A protocol and a communication mechanism intended for time and safety critical applications using a radio channel for information transport are considered jointly. The protocol is based on a scheme of retransmissions done on demand within a given time window. Each retransmission is coded with a varying number of redundant symbols. The set of blocks used for retransmission is controlled by two quality-of-service parameters: deadline for the transmission and the probability that the correct decoded message will reach the recipient before this deadline. Analysis of a protocol model indicates that it is possible to transmit time critical information in a mobile wireless system with very low error probabilities in an industrial environment.

The paper presents results of simulations done with the CCR-EDF (Control Channel based Ring network with EDF scheduling) pipelined ring network together with a case study of system area networks for radar signal processing. The topology of the network is a pipelined unidirectional fibre-ribbon ring that supports several simultaneous transmissions in non-overlapping segments. Access to the network is divided into slots. In each slot the node that has the highest priority message is permitted to transmit. This feature of the medium access protocol gives the network the functionality for earliest deadline first scheduling. Different classes of traffic are supported for the user. These are guaranteed logical real-time channels (LRTC), best effort (BE) channels and non real-time (NRT) traffic. The case study used is from an airborne radar signal processing (RSP) application. Results of the simulations indicate that the CCR-EDF network works well with the RSP application studied.

The Vehicle Alert System (VAS) project focuses on cooperative alert services based on timely and reliable communication under the challenging circumstances pertaining to a highly mobile vehicular network. Through a cross-layer design, we gain the flexibility needed to adapt the system to the individual requirements of three chosen application scenarios that represent different situations where cooperation between vehicles can make a significant impact. The VAS project is a collaboration involving academic as well as industrial partners and the final stage of the project is a demonstrator that implements results from the research.

In March 2007, an agreement was made for interchange of experiences between CVIS and the Centre for Research on Embedded Systems (CERES) at Halmstad University in Sweden. The majority of the work relating to this collaboration has been conducted within the CERES project Vehicle Alert System (VAS), aiming to use vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications to provide different types of warning messages. The main focus of the VAS project is on communication and in particular the lower layers of the communication stack are investigated. VAS involves academic researchers from Halmstad University as well as researchers from Volvo Technology, SP Technical Research Institute of Sweden and the company Free2move. This report presents the results of the VAS project, its publications, and other issues of interest both to the CVIS consortium as well as a broader scope.

In this paper, initial simulations are presented showing that the upcoming IEEE 802.11p standard is not suitable for traffic safety applications requiring reliable, low delay communication between vehicles. The medium access control procedure is one of the most important parts in the design of delay-constrained communication systems, and emerging vehicle safety applications put new stringent demands on timely and reliable delivery of data packets. The medium access procedure used in 802.11p is carrier sense multiple access, which is inherently unsuitable for time-critical data traffic since it is contention-based and cannot provide a finite upper bound on the time to channel access. The simulation results indicate that with IEEE 802.11p, channel access cannot be granted in a manner that is sufficiently predictable to support reliable, low-delay communications between vehicles on a highway.

In this paper the medium access control (MAC) method of the upcoming vehicular communication standard IEEE 802.11p has been simulated in a highway scenario with periodic broadcast of time-critical packets (so-called heartbeat messages) in a vehicle-to-vehicle situation. The 802.11p MAC method is based on carrier sense multiple access (CSMA) where nodes listen to the wireless channel before sending. If the channel is busy, the node must defer its access and during high utilization periods this could lead to unbounded delays. This well-known property of CSMA is undesirable for time critical communications. The simulation results reveal that a specific node/vehicle is forced to drop over 80% of its heartbeat messages because no channel access was possible before the next message was generated. To overcome this problem, we propose to use self-organizing time division multiple access (STDMA) for real-time data traffic between vehicles. This MAC method is already successfully applied in commercial surveillance applications for ships (AIS) and airplanes (VDL mode 4). Our initial results indicate that STDMA outperforms CSMA for time-critical traffic safety applications in ad hoc vehicular networks.

Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the intelligent transportation systems (ITS) sphere. Many of these new applications require real-time communication with high reliability, meaning that packets must be successfully delivered before a certain deadline. Applications with early deadlines are expected to require direct V2V communications, and the only standard currently supporting this is the upcoming IEEE 802.11p, included in the wireless access in vehicular environment (WAVE) stack. To meet a real-time deadline, timely and predictable access to the channel is paramount. However, the medium access method used in 802.11p, carrier sense multiple access with collision avoidance (CSMA/CA), does not guarantee channel access before a finite deadline. In this paper, we analyze the communication requirements introduced by traffic safety applications, namely, low delay, reliable, real-time communications.We show by simulation of a simple, but realistic, highway scenario, that vehicles using CSMA/CA can experience unacceptable channel access delays and, therefore, 802.11p does not support real-time communications. In addition, we present a potential remedy for this problem, namely, the use of self-organizing time division multiple access (STDMA). The real-time properties of STDMA are investigated by means of the same highway simulation scenario, with promising results.

Emerging traffic safety applications requiring low delay communications will need vehicle ad-hoc networks. The only communication standard currently supporting this is IEEE 802.11p. However, 802.11p uses the medium access method CSMA/CA, which has a major drawback: unbounded worst case channel access delay. We therefore propose an algorithm already in commercial use in the shipping industry: STDMA. With STDMA, nodes always get predictable channel access regardless of the number of competing nodes and the maximum delay is deterministic. In this paper we elaborated with different parameter settings for the two protocols with the aim of improving performance without altering the standards.

Based on communication and cooperation between vehicles and roadside infrastructure, Intelligent Transport Systems (ITS) safety applications offer great potential to avoid traffic accidents or at least reduce their impact. As these applications usually are delay-sensitive, the delay introduced by waiting for access to the wireless communication channel should both be reduced and provided with an upper bound. The proposed IEEE 802.11p standard for short to medium range vehicular communication does not offer these guarantees. In previous work, we presented a MAC (Medium Access Control) enhancement supporting delay-sensitive, safety-critical V2I (Vehicle-to-Infrastructure) applications. Since the proposed enhancement requires a deterministic and fast mechanism to associate a vehicle to a roadside unit (RSU) so that it can be integrated into the centralized polling schedule, we now target the handover and connection setup between a vehicle and an RSU. Although the first connection setup with an RSU still underlies the randomness of the original 802.11p MAC method, we provide a deterministic solution to further enhance the handover procedures by introducing a fast, proactive handover mechanism. We show that the overhead of our solution is limited and still allows our MAC protocol to support safety-critical V2I applications in a densely trafficked highway scenario.

Support for real-time traffic is crucial to many ITS (Intelligent Transport Systems) safety applications. At the same time it is desirable to support a number of non-safety applications. Based on a merge assistance scenario supported by roadside infrastructure, we propose dynamic data traffic priority classes based on parameters like position, speed and road traffic density. Moreover, we discuss both how to schedule data traffic in order to support the QoS demands of both safety-critical and non-safety critical traffic classes and how to analyze the real-time performance of the network.

Support for real-time traffic is crucial to many ITS (Intelligent Transport Systems) safety applications. At the same time it is desirable to provide a number of non-safety services. In this paper, we propose a communication system for safety-critical V2I (Vehicle-to-Infrastructure) communication based on an extension to the upcoming IEEE 802.11p MAC standard. Real-time analysis provides the tool to adapt the resources set aside for collision-free, safety-critical data traffic to the communication needs of the current number of supported vehicles. The remaining bandwidth is available to other services according to the contention-based random access method defined in the standard. The performance of the proposed concept is evaluated through a simulation analysis based on a merge assistance scenario supported by roadside infrastructure.

We present a router architecture with electronic queuing and a passive optical multi-channel network, which is based upon a single-hop star topology with an arrayed waveguide grating (AWG) at its center. The AWG's property of spatial wavelength reuse and both fixed-tuned and tunable transceivers enable simultaneous control and data transmission. Our proposed medium access control protocol supports traffic differentiation and utilizes EOF (earliest deadline first) to schedule the traffic from input ports to output ports on the router. Our simulations show that the router treats QoS (quality of service) traffic well.

In this paper, an architecture and a Medium Access Control (MAC) protocol for a multi-wavelength optical communication network, applicable in short range communication systems like System Area Networks (SANs), are proposed. The main focus lies on guaranteed support for hard and soft real-time traffic. The network is based upon a single-hop star topology with an Arrayed Waveguide Grating (AWG) at its center. Traffic scheduling is centralized in one node (residing together with the AWG in a hub), which communicates through a physical control channel. The AWG's property of spatial wavelength reuse and the combination of fixed-tuned and tunable transceivers in the nodes enable simultaneous control and data transmission. A case study with defined real-time communication requirements in the field of Radar Signal Processing (RSP) was carried out and indicates that the proposed system is very suitable for this kind of application.

This paper presents an effort to support emerging Wireless Sensor Networks applications composed by different types of sensor nodes. The work is composed by two parts, in which the first is dedicated to provide cooperation abilities to sensor nodes, while the second is a customizable hardware platform intended to provide different types of sensor nodes, from those more resource constrained up to the resource-rich ones. A description of a testbed demonstra- tor of the proposed system is provided and comparisons with previous published simulation results denote the feasibility of the proposal.

Teams of small Unmanned Aerial Vehicles (UAVs) are being largely proposed to be used in different areas for both military and civilian applications. Their integration in wider sensor networks is also being considered in order to provide a better cost-benefit ration. However, coordination among UAV teams is not a trivial problem in an ad hoc network. This paper presents a decentralized coordination strategy to orient the actions of a team of UAVs, which take part in a wider sensor network, relying on ad hoc network communication. The proposed sensors network inclused static sensors that issue alarms indicating the presence of possible targets that must be handled by one of the UAVs and possibly relay messages among them. Preliminary results of the proposed approach are presented and are contrasted with results provided by a centralized solution for the problem.

Sensor networks are being used in several emerging applications not even imagined some years ago due to advances in sensing, computing, and communication techniques. However, these advances also pose various challenges that must be faced. One important challenge is related to the autonomous capability needed to setup and adapt the networks, which decentralizes the control of the network, saving communication and energy resources. Middleware technology helps in addressing this kind of problem, but there is still a need for additional solutions, particularly considering dynamic changes in users' requirements and operation conditions. This paper presents an agent-based framework acting as an integral part of a middleware to support autonomous setup and adaptation of sensor networks. It adds interoperability among heterogeneous nodes in the network, by means of autonomous behavior and reasoning. These features also address the needs for system setup and adaptations in the network, reducing the communication overhead and decentralizing the decision making mechanism. Additionally, preliminary results are also presented.

A well know problem in the Wireless Sensor Network (WSN) research area is the usage of appropriate strategies to setup the sensor nodes such that they may accomplish sensing missions. This problem refers to the selection of appropriate nodes to perform the different tasks required to the missions' accomplishment and may be thus characterized as an instance of the task and resource allocation problem. Traditional approaches consider pre-planned strategies, which are not flexible to deal with changes in the network and environment operating conditions. This paper presents an enhanced agent-oriented strategy, which consists of a usage of mobile intelligent agents to disseminate missions and nodes' information over the network, as well as stationary software agents installed in the sensor nodes to provide advanced reasoning apparatus for decision making purposes. The proposed enhancement complements the original agent-based approach with robustness features required to overcome extreme adverse conditions in which an ordinary WSN presents poor results. Results from simulations provide evidences of the efficiency of the complete enhanced approach.

An important problem in Wireless Sensor Networks (WSN) is the occurrence of failures that lead to the disconnection of parts of the network, compromising the final results achieved by the WSN operation. A way to overcome such problem is to provide a reliable connection to support the connectivity via other types of nodes that communicate with the sensor nodes. This paper proposes the usage of a network composed by Unmanned Aerial Vehicles (UAVs) as a relay network to guarantee the delivery of data produced by WSN nodes on the ground to the users. Results from simulations of the proposed technique are provided and discussed.

A new challenge in the sensor network area is the coordination of heterogeneous sensors (with different sensing, mobility and computing capabilities) in an integrated network. This kind of sensor networks have clearly high relevance in surveillance systems, in which both low-end static ground sensor nodes and more sophisticated sensors carried by mobile platforms, such as Unmanned Aerial Vehicles (UAVs), cooperate. This paper provides an analysis of two different strategies to guide the collaboration among the sensor nodes mentioned above, applied to area surveillance systems. The first analyzed problem is related to the choice of the UAV instance that will respond to a given alarm issued by a ground sensor node. The second issue is the estimation of the response time until any UAV can be engaged in handling an alarm and effectively handles it. Two strategies are introduced and compared: one based on a pheromone inspired approach and another based on utility functions inspired on risk profiles that models decisions of investors in the stock market. ©2009 IEEE.

This paper presents a comparison among different strategies to coordinate the use of heterogeneous wireless sensors aimed for area surveillance. The heterogeneity among the sensor nodes is related to their sensing and mobility capabilities. The goal of the strategies is to provide coordination among the different nodes, in order to make the wireless sensor network perform its missions with higher efficiency. Strategies combine advantages of bio-inspired and utility-based approaches to coordination. Simulations of scenarios with different characteristics were performed and the results are compared and analyzed.

A current trend that is gaining strength in the wireless sensor network area is the use of heterogeneous sensor nodes in one coordinated overall network, needed to fulfill the requirements of sophisticated emerging applications, such as area surveillance systems. One of the main concerns when developing such sensor networks is how to provide coordination among the heterogeneous nodes, in order to enable them to efficiently respond the user needs. This study presents an investigation of strategies to coordinate a set of static sensor nodes on the ground cooperating with wirelessly connected Unmanned Aerial Vehicles (UAVs) carrying a variety of sensors, in order to provide efficient surveillance over an area of interest. The sensor nodes on the ground are set to issue alarms on the occurrence of a given event of interest, e.g. entrance of a non-authorized vehicle in the area, while the UAVs receive the issued alarms and have to decide which of them is the most suitable to handle the issued alarm. A bio-inspired coordination strategy based on the concept of pheromones is presented. As a complement of this strategy, a utility-based decision making approach is proposed.

The emerging applications using sensor networks technologies constitute a new trend requiring several different devices to work together and this partly autonomously. However, the integration and coordination of heterogeneous sensors in these emerging systems is still a challenge, especially when the target application scenario is susceptible to constant changes. Such systems must adapt themselves in order to fulfill requirements that can also change during the system runtime. Due to the dynamicity of this context, system adaptations must take place very quickly, requiring system autonomous decisions to perform them without any human operator intervention, besides the first directions to the system. Thus a reflective behavior must be provided. This paper presents a reflective middleware that supports reflective behaviors to address adaptation needs of heterogeneous sensor networks deployed in dynamic scenarios. This middleware presents specific handling of users’ requirements by representing them as missions that the network must accomplish with. These missions are then translated to network parameters and distributed over the network by means of the reasoning about network nodes capabilities and environment conditions. A multi- agent approach is proposed to perform this initial reasoning as well as the adaptations needed during the system runtime.

In this report, we present a real-time analytical framework and the performance evaluation on our analysis. We propose a feasibility analysis of periodic hard real-time traffic in packet-switched networks using First Come First Served (FCFS) queuing but no traffic shapers. We choose switched Ethernet as an example to present the idea of our analysis and our experimental evaluations in this report.The remainder of the report is organized as follows. In Chapter 2, we define the network models, important concepts and terminology for real-time analysis. Chapter 3 presents our real-time analysis for isolated network elements. Chapter 4 gives end-to-end real-time analysis. Chapter 5 presents the performance evaluation of our results by simulation and comparison study and summarizes this report.

Many approaches have been developed to give an estimation of the upper bound of the end-to-end delay or the response-time for real-time application, e.g., the Network Calculus (NC) model and the scheduling analysis. In this paper, we present an approach based on scheduling analysis to support guaranteed real-time services over standard switched Ethernet. Furthermore, we conduct a comparative study between these two admission control schemes, our novel algorithm and an NC-based algorithm. The simulation analysis shows that our feasibility analysis gives up to 50% higher utilization than the popular NC. Another advantage of our solution is that no additional hardware or software modification of the switch and the underlying standard. In our proposal, the traffic differentiation mechanism introduced by the IEEE 802.1D/Q standard and the standard hardware-implemented First Come First Served (FCFS) priority queuing are used in the switch and the source nodes. We have derived a feasibility analysis algorithm to ensure that the real-time requirements can be met. The algorithm also gives, as a sub-result, the needed buffer space in the end nodes and the switch. Moreover, our feasibility analysis supports variable-sized frames and switches with different bit-rates ports.

In this report, we survey different architectural features of network components for packet-switched networks. Especially, we have a real-time perspective in the study. We also discuss how different architectural features vary with different implementations of two standards, RapidIO and switched Ethernet.

In this paper, we propose a feasibility analysis of periodic hard real-time traffic in packet-switched networks using first come first served (FCFS) queuing but no traffic shapers. Our work constitutes a framework that can be adopted for real-time analysis of switched low-cost networks like Ethernet without modification of the standard network components. Our analysis is based on a flexible network and traffic model, e.g., variable-sized frames, arbitrary deadlines and multiple switches. The correctness of our real-time analysis and the tightness of it for network components in single-switch networks are given by theoretical proofs. The performance of the end-to-end real-time analysis is evaluated by simulations. Moreover, our conceptual and experimental comparison studies between our analysis and the commonly used Network Calculus (NC) shows that our analysis can achieve better performance than NC in many cases.

Background: The purpose of this study was to determine if 3D printed lenses with wavelength specific anti-reflective (AR) surface structures would improve beam intensity and thus radar efficiency for a Printed Circuit Board (PCB)-based 60 GHz radar. This would have potential for improved low-cost radar lenses for the consumer product market. Methods: A hyperbolic lens was designed in 3D Computer Aided Design (CAD) software and was then modified with a wavelength specified AR structure. Electromagnetic computer simulation was performed on both the ‘smooth’ and ‘AR structure’ lenses and compared to actual 60 GHz radar measurements of 3D printed polylactic acid (PLA) lenses. Results: The simulation results showed an increase of 10% in signal intensity of the AR structure lens over the smooth lens. Actual measurement showed an 8% increase in signal of the AR structure lens over the smooth lens. Conclusions: Low cost and readily available Fused Filament Fabrication (FFF) 3D printing has been shown to be capable of printing an AR structure coated hyperbolic lens for millimeter wavelength radar applications. These 3D Printed AR structure lenses are effective in improving radar measurements over non-AR structure lenses. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

In wireless industrial networks, providing reliable and timely communication is crucial. Previous research has shown that relaying can be used to achieve this goal. However, we have found that different types of wireless channels encountered in industrial environments affect the benefits as well as the best behavior and position of relay nodes. We consider two types of behavior: the relay node always retransmits or it only retransmits if it has obtained a correct copy of the packet. We evaluate different positions of the relay node by conducting simulations for two types of fading channels: with and without line of sight. The results clearly show that the benefits, the best behavior and position of a relay node depends on the wireless channel, whether or not the bit errors appear randomly or in bursts and also on the distance between the source and the final destination. © 2012 IEEE.

There is a strong interest of using the cheap and simple Ethernet technology for industrial and embedded systems. This far, however, the lack of real-time services has prevented this change of used network technology. This paper presents enhancements to full-duplex switched Ethernet for the ability of giving throughput and delay guarantees. The switch and the end-nodes controls the real-time traffic with Earliest Deadline First (EDF) scheduling on the frame level. No modification to the Ethernet standard is needed in the network that supports both real-time and non-real-time TCP/IP communication. The switch is responsible for admission control where feasibility analysis is made for each link between source and destination. The switch broadcasts Ethernet frames regularly to clock synchronize the end nodes and to implement flow control for non-real-time traffic.

There is a strong interest of using the cheap and simple Ethernet technology for industrial and embedded systems. This far, however, the lack of real-time services has prevented this change of used network technology. This paper presents enhancements to full-duplex switched Ethernet for the ability of giving throughput and delay guarantees. The switch and the end-nodes control the real-time traffic with Earliest Deadline First (EDF) scheduling on the frame level. No modification to the Ethernet standard is needed in the network that supports both real-time and non-real-time TCP/IP communication. The switch is responsible for admission control where feasibility analysis is made for each link between source and destination. The switch broadcasts Ethernet frames regularly to clock synchronize the end nodes and to implement flow control for non-real-time traffic. We have characterized the performance of the network in terms of channel acceptance ratio by simulations with different number of nodes connected to the switch.

This paper presents work on a switched Ethernet network extended to allow for earliest deadline first (EDF) scheduling. We show by example that asymmetric deadline partitioning between the links of a real-time channel can increase the utilization substantially, still not violating the real-time guarantees. We also report measurements on a software implementation of the switch on an ordinary PC.

When implementing computation-intensive algorithms on finegrained parallel architectures, adjustment of resource to performance tradeoff is a big challenge. This paper proposes a methodology for dealing with some of these performance tradeoffs by adjusting parallelism at different levels. In a case study, interpolation kernels are implemented on a fine-grained architecture (FPGA) using a high level language (Mitrion-C). For both cubic and bi-cubic interpolation, one single-kernel, one cross-kernel and two multi-kernel parallel implementations are designed and evaluated. Our results demonstrate that no single level of parallelism can be used for trade-off adjustment. Instead, the appropriate degree of parallelism on each level, according to available resources and the performance requirements of the application, needs to be found. Basing the design on high-level programming simplifies the trade-off process. This research is a step towards automation of the choice of parallelization based on a combination of parallelism levels.

In this report, some high-performance interconnection networks are briefly commented/evaluated against a specific radar signal processing system selected as a general representative system

In future parallel radar signal processing systems, with high bandwidth demands, new interconnection technologies are needed. The same reasoning can be made for other signal processing applications, e.g., those involving multimedia. Fiber-optic networks are a promising alternative and a lot of work have been done. In this paper, a number of fiber-optic interconnection architectures are reviewed, especially from a radar signal processing point-of-view. Two kinds of parallel algorithm mapping are discussed: (i) a chain of pipeline-stages mapped, more or less directly, one stage per computation node and (ii) SPMD (Same Program Multiple Data). Several network configurations, which are simplified due to the nature of the applications, are also proposed. © Springer-Verlag Berlin Heidelberg 1999

Future parallel computer systems for embedded real-time applications,where each node in itself can be a parallel computer, are predicted to havevery high bandwidth demands on the interconnection network. Otherimportant properties are time-deterministic latency and guarantees to meetdeadlines. In this thesis, a fiber-optic passive optical star network with amedium access protocol for packet switched communication in distributedreal-time systems is proposed. By using WDM (Wavelength DivisionMultiplexing), multiple channels, each with a capacity of several Gb/s, areobtained.

A number of protocols for WDM star networks have recently been proposed.However, the area of real-time protocols for these networks is quiteunexplored. The protocol proposed in this thesis is based on TDMA (TimeDivision Multiple Access) and uses a new distributed slot-allocationalgorithm with real-time properties. Services for both guarantee-seekingmessages and best-effort messages are supported for single destination,multicast, and broadcast transmission. Slot reserving can be used toincrease the time-deterministic bandwidth, while still having an efficientbandwidth utilization due to a simple slot release method.

By connecting several clusters of the proposed WDM star network by abackbone star, thus forming a star-of-stars network, we get a modular andscalable high-bandwidth network. The deterministic properties of thenetwork are theoretically analyzed for both intra-cluster and inter-clustercommunication, and computer simulations of intra-cluster communicationare reported. Also, an overview of high-performance fiber-opticcommunication systems is presented.

Parallel and distributed computing systems become more and more powerful and hence place increasingly higher demands on the networks that interconnect their processors or processing nodes. Many of the applications running on such systems, especially embedded systems applications, have real-time requirements and, with increasing application demands, high-performance networks are the hearts of these systems. Fiber-optic networks are good candidates for use in such systems in the future.

This thesis contributes to the relatively unexplored area of fiber-optic networks for parallel and distributed real-time computer systems and  suggests and evaluates several fiber-optic networks and protocols. Two different technologies are used in the networks, WDM (Wavelength Division Multiplexing) and fiber-ribbon point-to-point links. WDM offers multiple channels, each with a capacity of several Gbit/s. A WDM star network in which protocols and services are efficiently integrated to support different kinds of real-time demands, especially hard ones, has been developed. The star-of-stars topology can be chosen to offer better network scalability.

The WDM star architecture is attractive but its future success depends on components becoming more commercially mature. Fiber-ribbon links, offering instead an aggregated bandwidth of several Gbit/s, have already reached the market with a promising price/performance ratio. This has motivated the development and investigation of two new ring networks based on fiber-ribbon links. The networks take advantage of spatial bandwidth reuse, which can greatly enhance performance in applications with a significant amount of nearest downstream neighbor communication. One of the ring networks is control channel based and not only has support for real-time services like the WDM star network but also low level support for, e.g., group communication.

The approach has been to develop network protocols with support for dynamic real-time services, out of time-deterministic static TDMA systems. The focus has been on functionality more than pure performance figures, mostly on real-time features but also on other types of functionality for parallel and distributed systems. Worst-case analyses, some simulations, and case studies are reported for the networks. The focus has been on embedded supercomputer applications, where each node itself can be a parallel computer, and it is shown that the networks are well suited for use in the radar signal processing systems studied. Other application examples in which these kinds of networks are valuable are distributed multimedia systems, satellite imaging and other image processing applications.

Interconnection networks have a key role in distributed processing systems of today but to follow the evolution in processing power, new technologies are needed. Multiple-channel fiber-optic communication can solve the emerging demand of bandwidth. New protocols must, however, be used to coordinate the use of multiple high-speed channels. This paper describes protocols and fiber-optic network architectures that are considered to be useful as flexible interconnection networks in future parallel and distributed computing systems. Also, a short overview of system components and system technologies is presented.

Optical interconnection networks is a promising design alternative for future parallel computer systems. Numerous configurations with different degrees of optics, optoelectronics, and electronics have been proposed. In this paper, some of these interconnection networks and technologies are briefly surveyed. Also, a discussion of their suitability in radar signal processing systems is provided, where several different ways of coarse algorithm mapping are considered.

More and more real-time systems are complex and distributed systems consisting of many sub-systems that must cooperate. In other words, those sub-systems must communicate with each other and to do this, still fullling the overall system specfication, real-time communication must be supported. Moreover, real-time communication is also becoming widely needed in networks like the Internet, spanning over large distances. In for example Internet, the support for different traffic classes is often described as supporting different QoS (Quality of Service) levels and does normally include some kind of specifcation to meet real-time demands. Real-time communication often relies on some kind of scheduling like EDF (Earliest Deadline First), but there are some important differences compared to standard single-processor scheduling. First, the transmission of a packet is, in most cases, non-preemptive. The ongoing transmission, and possibly also some of the already queued messages, can then not be interrupted when a more important message (e.g., with a shorter relative deadline) arrives or is generated. Moreover, a network, instead of a single link, makes the situation much more complex and one must consider things like medium access method, topology, multiple users on multiple nodes, non-deterministic access delay etc.

Ring networks made of fiber-ribbon point-to-point links are proposed. The first network is a control-channel based network in which one fiber in each link joins with others to form a control-channel ring. This ring improves performance of the network by sending medium access control information immediately before the data transmissions. High throughputs can be achieved in the network due to pipelining, i.e., several packets can travel through the network simultaneously but in different segments of the ring. The network can meet tough performance demands in, e.g., massively parallel signal processing systems, which is shown by example. Also, real-time demands can be met using slot reserving. The network, called CC-FPR (control-channel based fiber-ribbon pipeline ring), can be built today using off-the-shelf fiber optic components. The increasingly good price/performance ratio for fiber-ribbon links indicates a high potential for the success of the proposed kind of networks; a prototype is currently under development. The second network is similar to first except that it divides the network into two subnetworks, one for packet-switched traffic and one for circuit-switched traffic. When the main data flow in the network does not change rapidly, this is a good choice for a simple but powerful network.

In this paper, we present how real-time services are implemented in a control-channel based ring network built up of fiber-ribbon point-to-point links. Services for best effort messages, guarantee seeking messages and real-time virtual channels are supported for single destination, multicast and broadcast transmission by the network. Slot-reservation is used for the implementation of real-time virtual channels. High aggregated throughput can be achieved due to pipelining, i.e., data can be transmitted simultaneously in different segments of the ring. An analysis of worst-case latency and deterministic throughput, which are important measures for real-time service implementation, is provided. The network is analyzed for two variants of time-slot organization, one that offers higher throughput and one that offers lower latency in some situations. We also show how the network offers low-level support for parallel computing, i.e.,  barrier-synchronization and global reduction. The control channel is used when realizing these functions, which implies no modification of the original network architecture. Low-level support for reliable transmission is also offered in a similar manner. This includes acknowledge / negative acknowledge and flow-control.

In this paper, we present how real-time services are implemented in a control-channel based ring network built up of fiber-ribbon point-to-point links. Services for best effort messages, guarantee seeking messages and real-time virtual channels are supported for single destination, multicast and broadcast transmission by the network. Slot-reservation is used for the implementation of real-time virtual channels. High aggregated throughput can be achieved due to pipelining, i.e., data can be transmitted simultaneously in different segments of the ring. An analysis of worst-case latency and deterministic throughput, which are important measures for real-time service implementation, is provided. The network is analyzed for two variants of time-slot organization, one that offers higher throughput and one that offers lower latency in some situations. We also show how the network offers low-level support for parallel computing, i.e.,  barrier-synchronization and global reduction. The control channel is used when realizing these functions, which implies no modification of the original network architecture. Low-level support for reliable transmission is also offered in a similar manner. This includes acknowledge / negative acknowledge and flow-control.

Employing wireless communication in industrial applications requires methods that deal with the high fraction of packet errors common to wireless transmissions. At the same time, industrial applications have real-time demands that protocols like TCP are unable to support. This paper combines ARQ (automatic repeat request) with real-time worst-case scheduling analysis to achieve both high reliability and real-time support. One or several retransmission attempts of erroneous data packets are handled, while still not jeopardizing stated delay guarantees of other packets. We present the real-time analysis for a full-duplex link using our retransmission scheme. In simulation studies, we demonstrate a possible reduction of the message error rate by several orders of magnitude for bit error rates typically experienced in wireless communication.

This paper presents a framework for how to use ARQ (automatic repeat request) in combination with real-time worst-case scheduling analysis to be able to support reliable hard real-time communication. We show how to handle retransmissions of erroneous data packets, while still not jeopardizing stated delay guarantees of other packets. We demonstrate this by taking a point-to-point link as an example. Through our simulation studies we have shown that a reduction of the message error rate by several orders of magnitude is possible with a reasonable utilization penalty.

Increased mobility coupled with a possible reduction of cabling costs and deployment time makes wireless communication an attractive alternative for the automation industry and related application areas. Methods compensating for the high probability of bit errors accompanying wireless transmissions are, however, needed. This is predominantly important in industrial applications with strict reliability and timing requirements, which cannot be met by standard communication protocols as e.g. TCP. In this paper, way of combining retransmissions with real-time worst-case scheduling analysis is presented that can offer both a high grade of reliability and hard real-time support. The presented solution handles one or several retransmission attempts of erroneous data without jeopardizing already guaranteed delay bounds of other packets. A real-time analysis for a full-duplex, asymmetric link, utilizing the novel retransmission scheme and supporting both piggybacked and nonpiggybacked acknowledgements, is provided. A simulation study is presented that evaluates the performance of the retransmission scheme for bit error rates typically experienced in wireless communication. The results clearly indicate a possible reduction of the message error rate by several orders of magnitude.

In modern factory automation systems, data communication plays a vital role. Different nodes like control systems, sensors and actuators can communicate over a wireless or wired industrial network. The data traffic generated is often scheduled for periodic transmission, where each single message or packet must arrive in time. For this real-time communication, methods have been developed to support communication services with a guaranteed throughput and delay bound for such periodic traffic, but merely under the assumption of error-free communication. However, the possibility for errors in the transmission still exists due to, e.g. noise or interference. A node receiving sensor values from a sensor in the system might then be forced to rely upon an older sensor value from the latest period, possibly leading to inaccuracies in control loops which can compromise the functioning of the system. In safety-critical systems, redundant networks or communication channels are frequently added to cope with errors, leading to more expensive systems. In this chapter, we will describe an alternative approach where erroneous data packets are retransmitted in a way that does not jeopardise any earlier stated real-time guarantees for ordinary transmissions. Using our framework, the reliability of real-time communication can be increased in a more cost-efficient way. We describe in this chapter an overview of our framework for reliable real-time communication, while details of our approach can be found in our earlier publications. In the light of the emerging use of wireless communication, the framework proves to be especially useful due to the high bit error rate inherent to the wireless medium. However, the framework is naturally also attractive for wired communication systems.

Intelligent transport systems provide a multitude of possibilities when it comes to increasing traffic safety on our roads. Many of the proactive traffic safety applications under development today demand timely and reliable treatment of deadline dependent data traffic. Unfortunately it is not possible to provide any timing guarantees when using the current IEEE 802.11p standard for wireless access in vehicular environments. Additionally, a difficult wireless channel environment makes successful data transmissions very challenging. We suggest adding a real-time layer, comprising a deterministic medium access control protocol and transport layer retransmissions, on top of IEEE 802.11p in order to enable guaranteed real-time behaviour and to improve reliability. In a simulation study we show that the packet error rate can be decreased by several orders of magnitude while being able to guarantee timely treatment of both ordinary transmissions and retransmissions by the help of a real-time schedulability analysis.