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Lakeside Park, Austria

Tyrrell A.,DOCOMO Communications Laboratories Europe GmbH | Auer G.,DOCOMO Communications Laboratories Europe GmbH | Bettstetter C.,Klagenfurt University | Bettstetter C.,Lakeside Labs GmbH
IEEE Transactions on Mobile Computing | Year: 2010

This paper presents a biologically inspired approach for distributed slot synchronization in wireless networks. This is facilitated by modifying and extending a synchronization model based on the theory of pulse-coupled oscillators. The proposed Meshed Emergent Firefly Synchronization (MEMFIS) multiplexes synchronization words with data packets and adapts local clocks upon the reception of synchronization words from neighboring nodes. In this way, a dedicated synchronization phase is mitigated, as a network-wide slot structure emerges seamlessly over time as nodes exchange data packets. Simulation results demonstrate that synchronization is accomplished regardless of the arbitrary initial situation. There is no need for the selection of master nodes, as all nodes cooperate in a completely self-organized manner to achieve slot synchrony. Moreover, the algorithm is shown to scale with the number of nodes, works in meshed networks, and is robust against interference and collisions in dense networks. © 2010 IEEE. Source


Marchenko N.,Klagenfurt University | Bettstetter C.,Klagenfurt University | Bettstetter C.,Lakeside Labs GmbH
IEEE Transactions on Vehicular Technology | Year: 2014

An important building block in cooperative diversity is relay selection, which has to ensure that a well-suited node is employed as a relay. The required coordination among nodes causes signaling overhead, which in turn can significantly devalue the performance benefits gained by cooperative diversity. A relay update policy defines when a new relay is selected; it can balance the tradeoff between performance and overhead. This tradeoff is studied using mathematical methods. We consider three relay selection schemes, i.e., permanent, reactive, and adaptive, which have different relay update rules. We develop an analytical framework using semi-Markov processes to evaluate the throughput and energy efficiency of cooperative automatic repeat request (ARQ) protocols in time-correlated multipath fading channels. Results reveal potential performance gains of different selection schemes under various conditions. The reactive and adaptive schemes make use of better suited relays due to frequent selections. If their selection overhead, however, is significant, a permanent relay can achieve higher throughput due to negligible overhead. The impact of temporal correlation of fading channels on throughput and energy efficiency is also shown. These insights can be applied for development of cooperative communication protocols. © 2013 IEEE. Source


Adam H.,Klagenfurt University | Yanmaz E.,Klagenfurt University | Bettstetter C.,Klagenfurt University | Bettstetter C.,Lakeside Labs GmbH
IEEE Transactions on Mobile Computing | Year: 2014

We specify and evaluate a protocol for cooperative relay communications in wireless networks targeted for low-budget and energy-constrained off-the-shelf hardware. The protocol located at the Medium Access Control (MAC) layer integrates radio resource reservation, relay selection, and packet flow. Performance is evaluated with different parameters, such as node density, channel coherence time, and data packet size. Higher network-wide reliability and throughput compared to noncooperative protocols can be achieved in dense networks and unreliable channels. At the same time, throughput does not degrade in sparse networks or good channel conditions. © 2002-2012 IEEE. Source


Marchenko N.,Klagenfurt University | Andre T.,Klagenfurt University | Brandner G.,Klagenfurt University | Masood W.,Klagenfurt University | And 2 more authors.
IEEE Transactions on Industrial Informatics | Year: 2014

Strict reliability and delay requirements of factory monitoring and control applications pose challenges for wireless communications in dynamic and cluttered industrial environments. To reduce outage in such fading-rich areas, cooperative relays can be used to overhear source-destination transmissions and forward data packets that a source fails to deliver. This paper presents the results of an experimental study of selective cooperative relaying protocols that are implemented in off-the-shelf IEEE 802.15.4-compatible devices and evaluated in an industrial production plant. Three practical relay update schemes, which define when a new relay selection is triggered, are investigated: 1) periodic; 2) adaptive; and 3) reactive relay selections. The results show that all relaying protocols outperform conventional time diversity retransmissions in delivery ratio and number of retransmissions for packet delivery. Reactive selection provides the best overall delivery ratio of nearly 99% over the tested network. There is a tradeoff, however, between achievable delivery ratio and required selection overhead. This tradeoff depends on protocol and network parameters, and is studied via protocol emulation using empirical channel values. © 2005-2012 IEEE. Source


Adam H.,Klagenfurt University | Yanmaz E.,Klagenfurt University | Bettstetter C.,Klagenfurt University | Bettstetter C.,Lakeside Labs GmbH
IEEE Transactions on Mobile Computing | Year: 2013

Several communication protocols and applications require a node to know how many neighboring nodes exhibiting a certain attribute it has. Conventionally, such neighbor information is obtained by explicit message exchange between nodes, which is reliable but inefficient in densely connected networks in terms of overhead and delay. An alternative approach is to perform an estimation of the neighbor cardinality using probabilistic methods. This paper pursues such an approach by proposing neighbor cardinality estimators that require no coordination among polled nodes but are based on a simple random access scheme with busy tones, where the number of empty slots is exploited to infer about the neighbor cardinality. We compare three estimators with different levels of adaptability and feedback from the query node and discuss their suitability for IEEE 802.11 and low power sensors. Performance is studied in terms of estimation accuracy and delay. © 2002-2012 IEEE. Source

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