Quadrature amplitude modulation synchronization method

Claim 2

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency, each channel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal, an improved method of providing timing and frequency synchronization information to a QAM receiver, said method comprising the steps of: providing QAM signal synchronizing symbol sequences to substantially each of said N secondary information signals, accompanying transmission of information from said first information signal such that the QAM receiver can detect QAM signal timing and frequency synchronization for said QAM subchannels from said QAM signal synchronizing symbol sequences; when N is even, arranging an even number of said N QAM subchannels into a number of pairs of frequency bands, said pairs of frequency bands displaced evenly about said center frequency; and when N is odd, arranging an even number of said N QAM subchannels into a number of paired frequency bands, said paired frequency bands centered about a predetermined frequency, an unpaired QAM subchannel being substantially centered about said center frequency.

Claim 3

The method of claim 1 further comprised of the steps of: for at least one of the paired QAM subchannels: loading the QAM signal synchronizing symbol sequence in one QAM subchannel of a pair of QAM subchannels with a first complex signal sequence and; loading the QAM signal synchronizing symbol sequence in the other QAM subchannel of a pair of QAM subchannels with a complex conjugate of said first complex signal sequence.

Claim 4

The method of claim 1 further comprised of the steps of: loading said unpaired QAM subchannel with a real-valued sequence.

Claim 5

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency, each channel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal, an improved method of providing timing and frequency synchronization information to a QAM receiver, said method comprising the steps of: a) down-converting a transmitted QAM signal having a sequence of predetermined synchronization symbols appended to said QAM signal, to produce a complex zero-IF signal centered substantially about zero hertz; b) filtering said complex zero-IF signal by a first filter possessing a response substantially matched to a composite transmitted signal, said composite transmitted signal obtained by adding said predetermined synchronization symbols to substantially each of said N QAM subchannels; c) computing the square of the amplitude of the signal output from said first filter to obtain a first intermediate signal; d) comparing the magnitude of said first intermediate signal against a first threshold value; and e) identifying occurrences of said first intermediate signal that exceed said first threshold value as being substantially optimum sampling times for QAM symbols.

Claim 6

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency, each channel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal, an improved method of providing timing and frequency synchronization information to a QAM receiver, said method comprising the steps of: a) down-converting a transmitted QAM signal having a sequence of predetermined synchronization symbols appended to said QAM signal, to produce a complex zero-IF signal centered substantially about zero hertz; b) filtering said complex zero-IF signal by a first filter possessing a response substantially matched to a composite transmitted signal, said composite transmitted signal obtained by adding said predetermined synchronization symbols to substantially each of said N QAM subchannels; c) computing the square of the amplitude of the signal output from said first filter to obtain a first intermediate signal; d) comparing the magnitude of said first intermediate signal against a first threshold value; and e) identifying occurrences of said first intermediate signal that exceed said first threshold value as being substantially optimum sampling times for QAM symbols.

Claim 7

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency f 0 , each subchannel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal and each subchannel having a predetermined synchronizing sequence of complex-valued symbols appended to it, each of said complex-valued symbols having an associated magnitude and phase angle, said complex-valued symbols having an expected phase angle difference between successive symbols, an improved method of providing an automatic frequency control signal to a quadrature-amplitude receiver proportional to a frequency offset between f 0 of a transmitter and f 0 of said receiver, said method comprising the steps of: obtaining temporally adjacent QAM signal synchronizing sequence symbols in substantially each of said QAM subchannels; forming a series of products representative of a combination of each QAM signal synchronizing sequence symbols and a quantity substantially equal to a complex conjugate of a previous QAM signal synchronizing sequence symbol; rotating each of said products by an amount substantially equal to the negative of an expected phase angle difference between corresponding synchronizing sequence symbols forming a series of rotated products; obtaining a phase angle representative of a sum of the series of rotated products; obtaining the phase angle of the sum of the series of rotated products by a first quantity substantially equal to 2πT, where T is time between successive synchronizing symbols in the subchannel and where phase angles are measured in radians to produce a frequency error signal; and filtering said frequency error signal producing thereby an AFC control signal.

Claim 8

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency f 0 , each subchannel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal and each subchannel having a predetermined synchronizing sequence of complex-valued symbols appended to it, each of said complex-valued symbols having an associated magnitude and phase angle, said complex-valued symbols having an expected phase angle difference between successive symbols, an improved method of providing an automatic frequency control signal to a quadrature-amplitude receiver proportional to a frequency offset between f 0 of a transmitter and f 0 of said receiver, said method comprising the steps of: obtaining temporally adjacent QAM signal synchronizing sequence symbols in substantially each of said QAM subchannels; forming a series of products representative of a combination of each QAM signal synchronizing sequence symbols and a quantity substantially equal to a complex conjugate of a previous QAM signal synchronizing sequence symbol; rotating each of said products by an amount substantially equal to the negative of an expected phase angle difference between corresponding synchronizing sequence symbols forming a series of rotated products; obtaining a phase angle representative of a sum of the series of rotated products; obtaining the phase angle of the sum of the series of rotated products by a first quantity substantially equal to 2πT, where T is time between successive synchronizing symbols in the subchannel and where phase angles are measured in radians to produce a frequency error signal; and filtering said frequency error signal producing thereby an AFC control signal.

Claim 9

The method of claim 5 wherein said series of products is formed by multiplying each QAM signal synchronizing sequence symbol by said quantity substantially equal to said complex conjugate of said previous QAM signal synchronizing sequence symbol.

Claim 10

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency f 0 , each subchannel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal and each subchannel having a predetermined synchronizing sequence of complex-valued symbols appended to it, each of said complex-valued symbols having an associated magnitude and phase angle, said complex-valued symbols having an expected phase angle difference between successive symbols, an improved method of providing an automatic frequency control signal to a quadrature-amplitude receiver proportional to a frequency offset between f 0 of a transmitter and f 0 of said receiver, said method comprising the steps of: detecting QAM signal synchronizing sequence symbols in at least one of said N QAM subchannels; calculating actual phase angle differences between pairs of temporally adjacent synchronizing sequence symbols; for each of said N QAM subchannels, obtaining an expected phase angle difference between successive synchronizing symbols from the actual phase angle difference between temporally adjacent synchronizing symbols, forming thereby a series of numbers representing phase angle errors; forming a weighted average of the phase angle errors obtained from substantially all subchannels; and producing a frequency error signal using said weighted average of the phase angle errors to thereby create a signal proportional to the frequency offset between f 0 of said transmitter and f 0 of said receiver.

Claim 11

In a multicarrier information system wherein information in a first information signal is subdivided into N secondary information signals, each of said N secondary information signals including a substantially periodic stream of discrete samples of the information in said first information signal and occupying separate frequency ranges, each of said N secondary information signals carrying a fractional amount of the information in said first information signal and modulating a carrier signal using quadrature-amplitude modulation (QAM) forming thereby N QAM subchannels substantially centered about a center frequency f 0 , each subchannel carrying discrete and periodic QAM symbols, each QAM symbol representing a portion of said first information signal and each subchannel having a predetermined synchronizing sequence of complex-valued symbols appended to it, each of said complex-valued symbols having an associated magnitude and phase angle, said complex-valued symbols having an expected phase angle difference between successive symbols, an improved method of providing an automatic frequency control signal to a quadrature-amplitude receiver proportional to a frequency offset between f 0 of a transmitter and f 0 of said receiver, said method comprising the steps of: detecting QAM signal synchronizing sequence symbols in at least one of said N QAM subchannels; calculating actual phase angle differences between pairs of temporally adjacent synchronizing sequence symbols; for each of said N QAM subchannels, obtaining an expected phase angle difference between successive synchronizing symbols from the actual phase angle difference between temporally adjacent synchronizing symbols, forming thereby a series of numbers representing phase angle errors; forming a weighted average of the phase angle errors obtained from substantially all subchannels; and producing a frequency error signal using said weighted average of the phase angle errors to thereby create a signal proportional to the frequency offset between f 0 of said transmitter and f 0 of said receiver.

Claim 12

The method of claim 7 wherein the step of producing said frequency error signal comprises dividing the weighted average of the phase angle errors by a first quantity substantially equal to 2πT to produce said frequency error signal, where T is time between successive synchronizing symbols in the subchannel and where phase angles are in radians.

Claim 13

The method of claim 7 further comprising the step of filtering said frequency error signal, producing thereby an AFC control signal.