Abstract:
A system is disclosed including a transmitter and receiver for the communication of security codes which may be validated at the receiver to operate equipment. In one embodiment, the transmitter transmits a security code at two frequencies contemporaneously to the receiver which may receive both frequencies and resolve the security code therefrom. The receiver may lock onto one frequency when parts of a security code are detected to the exclusion of the other frequency. In another embodiment, the transmitter selectively transmits security codes at a default frequency which is selected because of a recorded count of prior apparent successful transmission.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the transmission and reception of wirelessly transmitted control signals. 
   BACKGROUND OF THE INVENTION 
   Systems are known in which equipment activation signals are wirelessly transmitted to a receiver which responds thereto by activating the equipment. Such signals are used, for example, to allow remote unlocking or opening of a barrier separating a user from a protected or secure area. The transmitted signals generally include an access or security code which is analyzed by the receiver to identify whether the user causing the signal transmission has permission for access to the protected area. 
   Frequently, the wireless access signals are transmitted by means of a radio frequency (rf) carrier. In many cases, these systems are used in consumer products which dictate that costs and energy consumption are kept to a minimum. It has been discovered that such communication systems may, from time to time, lose their effectiveness due to interfering rf signal transmission by other more powerful transmitters. For example, a barrier movement operator such as a garage door operator, may transmit relatively low power rf signals including a security code to a barrier controller which responds thereto by selectively moving the barrier. One common frequency for the transmission of such security codes is 390 MHZ. Should a higher power rf transmitter be operating nearby at or nearly at the 390 MHZ frequency the receiver at the barrier movement operator may be overloaded and unable to respond properly to a transmitted security code. As should be apparent, this results in the user being unable to control the barrier with his or her remote security transmitter. Further, when the powerful transmitter operates, the inability to control the barrier may appear as an intermittent problem because sometimes the code transmission controls the barrier and sometimes it does not. 
   A need exists for a wireless code transmission and reception system which is less prone to interfering signal transmission. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood from the following description when read in conjunction with the drawing in which 
       FIG. 1  is a block diagram of a barrier movement operator; 
       FIG. 2  is a block diagram of a transmitter of the type shown in  FIG. 1 ; 
       FIG. 3  is an illustration of an embodiment of a transmitter circuit for  FIG. 2 ; 
       FIG. 4  is an illustration of another embodiment of a transmitter circuit for use in  FIG. 2 ; 
       FIG. 5  is an illustration of an embodiment of a multi-frequency receiver circuit; 
       FIG. 6  is an illustration of another embodiment of a multi-frequency receiver circuit; 
       FIG. 7  is a graphical representation of the ref transmission and reception of security code portions; 
       FIG. 8  is a graphical representation of an alternative to the transmission and reception shown in  FIG. 7 . 
       FIG. 9  is a functional flow diagram of the plurality of radio frequencies a method selecting a frequency for transmission based on a count of the plurality of radio frequencies the number of the plurality of radio frequencies usages of the plurality of radio frequencies each frequency; and 
       FIG. 10  is a function flow diagram of the arrangement of  FIG. 9  which includes the ability to lock the transmitter into a selected frequency. 
   

   DESCRIPTION 
     FIG. 1  is a functional block diagram of a security system gaining advantage of the principles described herein. The system of  FIG. 1  uses rf transmitted security codes to control the position of a barrier such as a door, a gate or a garage door. From  FIG. 1  it can be seen that the present system might also be used to control a lock on a door or barrier or the like. 
     FIG. 1  illustrates a barrier movement operator  11  which includes an rf receiver  13  which receives rf security code transmissions from a transmitter  15  via an antenna arrangement  17 . In the present embodiment each transmission includes data identifying the security code, or portion thereof, and information such as a start and sync character to synchronize the receiver with the incoming message. The receiver detects the synchronizing information and the security code portion which is forwarded to a controller  19 . The data in a transmission may include a number of digits or digit portions which are sequentially conveyed by the receiver  13  to the controller  19 . Controller  19  receives the digits and digit portions from receiver  13  and analyzes them to determine from the received format whether a security code portion is in fact being received. The controller  19  then continues to accumulate the digits of a received security code. A received security code is then compared with one or more approved security codes which are stored in a memory  21  of the controller to determine whether approval should be given to the received security code. If such approval is given a motor  23  is energized to move a barrier  25  in a manner determined by the controller. It should be remembered that other actions such as unlocking a barrier could also be initiated by the controller  19 . 
   In the present example, transmitter  15  is capable of transmitting each security code portion at at least two different rf frequencies. For the sake of understanding, the present example discusses the transmission of security codes at two frequencies, 390 MHZ and 315 MHZ. Other numbers of frequencies and other frequencies may be used in accordance with the principles discussed herein and the amount of redundancy desired.  FIG. 2  represents a block diagram of a transmitter  15  which includes one or more push buttons  27  which signal to a controller  29  of the transmitter, that a security code is to be transmitted. Controller  29  then controls a transmitter  33  to send a security code stored in a transmitter memory  31  at the two frequencies 315 MHZ and 390 MHZ. Transmitter  33  responds to the control from controller  29  by contemporaneously rf transmitting security code portions at the two frequencies. The codes are said herein to be contemporaneously transmitted because they are sent during the same period of time, but transmission may not take place in lock step or synchronously, although such may be the case. Also, the security code is transmitted in portions each of which may include an entire security code or less than an entire security code in accordance with priority established formats. For example, a security code may comprise 40 trinary digits which are transmitted as two 20 digit security code portions to be accumulated at the receiver  13  and controller  19 . 
     FIG. 3  is a block diagram of a multiple transmitter circuit transmitter  33 . As shown in  FIG. 3  transmitter  33  comprises two transmitter circuits each of which is configured to transmit security codes at a predetermined frequency. In  FIG. 3  a transmitter circuit  35  is configured to transmit at 315 MHZ and a transmitter circuit  37  is configured to transmit security codes at 390 MHZ. To send a security code, controller  29  transmits the digits of the security code to transmitter  33  via a communication path  39  with appropriate timing for transmission. The security code on conductor  39  is applied to both transmitter circuits  35  and  37  and is thus, contemporaneously transmitted at 315 MHZ and 390 MHZ. 
     FIG. 4  illustrates a transmitter  33  which comprises a single frequency agile transmitter circuit  41  which is capable of transmitting security codes at multiple frequencies. When a security code is to be transmitted using the transmitter of  FIG. 4 , the controller pre sets the transmitter circuit via communication path  39  to transmit at a first rf frequency e.g., 315 MHZ and sends the digits of a security code portion to the configured transmitter circuit  41  via the same communication path. When the transmission at the first rf frequency is completed, the controller  29  controls the transmitter circuit  41  to transmit at the second rf frequency e.g., 390 MHZ and sends the security code portion to the so configured transmitter circuit  41 . 
   The receiver  13  is shown in block diagram form in  FIGS. 5 and 6 . The example of  FIG. 5  includes a receiver  13  which comprises two fixed frequency receiver circuits  43  and  45 . The controller  19  of barrier movement operator  11  periodically surveys reception by the receiver circuits  43  and  45  to determine whether a security code may be being received at their respective frequencies and, if so, controller  19  accumulates received security code digits. The receiver  13  of  FIG. 6  includes one frequency agile receiver circuit  47  which may be periodically switched back and forth to receive security codes at the possible frequencies of reception. In the present example, receiver circuit  47  is alternatively switched between 315 MHZ and 390 MHZ to identify security codes at one or both of those frequencies. 
     FIG. 7  illustrates the operation of the transmitter and receiver to complete the sending and reception of security codes. The top line  49  of  FIG. 7  represents the reception of security codes at 315 MHZ while the second line  51  represents the reception of security codes at 390 MHZ. As illustrated in line  49 , the individual segments  50  represent security code portions as do the individual segments  52  of line  51 . Transmission and reception at 315 MHZ (line  49 ) is given a cross-hatched appearance while transmission and reception at 390 MHZ is not and is represented as open space between segments. Line  53  represents the time during which the controller is detecting signals transmitted at the two frequencies on line  53  the time for detecting 315 MHZ signals is represented as cross hatched times  55  and the timing for detecting signals transmitted at 390 MHZ is represented as plane time segments  57 . Controller alternates between the two frequencies and when appropriate digits are detected, it connects to the single frequency at which the digits were first detected to accumulate the transmitted security code portions. In this way, when one frequency is being interfered with, the security code at the other frequency will be detected. The switch from alternating between frequencies being detected and a constant detection of signals transmitted at 315 MHZ is represented at line  59  of  FIG. 7 . 
   It may be desirable to transmit security codes with time spacing between the transmission of security code portions as is illustrated at line  61  of  FIG. 8 . In the example, security code portions are transmitted for a period of approximately 40 msec ( 63 ) with an approximately 60 msec guard time  65 . Line  61  represents transmission at 315 MHZ. Security code portions are also transmitted at 390 MHZ in 40 msec transmissions  67  separated by approximately 60 msec ( 65 ) of no transmission. Advantageously, the transmission at one frequency occurs during the non-transmission at the other frequency. As represented in  FIG. 8  the active transmission of security code portions at 315 MHZ ( 63   a ,  63   b ,  63   c ) occurs when active transmission at 390 MHZ ( 67   a ,  67   b  and  67   c ) is not occurring. In this way the security codes can be contemporaneously transmitted in a non-interfering manner simplifying the use of frequency agile transmitter and receiver circuits. Also, by operation of controller  29  of transmitter  15  substantially the same code portion will be transmitted as shown by the couplets ( 63   a ,  67   a ); ( 63   b ,  67   b ) and ( 63   c ,  67   c ). The reception of transmission is similar to that shown in  FIG. 7  in that when valid code digits are found at one frequency e.g., 315 MHZ, the reception may convert to that frequency alone for further reception. 
   A system of the above described type will include one or more transmitters of the type shown in  FIG. 2  and a barrier movement operator as shown in  FIG. 1  which includes a multiple frequency rf receiver. As a part of the normal operating routine, the controller of the barrier movement operator alternatively checks whether there are incoming code digits at the 315 MHZ and 390 MHZ frequencies. When a user wants to gain access to the secure area he or she presses the button  27  of the transmitter to initiate code transmission. In response to the button press, controller  29  of the transmitter  15  controls the transmitter operation to contemporaneously transmit security code portions at both frequencies. The contemporaneous transmission may be as shown in  FIG. 7 , lines  49 – 51  or as shown in  FIG. 8 , lines  61  and  69  or other methods of contemporaneous transmission. 
   The receiver, which is checking for incoming security codes, will detect the presence of such a code at within 315 or 390 MHZ. Upon such detection the receiver will continue to focus on the frequency at which code presence was detected to accumulate or enter security code. The accumulated code is then validated by comparing with security codes of authorized transmitters previously stored in the barrier movement operator. Upon validation the controller  19  of receiver  11  may energize motor  23  to change the position of a barrier. As is well known in the art, other functions could also be enacted by the security code such as unlocking a barrier or enabling lights. 
   The preceding embodiments use multi-frequency transmitters and receivers to contemporaneously transmit security codes at a plurality of frequencies. In an alternative embodiment multi-frequency transmitters and receivers can also be used to avoid radio frequency interference by a method and arrangement for transmitting security codes at a first one of a plurality of frequencies, then, should a user indicate that the security code transmission did not provide access to the secure area, transmitting the security code at a second of a plurality of frequencies. 
   As a first example of the present embodiment, a user may press push button  27  to initiate the transmission of a security code. In response to the button press, the transmitter  15  obtains a security code and transmits the obtained security code at a default rf frequency. The controller  29  of the transmitter determines which of the possible rf frequencies of transmission is the default frequency by responding to user interaction. When the button press being responded to occurs within a predetermined period of time, e.g., 4–40 seconds of the last button press, the controller changes the default frequency for transmission to another of the transmitter&#39;s frequencies. A second press within the predetermined period of time is likely to indicate that the immediately prior transmission was not effective and the default frequency is changed to a second frequency to protect against rf interference. Alternatively, when the second button press occurs after the expiration of the predetermined period of time, given the results of human factors studies, it is likely that the prior transmission was successful. Accordingly, the default frequency is not changed and the second transmission is completed using the same rf frequency as the next prior transmission. 
     FIG. 9  is a functional block diagram of a second example of operation in accordance with the second embodiment. In the example of  FIG. 9  a count is maintained for each of the plurality of possible frequencies. Although the present example relates to two possible frequencies, extending the principles taught to a greater number of frequencies is within the scope of the present example. Each count is incremented or decremented based on the time that a second button actuation occurs after a first button actuation to roughly track the probable success and failure rates at each frequency. When a security code is to be transmitted, the frequency with the highest count is selected as the default frequency for transmission representing the most apparent successful uses. 
     FIG. 9  represents the frequency selection in a transmitter which maintains frequency usage counts and begins with a step  71  in which the user press of a switch is detected. Next, in step  73  a determination is made as to whether the time elapsed since the last switch press exceeds a predetermined time. As in the previous embodiments the predetermined time is relatively short, to reflect the differences between button presses which are made because the prior button did not seem effective and the normal rate of effective button presses. The predetermined time may, for example, be in the range of 4–40 seconds. When the elapsed time exceeds the predetermined amount, flow proceeds to step  74  in which a count value associated with the last frequency used for transmission is incremented. 
   Alternatively, when step  73  identifies that the elapsed time between actuations does not exceed the threshold, a step  75  is performed in which the count value associated with the last frequency used, is decremented. After either step  74  or step  75 , a step  76  is performed in which the various counts for the various possible output frequencies are compared and the frequency associated with the largest count is selected. Next, the security code to be transmitted is transmitted (step  77 ) using the frequency selected in step  76  and this portion of the operation of the transmitter ends in block  78 . It should be mentioned that step  76  will include a predetermined frequency e.g., 390 MHZ to be used when the count values for two frequencies are equal at the highest count. 
     FIG. 10  is a flow diagram of transmitter operation which includes a frequency lock function in addition to the steps shown in  FIG. 9 . The frequency lock function allows a transmitter to semi-permanently define one frequency as the default frequency when the number successful of usages of a particular frequency indicates that it is the most likely to yield satisfactory results.  FIG. 10  begins with the detection of a switch actuation in step  81  and proceeds to a decision step  82  to determine if a frequency has already been locked in the transmitter for future use. When step  82  identifies that a frequency has been locked into the transmitter for future use, flow proceeds to step  95  where the frequency for transmission is set to the locked frequency and flow continues to a step  87  in which the code is transmitted using the locked frequency. When step  82  determines that no locked frequency exists, steps  83  and  84  or  85  are performed to increment or decrement the per frequency counts as in the example of  FIG. 9 . Whenever the count is incremented in step  84  a decision step  91  is performed to determine whether the count for the just incremented frequency exceeds a predetermined lock threshold. When the lock threshold has been exceeded, flow proceeds step  93  in which the frequency is locked for future use and flow continues to transmit step  87  via the step  95 . Whenever the count associated with a frequency is decremented in step  85  and whenever step  91  indicates that the lock threshold has not been achieved, the frequency with the highest count is selected in step  86  and transmission occurs at the selected frequency in step  87 . 
   The decision step  91  is shown to compare the count of a frequency to a threshold to determine whether or not to lock a frequency. It should be mentioned that the step  91  may be changed to compare the counts of the frequencies and to lock in a frequency when the counts show a predominant usage of one frequency over another. Further, it is possible that the performance of the flow in  FIG. 10  will lock a frequency into the transmitter at a time when no rf interference exists, but later a source of rf interference at the locked frequency arises. To protect from such, the flow diagram of  FIG. 10  may be modified to unlock a locked frequency when a predetermined number of apparently non-successful transmissions have occurred so that the transmitter can begin to select frequencies as before. Another possibility is to provide a means actuatable by the user, such as a dedicated switch or a combination of switch actuations, to unlock a frequency. 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.