WO2024120886A1 - Premier et second dispositifs de communication et procédés - Google Patents

Premier et second dispositifs de communication et procédés Download PDF

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Publication number
WO2024120886A1
WO2024120886A1 PCT/EP2023/083308 EP2023083308W WO2024120886A1 WO 2024120886 A1 WO2024120886 A1 WO 2024120886A1 EP 2023083308 W EP2023083308 W EP 2023083308W WO 2024120886 A1 WO2024120886 A1 WO 2024120886A1
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Prior art keywords
communication device
tone mapping
ofdm
constellation
constellation points
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PCT/EP2023/083308
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English (en)
Inventor
Pukar SHAKYA
Thomas Handte
Daniel VERENZUELA
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Sony Group Corporation
Sony Europe B.V.
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Publication of WO2024120886A1 publication Critical patent/WO2024120886A1/fr

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    • 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
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1867—Arrangements specially adapted for the transmitter end
    • H04L1/1893—Physical mapping arrangements
    • 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
    • H04L1/0071—Use of interleaving

Definitions

  • the present disclosure relates to first and second communication devices and methods, in particular for use in wireless LAN (WLAN) systems.
  • WLAN wireless LAN
  • WLAN features hybrid automatic repeat request (HARQ) type I which features a combination of forward error correction (FEC) and automatic repeat request (ARQ) protocol.
  • HARQ hybrid automatic repeat request
  • FEC forward error correction
  • ARQ automatic repeat request
  • any MAC layer data unit to be transmitted is first supplied with a frame check sequence (FCS) and then encoded by a forward error correction encoder such as low- density parity-check (LDPC) code.
  • FCS frame check sequence
  • LDPC low- density parity-check
  • the receiver Upon reception, the receiver (herein also called “second communication device") performs FEC decoding and subsequently checks the validity of FCS. If the FCS is valid, the automatic repeat request (ARQ) mechanism transmits a positive acknowledgement (ACK) to the transmitter (herein also called “first communication device") to indicate successful reception. If the FCS is invalid, the ARQ mechanism transmits a negative acknowledgement (N-ACK) or nothing to the transmitter to indicate that a retransmission of the MAC layer data unit is needed.
  • ACK positive acknowledgement
  • N-ACK negative acknowledgement
  • HARQ type I may fail to provide reliable communication because initial transmission and retransmissions may fail.
  • WLAN is deployed in indoor scenarios where the wireless channel is a slowly fading time varying channel.
  • HARQ soft combining such as Chase combining
  • a MAC layer data unit that has been failed to be received or decoded in an initial transmission also called original transmission
  • a first communication device configured to communicate with a second communication device, the first communication device comprising circuitry configured to obtain MAC layer data units and encode said MAC layer data units into encoded data units; perform constellation mapping to map bits of said one or more encoded data units to be transmitted to the second communication device onto constellation points of a constellation; perform first tone mapping to map said constellation points onto first orthogonal frequency division multiplex (OFDM) subcarriers; modulate said first OFDM subcarriers to obtain first OFDM symbols; transmit said OFDM symbols to the second communication device; obtain an error indication indicating at least one erroneous MAC layer data unit that failed to be received or decoded by the second communication device; perform second tone mapping to map the constellation points corresponding to the at least one erroneous MAC layer data unit onto second OFDM subcarriers differently than the constellation points in the first tone mapping step; modulate said second OFDM subcarriers obtained in the second tone mapping step to obtain second OFDM symbols; and retransmit said second OFDM
  • a second communication device configured to communicate with a first communication device, the second communication device comprising circuitry configured to receive first orthogonal frequency division multiplex (OFDM) symbols from the first communication device; demodulate said first OFDM symbols into first OFDM subcarriers, perform first tone demapping to demap constellation points of a constellation from said first OFDM subcarriers; perform constellation demapping to demap one or more encoded data units from the constellation points; provide an error indication to the first communication device indicating at least one erroneous media access control (MAC) layer data unit that failed to be received or decoded by the second communication device; receive retransmitted second OFDM symbols from the first communication device; demodulate said second OFDM symbols into second OFDM subcarriers; and perform second tone demapping to demap the constellation points corresponding to the at least one erroneous MAC layer data unit from said second OFDM subcarriers differently than the constellation points in the first tone demapping step.
  • OFDM orthogonal frequency division multiplex
  • a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non-transi- tory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.
  • One of the aspects of the disclosure is to provide an increased frequency diversity between the original transmission and one or more retransmissions of the same data, which is achieve by mapping I allocating the constellation points to OFDM subcarriers differently than in the previous (re)transmission of the same data.
  • the originally transmitted and the retransmitted encoded data units can then be soft combined bitwise, in particular their log likelihood ratio (LLR) values.
  • LLR log likelihood ratio
  • Fig. 1 shows a diagram of a known communication scheme in WLAN.
  • Fig. 2 shows a diagram illustrating a known encoding and decoding scheme for
  • WLAN for an LDPC code.
  • Fig. 3 shows a diagram of a PPDU and its relation to a MPDU and codeword(s).
  • Fig. 4 shows an embodiment of a MAC header of a MPDU.
  • Fig. 5 shows a VHT-SIG-B and service field relationship.
  • Fig. 6 shows a simplified diagram of systematic encoding the data field of a PPDU.
  • Fig. 7 shows a diagram of an embodiment of a Chase combining scheme for two retransmissions.
  • Fig. 8 shows a diagram illustrating more details of the transmitter side of an encoding and decoding scheme in WLAN.
  • Fig. 9 shows a diagram illustrating an embodiment of an encoding and decoding scheme.
  • Fig. 10 shows a diagram illustrating an embodiment of the operation of an accumulate unit as used in the encoding and decoding scheme shown in Fig. 9.
  • Fig. 11 shows a simplified diagram of systematic encoding the data field of a PPDll according to another embodiment.
  • Fig. 12 schematically illustrates an embodiment of the HARQ Type III combining scheme.
  • Fig. 13 shows a schematic diagram of another embodiment of an encoding and decoding scheme.
  • Fig. 14 shows a schematic diagram of still another embodiment of an encoding and decoding scheme.
  • Fig. 15 shows a diagram of another embodiment of a Chase combining scheme for two retransmissions.
  • Fig. 16 shows a schematic diagram of an embodiment of an encoding and decoding scheme according to the present disclosure using Tx count.
  • Fig. 17 shows a diagram illustrating the operation of the HARQ tone mapper according to a first embodiment.
  • Fig. 18 shows a diagram illustrating the operation of the HARQ tone mapper according to a second embodiment.
  • Fig. 19 shows a diagram illustrating the operation of the HARQ tone mapper according to a third embodiment.
  • Fig. 20 shows a flowchart illustrating the process for three options of HARQ tone mapping according to the present disclosure.
  • Fig. 21 shows a diagram of an embodiment of a Chase combining scheme according to the present disclosure for one retransmission.
  • Fig. 22 shows a flowchart of an embodiment of a first communication method according to the present disclosure.
  • Fig. 23 shows a flowchart of an embodiment of a second communication method according to the present disclosure.
  • WLAN features HARQ type I which features a combination of FEC and ARQ protocol as illustrated in Fig. 1 showing a diagram of a known communication scheme.
  • Any MAC layer data unit to be transmitted is first supplied with a frame check sequence (FCS) and then encoded by a forward error correction encoder such as low-density parity-check (LDPC) code into a codeword (also called data unit) comprising an information part and a parity part.
  • FCS frame check sequence
  • LDPC low-density parity-check
  • the data packet as shown in Fig. 1 is a MAC layer data unit that comprises a MAC header, user data and CRC bits.
  • a MAC layer data unit is encoded into one or more data units (or codewords).
  • the FCS contains CRC bits in order to detect if there is any bit error within the MAC layer data unit and the FEC encoder adds additional redundancy (parity bits) enabling the receiver to perform (bit) error correction.
  • the bit error correction works on data unit or codeword basis.
  • the receiver performs FEC decoding of data units or codewords and subsequently checks the validity of FCS of the received MAC layer data unit. If the FCS is valid, the ARQ mechanism transmits a positive acknowledgement ACK to the transmitter to indicate successful reception. If the FCS is invalid, i.e., if there are bit errors as shown in the originally transmitted data unit and in the first retransmission, the ARQ mechanism transmits a negative acknowledgement N-ACK (or nothing, preferably after a timeout) to indicate that a retransmission of the MAC layer data unit is needed. After a certain number of retransmissions, e.g., depending on a lifetime of a MAC layer data unit, the transmission was either successful or not in which case the MAC layer data unit is discarded at the transmitter side.
  • LDPC encoding is done based on the fixed block length or codeword (CW) (also called data unit herein) length, i.e., either 648, 1296 or 1944.
  • CW codeword
  • the varying number of bits to be transmitted e.g., because of different MAC layer data unit sizes and/or aggregated MAC layer data units
  • an encoding and decoding scheme is preferred at transmitter or receiver, respectively.
  • the encoding and decoding scheme 1 for WLAN is schematically shown in Fig. 2 for an LDPC code.
  • the source provides the scrambled data of payload bits and FCS (CRC bits). These data are subsequently encoded and OFDM modulated to transmit over a wireless channel.
  • LDPC codes operate with a codeword length. Therefore, when the user data has a variable size, pre-and post-processing is needed in order to fit the varying number of bits to one or more codewords.
  • the LDPC encoding process in WLAN simultaneously fit the scrambled bits into a required minimum number of OFDM symbols and an integer number of codewords.
  • the pre-processing unit 11 determines the required minimum number of OFDM symbols (/V S ) according to the total number of scrambled bits coming from the source 10. This unit also determines the codeword (CW) length (L LDPC ) and computes the number of codewords (N cw ) based on total number of scrambled bits. It shall be noted in this context that WLAN LDPC encoding offers three different code word size LDPC codes. They are selected depending on total number of scrambled bits. Typically, the largest code word size of 1944 bits is used, because a typical data unit length is 1500 bytes or 12000 bits.
  • N shrt Shortening bits are bits of fixed value that are added to the information part of each codeword before the encoding, but which are discarded before transmission.
  • the receiver includes those bits of fixed value before decoding. These shortened bits are not always possible to be equally distributed to the number of codewords.
  • the first mod(N shrt , N cw ) codewords contain one more shortening bit than remaining codewords.
  • the minimum number of shortening bits per codeword N spcw [N shrt /N cw are inserted.
  • the output of the pre-processing unit 11 is systematically encoded with the LPDC encoder 12 with the designated code rate (/?) as per modulation and coding scheme (MCS) to obtain the codewords.
  • the inserted shortening bits in the information part of codewords are removed and either puncturing of the parity part of codewords (if the encoded bits are more than OFDM symbols can carry) or a repetition of the information part of codewords (if the encoded bits are less to fit the OFDM symbols) is performed.
  • the total number of parity bits to be punctured to fit in OFDM symbols is too large, the coding performance will degrade. To avoid this, an extra OFDM symbol will be added if either of the following two conditions is met:
  • the output of post-processing unit 13 is then modulated as per MCS and undergoes IFFT in a modulation and IFFT unit 14 before it is transmitted over a wireless channel 2 as an OFDM signal.
  • the inverse processes of the encoding procedure are carried out in an inverse post-processing unit 21 , an LDPC decoder 22 and an inverse pre-processing unit 23 to retrieve the payload bits provided to the sink 24.
  • the LDPC decoder 22, in WLAN uses the belief propagation algorithm to decode a binary systematic LDPC code, whose input is the soft decision bitwise LLR values from a demodulator 20.
  • the received signal after passing through the demodulator 20, is sampled, and real values are measured for soft decision demapping. These real values are soft decision value of received bits for the corresponding bits in the M-ary modulated constellation points and are termed as bitwise log-likelihood ratio (LLR) values.
  • LLR bitwise log-likelihood ratio
  • LLR is the ratio of probabilities of a 0 bit being transmitted to the 1 bit being transmitted for a received signal and can be expressed as equation (1) where b is the transmitted bit (one of k bits in an M- ary symbol) and r is received signal with coordinates (x,y) in constellation diagram.
  • the LLR value of code bit after passing a signal over additive white gaussian noise is expressed by equation (2) where S o /S 1 is the constellations point with bit 0/1 at the given bit position, s x /s y is the in-phase/quadrature coordinate of the constellation point, a 2 is the noise variance of the baseband signal.
  • an LLR value is a real number that indicates per bit the reliability of said bit. The more positive the value, the more likely a 0 bit was detected, whereas the more negative, the more likely a 1 bit was detected. A LLR value of zero means that both bits are equally probable.
  • HARQ Type I fails to provide reliable communication, because initial transmission and retransmissions may fail. Discarding the failed data unit at the receiver leads to a waste of resources that have been used for the transmission. Hence, instead of discarding the erroneous data unit, it can be utilized to extract some relevant information that may help in decoding the data unit in successive retransmissions. In this regard, it is favorable to achieve a combination gain by combining initial transmission and one or more retransmission(s).
  • Soft combining is one of the techniques to combine log-likelihood ratio (LLR) values of failed data unit with a retransmitted data unit, which can help the decoder to decode it correctly.
  • LLR log-likelihood ratio
  • HARQ with soft combining can be done in two ways, i.e. Chase combining (CC) and Incremental Redundancy (IR). Both are categorized as HARQ Type II.
  • CC and HARQ Type III will be considered:
  • CC the same information as the erroneous data unit will be retransmitted again, and LLR values of initial transmission and retransmissions will be combined at the receiver side.
  • HARQ Type Ill a combination of both CC and IR techniques is considered, in which, within the information part, LLR values are combined, but new parity information in retransmission is considered.
  • the combination may be done on a one data unit or codeword basis.
  • a MAC layer data unit is often encoded in multiple data units or codewords, the combination process may repeat for all data units or codewords which contain the MAC layer data unit.
  • HARQ Type II (Chase combining) will be explained.
  • Chase combining technique according to which an original transmission and retransmissions are generally identical, can be applied to the data field of the physical protocol data unit (PPDU) in the physical (PHY) layer with the requirement that the retransmitted copy shall be exactly the same as the previously failed data field of the PPDU.
  • PPDU physical protocol data unit
  • PHY physical
  • MAC medium access control
  • the MAC header of the MPDU may comprise a Retry bit field, which is set to 1 (initially 0) if retransmission is made.
  • the other field such as Duration ID may also change according to the NAV setting in retransmission.
  • a Retry bit and a Duration ID field illustrated in Fig. 4 showing an embodiment of a MAC header of a MPDU
  • the FCS field will also change accordingly.
  • the data field of a PHY protocol data unit consists of the service field whose last 8 bits are for CRC check generated for the VHT-SIG-B field from the PHY preamble.
  • PPDU PHY protocol data unit
  • the VHT-SIG-B field may change if any content, for e.g. bandwidth, of it changes in retransmission that will lead to a different CRC in service field.
  • a scrambler initialization should be the same for initial transmission and retransmissions.
  • the data field of the PPDU is scrambled with a length-127 PPDU-synchronous scrambler in case of VHT 802.11ac/ HE 802.11ax and with a length-2047 PPDU-synchronous scrambler in case of EHT 802.11 be.
  • the scrambled data is encoded to codewords as designated MCS.
  • the data unit 30 comprises an information part 31 and a parity part 32.
  • the information part 31 comprises a payload part 33 and a CRC 34 (under the assumption that the entire data field of a PPDll fits into a single code word; otherwise, a codeword holds a fraction of the information part).
  • MAC layer data unit holding CRC
  • a MAC layer data unit is encoded in multiple data units I codewords. This is e.g. illustrated in Fig. 3. Therefore, if an error is detected at the receiver using CRC, it can generally not be determined which data unit / codeword is wrong, but it is just known that at least one of it was erroneous.
  • the same entire data field is retransmitted under the constraints above.
  • the entire data field shall be bit-wise equal. This implies that in a retransmission the scrambler seed is unchanged, i.e., the scrambler state is the same as the one used for the initial transmission, and all data units are the same and in the same order, which implies that length of each data unit, MAC header, delimiters (if present), and frame body is unchanged.
  • the PHY header may be different and padding that does not have an impact on the encoding length may be different.
  • Fig. 7 schematically illustrates an embodiment of Chase combining scheme including two retransmissions. In other embodiments only one or more than two retransmissions may be made.
  • the erroneously received data unit 40 (indicated in Fig. 7 by error bits 45 in the respective information part 41 of the received data unit) is stored instead of discarding it.
  • the transmitter In response to a N-ACK, representing an indication indicating at least one erroneous data unit that failed to be received or decoded by the receiver, the transmitter retransmits the same data unit 30 again (in this case two times, indicated as data units 30a, 30b) leading to another erroneously received data unit 40a and a correctly received data unit 40b, which is confirmed by transmitting ACK to the transmitter. The transmitter will then send the next (different) data unit 35.
  • the receiver Since in Chase combining, all retransmitted data units are bit-wise identical to the initial transmitted data unit consisting of the same information, the receiver combines the loglikelihood ratio (LLR) values L (k) (where k is number of transmission or Tx count) of the same bits received in the initial transmission and the corresponding retransmissions, i.e. data units 40, 40a, 40b received from the transmissions of data units 30, 30a, 30b. Due to the time-varying channel, the receiver may take advantage of the channel variation in each retransmission, and combining all retransmitted versions of the same data unit will help in obtaining temporal diversity. This diversity gain due to channel variation may increase the likelihood of successful decoding at the receiver. Thus, the LLRs of the erroneous data unit and the corresponding retransmission of the erroneous data unit are combined and the data unit is finally decoded based on the accumulated LLRs.
  • LLR loglikelihood ratio
  • the retransmissions would have the same frame body of MAC data unit (also called “MAC layer data unit” herein) but different MAC header (different setting of retry bit).
  • the encoding process into codewords also called “encoded data units” or simply “data units” herein
  • the MAC data units are encoded into codewords (data units), so that each codeword is the same and contains the same part of a MAC data unit in the initial transmission and the corresponding retransmission.
  • a PPDU may be different to such an extent that it does not affect decoding of the data units that are encoded.
  • Fig. 8 schematically shows a WLAN PHY block diagram for processing the data field of a PPDU with LDPC encoding. It shows more details of the blocks of the transmitter side of the encoding and decoding scheme 1 shown in Fig. 2 and accordingly uses the same reference signs.
  • any sub-block within the MOD + IFFT block 14 can potentially be changed for HARQ retransmission in comparison to the initial transmission.
  • all sub-blocks of the source block 10 and the pre-processing, LDPC encoding and post-processing block 11-13 shall be unchanged.
  • Fig. 9 shows a schematic diagram of the encoding and decoding scheme 3 for Chase combining according to an embodiment.
  • This scheme is similar to the concept shown in Fig. 2, but additionally comprises an accumulate unit 25 at the receiver side to perform Chase combining. All the units except the accumulate unit 25 generally operate and function as described above for the known concept and as generally known.
  • Fig. 10 shows a diagram illustrating an embodiment of the operation of the accumulate unit 25.
  • LLR values 51 i.e., the output of inverse post-processing unit 21
  • LLR values 50 of a newly transmitted copy of the codeword.
  • Fig. 10 illustrates the processing for a single codeword.
  • a data field of PPDU is typically encoded to a number of multiple codewords in which case the same process repeats for all codewords independently.
  • the accumulation unit 25 generally combines related codewords, i.e., the first codeword (or data unit) of data field of PPDU is combined with the first codeword (or data unit) of an earlier received and equal (in the sense as explained above) data field of PPDU.
  • the combined soft output values are fed to the LDPC decoder 23 which takes the advantages of combination gain and increase of the likelihood of successful decoding.
  • the output of the LDPC decoder 22 is inverse pre-processed in inverse pre-processing unit 23, and payload bits are retrieved at the receiver (sink 24).
  • HARQ Type III This is another scheme of soft combining that includes both Chase combining and incremental redundancy technique.
  • the systematic information bits of one or more codeword(s) are included in every transmission so that each transmission can be decoded independently of the previous transmissions.
  • only parity bits are varied from one transmission to another.
  • the systematic information part is Chase combined whereas new parity sets in each transmission provide incremental redundancy.
  • Fig. 11 shows a diagram of a PPDll 60 used according to HARQ Type III.
  • the raw data unit 60 comprises a raw codeword having an information part 61 and a parity part 62.
  • the information part 61 comprise a payload part 63 and a CRC 64.
  • the raw data unit 60 is generated from the information part 61 by systematic encoding.
  • the parity part 62 can be split into several (in this example three) parity portions (or sets) 62a, 62b, 62c (indicated as p (0 pW and p (2) ), e.g., by puncturing.
  • a data unit (codeword) thus comprises the information part 61 and one of the parity portions 62a, 62b, 62c (in Fig. 11 the codeword 65a is shown comprising the information part 61 and the parity portion 62a).
  • Fig. 12 schematically illustrates an embodiment of the HARQ Type III combining scheme, in this example with a maximum number of two retransmissions.
  • CT? 3/4
  • the information part 61 is sent with another (new) set of parity bits 62b (p (1) ) or 62c (p ).
  • the receiver receives data units 70a, 70b, 70c and provides feedback to the transmitter about the reception status of the data units in the form of N-Ack or Ack, as explained above with reference to Fig. 7. After confirmation of a correct reception or decoding, the transmitter will send the next (new) data unit 65. As shown in the last line, errors 75 appear in the information parts 71a, 71b of the first two received data units 70a, 70b.
  • the information parts of the received data units 70a, 70b, 70c is Chase combined, and the parity bits of the different parity sets p (0 pW and p (2) are redistributed at their original location where they have been punctured.
  • a low density parity check (LDPC) tone mapper is generally used to map the consecutive constellation points or quadrature amplitude modulation (QAM) symbols to non-consecutive OFDM subcarriers (inverse fast Fourier transformation, IFFT).
  • D TM The tone mapping distance between the OFDM subcarriers, which is denoted by D TM , is fixed and is the function of a selected resource unit (RU) size.
  • RU resource unit
  • the tone mapping of consecutive constellation points to non-consecutive OFDM subcarriers is done only in LDPC encoded PHY formats based on the allocated resource unit size.
  • the LDPC tone mapping distance parameter D TM is constant for each resource unit size. Table 1 shows the value of D TM for different resource units according to the standard document specifications in IEEE 802.11 be.
  • LDPC tone mapping is performed on each encoded stream by using the LDPC tone mapper by permuting the streams of constellation points (d) generated by constellation mapper as shown in Fig. 8.
  • the input to the LDPC tone mapper is d k and output is defined by equation (3).
  • the transmitter used the specific D TM as per the resource unit allocated to transmit the data unit. Upon failure of this data unit as per negative acknowledgement received from the receiver side, the transmitter will retransmit the data unit again with the same D TM provided that resource unit size is same. The erroneously received data units at the receiver will be discarded.
  • Fig. 13 shows a schematic diagram of another embodiment of an encoding and decoding scheme 4. It illustrates the compact and complete communication between source 10 and sink 24 including the encoding procedure with mapping of constellation points from a constellation mapper 15 to an LDPC tone mapper 16 at the transmitter side. On the receiver side the decoding procedure with the inverse process done by an LDPC tone demapper 27 to map the received constellations points to a constellation demapper 26.
  • the LDPC tone mapper 16 uses a fix tone mapping distance D TM for the specific bandwidth (Resource Unit) used as shown in Table 1 . If the same D TM is used for the initial transmission and for retransmissions for the failed (erroneous) data unit, then HARQ soft combining cannot exploit the frequency diversity, nor it has exploited the time diversity due to the generally slow fading time varying channel. As explained above, one of the ideas of implementing HARQ soft combining is to combine the different LLR values of the same bit by exploiting some diversity which may be useful to correctly decode data at the receiver.
  • Fig. 14 shows a schematic diagram of another embodiment of an encoding and decoding scheme 5. It illustrates the source to sink communication chain including a HARQ Chase combining approach with an LDPC tone mapper 16 of fixed D TM in a slow fading time varying wireless channel 2. Accordingly, an accumulation unit 25 as shown in Fig. 9 is provided in addition to the elements of the encoding and decoding scheme shown in Fig. 13.
  • D TM bitwise LLR values
  • the erroneously received data unit at the receiver side can be stored in a buffer and can later be combined with HARQ soft combining techniques instead of discarding it.
  • the soft combining technique of using log-likelihood ratios of a failed data unit and of the retransmitted data unit or of information related to the failed data unit can provide a combination gain that will help the decoder to decode the data unit successfully.
  • WLAN is often deployed in an indoor scenario, where the channel is considered to be a slow fading time-varying channel.
  • Coherence time is the time duration during which the channel impulse response is considered to be constant which depends on Doppler effects, i.e., on how fast transmitter, receiver and/or surrounding reflectors are moving. If the channel has not changed significantly, the retransmitted copy of the originally transmitted data unit may not provide a significant combining gain.
  • the tone mapping procedure of mapping constellation points to OFDM subcarriers is changed according to an embodiment of the present disclosure. While retransmitting the same constellation points (e.g. QAM symbols) in a different tone (data subcarrier), it will face different channel conditions than in the initial transmission so that frequency diversity can be achieved.
  • Fig. 16 shows a schematic diagram of a corresponding embodiment of an encoding and decoding scheme 6 according to the present disclosure, where the HARQ tone mapper unit 17 and the HARQ tone demapper unit 28 use the Tx count.
  • the HARQ Tone mapper unit 17 can be configured and implemented in different ways. Three possible options of a constellation points mapping procedure will be explained in the following. Other options may be used in other embodiments as well.
  • the tone mapping distance D TM may be changed.
  • all possible D TM values for each Rll are initially found based on the number of data subcarriers N SD , i.e. based on its size.
  • the idea here is to use different D TM values that have not been used in previous transmissions.
  • previously used D TM values can be used again after a later (e.g. third) retransmission has taken place
  • the assumption is that the channel would have been changed distinctly after the third retransmission.
  • Table 2 shows the possible D TM values for each Rll based on N SD used for retransmissions.
  • D TM values may be taken as they are defined in a WLAN standard specification.
  • possible D TM values are chosen as described above.
  • Fig. 17 showing a diagram illustrating the operation of the HARQ tone mapper.
  • the data subcarrier gap is changed from 9 (as used according to Fig. 17A for the initial transmission) to 13 (as used according to Fig. 17B for the first retransmission).
  • the first constellation point is mapped to a first data subcarrier
  • the second constellation point is mapped to a tenth data subcarrier, and so on (see Fig. 17A).
  • the first constellation point is mapped to a first data subcarrier as well, but the second constellation point is mapped to a fourteenth data subcarrier, and so on (see Fig. 17B).
  • cyclic shifting the LDPC one mapper is used.
  • the maximum possible cyclic shift distance is found by dividing the total number of data subcarriers N SD by two. Based on the number of retransmissions, the following equation (5) is used to find the tone mapping cyclic shifter TM CS .
  • the idea is to map the constellation points to the data subcarriers after cyclic shifting the LDPC tone mapper indices by TM CS .
  • Table 3 shows the cyclic shifter (TM CS ) values that can be used for cyclic shifting the LDPC tone mapper indices based on Tx count.
  • j 1, 2, 3 for the first three retransmissions.
  • the tone mapper distance is maintained with 9 data subcarriers.
  • pseudorandom tone mapping indices are used.
  • a look-up table may be created for the pseudorandom tone mapping (TM PR ) indices of size N SD for corresponding Tx count (> 0).
  • the indices can be generated by using a random seed for initializing the pseudorandom number generator at both transmitter and receiver side.
  • Pseudorandom numbers are mostly generated by an algorithm which uses some kind of recursive method that is initiated with a base value. This base value is particularly determined by an input called seed.
  • the pseudorandom numbers generated by this recursive algorithm is fixed for the particular seed fed as an input.
  • the default used algorithm in most statistical software is the Mersenne Twister algorithm MT19937.
  • the random seed may already be known to the receiver or may be transmitted beforehand, e.g. in a PHY preamble.
  • the pseudorandom tone mapping may be turned off, i.e., the first row of Table 4 is 1 , 2, 3, 4, ... , 10 and the corresponding D TM applies.
  • Fig. 19 shows a diagram illustrating the operation of the HARQ tone mapper according to a third embodiment of the present disclosure using the mapping of the pseudorandom tone mapper.
  • the first constellation point is mapped to the sixth data subcarrier
  • the second constellation point is mapped to the third data subcarrier, and so on (pseudo randomly).
  • the first constellation point is mapped to the seventh data subcarrier
  • the second constellation point is mapped to the second data subcarrier, and so on.
  • Fig. 20 shows a flowchart illustrating the process for all three options of HARQ tone mapper as described above.
  • tone mapping is carried out as defined in the standard specification.
  • Tx count increases (Tx > 0)
  • tone mapping procedures are carried out for the retransmissions.
  • a HARQ tone demapper is used to reverse the effect of the HARQ tone mapper procedure.
  • the LLR values of the same bit coming from different data subcarriers, experiencing different channel conditions are Chase combined and hence achieve frequency diversity to have a reliable and sustainable communication in a slow fading time varying channel.
  • OFDM subcarriers generally include both data subcarriers and pilot subcarriers. According to the present disclosure, the tone mapping is primarily applied to the data subcarriers only, whereas the location of pilot subcarriers is generally fixed.
  • Fig. 21 shows a diagram of an embodiment of a Chase combining scheme according to the present disclosure for one retransmission.
  • the decoder at the receiver side receives data units 90, 90a, based on which it is able to decode the data unit correctly after the first retransmission, i.e., differently from the scheme depicted in Fig.
  • mapping procedures apply only to the data field of a PPDll but not to the preamble of a PPDll to maintain backwards compatibility. This comes with no loss, because the preamble is anyway encoded with BCC.
  • HARQ tone mapping can operate in different options and the receiver should be aware of the option that has been used for tone mapping the constellation points to data subcarriers so that the receiver can apply the reverse tone demapping operation.
  • This information may e.g. be provided to the receiver in the PHY preamble.
  • Such information may include one or more of: which option has been chosen to implement HARQ tone mapping; Tx count to demap corresponding in all three options; for option 1 , after which Tx count the used D TM is used again; for option 2, after which Tx count the cyclic shifters are repeated again; for option 3, the random seed for pseudorandom tone mapping indices generator, if initially not known to the receiver.
  • FIG. 22 A flowchart of an embodiment of a transmission method 100 (first communication method) according to the present disclosure is shown in Fig. 22.
  • step 101 MAC layer data units are obtained, e.g. from a higher layer or another entity, which are encoded into encoded data units, e.g. by LDPC encoding.
  • step 102 constellation mapping is performed to map bits of said one or more encoded data units to be transmitted to the second communication device (a receiving device) onto constellation points of a constellation, e.g. of a QAM constellation.
  • first tone mapping is performed to map said constellation points onto first OFDM subcarriers.
  • step 104 said first OFDM subcarriers are modulated to obtain first OFDM symbols. Said first OFDM symbols are then transmitted (initial transmission) to the second communication device in step 105.
  • step 106 If an error indication is obtained from the second communication device in step 106, where the error indication indicates at least one erroneous MAC layer data unit that failed to be received or decoded by the second communication device, a second tone mapping is performed in step 107 to map the constellation points corresponding to the at least one erroneous MAC layer data unit onto second OFDM subcarriers differently than the constellation points in the first tone mapping step 103.
  • step 108 said second OFDM subcarriers obtained in the second tone mapping step are modulated to obtain second OFDM symbols, which are then transmitted (retransmission) to the second communication device in step 109.
  • step 106 it may be checked in step 106 if a further error indication is obtained from the second communication device, which would require further retransmission(s).
  • a further error indication e.g. 2, 3, 4 or any other predetermined number.
  • the method proceeds with step 101 or 102 to obtain further MAC layer data units or start processing already obtained further MAC layer data units.
  • step 201 first OFDM symbols are received from the first communication device (a transmission device), which corresponds to the initial transmission.
  • step 202 said first OFDM symbols are demodulated into first OFDM subcarriers.
  • step 203 first tone demapping is performed to demap constellation points of a constellation from said first OFDM subcarriers.
  • constellation demapping is performed to demap one or more data units from the constellation points.
  • step 209 If at least one erroneous MAC layer data unit failed to be received or decoded by the second communication device, which may be checked in step 209, a corresponding error indication is provided to the first communication device indicating this in step 205. In response, retransmitted second OFDM symbols are received from the first communication device in step 206, which are then demodulated into second OFDM subcarriers. In step 207 second tone demapping is performed to demap the constellation points corresponding to the at least one erroneous MAC layer data unit from said second OFDM subcarriers differently than the constellation points in the first tone demapping step 203.
  • step 209 After constellation demapping in step 204 it may be checked in step 209 if a further error appeared, which would require further retransmission(s). Optionally, there may be an upper limit of retransmissions, e.g. 2, 3, 4 or any other predetermined number. If no (first or further) error is detected in step 209, the method proceeds with step 201 to received further first OFDM symbols, i.e. next data.
  • a circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).
  • First communication device configured to communicate with a second communication device (Rx), the first communication device comprising circuitry configured to obtain media access control (MAC) layer data units and encode said MAC layer data units into encoded data units; perform constellation mapping to map bits of said one or more encoded data units to be transmitted to the second communication device onto constellation points of a constellation; perform first tone mapping to map said constellation points onto first orthogonal frequency division multiplex (OFDM) subcarriers; modulate said first OFDM subcarriers to obtain first OFDM symbols; transmit said first OFDM symbols to the second communication device; obtain an error indication indicating at least one erroneous MAC layer data unit that failed to be received or decoded by the second communication device; perform second tone mapping to map the constellation points corresponding to the at least one erroneous MAC layer data unit onto second OFDM subcarriers differently than the constellation points in the first tone mapping step; modulate said second OFDM subcarriers obtained in the second tone mapping step to obtain second OFDM symbols; and retransmit said second OFDM OFDM
  • the circuitry is configured to change a tone mapping distance in the second tone mapping step compared to the first tone mapping step, the tone mapping distance indicating the distance between OFDM subcarriers onto which consecutive constellation points are mapped.
  • First communication device configured to process at least partly the same MAC layer data units in one or more further iterations for performing one or more further retransmissions, wherein in one or more iterations for one or more of said further retransmissions the tone mapping distance is changed compared to the original transmission and one or more earlier retransmissions.
  • circuitry is configured to apply, as the second tone mapping, a cyclic shift to the first OFDM subcarriers generated by the first tone mapping step.
  • First communication device wherein the circuitry is configured to select a cyclic shift value indicating the amount of cyclic shift from a table of predetermined cyclic shift values for different numbers of subcarriers per resource unit.
  • circuitry is configured to process at least partly the same MAC layer data units in one or more further iterations for performing one or more further retransmissions, wherein in one or more iterations for one or more of said further retransmissions the cyclic shift value is changed compared to the original transmission and one or more earlier retransmissions.
  • circuitry is configured to pseudo-randomly change OFDM subcarrier indices of the second OFDM subcarriers, onto which the constellation points corresponding to the at least one erroneous MAC layer data unit are mapped in the second tone mapping step.
  • First communication device wherein the circuitry is configured to select the changed OFDM subcarrier indices in the second tone mapping step from a table of predetermined OFDM subcarrier indices for different numbers of subcarriers per resource unit.
  • First communication device wherein the circuitry is configured to compute the changed OFDM subcarrier indices in the second tone mapping step based on a seed value, the seed value defining a pseudo-random indices sequence.
  • First communication device wherein the circuitry is configured to process at least partly the same MAC layer data units in one or more further iterations for performing one or more further retransmissions, wherein in one or more iterations for one or more of said further retransmissions the OFDM subcarrier indices are changed compared to the original transmission and one or more earlier retransmissions.
  • the circuitry is configured to process at least partly the same MAC layer data units in one or more further iterations for performing one or more further retransmissions, wherein in one or more iterations for one or more of said further retransmissions the second tone mapping is changed per retransmission and wherein after a predetermined or selected number of retransmissions the first tone mapping is used again for the subsequent retransmission.
  • circuitry is configured to select one of different options for changing the tone mapping from a set of different options and to transmit to the second communication device an indication of the selected option.
  • First communication device wherein one or more first encoded data units carried in first OFDM symbols in an initial transmission each comprise an information part and at least a portion of a parity part and wherein in a retransmission one or more retransmitted second encoded data units carried in second OFDM symbols have at least an identical information part as the one or more first encoded data units.
  • circuitry is configured to perform, before performing second tone mapping, further constellation mapping to map at least partly different of the bits of said one or more encoded data units corresponding to the at least one erroneous MAC layer data unit onto the constellation points of the constellation used in the initial constellation mapping.
  • Second communication device configured to communicate with a first communication device (Tx), the second communication device comprising circuitry configured to receive first orthogonal frequency division multiplex (OFDM) symbols from the first communication device; demodulate said first OFDM symbols into first OFDM subcarriers; perform first tone demapping to demap constellation points of a constellation from said first OFDM subcarriers; perform constellation demapping to demap one or more encoded data units from the constellation points; provide an error indication to the first communication device indicating at least one erroneous media access control (MAC) layer data unit that failed to be received or decoded by the second communication device; receive retransmitted second OFDM symbols from the first communication device; demodulate said second OFDM symbols into second OFDM subcarriers; and perform second tone demapping to demap the constellation points corresponding to the at least one erroneous MAC layer data unit from said second OFDM subcarriers differently than the constellation points in the first tone demapping step.
  • OFDM orthogonal frequency division multiplex
  • Second communication device wherein the circuitry is configured to determine how to perform the second tone demapping based on an indication from the first communication device indicating how second tone mapping applied by the first communication device for the retransmission has changed compared to the first tone mapping applied by the first communication device for the original transmission or indicating one of different options for changing the tone mapping from a set of different options.
  • Second communication device wherein the circuitry is configured to accumulate log-likelihood ratios (LLRs) of the erroneous data unit and the corresponding retransmission of the erroneous data unit; and decode the data unit based on the accumulated LLRs.
  • LLRs log-likelihood ratios
  • Second communication device according to embodiment 17, 18 or 19, wherein the circuitry is configured to provide said error indication by explicitly transmitting a response to the first communication device indicating the at least one erroneous MAC layer data unit or by not transmitting a response to the second communication device within a predetermined period.
  • Second communication method of a second communication device (Rx) configured to communicate with a first communication device (Tx), the second communication method comprising: receiving first orthogonal frequency division multiplex (OFDM) symbols from the first communication device; demodulating said first OFDM symbols into first OFDM subcarriers; performing first tone demapping to demap constellation points of a constellation from said first OFDM subcarriers; performing constellation demapping to demap one or more data units from the constellation points; providing an error indication to the first communication device indicating at least one erroneous media access control (MAC) layer data unit that failed to be received or decoded by the second communication device; receiving retransmitted second OFDM symbols from the first communication device; demodulating said second OFDM symbols into second OFDM subcarriers; and performing second tone demapping to demap the constellation points corresponding to the at least one erroneous MAC layer data unit from said second OFDM subcarriers differently than the constellation points in the first tone demapping step.
  • OFDM orthogonal frequency division multiplex
  • a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 21 or 22 to be performed.
  • a computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 21 or 22 when said computer program is carried out on a computer.

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

Un premier dispositif de communication qui est configuré pour communiquer avec un second dispositif de communication comprend un ensemble circuit configuré pour obtenir des unités de données de couche de commande d'accès au support (MAC) et coder lesdites unités de données de couche MAC en unités de données codées ; effectuer une mise en correspondance de constellation pour mettre en correspondance des bits de ladite ou desdites unités de données codées à transmettre au second dispositif de communication sur des points de constellation d'une constellation ; effectuer une première mise en correspondance de tonalité pour mettre en correspondance lesdits points de constellation sur des premières sous-porteuses OFDM ; moduler lesdites premières sous-porteuses OFDM pour obtenir des premiers symboles OFDM ; transmettre lesdits premiers symboles OFDM au second dispositif de communication ; obtenir une indication d'erreur indiquant au moins une unité de données de couche MAC erronée dont la réception ou le décodage par le second dispositif de communication a échoué ; effectuer une seconde mise en correspondance de tonalité pour mettre en correspondance les points de constellation correspondant à ladite au moins une unité de données de couche MAC erronée sur des secondes sous-porteuses OFDM différemment des points de constellation dans la première étape de mise en correspondance de tonalité ; moduler lesdites secondes sous-porteuses OFDM obtenues dans la seconde étape de mise en correspondance de tonalité pour obtenir des seconds symboles OFDM ; et retransmettre lesdits seconds symboles OFDM au second dispositif de communication.
PCT/EP2023/083308 2022-12-06 2023-11-28 Premier et second dispositifs de communication et procédés WO2024120886A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100180173A1 (en) * 2009-01-13 2010-07-15 Texas Instruments Incorporated Hybrid-ARQ (HARQ) with Scrambler and Diversity
US20100195764A1 (en) * 2007-07-30 2010-08-05 Kyocera Corporation Ofdm transmission apparatus, ofdm receiving apparatus and interleaving method
US20200137827A1 (en) * 2018-12-28 2020-04-30 Laurent Cariou Extremely high throughput hybrid automatic repeat request

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100195764A1 (en) * 2007-07-30 2010-08-05 Kyocera Corporation Ofdm transmission apparatus, ofdm receiving apparatus and interleaving method
US20100180173A1 (en) * 2009-01-13 2010-07-15 Texas Instruments Incorporated Hybrid-ARQ (HARQ) with Scrambler and Diversity
US20200137827A1 (en) * 2018-12-28 2020-04-30 Laurent Cariou Extremely high throughput hybrid automatic repeat request

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