Catálogo de publicaciones - libros

The benefits of using smart antennas in a wireless mobile system have been thoroughly studied in recent years, showing an improvement in the antenna gain, a reduction of interfering power and, as a consequence, an increase in the system capacity. The real implementation and measurement of a smart antenna for the UMTS system are presented in this paper. Implementation impairments produce undesirable effects, such as frequency mismatch and coupling between RF channels. In order to minimize these effects, some simulations of the real system and the main non-ideal effects were carried out, so the analysis of these effects were affordable. Some solutions to the real implementation impairments were proposed and simulated, and the ones with better performance have been implemented and the obtained results are reported in this paper. Since traditional measurement methods are no longer suitable for the characterization of a smart antenna, a new method to measure the performance of the system is also introduced. The results show the feasibility of the system, which outperforms the performance of a conventional sectored antenna. An improvement of 6 dB in gain and 12.5 dB in carrier to interference ratio (CIR) was obtained with this prototype. The measurements were also validated by comparison with simulation results.

In concert with numerous other western world nations, in Sweden military doctrine is changing focus from a platform-oriented towards a network-based approach. Military platforms become participants in “the network”, share information, and provide services that allow them to sense, decide, and act beyond their individual capabilities in a cooperative and distributed manner. The information exchange occurs through an information infrastructure, the so called “infostructure”, which constitutes a communication network spanned by the participating nodes. Although technologically not far beyond the edge of today’s state of the art, are functional and technological requirements on the infostructure high: Mobile units exposed to lethal threats and electronic countermeasures shall connect and disconnect rapidly and reliably to build networks in an adhoc manner, ensuring secure and fault tolerant communication with sufficiently high quality of service. Nodes in the infostructure consist of heterogeneous systems provided by numerous nations, providing various types of end-user and communication services. Various alternative approaches can be taken for the creation of the infostructure, which must be expected to become a highly complex system, challenging to control and administrate. Modeling and Simulation are considered to be the mandatory enablers to optimize its design, maintenance, use, and improvement. This concept paper describes a vision of the infostructure, operational conditions, and desired properties, and identifies challenges which must be met on order to early avoid dead-end roads. Finally, it outlines application areas for communication related Modeling and Simulation to support the transition to and continuous improvement of a Network Based Defense.

Even though the problem of developing adequate models for self-similar data traffic is relatively old, it still remains unresolved. One of the limitations of the existing models is their lack of general applicability. Many traffic models re validated using a single trace only, such that the developed model may well fit the traffic of this trace, but not necessary of another one. Therefore, it is mandatory to use more than one trace for model validation, and in order to fit the collected traffic, specific descriptors of the traffic features have to be chosen (e.g. Hurst parameter, index of disperson of counts, etc.). The used traces should stem from different areas, reflecting various user behaviour. In this paper, we present a tool box which helps modelers to analyse measured traces and to validate their developed Markovian traffic models.

A virtual circuit is a connection between two users, devices, or terminals that Junctions as if it were a direct connection. Forwarding, switching, and/or routing over directly-connected circuits takes place at intermediate devices within the virtual circuit, but the details are hidden from the end points. Virtual circuits are widely used in many telecommunications and networking architectures; viz.: in wireline (PSTN, ISDN, BISDN) and wireless (GSM) telephony; in packet-switched networks at various layers (e.g., transport layer connections); in Multiprotocol Label Switched (MPLS) networks where tunnels are a type of virtual circuit; in Asynchronous Transfer Mode (ATM) networks where permanent and switched virtual circuits are fundamental components; in optical networks where wavelength routing and burst switching are abstract forms of provisioned virtual circuits; and in emerging multi-service networks where managed Ethernet virtual circuits are used to bridge legacy technologies like frame relay and ATM. The names of the service stages, branches, and exits used herein to describe and model virtual circuits are borrowed directly from telephony and teletraffic engineering. For example, ‘blocking’ is a branch point in virtual circuit provisioning with counterparts in telephony, ATM, MPLS, Ethernet, and optical networks. The terminology is a convenient way to define a conceptual teletraffic model for these networks. Most of the service stages, branches and exits defined herein have direct counterparts in the data and/or control planes of multi-service networks. In this paper, we define a conceptual model that is sufficiently general for a broad family of virtual circuit switching systems, and we use the model to derive expressions for traffic intensity, blocking probability, and quality of service (QoS) dimensioning of resources. The results are applicable to a number of virtual circuit switching systems and paradigms, and can be used as a basis for terminal and network teletraffic engineering tools for multi-service networks.