Patent Publication Number: US-7899130-B2

Title: Transmitter for operating multiple devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 10/193,525, filed on Jul. 9, 2002 now U.S. Pat. No. 7,254,182. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to remote control systems, and specifically to a transmitter or transceiver that is programmable and capable of operating multiple devices by transmitting multiple codes at multiple frequencies, using multiple transmission formats. 
     2. Background of the Invention 
     Transmitter-receiver controller systems are widely used for remote control and/or actuation of devices or appliances such as garage door openers, gate openers, security systems, and the like. For example, most conventional garage door opener systems use a transmitter-receiver combination to selectively activate the drive source (i.e., motor) for opening or closing the door. The receiver is usually mounted adjacent to the motor and receives a coded signal (typically radio frequency) from the transmitter. The transmitter is typically carried by a user and selectively activated by the user to open or close the garage door. These type of remote control systems typically employ VHF/UHF radio frequency transmissions. 
     In general, a remote control system has a remote transmitter and a receiver coupled to the device, which is to be controlled. When activated, the transmitter emits a modulated signal, which is recognized by the receiver to activate the device. In VHF/UHF-based systems, a transmitter typically emits a pulse-modulated VHF/UHF signal. The signal embodies a modulation pattern as a sequence of “signal on” and “signal off” intervals. The modulated signal emitted by the transmitter is recognized by the receiver. The modulation pattern of remote control systems is typically unique to restrict unauthorized access to the device being controlled. 
     Alternatively, the modulation pattern may be comprised of a rolling code signal which changes for each transmission, as a function of a predetermined algorithm. Each new rolling code is generated using a rolling code generator, where both the transmitter and its corresponding receiver will contain the same rolling code generator. In such systems, the receiver will only be activated if it receives one of a limited number of possible rolling codes from the transmitter. Since both the transmitter and the receiver are advancing through a rolling code sequence using the same rolling code engine, the transmitter will typically be able to provide an acceptable code to the receiver. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and apparatus is disclosed. In one embodiment, the transmitter comprises a first switch and a memory programmed with transmission values and corresponding transmission frequencies for a plurality of receivers, where the transmission values are representative of at least one of a device code and a modulation format. In one embodiment, the transmission values include transmission values for a fixed-code type receiver and a rolling-code type receiver. The apparatus further includes a receiving circuit for receiving a sample signal having sample transmission values, and a controller coupled to the first switch, the memory and the receiving circuit. The controller compares the sample transmission values from the sample signal to the transmission values in the memory for the plurality of receivers, and associates the first switch with a first set of transmission values and corresponding transmission frequencies in memory for a first receiver of the plurality of receivers when the first set of transmission values stored in memory for the first receiver match the sample transmission values from the sample signal. 
     Other embodiments are disclosed and claimed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a simplified block diagram of a transmitter-receiver system consistent with the principles of the invention. 
         FIG. 1B  illustrates a block diagram of a transmitter utilizable in the transmitter-receiver system of  FIG. 1A , according to one embodiment of the invention. 
         FIG. 2  is a detailed schematic of the transmitter of  FIG. 1B , according to one embodiment of the present invention. 
         FIG. 3  illustrate a schematic of one embodiment of one aspect of the transmitter of  FIG. 1B . 
         FIG. 4  illustrate a schematic of one embodiment of another aspect of the transmitter of  FIG. 1B . 
         FIG. 5  illustrates a flow diagram of a process for utilizing the transmitter of  FIG. 1B , according to one embodiment of the present invention. 
         FIGS. 6A-6C  is a flow diagram of one embodiment for programming a transmitter consistent with the principles of the present invention. 
         FIGS. 7A-7B  illustrates a flow diagram of a data transmission process between a transmitter and receiver, according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention comprises a transmitter that is programmable to transmit one or more device codes, using one or more transmission formats, at one or more transmission frequencies to control one or more respective devices. In one embodiment, the transmitter includes a controller and memory for storing receiver transmission values, wherein the stored transmission values may include multiple device codes and transmission formats. In another embodiment, the transmitter has a read-to-match mode and a transmission mode. While in the transmission mode, the transmitter may load a set of transmission values and corresponding transmission frequencies into a memory from an internal storage, where the set of transmission values and corresponding transmission frequencies loaded correspond to a specific input by a user. In one embodiment, a signal based on the transmission values and corresponding transmission frequencies is then transmitted to operate one or more desired receivers. In another embodiment, the stored transmission values may be used to operate both fixed-code type receivers and rolling-code type receivers. It should be appreciated that the transmitter may also be a transceiver. 
     Another aspect of the invention is to provide a transmitter having a read-to-match mode, wherein the transmission values in a sampled signal may be compared and matched to the transmission values stored in a memory of the transmitter. Upon matching the transmission values in the sampled signal to one of a plurality of stored transmission values, a selected switch on the transmitter may be programmed to actuate a receiver which is responsive to the transmission values in the sampled signal. 
     Yet another aspect of the present disclosure is to enable the transmitter to correct or fine tune a transmission frequency at which the transmission values are being sent by comparing the transmission frequency to a reference frequency. 
     Referring now to the figures, and specifically to  FIG. 1A , illustrating a system diagram of a transmitter  100  that can transmit multiple device codes using multiple transmission formats or protocols, at multiple transmission frequencies. One or more receivers  105  are adapted to receive the signals  102  from the transmitter  100 , interpret the signals and produce an output signal to drive a corresponding utility device  110 . The transmitter  100  of the invention is programmable to transmit one or more rolling device codes or fixed device codes using one or more transmission formats at one or more frequencies. Additionally, the transmitter  100  includes multiple switches (e.g., 4) that can be assigned to control multiple utility devices  110  via receivers  105 . Thus, each switch can be assigned to transmit a signal having any combination of a device code, transmission format, and transmission frequency. In one embodiment, the transmission format is a pulse-code modulation pattern. However, in alternative embodiments, the transmission format may be any known transmission pattern, for example, frequency shift keying, pulse amplitude modulation, pulse width modulation, or a rolling code modulation pattern. 
     In a representative utilization, the transmitter  100  is a remote control device which can be used with a receiver  105  as part of a garage door opening system. In this representative utilization, the corresponding utility device  110  may be the garage door mechanism, including the motor, drive mechanism, lighting apparatus and/or the like. For example, the utility device  110  opens or closes a garage door when activated by a corresponding receiver  105  upon receipt of the appropriate signal from the transmitter  100 . While a garage door opening mechanism is illustrative, many other types of utility devices may be controlled by such remote transmitter-receiver system such as gates, light systems, security systems, etc. In another embodiment, the transmitter  100  is a transceiver. 
     When activated, the programmable transmitter  100  generates a signal  102  having a predetermined transmission frequency and a unique data transmission format, where the timing parameters and modulation characteristics related to encoded data are unique to the design of the particular transmitter. As mentioned above, one or more receivers  105  are adapted to receive and decode the signals generated by the transmitter  100  to actuate a corresponding utility device  110 . In one embodiment, the transmitter  100  and the receivers  105  transmit and receive at a single transmission frequency, using a single data transmission format. In alternative embodiments, multi-format and/or multi-frequency systems may be implemented. As will be discussed in more detail below, the transmission frequency at which the signal is sent may be adjusted or fine tuned so as to ensure that the signal  102  is being sent at the expected frequency. 
       FIG. 1B  is a block diagram depicting a transmitter  100 , according to one embodiment. Referring to  FIG. 1B , the transmitter  100 , which may also be referred to a transceiver, includes a processor  115 , a memory  120 , which includes a random-access memory (RAM)  125  and a read-only memory (ROM)  130 . The processor  115  may take any form, such as a microprocessor, microcontroller, digital signal processor (DSP), reduced instruction set computer (RISC), application specific integrated circuit (ASIC), and the like. ROM  130  may include one or more of flash memories, electrically erasable programmable read-only memory (EEPROM) and non-volatile RAM (NVRAM). The ROM  130  may store the program that controls the processor  115 , as well as other information including, but not limited to, (i) values representative of the pre-selected transmission frequencies, (ii) values representative of data transmission formats, (iii) device codes, (iv) rolling code settings, etc. 
     The transmitter  100  further includes input(s)  135 , which may include an alphanumeric keypad, buttons or other known means of input. Transmitter  100  further includes light emitting diodes (LEDs)  140  and  145 . In another embodiment, however, LEDs  140  and  145  may be replaced or supplemented with any type of known display device, including a liquid crystal display (LCD) screen (not shown). The transmitter of  FIG. 1B  further includes a transmission circuit  150 , which is connected to the processor  115  via a digital-to-analog converter (DAC)  155 . It should be appreciated that the transmitter  100  may further include a portable battery or other power source (not shown) which powers the transmitter  100  upon actuation of an input. 
     The transmission circuit  150  includes a voltage-controlled oscillator (VCO)  160  and antenna  165  for transmitting signal  102  to receivers  105 . The processor  115  may produce a digital signal, which is converted to an analog voltage by DAC  155 . The output from the DAC  155  may then be applied to tune VCO  160  to a desired frequency. The VCO  160 , working in conjunction with antenna  165 , may then be used to provide signal  102  to one or more of the receivers  105  for controlling the utility devices  110 . In another embodiment, the transmission circuit  150  may be operable to transmit infrared (IR) signals. 
     While the present disclosure refers to transmitter  100  as being a transmitter, it should equally be appreciated that transmitter  100  may be a transceiver. To that end, transmitter  100  may further include a receiving circuit  170 , comprised of an antenna  177 , broadband receiver  175  and a wave shaper circuit  180 . In one embodiment, the broadband receiver  175  receives an RF signal from a template transmitter  185  using antenna  177 . A sample of the signal received by the broadband receiver  175 , which may also include a wide-band pre-scaler circuit and an amplifier, is then provided to the input of the wave shaper circuit  180 . The wave shaper circuit  180 , whose output is coupled to the processor  115 , may then wave shape and level shift the received sample signal so as to enable accurate reading of the signal by the processor  115 . 
     The input  135  may include a plurality of keys or switches which may be programmed to correspond to a particular transmission format. The processor  115  may be programmed to store the transmission format corresponding to the keys of input  135  in memory  120 . Once a given input  135  is programmed with a device code, modulation pattern, and data transmission frequency, actuation of the switch causes the processor  115  to retrieve the values from RAM  125  and/or ROM  130  and generate a pulse-modulated signal or FSK signal using the programmed modulation pattern at the programmed transmission frequency. 
     When data transmission is activated, the processor  115  retrieves the device identification code, transmission format, and values representative of a transmission frequency, assigned or associated with the switch pressed, from ROM  130 . The processor  115  outputs values to the DAC  155  to control the VCO  160  to generate the transmission frequency. Consequently, a signal  102  is transmitted with the desired device code and modulation pattern, with a desired transmission frequency. 
     As discussed above, the ROM  130  may be used to store one or more transmission formats for operating one or more respective rolling code receivers or fixed code receivers. The stored transmission formats may further include any number of fixed code formats, including a pulse-width modulated (PWM) format or a frequency shift key (FSK) format. 
     The stored transmission formats may further include a Type A rolling code format and/or a Type B rolling code format. On one embodiment, the Type A and Type B rolling code transmission formats may be the rolling code formats used Chamberlain® brand rolling code transmitter-receiver systems and Genie® brand rolling code transmitter-receiver system. U.S. Pat. No. 6,956,460, entitled “Transmitter for Operating Rolling Code Receivers,” which is assigned to the assignee hereof and hereby incorporated by reference, discloses a method for using a set of fixed codes to operate a rolling code receiver. This set of fixed codes, along with the device code, modulation pattern and transmission frequency, may comprise the transmission format for a rolling code transmitter. 
     Transmitter  100  further includes a data code circuit  190 , which may be comprised of a plurality of dual in-line package (DIP) switches and/or a pin pad. A number of transmitter-receiver systems determine their modulation patterns by setting a plurality of DIP switches on the transmitter and by similarly setting a plurality of DIP switches on the corresponding receiver. In this manner, a device code, in the form of a particular DIP switch or pin pad setting, may be used to program a transmitter to be able to communicate with a particular receiver and vice versa. For convenience this DIP switch or pin pad setting will be referred to herein as the device code or the device code setting. While the data code circuit  190  may be operated by processor  115 , the data code circuit  190  settings may also be manually adjusted. In one embodiment, manual adjustment of DIP switches of the data code circuit  190  may be made to set the device code setting for transmitter  100  to correspond to the settings of one of receivers  105 . 
     Finally, receiving circuit input  195  provides the processed sample signal from receiving circuit  170  to processor  115 . 
     Referring now to  FIG. 2 , in which a detailed schematic of transmitter  100  is illustrated.  FIG. 2  shows processor  115  coupled to data code circuit  190 , memory  120 , input  135 , DAC  155  and voltage regulator  157 . In addition, processor  115  is coupled to receiving circuit input  195 , through which sampled signals are provided to the processor  115 . 
       FIG. 3  is a schematic of broadband receiver  175 . Broadband receiver  175 , using antenna  177 , receives an RF signal and passes it to wave shaper  180 , as shown in  FIG. 4 . After processing the received signal, wave shaper  180  provides the signal to processor  115 , via receiver circuit input  195 . It should be appreciated that the received signal may be further processed by other components known in the art, such as an amplifier, before it is provided to the processor  115 . 
     Referring now to  FIG. 5 , in which a process  500  for utilizing transmitter  100  is depicted. The process begins when transmitter  100  is powered on at block  505 . In the embodiment of  FIG. 5 , this is indicated by illuminating red LED  140 . However, it should be appreciated that any number of known means of indication may be used. A determination is then made at decision block  510  as to whether there has been a user input. In one embodiment, the decision block  510  determines if a user has activated input  135 , which may comprise one or more buttons or keys. Once a user input is detected, a determination is made at block  515  as to whether the input exceeds a predetermined time. In one embodiment, this determination is based on how long a user holds down a key/button on input  135 . The predetermined time is 5 seconds, in one embodiment, but may be longer or shorter period of time. For present discussion purposes only, it will be assumed that input  135  has input keys  1 -N, where N is any positive nonzero integer. However, it should be appreciated that other input means may also be used, including, but not limited to, a touch screen, voice activation, etc. 
     If the input does not exceed the predetermined time, then the process of  FIG. 5  continues to block  520  where the transmitter enters Data Transmission Mode. If, on the other hand, the input does exceed the predetermined time, then this is an indication that the user desires to enter Read-to-Match Mode and the process continues to block  525  to enter Read-to-Match Mode. 
     Assuming that there has been an input exceeding the predetermined time at block  515 , entry into the Read-to-Match Mode is indicated at block  605  on  FIG. 6A  when the green LED  145  begins to flash, according to one embodiment. The Read-to-Match process  600  then initializes a timeout timer at block  610 . In one embodiment, the timeout timer is used to exit the Read-to-Match Mode after a predetermined timeout period. In one embodiment, this predetermined timeout period is 8 seconds, although it should be appreciated that the timeout period may be a longer or shorter period of time. 
     Process  600  continues with decision block  615 , where a determination is made as to whether process  600  has timed out (e.g., whether the predetermined timeout has elapsed). If so, process  600  continues to block  620  where the transmitter may be powered off and/or the selected input key may be set to a predetermined transmission format. In one embodiment, the predetermined transmission format is a rolling code format, such as the rolling code format provided by Skylink, of Ontario, Canada. In one embodiment, the predetermined transmission formats are based on inputs to the data code circuit  190 . 
     Where decision block  615  determines that the timeout period has not elapsed, process  600  continues to decision block  625 , where a determination is made as to whether a signal from a template transmitter  185  has been detected. It should be appreciated that the template transmitter  185  may be any rolling code or fixed code transmitter that, when activated, transmits a signal  102  which may then be received by receiving circuit  170 . In particular, the received signal may be received by broadband receiver  175  and, thereafter, provided to wave shaper  180 , as previously discussed. 
     Once a signal is detected, the signal may be sampled and temporarily held in memory at block  630 . In one embodiment, the sampled signal is held in RAM  125 . It should be appreciated that any known means of sampling a RF signal may be used. Once the signal sampling has been completed (as determined by block  635 ), process  600  continues to  FIG. 6B . 
     Referring now to  FIG. 6B , process  600  continues with a determination, at block  640 , as to whether the sampled signal corresponds to the signal of a Type A rolling code system. If so, process  600  continues to block  645  where the selected key on input  135  is set to the Type A rolling code format. Alternatively, if it is determined at block  640  that the signal sample does not correspond to the Type A rolling code format, then process  600  continues to decision block  650 . At decision block  650 , a determination is made as to whether the signal sample is of the Type B rolling code format. If so, then process  600  continues to block  655  where the selected key on input  135  is set to correspond to the Type B rolling code format. As mentioned previously, in one embodiment Type A and Type B rolling code formats refers to the Chamberlain® brand rolling code format and the Genie® brand rolling code format. 
     When a determination is made that the sample signal is of either the Type A or the Type B rolling code format, the selected key is set to that appropriate rolling code format. In one embodiment, setting an input key to a particular format consist of programming the selected key, of input  135 , to be a reference pointer to preloaded data in memory  120 . Thus, in the case of the rolling code formats, the selected key is set to pre-loaded rolling code data in memory  120 , where the rolling code data consists of modulation pattern data, frequency data, code setting data, and other code data, as described in U.S. Pat. No. 6,956,460, entitled “Transmitter for Operating Rolling Code Receivers,” for activating a corresponding rolling code receiver. Process  600  would then continue to  FIG. 6C , as will be discussed below in more detail. 
     If, on the other hand, a determination is made at decision block  650  that the signal sample is not of the Type B rolling code format, then process  600  continues to block  660 , where a determination is made as to whether the signal sample is in a predetermined type of fixed code format. In one embodiment, the signal sample is checked to see if it is a pulse-width modulated (PWM) signal. If so, then process  600  may continue to block  665 . At block  665 , signal data may be loaded from ROM  130  into RAM  120 . A comparison may then be undertaken to determine if the signal sample corresponds to any of the pre-loaded signal formats stored in transmitter  100  (block  670 ). Once a match is found, the selected key is set to the matching signal format in memory  120  at block  675 . In addition, where it is determined that the sample signal is a frequency shift key (FSK) signal, the input key may set automatically set to refer to FSK signal data in memory  120 . 
     Alternatively, if no match is found for the sampled signal or the sampled signal is not a fixed code signal, as determined at block  660 , then process  600  continues to block  680 . At block  680 , the transmitter may be powered down or, alternatively, the selected key may be set to a default code format. In one embodiment, the default code format us the FSK format, while in an another embodiment the default format is the Skylink rolling code format. 
     At this point, process  600  proceeds to block  685  of  FIG. 6C . At block  685 , any device code information in the sampled signal is identified. As discussed previously, the device code information represents the DIP switch or pin pad settings of a transmitter-receiver pair. Such device code data is then saved to memory, which in one embodiment is ROM  130  (block  690 ). At this point, process  600  is complete and the transmitter exits the Read-to-Match Mode at block  695 . 
     Referring now back to block  515  of  FIG. 5 , if the user input does not exceed the predetermined time, then process  500  would continue to block  520 , where Data Transmission Mode would be entered and Data Transmission process  700  of  FIG. 7A  would begin. As seen in  FIG. 7A , Data Transmission process  700  begins with the identification of which input key was pressed (block  705 ). In one embodiment, a user selects an input key by selecting one of the keys on input  135 . Where the user desires to activate a particular receiver, the user selection would correspond to an input key which has previously been programmed to activate the desired receiver. In one embodiment, the selected input key was programmed using the Read-to-Match process  600 , while in another embodiment the input key was pre-programmed during manufacture. 
     Assuming that the user has selected to enter Data Transmission Mode by not exceeding the predetermined input time at block  515 , the process continues with  FIG. 7A . In particular, at block  705  a determination is made as to which key of input  135  was selected by the user. In one embodiment, each of the input keys  1 -N on input  135  is programmable to generate a desired device code, using a desired modulation format, at a desired transmission frequency. Thus, the input keys can be used in conjunction with N different receivers  105  to control N different utility devices  110 . For example, where there are four input keys on input  135 , input keys  1  and  2  may be programmed to control two different garage door openers, input key  3  may be programmed to arm/dis-arm a security system, and input key  4  may be used to control a gate. Alternatively, more than one key may be used to control different features of a utility device  100 . For example, input keys  1  and  2  may be programmed to control different zones of an alarm system, and input keys  3  and  4  may be used to control different lights within a dwelling. Many other embodiments exist for programming and usage of the input keys  1 -N. 
     Continuing to refer to  FIG. 7A , once the selected input key is determined at block  705 , the corresponding modulation pattern and frequency may be identified at block  710 . A determination should also be made as to whether there is a device code stored in memory  120  for the selected input key (block  715 ). If there is a stored device code for the selected input key of input  135 , this value may be loaded into RAM  125  at block  720 . If alternatively, there is no device code in memory corresponding to the selected key, then a user may be prompted to manually enter the device code via data code circuit  190  (block  725 ). As mentioned previously the device code may be set using the data code circuit  190 , which may include a series of DIP switches or a pin pad. 
     Thereafter, the transmission values, such as the modulation pattern and frequency, are loaded into RAM  125  at block  730 . It should be appreciated, however, that the transmission values of block  730  may also be accessed and loaded prior to the device code of block  720 . In any event, the transmission values may then be used to tune the VCO to the desired frequency or frequencies at block  735 . 
     The process of  FIG. 7A  continues to block  740  on  FIG. 7B , where the transmission format, including the modulation pattern, corresponding to the selected input key is loaded into an output buffer, which in one embodiment is part of transmission circuit  150 . It should be appreciated that, in an alternate embodiment, the output buffer may be part of memory  120 . However, for convenience, the following description of  FIG. 7B  will refer to it only as the ‘output buffer.’ 
     A bit-by-bit verification process may then be undertaken at block  745 . In particular, a bit to be provided by the transmission circuit  150  as part of the output signal  102  is checked at decision block  750 . If a determination is made that the bit is a positive bit, the timing for positive bits for the appropriate transmission format is loaded into the output buffer (block  755 ). If the bit is not a positive bit, process  700  continues to decision block  760 , where the bit is checked to see if it is a neutral bit, such as may be the case for a trinary bit format. If decision block  760  determines that the bit is a neutral bit, then process  700  moves to block  765  where the timing for neutral bits is loaded into the output buffer. Similarly, where the bit is a not a neutral bit, then the timing for negative bits is loaded at block  770 . The high pulses and low pulses (e.g., leading edge and trailing edge) for the output signal  102  are then transmitted at blocks  775  and  780  by the transmission circuit  150 . 
     Decision block  785  involved a determination of whether all bits in the signal  102  have been transmitted. If not, process  700  reverts to block  745  and the verification and loading process continues for the next bit. If, on the other hand, all bits have been transmitted then process  700  continues to block  790  where the space time is output, where space time is the separation time between data transmissions. If the Data Transmission process is to be repeated, then block  795  directs process  700  back to block  740  where the transmission format may be loaded into the output buffer. If the process is not to be repeated, then process  700  ends. 
     As mentioned previously, another aspect of the present disclosure is for the transmitter to correct or fine tune the transmission frequency at which the transmission values are being sent by comparing the transmission frequency for the transmission values to a reference frequency. As discussed above, the signal  102  sent by the transmitter  100  is comprised of the desired transmission format and is sent at one or more frequencies based on the predetermined transmission frequencies stored in memory  120 . In one embodiment, the predetermined transmission frequencies correspond to the frequencies used by particular manufacturers for particular models of receivers. 
     However, due to the potential presence of environmental factors that may tend to affect RF signal transmissions, the actual frequency at which the transmitter  100  is sending the signal  102  (or the actual frequency at which the signal  102  is being received) may not correspond to the predetermined frequency for the particular transmission format being sent. Thus, in one embodiment, the transmitter  100  compares the actual transmission frequency of signal  102  to a predetermined reference signal. While in one embodiment, the reference signal may be based on the clock frequency for processor  115 , it should be appreciated that any transmission frequency may be used. 
     The process of detecting and correcting a degraded transmission frequency begins when the transmitter  100  sends a signal  102 , comprised of the selected transmission format, at its pre-determined transmission frequency. As mentioned previously, the transmitter  100  is also a transceiver in one embodiment. Thus, in addition to having one or more of the receivers  105  receive the signal  102 , the signal  102  may also be received by the receiving circuit  170 . In one embodiment, the transmitter  100  saves the actual received frequency of the signal  102  to memory  120 . Thereafter, processor  115  may undertake to compare the frequency of the received signal  102  to the frequency of the reference signal. It should be appreciated that this comparison function may be performed in software or in hardware. When implemented in hardware, an analog-to-digital converter (“ADC”) may be used to provide a digitized signal to the processor  115 . 
     Given that the signal  102  should be received at the predetermined frequency for the selected transmission format, comparing the actual frequency of the received signal  102  to the reference frequency should produce a distinct result if there has been no signal degradation. By way of a non-limiting example, assume the reference frequency is 300 MHz and the transmission frequency of the selected transmission format is 390 MHz. In this case, a comparison of the received transmission frequency and the reference frequency should yield a net difference of 90 MHz. Thus, where the frequency comparison produces a net frequency difference of 90 MHz, no adjustment is needed since the signal  102  is being received at the correct predetermined transmission frequency. However, where the comparison yields a different result (e.g., difference of 92 MHz), processor  115  can then direct VCO  160  to adjust the transmission frequency so as to correct this detected variance. In another embodiment, rather than adjust the VCO  160 , the predetermined transmission frequency in memory  120  for the given transmission format is updated. 
     Continuing with the above example, the next time the transmitter  100  sends the particular selected transmission format, it will send it at a frequency of 388 MHz, rather than the predetermined transmission frequency of 390 MHz. As before, transmitter  100  will undertake to compare the frequency at which the transmission format is received to the frequency of the reference signal. If this comparison yields a net difference of 90 MHz, then no further adjustment instruction need be provided to the VCO  160  (or no further updating of the predetermined transmission frequency need be made). If, on the other hand, there continues to be a net difference of more or less than 90 MHz, the VCO  160  will further adjust the transmission frequency for the particular transmission format for subsequent transmission. This iterative process continues until the net difference between the transmission frequency and reference frequency converges to 90 MHz. 
     It should be appreciated that the frequencies used in this example are for illustration only. It should further be appreciated that it may be desirable to set a tolerance for the net frequency difference. In one embodiment, the tolerance is plus or minus 1 MHz. In another embodiment, the tolerance is set at between 0.1 and 1.0 MHz. If the computed net difference is within the set tolerance range, no further adjustment to the VCO  160  (or updating of the predetermined transmission frequency) will be made, according to one embodiment. 
     While the preceding description has been directed to particular embodiments, it is understood that those skilled in the art may conceive modifications and/or variations to the specific embodiments and described herein. Any such modifications or variations which fall within the purview of this description are intended to be included therein as well. It is understood that the description herein is intended to be illustrative only and is not intended to limit the scope of the invention. Rather the scope of the invention described herein is limited only by the claims appended hereto.