Encoding scheme for producing magnetic field signals having desired spectral characteristics
First Claim
1. A method, for producing an encoded information signal having attenuated low frequency spectral components and a substantially constant average energy, the method producing an M bit code word for each N bits of the information signal according to the following conditions:
- (a) each code word includes an equal number of logic zero bits and logic one bits;
(b) each code word includes no more than two consecutive identical bits; and
(c) M is greater than N wherein the producing an M bit code word for each N bits of the information signal is also according to the following condition;
(d) each code word, representative of a particular combination of N bits, is different by at least two bits than any other code word, representative of a different combination of N bits.
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Abstract
Methods and systems for producing an encoded information signal having attenuated low frequency spectral components and a substantially constant average energy. An M bit code word is produced for each N bits of an information signal according to the following conditions: (a) each code word includes an equal number of logic zero bits and logic one bits; (b) each code word includes no more than two consecutive identical bits; and (c) M is greater than N. For example, M equals eight and N equals four. Such an encoded information signal is especially useful for generating a magnetic field signal usable for locating an underground object. This is in part because information sidebands of the magnetic field signal to have desired spectral characteristics that are useful in environments that often include harmonically derived interference signals at regular 50 Hz (±0.1 Hz) or 60 Hz (±0.1 Hz) intervals caused by power lines.
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Citations
42 Claims
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1. A method, for producing an encoded information signal having attenuated low frequency spectral components and a substantially constant average energy, the method producing an M bit code word for each N bits of the information signal according to the following conditions:
- (a) each code word includes an equal number of logic zero bits and logic one bits;
(b) each code word includes no more than two consecutive identical bits; and
(c) M is greater than N wherein the producing an M bit code word for each N bits of the information signal is also according to the following condition;
(d) each code word, representative of a particular combination of N bits, is different by at least two bits than any other code word, representative of a different combination of N bits. - View Dependent Claims (2, 3, 4, 5, 6)
- (a) each code word includes an equal number of logic zero bits and logic one bits;
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7. A method for generating a magnetic field signal usable for locating an underground object, comprising:
- (a) generating a reference signal having a reference signal frequency substantially equal to the integer multiple of 300 Hz;
(b) receiving an information signal;
(c) encoding the information signal to produce an encoded information signal meeting the following conditions (c.1) each code word includes an equal number of logic zero bits and logic one bits, and (c.2) each code word includes no more than two consecutive identical bits; and
(d) modulating the reference signal with the encoded information signal at a predetermined bit rate to produce a drive signal including (d.1) a carrier component having a carrier component frequency equal to the reference signal frequency and a substantially constant average energy, and (d.2) at least one information sideband including sideband energy, the encoding and bit rate causing a substantial portion of the sideband energy to be contained between the carrier component frequency and a frequency spaced 50 Hz from the carrier component frequency; and
(f) driving a transponder with the drive signal to generate the magnetic field signal, the magnetic field signal having a magnetic field signal carrier component having a frequency equal to the carrier component frequency and at least one magnetic field signal information sideband including magnetic field signal sideband energy, a substantial portion of the magnetic field signal sideband energy contained between the carrier component frequency and the frequency spaced 50 Hz from the carrier component frequency. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
- (a) generating a reference signal having a reference signal frequency substantially equal to the integer multiple of 300 Hz;
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22. An encoder to produce an encoded information signal including attenuated low frequency components and a substantially constant average energy, the encoder comprising:
- code storing means for storing a plurality of different codes words each representative of a different combination of N bits, wherein each of the plurality of different code words meet the following conditions;
(a) each code word includes an equal number of logic zero bits and logic one bits; and
(b) each code word includes no more than two consecutive identical bits; and
selecting means for selecting one of the plurality of different code words for each N bits of the information signal. - View Dependent Claims (23, 24, 25, 26, 27, 28)
- code storing means for storing a plurality of different codes words each representative of a different combination of N bits, wherein each of the plurality of different code words meet the following conditions;
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29. A system for generating a magnetic field signal usable for locating an underground object, comprising:
- a reference signal generator to produce a reference signal having a reference signal frequency substantially equal to the integer multiple of 300 Hz;
an encoder to encode an information signal to produce an encoded information signal meeting the following conditions (a.1) each code word includes an equal number of logic zero bits and logic one bits, and (a.2) each code word includes no more than two consecutive identical bits;
a modulator to modulate the reference signal with the encoded information signal at a predetermined bit rate to produce a drive signal including (b.1) a carrier component having a carrier component frequency equal to the reference signal frequency, and (b.2) at least one information sideband including sideband energy, the encoding and bit rate causing a substantial portion of the sideband energy to be contained between the carrier component frequency and a frequency spaced 50 Hz from the carrier component frequency; and
a transponder to generate the magnetic field signal when driven by the drive signal, the magnetic field signal having a magnetic field signal carrier component having a frequency equal to the carrier component frequency and at least one magnetic field signal information sideband including magnetic field signal sideband energy, a substantial portion of the magnetic field signal sideband energy contained between the carrier component frequency and the frequency spaced 50 Hz from the carrier component frequency. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36)
- a reference signal generator to produce a reference signal having a reference signal frequency substantially equal to the integer multiple of 300 Hz;
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37. A method for encoding data, comprising the steps of:
- (a) encoding each four bits of the data into an eight bit code word that is representative of the respective four bits, wherein each eight bit code word includes an equal number of logic one bits and logic zero bits;
(b) grouping a first plurality of the eight bit code words into a first group and a second plurality of the eight bit code words into a second group; and
(c) adding a first header to the first group to produce a first frame and a second header to the second group to produce a second frame, wherein each header comprises an eight bit header code that is different from any of the eight bit data codes in its respective frame, and wherein the second header is a compliment of the first header, whereby a total bits of the first and second frames together include an equal number of logic one bits and logic zero bits. - View Dependent Claims (38, 39, 40, 41)
- (a) encoding each four bits of the data into an eight bit code word that is representative of the respective four bits, wherein each eight bit code word includes an equal number of logic one bits and logic zero bits;
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42. A method for producing a magnetic field signal, comprising:
- (a) encoding an information signal to produce an encoded information signal having attenuated low frequency spectral components and a substantially constant average signal energy;
(b) modulating a reference signal with the encoded information signal at a predetermined bit rate to produce a drive signal including (b.1) a carrier component having a substantially constant average energy and a carrier component frequency equal to the reference signal frequency, and (b.2) at least one information sideband including sideband energy, the encoding and bit rate causing a substantial portion of the sideband energy to be contained between the carrier component frequency and a frequency spaced 50 Hz from the carrier component frequency; and
(c) driving a transponder with the drive signal to generate the magnetic field signal, the magnetic field signal having a magnetic field signal carrier component and at least one magnetic field signal information sideband, wherein the magnetic field signal carrier component has a substantially constant average energy and a frequency equal to the carrier component frequency, and wherein the at least one magnetic field signal information sideband includes magnetic field signal sideband energy, a substantial portion of the magnetic field signal sideband energy contained between the carrier component frequency and the frequency spaced 50 Hz from the carrier component frequency.
- (a) encoding an information signal to produce an encoded information signal having attenuated low frequency spectral components and a substantially constant average signal energy;
Specification