UllltEd States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,907,582
`
`
`Yi
`[45] Date of Patent:
`May 25, 1999
`
`USODS907582A
`
`[54] SYSTEM FOR TURBO-CODED SATELLITE
`DIGITAL AUDIO BROADCASTING
`
`[75]
`
`inventor: Byung Kwan Yi, Derwood, Md.
`‘
`.
`-
`-
`[73] Assignee. 3rbllal Screnees Corporation, Dulles,
`3'
`
`[21] Appl. No.: 081903.045
`,
`Filed:
`
`AHB- 11: 1997
`
`[22]
`
`5,446,747
`5,485,485
`5,544,156
`
`3/1995 Berrall
`thQé Briskmnn :1 al.
`8.11996 Teder et a].
`.....
`
`311145
`375mm
`3rw342
`
`..
`
`
`3701476
`1011996 aney et a].
`5,570,356
`..... 3751216
`1911996 Dapper et a].
`..
`5,538,022
`
`811997 Lou et al.
`3701334
`5,657,325
`5,671,221 W199? Yang IIIIIIIIIII
`370l320
`
`5,591,914 11,199? minim}.
`370/203
`
`..
`...... 4559.1
`5,729,325
`3/1993 Knstreski el al.
`
`
`5,751,761
`$1998 Gilhousen
`3751200
`511993 Dent ............. 37mm
`5,764,646
`
`5,771,225
`6/1998 szu
`mama
`
`Int. Cl.Ii
`[51]
`[52] US. Cl.
`
`...................................................... H04] 13.100
`375(259; 375/200; 370E342;
`370fl08
`375mm, 259,
`[53] Fleld or Search
`3753250: 257. 347; 3701203. 209- 320-
`342. 485; 455/92, 103- 132. 133- 137,
`12-1, 427, 505
`
`[561
`
`Referenm Cited
`U.S. PATENT DOCUMENTS
`
`4,331,241
`5,191,598
`5,278,863
`5,283,780
`5,315,533
`5 319 673
`5,406,570
`5,408,502
`5,433,590
`
`....................... 3750.60
`1111939 Pommier et a].
`..
`3(1993 Backstrom et al.
`------ 375547
`
`”1994 Briskman ..............
`----- 315/200
`271994 Sehuchman eta].
`.
`
`""" 233,133
`994
`it
`t
`l.
`.......
`______ 375nm
`2:99,, 31:35:: am
`
`
`371143.11
`431995 Berton mt.
`#1995 How ........................ 375%
`
`871995 'I‘zukerman et al.
`375.5259
`
`Primary Examiner—Young T. T86
`Attorney, Agent, or Firm—McDonnell. Will &. Emery
`
`ABSTRACT
`[57]
`Asystem and method for broadcasting an audio signal in a
`turbo-coded satellite digilal audio broadcasting system is
`provided that utilizes the combination of a turbo coding
`system having code combining and code diversity tech-
`oiques to lower the power required for transmittal and to
`transmit at a higher code rate of 5‘3 by utilizing the punc-
`turing sequence and a pilot signal assisted orthogonal
`CDMA; the invention includes an lJIIPl'OVCd mcivgr SySlCm
`that uses modified RAKE receivers in order to mitigate the
`Rayleigh multipalh fading, shadowing, and temporal block-
`age and improve performance. The invention further uses a
`.
`.
`terrestnal gap filler network havtng a reduced amount of gap
`fillers
`
`3] Claims, l5 Drawlng Sheets
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 1
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 1
`
`

`

`U.S. Patent
`
`May 25,1999
`
`Sheet 1 of 6
`
`5,907,582
`
`
`
`roodmiingStation
`
`B
`
`M
`
`A!
`
`
`
`104
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 2
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 2
`
`

`

`US. Patent
`
`May 25,1999
`
`Sheet 2 or 6
`
`5,907,582
`
`
`
`0 ”6
`I‘d.-
`2
`
`I26
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`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 3
`
`112
`
`ChonnellJ
`
`Long PM
`Sequence #1
`
`PM
`
`I20
`
`122
`
`Channel I
`
`Channel?
`
`Audio
`Encoder
`‘
`
`120
`
`Audio
`
`dk
`
`I...
`
`I20
`
`dk
`
`Turbo
`Encoder
`
`124
`
`122
`
`124
`
`Turbo
`Encoder —
`
`126
`
`.II.
`
`1 2
`
`Channel 3]
`
`Audio
`Encoder
`
`dk
`
`124
`Turbo
`Encoder -I
`
`114
`
`126
`
`Long PM
`
`Channel 32 Sequence #2
`
`PH
`
`lflZ
`
`FIG. 2
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 3
`
`

`

`US. Patent
`
`May 25, 1999
`
`Sheet 3 of 6
`
`5,907,582
`
`.2235.
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 4
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 4
`
`
`

`

`US. Patent
`
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`To:
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 5
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 5
`
`
`
`

`

`U.S. Patent
`
`May 25, 1999
`
`Sheet 5 of 6
`
`5,907,582
`
`“1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIJ_E2:33a.5:2:12;.a._23$55.25572."cussum~m+fefransom"u._Iu____u_._m.3330“_ana_a:2:asm
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`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 6
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 6
`
`
`
`
`
`

`

`US. Patent
`
`May 25, 1999
`
`Sheet 6 of 6
`
`5,907
`
`,582
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`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 7
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 7
`
`
`
`
`
`
`
`

`

`1
`SYSTEM FOR TURBO-CODED SATELLITE
`DIGITAL AUDIO BROADCASTING
`
`BACKGROUND OF THE INVENTION
`1. Field of die Invention
`
`This invention relates to a Digital Audio Broadcasting
`(DAB) system for the wide-area distribution of multiple
`channels of audio programming, and in particular to a DAB
`system and method having improved receiver performance
`through coding gain from code diversity and packet
`combining, and distributed gap filler network.
`2. Description of the Prior Art
`Several DAB methods and systems have been proposed
`for Direct Broadcast Satellite Radio that essentially broad-
`casts digital audio signals for reception by fixed and mobile
`receivers. Such DAB systems and methods heretofore have
`yet
`to overcome problems that afl'ect
`the overall system
`performance so as to make it commercially feasible. The
`most significant problems in DAB systems are signal
`shadowing, fading, and temporal blockage. Shadowing
`problems are dominated by factors such as the intermittent
`blockage of the line of sight to the receiver from the satellite
`by natural or man-made objects. For example, in suburban
`enVironments tree shadoWing is the prominent signal
`impairment. while in urban environments, buildings cause
`the major shadowing effect. Fading problems are mainly
`caused by multipath signals to the mobile receiver in sub-
`urban and urban environments. Signal fading can be miti-
`gated by adapting temporal diversity techniques such as time
`diversity and spatial diversity. Conventional time diversity
`schemes operate on the same signal so as to randomize the
`outage patterns through interleaving, data repetition, andjor
`some form of channel coding. Conventional spatial diversity
`techniques operate on the same signal using a dual satellite
`scheme andfor an antenna diversity technique for remedying
`shadowing and temporal blockages.
`Conventional DAB systems and methods have sought to
`mitigate the problems of multipath fading and foliage
`attenuation by employing two geosynchronous satellites.
`U.S. Pat. Nos. 5,319,673 and 5,278,863 to Briskman dis-
`close a polarization diversity technique in a spread spectrum
`system (either direct sequence or
`frequency hopping
`schemes) that employs frequency diversity to combat fading
`in a frequency selective channel. A conventional Code
`Division Multiple access (CDMA) system, using two geo-
`synchronous satellites and a dual diversity technique is
`utilized. however,
`the Briskman system cannot provide
`seamless high performance service over the entire coverage
`area, since conventional CDMA system performance is
`limited by self-interference. Self-interference is induced by
`the cross-correlations of the Pseudo Noise (PN) sequences
`used for the diiferent program channels. Furthermore, the
`Briskman system employs a dual polarization approach to
`separate signals from two satellites. the receiver then select-
`ing the stronger of the two broadcasts of the same signal.
`While a dual satellite system increases the probability that a
`mobile or fixed receiver has line-of-sight contact with one of
`at least two satellites, Ihe unselected satellite’s signal must
`be separated and eliminated from further signal processing.
`otherwise. the weaker signal acts like added noise to the
`stronger signal. Additionally. preserving the polarization in
`
`10
`
`15
`
`35
`
`45
`
`St]
`
`55
`
`till
`
`65
`
`5,907,582
`
`2
`
`the mobile signal path is very difficult because the reflected
`signals tend to invert the polarization. Therefore, conven-
`tional DAB systems are inefficient in power and bandwidth
`usage whereby performance is inadequate for subscription-
`grade quality of service.
`Finally, even with two satellites, signal blockage,
`shadowing, and fading problems continue to occur in urban
`and suburban environments. Conventional DAB systems
`have sought to solve this problem by employing a network
`of gap filler transmitters to provide the signal when both
`satellites are blocked from view. However, such network of
`gap fillers transmitting the same broadcast signal increases
`the self-interference problem, which in turn increases the
`cost and complexity of the gap filler network because of the
`desire to use increased transmit power levels to combat
`self-interference. Previous attempts to solve this. problem
`have been inadequate for subscription grade service given
`the intended DAB service area (continental United States)
`and the pervasiveness of the shadowingr‘fading problem; this
`has created new cost problems whereby gap fillers are
`required in virtually all urban and suburban locations.
`Therefore,
`the DAB method and system of the present
`invention advantageously provides a way to reduce the
`number and cost of such gap fillers and a critical solution to
`the overall network design problem. The DAB method and
`system of the present invention advantageously utilizes code
`diversity (whereby two different non-self-interfering turbo
`encoded signals are transmitted and substantially combined
`inside the receiver)
`to provide improved performance
`through higher coding 36115, fewer gap fillers. and reduced
`transmit power level requirements from either of each of the
`satellite or the gap fillers.
`Other DAB systems have used dual antennas and a
`Viterbi-algorithm method over a fading channel to reduce
`the afl'ects of signal fading in the received signal. US. Pat.
`No. 5,191,593 to nicksuam et al. discloses a system for
`receiving radio signals on at least two mutually spaced
`antennas and a receiver to process samples of the signal
`using a Viterbi-algorithm thereby reducing signal fading.
`Various antenna diVersity schemes also have been used and
`these are characterized by the orthogonal polarization of the
`broadcast signals. For example, in US. Pat. No. 5,485,485
`to Briskman, a dual antenna system is disclosed that selects
`the stronger of two signals having substantially the same
`content and frequency. The dual antenna approach requires
`two physical antennas on the mobile receiving station which
`is inconvenient and expensive as multiple antennas are
`installed on the vehicle ’s roof, and their employment illus-
`trates the severity of the reception problems of conventional
`DAB systems. Additionally, the performance gain due to a
`dual-antenna system is minimal unless the receiver uses
`extensive signal processing techniques to accurately com-
`pensate for the angle of arriVal. The method and system of
`lhe present invention solves these problems by advanta-
`geously utilizing RAKE receivers to combine multipath
`signals from satellites and gap filters at the DAB receiver.
`U.S. Pat. No. 5,544,156 to Teder el al. discloses a system
`and method for coherently demodulating an uplink signal in
`a multiratc, CDMA system. However, the receiver perfor-
`mance of the conventional CDMA andfor Viterbi based
`coding systems is limited by multiple access channel inter-
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 8
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 8
`
`

`

`3
`
`4
`
`5,907,582
`
`ference and does not provide performance and coding gains
`at the level provided by the present invention. As a result, the
`present invention uses a Turbo Code method and system
`along with Orthogonal Code Division Multiple Access
`(0CDMA) techniques to advantageously eliminate the
`efi'ects of multiple access interference and provide high
`coding gain, which results in robust DAB reception at lower
`overall power levels.
`Finally, an error coding system using turbo codes, i.e.,
`codes that associate with parallel concatenation of two
`convolutional codes separated by an interleaver, is disclosed
`in US. Pat. No. 5,446,747 to Berrou and U.S. Pat. No.
`5,406,570 to Berrou et al. While such systems have accept-
`able coding gain they do not address the dual-signal path
`case or the benefits provided through the use of code
`combining and code diversity. These codes do not transmit
`interleaved data elements, but only transmit uninterleavecl
`data elements and parity check elements from both uninter-
`leaved and interleaved sequences. The present invention
`transmits uninterleaved and interleaved data elements With
`
`corresponding coded data elements to two separate signal
`paths, and at the turbo decoder, combines these two elements
`advantageome to achieve an effective overall code rate V4
`from the simultaneous reception and combination of [We
`code rate ’15 signals,
`thereby providing significantly
`improved performance.
`The present
`invention is aimed at overcoming these
`diflerent drawbacks of the prior art.
`
`SUMMARY OF THE INVENTION
`
`It is an object of the present invention to proVide an
`improved DAB method and system using an implementation
`of turbo code over two complementary satellite links in the
`DAB system to allow the reduction of the satellite trans-
`mitter output power.
`It is an object of the present invention to increase the
`coverage area with a minimum number of gap fillers using
`the high coding gain of the turbo code.
`Another object of the present invention is to provide code
`diversity at a code rate of 95 coupled with packet combining
`to result in an overall system code rate of Va. Acode diversity
`scheme, coupled with a code combining scheme advanta-
`geously provides improved performance through very high
`coding gain. allows the reduction of transponder output
`power, and pIOVides seamless service over the coverage area
`with a minimum number of required gap fillers. Code
`diversity and packet combining are used to mitigate Ray-
`leigh multipath fading, shadowing, and temporal blockage.
`Yet another object of the present invention is to provide a
`DAB system using a synchronous Orthogonal Code Divi-
`sion Multiple Access (OCDMA) scheme for DAB
`applications, e.g. CD Quality Radio, messaging transmis-
`sion and lntemet download server, so as to completely
`eliminate self interference from other audio channels
`
`encountered with the use of a conventional CDMA system.
`Another object of the present invention is to provide a
`DAB system having dual RAKE receivers, arranged
`whereby one RAKE receiver is used to combine the satellite,
`gap filler, and multipath signals associated with each of two
`complementary satellite data streams.
`
`5
`
`JD
`
`15
`
`35
`
`#5
`
`SI]
`
`55
`
`60
`
`65
`
`It is a further object of the present invention to provide
`high powered pilot channels to assist the receiver to acquire
`synchronization of the signals from multiple satellites and
`gap filler transmitters.
`Finally, the present invention can provide advantageously
`a terrestrial gap filler netWorlt. for retransmission of the
`uplinked satellite signals in areas where there is a high
`probability that signals from both satellites might be
`blocked, with proper built-in signal propagation delay to
`compensate for the signal delay through the satellite path. A
`variable delay is applied to each gap filler signal so as to
`accommodate propagation delays on the satellite patio,
`including Doppler shift associated with the normally
`encountered daily motion of the satellites in their respective
`geosynchronous orbit locations. In this way, each gap filler
`transmitter in a given service area retransmits the same
`signals as the two satellites so as to align the satellite-
`delivered and gap filler delivered signals in time at each
`receiver in the gap filler’s service area. So long as the delay
`spread is maintained to less than one bit period, orthogo-
`nality of the 0CDMA signals is maintained at the RAKE
`receiver, and the satellite, gap filler, and multipatlt reflection
`signals can be combined in the receiver to overcome the
`problems of conventional systems.
`Accordingly,
`the present
`invention provides a digital
`audio broadcasting (DAB) system adapted to broadcast
`signals of digital radio information and to reduce multipath
`fading, signal shadoWing and temporal blockage batting a
`broadcast source haying a transmitter for transmitting a first
`turbo encoded broadcast signal and a second turbo encoded
`broadcast signal that includes the digital radio information,
`whereby the first and second turbo encoded broadcast sig-
`nals are transmitted at a code rate of ’5 on at least one
`
`predetermined path, for example, the first turbo encoded
`broadcast sigial on a first path to a first satellite, the second
`turbo encoded signal on a second path to a second satellite
`source, andfor the first and second turbo encoded broadcast
`signals to a network of gap filters that have delay circuitry
`for delaying the first and second turbo encoded broadcast
`signals to compensate for propagation signal delay through
`the first and second satellites. The first
`turbo encoded
`
`broadcast signal consists essentially of uninterleaved data
`and parity check elements. The second turbo encoded broad-
`cast signal consists essentially of interleaved data and parity
`check elements. The system has at least one transmitter for
`transmitting the first and second turbo encoded broadcast
`signals on separate signal paths to each of the first and
`second satellite sources, respectively, and for tramitting
`the first and second satellite sources to the network of gap
`fillers. The system has a plurality of receivers for receiving
`the first and second turbo encoded broadcast signals, the
`receivers are located at or near the surface of the earth, each
`of the receivers has circuitry for outputting the digital radio
`information from the first and second turbo encoded broad-
`
`cast signals. The receiver includes an antenna connected for
`receiving radio frequency (RF) signals consisting of spread
`signals of the first and second turbo encoded broadcast
`signals. The receiver has downconverter means for convert-
`ing the RF signal to the baseband frequency of the first and
`second DAB encoded broadcast signals.
`Aceordingly the present invention provides a method of
`communicating an audio signal
`from a transmitter to a
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 9
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 9
`
`

`

`5 ,907,5 82
`
`5
`
`receiver using Turbo Coding in a digital audio broadcast
`(DAB) system. The method includes encoding the audio
`signal according to the Turbo Code at a V5 rate punctured to
`a code rate of '13, combining a first pilot signal and a
`predetermined number of channels of encoded audio signals
`using an orthogonal CDMA (OCDMA) modulator, whereby
`the OCDMA modulator consists essentially of an orthogonal
`Walsh sequence oan, W1, W2, . .
`. W3, to form a first turbo
`encoded broadcast signal containing the first pilot signal and
`the encoded audio signals of the predetermined channels,
`transmitting the first turbo encoded broadcast signal on a
`first path having the first pilot signal transmitted at a higher
`power. The method includes encoding the audio signal
`having been interleaved according to the Turbo Code at a to
`rate punctured to a rate of to, combining a second pilot signal
`and the interleaved encoded audio signals of the channels
`using the 0CDMA modulator, the OCDMA modulator con-
`sists essentially of an orthogonal Walsh sequence of W32,
`W33, W34,
`-
`.
`.
`, W63 to form a second turbo encoded
`broadcast signal containing the second pilot signal and the
`interleaved encoded audio signal of the predetermined
`channels, and the second turbo encoded broadcast signal is
`transmitted on a second path having the second pilot signal
`W32 transmitted at a higher power. The method includes, at
`the receiver, receiving the first and second turbo encoded
`broadcast signals, demodulating a selected channel of the
`first and second turbo encoded broadcast signals using said
`orthogonal Walsh sequence, whereby the demodulation of
`the first and second turbo encoded broadcast signals is
`adapted to use separate RAKE receivers so as to optimally
`combine the audio signal from the first and second turbo
`encoded signals received from the first and second paths.
`The method demultiplexes the first and second turbo
`encoded broadcast signals so as to separate systematic audio
`signals from multiplexed systematic sequences and parity
`sequences, and further the combining of an uninterleaved
`systematic sequence X, and interleaved systematic sequence
`X2 in conjunction with a code diversity combining of the
`first and second turbo encoded broadcast signals achieves an
`overall code rate V4.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features and advantages of the present invention will
`become more clearly appreciated from the following
`description, taken in conjunction With the accompanying
`drawings, in which like elements are denoted by like refer-
`ence numerals and in which:
`FIG. 1 is a schematic illustration of a DAB method and
`system;
`FIG. 2 illustrates a DAB transmission method and system
`indicating the flow of audio data in the DAB system;
`FIG. 3 illustrates a method and system of turbo encoding
`the program data signal for transmission of a channel of
`audio data in relation to FIG. 2;
`FIG. 4 illustrates and is used in explaining the method of
`implementing a punctured pattern for the output of the turbo
`encoder and the creation and subsequent transmission of the
`two complementary data signals in relation to FIGS. 2 and
`3;
`
`FIG. 5 illustrates a DAB receiver and method of receiving
`the audio data signals in the DAB system; and
`
`6
`FIG. 6 illustrates and is used in explaining a method of
`decoding the audio data signal received in relation to FIG.
`5.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`10
`
`15
`
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`
`35
`
`45
`
`50
`
`55
`
`65
`
`As illustrated in FIG. 1, a DAB system 100 is described
`according to an embodiment of the present invention. The
`DAB system It!) provides for the improved digital broad-
`casting of a signal having program data and information,
`such as, for example, digital radio information, CD Quality
`Audio, Messaging, Internet dournloads and the like. The
`DAB system 100 has an uplink earth station or transmitter
`102 designed for fixed-feeder transmission (SHF or higher
`frequency) to a plurality of separately spaced satellites in
`geosynchronous orbits, which for ease of illustration are
`shown by dual satellites 104 and 106. The transmitter 102
`can provide a plurality of uplinlt audio data signals A, for
`example. uplink signals A, and A9 to each of satellites 104
`and 106 spaced apart
`in a geosynchronous orbit. Such
`satellite transmissions can be by way of fixed-feeder tram-
`mission links to the geosynchronous satellites or to a web or
`network of low orbital satellites enabling sm'tching trans-
`mission such as GPS and the like. The DAB system 100 also
`has a plurality of receivers 108, whether fixed or mobile, for
`receiving such audio data signalsA, after they are retrans-
`mitted to a footprint or coverage area represontcd as a
`plurality of downlink paths from the satellites 104 and 106.
`The DAB system 100 advantageously can broadcast signals
`A, terrestrially from the uplink station 102 to a plurality of
`gap fillers 110 along land-lines. optical networks, micro-
`wave ground oetworks or the like. The gap fillets 110
`transmit both uplink signals A, and A2, in connection With
`a continuously adaptive propagation delay scheme to
`accommodate timing shifts caused by variations in the
`satellite paths. Gap fillers operate to fill gaps in the reception
`of the satellite signal data, for example, high density areas
`having acute problems of fading or shadoWing. Such gaps
`can be the result of signal path blockage or fading such as,
`for example, urban areas where there is a high probability
`that buildings will block signals A, or A2, or both.
`The adaptive propagation delay [12 system compensates
`for the difference between the propagation delay through
`satellites and the propagation delay through the terrestrial
`gap filler 110 network. The delay system includes, in this
`case, two delays; one to align the gap filler’s transmission of
`the AJ signal with the A, signal transmitted by satellite 104.
`and one to align the gap filler's transmission of the A.z signal
`with the Ag signal transmitted by satellite 106. The arrival
`delay spread of the signals from satellites, gap filler
`transmitter, and reflected multipaths is thereby maintained
`within one bit period to preserve the orthogonality of the
`synchronous 0CDMA system, to eliminate self-interference
`at the RAKE receiver. In this manner, the DAB system 100
`can transmit the audio data signals. Additionally, the present
`invention advantageously can allow for the transmission and
`reception of the digitized program data and information in a
`highly efiicient, reliable and cost efiective manner, so as to
`better manage transmitter power and bandwidth resources.
`According to an embodiment of the present invention, the
`DAB system 100 utilizes a Lime diversity wheme that
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 10
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 10
`
`

`

`5,907,582
`
`7
`implements a Tlurbo Code (TC) iterative channel coding
`scheme. The 'Itlrbo Coding scheme combines several simple
`codes in parallel to communicate audio program data and
`information in the signals to each uplinlt path (A1, Ah) so as
`to provide for receiver performance at or near theoretical
`Shannon’s limit, such as, for example, in the range of 0.3 to
`0.7 dB signal-to-noise ratio at a bit error rate of 10.5 for the
`Binary Phase Shift Keying (BPSK) modulation scheme. The
`DAB system 100 advantageously provides a high perfor-
`mance TC scheme achieving the code rate of V4 as described
`herein in relation to FIGS. 2-4. In this manner, the present
`invention advantageously provides temporal diversity
`through a TC implementation, thereby reducing the satellite
`transmitter output power and resulting in improved coverage
`area with a minimum number of gap fillers.
`As shown in FIG. 2,
`the transmitter 102 includes a
`plurality of channels for sending the audio data signal, for
`example, a 31 Channel DAB transmission system. For ease
`of illustration, Channels 3 through 30 are not shown. The
`transmitter 102 includes pilot signal generators 112 and 114
`for generating pilot signals P51 and P82. The pilot signal
`generators send pseudo-random noise (PH) sequences PIN]1
`and PN2 on Channels 0 and 32. The PN sequences PNl and
`PH2 are Spread by Walsh aides WcI and W32. Subsequently,
`pilot signal PS1 on Channel 0 is combined with the first
`turbo encoded audio signal and sent as a first turbo encoded
`broadcast signal via signal path A]. Pilot signal PS2 on and
`Channel 32 is combined with a second turbo encoded audio
`
`signal and sent as a second turbo encoded broadcast signal
`via signal path A2. The pilot signals are transmitted at a
`higher power or rate than the individual signals of the audio
`data channels. Pilot signals PS1 and P5,, are used by the
`receiver 108 to acquire and maintain synchronization of the
`first and second turbo encoded broadcast signals for each
`channel on the A, and A: paths, and to obtain the predeter-
`mined number of strongest multipath signals for the RAKE
`receiver.
`
`As is illustrated in FIGS. 2 and 3, the transmitter 102
`provides Channels 1 through 31 with the broadcast program-
`ming or digital audio data and information from the source
`channels to respective audio encoders 120. The output of
`each audio encoder for channels 1—31 is provided to a turbo
`encoder 122. Each turbo encoder 122 has two separate
`outputs designated 124 and 126. Non-interleaved outputs
`multiplexed with parity bits on output 124 are spread by
`Welsh codes W, through WM and combined together with
`the spread pilot signal W0, for transmission as signal AJ to
`satellite 104 and to the gap filler 110. Interleaved outputs are
`similarly multiplexed with parity bits on output 126, are
`spread with Walsh codes W33 and W63 and combined with
`the other spread pilot signal W32, for transmission as signal
`A: to satellite 106, and to the gap filler 110.
`The spread circuitry 116 operates according to an orthoga-
`nal Code Division Multiple Access (0CDMA) scheme to
`spread the PN sequences generated for pilot signals PS1 and
`P52, encoded audio program data and information, or inter-
`leaved encoded audio program data and information with a
`Walsh code sequence in a known manner and represented
`herein by the sequence W0, W1, W2, .
`.
`. W63 for a system
`supporting 31 channels of CD-quality stereo audio. The pilot
`signals PS, and PS2 generated for Channels 0 and 32 are
`
`8
`
`directly spread by the Walsh sequences W0 and W32 without
`turbo encoding. Encoded audio data and information on
`Channels 1 through 31 are spread and sequenced with Welsh
`codes W, through W31 for transmission Via the A] path.
`Similarly, encoded and interleaved audio data and informa-
`tion on channels 33 through 63 are spread and sequenced
`with Walsh codes W33 through W63 for transmission via the
`A; path. All 64 Walsh sequences are generated by the
`Hadamard matrix, and each sequence is thus orthogonal to
`every other sequences including delayed versions of itself.
`unless the delay spread exceeds one bit period. The orthogo-
`nality results in the self interference free spread spectrum
`operation of the OCDMA. The spread circuitry 116 outputs
`the spread sequence of Channels 0 through 31 to the
`combiner 113 for ultimate transmission to satellite 104 and
`
`to the gap filler 110, and Channels 32 through 63 to
`combiner 113 for ultimate transmission to satellite 106 and
`to gap filler 110.
`As shown in FIG. 3, the turbo encoder 122 includes an
`interleavcr 132 beIWeen two constituent recursive convolu-
`
`tional encoders 134 and 136 to permute incoming digital
`audio information sequence in random fashion. The permu-
`tation breaks the cross correlation between the two turbo
`
`encoded sequences. The operation of the constituent encod-
`ers 134 and 136 can be described by the polynomial
`representation,
`
`[1. astral-{1. 1+o‘n+o+o‘+n’+o‘)
`
`(1)
`
`Conventional octal representation for the illustrated code is
`(31, g1)-(21, 37). Here, the g1 represean the feed forward
`connection, and the g2 represents the feed back connection.
`The constituent codes are illustrated as identical with each
`having four memory elements (D). However, the present
`invention is not limited by this particular polynomial nor by
`the number of memory elements. The parity sequence out—
`puts of two encoders 134 and 136 are input to puncturers 138
`and 140 to generate two different punctured sequences
`described in greater detail in FIG- 4. These punctured parity
`sequence outputs are multiplexed with X, and X2 represent-
`ing the unaltered source sequences (1,, and d“ at MUX 142
`and at MUX 144, respectively. The turbo encoder 122
`miated With each audio channel can advantageously
`process broadcast programming or encoded audio data
`according to puncturing patterns discussed herein to com-
`bine the audio data and the parity data onto two carriers for
`subsequent advantageous use by an iterative decoding pro-
`cess in the turbo decoder 172 of each receiver 108.
`
`In operation, the original audio program data sequences,
`represented as d,‘ in FIG. 3, are supplied to the turbo encoder
`122, Which outputs an unaltered copy of the systematic
`audio data X, to one input of MUX 142. The audio data d,
`is also supplied to the first constituent recursive encoder 134,
`Which supplies parity output Y,, to one input of the first
`puncturer 138 and to one input of the second puncturer 140.
`The audio data clJr are also supplied to intedeaver 132. The
`second constituent encoder 136 is supplied with an inter-
`leaved audio program data signal d”. Unaltered interleaved
`signal db. is supplied in systematic form as sequence X; to
`one input of MUX 14-4 for ultimate transmission to signal
`path 126. A copy of db- is supplied to the second constituent
`encoder 136, which encodes each interleaved bit of audio
`data and generates a parity sequence Y; which is supplied to
`both puncturers 138 and 140.
`
`10
`
`15
`
`3|]
`
`35
`
`45
`
`SI}
`
`55
`
`65
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 11
`
`Petitioner Sirius XM Radio Inc. - Ex. 1006, p. 11
`
`

`

`5,907,582
`
`9
`The parity outputs ‘1’1 and Y2 generated by audio data (1,,
`and d...- are punctured according to the puncturing pattern
`
`["1]
`
`[I a]
`
`10
`as a result of the puncturing pattern
`
`a
`1
`I. u]-
`
`by the first puncturer 138 in an alternating y1 and y2 bit
`output sequence. The parity outputs Y1 and