Method and system for modulating and detecting high datarate symbol communications
DCFirst Claim
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1. A receiver comprising:
- a demodulator for receiving symbol signal frames and producing quadrature demodulated output signals;
a mapping look-up unit coupled to said demodulator for receiving said quadrature demodulated output signals and determining a three-bit symbol decode associated with points on a predetermined constellation, wherein said constellation has the property of having a first and second point of differing amplitude and zero reference phase, a third point having an amplitude equal to an amplitude of said first point and a 180 degree reference phase, a fourth point having an amplitude equal to an amplitude of said second point and a 180 degree reference phase, fifth and sixth points having real magnitudes substantially equal to said amplitude of said first point and equal imaginary magnitudes of opposite sign, and seventh and eighth points having real magnitudes substantially equal to a negation of said amplitude of said first point and equal imaginary magnitudes of opposite sign, wherein said mapping look-up unit produces probability values for each bit in said three-bit symbol decode from log-likelihood grouping maps for determining membership within a grouping associating said points with values of each bit of said three-bit symbol decode, whereby magnitudes of said quadrature demodulated output signals determine whether or not each symbol signal frame has membership in a first subgroup corresponding to a logical zero or membership in a second subgroup corresponding to a logical one for each grouping; and
a codec coupled to an output of said mapping lookup unit for receiving said probability values for each bit and determining values of each bit.
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Abstract
A method and system for modulating and detecting high datarate symbol communications provides superior performance in channels having a fixed spectral efficiency. A quadrature amplitude modulation (QAM) constellation and an optimized mapping are employed to encode/detect a communications signal and error correction is provided using high speed forward error correction techniques. A log likelihood detection scheme and/or a novel phase detector may be employed to further enhance performance.
16 Citations
25 Claims
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1. A receiver comprising:
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a demodulator for receiving symbol signal frames and producing quadrature demodulated output signals; a mapping look-up unit coupled to said demodulator for receiving said quadrature demodulated output signals and determining a three-bit symbol decode associated with points on a predetermined constellation, wherein said constellation has the property of having a first and second point of differing amplitude and zero reference phase, a third point having an amplitude equal to an amplitude of said first point and a 180 degree reference phase, a fourth point having an amplitude equal to an amplitude of said second point and a 180 degree reference phase, fifth and sixth points having real magnitudes substantially equal to said amplitude of said first point and equal imaginary magnitudes of opposite sign, and seventh and eighth points having real magnitudes substantially equal to a negation of said amplitude of said first point and equal imaginary magnitudes of opposite sign, wherein said mapping look-up unit produces probability values for each bit in said three-bit symbol decode from log-likelihood grouping maps for determining membership within a grouping associating said points with values of each bit of said three-bit symbol decode, whereby magnitudes of said quadrature demodulated output signals determine whether or not each symbol signal frame has membership in a first subgroup corresponding to a logical zero or membership in a second subgroup corresponding to a logical one for each grouping; and a codec coupled to an output of said mapping lookup unit for receiving said probability values for each bit and determining values of each bit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for receiving a communications signal bearing three-bit symbol encodes associated with points on a predetermined constellation, wherein said constellation has the property of having a first and second point of differing amplitude and zero reference phase, a third point having an amplitude equal to an amplitude of said first point and a 180 degree reference phase, a fourth point having an amplitude equal to an amplitude of said second point and a 180 degree reference phase, fifth and sixth points having real magnitudes substantially equal to said amplitude of said first point and equal imaginary magnitudes of opposite sign, and seventh and eighth points having real magnitudes substantially equal to a negation of said amplitude of said first point and equal imaginary magnitudes of opposite sign, said method comprising:
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demodulating a stream of symbol signal frames and producing quadrature demodulated output signals; retrieving log-likelihood probability values estimating a likelihood of each symbol signal frame being transmitted as each point of said constellation, each of said probability values retrieved in conformity with values of said quadrature demodulated output signals and for an associated one of said points; and determining symbols associated with said signal frames in conformity with said probability values. - View Dependent Claims (15, 16, 17, 18, 19)
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20. A receiver comprising:
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a demodulator for receiving symbol signal frames and producing quadrature demodulated output signals; a mapping look-up unit coupled to said demodulator for receiving said quadrature demodulated output signals and determining a three-bit symbol decode associated with points on a predetermined constellation, wherein said constellation has eight points having complex magnitudes of (K/2,0), (3K/2,0), (K/2, K), (−
K/2, K), (−
K/2,0), (−
3K/2,0), (−
K/2, K) and (K/2, K), respectively for a particular rotation of said constellation, where K is an arbitrary coefficient for determining an overall amplitude of said constellation, wherein said mapping look-up unit produces probability values for each bit in said three-bit symbol decode from log-likelihood grouping maps for determining membership within a grouping associating said points with values of each bit of said three-bit symbol decode, whereby magnitudes of said quadrature demodulated output signals determine whether or not each symbol signal frame has membership in a first subgroup corresponding to a logical zero or membership in a second subgroup corresponding to a logical one for each grouping, wherein a grouping associated with a first bit of said three-bit symbol decode divides said constellation between a first subgroup including said first, second, fifth and seventh points and a second subgroup comprising all points that are not members of said first subgroup, wherein a grouping associated with a second bit of said three-bit symbol decode divides said constellation between a third subgroup including said first, third, seventh and eighth points and a fourth subgroup comprising all points that are not members of said third subgroup, and wherein a grouping associated with a third bit of said three-bit symbol decode divides said constellation between a fifth subgroup including said first, third, fifth and sixth points and a sixth subgroup comprising all points that are not members of said fifth subgroup; anda forward error correction block coupled to an output of said mapping look-up unit for receiving said three-bit symbol decode from said mapping look-up unit and providing a corrected data stream in response to a sequence of three-bit symbol decodes. - View Dependent Claims (21)
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22. A carrier generation circuit for providing a reference signal for demodulating a received sequence of symbol frames decoded as quadrature demodulated signals, said circuit comprising:
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an oscillator having an output for providing said reference signal and an control input for receiving a phase error signal; a switching circuit having an output coupled to said control input of said oscillator for selectively applying an input phase error signal in response to a switch control input signal; a phase error magnitude circuit having inputs coupled to said quadrature demodulated signals for generating said input phase error signal and an output coupled to said switching circuit; and an amplitude detector having inputs coupled to said quadrature demodulated signals and an output coupled to said switch control input signal, whereby a phase of said oscillator is controlled in conformity with a subset of said symbol signal frames in conformity with a detected amplitude of said quadrature demodulated signals. - View Dependent Claims (23, 24, 25)
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Specification