A CAN/IEEE 802.11b wireless Lan local bridge design

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Abstract

Employing CAN in distributed real-time control applications sometimes critically requires increasing the size of distributed area, and communication with both other LANs and independent CAN segments. An interworking device with wireless support to extend CAN segments, utilizing an IEEE 802.11b WLAN is a practical solution for such an industrial environment. A key objective of this research work is to design and implement an interworking device called Wireless Interworking Unit (WIU) enabling remote CAN2.0A nodes to communicate over IEEE 802.11b WLAN using encapsulation method. Computer modeling and simulations of the proposed WIU are carried out using OPNET Modeler. The SAE Benchmark has been utilized in the networking models to evaluate the simulation results obtained. Considering the total end-to-end delay results of especially remote CAN messages for above 40 kbit/s bus rates, effect of the designed WIU is proved not causing to exceed the required arrival time deadline set by the SAE Benchmark.

Introduction

The Controller Area Network (CAN) is a contention-based serial communication bus with high performance, high speed, high reliability, and low cost for distributed real-time control applications in both the automotive and the industrial control. Increasing use of several CAN networks in modern industrial plants results in need for interworking between CAN networks as well as between CAN and other major public/private networks. There may be certain difficulties in some industrial scenarios where such a traditional wired backbone is deployed to provide this type of required interconnection functions. For example, when an existing plant, in which cable laying would be quite difficult, requires installation of new communication systems. In addition, there could be some other cases where the use of a wired backbone solution is not feasible, for example, in an integrated factory where several robots work under the control of one or more supervision systems. In such a scenario, each robot may have more than one CAN FieldBus interconnecting the local sensors. Consequently these CAN networks can apparently not be interconnected using conventional wired systems. Having a wireless backbone as an alternative in such environments to interconnect CAN networks would be exceptionally valuable [1], [2], [3], [4], [5]. [5] proposes a wireless Internet working model between TTCAN nodes over Bluetooth for in-car communications, which well suits only for low distance CAN data traffics. Similarly, [1] introduces a CAN over wireless ATM architecture, considering both the CAN messages requiring quality of service support and integration with broadband networks with high expenses. These facts point out a cost-effective implementation of wireless networking necessity of CAN nodes also with any other CAN nodes outside-car, such as proposed in our work over IEEE 802.11b wireless LANs.

As indicated in [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], one wireless network which currently possesses the features needed in an industrial control system, that is, easy integration with several communication systems and capability to ensure critical time constraints, is the IEEE 802.11 standard. The work presented in this paper particularly deals with extending CAN2.0A segments using the IEEE 802.11b WLAN. A new WIU model provided with CAN2.0A/ IEEE 802.11b Internet working functions is proposed in this research study.

Section 2 explains briefly CAN and IEEE 802.11 WLAN and introduces the proposed WIU model including WIU CAN data transfer algorithm, WIU-WLAN data transfer algorithm and WIU learning and transferring subprocesses. Section 3 presents computer simulation modeling of the proposed system, principally consisting of WIU node model and WIU process model with WIU CAN and IEEE 802.11 WLAN process model algorithms, where OPNET Modeler is utilized. Simulation results of the proposed WIU in a CAN Internet working environment followed by its performance evaluation with final remarks are presented and discussed in Section 4.

Section snippets

Interconnecting CAN segments over IEEE 802.11 WLAN

To design a Wireless Interworking Unit (WIU) providing interconnection of CAN Segments over IEEE 802.11 WLAN, first of all two different types of network characteristics should be considered.

Computer simulation implementation of the model

In this section, computer simulation modeling stages of the proposed WIU are presented using OPNET Modeler Radio Module 11.5. These are the network (Fig. 4), node (Fig. 9) and process (Fig. 10, Fig. 12) models.

The node model of the proposed CAN2.0A/IEEE 802.11b WIU is depicted in Fig. 9. The CAN_proc node executes functions of the CAN Interface Entity (CIE) and the CAN Learning, Filtering and Translating Entity (CLFTE), which are shown in the functional block diagram (Fig. 6). Similarly, the

Simulation results and performance evaluation of the WIU model

1The example networking scenario implemented using OPNET Modeler was simulated under various traffic loads. For more realistic simulation and performance analysis of the proposed model, the SAE (Society of Automotive Engineers) Benchmark for real-time distributed system is utilized. SAE Benchmark describes a set of signals sent between several different subsystems in a prototype electric car (Table 1). Although, the SAE Benchmark was defined for use in automotive environment, the set of signals

Conclusions

This paper presents a proposed Wireless Interworking Unit (WIU) and its design stages in order to grant a service achieving the wireless interconnection of independent CAN2.0A segments over IEEE 802.11b WLAN. Considering their easy and common employment in many industrial areas, CAN nodes emerge inevitably to need such a wireless interworking approach for greater flexibility for their applications to be controlled and/or programmed remotely. Such a standard WIU solution with this

Acknowledgement

The authors would like to thank the editor and anonymous reviewers for their invaluable comments and suggestions. This research has been supported by TUBITAK (Scientific and Technological Research Council of Turkey) under contract EEEAG/105E059.

Cuneyt Bayilmis received the M.Sc. degree from Sakarya University, Turkey, in 2001 and Ph.D. degree in Kocaeli University, Turkey in 2006. His active research interests are CAN, WLAN, Internet working and microcontrollers.

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    Cuneyt Bayilmis received the M.Sc. degree from Sakarya University, Turkey, in 2001 and Ph.D. degree in Kocaeli University, Turkey in 2006. His active research interests are CAN, WLAN, Internet working and microcontrollers.

    Ismail Erturk received the M.Sc. and Ph.D. degrees from Sussex University, UK in 1996 and 2000, respectively. His research interests are ATM, wireless data communications, CAN, LANs/WANs, IP and QoS, MPLS, Internet working and real-time multimedia applications.

    Celal Ceken received the M.Sc. and Ph.D. degrees from Kocaeli University, Turkey in 2001 and 2004, respectively. His active research interests include wireless communications, broadband networks, ATM networks, sensor networks and high speed communication protocols.

    Ibrahim Ozcelik received the M.Sc. and Ph.D. degrees from Sakarya University, Turkey in 1997 and 2002, respectively. His research interests are data communications, computer networks, FieldBuses, mobile agent, PC based data acquisition and microprocessors.

    A preliminary version of this study was presented in 19th International Symposium on Computer and Information Sciences, Turkey, 27–29 October, 2004.

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