Ángela Hernández

A Framework for UWB-Based Communication and Location Tracking Systems for Wireless Sensor Networks

Ultra wideband (UWB) radio technology is nowadays one of the most promising technologies for medium-short range communications. It has a wide range of applications including Wireless Sensor Networks (WSN) with simultaneous data transmission and location tracking. The combination of location and data transmission is important in order to increase flexibility and reduce the cost and complexity of the system deployment. In this scenario, accuracy is not the only evaluation criteria, but also the amount of resources associated to the location service, as it has an impact not only on the location capacity of the system but also on the sensor data transmission capacity. Although several studies can be found in the literature addressing UWB-based localization, these studies mainly focus on distance estimation and position calculation algorithms. Practical aspects such as the design of the functional architecture, the procedure for the transmission of the associated information between the different elements of the system, and the need of tracking multiple terminals simultaneously in various application scenarios, are generally omitted. This paper provides a complete system level evaluation of a UWB-based communication and location system for Wireless Sensor Networks, including aspects such as UWB-based ranging, tracking algorithms, latency, target mobility and MAC layer design. With this purpose, a custom simulator has been developed, and results with real UWB equipment are presented too.

Downlink scheduling for intercell interference fluctuation mitigation in partial-loaded broadband cellular OFDMA systems

In this paper, we analyze the problem of strong intercell interference (ICI) fluctuations in OFDMA networks with frequency reuse of one and their effects on system performance. Our goal is to outperform fractional frequency reuse scheme by proposing a joint time and frequency resource scheduling algorithm that limits ICI fluctuations both in full and partially loaded scenarios. Adaptive MCS selection according to channel conditions in addition to traffic requirements is considered. Simulation results show that our proposed scheme enhances the system performance and the user satisfaction.

Accurate indoor wireless location with IR UWB systems a performance evaluation of joint receiver structures and TOA based mechanism

Impulse radio (IR) ultra wide-band (UWB) is one of the most promising wireless technologies to develop both indoor and outdoor location and tracking applications. Due to its high bandwidth and short duration pulses, UWB potentially allows a great accuracy in distance measurements based on time of arrival (TOA) estimations. The main objective of this paper is to compare and to provide a qualitative and quantitative evaluation of different TOA-based distance estimation mechanisms joint to receiver architectures proposed for UWB systems. This comparison has been done in terms of accuracy and the effect of characteristic parameters of the transmitted signal, propagation conditions and signal-to-noise ratio has been analyzed. With this purpose a simulation tool has been developed, where the different receiver architectures, estimation mechanisms and channel models proposed on 802.15.4a have been implemented.

A Neuro-Fuzzy System for Extracting Environment Features Based on Ultrasonic Sensors

In this paper, a method to extract features of the environment based on ultrasonic sensors is presented. A 3D model of a set of sonar systems and a workplace has been developed. The target of this approach is to extract in a short time, while the vehicle is moving, features of the environment. Particularly, the approach shown in this paper has been focused on determining walls and corners, which are very common environment features. In order to prove the viability of the devised approach, a 3D simulated environment has been built. A Neuro-Fuzzy strategy has been used in order to extract environment features from this simulated model. Several trials have been carried out, obtaining satisfactory results in this context. After that, some experimental tests have been conducted using a real vehicle with a set of sonar systems. The obtained results reveal the satisfactory generalization properties of the approach in this case.

Interference Management through Resource Allocation in Multi-Cell OFDMA Networks

This work addresses the problem of inter-cell interference (ICI) management in the context of single frequency broadband OFDMA-based networks. Five proposals, based on a combination of ICI coordination/avoidance techniques along with a set of heuristic adaptive power and subcarrier allocation algorithms, have been considered in order to achieve better interference performance and resource utilization in a multi-cellular environment. Connected with a proper power mask based design, the potential gain of a flexible frequency sectorization solution, halfway between fractional/soft frequency reuse and pure frequency sectorization, is explored.

Active Methodologies in a Queueing Systems Course for Telecommunication Engineering Studies

This paper presents the results of a one-year experiment in incorporating active methodologies in a Queueing Systems course as part of the Telecommunication Engineering degree at the University of Zaragoza, Spain, during the period of adaptation to the European Higher Education Area. A problem-based learning methodology has been introduced, and the academic results showed that students achieved higher grades (improvement ranging from 27% up to 50%). The additional effort of students and faculty staff has also been evaluated.

Evaluation of TOA estimation algorithms in UWB receivers

UWB technology is especially suitable for location and tracking applications due to its high bandwidth, which allows a great accuracy on Time Of Arrival (TOA) estimation. Nevertheless, the achievement of this goal on multipath environments requires the design of efficient detection algorithms. The main objective of this paper is to compare and to provide a qualitative and quantitative evaluation of different TOA-based distance estimation mechanisms joint to receiver architectures proposed for UWB systems. This comparison has been done in terms of accuracy and the effect of characteristic parameters of the transmitted signal, propagation conditions and signal-to-noise ratio has been analyzed. With this purpose a simulation tool has been developed and the different receiver architectures and estimation mechanisms have been implemented, as well as the different channel models proposed on 802.15.4a.

Interference management and cell range expansion analysis for LTE picocell deployments

Heterogeneous networks are one of the solutions employed in next generation mobile networks to improve coverage and enhance spectral efficiency. This paper focuses on in-band heterogeneous deployments based on picocells, so interference coordination is necessary in order to increase system capacity. In addition, traditional association methods have to be revised. Several radio resource management and intercell interference coordination schemes are proposed and evaluated in this work. Moreover, to enhance data offloading in picocell deployments, cell range expansion (CRE) techniques have been introduced and the impact of the selected bias values is evaluated in several scenarios.

Analytical and Experimental Performance Evaluation of BLE Neighbor Discovery Process Including Non-Idealities of Real Chipsets

The purpose of this paper is to evaluate from a real perspective the performance of Bluetooth Low Energy (BLE) as a technology that enables fast and reliable discovery of a large number of users/devices in a short period of time. The BLE standard specifies a wide range of configurable parameter values that determine the discovery process and need to be set according to the particular application requirements. Many previous works have been addressed to investigate the discovery process through analytical and simulation models, according to the ideal specification of the standard. However, measurements show that additional scanning gaps appear in the scanning process, which reduce the discovery capabilities. These gaps have been identified in all of the analyzed devices and respond to both regular patterns and variable events associated with the decoding process. We have demonstrated that these non-idealities, which are not taken into account in other studies, have a severe impact on the discovery process performance. Extensive performance evaluation for a varying number of devices and feasible parameter combinations has been done by comparing simulations and experimental measurements. This work also includes a simple mathematical model that closely matches both the standard implementation and the different chipset peculiarities for any possible parameter value specified in the standard and for any number of simultaneous advertising devices under scanner coverage.

Resource allocation and interference management strategies for inband relaying in LTE-A

Relaying is seen as a cost-effective solution to increase the coverage and improve the capacity for long term evolution-advanced networks. However, the resource allocation among different nodes and links and the inter-cell interference coordination (ICIC) are important challenges in order to make the most of the potential benefits of relay deployments. This paper focuses on Type 1 half-duplex inband relaying. Several strategies related to radio resource partition and frequency reuse between nodes and links are reviewed, proposed and evaluated in this work, considering the real impact of the overhead introduced by backhaul links on the system performance and the ICIC schemes applied among macrocells. We also propose a way to multiplex the transmissions addressed to several relay nodes with the aim of improving the resource allocation and the network performance.