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`USN-3061997131
`
`(121 United States Patent
`Eberlein et al.
`
`[10} Patent No.:
`
`(45} Date of Patent:
`
`US 7,061,997 BI
`Jun. 13, 2006
`
`(54) METHOD AND APPARATUS FOR FINE
`FREQUENCY SYNCHRONIZATTON IN
`MULTl—(TARRIER DIE-MODULATION
`SYSTEMS
`
`(75}
`
`inventors: Ernst Eben-loin. Grossenseebach (DE):
`Sabah Badri. Erlangen (DE); Stefan
`Lipp. Eriangen (DE): Stephan
`Buchbulr. Munich (DE): Albert
`lieuberger. lirlangcn (Di-l): Heinz
`Gerhaeuser. Waiscltenl'eld (DIE)
`(73) Assignee: Fraunhofer-Gesellschal‘t znr
`Foerderung der angewandten
`Forsehung e.V.. Munich. (DE)
`
`( “ ] Notice:
`
`Subject to any disclaimer. the temt oitltis
`patent is extended or adjusted under 35
`U.S.C‘. 154(b) by 0 days.
`
`(21 ) Appl. No.:
`
`09f673,270
`
`(22)
`
`PCT Filed:
`
`Apr. [4. l998
`
`(86) PCT No.:
`
`PCTIEP98H|2184
`
`§ 37] (e)(l).
`(2). (4) Date:
`
`Nov. 29, 2000
`
`(87) PCT Pub. No: W099i‘53667
`
`PCT Pub. Date: Oct. 21. I999
`
`(51)
`
`Int. (.1.
`H03!) 3/22
`H0” [1100
`
`(2006.01)
`(2006.01)
`
`375f3322370i210
`(52) U.S. C1.
`3753332.
`(58} Field of Classification Search
`3751200: 370(203. 200. 20?. 480. 210
`See application tile for complete search history.
`
`(56)
`
`References Cited
`
`U .S. PATENT DOCUMENTS
`4.347.483 A "
`8519112
`lilasrn etal.
`5.267.273 A “
`11:]!193 [)arloisel a].
`
`331-12
`
`.
`
`5.345.440 A "
`
`9"1994 Giedhiiiet ai.
`
`370.210
`
`(Continued)
`
`EP
`
`l-‘OREIGN PA'I'i-IN’I' lXX‘lJMliN’I'S
`082 2682
`2-"1998
`
`(Continued)
`
`0'” “ER 1’Ul11..1('ATlONS
`
`Keller and Harlan: “Orthogonal liraiuency Division Multi-
`plex Synchronisation Techniques for Wireless Local Area
`Networks". {EEE International Srntpost‘ma on Personal.
`indoor and Mobile Radio Conmmm‘r'on‘ons. pp. 963-967
`(Oct. 1996).
`
`((‘o nt inued)
`
`Prt‘mert- Examiner—Stephen Chin
`Assistant Examiner—Cicely Ware
`(74) Afloflfc'l'. Agent. or Firm- --Roy!ance.Abrams.Berdo &
`Goodman. I..L.I’.
`
`(57)
`
`ABSTRACT
`
`A method and an apparatus relating to a fine frequency
`synchronization compensating for a carrier frequency devia-
`tion li-om an oscillator frequency in a multi-carrier demodu-
`lation system of the type capable of carrying out a differ-
`ential phase decoding oi‘multi-carrier modulated signals. the
`signals comprising a plurality of symbols. each symbol
`being defined by phase dilierences between simultaneous
`carriers having. different
`licquencies. A phase dili'erence
`between phases of the same carrier in different symbols is
`determined. 'I'herutiicr. a frequency oii'sct is dctemiined by
`eliminating phase shill uncertainties related to the transmit-
`ted information from the phase difl’erenee making use of a
`M-PSK decision device. Finally. a feedback correction of
`the carrier frequency deviation is performed based on the
`determined frtaincncy oil's-ct. Alternatively. an averaged in:-
`queney offset can be determined by averaging determined
`frequency offsets of a plurality of carriers. Then. the feed-
`back correction of the frequency deviation is performed
`based on the averaged frequency oil‘set.
`
`7 (flalms. 13 Drawing Sheets
`
`
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 1
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 1
`
`

`

`US 7,061,997 B].
`Page 2
`
`U .S. PA'I‘EN'I'
`
`DOCTU MliN'l'S
`
`Zou and Wu. “C‘OF13M: An Overview“. iEL-‘E Yi'ansactt‘ons
`
`5.094.389 A ‘“
`5.771.224 A
`6.192.068 BI “
`6.2[9333 Bl '
`6.226.337 BI ‘
`
`370x208
`[2-1997 Seki et al.
`370.3206
`6.-'1998 Saki et al.
`
`375-130
`2:200! Faltoucheet a].
`4.-'200I Aim ........................... 370.3203
`5:"200I Klan]: et al.
`375.5367
`
`.lP
`JP
`W0
`W0
`
`FOREIGN PATENT DOCUMENTS
`8265293
`10." I 996
`l04l99l
`2.1998
`9205 646
`4.-' I 992
`9800946
`I. I 998
`
`OTHER PUBLICATIONS
`
`Moose. “A Technique for Orthogonal Frequency Division
`Multiplexing Frequency Oflset Correction“. JEEE Transac-
`tions on Communications. vol. 42. No. 30. pp. 2908—2914
`(Oct. 1994}.
`Classen and Meyr. "Synchronization Algorithms for an
`OFDM System for Mobile Cortmlunication". Condierung
`fit! Quelle. Kanal and Ubertmgung: ITG-Fachben'cht. pp.
`105-114 (Oct. 1994).
`"Low-Overhead. Low-(Tomplexity
`Schmidl
`and Cox.
`[Burst] Synchronimtion for 01'-'[)M‘. Prov. iEEE Int. (font
`on Common. pp. 1301-1306 (I996).
`
`l~8 (Mar. 1995}.
`on Brandmsring. vol. 4!. No. 1. pp.
`Palncherla. “DSP-ttP Routine Computes Magnitude“. EDN
`Eileen-ice! Design News. vol. 34. No. 22. pp. 225-226 (Oct.
`1989).
`Adams and Brady. “Magnitude Appmxmations for Micro-
`processor Implementation“. IEEE Micro. vol. 3. No. 5. pp.
`27-31 (Oct. 1983).
`Luise and Regiannini. “Carrier Frequency Acquisition and
`‘I‘rackirtg For OFDM Systems". JEEE Truman-lions on Cam-
`mrmir‘aiions. Vol. 44. No. ll. pp. 1590-1598 (Nov. 1996).
`Tuisel and Kammcyer. “(‘an'ier-Remvery for Mttlticarrier-
`Transmission Over Mobile Radio Channels“. Int. Coryf on
`Amusiics. Speech and Signal Processing (ICASSP 92). San
`Francisco. Band 4. pp. 677-680 [1992).
`Moose. “Dill'crenlially Coded Multi-l-‘requeney Modulation
`for
`Digital
`Communications".
`Sigaai
`Processing
`V—Theories and Applications. Proceedings of EUSIPC'O-
`90
`Fifth European
`Signal
`Processing Conference.
`Barcelona. Spain. vol. 1]]. pp. 1807-1810 (Sep. 1990).
`
`“ cited by examiner
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 2
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 2
`
`

`

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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 3
`
`
`
`

`

`US. Patent
`
`Jun. 13, 2006
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 4
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`

`

`US. Patent
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`Jun. 13, 2006
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 5
`
`

`

`US. Patent
`
`Jun. 13, 2006
`
`Sheet 4 of 13
`
`US 7,061,997 Bl
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`frequency
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`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 6
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 6
`
`

`

`US. Patent
`
`Jun. 13, 2006
`
`Sheet 5 of 13
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`US 7,061,997 Bl
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 7
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 7
`
`

`

`US. Patent
`
`Jun. 13, 2006
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 8
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`

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`US. Patent
`
`Jun. 13, 2006
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 9
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 10
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 11
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 12
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 14
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`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 15
`
`
`

`

`US 1061,99? Bl
`
`1
`METHOD AND APPARATUS FOR FINE
`FREQUENCY SYNCHRONIZA‘I'ION IN
`MULTl-(TARRIER DEMODULA'I'ION
`SYSTEMS
`
`This application is a 371 of P('ffEP98l02184 Apr. 14.
`1998.
`
`FIELD OF THE INVENTION
`
`The present invention relates to methods and apparatus
`for performing a line frequency synchronization itt multi-
`carrier demodulation systems. and in particular to methods
`and apparatus for periorming a line frequency synchmnim-
`tion compensating for a carrier frequency deviation from an
`oscillator frequency in a multi-carrier demodulation system
`of the type capable of carrying out a differential phase
`decoding of ntulti-carrier modulated signals. wherein the
`signals comprise a plurality of symbols. each symbol being
`defined by phase differences between simultaneous carriers
`having difl‘erent frequencies.
`
`BACKGROUND OF THE INV’lENfION
`
`In a multi carrier transmission system {MCM. OFDM}.
`the effect of a carrier frequency offset is substantially more
`considerable than in a single carrier transmission system.
`MCM is more sensitive to phase noise and frequency oll‘set
`which occurs as amplitude distortion and inter carrier inter—
`ference (ICl ). The inter carrier interference has the effect that
`the subcarriers are no longer orthogonal in relation to each
`other. Frequency offsets occur after power on or also later
`due to Frequency deviation of the oscillators used for down-
`conversion into baseband. Typical accuracies for the fre-
`quency of a free running oscillator are about :50 ppm of the
`carrier frequency. With a carrier frequency in the S—band of
`2.34 Ghz. for example. there will be a maximum local
`oscillator (LO)
`frequency deviation of above 100 ltI-lz
`(1 I725 ltI-lx}. The above named effects result
`in high
`requirements on the algorithm used for frequency offset
`correction.
`
`DESCRIPTION OF PRIOR ART
`
`Most prior art algorithms for frequency synchronization
`divide frequency correction into two stages.
`in the first
`stage. a coarse synchronization is performed. In the second
`stage. a fine correction can be achieved. A frequently used
`algorithm for coarse synchronization of the carrier fre-
`quency uses a synchronisation symbol which has a special
`spectral pattern in the frequency domain. Such a synchro-
`nization symbol
`is.
`for example.
`a CAZAC sequence
`(CAZAC=Constant Amplitude
`zero Autocorrelation}.
`'lhrough comparison, Le.
`the correlation of the power
`spectrum of the received signal with that of the transmitted
`signal.
`the frequency carrier offset can be warsely esti—
`mated. 'I'hesc prior art algorithms all work in the frequency
`domain. Reference is made.
`for example.
`to Ferdinand
`Clalien. Heinrich Meyr. “Synchronization Algorithms for an
`OFDM System for Mobile Communication". lTG-Fachta-
`gung 130. Codierung fiir Quelle. Kanal uttd llbertragung.
`pp. l05- 113. Oct. 26 28. 1994: and Timothy M. Schmidl.
`Donald C‘. Cox. "Low-overhead. Low-Complexity [Burst]
`synchronization for OFDM".
`in Proceedings of the IEEE
`international conference on communication 1CC 1996. pp.
`1301—1306 (1996).
`
`lo
`
`20
`
`3-0
`
`35
`
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`
`45
`
`50
`
`55
`
`(If)
`
`65
`
`2
`
`For the coarse synchronization of the carrier frequency.
`Paul H. Moose. "A Technique for orthogonal Frequency
`Division Multiplexing Frequency oli'set Correction“. HERE
`Transaction on communications. Vol. 42. No.
`[0. October
`1994. suggest increasing the spacing between the subcarriers
`such that the subcarrier distance is greater than the maxi-
`mum l‘requertcy ditliarence between the reteived and trans-
`mitted carriers. The subcarrier distance is increased by
`reducing the number of sample values which are trans-
`formed by the Fast Fourier Transform. This corresponds to
`a reduction of the number of sampling values which are
`transitioned by the Fast Fourier Transform.
`WC) 9205646 A relates to methods for the reception of
`orthogonal frequency division multiplexed signals compris-
`ing data which are preferably difl'erentially coded in the
`direction of the time axis. Phase drifi of the demodulated
`
`samples from one block to the next is used to indicate the
`degree of local oscillator frequency error. Phase drift
`is
`assessed by multiplying complex valuos by the complex
`conjugate of an earlier sampte demodulated from the same
`OFDM carrier and using the resulting measure to steer the
`local oscillator frequency via a frequency locked loop.
`
`SUMMARY OF THE INVEN'I'ION
`
`It is an object ofthe present invention to provide methods
`and apparatus for performing a fine frequency synchroniza-
`tion which allow a fine frequency synchronization compen-
`sating for a carrier licquency deviation frotn an oscillator
`frequency in a MCM transmission system which makes use
`of MCM signals in which information is dilferential phase
`encoded between simultaneous sub-carriers having different
`frequencies.
`In accordance with a first aspect. the present invention
`provides a method of pcrfonuing a line frequency synchro-
`nization compensating for a carrier frequency deviation
`from an oscillator frequency in a multi-can'ier demodulation
`system of the type capable of can'ying out a diflemntial
`phase decoding of mulIi-carrier modulated signals. the sig-
`nals comprising a plurality of symbols. each symbol being
`defined by phase differences between simultaneous carriers
`having different
`frequencies.
`the method comprising the
`steps of:
`determining a phase difference between phases of the same
`carrier in different symbols:
`determining a frequency olfset by eliminating phase shift
`uncertainties related to the transmitted information from
`
`the phase difference making use of a M-PSK decision
`device: and
`
`perfon'ning a feedback correction of the carrier frequency
`deviation based on the determined frequency offset.
`In accordance with a second aspect. the present invention
`provides a method of pcrfonning a line frequency synchro-
`nization compensating for a carrier frequency deviation
`from an oscillator frequency in a ntulti-canier demodulation
`system of the type capable of can'ying out a differential
`phase decoding of mulli-carrier modulated signals. the sig-
`nals comprising a plurality of symbols. each symbol being
`defined by phase difierences between simultaneous carriers
`having different
`frequencies.
`the method comprising the
`steps of:
`determining respective phases of the same carrier in differ-
`ent symbols:
`eliminating phase shift uncertainties related to the transmit-
`ted information from the phases to determine respective
`phase deviations making use of a MoPSK decision device:
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 16
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 16
`
`

`

`US 7,061.99? Bl
`
`3
`determining a frequency offset by determining a phase
`difference between the phase deviations: and
`performing a feedback correction of said carrier frequency
`deviation based on the determined frequency ofl'set.
`In accordance with a third aspect. the present invention
`pmvidts an apparatus for performing. a fine frequency
`synchronisation compensating for a carrier frequency devia-
`tion from an oscillator
`frequency.
`for a multi-carrier
`dctnodulation system of the type capable of carrying out a
`differential phase decoding of multi-carrier modulated sig-
`nals. the signals comprising a plurality of symbols. each
`symbol being defined by phase differences between simul-
`taneous carriers having different frequencies. the apparatus
`comprising:
`means for determining a phase difference between phases of
`the same carrier in different symbols:
`M-PSK decision device for determining a frequency oh'set
`by eliminating phase shift uncertainties related to the
`transmitted information front the phase difference: and
`means for performing a feedback correction ofthe frequency
`deviation based on the determined frequency offset.
`In accordance with a fourth aspect. the present invention
`provides an apparatus for perfonning a fine frequency
`synchroniration compensating for a carrier frequency devia-
`tion from an oscillator
`frequency.
`for a multi-carricr
`demodulation system of the type capable of carrying out a
`diflercntial phase decoding of multi-can'ier modulated sig-
`nals. said signals comprising a plurality of symbols. each
`symbol being defined by phase differences between simul-
`taneous carriers having different frequencies. the apparatus
`comprising:
`means for determining respective phases ofthe same carrier
`in difl'erent symbols:
`M-PSK decision device liar eliminating phase shill uncer-
`tainties related to the transmitted infonnation from the
`
`phases to detcnninc respective phase deviations:
`means for determining a frequency offset by determining a
`phase difference between the phase deviations: and
`means for performing a feedback correction ofthc frequency
`deviation based on the determined frequency offset.
`The present invention relates to methods and apparatus
`for performing a fine frequency synchronization compen-
`sating liar a carrier frequency deviation from an oscillator
`frequency. This line frequency synchronization is preferably
`performed after completion ofa coarse frequency synchro-
`ni'zation. such that the frcqucncy offsets after the coarse
`frequency synchronization are smaller than half the sub-
`carrier distance in the MCM signal. Since the frequency
`offsets which are to be corrected by the inventive fine
`frequency synchronization methods and apparatus. a correc-
`tion of the frequency offsets by using a phase rotation with
`differential decoding and dc-mapping in the time axis can be
`used. The frequency offsets are detected by determining. the
`frequency diflerences between time contiguous sub-carrier
`sytubols along the time axis. The frequency error is calcu-
`lated by measuring the rotation of the l-Q Cartesian coor-
`dinates of each sub-carrier and. in preferred embodiments.
`averaging them over all n sub-carriers of a MCM symbol.
`Firstly. the phase ambiguity or uncertainty is eliminated
`by using a M-PSK decision device and correlating the output
`ofthe decision device with the input signal for a respective
`sub-carrier symbol. Thus. the phase offset for a sub-carrier
`symbol is determined and can be used for restructuring the
`Ii'equency cum in form ofa Iced-backward structure. Alter-
`natively. the phase ofl'sets of the sub-carrier symbols of one
`MC M symbol cart be averaged over all of the active carriers
`
`4
`
`of a MCM symbol. wherein the averaged phase offset is used
`to restructure the frequency error.
`In accordance with the present invention. the determina-
`tion of the frequency offset is perfonned in the frequency
`domain. The feedback correction in accordance with the
`
`inventive fine frequency synchronization is performed in the
`time domain. To this end. a ditltarcntiai decoder in the time
`domain is provided in order to detect frequency offsets of
`sub-carriers on the basis of the phases of timely successive
`sub-carrier symbols of different MCM symbols.
`
`It!
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the following. preferred embodiments of the present
`invention will be explained in detail on the basis of the
`drawings enclosed. in which:
`FIG. 1 shows a schematic overview ofa MC M transmis-
`sion system to which the present application can be applied:
`FIGS. 2A and 213 show schematic views representing a
`scheme for differential mapping in the time axis and a
`scheme for differential mapping in the frequency axis:
`FIG. 3 shows a functional block diagram for performing
`a difl'erential mapping in the frequency axis:
`FIG. 4 shows a representation of time variation of all
`sub-can'icrs in MCM symbols:
`FIG. 5 shows a QPSK-constellation for each sub-carrier
`with a frequency offset:
`FIG. 6 shows a general block diagram illustrating the
`position of the inventive line frequency synchmniration
`device in a MC‘M receiver.
`FIG. 7 shows a block diagram ofthc line frequency error
`detector shown in FIG. 6:
`
`FIG. 8 shows a block diagram of a MCM receiver
`comprising a coarse frequency syncluonizzttion unit and a
`line frequency synchronization unit;
`FIG. 9 shows a block diagram ofa unit for performing a
`coarse frequency synchmnimtion:
`FIG. 10 shows a schematic view of a reference symbol
`used for perlonning a coarse frequency synchronization:
`FIG. 11 shows a schematic view of a typical MCM signal
`having a frame structure:
`FIG. 12 shows scatter diagrams of the output of an
`(differential de-rnapper of an MCM receiver for illustrating
`the reflect ofan echo phase offset correction:
`FIG. 13 shows a schematic block diagram for illustrating
`the position and the functionality of an echo phase offset
`correction unit;
`FIG. 14 shows a schematic block diagram of a preferred
`form ofan echo phase offset correction device: and
`FIG. l5 shows schematic views for illustrating a projec-
`tion perfomred by another echo phase offset correction
`ulgoritlun.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`the
`invention in detail.
`Before discussing the present
`mode of operation of a MCM transmission system is
`described referring to FIG. 1.
`Referring to FIG. 1. at 100 a MCM transmitter is shown
`that substantially corresponds to a prior an MCM transmit-
`ter. A description of such a MCM transmitter can be found.
`for example. in William Y. Zou. Yryan Wu. “('UFDM: AN
`OVERVIEW". IEIEE Transactions on Broadcasting. vol. 41.
`No. 1. March 1995.
`A data source 102 provides a serial bitstream 104 to the
`MCM transmitter. The incoming serial bitstream 104 is
`
`20
`
`3-0
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`(If)
`
`65
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 17
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 17
`
`

`

`US 1061,99? Bl
`
`5
`applied to a bit-carrier mapper 106 which produces a
`sequence of spectra 108 from the incoming serial bitstream
`104. An inverse fast Fourier transform (IFF'I‘) 110 is per-
`formed on the sequence ofspectra 108 in order to produce
`a MCM time domain signal 112. The MCM time domain
`signal fomts the useful MCM symbol of the MGM time
`signal. To avoid inter-symbol interterence (IS!) caused by
`multipath distortion. a unit 114 is provided for inserting a
`guard interval of fitted length between adjacent MC M sym-
`bols in time. In accordance with a preferred embodiment of to
`the present
`invention.
`the last pan of the useful MCM
`symbol is used as the guard interval by placing same in front
`of the useful symbol. The resulting MCM symbol is shown
`at 115 in FIG. 1 and corresponds to a MCM symbol 160
`depicted in FIG. 11.
`FIG. 11 shows the construction ofa typical MC M signal
`having a frame structure. One frame of the MC M time signal
`is composed of a plurality of MCM symbols 160.
`ltach
`MC‘M symbol 160 is formed by an useful symbol 162 and
`a guard interval 164 associated therewith. AS shown in FIG.
`11. each frame comprises one reference symbol 166. The
`present invention can advantageously he used with such a
`MCM signal. however. such a signal structure being not
`necessary for performing the present invention as long as the
`tnmsmitted signal comprises a useful portion and at least one
`reference symbol.
`In order to obtain the final frame structure shown in FIG.
`11. a unit 116 for adding a reference symbol
`for much
`predetermined number of MCM symbols is provided.
`In accordance with the present invention. the reference
`symbol is an amplitude modulated hit sequence. Thus. an
`amplitude modulation ofa bit sequence is performed such
`that the envelope of the amplitude modulated bit sequence
`defines a reference pattern of tlte reference symbol. This
`reference pattem defined by the envelope of the amplitude
`modulated bit sequence has to be detected when receiving
`the MC M signal at a MCM receiver. In a preferred embodi-
`ment of the present invention. a pseudo random bit sequence
`having good autocorrelation properties is used as the bit
`sequence that is amplitude modulated.
`The choice of length and repetition rate of the reference
`symbol depends on the properties of the channel through
`which the MCM signal is transmitted. e.g. the coherence
`time of the channel. In addition. the repetition rate and the
`length of the reference symbol. in other words the number
`of useful symbols in each frame. depends on the receiver
`requirements concerning mean time for initial synchroniza-
`tion and mean time for resynchronization after synchroni-
`zation loss due to a channel fade.
`
`20
`
`3-0
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`(II)
`
`65
`
`The resulting MC M signal having the structure shown at
`118 in FIG.
`1
`is applied to the transmitter front end 120.
`Roughly speaking. at the transmitter front end 120, a digital;Ir
`analog conversion and an tip-converting of the MCM signal
`is performed. Thereafter. the MC M signal
`is transmitted
`through a channel 122.
`Following. the mode of operation ofa MC‘M receiver 130
`is shortly described referring to FIG. 1. The MCM signal is
`received at the receiver front end 132. In the receiver front
`end 132. the MCM signal is down—convened and. timber-
`more. an analogfdigital conversion of the down-converted
`signal is performed.
`The down-converted MCM signal is provided to a symbol
`framel'carrier frequency synchronization unit 134.
`A first object of the symbol
`framel'carrier
`frequency
`synchronization unit 134 is to perform a frame synchroni-
`zation on the basis of the amplitude-modulated reference
`symbol. This frame synchronization is performed on the
`
`6
`basis of a correlation between the amplitude—demodulated
`reference symbol and a predetermined reference pattern
`stored in the MCM receiver.
`
`A second object of the symbol frameicarrier frequency
`synchronimtion unit is to perform a coarse frequency syn-
`chronization of the MC M signal. To this end. the symbol
`frantefcarricr t'reqnency synchronization unit 134 serves as a
`coarse frequency synchrtmization unit
`for detcmtining a
`coarse frequency offset of the carrier frequence caused. for
`example. by a difl‘erence of the fiequencies between the
`local oscillator of the transmitter and the local oscillator of
`
`the receiver. The determined frequency is used in order to
`pert'omt a coarse frequency correction. ‘Ihe mode of opera-
`tiun of the coarse frequency synchmuization unit
`is
`described in detail referring to FIGS. 9 and 10 hereinafter.
`As described above. the frame synchronization unit 134
`detemtines the location of the reference symbol in the MCM
`symbol. Based on the determination of the frame synchro-
`nization unit [34. a reference symbol extracting unit 136
`extracts the framing infonuation. i.e. the reference symbol.
`from the MC M symbol coming from the receiver front end
`132. After the extraction of the reference symbol. the MCM
`signal is applied to a guard interval removal unit 138. The
`result of the signal processing performed hereherto in the
`MGM receiver are the useful MCM symbols.
`The useful MCM symbols output from the guard interval
`removal unit 138 are provided to a fast Fourier transfomt
`unit 140 in order to provide a sequence of spectra from the
`useful symbols. Thereafter. the sequence of spectra is pro-
`vided to a carrier-bit mapper 142 in which the serial bit-
`stream is recovered. This serial bitstream is provided to a
`data sink 144.
`two modes for
`Next. referring to FIGS. 2A and 28.
`differential mapping are described.
`In FIG. 2A. a first
`method o fdilferential mapping along the time axis is shown.
`AS can be seen from FIG. 2A. a MUM symbol consists of
`K subcarricrs. The sub-carriers comprise dillerent frequen-
`cies and are. in a preferred embodiment. equally spaced in
`the frequency axis direction. When using differential map-
`ping along the time axis. one or more bits are encoded into
`phase andi'or amplitude shifts between two sub-carriers of
`the same center frequency in adjacent MCM symbols. The
`arrows depicted between the sub-carrier symbols correspond
`to information encoded in amplitude andfor phase shifts
`between Mo sub-carrier symbols.
`A second method ofdifl'ercntial mapping is shown in FIG.
`28. The present invention is adapted for MCM transmission
`system using the mapping scheme shown in FIG. 28. Tltis
`mapping scheme is based on a differential mapping inside
`one MC M symbol along the frequency axis. A another of
`MCM symbols 200 are shown in FIG. 213. Each MC M
`symbol 200 comprises a number ofsub-can'ier symbols 202.
`The armws 204 in FIG. 2B iIIUstrate information encoded
`between two sub-carrier symbols 202. As can be seen from
`the arrows 204. this mapping scheme is based on a dilfer—
`ential mapping within one MCM symbol along the fre»
`quency axis direction.
`In the embodiment shown in F IG. 213. the first sub-carrier
`(lo—0)
`in an MCM symbol 200 is used as a reference
`sub-carrier 206 (shaded) such that information is encoded
`between the reference sub-carrier and the first active carrier
`
`208. The other information of a MC M symbol 200 is
`encoded between active carriers. respectively.
`Thus. for every MCM symbol an absolute phase reference
`exists.
`In accordance with FIG. 23. this absolute phase
`reference is supplied by a reference symbol inserted into
`every MC"M symbol (k=0). The reference symbol can either
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 18
`
`Petitioner Sirius XM Radio Inc. - Ex. 1007, p. 18
`
`

`

`US 1061,99? Bl
`
`7
`have a constant phase for all MCM symbols or a phase that
`varies from MC‘M symbol to MUM symbol. A varying phase
`cart be obtained by replicating the phase from the last
`subcarrier of the MC M symbol preceding in time.
`In FIG. 3 a preferred embodiment of a device for per-
`forming a differential mapping along the frequency axis is
`shown. Referring to FIG. 3. assembly of MCM symbols in
`the frequency domain using ditl'erential mapping along the
`frequency axis according to the present
`invention is
`described.
`
`FIG. 3 shows the assembly of one MCM symbol with the
`following parenteters:
`NFI‘T designates the number of complex coefficients of the
`discrete Fourier transform. number of sttbcartiers respec-
`tively.
`K designates the number of active carriers. The reference
`carrier is not included in the count for K.
`
`According to FIG. 3. a quadrature phase shift keying
`(QP‘SK) is used for mapping the bitstream onto the complex
`symbols. However. other M-ary mapping schemes (MPSK)
`like 2-PSK. 8-PSK. ltS-QAM. 16-APSK. 64-APSK etc. are
`possible.
`Furthermore. for ease of filtering and minimization of
`aliasing effects some subcarriers are not used for encoding
`information in the device shown in FIG. 3. ’I'ltcse subcul't'l-
`ers, which are set
`to zero, constitute the so-called guard
`bands on the upper and lower edges of the MC M signal
`spectrum. At the in