WO2005048519A1 - Procede, systeme et dispositif de communication - Google Patents

Procede, systeme et dispositif de communication Download PDF

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Publication number
WO2005048519A1
WO2005048519A1 PCT/IB2004/052349 IB2004052349W WO2005048519A1 WO 2005048519 A1 WO2005048519 A1 WO 2005048519A1 IB 2004052349 W IB2004052349 W IB 2004052349W WO 2005048519 A1 WO2005048519 A1 WO 2005048519A1
Authority
WO
WIPO (PCT)
Prior art keywords
data packets
subset
undecodable
information
data
Prior art date
Application number
PCT/IB2004/052349
Other languages
English (en)
Inventor
Matthew P. J. Baker
Timothy J. Moulsley
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB0326366A external-priority patent/GB0326366D0/en
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2005048519A1 publication Critical patent/WO2005048519A1/fr

Links

Classifications

    • 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
    • H04L1/1812—Hybrid protocols; Hybrid automatic repeat request [HARQ]
    • H04L1/1816—Hybrid protocols; Hybrid automatic repeat request [HARQ] with retransmission of the same, encoded, message
    • 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
    • H04L1/0041—Arrangements at the transmitter end
    • 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
    • H04L1/0057—Block codes
    • 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
    • H04L1/0059—Convolutional codes
    • 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
    • H04L1/0064—Concatenated codes
    • H04L1/0065—Serial concatenated codes
    • 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
    • H04L1/08—Arrangements for detecting or preventing errors in the information received by repeating transmission, e.g. Verdan system
    • 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
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1657—Implicit acknowledgement of correct or incorrect reception, e.g. with a moving window

Definitions

  • the invention relates to a method of communicating information, to a device for use in a communication system, and to a communication system comprising such a device.
  • the invention is particularly, but not exclusively, suitable for use in the communication of information from a single device to a plurality of devices.
  • FIG. 1 A known way of encoding information is illustrated in Figure 1.
  • Information is encoded in data packets, each data packet comprising a code word of an inner code having k symbols for information I and r parity check symbols P, which may include, for example, a cyclic redundancy checksum (CRC).
  • Each row of Figure 1 represents a data packet and the total amount of information occupies k' such data packets, as represented by the upper k' rows in Figure 1.
  • To the k' data packets are added further packets k'+1 to N which contain parity check symbols P' which encode the symbols of the upper k' rows of Figure 1 to form an outer code.
  • the outer code encodes a plurality of data packets.
  • error detection and/or error correction can be performed on each information carrying data packet using the inner code parity check symbols P, and error correction can be performed across all the data packets using the outer code.
  • the objective of such a coding scheme is to combine the capability of the inner and outer codes, enabling errors that cannot be fully corrected by one code to be corrected by the other code or the combination of codes.
  • Either the inner code or outer code may be decoded first by a receiving device.
  • Such a coding scheme is under consideration, for example, for providing a Multi-Media Broadcast and Multicast Service (MBMS) for the Universal Mobile Telecommunication System (UMTS).
  • MBMS Multi-Media Broadcast and Multicast Service
  • UMTS Universal Mobile Telecommunication System
  • the data packets will be broadcast over a Radio Access Network (RAN) to large numbers of users in each coverage cell, and so the transmission power cannot be set individually for each user.
  • RAN Radio Access Network
  • a powerful coding scheme such as that described above with reference to Figure 1 can contribute to reducing the transmit power requirement.
  • the receiving device can transmit a positive acknowledgment (ACK) or a negative acknowledgement (NACK) for each data packet to indicate to the sending device whether or not that data packet has been successfully received, and consequently whether or not a retransmission of that data packet is required.
  • ACK positive acknowledgment
  • NACK negative acknowledgement
  • the receiving device can transmit a single ACK or NACK to indicate whether or not the whole group of N data packets has been successfully received, and consequently whether or not a retransmission of the whole group of N data packets is required.
  • this may result in the retransmission of some data packets that have already been successfully decoded.
  • the number of data packets retransmitted can be reduced if a selective retransmission scheme is employed in which a receiving device transmits an indication of which data packets it has failed to decode successfully after decoding both the inner and outer codes, and the sending device retransmits only those indicated data packets.
  • An object of the invention is to reduce the amount of transmission in a communication system.
  • a method of communicating information from a first device to a second device comprising: encoding information in a group of data packets, wherein each data packet comprises an inner error detection or correction code and the group comprises an outer error correction code; transmitting the group of data packets from the first device; receiving the group of data packets at the second device; decoding the group of data packets using the inner and outer codes to recover the information; if a plurality of the data packets are undecodable such that the information is not recovered, determining a subset of the plurality of undecodable data packets which would, if each data packet of the subset were decodable, enable the information to be recovered; and retransmitting the subset of data packets from the first device.
  • Either the second device (also referred to as the receiving device) may transmit an indication of the plurality of undecodable data packets, and the first device (also referred to as the sending device) determines the subset of those data packets to be retransmitted, or the second device may determine the subset of the undecodable data packets and transmit an indication of the subset to the first device.
  • a device for sending data in a communication system comprising: encoding means for encoding information in a group of data packets, wherein each data packet comprises an inner error detection or correction code and the group comprises an outer error correction code; transmitter means for transmitting the encoded information; receiver means for receiving an indication of a plurality of data packets that are undecodable by a receiving device; processing means for determining a subset of the plurality of undecodable data packets which would, if each data packet of the subset were decodable, enable the information to be recovered by the receiving device; and wherein the transmitter means is adapted to transmit the determined subset of data packets.
  • a device for receiving data in a communication system in which information is encoded in a group of data packets, wherein each data packet comprises an inner error detection or correction code and the group comprises an outer error correction code comprising: receiving means for receiving the group of data packets; decoding means for decoding the group of data packets using the inner and outer codes to recover the information; processing means adapted to, if a plurality of data packets are undecodable such that the information is not recovered, determine a subset of the plurality of undecodable data packets which would, if each data packet of the subset were decodable, enable the information to be recovered; and transmitting means for transmitting from the second device an indication of the subset of data packets.
  • a communication system comprising a device in accordance with the second aspect of the invention for sending data and a further device for receiving the data and requesting retransmission of undecodable data packets.
  • a communication system comprising a device in accordance with the third aspect of the invention for receiving data and a further device for sending the data and retransmitting requested data packets.
  • the invention is based on the realisation that it is not necessary to retransmit every undecodable data packet, but that retransmission of merely a subset of the undecodable data packets is sufficient because the combination of the inner and outer codes can enable previously undecodable data packets to become decodable after retransmission of the subset. In this way, the invention enables a reduction in the amount of transmission in a communication system.
  • Figure 1 illustrates information encoded with an inner code and an outer code
  • Figure 2 is a flow chart illustrating a method of communicating information
  • Figure 3 is a block schematic diagram of a device for sending data
  • Figure 4 is a block schematic diagram of a device for receiving data
  • Figure 5 is a block schematic diagram of a communication system comprising the device of Figure 3
  • Figure 6 is a block schematic diagram of a communication system comprising the device of Figure 4.
  • a method of communicating information from a first, sending device to a second, receiving device commences at step 110 where, at the sending device, information is encoded with an inner error detection or correction code and then at step 120 the encoded data is further encoded with an outer error correction code, resulting in a group of data packets.
  • the group of data packets is transmitted by the sending device, and at step 140 the transmitted data packets are received by the receiving device.
  • the inner codes of the received data packets are decoded by the receiving device, and then at step 160 the outer code of the received data packets is decoded.
  • the receiving device determines whether all of the transmitted data packets have been decoded successfully, including data packets decoded successfully from any previous transmissions, such that the information, either the whole information or a predetermined amount, can be recovered. If all of the transmitted data packets have been decoded successfully, then the process ends at step 180. If a plurality of the transmitted data packets are undecodable due to transmission errors, including data packets decoded from any previous transmissions, such that the information cannot be recovered, then at step 190 a subset of the plurality of undecodable data packets is determined which would, if each data packet of the subset were decodable, enable the information to be recovered.
  • Step 190 may be performed either by the sending device, in response to the receiving device transmitting an indication of the plurality of undecodable data packets, or by the receiving device, in which case the receiving device transmits to the sending device an indication of the data packets in the subset.
  • the subset may, depending on the extent of the errors, comprise only one data packet. If only one of the transmitted data packets is undecodable, then determination of the subset is trivial and only that data packet is retransmitted.
  • criterion may be, for example: all or a predetermined amount of the information has been recovered, all or a predetermined percentage of data packets have been successfully decoded, or a maximum number of retransmissions has been made, or a time limit expires.
  • the inner code may be decoded before the outer code, in which case the order of steps 150 and 160 is reversed. Additionally or alternatively, the order of steps 110 and 120 may be reversed in the sending device.
  • a device 200 for sending data comprises a first encoder 220 for receiving information on an input 210 and encoding the information in data packets using an inner error detection or correction code.
  • An output of the first encoder 220 is coupled to an input of a second encoder 230 which receives the encoded data packets from the first encoder 220 and encodes the data packets using an outer error correction code, and delivers a group of data packets to a transmitter 240 for transmission via an antenna 250.
  • the receiver 260 is coupled to a processing means 270 for processing the received indication.
  • a device 300 for receiving data comprises a receiver 320 coupled to an antenna 310 for receiving a group of data packets, wherein each data packet comprises information encoded in an inner error detection or correction code and the group comprises an outer error correction code.
  • An output of the receiver 320 is coupled to an input of a first decoder 330 for decoding either the inner or outer code.
  • An output of the second decoder 330 is coupled to an input of a second decoder 340 for decoding the other code (outer or inner).
  • An output of the second decoder 340 is coupled to a processing means 350. If a plurality of the data packets are undecodable such that the whole of the information, or a predetermined amount of the information, is not successfully recovered, including data packets decoded successfully from any previous transmissions, the processing means 350 determines a subset of the plurality of undecodable data packets which would, if each data packet of the subset were decodable, enable the information to be recovered successfully.
  • the processing means 350 is coupled to a transmitter 360 for transmitting via the antenna 310 an indication of the subset of data packets.
  • a communication system 400 comprising the sending device 200 of Figure 3 and a receiving device 410.
  • the receiving device 410 determines, and transmits an indication of, which received data packets are undecodable, taking account of data packets received in any previous transmission, and the sending device 200 determines which subset of those undecodable data packets is retransmitted.
  • the receiving device 410 does not transmit a NACK for a group of data packets until the decoding operation on both the inner and the outer codes has been carried out for the group of data packets.
  • the receiving device 410 determines which of the constituent data packets are undecodable, indicated for example by an incorrect CRC check in the data packets, and transmits a multi-bit NACK codeword.
  • This NACK codeword gives the sending device the identity of only those received data packets that were undecodable.
  • FIG 6 there is illustrated a communication system comprising the receiving device 300 of Figure 4 and a sending device 510.
  • the receiving device 300 determines which subset of the undecodable data packets is to be retransmitted, taking account of data packets received in any previous transmission, and the transmits an indication of those data packets to the sending device 510 in order to request retransmission.
  • the sending device 510 retransmits those requested data packets.
  • a communication system comprising a plurality of receiving devices,
  • a sending device 200 may compile a list of the data packets identified by the various receiving devices, 300 or 410, as being undecodable, and then select for retransmission a subset of the undecodable data packets in the compiled list sufficient to enable each receiving device, 300 or 410, or a plurality of the receiving devices to complete decoding of the full set of N data packets using the inner and outer codes.
  • the subset of undecodable data packets is selected, consider the situation in which there are e undecodable data packets after the inner and outer codes have been decoded, and the outer code is capable of correcting any t errors (e> t ) in each code word of the outer code.
  • the retransmitted subset could comprise any e-t of the undecodable data packets.
  • the subset may comprise more than e-t of the undecodable data packets, but fewer than e.
  • the subset of undecodable data packets may be selected to take advantage of the maximum error correcting capability of the outer code, thereby minimising the number of data packets retransmitted.
  • data is packaged into physical layer data packets each lasting 20ms.
  • Each such packet includes FEC (Forward Error Correction) symbols and a CRC.
  • FEC Forward Error Correction
  • CRC Forward Error Correction
  • the receiving device 410 receives, and attempts to decode, each physical layer data packet individually. If the CRC fails for one or more of the 16 data packets, the receiving device 410 then proceeds to use the parity information from the Reed Solomon code to attempt to recover the corrupt packets. If this process does not result in the remaining CRCs of the physical layer data packets passing, the receiving device 410 transmits a multi-bit NACK indication to the sending device 200.
  • a NACK codeword containing 4 information bits per physical layer packet would be sufficient to indicate unambiguously to the sending device 200 the identity of the physical layer data packets which have failed.
  • the sending device 200 selects the subset to encode and retransmit.
  • the NACK codeword may itself be protected with an error-correcting code and/or a CRC.
  • the number of bits required for the NACK codeword may be reduced by signalling only an indication of which sub-groups of the group of N data packets contain errors. For example, if the 16 data packets were considered as 8 sub-groups of 2, a 3-bit codeword per sub-group would suffice for the NACK.
  • the number of bits required for the NACK is therefore a trade-off between the signalling energy required for the NACKs and the number of data packets which have to be retransmitted. Note that any physical layer data packets which are retransmitted could be retransmitted as part of the next group of data packets.
  • all receiving devices 410 could be required to transmit their NACKs before all the parity data packets have been transmitted. In reliable radio channels, this could allow the sending device 200 to avoid transmitting the last few parity data blocks if no NACKs were received.
  • the receiving devices in a cell are sub-divided into groups, each of which is allocated a specific time period in which to transmit their NACKs. The time periods are arranged sequentially in a time-division manner.
  • the sending device detects a NACK for a particular physical layer data packet or sub-group of data packets, it can indicate to all receiving devices that the relevant data packet or packets will be retransmitted, so that receiving devices which have been assigned to subsequent time periods do not need to transmit NACK for those packets.
  • the inner and outer codes may comprise a block code or a convolutional code, or another type of code, including a composite of more than one code.
  • a second outer code may be used to further encode the retransmitted data packets.

Abstract

Dans un protocole ARQ, les informations sont codées dans des paquets de données au moyen d'un premier code interne (110), après quoi les paquets de données codées subissent un codage additionnel au moyen d'un second code externe (120). Un dispositif récepteur (410) déchiffre les deux codes (150, 160) pour restituer les informations. Si, après que les deux codes ont été appliqués, une pluralité de paquets de données n'est toujours pas déchiffrable, un sous-ensemble des paquets de données non déchiffrables (190) est retransmis, et les paquets de données non déchiffrables qui ne sont pas retransmis sont restitués par application de la fonctionnalité de correction d'erreurs du codage. Le sous-ensemble particulier de parquets de données non déchiffrables qui a été sélectionné pour la retransmission est choisi de façon à assurer que les paquets de données non déchiffrables et non retransmis soient déchiffrables après la retransmission. Ledit sous-ensemble destiné à la retransmission peut être déterminé par le dispositif récepteur ou par un dispositif émetteur.
PCT/IB2004/052349 2003-11-12 2004-11-09 Procede, systeme et dispositif de communication WO2005048519A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0326366.2 2003-11-12
GB0326366A GB0326366D0 (en) 2003-11-12 2003-11-12 Communication method,system and device
GB0419122A GB0419122D0 (en) 2003-11-12 2004-08-27 Communication method, system and device
GB0419122.7 2004-08-27

Publications (1)

Publication Number Publication Date
WO2005048519A1 true WO2005048519A1 (fr) 2005-05-26

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Cited By (7)

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WO2007051792A1 (fr) * 2005-11-03 2007-05-10 Continental Teves Ag & Co. Ohg Circuit de commutation de signal mixte destine a un systeme de commande ou de regulation electronique securise
US20100005360A1 (en) * 2008-07-07 2010-01-07 Cisco Technology, Inc. Importance-based fed-aware error-repair scheduling
US8462847B2 (en) 2006-02-27 2013-06-11 Cisco Technology, Inc. Method and apparatus for immediate display of multicast IPTV over a bandwidth constrained network
US8588077B2 (en) 2006-09-11 2013-11-19 Cisco Technology, Inc. Retransmission-based stream repair and stream join
US8711854B2 (en) 2007-04-16 2014-04-29 Cisco Technology, Inc. Monitoring and correcting upstream packet loss
US8769591B2 (en) 2007-02-12 2014-07-01 Cisco Technology, Inc. Fast channel change on a bandwidth constrained network
US8787153B2 (en) 2008-02-10 2014-07-22 Cisco Technology, Inc. Forward error correction based data recovery with path diversity

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007051792A1 (fr) * 2005-11-03 2007-05-10 Continental Teves Ag & Co. Ohg Circuit de commutation de signal mixte destine a un systeme de commande ou de regulation electronique securise
US8462847B2 (en) 2006-02-27 2013-06-11 Cisco Technology, Inc. Method and apparatus for immediate display of multicast IPTV over a bandwidth constrained network
US8588077B2 (en) 2006-09-11 2013-11-19 Cisco Technology, Inc. Retransmission-based stream repair and stream join
US9083585B2 (en) 2006-09-11 2015-07-14 Cisco Technology, Inc. Retransmission-based stream repair and stream join
US8769591B2 (en) 2007-02-12 2014-07-01 Cisco Technology, Inc. Fast channel change on a bandwidth constrained network
US8711854B2 (en) 2007-04-16 2014-04-29 Cisco Technology, Inc. Monitoring and correcting upstream packet loss
US8787153B2 (en) 2008-02-10 2014-07-22 Cisco Technology, Inc. Forward error correction based data recovery with path diversity
US20100005360A1 (en) * 2008-07-07 2010-01-07 Cisco Technology, Inc. Importance-based fed-aware error-repair scheduling
US9312989B2 (en) * 2008-07-07 2016-04-12 Cisco Technology, Inc. Importance-based FEC-aware error-repair scheduling

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