| 1. |
- Barac, Filip, et al.
(författare)
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Channel Coding and Interleaving in Industrial WSN : Abiding to Timing Constraints and Bit Error Nature
- 2013
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Ingår i: Proceedings - M and N 2013: 2013 IEEE International Workshop on Measurements and Networking. - 9781467328739 ; , s. 46-51
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Konferensbidrag (refereegranskat)abstract
- Forward Error Correction is a preemptive manner of improving communication reliability. Albeit not a part of IEEE 802.15.4-2006 standard, its application in Industrial Wireless Sensor Networks has been widely considered. Nevertheless, this study is the first performance analysis on real error traces with sufficiently lightweight channel codes, with respect to IEEE 802.15.4-2006 and industrial wireless communication timing constraints. Based on these constraints and bit error properties from the collected traces, the use of Reed-Solomon (15,7) block code is suggested, which can be implemented in software. Experiments show that bit error nature on links affected by multipath fading and attenuation in industrial environments is such that RS(15,7) can correct ≥95% of erroneously received packets, without the necessity for interleaving. On links under IEEE 802.11 interference, typically up to 50% of corrupted packets can be recovered by combining RS(15,7) with symbol interleaving, which has proven to be more effective than its bit counterpart. The optimal interleaving depth is found empirically and it is shown that simple bit-interleaved 1/3 repetition code achieves at least 90% of correcting performance of RS(15,7) code on uninterfered links that operate ≥10 dB above the sensitivity threshold.
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| 2. |
- Barac, Filip, 1983-, et al.
(författare)
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Channel Diagnostics for Wireless Sensor Networks in Harsh Industrial Environments
- 2014
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 14:11, s. 3983-3995
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Tidskriftsartikel (refereegranskat)abstract
- Wireless sensor network communication in industrial environments is compromised by interference, multipath fading, and signal attenuation. In that respect, accurate channel diagnostics is imperative to selecting the adequate countermeasures. This paper presents the lightweight packet error discriminator (LPED) that infers the wireless link condition by distinguishing between errors caused by multipath fading and attenuation, and those inflicted by interfering wideband single-channel communication systems (e.g., IEEE 802.11b/g), based on the differences in their error footprints. The LPED uses forward error correction in a novel context, namely, to determine the symbol error density, which is then fed to a discriminator for error source classification. The classification criteria are derived from an extensive set of error traces collected in three different types of industrial environments, and verified on a newly collected set of error traces. The proposed solution is evaluated both offline and online, in terms of classification accuracy, speed of channel diagnostics, and execution time. The results show that in ≥91% of cases, a single packet is sufficient for a correct channel diagnosis, accelerating link state inference by at least 270%, compared with the relevant state-of-the-art approaches. The execution time of LPED, for the worst case of packet corruption and maximum packet size, is below 30 ms with ≤3% of device memory consumption. Finally, live tests in an industrial environment show that LPED quickly recovers from link outage, by losing up to two packets on average, which is only one packet above the theoretical minimum.
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| 3. |
- Barac, Filip, et al.
(författare)
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CLAP: Chip-Level Augmentation of IEEE 802.15.4 PHY for Error-Intolerant WSN Communication
- 2015
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Ingår i: IEEE Vehicular Technology Conference. - Glasgow, Scotland : IEEE Vehicular Technology Society. ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Communication reliability is the ultimate priority in safety-critical wireless sensor network (WSN) communication. Surprisingly enough, the enormous potential of error control on direct sequence spread spectrum (DSSS) chips in IEEE 802.15.4 has been completely overlooked by the WSN community, possibly due to incorrect presumptions, such as the concerns about computational overhead. Current error-correction schemes in WSN counteract the error process once the errors have already propagated to bit- and packet-level. Motivated by the notion that errors should be confronted at the earliest stage, this work presents CLAP, a novel method that tremendously improves the error correction in WSN by fortifying the IEEE 802.15.4 Physical layer (PHY) with straightforward manipulations of DSSS chips. CLAP is implemented on a software-defined radio platform, and evaluated on real error traces from heavily WLAN-interfered IEEE 802.15.4 transmissions at 3 different environments. CLAP boosts the number of corrected packets by 1.78-6.88 times on severely interfered links, compared to two other state-of-the-art schemes. The overhead in terms of computational complexity is about 10% of execution time of the OQPSK demodulator in the legacy IEEE 802.15.4 receiver chain.
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| 4. |
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| 5. |
- Barac, Filip
(författare)
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Error mitigation in industrial wireless sensor networks : Corrupted packet forensics and recovery
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless sensor networks (WSN) are gradually penetrating the industrial automation domain. This process is, however, inhibited by a number of challenges that need to be considered and addressed before WSN can serve the most demanding industrial applications. In the context of process automation, existing technology can only serve the three least critical application classes related to non-critical monitoring of slowly-changing physical variables. The main issue in that respect is the insufficient communication timeliness and reliability, caused by the influence of harsh radio environment and the infeasibility of applying advanced communication techniques, due to the poor computational power of low-cost specialized hardware. The goal of this work is to improve wireless communication reliability in industrial environments, where the proposed solutions are generally applicable to other WSN domains as well as radio environments. This research is based on the notion that corrupt packets contain valuable channel state information that can be leveraged to improve communication robustness. The research methodology used in this work is rather unconventional, compared to existing research, but also highly intuitive, bearing in mind that counteracting a phenomenon requires a thorough knowledge of its properties. In order to rectify the aforementioned challenges, this work makes the following three contributions. The first contribution is a comprehensive analysis of communication errors recorded in practically relevant scenarios in a number of industrial environments. The related literature is seemingly rich, but essentially poor, due to inadequate measurement objectives, environments, and scenarios. The main research outcome of this measurement campaign is a set of practically relevant conclusions, which can be used for the design of coding, interleaving and packet recovery schemes. The second contribution is the design of two packet recovery schemes, based on the knowledge about error patterns obtained in the industrial measurement campaign. The first scheme is a proposal for redefinition of the IEEE 802.15.4 physical layer, where digital errors are counteracted at the earliest stage in the receiver chain. The second scheme exploits the determinism in packet structure inherent to industrial communication. Both schemes significantly improve the correctability of corrupted packets received. The third contribution is a channel diagnostics algorithm that determines whether a packet was corrupt by multipath fading and attenuation or by wireless local area network interference. The algorithm is derived from the error traces collected in three industrial environments and tested at a fourth, previously unused, industrial site. The results of live tests verify the ability of the proposed algorithm to promptly reestablish communication after a sudden deterioration of channel quality.
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| 6. |
- Barac, Filip, et al.
(författare)
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LPED: Channel Diagnostics in WSN Through Channel Coding and Symbol Error Statistics
- 2014
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Ingår i: IEEE ISSNIP 2014 - 2014 IEEE 9th International Conference on Intelligent Sensors, Sensor Networks and Information Processing, Conference Proceedings. - Singapore : IEEE Sensors Council. - 9781479928422 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Three major obstacles to wireless communication are electromagnetic interference, multipath fading and signal attenuation. The former stems mainly from collocated wireless systems operating in the same frequency band, while the latter two originate from physical properties of the environment. Identifying the source of packet corruption and loss is crucial, since the adequate countermeasures for different types of threats are essentially different. This problem is especially pronounced in industrial monitoring and control applications, where IEEE 802.15.4 communication is expected to deliver data within tight deadlines, with minimal packet loss. This work presents the Lightweight Packet Error Discriminator (LPED) that distinguishes between errors caused by multipath fading and attenuation, and those inflicted by IEEE 802.11 interference. LPED uses Forward Error Correction to determine the symbol error positions inside erroneously received packets and calculates the error density, which is then fed to a discriminator for error source classification. The statistical constituents of LPED are obtained from an extensive measurement campaign in two different types of industrial environments. The classifier incurs no overhead and in ≥90% of cases a single packet is sufficient for a correct channel diagnosis. Experiments show that LPED accelerates link diagnostics by at least 190%, compared to the relevant state-of-the-art approaches.
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| 7. |
- Barac, Filip, et al.
(författare)
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PREED: Packet Recovery by Exploiting the Determinism in Industrial WSN Communication
- 2015
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Ingår i: Proceedings - IEEE International Conference on Distributed Computing in Sensor Systems, DCOSS 2015. - Fortaleza, Brazil : IEEE Computer Society. ; , s. 81-90
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Konferensbidrag (refereegranskat)abstract
- The requirements of safety-critical wireless sensornetwork (WSN) applications, such as closed-loop control andtraffic safety, cannot be met by the IEEE 802.15.4-2006 standardnor its industrial WSN (IWSN) derivatives. The main problem inthat respect is the communication reliability, which is seriouslycompromised by 2.4-GHz interference, as well as multipathfading and attenuation (MFA) at industrial facilities. Meanwhile,communication blackouts in critical WSN applications maylead to devastating consequences, including production halts,damage to production assets and can pose a threat to safetyof human personnel. This work presents PREED, a method toimprove the reliability by exploiting the determinism in IWSNcommunication. The proposed solution is based on the analysisof bit error traces collected in real transmissions at four differentindustrial environments. A case study on WirelessHART packetformat shows that PREED recovers 42%-134% more packetsthan the competing approaches on links compromised by WLANinterference. In addition, PREED reduces one of the most trivialcauses of packet loss in IWSN, i.e. the corruption offrame lengthbyte, by 88% and 99%, for links exposed to WLAN interferenceand MFA, respectively.
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| 8. |
- Barac, Filip, et al.
(författare)
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Scrutinizing Bit- and Symbol-Errors of IEEE 802.15.4 Communication in Industrial Environments
- 2014
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 63:7, s. 1783-1794
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Tidskriftsartikel (refereegranskat)abstract
- The knowledge of error nature in wireless channels is an essential constituent of efficient communication protocol design. To this end, this paper is the first comprehensive bit- and symbol-level analysis of IEEE 802.15.4 transmission errors in industrial environments. The intention with this paper is to extract the error properties relevant for future improvements of wireless communication reliability and coexistence of radio systems in these harsh conditions. An extensive set of bit-error traces was collected in a variety of scenarios and industrial environments, showing that error behavior is highly dependent on the cause of packet corruption. It is shown that errors inflicted by multipath fading and attenuation exhibit different properties than those imposed by IEEE 802.11 interference. The statistical behavior of these two patterns is concurrently investigated in terms of differences in bit-error distribution, error burst length, channel memory length, and the scale of packet corruption. With these conclusions at hand, abiding to the computational constraints of embedded sensors and the statistical properties of bit-errors, a Reed-Solomon $(15,k)$ block code is chosen to investigate the implications of bit-error nature on practical aspects of channel coding and interleaving. This paper is concluded by a number of findings of high practical relevance, concerning the optimal type, depth, and meaningfulness of interleaving.
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| 9. |
- Barac, Filip, 1983-, et al.
(författare)
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Ubiquitous, yet Deceptive: Hardware-Based Channel Metrics on Interfered WSN Links
- 2015
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 64:5, s. 1766-1778
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Tidskriftsartikel (refereegranskat)abstract
- The ease of acquiring hardware-based link quality indicators is an alluring property for fast channel estimation in time- and safety-critical Wireless Sensor Network (WSN) applications, such as closed-loop control and interlocking. The two rudimentary hardware-based channel quality metrics, Received Signal Strength (RSS) and Link Quality Indicator (LQI), are the key constituents of channel estimation and a plethora of other WSN functionalities, from routing to transmit power control. Nevertheless, this study highlights three deficient aspects of these two indicators: 1) overall deceptiveness, i.e. the inability to reveal the presence of interference, falsely indicating excellent channel conditions in an unacceptably high fraction of cases; 2) the burstiness of missed detections, which compromises the attempts to eliminate the deceptiveness by averaging; 3) high mutual discrepancy of the two indicators, observed in 39-73% of packets, throughout different scenarios. The ability of RSS and LQI to indicate IEEE 802.11 interference is scrutinized in a variety of scenarios in typical industrial environments, using commercialoff- the-shelf hardware and realistic network topologies, giving the findings of this study a high general validity and practical relevance.
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| 10. |
- Dobslaw, Felix, et al.
(författare)
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A Reliability-Aware Cross-layer Optimization Framework for Wireless Sensor Networks.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- One of the biggest obstacles for a broad deploymentof Wireless Sensor Networks for industrial applications is the dif-ficulty to ensure end-to-end reliability guarantees while providingas tight latency guarantees as possible. In response, we proposea novel centralized optimization framework for Wireless SensorNetworks that identifies TDMA schedules and routing combi-nations in an integrated manner. The framework is shown toguarantee end-to-end reliability for all events send in a schedulingframe while minimizing the delay of all packet transmissions. Itcan further be applied using alternative Quality of Service ob-jectives and constraints including energy efficiency and fairness.We consider network settings with multiple channels, multiplesinks, and stringent reliability constraints for data collectingflows. We compare the results to those achieved by the onlyscalable reliability-aware TDMA scheduling algorithm to ourknowledge, SchedEx, which conducts scheduling only. By makingrouting part of the problem and by introducing the conceptof source-aware routing, we achieve latency improvements forall topologies, with a notable average improvement of up to31percent.
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