Ex. PGS 1036
`
`Ex. PGS 1036
`
`
`
`
`
`

`
`United States Patent [191
`Rouquette
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`5,200,930
`Apr. 6, 1993
`
`US005200930A
`(11} Patent Number:
`[45] Date of Patent:
`
`(54] TWO-WIRE MULTI-CHANNEL STREAMER
`COMMUNICATION SYSTEM
`Inventor: Robert E. Rouquette, Kenner, La.
`
`(75]
`
`(56}
`
`[73} Assignee: ne Laitram Corporation, Harahan,
`La.
`(21] Appl. No.: 125,007
`Jaa. 24, 1992
`(22} Filed:
`lat. a.~ ............................................... GOlV 1122
`[51)
`(52] u.s. a ....................................................... 367n6
`(58] Fteld of Search ............................. 367/20, 76, 80;
`340/870.18, 870.26, 854.9
`References Cited
`U.S. PATENT DOCUMENTS
`3,958,216 5/1976 Chapman .............................. 367/SO
`4,219,810 8/1980 Joosten ................................ 340/853
`4,912,684 3/1990 Fowler .................................. 367176
`4,967,400 10/ 1990 Woods .................................. 367/21
`Primary Examiner-Ian J. Lobo
`Attorney, Agent, or Firm-James T. Cronvich
`[57)
`ABSTRA.cr
`For use with marine seismic streamers, a two-wire,
`multi-channel communication system capable of han(cid:173)
`dling the high throughput necessary for effective Com(cid:173)
`munication between a central controller aboard a tow
`vessel and the many sensors deployed along the
`
`streamer. The central controller includes an intelligent
`modem with the capability of transmitting and receiv(cid:173)
`ing frequency-modulated message signals on one or
`more signal lines, such as conventional twisted-pair
`wires, over a number of individual inbound and out(cid:173)
`bound frequency channels. In the preferred embodi(cid:173)
`ment, seventeen channels are spread over a frequency
`band ranging from about 20 kHz to 100 kHz, thereby
`making available for co!DJ!lunication a bandwidth much
`wider than available in conventional single-channel
`· streamer communication. In this way, many positioning
`sensors, such as compasses, depth sensors, cable-level(cid:173)
`ing birds, and acoustic-ranging transceivers, attached to
`the streamer and each having a transmitter and receiver
`tuned to one of the modem's inbound and outbound
`channels, respectively, can be put in communication
`with the modem. To take advantage of its high through(cid:173)
`put capability, the intelligent modem refers to a stored
`table of individual sensor parameters, such as sensor
`type, transmit channel, and receive channel, to schedule
`an efficient scan of the sensors. As a diagnostic tool, the
`communication system also monitors the quality and
`performance of the communication link by measuring
`and recording such parameters as the transmitted and
`received signal strengths, signal-to-noise ratios, and
`number of incorrectly received messages.
`
`25 Claims, 9 Draw:iDg Sbeets
`
`TO
`CONTROLLER
`
`TO
`TAL END
`SENSORS
`
`Ex. PGS 1036
`
`

`
`0
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`
`I
`;
`
`38
`
`22
`24A ZA a14
`FIG. I
`
`TO
`CONTROLLER
`
`FIG.2
`
`TO
`TAIL END
`SENSORS
`
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`
`0
`0
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`
`Ex. PGS 1036
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`
`SIGNAL
`STRENGTH
`(dBV)
`-10.00 I
`
`I
`
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`
`-30.0
`
`-50.0
`
`-70.0
`
`-90.0
`
`il '
`
`'/
`
`10.00k
`
`70.00k
`50.00k
`30.00k
`RCV SS Vs. FREQ. IN Hz (LOW Q COILS)
`FIG.JA
`
`90.00k
`
`Okm
`
`8km
`
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`Ex. PGS 1036
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`10.00k
`
`50.00k
`OO.OOk
`RCV SS Vs FREQ.IN Hz
`FIG.JB
`
`90.00k
`70.00k
`(HIGH Q COILS)
`
`
`
`Ex. PGS 1036
`
`

`
`GROUP DELAY
`()-l~)
`
`450
`
`350
`
`250
`
`150
`
`50
`
`1\
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`50.00k
`30.00k
`10.00k
`GROUP DELAY Vs FREQ. IN Hz
`FIG. 4A
`
`~ • 00.
`
`•
`
`A5]10km
`~8km
`=--raJ 6km
`:--I2J 4km
`~2km
`"ill) Okm
`
`9000k
`70.00k
`(LOW Q COILS)
`
`
`
`Ex. PGS 1036
`
`

`
`GROUP DELAY
`(}J.S)
`
`450~--~--~--+---+---+---+---+---+---+-~
`
`~ • 00. •
`
`350r---~~~--+---+---+---+---+---+---+-~
`
`250r---~~~--~--+---~--+---+---+---+-~
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`r----f--""~!':..HlH+i\.-+~ ~~ ........ d----:::_-:_t_-:_~~-=-~~-=--:1-=-=1-==:t:=::!~ 8k m
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`50
`../" \ . .._ ........._
`_./ l -----+---.f---+---+----1----1----1------t~ 4k m
`10.00k
`30.00k
`50.00k
`70.00k
`"mJ Ok m
`GROUP DELAY Vs FREQ. IN Hz
`(HIGH Q COILS)
`FIG.4B
`
`90.00k "'"'J 2k m
`
`
`
`Ex. PGS 1036
`
`

`
`M
`
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`M
`
`COMM
`PROCESSOR
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`84-D LINED
`84.£ LINE E
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`84
`B4H LINE G
`LINE H
`
`90
`
`c
`PHYSICAL LAYER D
`
`PHYSICAL LAYER E
`
`PHYSICAL LAYER F
`
`PHYSICAL LAYER G
`PHYSICAL LAYER H
`
`I FIG. 5
`
`Ex. PGS 1036
`
`

`
`FROM
`MODEM
`TRANSMITTER ·
`128
`PROCESSOR
`.-- ---------------------,
`LEVEL --~~--------------~~
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`
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`
`Ide
`
`Vdc
`
`LOG AMP
`AND
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`
`SIGNAL
`STRENGTH
`TO MODEM
`PROCESSOR
`FIG. 6
`
`/440
`
`Ex. PGS 1036
`
`

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`S1 hfsiGNAL STRENGTH 1
`51€ rtSI:AL STRENGTH 2
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`
`FIG. 7
`
`
`
`Ex. PGS 1036
`
`

`
`OUTBOUND POLL CH. I
`
`INBOUND RESPONSE ·
`
`CH. 2
`
`CH. 3
`
`CH. 4
`CH. 5
`
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`FIG.B
`
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`
`1 2 3 4 5
`
`6 7 8 9 10
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`11 12 13 14 15
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`16 17
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`X A
`LOWEST CARRIER FREQUENCY------ HIGHEST CARR. FAEQ.
`TAIL END .
`HEAD END
`
`X A A A R
`
`FIG. 9
`
`Ex. PGS 1036
`
`

`
`1
`
`5,200,930
`
`TWO·WIRE MULTI-CHANNEL STREAMER
`COMMUNICATION SYSTEM
`
`FIELD OF THE INVENTION
`This invention relates to multiple sensor communica-
`tion and, more particularly, to apparatus and methods
`for achieving multi-channel communication with many
`sensor devices connected across a two-wire communi-
`cation path in a seismic streamer cable.
`
`2
`particularly in multi-streamer applications, is necessary
`to support the increased accuracy being demanded of
`seismic surveys. Each bydroacoustic transceiver typi(cid:173)
`cally transmits much more data to the controller than
`S other sensors, such as compasses and depth sensors.
`Second, maximum streamer lengths of 10 km are ex-
`pected to become commonplace, in contrast to 6 km
`today. Longer streamers accommodate more sensors on
`a single twisted pair with the concomitant increase in
`10 data traffic. Third, in the continuing quest for greater
`accuracy, today's typical spacings of every 300m for
`BACKGROUND OF THE INVENTION
`depth sensors and compasses may well be replaced by
`In a marine seismic survey, a surveying vessel tows
`spacings of 100m, for a threefold increase in the number
`one or more seismic cables or streamers. Each streamer
`of these sensing devices. Fourth, to avoid interference
`is outfitted with distributed seismic transducers, namely 15 with seismic measurement activity, availability of the
`communication system for data traffic may be limited to
`hydrophones, and position-control devices and posi-
`tion-determining sensors, such as cable-leveling bird.s,
`two seconds or less every seismic shot interval, which is
`comrasses, dept~ (pressure) sensors, and hydroacoUStlC
`typically ten seconds. Thus, in view of the expected
`rangmg transceivers. Data from the hy~rop~ones are
`expanded use of acoustics, longer streamers, closer sen-
`sent t~ a contr?ller on board the v~l VIa a ~gb-speed 20 sor spacing, and narrower data transmission intervals,
`data link, wJ?~h could be an optical-fiber link. Da~ prior art two-wire streamer communication systems
`from the pos1t10n sensors, on the other hand, are typ1-
`ill be · ad
`t
`b dl th
`·
`eased d ta t
`fli
`e mer
`a
`ra tc.
`m equa e to an e
`· d
`b
`ll
`·
`·
`·
`w
`call
`y transnutte tot e contro er vta a two-wrre, twtst-
`As'd f
`be'
`bl t handl th ·
`d d
`1 e ~om mg una. e 0
`~ ~ mcrease
`ed-pair line, each wire of the pair being no larger than
`ata
`size 22 A WG. Sensors are connected along the twisted 25 traffic, p~or art two:-~e co~urucatt?n systems d?
`not predtct ~mmlln!ca~on failures. Failure to te~-
`pair in one of two ways. First, in-streamer sensors are
`nate the twts~ed-parr line properly ~uses standmg
`connected in parallel directly across the twisted pair.
`wa~C:S on the line th~t can null out the stgnals at se~sor
`Typically, in-streamer sensors are also powered over
`the twisted pair. Second, outlying sensors, such as those
`posttlons along the Ime. Broken or sho.rte~ conne.ctiOns
`sensors residing in cable-leveling birds or hydroacoustic 30 are another source of faulty commurucat10ns. Fmally,
`saltwater leakage causes deterioration of the communi-
`transceivers, are individually coupled to the twisted
`pair by means of a coupling coil connected in parallel
`cation link over time. Prior art communication systems
`across the twisted pair. Each outlying sensor bas an
`do not recognize deterioration of the communication
`link until it is all but dead.
`individual, associated coil in the streamer.
`The coupling coils in the streamer are conventionally 35
`Therefore, one object of the invention is reliable, high
`timed to the same frequ·!ncy and typically have a fairly
`throughput data communication over existing twisted-
`high selectivity, or Q, giving the two-wire communica-
`pair lines with many sensors distributed along marine
`seismic streamers up to 10 km long. It is a further object
`tion system a narrow bandwidth and a relatively low
`data rate. The high Q further makes tuning of the trans-
`of the invention to permit early diagnosis of deteriorat-
`mitting frequency critical for effective communication. 40 ing communication so that prompt corrective action
`Because noise generated in the neighboring power sys-
`can be taken.
`tern for the high-speed hydrophone data link occurs at
`a dominant frequency of about 2 kHz with harmonic
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a further understanding of the nature and objects
`level decreasing with frequency to beyond 100 kHz,
`typical two-wire communication takes place at about 25 45 of the present invention, reference should be made to
`the following detailed description, including the accom-
`kHz. Conventional communication is achieved my
`means of. f~equency-shift-keying .<FSK) modulation.
`panying drawings, in which:
`Other vanatt?ns of.angle modulatiOn,. such as quad~a-
`FIG. 1 is side view of a seismic surveying vessel
`ture-phase-shift keymg (QPSK) and btpolar-pbase-shift
`.
`.
`.
`fr
`nl used Carri
`CF\ towmg a streamer outfitted wtth sensmg and streamer
`k
`·
`(BPSK)
`al
`er e- .7\J control devices in communication with a controller
`• are
`so commo Y
`·
`eym~
`f
`quenctes on the order of 20kHz-30kHz are common.
`abo d th
`'tb b
`·
`1 ·
`dan
`~ vesse ~ accor
`~ e ~ven ton;
`Proper timing of the carrier frequency is critical to
`ar
`ce Wl
`. FIG. llS a p~ cuta~ay .schematic vtew of a~-
`achieve a signal-to-noise ratio adequate for effective
`tion of .a conv~ntional se~~ str~er represen~g
`communication. Thus, present-day two-wire streamer
`communication relies heavily on a properly timed sys- 55 two tWisted-parr commurucation lines, one sbowmg
`parallel-connected coupling coils, in-line devices, and a
`tern.
`line termina~on; .
`.
`.
`Prior art two-wire communication with position sen-
`sors on streamers bas generally been realized by half.
`FIG. 3A 1S a f~y of curves represen~g th~ stgnal
`strength as a function of frequency for vanous distances
`duplex, single-channel communication schemes. Conse-
`quently, only one sensor is allowed to send data at a 60 from a 20 dBV (10 V) signal source for a conventional
`22 A WG twisted-pair communication line with a num-
`time. Likewise, no sensor may send data while the con-
`ber of low Q coupling coils distributed therealong;
`troller is communicating. Such limitations have only
`FIG. 3B is a family of curves as in FIG. 3A, but for
`recently become important. Several developments
`promise to make the half-duplex, single-channel com-
`a higher Q coupling coil, along with the interference
`munication system inadequate to meet expected de- 65 spectrum in the streamer environment;
`mands in position-determining requirements. First, by-
`FIG. 4A is a family of curves representing the group
`of delay as a function of frequency for various distances
`droacoustic ranging systems are seeing more wide-
`spread use. The positioning accuracy they provide,
`from a signal source, corresponding to the line with low
`
`
`
`Ex. PGS 1036
`
`

`
`5,200,930
`
`4
`3
`Q coupling coils having the signal strength characteris(cid:173)
`DETAILED DESCRIPTION OF THE
`tic of FIG. 3A;
`INVENTION
`FIG. 4B is a family of curves as in FIG. 4A, but
`corresponding to the high Q coupling coil having the
`A seismic surveying vessel 20 is depicted in FIG. 1
`5 towing a seismic streamer 22 beneath the sea surface 21.
`signal strength characteristic of FIG. 3B;
`Distributed along the length of the streamer 22 are
`FIG. 5 is a partial schematic block diagram of a pre-
`in-streamer sensors 24A-D, su~h as compasses and
`ferred embodiment of the communication apparatus of
`depth sensors, and outboard devtces, such as cable-lev-
`the invention·
`eling birds 26A-~ and acoustic r~ging tr~ivers
`FIG. 6 is; schematic block diagram of another em-
`bodiment of the invention showing some compo- 10 28A-B. For brevtty, all such dev1ces are hereinafter
`referred to generally as sensors. The outboard sensors
`nents in more detail than in FIG. 5;
`FIG. 7 is a schematic diagram of a multiplexer circuit
`are connected to the streamer 22 by means of.collars 27
`used in the invention to monitor electrical transmission
`clamped around the streamer. The streamer mcludes a
`te
`front-end marker buoy 30 tethered to the streamer 22 by
`.
`d
`tl
`1 32
`d
`tail
`d b
`34
`th eel
`h
`an recep on parame rs;
`h
`. f
`FIG 8 ·
`·
`·
`d
`d"
`15 a tet er cab e
`an a
`-en
`uoy
`te er
`to t e
`1
`15 a timmg
`•a gram epic ~g an ex~p ary
`end of the streamer 22 by a tether cable 36. The sensors
`•
`•
`~lling and response sequence accordmg to the mven-
`l4, 26, and 28 are all in communication with a central
`non; and .
`.
`controller 38 on board the vessel 20. Hydrophones (not
`. FIG. 9 lS a chart sho~~ the preferred c?annel. as-
`shown) are also distributed along the streamer 22 for
`s1gnment of the commurucatlon system of the mventlon. 20 detecting seismic energy generated by a seismic source
`SUMMARY OF THE INVENTION
`(also not shown) and reflected off geologic structures in
`the earth's surface. The birds 26A-B, such as the Model
`These and other objects are achieved by the present
`5000 manufactured by DigiCOURSE, Inc., the subsid-
`iary of the assignee of this invention, are used to control
`invention, which provides a multi-channel, two-wire
`communication system for sending commands and data 25 the depth of the streamer 22. Outfitted with heading
`sensors and depth sensors, a bird 26 can also communi-
`requests to and receiving data rom many positioning
`sensors and cable-leveling devices distributed along a
`cate beading and depth data to the on-board controller
`seismic streamer. The apparatus of the invention in-
`38 for use in predicting the shape of the streamer 22.
`eludes a central controller comprising an intelligent
`The acoustic ranging transceivers 28A-B transmit tran-
`modem that can scan the many streamer devices for 30 sit time information to the controller 38 also for use in
`cable-positioning data each seismic shot interval. By
`estimating the shape of the streamer 22. Of course, a
`typical deployment would include many more of such
`referring to an equipment table stored in memory, the
`sensors and more streamers than shown in FIG. 1.
`intelligent modem polls each device in an efficient and
`orderly fashion by transmitting message signals over an
`Communication between the sensors and the on-
`outbound channel. Responses from the polled devices in 35 board controller is effected over one or more two-wire
`lines running through the streamer as shown in FIG. 2.
`the form of message signals are received by the modem
`over one or more inbound channels difierent from the
`The cutaway side view of a portion of a streamer 40
`outbound channel. According to a preferred embodi-
`reveals, in this example, two twisted-pair lines 42A-B.
`An outboard bird 44, clamped to the streamer 40 by a
`ment, a modem has the capability of transmitting out-
`bound commands or data request messages one of four 40 collar (not shown), co~uni~tes wit~ the on-board
`~ntroller by ~eans o~ mductive coupling betw:en an
`channels as frequency-modulated signals and of receiv-
`m:st~eamer P:UUary co~ 46A and a second~ coil 48~
`ing frequency-modulated response messages on one of
`thirteen inbound channels.
`Within the brrd 44 or 1ts collar. A capaCitor 45A, m
`My measurements and modeling of the loss and group
`series with the primary coil 46A, blocks dire:t current
`delay characteristics of conventional 22 A WG and 45 used. to power m:streamer ~nsors. Control s1gnals. are
`rece1v~ by the brrd electromcs 50 to control the wmgs
`smaller twisted-pair, coupling-coil-laden streamer com-
`o~ the brrd ~d, thereby, the dep~h of the st~eamer. The
`munication lines revealed relatively flat loss and group
`brrd electromcs also meas~e v~ous operating parame-
`delay characteristics above conventional coil resonant
`frequencies of 20 kHz-25 kHz up to about 100kHz. My
`ters, such as depth, heading, wmg angle, temperature,
`. terfi
`50 and battery statllS, and send such data to the controller
`te
`ts f th
`furth
`In
`er measuremen o
`e power sys m m
`erence
`imil"
`th
`ll
`ealed ·gnat t
`1 1
`t
`ti
`ad
`upon request.
`as
`ar manner,
`e contro er com-
`·
`te
`spec rum eve rev
`. s•.
`• o-nolSe ~ os
`equa
`municates over the same line 42A with an acoustic
`for successful commurucation at frequencies from abo~t
`ranging transceiver 52 and its internal electronics pack-
`2~ kHz up to 100 ~· Th7 novel streamer commuru-
`age 54 by means of a similar primary coil46B and ca-
`catlon system. of the mvent10n takes advantage or t:!te 55 pacitor 45B and secondary coil 48B. As can be seen,
`
`each outboard device is put into communication with
`newly r~gnized loss and group delay. characterutics
`the line 42A by means of a corresponding coil 46 con-
`-:nd the mterference spectrum by operating over a mul-
`nected in parallel across the twisted-pair line. In-
`!itllde of c~els between abo~t 20 kHz ~d 100 kHz,
`streamer devices, such as a heading sensor 56, are con-
`mstead of a s~~le channel as ~ conventionally done,
`thereby perm1ttmg the much higher daf:-. ~oughput 60 nected directly in parallel across the lines of the line
`~tes n~ ~or adv~ced cable-~1tionmg solu-
`42B. To prevent line reflections that can cause nulls in
`tions. The mvention additionally provtdes an operator
`the communication signals, the line 42B is terminated
`with its characteristic impedance 58. Thus, a twisted-
`on board the survey vessel with communication quality
`and performance measures, such as inbound and out-
`pair line over which cable-position sensors communi-
`bound signal strengths and signal-to-noise ratios, ac line 65 cate with the on-board controller contains a number of
`impedance, de line load, false carrier detections, and
`coupling coils or in-streamer devices all connected in
`message errors for detection of streamer problems ear-
`parallel across the line. Each sensor has a unique ad-
`dress or serial number identifier for communication
`lier than heretofore possible.
`
`
`
`Ex. PGS 1036
`
`

`
`5,200,930
`
`6
`5
`78 interface the modem processor 70 with a communi-
`addressing. An individual10 km twisted-pair line could
`include up to 377 parallel sensors. For long streamers
`cation processor 80 in communication with other on-
`board processing equipment. (The central controller 38
`having more sensors than a single twisted-pair line can
`in FIG. 1 includes the modem processor 70 and the
`handle, additional lines could be used as exemplified by
`the two twisted-pairs 42A and 42B in FIG. 2.
`5 communication processor 80.) Preferably, data are
`passed between the communication processor 80 and
`In a conventional twisted-pair communication sys-
`tem, with a wire size of 22 A WG and having a number
`the modem processor 70 through designated memory
`of identical low Q coupling coils distributed therealong,
`areas in a dual-ported RAM 82 shared by the two pro-
`cessors. Interrupts from the communication processor
`the signal strength characteristic is typified by FIG. 3A.
`For convenience of comparison with the interference 10 80 signifying the start of a sensor scan cycle are also
`passed to the modem processor 70 over the system bus
`spectrum, the signal strength of a signal 10 transmitted
`at a level of 20 dBV, or 10 V, by a signal source is
`76.
`plotted as a function of frequency for various distances
`The modem processor 70 communicates with the
`from the source, instead of the reciprocal loss character-
`individual sensors over twisted-pair lines 84A-H each
`istic. The signal strength characteristic for a line having 15 containing a number of parallel-connected coils or in-
`a number of high Q coils is shown in FIG. 3B. For
`streamer sensors. For simplicity each twisted-pair line is
`e_xample, in FIG. 3A, at SO~ with low Q coils, the
`represented by a single line in FIG. 5. Each line is con-
`s!gnal strengt~ (-50 dB) at a dtstance of~ km from the
`nected to an individual modem physical layer 86A-H.
`stgnal source 1s about 19 dB less than the stgnal strength
`A
`"cal h "cal
`·
`·
`.
`f 4 km I . .
`typ1
`p ys1
`layer compnses a transmit path, a
`( 31 dB) t d ·
`· t lS tmportant t~ notice 20 receive path, and an isolation transformer 88.
`tstanc::e 0
`-
`a a
`that, although the signal strength decreases wtth fre-
`·tte 90
`Th
`t
`·t
`d" "tal t
`th · 1 d
`.
`e ransmi pa me u es a
`Igt
`ransmi
`r
`rfi
`d
`th
`11 d b
`th
`od
`70 Th d" "tal
`quency, so oes
`e mte erence spectrum level 60,
`t
`1~
`con ro. e Y . e m em processor
`which decreases with frequency from 20 kHz to 100
`·
`e
`,_..,._ as sho
`· FIG 3B Furth
`th
`transmitter 90 15 programmed or preset to synthesiZe a
`a1
`·
`f
`od 1 d di "tal
`wn m
`.
`.
`ermore,
`e group
`·
`.LnL,
`delay characteristic between 20 kHz and 100 kHz for 25 requen~y-m . u ate
`~ sign
`at Its output, t~e
`modulat10~ ?em~ a f~ct10n ?f the data to be transmit-
`both high and low Q coils, shown in FIGS. 4A and 4B,
`ted. The digttal stgnal15 apphed toaD/ A conve~er 92
`is relatively flat. A non-flat group delay characteristic
`to _pr~uce an analog frequency-modulated SI~~·
`for which the delays of the upper and lower frequencies
`of a frequency-modulated signal differ by more than
`which 15 flltered by a bandpass fllter 94 to remove digt·
`about 0.1 ms at 2400 baud degrades the performance of 30 tal noise an~ o~t-of-channel ~ignal, and amplified b~ a
`power. amplifier 96 before bemg coup!e~ onto the line
`conventional modems. Thus, a significant bandwidth is
`84A vta the trans~ormer 88 for transmission to !he sen-
`available for frequency-modulated communication over
`existing twisted-pair lines above the coil resonant fre-
`sors. Data transmitted by a sensor are coupled mto the
`quency of about 20 kHz.
`physical layer 86~ t!rrough the transforme~ 88. A band-
`Instead of limiting communication to the relatively 35 pass fl.lte~ ~ ~liminates low-frequency mte~erence,
`narrow bandwidth of the coil resonance characteristic .
`such as setsmic mterference and power system mterfer-
`ence, and tr~mit~er interfer~nce from the receiver.
`the present invention takes advantage of the wide band:
`The ftltered stgnal 15 buffered m a pre-amp 100 before
`width available above 20 kHz to communicate effi-
`being applied to. an ~/D C?nverte~ ~02, ~hich converts
`ciently with many sensors. The preferred communica-
`tion scheme is a multi-channel approach, in which 17 40 the analog recetv~ ~1gnal m!o a d1gttal signal to be de-
`individual narrow-band channels from about 20 kHz to
`modulated by a d1gttal recetver 104. The demodulated
`100 kHz are used to permit full-duplex communication
`data are then sent to the modem processor 70 from the
`physical layers 86A-H over UART ports 106A-H.
`with many sensors distributed along a streamer. Chan-
`nels are limited to below 100 kHz, because, at higher
`Although only two lines 108A-H and 109A-H are
`frequencies, the two-wire line behaves more like a dis- 45 shown for each UART port 106A-H, a full RS-Z32C
`handshaking link is implemented, as will be described
`tributed parameter transmission line than a lumped pa-
`rameter circuit. Such a multi-channel approach permits
`hereinafter. Although the block diagram of FIG. 5
`sensors operating on separate channels to communicate
`shows eight physical layers, it should be recognized that
`simultaneously. Because of the signal strength charac-
`realizations having more physical layers are within the
`teristics and interference spectrum shown in FIG. 3, so scope of the invention.
`In a preferred embodiment, the transmitter 90 and the
`channels are assigned to sensors according their dis-
`tances from the on-board controller for best signal-to-
`receiver 104 are realized by a multiplicity of digital-sig-
`interference ratios. Lower frequency channels are as-
`nal-processing (DSP) integrated circuits, such as the
`signed to those sensors farthest from the controller. One Model TMS320C40 manufactured by Texas Instru-
`skilled in the art will recognize that the invention could 55 ments, Inc., Dallas, Tx. Such a device allows great
`likewise be used with communication lines other than
`flexibility in selecting carrier frequencies and modula-
`tion schemes. In this embodiment, however, a minimum
`twisted-pair lines, as long as they exhibit similar signal
`strength and group delay characteristics.
`frequency-shift-keying modulation (MSK) scheme is
`used whereby a logic low data bit causes a frequency of
`A block diagram of the multi-channel communication
`system of the preferred embodiment of the invention is 60 fc-600 Hz to be transmitted and a logic high data bit
`causes a frequency of fc+600 Hz to be transmitted
`shown in FIG. 5. Communication with streamer sensors
`is realized by a modem configt1red around a modem
`where fcis the transmit channel center frequency. Data
`processor 70 having a RAM scratchpad memory 74 and
`bit rates of 2400 baud make the system compatible with
`the group delay characteristic of the channel. As a
`non-volatile memory 72, such as ROM, for program
`storage. The modem processor sends and receives sen- 65 transceiver, the DSP integrated circuit is capable offull
`sor commands and data from the other processing
`duplex operation, i.e., simultaneous transmission and
`equipment on board the survey vessel over a parallel
`reception, as well as simultaneous multi-channel recep-
`system bus 76, such as a VME bus. Bus control circuits
`tion.
`
`
`
`Ex. PGS 1036
`
`

`
`5,200,930
`
`7
`8
`modulated transmit signal is summed with de power for
`In another embodiment, shown in the schematic
`block diagram of FIG. 6, the transmit and receive func-
`in-streamer devices and sent down the communication
`tions of the physical layer are performed by analog and
`line for decoding by the appropriately addressed sen-
`sors. In a full-duplex system, responses from various
`digital circuitry not including a DSP integrated circuit.
`Each transmitter 111A-B includes a digital phase accu- 5 sensors may occur simultaneously on different channels.
`mulator 110 whose output is a digital count incremented
`Simultaneous receive channels are implemented in the
`embodiment of FIG. 6 by additional receivers for each
`at a rate determined by the transmit clock signal 112,
`the transmit channel frequency setting 114, and the data
`receive channel. A description of the operation of one
`bit 116 to be transmitted. The transmit clock signal may
`receiver suffices to describe the operation of all, which
`be derived from a bus clock signal 118 by a frequency 10 are identical, except for being tuned to receive on sepa-
`rate channels. Four receivers 144A-D are shown in
`divider 120. For a given transmit clock rate and a se-
`lected transmit channel, the rate of the digital count out
`FIG. 6. The input to each receiver is taken from the
`of the phase accumulator is determined by the transmit
`transformer 136. Although the receivers are shown
`connected to the modem side of the transformer 136 in
`data. Preferably, the transmit data 116 are sent serially
`to the phase accumulator 110 from a TX line of a 15 FIG. 6, they could alternatively be coupled through
`UART on the modem processor using standard NRZ
`individual transformers connected to the line side of the
`transformer 136. Each receiver, as exemplified by re-
`asynchronous serial communication, including start and
`stop bits. The sequence of data logic levels, alternating
`ceiver 144A, includes an adjustable notch filter 146 for
`between highs and lows, adjusts the output count be-
`attenuating the transmit frequency coupled into the
`tween two rates, which are converted into two respec- 20 receiver. The fl.ltered signals from the streamer sensors
`tive frequencies by sine ROM 122 and D/ A converter
`are buffered in a pre-amp 148 and further filtered in an
`124, thereby producing an MSK-modulated signal at
`adjustable bandpass filter 150 tuned to the designated
`the output of the D/ A converter 124. The phase accu-
`receive channel frequency. The filtered signal is then
`mulator and sine ROM functions can be implemented
`limited in a limiter 152 to preserve phase information
`by a single integrated circuit, such as an HSP45102 25 representing the data and demodulated in an FM de-
`modulator 154. In the embodiment described by refer-
`numerically controlled oscillator, manufactured by the
`Harris Corporation, Melbourne, Fla. For a logic low
`ence to FIG. 6, the signals from the sensors to the
`data bit, the frequency is selected to be fC"'600 Hz; for a
`modem are MSK-modulated signals similar to the sig-
`logic high data bit, the frequency is selected to be
`nals transmitted to the sensors as previously described.
`fc+600 Hz, where fc is the transmit channel center fre- 30 In fact, in the preferred embodiment, each sensor has
`one transmit path and one receive path similar to those
`quency. The start of the conversion process in the D/ A
`converter 124 is controlled by the transmit clock input
`on the modem. The demodulator 154 is tuned to the
`signal 112, which is the clocking rate of the digital sig-
`designated receive channel by means of a receive clock
`nal. The modem processor can also control the ampli-
`signal 156 and a signal representing the receive channel
`tude of the output of the D/ A converter and, hence, the 35 setting 158. The receive clock signal 156 may be de-
`transmitted energy, by means of a level adjust signal
`rived from a I-us clock signal 118 by a frequency divider
`128. The analog signal out of the AID converter 124 is
`160. The demodulator 154 can be realized by an inte-
`fl.ltered by an adjustable bandpass filter 130, which re-
`grated circuit, such as the 74HC297 digital phase-
`moves digital quantization noise and out-of-channel
`locked-loop manufactured by Texas Instruments. The
`signals. The fl.ltered analog signal is amplified in a 40 demodulator 154 indicates to the modem processor that
`power amplifier 132 terminated in adjustable line-
`the carrier has been detected via a CARRIER DE-
`matching impedance 134 for maximum power transfer
`TECT signal 162. The demodulated receive data 164 is
`to the communication line. Other similar transmitters,
`sent to an RX line on a modem processor UART in the
`operatin