United States Patent [191
`Balasubramaniam
`
`llllllIlllllllIllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`5,586,150
`Dec. 17, 1996
`
`US005586150A
`Patent Number:
`[11]
`[45] Date of Patent:
`
`[54] NIETHOD AND APPARATUS FOR SYMBOL
`SYNCHRONIZATION IN MULTI-LEVEL
`DIGITAL FM RADIO
`
`[75] Inventor: Rajupandaram K. Balasubramaniam,
`2420 NW. Rolling Green Dr. #30,
`Corvallis, Oreg. 97330
`
`[73] Assignee: Rajupandaram K. Balasubramaniam,
`Corvallis, Oreg.
`
`[21] Appl. No.: 157,996
`[22] Filed:
`Nov. 24, 1993
`
`[51] Int. Cl.6 .............................. .. H04L 7/00; H04L 7/02;
`H04L 25/49
`[52] U.S. Cl. ........................ .. 375/354; 375/357; 375/359;
`375/293
`[58] Field of Search ................................... .. 375/106, 107,
`375/17, 20, 354, 357, 359, 286, 287, 293;
`370/1001, 105.1, 105.2
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,702,008 10/1972 Groth.
`4,028,497
`6/1977 Saburi.
`4,054,863 10/1977 Goodman et a1. .
`4,100,499
`7/1978 Monrolin .
`4,117,267
`9/1978 Haberle et al. .
`4,161,786 7/1979 Hopkins et al. .
`4,204,093
`5/1980 Yeh ...................................... .. 370/951
`4,251,865
`2/1981 Moore et al. .
`4,312,075
`1/1982 Murano et al. ....................... .. 375/106
`4,322,845 3/1982 Fennel, Jr. et a1. ................... .. 370/104
`4,352,183
`9/1982 Davis et a1. .
`4,357,700 11/1982 Alvarez, III et a1. .
`4,414,661 11/1983 Karlslrom .......................... .. 370/1001
`4,491,947
`1/1985 Frank ........ ..
`370/941
`4,527,279
`7/1985 Yasuda et a1.
`..... .. 375/114
`4,538,147
`8/1985 Grow ............................... .. 340/825.05
`4,538,261
`8/1985 Kurne.
`4,564,838
`1/1986 Boulogne et a1. .
`455/54
`.
`4,573,207
`2/1986 Smith et a1.
`4,578,800
`3/1986 Yasuda et a1. ........................ .. 375/106
`
`FOREIGN PATENT DOCUMENTS
`
`1566305 4/1980 United Kingdom .
`
`OTHER PUBLICATIONS
`
`Goodman, D. & Wei, S. “Factors Affecting the Bandwidth
`E?iciency of Packet Reservation Multiple Access,” Pro
`ceedings of the 1989 IEEE Vehicular Tech. Conf., pp.
`292-299.
`Jalloul, L., Nanda, S., & Goodman, D. “Packet Reservation
`Mulitple Access over Slow and Fast Fading Channels,”
`IEEE, 1990, pp. 354-359.
`Eizenhofer, A. & von Harten, G. “BCMA: Backlog Con
`trolled Multiple Access,” Proceedings of 1988 IEEE Vehicu
`lar Tech. Conf. pp. 285—290.
`Goodman, D., Valenzuela, R. Gayliard, K. & Rarnamurthi,
`B. “Packet Reservation Multiple Access for Local Wireless
`Communications”, Proceedings of 1988 IEEE Vehicular
`Tech. Conf., pp. 701-706.
`Sollenberger, N. R.; Chuang, Justin C-I, IEEE 19, “Low
`Overhead Symbol Timing and Carrier Recovery for TDMA
`Portable Radio Systems”, pp.; pre-publication copy
`obtained May, 1990.
`
`(List continued on next page.)
`Primary Examiner—Stephen Chin
`Assistant Examiner-—Hai H. Phan
`
`ABSTRACT
`[57]
`A block demodulation method and apparatus that provides
`for synchronizing bursts of incoming data without a special
`symbol synchronization word, and minimal frame synchro
`nization overhead. An entire burst, comprising ramp up
`time, a preamble, guard times, data and ramp down time, is
`captured and stored in the form of baseband samples of the
`signal burst. The burst samples are then ?ltered to reduce
`pattern jitter. Thereafter, the samples are squared to derive
`the symbol clock. Then, the samples are differenced and
`cyclically accumulated. The cyclicly accumulated samples
`are examined to ?nd a valid zero crossing. In the event that
`the aforementioned method does not identify a valid zero
`crossing, two additional methods for ?nding a valid zero
`crossing are employed.
`
`(List continued on next page.)
`
`22 Claims, 5 Drawing Sheets
`
`38
`
`BURST
`CAPTURE
`
`52
`
`42
`
`44
`
`SYMBOL
`DETECTION
`
`M-CYCLIC
`ACCUMULATOR
`
`55
`FORM
`-> HISTOGRAM ->|
`
`/
`
`OVER 4 BINS
`
`ea
`Y /
`M-C cuc
`ACCUMULATOR
`
`|—>L
`
`70
`12
`/
`|—->|:THRE$HOUJ
`FIND
`MAXIMUM
`‘vol
`
`50
`7a
`16
`Z4
`1
`CONSTRUCT
`FORM
`FIND
`M-CYCLIC
`/
`_. DWFERENCE _. WWW — -
`ACCUMULATOR
`MAXIMUM
`OVER M
`OVER 7 BINS
`
`7 LEVEL EYE
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 1 of 11
`
`

`
`5,586,150
`Page 2
`
`US. PATENT DOCUMENTS
`
`4/1986 Kittel.
`4,583,217
`9/1986 Davis et a1. ......................... .. 370/95.l
`4,612,637
`2/1987 Raychaudhun' ........ ..
`370/95.1
`4,641,304
`3/1987 Serfaty et a1. ........................ .. 307/269
`4,651,026
`6/1987 Bourgonje et a1. .
`4,672,606
`7/1987 Kelch et a1. .
`4,683,531
`8/1987 Eizenhofer et a1. .................. .. 375/107
`4,688,210
`4,712,229 12/1987 Nakamura ............................... .. 379/58
`4,736,371
`4/1988 Tejirna et al. .
`4,742,512
`5/1988 Akashi et a1. ........................ .. 370/104
`4,745,600
`5/1988 Herman etal. ..
`.. 370/95.l
`4,754,453
`6/1988 Eizenhofer ..... ..
`.. 370/95.1
`4,756,007
`7/1988 Qureshi et a1. ..
`375/8
`4,763,322
`8/1988 Eizenhofer ..... ..
`. 370/110.1
`4,774,707
`9/1988 Raychaudhuri ..
`370/95.1
`4,775,974 10/1988 Kobayashi ..... ..
`370/104
`4,782,484 11/1988 Limb .......... ..
`370/100
`4,799,252
`1/1989 Eizenho?ler ..
`.... .. 379/59
`4,803,681
`2/1989 Takahashi ........................... .. 370/85
`4,807,257
`2/1989 Schouhamer Immink et a1.
`375/106
`4,815,073
`3/1989 Grauel et al. .................. ..
`.. 370/95.1
`4,817,089
`3/1989 Paneth et a1.
`370/109
`4,849,991
`7/1989 Arnold et al.
`375/106
`4,850,033
`7/1989 Eizenhofer ....................... .. 455/56
`4,887,266 12/1989 Neve et a1. .......................... .. 370/95.1
`4,888,765 12/1989 Dyke .......... ..
`370/95.1
`4,890,299 12/1989 Dolivo et a1.
`375/18
`
`4,896,334
`
`1/1990 Sayar . . . . . . . . . . .
`
`3/1990 Scoles et a1.
`4,907,224
`6/1990 Sonetaka .... ..
`4,937,818
`4,940,974 7/1990 Sojka ......... ..
`4,941,155
`7/1990 Chuang et al.
`
`. . . . .. 375/20.
`
`.. 370/85.2
`370/95.3
`370/95.2
`375/106
`
`4,949,395
`. . . . .. 455/33
`8/1990 Rydbeck . . . . . .
`4,953,185
`375/106
`8/1990 Goode ........ ..
`4,984,255
`1/1991 Davis et a1. .......................... .. 375/106
`4,987,571
`l/1991 Haymond et al. ................... .. 370/85.3
`5,003,534
`3/1991 Gerhardt et a1.
`370/94.1
`5,008,883
`4/1991 Eizenhdfer et a1. .
`370/95.1
`5,012,469
`4/1991 Sardana .......... ..
`.. 370/95.3
`5,070,536 12/1991 Mahany et al.
`455/67.1
`5,072,445 12/1991 Nawata ................................. .. 375/109
`5,081,622
`1/1992 Nassehi et a1. ...................... .. 370/85.2
`5,084,891
`1/1992 Ariyavisitakul et a1.
`.... .. 371/42
`
`5,103,445
`
`4/1992 Ostlund . . . . . . . . . . . . . . . .
`
`. . . . .. 370/79
`
`6/1992 Gerhardt et a1. ..................... .. 370/85.2
`5,121,387
`5,166,929 11/1992 Lo .
`
`5,172,375 12/1992 Kou . . . . . .
`. . . . . .. 370/95.3
`5,199,031
`3/1993 Dahlin ................................ .. 370/110.1
`
`OTHER PUBLICATIONS
`
`Furuya, Y.; Akashi, F.; Murakaurni, S., IEEE 1983, “A
`Practical Approach Toward Maximum Likelihood Sequence
`Estimation for Band-Limited Nonlinear Channels”, pp.
`200-207.
`Dechambre, M. & Levy, A. J ., “Limits of Data Rates in the
`Urban Mobile Channel”, Proceedings of 1987 IEEE Vehicu
`lar Tech. Conf., pp. 541-546.
`Feher, K. “MODEMS for Emerging Digital Cellular-Mobile
`Radio System”, IEEE Transactions on Vehicular Technol
`ogy, vol. 40, No. 2, May 1991, pp. 355-365.
`Akaiwa, Y., Takase, 1., Kojima, S., lkoma, M., & Saegusa,
`N. “Performance of Baseband-Bandlimited Multilevel PM
`with Discriminator for Digital Mobile Telephony”, Trans
`lations of IECE 0 Japan, vol. E64, No. 7, Jul. 1987, pp.
`463-469.
`
`Kleinrock, L. & Tobagi, F. “Random Access Techniques for
`Data Transmission Over Packet-Switched Radio Channels”,
`Proceedings of 1975 National Computer Conf., pp.
`187-201.
`Rosner, R. D., Packet Switching: Tomorrow’s Communica
`tions Today, Belmont, CA 1982, Chapters 13-15.
`Lee, W. C. Y., Mobile Communications Design Fundamen
`tals, New York, NY 1993, pp. 1-44, 169-173.
`Schoute, F. C., “Dynamic Frane Length ALOHA” ieee
`Trans. Comm. vol. Com. -31, No. 4, pp. 565-568, 1983.
`Onozato, Y. & Kato, T. “Stability Analysis of Combined
`Random/Reservation Access Methods”, Electronics and
`Communications in Japan, Part 1, vol. 72, No. 4, 1989, pp.
`10-17.
`Benelli, G. “Some New Retransmission Strategies for Mul
`tipacket Slotted ALOHA Protocol”, IEEE Proceedings, vol.
`135, Pt. F, No. 6, Dec. 1988, pp. 585-593.
`Wong, E. & Yum, T. “The Controlled-SRMA Protocol for
`Packet Satellite Communication”, Record of the 1988 IEEE
`International Conference on Communications, vol. 2, pp.
`812-818.
`Davie, M. & Smith, J. “A Cellular Packet Radio Data
`Network”, Electronics & Communication Engineering Jour
`nal, vol. 3, No. 3, Jun. 1991, pp. 137-143.
`RAM Mobile Data, Inc., “An Overview of The RAM
`Mobile Data, Inc. Mobitex Packet Radio Networks”, Aug,
`1990, pp. 21-23, 27, 28, 31-34, 51-52.
`Motorola European Research Laboraory, “Mobile Digital
`Tmnked Radio System”, Feb., 1991, pp. 1-7.
`Bustillo, et al. “Datamobile: A Practical Implementation of
`TRADAMO Mobile Data Transmission Protocol”, Proceed~
`ings of the 1989 IEEE Vehicular Tech. Conf., pp. 35-37.
`H Morrow/United Parcel Service, “Technical Presentation,”
`FCC PR Docket No. 89-552, Dec., 1990, pp. l-25.
`Fielding et al., “Comments of United Parcel Service, Inc.,”
`Mar. 1990, FCC PR Docket No. 89-552, RM-6595, pp.
`1-50, 1-33.
`I
`Federal Communications Commission, “Notice of Proposed
`Rule-making,” P.R. Docket 89-552 RM-6595, Dec. 1989,
`pp. 1-20.
`Federal Communications Commission, “Report and Order,”
`RR. Docket No. 89-552, RM-6595, pp. 1-35.
`MPT 1327, “A Signalling Standard for Tmnked Private
`Land Mobile Radio Systems,” Jan., 1988, pp. cover page,
`1-8, 1-13, 6-7, 7-1 through 7-10, 14-1 through 14-10,
`15-1 through 15-3, 17-1 through 17-56, A7-1, A7-2.
`United Parcel Service, “Technical Reply Comments of
`United Parcel Service, Inc.,” FCC PR Docket No. 89-552,
`Apr. 1990, pp. 1-28, 1-5.
`James K. Cavers, “The Performance of Phase Locked Trans
`parent Tone-in-Band with Symmetric Phase Detection”,
`IEEE Transactions on Communications, vol. 39, No. 9, Sep.
`1991, pp. 1389-1399.
`“Phase Locked Transparent
`James
`K.
`Cavers,
`Tone-in-Band: An Analysis”, Proceedings IEEE Vehicular
`Technology Conference 1989, pp. 73-77.
`Shigeru Ono, Noriaki Kondoh, and Yoshihito Shimazaki,
`“Digital Cellular System With Linear Modulation”, Pro
`ceedings IEEE Vehicular Technology Conference 1989, pp.
`44-49.
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 2 of 11
`
`

`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 3 of 11
`
`

`
`US. Patent
`
`Dec. 17, 1996
`
`Sheet 2 0f 5
`
`5,586,150
`
`31 /
`
`24 ms DURATION
`
`1/2
`Zms ms zms
`
`18 ms
`USER DATA + PARITY
`
`1/2
`ms
`
`K \PREAMBLE GUARD SYMBOL-j j
`
`GUARD SYMBOL
`RAMP UP TIME
`PROPAGATION DELAY
`
`RAMP DOWN TIME
`_
`Flg. 2
`
`-
`
`DIAGRAM _
`
`BIN # 1
`
`>~FM SYMBOLS
`
`_
`
`~
`
`_ BIN # 2
`
`_ BIN # 3
`=-*FM SYMBOLS
`
`BIN # 4
`
`#1 #2 #3#4#5 #6 #7 #8‘_\
`C
`HISTOGRAM
`
`CHOOSE MAXIMUM VALUE AS
`OPTIMUM SAMPLING POINT
`Fig. 5
`
`CQUNTS (ONE
`PER SAMPLE
`POSITION.)
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 4 of 11
`
`

`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 5 of 11
`
`

`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 6 of 11
`
`

`
`US. Patent
`
`Dec. 17, 1996
`
`Sheet 5 of 5
`
`5,586,150
`
`SEVEN
`LEVEL
`"EYE"
`DIAGRAM
`
`.
`
`BIN#1
`
`\FM SYMBOLS
`
`BIN # 3
`
`\ BIN#4
`
`BIN#5
`
`7- FM SYMBOLS
`
`BIN # 6
`
`BIN#7
`
`82 \
`#1 #2 #3 #4 #5 #6 #7 #8 x
`C
`HISTOGRAM
`
`CHOOSE MAXIMUM VALUE AS
`OPTIMUM SAMPLING POINT
`Fig. 6
`
`COUNTS (ONE
`PER SAMPLE
`POSITION.)
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 7 of 11
`
`

`
`1
`METHOD AND APPARATUS FOR SYMBOL
`SYNCHRONIZATION IN MULTI-LEVEL
`DIGITAL FM RADIO
`
`5,586,150
`
`2
`In the event that the aforementioned second method does
`not provide a histogram value greater than a predetermined
`threshold, a third method is employed. The third method is
`similar to the second method, except that a predetermined
`odd number of baseband levels, greater than the actual
`number of PAM levels is employed. The samples are used to
`construct a second set of burst samples which are obtained
`as a difference of the original samples, spaced one symbol
`apart. The histogram method is again employed using bins
`in number equalling the predetermined, odd number of
`levels of the second set of samples.
`Therefore, it is a principal object of the present invention
`to provide a novel and improved method and apparatus for
`symbol synchronizing bursts of digital signaling or data.
`It is another object of the present invention to provide
`such a method and apparatus wherein minimal overhead is
`required so as to maximize channel e?‘iciency.
`The foregoing and other objects, features, and advantages
`of the invention will be more readily understood upon
`consideration of the following detailed description of the
`invention, taken in conjunction with the accompanying
`drawings.
`
`10
`
`20
`
`BACKGROUND OF THE INVENTION
`
`This invention relates to packet data radio communication
`systems, and particularly to such systems where there is a
`need at a radio receiver to receive incoming relatively short
`bursts of data.
`In a land mobile data communication system there typi
`cally will be a number of base stations at ?xed locations
`covering predetermined geographic areas and a much larger
`number of mobile stations in vehicles that travel within and
`between those geographic areas. Where packet data com
`munication or digital control signalling is used, base stations
`will, in effect, broadcast to the mobile stations, and the
`mobile stations will transmit signals to the base stations in
`bursts, as required by the circumstances. When signal burst
`duration is minimized to maximize radio channel capacity,
`each signal burst tends to require controlled amplitude
`envelope rise and fall times, or “ramp up” and “ramp down”
`time, and typically contains various control symbols as well
`as information data packets.
`Ordinarily, synchronization for each such burst must be
`performed using only the waveform of the individual burst.
`Thence, each such burst conventionally includes a preamble
`having a symbol timing synchronization word (“STSW”),
`and a frame timing synchronization word (“FTSW”) for
`modulation symbol detection and data block or frame syn
`chronization. However, this approach requires many pre
`amble symbols which, by consuming channel time that
`could be used for transmitting information, i.e., the preamble
`symbols are “overhead” which reduces channel e?iciency,
`especially in bursty communications.
`Therefore, there is a need for a method and apparatus for
`synchronizing bursts of incoming data that does not require
`high overhead and, thereby, provides greater channel e?i
`ciency, and wherein symbol synchronization is derived from
`the information symbols rather than from the use of a special
`preamble.
`
`25
`
`30
`
`35
`
`SUMMARY OF THE INVENTION
`
`45
`
`50
`
`The present invention overcomes the aforementioned
`problem and meets the aforementioned need by providing a
`block demodulation method and apparatus that provides for -
`synchronizing bursts of incoming data without a special
`symbol synchronization word, and minimal frame synchro
`nization overhead. An entire burst, comprising ramp up
`time, a preamble, guard times, data and ramp down time, is
`captured and stored in the form of baseband samples of the
`signal burst. The burst samples are then ?ltered to reduce
`pattern jitter. Thereafter, the samples are squared to derive
`the symbol clock. Then, the samples are di?’erenced and
`cyclically accumulated. The cyclicly accumulated samples
`are examined to ?nd a valid zero crossing.
`In the event that the aforementioned method does not
`identify a valid zero crossing, a second method is employed.
`In the second method, a histogram is constructed whereby
`the number of times a sample of a baseband data symbol
`falls within any one of a predetermined number of bins
`associated with an equivalent number of pulse amplitude
`modulation (“PAM”) levels is found for each of the sample
`points. The sample point having the maximum such number
`is used as the symbol timing reference.
`
`55
`
`60
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a radio transmitter which
`produces a radio signal having data bursts, according to the
`present invention.
`FIG. 2 is a diagram of a data burst, according to the
`present invention.
`FIG. 3 is a block diagram of a radio receiver which
`employs a method and apparatus for synchronizing bursts of
`incoming data, according to the present invention.
`FIG. 4 is a block diagram of an apparatus, according to the
`present invention.
`FIG. 5 is an illustration of an eye diagram of four level
`data symbols and the manner in which a four level histogram
`is constructed from burst samples, according to the present
`invention.
`FIG. 6 is an illustration of an eye diagram of seven level
`data symbols and the manner in which a seven level histo
`gram is constructed from burst samples, according to the
`present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`A signal according to the present invention may be
`produced by a radio transmitter 9 of the type shown in FIG.
`1. Information bits 11, comprising user data, are provided at
`input 12. The bits 11 are encoded to form encoded bits 13,
`preferably by a Reed-Solomon encoder 10, as is commonly
`understood in the art. A data burst 15 is then formed by a
`burst compiler 14. The data burst 15 comprises the encoded
`bits 13, as well as predetermined preamble bits 17 and guard
`bits 19. The values of the preamble bits 17 preferably are
`system con?gurable. The preamble bits 17 and the guard bits
`19 are provided at inputs 16 and 18, respectively. The
`preamble bits 17 are used to provide frame synchronization
`information, as the use of multi-level FM modulation elimi
`nates need for carrier phase synchronization and the present
`invention eliminates the need to use a special preamble for
`symbol timing synchronization.
`The data burst 15 as formed by burst compiler 14 is
`applied to a Gray level encoder 20 for encoding the bits into
`a predetermined number of levels. Although two-to-four
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 8 of 11
`
`

`
`5,586,150
`
`3
`level encoding is shown, it is to be recognized that the data
`burst 15 may be encoded using other numbers of levels
`without departing from the principles of the invention. An
`encoded burst 21 is output from the encoder 20 and is
`applied to a square root raised cosine ?lter 22 to shape the
`energy spectrum of the encoded burst 21. It is to be recog
`nized that although a square root raised cosine ?lter is
`shown, other ?lters may be used without departing from the
`principles of the invention.
`The output of the ?lter 22 is applied to an FM modulator
`24, having a modulation index input 26. The PM modulator
`24 modulates a carrier signal so as to provide a transmitted
`modulation burst which, using an antenna 28, is transmitted
`over a channel 29.
`A signal comprising a transmitted modulation burst 31, as
`received by the receiver, is shown in FIG. 2. The channel 29
`is divided into slots of predetermined duration, e. g., a
`duration of 24 milliseconds. Each transmitted modulation
`burst 31 has a predetermined, effective duration shorter than
`the duration of a corresponding slot and falls within the
`duration of that slot. In one embodiment, each transmitted
`modulation burst 31 comprises predetermined components,
`including a leading half-millisecond guard symbol, a 2
`millisecond preamble, 18 milliseconds of user data plus
`parity bits, and a trailing half-millisecond guard symbol. The
`difference in time between the slot’s duration and the
`duration of the above-described components accommodates
`propagation delay over the channel 29, as well as the
`ramp-up/down of the mobile power ampli?er. Although a
`transmitted modulation burst 31 may be con?gured as
`shown, it is to be recognized that the burst 31 may have other
`con?gurations without departing from the principles of the
`invention.
`A suitable receiver 37 for receiving signals 33 comprising
`one or more transmitted modulation bursts 31 and for
`employing the invention is shown in FIG. 3. It comprises a
`band pass ?lter 30, having an input 32 for inputting the
`received signal 33. The output of the band pass ?lter 30 is
`applied to a limiter/discriminator circuit 34 which converts
`the FM modulated burst into a PAM baseband pulse train of
`symbols, each symbol having a predetermined number of
`levels as described above. The circuit 34 also provides for
`sampling the baseband pulse train at a predetermined rate so
`as to produce M samples per modulation symbol. The
`samples are applied to a ?lter 36 of a type corresponding to
`that used in the radio transmitter 9 described above.
`An encoded burst, corresponding to an encoded burst 21
`of the radio transmitter 9 described above, is captured from
`the output of the ?lter 36 by a burst capture function 38. The
`output of the burst capture function is applied both to a
`symbol synchronization function 40 and, through a gate 42,
`to a symbol detection function 44. The burst capture func
`tion 38 uses a slot timing signal 35 provided by the receiv
`er’s associated transmitter, that transmitter preferably trans
`mitting continuously.
`The symbol detection function 44 maps each symbol to
`one of a predetermined number of PAM levels that, in
`number, correspond to the number of levels employed by the
`transmitter 9. Once the symbols are detected, they are
`applied to a Gray level decoder 46 for decoding from the
`predetermined number of levels into two levels, i.e., into
`bits. The output of the decoder 46 comprises data bursts
`corresponding to data bursts 15 of the transmitter 9. The
`frame synchronizer 48 identi?es the frame synchronization
`bits obtained from the output of the decoder 46. The encoded
`bits 13 are provided to a decoder so as to be decoded into
`
`15
`
`20
`
`30
`
`50
`
`55
`
`65
`
`4
`information bits 11. The type of decoder used by the receiver
`37 preferably corresponds to the encoder 20 of the trans
`mitter 9, e.g., a Reed-Solomon decoder 50 as is commonly
`understood in the art.
`.
`Turning now to FIG. 4, the symbol synchronization
`function 40 is broken down into a more detailed block
`diagram of functional elements. These functional elements
`represent three alternative methods for deriving a symbol
`clock to be used for data detection.
`The ?rst alternative method includes a pre-?lter function
`52 which ?lters the burst applied to it from the burst capture
`function 38 so as to reduce pattern j itter. A squaring function
`54 removes the modulation. A differentiator 56, using the
`central difference method, is used to obtain the symbol
`clock. The differenced samples are accumulated in an M-cy
`clic accumulator 58 to average out the variations in corre
`sponding samples over time. A zero crossing detector 60
`identi?es, from the data in the accumulator 58, a zero
`crossing, if possible. A test-for-a valid-zero-crossing func
`tion 62 determines whether the symbol clock obtained may
`to be used for detection. A valid zero crossing is indicated
`when the maximum valued sample in the accumulator 58 is
`greater than a predetermined threshold while the minimum
`valued sample in the accumulator is smaller than the nega
`tive of that threshold. In addition, however, the samples in
`the accumulator are used to invalidate an otherwise valid
`zero crossing that is found using this threshold method; the
`invalidation occurring when the samples indicate the exist
`ence of more than one zero crossing. In one embodiment,
`each zero crossing indicated by the samples found by (i)
`identifying a sign transition (positive to negative or negative
`to positive) between adjacent samples, e.g., ?rst and second
`samples, and (ii) con?rming that a sample at a predeter
`mined point prior to the ?rst sample has the same sign as the
`?rst sample and that a sample at a predetermined point after
`the second sample has the same sign as the second sample.
`In the case of the ?rst and last accumulated values, this
`operation applies in a cyclical fashion, e.g., accumulated
`value 1 is considered to follow accumulated value M.
`If a valid zero crossing is found and con?rmed, a linear
`interpolation is used on the two samples on either side of the
`zero crossing to determine the timing for controlling opera
`tion of gate 42 for symbol detection. On the other hand, if
`no valid zero crossing is found using this approach, then a
`second alternative method is used to derive a symbol clock.
`In the second alternative method, no valid zero crossing
`has been found using the ?rst alternative method. Accord
`ingly, the output of the function 62 is “NO.” The “NO”
`output is employed to close a switch 88 initiating the circuit
`of the second alternative method, particularly initiating
`function 66. The samples from the burst are used by function
`66, which provides for a predetermined number of bins 84
`as shown in FIG. 5, wherein each bin corresponds to a range
`of values corresponding to one of the predetermined number
`of levels. Function 66 also provides for a histogram being
`formed to determine the symbol clock. In a preferred
`embodiment the number of bins equals the number of
`modulation levels. Although as shown in FIG. 5 four bins
`and levels are used, it is to be recognized that other numbers
`of each may be used without departing from the principles
`of the invention. It is also to be recognized that, although the
`bins 84 as shown are substantially centered over the corre
`sponding modulation level, other arrangements may be used
`without departing from the principles of the invention. The
`size of the bins is dictated by the expected intersymbol
`interference (“ISI”) obtained in the channel.
`In operation, whenever a sarnple’s value falls within one
`of the predetermined bins, the corresponding histogram
`
`ARRIS GROUP, INC.
`IPR2015-00635 , p. 9 of 11
`
`

`
`5,586,150
`
`5
`count 82 for that sample is incremented. The histogram
`counts corresponding to each of the M samples are accu
`mulated in an M-cyclic accumulator 68. The above proce
`dure is repeated for each sample of a burst.
`Using the accumulated counts, a symbol clock is found by
`determining whether the maximum count value in the accu
`mulator exceeds a predetermined threshold. The maximum
`count value is determined in function 70. The comparison of
`the count against the threshold is performed in function 72.
`The sample number corresponding to the maximum count in
`the accumulator 68 represents the optimum sample point for
`use in detection. This sample’s position, i.e., a sequential
`number in the M samples taken per symbol, is supplied to
`gate 42 for converting the burst data into symbols, as
`described above for the ?rst alternative method.
`If no symbol clock is found in the second alternative
`method, a third alternative method is employed. The output
`of function 72 is “NO.” The “NO” output is employed to
`close a switch 90 initiating the circuit of the third alternative
`method, particularly initiating a difference function 74. The
`difference function 74 ?nds differences between each pair of
`samples which are M samples (i.e., one symbol) apart. If the
`number of modulation levels is denoted as L, the difference
`function 74 produces a new set of samples having 2 L—l
`levels. The new set of samples is applied to a second
`histogram function 76. The operation of this histogram
`function 76 is illustrated in FIG. 6. In a manner substantially
`the same as the histogram function used in the second
`alternative method described above, 2 L-l bins are pro
`vided, wherein each bin corresponds to a range of values
`corresponding to one of the 2 L—l levels and a histogram is
`formed in function 76 to determine the symbol clock. The
`histogram counts corresponding to each sample of the new
`set of samples are accumulated in an M-cyclic accumulator
`78, and the maximum count value in the accumulator 78 is
`found in function 80. This maximum value corresponds to
`the optimum sample point for use in detection, and is
`supplied to the gate 42 as described above.
`Although the aforementioned three alternatives have been
`shown together in FIG. 4, it is particularly pointed out, as is
`apparent therefrom and from the foregoing, that the alter
`native methods are employed sequentially and, therefore,
`may form a pipeline. Thence, while one alternative method
`is being employed for a particular burst, subsequent methods
`are not being employed for that burst yet may be performing
`a symbol synchronization function for a previously captured
`burst.
`As shown in FIG. 6, an exemplary application of the third
`alternative method is shown in the context of four level
`modulation. The method results in seven levels being
`formed, each of which has a corresponding bin 86. Each
`modulation symbol corresponds to eight samples (M=8). It
`is to be recognized that this method may be used even
`though the number of samples per modulation symbol is
`other than the eight and the number of modulation levels is
`other than four, without departing from the principles of the
`invention.
`Although the three alternative methods generally are
`described above as being used sequentially, it is to be
`recognized that any one method can be used separately of
`the other two methods and in other combinations with said
`other two methods.
`While the invention has been described with reference to
`functional blocks and elements that may be constructed of
`hard wired analog and digital circuitry, most of the function
`blocks and elements are preferably implemented by digital
`signal processing in a programmed digital processor.
`
`10
`
`20
`
`25
`
`30
`
`35
`
`60
`
`65
`
`6
`The terms and expressions which have been employed in
`the foregoing speci?cation are employed therein as terms of
`description and not of limitation, and there is no intention in
`the use of such terms and expressions of excluding equiva
`lents of the features shown and described or portions thereof,
`it being recognized that the scope of the invention is de?ned
`and limited only by the claims which follow.
`I claim:
`1. A method for deriving a ?rst symbol clock associated
`with a ?rst received multilevel FM radio signal burst of
`symbols using samples of the burst itself, comprising the
`steps of:
`capturing said ?rst received multilevel FM radio signal
`burst to produce burst samples;
`squaring said burst samples to produce squared burst
`samples;
`differentiating said squared burst samples;
`cyclically accumulating said di?erentiated squared burst
`samples to produce accumulated samples;
`identifying a zero crossing in said accumulated samples;
`and
`deriving said symbol clock from said zero crossing.
`2. The method of claim 1, wherein said identifying step
`comprises determining a sign transition between a ?rst
`accumulated sample and a second accumulated sample, said
`?rst and second accumulated samples being adjacent one
`another.
`3. The method of claim 2, wherein said identifying step
`further comprises con?rming that a third accumulated
`sample at a predetermined point relative to said ?rst accu
`mulated sample has the same sign as said ?rst accumulated
`sample, and that a fourth accumulated sample at a prede
`termined point relative to said second accumulated sample
`has the same sign as said second accumulated sample.
`4. The method of claim 1, further comprising the step of
`testing the validity of said zero crossing so as to ?nd a valid
`zero crossing.
`5. The method of claim 4, wherein said testing step
`comprises at least one of:
`(a) con?rming that said accumulated samples have a
`maximum value thereamong that is greater than a
`predetermined threshold and that said accumulated
`samples have a minimum value thereamong that is
`greater than a negative of said predetermined threshold;
`and
`(b) identifying no more than one zero crossing in said
`accumulated samples.
`6. The method of claim 1, wherein said deriving step
`comprises deterrrrining which of said burst samples is posi
`tioned closest to said zero crossing, and using the position
`ing of said determined burst sample as a symbol timing
`reference, said symbol timing reference being used for
`controlling operation of a gate associated with detecting and
`decoding each of said symbols represented as said burst
`samples.
`7. A method for deriving a symbol clock associated with
`a ?rst received multilevel FM radio signal burst of symbols
`using samples of the burst itself, comprising the steps of:
`capturing said ?rst received multilevel FM radio signal
`burst to produce burst samples;
`forming a histogram from said burst samples, said histo
`gram having a selected number of counter increments;
`cyclica