Remote keyless entry system with two-way long range communication

CROSS REFERENCE TO RELATED APPLICATIONS

0001Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

0002Not Applicable.

BACKGROUND OF THE INVENTION

0003The present invention relates in general to remote keyless entry systems for motor vehicles, and, more specifically, to increasing transmission range between a vehicle base station and a handheld portable transceiver fob without exceeding regulatory average field strength limitations.

0004Remote keyless entry (RKE) systems for use with motor vehicles are well known in the art. Such systems typically include at least one remote control device, which typically takes the form of a key fob. The key fob includes a wireless transmitter for use by the vehicle owner or user to transmit wireless, usually radio frequency (RF), vehicle device function signals and includes a number of vehicle function buttons for use in transmitting such signals. A receiver and controller are typically provided in the vehicle for receiving the vehicle device function signals and controlling one or more vehicle devices in order to effect the desired vehicle function.

0005Vehicle devices which have been remotely controlled in such a fashion include door lock mechanisms, a vehicle trunk, interior and/or exterior vehicle lights, and a vehicle horn or other alarm. More recently, remote vehicle starting (sometimes together with remote temperature control) has been introduced. Prior RKE systems have typically utilized one-way transmissions from the portable fob to the vehicle. However, two-way communication systems are increasingly being used to facilitate user feedback for remote starting functions (e.g., reminders that a vehicle is running, and providing a remote indication of the vehicle temperature that has been achieved) and for providing guiding information as part of a vehicle locating system, for example. A two-way RICE system is shown, for example, in U.S. Pat. No. 6,724,322, entitled “Remote System For Providing Vehicle Information To A User,” issued to Tang et al. on Apr. 20, 2004, incorporated herein by reference.

0006A key fob must be small in size in order to facilitate carrying in a user's pocket or purse. Thus, miniaturized circuits and a small battery size are employed. Energy efficient microelectronic circuits and methods of operation are necessary in order to minimize battery consumption and maximize battery life. The key fob must also accommodate a transmit/receive antenna that is preferably hidden within the key fob because of esthetic and durability concerns. Therefore, the antenna gain that can normally be achieved is fairly low. The low antenna gain has constrained the operating range over which broadcasts between the portable fob and the vehicle base station can be reliably received.

0007One method to increase effective range would be to increase the transmitter power. However, government regulations aimed at reducing the likelihood of interference with other transmissions are in place which limit the allowed transmitter power. Prior art transmitters have operated near the regulatory limits and yet operating range has been less than desired for remote monitoring of a vehicle, such as when the vehicle has been remotely started.

SUMMARY OF THE INVENTION

0008The present invention has the advantage of increasing operating range without modifications to the antenna and while operating within regulatory power limits.

0009In one aspect of the invention, a method is provided for transmitting vehicle information from a base station mounted in a vehicle to a portable RKE fob via a radio-frequency signal within a specified average field strength limit. A multi-byte vehicle message is formed and then coded into a multi-bit coded message. The multi-bit coded message is framed into a plurality of packets. The radio-frequency signal is wirelessly transmitted from the base station with a plurality of spaced packet windows having a predetermined duty cycle, each packet window including a respective one of the plurality of packets. The radio-frequency signal within each of the packet windows has a predetermined field strength greater than the average field strength limit and a substantially zero field strength between the packet windows. The predetermined duty cycle results in an actual average field strength for transmitting all of the packets not exceeding the average field strength limit. The plurality of packets are received within the portable RKE fob. The vehicle message is recovered in the RKE fob in response to the received plurality of packets.

BRIEF DESCRIPTION OF THE DRAWINGS

0010<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing the two-way communication system of the present invention.

0011<figref idref="DRAWINGS">FIG. 2</figref> is a flowchart showing a first preferred embodiment of a message sequence of the present invention.

0012<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram showing a preferred embodiment for message assembly, encoding, and framing.

0013<figref idref="DRAWINGS">FIG. 4</figref> is a waveform diagram showing the spaced packet windows and increased field strength transmissions of the present invention.

DETAILED DESCRIPTION OF PREFERRED. EMBODIMENTS

0014RKE transmitters are regulated as intentional radiators. Most existing RKE systems operate at 315 MHz or at 433 MHz. Each particular transmitter design is certified, so that individual licenses are not necessary for their operation. In the United States, for example, the FCC regulates these remote control devices by imposing a field strength limitation for the fundamental frequency at 315 MHz of 6,040 microvolts per meter measured at 3 meters. Compliance with the limits on field strength may be demonstrated based on the average value of the measured emissions. Therefore, a peak signal strength greater than the specified field strength limit is permissible provided the average emissions are within the limits. The regulations providing for the field strength limitation are found in FCC regulations under Title 47, Part 15, Section 15.231. FCC rules further provide in Section 15.35 that when an average radiated emission limit is specified there is also a limit on peak emissions corresponding to 20 dB above the maximum permitted average limit.

0015The data contained in a typical message sent by an RKE fob to the vehicle base station includes a transmitter identifier and an operation code. The transmitter identifier may comprise an encrypted identification code generated using a rolling code algorithm, as is known in the art, to prevent interception and subsequent unauthorized access to a vehicle. The operation code identifies a desired vehicle function as determined by the particular push button pressed on the fob, such as unlocking the doors. The data is typically encoded in a return to zero signal pattern, such as Manchester encoding. A message protocol is utilized which typically defines a preamble (to allow the receiver to detect an incoming message and synchronize its clock), a start bit, and a data field having a prescribed number of bits. When the push button is held down on the RKE fob, the corresponding data message is broadcast all at once. A typical transmission may last about 60 milliseconds, for example.

0016The duty cycle of a transmitter is defined as the ratio of transmitter on time to the transmitter cycle time (i.e., the minimum time between transmissions). A typical transmitter cycle time may be greater than about one hundred milliseconds. Using Manchester coding, the transmitter on time is one-half during a transmission. Therefore, a typical duty cycle in the prior art is equal to about 20·log(30 mS/100 mS) or about 10.5 dB. Consequently, the prior art transmission could utilize peak field strength which was about 10 dB greater than the average field strength limit, but no higher.

0017The present invention provides a modified message protocol for optimizing transmissions to utilize peak field strength that takes full advantage of the allowable peak values above the specified average. Specifically, the present invention reduces the data rate by framing a particular message into a plurality of packets and then separately transmitting the packets utilizing a duty cycle that can preferably take full advantage of the difference between the peak limit and the average limit for field strength. The corresponding reduction in data rate is well worth the improved operating range since the additional delay of a few hundred milliseconds is hardly noticeable to the user. The range is additionally improved by using error control coding (e.g., Hamming code) which results in a range improvement of about 1 dB.

0018Referring now to <figref idref="DRAWINGS">FIG. 1</figref>, a motor vehicle <b>10</b> includes a remote keyless entry (RKE) module <b>11</b> for communicating with a portable RKE fob <b>12</b> carried by a user. Two-way radio frequency (RF) communication is achieved using a pair of transceivers <b>13</b> and <b>14</b> in module <b>11</b> and fob <b>12</b>, respectively. Fob <b>12</b> further includes an antenna <b>15</b> connected to transceiver <b>14</b> which may take the form of a monopole antenna formed as a conductor trace on a printed circuit board within fob <b>12</b>, for example. A message controller <b>16</b> is coupled to transceiver <b>14</b>, push buttons <b>17</b> and <b>18</b>, and a display <b>19</b>. Message controller <b>16</b> preferably includes a programmed micro-controller responsive to push buttons <b>17</b> and <b>18</b> for generating either remote commands (e.g., door lock or unlock, engine start, etc.) or status request messages to be sent to vehicle module <b>11</b>. Message controller <b>16</b> also recovers vehicle data from messages received from vehicle module <b>11</b> for presentation on display <b>19</b> (e.g., the engine running status or internal temperature of vehicle <b>10</b>). Besides vehicle status, the vehicle message may provide calibratable parameters (e.g., a center frequency to be used for transmissions or a wake-up interval for monitoring for transmissions) or diagnostic information (e.g., received signals strength of messages). Display <b>19</b> may, for example, comprise an LCD display.

0019Transceiver <b>13</b> in vehicle module <b>11</b> is connected to an antenna <b>20</b> and a vehicle message controller <b>21</b>. Antenna <b>20</b> may comprise a monopole antenna packaged within a wire bundle of the electrical system of vehicle <b>10</b>. A greater antenna length and a higher antenna gain is achievable within vehicle <b>10</b> as compared with antenna <b>15</b> in fob <b>12</b>.

0020Message controller <b>21</b> is coupled to a security system <b>22</b> and to a vehicle system <b>23</b> such as an engine control module or a climate control module, for example. Vehicle message controller <b>21</b> responds to messages from fob <b>20</b> received by transceiver <b>13</b> in order to validate a message and then act upon any corresponding vehicle actions to be taken. For example, security system <b>22</b> may comprise electronic door locks, which may either be locked or unlocked in response to a message decoded by message controller <b>21</b>. In response to a status request message from fob <b>12</b>, message controller <b>21</b> may access vehicle system <b>23</b> in identifying an appropriate response to be generated by message controller <b>21</b> for broadcasting to fob <b>12</b>. Vehicle message controller <b>21</b> may also initiate transmissions to fob <b>12</b> in order to transfer calibratable parameters or diagnostic information without being requested by fob <b>12</b>.

0021A typical message sequence is shown in <figref idref="DRAWINGS">FIG. 2</figref>. In step <b>30</b>, a user presses a fob button to request a particular vehicle status, such as the vehicle interior temperature or the running status of the engine, a vehicle alarm status for identifying a triggered alarm, or the locked or unlocked status of a particular vehicle door. A corresponding status request message is sent from the fob to the vehicle RKE module in step <b>31</b>. The RKE module retrieves the appropriate information in step <b>32</b> and then generates a status message in step <b>33</b> according to a predefined message protocol. In step <b>34</b>, the status message is encoded and framed into a plurality of packets, each packet containing a portion of the status message. The packets are broadcast to the fob in step <b>35</b> using a duty cycle selected to allow increased peak field strength to be utilized for broadcasting each packet. The status message is received by the fob and then deframed and decoded in step <b>36</b>. In step <b>37</b>, the information from the broadcast status message is displayed on the fob.

0022Functional blocks within the message controllers for generating the packets based on the data to be transmitted is shown in <figref idref="DRAWINGS">FIG. 3</figref>. A vehicle message (or a status request message) is assembled in a block <b>40</b> in response to a fob identifier and vehicle parameters such as a security status (e.g., alarms status or door lock status), vehicle information (e.g., engine running status or vehicle temperature), calibratable parameters, or diagnostic information. A typical vehicle status message may include 3 bytes wherein byte #<b>1</b> includes vehicle security status, byte #<b>2</b> includes vehicle temperature, and byte #<b>3</b> includes a transmitter identifier. A vehicle message may preferably also include other bytes or message portions which include a fob ID code in a rolling code format. A one-byte cyclic redundancy check is calculated in a block <b>41</b> and added to the vehicle status message in a summer <b>42</b>. To provide error correction as is known in the art, the four-byte message may be encoded using a hamming code in a block <b>43</b>. A 7, 4 hamming code is preferably used. The multi-bit hamming result is provided to a Manchester encoder <b>44</b> for generating a multi-bit Manchester encoded message. Alternatively, any alternative non-return-to-zero encoding message or any other suitable bit encoding may be employed. A framer <b>45</b> separates the multi-bit coded message into a plurality of packets for separate transmission in spaced packet windows having a predetermined duty cycle. Each packet may preferably have a preamble and/or start bits prepended to it.

0023In a preferred example of the present invention having a status message including a CRC byte providing a total of 32 bits (i.e., four 8-bit bytes), application of a 7, 4 hamming coding produces 56 bits. The 56 bits are preferably broken into four separate packets including 13 data bits, 18 data bits, 18 data bits, and 7 data bits, respectively. The first packet begins with a preamble comprising a predetermined number of repetitions of a predetermined bit. The preamble is followed by a pair of start bits and then the data field for the first packet. Subsequent packets begin with the pair of start bits followed by their respective data bits. Each packet window may have a width of about 20 milliseconds and the packets may be repeated at a packet period of 100 milliseconds, resulting in a duty cycle of 10%. Using a data rate of about 2 kilobits per second during each packet, each bit period comprises about 0.5 milliseconds.

0024As shown in <figref idref="DRAWINGS">FIG. 4</figref>, packets <b>50</b>, <b>51</b>, and <b>52</b> have respective packet window widths of 20 milliseconds separated by a packet period of 100 milliseconds. Using Manchester coding, the transmitter is on during one-half of each 20 millisecond packet window. Each packet is transmitted with a peak field strength <b>53</b> greater than the specified average field strength limit <b>54</b>. If the duty cycle (i.e., the ratio of half a packet window width to the packet period) is substantially equal to a reciprocal of the ratio of the peak field strength limit to the average field strength limit then the maximum allowable peak field strength limit is utilized. Thus, the transmission takes is full advantage of the permissible peak field strength to generate the greatest possible operating range. In the case of the FCC requirement that peak emission is limited to being 20 dB above the maximum permitted average limit, the peak field strength may be 10 times as great as the average field strength. Thus, at a duty cycle of 10%, the peak field strength is allowed to approach the maximum peak limit without reducing the data rate any more than necessary.

0025The packetized transmissions of the present invention can be used for either or both of the transmissions from the vehicle to the fob or from the fob to the vehicle. Since antenna gain and power consumption constraints in the vehicle are less severe than in the fob, the operating range for messages from the fob to the vehicle are less severely limited. Therefore, the present invention may be more beneficial when applied to messages being broadcast from the vehicle to the fob. In other words, greater receiver sensitivity may be more easily obtained in the vehicle receiver by achieving a greater antenna gain, reducing receiver bandwidth, and providing a higher amplifier gain in the vehicle receiver than are possible in the fob.

0026The fob ID shown in <figref idref="DRAWINGS">FIG. 3</figref> is optional for insuring that a vehicle message is received by and displayed by only the fob requesting the information. The fob ID may comprise a random number generated by the fob and inserted into the vehicle status request message. The randomly generated number is received by the vehicle receiver and then included in the responsive vehicle message to be detected by the fob and correlated to the previous request message. A fob receiving the vehicle status message and not having a matching fob identifier in its memory would not display or otherwise use the vehicle message. A rolling code fob ID contains several bytes due to the large number of possible transmitters that are deployed in service. A short (e.g., one byte) fob ID is sufficient for restricting the reception of a vehicle message to the intended fob because the number of fobs within range of a vehicle is a much lower number.