it varies from 20 to 26 users/cell in urban scenarios, while with 288 channels/cell, although the number of channels is only 25 % lower, the supported number of users decreases 50 %. High terminal mobility strongly degrades the performance in the roads scenario.