PCT
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification 7 :
`WO 00/36783
`H04L 1/06, H04B 7/06
`
`(11) International Publication Number:
`
`Al
`
`(43) International Publication Date:
`
`22 June 2000 (22.06.00)
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`(21) International Application Number:
`
`PCT/EP98/07850
`
`(22) International Filing Date:
`
`3 December 1998 (03.12.98)
`
`(71) Applicant (for all designated States except US): FRAUN(cid:173)
`HOFER-GESELLSCHAFf ZUR FORDERUNG DER
`ANGEWANDTEN FORSCHUNG E.V. [DE/DE]; Leon(cid:173)
`rodstrasse 54, D-80636 Mtinchen (DE).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only):
`EBERLEIN, Ernst
`[DE/DE]; Waldstrasse 28b, D-91091 Grossenseebach
`(DE). BREILING, Marco [DE/DE]; Johann Jiirgen Strasse
`6, D-91052 Erlangen (DE). STOESSEL, Jan [DE/DE];
`Parkstrasse 2, D-90409 Niimberg (DE). GERHAUSER,
`Heinz [DE/DE]; Saugendorf 17, D-91344 Waischenfeld
`(DE).
`
`(74) Agent: SCHOPPE, Fritz; Schoppe & Zimmermann, Postfach
`71 08 67, D-81458 Mtinchen (DE).
`
`(81) Designated States: AL, AM, AT, AU, AZ, BA, BB, BG, BR,
`BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE,
`GH, GM, HR, HU, ID, IL, IS, JP, KE, KG, KP, KR, KZ,
`LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW,
`MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL,
`TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW, ARIPO
`patent (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR,
`IE, IT, LU, MC, NL, PT, SE), OAPI patent (BF, BJ, CF,
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`Published
`With international search report.
`
`(54) Title: APPARATUS AND METHOD FOR TRANSMITTING INFORMATION AND APPARATUS AND METHOD FOR
`RECEIVING INFORMATION
`
`240a
`
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`I~ I
`I
`I
`I
`I
`I
`I
`I
`I
`400
`I
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`I
`I
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`----TransmlWng------
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`100
`apparatus
`200
`apparatus
`
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`milting
`
`140
`
`Coclerate<½
`
`(57) Abstract
`
`An apparatus (100) for transmitting information comprises a bitstream source (110) for providing a bitstream representing the
`information, a redundancy adding encoder (120) for generating an encoded bitstream, which is arranged to output, for a first number of
`input bits and a second number of output bits. The apparatus (100) further comprises means (130) for partitioning the second number of
`output bits into the two portions of output bits and means (140) for transmitting the output bits of the first portion via a first channel (300)
`and the output bits of the second portion via second channel ( 400) being spatially different from the first channel (300). An inventive
`receiving apparatus (200) combines (230) the signals received via the first and second channels (300, 400) and uses both channel signals
`for channel decoding (220) by removing redundancy.
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`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`cu
`CZ
`DE
`DK
`EE
`
`Albania
`Atmenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cote d'Ivoire
`Cameroon
`China
`Cuba
`Czech Republic
`Getmany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`GE
`GH
`GN
`GR
`HU
`IE
`IL
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`LI
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People's
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`The fotmer Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`SI
`SK
`SN
`sz
`TD
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`us
`uz
`VN
`YU
`zw
`
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenistan
`Turkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`Yugoslavia
`Zimbabwe
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`WO 00/36783
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`Apparatus and Method For Transmitting Information
`and
`Apparatus and Method For Receiving Information
`
`Specification
`
`invention relates
`to concepts
`The present
`concepts
`in particular,
`broadcasting and,
`for
`fading
`channels
`broadcasting
`suited
`communication.
`
`for digital
`for digital
`for wireless
`
`Satellite-based broadcasting systems provide an adequate
`communication link only in rural areas,
`in which only a
`small number of e.g. bridges exist. Additionally, rural
`areas usually do not have skyscrapers. Skyscrapers as well
`as bridges or, generally, densly built-up areas are
`obstacles to satellite-based communication systems, since
`carrier
`frequencies used
`for
`such communication
`links
`involve that a channel between a sender, e.g., a satellite,
`and a receiver, i. e. a mobile or stationary receiver, is
`characterised by the line of visual contact (line of sight)
`between the sender and the receiver. If a skyscraper comes
`into the line of visual contact, i.e. ,
`the transmission
`channel between the satellite and the receiver, which may be
`positioned in a car, the received signal power will decrease
`substantially.
`
`Generally, it can be stated that in wireless systems (radio
`systems), changes
`in the physical environment cause the
`channel
`to
`fade. These changes
`include both relative
`movement
`between
`transmitter
`and
`receiver
`and moving
`scatters/reflectors in the surrounding space. In theoretical
`studies of wireless systems, the real channels are usually
`modelled so that they result in trackable analysis. The two
`major classes of
`fading characteristics are known as
`Rayleigh and Rician. A Rayleigh-fading environment assumes
`no
`line of sight and no fixed reflectors/scatters. The
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`expected value of the fading is zero. If there is a line of
`sight, this can be modelled by Rician-fading, which has the
`same characteristics as the Rayleigh-fading, except for a
`non-zero expected radio.
`
`Modern digital broadcasting systems know several means for
`reducing the impact of a channel fa ding. These concepts
`comprise channel coding on the one hand and several kinds of
`diversity on
`the other hand. The European standard for
`digital
`audio broadcasting
`(DAB),
`set out
`in Radio
`Broadcasting Systems; Digital Audio Broadcasting
`(DAB) To
`Mobile, Portable and Fixed Receivers, ETS 300 401, ETSI -
`European Telecommunications Standards Institute, Valbonne,
`France,
`February
`1995,
`uses differential
`quadrature
`phase-shift keying
`(DQPSK)
`as modulation
`technique. The
`channel encoding process is based on punctured convolutional
`coding, which
`allows
`both
`equal
`and
`unequal
`error
`protection. As a mother code, a convolutional code having a
`code
`rate of 1/4,
`a constraint
`length 7,
`and octal
`polynominals is used. The puncturing procedure allows the
`effective code rate to vary between 8/9 and 1/4. Channel
`coding by means of punctured convolutional
`codes
`is
`described in "Punctured Convolutional Codes of Rate (n-1)/n
`and Simplified Maximum Likelihood Decoding", J. Bibb Cain et
`al., IEEE Transactions on Information Theory, Vol. IT-25,
`No. 1, January 1979.
`
`Punctured convolutional codes can be used in connection with
`many modulation techniques, such as OFDM, BPSK, QAM, etc.
`
`in
`techniques are outlined
`Different channel encoding
`"Channel Coding with Multilevel/Phase Signals", Gottfried
`Ungerboeck, IEEE Transactions on Information Theory, Vol. IT
`28, No. 1, pages 55 to 66, January 1982.
`
`Bitstreams encoded by means of a convolutional encoder can
`be decoded by a decoder,
`in which the well-known Viterbi
`algorithm is implemented. This algorithm is capable of using
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`"TCM on
`(see P. Hoeher
`information
`the channel state
`Frequency-Selective Length-Mobile Fading Channels", Proc.
`Tirrenia
`International Workshop Digital Communication,
`Tirrenia, Italy, September 1991). The Viterbi algorithm can
`be modified to provide reliability estimates together with
`the decoded
`sequence. This enables soft decoding. By
`applying a soft-output Viterbi algorithm, an improvement of
`about 2 dB
`is obtained
`in comparison
`to systems
`that
`implement "hard" decision.
`
`a simplified overview of a
`to Fig. 6,
`reference
`With
`transmitter receiver system described in the European DAB
`Standard is illustrated. The transmitter receiver system
`generally comprises a transmitter section 60 and a receiver
`section 70. The transmitter section 60,
`in the simplest
`case, comprises a bitstream source 62, a channel encoder 64
`transmitter 6 6. The receiver section 7 o,
`and a
`in the
`simplest case, comprises a receiver 72 and a channel decoder
`74.
`
`Fig. 7 illustrates a transmitting receiving setup providing
`for
`time diversity as well as
`space diversity. The
`transmitter section 60' comprises the bitstream source 62
`and the encoder 64 that have already been described with
`respect to Fig. 6. In addition, the receiver section 60'
`comprises a first transmitter 66a and a second transmitter
`66b. Both transmitters 66a and 66b are fed by the same
`signal output by the encoder 64 that is duplicated by a
`duplicator 67.
`
`To obtain time diversity, a delay element 68 is coupled
`between the duplicator 67 and the second transmitter 66b.
`
`In the case of satellite communication, the transmitters 66a
`and 66b are realised by
`two satellites that reside on
`different orbital positions spaced apart from each other.
`
`The first channel is defined by the line of sight between
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`the first transmitter and the receiver, for example, a car,
`whereas the second channel is defined by the line of sight
`between
`the
`second
`transmitter 66b
`and
`the car
`that
`comprises the receiving section 70'. In the scenario,
`in
`which the car travels on a street to the right and to the
`left of which are high buildings,
`the possibility
`is
`increased that the car will receive the transmitted signal
`from at least one satellite.
`
`When the case is considered, in which the car is driving
`through a tunnel or under a bridge, the lines of sight to
`both transmitters 66a and 66b are interrupted. The time
`diversity method implemented by this system shown in Fig. 7,
`however, ensures that the receiver will not be affected by
`the interrupted channel, since the transmission signal is
`delayed by the delay stage 68. Optimally, no transmission
`interruption will result, when the delay time is equal to or
`greater than the travelling time of the car through the
`tunnel or under the bridge. Thus,
`the receiving section
`will, once again, receive the transmission signal sent by
`the transmitter 66a, when it was under the bridge, via a
`channel 2. Naturally, the receiving section 70' comprises
`another delay stage 78. As it is shown in Fig. 7, the delay
`stage 78 of the receiving section has to be in the channel
`that has not been delayed in the transmitter section. Thus,
`the signals at the output of the receivers 72a and 72b are
`identical, when the delay values of the delay stages 78 and
`68 are equal.
`
`A decision stage 79, which is symbolised as a switch in Fig.
`7, determines which channel provides the signal with the
`better signal to noise ratio. When it is determined that
`channel 1 provides the stronger signal, the decision stage
`79
`is operative to conduct
`the signal received by
`the
`receiver 72a
`into
`the channel decoder 74 When it is
`determined in block 79 that the signal transmitted over the
`other channel (channel 2) is the stronger one, the decision
`stage 79 is operative to conduct the signal received by the
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`receiver 72b to the channel decoder 74.
`
`To summarise, the system illustrated in Fig. 7 comprises the
`following essential features:
`
`the signal output by the encoder 64 is duplicated by the
`duplicator 67;
`
`exactly the same signals, whether delayed or not, are
`transmitted via both channels;
`
`the signals transmitted over both channels are derived
`from the bitstream output by the bitstream source 62 in
`exactly the same way by means of the encoding process
`carried out
`in
`the
`redundancy
`adding
`encoder
`64
`(repetition code);
`
`the decision stage 79 compares the signal to noise ratio
`of both channels and selects the channel in which the
`to noise ratio is
`signal having
`the better signal
`transmitted;
`
`transmitted via
`signal
`the
`discarded; and
`
`the other
`
`channel
`
`is
`
`the channel decoder 74 only uses one channel, i.e., the
`channel determined by the decision stage 79, for channel
`decoding.
`
`Besides the technique of channel encoding using a redundancy
`adding encoder like a convolutional encoder, different types
`of diversity, e.g., time diversity and space diversity, can
`be implemented to ease the impact of fading channels.
`
`The bitstream source 62 can be implemented as an audio
`encoder as defined by
`ISO-MPEG. It provides a bitstream
`comprising useful information, i.e., encoded spectral values
`of a block of audio samples, and side
`information. To
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`enhance the robustness of the communication link, a forward
`error correction encoding is performed by the convolutional
`encoder 64. In general, the convolutional encoding procedure
`generates redundancy in the transmitted datastream in order
`to provide ruggedness against transmission distortion.
`
`Usually, convolutional encoders consist of a specific number
`of shift
`registers and
`a
`number of XOR gates. The
`convolutional encoder described in the ETS Standard is a
`convolutional encoder having a code rate of 1/4. This means
`that the convolutional encoder produces four output bits for
`one input bit. As it is well known in the art, each output
`bit is derived from the current input bit and a specific
`combination of a certain number of preceding input bi ts
`stored in the shift registers. The specific combination of
`the current input bit and certain preceding input bits for
`each encoder output bit
`is defined by
`the so-called
`generator polynominals. The octal forms of the generator
`polynominals defined in the ETS 300 401 are 133, 171, 145
`and 133.
`
`The encoded bitstream can be punctured for raising the code
`rate from 1/4 to another code rate, e.g., 8/9. "Puncturing"
`means that certain bits in the convolutional encoder output
`bits are discarded and not forwarded to the transmitter 66.
`Thus, puncturing operates to again reduce redundancy in an
`encoded bitstream, which has been added by the convolutional
`encoder.
`
`The transmitter 66 may comprise usual transmitter elements,
`such as a QPSK modulator, an IFFT block (IFFT= Inverse Fast
`Fourier Transform)
`for performing orthogonal
`frequency
`di vision multiplexing,
`a
`guard
`interval
`inserter,
`a
`synchronisation sequence inserter and modulation means for
`modulating the signal onto a high frequency carrier.
`
`Analogously, the receiver 72 comprises an HF front end, an
`analog/digital converter, and a QPSK demodulator. The signal
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`output by the receiver is input in the decoder 7 4 . The
`decoder 7 4
`is operative to decode the encoded bi tstream
`output by the receiver 72. In modern communication systems,
`the decoder 74
`implements
`the above-outlined soft-input
`Viterbi algorithm. As it has already been outlined,
`the
`Viterbi decoder performs a maximum likelihood decoding using
`the channel
`state
`information, which
`is also called
`"metric". Different algorithms are known for Rician and
`Rayleigh channels.
`
`Especially in satellite-based communication systems, design
`engineers are confronted with strong demands for reducing
`transmitter power. Reduced
`transmitter power directly
`translates
`into system costs. Generally,
`the costs for
`designing and transporting the satellite(s) into its (their)
`orbital position(s) are directly proportional to the power
`supply needed on board of the satellite. Higher transmitter
`power on board of the satellite also means higher energy
`producing capabilities of the satellite. Thus, it can be
`stated that, under costs aspects, reducing transmitter power
`is essential.
`
`Therefore, the system described in Fig. 7 is disadvantageous
`in that,
`in the receiver, only one channel is used for
`retrieving
`information, whereas
`the other
`channel
`is
`discarded. In extreme situations, in which one channel has
`faded totally, no transmitter power from one transmitter,
`i.e., one satellite, will reach the receiver. Normally,
`however, the channels will not fade totally. Instead, both
`channels will fade more or less. Thus, the decision stage 79
`has to select one out of two useful signals. When the case
`is considered that both signals output by the receivers 72a
`and 72b have identical signal to noise ratios, only one
`signal is selected, whereby the transmitter power from the
`satellite transmitting via
`the other channel is wasted
`totally.
`
`It is the object of the present invention to provide an
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`PCT/EP98/07850
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`apparatus and method for transmitting information and an
`apparatus and method for receiving information, which result
`in better receiver output signal quality and/or reduced
`transmitter power demands.
`
`This object is attained by an apparatus for transmitting
`information in accordance with claim 1, an apparatus of
`receiving information in accordance with claim 11, a method
`of transmitting information in accordance with claim 20, and
`a method of receiving information in accordance with claim
`30.
`
`The present invention is based on the finding that, although
`there are two physically different channels both channels
`are considered as one single channel from the viewpoint of
`the channel decoder located in the receiving section. This
`means that the channel decoder in the receiving section does
`not know
`that
`the signals
`it decodes
`stem
`from
`two
`physically, i. e. spatially, different channels. However,
`the
`inventive system,
`in fact, provides
`two different
`physical channels to allow for time and/or space diversity.
`The space diversity can be obtained by
`two terrestrial
`transmitters, by
`two satellite transmitters or by one
`satellite transmitter and one terrestrial transmitter.
`
`In accordance with the present invention, an apparatus for
`transmitting information comprises a bitstream source for
`providing
`a bitstream
`representing
`the
`information. A
`redundancy
`adding
`encoder
`for generating
`an
`encoded
`bitstream based on the bitstream provided by the bitstream
`source is arranged to output, for a first number of input
`bits, a second number of output bits, the second number of
`output bits having at least twice as many output bits as the
`first number of input bits, and wherein the second number of
`output bits includes
`two portions of output bits, each
`portion of output bits individually allowing the retrieval
`of
`information represented by the first number of input
`bits, and the first portion of output bits being coded based
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`on the bi tstream in a different way with respect to the
`second portion of output bits. A means for partitioning
`receives the output of the redundancy adding encoder and
`partitions the second number of output bi ts into the two
`portions of output bits. Means for transmitting transmit the
`output bits of the first portion via a first channel and the
`output bi ts of the second portion via a second channel,
`wherein the second channel is spatially different from the
`first channel.
`
`In accordance with another aspect of the present invention,
`an apparatus for receiving information comprises receiving
`means for receiving the first portion of bits via a first
`channel and the second portion of bits via a second channel,
`combining means for combining
`the first and
`the second
`portions and decoding means for decoding the coded bitstream
`by
`removing
`redundancy
`from
`the coded bitstream,
`the
`decoding means using the first and second portions of bits
`combined by the combining means.
`
`inventive transmitter receiver concept provides the
`This
`following advantages:
`
`two channels allow time and/or space diversity;
`
`the partitioner partitions rather than duplicates the
`output signal of the encoder into two portions of output
`bits;
`
`than
`rather
`the receiver combines
`in
`the combiner
`selects the signals received
`from both channels and
`feeds the combined signal into the channel decoder;
`
`the signals from both channels are used for decoding all
`the time;
`
`in the best case, in which the signal powers in both
`channels are
`identical,
`transmitter power used
`for
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`
`transmitting via each channel can be halved at least,
`thus, halving system costs with respect to the system
`illustrated in Fig. 7; and
`
`when the transmitter powers are not changed, the signal
`quality
`output
`by
`the
`channel
`decoder
`can
`be
`considerably improved.
`
`The foregoing and other objects, features and advantages of
`the invention will become more readily apparent from the
`following detailed description of preferred embodiments
`which proceeds with reference to the drawings.
`
`Fig. 1
`
`transmission
`a
`a principle overview of
`shows
`the present
`receiving system
`in accordance with
`invention, comprising an inventive transmitter and
`an inventive receiver.
`
`Fig. 2
`
`the
`a more detailed block diagram of
`shows
`transmission receiving system shown in Fig. 1, in
`which time and space diversity are embodied.
`
`Fig. 3
`
`shows a detailed block diagram of an
`transmitter section.
`
`inventive
`
`Fig. 4
`
`input bit sequence and an output bit
`shows an
`in an
`pattern of a convolutional encoder used
`inventive transmitter section.
`
`Fig. 5
`
`shows a detailed view of an
`section.
`
`inventive receiver
`
`Fig. 6
`
`shows a generalised block diagram of a prior art
`transmitting receiving system.
`
`Fig. 7
`
`transmitter receiver
`shows a block diagram of a
`system
`implementing
`time and space diversity,
`in
`which
`the output of
`the
`transmitter encoder
`is
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`PCT/EP98/07850
`
`duplicated and a channel selection is performed in
`the receiver.
`
`In Fig. 1 a general block diagram of an inventive apparatus
`for
`transmitting
`100
`and
`an
`inventive apparatus
`for
`receiving 200 is illustrated. The transmitting apparatus 100
`comprises
`a bitstream source 110,
`a
`redundancy adding
`encoder 120 and a partitioner 130. The bitstream source 110
`may be an MPEG encoder as described above. The encoder 120
`is generally a redundancy adding encoder for generating an
`encoded bitstream on its output, wherein the encoder 120 is
`arranged to output, for a first number of input bi ts, a
`second number of output bi ts, the second number of output
`bits having at least twice as many output bits as the first
`number of
`input bits. This means that the encoder 120
`implements a code rate equal to or less than 1/2. As it is
`known in the art, the code rate is defined by the number of
`input bits divided by the number of output bits produced by
`the encoder based on the number of input bi ts. In other
`words, a code rate 1/2 means that for each input bit, two
`output bits are produced. Analogously, a code rate of 1/3
`means
`that for each
`input bit,
`three output bits are
`produced. similarly, a code rate of 3/8 means that for three
`input bits, eight output bits are produced.
`
`The code rate of the encoder 120 is set to be smaller than
`1/2, such that the second number of output bits can be
`sub-divided into two portions of output bits, such that each
`portion of output bits individually allows the retrieval of
`information represented by the first number of input bits
`This means that a decoder 220
`located in the receiving
`apparatus is able to retrieve information represented by the
`bitstream output by the bitstream source 110 when only one
`channel, i.e., channel 1 300 or channel 2 400 provides a
`useful signal, whereas the other channel has faded totally.
`
`Another feature of the encoder 120 is that the first portion
`of output bit is coded based on the bitstream in a different
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`way with respect to the second portion of output bi ts. In
`contrast to a simple repetition code in which redundancy is
`doubled by simply duplicating a signal to transmitted coded,
`the channel decoder 220 capabilities are enhanced, since the
`signal is transmitted over the channels 300 and 400 are
`derived from the bi tstream output by the bi tstream source
`110 independently of each other. The partitioner 130 feeds
`means
`for
`transmitting 140
`for
`transmitting
`the first
`portion of output bits via the first channel 300 and the
`second portion of output bits via the second channel 400. It
`is to be noted that both channels 300 and 400 are spatially
`different from each other.
`
`As usual, a channel between the transmitter and the receiver
`is defined by the line of sight connection between the
`transmitter and
`the
`receiver. Thus,
`two channels are
`different from each other when a mobile receiver has moved
`with
`respect
`to
`a
`single
`transmitter, or when
`two
`transmitters exist positioned in different locations, e.g.,
`orbital positions. In this case, it does not play any role
`whether the receiver is a mobile or a stationary receiver.
`
`one
`comprise
`140 may
`transmitting means
`the
`Thus,
`transmitter, e.g., one satellite and a delay stage, such
`that two different channels are created between the single
`transmitter and a mobile receiver, when the mobile receiver
`is at a first position and between the single transmitter
`and the mobile receiver when the mobile receiver has moved
`to a second position after the period defined by the delay
`stage
`in
`the
`transmitter. This concept is called
`time
`diversity
`for mobile
`receivers. Naturally,
`it is not
`possible to create two channels different from each other
`between a single stationary transmitter and a stationary
`receiver.
`
`Alternatively, as it is described with reference to Fig. 2,
`the
`transmitting means
`140
`comprise
`two
`transmitters
`positioned
`in different
`locations,
`to obtain
`space
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`diversity.
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`
`The receiving apparatus 200 illustrated in Fig. 1 comprises
`receiving means
`240a
`and
`240b,
`the
`receiving means
`comprising a first receiver 240a for receiving the first
`portion of output bits transmitted via the first channel 300
`and a second receiver 240b for receiving the second portion
`of output bits via the second channel 400.
`
`In accordance with the present invention, the output signals
`of the receiving means 240a and 240b are combined in a
`combiner 230 such that the output signals of both receivers
`are used in the channel decoder 220.
`
`in
`receiving system
`transmission
`illustrates a
`2
`Fig.
`accordance with the preferred embodiment of the present
`invention. The transmitting apparatus comprises, as already
`described in Fig. 1, the bitstream source 110, the encoder
`120 generally
`termed as
`forward error correction,
`the
`partitioner 130 and transmitting means comprising a first
`satellite 140a, a second satellite 140b and a delay stage
`140c.
`
`The receiving apparatus comprises the channel decoder 220,
`the combiner 230 and the receiving means (Rx) comprising the
`first and second receivers 240a, 240b and a delay stage
`240c. The transmitting apparatus and the receiving apparatus
`are "connected" by the first channel 300 and the second
`channel 400.
`
`the delay stages 140c and 240c, which are
`By using
`in
`opposite
`channels,
`time diversity
`is
`positioned
`implemented in the transmission receiving system shown in
`Fig. 2. Furthermore, by means of the provision of
`two
`transmitters, i.e., the first satellite 140a and the second
`satellite 140b, space diversity or spatial diversity is
`implemented
`into
`the
`inventive
`transmission
`receiving
`system.
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`
`With reference to Fig. 3, a more detailed block diagram of
`the transmitting apparatus is described. The encoder 120 in
`the transmitting apparatus is implemented as a convolutional
`encoder in accordance with the present invention. As it is
`shown in Fig. 3, the convolutional encoder comprises three
`generator polynominals, i.e., a first generator polynominal
`gl 121, a second generator polynominal g2 122 and a third
`generator polynominal g3
`123. Thus,
`the convolutional
`encoder 120 has a code rate of 1/3, since, for one input
`bit,
`the
`encoder
`produces
`three output bi ts.
`The
`transmitting apparatus shown in Fig. 3 further comprises a
`puncturing unit 125 that reduces the number of bits, i.e.,
`the number of output bits, such that an even number of
`output bits to be transmitted over the first and second
`channel is obtained. The puncturing unit 125 is connected to
`the partitioner 130, that, in accordance with the preferred
`embodiments
`of
`the
`present
`invention,
`comprises
`a
`parallel-to-serial
`converter
`and
`a
`demultiplexer
`to
`demultiplex
`the
`serial
`bitstream
`produced
`by
`the
`parallel-to-serial converter into two bitstreams. The block
`diagram in Fig. 3 further comprises the delay stage 140c of
`the transmitting means. The first transmitter and the second
`transmitter are not shown in Fig. 3.
`
`Thus, the first portion of output bi ts is transmitted via
`the first channel, whereas the second portion of output bits
`is delayed by the delay stage, transmitted via the second
`channel.
`
`the
`functionality of
`the
`4,
`to Fig.
`reference
`With
`convolutional encoder 120, the puncturing unit 125 and the
`partitioner 130 will be described. In Fig. 4, an input bit
`sequence having bits 401, 402 and 403 is illustrated. The
`convolutional encoder 120 will produce
`three parallel
`arranged output bits 411, 412 and 413 for each input bit
`401, 402 and 403. The notation of the output bits 411 to 413
`relates to the channel, over which the respective bit is
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`transmitted. Thus, bi ts termed E are transmitted over the
`early satellite, i.e., satellite 140a (Fig. 2), whereas the
`bits termed Lare transmitted over the late satellite, i.e.,
`the satellite 140b (Fig. 2), which input is delayed by the
`delay stage 140c. The bit termed X is not transmitted at
`all. This bit is discarded by the puncturing unit 125 to
`obtain a second number of output bi ts, which is an even
`number. In accordance with the preferred embodiment of the
`present invention, an even number of output bi ts to be
`transmitted by
`the
`transmitting means 140
`(Fig. 1)
`is
`required, since two channels exist and the number of bi ts
`transmitted over each channel are equal in the preferred
`embodiment. It has to be noted that equal numbers of bits in
`each channel are not esential for the present invention.
`
`into a
`fed
`is
`the puncturing unit 125
`The output of
`parallel-to-serial converter included in the combiner 130
`(Fig. 3) such that a serial bitstream, i.e., the second
`number of output bits,
`is obtained. The demultiplexer
`included in the partitione