Marco Ajmone Marsan

Politecnico di Torino, Torino, Piedmont, Italy

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Publications (298)125.66 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the first systematic investigation of the potential performance gains for crowdsourcing systems, deriving from available information at the requester about individual worker earnestness (reputation). In particular, we first formalize the optimal task assignment problem when workers' reputation estimates are available, as the maximization of a monotone (submodular) function subject to Matroid constraints. Then, being the optimal problem NP-hard, we propose a simple but efficient greedy heuristic task allocation algorithm. We also propose a simple ``maximum a-posteriori`` decision rule. Finally, we test and compare different solutions, showing that system performance can greatly benefit from information about workers' reputation. Our main findings are that: i) even largely inaccurate estimates of workers' reputation can be effectively exploited in the task assignment to greatly improve system performance; ii) the performance of the maximum a-posteriori decision rule quickly degrades as worker reputation estimates become inaccurate; iii) when workers' reputation estimates are significantly inaccurate, the best performance can be obtained by combining our proposed task assignment algorithm with the LRA decision rule introduced in the literature.
    11/2014;
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    ABSTRACT: Traditionally, energy efficiency aspects have been included in the wireless access network design space only in the context of power control aimed at interference mitigation, and for the increase of the terminal battery lifetime. Energy consumption of network components has also, for a long time, not been considered an issue, neither in equipment design, nor in network planning and management. However, in recent years, with the user demand increasing at nearly exponential pace, and margins rapidly shrinking, concerns about energy efficiency have been raised, with the objective to reduce network operational costs (not to mention the environmental issues). Installing more energyefficient hardware does not seem to fully solve the problem, since wireless access networks are almost invariably (over)provisioned with respect to the peak user demand. This means that efficient resource management schemes, capable of controlling how much of the network infrastructure is actually needed and which parts can be temporarily powered off to save energy, can be extremely effective and provide quite large cost reductions. Considering that most of the energy in wireless access networks is consumed in the radio part, a dynamic provisioning of wireless access network resources is crucial, to achieve energy-efficient operation. The consensus on this approach in the research community has been wide in the last few years, and a large number of solutions was proposed. In this paper, we survey the most important proposals, considering the two most common wireless access technologies, namely cellular and WLAN. Main features of the proposed solutions are analyzed and compared, with an outlook on their applicability in typical network scenarios that also include cooperation between both access technologies. Moreover, we provide an overview of the practical implementation aspects that must be addressed to achieve truly energy-efficient wireless access networks, including current standardization work, and trends in the development of energy-efficient hardware.
    IEEE Communications Surveys &amp Tutorials 10/2014; 16(4):2259-2285. · 4.82 Impact Factor
  • Marco Ajmone Marsan, Michela Meo
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    ABSTRACT: In this paper we exploit simple approximate queueing models to assess the effectiveness of the approaches that have been proposed to save energy in dense wireless local area networks (WLANs), based on the activation of access points (APs) according to the user demand. In particular, we look at a portion of a dense WLAN, where several APs are deployed to provide sufficient capacity to serve a large number of active users during peak traffic hours. To increase capacity, some APs are colocated and provide identical coverage; we say that these APs belong to the same group, and they serve users in the same area. The areas covered by different AP groups only partially overlap, so that some active users can only be served by a group of APs, but a fraction of active users can be served by more groups. Due to daily variations of the number of active users accessing the WLAN, some APs can be switched off to save energy when not all the capacity is needed. A real example of this setting is provided by a floor of one building of Politecnico di Torino in Italy, where a student library is located. The approximate analytical models indicate that the energy saving achievable with the proposed approaches is quite substantial, over 40% if at least one AP for each group is always kept on, even with no traffic, to be ready to accept incoming users, and it grows to almost 60% if all APs can be switched off at night, using a separate technology to activate an AP when the first user requests association in the morning.
    Computer Networks 06/2014; 66:82–93. · 1.23 Impact Factor
  • Gianluca Rizzo, Balaji Rengarajan, Marco Ajmone Marsan
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    ABSTRACT: Sleep modes are one of the most widely investigated techniques to decrease energy consumption in cellular access networks. However, the application of such algorithms on the base station (BS) equipment of today presents several challenges. Indeed, currently installed BSs are unfit for frequent on/off cycles. This may lead to increased failure rates and malfunctioning, ultimately resulting in significant CAPEX and OPEX increases for mobile network operators (MNOs). This situation calls for a new generation of flexible BSs endowed with a ”hot standby” mode, which guarantees quick activation times without affecting BS availability. However, when such new BS models become available, MNOs will need to determine a migration path to a new network deployment with progressive replacement of old BS equipment. In this paper, we propose an approach to quantify the benefits obtained by MNOs with the deployment of flexible BSs, in terms of maximum energy efficiency achievable with a given fraction of flexible BSs in their network. More specifically, we propose a method for estimating, for a given percentage of flexible BSs, the energy optimal density of static and flexible BSs, which is sufficient to serve a given set of active users with predefined performance guarantees. We show how to apply our method to derive bounds on the maximum energy saving achievable through sleep modes, as a function of the fraction of flexible BSs. We determine the effect of uncertainty in traffic predictions on sleep modes performance, and we derive indications for optimal network planning strategies.
    2014 ICC - 2014 IEEE International Conference on Communication Workshop (ICC); 06/2014
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    ABSTRACT: The growing ubiquity and pervasiveness of sensors and smart devices, with the consequent availability of a large amount of "local" and contextualized information, are giving rise to a wealth of "context-aware" applications and services. In this work we consider an opportunistic communication scheme called Floating Content (FC), which was specifically designed for serverless distributed context-aware applications. So far, the performance analysis of FC, and in particular of content lifetime and availability, was based on simplified system models and fluid system analysis. The resulting performance estimates did not account for the effects of propagation characteristics, mobility patterns, and communication protocols, all factors known to significantly affect the performance of opportunistic communication schemes. This article studies the main issues related to the performance of FC service in a realistic office setting through a first experimental evaluation of a mobile app for Android devices. Our experimental results confirm the feasibility of FC service for supporting practical context-aware mobile applications in office settings.
    IEEE Communications Magazine 01/2014; 52(6):49-54. · 3.66 Impact Factor
  • Context-Aware Systems and Applications, 01/2014: pages 198-208; Springer International Publishing.
  • Balaji Rengarajan, Gianluca Rizzo, Marco Ajmone Marsan
    Computer Networks. 01/2014;
  • Marco Ajmone Marsan, Michela Meo
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    ABSTRACT: In this paper we investigate the potential energy saving inherent in the network sharing approach, whereby all (or significant parts) of the network infrastructures existing in a country can be shared by different network operators. In our study we consider European mobile network operators, and we use simple analytical models to show that in most European countries the amount of energy necessary to run mobile networks can be reduced by 35 to 60% with respect to the case in which each operator manages a separate network infrastructure.
    GLOBECOM 2013 - 2013 IEEE Global Communications Conference; 12/2013
  • Marco Ajmone Marsan, Luca Chiaraviglio, Delia Ciullo, Michela Meo
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    ABSTRACT: In this paper we study base station sleep modes that, by reducing power consumption in periods of low traffic, improve the energy efficiency of cellular access networks. We assume that when some base stations enter sleep mode, radio coverage and service provisioning are provided by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This may be an optimistic assumption in the case of the sparse base station layouts typical of rural areas, but is, on the contrary, a realistic hypothesis for the dense layouts of urban areas, which consume most of the network energy. We consider the possibility of either just one sleep mode scheme per day (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several sleep mode schemes per day, with progressively fewer active base stations. For both contexts, we develop a simple analytical framework to identify optimal base station sleep times as a function of the daily traffic pattern. We start by considering homogeneous networks, in which all cells carry the same amount of traffic and cover areas of equal size. Considering both synthetic traffic patterns and real traffic traces, collected from cells of an operational network, we show that the energy saving achieved with base station sleep modes can be quite significant, the actual value strongly depending on the traffic pattern. Our results also show that most of the energy saving is already achieved with one sleep mode scheme per day. Some additional saving can be achieved with multiple sleep mode schemes, at the price of a significant increase in complexity. We then consider heterogeneous networks in which cells with different coverage areas and different amounts of traffic coexist. In particular, we focus on the common case in which some micro-cells provide additional capacity in a region covered by an umbrella macro-cell, and we prove that the optimal scheduling of micro-cell sleep times is in increasing order of load, from the least loaded to the most loaded. This provides a valuable guideline for the scheduling of sleep modes (i.e., of low-power configurations) in complex heterogeneous networks.
    Computer Networks 12/2013; 57(17):3276–3290. · 1.23 Impact Factor
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    ABSTRACT: Cellular networks have been traditionally dimensioned to fulfill the desired quality of service (QoS) requirements at all times, and consequently their deployment has been planned to meet the expected peak of the user demand. However, with the user demand recently increasing at exponential pace, concerns about the cellular networks energy consumption have been raised. In response, energy-efficient resource management schemes have been proposed, which take into account energy consumption, and control how much of the network infrastructure is actually needed at different times, and how much can be temporarily powered off to cut energy consumption. Since most of the energy consumed in cellular networks is used by base stations (BSs), algorithms for managing BSs seem to be the most urgent development to achieve energy-efficient operation. This paper provides a quick overview of the BS management techniques that were recently proposed for cellular networks. In addition, an outlook on real implementation aspects, including current commercial products, and trends in the development of energy-efficient hardware is also given.
    The 24th Tyrrhenian International Workshop on Digital Communications; 09/2013
  • Source
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    ABSTRACT: Optimizing the tradeoff between power saving and Quality of Service (QoS) in the current Internet is a challenging research objective, whose difficulty stems also from the dominant presence of TCP traffic, and its elastic nature. In a previous work we have shown that an intertwining exists between capacity scaling approaches and TCP congestion control. In this paper we investigate the reasons of such intertwining, and we evaluate how and how much the dynamics of the two algorithms affect each other's performance. More specifically, we will show that such an interaction is essentially due to the overlap of the two closed loop controls, with different time constants.
    Energy Efficient and Green Networking (SSEEGN), 2013 22nd ITC Specialist Seminar on; 01/2013
  • S. Ali, G. Rizzo, B. Rengarajan, M. Ajmone Marsan
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    ABSTRACT: Context-awareness is a peculiar characteristic of an ever expanding set of applications that make use of a combination of restricted spatio-temporal locality and mobile communications, to deliver a variety of services to the end user. It is expected that by 2014 more than 1.5 billion people would be using applications based on local search (search restricted on the basis of spatio-temporal locality), and that mobile location based services will drive revenues of more than $15 billion worldwide. A common feature of such context-aware applications is the fact that their communication requirements significantly differ from ordinary applications. For most of them, the scope of generated content itself is local. This locally relevant content may be of little concern to the rest of the world, therefore moving this content from the user device to store it in a well-accessible centralized location and/or making this information available beyond its scope represents a clear waste of resources (connectivity, storage). Due to these specific requirements, opportunistic communication can play a special role when coupled with context-awareness. The benefit of opportunistic communications is that it naturally incorporates context as spatial proximity is closely associated with connectivity.
    Computer Communications Workshops (INFOCOM WKSHPS), 2013 IEEE Conference on; 01/2013
  • B. Rengarajan, G. Rizzo, M. Ajmone Marsan, B. Furletti
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    ABSTRACT: We consider the problem of minimizing the energy consumed in a cellular access network, under loads that slowly vary over space and time, while guaranteeing quality of service (QoS). In particular, we formalize the problem of jointly optimizing the base stations (BS) power levels and the association of users to BSs, while guaranteeing a minimum throughput to each user, and a target value of blocking probability. We propose abstractions that enable tracking of long-term spatial load distributions, and a practical algorithm for energy efficient user association and base station power allocation. Our algorithm is applicable to arbitrary (planar) BS layouts, to settings with interference, to different BS energy models, and to arbitrary user distributions over the service area. Through extensive simulations using measured data, and realistic BS deployments, we show that our algorithm leads to substantial energy savings both with traditional BS designs and with energy-proportional equipment, and we demonstrate the potential of BS sleep modes to achieve network-level energy proportionality.
    World of Wireless, Mobile and Multimedia Networks (WoWMoM), 2013 IEEE 14th International Symposium and Workshops on a; 01/2013
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    ABSTRACT: In this paper we study cellular access networks which solely rely on renewable energy. We consider a cellular network in which a mesh of base stations (BSs) that are powered with renewable sources, and interconnected with wireless backhaul links, cover the service area, and provide connection to few, typically remote, wired network accesses to the national and international backbone. In particular, we study how to dimension BS power generators and energy storage. We start by discussing the BS energy need, that depends on both the BS consumption model and the BS traffic profiles. Focusing then on some specific locations, we consider the use of photovoltaic (PV) panels, and dimension them based on the daily energy need of the BS and on typical radiative power of sun in the considered locations. Once the PV system has been dimensioned, we also evaluate the energy storage capacity that is needed to absorb energy production variability due to both daily and seasonal radiative power variations. Finally, we investigate the effectiveness of integrating the PV system with wind turbines, as well as the benefit induced on the system by base station sleep modes.
    Communications Workshops (ICC), 2013 IEEE International Conference on; 01/2013
  • S. Ali, G. Rizzo, B. Rengarajan, M. Ajmone Marsan
    [Show abstract] [Hide abstract]
    ABSTRACT: Context-awareness is a peculiar characteristic of an ever expanding set of applications that make use of a combination of restricted spatio-temporal locality and mobile communications, to deliver a variety of services to the end user. It is expected that by 2014 more than 1.5 billion people would be using applications based on local search (search restricted on the basis of spatio-temporal locality), and that mobile location based services will drive revenues of more than $15 billion worldwide. A common feature of such context-aware applications is the fact that their communication requirements significantly differ from ordinary applications. For most of them, the scope of generated content itself is local. This locally relevant content may be of little concern to the rest of the world, therefore moving this content from the user device to store it in a well-accessible centralized location and/or making this information available beyond its scope represents a clear waste of resources (connectivity, storage). Due to these specific requirements, opportunistic communication can play a special role when coupled with context-awareness. The benefit of opportunistic communications is that it naturally incorporates context as spatial proximity is closely associated with connectivity.
    INFOCOM, 2013 Proceedings IEEE; 01/2013
  • 01/2013;
  • Thorsten Herfet, Marco Ajmone Marsan
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    ABSTRACT: Data aggregation has been the focus of many researchers as one of the most important applications in Wireless Sensor Networks. A main issue of data aggregation is how to construct efficient schedules by which data can be aggregated without any interference. ...
    Computer Communications. 11/2012; 35(18):2236.
  • Marco Ajmone Marsan
    European Conference and Exhibition on Optical Communication; 09/2012
  • Ana Paula Couto da Silva, Michela Meo, Marco Ajmone Marsan
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    ABSTRACT: The increasing concern about the energy consumption of communication networks is driving the research community to identify approaches to save energy in the networks of today. For instance, considering wireless local area networks (WLANs), the activation of network resources can be driven by the user demand, avoiding having to always power on all Access Points (APs). In this paper, we consider a portion of a dense WLAN system, where many APs are deployed to provide sufficient capacity to serve a large number of active users during peak traffic hours. To provide large capacity, a number of APs are colocated in the same position and provide identical coverage; we say that these APs belong to the same group, and they serve users in the same area. The areas covered by different groups only partially overlap, so that some active users can only be served by a group of APs, but a fraction of active users can be served by several groups. Due to daily variations of the number of active users accessing the WLAN, some APs can be switched off to save energy when not all the capacity is needed. The main focus of our study is the investigation of the type of algorithm that should be used for the association of active users with APs in order to increase the amount of saved energy in dense WLANs. Results show that when some system state information is available, such as the number of users associated with each AP, the energy consumption can decrease up to 20%. Furthermore, our study gives comprehensive insights on the trade-off between the opposite needs to save energy and provide quality of service to the users.
    Computer Networks (1976) 07/2012; 56(10):2522–2537.

Publication Stats

6k Citations
125.66 Total Impact Points

Institutions

  • 1982–2013
    • Politecnico di Torino
      • • DET - Department of Electronics and Telecommunications
      • • DAUIN - Department of Control and Computer Engineering
      Torino, Piedmont, Italy
  • 2012
    • The Optical Society
      Society Hill, New Jersey, United States
  • 2009
    • Federal Technological University of Parana
      Curityba, Paraná, Brazil
  • 2007
    • University of Massachusetts Amherst
      • School of Computer Science
      Amherst Center, MA, United States
  • 1988–2006
    • University of Milan
      • Department of Computer Science
      Milano, Lombardy, Italy
  • 2004–2005
    • Università degli Studi di Trento
      Trient, Trentino-Alto Adige, Italy
    • University of Bradford
      • Department of Computing
      Bradford, ENG, United Kingdom
  • 1996–2001
    • Federal University of Rio de Janeiro
      Rio de Janeiro, Rio de Janeiro, Brazil
  • 1986–2001
    • Università degli Studi di Torino
      • Dipartimento di Informatica
      Torino, Piedmont, Italy
    • Politecnico di Bari
      Bari, Apulia, Italy
  • 2000
    • Università della Calabria
      Rende, Calabria, Italy
  • 1989–1995
    • Budapest University of Technology and Economics
      Budapeŝto, Budapest, Hungary