Mikael Björkbom

Localization Services for Online Common Operational Picture and Situation Awareness

Many operations, be they military, police, rescue, or other field operations, require localization services and online situation awareness to make them effective. Questions such as how many people are inside a building and their locations are essential. In this paper, an online localization and situation awareness system is presented, called Mobile Urban Situation Awareness System (MUSAS), for gathering and maintaining localization information, to form a common operational picture. The MUSAS provides multiple localization services, as well as visualization of other sensor data, in a common frame of reference. The information and common operational picture of the system is conveyed to all parties involved in the operation, the field team, and people in the command post. In this paper, a general system architecture for enabling localization based situation awareness is designed and the MUSAS system solution is presented. The developed subsystem components and forming of the common operational picture are summarized, and the future potential of the system for various scenarios is discussed. In the demonstration, the MUSAS is deployed to an unknown building, in an ad hoc fashion, to provide situation awareness in an urban indoor military operation.

Ultra-reliable and real-time communication in local wireless applications

This paper presents a wireless MAC and networking protocol called Real-time Network Protocol (RNP) for ultra-reliable and real-time communication in wireless applications using a small number of nodes. RNP is a collaborative and hybrid TDMA/CSMA MAC protocol with implicit routing, designed especially for small, fast, and time-constrained Wireless Sensor and Actuator Networks in harsh industrial environments. The design is targeted for industrial applications where reliability is the top priority and special attention is put on selection of retransmission method and cooperation between the nodes to collect data periodically. For reliability in RNP several diversity techniques using collaborative retransmission, piggybacking and spatial diversity are proposed. Using analysis, simulations, and a real deployment in an industrial setting, it is shown that RNP achieves high reliability and outperforms alternative designs.

Step adaptive controller for networked MIMO control systems

This paper considers controller tuning for multivariable processes in networked control systems (NCSs) and presents a novel control strategy. In MIMO NCS systems the controller has to manage both the cross-interactions between different loops, and the delays and losses induced by the network. We investigate the effect of cost function weighting and cross-interaction restriction in MIMO systems by simulation-based optimization of controller parameters. Based on this, a step adaptive controller is developed, which changes its tuning parameters depending on whether step response or cross-interaction elimination is desired. We also analyze the proposed control scheme from the networked control perspective via the jitter margin. The step adaptive controller is compared with other MIMO control methods, both in a traditional MIMO case, but also in a NCS setup with the communication and control co-simulator PiccSIM. The results show that the step adaptive controller performs well in comparison to methods presented previously in the literature, and it can suppress the cross-interaction efficiently.

Multichannel Communications in Wireless Automation: Interdependencies between Communication and Control Parameters

Exploitation of wireless communications in various automation applications brings indisputable benefits, which has proliferated research efforts in the field during the recent years. However, underlying wireless communication systems introduce problems to the wireless control systems, such as variable delays, information loss, and limited throughput. By using multiple frequency bands simultaneously, the performance of a wireless network can be enhanced. Since many control applications have strict requirements on delay and delay variations, it is important to understand the impact of communication systems on the performance of wireless automation systems with respect to delay. Hence, in this paper, we study how different communication parameters, such as packet arrival rate, number of channels, and packet size, affect the performance of control systems. We also derive bound on control system performance given the network properties. Our results show the tradeoff between the performance of the wireless multichannel communication system and the automation system. These results can, for example, be further exploited in system design to find out the maximum packet arrival rate with given control parameters.

Networked PID control: Tuning and outage compensation

This paper deals with architecture and algorithm design of networked control systems (NCSs) to cope with network outages. A Networked PID controller and an internal model control based tuning scheme is proposed, using the jitter margin to ensure stability despite dropped packets. For longer periods of disconnection, an outage heuristic is proposed. The control design and outage heuristic need only the step response of the process and is as such simple to apply in practice. The effect of these outages on the stability and performance of the closed-loop control system are evaluated, and compared with alternative schemes via extensive simulations. The simple Networked PID with the outage heuristic is shown to perform well, compared to other techniques proposed in the NCS literature.

Technologies and Methodologies Enabling Reliable Real-Time Wireless Automation

Wireless automation is an emerging field of research, engineering and industrial development that aims at significant savings in installation times and costs of cabling in automation systems, while providing a new level of flexibility for system design, reconfiguration, and agility. It is applicable to both new automation systems and retrofit applications. The use of wireless technologies is rather common in consumer applications, consider, for example, cellular phones, cordless desktops, etc., but the strict real-timeliness and reliability requirements of automation systems have limited the use of wireless technology in industrial environments. There are, however, a variety of existing industrial applications of Bluetooth, ZigBee and WLAN networks, but very rarely these are used in time-critical applications. The bulletproof wireless technologies are few, and hence the technologies have not yet spread to wide use in industrial automation. The main concerns in this respect are related to the problem of how the reliability and real-timeliness of wireless communications could be guaranteed. Wireless automation considers a wide range of technologies that are used in an automation system to enable wireless communications on one or several levels of the system, including factory, automation system, and field device levels. The wireless communications are used to deliver measurements and control values, device configuration information and other process data between the devices, control rooms and servers. This chapter reviews the wireless automation standards and related technologies, but also certain medium access control (MAC) and routing protocols and control design approaches are discussed that together could solve the problem of achieving a reliably working real-time wireless automation system. We will also consider simulation of wireless automation systems, which is essential for the network and automation system co-design validation, and evaluate some candidate system designs with a suitable simulator. The focus is on the field device level, and hence the technologies used for device to device wireless communication for control purposes are addressed. The main contributions of this chapter include a review of current technologies used in wireless automation. We also discuss and propose a new MAC and mesh routing protocol (limited broadcast protocol, LBP) to enhance the reliability and real-time performance of wireless automation systems. We will also demonstrate how the modelling and simulation of packet drops could be done and integrated in the co-design procedure of wireless automation systems. Finally, we will investigate some practical control solutions and designs for wireless automation with a full-scale simulator to validate the proposed designs.

On suboptimal Kalman filtering in case of cluttered observations

This paper examines Kalman filtering and three suboptimal methods in the case of delayed and out-of-sequence measurements in networked or wireless systems. The motivation for suboptimality for Kalman filtering stems from the low computational resources of wireless devices. Optimality is reduced by using a history of a finite horizon. It is shown that the suboptimal filtering with full iteration within the update window performs very similar to the optimal filter, even with a short history window.

Optimization of control transmissions by event-driven model prediction

In this paper we study the optimization of control transmissions in event-driven control systems, with respect to the control performance and number of communication events. The control signal transmissions are decided based on optimization in a model predictive framework, called Model Predictive Triggering (MPT). MPT is developed because the typical send-on-delta approach does not take into account control performance. Several transmission cost functions criteria are compared. We show and compare the performance of the different alternatives using simulation, including a conventional model predictive control approach. The MPT method is shown to be the effective considering the transmission count and control performance, with tuning parameters to select a suitable trade-off between communication and control.

A-stack: A real-time protocol stack for IEEE 802.15.4 radios

This paper presents the A-Stack, a real-time protocol stack for time-synchronized, multi-channel and slotted communication in multi-hop wireless networks. The stack is developed to meet the reliability, latency and accuracy requirements of real-time applications such as wireless automation and wireless structural health monitoring and to provide a flexible development environment for such applications. It includes MAC, routing and time-synchronization protocols as well as a node-joining algorithm. The stack is further supplemented with PC tools for optimizing the network as per the target application for easy prototyping. The design and operational aspects of the stack are verified under various deployment scenarios where the long term system and communication reliability are also tested.

Advanced Communication Solutions for Reliable Wireless Sensor Systems

State-of-the-art Wireless Sensor Network (WSN) technology enables design and implementation of novel, intriguing applications that can be used to address numerous industrial, environmental, societal and economical challenges and thus, the importance and potential of WSNs are constantly growing. Wireless sensor nodes constituting a WSN consist of a sensor interface, microcontroller, memory and battery units together with a radio module. Hence, wireless sensor nodes are able to carry out distributed sensing and data processing, and to share the collected data using radio communications. In the beginning the development of wireless sensors was driven by military applications but the introduction of civilian wireless sensor systems has greatly diversified application domain which has further boosted research efforts in the field of wireless sensor networks. Present state of the evolution of wireless sensor nodes allows utilization of smart sensors to enhance the performance and robustness of WSNs.