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
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0036—Systems modifying transmission characteristics according to link quality, e.g. power backoff arrangements specific to the receiver
  • H04L1/0038—Blind format detection
• • 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
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
• • 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
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0014—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the source coding
• • 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
  • H04L1/0046—Code rate detection or code type detection
• • 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
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
  • H04L1/0032—Without explicit signalling
• • 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
  • H04L1/0059—Convolutional codes

Definitions

• the present invention relates to a method of transmitting digital packets which have been the subject of transmission coding, a method according to which the nature of the coding used is not transmitted.
• the field of the invention is therefore that of digital transmissions by means of packets liable to have undergone different encodings, however all belonging to a set of available encodings.
• a transmitter uses transmission coding to produce a packet from a message
• this field will be presented with reference to digital cellular radio systems of the GSM type. These systems have the advantage of being widely used and the support of a concrete example will make it possible to clarify the description of the invention.
• an analog speech signal is digitized in 13-bit samples at the rate of 8 kHz, or a speed of 104 kilobits per second.
• GSM currently provides three types of source coding to reduce the bit rate of this digital signal. Full-speed coding, enhanced full-speed coding and half-speed coding, producing a signal at 13, 12.2 and 5.6 kilobits per second respectively from the previous signal.
• the signal undergoes channel coding to protect it from the vagaries of radio transmission.
• the resulting signal has a bit rate of 22.8 kilobits per second in the case of full speed and 11.4 in the case of half speed.
• the immediate solution consists in reserving, within the packet, positions or mode bits to ensure this function.
• the receiver begins by detecting these mode bits to determine the decoding means suitable for the transmission coding which has been applied by the transmitter.
• mode bits must also undergo special coding, mode coding, intended to ensure their protection during transmission.
• the mode coding unlike transmission codings, must be unique so that the receiver can unambiguously identify the transmission coding used.
• the mode bits must therefore be coded independently of the useful content of the message which is subject to transmission coding. This mode coding is of course intended for the most difficult transmission conditions. severe and it is common to use a convolutional code in this case.
• the minimum length of the coded word must be equal to five times the product of the constraint length by the inverse of the coding rate. It follows that for a rate 1/3 and for a constraint length equal to 5, appropriate typical values, the minimum size of the coded mode is 75 bits. We realize that if we provide 4 transmission codes, information which results in two bits for the mode, it is necessary to use 75 bits of the packet to transmit this information under the best conditions.
• the transmission efficiency is defined as the ratio of the number of bits carrying the information to be transmitted to the number of bits transmitted, it appears that this efficiency is far from optimal.
• US Pat. No. 5,230,003 teaches a decoding system studied to distinguish signals encoded according to different available encodings, the encoding used not being transmitted.
• a decoder is required for each coding available. The number of decoders can become large when many codings are used.
• reception equipment for receiving a digital packet which has been the subject of a transmission coding selected from among a plurality of available codings, and it includes decoding means for decoding this packet according to the coding of transmission; transmission coding belonging to a reduced set of possible codings, this equipment comprises for each of the possible codings a decoder receiving a part of the packet to produce the reliability of the associated decoding, and it further comprises means for identifying the decoding means as those which correspond to the decoder having produced the best reliability.
• the invention also relates to transmission equipment intended to transmit a sequence of coded messages by means of packets, the last message of this sequence being subjected to a coding identified in a set of codings available and different from the coding applied to the first message of thereafter, these packets comprising on the one hand a section useful for receiving data and on the other hand guard bits, this equipment comprising means for arranging each of the coded messages in the whole of the useful section of the corresponding packet; moreover, the coding applied to the last message belongs to a reduced set of possible codings.
• the first packet of a transmission is assigned a predetermined available coding.
• the possible encodings are the following available encoding, that which is identical to, and that which precedes the encoding of the preceding packet.
• the possible codings are convolutional codings each affected by a separate coding scheme.
• the identification of the decoding means can be carried out by means of two coding rates.
• FIG. 1 the diagram of a receiver allowing the implementation of the invention
• the mode which indicates the transmission coding to which a packet has been subjected is not transmitted by the transmitter.
• Mode selection is based on the estimated signal-to-noise ratio of the link between the transmitter and the receiver. This report therefore results from measurements made at the receiver and which are passed on to the transmitter so that the latter selects the appropriate transmission coding.
• the signal-to-noise ratio measurements are part of the state of the art so that they will not be more detailed.
• the transmitter selects one of the modes according to the signal to noise ratio C / I estimated as follows: - mode 1: C / I> 13 dB
• the convolutional channel codings of the different modes produce packets which have the following characteristics:
• the receiver is designed to decode according to any one of the modes using the Viterbi algorithm.
• This algorithm produces, for an analyzed word, a decoded word as well as a metric.
• This metric indicates the distance between the analyzed word and a reference word which, subjected to this algorithm, produces the same decoded word. This metric is therefore a measure of the reliability of the decoding.
• the maximum likelihood detection algorithm proceeds according to a fully specified coding scheme, namely in particular the rate of the code, the polynomials used and the position in the packet of the different coded bits. It calculates for different possible sequences of bits the metrics that they present with respect to the word analyzed in order to finally retain the sequence of bits affected by the highest metric.
• this algorithm operates according to a coding scheme which does not correspond to the coding used for the analyzed word, the various sequences of bits will present metrics which are substantially similar. If, on the other hand, the chosen coding scheme is adapted to the word analyzed, a particular series of bits will have a much higher metric than the others, and this is therefore the solution sequence.
• the receiver will therefore take advantage of the disparities in the different channel codings to detect the transmission coding used in a received packet. To this end, it will try to decode this packet according to each of the channel codings to retain the one which has the highest metric at output.
• a received packet can only be affected by the preceding mode, the same mode or the mode following that of the previous packet: a mode 4 packet may be followed by a mode 3 or 4 packet, and a mode 2 packet may be followed by a mode 1, 2 or 3 packet. It is further provided that the first packet received must be mode 4 so that there is no ambiguity at the start of the transmission.
• This receiver includes a TRUNC truncation circuit which receives a packet B to keep part of it S, the first 138 bits in this case.
• the receiver keeps in memory the coding mode Pr of the previous packet.
• It includes a first DECl decoder which decodes the part S of the packet according to the mode (Pr-1) to produce the corresponding metric Met (Pr-1).
• It includes a second decoder DEC2 which decodes the part S of the packet according to the Pr mode to produce the corresponding metric Met (Pr).
• Pr-l the third decoder DEC3 is of no interest and its output metric Met (Pr + 1) is also made zero.
• the receiver also includes a comparison circuit COMP which searches for the winning mode m having produced the highest metric:
• Met (m) Max [Met (Pr-l), Met (Pr), Met (Pr + l)]
• This receiver naturally includes decoding means MD which receive the entire packet B to produce a word decoded by application of the Viterbi algorithm parameterized according to the winning mode m.
• these decoding means are not necessarily produced with an independent circuit.
• these decoding means may be limited to decoding the part of the packet which has not already been decoded by the decoder having produced the highest metric.
• this differentiation value F takes the following values:
• the two modules are loaded again with the first 72 bits of the packet. If the differentiation value F is 3, the winning mode m is the only possible one which has the rate 1/3, that is to say mode 4. If, on the other hand, the differentiation value is equal to 2, the two modules are now loaded with the following 72 bits of the packet. If the new differentiation value F is 3, the winning mode m is mode 3 while in the opposite case, it is mode 2 which is winning.
• the 72 bits following the I38 th packet bit are taken into account. If the differentiation value F is 3, the winning mode m is the only possible one which has a rate 1/3, that is to say mode 3. If on the other hand the differentiation value is equal to 2, we load now the two modules with the 72 bits following the 234 th bit of the packet. If the new differentiation value is 3, the winning mode m is mode 2 and if not, it is mode 1 which is winning.
• the two modules are loaded with the 72 bits which follow the 234 th packet bit. If the differentiation value F is 3, the winning mode is mode 2 while in the opposite case, it is mode 1 which is winning.
• the different modes are distinguished here by the coding rates which differ according to the position of the bit in the packet.
• the different modes should have a different coding scheme, whether it be the coding rate, the nature of the polynomials or the position of the coded bits.
• the invention applies regardless of the type of coding used and is not limited to convolutional codes. It is only important to be able to distinguish on reception, with good reliability, the nature of the coding of a received packet by searching for that of the possible codes from which it is most probably derived.
• the invention further relates to a transmitter intended to transmit packets to the receiver.
• This transmitter has the advantage of being simplified since it does not transmit the nature of the transmission coding used for the packet.
• a packet results from the coding of the succession of a head section, a useful section, and a tail section.
• K convolutional code of constraint length
• the guard bits therefore frame the useful section.
• This useful section corresponds to the exploitable part, it being understood that the guard bits cannot be used to transmit information.
• Guard bits that are predetermined are used only during decoding. According to the invention, the entire useful section can be used to transmit the data which is the subject of the transmission between the transmitter and the receiver. The nature of the transmission coding is not included in the useful section, even when the coding has changed compared to the previous packet.
• the transmitter therefore comprises a control circuit CC which receives the nature N of the coding to be applied to the message W which should be conveyed by means of the next packet. It also includes a coding unit COD which receives this message W to code it as a function of the coding parameters Pa supplied by the control circuit CC. In this case, the control circuit CC produces the coding scheme based on the required channel coding.
• the transmitter also includes a register ⁇ which corresponds to the useful section of the packet. This register is loaded in full with the coded message MC originating from the coding member COD.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Quality & Reliability (AREA)
• Error Detection And Correction (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Communication Control (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9527193

Family Applications (1)

Country Status (6)

Citations (6)

• 1998
  • 1998-06-03 FR FR9807255A patent/FR2779591B1/fr not_active Expired - Fee Related
• 1999
  • 1999-06-03 CN CN 99808584 patent/CN1309854A/zh active Pending
  • 1999-06-03 EP EP99925057A patent/EP1084544A1/fr not_active Withdrawn
  • 1999-06-03 WO PCT/FR1999/001314 patent/WO1999063700A1/fr not_active Application Discontinuation
  • 1999-06-03 JP JP2000552803A patent/JP2002517946A/ja active Pending
  • 1999-06-03 CA CA002334097A patent/CA2334097A1/fr not_active Abandoned

Patent Citations (6)

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