United States Patent
`
`{191
`
`[11] Patent Number:
`
`5,732,105
`
`Andren et a].
`
`[45] Date of Patent:
`
`Mar. 24, 1998
`
`USOOS732105A
`
`[54]
`
`[75]
`
`METHOD OF ESTIMATING SIGNAL
`QUALITY IN A DPSK DEMODUIATOR
`
`[56]
`
`References Cited
`U.s. Pm DOCUMENTS
`
`Inventors: Call Frank Andi-en. Indialantic: Perry
`Wesley Fmgge. Palm Bay; Leonard
`Victor Lucas. Palm Bay; Jim Snell.
`Palm Bay. all of Fla.
`
`[7'3]
`
`Assignee: Harris Corporation, Melbourne. Fla.
`
`[21]
`
`AppL No.: 509,586
`
`[22]
`
`Filed:
`
`Jul. 31, 1995
`
`[51]
`
`[52]
`
`[53]
`
`Int. CI.‘5 .. ........................ H04]! 5’46; H043 17100
`US. Cl. _.. ................... 375I226: 3751327; 375830:
`375.840: 375855: 3751371; 329804
`Field of Search ..............
`3753226. 224,
`3751227. 283. 284. 285, 324, 327. 330.
`340. 346. 355. 371. 373. 376; 3291304
`
`5.001.724
`5,490.17?
`
`321991 Birgenhda'dal. ................ 373226
`219% LaRosaet :1. _- 375540
`
`Primary Examiners—Don N. Vo
`Artur-neg; Agent, or Firm—Rogers 8:. Killeen
`[57]
`ABSTRACT
`
`Amethod of estimating signal quality in a radio demodulator
`receiving an input stream of symbols includes the steps of
`sampling a phase-only portion of each of the symbols in the
`input stream. determining a phase error for each of the
`samples of the phase-only portions. and calculating a signal
`quality estimate from a plurality of the sample phase errors.
`The signal quality estimate may be an average magnitude of
`a predetermined number of sample phase errors. The input
`stream may be symbols in the preamble. or symbols in the
`data signal that follows.
`
`15 Claims, 1 Drawing Sheet
`
`CLEAR CHANNEL
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`ASSESSMENT
`
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`INPUT TO CHIP
`
`
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`SIGNAL QUALITY 2
`
`
`
`
`
`CORRELATOR
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`52AMP.
`ISTAP
`SECTION
`
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`
`I 4
`
`SAMP
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`
`SUBRATE
`DATA
`
`
`DESCRAM
`
`
`
`
`
`A‘JG PHASE
`FREO.
`
`
`AVG PHASE FREQ.
`
`
`ID
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 1
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 1
`
`

`

`US. Patent
`
`Mar. 24, 1993
`
`5,732,105
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`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 2
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 2
`
`
`
`
`
`

`

`1
`METHOD OF ESTMATING SIGNAL
`QUALITY IN A DPSK DEMODULATOR
`BACKGROUND OF THE INVENTION
`
`This application is related to application Ser. No. 081509.
`587 entitled Short Burst Acquisition Circuit for Direct
`Sequence Spread Spectrum links; application Ser. No.
`081509.588 entitled Fast Acquisition Bit Timing Loop
`Method and Apparatus; application Ser. No. 085091.589
`entitled Short Burst Direct Acquisition Direct Sequence
`Spread Spectrum Receiver; application Set. No. 08509590
`entitled ND Reference Level Adjustment Circuit to Main-
`tain Optimum Dynamic Range at the AD all of which are
`incorporated by reference. and are filed concurrently here-
`with and assigned to the assignee hereof.
`The present invention is related to demodulators for radio
`receivers. and more particularly to a DPSK demodulator for
`a direct sequence spread spectrum radio receiver in which
`signal quality estimates include phase-only processing.
`Design of demodulators for diiferential binary phase shift
`keyed (DBPSK) and differential quadrattn’e phase shift
`keyed (DQPSK) data typically involves a trade-off between
`circuit complexity and performance. More specifically, sig-
`nal quality estimates may be used in the demodulator to set
`the performance level of the demodulator; the more accurate
`the signal quality estimates. the better the petionnance of the
`demodulator. Additionally. the signal quality may be used in
`the acquisition decision process. The more accurate the
`signal quality estimates. the closer the decision point can be
`set to optimize the ratio of the probability of (correct)
`acquisition to the probability of false alarm. However. the
`circuit in the demodulator for providing the signal quality
`estimates increases in complexity and size as the accuracy of
`the signal quality estimate improves. Thus. the size and
`complexity of the demodulator are undesirably increased as
`its perfennance is improved.
`A typical data transmission received at a DPSK receiver
`includes a data signal preceded by a preamble. The receiver
`is expected to acquire the preamble before attempting to
`demodulate the data signal that follows. The signal quality
`estimate is used to set various demodulator features. and is
`determined first during the preamble and updated during the
`data signal. In the prior art. signal quality estimates typically
`are hit sync amplitudes derived from correlators that receive
`Iand Q components of the input stream of symbols (the term
`symbol is used herein to refer to the units used in the
`preamble format. e.g., spread specn-umBPSK. or in the data
`signal format. e.g.. DBPSK or DQPSK). However. bit sync
`amplinides provide an incomplete picuire of signal quality.
`For example. they do not directly indicate any phase rela-
`tionships.
`Accordingly. it is an object of the present invention to
`provide a novel method of estimating signal quality in a
`radio receiver that
`takes advantage of phase-only
`processing. thereby obviating the problems of the prior art.
`It is another object of the present invention to provide a
`novel method of estimating signal quality in a DPSK
`demodulator in which the phase-only portions of input
`symbols are sampled so that a phase error may be deter-
`mined for each of the symbols.
`It is yet another object of the present invention to provide
`a novel method of estimating signal quality in a DPSK
`demodulator in which phase errors derived from a plurality
`of samples of phase-only portions of input symbols are used
`as signal quality estimates.
`It is still another object of the present invention to provide
`a novel method of estimating signal quality in a DPSK
`
`5,732,105
`
`2
`
`demodulator in which each symbol in a sn'eam of symbols
`is sampled once and converted to polar coordinate form, in
`which a phase error for each of the samples is determined
`using a phase-only portion of the polar coordinate form. and
`in which a signal quality estimate is an average magnitude
`of a predetermined number of the sample phase errors.
`It is a further object of the present invention to provide a
`novel method of estimating signal quality in a radio
`demodulator in which phase errors derived from a plurality
`of samples of phase-only portions of input symbols are
`provided from a phase locked loop.
`These and many other objects and advantages of the
`present invention will be readily apparent to one skilled in
`the art to which the invention pertains from a perusal of the
`claims. the appended drawings. and the following detailed
`description of the preferred embodiments.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`5
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`JD
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`15
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`30
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`35
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`45
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`55
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`FIG. 1 is a block diagram of an embodiment of the
`demodulator of the present invention.
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`An embodiment of the present invention for estimating
`signal quality in a radio demodulator receiving an input
`sheath of symbols may include the steps of sampling a
`phase-only portion of each of the symbols in the input
`stream. determining a phase error for each of the samples of
`the phase-only portions. and calculating a signal quality
`estimate from a plurality of the sample phase errors. “to
`input stream may be symbols in the preamble. or symbols in
`the data signal that follows.
`In a preferred embodiment. the input stream of symbols is
`provided in l and Q components. and the I and Q compo—
`nents are combined for each of the symbols. The combined
`1 and Q components for each of the symbols may be sampled
`at the rate of one sample per symbol. and the samples
`converted to a form that separates the magnitude and the
`phase. such as polar coordinate form. The phase-only por-
`tion of the polar coordinate firm may be provided to a phase
`locked loop for determination of a phase aror fcr each of the
`samples. 'I’hu'eafter, an estimate of the signal quality may be
`provided by calculating an average magnitude of a plurality
`of the sample phase errors.
`Dining the period when the signal is still being acquired
`(the preamble is still being received), the average magnitude
`may include the sample phase errors in a block of the
`symbols from the preamble received from an antenna. When
`more than one antenna is present. signal quality estimates
`may be provided for each antenna by using subsequent
`blocks of symbols from the Ixearnble. Once the signal has
`been acquired and data are being demodulated. the signal
`quality estimate may be the average magnitude of a prede-
`termined number of the sample phase errors. for example the
`average magnitude of phase errors from samples of 128 data
`symbols.
`The use of the phase errors provides a robust signal
`quality estimate, even when the input signal is weak because
`the phase errors do not rely on signal amplitude. Funher. the
`conversion to phase-only provides advantages to the rest of
`the demodulation functions. For example. the samples are
`real numbers. rather than complex numba-s. so that phase
`rotation of the carrier can be compensated by a simple
`addition tamer than a complex multiply. The decision sn'uc-
`ture for removing the DBPSKIDQPSK modulation involves
`additions and does not require comparators or complicated
`logic.
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 3
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 3
`
`

`

`5,732,105
`
`3
`In a further embodiment. an average phase of a predeter-
`mined number of the symbols may be determined from the
`phase-only portions of the symbols. The average phase may
`be provided to the phase locked loop to remove frequency
`ofisets.
`
`In yet a further embodiment. an average of the magnitude-
`Only portions of the polar coordinate form of the symbols
`[also denoted the bit sync amplitude) may be provided as a '
`further signal quality estimate.
`By way of further explanation. and with reference to FIG.
`1. symbols in a received signal may be provided to a
`demodulator 10 for processing. I and Q components may be
`provided through analog to digital converters 12 and 14 to
`correlators 16 and 18 to remove the symbol spreading
`sequence. Outputs from correlators 16 and 18 may be
`combined and converted from cartesian to polar coordinate
`form in converter 20. The stream from converter 20 may be
`decimated to the symbol rate and the phase may be corrected
`for frequency ofl‘set before PSK demodulation in PSK
`demodulator 22. Phase errors from PSK demodulator 22 are
`fed to a numerically controlled oscillator 24 through a
`leadl'lag filter 26 to achieve phase lock in phase locked loop
`27.
`
`10
`
`15
`
`Frequency ofl’set is measured during signal acquisition
`and stored in processor 28 for use in demodulation. The
`frequency otiset is estimated by averaging the phase rotation
`from symbol to symbol and then provided to phase locked
`loop 27 as an initial condition to accelerate phase lock.
`thereby saving time over the classical phase locked loops
`used in the prior art. The average magnitude of the phase
`errors for the symbols may be determined in calculating
`block 30 and provided as a signal quality estimate.
`The magnitude of the output from converter 20 also may
`be provided to integrator 32 for integration. As will be
`appreciated. this eliminates the need (and the hardware) in
`the prior art to Doppler shift or to correct for oscillator offset
`prior to the carelator. The integrated output is provided to
`timer 34 for determination of symbol tinting and bit sync
`amplitude. The bit sync amplitude is an average magnitude
`of the symbols in polar coordinates and is a measure of
`signal amplitude that also may be provided as a signal
`quality estimate.
`During data demodulation the phase locked loop tracks
`and removes frequency offsets by subtracting the average
`phase. The demodulator switches from difierential demodu-
`lation dining acquisition to coherent demodulation followed
`by difl‘erential detection during data demodulation. This
`switch improves bit error rate performance.
`Mile preferred embodiments of the present invention
`have been described. it is to be understood that the embodi-
`ments described are illustrative only and the scope of the
`invention is to be defined solely by the appended claims
`when accorded a full range of equivalence. many variations
`and modifications naturally occurring to those of sltill in the
`art from a perusal hereof.
`What is claimed is:
`
`1. A method of estimating signal quality in a DPSK
`demodulator receiving an input stream of symbols.
`the
`method comprising the steps of sampling a phase-only
`portion of each of the symbols in the input stream, deter-
`mining a phase error for each of the samples. and calculating
`a signal quality estimate from a plurality of the sample phase
`errors.
`
`2- The method of claim 1 further comprising the step of
`converting the symbols to a magnitude and phase form
`before sampling.
`
`35
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`45
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`50
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`55
`
`4
`3.1‘he method ofclaimlwherein the stepofdetermining
`a phase error comprises the step of providing the phase-only
`portion to a phase locked loop for determination of the phase
`error for each of the samples.
`4. The method of claim 3 further comprising the step of
`determining an average phase of a predetermined number of
`the symbols from the phase-only portions of the symbols.
`5. The method of claim 4 further comprising the step of
`providing the average phase to the phase locked loop.
`6. The method of claim 1 wherein the signal quality
`estimate is an average magnitude of a predetermined number
`of the sample phase errors.
`‘7. A method of estimating signal quality in a DPSK
`demodulator in which the estimate of signal quality is used
`to establish a level of demodulation acquisition
`performance. the method comprising the steps of:
`
`(a) sampling each symbol in a stream of symbols input to
`a DPSK demodulator;
`
`(b) conva'ting the samples to polar coordinate fonn:
`to) determining a phase error for each of the samples
`using a phase-only portion of the polar coordinate
`form; and
`
`is
`
`(d) calculating a signal quality estimate from a plurality of
`the sample phase errors.
`8. The method of claim 7 wherein the stream of symbols
`is a stream of data to be demodulated.
`9. The method of claim 8 wherein the signal quality
`estimate is an average magnitude of a predetermined number
`of the sample phase errors.
`10. The method of claim 7 wherein the stream of symbols
`is a preamble to a data signal.
`11. The method of claim 10 wherein the signal quality
`estimate is an average magnitude of the sample phase errors
`in a block of the symbols received from a first antenna.
`12. The method of claim 7 wherein each symbol
`sampled once.
`13. A method of estimating signal quality in a data radio
`demodulator comprising the steps of:
`(a) providing I and Q components of a stream of data
`symbols to a data radio demodulator;
`(b) combining the I and Q components for each of the
`symbols:
`(c) sampling the combined I and Q components for each
`of the symbols at the rate of one sample per symbol
`(d) converting the samples to polar coordinate form;
`(e) providing a phase-only portion of the polar coordinate
`form to a phase locked loop for determination of a
`phase error for each of the samples:
`(f) calculating an average magnitude of a plurality of the
`sample phase errors; and
`(g) providing the average magnitude to an input to the
`demodulator as a signal quality estimate.
`14. The method of claim 13 ftn‘ther comprising the steps
`of determining an average phase of a predetermined number
`of the symbols from the phase-only portions of the symbols,
`and providing the average phase to the phase locked loop.
`15. The method of claim 14 further comprising the step of
`providing an average of magnitude-only portions of the
`symbols to the input to the demodulator as a further signal
`quality estimate.
`
`attest
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 4
`
`Petitioner Sirius XM Radio Inc. - Ex. 1005, p. 4
`
`