NO803526L - PROCEDURE FOR CUSTOMIZING A DIGITAL TONE SIGNAL TO A DATA FLOW - Google Patents

Abstract

1. Method for the clock rate matching of a voice frequency signal occuring in digital form to a data flow which is organized in pulse frames and superpulse frames, which serves for digital speech transmission of telephone quality, is provided with signalling bits for signalling transmission, and whose clock rate is plesiochronous to the clock rate of the digital voice frequency signal, characterized in that code words, which represent sample specimens of the voice frequency signal, are continually transmitted in a time slot covering a plurality of telephone channels, (K1, K2, K3 in fig. 1) and in the corresponding time slots of the following pulse frames, that the clock rate matching within this sequence is effected by bitwise displacement, and that in each super-frame, at those locations (Z1, Z2, Z3 in fig. 1) of the signalling bits (in ZK16) which have been released when the digital voice frequency signal is transmitted over a plurality of telephone channels (K1, K2, K3 in fig. 1) and which are assigned to said channels, there is transmitted - one positive and one negative clock rate matching signal (++or-- in fig. 2 to 4 in R1 and R2), and - in each case in pulse frame R3, the digital coded bit number of the particular reference difference (B = 5 in fig. 2, 5 and 6 in fig. 3 and 5 respectively, and 4 in fig. 4) of the voice frequency signal words (Tn1, Tn3, Tn5 to Tn31) relative to the beginning of the particular first (ZK1 to ZK3) which are used to transmit the voice frequency signal in question, and - for negative clock rate matching, the bit which has been gated out of the coded voice frequency signal (X in fig. 4).

Description

Procedure for timing adaptation of a digital tone signal to a data stream.

The present invention relates to a method for timing adjustment of a tone signal that exists in digital form, to a data stream organized in pulse frames and superframes, for digital speech transmission of telephony quality and with characteristic bits for characteristic transmission, whose rate is plessynchronous to the digital tone signal's rate, i.e. that the two taktfre--4 -7 quences have an insignificant deviation of e.g. 10 - 10

If the transformation of an analogue tone broadcast signal into digital form is controlled e.g. with the rate of a digital signal connection for 2-Mbit/s signals (DSV2, until now PCM30), the insertion of the resulting data stream into the pulse frames in DSV2 and the use of any subsequent further digital hierarchy steps are unproblematic. However, use cases can be imagined where the analogue/digital conversion (A/D conversion) takes place spatially at a distance from the devices in DSV2 and the utilization of their clocks is not possible for various reasons. For A/D conversion, only a locally sourced clock that is plesiochronous to the clock in DSV2 can then be used. In these cases, a tempo adjustment is necessary.

For summarizing the data streams in several digital "subsystems" with mutually plesiochronous clocks into a "supersystem", several clock matching methods are known. These methods can be divided into those with and those without information loss. If, for the aforementioned use case, one wanted to take into account a beat adjustment with loss of information, then this, in order not to lose word synchronicity, would mean the omission or repetition of an entire code word from time to time. Investigations carried out by the applicant have shown that the result of these precautions was a quality deterioration of the tone signal unacceptable to the listener when the beat deviation is greater than 10 <-7> Beat adjustment procedures without information loss during bitwise beat adjustment are known from "Nachrichtentechnischen Fachberichten Nr. 42, 1972" , PCM technology, VDE-Verlag GmbH Berlin-Charlottenburg, pages 235 - 244 and from the journal

"Elektronik", booklet 6/1978, pages 78-83. In this connection, at an agreed place in the frame - mostly in an "supersystem" - blank bits are added (positive beat adjustment) or information bits are sorted out (negative beat adjustment).

This sequence must be fed to the receiver with the help of additional capacity that is available in the pulse frame, which reverses the manipulation that was carried out on the transmitter side, and again produces the original beat. Alongside the methods of positive clock adaptation or negative clock adaptation, where the clock frequency in the "subsystem" in the first method is lower and in the second method is higher than the clock frequency of the available data stream, there is a combination of the two possibilities as positive/negative beat matching. In this connection, relative tempo deviations can be processed in a positive and negative direction.

The multiplex system known from the "Taschenbuch

der Fernmeldepraxis 1979", pages 13 - 41, is suitable both for digital transmission of tone signals and for combined transmission of tone and telephony signals in the pulse frame in DSV2.

Fig. 1 shows the known structure of the pulse frame and the upper frame in a DSV2. This pulse frame with a duration of 125 jas contains 256 bits, which corresponds to a data stream of

2048 kbit/s. The pulse frame is divided into 32 time channels ZKO - ZK31. The first time channel ZKO alternately serves to transmit a message and a frame characteristic word (RSy).

The seventeenth time channel ZK16 is mainly arranged for the transmission of the selection characteristics Zl - Z15, Z17 - Z31 for the thirty telephone channels Kl - K15, K17 - K31. Sixteen successively transmitted pulse frames RO - R15 form a superframe. The synchronization of the upper frame takes place by an upper frame synchronization word OR - Sy in the seventeenth time channel ZK16 in the first pulse frame RO. For the sake of overview is

the 16 pulse frames in an upper frame in fig. 1 drawn below each other.

The proposal known from the "Taschenbuch der Fernmeldepraxis" allows mixed coverage of DSV2 with telephony and tone channels. The first time channels ZKO and the seventeenth time channels ZK16 are thus not affected by the tone transmission.

With this digital tone transmission, high-quality channels with a 15 kHz bandwidth and medium-quality channels with a 7 kHz bandwidth are used. In the former case the sensing frequency is 32 kHz and in the latter case 16 kHz. Both are multiples of the sensing frequency of 8 kHz for telephony signals. Each sensing value with the protection bits against the bit errors that occur on the transmission path occupies a word of 12 bits in length. In a pulse frame, four 12-bit code words must therefore be arranged for a 15-kHz tone channel and two 12-bit code words for a 7-kHz tone channel. When transmitting a 15-kHz tone channel, six time channels ZK1 - ZK3, ZK17 - ZK19 are therefore covered per eight bits, and in the transmission of a 7-kHz tone signal three time channels ZK1 - ZK3. If additional tone channels are to be transmitted, additional time channels ZK4 - ZK6, ZK20 - ZK22 resp. ZK4 - ZK6. The bits in two consecutive code words are also shuffled together to protect against double errors on the transmission path. A 15-kHz tone channel thus has an information flow of 384 kbit/s, and there is an interface between the encoder/decode device of the tone signal and DSV2 with a data transfer rate of 384 kbit/s (for a 7-kHz tone channel: 192 kbit/s).

The known method has the disadvantage that it only requires a synchronous introduction of the information in coded tone channels in the frame in a DSV2. However, this is not always possible, as for example: at a digital cut point, between a broadcast studio and the Post Office's digital network when the rates have a permissible deviation of ^ 10 from each other,

in national digital networks, at the intersections between

those parts of this network which are not, or not yet, operated synchronously, and where the clock deviation is ^> 10 , and

in the exchange of digital tone signals between international networks which are indeed synchronous in themselves, but in relation to each other are plesiosynchronous with a time difference of >10~<7>.

The present invention is based on the task of specifying a method for beat matching, where the code word limits for the digital tone signals can shift within the allocated time channels and the chronological position of the code word limits can be easily deduced on the receiver side.

This task is solved by the invention defined in the main claim.

The sub-claims relate to advantageous further developments of the invention.

The invention provides the advantage that a multiplex system

which is arranged for the transmission of synchronously coded tone channels, without changing the frame structure, can also be used in connection with plesiochronous mode of operation of the clock generator in question. The tempo adjustment according to the invention enables extensive smoothing of the tempo of the digitally transmitted tone signals to be recovered again, as well as the identification of the start of the code word for the digital tone signal required for the digital/analogue conversion.

A further advantage obtained, by. that. parts of a synchronous network within an inherently plesiochronously driven transmission network can be realized for digital tone signal transmission with a bit transmission rate of e.g. 192 kbit/s or multiples of this, whereby time-multiplex transmission or cross-linking is enabled.

It is also advantageous that the invention provides additional security against transmission errors because the range difference in interference-free operation can only change by the value - .1 and this change is also only allowed to take place after two identical clock matching signals sent in two successive superframes, i.e. when a positive resp. negative beat adaptation took place. Transmission errors can thus be easily identified and corrected.

The invention will be described in more detail with reference to figures 2-4. Fig. 2 shows the structure of the data stream in a DSV2 with a plesiochronous 7-kHz tone signal transmission in synchronous mode, Fig. 3 shows a possible structure of the data stream with a positive, and Fig. 4 with a negative clock adaptation of the digital 7-kHz tone signal.

In fig. 2 - 4, three and three upper frames are drawn below one another, which follow each other in time, and each of which consists of sixteen pulse frames RO - R15, which in turn are made up of 3 2 time channels ZKO - ZK31 of 8 bits. In each upper frame, e.g. the time channels ZKl - ZK3 coated with 32 tone signal words or code words TnO - Tn32 a 12 bits in a 7-kHz tone signal. The codeword Tn32 complements the codeword TnO in the following superframe to 12 bits. Due to the occupation of these three time channels ZK1 - ZK3 with the coded tone signal, the three times four bit positions released in the time channel ZK16 (originally the selection characteristics Z1 - Z3 and four bits in the pulse frames RI, R2 and R3) can be used for beat matching . The first 8 bits in the pulse frames Ri and R2 are alternated per overframe driven with a positive and a negative clock matching signal, ++ and — respectively. The rate adaptation signal ++ resp. —■is thus distributed over the pulse frames RI and R2. The remaining four bit positions in the pulse frame R3 provide digitally coded the respective, in synchronous state constant reference difference B for the tone signal codewords Tn1, Tn3, Tn5 - Tn31 in relation to the start of the time channel ZKl. Is e.g. reference trial cell<n>B = 5, then it is transmitted as bit sequence OLOL. The negative timing signal — is the inverted positive timing signal ++.

With the available 4 bit positions in the pulse frame R3, the 12 possible different reference differences B for 12-position tone signal words can be transmitted redundantly. The permanent transmission of the existing reference difference at all times makes it possible, after an interruption of the connection, to determine the relative position of the coded tone signal words on the receiving side.

The synchronous state "no clocking required" does not need to be transmitted separately, since the regular sequence ++ -- ++ — etc. of the alternating positive and negative clocking signals does not trigger any reaction in the receiver.

In fig. 3 shows the case for a positive beat deviation, i.e. the tone signal's beat frequency is lower than the proportional beat frequency in DSV2. If the time shift between the two clocks is 1 bit, then, according to the invention, positive clock matching signals are transmitted in two successive superframes. The reference difference B that follows the second positive clock adaptation signal increases from e.g. 5 bits with the value 1 to six (OLLO), and at a location agreed with the receiver, here the first bit after the frame characteristic word RSy in the pulse frame R3, an informationless blank bit L is added. The code word Tn7 is thereby shifted six times for the first time bits in relation to the start of the time channel ZKl in the pulse frame R3. Synchronization is thereby given again, and alternating positive and negative clock adaptation signals are transmitted in the subsequent overframes, with the negative clock adaptation signal first.

By that in fig. 4 shows negative'beat deviation, the beat frequency of the tone signal is greater than the proportional beat frequency in DSV2. In order to signal this state, negative clock adjustment signals are transmitted in two consecutive superframes. Since a bit X extracted from the tone signal must be transmitted outside the time channels ZK1 - ZK3 reserved for the tone signal, it should be understood that the second negative clock matching signal only has a length of 7 bits, and that this extracted bit X is transmitted at the position of the original eighth bit at the clock matching signal. The code word Tn6 within the pulse frames R2 and R3 for the second upper frame in fig. 4, thereby only has a length of 11 bits and is completed to the required 12 bits using the X bit.

The codeword Tn7 within this superframe now has a reference difference B of 4 (0L00). This now existing reference difference is transmitted in the pulse frame R3 first to the receiver.

Here, too, after the clock adjustment, alternating positive and negative clock adjustment signals (with a positive start) are transmitted in the subsequent overframes with the constant reference difference B = 4 until the next clock adjustment.

When transmitting a 15 kHz tone signal, e.g. in the six time channels ZK1, ZK2, ZK3, ZK17, ZK18 and ZK19, a further 12 bits are free at the positions of the selection characteristics Z17 - Z19. These can take over other tasks such as e.g. the alarm transmissions.

In cases where an alarm transmission is desired with a 7-kHz tone signal, a 7-bit word can generally be used as the beat matching signal. 1 bit is then available for special signal purposes (alarm) or for the transmission of the negative clock adjustment for the sorted out bit X. This special signal transmission is possible because in the case of a relative clock deviation of e.g. 5 • 10 -7 in the worst case it was only necessary to transmit a sorted bit X in every thirteenth superframe.

The rate adaptation signals ++ or — is in the design example a code word with 8 or 7 positions that are complementary in relation to each other. Their signal distance is thus 8 resp. 7. It is therefore possible to correct up to three appearing errors in these code words.

Claims (4)

1. Procedure for timing adjustment of a tone signal that exists in digital form, to a data stream organized in pulse frames and superframes, for digital voice transmission of telephony quality and with characteristic bits for characteristic transmission, where the tempo of the data stream is plesiochronous with the digital tone signal's tempo, characterized by the timing adjustment taking place bitwise, and that at the positions (Zl, Z2, Z3 in fig. 1) for the characteristic bits (in ZK16) which during the transmission of the digital tone signal over several telephone channels (Kl, K2 and K3 in fig. 1) are free and are assigned to these, per upper frame is transferred a positive or a negative clock matching signal (++ respectively -- on fig. 2 - 4 in Ri and R2), further (each time in the pulse frame R3) the digitally coded bit number for the respective reference difference (B = 5 in Fig. 2, 5 or 6 in fig. 3 and 5 respectively. 4 on fig. 4) for the tone signal words (Tnl, Tn3, Tn5 - Tn31) opposite the start of the first (ZKl) of the time channels (ZKl - ZK3) used for the transmission of the respective tone signal, as well as, for negative beat matching, the one from the coded tone signal sorted bit (x in fig. 4). 2. Method as stated in claim 1, characterized in that in the event of a match between the rates of the data stream and the digital tone signal (fig. 2) in successive upper frames • - the reference difference (B) remains constant and the clock adaptation signal (++ or --) is alternately positive and negative from overframe to overframe. 3. Method as stated in claim 1, characterized in that in the case of a positive clock adaptation (fig. 3), the clock adaptation signals (++) for two follow each other gende overframes both positive, and the reference difference (B = 5 + 1 = 6), which in relation to the previous one is increased by the value 1, is transmitted first in the second overframe. 4. Method as stated in claim 1, characterized in that in the case of a negative clock adjustment (fig. 4), the clock adjustment signals (—) are for two on.each other gende overframes both negatives, and the reference difference (B = 5 - 1 = 4), which in relation to the previous one is increased by the value 1, is transmitted first in other overframe, and moreover, other is negative clock matching signal shortened by a bit, and the bit (x) extracted from the coded tone signal is transferred led instead.