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  • 1.
    Girs, Svetlana
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Willig, Andreas
    University of Canterbury, Canterbury, New Zealand.
    Uhlemann, Elisabeth
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems. Halmstad University, Halmstad, Sweden.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    On the Role of Feedback for Industrial Networks Using Relaying and Packet Aggregation2013Report (Other academic)
    Abstract [en]

    To be accepted for use in industrial applications, wireless technologies must offer similar performance in terms of reliability and timeliness as provided by current wired solutions. Wireless channels, introducing time-varying packet error rates, impose a significant challenge to fulfill these requirements. One way to improve reliability in industrial wireless networks is to use relaying, whereas packet aggregation is a method that can reduce delay. Hence, in this paper, we propose to use a combination of relaying and packet aggregation. Based on the type of feedback provided by the controller, the relay node can choose the most suitable way to use its allocated time slots such that more packets can reach the controller before their deadlines. The results show that allowing this kind of flexibility at the relay node results in performance improvements. The more flexibility, the greater the gain, and thus further improvements can be made by adjusting the schedule to take different types of feedback into account.

  • 2.
    Uhlemann, Elisabeth
    et al.
    Högskolan i Halmstad, Inbyggda system (CERES).
    Willig, Andreas
    Technical University of Berlin.
    Hard decision packet combining methods for industrial wireless relay networks2008In: Second International Conference on Communications and Electronics, 2008. ICCE 2008, Piscataway, N.J.: IEEE Press , 2008, p. 104-108Conference paper (Refereed)
    Abstract [en]

    We consider wireless relay networks for use in industrial applications with strict requirements on both reliable and timely communications. In most cases commercially available transceivers must be used, which implies that only hard decision detector outputs are available. Since relay networks typically use retransmissions of erroneous packets, packet combining methods have the potential to increase the information reliability without excessive delay. We evaluate three different hard decision packet combining methods for different placement of the source, the relay node and the destination. Packet combining can in general be improved with knowledge of the current channel state information, which, however, is often not available. In this paper we find a packet combining method which does not use channel state information but which delivers similar performance as the scheme that has knowledge of the channel state.

  • 3.
    Uhlemann, Elisabeth
    et al.
    Högskolan i Halmstad, Inbyggda system (CERES).
    Willig, Andreas
    Technical University of Berlin.
    Joint design of relay and packet combining schemes for wireless industrial networks2008In: IEEE Vehicular Technology Conference 2008, IEEE Press , 2008, p. 2441-2445Conference paper (Refereed)
    Abstract [en]

    Wireless industrial networks differ in many respects from other types of wireless networks. In particular, since many applications impose tight real-time and reliability requirements at the same time, and packet sizes tend to be small. In this paper we design a simple and practically implementable protocol in which relaying and packet combining work together to improve the probability that packets are delivered within a prescribed deadline over fading channels. The results indicate that such a combination can be fruitfully employed in wireless industrial networks.

  • 4.
    Willig, Andreas
    et al.
    University of Canterbury, Christchurch, New Zealand.
    Uhlemann, Elisabeth
    Högskolan i Halmstad, Inbyggda system (CERES).
    Deadline-Aware Scheduling of Cooperative Relayers in TDMA-Based Wireless Industrial Networks2014In: Wireless networks, ISSN 1022-0038, E-ISSN 1572-8196, Vol. 20, no 1, p. 73-88Article in journal (Refereed)
    Abstract [en]

    In this paper we consider a scenario in which a set of source nodes wishes to transmit real-time data packets periodically to a central controller over lossy wireless links, while using a TDMA-based medium access control protocol. Furthermore, a number of relay nodes are present which can help the source nodes with packet retransmissions. The key question we consider in this paper is how to schedule the TDMA slots for retransmissions while taking advantage of the relay nodes, so that the average number of packets missing their deadlines is minimized. We provide a problem formulation for the general deadline-aware TDMA relay scheduling problem. Since the design space of the general problem is large, we also present one particular class of restricted TDMA relay scheduling problems. We suggest and numerically investigate a range of algorithms and heuristics, both optimal and suboptimal, of the restricted scheduling problem, which represent different trade-offs between achievable performance and computational complexity. Specifically, we introduce two different Markov Decision Process (MDP) based formulations for schedule computation of the restricted TDMA relay scheduling problem. One MDP formulation gives an optimal schedule, another (approximate) formulation gives a sub-optimal schedule which, however, comes very close to the optimal performance at much more modest computational and memory costs.

  • 5.
    Willig, Andreas
    et al.
    University of Canterbury.
    Uhlemann, Elisabeth
    Högskolan i Halmstad, Inbyggda system (CERES).
    On relaying for wireless industrial communications: Is careful placement of relayers strictly necessary?2012In: IEEE International Workshop on Factory Communication Systems, 2012, p. 191-200Conference paper (Refereed)
    Abstract [en]

    Relaying is a very promising technique to improve the reliability of data transmission in wireless (industrial) networks. With relaying, relay nodes support source nodes in carrying out retransmissions. A common assumption is that relayers should be placed at “good” positions (e.g. in the middle between source and destination) to achieve benefits. In this paper we tackle the question of whether it is strictly necessary to place relayers at “good” positions (which often requires extensive measurements). We present results indicating that the benefits of relaying are achievable even with randomly placed relayers, as long as enough of them are deployed. Specifically, we present results suggesting that with a sufficient (and still not too high) number of randomly deployed relayers, the probability that all packets, sent by source nodes to a central controller in a TDMA round, reach the controller is larger than for the case with source-only retransmissions. This finding holds true both in the absence and the presence of feedback.

  • 6.
    Willig, Andreas
    et al.
    Technische Universitt Berlin, Berlin, Germany.
    Uhlemann, Elisabeth
    Högskolan i Halmstad, Inbyggda system (CERES).
    PRIOREL-COMB: A protocol framework supporting relaying and packet combining forwireless industrial networking2008In: WFCS 2008: 2008 IEEE International Workshop on Factory Communication Systems : proceedings : May 21st-23rd, 2008, Steigenberger Hotel de Saxe, Dresden, Germany / [ed] Gianluca Cena and Françoise Simonot-Lion, Piscataway, NJ: IEEE Press , 2008, p. 45-54Conference paper (Refereed)
    Abstract [en]

    The PRIOREL-COMB framework presented here integrates support for relaying and packet combining into wireless industrial networks. The selection of suitable relay nodes is made using distributed algorithms which includes different eligibility tests as well as different priority assignments. The framework improves performance in terms of probability to successfully deliver packets before their deadline and it can be implemented on top of commercial transceivers without modification of the physical layer. This class of protocols will therefore be a valuable addition to future wireless industrial communication systems.

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