Enrica Zola | Universitat Politecnica de Catalunya (original) (raw)

Papers by Enrica Zola

Lecture Notes in Computer Science, 2015

International Journal of Handheld Computing Research, 2013

Lecture Notes in Computer Science, 2013

Recent Advances in Communications and Networking Technology, 2014

Lecture Notes in Computer Science, 2014

Recent advances in wireless technology, such as software defined radio, lead to the possibility t... more Recent advances in wireless technology, such as software defined radio, lead to the possibility to explore new Internet connectivity models derived from the willingness of the end-user to share some Internet services. These networking architectures are known as User-centric Networks (UCNs). This chapter addresses energy-awareness in terms of multihop routing for wireless networks having the motivation to explain fundamental concepts, parameters and metrics, as well as how to address energy-awareness while keeping backward compatibility with current shortest-path routing approaches. The chapter starts by giving insight to notions concerning energy-awareness from a routing perspective, to then describe concepts that could assist in making multihop routing more efficient in terms of energy-awareness, showing the benefits in terms of performance. The chapter then describes the most recent metrics that are capable of providing some form of energy-awareness based on existing notions such as energy consumption models, energy capacity of a node, as well as based upon residual energy of a node. A section is dedicated to an analysis concerning implementation aspects.

IEEE Communications Letters, 2014

ABSTRACT The deployment of a large number of access points in public areas presents a new paradig... more ABSTRACT The deployment of a large number of access points in public areas presents a new paradigm in which a given station may be served by more than one access point at a time. Recently, a network model has been proposed to derive the optimal association strategy for the stations by solving a linear optimization problem. According to that model, a station cannot download data while performing a handover. In this letter, we demonstrate that even in static conditions (i.e., no mobility and constant load in the cell), that association strategy can force a handover. We thus propose a multi-objective optimization function that maximizes the download rates and minimizes the number of handovers. As a handover implies an extra cost due to necessary signaling to be exchanged, we propose a new handover cost function that takes into account the extra bandwidth. Using the new strategy, the system throughput slightly decreases while the number of handovers reduces.

ERCIM, the European Research Consortium for Informatics and Mathematics, aims to foster collabora... more ERCIM, the European Research Consortium for Informatics and Mathematics, aims to foster collaborative work within the European research community and to increase co-operation with European industry. In the ERCIM eMobility workshop, current progress and future developments in the area of eMobility should be discussed and the existing gap between theory and application closed.

ABSTRACT Postprint (published version)

A través del proyecto Education Roaming (eduroam), muchas universidades europeas permiten que sus... more A través del proyecto Education Roaming (eduroam), muchas universidades europeas permiten que sus usuarios puedan desplazarse entre ellas, disponiendo en todo momento de los servicios móviles igual que estuviesen en su propia universidad. La Universitat Politècnica de Catalunya (UPC) participa en este proyecto. Analizando los syslog de los puntos de acceso de la biblioteca principal del Campus Nord, se ha estudiado la actividad de los usuarios en la red WLAN de la UPC durante una semana y se ha extraído información sobre el comportamiento de los usuarios. A pesar de la difusión de dispositivos portátiles ligeros que facilitan su uso entre la gente joven mientras se va desplazando, en general los usuarios no se mueven mucho. No obstante la buena cobertura proporcionada por la infraestructura de red, los usuarios sufren muchos problemas de conectividad. Los resultados de nuestro trabajo pueden resultar útiles para mejorar la calidad de la red inalámbrica y para diseñar nuevas aplicaci...

ABSTRACT Time-based multilateration in IEEE 802.11 networks usually involves custom hardware desi... more ABSTRACT Time-based multilateration in IEEE 802.11 networks usually involves custom hardware designs, which tend to slow down the implementation and deployment of the location system. This paper presents software for calculating time-based location observables. This software enhances the SoftMAC layer of the Linux operating system by adding location-related measuring capabilities. A plugin for calculating the round trip time between two network entities is included in the software definition. Real data have been collected to test the performance of the proposed system. Despite the relevant noise present in the measurements, the results prove that the round trip time measurements achieved are useful to estimate distances achieving estimates with RMS of the error close to 2 meters.

Proceedings of the 6th ACM workshop on Performance monitoring and measurement of heterogeneous wireless and wired networks - PM2HW2N '11, 2011

Wireless local area networks (WLAN) are common in universities and their popularity grows every d... more Wireless local area networks (WLAN) are common in universities and their popularity grows every day. Understanding the trends in the use of these networks (i.e. how much, when and where traffic is present) is becoming more relevant. Interesting results can be extracted by analyzing WLAN traces from real scenarios. In this work, three buildings are studied on two campuses in Barcelona (Spain) and its surroundings. This is the first study providing the user behavior in a European campus. Similar trends are observed in the three buildings, despite the different amount of users, purpose of the building and size of the campus. Daily and weekly patterns are shown. The population accessing the networks is mostly composed of infrequent users: less than half of the devices access the WLAN more than four days during the three months studied. Many users visiting one building associate with only one access point: despite the widespread use of lightweight devices many users are static. The main difference among different buildings is the fidelity of users: users on a small campus are more likely to reappear on different days than on a large campus, where the population is more heterogeneous. The results of this analysis provide general tools for characterizing campus-wide WLAN and a better understanding of usage and performance issues in a mature wireless network in Europe.

2012 2nd Baltic Congress on Future Internet Communications, 2012

ABSTRACT The handoff process allows users to move while their communication is handled by differe... more ABSTRACT The handoff process allows users to move while their communication is handled by different antennas in the network. A proper configuration of network's parameters is required in order to guarantee a given QoS for both moving and static users. Prediction of the next cell to which a user may need to connect in the near future may help to better allocate resources in the network and to guarantee the continuity of the communication. In previous works, analytical results for these predictions for nodes moving according to the Random Waypoint mobility model have been presented. However, the mathematical analysis is only possible for simple cases with ideal conditions of propagation and handoff strategy. In this paper, simulation results for the proposed model are presented under different radio channel conditions and handoff strategies. First, the study validates the existing analytical model for ideal conditions. Second, the results prove that the probability of handoff increases under non-ideal radio channel conditions. Moreover, a different handoff strategy may lead to relevant differences in the prediction, thus proving that the handoff strategy has a strong impact on the network performance.

2011 IEEE 36th Conference on Local Computer Networks, 2011

Users in a cellular network are allowed to move freely while the network handoffs their calls or ... more Users in a cellular network are allowed to move freely while the network handoffs their calls or data transfers among different access points. Studies demonstrate that the mobility pattern followed by the users has an impact on some metrics strongly related to the performance (i.e., handoff rate, cell residence time, etc). Some aspects of the Random Waypoint mobility model have been studied in depth, but relating those studies with different possible layouts for the access points still remains an open issue. The interest in forecasting the next cell where the device may be handed off is twofold: 1. it gives a deeper insight into the statistical study of the mobility model; 2. it is useful to manage the resource allocation to improve the performance. The goal of this paper is to provide an analytical framework for these predictions in a symmetric layout composed of four circular cells covering a circular area. Equations are provided along with numerical examples for a given scenario.

2009 IEEE Sarnoff Symposium, 2009

Several mobility models are available for simulating WLAN, with different impacts on network perf... more Several mobility models are available for simulating WLAN, with different impacts on network performance. This work deals with the impact of the assumed mobility model on two key teletraffic variables involved in the planning of the network: the cell residence time (i.e., time connected to an access point) and the handoff rate. These two variables are studied in different scenarios for WLANs designed for pedestrians. For this purpose, discrete event simulations are run with different mobility patterns and number of access points. The time between changes of access point (i.e., handoffs) is studied as a random variable. This research proves the importance of correctly selecting the assumed mobility pattern, as it has a strong impact on the number of handoffs. The probability density function of the cell residence time is also studied as a combination of a distribution that models fast disassociation events (i.e., short ping-pongs between two access points) and a gamma or lognormal distribution, depending on the mobility pattern, which model longer dwells.

Users in a cellular network can move while their connections are handed off to different access p... more Users in a cellular network can move while their connections are handed off to different access points. Studies prove that the mobility pattern followed have a strong impact on performance metrics (i.e., handoff (HO) rate, cell residence time). Recently, some key aspects of the Random Waypoint mobility model have been studied in depth, but relating those studies with different cellular layouts has not been reported. Interest in forecasting the cell to which a device may be handed off depending on the movement pattern is twofold. First, it gives insight into properties and statistics of the mobility model. Second, and from a more practical perspective, it is useful to manage resource allocation and reservation strategies in order to smooth the HO process. The goal of this article is to provide an analytical framework for these predictions in a simple layout. Given a node's current location and the timestamp and location of the last waypoint, an approximation for HO during time Δt is derived. The analysis is provided along with numerical examples and simulations for a symmetrical layout and uniform speed distribution. Results shed light on how useful more advanced strategies can be.

6th Joint IFIP Wireless and Mobile Networking Conference (WMNC), 2013

ABSTRACT The IEEE 802.11 standard defines the different bit rates and modulation schemes to which... more ABSTRACT The IEEE 802.11 standard defines the different bit rates and modulation schemes to which a WLAN device may adapt according to the channel quality. User mobility may also have an impact on the available bit rate. This paper presents a study of the bit rate evolution along time for devices that move according to the Random Waypoint mobility pattern in WLAN cells. Simulation has been applied in order to obtain statistical results that permit to characterize the evolution of the bit rate behavior along time and to compute average results in the ideal case (without interference) and in the presence of interfering devices. Our results can be useful in the solution of optimization problems in which decision on where to connect must be taken based on some minimum guaranteed bit rate. They also can be useful in the design of inter and intra-cell handover methods and load balancing schemes.

2013 12th Annual Mediterranean Ad Hoc Networking Workshop (MED-HOC-NET), 2013

ABSTRACT Several techniques have been proposed for positioning nodes over IEEE 802.11 networks, b... more ABSTRACT Several techniques have been proposed for positioning nodes over IEEE 802.11 networks, but only few consist in time-based multilateration, mainly due to the protocol stack not supporting accurate timestamps. One frequent solution is to develop the hardware required for providing accurate timestamps. However, this approach tends to slow down the research and the ulterior deployment of the location techniques, since the performance of these techniques is bounded to a specific hardware design. This paper presents a measuring system aimed at providing location observables that can be used in time-based multilateration techniques. The system, which follows a software approach, is based on enhancing the SoftMAC layer of Linux with location-measuring capabilities. The system is conceived for supporting any kind of time-based measurements, by adding as many plugins as measured observables. Two plugins have been initially developed. The first one computes the round trip time of a message from a station to an access point and back again to the station. The second plugin calculates time-differences of arrival suitable for being used in the passive TDOA technique. This work provides the definition of the measuring system. Real data has been collected to test the system. The results indicate that the measurements provided by the system can be used for location purposes, i.e. they follow the physical laws in which metrics are based (e.g. they grow along with the distance between the nodes).

6th Joint IFIP Wireless and Mobile Networking Conference (WMNC), 2013

ABSTRACT Indoor positioning has focused the interest of researchers for years. Although there are... more ABSTRACT Indoor positioning has focused the interest of researchers for years. Although there are several techniques proposed, they are difficult to reproduce and consequently to contrast and improve. This paper presents a modular location platform, which enhances the SoftMAC implementation in Linux with positioning capabilities. This platform can be deployed in any device running Linux kernel 2.6 or higher. The core of the platform is its software-based measuring system. This measuring system supports the 2-way TOA technique, but any time-based multilateration technique (e.g. passive TDOA) can be incorporated with minimum changes. Real data have been gathered to assess the performance of the measuring system. The RTTs estimated grow with the distance, which demonstrates the feasibility of the system.

Lecture Notes in Computer Science, 2015

International Journal of Handheld Computing Research, 2013

Lecture Notes in Computer Science, 2013

Recent Advances in Communications and Networking Technology, 2014

Lecture Notes in Computer Science, 2014

Recent advances in wireless technology, such as software defined radio, lead to the possibility t... more Recent advances in wireless technology, such as software defined radio, lead to the possibility to explore new Internet connectivity models derived from the willingness of the end-user to share some Internet services. These networking architectures are known as User-centric Networks (UCNs). This chapter addresses energy-awareness in terms of multihop routing for wireless networks having the motivation to explain fundamental concepts, parameters and metrics, as well as how to address energy-awareness while keeping backward compatibility with current shortest-path routing approaches. The chapter starts by giving insight to notions concerning energy-awareness from a routing perspective, to then describe concepts that could assist in making multihop routing more efficient in terms of energy-awareness, showing the benefits in terms of performance. The chapter then describes the most recent metrics that are capable of providing some form of energy-awareness based on existing notions such as energy consumption models, energy capacity of a node, as well as based upon residual energy of a node. A section is dedicated to an analysis concerning implementation aspects.

IEEE Communications Letters, 2014

ABSTRACT The deployment of a large number of access points in public areas presents a new paradig... more ABSTRACT The deployment of a large number of access points in public areas presents a new paradigm in which a given station may be served by more than one access point at a time. Recently, a network model has been proposed to derive the optimal association strategy for the stations by solving a linear optimization problem. According to that model, a station cannot download data while performing a handover. In this letter, we demonstrate that even in static conditions (i.e., no mobility and constant load in the cell), that association strategy can force a handover. We thus propose a multi-objective optimization function that maximizes the download rates and minimizes the number of handovers. As a handover implies an extra cost due to necessary signaling to be exchanged, we propose a new handover cost function that takes into account the extra bandwidth. Using the new strategy, the system throughput slightly decreases while the number of handovers reduces.

ERCIM, the European Research Consortium for Informatics and Mathematics, aims to foster collabora... more ERCIM, the European Research Consortium for Informatics and Mathematics, aims to foster collaborative work within the European research community and to increase co-operation with European industry. In the ERCIM eMobility workshop, current progress and future developments in the area of eMobility should be discussed and the existing gap between theory and application closed.

ABSTRACT Postprint (published version)

A través del proyecto Education Roaming (eduroam), muchas universidades europeas permiten que sus... more A través del proyecto Education Roaming (eduroam), muchas universidades europeas permiten que sus usuarios puedan desplazarse entre ellas, disponiendo en todo momento de los servicios móviles igual que estuviesen en su propia universidad. La Universitat Politècnica de Catalunya (UPC) participa en este proyecto. Analizando los syslog de los puntos de acceso de la biblioteca principal del Campus Nord, se ha estudiado la actividad de los usuarios en la red WLAN de la UPC durante una semana y se ha extraído información sobre el comportamiento de los usuarios. A pesar de la difusión de dispositivos portátiles ligeros que facilitan su uso entre la gente joven mientras se va desplazando, en general los usuarios no se mueven mucho. No obstante la buena cobertura proporcionada por la infraestructura de red, los usuarios sufren muchos problemas de conectividad. Los resultados de nuestro trabajo pueden resultar útiles para mejorar la calidad de la red inalámbrica y para diseñar nuevas aplicaci...

ABSTRACT Time-based multilateration in IEEE 802.11 networks usually involves custom hardware desi... more ABSTRACT Time-based multilateration in IEEE 802.11 networks usually involves custom hardware designs, which tend to slow down the implementation and deployment of the location system. This paper presents software for calculating time-based location observables. This software enhances the SoftMAC layer of the Linux operating system by adding location-related measuring capabilities. A plugin for calculating the round trip time between two network entities is included in the software definition. Real data have been collected to test the performance of the proposed system. Despite the relevant noise present in the measurements, the results prove that the round trip time measurements achieved are useful to estimate distances achieving estimates with RMS of the error close to 2 meters.

Proceedings of the 6th ACM workshop on Performance monitoring and measurement of heterogeneous wireless and wired networks - PM2HW2N '11, 2011

Wireless local area networks (WLAN) are common in universities and their popularity grows every d... more Wireless local area networks (WLAN) are common in universities and their popularity grows every day. Understanding the trends in the use of these networks (i.e. how much, when and where traffic is present) is becoming more relevant. Interesting results can be extracted by analyzing WLAN traces from real scenarios. In this work, three buildings are studied on two campuses in Barcelona (Spain) and its surroundings. This is the first study providing the user behavior in a European campus. Similar trends are observed in the three buildings, despite the different amount of users, purpose of the building and size of the campus. Daily and weekly patterns are shown. The population accessing the networks is mostly composed of infrequent users: less than half of the devices access the WLAN more than four days during the three months studied. Many users visiting one building associate with only one access point: despite the widespread use of lightweight devices many users are static. The main difference among different buildings is the fidelity of users: users on a small campus are more likely to reappear on different days than on a large campus, where the population is more heterogeneous. The results of this analysis provide general tools for characterizing campus-wide WLAN and a better understanding of usage and performance issues in a mature wireless network in Europe.

2012 2nd Baltic Congress on Future Internet Communications, 2012

ABSTRACT The handoff process allows users to move while their communication is handled by differe... more ABSTRACT The handoff process allows users to move while their communication is handled by different antennas in the network. A proper configuration of network's parameters is required in order to guarantee a given QoS for both moving and static users. Prediction of the next cell to which a user may need to connect in the near future may help to better allocate resources in the network and to guarantee the continuity of the communication. In previous works, analytical results for these predictions for nodes moving according to the Random Waypoint mobility model have been presented. However, the mathematical analysis is only possible for simple cases with ideal conditions of propagation and handoff strategy. In this paper, simulation results for the proposed model are presented under different radio channel conditions and handoff strategies. First, the study validates the existing analytical model for ideal conditions. Second, the results prove that the probability of handoff increases under non-ideal radio channel conditions. Moreover, a different handoff strategy may lead to relevant differences in the prediction, thus proving that the handoff strategy has a strong impact on the network performance.

2011 IEEE 36th Conference on Local Computer Networks, 2011

Users in a cellular network are allowed to move freely while the network handoffs their calls or ... more Users in a cellular network are allowed to move freely while the network handoffs their calls or data transfers among different access points. Studies demonstrate that the mobility pattern followed by the users has an impact on some metrics strongly related to the performance (i.e., handoff rate, cell residence time, etc). Some aspects of the Random Waypoint mobility model have been studied in depth, but relating those studies with different possible layouts for the access points still remains an open issue. The interest in forecasting the next cell where the device may be handed off is twofold: 1. it gives a deeper insight into the statistical study of the mobility model; 2. it is useful to manage the resource allocation to improve the performance. The goal of this paper is to provide an analytical framework for these predictions in a symmetric layout composed of four circular cells covering a circular area. Equations are provided along with numerical examples for a given scenario.

2009 IEEE Sarnoff Symposium, 2009

Several mobility models are available for simulating WLAN, with different impacts on network perf... more Several mobility models are available for simulating WLAN, with different impacts on network performance. This work deals with the impact of the assumed mobility model on two key teletraffic variables involved in the planning of the network: the cell residence time (i.e., time connected to an access point) and the handoff rate. These two variables are studied in different scenarios for WLANs designed for pedestrians. For this purpose, discrete event simulations are run with different mobility patterns and number of access points. The time between changes of access point (i.e., handoffs) is studied as a random variable. This research proves the importance of correctly selecting the assumed mobility pattern, as it has a strong impact on the number of handoffs. The probability density function of the cell residence time is also studied as a combination of a distribution that models fast disassociation events (i.e., short ping-pongs between two access points) and a gamma or lognormal distribution, depending on the mobility pattern, which model longer dwells.

Users in a cellular network can move while their connections are handed off to different access p... more Users in a cellular network can move while their connections are handed off to different access points. Studies prove that the mobility pattern followed have a strong impact on performance metrics (i.e., handoff (HO) rate, cell residence time). Recently, some key aspects of the Random Waypoint mobility model have been studied in depth, but relating those studies with different cellular layouts has not been reported. Interest in forecasting the cell to which a device may be handed off depending on the movement pattern is twofold. First, it gives insight into properties and statistics of the mobility model. Second, and from a more practical perspective, it is useful to manage resource allocation and reservation strategies in order to smooth the HO process. The goal of this article is to provide an analytical framework for these predictions in a simple layout. Given a node's current location and the timestamp and location of the last waypoint, an approximation for HO during time Δt is derived. The analysis is provided along with numerical examples and simulations for a symmetrical layout and uniform speed distribution. Results shed light on how useful more advanced strategies can be.

6th Joint IFIP Wireless and Mobile Networking Conference (WMNC), 2013

ABSTRACT The IEEE 802.11 standard defines the different bit rates and modulation schemes to which... more ABSTRACT The IEEE 802.11 standard defines the different bit rates and modulation schemes to which a WLAN device may adapt according to the channel quality. User mobility may also have an impact on the available bit rate. This paper presents a study of the bit rate evolution along time for devices that move according to the Random Waypoint mobility pattern in WLAN cells. Simulation has been applied in order to obtain statistical results that permit to characterize the evolution of the bit rate behavior along time and to compute average results in the ideal case (without interference) and in the presence of interfering devices. Our results can be useful in the solution of optimization problems in which decision on where to connect must be taken based on some minimum guaranteed bit rate. They also can be useful in the design of inter and intra-cell handover methods and load balancing schemes.

2013 12th Annual Mediterranean Ad Hoc Networking Workshop (MED-HOC-NET), 2013

ABSTRACT Several techniques have been proposed for positioning nodes over IEEE 802.11 networks, b... more ABSTRACT Several techniques have been proposed for positioning nodes over IEEE 802.11 networks, but only few consist in time-based multilateration, mainly due to the protocol stack not supporting accurate timestamps. One frequent solution is to develop the hardware required for providing accurate timestamps. However, this approach tends to slow down the research and the ulterior deployment of the location techniques, since the performance of these techniques is bounded to a specific hardware design. This paper presents a measuring system aimed at providing location observables that can be used in time-based multilateration techniques. The system, which follows a software approach, is based on enhancing the SoftMAC layer of Linux with location-measuring capabilities. The system is conceived for supporting any kind of time-based measurements, by adding as many plugins as measured observables. Two plugins have been initially developed. The first one computes the round trip time of a message from a station to an access point and back again to the station. The second plugin calculates time-differences of arrival suitable for being used in the passive TDOA technique. This work provides the definition of the measuring system. Real data has been collected to test the system. The results indicate that the measurements provided by the system can be used for location purposes, i.e. they follow the physical laws in which metrics are based (e.g. they grow along with the distance between the nodes).

6th Joint IFIP Wireless and Mobile Networking Conference (WMNC), 2013

ABSTRACT Indoor positioning has focused the interest of researchers for years. Although there are... more ABSTRACT Indoor positioning has focused the interest of researchers for years. Although there are several techniques proposed, they are difficult to reproduce and consequently to contrast and improve. This paper presents a modular location platform, which enhances the SoftMAC implementation in Linux with positioning capabilities. This platform can be deployed in any device running Linux kernel 2.6 or higher. The core of the platform is its software-based measuring system. This measuring system supports the 2-way TOA technique, but any time-based multilateration technique (e.g. passive TDOA) can be incorporated with minimum changes. Real data have been gathered to assess the performance of the measuring system. The RTTs estimated grow with the distance, which demonstrates the feasibility of the system.