Alfonso Fernandez-Duran

Long term evolution in high speed railway environments: Feasibility and challenges

Long Term Evolution (LTE) is considered to be the natural evolution for the current Global System for Mobile Communications-Railways (GSM-R) in high speed railway environments, not only for its technical advantages and increased performance, but also due to the current evolution of public communication systems. In railway environments, mission critical services, operation assistance services, and passenger services must be supported by reliable mobile communication systems. Reliability and availability are key concerns for railway operators and as a consequence, railway operators are usually conservative adopters of information and communication technologies (ICT). This paper describes the feasibility of LTE as a successor to GSM-R for new railway mobile communication systems. We identify key features of LTE as a technology and analyze its ability to support both the migration of current railway services and the provisioning of potential future ones. We describe the key challenges to address specific requirements for railway communication services including the provisioning of voice service in LTE networks, handover performance, multicast multimedia transmission, and the provisioning of group communications service and railway emergency calls.

Management architecture for location-aware self-organizing LTE/LTE-a small cell networks

This article proposes a novel architecture for next-generation cellular networks in indoor scenarios. The objective of this model is to support SON mechanisms based on the knowledge of the user equipment location in a small cell network, the use of such information being a key enabler for advanced SON methods. The defined design is the basis for systems providing innovative location-aware SON techniques that make use of user localization in medium/large indoor areas (e.g., malls or corporate buildings). The functional and physical characteristics of this architecture and their technical implications are analyzed. Proposed innovations to generic mobile architecture are described as well as specific implementation for LTE/LTE-A standards. Interoperability with standard management systems and localization services, congestion avoidance, and data offloading are the key drivers of the design. Finally, the capabilities of the proposed architecture are demonstrated through the performance analysis of a simple key use case for location-aware self-optimization.

Design of in-building wireless networks deployments using evolutionary algorithms

In this article, a novel approach to deal with the design of in-building wireless networks deployments is proposed. This approach known as MOQZEA (Multiobjective Quality Zone Based Evolutionary Algorithm) is a hybrid evolutionary algorithm adapted to use a novel fitness function, based on the definition of quality zones for the different objective functions considered. This approach is conceived to solve wireless network design problems without previous information of the required number of transmitters, considering simultaneously a high number of objective functions and optimizing multiple configuration parameters of the transmitters.

Enhanced in-building fingerprint positioning using femtocell networks

The volume of traffic generated in indoor environments is increasing exponentially, and emerging femtocell networks are being deployed to meet associated challenges. These specific in-building deployments provide an opportunity for improving the performance of indoor positioning systems. Femtocell networks can be used to support accurate and reliable location services based on received-power and fingerprint location techniques. In fingerprint positioning methods, calibration and recalibration procedures are extremely time-consuming tasks. To address this problem, we developed a novel scenario-dependent procedure that reduced calibration points. We also analyzed several indoor propagation models, evaluating their suitability to reduce the effort required for calibration as well as their applicability for the recalibration procedures necessary to update previously recorded fingerprints. Our procedure includes both a simulation and a measurement phase, and obtains important improvements in accuracy, precision, and reliability while reducing the time and effort associated with both calibration and recalibration procedures.

Location-aware self-organizing methods in femtocell networks

The evolution of cellular technologies has been followed by a continuous increase in their capacity and complexity. As a consequence, network management has become a challenge for network operators, especially at indoor environments. In these scenarios the percentage of calls and traffic is much higher than outdoors. Hence, intelligent and automatic mechanisms for network operation and maintenance are deemed necessary, leading to the so-called Self-Organizing Networks (SON). SON mechanisms analyze network indicators like counters, alarms, etc. in order to improve the network performance. Furthermore, in indoor scenarios, the recent advances in indoor positioning systems allow the integration of terminal position in the definition of novel SON techniques. The availability of this additional information provides knowledge about terminal distributions, mobility patterns, etc., which is useful data to enhance the efficiency and performance of SON techniques. In this sense, this paper proposes and develops location-aware SON techniques for indoor femtocell networks. In particular, novel self-optimization and self-healing algorithms are defined, which are supported by an indoor cellular-positioning system. Such mechanisms are evaluated in a real testbed environment.

Dimensioning method for conversational video applications in wireless convergent networks

New convergent services are becoming possible, thanks to the expansion of IP networks based on the availability of innovative advanced coding formats such as H.264, which reduce network bandwidth requirements providing good video quality, and the rapid growth in the supply of dual-mode WiFi cellular terminals. This paper provides, first, a comprehensive subject overview as several technologies are involved, such as medium access protocol in IEEE802.11, H.264 advanced video coding standards, and conversational application characterization and recommendations. Second, the paper presents a new and simple dimensioning model of conversational video over wireless LAN. WLAN is addressed under the optimal network throughput and the perspective of video quality. The maximum number of simultaneous users resulting from throughput is limited by the collisions taking place in the shared medium with the statistical contention protocol. The video quality is conditioned by the packet loss in the contention protocol. Both approaches are analyzed within the scope of the advanced video codecs used in conversational video over IP, to conclude that conversational video dimensioning based on network throughput is not enough to ensure a satisfactory user experience, and video quality has to be taken also into account. Finally, the proposed model has been applied to a real-office scenario.

Application of extreme value distribution to model propagation fading in indoor mobile radio environments

In indoor mobile radio environments, the signal strength received in a mobile terminal vary due to amplitude fading that can be modelled by several distributions, such as Lognormal, Rayleigh, Rice, Nakagami, Suzuki or Weibull. Unfortunately, the application of these models does not allow to obtain analytical expressions that relate a signal strength value with mean value and typical deviation of the signal strength and the probability of signal strength to exceed the fixed value. In this paper, Extreme Value distribution is proposed to model fading in indoor propagation environments, in order to achieve closed analytical expressions to characterize probability distribution function and cumulative distribution function of signal strength and, by means of this, to relate by analytical expressions the signal threshold and the probability of signal strength to be above that threshold.

Zero-IF receiver architecture for multistandard compatible radio systems. GIRAFE project

This paper covers the results of the radio architecture studies towards common multistandard compatible radio front-ends (operating in the 2 GHz band) carried out within the RACE Project 2123 GIRAFE (Gigahertz Radio Front Ends) which is a research project in the area of mobile telecommunications focused on the application of advanced microelectronics integration and packaging techniques for RF components to be used in terminals of future mobile communications systems. These terminals will be based on combinations of available second generation systems in Europe (GSM, DCS1800, DECT and INMARSAT). The objective is to create a set of RF building blocks (RX and TX mixers, 90/spl deg/ phase shifters, VCO and prescaler) and develop multistandard RF front-ends in a high frequency bipolar process, complemented by the investigation and adaptation of novel packaging techniques which have a major impact in manufacturing low cost, high volume RF components.

Morphological Sampling Scheme for Analysis and Optimization of Wireless Indoor Environments

Algorithms used in the optimization of wireless deployments have computational time as one of their main drawbacks. This computational time is very dependent on the test points established to characterize a deployment scenario. The approach commonly used to define sample points is based on a regular grid, which leads to a remarkable number of sample points if accuracy is required. In this paper, a novel scenario-dependent sampling scheme based on mathematical morphology is presented. Its performance is evaluated and compared to regular sampling, outperforming typical schemes reducing computational time while maintaining very accurate results.

Automatic planning tool for deployment of indoor wireless local area networks

This paper presents an automatic planning software tool for indoor wireless networks. As a consequence of increasing number of wireless interface based systems, automation of deployments becomes actually relevant. There are a lot of parameters that influences network performance, so designers have to take them into account. The larger the network is, the more complex its planning results are. Planning determines performance, and getting it manually is not efficient. Mentioned tool automatically looks for an optimal planning solution, in terms of base stations distribution and frequency planning. It consists of analyzing data obtained by means of environment simulation. The user is able to decide the optimization criterion and the algorithm for searching solutions. This tool obtains an optimal solution in a short period of time, and it shows results such as power received at each user spatial point, interference level or traffic load for each station.