Abstract:
The present invention is directed to a radio designed to receive both analog and digital subchannels from radio stations that are broadcasting either an analog only signal, a digital only signal, or a hybrid signal containing both analog and digital subchannels. It allows a user to direct the radio to search for either the next active analog or digital subchannel, or alternately to ignore the analog subchannels and search only for digital subchannels. This is accomplished using a single button for either functionality when searching through incrementing frequencies. Another button may be added for decrementing frequencies with the same basic functionality. In the present invention, when the user presses the “Scan Up” button once for a short period of time, the radio will search for the next active analog or digital subchannel above the current location of the virtual channel map. But if the user presses the button twice in quick succession or holds the button down for a longer period of time, the radio will search only for the next digital subchannel above the current location in the virtual channel map.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. Provisional Application No. 60/506,707, filed Apr. 4, 2006, entitled “Method and Apparatus for Scanning for Digital Subchannels in a Hybrid Analog/Digital Broadcast,” the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to radio and television receiver technology. More specifically, it relates to a method of selecting the desired subchannel from a plurality of subchannels available on a single station.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the past, radio frequency broadcasts of audio or audio-video programming have used analog technology with a single program per carrier frequency (often referred to as a station). The advent of digital technology provided the capability to offer multiple, simultaneous programs on a single station. Some digital broadcast standards such as the in-band on-channel (IBOC) system developed by iBiquity Digital Corporation for AM and FM radio allow several completely independent, simultaneous programs to be added as digital subchannels to be added to the analog subchannel, combined into a single broadcast signal and sent out in one channel&#39;s frequency allocation.  
         [0004]     Users have grown accustomed to the model where there is a one-to-one correspondence between the programming and the carrier frequency. For radio broadcasts, they are required to tune to the actual carrier frequency to hear the station; tuning to 90.3 MHz actually sets the tuner to demodulate the carrier at 90.3 MHz. Once a digital carrier with multiple simultaneous programs is broadcast, as allowed by the IBOC standard, the tuning model must be enhanced. While a station frequency is still required, another parameter to select the desired program, or subchannel, from the plurality of programs included in the signal is also required. In the IBOC standard this would allow a station to at 90.3 MHz to have the analog subchannel, the main digital subchannel (HD-1) that usually carries the same audio program as the analog subchannel, and multiple additional subchannels (HD-2, HD-3, . . . HD-7). Most receivers insert the added subchannels as virtual channels between the analog channels. For example, if the user hits the “Tune Up” button while listening to a radio station at 90.3 with three subchannels called main program, HD-2 and HD-3, many IBOC compatible radio receivers will tune from the main program at 90.3 to 90.3 HD-2 and then to 90.3 HD-3 before tuning to 90.5.  
         [0005]     Many radios also have a “Scan” functionality that allows the user to tell the radio to find the next active channel instead of requiring the user to manually direct the radio to tune to each possible frequency sequentially. When the “Scan Up” button is pressed on such a radio, the radio will start automatically checking each possible frequency allotment to see if there is an active carrier signal starting from the currently tuned frequency. It will keep incrementing the frequency until it finds an active carrier. It will then stop incrementing the frequency and play the station that it finds. This provides an easy way for the user to rapidly scan through the choices that are available to him. Some radios supporting the IBOC standard add the digital subchannels into their virtual channel map so that if a user is tuned to the radio station at 90.3 MHz described above, hitting the “Scan Up” button causes the radio to change from the main program at 90.3 to 90.3 HD-2 and then to 90.3 HD-3 before starting to scan for an active analog carrier at 90.5 MHz or above. There is no method in existing scan buttons to skip analog subchannels and have the radio scan only for digital subchannels  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a radio designed to receive both analog and digital subchannels from radio stations that are broadcasting either an analog only signal, a digital only signal, or a hybrid signal containing both analog and digital subchannels. It allows a user to direct the radio to search for either the next active analog or digital subchannel, or alternately to ignore the analog subchannels and search only for digital subchannels. This is accomplished using a single button for either functionality when searching through incrementing frequencies. Another button may be added for decrementing frequencies with the same basic functionality. In the present invention, when the user presses the “Scan Up” button once for a short period of time, the radio will search for the next active analog or digital subchannel above the current location of the virtual channel map. But if the user presses the button twice in quick succession or holds the button down for a longer period of time, the radio will search only for the next digital subchannel above the current location in the virtual channel map. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a block diagram of an exemplary radio broadcast station suitable for generating a signal to be used by the present invention  
         [0008]      FIG. 2  is a representation of an exemplary radio receiver capable of utilizing the present invention.  
         [0009]      FIG. 3  is a block diagram of a radio receiver utilizing the present invention.  
         [0010]      FIG. 4  is a more detailed block diagram of the preferred embodiment of a radio receiver utilizing the present invention.  
         [0011]      FIG. 5  is a block diagram of the functions implemented in the firmware running on the Digital Signal Processor in the preferred embodiment of a radio receiver utilizing the present invention.  
         [0012]      FIG. 6  is a flow-chart diagram of the present invention.  
         [0013]      FIG. 7  is a flow chart diagram of the preferred embodiment of the present invention.  
         [0014]      FIG. 8  is a diagram showing the how the two different scanning behaviors would tune through a set of available radio stations. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Reference will now be made to the accompanying drawings to further describe the preferred embodiment of the present invention. While the invention will be described in light of the preferred embodiment, it will be understood that it is not intended to limit the invention to those embodiments. The invention is intended to cover all modifications, alternatives or equivalents which may included within the spirit or scope of the invention as defined by the appended claims.  
         [0016]     The following detailed descriptions give many specific details in order to provide a thorough understanding of the present invention. It will be recognized by one of ordinary skill in the art that the present invention may be practiced without those specific details. In other cases, well known methods, processes and techniques have not been described in detail so as not to obscure aspects of the present invention.  
         [0017]     Referring now to  FIG. 1 , a radio broadcast station  100  is broadcasting a radio signal  108  comprised of several programs  101 . These programs  101  can consist of news, sports coverage, talk, music or any other type of audio information. In this particular embodiment which is consistent with the FCC approved in-band on-channel (IBOC) system developed by iBiquity Digital Corporation, there is a single analog audio program “A”  110  that is modulated onto a carrier signal by the analog modulator  104  as the analog subchannel, amplified to a high power signal by the transmitter  106  and broadcast through the antenna  107 . In this exemplary embodiment of a radio station  100 , the analog modulator  104  uses frequency modulation (FM) on a 87.9 to 109.9 MHz carrier or amplitude modulation (AM) on a 540 to 1700 kHz carrier to generate a signal compatible with readily available AM/FM radio receivers in the United States.  
         [0018]     In this embodiment, the analog program “A”  110  is converted to the first digital subchannel  111  by the analog to digital converter (ADC)  102 . The main digital subchannel  111  contains the same audio program as analog program “A”  110  but in a digital form. The exemplary radio station  100  can also include additional programs  101  encoded as digital subchannels which are shown in  FIG. 1  as digital subchannel “2”  112 , digital subchannel “3”  113  and digital subchannel “N”  114 . The total number of digital subchannels available on a radio broadcast station  100  may be limited by the particular implementation. The IBOC system allows for up to 8 total digital subchannels to be included on a single station. Further discussion will assume that a station includes three digital subchannels, the main digital subchannel  111 , digital subchannel “2”  112  which is sometimes referred to as HD-2 and digital subchannel “3”  113  which is sometimes referred to as HD-3. Digital subchannel “N”  114  is shown to illustrate that more than three digital subchannels may be allowed. These digital subchannels  111 - 114  can be simple pulse-code modulated (PCM) data or, more commonly, they are compressed using a lossy compression algorithm such as the High Definition Codec (HDC) algorithm used in the IBOC system.  
         [0019]     The entire set of digital subchannels  111 - 114  are then combined into a single digital stream  109  by the multiplexer  103 . There are many variations of how the digital subchannels  111 - 114  can be combined to provide for error robustness and correction but in its simplest form, the multiplexer  103  takes time slices of each digital subchannel  111 - 114  and combines them into a single, higher-speed, digital stream  109  using time-domain multiplexing. The digital stream  109  is then modulated by the digital modulator  105 . In this exemplary embodiment, this modulation is accomplished by using orthogonal frequency domain multiplexing (OFDM) which employs a large number of narrowband subcarriers located in the sidebands of the analog carrier frequency but other technology could be used. The output of the digital modulator  105  is then combined with the output of the analog modulator  104  and amplified by the transmitter  106 . The combined signal is then transmitted as the IBOC radio signal  108  by the antenna  107 .  
         [0020]     While the analog audio program  110  can be recovered from the radio signal  108  by a standard AM/FM receiver simply by tuning the receiver to the proper frequency, additional functionality must be included in the receiver to be able to recover a digital stream.  FIG. 2  provides a view of the MultiStream™ HD receiver from Radiosophy as an exemplary receiver  200  capable of an audio program recovered from a digital subchannel in the IBOC radio signal  108 . It includes a power switch  207 , an antenna  209  for receiving the radio signal  108 , a display  201  for identifying the currently selected frequency and other textual information, a button  202  for selecting whether to tune the 540-1700 kHz AM band or the 87.9-107.9 FM band and a button  203  for selecting a menu function in the receiver. It also includes two methods for selecting which frequency to tune. Tuning switch  204  allows the user to step through the selected frequency band to all allowable frequency locations. It will step up or down through the band by 10 kHz steps if the AM band is selected and by 200 kHz steps if the FM band is selected. Scanning switch  205  tells the radio to tune to the next active frequency. It can be rocked up to indicate that the radio should search up through the virtual channel map to find the next active subchannel or it can be rocked down to indicate that the radio should search down through the virtual channel map to find the next active subchannel. The tuning switch  204  and scanning switch  205  will also step sequentially through the available digital subchannels in the IBOC radio signal  108 . The radio  200  also includes a set of preset buttons  208 . These buttons allow the user to store a frequency and subchannel identifier to be associated with each button allowing the user to rapidly select the same frequency and subchannel in the future.  
         [0021]     The radio receiver  200  may also include a remote control  210 . This remote control  210  may include a power button  217 , tuning buttons  214 , scanning buttons  215  and preset buttons  218 . It might include other buttons as well. When a button is pressed on the remote control, a specific code sent to the infrared (IR) transmitter  216  causing modulated IR radiation  220  to be emitted. The infrared window  206  on the radio receiver  200  allows the modulated IR radiation  220  to enter the case where it can be received and interpreted. The radio  200  then interprets the specific code to determine which button on the remote control  210  was pressed. It then performs the same action as if the corresponding button on the radio  200  was pressed.  
         [0022]      FIG. 3  shows a simplified, high-level block diagram  300  of the radio receiver  200 . It includes the antenna  209  that feeds the radio signal  108  to the receiving circuitry  302 . The receiving circuitry  302  tunes to the selected frequency, demodulates the signal and feeds it to the demultiplexer (demux)  303 . The demux  303  selects desired digital subchannel from the signal based on the selected subchannel and passes it to the amplifier  305  which drives the speaker  306  to generate the audio program for the listener. Control Circuitry  307  can interpret user input from a scan switch  308 , and control the receiving circuitry  302 , the demux  303  and amplifier  305  to allow the user to select the desired program.  
         [0023]     A more detailed block diagram  400  of the preferred embodiment of the radio receiver  200  is shown in  FIG. 4 . All the elements of the simplified block diagram  300  are present in the detailed block diagram  400  although there is not necessarily a one-to-one correspondence for all the blocks. The receiving circuitry  302  is implemented by the tuner module  401 , analog to digital converter (ADC)  402  and firmware running in the digital signal processing subsystem (DSP)  403 . The tuner module  401  converts the selected carrier frequency to an intermediate frequency signal that is passed to the ADC  402  where it is digitized before being fed into the DSP  403 . The demux  303  is implemented as one of several functions of the firmware in the DSP  403  and the amplifier  305  is comprised of the digital to analog converter (DAC)  404  and analog amplifier  405 . Control circuitry  307  is implemented as firmware running in the microprocessor (μProc)  407  and the scan switch  308  is implemented as scan up switch  408  in a switch matrix  410 . Block diagram  400  shows some additional detail including a display  201 , a scan down button  409  in the switch matrix  410  and an IR receiver  406  that is positioned behind the IR window  206 . Scan up and down switches  408  and  409  are the up and down position of the scanning switch  205 .  
         [0024]     In the preferred embodiment, the tuner module  401  is a TDGA2X010A from Alps Electric Ltd., the ADC  402  is an AFEDRI8201 from Texas Instruments, the DAC  404  is a PCM 1782 from Texas Instruments and the analog amplifier  405  is a TDA8567Q from Philips Semiconductors. The display  201  is a 128×64 dot LCD with backlight such as a BF-MG12864DLBS-19C-1 from Bona Fide Technology Ltd. and the IR receiver  406  is a MIM-5385K1 F from Unity Opto Technology Company Ltd. The DSP  403  is implemented using a TMS320DRI350 Digital Baseband for HD Radio chip from Texas Instruments connected to a 32 Mbit Flash ROM used to store firmware instructions and a 64 Mbit SDRAM to be used for working memory. The μProc  407  is implemented using a PIC18F4550 integrated microcontroller from Microchip Technology Inc. that has 32 kbytes of non-volatile program memory and 2 kbytes of random access memory (RAM). The μProc  407  controls the tuner module  401 , the ADC  402 , the DSP  403 , the DAC  404  and the analog amplifier  405  using combination of dedicated general purpose I/O lines and an I 2 C bus. The μProc  407  runs software instructions, or firmware, that have been stored in the internal non-volatile program memory allowing it to scan the switch matrix  410  to determine whether scan up switch  408 , scan down switch  409 , or any other buttons on the radio  200  have been pressed. The firmware running in the μProc  407  can also interpret the output of the IR receiver  406  to determine if a button on the remote control  210  has been pressed. Whenever a scan switch is activated, the μProc  407  detects which button is pressed, and then scans up or down through the virtual channel map by controlling the tuner module  401  and DSP  403 .  
         [0025]     A block diagram of the firmware  500  running on the DSP  403  is shown in  FIG. 5 . The digitized intermediate frequency data  510  is passed to the analog demodulator  501  firmware block and the digital demodulator  502  firmware block. These blocks perform digital signal processing algorithms on the incoming data  510  to determine if a valid analog and/or digital signal is available. This information is then made available to the μProc  407  to use to decide whether to continue scanning or to stop at the current frequency. If the analog program is to be selected, the analog modulator  501  is commanded to start fully demodulating the incoming data  510  to digital audio data  511  which is then passed to the output selector  505 . In the preferred embodiment, the analog demodulator  501  firmware block has the ability to demodulate either an AM or FM signal at the command of the μProc  407 . The μProc  407  also commands the output selector  505  to select the digital data  511  representing the analog audio program to be the digital audio output  515  to send to the DAC  404 .  
         [0026]     If a digital subchannel is to be selected, the μProc  407  commands the digital demodulator  502  to start fully demodulating the digital data  512  from the incoming digitized intermediate frequency data  510 . In the preferred embodiment, the digital demodulator  502  firmware block implements an algorithm to extract the digital data  512  from an OFDM signal. The extracted digital data  512  is then passed to the demultiplexer  503  firmware module. The demultiplexer  503  may perform error correction on the data. Then, based on the desired subchannel, the μProc  407  will command it to extract an individual digital subchannel  513  from the demodulated digital data  512 . In the preferred embodiment, there is information embedded in the digital data  512  to tag each block of data as being associated with a particular individual digital subchannel. In an alternative embodiment, the individual digital subchannels are simply time domain multiplexed with a pre-determined data block size so that a given data subchannel is made up of a block of “A” bits with “B” bits skipped before the next block of relevant data is found. The exact scheme required is determined by the method used at the broadcast location to multiplex the data and one skilled in the art could apply many different methods to accomplish the same task of extracting an individual digital subchannel  513  from the digital data  512 .  
         [0027]     If the selected individual digital subchannel  513  consists of compressed audio it will need to be decoded. The decoder  504  firmware block implements the appropriate algorithms to decompress the individual digital subchannel  513  into an uncompressed digital audio stream  514 . In the preferred embodiment the decoder  504  implements a the High Definition Coded (HDC) as defined by the IBOC system but many different compression schemes could be used or, if the individual digital subchannels consist of uncompressed PCM audio data, the decoder  504  could pass the data through untouched. The output selector  505  is then commanded to select the uncompressed digital audio stream  514  as the digital audio  515  to send to the DAC  404 .  
         [0028]     Referring now to  FIG. 6 , which shows a flow chart  600  of the present invention, the radio  200  is powered on at  601  and it selects the last stations and subchannel played before being turned off at  602  to play again at  603 . The radio  200  then waits for a scan command. It determines which type of scan command was received at  604 . In the preferred embodiment, the scan command is a press of a scan button  205  and there are two ways that the user may actuate it. The first way is for the user to press it once for less than a predetermined length of time. In the preferred embodiment, the predetermined length of time is one second. If the user presses the scan button  205  in the first way, the radio will search for the next active subchannel of any type and select it at  605 . It will then play the audio program contained in that subchannel at  603 .  
         [0029]     The second way the user can actuate the scan button  205  is to press it twice quickly within the predetermined length of time or to press and hold it for the entire predetermined length of time or some other method to differentiate the second way from the first way. In the preferred embodiment, the user should press the scan button  205  twice within one second to indicate the second way. If the second way is indicated, the radio  200  will search for the next available digital subchannel and select it at  606 . It will then play the audio program contained in that subchannel at  603 . It should be noted that it may be necessary for the radio to look for the presence of the analog subchannel (or analog carrier frequency) to be able to determine whether to attempt to look for a digital subchannel. The fact that the radio must look for the presence of the analog subchannel does not preclude it from only playing the audio content of the digital subchannels and not subjecting the user to the lower quality content from the analog subchannels.  
         [0030]     Flow chart  700  in  FIG. 7  describes the preferred embodiment in more detail. The radio  200  is turned on at  701  and selects that last station and subchannel “N” played at  702  where “N” refers to a logical subchannel. The logical subchannel can refer to the analog subchannel (N=0), the main digital subchannel (N=1) or other digital subchannels (2≦N≦8 for the IBOC system). It starts to play the audio program from the selected station and subchannel “N” at  703 . When the user presses the scan button, the radio will determine if there is a digital carrier containing digital subchannels on the currently selected station and determine whether there is another logical digital subchannel “N+1” available at  704 . If there is, it will select subchannel “N+1” at  705  and play the new audio from that subchannel at  703 . If there is no digital carrier or if logical subchannel “N+1” is not available on this station when the scan button is pressed, the radio  200  will mute the audio output and begin to search through the possible carrier frequencies at  706  looking for a modulated carrier with enough signal strength to allow it to be received and selects it. When it finds an active carrier signal, it will determine whether the scan was a short single press at  707  indicating that both analog and digital subchannels should be searched. If it is a short single press, the radio selects the analog subchannel of the selected carrier at  709 . It then unmutes and plays the audio program at  710 . It then looks for a digital subcarrier on the selected frequency at  711  to see if there are any digital subchannels. If there are not, it continues to play the analog subchannel at  703  and waits for the next scan command. If there are digital subchannels available, the radio will switch to the first digital subchannel at  712 . This is a standard function within the IBOC system as the first digital subchannel has the same audio program as the analog subchannel and the radio is required to blend over from the analog subchannel to the first digital subchannel automatically to give the user the benefit of the improved sound quality of the digital signal. Once the first digital subchannel has been selected, the radio  200  continues to play the audio at  703  and waits for the next press of the scan button.  
         [0031]     If the press of the scan button was not a short single press but was instead a long press or a double-press, the radio  200  will detect this at  707  as an indication that the user wants to find the next available digital subchannel and it should ignore all analog subchannels. It will then look for a digital subcarrier on the newly selected carrier at  708 . If it does not find a digital subcarrier, it will start scanning for the next carrier frequency with a strong enough signal to be received at  706 . When it finds that next carrier frequency, it will remember that the scan was a digital only scan request at  707  and look for the digital subcarrier again at  708 . It will keep doing this until a carrier frequency with a digital subcarrier is found. Once that happens, the radio  200  will select the first digital subchannel on that frequency at  712  and then unmute and play the audio program on that subchannel at  703 .  
         [0032]     There may also be delays required to allow the radio  200  time to find the next subchannel. There is a finite amount of time required for the radio to evaluate each possible carrier frequency to see if it has a receivable signal and once a receivable signal has been found, additional delays may be required to determine whether a digital subcarrier is available on that station. The delays are not explicitly discussed here as one skilled in the art can determine the exact delay required for the specific implementation.  
         [0033]     The possible carrier frequencies to be scanned depends on what type of radio signals are to be received by the radio  200 . In the preferred embodiment, the radio can receive either FM signals at a carrier frequency in the range of 87.9 to 109.9 MHz, incrementing by 200 kHz or AM signals with a 540 to 1700 kHz carrier incrementing by 10 kHz. The radio could either scan up or down through the selected frequency range and in the preferred embodiment, has two different scan switches  408  and  409  that can be actuated by rocking the scan button  205  either up or down to let the user indicate which direction to scan. It also will treat the frequency range as a circular range so that if it is scanning up and it hits the top of the range, it will continue to look again from the bottom of the range. It likewise will continue from the top when it hits the bottom if scanning down.  
         [0034]      FIG. 8  shows represents for different radio stations and assumes that those four stations are the only stations available to the radio  200 . The first station  810  is broadcasting at 89.1 MHz and has an analog subchannel  818  with no digital subchannels. The second station  830  is broadcasting at 90.3 MHz and has an analog subchannel  838 , an HD-1 digital subchannel  831  containing the same audio program as the analog subchannel  838 , an HD-2 digital subchannel  832  and an HD-3 digital subchannel  833  with different audio programs. The third station  850  is contains a single analog subchannel  858  and is broadcasting at 91.5 MHz and the fourth station  870  is broadcasting at 92.7 MHz with an analog subchannel  878  and a single digital subchannel  871  containing the same audio content.  
         [0035]     The differently styled lines indicated the action taken by the radio  200  in response the scan up button being pressed. The radio will automatically switch from the analog subchannel to the first digital subchannel when a digital carrier is detected. This is indicated by arrow of type  804 . An example of this transition are changing from the analog subchannel  838  to the HD-1 subchannel  831  of the second station  830 . This type of transition occurs automatically with no intervention from the user. If the user presses the scan up button for a single/short press, transitions as shown by line of the type  802  occur. This indicates that the user wishes to go to the next subchannel of either analog or digital. An example of this is the transition from the first station&#39;s  810  analog subchannel  818  to the analog subchannel  838  of the second station  830 . If the user double-presses the scan up button while listening to the first station&#39;s  810  analog subchannel  818 , the radio will change to the first digital subchannel  831  of second station  830  as shown by line type  803 . In other cases, the radio  200  will select the same next subchannel with either a single or a double press of scan up. This is represented by line type  801  and is shown in the transition from the HD-1 subchannel  831  to the HD-2 subchannel  832  of the second station  830 .  
         [0036]     The listing below shows the subchannel transitions for a set of single presses of the scan up button if the user starts at the analog subchannel  818  of the first station  810 . 
    First station  810 , Analog  818      Second station  830 , Analog  838  automatically transitioning to HD-1  831      Second station  830 , HD-2  832      Second station  830 , HD-3  833      Third station  850 , Analog  858      Fourth station  870 , Analog  878  automatically transitioning to HD-1  871      First station  810 , Analog  818     
 
         [0044]     The listing below shows the subchannel transitions for a set of double-presses of the scan up button is the user starts at the analog subchannel  818  of the first station  810 . Note that the radio will not return to the same analog subchannel  818  as the double-press will only to digital subchannels. 
    First station  810 , Analog  818      Second station  830 , HD-1  831      Second station  830 , HD-2  832      Second station  830 , HD-3  833      Fourth station  870 , HD-1  871      Second station  830 , HD-1  831     
 
         [0051]     Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed.