WO1998007284A2 - Transcodeur et procede pour codage non en cascade - Google Patents

Transcodeur et procede pour codage non en cascade Download PDF

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Publication number
WO1998007284A2
WO1998007284A2 PCT/EP1997/003966 EP9703966W WO9807284A2 WO 1998007284 A2 WO1998007284 A2 WO 1998007284A2 EP 9703966 W EP9703966 W EP 9703966W WO 9807284 A2 WO9807284 A2 WO 9807284A2
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WO
WIPO (PCT)
Prior art keywords
transcoder
encoded samples
double
information
encoded
Prior art date
Application number
PCT/EP1997/003966
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English (en)
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WO1998007284A3 (fr
Inventor
David Fraser Chambers
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Motorola Limited
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
Application filed by Motorola Limited filed Critical Motorola Limited
Priority to AU41155/97A priority Critical patent/AU4115597A/en
Publication of WO1998007284A2 publication Critical patent/WO1998007284A2/fr
Publication of WO1998007284A3 publication Critical patent/WO1998007284A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/18—Service support devices; Network management devices
    • H04W88/181—Transcoding devices; Rate adaptation devices

Definitions

  • This invention relates, in general, to a communication system arranged to implement a transcoding operation, and is particularly, but not exclusively, applicable to method and associated signalling scheme arranged to provide a non-tandem voice coding operation in a cellular communication network.
  • GSM Global System for Mobile
  • a double encoding process In mobile communication systems, a double encoding process currently takes place. Specifically, a mobile unit will first encode speech for transmission to base station equipment over a radio frequency link, for example. Subsequently, the fixed infrastructure equipment will further encode the signals for transmission at the base station to ensure efficient and robust communication over an air-interface.
  • a mobile unit encodes a speech communication at a rate of 16kbit/s, which includes 13kbit s of sampled speech and 3kbit s of ancillary information, such as parity check and correction bits (and the like) and synchronisation information.
  • This 16kbit/s speech is multiplexed into a time-slot containing three other speech calls to produce a channel of 64kbit s on a landline, and this channel is communicated by a base station controller (BSC) to at least one fixed base transceiver station (BTS).
  • BSC base station controller
  • BTS fixed base transceiver station
  • the BTS serves a cell that is typically partitioned into distinct sectors each administered by individual transceivers, while a BSC serves a group of cells.
  • a transcoder (which provides a transposition in the coding scheme received by the BTS) de-multiplexes the channel and then encodes each speech communication as a 64kbit/s pulse code modulated (PCM) format for transparent and sequential transmission through a first Mobile Switching Centre (MSC), a second MSC and then to a second transcoder for PCM decoding for onward routing to a BSC, BTS and ultimately, perhaps, to another subscriber unit.
  • PCM pulse code modulated
  • a TRAU Transcoder Rate Adaption Unit
  • ms milliseconds
  • speech is sampled at a rate of 8000 samples per second. Therefore, bearing in mind that each sample is an 8-bit word, each TRAU frame consists of one-hundred and sixty 8-bit samples. Subsequently, transcoder operation codes these one-hundred and sixty samples as an 8-bit PCM word to provide 1280 bits of PCM information per frame (equivalent to 64kbit s).
  • the structure of the 8-bit PCM frame is indicative of a signal level, with the Least Significant Bit (LSB) being of relatively little importance in the re-construction of encoded information when compared with the relative importance of successive bits.
  • the Most Significant Bit (MSB) has the greatest effect on the re-construction of encoded information, since its bit- value in an 8-bit binary word is indicative of a level one-hundred and twenty- eight times greater than the bit- value of the LSB.
  • a method of communicating information through a transcoder arranged selectively to perform a non-tandem coding operation comprising the steps of: a) receiving the information in frames containing encoded samples; b) initially re-encoding the frames of encoded samples to produce frames of double-encoded samples containing information bits having varying importance with respect to reproduction of the information; c) periodically selecting a frame of double-encoded samples and modifying at least one information bit having relatively minor importance to the reproduction of the information within at least some of the double- encoded samples of the frame to embed a predetermined data pattern indicative of a transcoder type within the frame of double-encoded samples; d) communicating the frames of double-encoded samples to a second transcoder; e) determining whether the second transcoder responds to the predetermined data pattern to indicate transcoder compatability; and f) entering non-tandem coding operation when the second transcoder responds, whereby information is communicate
  • the second transcoder enters non- tandem coding operation in response to detecting the predetermined bit pattern, but it may enter non- tandem coding operation on a frame-by-frame basis.
  • a transcoder for communicating information to a second transcoder by selectively performing a non-tandem coding operation
  • the transcoder comprising: means for receiving the information in frames containing encoded samples; means, coupled to the means for receiving, for selectively re-encoding the frames of encoded samples to produce frames of double-encoded samples containing information bits having varying importance with respect to reproduction of the information; memory for storing a predetermined data pattern indicative of a transcoder type; means, coupled to the means for selectively re-encoding and the memory, for periodically selecting a frame of double-encoded samples and for modifying at least one information bit having relatively minor importance to the reproduction of the information within at least some of the double-encoded samples of the frame to embed the predetermined data pattern; means for selectively decoding the double-encoded samples; means, coupled to the second transcoder and the means for selectively decoding the double-encoded samples, for searching for the predetermined data pattern and for responding thereto
  • the transcoder and the second transcoder may be the same transcoder.
  • FIG. 1 is a block diagram of a communication system having transcoders arranged to implement a non-tandem voice coding operation according to a preferred embodiment of the present invention.
  • FIG. 2 is a flow diagram illustrating the performance of the non-tandem voice coding operation according to a preferred embodiment of the present invention.
  • FIG. 3 is a block diagram of a transcoder according to a preferred embodiment of the present invention.
  • FIG. 4 illustrates an exemplary format for an embedded data pattern used by the present invention.
  • FIG. 1 a block diagram of a communication system 10 having transcoders arranged to implement a non- tandem voice coding operation according to a preferred embodiment of the present invention.
  • the communication system 10 is shown in simplified form and is illustrative of a call routing mechanism between subscriber units within the communication system.
  • the subscriber units may be mobile units or may be fixed site terminads, and may be located with a coverage area served by a common BTS or in distinct cells.
  • a first subscriber unit 12 communicates data 16 (on an up-link) to a first BTS 14 over a communication link, such as a radio frequency channel or a fibre-optic link.
  • the first BTS 14 is coupled to a first BSC 18, which first BSC 18 is coupled to a first transcoder (XCDRi) 20.
  • Data 16 is therefore passed in sequence from the first subscriber unit 12 to the first transcoder 20.
  • XCDRi first transcoder
  • the first transcoder 20 is coupled to the first MSC 22 through a traffic channel resource 24 and a control channel resource 26.
  • the control channel resource is bi-directional and is arranged principally to transfer control information for system management between the first transcoder 20 and the first MSC 22.
  • a second distantly located MSC 28 is further coupled to the first MSC 22 via a traffic channel resource 30 and a control channel resource 32, while a second transcoder (XCDR2) 34 is coupled to the second MSC via a traffic channel resource 36 and a control channel resource 38.
  • the second transcoder 34 is coupled to a second BSC 40, which in turn is coupled to a second BTS 42.
  • the second BTS is arranged to relay the original data 16 to a second subscriber unit 44 over an appropriate communication medium 46.
  • the communication system 10 is illustrated and described with only limited amounts of infrastructure and subscriber equipment, although it will be readily appreciated that the system will comprise many subscriber units and many transcoders, for example.
  • Transcoder XCDRi receives an encoded speech signal (such as the 16kbit s multiplexed used speech in GSM) at block 52, and then determines at block 54 whether or not it is also receiving a transcoder ID (or address) on a control channel resource; the purpose of this transcoder address will be described subsequently.
  • an encoded speech signal such as the 16kbit s multiplexed used speech in GSM
  • block 54 determines at block 54 whether or not it is also receiving a transcoder ID (or address) on a control channel resource; the purpose of this transcoder address will be described subsequently.
  • flow proceeds to block 56 where the encoded speech is further encoded by a PCM process (or the like).
  • transcoder XCDRi determines the fr ⁇ ime number of the particular on-going communication, and subject to that frame number being the n* frame or integer multiple thereof (as determined at block 58), the transcoder XCDRi steals the least significant bit of all PCM words in that frame and substitutes these least significant bits with a data pattern indicative of the transcoder type of XCDRi at block 60 (and thereby modifies the information content of the sample).
  • the PCM encoded information is relayed (or transmitted) 62 to XCDR2. If the determination at block 58 reveals that the frame is not an integer multiple of n, then instead flow immediately proceeds to block 62 where the PCM encoded information, in this instance, is relayed to XCDR 2 .
  • the effect of stealing the LSBs of an entire frame in every n th frame (say one frame in every eight frames), and then to substitute each bit value of each LSB in a periodically selected frame with a successive bit of a predetermined data pattern (having an absolute length in bits similar to the number of samples per frame) has a negligible effect on signal re-construction (since LSBs are of relatively minor importance with respect to the sampling level of the entire word) but advantageously provides an embedded (in-band) slow-rate data channel within a speech channel environment.
  • the structure of the periodically inserted, predetermined data pattern is discussed subsequently in relation to FIG.
  • the predetermined data pattern is assigned according to the type of transcoder and is therefore retained within the transcoder for encoding and identification purposes. More specifically, according to the present invention, if is possible to identify the encoding transcoder then it is possible to achieve vo-coder by-pass (i.e.
  • non- tandem operation by either modifying the operation of the decoding transcoder or, preferably, by eliminating entirely the need for transcoder encoding and decoding in the event that the interconnected transcoders are structurally identical and that they are therefore capable of supporting direct information transfer at merely a speech encoded level.
  • a second transcoder XCDR 2 is arranged to receive 64 both PCM (double) encoded and direct speech (single) encoded information. Subsequent to receiving information, the second transcoder XCDR 2 determines whether a local By-Pass Flag has been set 66, and in the negative advances to block 68 where the second transcoder realises that the received information is PCM encoded and therefore attempts to detect the XCDRi data patterns embedded within the speech channel. If the XCDRi data pattern is not detected, then decoding 70 of the PCM information signal occurs and then the remaining speech encoded information is routed to an appropriate BSC at block 72.
  • transcoder XCDR2 transmits an identification or acknowledgement 78 on the signalling channel (i.e.
  • the signalling is ostensibly transparent to MSCs in the communication system 10, although MSCs may be utilised to route and generally control signalling on the numerous control channel resources.
  • the identification or acknowledgement may be an address of the transcoder, a pseudo random number or a dedicated handshake (or bit) response, for example.
  • transcoder XCDRi The effect of the transmission of the XCDR2 identification at block 78 can be seen in relation to the upper portion of the flow diagram used by transcoder XCDRi.
  • an affirmative response is provided in block 54, and the transcoder XCDRi enters a vo-coder by-pass mode (i.e. it commences non-tandem operation) 82 and therefore routes encoded speech (subsequently received at block 52) directly through transcoder XCDRi without double encoding with PCM, or the like.
  • the preferred embodiment of the present invention also contemplates that, prior to transmission (by-passing in this instance) of the single encoded speech from transcoder XCDRi at block 62, at least some bits of the most important bits (four in the preferred embodiment) are substituted 84 by transcoder XCDRi with a predetermined MSB pattern.
  • the predetermined MSB pattern is then utilised by the receiving transcoder (XCDR2 in this case) to confirm that non-tandem operation is occurring.
  • transcoder XCDR2 executes a vo-coder by-pass mode and enters non-tandem operation at block 88 and therefore routes speech encoded information directly to an interconnected BSC without the need for PCM (or similar) decoding in the transcoder. Subsequent to the execution of the vocoder bypass, transcoder XCDR2 will, optionally, re-transmit 90 its identification on the signalling channel to re-confirm on-going non- tandem operation. In the event that the predetermined MSB pattern is not detected at block 86, flow proceeds to block 68.
  • the purpose of the setting of the MSBs to a predetermined pattern at block 84 becomes prominent at a point in time when an originating transcoder terminates a non-tandem communication or establishes a new communication with an unknown transcoder.
  • the receiving transcoder By simply dropping the predetermined MSB pattern, the receiving transcoder immediately defaults to the appropriate double decoding format, e.g. PCM decoding, and is therefore immediately able to receive and decode the information frame.
  • feedback of the transcoder identification re-enforces bi-directional flow between the transcoders, and is of further benefit in relation to handover operation. Specifically, if the identification is conimunicated back to a transcoder originally responsible for the communication but a handover has already taken place, then no XCDR2 identification is received by the new transcoder (now responsible for the communication) and, as such, the next speech frame is automatically encoded with a double PCM format (in the specific example of GSM) meaning that no predetermined MSB pattern is imposed and the receiving transcoder defaults to a PCM decode.
  • a double PCM format in the specific example of GSM
  • transcoder XCDR2 need not necessary establish the by-pass mode upon identifying the existence of the predetermined data pattern, and that block 76 may therefore be omitted.
  • the XCDR2 identification is still transmitted, and transcoder XCDRi still enters the by-pass mode at block 82, and also sets the MSB pattern at block 84. Thereafter, it is receipt of the predetermined MSB pattern (rather than the preferred flow through block 66) that triggers the execution of the by-pass mode in transcoder XCDR2, and that in this case the the requirement for the By-Pass Flag can also be eliminated.
  • FIG. 3 is a block diagram of a transcoder 100 according to a preferred embodiment of the present invention.
  • the transcoder 100 comprises processor intelligence 102 that is capable of controlling the operation of the transcoder 100.
  • the transcoder 100 comprises a first input 104 which acts to receive encoded speech signals 106 from a BSC.
  • the encoded speech signals 106 are applied to a first switching network 108 arranged to selectively route the encoded speech signals 106 to a first output 110, under the control of the processor intelligence 102, via one of a PCM encoding function 112 or an encoding by-pass route 114.
  • the encoded speech signals 106 are passed via the encoding by- pass route 114, the encoded speech signals are further processed by the processor intelligence 102, through interconnection 116, to substitute the four most important bits (in the preferred embodiment) of the encoded speech signals 106, as previously described.
  • the double-encoded (PCM) signals are selectively (periodically) further processed by the processor intelligence 102 to embed the predetermined data pattern through connection 117.
  • the output 110 is coupled to a MSC.
  • the transcoder 100 further comprises a second input 120 coupled through at least one MSC (not shown) to another transcoder (not shown) in the commumcation system.
  • the second input provides single encoded speech signals or double encoded PCM signals 122 (in the specific and exemplary instance of a GSM environment) to the transcoder 100.
  • the single encoded speech signals or double encoded PCM signals 122 are typically input into a buffer to facilitate configuration of the transcoder into an appropriate operating mode, and in this respect the single encoded speech signals or double encoded PCM signals 122 are tapped 125 prior to the buffer 124 in order that the connected processor intelligence 102 can ascertain the presence or absence of the predetermined MSB data pattern (step 86 in the flow diagram).
  • the single encoded speech signals or double encoded PCM signals 122 are applied to a second switching network 126 arranged to selectively route the buffered signals to a second output 128, under the control of the processor intelligence 102, via one of a PCM decoding function 130 or an decoding by-pass route 132.
  • An output from the PCM decoding function 130 is tapped 134 for use by the processor intelligence 102 in determining the existence of the predetermined data pattern of the embedded slow-rate data channel, as required in step 68 in the flow diagram of FIG. 2.
  • the processor intelligence 102 is further coupled to a memory 136 for storing, amongst other things, the predetermined data pattern 138 (used to identify the transcoder type and hence the capability of non- tandem operation), and a By-Pass Flag indicator 140 (required in step 66 of the flow diagram).
  • the memory will also typically contain additional storage capacity and registers 142 for general use, as will be appreciated by the skilled addressee. In the case where the identification sent on the signalling channel (required in steps 78 and 90) is the transcoder address, this address will typically be stored in the memory 136.
  • the processor intelligence 102 is also responsive a control channel resource 144 that relays information to MSCs and other transcoders, which information controls system operation and function, as previously described.
  • FIG. 4 there is illustrated an exemplary format 160 for an embedded data pattern used by the present invention.
  • the predetermined data pattern (indicative of the transcoder type) should ideally contain no more than one-hundred and sixty bits.
  • Each of the bits in the predetermined data pattern is sequentially substituted for each LSB of each 8-bit sample of a selected frame to modify its information content and to produce the slow-rate embedded data channel.
  • a typical structure for the predetermined data pattern might include a synchronisation pattern 162, voice coding data bits 164, signalling state bits 166, spare bits 168 that may be used as an addressee field for the transcoder originating the information transfer and parity check bits 170 for error detection and correction purposes.
  • the voice coding data bits 164 would preferably identify a frame type (such as frame having either a GSM frame format, a GSM extended frame format, or a half-rate or a full-rate format) and may contain four or more bits to allow sufficient scope for defining fr ⁇ ime types likely to be encountered.
  • the signalling state bits 166 represent an additional indication of transcoder intention, and may be used to identify that the encoding scheme is either double encoded PCM, is speech 16kbit/s speech encoded or is about to change between these two extremes. As such 2-bits of information would be sufficient, with values accordingly assigned from logical 00 to logical 11. In terms of the predetermined data pattern, a technique such as HDLC (High-speed Data Link Control line) framing may be used where maximum protection is required.
  • HDLC High-speed Data Link Control line
  • the method used to identify when to apply non- tandem operation is based on sending a predetermined data pattern in-band on the least significant bits of a selected frame of the 64kbit/s voice circuits that are passed through the MSC.
  • the in-band (embedded data channel) will be ostensibly undetectable to normal voice calls.
  • 16kbit/s encoded Transcoder Rate Adaption Unit (TRAU) frames are passed directly over two bits of the 64 ⁇ 1 ⁇ 8 circuit.
  • the transcoder is normally flow controlled by the BTS channel coding process.
  • the Skbit ancillary (or header) information is adapted to ensure that up-link and down-link communications are appropriately structured to guarantee proper routing and recognition.
  • a preferred embodiment of the present invention contemplates the use of the channel coding process to implement flow control function normally dealt with by transcoders in a mobile-to-mobile subscriber unit mode, i.e. the synchronisation of the TRAU frame generation process is usually controlled by the channel coder and implemented in the transcoder. The channel coder must now be able to perform both function ⁇ u d so is adapted accordingly.
  • the present invention therefore advantageously provides a system with improved voice quality by avoiding the requirement for double decoding with a 64kbit s PCM format (for example), and provides a simple, robust and inexpensive mechanism for achieving non- tandem operation between transcoders. Furthermore, the technique of the present invention is valid for use with all current and future GSM codecs (including half rate, full-rate and extended full-rate formats), and may be used in other telecommunication networks where voice coding and/or compression is used for different phases (within the infrastructure) of a call.
  • the significance of a particular bit in relation to a particular word is dependent upon the length and structure of the word in question (which length ⁇ tnd structure is determined by the particular application), and that it is therefore only important to select a bit that is of sufficiently minor importance so as not to corrupt significantly the information relayed in the original word.
  • the present invention is not limited to this structure and therefore contemplates the positioning of the transcoders in other locations within the illustrated infrastructure, particularly in a position between the BTS and BSC.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Le fonctionnement non en tandem des transcodeurs d'un réseau de communication se fait par identification de la compatibilité des transcodeurs, ainsi que le montre la figure 2. Un premier transcodeur code d'abord en double les informations par transcodage, par exemple, des signaux vocaux codés en simple (52) en modulation par impulsions et codage (MIC) (56). Périodiquement (60), le bit le moins significatif de chaque mot suivant d'une trame codée en double est remplacé par des bits séquentiels d'une configuration de données prédéterminée (indiquant la compatibilité), de façon à produire un canal de données à bas débit intégré. Un second transcodeur, conçu à l'origine pour recevoir des trames codées en double (68), recherche la configuration de données prédéterminée et se reconfigure lui-même de façon à passer en mode dérivation de vocodeur (74-76) s'il trouve ladite configuration. Grâce à un mécanisme de rétroaction (78, 90, 54), le premier transcodeur adopte un mode dérivation de vocodeur (82-84), ce qui achemine directement les signaux vocaux codés en simple (52), par exemple, et les fait passer par le premier et le second transcodeur sans qu'il soit nécessaire d'appliquer un double codage et le décodage qui lui est associé.
PCT/EP1997/003966 1996-08-09 1997-07-21 Transcodeur et procede pour codage non en cascade WO1998007284A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU41155/97A AU4115597A (en) 1996-08-09 1997-07-21 Transcoder and method for a non-tandem coding operation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9616734A GB2316277B (en) 1996-08-09 1996-08-09 Transcoder and method for a non-tandem coding operation
GB9616734.1 1996-08-09

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WO1998007284A2 true WO1998007284A2 (fr) 1998-02-19
WO1998007284A3 WO1998007284A3 (fr) 1998-03-26

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GB (1) GB2316277B (fr)
HK (1) HK1008627A1 (fr)
WO (1) WO1998007284A2 (fr)

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Publication number Priority date Publication date Assignee Title
US6091969A (en) * 1998-08-21 2000-07-18 Motorola, Inc. Method and apparatus for inband signaling control of vocoder bypass
JP4271862B2 (ja) * 1998-08-21 2009-06-03 モトローラ・インコーポレイテッド 帯域内シグナリングを利用するボコーダ・バイパスの制御のための方法および装置
FR2792156B1 (fr) * 1999-04-06 2001-06-15 Cit Alcatel Procede et dispositif de transmission de donnees sur un canal de parole
GB2353192B (en) 1999-08-11 2004-02-25 Ericsson Telefon Ab L M Transcoder rate controller
WO2009000292A1 (fr) * 2007-06-25 2008-12-31 Telefonaktiebolaget Lm Ericsson (Publ) Technique de réduction des opérations de transcodage dans un système de télécommunication

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WO1996016521A1 (fr) * 1994-11-21 1996-05-30 Nokia Telecommunications Oy Systeme de communication mobile numerique
WO1996019907A1 (fr) * 1994-12-19 1996-06-27 Northern Telecom Limited Systeme pour le contournement de codeur-decodeur a prediction lineaire a excitation par somme vectorielle, dans une connexion amrt de station mobile a station mobile
WO1996023297A1 (fr) * 1995-01-25 1996-08-01 Qualcomm Incorporated Procede et appareil destine a la detection et au contournement du codage de la voix en tandem

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GB2316277B (en) 2001-03-14
WO1998007284A3 (fr) 1998-03-26
GB2316277A (en) 1998-02-18
HK1008627A1 (en) 1999-05-14
AU4115597A (en) 1998-03-06
GB9616734D0 (en) 1996-09-25

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