WO2018052580A1 - Récupération de symboles lorsqu'un récepteur a connaissance a priori de certains bits d'une unité de données reçue - Google Patents

Récupération de symboles lorsqu'un récepteur a connaissance a priori de certains bits d'une unité de données reçue Download PDF

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Publication number
WO2018052580A1
WO2018052580A1 PCT/US2017/046003 US2017046003W WO2018052580A1 WO 2018052580 A1 WO2018052580 A1 WO 2018052580A1 US 2017046003 W US2017046003 W US 2017046003W WO 2018052580 A1 WO2018052580 A1 WO 2018052580A1
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Prior art keywords
symbol
bits
unmapped
receiver
constellation
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PCT/US2017/046003
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English (en)
Inventor
Parthiban ANNAMALAI
Jyotsna BAPAT
Debabrata Das
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Intel Corporation
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Publication of WO2018052580A1 publication Critical patent/WO2018052580A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L23/00—Apparatus or local circuits for systems other than those covered by groups H04L15/00 - H04L21/00
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0061—Error detection codes

Definitions

  • aspects of the present disclosure relate generally to communication receivers, and more specifically to recovering symbols when a receiver has a priori knowledge of some bits of a received data unit.
  • Symbols are the basis for transmission of digital data in many communication systems.
  • a symbol represents the basic unit which is used to modulate a carrier signal, with the resulting modulated signal being then further processed for transmission according to the pertinent communication technology.
  • a symbol can contain one or more bits of data.
  • Transmitters often seek to transmit data units, with each data unit containing a sequence of bits.
  • Each data unit is defined to have boundaries according to a pre-specified format, with the format further specifying the convention for interpreting the bits in specific positions of the data unit.
  • the sequence of bits are grouped into a sequence of symbols, with each symbol thereafter being used to modulate the carrier signal.
  • a transmitter transmits the modulated carrier, and a receiver thereafter seeks to demodulate the carrier to recover the bits constituting each of the received symbols.
  • a receiver may have a priori knowledge of some of the bits (i.e., values in specific positions of a data unit), for example based on a protocol specification or prior communications. Aspects of the present disclosure relate to recovering symbols when a receiver has a priori knowledge of some bits of a received data unit.
  • Figure 1 is a block diagram of an example environment in which several aspects of the present disclosure can be implemented.
  • Figure 2 is a flowchart illustrating an exemplary manner in which symbols of a received data unit are recovered when a receiver has a priori knowledge of some bits in the received data unit, according to aspects of the present disclosure.
  • Figure 3A is a block diagram of an exemplary transmitter according to an aspect of the present disclosure.
  • Figure 3B is a block diagram of an exemplary receiver according to an aspect of the present disclosure.
  • Figure 4 is an exemplary diagram illustrating the fields of a master information block according to LTE in an embodiment.
  • Figure 5 is a diagram of a constellation for QPS as used in LTE.
  • Figure 6 a block diagram representing an exemplary wireless device in which several aspects of the present disclosure can be implemented.
  • a receiver provided according to an aspect of the present disclosure generates an unmapped symbol encoded according to a symbol constellation in a received signal.
  • the receiver may determine whether a bit value constituting bits of the unmapped symbol is known a priori, and generates a de-mapped symbol representation for the unmapped symbol from a sub-region of the constellation map constrained by the bit value, if the bit value is known. For example, if one of two bits of the symbol are known, only half the constellation map is considered in generating the de-mapped symbol representation. As only a smaller region is considered in determining the de- mapped symbol representation, errors introduced by transmission channel may be reduced with less processing.
  • Figure 1 is a block diagram representing an example environment in which several aspects of the present disclosure can be implemented.
  • the example environment is shown containing only representative devices and systems for illustration. However, real world environments contain more systems/devices.
  • the example environment of Figure 1 is provided in the context of wireless communications, aspects of the present disclosure can be operative in environments containing wired devices also. Examples of such wired devices include those operative based on ADSL (Asymmetric Digital Subscriber Loop) modems, Symmetric DSL modems, etc.
  • Figure 1 shows a cell 100 containing base station (BS) 110 and wireless devices (WD) 120, 130 and 140.
  • BS base station
  • WD wireless devices
  • BS 110 is a fixed communications unit of a corresponding mobile network deployed by a cellular network operator and provides the last-mile (or last hop) communications link to wireless devices that are within communications range (i.e., within the coverage area represented by cell 100) of BS 1 10, and that have subscribed to services from the cellular network operator of BS 110.
  • BS 110 may be connected to other devices/systems in the corresponding cellular network infrastructure to enable wireless devices (e.g., 120, 130 and 140) within coverage range to communicate with devices, with landline communications equipment in a conventional PSTN (Public Switched Telephone Network), public data networks such as the Internet, etc.
  • PSTN Public Switched Telephone Network
  • the base station and the wireless devices of Figure 1 may operate according to any of cellular network standards/ specifications for wireless mobile communications such as, for example, GSM (Global System for Mobile Communications), LTE (Long Term Evolution, including frequency division duplex (FDD) and/or time division duplex (TDD) modes, UMTS (Universal Mobile Telecommunications System), CDMA (Code Division Multiple Access), W- CDMA (Wideband CDMA), 5G, etc.
  • GSM Global System for Mobile Communications
  • LTE Long Term Evolution, including frequency division duplex (FDD) and/or time division duplex (TDD) modes
  • UMTS Universal Mobile Telecommunications System
  • CDMA Code Division Multiple Access
  • W- CDMA Wideband CDMA
  • 5G etc.
  • a BS In the context of LTE (Long Term Evolution), a BS is referred to as an eNodeB.
  • the term 'base station' as used herein covers base stations as well as eNodeBs. Further, although noted as covering corresponding normal cell areas, the base stations of Figure 1 can also be designed to cover a much smaller area such as, for example, a macrocell, a microcell, a picocell, a femtocell, a home eNodeB, etc.
  • Macro/micro/femtocells/picocells/home eNodeBs are special cellular base stations (operating over smaller cell areas than normal cells) that are often deployed in small areas to add extra cell capacity. For example, such small cells can be deployed temporarily during sporting events and other occasions where a large number of cell phone users are expected to be concentrated in one spot.
  • Wireless devices (WD) 120 and 130 represent user equipment (UE) capable of Machine- type Communication (MTC) (e.g., electric utility meter, sensors, actuators, etc.), and typically do not contain user or operator interfaces such as keyboard, display, etc.
  • WD 120 and WD 130 may communicate wirelessly with MTC server(s) (not shown) and/or other MTC device(s) via BS 110.
  • WD 140 is shown as a mobile phone. Although not shown, cell 100 may contain many more wireless devices such as tablets, etc.
  • Mobile phone 140 may be used for wireless communication such as voice calls, data services such as web browsing, receiving and sending emails, etc.
  • a wireless device located within the boundaries of a geographical area termed a 'cell' (here cell 100) served by a base station (here BS 110) of a mobile cellular network, interfaces with the base station, which provides the corresponding user the facility of voice and data based services.
  • the wireless device is said to 'be camped' on the cell covered by the base station.
  • the wireless device is referred to as a subscriber, and generally has a unique identity/ account with the mobile cellular network operator.
  • BS 110 may transmit data units containing symbols to the wireless devices in cell 100.
  • a receiver of a wireless device e.g., WD 120
  • FIG. 2 is a flowchart illustrating the manner in which symbols of a received data unit are recovered when a receiver has a priori knowledge of some bits in the received data unit, according to aspects of the present disclosure.
  • the flowchart is described with respect to wireless device 120 of Figure 1, merely for illustration. However, various features described herein can be implemented in other environments and using other components as well, as will be apparent to one skilled in the relevant arts by reading the disclosure provided herein.
  • the flowchart starts in step 201, in which control passes immediately to step 210.
  • WD 120 receives an unmapped symbol encoding a set of bits present at respective positions in an ordered sequence of bits of a data unit.
  • the term unmapped implies that the signal/data being processed represents the signal corresponding to the symbol period, including any potential distortions when received on the wireless/transmission medium.
  • WD 120 receives a signal spanning an OFDM symbol duration.
  • WD 120 performs a Fourier transform of the received signal, and obtains phase and amplitude of each of the transmitted sub-carriers (representing the transmitted QPSK symbols plus any distortions).
  • Each sub-carrier, thus obtained, represents an unmapped symbol, and is typically represented by a complex number.
  • synchronous or IQ demodulation may be performed, and the demodulated symbol may be a voltage or a number.
  • Various other techniques may use other corresponding approaches to generate the unmapped symbol.
  • the unmapped symbol may be compared to a pre-determined symbol constellation to extract the individual bits of the symbol, as noted below.
  • the unmapped symbol received in step 210 encodes a set of bits at respective positions in an ordered sequence of bits of a data unit.
  • the bits representing the symbol have predetermined positions in the sequence of bits (as transmitted on the air or wireless medium, and also as received by WD 120) representing the data unit. Control then passes to step 230.
  • step 230 WD 120 checks if the bit value at any of the positions is known a priori to WD 120. In other words, WD 120 checks if any of the bits in the symbols is a bit whose value (logic zero or logic one) is known a priori to WD 120. If the bit value at any of the positions is known, control passes to step 250. If the bit value at any of the positions is not known, control passes to step 270.
  • step 250 WD 120 generates a de-mapped symbol representation for the unmapped symbol from a sub-region of a constellation map constrained by the known bit values. It may be appreciated that if WD 120 knows the value of at least one of the multiple bits in the symbol, then only those portions of the constellation map that contain the known bit need to be considered in determining the remaining bits of the symbol.
  • the process of determining either the bit values themselves (hard bits), or numbers (soft bits) indicating the confidence with which the bit values are known is termed symbol de-mapping, and may involve comparison of the unmapped symbol (as noted in step 210) with all the regions of the constellation map.
  • step 270 WD 120 generates the de-mapped symbol representation of the unmapped symbol from the (entire) constellation map.
  • WD 120 needs to consider the entire constellation map used of the modulation technique to determine the values of the hard bits or soft bits for the symbol. Control then passes to step 290.
  • step 290 WD 120 checks if additional (i.e., more) symbols of the data unit are yet to be recovered. If so, control passes to step 210, and the corresponding steps of the flowchart may be executed. If there are no more symbols of the data unit to be recovered, control passes to step 299, in which the flowchart ends.
  • step 250 corrects possible errors in some bits (the bits known a priori) due to propagation path effects (noise in the transmission path/wireless medium), errors in transmitter, errors in demodulation in the receiver, receiver noise, etc.
  • bit error rate (BER) and in turn, the block error rate (BLER) of the receiver of WD 120 is reduced. Consequently, for the same transmitted power, greater communication range of reception can be achieved. In other words, the geographical area represented by cell 100 can be increased.
  • FIG. 3A is a block diagram of a transmitter (300) in BS 110.
  • Transmitter 300 is designed consistent with OFDM technology (which uses multi-carrier modulation techniques) employing QPSK modulation, as specified for example by LTE technology (described in detail in 3GPP (3rd Generation Partnership Project) technical specification document TS 36.331 V13.1.0 (2016-03)).
  • Transmitter 300 is shown containing CRC append block 305, convolution encoder 310, block interleaver 315, rate matcher 320, QPSK mapper 325, OFDM symbol mapper 330, RF block 335 and antenna 336.
  • the combination of CRC append block 305, convolution encoder 310, block interleaver 315, rate matcher 320, QPSK mapper 325 and OFDM symbol mapper 330 represents the baseband portion of transmitter 300.
  • CRC append block 305 receives, on path 301 (which may be connected to a processing block, not shown in Figure 3A), a block of data (data unit) that is sought to be transmitted on a wireless medium.
  • the data unit contains an ordered sequence of bits, and the position of some bits in the sequence is known to receiver 380.
  • One example of a block of data received on path 301 is a MIB (Master Information Block) in the context of LTE, and is described further below.
  • CRC append block 305 computes the CRC (cyclic redundancy check) of the block of data, and appends the CRC to the block of data.
  • CRC append block 305 forwards the block of data with CRC appended to convolution encoder 310.
  • Convolution encoder 310 performs channel coding according to the technique specified by the corresponding standard (here LTE) by adding redundant bits to the block of data received from CRC append block 305 to generate an encoded data block.
  • Convolution encoder 310 is shown as a (n, k, K) encoder, wherein n represents the number of code bits, k represents the number of data bits, and is the constraint length resulting in (K-l) memory registers of the encoder. In an embodiment (n, k, ) corresponds to (3, 1, 7). Convolution encoder 310 forwards the encoded data block to block interleaver 315.
  • Block interleaver 315 receives the encoded data block from convolution encoder 310, and re-arranges (re-orders or scrambles) the data in a different (but known) sequence. Typically, block interleaver 315 sequentially writes the bits in the received encoded block into a matrix row- by-row, and then reads out the data column-by-column. Such interleaving is done with the aim of reducing the impact of burst errors that may be introduced by the transmission channel (here a wireless medium). Block interleaver 315 forwards the interleaved block of data to rate matcher 320.
  • Rate matcher 320 operates to fit the received block of data within transmission resources (length of transmission time slot, bandwidth of frequency band allotted) that are allotted to transmitter 300 for transmission. Thus, for example, if the transmission time slot obtained is larger than that required to fit the received block of data, rate matcher 320 replicates the block of data so as to fit in the time slot. As another example, if the block of data is much larger than can be fitted in the time slot, rate matcher 320 may puncture (remove some bits from) the data block so that it fits in the time slot. Rate matcher 320 may perform similar fitting (or matching) operations with respect to allotted frequency band as well. Rate matcher 320, forwards the rate- matched block of data to QPSK mapper 325.
  • transmission resources length of transmission time slot, bandwidth of frequency band allotted
  • QPSK mapper 325 selects (successive adjacent) pairs of bits in the rate-matched block of data received from rate matcher 320, and depending on the value of each pair (whether 00, 01, 10, or 11) selects one of four symbols (represented by a complex number) from the constellation used for QPSK. Thus, QPSK mapper 325 generates N/2 complex numbers (QPSK symbols) from N bits in the rate-matched block of data.
  • a QPSK symbol is a numerical representation of the amplitude and phase of a carrier (or sub-carrier in the case of OFDM).
  • QPSK mapper 325 forwards the QPSK symbols corresponding to the rate-matched block of data to OFDM symbol mapper 330.
  • OFDM symbol mapper selects a subset (P) of subcarriers (the size P and their distribution being specified by the corresponding standard such as LTE) from the total number of used subcarriers in N-point IFFT and maps the QPSK symbols received from QPSK mapper and generates one OFDM symbol.
  • OFDM symbol mapper 330 is implemented as an IFFT (Inverse Fast Fourier Transform), and a generated OFDM symbol is the sum of the P symbols. OFDM symbol mapper 330 thus converts the set of QPSK symbols into a set of OFDM symbols (each of which is represented by a complex number), and forwards the OFDM symbols (representing the block of data received on path 301) to RF block 335.
  • one or more LTE frames may be required to transmit the set of OFDM symbols representing the block of data, and OFDM symbol mapper 330 is assumed to also perform formatting of data into LTE frames and sub-frames.
  • RF block 335 converts each OFDM symbol (complex number) into an RF (Radio Frequency) signal, which is then transmitted by antenna 336 on a wireless medium.
  • RF block 335 may perform digital-to-analog, addition to cyclic prefixes/guard bands, up-conversion, filtering and power amplification in converting an OFDM symbol to a corresponding RF signal that is transmitted.
  • One or more LTE frames corresponding to a block of data received on path 301 is thus transmitted by transmitter 300.
  • the one or more LTE frames viewed as a sequence also contain an ordered sequence of bits, and the position of some bits in such as a sequence also is known to receiver 380.
  • Figure 3B is a block diagram of a receiver in WD 120.
  • WD 130 and WD 140 of Figure 1 also contain similar receivers.
  • Receiver 380 of Figure 3B is shown containing antenna 341, RF block 340, OFDM symbol de-mapper 345, QPSK symbol de-mapper 350, rate de-matcher 355, block interleaver 360, Viterbi decoder 365 and CRC checker 370.
  • OFDM symbol de-mapper 345 represents the baseband portion of receiver 380, and respectively perform the inverse operation of OFDM symbol mapper 330, QPSK mapper 325, rate matcher 320, convolution encoder 310 and CRC append block 305, and are only briefly described below.
  • RF block 340 receives one or more LTE frames (received signal) corresponding to a block of data received on path 301 (of transmitter 300) and transmitted by transmitter 300 in the form of RF signals from antenna 341.
  • RF block 340 may perform operations such as low-noise amplification, filtering, down-conversion, and anal og-to- digital conversion to generate a set of OFDM symbols in the form of complex numbers (digital values) from the RF signals received.
  • the set of OFDM symbols is ideally the same as that generated by OFDM symbol mapper 330 of transmitter 300, but which may be degraded by noise from various sources in the channel from antenna 336 to antenna 341.
  • RF block 340 forwards the set of OFDM symbols to OFDM demodulator 345.
  • OFDM demodulator 345 performs multi-carrier demodulation (e.g., using FFT (Fast Fourier transform)) to extract QPSK symbols from each received OFDM symbol, and generates a set of QPSK symbols representing the one or more LTE frames received by RF block 340.
  • the extracted QPSK symbols may contain noise added by the wireless channel between antenna 336 and antenna 341, and therefore may not map exactly to a corresponding point in the QPSK constellation.
  • the extracted symbols are therefore noted herein as unmapped symbols, since which constellation point (or what soft bits are to be generated to represent the unmapped symbol) that an extracted symbol corresponds to is yet to be determined.
  • OFDM demodulator 345 forwards the set of unmapped QPSK symbols to QPSK de-mapper.
  • the set of unmapped QPSK symbols may be in the form of respective complex numbers (an example of an unmapped symbol), each representing the amplitude and phase of a sub-carrier according to OFDM).
  • OFDM demodulator 345 When the context is other than LTE, OFDM demodulator 345 is, in general, replaced by a corresponding demodulator suitable for the modulation technique used in transmitter 300.
  • the demodulator operates to extract encoded symbols (which may contain noise, and are therefore in in unmapped form) from the RF signal received from RF block 335.
  • the demodulator generates unmapped symbols, and forwards the unmapped symbols to a symbol de-mapper such as QPSK symbol de-mapper 350.
  • a symbol de-mapper such as QPSK symbol de-mapper 350.
  • OFDM demodulator 345 (or demodulator in general) generates a complex number (e.g., 32 or 64 bit value) representing an extracted symbol, though in alternative embodiments the unmapped symbol can be represented in analog forms such as voltage or current.
  • QPSK symbol de-mapper 350 operates to de-map each QPSK symbol (unmapped symbol) in the set of received QPSK symbols.
  • QPSK symbol de- mapper is implemented as a hard de-mapper, and generates a corresponding set of bit pairs (one of 00, 01, 10 and 11) depending on the value of the corresponding complex number representing a received QPSK symbol.
  • a received QPSK symbol may not exactly map to any one of four points in the QPSK constellation, i.e., the amplitude and phase represented by the complex number corresponding to a QPSK symbol may not exactly match any of the amplitudes and phases of the four constellation points (00, 01, 10 and 11). Therefore, QPSK symbol de-mapper 350 may need to select that constellation point that best matches a received QPSK symbol, as illustrated further below, and outputs a bit pair (hard bits) representing the corresponding QPSK symbol.
  • blocks 355, 360, and 365 are designed to operate on hard bits (i.e., binary bit pair representing each symbol).
  • QPSK symbol de-mapper 350 is implemented as a soft de-mapper.
  • QPSK symbol de-mapper 350 instead of directly mapping the symbol to a bit pair (00, 01 , 10 or 11) that the received QPSK symbol is deemed to represent, QPSK de-mapper 350, generates a set of soft bits, that in addition to indicating the corresponding symbol, also indicate a confidence measure indicating the confidence that QPSK symbol de-mapper 350 has that the soft bits represent the QPSK symbol.
  • QPSK symbol de-mapper 350 maps I and Q values of the complex representation of a QPSK symbol to one of a set of soft bits, as illustrated further below.
  • blocks 355, 360, and 365 are designed to operate on soft bits, and only the output of Viterbi decoder 365 provides the final binary bits of a received symbol.
  • QPSK symbol de-mapper 350 (which may be generically viewed as a symbol de-mapper), operates to determine whether a received QPSK symbol contains a bit value that is known a priori to receiver 380. If so, QPSK symbol de-mapper 350 either generates a bit pair (00, 01, 10 or 11) or generates a set of soft bits for the symbol from a sub-region of the QPSK constellation map constrained by the bit value, as illustrated with examples below. QPSK symbol de-mapper 350 forwards the generated bit pairs (or soft bits) (corresponding to a block of data) to rate de-matcher 355.
  • Rate de-matcher 355 performs the inverse operation as that performed by rate matcher 320 of transmitter 300. Thus, if replication of data was done by rate matcher 320, then rate de- matcher 355 discards the replicated data, and tries decoding the remaining copy of the data. If decoding is unsuccessful, rate de-matcher 355 uses the other copies (discarded earlier) of the data either coherently or non-coherently to improve the decoding probability.
  • rate de-matcher 355 adds data bits to the received bit-pairs Typically, rate de-matcher 355 inserts zeroes ( ⁇ ') in the punctured bit locations, when QPSK symbol de-mapper 350 is implemented as a hard de-mapper. Rate de-matcher 355 forwards the rate de-matched block of data to block de-interleaver 360.
  • Block de-interleaver 360 operates to unscramble the bit pairs or soft bits in the block of data received from rate de-matcher 355.
  • the technique used by block de-mterleaver 360 is the reverse of that used in block interleaver 315.
  • Block de-interleaver 360 forwards the de-interleaved block of data to Viterbi decoder 365.
  • Viterbi decoder 365 performs channel decoding on the received de-interleaved block of data to generate a decoded block of data.
  • the operations of Viterbi decoder reverse those performed by convolution encoder 310.
  • Viterbi decoder 365 forwards the decoded block of data (in the form of binary numbers) to CRC checker 370.
  • CRC checker 370 computes the CRC of the received decoded block of data, compares the computed CRC with the CRC field in the decoded block of data to check if there are errors. CRC checker 370 removes the CRC field from the block of data and forwards the block of data on path 371 , also indicating if there is a CRC error. A processing block may be connected to path 371 and may further process the block of data. [062] Assuming there are no errors in data transmission, the block of data sent by receiver 380 on path 371 would ideally be identical to that received by transmitter 300 on path 310.
  • transmitter 300 and receiver 380 are shown merely by way of example.
  • the implementation details of transmitter 300 and receiver 380 can be different when other technologies or standards are used to implement them.
  • receiver 380 is a wired device (e.g., DSL (Digital Subscriber Line) modem
  • antenna 341 is not used and the wired medium is directly connected to a medium interface block used in place of RF block 340.
  • the medium interface block performs the necessary electrical and protocol/format conversions, such as for example, front-end amplification, filtering, analog-to-digital conversion, etc., as suited for the specific technology, and provides unmapped symbols as its output.
  • a corresponding demodulator is used in place of OFDM demodulator 345, which extracts symbols contained in the signal received from the medium interface block, and provides unmapped symbols to a symbol de- mapper used in place of QPS de-mapper 350.
  • the remainder of the blocks of receiver 380, as well as the blocks of transmitter 300 are implemented consistent with the wired technology (e.g., DSL) used for data transfer.
  • One example of the block of data on path 301 is a master information block (MIB) according to LTE.
  • the MIB includes a limited number of most essential and most frequently transmitted parameters that are needed to acquire other information from the cell (or BS 110), and the information in the MIB is required by WD 120 to camp on cell 100.
  • FIG 4 illustrates the various fields in a MIB according to LTE (Long Term Evolution).
  • MIB 400 contains three octets (octet 1, octet 2 and octet 3) which correspond to 24 bits of data.
  • Row Rl indicates the bit position (1 to 8) of the corresponding fields.
  • field 410 corresponds to bits 7 and 8 of octet 1, and so on.
  • MIB contains DL (downlink) bandwidth (field 430) of cell 100, PHICH configuration (field 420) and the System Frame Number (SFN) (fields 410 and 450).
  • DL bandwidth 430 specifies the bandwidth of the downlink channel (BS110 to a WD), and occupies bits 1, 2 and 3 of octet 1.
  • System frame number (SFN) field 410 contains the 7 th and 8 th bits of the system frame number.
  • System frame number (SFN) field 450 contains bits 1 through 6 of the system frame number.
  • PHICH configuration field 420 provides configuration information in relation to Physical Hybrid-ARQ Indicator Channel, in accordance with LTE standard.
  • Fields 440 and 460 are spare bits and are always set to binary zero. Thus, the ten bits of fields 440 and 460 are always known (a priori) to receiver 380 of WD 120. Further, the bits of fields 410 and 450 are not known to receiver 380 only the first time MIB is decoded. Subsequent values of the SFN can be computed by receiver 380 by simply incrementing the previously received SFN value.
  • the 24 bits translate to 40 bits at the output of CRC append block 305 due to the appending of the CRC. Of the 40 bits, again 10 bits are always known, while the 8 SFN bits are conditionally known, to receiver 380. Again, the sum of always known and conditionally known bits is 18 bits.
  • the 40 bits translate to 120 bits at the output of convolution encoder 310 (assuming encoder 310 is a (3, 1, 7) encoder. Due to the 6 memory registers in convolution encoder 310, the known 10 bits translate to only 12 known bits (4 known bits multiplied by the coding rate of 1/3). The sum of always known and conditionally known bits is 36 bits.
  • the 120 bits translate to 120 bits at the output of block interleaver 315.
  • the number of always known bits remains 12 bits, and the sum of always known and conditionally known bits remains 36 bits.
  • the bit positions are however scrambled by block interleaver 315. But the specific interleaving operation is known to receiver 380.
  • the 120 bits translate to 1920 bits at the output of rate matcher 320 Of the 1920 bits, the number of always-known bits is 192, and the sum of always-known and conditionally known bits is 576.
  • the 1920 bits translate to 960 symbols at the output of QPSK mapper 325.
  • the number of symbols with at least one always-known bit is 192 symbols.
  • the sum of the number of symbols with at least one always-known bit and one conditionally known bit is 576 symbols.
  • the position of each of the always-known bits in the set of unmapped QPSK symbols provided as output of OFDM demodulator 345 is known to receiver 180. Further, after first-time receipt of the system frame number, the location of each of the conditionally-known bits in the set of QPSK symbols provided as output of OFDM demodulator 345 is also known to receiver 180 once the condition has been satisfied.
  • a technology/standard e.g., LTE
  • the symbol de-mapper (e.g., QPSK symbol de-mapper 350) of receiver 180 can operate as described above with respect to the flowchart of Figure 2 to generate the bit-pair or soft bits representing a QPSK symbol received from OFDM symbol de- mapper 350 from a sub-region of the QPSK constellation map obtained by constraining the map by the known bit value(s), or from the entire constellation map, as illustrated next with respect to Figure 5.
  • Figure 5 shows the constellation map for QPSK as used in LTE.
  • the four constellation symbols lie on the unit circle (C I) and are Q0, Ql , Q2 and Q3, which respectively correspond to the bit-pair values of 00, 01, 11 and 10.
  • the symbols Q0, Ql , Q2 and Q3 are located in quadrants 1, 2, 3 and 4 respectively.
  • the left-most (most significant) bit represents bit number ' ⁇ + ⁇
  • the nght-most (least significant bit) represents bit number 'n'.
  • the constellation map includes points on the unit circle CI, points inside the unit circle, as well as points outside the unit circle.
  • Each symbol received by QPSK symbol de-mapper 350 has an I component and a Q component, and the I and Q axes are indicated in Figure 5.
  • the I and Q values of the constellation points as used in LTE are indicated in Table 1 below (wherein b(n) and b(n+l) are successive bit pairs in a received symbol), wherein i represents the square root operator:
  • each symbol in the set of symbols output by OFDM demodulator 345 should (exactly) correspond to one of the 4 constellation points Q0-Q3.
  • a symbol may get corrupted such that at the output by OFDM demodulator 345 the symbol does not exactly correspond to any of the 4 constellation points.
  • noise can cause a symbol to have I and Q components such that the symbol can lie anywhere on the constellation map (although, typically only on, or within, the unit circle).
  • a symbol Ql (01) transmitted by transmitter 300 may, at the output of OFDM symbol de-mapper 345, lie (incorrectly) in any of the other three quadrants 1, 3 and 4, leading to errors in receiver 380.
  • receiver 180 if knowledge of one or more bits of a transmitted symbol is available at receiver 180, then receiver 180 (specifically QPSK symbol de- mapper 350) utilizes such a priori knowledge to constrain the estimate of the symbol to a smaller region (sub-region) of the constellation map.
  • QPSK symbol de-mapper 350 generates the hard or soft bits representing the unmapped symbol from a sub-region (quadrant 1 and 4 only) of the constellation map constrained by the known bit value in the symbol (step 250 of Figure 2).
  • QPSK symbol de-mapper 350 may de-map Q component of the unmapped symbol (whose I component is known to be iNl) to that of the nearest constellation point (here constellation point Q0 (00)) in the constrained sub-region (dotted region in Figure 5) of the constellation map.
  • QPSK de-mapper 350 may de-map the unmapped symbol 510 to bit pair (00).
  • QPSK symbol de-mapper 350 When implemented as a soft de-mapper, QPSK symbol de-mapper 350 generates the I and Q values of the unmapped symbol to equal that of point 520. Thus, QPSK de-mapper 350 assigns to the unmapped symbol, an I component soft bits value representing 1/V2 with no error (error free), and assigns a Q component soft bits value depending on the Euclidian distance of the received Q component from the nearest constellation symbol. In the example, such distance is the distance between point 520 and the constellation point Q0 (00). Depending on the specific number of bits used to encode the soft decision, the de-mapped I and Q soft bits will have corresponding values. As an example, assuming 3 bits are used to encode each of the soft bits corresponding to the I and Q components, the de-mapping relationship shown in Table 2 below may be used:
  • QPSK symbol de-mapper 350 may de-map the I component of the unmapped symbol received as 510 to soft bits (000), and the Q components to soft bits (010) (medium confidence).
  • the output of QPSK symbol de-mapper 350, whether implemented as a hard de-mapper or a soft de-mapper is termed herein as the 'de-mapped symbol representation' of an unmapped symbol, and the de-mapped symbol representation may contain fewer bits than used to represent an unmapped symbol.
  • QPSK symbol de-mapper 350 may use as many bits as there are in the received I and Q components of an unmapped symbol for representing the de-mapped symbol.
  • QPSK de-mapper may retain an unknown component (I or Q) to have the same number of bits as received by QPSK symbol de-mapper 350
  • QPSK symbol de-mapper may retain the Q component as it is and simply forwards to rate de-matcher 355, the unchanged Q component and the value 1/V2 for the I component.
  • the unmapped symbol may fall into one of four classes, as indicated in the Table 3 below:
  • a class 1 symbol corresponds to the LSB being known to be a zero, while the MSB is not known.
  • a class 2 symbol corresponds to the MSB being known to be a zero, while the LSB is not known.
  • a class 3 symbol corresponds to the LSB being known to be a one, while the MSB is not known.
  • a class 4 symbol corresponds to the MSB being known to be a one, while the LSB is not known.
  • QPSK symbol de-mapper 350 may constrain the region of the constellation map from which to estimate the bit pair (hard bits) or soft bits corresponding to a received unmapped symbol as indicated in the Table 3.
  • QPSK symbol de-mapper 350 constrains the region of the constellation map which is to be considered to de-map the symbol to quadrants 1 and 4. If the unmapped symbol is a class 4 symbol, QPSK symbol de-mapper 350 constrains the region of the constellation map which is to be considered to de-map the symbol to quadrants 3 and 4, and so on.
  • QPSK symbol de-mapper 350 considers all four quadrants of the constellation map to generate the value of the symbol (step 270 of Figure 2). As an example, if the location of the received symbol in the constellation is point 590, and QPSK symbol de-mapper 350 does not have prior knowledge of either of the bits in the symbol, then QPSK symbol de-mapper 350 considers all regions of the constellation map to determine which of the four points Q0, Ql, Q2 and Q3 the received symbol is.
  • QPSK symbol de-mapper 350 may compare the I and Q components of a received unmapped symbol with the (ideal) I and Q values noted in Table 1, and accordingly de-map the unmapped symbol to one of the constellation points. If the I and Q components are corrupted by noise, QPSK symbol de-mapper may merely compare the sign bit of the I and Q components with those of the 4 constellation points, and de-map the unmapped symbol to that point whose sign bits for I and Q components match those of the received unmapped symbol.
  • QPSK symbol de-mapper 350 may use the Euclidian distance of the I and Q components of a received unmapped symbol to the I and Q components of the 4 constellation points to determine the soft bits to represent the received unmapped symbol.
  • the constraining techniques of the present disclosure reduces the number of errors in the block of data recovered by QPSK symbol de-mapper 350. Further, the techniques described above reduce the input bit error to Viterbi decoder 365, thereby enabling further reduction in the error in the output block of data on path 371 (since Viterbi decoder 356 itself performs further error correction).
  • WD 120 attempts to camp in a strongest cell and the always-known bits can be utilized during the cell selection stage to reduce BER.
  • the system frame number (fields 410 and 450 of MIB 400 of Figure 4) is known, and both the always-known bits and the conditionally-known bits (those bits corresponding to the system frame number) enable WD 120 to improve the SNR (and reduce BER) and stay connected to the cell.
  • FIG. 6 is a block diagram representing an example wireless device in which several aspects of the present disclosure can be implemented.
  • Wireless device 120 is shown containing processing block 610, non-volatile memory 620, input/output (I/O) block 630, random access memory (RAM) 640, real-time clock (RTC) 650, SIM (Subscriber Identity Module) module 660, transmit (Tx) block 670, receive (Rx) block 680, switch 690, and antenna 695.
  • Some or all units of wireless device 120 may be powered by a battery (not shown).
  • wireless device 120 is mains-powered and contains corresponding components such regulators, filters, etc.
  • wireless device 120 may contain more or fewer blocks depending on specific requirements. Although only one transmitter (670) and one receiver (680) are shown for conciseness, WD 120 may contain more than one transmitter and receiver also.
  • processing block (or circuitry) 610, non-volatile memory 620, input/output (I/O) block 630, random access memory (RAM) 640, real-time clock (RTC) 650, Tx block 670 and Rx block 680 may be implemented in integrated circuit (IC) form.
  • SIM module 660 is designed to identify the specific subscribers and related parameters to facilitate the subscriber to access various services provided via the wireless communication network.
  • SIM module 660 contains a physical holder (into which a SIM card (SIM), can be inserted) and electrical/electronic circuits which together retrieve various data parameters stored on the inserted SIM cards.
  • a SIM card may provide the international mobile subscriber identity (IMSI) number (also the phone number) used by a network operator to identify and authenticate a subscriber.
  • IMSI international mobile subscriber identity
  • the SIM is 'inserted' into such holder before wireless device 120 can access the services provided by the network operator for the subscriber configured on the SIM.
  • a SIM may store address book/telephone numbers of subscribers, security keys, temporary information related to the local network, a list of the services provided by the network operator, etc.
  • SIM module 660 may accordingly be implemented to support virtual SIM.
  • a physical SIM may be supported in combination with one or more virtual SIMs within the wireless device.
  • the module may be implemented to support such altemative embodiments as well.
  • Processing block 610 may read the IMSI number, security keys etc., in transmitting and receiving voice/data via Tx block 670 and Rx block 680 respectively.
  • the SIM in SIM module 660 may subscribe to data and voice services according to one of several radio access technologies such as GSM, LTE (FDD as well as TDD), CDMA, WCDMA, 5G, etc., as also noted above.
  • RTC 650 operates as a clock, and provides the 'current' time to processing block 610. Additionally, RTC 650 may internally contain one or more timers I/O block 630 provides interfaces for user interaction with wireless device 120, and includes input devices and output devices. The input devices may include a keypad and a pointing device (e.g., touch-pad). Output devices may include a display with touch-sensitive screen.
  • I/O block 630 may not be implemented at all, or be implemented, for example, as a communications port, such as a serial port.
  • Antenna 695 operates to receive from, and transmit to, a wireless medium, corresponding wireless signals (representing voice, data, etc.) according to one or more standards such as LTE.
  • Switch 690 may be controlled by processing block 610 (connection not shown) to connect antenna 695 to one of blocks 670 and 680 as desired, depending on whether transmission or reception of wireless signals is required.
  • Switch 690, antenna 695 and the corresponding connections of Figure 6 are shown merely by way of illustration. Instead of a single antenna 695, separate antennas, one for transmission and another for reception of wireless signals, can also be used.
  • Tx block 670 corresponds to RF block 335 of Figure 3A, and receives, from processing block 610, digital signals representing information (voice, data, etc.) to be transmitted on a wireless medium (e.g., according to the corresponding standards/specifications), generates a modulated radio frequency (RF) signal (according to the standard), and transmits the RF signal via switch 690 and antenna 695.
  • Tx block 670 may contain RF circuitry (mixers/up-converters, local oscillators, filters, power amplifier, etc.) as well as baseband circuitry for modulating a carrier with the baseband information signal.
  • Tx block 670 may contain only the RF circuitry, with processing block 610 performing the modulation and other baseband operations (in conjunction with the RF circuitry).
  • Rx block 680 corresponds to RF block 340 of Figure 3B, and represents a receiver that receives a wireless (RF) signal bearing voice/data and/or control information via switch 690, and antenna 695, demodulates the RF signal, and provides the extracted voice/data or control information to processing block 610.
  • Rx block 680 may contain RF circuitry (front-end filter, low-noise amplifier, mixer/down-converter, filters) as well as baseband processing circuitry for demodulating the down-converted signal.
  • Rx block 680 (the receive chain) may contain only the RF circuitry, with processing block 610 performing the baseband operations in conjunction with the RF circuitry
  • Non-volatile memory 620 is a non-transitory machine readable medium, and stores instructions, which when executed by processing block 610, causes wireless device 120 to operate as described herein.
  • the instructions enable wireless device 120 to operate as described with respect to the flowchart of Figure 2.
  • the instructions may either be executed directly from non-volatile memory 620 or be copied to RAM 640 for execution.
  • RAM 640 is a volatile random access memory, and may be used for storing instructions and data.
  • RAM 640 and non-volatile memory 620 (which may be implemented in the form of readonly memory/ROM/Flash) constitute computer program products or machine (or computer) readable medium, which are means for providing instructions to processing block 610.
  • Processing block 610 may retrieve the instructions, and execute the instructions to provide several features of the present disclosure.
  • Processing block 610 may contain multiple processing units internally, with each processing unit potentially being designed for a specific task. Alternatively, processing block 610 may represent a single processing unit executing multiple execution threads. Processing block (or circuitry) 610 performs (in addition to other tasks) the operations of blocks 305, 310, 315, 320, 325, and 330 of Figure 3A and blocks 340, 345, 350, 355, 360, 365 and 370 of Figure 3B. In general, processing block 610 executes instructions stored in nonvolatile memory 650 or RAM 640 to enable wireless device 120 to operate according to several aspects of the present disclosure, described in detail herein, and specifically the operations of the steps of the flowchart of Figure 2.
  • references throughout this specification to "one aspect of the present disclosure”, “an aspect of the present disclosure”, or similar language means that a particular feature, structure, or characteristic described in connection with the aspect of the present disclosure is included in at least one aspect of the present disclosure of the present invention.
  • appearances of the phrases “in one aspect of the present disclosure”, “in an aspect of the present disclosure” and similar language throughout this specification may, but do not necessarily, all refer to the same aspect of the present disclosure.
  • the following examples pertain to above or further embodiments.
  • Example 1 corresponds to a receiver containing a demodulator and a symbol de-mapper.
  • the demodulator demodulates a received symbol that has been encoded according to a symbol constellation, and generates an unmapped symbol.
  • the symbol de-mapper determines if a bit value of one or more bits in the symbol is known a priori, and if so generates a de-mapped symbol representation for the unmapped symbol from a sub-region of the constellation map constrained by the (known) bit value.
  • Example 2 corresponds to the receiver of example 1, in which if the receiver does not have a priori knowledge of any of the bits of the unmapped symbol, then the receiver generates the de- mapped symbol representation for the unmapped symbol based on the entire constellation map.
  • Example 3 corresponds to the receiver of example 1 or example 2, wherein the received signal represents a sequence of symbols including the unmapped symbol, and the symbol de- mapper is operable to generate a sequence of de-mapped symbol representations, each corresponding to a respective symbol of the sequence of symbols.
  • Example 4 corresponds to a receiver of any of examples 1 -3, in which a transmitter adds a CRC checksum to a data unit as well as redundant bits to the data unit for error correction.
  • the sequence of symbols, the CRC checksum and the redundant bits together represent the data unit.
  • the receiver includes a channel decoder that processes the de-mapped symbol representations and recovers bits constituting the data unit and the CRC checksum.
  • the receiver includes a CRC checker that computes the CRC of the data unit, and compares the computed CRC with the CRC checksum.
  • Example 5 corresponds to the receiver of any of examples 1-4, wherein the symbol constellation is according to QPSK (quadrature phase shift keying), wherein the symbol de- mapper comprises a QPSK de-mapper, wherein the received signal is generated at the transmitter according to a multi-carrier modulation technique, wherein the demodulator generates the unmapped symbol according to multi-carrier demodulation technique,
  • QPSK quadrature phase shift keying
  • Example 6 corresponds to the receiver of any of examples 1-5, wherein the multicarrier modulation technique is OFDM (orthogonal frequency division multiplexing) and the data unit is a master information block (MIB) according to LTE (long term evolution), wherein the bit value known a priori is a bit in the MIB.
  • OFDM orthogonal frequency division multiplexing
  • MIB master information block
  • LTE long term evolution
  • Example 7 corresponds to the receiver of any of examples 1-6, wherein the de-mapped symbol representation is in the form of a bit pair equaling a corresponding one of constellation points in the constellation map.
  • Example 8 corresponds to the receiver of any of examples 1-6, wherein the de-mapped symbol representation is in the form of soft bits representing both the bits constituting the unmapped symbol as well as a confidence measure representing the confidence level with which the soft bits represent both the bits.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
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Abstract

L'invention concerne un récepteur qui génère un symbole non mappé codé selon une constellation de symboles dans un signal reçu. Le récepteur peut déterminer si une valeur binaire constituant des bits du symbole non mappé est connue a priori, et générer une représentation de symbole dé-mappée pour le symbole non mappé à partir d'une sous-région d'une carte de constellation contrainte par la valeur de bit, si la valeur de bit est connue. Par conséquent, des erreurs introduites par le canal de transmission peuvent être réduites avec moins de traitement.
PCT/US2017/046003 2016-09-13 2017-08-09 Récupération de symboles lorsqu'un récepteur a connaissance a priori de certains bits d'une unité de données reçue WO2018052580A1 (fr)

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Cited By (1)

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WO2022011589A1 (fr) * 2020-07-15 2022-01-20 Zte Corporation Codage et modulation de canal

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US20130208836A1 (en) * 2012-02-14 2013-08-15 Hitachi Kokusai Electric Inc. Receiver and received signal decoding method
US20150063502A1 (en) * 2012-01-30 2015-03-05 Telefonaktiebolaget L M Ericsson (Publ) Methods of communicating data including symbol mapping/demapping and related devices
US20150124912A1 (en) * 2013-11-01 2015-05-07 MagnaCom Ltd. Reception of inter-symbol-correlated signals using symbol-by-symbol soft-output demodulator
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US20120033721A1 (en) * 2008-10-31 2012-02-09 Oliver Isson Receiver with ICI Noise Estimation
US20150063502A1 (en) * 2012-01-30 2015-03-05 Telefonaktiebolaget L M Ericsson (Publ) Methods of communicating data including symbol mapping/demapping and related devices
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US20150124912A1 (en) * 2013-11-01 2015-05-07 MagnaCom Ltd. Reception of inter-symbol-correlated signals using symbol-by-symbol soft-output demodulator

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