Broadcast encoding system and method

A method for adding a binary code bit to a block of a signal having a spectral amplitude and a phase, both the spectral amplitude and the phase varying within a predetermined signal bandwidth, the method comprising the following steps:

• a) selecting, within the block, (i) a reference frequency within the predetermined signal bandwidth, (ii) a first code frequency having a first predetermined offset from the reference frequency, and (iii) a second code frequency having a second predetermined offset from the reference frequency;
• b) comparing the spectral amplitude of the signal near the first code frequency to the spectral amplitude of the signal near the second code frequency;
• c) selecting a portion of the signal at one of the first and second code frequencies at which the corresponding spectral amplitude is smaller to be a modifiable signal component, and selecting a portion of the signal at the other of the first and second code frequencies to be a reference signal component;
• and,
• d) selectively changing the phase of the modifiable signal component so that it differs by no more than a predetermined amount from the phase of the reference signal component.

A method of reading a digitally encoded message transmitted with a signal having a time-varying intensity, the signal characterized by a signal bandwidth, the digitally encoded message comprising a plurality of binary bits, the method comprising the following steps:

• a) selecting a reference frequency within the signal bandwidth;
• b) selecting a first code frequency at a first predetermined frequency offset from the reference frequency and selecting a second code frequency at a second predetermined frequency offset from the reference frequency;
• and,
• c) finding which one of the first and second code frequencies has a spectral amplitude associated therewith that is a maximum within a corresponding frequency neighborhood and finding which one of the first and second code frequencies has a spectral amplitude associated therewith that is a minimum within a corresponding frequency neighborhood in order to thereby determine a value of a received one of the binary bits.

A method of reading a digitally encoded message transmitted with a signal having a spectral amplitude and a phase, the signal characterized by a signal bandwidth, the message comprising a plurality of binary bits, the method comprising the steps of:

• a) selecting a reference frequency within the signal bandwidth;
• b) selecting a first code frequency at a first predetermined frequency offset from the reference frequency and selecting a second code frequency at a second predetermined frequency offset from the reference frequency;
• c) determining the phase of the signal within respective predetermined frequency neighborhoods of the first and the second code frequencies;
• and,
• d) determining if the phase at the first code frequency is within a predetermined value of the phase at the second code frequency and thereby determining a value of a received one of the binary bits.

An encoder arranged to add a binary bit of a code to a block of a signal having an intensity varying within a predetermined signal bandwidth comprising:

• a selector arranged to select, within the block, (i) a reference frequency within the predetermined signal bandwidth, (ii) a first code frequency having a first predetermined offset from the reference frequency, and (iii) a second code frequency having a second predetermined offset from the reference frequency;
• a detector arranged to detect a spectral amplitude of the signal in a first neighborhood of frequencies extending about the first code frequency and in a second neighborhood of frequencies extending about the second code frequency;
• and,
• a bit inserter arranged to insert the binary bit by increasing the spectral amplitude at the first code frequency so as to render the spectral amplitude at the first code frequency a maximum in the first neighborhood of frequencies and by decreasing the spectral amplitude at the second code frequency so as to render the spectral amplitude at the second code frequency a minimum in the second neighborhood of frequencies.

An encoder arranged to add a binary bit of a code to a block of a signal having a spectral amplitude and a phase, wherein both the spectral amplitude and the phase vary within a predetermined signal bandwidth, and wherein the encoder comprises:

• a selector arranged to select, within the block, (i) a reference frequency within the predetermined signal bandwidth, (ii) a first code frequency having a first predetermined offset from the reference frequency, and (iii) a second code frequency having a second predetermined offset from the reference frequency;
• a detector arranged to detect the spectral amplitude of the signal near the first code frequency and near the second code frequency;
• a selector arranged to select the portion of the signal at one of the first and second code frequencies at which the corresponding spectral amplitude is smaller to be a modifiable signal component, and to select the portion of the signal at the other of the first and second code frequencies to be a reference signal component;
• and,
• a bit inserter arranged to insert the binary bit by selectively changing the phase of the modifiable signal component so that it differs by no more than a predetermined amount from the phase of the reference signal component.

A decoder arranged to decode a binary bit of a code from a block of a signal transmitted with a time-varying intensity comprising:

• a selector arranged to select, within the block, (i) a reference frequency within the signal bandwidth, ii) a first code frequency at a first predetermined frequency offset from the reference frequency, and (iii) a second code frequency at a second predetermined frequency offset from the reference frequency;
• a detector arranged to detect a spectral amplitude within respective predetermined frequency neighborhoods of the first and the second code frequencies;
• and,
• a bit finder arranged to find the binary bit when one of the first and second code frequencies has a spectral amplitude associated therewith that is a maximum within its respective neighborhood and the other of the first and second code frequencies has a spectral amplitude associated therewith that is a minimum within its respective neighborhood.

A decoder arranged to decode a binary bit of a code from a block of a signal transmitted with a time-varying intensity comprising:

• a selector arranged to select, within the block, (i) a reference frequency within the signal bandwidth, (ii) a first code frequency at a first predetermined frequency offset from the reference frequency, and (iii) a second code frequency at a second predetermined frequency offset from the reference frequency;
• a detector arranged to detect the phase of the signal within respective predetermined frequency neighborhoods of the first and the second code frequencies;
• and,
• a bit finder arranged to find the binary bit when the phase at the first code frequency is within a predetermined value of the phase at the second code frequency.

A method of reading a data element from a received signal comprising the steps of:

• a) computing a Fourier Transform of a first block of n samples of the received signal;
• b) testing the first block for the data element;
• c) setting an array element SIS[a] of an SIS array to a predetermined value if the data element is found in the first block;
• d) updating the Fourier Transform of the first block of n samples for a second block of n samples of the received signal, wherein the second block differs from the first block by k samples, and wherein k<n;
• e) testing the second block for the data element;
• and,
• f) setting an array element SIS[a+1] of the SIS array to the predetermined value if the data element is found in the first block.

A method for adding a binary code bit to a block of a signal varying within a predetermined signal bandwidth, the method comprising the following steps:

• a) selecting a reference frequency within the predetermined signal bandwidth, and associating therewith both a first code frequency having a first predetermined offset from the reference frequency and a second code frequency having a second predetermined offset from the reference frequency;
• b) measuring the spectral power of the signal within the block in a first neighborhood of frequencies extending about the first code frequency and in a second neighborhood of frequencies extending about the second code frequency, wherein the first frequency has a spectral amplitude, and wherein the second frequency has a spectral amplitude;
• c) swapping the spectral amplitude of the first code frequency with a spectral amplitude of a frequency having a maximum amplitude in the first neighborhood of frequencies while retaining a phase angle at both the first frequency and the frequency having the maximum amplitude in the first neighborhood of frequencies;
• and,
• d) swapping the spectral amplitude of the second code frequency with a spectral amplitude of a frequency having a minimum amplitude in the second neighborhood of frequencies while retaining a phase angle at both the second frequency and the frequency having the maximum amplitude in the second neighborhood of frequencies.