Patent Publication Number: US-2005117068-A1

Title: System and method for the wireless transmission of audio and video information

Description:
CROSS REFERENCE  
      This application is based on, and claims priority of, provisional application Ser. No. 60/507,608 which was filed by applicants on Sep. 30, 2003. 
    
    
     BACKGROUND  
      The present invention relates to a system and method for transmitting audio and video signals over a wireless network and, more particularly, to such a system and method featuring encryption and diversity and transmission at a relatively low cost.  
      There are many applications in which the wireless transmission of audio and video signals would be highly desirable. For example, in commercial or home entertainment applications the standard technique of providing hard wiring between audio source components and amplifiers and/or loudspeakers, as well as between video source components and video displays is often difficult, time consuming and inconvenient. These same problems also exist in commercial or professional venues such as live concerts, down hole oil and gas recovery systems, and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a flowchart of one embodiment of a method for transmitting a signal containing audio and video information.  
       FIG. 2  is a flowchart of one embodiment of a method for receiving a signal transmitted using the method of  FIG. 1 .  
       FIG. 3  is a schematic diagram of one embodiment of a system within which the methods of  FIGS. 1 and 2  may be implemented.  
       FIG. 4  is a diagram of a signal that may be used with the system of  FIG. 3 . 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIG. 1 , in one embodiment, a method  10  may be used to transmit audio and video information using a wireless signal. As will be described below in greater detail with specific examples, the method  10  enables composite video signals as well as luminance and chrominance video signals (hereinafter collectively referred to as “analog video signals”) to be wirelessly transmitted along with a digital audio signal in a single combined signals. The analog video signals are maintained in their original analog form, and the audio signals are either received in the digital domain, or if received in an analog domain, are converted to digital. The combination of the digital audio signals and the analog video signals (hereinafter collectively referred to as “combined signals”) may be analyzed for errors at the receiver location using the digital audio signal component. In a diversity system having multiple reception channels, a receiver may use the error analysis to select a channel providing the best (e.g., most error free) reception. In addition, the digitized audio signal may be used to provide encryption/validation functionality for the combined signals. For example, validation of the audio signal&#39;s encryption may be used to validate the combined signals. Accordingly, the analog video signals may remain in the analog and still enjoy the benefits of diversity and encryption provided by the digital audio signal.  
      In steps  12  and  14 , the analog video signals are received from a video source and an audio signal is received from an audio source. The audio signal is digitized in step  16  (assuming that the audio signal is not already in digital form) and combined with the video signals in step  18 . In step  20 , the combined signals is transmitted via a wireless transmitter. As will be described below, various other actions may be taken, including encrypting the digital audio signal.  
      Referring to  FIG. 2 , one embodiment of a method  30  illustrates a process by which a wirelessly transmitted combined signals (such as that transmitted using the method  10  of  FIG. 1 ) may be received and separated into its component signals. More specific examples of various steps of  FIG. 2  will be described later.  
      In step  32 , a combined signal is received that contains the analog video signals and a digital audio signal. In step  36 , if the receiver includes a diversity system that provides multiple reception channels (as determined in step  34 ), the best channel (e.g., the channel with the highest level of error free transmission) is selected and the incoming signal is pulled from that channel. In step  40 , if the audio signal is encrypted (as determined in step  38 ), the audio portion of the signal is decrypted. This step may include validation of the audio signal (and the associated video signals), with the receiver ensuring that the destination has permission to receive the unencrypted signal, and the accompanying analog video signal. In step  42 , the analog video signals and the digital audio signals are separated from the combined signals. In step  44 , the digital audio signal is converted into an analog audio signal (if needed). In steps  46  and  48 , respectively, the analog video signals are sent to a video destination and the audio signal is sent to an audio destination.  
      Referring to  FIG. 3 , an embodiment of the present invention is shown in connection with an audio/video home or commercial entertainment system  49  for the purpose of example only. The embodiment includes a processor/transmitter  50  having a conventional video input terminal, or jack, to which one end of a cable  52  is connected, via a conventional connector. The other end of the cable  52  is connected, also via a conventional connector, to a video source  54  which could be a television receiver, a cable television source, a satellite receiver/processor, a DVD player, a video recording/playback deck, a camera, or any other source. The analog video signals from the source  54  and passed to the processor/transmitter  50 , via the cable  52 .  
      The processor/transmitter  50  also has two conventional audio input terminals, or jacks, to which one end of each of two audio cables  56   a  and  56   b  are respectively connected, via conventional connectors. The other ends of the cables  56   a  and  56   b  are connected to an audio source  58  which could be one of the same sources set forth above, or a tape deck, a CD player, a DAT player, a record player, a FM or AM tuner, or any other type of audio source.  
      The audio source signals are outputted from the source  58  and passed to the processor/transmitter  50 , via the cables  56   a  and  56   b.  It can be appreciated that the two audio signals could represent a stereo signal and that the number of inputs, connectors and cables could be increased to accommodate any number of channels, or discrete signals, in a multichannel audio surround system, such as SACD (super audio compact disc) surround and DVD (digital versatile disc) audio surround, all of which are conventional. Also, the source  58  could output a single digital audio signal such as 5.1 Dolby digital, DTS or the like, in which case the cable  56   a  (or  56   b ) would be adapted to pass the latter signal to the processor/transmitter  50 .  
      The processor/transmitter  50  includes circuitry, in the form of limiters, modulators, converters, generators, multiplexers, transformers, and associated circuitry to process the video signals received at the video input and the audio signals received at the audio inputs in the following manner.  
      If the analog video signal received from the video source  54  consists of luminance and chrominance signals, the luminance signal is processed to maintain DC integrity and is band-limited with a low pass filter (such as 6 MHz). A modulator modulates the chrominance signal onto a carrier frequency (such as 15 MHz), band-limited between a predetermined range (such as between 12 and 18 MHz), the modulated signal is added to the luminance signal, and the combined signals are transmitted from the processor/transmitter  50  in a manner to be described.  
      If the analog video signal received from the video source  54  consists of a composite signal, the composite signal is processed to maintain DC integrity and is band-limited with a low pass filter (such as 6 MHz) and the signal is transmitted from the processor/transmitter  50  in a manner to be described.  
      The processor/transmitter  50  also includes circuitry, including analog-to-digital converters, digital circuitry, clock frequency generators, multiplexers, synchronizers, spreaders, encryptors, transformers, and associated circuitry to process the audio signals received at the audio inputs in the following manner.  
      If the audio signals are analog, they are converted to corresponding digital signals utilizing analog-to-digital converter integrated chips and applied to a digital circuit such as an ASIC (application-specific integrated circuit—a chip designed for a particular application. The digital processing includes the steps of: 
          1. generating the clock frequencies to run the analog-to-digital converters;     2. multiplexing the data portions of the digitized audio signals into one bit stream;     3. adding synchronizing information to the bit stream; and     4. adding a spreading code and/or an encryption code to the bit stream.        

      The assembled bit stream is then transformed into a transmission code that is bandwidth limited from a certain frequency range (such as 6 MHz to 12 MHz, for example). Examples of acceptable transmission codes include bi-phase digital coding, di-phase coding, Manchester coding, DDS (digital direct sequence—a type of spread spectrum coding) combined with FSK (frequency shift keying—a method of modulation where the frequency is shifted to higher frequencies, then to lower frequencies to signify a logic “1” or “0”) modulation of a 9 MHz or other carrier, frequency modulation of a 9 MHz or other carrier, or ASK (amplitude shift keying, a type of modulation where the amplitude of a radio signal is shifted up and down in amplitude in order to signify a logic “1” or “0”) modulation of a carrier.  
      With additional reference to  FIG. 4 , and assuming that the analog video signal consists of luminance signals and chrominance signals, a chart  80  provides an amplitude/frequency illustration of how these signals, and the audio signal is combined. In this embodiment, the band-limited digital audio signal  84  is added to the luminance video signal  82 , and chrominance video signal  86  from the above video circuitry in the processor/transmitter  50  with the above frequency range (6 MHz to 12 MHz) of the digital audio signal lying between the frequency range (up to 6 MHz) of the luminance video signal and the frequency range (12 MHz to 18 MHz) of the chrominance video signal. A dotted line  88  illustrates that the transmitted band is 20 MHz wide.  
      It is understood that this particular arrangement of signals (e.g., luminance, audio, and chrominance in sequentially increasing frequency slots) is for purposes of illustration only and the signals may be arranged differently. In the present example, the luminance signal is placed in the lowest frequency slot because this is the spectrum location from which the luminance signal is received using an S-video cable. The audio is placed in the middle frequency slot because this matches the spectrum where the digital audio signal will appear using at least some of the previously referenced modulation schemes. When the chrominance signal is received, it is overlapping the luminance signal and needs to be shifted. By shifting the chrominance signal to the highest frequency slot, only one of the three signals needs to be shifted. This may reduce the cost of the system  49  by avoiding unnecessary shifting. However, it is understood that any of the signals may be moved to any of the frequency slots, and that different arrangements of signals may be desired to handle different situations (e.g., if a different modulation scheme is used).  
      If the analog video signal is a composite signal it would be in the lowest frequency slot, as defined above, there would not be a highest frequency slot.  
      Referring again specifically to  FIG. 3 , the combined signals are modulated onto an RF (radio frequency) carrier such as at a frequency between 5.725 GHz and 5.825 GHz according to FCC or international requirements. The RF carrier is generated by a frequency synthesizer and transmitted from the processor/transmitter  50  in this form. To this end, the processor/transmitter  50  includes, or is connected to, an antenna  59 , for transmitting the signals from the processor/transmitter. The antenna  59  can be of the type disclosed in pending U.S. patent application Ser. No. 10/215,704 assigned to the same assignee as the present application, the disclosure of which is incorporated by reference.  
      A receiver/processor  60  is provided in proximity to the processor/transmitter  50  and includes, or is connected to, two antennas  62   a  and  62   b.  It is understood that, although the antennas  62   a  and  62   b  are illustrated separately, they may be contained on a single antenna board. The antennas  62   a  and  62   b  may be similar or identical to the antenna  59  and are adapted to receive the transmitted signals from the latter antenna and pass the signals to the receiver/processor  60 . In this context, the receiver/processor  60  includes a diversity system of the type taught in U.S. Pat. No. 6,788,751 and in U.S. patent application Ser. No. 09/552,471, the disclosures of which is incorporated by reference. The diversity system is discussed below.  
      The receiver/processor  60  also includes circuitry, including one or more amplifiers, filters, mixers, generators, synthesizers, filters, demodulators or discriminators, combiners, equalizers, bufferers, encryption pass/fail switches, and associated circuitry, to process the video and audio signals received from the processor/transmitter  50  in the following manner.  
      Two RF signals, each including the combined audio and video signals, from the two antennas  62   a  and  62   b,  respectively, are received by the receiver/processor  60  utilizing the diversity system discussed above. In particular, and as disclosed in the above mentioned U.S. patent and patent application, this diversity system, in general, involves processing and analyzing the two combined signals from the two antenna  62   a  and  62   b,  respectively, and selecting the optimum signal in accordance with the following.  
      The processing at the receiver/processor  60  includes amplifying the resulting RF signal, including the combined audio and video signals, by a low noise amplifier stage, band-pass filtered, and applying it to the RF input of a double balanced mixer. An LO (local oscillator—a oscillator that is used to combine with other frequencies to form sum and difference frequencies) signal is generated by a frequency synthesizer and applied to an appropriate input of the double balanced mixer. The RF signal is mixed with a local oscillator (LO) frequency signal in the mixer to generate a resultant intermediate frequency (IF) signal that is generally at a lower frequency so filtering, amplification and demodulation are easier.  
      The intermediate frequency signal is outputted from the double balanced mixer, is amplified as necessary to achieve the required sensitivity, and is band-pass filtered at the intermediate (sum or difference) frequency. The intermediate frequency signal is either mixed again to establish a second intermediate frequency or the first intermediate frequency is demodulated or discriminated utilizing standard techniques to retrieve the compiled analog video signals and the digital audio signal.  
      If the analog video signals are luminance and chrominance video signals, the resulting RF signal is DC restored, amplitude-equalized and buffered and the chrominance signal is demodulated, amplitude-equalized, and buffered. The receiver/processor  60  outputs the separate luminance and chrominance video components of the process signal via a conventional video output terminal, or jack, to which one end of a video cable  64  is connected. The cable  64  can be a standard video cable, such as an S-video cable, and its other end is connected to a video display  66  such as a television set, a plasma monitor, a front projector, a rear projector, a LCOS monitor, a LCD monitor, or the like.  
      The receiver/processor  60  also includes circuitry, including a digital processor, a digital-to-analog converter, and associated circuitry, to process the audio signals in the resulting RF signal in the following manner.  
      The digital audio signals are processed by the digital processor whose functions include: 
          1. clock recovery,     2. de-encryption,     3. demultiplexing,     4. error detection, correction, and concealment,     5. diversity selection (if applicable), and     6. I 2 S (a standard digital audio format which uses 3 wires, data, data clock and Left-Right clock formatting).        

      The I 2 S-formatted signals are converted to analog audio information by means of the digital-to-analog converters, are filtered and are outputted from the receiver/processor  60  via two conventional audio output terminals, or jacks, to which one end of each of two audio cables  68   a  and  68   b  are respectively connected. The other ends of the cables  68   a  and  68   b  are connected to an audio amplifier  70  for amplifying the audio signals. It is understood that the audio amplifier  70  could be associated with, or separate from, the display  66  or the receiver/processor  60 . In any case, the amplifier  70  amplifies the signals received from the receiver/processor  60 , and is connected to loudspeakers (not shown) for reproducing the audio signal in a conventional manner. The loudspeakers can be built into the display  66  or could be stand-alone.  
      The number of audio signals passed from the receiver/processor  60  to the amplifier  70  could vary to accommodate any number of channels, or discrete signals, in a multichannel audio surround system, such as SACD surround and DVD audio surround, all of which are conventional. Also, the receiver/processor  60  could output a single digital audio signal such as 5.1 Dolby digital, DTS, or the like.  
      It is understood that the circuitry of the receiver/processor  60 , from the low noise amplifier to the demodulator or discriminator, can be duplicated one or more times to create multiple receiving devices which correspond in number to the number of antennas, which in this example are antennas  62   a  and  62   b.  In this context, two or more of the above functions can be combined for diversity in the manner discussed above and taught in the above-mentioned patent and patent application.  
      The above embodiment permits a relatively low cost, wireless transmission of audio and video featuring encryption for privacy, digital audio for high quality audio, synthesized tuning for selectivity and stability, and in the case where the analog video signals are separated luminance and chrominance signals, these signals are separated for high video quality.  
      It is understood that variations may be made in the above without departing from the scope of the invention. For, example the number of antennas and the number of corresponding receiver/processor circuits can be increased within the scope of the invention. Also, the expression “signal” is used above in a broad sense and, as such, is meant to cover one signal or a plurality of signals. Further, any conventional type of antennas and diversity systems can be used. Moreover, the embodiment described above is not limited to use with a home audio/video entertainment system, but rather is applicable to any other environment in which wireless transmission of signals is desired. Also, it is understood that the above embodiment is equally applicable to stand-alone audio applications as well as stand-alone video applications. In addition, various steps of the described methods may be executed in a different order or executed sequentially, combined, further divided, replaced with alternate steps, or removed entirely. Also, various functions illustrated in the methods or described elsewhere in the disclosure may be combined to provide additional and/or alternate functions.  
      Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many other modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.