CA1157592A - Method of clock rate matching plesiochronous signals - Google Patents
Method of clock rate matching plesiochronous signalsInfo
- Publication number
- CA1157592A CA1157592A CA000365191A CA365191A CA1157592A CA 1157592 A CA1157592 A CA 1157592A CA 000365191 A CA000365191 A CA 000365191A CA 365191 A CA365191 A CA 365191A CA 1157592 A CA1157592 A CA 1157592A
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- Prior art keywords
- clock rate
- audio signal
- rate matching
- signal
- bit
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/07—Synchronising arrangements using pulse stuffing for systems with different or fluctuating information rates or bit rates
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Time-Division Multiplex Systems (AREA)
- Synchronisation In Digital Transmission Systems (AREA)
- Electrophonic Musical Instruments (AREA)
- Ultra Sonic Daignosis Equipment (AREA)
Abstract
ABSTRACT
A method of clock rate matching a digitalised analogue signal to a data flow having a pulse frame structure which includes channels (ZKO to ZK31) for the data (Kl to K31)and additional transmission capacity for signals (UR-Sy, Zl to Z17) other than data., the digitalised analogue signal (TnO to Tn31) and data flow having mutually plesiochronous clock rates, said method including the steps of inserting the digital bits of the digitalised analogue signal (TnO to Tn31) into respective bit time slots of a plurality of consecutive channels of each pulse frame, inserting into vacant bit time slots of the additional transmission capacity (ZK16) a clock rate matching signal (++,--) indicating whether the clock rates are effectively synchronous within predetermined limits or have a positive (++,++) or negative (--,--) deviation relative to each other outside said limits, and a reference bit position difference signal (B) indicative of the number of bits in-a pre-determined portion (ZKl) of the channels (ZKl to ZK3) in each pulse frame occupied by the digitalised analogue signal, adjusting, when said deviation is outside said limits, the number of bits (B) in said predetermined channel portion (ZKl) such that said-clock rate matching signa1 (++,--) will again indicate effectively synchronous clock rates, and, where necessary inserting into a vacant portion (R2,ZK16) of said additional transmission capacity, a portion (X) of the digit-alised analogue signal omitted from said predetermined channel portion (ZKl) as a result of said adjustment.
A method of clock rate matching a digitalised analogue signal to a data flow having a pulse frame structure which includes channels (ZKO to ZK31) for the data (Kl to K31)and additional transmission capacity for signals (UR-Sy, Zl to Z17) other than data., the digitalised analogue signal (TnO to Tn31) and data flow having mutually plesiochronous clock rates, said method including the steps of inserting the digital bits of the digitalised analogue signal (TnO to Tn31) into respective bit time slots of a plurality of consecutive channels of each pulse frame, inserting into vacant bit time slots of the additional transmission capacity (ZK16) a clock rate matching signal (++,--) indicating whether the clock rates are effectively synchronous within predetermined limits or have a positive (++,++) or negative (--,--) deviation relative to each other outside said limits, and a reference bit position difference signal (B) indicative of the number of bits in-a pre-determined portion (ZKl) of the channels (ZKl to ZK3) in each pulse frame occupied by the digitalised analogue signal, adjusting, when said deviation is outside said limits, the number of bits (B) in said predetermined channel portion (ZKl) such that said-clock rate matching signa1 (++,--) will again indicate effectively synchronous clock rates, and, where necessary inserting into a vacant portion (R2,ZK16) of said additional transmission capacity, a portion (X) of the digit-alised analogue signal omitted from said predetermined channel portion (ZKl) as a result of said adjustment.
Description
1 1575~2 The invention relates to a method of clock rate matching plesiochro-nous signals, particularly clock rate matching in respect of a digitalised (converted into digital form) analogue signal to a data flow having a pulse frame structure which includes channels for the data and additlonal transmission capacity for signals other than data, the digitalised analogue signal and data flow having mutually plesiochronous clock rates. The data flow can be organis-ed in frames and super frames for telephone quality digital speech transmis-sion with characteristic bits for characteristic transmission whose clock rate is plesiochronous to the clock rate of the digital audio signal, thus the two clock frequencies possess a slight deviation of e.g. 10 ~ to 10 7. The digi-talised analogue signal may be an audio signal as referred to hereinafter.
The term "audio signal" is to be understood to include sound programs, such as transmitted from a concert hall to a broadcast transmitter, with a bandwidth of, for example, 7 kHz or 15 kHz.
If the conversion of an analogue sound broadcast signal into digital form is controlled for example using a clock rate of a digital signal connec-tion for 2Mbit/s-signals ~Siemens system DSV2, previously PCM30), the insertion of the audio signal data flow into the pulse frame of the DSV2 system and the co-exploitation of the possibly following further digital hierarchy stages is non-problematical. H~wever applications are conceivable in which the analogue/
digital conversion (A/D conversion) of the audio signal takes place at a dis-tance from the devices of the DSV2 system and for various reasons it is not pos-sible to use the same clock rate. Ihe ~/D conversion must ~hen be carried out using a locally produced clock rate which is plesiochronous to the clock rate of the DSV2 system.
~ 157592 In these situations clock rate matching is necessary to achieve insertion of the digital audio signal into the pulse frames of the DSV2 system.
A plurality of clock rate matching methods are known for combining the data flows of a plhrality of digital "sub-systems" having clock rates which are plesiochronous to one another to form a "super system". These methods may be split into those which do involve and those which do not involve information loss. If it were desired to use clock rate matching involving information loss in tha audio signal insertion mentioned above, in order not to lose word synchronism it would be necessary to tolerate the omission or the repetition of an entire code word from time to time. Investigations carried out by the present applicants have indicated that this measure would result in a fall in quality in the audio signal which wo~ld be unacceptable to the listener when the clock rate deviation exceeds 10 7.
Clock rate matching methods which do not involve information loss in which the clock rate matching takes place bit-wise are known from the "Nachrichtentechnischen Fachher-ichten No. 42, 1972", PCM-Technik, VDE-Verlag GmbH Berlln-Charlottenburg, pages 235,244 and from the magazine "Elektronik", Vol. 6/1978, pages 78 to 83. In these methods, at an agreed point within the frame - generally of a "super system" - blank bits are interposed (positive clock rate matching) or information bits are gated out ~negative clock rate matching). This procedure must be communicated by means of additional capacity available -1 ~57~92 in the pUlse Erame to the rece~ver which cancels the manipu]ation whlch has been effected at the transmitting end and reproduces the orlginal clock rate.
In addition to the procedures which use positive clock rate matching or nega-tive clock rate matchlng ancl in which in the case oE positive matching the clock frequency of the "suE system'~ is less than the clock frequency oE the available data flow whereas in negative matching the clock frequency of the "sub system" is higher than that of the available data flow, the two possibi-lities can be combined as positive/negative clock rate matching. In this case it is possible to compensate relative clock rate deviations in both positive and negative directions.
The multiplex system which is disclosed in the "Taschenbuch der Fernmeldepraxis 1979" pages 13 to 41 is suitable both for digital transmission of audio signals and for the comE.ined transmission of audio signals and tele-phone signals in the pulse frame of the DSV2 system.
~ccording to a broad aspect of the invention there is provided a method for clock rate matching a digitalized audio signal to a data flow organized in pulse frames and super frames for telephone quality digital speech transmission and with characteristic bits for characteristic trans-mission whose clock rate is plesiochronous to the clock rate of the digital audio signal, characterized in that sampling tests of the audio signal repres-enting code words are transmitted continuously in a time slot comprising several telephone channels and in corresponding time slots of following pulse frames, that the clock rate matching within this series takes place through bit-wise delay, and that in each super frame a positive and a negative clock rate matching signal, in a predetermined pulse frame a digitally coded bit number of a respective reference bit position difference of the audio signal words compared with the start of the respective first time channels used for .
~ ~ ~7592 transmisslon oE the relevant audio signal~ and in addition, a bit gated out of the coded audio signal for negative clock rate matching are transmitted to associated positlons that became free during transmission of the digital audio signal over several telephone channels of the characterlstic bit.
Fig. 1 illustrates the known structure of the pulse frame and of the super frame of a DSV2 system. This pulse frame of 125,us duration con~
tains 256 bits; this corresponds to a data flow of 204~kbit/s. The pulse frame is divided into 32 channels ZK0 to ZK31. The first time channel ZK0 serves alternately to transmit a message word and a frame code word (RSY).
The seventeenth time channel ZK16 is provided mainly to transmit dialled characteristics Zl to Z15, Z17 to Z31 of the thirty telephone channels Kl to K15, K17 to K31. Sixteen consecutively transmitted pulse frames R0 to ~15 form one super frame. The synchroni~ation of the super frame is effected by -4a-means of a super frame synchronising word UR-Sy in the seventeenth time channel ZK16 of the first pulse ~rame RO. For the sake of clarity the sixteen pulse frames of a supér frame in Fig. 1 have been represented ona below another.
- The proposal disclosed in the "Taschenbuch der Fern-meldepraxis" per~its mixed use of the DSV2 system for telephone channels and audio channels. In this case the first time channels ZKO and the seventeenth time channels ZK16 are not affected by the audio transmission.`
In this digital audio transmission, channels of high quality possessing 15 kHz band width and channels of average quality possessing 7 kHz band width must be provided. In the former case the sampling frequency is 32 kHz and in the latter case 16 kHz. Both represent multiples of the samp ~ g fr~Y~cy of 8 kHz for telephone si~ls. Each sample value with the prote ~ on bits in respect of the bit errors occurring on the transmission path requires a word of 12 bits length. Therefore in one pulse frame four code words each comprising 12 bits must be accommodated for a 15 kHz audio channel and two code words each comprising 12 bits must be accommodated for a 7 kHz audio channel. Therefore six time channels ZK1 to ZK3, ZK17 to ZKl9 each comprising eight bits are used for the transmission of a 15 kHz audio channel and three time channels ZKl to ZK3 are used for the transmission of a 7 kHz audio signal. If further audio signals are to be transmitted, further time channels ZK4 to ZK6, ZK20 to ZX22 and ZK4 to ZK6 etc. are used~ The bits of two consecutive code words are also interlocked in order to provide protection against double ~ 1575~2 errors on the transnission path. As a result a 15 k~lz audio channel has an informa~ion flow of 384 kb:lt/s and an interface having a data rate of 384 kbit/s (ln the case Oe a 7 kHæ audlo channel: 192 kbit/s) is provlded between the coder/decoder devlce of the audlo signal and the DSV2 system.
Thls known method of operation has the dlsadvantage that it merely provides a synchronous insertion of the information of coded audio channels into the frame of a DSV2 system. However, this is not always possible such as for example:
- at a digital interface between a broadcasting studio and the digital network of the postal administration (or o~her authority) when the clock rates possess a permissible deviation of greater than 10 7 from one another, - in national digital networks at the interfaces between parts of these networks which are not or not yet operating in synchronism and where the clock rate deviation is greater than 10 7 and - when digital audio signals are exchanged between international networks which although in themselves synchronous, are mutuall~ plesiochronous with a clock rate deviation of greater than 10 7.
In the periodical "Frequenzl' 32, (1978) 10, pages 281 - 287 a system PCM 30 D is described, wherein for each channel within a super pulse frame packin~ information is transmitted in half of the sixteenth channel.
The channel boundaries in the pulse frame remain constant during operation.
According to this invention there is provided a me-thod of clock rate matching a digitalized analogue signal to a data flow having a pulse frame structure which includes channels for the data and additional trans~
mission capacity for signals other than data, the digitalized analogue signal and data flow having mutually plesiochronous clock rates, said method includ-ing the -6-~' .
t 1~59~
steps of inSertin~ the digital bi-ts of the digitalised analogue signal into respective bit time slots of a plurality of consecutive channels of each pulse frame, inserting into vacant bit time slots of the additional transmission capacity a clock rate matching signal indicating whether the clock rates are effectively synchronous within predetermined limits or have a positive or negative deviation relative to each other outside said limits, and a reference bit posi~ion difference signal indicative of the number of bits in a predetermined portion of the channels in each pulse frame occupied by the digit-alised analogue signal, adjusting~ when sa:id deviation is outside said limits, the number of bits in said predetermined channel portion such that said clock rate matching signal will again :indicate effectively synchronous clock rateS, and, where necessary, inserting into a vacant portion of said additional transmission capacity, a portion of the digit-alised analogue signal omitted from said predetermined channel portion as a result of said adjustment.
In one embodiment there is provided a method of clock rate matching a digital audio signal to a data flow organised in pulse frames and super frames for telephone quality digital speech transmission involving transmission of channel-associated signals as sic~nalling bits in each pulse frame, the digital audio signal and data flow having plesiochronous clock rates, said method including the steps of inserting the digital bits of the audio signal into respective bit time slots of a plurality of consecutive channels of each pulse frame of a ` ~157~92 super frame, inserting into the vacant signalling bit time slots associated with the channels ~nto which the audio signal has been in-serted, a clock rate matching signal, indicat:ing whether tlle clock rates are synchronous or have a positive or a negative deviat:ion relative to each other, and a reference bit position different ~ig-nal indicative of the number of bit time slots occupied between the beginning of the first audio signal occupied channel and the beginning of the ne~t following audio signal word, adjusting by one of the number of bits in said first audio signal occupied channel portion when said deviation corresponds to one bit time slot length, such that said clock rate matching signal can indicate synchronous clock rates and, where necessary, inserting into a vacant signalling bit time slot a bit of the audio signal omitted from said predetermined first channel portion as a result of said adjustment.
~n embodiment of this invention will now be described, by way of example, with reference to the accompanying drawings in which:-Figure 1 is a table illustrating a known form of super frame of a known data transmission system (Siemens system DSV2);
Figure 2 is a set of tables illustrating the structure of the data flow of a DSV2 system in the case of plesiochrono-us 7 kHz audio signal transmission in the synchronous state;
Figure 3 is a set of tables illustrating the structure of the data flow of the DSV2 system in the case of a positive clock rate matching of the digital 7 kHz audio signal; and Figure 4 is a set of tables illustrating the structure of the data flow of the DSV2 system in t~e case of a negative clock rate matching of the digital 7 kHz audio si~nal.
1 ~57~92 Referring to Figs. 2 to 4, three consecutive super frames have been represented one below another, each consisting of sixteen pulse frames RO to R15 which are in turn constructed from thirty-two time channels ZKO to ZK31 each containing 8 bits.
In each super frame the time channels ZKl to ZK3 (~or example) are filled with thirty-two audio signal words or code words TnO
to Tn32 each comprising 12 bits of a 7 kHz audio signal.
As can be seen from Fig. 2, each pulse frame contains a first audio signal word portion followed by a complete audio signal word followed by a second audio signal portion which supplements the first audio signal word portion of the next following pulse frame to form a complete word. The code word Tn32 supplements the code word TnO of the ollowing supex frames to form 12 hits.
By filling the three time channels ZKl to ZK3 with the coded audio signal it is possible to use the 3 times 4 bit positions which have become free in the time channels ZK16 (originally the dialled characteristics Zl to Z3 each comprising 4 bits) in pulse frames Rl,R2 and R3 for clock rate matching.
In the channels ZK16 of each super frame the first 8 bits (in the pulse frames Rl and R2) are alternately filled with a positive and a negative clock rate matching signal ++ and --.
Thus the clock rate matching signal ++ and -- is divided between the pulse frames Rl and R~. The remaining 4 bit positions in the pulse frame R3 indicate, in digital coded form, a reference bit position diference B (which in the synchronous state remains constant) between the audio signal code words Tnl, Tn3, Tn5 to Tn31 and the beginning of the time channel ZKl. If, for example, the reference bit position difference B = 5, it is transmitted as a bit sequence OLOL. The negative clock rate matching signal -- represents the inverted positive clock rate matching signal ~+.
_g_ ~15759~
The available 4 bit positions in the pulse frame R3 can be used for ~he redundant transmission of any one of the 12 different reference bit position differences B possible in 12-position audio signal words. The continuity of transmission of the existing reference bit position difference allows the relative positions of the coded audio slgnal words to be determined at the receiving end following an interruption in the connection.
The synchronous state "no clock rate matching necessary"
does not requlre to be seperately txansmitted as the regular sequence +~ -- etc. of the alternately positive and negative clock xate matching signals does not trigger any reaction in the receiver.
Fig. 3 illustrates the situation of a positive clock rate deviation, i.e. here the clock frequency of the audio signal is less than the corresponding clock frequency o the DSV2 system. If the time shi~t between the two clock rates is l bit, positive clock rate matching signals are transmitted in two consecutive super frames. The reference bit position difference B which follows the second positive clock rate matching signal is increased fromj for example, 5 bits hy a bit value 1 to 6 (OLLO) and an information-free blank bit L is inserted at a position previously agreed upon with the receiver, here as the first bit following the frame code word RS~ in the pulse frame R3. As a result the code word Tn7 is displaced for the first time by 6 bits relative to the beginning of the time channel ZKl in the pulse frame R3. This restores synchronism and in the following super frames positive and negative clock rate matching signals are transmitted alternately and commencing with the negative clock rate matching signal.
In the case of the negative clock rate deYiation S illustrated in Fig. 4 the clock fr~cy of the all~;o si~ is gr~ater than the corresponding clock frequency of the DSV2 s~stem. In order to signal this state, negative clock rate matching signals are transmitted in two consecutive super rames. As a b`it X
gated out of the audio signal must be transmitted outside the time channels ZKl to ZK3 reserved for the audio signal, it is previously agreed that the second negative clock rate matching signal need only have a length of 7 bits and that the gated out bit X is transmitted at the position of the original eighth bit of the negative clock rate matching signal. As a result the code word Tn6 in the pulse frames R2 and R3 of the second super frame in Fig. 4 only has a length of 11 bits and needs to be supplemented by the bit X to form the reguisite 12 bit word.
The code word Tn7 within this super frame now has a reference bit position difference B of 4 SOLOO). This reference bit position diference is transmitted for the first time to the receiver in the pulse frame R3 of the second super frame.
Positive and negative clock rate matching signals are transmitted alternately (commencing with the positive) in the following super frames with the reference bit position difference B = 4 which remains constant until the next clock rate matching procedure.
When a 15 kHz audio signal is transmitted for example in the six time channels ZKl, ZK2, ZK3, ZK17, ZK18, and ZXl9, 12 1 157~92 addit~onal hits are free at the positions of the omitted dialled characteristics Z17 to Zl9. These can assume other functions such as, for example, the transmission of alarms.
If an alarm transmission is also required in the case of a 7 kHz audio signal, it is generally possible to use a 7-bit word as clock rate matching signal. A single bit is then available mainly for special signal purposes (alarm) or for transmission, in the case of negative clock rate matching, of the gated out bit X. This special signal transmission ls possible since, in the event of a relative clock rate deviation of e.g. 5 . 10 7, under the most unfavourable circumstances a gated out bit X would only have to be transmitted in every thirteenth super frame.
In the embodiment described above the clock rate matching signals ~ and -- consist of 8-position and 7-position code words which are complementary to one another. Thus their Hamming distance is 8 and 7 respectively. As a result it is possible to correct up to three errors contained in these code words.
The embodiments described above offer the advantage that is is possible to use a multiplex system provided for the trans-mission of synchronously coded audio channels without chan~ing the frame structure for plesiochronous operation of the participatiny clock pulse generators. The clock rate matching ~ in the embodiments described above facilitates considerable smoothing of the clock rate to be restored in the transmitted digital audio signals and likewise the recognition of the start 1 ~57592 of the code words of the dlgital audio signal which is necessary for the digital/analogue conversion in the receiver.
A further advantage ls achieved in that wlthin A transmlssion m~twork which is in itselE operated plesiochronously, it is possible to produce parts oE a synchronous network for digital audio signal transmission using a bit rate of e.g. 192 kbit/s or a multiple thereoE, which provides switching or switch-through facilitles in the time multiple.
It is also advantageous that the invention provides an additional safeguard against transmission errors since the reference bit position difEer-ence between the start of a time channel ZK and the end of the audio signal code word inserted predominantly in this time channel in disturbance-free operation can only change in value by a step + 1 and this change can take place only after two identical clock rate matching signals transmitted in two consecutive super frames, i.e. when a positive and negative clock rate match~
ing is to be carried out. As a result transmission errors can be easily recogni~ed and corrected.
While this specification refers mainly to an audio signal, for the sake of simplicity, as the digital converted analogue signal, it is to be understood that the invention has application to the insertion of any digital converted analogue signal into the data flow of a system using a pulse frame structure with capacity for the clock matching and associated signals in addition to the digitalized analogue signal.
The term "audio signal" is to be understood to include sound programs, such as transmitted from a concert hall to a broadcast transmitter, with a bandwidth of, for example, 7 kHz or 15 kHz.
If the conversion of an analogue sound broadcast signal into digital form is controlled for example using a clock rate of a digital signal connec-tion for 2Mbit/s-signals ~Siemens system DSV2, previously PCM30), the insertion of the audio signal data flow into the pulse frame of the DSV2 system and the co-exploitation of the possibly following further digital hierarchy stages is non-problematical. H~wever applications are conceivable in which the analogue/
digital conversion (A/D conversion) of the audio signal takes place at a dis-tance from the devices of the DSV2 system and for various reasons it is not pos-sible to use the same clock rate. Ihe ~/D conversion must ~hen be carried out using a locally produced clock rate which is plesiochronous to the clock rate of the DSV2 system.
~ 157592 In these situations clock rate matching is necessary to achieve insertion of the digital audio signal into the pulse frames of the DSV2 system.
A plurality of clock rate matching methods are known for combining the data flows of a plhrality of digital "sub-systems" having clock rates which are plesiochronous to one another to form a "super system". These methods may be split into those which do involve and those which do not involve information loss. If it were desired to use clock rate matching involving information loss in tha audio signal insertion mentioned above, in order not to lose word synchronism it would be necessary to tolerate the omission or the repetition of an entire code word from time to time. Investigations carried out by the present applicants have indicated that this measure would result in a fall in quality in the audio signal which wo~ld be unacceptable to the listener when the clock rate deviation exceeds 10 7.
Clock rate matching methods which do not involve information loss in which the clock rate matching takes place bit-wise are known from the "Nachrichtentechnischen Fachher-ichten No. 42, 1972", PCM-Technik, VDE-Verlag GmbH Berlln-Charlottenburg, pages 235,244 and from the magazine "Elektronik", Vol. 6/1978, pages 78 to 83. In these methods, at an agreed point within the frame - generally of a "super system" - blank bits are interposed (positive clock rate matching) or information bits are gated out ~negative clock rate matching). This procedure must be communicated by means of additional capacity available -1 ~57~92 in the pUlse Erame to the rece~ver which cancels the manipu]ation whlch has been effected at the transmitting end and reproduces the orlginal clock rate.
In addition to the procedures which use positive clock rate matching or nega-tive clock rate matchlng ancl in which in the case oE positive matching the clock frequency of the "suE system'~ is less than the clock frequency oE the available data flow whereas in negative matching the clock frequency of the "sub system" is higher than that of the available data flow, the two possibi-lities can be combined as positive/negative clock rate matching. In this case it is possible to compensate relative clock rate deviations in both positive and negative directions.
The multiplex system which is disclosed in the "Taschenbuch der Fernmeldepraxis 1979" pages 13 to 41 is suitable both for digital transmission of audio signals and for the comE.ined transmission of audio signals and tele-phone signals in the pulse frame of the DSV2 system.
~ccording to a broad aspect of the invention there is provided a method for clock rate matching a digitalized audio signal to a data flow organized in pulse frames and super frames for telephone quality digital speech transmission and with characteristic bits for characteristic trans-mission whose clock rate is plesiochronous to the clock rate of the digital audio signal, characterized in that sampling tests of the audio signal repres-enting code words are transmitted continuously in a time slot comprising several telephone channels and in corresponding time slots of following pulse frames, that the clock rate matching within this series takes place through bit-wise delay, and that in each super frame a positive and a negative clock rate matching signal, in a predetermined pulse frame a digitally coded bit number of a respective reference bit position difference of the audio signal words compared with the start of the respective first time channels used for .
~ ~ ~7592 transmisslon oE the relevant audio signal~ and in addition, a bit gated out of the coded audio signal for negative clock rate matching are transmitted to associated positlons that became free during transmission of the digital audio signal over several telephone channels of the characterlstic bit.
Fig. 1 illustrates the known structure of the pulse frame and of the super frame of a DSV2 system. This pulse frame of 125,us duration con~
tains 256 bits; this corresponds to a data flow of 204~kbit/s. The pulse frame is divided into 32 channels ZK0 to ZK31. The first time channel ZK0 serves alternately to transmit a message word and a frame code word (RSY).
The seventeenth time channel ZK16 is provided mainly to transmit dialled characteristics Zl to Z15, Z17 to Z31 of the thirty telephone channels Kl to K15, K17 to K31. Sixteen consecutively transmitted pulse frames R0 to ~15 form one super frame. The synchroni~ation of the super frame is effected by -4a-means of a super frame synchronising word UR-Sy in the seventeenth time channel ZK16 of the first pulse ~rame RO. For the sake of clarity the sixteen pulse frames of a supér frame in Fig. 1 have been represented ona below another.
- The proposal disclosed in the "Taschenbuch der Fern-meldepraxis" per~its mixed use of the DSV2 system for telephone channels and audio channels. In this case the first time channels ZKO and the seventeenth time channels ZK16 are not affected by the audio transmission.`
In this digital audio transmission, channels of high quality possessing 15 kHz band width and channels of average quality possessing 7 kHz band width must be provided. In the former case the sampling frequency is 32 kHz and in the latter case 16 kHz. Both represent multiples of the samp ~ g fr~Y~cy of 8 kHz for telephone si~ls. Each sample value with the prote ~ on bits in respect of the bit errors occurring on the transmission path requires a word of 12 bits length. Therefore in one pulse frame four code words each comprising 12 bits must be accommodated for a 15 kHz audio channel and two code words each comprising 12 bits must be accommodated for a 7 kHz audio channel. Therefore six time channels ZK1 to ZK3, ZK17 to ZKl9 each comprising eight bits are used for the transmission of a 15 kHz audio channel and three time channels ZKl to ZK3 are used for the transmission of a 7 kHz audio signal. If further audio signals are to be transmitted, further time channels ZK4 to ZK6, ZK20 to ZX22 and ZK4 to ZK6 etc. are used~ The bits of two consecutive code words are also interlocked in order to provide protection against double ~ 1575~2 errors on the transnission path. As a result a 15 k~lz audio channel has an informa~ion flow of 384 kb:lt/s and an interface having a data rate of 384 kbit/s (ln the case Oe a 7 kHæ audlo channel: 192 kbit/s) is provlded between the coder/decoder devlce of the audlo signal and the DSV2 system.
Thls known method of operation has the dlsadvantage that it merely provides a synchronous insertion of the information of coded audio channels into the frame of a DSV2 system. However, this is not always possible such as for example:
- at a digital interface between a broadcasting studio and the digital network of the postal administration (or o~her authority) when the clock rates possess a permissible deviation of greater than 10 7 from one another, - in national digital networks at the interfaces between parts of these networks which are not or not yet operating in synchronism and where the clock rate deviation is greater than 10 7 and - when digital audio signals are exchanged between international networks which although in themselves synchronous, are mutuall~ plesiochronous with a clock rate deviation of greater than 10 7.
In the periodical "Frequenzl' 32, (1978) 10, pages 281 - 287 a system PCM 30 D is described, wherein for each channel within a super pulse frame packin~ information is transmitted in half of the sixteenth channel.
The channel boundaries in the pulse frame remain constant during operation.
According to this invention there is provided a me-thod of clock rate matching a digitalized analogue signal to a data flow having a pulse frame structure which includes channels for the data and additional trans~
mission capacity for signals other than data, the digitalized analogue signal and data flow having mutually plesiochronous clock rates, said method includ-ing the -6-~' .
t 1~59~
steps of inSertin~ the digital bi-ts of the digitalised analogue signal into respective bit time slots of a plurality of consecutive channels of each pulse frame, inserting into vacant bit time slots of the additional transmission capacity a clock rate matching signal indicating whether the clock rates are effectively synchronous within predetermined limits or have a positive or negative deviation relative to each other outside said limits, and a reference bit posi~ion difference signal indicative of the number of bits in a predetermined portion of the channels in each pulse frame occupied by the digit-alised analogue signal, adjusting~ when sa:id deviation is outside said limits, the number of bits in said predetermined channel portion such that said clock rate matching signal will again :indicate effectively synchronous clock rateS, and, where necessary, inserting into a vacant portion of said additional transmission capacity, a portion of the digit-alised analogue signal omitted from said predetermined channel portion as a result of said adjustment.
In one embodiment there is provided a method of clock rate matching a digital audio signal to a data flow organised in pulse frames and super frames for telephone quality digital speech transmission involving transmission of channel-associated signals as sic~nalling bits in each pulse frame, the digital audio signal and data flow having plesiochronous clock rates, said method including the steps of inserting the digital bits of the audio signal into respective bit time slots of a plurality of consecutive channels of each pulse frame of a ` ~157~92 super frame, inserting into the vacant signalling bit time slots associated with the channels ~nto which the audio signal has been in-serted, a clock rate matching signal, indicat:ing whether tlle clock rates are synchronous or have a positive or a negative deviat:ion relative to each other, and a reference bit position different ~ig-nal indicative of the number of bit time slots occupied between the beginning of the first audio signal occupied channel and the beginning of the ne~t following audio signal word, adjusting by one of the number of bits in said first audio signal occupied channel portion when said deviation corresponds to one bit time slot length, such that said clock rate matching signal can indicate synchronous clock rates and, where necessary, inserting into a vacant signalling bit time slot a bit of the audio signal omitted from said predetermined first channel portion as a result of said adjustment.
~n embodiment of this invention will now be described, by way of example, with reference to the accompanying drawings in which:-Figure 1 is a table illustrating a known form of super frame of a known data transmission system (Siemens system DSV2);
Figure 2 is a set of tables illustrating the structure of the data flow of a DSV2 system in the case of plesiochrono-us 7 kHz audio signal transmission in the synchronous state;
Figure 3 is a set of tables illustrating the structure of the data flow of the DSV2 system in the case of a positive clock rate matching of the digital 7 kHz audio signal; and Figure 4 is a set of tables illustrating the structure of the data flow of the DSV2 system in t~e case of a negative clock rate matching of the digital 7 kHz audio si~nal.
1 ~57~92 Referring to Figs. 2 to 4, three consecutive super frames have been represented one below another, each consisting of sixteen pulse frames RO to R15 which are in turn constructed from thirty-two time channels ZKO to ZK31 each containing 8 bits.
In each super frame the time channels ZKl to ZK3 (~or example) are filled with thirty-two audio signal words or code words TnO
to Tn32 each comprising 12 bits of a 7 kHz audio signal.
As can be seen from Fig. 2, each pulse frame contains a first audio signal word portion followed by a complete audio signal word followed by a second audio signal portion which supplements the first audio signal word portion of the next following pulse frame to form a complete word. The code word Tn32 supplements the code word TnO of the ollowing supex frames to form 12 hits.
By filling the three time channels ZKl to ZK3 with the coded audio signal it is possible to use the 3 times 4 bit positions which have become free in the time channels ZK16 (originally the dialled characteristics Zl to Z3 each comprising 4 bits) in pulse frames Rl,R2 and R3 for clock rate matching.
In the channels ZK16 of each super frame the first 8 bits (in the pulse frames Rl and R2) are alternately filled with a positive and a negative clock rate matching signal ++ and --.
Thus the clock rate matching signal ++ and -- is divided between the pulse frames Rl and R~. The remaining 4 bit positions in the pulse frame R3 indicate, in digital coded form, a reference bit position diference B (which in the synchronous state remains constant) between the audio signal code words Tnl, Tn3, Tn5 to Tn31 and the beginning of the time channel ZKl. If, for example, the reference bit position difference B = 5, it is transmitted as a bit sequence OLOL. The negative clock rate matching signal -- represents the inverted positive clock rate matching signal ~+.
_g_ ~15759~
The available 4 bit positions in the pulse frame R3 can be used for ~he redundant transmission of any one of the 12 different reference bit position differences B possible in 12-position audio signal words. The continuity of transmission of the existing reference bit position difference allows the relative positions of the coded audio slgnal words to be determined at the receiving end following an interruption in the connection.
The synchronous state "no clock rate matching necessary"
does not requlre to be seperately txansmitted as the regular sequence +~ -- etc. of the alternately positive and negative clock xate matching signals does not trigger any reaction in the receiver.
Fig. 3 illustrates the situation of a positive clock rate deviation, i.e. here the clock frequency of the audio signal is less than the corresponding clock frequency o the DSV2 system. If the time shi~t between the two clock rates is l bit, positive clock rate matching signals are transmitted in two consecutive super frames. The reference bit position difference B which follows the second positive clock rate matching signal is increased fromj for example, 5 bits hy a bit value 1 to 6 (OLLO) and an information-free blank bit L is inserted at a position previously agreed upon with the receiver, here as the first bit following the frame code word RS~ in the pulse frame R3. As a result the code word Tn7 is displaced for the first time by 6 bits relative to the beginning of the time channel ZKl in the pulse frame R3. This restores synchronism and in the following super frames positive and negative clock rate matching signals are transmitted alternately and commencing with the negative clock rate matching signal.
In the case of the negative clock rate deYiation S illustrated in Fig. 4 the clock fr~cy of the all~;o si~ is gr~ater than the corresponding clock frequency of the DSV2 s~stem. In order to signal this state, negative clock rate matching signals are transmitted in two consecutive super rames. As a b`it X
gated out of the audio signal must be transmitted outside the time channels ZKl to ZK3 reserved for the audio signal, it is previously agreed that the second negative clock rate matching signal need only have a length of 7 bits and that the gated out bit X is transmitted at the position of the original eighth bit of the negative clock rate matching signal. As a result the code word Tn6 in the pulse frames R2 and R3 of the second super frame in Fig. 4 only has a length of 11 bits and needs to be supplemented by the bit X to form the reguisite 12 bit word.
The code word Tn7 within this super frame now has a reference bit position difference B of 4 SOLOO). This reference bit position diference is transmitted for the first time to the receiver in the pulse frame R3 of the second super frame.
Positive and negative clock rate matching signals are transmitted alternately (commencing with the positive) in the following super frames with the reference bit position difference B = 4 which remains constant until the next clock rate matching procedure.
When a 15 kHz audio signal is transmitted for example in the six time channels ZKl, ZK2, ZK3, ZK17, ZK18, and ZXl9, 12 1 157~92 addit~onal hits are free at the positions of the omitted dialled characteristics Z17 to Zl9. These can assume other functions such as, for example, the transmission of alarms.
If an alarm transmission is also required in the case of a 7 kHz audio signal, it is generally possible to use a 7-bit word as clock rate matching signal. A single bit is then available mainly for special signal purposes (alarm) or for transmission, in the case of negative clock rate matching, of the gated out bit X. This special signal transmission ls possible since, in the event of a relative clock rate deviation of e.g. 5 . 10 7, under the most unfavourable circumstances a gated out bit X would only have to be transmitted in every thirteenth super frame.
In the embodiment described above the clock rate matching signals ~ and -- consist of 8-position and 7-position code words which are complementary to one another. Thus their Hamming distance is 8 and 7 respectively. As a result it is possible to correct up to three errors contained in these code words.
The embodiments described above offer the advantage that is is possible to use a multiplex system provided for the trans-mission of synchronously coded audio channels without chan~ing the frame structure for plesiochronous operation of the participatiny clock pulse generators. The clock rate matching ~ in the embodiments described above facilitates considerable smoothing of the clock rate to be restored in the transmitted digital audio signals and likewise the recognition of the start 1 ~57592 of the code words of the dlgital audio signal which is necessary for the digital/analogue conversion in the receiver.
A further advantage ls achieved in that wlthin A transmlssion m~twork which is in itselE operated plesiochronously, it is possible to produce parts oE a synchronous network for digital audio signal transmission using a bit rate of e.g. 192 kbit/s or a multiple thereoE, which provides switching or switch-through facilitles in the time multiple.
It is also advantageous that the invention provides an additional safeguard against transmission errors since the reference bit position difEer-ence between the start of a time channel ZK and the end of the audio signal code word inserted predominantly in this time channel in disturbance-free operation can only change in value by a step + 1 and this change can take place only after two identical clock rate matching signals transmitted in two consecutive super frames, i.e. when a positive and negative clock rate match~
ing is to be carried out. As a result transmission errors can be easily recogni~ed and corrected.
While this specification refers mainly to an audio signal, for the sake of simplicity, as the digital converted analogue signal, it is to be understood that the invention has application to the insertion of any digital converted analogue signal into the data flow of a system using a pulse frame structure with capacity for the clock matching and associated signals in addition to the digitalized analogue signal.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for clock rate matching a digitalized audio signal to a data flow organized in pulse frames and super frames for telephone quality digital speech transmission and with characteristic bits for characteristic transmission whose clock rate is plesiochronous to the clock rate of the digital audio signal, characterized in that sampling tests of the audio signal representing code words are transmitted continuously in a time slot comprising several telephone channels and in corresponding time slots of following pulse frames, that the clock rate matching within this series takes place through bit-wise delay, and that in each super frame a positive and a negative clock rate matching signal, in a predetermined pulse frame a digitally coded bit number of a respective reference bit position difference of the audio signal words compared with the start of the respective first time channels used for transmission of the relevant audio signal, and in addition, a bit gated out of the coded audio signal for negative clock rate matching are transmitted to associated positions that became free during transmission of the digital audio signal over several telephone channels of the characteristic bit.
2. A method according to claim 1 for clock rate matching a digital audio signal to a data flow organized in pulse frames and super frames for telephone quality digital speech transmission involving transmission of channel-associated signals as signalling bits in each pulse frame, the digital audio signal and data flow having plesiochronous clock rates, said method including the steps of inserting the digital bits of the audio signal into respective bit time slots of a plurality of consecutive channels of each pulse frame of a super frame, inserting into the vacant signalling bit time slots associated with the channels into which the audio signal has been inserted, a clock rate matching signal, indicating whether the clock rates are synchronous or have a positive or a negative deviation relative to each other, and a reference bit position difference signal indica-tive of the number of bit time slots occupied between the beginning of the first audio signal occupied channel and the beginning of the next following audio signal word, adjusting by one the number of bits in said first audio signal occupied channel portion when said deviation corresponds to one bit time slot length, such that said clock rate matching signal can indicate synchro-nous clock rates and, where necessary, inserting into a vacant signalling bit time slot a bit of the audio signal omitted from said predetermined first channel portion as a result of said adjustment.
3. A method according to claim 2 wherein while said clock rates are considered synchronous, the reference bit position difference signal is con-stant from one super frame to the next and the clock rate matching signal.
alternates between positive and negative deviation indications in respective consecutive super frames.
alternates between positive and negative deviation indications in respective consecutive super frames.
4. A method according to claim 3 wherein a positive deviation is con-sidered to exist when the clock rate of the audio signal is less than that of the data flow by a time corresponding to a bit time slot length and the positive deviation indication is provided by the clock rate matching signal in two consecutive super frames, a reference bit position difference signal which has been increased by unity over the value transmitted in previous super Frames being transmitted in the second of said two consecutive super frames.
5. A method according to claim 3 or 4 wherein a negative deviation is considered to exist when the clock rate of the audio signal is greater than that of the data flow by a time corresponding to a bit time slot length and the negative deviation indication is provided by the clock rate matching signal in two consecutive super frames, a reference bit position difference signal which has been decreased by unity being transmitted in the second of said two consecutive negative-indication super frames, the clock-rate matching signal in said second consecutive negative-indication super frame being shortened by one bit to provide transmission capacity for said audio signal bit omitted from said predetermined first channel as a result of said adjustment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2947226.2 | 1979-11-23 | ||
| DE2947226A DE2947226C2 (en) | 1979-11-23 | 1979-11-23 | Method for clock adjustment for a digital audio signal to a data flow |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1157592A true CA1157592A (en) | 1983-11-22 |
Family
ID=6086687
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000365191A Expired CA1157592A (en) | 1979-11-23 | 1980-11-21 | Method of clock rate matching plesiochronous signals |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0029586B1 (en) |
| JP (1) | JPS5924574B2 (en) |
| AT (1) | ATE4264T1 (en) |
| CA (1) | CA1157592A (en) |
| DE (1) | DE2947226C2 (en) |
| NO (1) | NO803526L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3146317A1 (en) * | 1981-11-23 | 1983-07-28 | Philips Kommunikations Industrie AG, 8500 Nürnberg | Method for forming a time-division multiplex signal from broadband channels or analog signals |
| DE3146466A1 (en) * | 1981-11-24 | 1983-09-01 | AEG-Telefunken Nachrichtentechnik GmbH, 7150 Backnang | Method for trunking sound broadcast signals |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2622107C2 (en) * | 1976-05-18 | 1982-04-22 | Siemens AG, 1000 Berlin und 8000 München | Method and arrangement for digital communication |
| DE2814351C2 (en) * | 1978-04-03 | 1987-03-12 | Felten & Guilleaume Fernmeldeanlagen GmbH, 8500 Nürnberg | Frame structure for a third-order digital time-division multiplex system |
| DE2826364C3 (en) * | 1978-06-16 | 1981-09-17 | Siemens AG, 1000 Berlin und 8000 München | Method for the transmission of error-protected audio program signals in the pulse frame of the PCM 30 telephone system |
-
1979
- 1979-11-23 DE DE2947226A patent/DE2947226C2/en not_active Expired
-
1980
- 1980-11-19 EP EP80107202A patent/EP0029586B1/en not_active Expired
- 1980-11-19 AT AT80107202T patent/ATE4264T1/en not_active IP Right Cessation
- 1980-11-21 CA CA000365191A patent/CA1157592A/en not_active Expired
- 1980-11-21 NO NO803526A patent/NO803526L/en unknown
- 1980-11-25 JP JP55165754A patent/JPS5924574B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0029586A1 (en) | 1981-06-03 |
| DE2947226A1 (en) | 1981-05-27 |
| JPS5924574B2 (en) | 1984-06-11 |
| DE2947226C2 (en) | 1982-11-25 |
| ATE4264T1 (en) | 1983-08-15 |
| EP0029586B1 (en) | 1983-07-20 |
| NO803526L (en) | 1981-05-25 |
| JPS5690645A (en) | 1981-07-22 |
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