Questions addressed are how to organize multiple autonomous robots to spatially distribute during exploration to decrease exploration time. What role does communication play? Self distribution is an important research questions to improve reliability and scalability.
Communication is vital for the interaction of the multi-robot system. It allows the robots to coordinate, cooperate, or collaborate. Reliable information flow in multi-cast networks allows robots to increase their exploration efficiency.
Cooperative relaying allows to significantly reduce the reliability between two communicating entities. A third node, the cooperative relay, overhears a transmission and retransmits on the behalf of the original sender.
We analyze the applicability of cooperative relays in multi-hop and multi-cast networks. Cooperative relays may aid the information flow in large networks while improving the reliability of the data link layer significantly.
Networks of micro aerial vehicles (MAVs) equipped with various sensors are increasingly used for civil applications, such as monitoring, surveillance, and disaster management. In this article, we discuss the communication requirements raised by applications in MAV networks. We propose a novel system representation that can be used to specify different application demands. To this end, we extract key functionalities expected in an MAV network. We map these functionalities into building blocks to characterize the expected communication needs. Based on insights from our own and related real-world experiments, we discuss the capabilities of existing communications tech- nologies and their limitations to implement the proposed building blocks. Our findings indicate that while certain requirements of MAV applications are met with available technologies, fur- ther research and development is needed to address the scalability, heterogeneity, safety, quality of service, and security aspects of multi-MAV systems.
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 article 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: periodic, adaptive, and 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. However, there is a tradeoff 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 measurements.
We evaluate the packet delivery performance of low- complex cooperative relaying in car-to-car communications by real-world measurements. The ratio and temporal correlation of packet delivery are evaluated for suburban and highway environments using three cars equipped with programmable radios and serving as sender, relay, and destination. We compare the relaying performance to that of pure time diversity and show how temporal autocorrelation of packet delivery is a key factor in whether or not relaying exhibits benefits. Results are relevant in the design of relay selection protocols, as they give guidelines for the affordable selection delay.
Through real-world measurements we evaluate the impact of multihop-aware cooperative relaying on end-to-end route performance in wireless multi-hop networks. In an exper- iment with 50 devices in an industrial environment cooperative relaying increases the end-to-end transmission reliability for multi-hop links to nearly 100 % while reducing the average packet delay. We suggest how to include relay selection in the route discovery process of ad hoc routing protocols such as Ad hoc On- Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) and perform two experiments. In the first experiment we discuss route discovery strategies focusing on small delay benefiting from reliable data link transmissions using cooperative relays. In the second experiment we compare reliability and delay for five different transmission powers with and without cooperative relaying.
This paper proposes and evaluates a modular architecture of an autonomous unmanned aerial vehicle (UAV) system for search and rescue missions. Multiple multicopters are coordinated using a distributed control system. The system is implemented in the Robot Operating System (ROS) and is capable of providing a real-time video stream from a UAV to one or more base stations using a wireless communications infrastructure. The system supports a heterogeneous set of UAVs and camera sensors. If necessary, an operator can interfere and reduce the autonomy. The system has been tested in an outdoor mission serving as a proof of concept. Some insights from these tests are described in the paper.
We present and evaluate new ROS packages for coordinated multi-robot exploration, namely communication, global map construction, and exploration. The packages allow completely distributed control and do not rely on (but allow) central controllers. Their integration including application layer protocols allows out of the box installation and execution. The communication package enables reliable ad hoc communication allowing to exchange local maps between robots which are merged to a global map. Exploration uses the global map to spatially spread robots and decrease exploration time. The intention of the implementation is to offer basic functionality for coordinated multi-robot systems and to enable other research groups to experimentally work on multi-robot systems. The packages are tested in real-world experiments using Turtlebot and Pioneer robots. Further, we analyze their performance using simulations and verify their correct working.
We assess the impact of cooperative relaying assisted hops on a multi-hop network. On the example of the reactive Dynamic Source Routing (DSR) protocol, we utilize cooperative relays to improve the link delivery probabilities of the individual hops allowing to significantly improve the end-to-end delivery ratio for large networks. First, we discuss two types to trigger retransmissions by cooperative relays in case direct transmissions between nodes fail. Second, we show that cooperative relaying assisted links lead to improved end-to-end delivery probabilities for multi-hop networks and determine the associated costs in terms of delay and consumed energy. For multi-hop routes with a large number of hops, cooperative relaying can decrease the costs while improving the end-to-end delivery ratio significantly making reliable communication possible where unassisted multi- hop communication is functionally not feasible.
With the introduction of multi-robot systems for exploration the question then arises, whether coordination among robots in such systems is required. We propose a model based on Markov processes to evaluate the need for coordination in multi-robot systems during the exploration of unknown environments and determine possible gains achievable through coordination. The model is illustrated by exploration of an indoor office environment. We qualitatively identify characteristics of environments which make coordination necessary and allow to quantitatively include them in the model. The expected gain through coordination highly depends on the environment. We further investigate the impact of team sizes. In favorable environments explicit coordination is not needed at the cost of increased team sizes. This helps to raise understanding of factors having an impact on coordination functions and making it possible to approximate a possible gain through coordination.
We evaluate by real-world measurements two cooperative relaying protocols for industrial sensor networks: the first one employs a periodic relay selection scheme, where relays are selected periodically from a candidate set at fixed time intervals, while the second one is an adaptive approach selecting relays depending on channel characteristics. We perform measurements of both protocols in a real-world industrial environment, and analyze and compare their performance characteristics in terms of frame delivery ratio and protocol overhead. Results show that the periodic protocol increases the frame delivery ratio considerably compared to direct transmission. Furthermore, the adaptive approach improves frame delivery even further. In particular, for cases where the frame error rate between source and destination is high, adaptive relaying improves frame delivery considerably beyond that of periodic relaying.
Cooperative relaying is a communication technique that has been shown to improve link reliability between com- municating 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.
Multihop and multipoint transmissions are two of the main features towards an increased spectral efficiency for the LTE-Advanced mobile radio system. Fixed wireless relays with in-band backhauling are considered as a multihop technique in LTE-Advanced. Relays improve cell capacity and cell edge user performance depending on the deployment. In this paper, at first, results for the peak spectral efficiency of LTE-Advanced are presented and secondly, an analytical model to calculate the cell spectral efficiency of relay enhanced cell deployments in the context of the IMT-Advanced evaluation is presented. T he developed model is applied to the LTE-Advanced system comparing different relay deployments with different frequency reuse schemes.
I am co-founder and first chair of the IEEE Student Branch Klagenfurt (SB). The SB was founded in 2011. In its first year the SB won the Most Active Student Branch Award. The SB organizes events, excursions, workshops, presentations for students of the primarily technical department.
The IEEE is an organization with more than 400,000 members. It is known for its standardization work, such as IEEE 802.11, i.e., WLAN. Additionally, the IEEE organizes conferences, publishes journals.
It is organized in ten regions, where Africa, Asia, and Europe form Region 8. The regions themselves are organized in sections. The Student Branch is a sub organization of the IEEE Austria Section.
This course is intended to familiarize students with current issues in multi-robot systems and to give an overview of common problems in robotics.
Students shall solve some of these problems. For example, students are asked to implement a controller that assures that, given an unknown environment, the complete environment is traversed and automatically mapped. While development and testing will be done in simulation, the controllers can be installed on real robots and demonstrated in a real-world environment.Contents:
The course "ICT Lab: Wireless Sensor Networks (WSNs)" is an introductory class to wireless sensor networks (WSNs). Students learn the basics of WSNs by implementing basic protocols in TinyOS using our Crossbow TelosB devices. Further the basics of IEEE 802.15.4 are covered, a widely spread IEEE standard for low-rate personal area networks (PAN) which is used as basis for ZigBee, ISA100.11a, and WirelessHART.Contents:
This is the tutorial for the lecture Wireless Networks in which some of the lecture's topics are covered in more detail. Further we will address some contents in a practical manner and cover some additional topics.Contents:
The course extends the lecture "Mobile Networks" and illustrates basic concepts of mobile systems in modern technologies such as LTE-Advanced. Further the class covers basics of synchronization and illustrates the synchronization algorithms in LTE-Advanced and ISA100.11a.Contents: