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WIRELESS COMMUNICATION IN AUTOMAIION Zdenek Bradac Petr FiedIer Petr Cach Radimir Vrb n Dept of Control and Instrumentation Faculty of Electrical Engineering and Communication Bmo University of Technology Bozetechova 2 CZ 61266 Bmo Czech Republic cach feec wtbr cz fiedlerp feec vutbr cz Dept of Microelectronics Faculty of Electrical Engineering and Communicatiori Bmo University of Technology Udolni 53 CZ 60200 Brno Czech Republic vrbar feec wtbr cz ABSTRACT The paper shows the challenges associated with attempts to utilize Bluetooth communication interface for automation purposes like control and data acquisition The paper describes major challenges selected approach first tests first experiences with Bluetooth on Linux and fmt prototypes of embedded devices used for testing Moreover the paper discusses some specific challenges associated with utilization of wireless communication techniques focused to Bluetooth in automation Finally the paper presents ideas formal methods that could he used to analyze and improve reliability of such system and approach time triggered approach with clock synchronization that could be used to improve the deterministicity of wireless communication channels 1 MTRODUCTION Bluetooth technology is the first widespread PAN Personal Area Network technology The primary focus of this technology is to consumer electronics However there are possible applications in the field of automation too Bluetooth itself does not support industrial applications so it was necessary to gain some experience to do some experiments and development The paper describes the effort to develop Bluetooth platform for a new Bluetooth applications To test basic feames of Bluetooth communication modules a Linux OS was used The Linux was the only platform that provides free source codes of Bluetooth protocols so it was possible to analyze the Bluetooth libraries in the form of source codes and port the code to embedded platforms The Bluetooth parf of Linux is called BlueZ The BlueZ modules contain Bluetooth stack and support Bluetooth modules from major manufacturers The BlueZ enables to immediately start experiments at various proto ol levels As the embedded applications need to suppoit the whole stack it was necessary to start at the HCI level The utilities that are part of the BIueZ allow tci analyze and monitor the Bluetooth communication over RS 232 and USB in the form ofhasic communication packets For the initial experimenrs we have chosen standard Bluetooth modules with USB interface made by MSI The experiments continued using Comtec Teleca SE modules that are equipped with both USB and RS 232 interfaces The first modules are based on Cambridge Silicon Radio chipset while the Comtec modules are based on Ericsson cbipset We found the compatibility among modules from different manufacturers to be very good The initial testing was done with manufachxer supplied software for Windows 2000 The Linux workstation equipped with a Bluetooth module was used to send requests to the modules on PCs with Windows 2000 These experiments were performed to gain some experience with HCI interhcelpmtocol However we found that the latest BlueZ libraries still do not have support for all Bluetooth features and profiles We have performed our tests using BlueZ version 2 0 which for example does not provide support for LAN profile that would enable wireless connection to standard LAN The experience gained with Linux OS and utilization of HCI interface over USB it was possible to create sample data acquisition application In this application there is one master data acquisition node and up to three slave sensoric nodes The master station is in a form of PC and the slave stations are based on simple microcontrollers The sample application thus forms a single Bluetooth piconet 2 LINUX BASED TESTING OF BLUETOOTH 0 7803 8163 7 03 17 00 0 2W3 I BE 659 ICECS 2003 Implementation of Bluetooth stack based just on the written specification is very difficult so the existence of Linux with free open source Bluetooth stack is very helpful The Bluetooth addendum for Linux called BlueZ is part of the Linnx kernel and is part of some recent distributions We have tested RedHat 7 2 and Suse 8 Linux distributions 2 1 BlueZ BlueZ is a software package for Linux which contains Bluetooth stack The BlueZ consists of Bluez Core core of Bluetooth stack HCI WART USB PCMCIA and virtual HCI drivers LZCAPmodule implementation of LZCAP Layer of Bluetooth stack SCO module implementation and control of SCO packets HCIDUMP monitoring tool configuration and test tools The available tools and drivers support Bluetooth modules connected using both standard interfaces USB and RS 232 The tools allow to set up and configure the Bluetooth devices including full set up of various communication parameters The effort to analyze source codes was not very efficient as the source code is not written on a fully platform independent manner and there are many Linux specific parts of code The major advantage of the Linux based approach was in the HCIDUMP utility that enabled to monitor the flow of commands and data toifrom Bluetooth modules HCIDUMP thus enabled to have hands on experience with Bluetooth without the need to fully understand the complex Bluetooth specification 3 EXPERIMENTAL APPLICATIONS The experiments have confirmed that modules from different vendors utilize the same HCI protocol and the same HCI commands Thus it enables to be manufacturer independent without the need to re write the software when there is a need to change a module vendor If the software utilizes only standard commands then the interoperability should be flawless Some cbipset manufacturers extend the standard HCI commands to support non standard features e g Ericsson Specific HCI commands however to bring the modules to operational state these non standard extensions are not needed Based on the first experiment there has been created a model software application which interconnected two personal computers using Bluetooth The modules were controlled directly using HCI commands without utilization of third party software All the newly created software libraries were written in ANSI C to ensure future portability to embedded world As the embedded application will build on RS 232 interface the experiments were performed using this interface too 3 1 The experimental applications The experimental application was targeted to run in the Windows 2000 environment while utilizing the newly created Bluetooth libraries The libraries were written in strict ANSI C as the source code was from the beginning intended for porting to MCSS 1 embedded platform The experimental application runs on Windows 2000 and directly controls the Comtec Teleca modules using RS 232 The control is performed strictly only by HCI commands sent over E 232 The application itself allows configuring and parameterizing of communication modules Application was built according our needs and wishes that stem out from our experience with HCIDUMP This application is used for Testing of protocols at the HCI level Monitoring of data transmissions REQUEST ANSWER Testing of correctness of implementation of basic HCI conunands Implementation of basic L2CAP functions for transmission of data packet Moreover the application supports commands for creation of a piconet from available nodes There have been selected a subset of necessary commands These commands are necessary for configuration and setup of modules inclusion of module into the communication network setup of communication between modules and commands that enable to transmit useful data Implemented commands include commands for search and identification of available Bluetooth nodes 4 EMBEDDED APPLICATION OF BLUETOOTH The above described experiments with wireless communication were foundation for creation of embedded application with single data logger gathering information from sensors via wireless interface The data logger then makes data available over Internet as it is equipped with Ethernet interface supported by TCPiIP protocols The master station can be a PC embedded PC or special data acquisition device Data concentrator SensvisionTM with Net Arm CPU The master station is a piconet Master and it has to be equipped by Bluetooth module with Multipoint capability The local stations are embedded devices based on MCSSl family microprocessors The frst prototypes are based on AbneVTemic AT89CSlCC01 4 1 Design of local sensor station Local station is based on AT89CSlCC01 microcontroller This microcontroller is equipped with external data memory for communication buffer and data structures needed by Bluetooth communication libraries The Comtec Teleca Bluetooth module is connected to the 660 embedded system using RS 232 interface the communication speed over the RS 232 is 57 600 kbps Each local station is equipped by two analog inputs with IO bit resolution Such resolution is suitable enough as this local station serves for testing of the suitability of the selected approach Intemet lntranet Ethemet r KS 232C lialt Environineiit process Figure 1 Experimental Bluetooth apllication 5 CHALLENGES ASSOCIATED WITH DISTRIBUTED WIRELESS COMMUNICATION STRUCTURES The wireless solutions due to their wireless nature bring new challenges especially in the field of reliability and security The wireless technologies are prone to jamming which negatively influences the reliability predictability and deterministicity Moreover unauthorized receptiodlransmission of data is difficult to detect so the wireless technologies have to deal with the security issues much more than it is necessary with classical fieldhuses The reliability of wirekss systems as for temporary or permanent failures can bc analyzed and solved using formal methods while the deterministicity of the wireless control systems can be asisured using time triggered control approach 5 1 Formal modelkpecificritinn of hierarchical decentralized control s ystem Many control systems for industrial controls of manufacturing or production are built as distributed control system There are used PLCs or other microprocessor based control systems smart sensors and actors connected together hy industrial serial fieldbuses or wireless communication buses These systems are often connected to a high li vel network together with workstations operator stations database servers etc In near future a huge amount of new systems will be based on that scheme These system are going to he larger and more complex but more difficult and sensitive to faults Very important problem is to achieve better safety functionality and reliability One of snhparts to achieve fault tolerance of a system is to create a mathematical model of packet s routing a program module mapping in hierarchical decentralized control systems The mathematical model has to be applicable for solving of optimisation problem routing problem and program module mapping There are several criteria which are corresponding with a miscellaneous configurations and requests The formal specification used for mathematical model s creation has to fill requests for easy and very fast solving of routing problem because the routing problem is only one of many sub problem like optimal program module mapping resonrces administration in time tuning of system and etc which are generating a huge and complex optimisation problem Definition of sufficient formal specification will consequently enable optimal routing and module mapping in the framework of hierarchical decentralized system It will also enable to solve optimisation tasks focused to balanced load of buses time optimal transfers and other optimisation functions based on different requirements and criteria 5 2 Graphical modellspecification of hierarchical decentralized control system It is possible to accept hypotheses that whole decentralized control system can he modelled by oriented weighted chart Formal specification of hierarchical decentralized control system has to be extended to model of different transfer and functional capabilities of serial buses and of resource description of control system elements This needs to carry new requirements on weighting and functional limitation of arcs of graph presentation Formal specification of hierarchical decentralized control system dlows using infinity value as weighting of arcs There are problems with discontinuities at enumerating of optimisation problems mainly with enumerating of criteria1 functionals Based 661 on above mentioned hypotheses is possible to introduce global model which consists of parts presenting serial communication nets distributed peripherals and embedded peripherals 5 3 Mathematical modellspecification of hierarchical decentralized control system Mathematical model of optimal routing problem as well as optimal module mapping problem are based on formal description of graphic chart presentation of hierarchical decentralized control system hy set of linear equations with constrains Let input to the mathematical model is given by set of two graphs first graph let describes HW resources of system and second one let describes SW requirement of program modules The weighted oriented graph describing decenmlized control system can be transformed to the mathematical representation by LP linear programming Some optimisation problems of decentralized control system need to use more complex methods like MILP mixed integer linear programming methods etc 5 4 Bluetooth vs Real time The suitability of Bluetooth technology for real time automation purposes is questionable At present time the valid Bluetooth specification is version 1 1 The present Bluetooth supports various transmission modes synchronous or asynchronous symmetric or asymmetric however functionality that would provide predictable QoS Quality of Services is expected to he added to Bluetooth version 2 0 Also the communication delays with Bluetooth may be varying which makes the utilization of Bluetooth for hard real time purposes not so straightforward For applications that require deterministic performance the application has to utilize some advanced control techniques For timely data acquisition it is wise to utilize clock synchronization methods to achieve unified time base among distributed data acquisition nodes 5 5 Clock synchronization and timetriggered approach Without clock synchronization it is not possible to guarantee ability to reconstnict state of the controlled system using data acquired from various distributed sensors using non deterministic communication channel With uniform time base it is possible to attach a time stamp to each acquired data Such time stamp allows to relate data acquired from distributed sensors without a need for deterministic communication channel Ability to reliably reconstruct state of the system is necessary for some control algorithms and it is vital for successful post mortem analysis in case of failures Moreover uniform time based is the first step to time triggered control which is very reliable control approach that is able to guarantee deterministic behaviour of systems in applications that utilize non deterministic communication channels Bluetooth technology allows to transfer TCP IP protocol Over the TCP IP there are defined clock synchronization protocols e g NTP SNTP that allow to achieve very precise and accurate clock synchronization with a common time base The time base can be synchronized either locally limited difference among clock values indicated by distributed nodes at the same time or the whole system can be synchronized to global time limited difference between global time and clock value of any distributed node With clock synchronization and realistic requirements on the Bluetoot