US 6,728,323 B1
`(10) Patent N0.:
`(12) United States Patent
`
`Chen et al. Apr. 27, 2004 (45) Date of Patent:
`
`
`USOO6728323B1
`
`(54) BASEBAND PROCESSORS, MOBILE
`TERMINALS, BASE STATIONS AND
`METHODS AND SYSTEMS FOR DECODING
`A PUNCTURED CODED RECEIVED SIGNAL
`USING ESTIMATES OF PUNCTURED BITS
`
`FOREIGN PATENT DOCUMENTS
`
`if
`W0
`
`figggfiég :2 13133:
`WO 99/41840
`8/1999
`OTHER PUBLICATIONS
`
`(75)
`
`Inventors: Dayong Chen, Cary, NC (US); Evin
`Fell, Cary, NC (US)
`.
`_
`.
`(73) ASSignee: Ericsson Inc., Research Triangle Park,
`NC (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U-S-C- 154(b) by 624 days.
`
`pp .
`21 A l N
`
`o.:
`
`,
`09/612 713
`
`International Search Report for PCT/SE01/01605.
`G. David Forney, The ViterbiAlgorithm, Proceedings of the
`IEEE, vol. 61, No. 3, Mar. 1973.
`George C. Clark, Jr., and J. Bibb Cain, Error—Correction
`Coding for Digital Communications, Proceedings of the
`IEEE M . 1973.
`.
`’
`ar
`.
`* Cited by examiner
`Primary Examiner—Khai Tran
`(74) Attorney, Agent, or Firm—Myers Bigel Sibley &
`ajovec
`S '
`
`(22)
`
`Filed:
`
`Jul. 10,2000
`
`(57)
`
`ABSTRACT
`
`(51)
`Int. Cl.7 ......................... H04L 27/06; H03M 13/03
`(52) US. Cl. ................................. 375/340; 714/790
`
`(58) Field of Search
`.......... 375/340 341
`375/316' 714/794 786 790 795’ 799’
`’
`’
`’
`’
`’
`References Cited
`
`(56)
`
`U~S- PATENT DOCUMENTS
`5,673,291 A
`9/1997 Dent
`.......................... 375/262
`5,878,090 A *
`3/1999 Stephens
`375/326
`
`5,983,384 A
`11/1999 Ross .........
`714/755
`................
`6,094,427 A *
`7/2000 Yi
`370/331
`
`6,157,683 A
`12/2000 Daribi et a1.
`.....
`375/341
`6,192,500 B1 *
`2/2001 Yang et al.
`.......
`714/786
`6,233,712 B1
`5/2001 Rhee et al.
`................. 714/789
`
`Methods, systems, baseband processors, mobile terminals
`and base stations are provided for decoding a punctured
`coded Signal are provided. The Signal iS received to provide
`received symbols. Symbol positions associated With punc-
`tured locations are initialized to default symbol values. The
`received symbols and the default symbol values are error
`correction decoded to provide first Signal estimates. Punc-
`tured location symbol estimates are generated based on the
`first Signal estimates and the received symbols are combined
`.
`.
`.
`.
`With the punctured location symbol estimates placed in
`corresponding punctured locations. The combined received
`symbols With the punctured location symbol estimates are
`error correction decoded to provide second Signal estimates.
`
`28 Claims, 6 Drawing Sheets
`
`APPLE 1047
`
` 1
`
`APPLE 1047
`
`1
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 1 0f 6
`
`US 6,728,323 B1
`
`Other User Interference
`Noise
`
`FIG. 1
`
`PRIOR ART
`
`
`
`
`
`
`
`Transmitter
`
`Radio
`Processor
`
`Baseband
`
`Post
`
`Processor
`
`Processing
`
`Receiver
`
`19
`
`Coded
`
`40
`
`Bits
`
`42
`
`
`
`information
`
`
`Bits
`
`FIG. 2
`
`PRIOR ART
`
`44
`
`
`
`Modulator
`
`
`
`2
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 2 0f 6
`
`US 6,728,323 B1
`
`
`
` ._.m<EOE—n—m.9“.
`
`A20«5:3
`
`A8,.«Noas
`
`Eccmco
`
`856:3 cos—minceam5>mm=m§
`
`356595:
`
`mo.—30%
`
`m:29.EQsmuoo
`
`m:396.63800
`
`253%
`
`3
`
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 3 0f 6
`
`US 6,728,323 B1
`
`
`
`4
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 4 0f 6
`
`US 6,728,323 B1
`
`5°°
`
`FIG. 5
`
`Receive Signal
`
`505
`
`530
`
`Locations
`
`510
`
`
` Initialize
`
`
`Punctured
`
`
`
`
`Error Correction
`
`
`
`Decode
`
`520
`
`Yes
`
`Re—encode
`
`
`
`
`
`Signal
`
`Estimates
`
`525
`
`Convert to Soft
`Information
`
`Combine Signal
`
`and Estimates
`
`535
`
` Fle-error
`
`Correction
`
`
`Decode
`
`540
`
`No
`
`Yes 545
`
`Request
`
`Re-transmit
`
`m
`
`5
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 5 0f 6
`
`US 6,728,323 B1
`
`m.GE
`
`coo
`
`n2mNZwrZw02mNZM.‘Zm
`
`mwmNW5%.
`
`mumNNIwrum
`
`mzmmzmEm
`
`6
`
`
`
`

`

`US. Patent
`
`Apr. 27, 2004
`
`Sheet 6 0f 6
`
`US 6,728,323 B1
`
`FIG. 7
`
`Decode Signal
`
`Combined Signal
`
`Combine Punctured
`
`Signal Estimates
`and Signal
`
`Fla-decode
`
`7
`
`

`

`US 6,728,323 B1
`
`1
`
`BASEBAND PROCESSORS, MOBILE
`TERMINALS, BASE STATIONS AND
`METHODS AND SYSTEMS FOR DECODING
`A PUNCTURED CODED RECEIVED SIGNAL
`USING ESTIMATES OF PUNCTURED BITS
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to signal communications
`and, in particular,
`to reception of encoded signals over a
`communications channel.
`
`10
`
`The use of wireless communications is expanding rapidly,
`particularly as more radio spectrum becomes available for
`commercial use and as wireless phones become more com-
`monplace. In addition, analog wireless communications are
`gradually being supplemented and even replaced by digital
`communications. In digital voice communications, speech is
`typically represented by a series of bits which may be
`modulated and transmitted from a base station of a wireless
`communications network to a mobile terminal device such
`
`as a wireless phone. The phone may demodulate the
`received waveform to recover the bits, which are then
`converted back into speech.
`In addition to voice
`communications, there is also a growing demand for data
`services, such as e-mail and Internet access, which typically
`utilize digital communications.
`There are many types of digital communications systems.
`Traditionally, frequency-division-multiple-access (FDMA)
`is used to divide the spectrum up into a plurality of radio
`channels corresponding to different carrier frequencies.
`These carriers may be further divided into time slots, gen-
`erally referred to as time-division-multiple-access (TDMA),
`as is done, for example, in the Digital-Advanced Mobile
`Phone Service (D-AMPS) and Global System for Mobile
`communication (GSM) standard digital cellular systems.
`Alternatively, if the radio channel is wide enough, multiple
`users can use the same frequencies using spread spectrum
`techniques and code-division-multiple-access (CDMA).
`A typical digital communications system 19 is shown in
`FIG. 1. Digital symbols are provided to the transmitter 20,
`which maps the symbols into a representation appropriate
`for the transmission medium or channel (e.g. radio channel)
`and couples the signal
`to the transmission medium via
`antenna 22. The transmitted signal passes through the chan-
`ne124 and is received at the antenna 26. The received signal
`is passed to the receiver 28. The receiver 28 includes a radio
`processor 30, a baseband signal processor 32, and a post
`processing unit 34.
`The radio processor typically tunes to the desired band
`and desired carrier frequency, then amplifies, mixes, and
`filters the signal to a baseband. At some point, the signal may
`be sampled and quantized, ultimately providing a sequence
`of baseband received samples. As the original radio signal
`generally has in-phase (I) and quadrature (Q) components,
`the baseband samples typically have I and Q components,
`giving rise to complex, baseband samples.
`The baseband processor 32 may be used to detect the
`digital symbols that were transmitted. It may produce soft
`information as well, which gives information regarding the
`likelihood of the detected symbol values. The post process-
`ing unit 34 typically performs functions that depend on the
`particular communications application. For example, it may
`convert digital symbols into speech using a speech decoder.
`Atypical transmitter is shown in FIG. 2. Information bits,
`which may represent speech, images, video, text, or other
`content, are provided to forward-error-correction (FEC)
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`encoder 40, which encodes some or all of the information
`bits using, for example, a convolutional encoder. The FEC
`encoder 40 produces coded bits, which are provided to an
`interleaver 42, which reorders the bits to provide interleaved
`bits. These interleaved bits are provided to a modulator 44,
`which applies an appropriate modulation for transmission.
`The interleaver 42 may perform a variety of types of
`interleaving.
`The modulator 44 may apply any of a variety of modu-
`lations. Higher-order modulations are frequently utilized.
`One example is 8-PSK (8-ary phase shift keyed), in which
`3 bits are sent using one of 8 constellation points in the
`in-phase (I)/ quadrature (Q) (or complex) plane. Another
`example is 16-QAM (16-ary quadrature amplitude
`modulated),
`in which 4 bits are sent at
`the same time.
`Higher-order modulation may be used with conventional,
`narrowband transmission as well as with spread-spectrum
`transmission.
`
`In a conventional baseband processor, a baseband
`received signal is typically provided to a demodulator which
`produces soft bit values. These soft bit values are generally
`provided to a de-interleaver which reorders the soft bit
`values to provide de-interleaved soft bits. These
`de-interleaved soft bits may then be provided to a forward
`error correction (FEC) decoder which performs,
`for
`example, convolutional decoding, to produce detected infor-
`mation bits.
`
`A second example of a conventional baseband processor
`employs multipass equalization, sometimes referred to as
`Turbo equalization,
`in which results, after decoding has
`completed, are passed back to the equalization circuit to
`re-equalize, and possibly re-decode,
`the received signal.
`Such a system is described, for example, in US. Pat. No.
`5,673,291 to Dent et al. entitled “Simultaneous demodula-
`tion and decoding of a digitally modulated radio signal using
`known symbols” which is hereby incorporated herein by
`reference. In multi-pass equalization, the processor typically
`initially performs conventional equalization and decoding.
`After decoding, the detected information bits are encoded
`and then re-interleaved to provide information to the mul-
`tipass equalizer and soft
`information generator which
`re-equalizes the received baseband signal using the detected
`bit values. Typically, because of diagonal interleaving or the
`fact that some bits are not convolutionally encoded, the
`second pass effectively uses error corrected bits, as deter-
`mined and corrected in the first pass, to help detection of
`other bits, such as bits which were not error correction
`encoded.
`
`Both single pass and multipass baseband processors as
`described above typically use conventional FEC decoders.
`Conventional FEC decoders typically treat each soft bit
`value as if it were independent of all other values. For
`example, in a Viterbi decoder for convolutional codes, soft
`bit values are generally correlated to hypothetical code bit
`values and added. As the soft bit values typically correspond
`to loglikelihood values, adding soft values corresponds to
`adding loglikelihoods or multiplying probabilities.
`By way of background, error correction codes, such as
`convolutional codes,
`in essence, provide error correction
`capability by generating one or more “parity” bits for
`transmission from each data bit to be transmitted. The ratio
`
`of data symbols to parity symbols is referred to as a coding
`rate. For example, if two parity bits are generated for each
`data bit, the code is known as a rate 1/2 code, with twice as
`many parity bits as original data bits being transmitted. If the
`rate of transmission is fixed, the time required to transmit
`8
`
`8
`
`

`

`US 6,728,323 B1
`
`3
`such parity bits is twice as long as the time required to
`transmit the original data bits. More generally, if r parity bits
`are generated for each data bit, the code is known as a rate
`1/r code. Typically, the parity bit transmission rate is adopted
`to be r times the message information bit rate.
`Tables of parity equations for various code rates and
`constraint lengths that result in optimum codes are published
`in the technical literature. See, e.g., G. Clarke, Jr., and J.
`Cain, Error-Correction Coding for Digital Communications,
`Appendix B, Plenum Press, New York (1981).
`The known methods for decoding convolutional codes
`include threshold decoding, Sequential Maximum Likeli-
`hood Sequence Estimation (SMLSE), and the stack algo-
`rithm. The SMLSE technique is commonly known as the
`Viterbi algorithm, which is described in the literature includ-
`ing D. Forney, “The Viterbi Algorithm”, Proc. IEEE, Vol. 61,
`pp. 268—278 (March, 1973).
`As noted above, r times more parity symbols than input
`data symbols are produced for a rate 1/r code, and, if all
`parity symbols are transmitted, an r-times redundancy has
`been provided to combat errors. It will, however, be appre-
`ciated that it is not necessary to transmit all of the parity
`symbols. If the transmitter and receiver have previously
`agreed on some regular method of determining which parity
`symbols are not transmitted, the code is then known as a
`punctured convolutional code. Punctured codes typically
`result in coding rates m/r, such as 13/29, where adaptation
`to a transmission rate that is r/m times the message infor-
`mation bit rate is required.
`Punctured convolutional codes are widely used in digital
`wireless systems, such as in GSM and in the emerging
`Enhanced General Packet Radio Service/Enhanced Data
`GSM Environment (EGPRS/EDGE). In these systems, con-
`volutional coding is typically first applied to a block of
`payload data to produce an initial signal block, sometimes
`referred to as an initial mother codeword. Subsequent punc-
`turing typically allows a single coder to derive multiple
`codewords corresponding to a variety of code rates. A
`codeword may then be transmitted by the sending end and
`subsequently received by the receiving end where decoding
`takes place.
`Such punctured codes may be processed at the receiving
`end using soft decoding. Soft decoding is based on soft
`information related to received symbols. The received sym-
`bols are characterized not only by their bit polarities, i.e.,
`one or zero, but also by a magnitude or quality measure
`generally referred to as soft information. Soft information
`with a large magnitude indicates that a one or zero,
`respectively, is received with high probability whereas soft
`information with a magnitude close or equal to 0 typically
`represents a received symbol that is ambiguous.
`Before decoding, the receiving decoder typically reverses
`the puncturing by filling the punctured symbol positions
`with zeros. As zero valued symbol typically does not convey
`any useful information to the decoder, the more symbols that
`are punctured, the less powerful the punctured codeword is
`compared with its original mother codeword.
`Puncturing may be used in incremental redundancy to
`divide a mother codeword into several increments of parity
`bits (incremental codewords). If a previously transmitted
`incremental codeword(s) cannot be decoded, additional
`incremental codewords may be sent until
`the combined
`incremental codewords can be successfully decoded to
`determine the original data block. For example, a received
`incremental codeword may be decoded and error correction
`applied. The error detection code (such as a cyclical redun-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`dancy check (CRC)) may then be used to check whether or
`not the decoded and error corrected symbols are error free.
`If there are still errors in the decoded and error corrected
`
`symbols, as indicated by the CRC test, the received incre-
`mental codeword is retained and transmission of an addi-
`
`tional incremental codeword is requested by the receiving
`end.
`
`Puncturing will now be further illustrated with reference
`to the schematic diagram of FIG. 3. A block of source (or
`payload) data symbols, which may include CRC and tail
`symbols, is illustrated at block 200. The source data symbols
`200 are convolutionally encoded, using a rate 1/3 code in the
`illustrated example, to produce an initial mother codeword
`210. As shown in FIG. 3, every third symbol (starting from
`the third symbol of the mother codeword) of the initial
`mother codeword 210 is punctured to provide an incremen-
`tal codeword 215 for transmission which has an effective
`
`coding rate of 1/2. Two additional incremental codewords
`can be generated, again by puncturing every third symbol of
`the initial mother codeword, but starting from the first of the
`second symbol respectively. Both of these incremental code-
`words include the coded symbols C13, C23 .
`.
`.
`, CN3 which
`were punctured in the first incremental codeword.
`
`SUMMARY OF THE INVENTION
`
`Methods for decoding a punctured coded signal are pro-
`vided. The signal is received to provide received symbols.
`Symbol positions associated with punctured locations are
`initialized to default symbol values. The received symbols
`and the default symbol values are error correction decoded
`to provide first signal estimates. Punctured location symbol
`estimates are generated based on the first signal estimates
`and the received symbols are combined with the punctured
`location symbol estimates placed in corresponding punc-
`tured locations. The combined received symbols with the
`punctured location symbol estimates are error correction
`decoded to provide second signal estimates.
`As will further be appreciated by those of skill in the art,
`while described above with reference to method aspects, the
`present
`invention may also be embodied as baseband
`processors, mobile terminals, base stations and systems.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram illustrating a conventional
`communication system.
`FIG. 2 is a block diagram illustrating a conventional
`transmitter.
`
`FIG. 3 is a schematic block diagram of coding using a
`punctured code according to the prior art.
`FIG. 4 is a block diagram illustrating a wireless commu-
`nication terminal including a baseband processor according
`to embodiments of the present invention.
`FIG. 5 is a flowchart illustrating baseband processing
`operations according to embodiments of the present inven-
`tion.
`
`FIG. 6 is a schematic block diagram further illustrating
`the operations shown in FIG. 5.
`FIG. 7 a flowchart illustrating baseband processing opera-
`tions according to further embodiments of the present inven-
`tion.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The present invention now will be described more fully
`hereinafter with reference to the accompanying drawings, in
`9
`
`9
`
`

`

`US 6,728,323 B1
`
`5
`which illustrative embodiments of the invention are shown.
`This invention may, however, be embodied in many different
`forms and should not be construed as limited to the embodi-
`ments set forth herein; rather, these embodiments are pro-
`vided so that this disclosure will be thorough and complete,
`and will fully convey the scope of the invention to those
`skilled in the art. As will be appreciated by those of skill in
`the art, the present invention may be embodied as methods
`or devices. Accordingly, the present invention may take the
`form of a hardware embodiment, a software embodiment or
`an embodiment combining software and hardware aspects.
`FIG. 4 illustrates exemplary mobile terminal 300 accord-
`ing to embodiments of the present invention. The mobile
`terminal 300 includes a transceiver (i.e.,
`receiver and
`transmitter) 372 that is operative to transmit and receive RF
`communication signals via an antenna 310 under control of
`a controller 370. The controller 370 includes a baseband
`
`processor 371 as well as other functional modules not
`illustrated in FIG. 4 but which will be understood to those
`of skill in the art related to wireless communications includ-
`
`ing both data and voice communication support. The con-
`troller 370 processes messages to produce physical layer
`bursts that are transmitted over physical wireless channels
`by the transceiver 372 via the antenna 310. The baseband
`processor 371 includes a forward error correction (FEC)
`decoder 374, such as a convolutional decoder, an error
`detector 376, such as a cyclical redundancy check (CRC)
`error detector, and a punctured symbol estimate generator
`378. The controller 370, such as a microprocessor, micro-
`controller or similar data processing device, may execute
`program instructions stored in a memory 360 of the mobile
`terminal 300, such as a dynamic random access memory
`(DRAM), electrically erasable programmable read-only
`memory (EEPROM) or other storage device. The controller
`370 is further operatively associated with user interface
`components of the mobile terminal 300 such as a display
`320, a keypad 330, a speaker 340, and a microphone 350,
`operations of which are known to those of skill in the art and
`will not be further discussed herein.
`
`The transceiver 372 provides a receiver that receives a
`punctured coded signal and provides the signal
`to the
`baseband processor 371. The error correction decoder 374 is
`configured to generate estimates of a received punctured
`coded signal from the punctured coded signal and from
`punctured location symbol estimates. The punctured symbol
`estimate generator 378 generates the punctured location
`symbol estimates from estimates of a received punctured
`coded signal and provides the punctured location symbol
`estimates to the error correction decoder 374. The receiver
`
`372 may be a demodulator configured to provide soft
`information to the baseband processor 371 as the received
`punctured coded signal. The error correction decoder 374
`may be a convolutional decoder. The convolutional decoder
`may, for example, be a rate 1/3 convolutional decoder
`wherein the punctured coded signal is punctured to a higher
`coding rate than 1/3 for transmission to the terminal 300. As
`noted above, the error detector 376 may be a CRC error
`detector, coupled to the error correction decoder 374, that
`detects errors in the estimates of a received punctured coded
`signal provided by the error correction decoder 374. The
`CRC detector 376 may be coupled to the punctured symbol
`estimate generator 378 and may initiate generation of punc-
`tured location symbol estimates by the punctured symbol
`estimate generator 378.
`It will be appreciated that the transceiver 372, the base-
`band processor 371 and other components of the mobile
`terminal 300 may be implemented using a variety of hard-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`ware and software. For example, operations of the trans-
`ceiver 372 and/or the baseband processor 371 may be
`implemented using special-purpose hardware, such as an
`application specific integrated circuit (ASIC) and program-
`mable logic devices such as gate arrays, and/or software or
`firmware running on a computing device such as a
`microprocessor, microcontroller or digital signal processor
`(DSP) as shown for the baseband processor 371 in FIG. 4.
`It will also be appreciated that, although functions of the
`transceiver 372 and/or the baseband processor circuit 371
`may be integrated in a single device, such as a single ASIC
`microprocessor, they may also be distributed among several
`devices. Aspects of the transceiver 372, the baseband pro-
`cessor 371 and the controller 370 may also be combined in
`one or more devices, such as an ASIC, DSP, microprocessor
`or microcontroller.
`
`It is further schematically illustrated in FIG. 4 that the
`mobile terminal 300 may receive communicated signals,
`such as the communication signal 382, from various com-
`munication service providers. It is to be further understood
`that a wireless communication system generating the com-
`munication signal 382 may include a variety of different
`configurations of components such as base stations, some-
`times referred to as “base transceiver stations,” mobile
`switching centers (MSCs),
`telecommunications switches,
`and other communications components.
`While the present invention was described with reference
`to a mobile terminal above,
`it is to be understood that
`baseband processors of the present invention may be utilized
`in a variety of communication devices, including wireless
`communication devices such as radiotelephones. As
`described with reference to FIG. 4, radiotelephones typically
`include a transmitter, a receiver, a user interface and an
`antenna system. The antenna system may include an antenna
`feed structure and one or more antennas. The antenna system
`may be coupled to the baseband processor through circuitry,
`such as an RF processor, configured to step up signals for
`transmission to an assigned transmission frequency or to
`step down received signals from a modulation frequency to
`a baseband frequency. However, the baseband processor in
`some applications may couple directly to the antenna sys-
`tems.
`
`As is well known to those of skill in the art, the transmitter
`converts the information which is to be transmitted by
`radiotelephone into an electromagnetic signal suitable for
`radio communications. The receiver demodulates electro-
`
`magnetic signals which are received by radiotelephone so as
`to provide the information contained in the signals to the
`user interface in a format which is understandable to the
`
`user. The receiver generally includes an RF processor and a
`baseband processor, in particular, a baseband processor of
`the present invention may be beneficially utilized as will be
`further described herein. A wide variety of transmitters,
`receivers, and user interfaces (e.g., microphones, keypads,
`displays) which are suitable for use with handheld radio-
`telephones are known to those of skill in the art, and such
`devices may be implemented in a radiotelephone including
`a baseband processor in accordance with the present inven-
`tion. Other than the baseband processor according to the
`present invention, the design of such a radiotelephone is well
`known to those of skill in the art and will not be further
`described herein. It
`is further to be understood that the
`
`present invention is not limited to radiotelephones and may
`also be utilized with other wireless and wired communica-
`
`tion receivers receiving punctured coded signals.
`Furthermore,
`it
`is to be understood that,
`in various
`embodiments, the present invention is directed to mobile
`10
`
`10
`
`

`

`US 6,728,323 B1
`
`7
`terminals and/or base stations utilizing baseband processors
`according to the present invention. As used herein, the term
`“base station” refers to a variety of relay components of a
`communication system which may communicate with a
`wireless terminal, such as base station controllers, mobile
`switching centers and the like.
`According to the present invention, methods, systems and
`baseband processors are provided that may decode punc-
`tured received signals by using signal estimates for signal
`positions corresponding to punctured locations from a first
`decoding pass during a second decoding pass of the punc-
`tured received signals. The estimates for the punctured
`locations may be provided by encoding the first pass output
`and inserting the punctured location estimates in the punc-
`tured locations along with the received signals and then
`again error correction decoding the combined signal. The
`second pass of decoding may be utilized when errors are
`detected during the first pass. Re-transmission may be
`avoided where the signal estimates from the second pass of
`decoding contain no errors.
`In embodiments of the present invention, methods for
`decoding a punctured coded signal are provided. The signal
`is received to provide received symbols. Symbol positions
`associated with punctured locations are initialized to default
`symbol values. The received symbols and the default symbol
`values are error correction decoded to provide first signal
`estimates. Punctured location symbol estimates are gener-
`ated based on the first signal estimates and the received
`symbols are combined with the punctured location symbol
`estimates placed in corresponding punctured locations. The
`combined received symbols with the punctured location
`symbol estimates are error correction decoded to provide
`second signal estimates. The error correction decoding may
`be convolutional decoding. The punctured location symbol
`estimates may be generated by encoding the first signal
`estimates to provide a corrected signal and determining the
`punctured location symbol estimates based on signals in
`locations in the corrected signal corresponding to the punc-
`tured locations.
`
`is
`it
`invention,
`In other embodiments of the present
`determined if the first signal estimates contain an error and
`punctured location symbol estimates are generated based on
`the first signal estimates if the first signal estimates contain
`an error. An error in the first signal estimate may be
`determined by detecting a CRC error in the first signal
`estimates.
`
`the
`invention,
`In further embodiments of the present
`received symbols, the default symbol values and the punc-
`tured location symbol estimates are soft information. The
`soft information may have a low confidence value, a high
`confidence one value and a high confidence zero value. The
`symbol positions associated with punctured locations may
`be initialized to the low confidence value. The punctured
`location symbol estimates may be determined by converting
`the encoded signal estimates to soft
`information. The
`encoded signal estimates may be converted to soft informa-
`tion by converting encoded signal estimates in the punctured
`locations having a one value to the high confidence one
`value and converting the punctured locations having a zero
`value to the high confidence zero value.
`In other embodiments of the present invention, the punc-
`tured coded signal is a signal coded at a low coding rate. The
`low coding rate may be a 1/2 coding rate. The combined
`received symbols with the punctured location symbol esti-
`mates may be error correction decoded to provide second
`signal estimates with performance equivalent to a lower
`coding rate, such as a rate 1/3.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`In further embodiments of the present invention, it is
`determined if the second signal estimates contain an error.
`Transmission of additional signal information is requested if
`the second signal estimates contain an error. Transmission of
`punctured signals associated with the received punctured
`coded signal may be requested. Alternatively,
`re-transmission of the punctured coded signal may be
`requested.
`In other embodiments of the present invention, methods
`are provided for decoding a punctured coded signal. A
`received punctured coded signal is error correction decoded
`to provide punctured location symbol estimates. The
`received punctured coded signal is error correction decoded
`using the punctured location symbol estimates to provide
`signal estimates of the received punctured coded signal.
`Error correction decoding may include combining symbol
`estimates of the received punctured coded signal with the
`punctured location symbol estimates placed in correspond-
`ing punctured locations and error correction decoding the
`combined received symbols with the punctured location
`symbol estimates to provide signal estimates of the received
`punctured coded signal.
`In further embodiments of the present invention, base-
`band processors are provided for decoding a punctured
`coded signal. The baseband processors include an error
`correction decoder configured to generate estimates of a
`received punctured coded signal from the punctured coded
`signal and from punctured location symbol estimates. A
`punctured symbol estimate generator generates the punc-
`tured location symbol estimates from estimates of a received
`punctured coded signal and provides the punctured location
`symbol estimates to the error correction decoder. Ademodu-
`lator configured to provide soft information as the received
`punctured coded signal may also be provided. The error
`correction decoder may be a convolutional decoder. The
`convolutional decoder may be a rate 1/3 convolutional
`decoder and the punctured coded signal may be punctured to
`a higher coding rate than 1/3. A CRC error detector may be
`coupled to the error correction decoder that detects errors in
`the estimates of a received punctured coded signal.
`Operations according to embodiments of the present
`invention for decoding a punctured coded signal will now be
`further described with reference to the flowchart illustration
`
`of FIG. 5 and the schematic block diagram illustration of
`FIG. 6. Operations begin at block 500 when the receiver 372
`receives the signal
`to provide received symbols to the
`baseband processor 371. An example of such a received
`symbol set is illustrated at block 600 of FIG. 6. Symbol
`positions associated with punctured locations are initialized
`to default symbol values (block 505). Such an initialized
`block is illustrated at block 605 of FIG. 6 where zero values,
`associated with low confidence received symbol
`information, are shown inserted in the codeword. The
`received symbols including the default initialized symbol
`values are error corrected decoded to provide first symbol
`estimates (block 510). Again referring to FIG. 6, an exem-
`plary set of first signal estimates (b1, b2 .
`.
`. bN is illustrated
`at block 610.
`
`Note that, as shown in the particular exemplary blocks of
`FIG. 6, the received signal is demodulated and deinterleaved
`to generate soft symbols of an incremental codeword of rate
`1/2. The soft symbols at the punctured positions are set to
`zero to provide a codeword that a rate 1/3 decoder can use
`to attempt to decode t