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Design of Reliable Communication Solutions for Wireless Sensor Networks: Managing Interference in Unlicensed Bands
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , vii, 142 p.
Series
Trita-ICT-COS, ISSN 1653-6347 ; 0901
National Category
Telecommunications
Identifiers
URN: urn:nbn:se:kth:diva-10257OAI: oai:DiVA.org:kth-10257DiVA: diva2:212727
Presentation
2009-05-14, Sal/Hall C1, KTH Electrum, Isafjordsgatan 26, KISTA, 14:00 (English)
Opponent
Supervisors
Available from: 2009-05-07 Created: 2009-04-23 Last updated: 2010-11-01Bibliographically approved
List of papers
1. Energy-efficient detection of intermittent interference in wireless sensor networks
Open this publication in new window or tab >>Energy-efficient detection of intermittent interference in wireless sensor networks
2010 (English)In: International Journal of Sensor Networks, ISSN 1748-1279, Vol. 8, no 1, 27-40 p.Article in journal (Refereed) Published
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.

Keyword
energy-aware spectrum sensing, interference detection, co-existence in unlicensed bands, WSNs, wireless sensor networks
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-25786 (URN)000281577500003 ()2-s2.0-77954917116 (Scopus ID)
Note
QC 20101101Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2010-11-01Bibliographically approved
2. Interference Aware Self-Organization for Wireless Sensor Networks: a Reinforcement Learning Approach
Open this publication in new window or tab >>Interference Aware Self-Organization for Wireless Sensor Networks: a Reinforcement Learning Approach
2008 (English)In: 2008 IEEE INTERNATIONAL CONFERENCE ON AUTOMATION SCIENCE AND ENGINEERING, VOLS 1 AND 2, NEW YORK: IEEE , 2008, 560-565 p.Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
NEW YORK: IEEE, 2008
Keyword
Arts computing, Computer networks, Energy efficiency, Hybrid sensors, Learning algorithms, Network protocols, Reinforcement, Reinforcement learning, Reliability, Sensor networks, Sensors
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-25788 (URN)10.1109/COASE.2008.4626424 (DOI)000261320400092 ()2-s2.0-54949119207 (Scopus ID)978-1-4244-2022-3 (ISBN)
Conference
IEEE International Conference on Automation Science and Engineering Arlington, VA, AUG 23-26, 2008 IEEE
Note
QC 20101101Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2010-11-01Bibliographically approved
3. Energy Optimal Neighbor Discovery for Single-Radio Single-Channel Wireless Sensor Networks
Open this publication in new window or tab >>Energy Optimal Neighbor Discovery for Single-Radio Single-Channel Wireless Sensor Networks
2008 (English)In: 2008 IEEE INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS (ISWCS 2008), NEW YORK: IEEE , 2008, 206-210 p.Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
NEW YORK: IEEE, 2008
Keyword
Cellular telephone systems, Communication systems, Dynamic programming, Energy efficiency, Energy policy, Global system for mobile communications, Mobile computing, Optimization, Routing protocols, Sensor networks, Systems engineering, Windows, Wireless telecommunication systems
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-25789 (URN)10.1109/ISWCS.2008.4726123 (DOI)000265213100042 ()2-s2.0-62449108775 (Scopus ID)978-1-4244-2488-7 (ISBN)
Conference
5th International Symposium on Wireless Communication Systems, Reykjavik, ICELAND, OCT 21-24, 2008 IEEE
Note
QC 20101101Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2011-03-25Bibliographically approved
4. Networked estimation under contention-based medium access
Open this publication in new window or tab >>Networked estimation under contention-based medium access
2010 (English)In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 20, no 2, 140-155 p.Article in journal (Refereed) Published
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.

Keyword
networked estimation, cross-layer analysis, cross-layer tradeoffs, MAC, protocols, sampling rates, communication bandwidth constraints, control-systems
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-19108 (URN)10.1002/rnc.1459 (DOI)000273545600003 ()2-s2.0-75749100976 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-01-27Bibliographically approved
5. Utility Based Adaptive Frequency Hopping
Open this publication in new window or tab >>Utility Based Adaptive Frequency Hopping
(English)Article in journal (Refereed) Submitted
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-25796 (URN)
Note
QC 20101101Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2010-11-01Bibliographically approved
6. SYNAPSE:  A network reprogramming protocol for wireless sensor networks using fountain codes
Open this publication in new window or tab >>SYNAPSE:  A network reprogramming protocol for wireless sensor networks using fountain codes
Show others...
2008 (English)In: 2008 5th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON, 2008, 188-196 p.Conference paper, Published paper (Refereed)
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.

National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-25795 (URN)10.1109/SAHCN.2008.32 (DOI)2-s2.0-51749123573 (Scopus ID)978-142441777-3 (ISBN)
Conference
5th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON 2008; San Francisco, CA; 16 June 2008 through 20 June 2008
Note
QC 20101101Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2010-11-01Bibliographically approved

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Citation style
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