System and method for transmitting digital data in the overscan portion of a video signal

Claim 2

In a system for transmitting a video signal, wherein said video signal has a horizontal overscan portion, apparatus for transmitting digital data within the horizontal overscan portion comprising: a) control means for receiving the video signal and for generating a control signal which is active during the horizontal overscan portion of a horizontal line interval of said video signal and inactive otherwise; b) carrier generating means for generating in-phase and quadrature phase carrier signals having a frequency within the band of frequencies occupied by said video signal; c) supply means for supplying bit-serial digital data at a predetermined rate; d) encoding means, coupled to the supply means for converting the bit-serial digital data into symbols, wherein each symbol represents more than one bit of the digital data; and e) modulating means, connected to the encoding means and carrier generating means and responsive to the control signal, for modulating both the in-phase and quadrature phase carrier signals with each of the symbols using quadrature amplitude modulation (QAM) during the horizontal overscan portion of the video signal.

Claim 3

Apparatus according to claim 1 wherein the encoding means comprises: QAM encoder means, coupled to the supply means, for encoding a group of N consecutive bits received from the supply means as a respective one of 2 N points in a QAM constellation by generating a first signal on an I channel and a second signal on a Q channel, wherein each pair of said first and said second signals has a respective pair of amplitude levels corresponding to the N consecutive bits, where N is an integer greater than 1 and each of the groups of N consecutive bits is one symbol; first pulse shaping means, coupled to the QAM encoder means, for shaping the first signal generated by the encoder means; second pulse shaping means, coupled to the QAM encoder means, for shaping the second signal generated by the encoder means; and, wherein the modulating means includes: phase shifting means, coupled to the carrier generating means, for generating the quadrature carrier signal by shifting the phase of the in-phase carrier signal by 90°; first multiplying means, coupled to the first pulse shaping means and the carrier generating means, for multiplying the shaped first signal with the in-phase carrier signal to produce a first output signal; second multiplying means, coupled to the second pulse shaping means and the phase shifting means, for multiplying the shaped second signal with the quadrature carrier signal to produce a second output signal; and adding means, connected to the first and second multiplying means, for adding the first output signal and the second output signal.

Claim 4

Apparatus according to claim 2 wherein N equals 5.

Claim 5

Apparatus according to claim 3 wherein said video signal has a vertical overscan portion, the control means generates a control signal which is active during at least a portion of the vertical overscan portion, and the symbols derived from the bit-serial digital data modulate the in-phase and quadrature carrier signals during the portion of the vertical overscan portion of the video signal.

Claim 6

Apparatus according to claim 4 wherein each of said first and second signals has six potential amplitude levels, thereby creating thirty-six pairs of amplitude levels.

Claim 7

Apparatus according to claim 5 wherein the video signal has a color subcarrier signal having a frequency of f sc , the QAM encoder means receives ones of the symbols at a rate of 4f sc /5, wherein the predetermined rate of the supply means is 2f sc and the in-phase and quadrature carrier signals have a frequency of f sc /2.

Claim 8

Apparatus according to claim 6 wherein the first and second pulse shaping means are filters each having a square-root raised cosine frequency response characteristic.

Claim 9

In a system for transmitting a video signal having a combination of digital data and video information, said system has a source of digital data, wherein said video signal has a color subcarrier signal with a frequency of f sc and said video signal has a horizontal overscan portion, a modulation system for modulating the digital data to be transmitted within the horizontal overscan portion, comprising: a) quadrature amplitude modulation (QAM) encoder means for encoding a group of N consecutive bits received rom the source as a respective one of 2 N points in a QAM constellation by generating a first signal on an I channel and a second signal on a Q channel, wherein said first and said second signals have successive amplitude levels corresponding to values of successive groups of the N consecutive bits, where N is an integer greater than 1; b) first pulse shaping means, coupled to the QAM encoder means, for shaping the first signal generated by the encoder means; c) second pulse shaping means, coupled to the QAM encoder means, for shaping the second signal generated by the encoder means; d) carrier generating means for generating a first carrier signal with a frequency of f sc /2; e) phase shifting means for generating a second carrier signal which is shifted in phase by 90° with respect to the first carrier signal; f) first multiplying means, coupled to the first pulse shaping means and the carrier generating means, for multiplying the shaped first signal with the first carrier signal to produce a first output signal; g) second multiplying means, coupled to the second pulse shaping means and the phase shifting means, for multiplying the shaped second signal with the second carrier signal to produce a second output signal; and h) adding means, connected to the first and second multiplying means, for adding the first output signal and the second output signal.

Claim 10

In a system for transmitting a video signal having a combination of digital data and video information, said system has a source of digital data, wherein said video signal has a color subcarrier signal with a frequency of f sc and said video signal has a horizontal overscan portion, a modulation system for modulating the digital data to be transmitted within the horizontal overscan portion, comprising: a) quadrature amplitude modulation (QAM) encoder means for encoding a group of N consecutive bits received rom the source as a respective one of 2 N points in a QAM constellation by generating a first signal on an I channel and a second signal on a Q channel, wherein said first and said second signals have successive amplitude levels corresponding to values of successive groups of the N consecutive bits, where N is an integer greater than 1; b) first pulse shaping means, coupled to the QAM encoder means, for shaping the first signal generated by the encoder means; c) second pulse shaping means, coupled to the QAM encoder means, for shaping the second signal generated by the encoder means; d) carrier generating means for generating a first carrier signal with a frequency of f sc /2; e) phase shifting means for generating a second carrier signal which is shifted in phase by 90° with respect to the first carrier signal; f) first multiplying means, coupled to the first pulse shaping means and the carrier generating means, for multiplying the shaped first signal with the first carrier signal to produce a first output signal; g) second multiplying means, coupled to the second pulse shaping means and the phase shifting means, for multiplying the shaped second signal with the second carrier signal to produce a second output signal; and h) adding means, connected to the first and second multiplying means, for adding the first output signal and the second output signal.

Claim 13

In a system for receiving a composite video signal, wherein said video signal contains modulated encoded digital data in its horizontal overscan portion, said data being encoded according to a quadrature amplitude modulation (QAM) encoding scheme in which the digital data is encoded as symbols which modulate two quadrature-phase related carrier signals having a frequency within a band of frequencies defied by the video signal, a system for decoding the digital data comprising: control means, which receives the video signal, for generating a control signal which is active during the horizontal overscan portion of a horizontal line interval of asid video signal and inactive otherwise; carrier reconstruction means for reconstructing the in-phase and quadrature phase carrier signals; extracting means, which receives the video signal and is coupled to the carrier reconstruction means, for extracting and decoding the modulated encoded digital data, wherein the extracting mans comprises: means, responsive to the control signal, for separating the modulated encoded data from the video signal; demodulation means for demodulating the modulated encoded data to produce an I channel signal representing the data values modulating the in-phase carrier signal and a Q channel signal representing the data values modulating the quadrature phase carrier signal; symbol clock reconstructing means for reconstructing a symbol clock having transitions which indicate instants at which symbols of the digital data occur in the I channel signal and in the O channel signal; first and second shaping means, coupled to the demodulation means, and symbol clock reconstruction means, for shaping the I channel signal and the Q channel signal, respectively to reduce interference between successive ones of said symbols; and QAM decoder means, coupled to the first and second shaping means, for decoding the shaped I and Q channel signals to recover the digital data symbols, wherein the combined amplitudes of the I and Q channel signals at instants determined by the symbol clock correspond to respective symbols, each symbol representing five bits of digital data.

Claim 14

In a system for receiving a composite video signal, wherein said video signal contains modulated encoded digital data in its horizontal overscan portion, said data being encoded according to a quadrature amplitude modulation (QAM) encoding scheme in which the digital data is encoded as symbols which modulate two quadrature-phase related carrier signals having a frequency within a band of frequencies defied by the video signal, a system for decoding the digital data comprising: control means, which receives the video signal, for generating a control signal which is active during the horizontal overscan portion of a horizontal line interval of asid video signal and inactive otherwise; carrier reconstruction means for reconstructing the in-phase and quadrature phase carrier signals; extracting means, which receives the video signal and is coupled to the carrier reconstruction means, for extracting and decoding the modulated encoded digital data, wherein the extracting mans comprises: means, responsive to the control signal, for separating the modulated encoded data from the video signal; demodulation means for demodulating the modulated encoded data to produce an I channel signal representing the data values modulating the in-phase carrier signal and a Q channel signal representing the data values modulating the quadrature phase carrier signal; symbol clock reconstructing means for reconstructing a symbol clock having transitions which indicate instants at which symbols of the digital data occur in the I channel signal and in the O channel signal; first and second shaping means, coupled to the demodulation means, and symbol clock reconstruction means, for shaping the I channel signal and the Q channel signal, respectively to reduce interference between successive ones of said symbols; and QAM decoder means, coupled to the first and second shaping means, for decoding the shaped I and Q channel signals to recover the digital data symbols, wherein the combined amplitudes of the I and Q channel signals at instants determined by the symbol clock correspond to respective symbols, each symbol representing five bits of digital data.

Claim 15

In a system for receiving a video signal having a combination of video information and quadrature amplitude modulated (QAM) encoded digital data in which multi-bit digital data symbols modulate in-phase and quadrature phase carrier signals, wherein said video signal has a color subcarrier with a frequency of f sc and said video signal has a horizontal overscan portion, a demodulation system for demodulating the modulated encoded digital data received during the horizontal overscan portion, apparatus comprising: demodulation means or demodulating the modulated encoded data to produce an I channel signal representing information modulating the in-phase carrier signal and a Q channel signal representing information modulating the quadrature phase carrier signal; symbol clock reconstruction means for reconstructing a symbol clock having transitions which indicate instants at which symbols of the digital data occur in the I channel signal and in the Q channel signal; first and second shaping means, coupled to the demodulation means and the symbol clock reconstruction means, for shaping the I channel signal and the Q channel signal, respectively to reduce interference between successive ones of said symbols; and QAM decoder means, coupled to the first and second shaping means, for decoding the shaped I and Q channel signals to recover the digital data symbols, wherein the amplitudes of each pair of values of the shaped I and Q channel signals occurring at an instant determined by the symbol clock corresponds to a respective one of the symbols, each symbol representing five binary bits of digital data.

Claim 16

In a system for receiving a video signal having a combination of video information and quadrature amplitude modulated (QAM) encoded digital data in which multi-bit digital data symbols modulate in-phase and quadrature phase carrier signals, wherein said video signal has a color subcarrier with a frequency of f sc and said video signal has a horizontal overscan portion, a demodulation system for demodulating the modulated encoded digital data received during the horizontal overscan portion, apparatus comprising: demodulation means or demodulating the modulated encoded data to produce an I channel signal representing information modulating the in-phase carrier signal and a Q channel signal representing information modulating the quadrature phase carrier signal; symbol clock reconstruction means for reconstructing a symbol clock having transitions which indicate instants at which symbols of the digital data occur in the I channel signal and in the Q channel signal; first and second shaping means, coupled to the demodulation means and the symbol clock reconstruction means, for shaping the I channel signal and the Q channel signal, respectively to reduce interference between successive ones of said symbols; and QAM decoder means, coupled to the first and second shaping means, for decoding the shaped I and Q channel signals to recover the digital data symbols, wherein the amplitudes of each pair of values of the shaped I and Q channel signals occurring at an instant determined by the symbol clock corresponds to a respective one of the symbols, each symbol representing five binary bits of digital data.