APPLICATION NOTE: APU007
Contents
1. 9 all geographies the manufacturer s vehicles are sold Batteries need to last a significant length of time pong Dovey typically 5 years depending on amount of use Cost The system should be as low cost as possible Reliability The system must reliably open start the vehicle It must be difficult for potential thieves to hijack Security communications between the key fob and the vehicle and thereby gain entry to the vehicle 2 2 How to meet these requirements with the DW1000 2 21 Distance from the vehicle Measuring the distance of the fob to the vehicle is not a problem DecaWave s technology allows distance to be measured to an accuracy of 10cm 4 A single transceiver in the vehicle can conduct a 2 way ranging exchange with the key fob when the appropriate key fob button is pressed and calculate the distance from the fob to the vehicle to an accuracy of 10cm See Figure 1 DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 4 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 k decaWave A single unit in the vehicle can conduct a two way ranging Fob exchange with the fob and calculate the distance between the fob and the vehicle Distance Figure 1 Measuring the distance2. decaWave APPLICATION NOTE APU007 APU007 APPLICATION NOTE AN INTRODUCTION TO AUTOMOTIVE KEYLESS ENTRY SYSTEMS Automotive Keyless Entry schemes and their implementation with DecaWave s DW1000 Wireless Transceiver Version 1 00 This document is subject to change without notice DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the author APUO007 An Introduction to Automotive Keyless Ent Systems 4 decaWave TABLE OF CONTENTS 1 INTRODUCTION bisccicccicieccccsseccccsssece cedscaccacssivcceunsccctessiace ENE DIE S EEA ON EANES aN aaas 3 2 IMPLEMENTATION OF KEYLESS ENTRY 4 2 1 REQUIREMENTS FOR A KEYLESS ENTRY SYSTEM 4 2 2 HOWTO MEET THESE REQUIREMENTS WITH THE DW1000 csscceceestececeeaeeeeeeaeeeeeeaaeeeeeeaeeeeseaaas 4 2 2 1 Distance from the 4 2 2 2 Operation only within a given distance from the 5 223 Detecting on which side of the vehicle the fob is located 6 2 2 4 Physical Implementation of the in vehicle 9 2 2 5 Consideration
3. as in indoor car parks Communications Range for vehicle access Generally required to be limited to within a relatively short distance of the vehicle DW1000 has excellent Non Line of Sight and Line of Sight range the system designer can decide on the distance within which the in vehicle system should take action on receipt of a valid exchange Communications Range for vehicle start The must be able to determine when the key fob is inside the vehicle so that the engine cannot be started until the driver is inside the vehicle DW1000 s highly accurate distance measurement capability allows the system to reliably determine if the fob is inside the vehicle Conformance with local regulations The technology employed must conform to regulations in all geographies the manufacturer s vehicles are sold DW 1000 is based on Ultra Wideband which is allowed on an unlicensed basis in most major geographies worldwide Consult DecaWave for more details Long Battery Life Batteries need to last a significant length of time typically 5 years depending on amount of use DW1000 s high data rates mean its on air time be kept shot it s power consumption can be minimized DW1000 s low cost allows cost effective fobs and in vehicle units to Cost The system should be as low cost as possible he constructed Reliability The system must reliably open start the vehicle The IEEE802 15 4 2011 UWB prot
4. not an issue since that is the way the system works The fob ranges to one in vehicle unit followed by the second it cannot range to both simultaneously It s our view that this is a good compromise solution provided the issue of communications between the micro and the two transceivers via SPI is handled correctly DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 10 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 k decaWave Antenna 1 Two unit system based on two antennas two transceivers and a decaWave single micro 1 lt DecaWave Distance Info to Transceiver in vehicle systems Antenna 2 DW1000 T decaWave Micro controller DecaWave Transceiver DW1000 Figure 10 Two Transceivers Single Micro implementation 2 2 4 3 Entirely Separate Units Antenna 1 Two unit system based two completely separate units decaWave SPI lt gt DecaWave Mi Transceiver Iero In vehicle comms Antenna 2 DW1000 controller bus CAN decaWave SPI lt _ gt DecaWave 7 Micro Transceiver controller DW1000 Figure 11 In vehicle unit based on two entirely separate sub units This is the obvious solution Each micro deals with it
5. 1 UWB standard This device is the first in a family of parts that will operate at data rates of 110 kbps 850 kbps and 6 8 Mbps The resulting silicon has a wide range of standards based applications for both Real Time Location Systems RTLS and Ultra Low Power Wireless Transceivers in areas as diverse as manufacturing healthcare lighting security transport inventory amp supply chain management Further Information For further information on this or any other DecaWave product contact a sales representative as follows DecaWave Ltd Adelaide Chambers Peter Street Dublin 8 t 353 1 6975030 e sales decawave com w www decawave com DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 16 of 16 author
6. aaeaea 7 FIGURE 6 MAXIMUM MEASUREMENT ERROR DETERMINES PHYSICAL SEPARATION OF IN VEHICLE 8 FIGURE 7 IN VEHICLE UNITS SEPARATED BY LESS THAN THE MAX MEASUREMENT 8 FIGURE 8 BASIC SINGLE UNIT IMPLEMENTATION scccccceceeeeseaececeeeceeeesaaaeeeceeeeeeeeaaaaececeeeseeeesaaaeeeeeeeeeeseaaaeees 9 FIGURE 9 POSSIBLE TWO UNIT IMPLEMENTATION BY SWITCHING ANTENNAS 9 FIGURE 10 TWO TRANSCEIVERS SINGLE MICRO 11 FIGURE 11 IN VEHICLE UNIT BASED ON TWO ENTIRELY SEPARATE SUB UNITS ccccccecececccececacececacaeacacacaeacaeeeees 11 FIGURE 12 LOCATION OF IN VEHICLE UNITS 13 DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 2 of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave 1 INTRODUCTION This is one in a series of notes on application areas for DecaWave s DW1000 Ultra Wideband wireless transceiver technology This note considers the use of DecaWave s DW1000 in Automotive Keyless Entry Systems Other notes in this series on www decawave com examine the application of DecaWave s technology to other market
7. areas such as Process Automation Healthcare Agriculture and so on DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 3 of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave 2 IMPLEMENTATION OF KEYLESS ENTRY SCHEMES The following are some general comments and notes on the implementation of Keyless Entry Schemes in particular wireless schemes based on DecaWave s Ultra Wideband technology DecaWave will be pleased to explore these issues with customers who wish to implement these or any other schemes 2 1 Requirements for a Keyless Entry System There are a number of fundamental requirements for a Keyless Entry System that can be summarized as follows Table 1 Requirements for a Keyless Entry System Parameter Requirement Must be capable of operating in crowded car parks Communications Performance both indenreand outdoors Communications Range for vehicle Generally required to be limited to within a relatively access short distance of the vehicle The must be able to determine when the key fob is inside the vehicle so that the engine cannot be started until the driver is inside the vehicle Communications Range for vehicle start The technology employed must conform to regulations Conformance with local regulations
8. ate through metal plates it can only propagate around them This has important implications for the location of the in vehicle units Positioning the units low down in the interior of the vehicle will severely restrict their visibility of the outside environment behind dashboards door panels etc are all poor locations for this technology Positioning the units high up in the headlining the courtesy light the sun visor mounts or other such elevated position will give a much better view of the outside environment via the windows glass and will give better performance The appropriate location for an individual vehicle can only be found through testing DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 12 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 Good locations open view of outside environment Poor locations restricted view of outside environment Figure 12 Location of in vehicle units 2 2 5 2 Antenna Radiation Patterns All of the discussions so far have assumed simple spherical antenna radiation patterns These may not be the best ones to use For example in the fob it may be better to use a much less omni directional pattern so an element of directionality is introduced and the fob must be
9. available A single unit in the vehicle cannot distinguish between a driver s side fob and a passenger side fob Q because only one piece of information is availble Fob is actually here But it could equally be here Figure 3 Detecting on which side of the vehicle the fob is located In order to determine on which side of the vehicle the fob is located two pieces of information are required two distances from two in vehicle units for example provided of course that these in vehicle units are positioned in an appropriate way Two in vehicle units mounted on the vehicle centre line cannot Fob is actually here distinguish on which side the fob is located But it could equally be here Figure 4 Two in vehicle units on vehicle centre line DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 6 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 decaWave If however the two units are mounted across the vehicle as shown in Figure 5 then it becomes possible to uniquely identify the side of the vehicle on which the fob is located Two in vehicle units offset across the vehicle can distinguish on Fob which side the fob is located by examining d1 and d2 Figure 5 Two in vehicle units mounted across the vehicle Table 2 Analysis
10. er a microcontroller and an antenna The microcontroller controls the transceiver and implements the two way ranging exchange with the fob Basic in vehicle single unit The micro provides measured distance information to other in vehicle systems for processing and analysis decaWave Distance Info to SPI in vehicle systems c Antenna DecaWave Micro Transceiver controller DW1000 Figure 8 Basic Single Unit Implementation There are a number of possibilities in terms of implementing the two units e Separate antennas but only one transceiver and one micro controller e Separate antennas and transceivers but only one micro controller e Entirely separate units 2 2 4 1 Separate Antenna Implementation Two unit system based on two Antenna 1 antennas and a single transceiver V micro decaWave Distance Info to Lo SPI in vehicle systems 0 4 c mo DecaWave Micro Transceiver controller DW1000 Antenna 2 Figure 9 Possible Two Unit Implementation by switching antennas DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 9of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave This implementation has the advantage that the comparison between the two distance measurements to the fob can be made i
11. from the fob to the vehicle 2 2 2 Operation only within a given distance from the vehicle DecaWave s technology allows Line of Sight ranges of greater than 250m however the in vehicle unit can be configured to only take action when the measured distance is less than a certain vehicle manufacturer defined value The fob and in vehicle unit can communicate up to the maximum Fob 1 can communicate ability of the technology 450m with in vehicle unit and in LOS BUT the in vehicle unit only vehicle unit takes action takes action when the measured distance is 2m or less Distance lt 2m to vehicle Distance gt defined value to vehicle Fob 2 can communicate with in vehicle unit but in vehicle takes no action Figure 2 Operation only within 2m of the vehicle by allowing communications DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 5 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 decaWave 2 2 3 Detecting on which side of the vehicle the fob is located A single two way ranging exchange between 1 in vehicle unit and a fob while sufficient to measure how far away the fob is from the vehicle is not sufficient to determine on which side of the vehicle the fob is located because only one piece of information a single distance is
12. he delay between the arrival departure of the signal at from the antenna and the instant it is time stamped by the receiver transmitter If they are not the same i e unit and one antenna located on one side of the vehicle and the other antenna located on the other side of the vehicle then different correction factors will need to be applied and these may need to be calibrated at manufacturing time to take account of cable manufacturing tolerances It is our view that this implementation will lead to production difficulties and an unreliable system implementation and should be avoided 2 2 4 2 Separate Antennas and Transceivers but only one Micro controller This system removes the antenna switching issues with the previous implementation It allows for the remote location of one transceiver antennas using the SPI interface although this range is limited because SPI was intended as an on circuit board serial communications interface scheme Because both distance measurements are calculated by one micro it is also capable of analysing these distances and determining on which side of the car the fob is located This information can then be provided to other in vehicle systems This may be a more orthogonal amp cleaner partitioning of functionality and may simplify other in vehicle systems The fact that one micro controls both transceivers means that only one can be actively communicating with a fob at any one time in fact this is
13. n the micro and the conclusion advised to the relevant in vehicle systems At first glance it would also appear that this implementation would be cheaper to implement The primary drawback with this system is the difficulty in switching antennas at the high frequencies involved and the inaccuracies that are introduced by the antenna connection and switching mechanisms Switching radio signals at the frequencies of interest 3 1 10 6GHz is difficult at best and should be avoided if at all possible The switching components are generally expensive given the frequencies at which they are operating Switching antennas necessitates a settling period before messages can be transmitted or received since there is no guarantee that the potential at one antenna is the same as the other at switching time so a transient may result which requires time to settle This will limit the number of transmissions receptions that can be made with each antenna Without system modelling it is impossible to say what impact this might have on overall performance For this system to work reliably the delays introduced by the antenna connections must be known and very tightly controlled This is difficult to do repeatably in cable environments but is much more controlled using printed circuit board connections Ideally these delays should be the same so that the same correction factor can be applied by the micro to remove the antenna delay from the calculations t
14. ocol incorporates a number of error checking methods to ensure communications is reliable TE Because the distance measurement is based on the exchange of very Security ai ee d accurate time stamps it is extremely difficult for a third party to hijack and thereby gain entry to the vehicle an exchange The IEEE802 15 4 2011 UWB standard supports AES 128 encryption DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the author Page 14 of 16 APUO007 An Introduction to Automotive Keyless Ent Systems 4 k decaWave 3 REFERENCES 3 1 Listing Reference is made to the following documents in the course of this Application Note Table 4 Table of References Ref Author Date Version Title 1 DecaWave 2 00 DW1000 Data Sheet 2 DecaWave 1 00 DW1000 User Manual DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 15 of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave 4 ABOUT DECAWAVE DecaWave is a pioneering fabless semiconductor company whose flagship product the DW1000 is a complete single chip CMOS Ultra Wideband IC based on the IEEE 802 15 4 201
15. of measured distances Condition in Fig 6 Conclusion d1 gt d2 Fob on driver s side USA d1 lt d2 Fob on passenger s side USA d1 d2 Fob on center line of vehicle a E ee A e Fob inside the vehicle The question then arises how close together can the in vehicle units be located If they can be mounted close enough together then it becomes possible to fabricate them as one unit for ease of installation into the vehicle This is where the 10cm distance measurement accuracy comes into play For the two in vehicle units to reliably determine correctly the side of the vehicle on which the fob is located the separation between the two in vehicle units must be greater than the maximum possible error in the distance measurement So with 10cm accuracy in the worst case the measurement from one in vehicle unit to the fob could be 10cm in error while the measurement from the other could be 10cm in error To avoid drawing incorrect conclusions from the measured data a minimum separation between the two units of 20cm is required We can illustrate this by drawing an error boundary of 10cm around the distance measured from each in vehicle unit to the fob DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 7 of 16 author APUO007 An Introduction to Automotive Ke
16. pointing in the general direction of the vehicle for communications to take place Similarly for the in vehicle units it may make sense to have oval radiation patterns rather than spherical because vehicles are generally longer than they are wide These decisions would require further analysis DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 13 of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave WuHyYDW1000i s IDEAL FOR KEYLESS ENTRY SYSTEMS DecaWave s DW1000 wireless transceiver usesUltra Wideband radio technology is compliant with the IEEE 802 15 4 2011 UWB standard and is implemented using CMOS technology For a full suite of sales amp technical information on the DW1000 see the DecaWave websitewww decawave com Looking at the requirements discussed above let s see how DecaWave s DW1000 technology addresses them Table 3 Meeting Keyless Entry System Requirements with the DW1000 Parameter Requirement What DW1000 brings Communications Performance Must be capable of operating in crowded car parks both indoors and outdoors Because DW1000 uses Ultra Wideband technology it is very immune to fading due Multipath propagation This is particularly important in indoor environments with significant amounts of metal such
17. s 12 WHYDW1000IS IDEAL FOR KEYLESS ENTRY 5 5 14 3 REFERENCES wisscccicccscectescsvcwscscsssveesosvevence sseutesesvedecsesvessacosvaveest svestacedvevcsseseessasosveveace 15 3 1 LISTING 224s ed ee 15 ABOUT DECAWAVE ES E 16 LIST OF TABLES TABLE 1 REQUIREMENTS FOR A KEYLESS ENTRY SYSTEM 4 TABLE 2 ANALYSIS OF MEASURED DISTANCES ssccssssecssscesssecssssecsseeecaeeessaecseseeceseeessaeesssuecseaseceaeessaaeeseaaeeseness 7 TABLE 3 MEETING KEYLESS ENTRY SYSTEM REQUIREMENTS WITH THE DW1000 14 TABLE 4 TABLE OF 22 15 LIST OF FIGURES FIGURE 1 MEASURING THE DISTANCE FROM THE FOB TO THE VEHICLE esccceececcceeeeeeeceaeaeaeaeacaeaeaeaeaeaeaeaeaeaeaeaea 5 FIGURE 2 OPERATION ONLY WITHIN 2M OF THE VEHICLE BY ALLOWING COMMUNICATIONS 5 FIGURE 3 DETECTING ON WHICH SIDE OF THE VEHICLE THE FOB IS 6 FIGURE 4 TWO IN VEHICLE UNITS ON VEHICLE CENTRE LINE ccccccceccceccceccceceacaeacacaeacacacacacacacaeacacaeaeaeaeaeacanaeaea 6 FIGURE 5 TWO IN VEHICLE UNITS MOUNTED ACROSS THE VEHICLE eccccccccccceceeeeecaeaeaeeeaeacaeacaeacacaeacacaeacaea
18. s own transceiver and supplies the distance measurement data either to a processor elsewhere in the vehicle to perform the data analysis or one of the two processors is designated as the data analysis processor and the other processor provides its measurements to it for analysis DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 11 of 16 author APU007 An Introduction to Automotive Keyless Entry Systems decaWave In this situation the communications between the micro controllers could be handled over the in vehicle communications bus CAN for example or via a separate dedicated connection from one controller to the other The advantage of this implementation is that it allows much greater freedom in the location of the units within the constraints of cost manufacturability and so on 2 2 5 Other Considerations 2 2 5 1 Location of the units in the vehicle We have already seen how the in vehicle units must be separated by more than 20cm to take account of the maximum possible ranging error There is another consideration to be borne in mind that of radio propagation DecaWave s technology is based on the propagation of radio waves from transmitter to receiver The technology is exceptionally good in non line of sight environments but like all radio schemes it will not propag
19. yless Ent Systems 4 k decaWave Provided the in vehicle units are separated by more then the max measurement error it is possible to determine the side of the vehicle on which the fob is located Figure 6 Maximum measurement error determines physical separation of in vehicle units If the in vehicle units are mounted closer together than the maximum measurement error then it is If the in vehicle units are separated not by less than the maximum measurement error there is possible to possibility of incorrectly eee i determining the side of the vehicle reliably on which the fob is located lt x ae determine a on which side of the vehicle the fob is located intersection also Figure 7 In vehicle units separated by less than the max measurement error DecaWave 2013 This document is confidential and contains information which is proprietary to DecaWave Limited No reproduction is permitted without prior express written permission of the Page 8 of 16 author APUO007 An Introduction to Automotive Keyless Ent Systems 4 k decaWave The conclusion from this analysis is that the two in vehicle units must be separated by at least 20 cm 2 2 4 Physical Implementation of the in vehicle unit So given that it is clear that two units are required inside the vehicle the question then arises as to how best to implement those units In its basic form a unit consists of the DecaWave transceiv
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