Aneeq Mahmood

A novel approach for Flexible Wireless Automation in Real-Time Environments

To widen the control over a factory from purely wire based to the wireless domain, both secure and reliable communication infrastructure with real-time capabilities is needed. Based on wireless communication technologies, such infrastructures may be used to gain new flexibility within any step of a manufacturing process hence enabling the development of revolutionary new applications. The international FlexWARE (flexible wireless automation in real-time environments) initiative establishes such a new infrastructure in order to fill this technological gap in the market. This paper gives an overview of the main ideas and the targeted goals.

Towards high accuracy in IEEE 802.11 based clock synchronization using PTP

The introduction of the precision time protocol has brought forth the possibility to have a standardised synchronization mechanism in networks, independent from the actual communication technology. However, it can be observed, for example in the annexes of the standard, that many implementations focus only on Ethernet based communication. The logical next step is to investigate how this protocol will fare when used for synchronizing clocks in a distributed manner over IEEE 802.11 based devices. The availability of features like roaming, the broadcast nature of the wireless medium and different hardware platform architectures require an investigation on how clock synchronization can be realized in wireless environments. This paper proposes an approach to import the precision time protocol to IEEE 802.11. Furthermore, standard nodes are enhanced with software timestamping, leading to a synchronization accuracy of a few microseconds.

Timestamping for IEEE 1588 based clock synchronization in wireless LAN

Clock synchronization is one of the enabling technologies for real-time networking. This paper is motivated by the need for WLAN support of real-time factory automation networks. These networks need synchronized clocks for the typical time-slotted arbitration schemes. As this type of service is not yet available wireless LANs, this work investigates possibilities for synchronizing clocks, based on higher layer synchronization approaches such as IEEE 1588 over WLAN. Different clock synchronization schemes are discussed in this study, some of those utilize the features of IEEE 802.11 and some of them not. In addition to that, this currently still ongoing work shows the difficulties of provision of highly accurate timestamps for the sake of synchronization.

Clock synchronization for IEEE 802.11 based wired-wireless hybrid networks using PTP

The current goal for real-time communication infrastructure in factory automation is to merge and balance the best of both worlds, i. e. the reliability of wired networks, and the flexibility of wireless technologies. Hybrid wired-wireless networks are proposed for establishing real-time communication infrastructures in factory automation. However, the provisioning of synchronized clocks is often taken for granted, and issues regarding the integration of wired and wireless synchronization are neglected. In this study, the requirements for providing clock synchronization for such networks are investigated for an IEEE 802.11 WLAN-based hybrid network with IEEE 1588 as the desired synchronization protocol. The paper also presents simulation and implementation results to assess the synchronization performance of WLAN-based hybrid networks.

Software support for clock synchronization over IEEE 802.11 wireless LAN with open source drivers

Between the wired and the wireless world a synchronization gap in terms of accuracy obviously exists due to the different possibilities of the technologies. This paper investigates means to access WLAN functionality in order to gain system-wide synchronization between access points and clients in order to establish a common notion of time in IEEE 802.11 systems. For this, a novel approach is presented, which uses beacons to transparently transport timing information even in high-loaded wireless LAN networks. Using the presented approach jitter accuracies in the microsecond range can be reached using the open Unix WLAN driver interfaces like madwifi or ath5k.

Impact of hard-and software timestamping on clock synchronization performance over IEEE 802.11

The possibility of equipping devices on the factory floor with wireless communication has brought up new applications and challenges. Among one of these challenges is clock synchronization which is required for easy network management and monitoring. The IEEE 802.11v amendment to IEEE 802.11 has opened the doors for establishing clock synchronization in industrial applications by providing mechanisms and guidelines for synchronization. This work addresses the synchronization means provided by the IEEE 802.11 standard, including the ones mentioned by IEEE 802.11v, and analyses the impact of both software and hardware timestamps on the synchronization performance through test-bed implementations. The results indicate that there are several elements which can affect the quality of both software and hardware time-stamps, which in turn affect the synchronization performance. Moreover, it is also shown that the timestamping accuracy itself is only one factor, and other factors such as control loop settings and synchronization interval also affect the final synchronization performance over WLAN.

Clock synchronization in wireless LANs without hardware support

One typical approach to provide industrial automation networks with real-time guarantees is to plan a communication timeframe, which relies on synchronized clocks at all communication participants. This paper investigates how to reach such a clock synchronization accuracy in a wireless LAN, where commercially available chipsets dictate the implementation possibilities. Furthermore, this paper proposes a synchronization scheme which is in its implementation - an addendum to the beacons - load-independent1.

Distribution of control functionality in energy-aware industrial building environment

Modern trends in automation require flexible production with an onus on saving energy. Till recently, the focus of production systems has been only saving production costs, but the growing concern over environmental impact of such system has led to a partial change in paradigm. The key for the future generation production system is to successfully integrate the manufacturing environment with energy optimisation. This relies on transparent representation of the building from the point of the Manufacturing Execution System (MES) that is not feasible using conventional centralized approaches to building thermal modeling and optimization. This work focuses on distributing the building automation system in a set of generic cells that encapsulate thermal energy models and optimization algorithms to minimize computational resources required for the system implementation on embedded devices. Combined with a notion of the global overview of the energy optimization with functional aggregation and dynamic clustering concepts, the proposed architecture provides a flexible energy saving solution that can be easily integrated in majority of conventional manufacturing systems as well as related factory buildings without compromising production operations.

On clock synchronization over wireless LAN using timing advertisement mechanism and TSF timers

The most recent version of the IEEE 802.11 standard, 802.11-2012 has extended the means of clock synchronization for wireless LANs. One of the mechanisms in the standard is called timing advertisement (TA). It involves calculating and maintaining the time offset with respect to the timing synchronization function (TSF) timer of the access point (AP). In the wireless stations, the TSF-based synchronization mechanism and the offset is combined to establish synchronization to an external timebase. However, such a method provides only loose synchronization unless the skew estimate between the external time source and the TSF timer of the AP is also conveyed to the nodes in the network, for which the standard provides no support. This study, in turn, provides another method, which is called SyncTSF, in which the external clocks at the AP and the nodes are synchronized to their respective TSF timers. Through analysis and measurements, it is shown that both SyncTSF and TA-based synchronization are limited by the frequency skews between the TSF timers of the AP and the nodes. Hence, for these methods to offer good synchronization accuracy, a mechanism to distribute frequency skews from the AP to the nodes should be provided.

Synchronizing an IEEE 1588 slave clock over both paths of a redundant Ethernet system

It is expected that there is only a single active path between an IEEE 1588 master and slave. This is based on the general operation scenario of an Ethernet network, which depends on a setup without network loops. In a redundant Ethernet system based on the Parallel Redundancy Protocol (PRP) or the High availability Seamless Redundancy protocol (HSR), this expectation is skewed. There are two simultaneously active paths between an IEEE 1588 master and slave clock in these systems. Selecting the better path for synchronization, by applying additional qualification criteria in the best master clock algorithm, e.g., the correction field, is a common solution for this problem. This paper proposes a solution to use both paths simultaneously for synchronization to provide a seamless switchover, if one path fails.