Mariano Molina-Garcia

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.

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.

Top challenges of LTE to become the next generation railway communication system

Railway environments cannot be away from the current evolution of public communication systems. The Long Term Evolution (LTE) mobile communication system is considered to be the natural evolution for current Global System for Mobile Communications Railways (GSM-R). LTE all IP networking technology plays a key role for the integration and convergence of heterogeneous networks and services, both the specific for the railway operative and the commercial broadband ones for passengers. The adoption of a new generation standard for railway communication must be based on an exhaustive feasibility study of the new system to become the railway mobile communication system. In this paper, LTE’s top challenges to address the specific requirements and features of railway communication services are evaluated. Under this scope, LTE features to implement the required railway functionalities, LTE technical challenges, spectrum harmonization, network deployment considerations and LTE capabilities to meet the railway service Reliability, Availability, Maintainability and Safety (RAMS) requirements, are assessed.

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.

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.

Planning and Sizing Tool for WiMAX Networks

A software tool for planning and sizing wireless networks based on standard 802.16 is presented in this paper. Due to the deployment of communication systems based on this standard, it is necessary a tool which allows an easy implementation and sizing of this type of networks. With this tool the user will be able to define technical specifications of transmitters and receivers, design parameters of the network and different propagation models, and evaluate point to point links and point to multipoint networks, obtaining results such as losses in the link, power received, signal noise rate, coverage or bit rates the network is able to handle. The versatility of the tool has been contrasted with experimental results obtained in a real deployment in a rural zone in Spain

Performance of LTE Mobile Relay Node Usage for Uplink Access in High Speed Railway Scenarios

Railway scenarios present several specific features that complicate the deployment of a radio communication network, especially for high speed trains. Nowadays, railway operators are evaluating the migration process from GSM-R to a new broadband system, like Long Term Evolution (LTE). In this paper, system-level simulations are carried out in order to evaluate overall network performance with Mobile Relay Node architecture for LTE uplink access in High Speed Railway scenarios. This implies developing specific tools for accurate characterization of such propagation environments.

Theoretical Analysis and Performance Simulation of In-Band LTE Mobile Relays in Railway Environments

Nowadays the number of vehicular users demanding mobile data services greatly increases due to the high penetration rate of smart phones, laptops and tablets. Under this scope, the 3GPP working group for LTE standardization, is paying more attention on vehicular scenarios, like railways environments. The proposed solution for improving performance in high speed railways scenario, is the mobile relay node. The authors focus on Type-1 in-band relays, which have been proposed for LTE-Advanced. In this work, authors investigate the issue of mobile relay capacity improvement for on-board train users and its impact on the overall network performance. Besides, the impact of several key configuration parameters of MRN, like the number of MBSFN sub frames, will be assessed.

Evolution of mean opinion Score due to handover events in IEEE 802.11 WLAN networks

Although networks based on IEEE802.11 was originally intended to transport best-effort data traffic, the appearance of IEEE802.11e has brought about the opportunity of supplying real time voice communications with strict requirements of quality of service. In WLAN IEEE802.11 networks, the handover process follow a “break-before-make” mechanism, provoking discontinuities in the communication, which have associated a variation of the packet loss rate, and, therefore, changes in the subjective quality of voice perceived by the user along the communication. It will be necessary to take into account this effect in the planning and sizing process of WLAN networks which have to deal with conversational services. With this purpose, in this paper is illustrated the influence of the horizontal handover events on the evolution of the MOS value for different VoIP codecs and several handover decision algorithms and durations.