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  • 1.
    Rabi, Maben
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Almström, Peter
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Analysis of networked estimation under contention-based medium access2008Ingår i: 17th World Congress, International Federation of Automatic Control, IFAC, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    We treat a problem in networked estimation where the focus is on sampling and transmitting measurements of the plant over a shared medium. The object is to choose the sampling rate at the sensor while taking the statistics of a contention based MAC protocol into account. In particular, we seek a trade-off between the reliable delivery of individual data packets and the input data load on the communication medium. Our analysis of the shared channel computes a probability of packet loss for an assumed IID loss process. This loss rate depends on the input packet stream intensities. We compute the estimation distortion with IID losses of periodically generated samples, as a function of the packet loss rate. This throws up a condition for stable estimator performance. We investigate the scalability limits of this stability as a function of the number of nodes. When stable estimation is possible, we provide a procedure that computes the input packet rate for the network that minimizes the average estimation distortion. We reproduce the analysis of estimation performance when the sensors sample asynchronously according to independent Poisson counters.

  • 2.
    Rabi, Maben
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Proutiere, Alexandre
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Networked estimation under contention-based medium access2010Ingår i: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 20, nr 2, s. 140-155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper studies networked estimation over a communication channel shared by a contention-based medium access protocol. A collection of N identical and physically decoupled scalar systems are sampled without sensor noise and transmitted over a common channel, using a contention-based medium access mechanism. We first carry out a calculation of the average distortion in estimation with irregular samples. Given the rate of packet generation at sensors, we characterize the traffic characteristics of the some contention-based MAC schemes. This lets us derive the statistics of inter-arrival times which in turn allows us to compute the packet loss rates and also the statistics of delay within a sample period. Using these results, we track the estimation performance as the sample generation rate and the number of contending nodes are varied. We provide a heuristic rule-of-thumb for choosing the sampling interval which minimizes the average distortion. By combining the network traffic characterization with that of the estimation performance, we show this rule performs pretty well. Carrying along the same lines, we are able to compute the scaling limits of estimation performance with respect to the number of contending nodes.

  • 3. Rossi, Michele
    et al.
    Bui, Nicola
    Zanca, Giovanni
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster, Kommunikationssystem, CoS.
    Crepaldi, Riccardo
    Zorzi, Michele
    SYNAPSE plus plus: Code Dissemination in Wireless Sensor Networks Using Fountain Codes2010Ingår i: IEEE Transactions on Mobile Computing, ISSN 1536-1233, E-ISSN 1558-0660, Vol. 9, nr 12, s. 1749-1765Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents SYNAPSE++, a system for over the air reprogramming of wireless sensor networks (WSNs). In contrast to previous solutions, which implement plain negative acknowledgment-based ARQ strategies, SYNAPSE++ adopts a more sophisticated error recovery approach exploiting rateless fountain codes (FCs). This allows it to scale considerably better in dense networks and to better cope with noisy environments. In order to speed up the decoding process and decrease its computational complexity, we engineered the FC encoding distribution through an original genetic optimization approach. Furthermore, novel channel access and pipelining techniques have been jointly designed so as to fully exploit the benefits of fountain codes, mitigate the hidden terminal problem and reduce the number of collisions. All of this makes it possible for SYNAPSE++ to recover data over multiple hops through overhearing by limiting, as much as possible, the number of explicit retransmissions. We finally created new bootloader and memory management modules so that SYNAPSE++ could disseminate and load program images written using any language. At the end of this paper, the effectiveness of SYNAPSE++ is demonstrated through experimental results over actual multihop deployments, and its performance is compared with that of Deluge, the de facto standard protocol for code dissemination in WSNs. The TinyOS 2 code of SYNAPSE++ is available at http://dgt.dei.unipd.it/download.

  • 4. Rossis, M.
    et al.
    Zancas, G.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Crepaldi, R.
    Harris III, A. F.
    Zorzi, M.
    SYNAPSE:  A network reprogramming protocol for wireless sensor networks using fountain codes2008Ingår i: 2008 5th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON, 2008, s. 188-196Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wireless reprogramming is a key functionality in Wireless Sensor Networks (WSNs). In fact, the requirements for the network may change in time, or new parameters might have to be loaded to change the behavior of a given protocol. In large scale WSNs it makes economical as well as practical sense to upload the code with the needed functionalities without human intervention, i.e., by means of efficient over the air reprogramming. This poses several challenges as wireless links are affected by errors, data dissemination has to be 100% reliable, and data transmission and recovery schemes are often called to work with a large number of receivers. State-of-the-art protocols, such as Deluge, implement error recovery through the adaptation of standard Automatic Repeat reQuest (ARQ) techniques. These, however, do not scale well in the presence of channel errors and multiple receivers. In this paper, we present an original reprogramming system for WSNs called SYNAPSE, which we designed to improve the efficiency of the error recovery phase. SYNAPSE features a hybrid ARQ (HARQ) solution where data are encoded prior to transmission and incremental redundancy is used to recover from losses, thus considerably reducing the transmission overhead. For the coding, digital Fountain Codes were selected as they are rateless and allow for lightweight implementations. In this paper, we design special Fountain Codes and use them at the heart of SYNAPSE to provide high performance while meeting the requirements of WSNs. Moreover, we present our implementation of SYNAPSE for the Tmote Sky sensor platform and show experimental results, where we compare the performance of SYNAPSE with that of state of the art protocols.

  • 5.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Design of Reliable Communication Solutions for Wireless Sensor Networks: Managing Interference in Unlicensed Bands2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Recent surveys conducted in the context of industrial automation have outlined that reliability concerns represent today one of the major barriers to the diffusion of wireless communications for sensing and control applications: this limits the potential of wireless sensor networks and slows down the adoption of this new technology. Overcoming these limitations requires that awareness on the causes of unreliability and on the possible solutions to this problem is created. With this respect, the main factor responsible for the perceived unreliability is radio interference: low-power communications of sensor nodes are in fact very sensitive to bad channel conditions and can be easily corrupted by transmissions of other co-located devices. In this thesis we investigate different techniques that can be exploited to avoid interference or mitigate its effects.We first consider interference avoidance through dynamic spectrum access: more specifically we focus on the idea of channel surfing and design algorithms that allow sensor nodes to identify interfered channels, discover their neighbors and maintain a connected topology in multi-channel environments. Our investigation shows that detecting and thus avoiding interference is a feasible task that can be performed by complexity and power constrained devices. In the context of spectrum sharing, we further consider the case of networked estimation and aim at quantifying the effects of intranetwork interference, induced by contention-based medium access, over the performance of an estimation system. We show that by choosing in an opportune manner their probability of transmitting, sensors belonging to a networked control system can minimize the average distortion of state estimates.In the second part of this thesis we focus on frequency hopping techniques and propose a new adaptive hopping algorithm. This implements a new approach for frequency hopping: in particular rather than aiming at removing bad channels from the adopted hopset our algorithm uses all the available frequencies but with probabilities that depend on the experienced channel conditions. Our performance evaluation shows that this approach outperforms traditional frequency hopping schemes as well as the adaptive implementation included in the IEEE 802.15.1 radio standard leading to a lower packet error rate.Finally, we consider the problem of sensor networks reprogramming and propose a way for ingineering a coding solution based on fountain codes and suitable for this challenging task. Using an original genetic approach we optimize the degree distribution of the used codes so as to achieve both low overhead and low decoding complexity. We further engineer the implementation of fountain codes in order to allow the recovery of corrupted information through overhearing and improve the resilience of the considered reprogramming protocol to channel errors.

  • 6.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Energy Optimal Neighbor Discovery for Single-Radio Single-Channel Wireless Sensor Networks2008Ingår i: 2008 IEEE INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS (ISWCS 2008), NEW YORK: IEEE , 2008, s. 206-210Konferensbidrag (Refereegranskat)
    Abstract [en]

    Neighbor discovery is a fundamental procedure that needs to be carried out in every wireless sensor network in order to enable communication capabilities. If nodes are mobile or multiple channels are used in the network, the same algorithm may be needed to be carried out several times during the network lifetime, consuming precious energy. In this paper we propose a way for optimizing a neighbor discovery procedure suitable for a single-radio single-channel scenario. Assuming a realistic energy model which accounts for energy required for transmitting discovery queries and listening for acknowledgements and explicitly accounting for collisions we exploit power control and the use of a contention window of variable size to minimize sensors' energy consumption while both transmitting and receiving. We formulate the neighbor discovery problem as a Markov decision process and through dynamic programming we compute an optimal policy defining the power level and the contention window size that must be used while broadcasting queries. This policy minimizes the energy cost of the discovery procedure for a given constraint on the maximum probability of having collisions. We further provide guidelines usefull for implementing sub-optimal policies which perform asymptotically optimal for high node densities and can be computed on-line by motes with low capabilities.

  • 7.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster (Stängd 20120101), Kommunikationssystem, CoS (stängd 2012-01-01). KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Energy-aware exploitation of white spaces in the time domain for wireless sensor networks2010Ingår i: Proceedings of the 2010 7th International Symposium on Wireless Communication Systems, ISWCS'10, 2010, s. 981-985Konferensbidrag (Refereegranskat)
    Abstract [en]

    Low power communications of sensor nodes operating in unlicensed bands are easily corrupted by transmissions of collocated wireless terminals whose interference can induce packet losses and consequently increase energy consumption of sensor devices. Dynamic spectrum access mechanisms can mitigate these problems however the energy aware design of these access schemes is a challenging task. In this paper we consider an energy constrained system comprising two sensor nodes that avoid interference by exploiting spectrum opportunities in the time domain. Using the distributions of idle period duration obtained during a measurement campaign we show how it is possible to design the access scheme deployed by sensors in an energy efficient manner. We compare different spectrum sensing strategies, showing that per-packet sensing results in significant energy overhead. We further provide a way for dimensioning the size of transmitted packets. Simulation results show that our approach outperforms other access strategies and allows to reduce energy consumption of 20 to 90 percent depending on channel conditions.

  • 8.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster, Kommunikationssystem, CoS.
    Quantifying and Modeling Spectrum Opportunities in a Real Wireless Environment2010Ingår i: IEEE Wireless Communications and Networking Conference, NEW YORK: IEEE , 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Interference avoidance schemes based on dynamic spectrum access can be exploited by wireless sensor networks in order to mitigate the interference induced by collocated wireless devices. Developing models that can accurately describe the variations of spectrum opportunities over frequency and time is a key challenge for the energy efficient design of those access schemes. Previous works addressing this problem have considered interference-controlled environments, where a single packet flown has been artificially generated and the spectrum opportunities arising among the bursty transmissions of the considered network have been characterized. In this paper we consider instead a real environment with heterogeneous wireless devices and perform measurements for analyzing spectrum utilization over the 2.4 GHz ISM band: we statistically characterize the distribution of idle periods and investigate how spectrum occupancy varies over a time-frame of several days. The results we obtain can be of great utility while simulating the performance of different access schemes or dimensioning spectrum sensing algorithms and provide insights that can be used to select the most appropriate interference avoidance approach.

  • 9.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Toward Reliable Wireless Sensor Networks: Energy-Aware Distributed interference Management for Unlicensed Bands2010Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Wireless sensor networks have been proposed as a cost effective and easy to deploy alternative to traditional wired systems in a multitude of application scenarios ranging from industrial automation to healthcare monitoring. They are expected to enable an unparalleled number of new services that will bring countless benefits to society. However, low power communications of sensor nodes operating in unlicensed bands face several challenges and are easily corrupted by transmissions of other collocated wireless networks. This problem has recently raised reliability concerns which have been tremendously enhanced by the proliferation of wireless devices we have been witnessing during the last years in the few available regions of the spectrum.

    This dissertation studies how to achieve reliable communications by proposing different ways for the energy aware management of the radio interference problem. The use of wireless sensing technologies has been envisaged in a broad variety of settings: for this reason it is not possible to identify a unifying solution for the problem of interference, but rather it is necessary to tailor the design of communication schemes accounting for the specific communication paradigm adopted by sensors, the traffic pattern generated by the expected application, as well as for the channel conditions experienced by nodes.

    When packet transmissions are addressed to a single receiver, cognitive access schemes can be utilized and sensors can opportunistically select for their transmissions when to access a certain channel or which channel to access so as to avoid interference. We provide an energy aware design for communication schemes implementing these ideas and evaluate their energy performance by means of experiments using real hardware. Our results indicate that the first approach should be considered only for sporadic packet transmissions over channels presenting limited interfering activities; channel adaptation should instead be preferred for large bulks of data or when the risk of operating in heavily interfered frequency bands is high. We further propose and evaluate a novel adaptive frequency hopping algorithm: this algorithm has been shown to be very efficient in mitigating the negative effects of interference allowing at the same time to avoid the use of the energy costly spectrum sensing algorithms required by cognitive access schemes. However, none of these three approaches may be suitable for scenarios where packet transmissions are addressed to multiple receivers. To deal with the packet losses that nodes may experience over noisy or interfered channels we envisage the use of fountain codes and show how it is possible to engineer such a coding solution so as to reduce the complexity and overhead introduced by the encoding and decoding procedures. The resulting codes provide an efficient way for disseminating data over multi-hop wireless sensor networks. Results obtained in this dissertation can be of great utility for designers of sensor applications who can use them in order to select the most energy efficient way to achieve reliable interference-aware communications.

  • 10.
    Stabellini, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Utility Based Adaptive Frequency HoppingArtikel i tidskrift (Refereegranskat)
  • 11.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Javed, Muhammad Umar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Experimental Comparison of Dynamic Spectrum Access Techniques for Wireless Sensor Networks2010Ingår i: VEHICULAR TECHNOLOGY CONFER, the Institute of Electrical and Electronic Engineers, Inc , 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Communication schemes exploiting dynamic spectrum access have been recently envisaged in the context of wireless sensor networks: these access techniques allow cognitive sensor devices to avoid transmissions of interfering networks by opportunistically exploiting spectrum holes in the time or frequency domain. Such spectrum opportunities need to be identified through spectrum sensing, however this might introduce significant energy overhead. Selecting the most appropriate spectrum sensing and access technique is therefore a key issue for the efficient design of these communication schemes. In this paper we present the experimental evaluation of two different cognitive approaches, respectively exploiting spectrum holes in the time and frequency domain. We quantify the average energy required by a two-node system for the successful delivery of a packet and investigate the effect of the energy overhead introduced by spectrum sensing. Our results show that the time domain approach results in poor performance even for relatively low values of channel occupancy; on the other hand channel surfing schemes introduce significant energy overhead due to spectrum sensing but allow to effectively avoid interference and should therefore be preferred to time-domain techniques when the risk of operating in heavily interfered channels is high or when a large amount of data has to be transmitted.

  • 12.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster (Stängd 20120101), Kommunikationssystem, CoS (stängd 2012-01-01).
    Parhizkar, Mohammad Mohsen
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Experimental comparison of frequency hopping techniques for 802.15.4-based sensor networks2010Ingår i: UBICOMM 2010 - 4th International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies, 2010, s. 110-116Konferensbidrag (Refereegranskat)
    Abstract [en]

    Frequency hopping communication schemes represent an attractive alternative for interconnecting low power wireless sensor nodes operating in unlicensed bands. The use of multiple communication channels can in fact mitigate the negative effects of interference induced by collocated wireless networks and potentially results in improved reliability.With this respect, quite a few adaptive variations, aiming at improving the resilience of frequency hopping toward interference have been recently proposed. In this paper we present the experimental evaluation of three different hopping schemes: we implement a traditional hopping algorithm and two adaptive variations on TMote Sky sensor motes and quantify their energy performance under different channel conditions. We also compare the effectiveness of these three hopping techniques against the one of a communication scheme making use of a single channel. Our results, obtained considering a two-node topology, indicate that our previously proposed utility based adaptive frequency hopping approach is the most effective in avoiding interference and can significantly reduce the overall energy consumption despite its higher complexity. The performed experiments also show that even though reliable single-channel communication might be possible, by using frequency hopping sensors can limit the performance degradation induced by interference while avoiding the energy overhead introduced by the spectrum sensing algorithms that nodes have to use for identifying clear channels.

  • 13.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Proutiere, Alexandre
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Evaluating delay and energy in sensor networks with sporadic and correlated traffic2007Ingår i: 7thScandinavian Workshop on Wireless Ad-Hoc Networks (ADHOC ´07), 2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wireless sensor networks are usually comprised of a set of sensors that are equipped with a wireless transmitter/ receiver and of a set of data sinks where the information gathered by sensors should be treated. The delay, from the time when events are sensed to the time when the information arrives at sinks, has to satisfy some specific requirements. These requirements depend on the underlying application targeted by the network, and typically consist in ensuring that the delay is less than a pre-defined threshold with high probability. A common issue in sensor networks is then to design distributed scheduling and routing algorithms so as to maximize the network lifetime while guaranteeing the delay requirements. This optimization problem has to account for the particular nature of traffic in sensor networks: the traffic there is (i) sporadic, in the sense that sensors do not have always packets to transmit, (ii) correlated, meaning that the sensors belonging to a common neighborhood may generate traffic simultaneously (e.g., a network sensing temperatures typically exhibits correlated traffic). In this work, we aim at providing analytical and simulation tools able to quantify the packet delays in sensor networks with sporadic and correlated traffic, for various types of distributed scheduling protocols. These tools may then be used to design protocols maximizing the lifetime of delay-constrained networks.

  • 14.
    Stabellini, Luca
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Shi, Lei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Al Rifai, Ahmad
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Espino, Juan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Magoula, Veatriki
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    A New Probabilistic Approach for Adaptive Frequency Hopping2009Ingår i: 2009 IEEE 20th International Symposium on Personal, Indoor and Mobile Radio Communications, NEW YORK: IEEE , 2009, s. 2147-2151Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This paper proposes Utility Based Adaptive Frequency Hopping (UBAFH), an adaptive hopping technique implementing a new paradigm for frequency hopping systems. Traditional adaptive algorithms aim at identifying bad channels that are consequently removed from the hopset. UBAFH instead utilizes all the available frequencies but assigns different usage probabilities to different channels according to the experienced channel conditions. Opportune upper and lower limits are used in order to bound these usage probabilities and achieve a desired level of frequency diversity. We simulate the behavior of UBAFH over frequency selective fading channels and compare the achieved packet error rate and throughput with the ones of IEEE 802.15.1 and with the adaptive frequency hopping implementation proposed by IEEE 802.15.2 showing that UBAFH outperforms both approaches.

  • 15.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Veronesi, Riccardo
    Tralli, Velio
    Increasing system capacity in GERAN by means of TRX power reduction2007Ingår i: 2007 IEEE Vehicular Technology Conference, Vols 1-6, 2007, s. 1162-1166Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we propose an efficient and simple method to improve system capacity in GSM/GPRS/EDGE radio systems. It exploits the power shaping concept and the parameter "TRX power reduction" already present in the standard and does not require major modifications to operators specific radio resource management algorithms. Power-shaping means assigning in advance (static allocation) a maximum power level to each channel before dynamically performing channel allocation. This is done by exploiting a set of suitably reused power profiles that partially organize the inter-cell interference in the available channels and make it partially predictable. This technique, thanks to the possibility of tightening the reuse factor, permits to increase the system capacity for both voice and data services if compared to most common reuse schemes or to the widely used concentric cells schemes. This is shown in the results where an interesting gain is achieved by power shaping with power reduction with respect to the other schemes.

  • 16.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster (Stängd 20120101), Kommunikationssystem, CoS (stängd 2012-01-01).
    Zander, Jens
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikation: Infrastruktur och tjänster (Stängd 20120101), Kommunikationssystem, CoS (stängd 2012-01-01).
    Energy-Aware Spectrum Sensing in Cognitive Wireless Sensor Networks: a Cross Layer Approach2010Ingår i: IEEE Wireless Communications and Networking Conference, WCNC, NEW YORK: IEEE , 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Low-power transmissions of sensor nodes are easily corrupted by interference generated by co-located wireless terminals that leading to packet losses might increase energy consumption and result in unreliable communications. Dynamic spectrum access mechanisms can mitigate these problems allowing cognitive sensor devices to sense the spectrum and access the wireless medium in an opportunistic way. With this respect, energy efficient algorithms for spectrum sensing have to be designed in order to meet the power constraints of wireless sensor networks. In this paper we consider an energy constrained system comprising two sensor nodes that avoid interference by exploiting spectrum holes in the time domain. We design the algorithm used for spectrum sensing so as to minimize the average energy required for the successful delivery of a packet. While carrying our this task we adopt a cross layer approach that accounts for the average channel occupancy and the power of interfering transmissions at the physical layer as well as for the size of packets used by sensors at the transport layer. Our results show that accounting for the short length of packets commonly used in sensor networks can significantly improve energy efficiency leading to gains of up to 50% if compared to other spectrum sensing algorithms envisaged in the literature.

  • 17.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Zander, Jens
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Energy-efficient detection of intermittent interference in wireless sensor networks2010Ingår i: International Journal of Sensor Networks, ISSN 1748-1279, Vol. 8, nr 1, s. 27-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Communications of low-power sensor nodes are easily corrupted by transmissions of collocated devices that inducing packet losses might increase data delay and energy consumption. Dynamic Spectrum Access mechanisms can mitigate these problems. These approaches allow frequency agile sensor nodes to avoid frequency bands experiencing high interference and select channels suitable for their transmissions. In this context, detecting interference and identifying spectrum opportunities in a reliable and efficient manner becomes a task of vital importance. In this paper we propose a new interference detection algorithm accounting both for energy and complexity constraints of sensor motes as well as for the intermittent nature of interference typically experienced by sensor networks in unlicensed bands. We develop an analytical framework that allows to explicitly characterise the performance of our algorithm and also implement it on the TMote Sky sensor platform. Experimental results clearly demonstrate the capabilities of the proposed scheme to identify interfered channels.

  • 18.
    Stabellini, Luca
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Zander, Jens
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Interference Aware Self-Organization for Wireless Sensor Networks: a Reinforcement Learning Approach2008Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON AUTOMATION SCIENCE AND ENGINEERING, VOLS 1 AND 2, NEW YORK: IEEE , 2008, s. 560-565Konferensbidrag (Refereegranskat)
    Abstract [en]

    Reliability is a key issue in wireless sensor networks. Depending on the targeted application, reliability is achieved by establishing and maintaining a certain number of network functionalities: the greatest among those is certainly the capability of nodes to communicate. Sensors communications are sensible to interference that might corrupt packets transmission and even preclude the process of network formation. In this paper we propose a new scheme that allows to establish and maintain a connected topology while dealing with this problem. The idea of channel surfing (already introduced in [1]) is exploited to avoid interference; in the resulting multi-channel environment nodes discover their neighbors in a distributed fashion using a reinforcement learning (RL) algorithm. Our scheme allows the process of network formation even in presence of interference, overcoming thus the limit of algorithms currently implemented in state of the art standards for wireless sensor networks. By means of reinforcement learning the process of neighbor discovery is carried out in a fast and energy efficient way.

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