Nikolaj Marchenko

An Experimental Study of Selective Cooperative Relaying in Industrial Wireless Sensor Networks

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.

Selecting a Spatially Efficient Cooperative Relay

Cooperative relaying is a communication technique in wireless networks where neighboring nodes assist communication pairs to mitigate the negative effects of multi-path fading. The resulting performance strongly depends on the selected relays. Although a cooperative relay provides benefits to a given source-destination pair, overall network performance might be degraded due to the increased level of interference. So far almost all relay selection mechanisms consider mainly channel conditions to the potential relays. In this paper we propose a contention-based relay selection mechanism that can take into account also spatial efficiency of potential relays. For that the degree as well as relative position of the nodes are used for selection. With the proposed method a high successful relay selection probability can be achieved, while significantly reducing the amount of additional spatial resources blocked by the cooperative relay.

Building blocks of cooperative relaying in wireless systems

SummaryThe concept of cooperative relaying promises gains in robustness and energy efficiency in wireless networks. This survey gives an introduction and overview of promising methods that can be used for cooperative relaying: relay selection protocols, cooperative channel and network coding, and physical layer aspects such as cooperative modulation. The particular methods can be seen as building blocks that can be configured and optionally used for designing a system. They offer a large number of design options for relaying systems. Based on available hardware features, expected environment, and required services an efficient system needs to be tailored using the right subset of available methods.ZusammenfassungDas Konzept des kooperativen Weiterleitens von Nachrichten ermöglicht eine Verbesserung der Robustheit und Energieeffizienz von drahtlosen Netzwerken. Dieser Artikel stellt einige vielversprechende Methoden für Netzwerke mit kooperativem Relaying vor. Im Speziellen werden Protokolle zur Relayauswahl, Kanalcodierung, Network Coding sowie kooperative Modulationstechniken behandelt. Die vorgestellten Methoden sind als Bausteine für ein Netzwerk mit kooperativem Relaying zu verstehen. Jede einzelne Methode kann optional und gemeinsam mit anderen verwendet werden und in den meisten Fällen zusätzlich noch dem Zweck entsprechend konfiguriert werden. Somit ergibt sich eine hohe Anzahl von Möglichkeiten, ein System mit kooperativem Relaying zu entwerfen. Das tatsächliche Design hängt letztendlich von Parametern wie der zur Verfügung stehenden Hardware, den Annahmen über die Zielumgebung sowie den Anforderungen der Applikation ab.

Cooperative ARQ With Relay Selection: An Analytical Framework Using Semi-Markov Processes

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.

Measurement-based analysis of cooperative relaying in an industrial wireless sensor network

Cooperative relaying is a communication technique that has been shown to improve link reliability between communicating entities. Most results in this area are obtained either analytically or via simulations. Rather few real-world experiments are conducted to backup theoretical results. This paper intends to go a step in this direction of applied research. We study the performance of cooperative relaying for industrial applications based on real-world measurements. These link-level measurements are conducted employing low-cost, off-the-shelf IEEE 802.15.4 devices in a factory characterized by a harsh and cluttered environment. Using the measured data, we emulate a simple cooperative relaying protocol to investigate the performance in terms of outage and packet delivery ratio and study parameters suitable for relay selection.

Incremental Cooperative Relaying in Time-Correlated Rayleigh Fading Channels

Incremental relaying is a communication technique enabling cooperative diversity in wireless networks. The relay forwards a correctly decoded packet only after getting the feedback that the destination failed to receive the data directly from the source. We model an incremental relaying protocol as a time-discrete finite-state Markov process and analyze its throughput performance in time-correlated radio channels with Rayleigh fading. We also determine two boundary cases: fully correlated and fully uncorrelated fading channel. The analysis shows that the throughput gains of incremental relaying to conventional Automatic Repeat-reQuest retransmission strongly depend on the channel correlation, relay position, and source-to-destination fading margin.

Impact of Relay Selection Overhead in Cooperative Diversity Protocols

Cooperative diversity employs relays to assist source-destination transmissions and has shown to improve link outage probability in multipath fading environments. In this paper, we model relay selection as a semi-Markov process to analyze the impact of relay selection overhead on throughput, delay, and jitter in a simple scenario. Results show that the selection overhead can significantly reduce benefits of reactive relay selection if data frames are small or only few nodes overhear data. In such scenarios, relaying with a preassigned relay can be more beneficial.

Cooperative Multicast with Low-Cost Radios

A simple cooperative diversity technique is applied to point-to-multipoint communication in wireless medium suffering from Rayleigh block fading. Such a concept is especially interesting if low-cost radios, which have no advanced capabilities for fading mitigation, are used. This paper analyzes the communication reliability in terms of outage and delivery ratio, and compares cooperative and non-cooperative schemes. Results from a simple setup show that already few preselected relays can lead to performance gains. A potential application field is link-layer broadcast in a network of energy-constrained embedded devices.

Distributed Binary Consensus in Networks with Disturbances

This article evaluates convergence rates of binary majority consensus algorithms in networks with different types of disturbances and studies the potential capacity of randomization to foster convergence. Simulation results show that (a) additive noise, topology randomness, and stochastic message loss may improve the convergence rate; (b) presence of faulty nodes degrades the convergence rate; and (c) explicit randomization of consensus algorithms can be exploited to improve the convergence rate. Watts-Strogatz and Waxman graphs are used as underlying network topologies. A consensus algorithm is proposed that exchanges state information with dynamically randomly selected neighbors and, through this randomization, achieves almost sure convergence in some scenarios.