F O R M 2
THE PATENTS ACT, 1970
(39 of 1970)
The patent Rule, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
“METHODS AND SYSTEMS FOR SECURED PASSIVE KEYLESS
ENTRY SYSTEM”
MINDA CORPORATION LIMITED, of E 5/2, Chakan Industrial Area, Phase III MIDC, Nanekarwdi, Taleka-Khed - 410501 dist.-Pune, Maharashtra
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
[0001] The present disclosure generally relates to the field of automobiles. More specifically, the present disclosure describes techniques for secured access to automobiles.
BACKGROUND OF THE INVENTION:
[0002] Passive Keyless Entry System (PKES) in vehicles allow keyless access which automatically locks /unlocks the vehicle doors without taking key out of a bag or pocket. Fig. 1 illustrates a vehicle 100 with PKES. If the driver triggers the door handle of a vehicle 100, then a low frequency (LF) signal (challenge signal) is transmitted from the vehicle 100 to a key frequency operated button 102 (keyfob). The keyfob 102 responds to the vehicle 100 by transmitting a radio frequency (RF) signal (response signal). The vehicle 100 decodes the RF signal received from the keyfob 102 and checks whether the keyfob 102 is registered. If the keyfob 102 is registered, then the vehicle 100 unlocks.
[0003] In a relay attack, messages are relayed from one location to another in order to make one entity appear closer to the other. The attack consists of first demodulating the signal, transmitting the demodulated signal using RF and then modulating it near the victim tag. In a relay attack, the attacker uses proxy devices to relay the communications between two legitimate entities without requiring any knowledge of the actual data being transmitted. Therefore, independent of any cryptographic primitives implemented it is possible to unlock the vehicle and drive away the vehicle even though the legitimate key is several hundred meters away from the vehicle.
[0004] Depending upon type of signal relayed, relay attacks are classified as LF Relay Attack and RF Relay Attack. Fig. 2 illustrates an exemplary embodiment of LF Relay Attack. In LF relay attack, a vehicle transmits an LF signal from the to the keyfob. The relay attack devices are composed of two components: RA1 and RA2. RA1 is responsible for receiving the LF signal from the vehicle and transmitting it to RA2. RA2 is responsible for receiving the signal from RA1 and

transmitting it to the keyfob present in user’s bag or pocket. The keyfob in response transmits an RF response signal to the vehicle and the vehicle on verifying the registration details of the keyfob unlocks the vehicle.
[0005] Fig. 3 illustrates an exemplary embodiment of the RF relay attack. An RF relay attack relays both an LF signal from the vehicle to the keyfob and an RF signal from the keyfob to the vehicle. For the RF relay attack, the possible attack distance is approximately up to 1 km as RF signal is also relayed using the relay attack devices RA1 and RA2.
[0006] Thus, there exists a need in the art to provide a technique which overcomes the above-mentioned problems to prevent LF-RF relay attack in passive keyless entry system.
OBJECTS OF THE INVENTION:
[0007] An object of the present invention is to determine whether a signal received from keyfob is authenticated or the relayed one.
[0008] Another object of the present invention is to determine the distance between the vehicle and keyfob.
[0009] Yet another object of the present invention is to unlock the vehicle only if keyfob is found to be within a particular range of the vehicle.
SUMMARY OF THE INVENTION:
[0010] The present disclosure overcomes one or more shortcomings of the prior art and provides additional advantages discussed throughout the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
[0011] In one non-limiting embodiment of the present disclosure, a method of unlocking a vehicle is disclosed. The method comprises transmitting, by an electronic control unit of the vehicle, a low frequency signal to a keyfob at a first

time stamp and receiving, by the electronic control unit, a radio frequency signal from the keyfob at a fourth time stamp. The radio frequency signal comprises a second time stamp indicating a time at which the low frequency signal is received at the keyfob and a third time stamp indicating a time at which the radio frequency signal is transmitted from the keyfob.
[0012] In another non-limiting embodiment of the present disclosure, the method further comprises determining, by the electronic control unit, a time of flight (TOF) based on the first, second, third and fourth time stamps and unlocking, by the electronic control unit, the vehicle if the determined TOF is less than a predetermined first threshold.
[0013] In yet another non-limiting embodiment of the present disclosure, the determining the TOF comprises determining, by the electronic control unit, a Received Signal Strength Indication (RSSI) of the radio frequency signal and if the determined RSSI is greater than a second threshold, determining the TOF. The method further comprises determining a distance (d) between the vehicle and the keyfob based on the determined TOF.
[0014] In yet another non-limiting embodiment of the present disclosure, an electronic control unit (ECU) for unlocking a vehicle is disclosed. The ECU comprises a transceiver unit configured to transmit a low frequency signal to a keyfob at a first time stamp and receive a radio frequency signal from the keyfob at a fourth time stamp. The radio frequency signal comprises a second time stamp indicating a time at which the low frequency signal is received at the keyfob and a third time stamp indicating a time at which the radio frequency signal is transmitted from the keyfob. The transceiver unit comprises a low frequency (LF) transceiver for transmitting the low frequency signal and a radio frequency (RF) transceiver for receiving the radio frequency signal.
[0015] In yet another non-limiting embodiment of the present disclosure, the ECU further comprises a memory unit operatively coupled to the transceiver unit and configured to store the first, second, third, and fourth time stamps. The ECU

further comprises a processor unit operatively coupled to the memory unit and configured to determine a time of flight (TOF) based on the first, second, third and fourth time stamps and unlock the vehicle if the determined TOF is less than a first threshold.
[0016] In yet another non-limiting embodiment of the present disclosure, the processor unit is configured to determine TOF by determining a Received Signal Strength Indication (RSSI) of the radio frequency signal and determining the TOF if the determined RSSI is greater than a second threshold. The processor unit is further configured to determine a distance (d) between the vehicle and the keyfob based on the determined TOF.
[0017] In yet another non-limiting embodiment of the present disclosure, a system for unlocking a vehicle is disclosed. The system comprises a keyfob, a low frequency transceiver for transmitting a low frequency signal to the keyfob at a first time stamp, and a radio frequency transceiver for receiving a radio frequency signal from the keyfob at a fourth time stamp. The radio frequency signal comprises a second time stamp indicating a time at which the low frequency signal is received at the keyfob and a third time stamp indicating a time at which the radio frequency signal is transmitted from the keyfob.
[0018] In yet another non-limiting embodiment of the present disclosure, the system further comprises a memory unit operatively coupled to the low frequency transceiver and the radio frequency transceiver and configured to store the first, second, third, and fourth time stamps. The system further comprises a processor unit operatively coupled to the memory unit and configured to determine a time of flight (TOF) based on the first, second, third and fourth time stamps and unlock the vehicle if the determined TOF is less than a first threshold.
[0019] In yet another non-limiting embodiment of the present disclosure, the processor unit is configured to determine TOF by determining a Received Signal Strength Indication (RSSI) of the radio frequency signal and determining the TOF if the determined RSSI is greater than a second threshold. The processor unit is

further configured to determine a distance (d) between the vehicle and the keyfob based on the determined TOF.
[0020] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF DRAWINGS:
[0021] Further aspects and advantages of the present invention will be readily understood from the following detailed description with reference to the accompanying drawings, where like reference numerals refer to identical or functionally similar elements throughout the separate views. The figures together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the aspects and explain various principles and advantages, in accordance with the present invention wherein:
[0022] Fig. 1-3 illustrates Passive Keyless Entry System (PKES) in a vehicle and various types of relay attacks, which is known to a person skilled in the art;
[0023] Fig. 4 illustrates a message flow diagram of communication between a vehicle and a keyfob, in accordance with an embodiment of the present disclosure;
[0024] Fig. 5 illustrates Received Signal Strength Indication (RSSI) value as function of distance, in accordance with an embodiment of the present disclosure;
[0025] Fig. 6 illustrates a timing flow diagram of communication between a vehicle and a keyfob, in accordance with an embodiment of the present disclosure;
[0026] Fig. 7 illustrates a flowchart of an exemplary method of unlocking a vehicle, in accordance with an embodiment of the present disclosure;

[0027] Fig. 8(a) illustrates a block diagram of an electronic control unit (ECU) and fig. 8(b) illustrates a block diagram of a transceiver unit, in accordance with an embodiment of the present disclosure;
[0028] Fig. 9 illustrates a system for unlocking a vehicle, in accordance with an embodiment of the present disclosure; and
[0029] Fig. 10 illustrates a flow chart of method performed at a keyfob, in accordance with an embodiment of the present disclosure.
[0030] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION OF DRAWINGS:
[0031] In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0032] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0033] The terms “comprises”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, system or method that comprises a list of components or steps does not include only those

components or steps but may include other components or steps not expressly listed or inherent to such setup or system or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
[0034] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
[0035] The present invention relates to a method of unlocking a vehicle. The method comprising transmitting a low frequency signal to a keyfob at a first time stamp and receiving a radio frequency signal from the keyfob at a fourth time stamp. The radio frequency signal comprises a second time stamp indicating a time at which the low frequency signal is received at the keyfob and a third time stamp indicating a time at which the radio frequency signal is transmitted from the keyfob. The method further comprises determining a Received Signal Strength Indication (RSSI) of the radio frequency signal and if the determined RSSI is greater than a second threshold, determining the TOF. The method furthermore comprises determining a time of flight (TOF) based on the first, second, third and fourth time stamps; and unlocking the vehicle if the determined TOF is less than a first threshold.
[0036] Fig. 4 illustrates a message flow diagram of communication between a vehicle and a keyfob, in accordance with an embodiment of the present disclosure.
[0037] In Passive Keyless Entry System (PKES), the unlocking of vehicle happens by transmitting LF- RF frames. The vehicle transmits beacons on a LF

channel to the keyfob. These beacons may comprise either short wake-up messages or larger challenge messages that contain the vehicle identifier. When a keyfob detects the beacon signal on the LF channel, it wakes up the processor or microcontroller of the keyfob. The transceiver of the keyfob may demodulate the beacon signal and the processor of the keyfob may process the demodulated signal.
[0038] The processor of the keyfob may then generate a response (an RF signal) to the challenge message if the vehicle identifier matches with pre-stored vehicle identifier stored in the keyfob. The response of the keyfob is transmitted on the RF channel. This response is received and verified by the vehicle. The vehicle demodulates the response and verify that the response is from the registered keyfob and the vehicle doors are unlocked.
[0039] Fig. 5 illustrates Received Signal Strength Indication (RSSI) value as function of distance, in accordance with an embodiment of the present disclosure.
[0040] RSSI is a measurement of the energy present in the received RF signal from keyfob. The RSSI may be measured by a radio frequency transceiver or normal transceiver. The rate at which the energy of the RF signal decreases when it is travelling a distance is a well-known physical property of the RF signal known to a person skilled in the art. RF signals experience a loss in signal strength as it travels through the medium such as free space or air. The amount of loss or attenuation in the signal’s strength is proportional to the square of the distance travelled. If the RSSI value of the received radio signal from keyfob is less than a predetermined signal strength value, then keyfob is not in the range of vehicle. The advantage of RSSI measurement is that the transmitter and the receiver do not require any sort of time synchronization between them. The RSSI signal may be obtained using standard hardware known to a person skilled in the art.
[0041] Fig. 6 illustrates a timing flow diagram of communication between a vehicle and a keyfob, in accordance with an embodiment of the present disclosure.

[0042] In an embodiment of the present disclosure, a vehicle transmits a challenge LF message at time stamp T1. The keyfob receives the challenge LF message at time stamp T2. The keyfob processes the challenge LF message and transmits a response RF message at time stamp T3. The vehicle receives the response RF message at time stamp T4. A time of flight (TOF) may be defined as time taken by a message to travel from one point to another. The TOF for the message exchanged between the keyfob and the vehicle may be determined using the following equation:
TOF= [(T4-T1) - (T3-T2)] / 2, where (T3-T2) is a processing time at the keyfob.
[0043] The TOF for the messages to travel from vehicle to keyfob may be used to determine the distance between the vehicle and the keyfob. The distance ‘d’ between vehicle to keyfob is given by:
d = TOF * c, where c is the speed of light.
However, the TOF and distance calculation between the keyfob and the vehicle is not limited to above exemplary embodiment. In another embodiment the TOF and the distance between the keyfob and the vehicle may be determined using a different procedure.
[0044] In an embodiment of the present disclosure, if the message is relayed between the vehicle and the keyfob then the time taken by vehicle to receive the message from keyfob increases. A distance of keyfob from vehicle may be estimated by calculating the TOF. When TOF value is more than a predetermined time threshold, then keyfob is not in the range of vehicle. In case of TOF based distance estimation, it is not possible for the attacker to succeed by just forwarding the signals, but the attacker is required to actively receive, interpret, reconstruct and transmit the appropriate signal back to the verifier. Thus, TOF based distance estimation facilitates prevention of relay attack in PKES and hence may be considered for proving proximity in wireless systems.

[0045] Fig. 7 illustrates a flowchart of an exemplary method 700 of unlocking a vehicle, in accordance with an embodiment of the present disclosure. The method 700 may comprise the following steps.
[0046] At block 701, a low frequency signal may be transmitted by the vehicle to the keyfob at a time stamp T1. The low frequency signal may be generated by an electronic control unit of the vehicle. The electronic control unit generates the low frequency signal in response to trigger signal generated by a user by pulling the door handle for unlocking. The low frequency signal may comprise a vehicle identifier that is unique to a particular vehicle. The vehicle identifier of the vehicle may be encrypted using any cryptography known to person skilled in the art. The encrypted vehicle identifier may be modulated by the transceiver of the vehicle and transmitted to the keyfob.
[0047] At block 703, a radio frequency signal may be received from the keyfob at time stamp T4. The radio frequency signal may comprise a second time stamp T2 indicating a time at which the low frequency signal is received at the keyfob and a third time stamp T3 indicating a time at which the radio frequency signal is transmitted from the keyfob. The radio frequency signal may also comprise registration details of the keyfob.
[0048] At block 705, a received signal strength indication (RSSI) of the received radio frequency signal is calculated. The RSSI may be calculated using any technique known to a person skilled in the art. At block 707, the RSSI of the received radio frequency signal received at the vehicle is compared with a second threshold. The second threshold may be a predetermined signal strength threshold stored in the electronic control unit (ECU) of the vehicle. At block 708, if the RSSI is less than the second threshold, then the keyfob is not in the range of the vehicle and the vehicle doors remain in the locked state.
[0049] At block 709, if the RSSI is greater that than the second threshold, the ECU of the vehicle determines the time of flight (TOF) based on the equation discussed above. The distance between the vehicle and the keyfob may be

determined based on TOF. The distance between the vehicle and the keyfob may also be determined based on the TOF as discussed above. At block 711, the TOF is compared with a first threshold. The first threshold may be predetermined time threshold stored in the ECU of the vehicle. At block 712, if the TOF is greater than the first threshold, then the keyfob is not in the range of the vehicle and the vehicle doors remain in the locked state.
[0050] At block 713, if the TOF is less than the first threshold, the keyfob is in the range of the vehicle and the ECU of the vehicle may unlock the door of the vehicle. Thus, RSSI and TOF value calculation facilitates prevention of relay attacks in PKES of vehicle. In one non-limiting embodiment of the present disclosure, the vehicle may be unlocked if the RSSI of the received radio signal is greater than a predetermined threshold. The steps of method 700 may be performed in an order different from the order described above.
[0051] Fig. 8(a) illustrates a block diagram of an electronic control unit (ECU)
800 and fig. 8(b) illustrates a block diagram of a transceiver unit 801, in
accordance with an embodiment of the present disclosure.
[0052] The ECU 800 may comprise a transceiver unit 801, a memory unit 803, and a processor unit 805 in communication with each other. The transceiver unit
801 may comprise an LF transceiver 810 and an RF transceiver 820. The
transceiver unit 801 may be configured to transmit a low frequency signal to a
keyfob at a first time stamp T1 and receive a radio frequency signal from the
keyfob at a fourth time stamp T4. The radio frequency signal may comprise a
second time stamp T2 indicating a time at which the low frequency signal is
received at the keyfob and a third time stamp T3 indicating a time at which the
radio frequency signal is transmitted from the keyfob.
[0053] The memory unit 803 may be configured to store the first, second, third and fourth time stamps for further processing. The processor unit 805 may be configured determine a time of flight (TOF) based on the first, second, third and fourth time stamps and unlock the vehicle if the determined TOF is less than a

first threshold. The processor unit 805 is configured to determine TOF by determining a Received Signal Strength Indication (RSSI) of the radio frequency signal and determining the TOF if the determined RSSI is greater than a second threshold. The TOF may be determined based on the procedure discussed above.
[0054] The processor unit 805 may be further configured to determine a distance (d) between the vehicle and the keyfob based on the determined TOF as discussed above. In one non-limiting embodiment of the present disclosure, the LF transceiver 810 may be configured to transmit the low frequency signal and the RF transceiver 820 may be configured to receive the radio frequency signal.
[0055] Fig. 9 illustrates a system 900 for unlocking a vehicle, in accordance with an embodiment of the present disclosure.
[0056] The system 900 may comprise an ECU 901 and a keyfob 911 in communication with each other. The ECU 901 may comprise an LF transceiver 903, an RF transceiver 905, a memory unit 907, and a processor unit 909 operatively coupled and in communication with each other. The keyfob 911 may comprise an LF transceiver 913, an RF transceiver 915, a memory 917, and a processor unit 919 operatively coupled and in communication with each other.
[0057] An LF transceiver 903 of the ECU may be configured to transmit a low frequency signal to the keyfob at a first time stamp T1. The low frequency signal may comprise a vehicle identifier. The LF transceiver 913 of the keyfob 911 may be configured to receive the low frequency signal at time stamp T2. The processor unit 919 of the keyfob 911 may be configured to validate the low frequency signal based on the vehicle identifier. The validation may comprise comparing the vehicle identifier with a pre-stored vehicle identifier stored in the memory 917 of the keyfob 911.
[0058] The RF transceiver 915 of the keyfob 911 may be configured to transmit the radio frequency signal if the vehicle identifier matches the pre-stored vehicle identifier. The radio frequency signal may comprise a second time stamp T2

indicating a time at which the low frequency signal is received at the keyfob 911 and a third time stamp T3 indicating a time at which the radio frequency signal is transmitted from the keyfob 911. The radio frequency signal may also comprise registration details of the keyfob.
[0059] The RF transceiver 905 of the ECU 901 may be configured to receive a radio frequency signal from the keyfob at a fourth time stamp T4. The memory unit 907 of the ECU 901 may be configured to store the first, second, third and fourth time stamps (T1, T2, T3, and T4). The processor unit 909 of the ECU 901 may be configured to determine a Received Signal Strength Indication (RSSI) of the radio frequency signal and determining the TOF if the determined RSSI is greater than a second threshold. The time of flight (TOF) may be determined based on the first, second, third and fourth time stamps using the procedure discussed above.
[0060] The processor unit 909 of the ECU 901 may be configured to unlock the vehicle if the determined TOF is less than a first threshold. The processor unit 909 of the ECU 901 may be configured to determine a distance (d) between the vehicle and the keyfob based on the determined TOF using the procedure discussed above. In a non-limiting embodiment of the present invention, the ECU 901 may be ECU of a vehicle situated inside the vehicle coupled to the doors of the vehicle.
[0061] Fig. 10 illustrates a flow chart of method 1000 performed at a keyfob, in accordance with an embodiment of the present disclosure.
[0062] At block 1010, an LF transceiver of the keyfob may receive a low frequency signal and capture a time stamp on reception. The low frequency signal may comprise a vehicle identifier associated with the vehicle. At block 1020, a processor unit of the keyfob may be configured to validate the low frequency signal based on the vehicle identifier. The validation may comprise comparing the vehicle identifier with a pre-stored vehicle identifier stored in the memory of the keyfob.

[0063] At block 1030, a RF transceiver of the keyfob may transmit the radio frequency signal if the vehicle identifier matches the pre-stored vehicle identifier. The radio frequency signal may comprise time stamp indicating a time at which the low frequency signal is received at the keyfob and another time stamp indicating a time at which the radio frequency signal is transmitted from the keyfob. The radio frequency signal may also comprise registration details of the keyfob. The transmitted radio frequency signal may be encrypted using a cryptography technique known to a person skilled in the art.
[0064] The memory of the processor unit may maintain software maintained and/or organized in loadable code segments, modules, applications, programs, etc., which may be referred to herein as software modules. The processor unit may comprise one or more processors. Each of the software modules may include instructions and data that, when installed or loaded on a processor and executed by the processor, contribute to a run-time image that controls the operation of the processors. When executed, certain instructions may cause the processor to perform functions in accordance with certain methods, algorithms and processes described herein.
[0065] The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope and spirit of the disclosed embodiments. Also, the words “comprising,” “having,” “containing,” and “including,” and other similar forms are intended to be equivalent in meaning and be open ended in that an item or items following

any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
[0066] Furthermore, one or more computer-readable storage media may be utilized in implementing embodiments consistent with the present disclosure. A computer-readable storage medium refers to any type of physical memory on which information or data readable by a processor may be stored. Thus, a computer-readable storage medium may store instructions for execution by one or more processors, including instructions for causing the processor(s) to perform steps or stages consistent with the embodiments described herein. The term “computer- readable medium” should be understood to include tangible items and exclude carrier waves and transient signals, i.e., are non-transitory. Examples include random access memory (RAM), read-only memory (ROM), volatile memory, nonvolatile memory, hard drives, CD ROMs, DVDs, flash drives, disks, and any other known physical storage media.
[0067] Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.

We Claim:
1. A method of unlocking a vehicle comprising:
transmitting, by an electronic control unit of the vehicle, a low frequency signal to a keyfob at a first time stamp T1;
receiving, by the electronic control unit, a radio frequency signal from the keyfob at a fourth time stamp T4, wherein the radio frequency signal comprises a second time stamp T2 indicating a time at which the low frequency signal is received at the keyfob and a third time stamp T3 indicating a time at which the radio frequency signal is transmitted from the keyfob;
determining, by the electronic control unit, a time of flight (TOF) based on the first, second, third and fourth time stamps; and
unlocking, by the electronic control unit, the vehicle if the determined TOF is less than a first threshold.
2. The method as claimed in claim 1, wherein the determining the TOF
comprises:
determining, by the electronic control unit, a Received Signal Strength Indication (RSSI) of the radio frequency signal; and
if the determined RSSI is greater than a second threshold, determining, by the electronic control unit, the TOF.
3. The method as claimed in claim 1, wherein the TOF is determined based
on:
TOF= [(T4-T1) - (T3-T2)]/2.
4. The method as claimed in claim 1, further comprising:
determining, by the electronic control unit, a distance (d) between the vehicle and the keyfob based on the determined TOF, wherein the distance (d) is determined based on:
d= TOF * c, where c is the speed of light.

5. An electronic control unit (ECU) for unlocking a vehicle comprising:
a transceiver unit configured to:
transmit a low frequency signal to a keyfob at a first time stamp T1; and
receive a radio frequency signal from the keyfob at a fourth time stamp T4, wherein the radio frequency signal comprises a second time stamp T2 indicating a time at which the low frequency signal is received at the keyfob and a third time stamp T3 indicating a time at which the radio frequency signal is transmitted from the keyfob;
a memory unit operatively coupled to the transceiver unit and configured to store the first, second, third and fourth time stamps; and
a processor unit operatively coupled to the memory unit and configured to:
determine a time of flight (TOF) based on the first, second, third and fourth time stamps; and
unlock the vehicle if the determined TOF is less than a first threshold.
6. The ECU as claimed in claim 5, wherein the processor unit is configured
to determine TOF by:
determining a Received Signal Strength Indication (RSSI) of the radio frequency signal; and
determining the TOF if the determined RSSI is greater than a second threshold.
7. The ECU as claimed in claim 5, wherein the TOF is determined based on:

8. The ECU as claimed in claim 5, wherein the processor unit is further
configured to:
determine a distance (d) between the vehicle and the keyfob based on the determined TOF, wherein the distance (d) is determined based on:

where c is the speed of light.
9. The ECU as claimed in claim 5, wherein the transceiver unit comprises:
a low frequency (LF) transceiver for transmitting the low frequency signal; and
a radio frequency (RF) transceiver for receiving the radio frequency signal.
10. A system for unlocking a vehicle, comprising:
a keyfob;
a low frequency transceiver configured to transmit a low frequency signal to the keyfob at a first time stamp T1;
a radio frequency transceiver configured to receive a radio frequency signal from the keyfob at a fourth time stamp T4, wherein the radio frequency signal comprises a second time stamp T2 indicating a time at which the low frequency signal is received at the keyfob and a third time stamp T3 indicating a time at which the radio frequency signal is transmitted from the keyfob;
a memory unit operatively coupled to the low frequency transceiver and the radio frequency transceiver and configured to store the first, second, third and fourth time stamps; and
a processor unit operatively coupled to the memory unit and configured to: determine a time of flight (TOF) based on the first, second, third
and fourth time stamps; and
unlock the vehicle if the determined TOF is less than a first
threshold.
11. The system as claimed in claim 10, wherein the processor unit is
configured to determine TOF by:
determining a Received Signal Strength Indication (RSSI) of the radio frequency signal; and
determining the TOF if the determined RSSI is greater than a second threshold.

12. The system as claimed in claim 10, wherein the TOF is determined based
on :

13. The system as claimed in claim 10, wherein the processor unit is further
configured to:
determine a distance (d) between the vehicle and the keyfob based on the determined TOF, wherein the distance (d) is determined based on: where c is the speed of light.