DE1815962B2 - SYNCHRONIZATION PROCESS FOR ADDRESS-CODED TELEPHONE SYSTEMS - Google Patents

Description

The invention relates to a synchronization process for operating an address-coded telephone system by means of analog or digital pulse modulation, wherein each information pulse by dividing it into a group of shorter pulses and coding in the time-frequency plane (= Matrix) can carry the full address of the partner and to ensure the high density of siaiion due to the many foreign impulses difficult address recognition by the partner through suitable processing of the information - for example modified delta modulation - a low pulse frequency is provided.

Such systems (which are often referred to in the English-language literature as »RADA« = »Random Access Discrete Address«) are essentially based on the The fact that a broadband channel is potentially available to a large number of participants at the same time. but is actually used only by a small number at any given moment. The relatively low canal load by the individual participant is not only achieved by the fact that he is only a small one Fraction of the time actually speaks, but particularly advantageous because he is also in the active state during the transmission process - the channel is only used for a short time in percentage terms.

The conversion of speech into a binary train of impulses must therefore take place in such a way that the middle The frequency of the resulting pulses remains small. B. with a modified delta modulation reach;

With the usual delta modulation, steep positive edges are reproduced using the pulse train (... 1111 ...), the negative edge through (... 0000 ...), while constant input signals due to the rapid change (... 0101 ...) of their clock frequency because it is above the pass band of the receiving low-pass filter.

The addition modulo-2 of an alternating signal (... 010101 ...) to the delta signal leaves the following Impulse groups arise:

... 101010.
... 010101.

... mm.

... 000000.

ascending
descending

constant

EirmatmssiüiKi

Constant signal levels can thus be characterized either by the ü sequence or by the 1 sequence.

If they are always represented in an advantageous manner by the 0 sequence on the transmit side, then they arise on the receive side after the same modulo-2 conversion probably here and there small errors of the size of a quantization level, however, the number of pulses to be transmitted is greatly reduced: at a clock frequency of the Delta modulator of 40 kHz, the mean pulse frequency of the modified delta signal drops to values of 2

... 3 KHz. In addition, this modified delta modulation has the advantage that two! Pulses can never occur in direct succession: they are always separated by at least one zero. This fact allows the double interval to be used on the transmission side for pulse broadening, increasing the number of addresses or reducing the peak power.

Faults that occur in clusters and simulate impulses in consecutive Taki intervals are converted into an (... 010101 ...) alternating signal via the modulo-2 adder stage of the receiver and are strongly suppressed in the receive low-pass filter.

The modulation system for the message that has just been outlined in its basic features still has to be supplemented by the ability to transmit addresses . The principle of the time-frequency matrix offers itself as a simple solution , among other things because the nature of the resulting systemic disturbances only slightly affects the voice transmission with this modulation system. With this conception, the entire available bandwidth B is divided into N channels ("channel raster"); each channel comprises η discrete frequencies ("frequency raster"), of which h frequencies are used to identify the address. Each original message pulse is replaced by a group of h pulses, each of which is broadcast on one of k possible time slots within the 50-HS interval. The receiver monitors the h him allocated frequencies and feeds the incoming pulses in the delay lines of the correct length, so that all pulses of a particular group for him occur simultaneously at the output of all the delay lines and mark so don original message pulse.

The allocation of different addresses to a single device as well as the receipt of the priority call is without Difficulties possible.

When the transmission medium is heavily loaded by many active devices and / or by multipath propagation there is a certain probability that incorrect address pulses will arise in each receiver, whereas the probability of suppressing a correct impulse is much smaller and practical neglected (phase and amplitude of an interferer should have exactly the right values).

The increased false address probability has two effects, the one without countermeasures make such a transmission system unusable;

1. If the receiver demodulation channel is constantly open, all false impulses that arise from the coincidence of the h outputs of the delay lines are demodulated and lead to loud noise.

2. It is no longer possible at the same time, a narrow Time gate that runs at a rate of 40 kHz only for a few us die the coincidence circuit to be provided for this is scanned and thus the majority of all interference is eliminated on the to synchronize the desired station.

With a satisfactory solution to the synchronization problem for the time gate, the effect of the Incorrect address increased due to the high station density Likelihood to be significantly reduced; even assuming a disorder of approx. 14 - 20% of all Sampling moments due to wrong impulses would still be intelligible with exact synchronization over 85%. at the same time (unlikely)

■! «

If 13% of all useful pulses were lost (range limit), word would still be intelligible of over 60% (corresponding to a signal-to-noise ratio of »16 dB or» 8 dB).

The invention is based on the object of eliminating the deficiencies of previously known systems of the type described above, in which a high system load from numerous active interferers was practically not expected, in the event of a high station density and the effect of a high probability of disturbed addresses to be reduced by additional synchronization. According to the invention, this is achieved in that, in order to increase the frequency of addressing by the calling subscriber station, which is reduced as a result of the information processing, and thus to improve the synchronization of the station called with this address with the calling station, each calling station periodically and in larger Zeitinierviullen a longer, dense pulse sequence (eg., 20 pulses in the shortest allowable time-pitch) emits ,, which pulse sequence is encoded in the time-frequency plane with the address of the called station, and that the relative duration of these lmpulslolgc selected so short that neither the overall system load increases significantly, nor is the corresponding loss of information practically perceived.

In a practically conveniently realizable embodiment of the invention, the procedure is as follows: triggered by pressing the transmission button and from this point in time every 3 seconds the transmitter automatically emits the appropriately addressed pulse sequence 1010 ... 10, consisting of 20 "ones" and 20 "zeros " consists. Such a "binary word" takes up a time interval of 20 times 50 \ is = 1 ms. It is inserted into the language every 3 seconds by the transmission line, and replaced by a corresponding gap at the receiving end after recognition. In the receiver, a binary pass-through memory (shift register with taps) with a resolution of 50 j.ls (approx. 200 cells) records the received signal.

As soon as there are 15 or more one at the right distance of 50 us in the transit memory (shift register), he regards the signal as intended for him, deletes the contents of the memory and is synchronized at the same time. If one demands that between the ones at least; for example, there are 5 zeros Incorrect synchronization due to permanent disturbance excluded.

In order to be able to drastically reduce the time and frequency of the system load the actual information pulses are completely freed from the address, so that the address recognition and the associated synchronization exclusively by means of the nested address-coded dense pulse trains (binary words).

In many cases it can also be expedient to provide means for recognizing several different addresses in the receiver of the called station, so that the receiver is automatically synchronized to the recognized address when one of these addresses is recognized.

After all, you can - um! ■. in the recipient of the The calling station receives a kind of »receipt« for correct reception on the other side and checks it to be able to - together with the synchronization of the recipient of the called station also their Sender is automatically based on the received address

can be set so that the received address is reproduced when sending from this station.

The probability of correct recognition P ₁ of the word given by the address-coded, dense pulse train is essentially determined by the expression:

C)

(I / T

Here, P is the probability that a message pulse will not be recognized. Assuming a word intelligibility of 80% for monosyllabic words, P = 0.135 (range limit). With this value we get:

in = 20 P ■ - = ■■ 0.135

This means that in over 95% of all extra cases the Synchronization with the first binary word takes place.

Conversely, such a word can also be faked by incorrect addresses. If one calculates with an average value of Pi \ the false address probability (systemic disturbances and range limits) of 17%, the result for the probability Pi of the pretense is:

- ■ Σ (T) ■

I Il ^v '

Olli

' I Λ

2 ■ OK

ι ι

20th
0.17

In comparison with the resolution of the memory (5 ns), this means that the When the system is heavily loaded, synchronization occurs on average every 4 minutes per address. To after such a start the receiver is blocked for 3 seconds, but opens again immediately when the next package is missing.

To make a possible loss of synchronization during the call unlikely, one could reduce the requirements in the synchronized state and, for example, only the Request receipt of 10 or less one.

With such a synchronization device, it is possible to establish connections even when the system is heavily loaded build and maintain. At the same time, it can be used to synchronize any encryption devices to serve.

In special cases it is:. »It is even possible to let the sender - in agreement with the receiver - do without the complete addressing of all message impulses after synchronization and to use only two or, in extreme cases, only one impulse instead of three or four. The "wrong address probability" does not increase significantly because the system load is correspondingly smaller (Pr i ~ 20 ... 25% with the same number of speakers and only one impulse). The main advantage is a corresponding reduction in the average transmission power.

Claims (6)

Patent claims: 1. Method for operating an address-coded telephone system using analog or digital Pulse modulation, with each information pulse by dividing it into a group of shorter ones Pulses and coding in the time-frequency level (= matrix) the complete address of the partner can carry and to ensure the high station density due to the many foreign impulses difficult address recognition by the partner due to suitable processing of the information - for example modified delta modulation - this ensures a low pulse frequency marked that in order to increase the as a result of the information processing with a reduced frequency of address transmission the calling subscriber station and thus for the purpose of improving the synchronization with it Address called station with the calling station each calling station periodically and in larger A longer, dense pulse sequence (e.g. 20 pulses in the shortest permissible time grid spacing) emits which pulse sequence in the time-frequency level is encoded with the address of the called station, and that the relative duration of this pulse train is chosen so short that neither the overall system load increased significantly, and the corresponding loss of information practically is perceived. 2. The method according to claim 1, characterized in that that the pulse sequence (binary word) encompassing the address code is transmitted in certain, Compared to the duration of the pulse train, large timing intervals (e.g. every 3 seconds) in the speech signal inserted and replaced by a corresponding gap on the receiving side after detection. 3. The method according to claim 1 or 2, characterized in that for the purpose of further, more drastic Reduction of the line and frequency system load the actual information impulses be completely freed from the address, so that the address recognition and associated Synchronization exclusively by means of the activated address-coded dense pulse trains (Binary words) is made. 4. The method according to claim 1 or 2 and 3, characterized in that the receiver called station a binary pass-through memory in the form of a tapped shift register is provided, the dai received signal picks up and in the presence of a larger Number of binary "one" signals following one another at the correct distance automatically deleted which simultaneously synchronizes the recipient of the called station to the address he follows. 5. The method according to claim 1 or 2, 3 and 4, characterized in that the receiver called station means for recognizing several different addresses are available and that the Recipients are automatically synchronized to the recognized address when one of these addresses is recognized will. 6. The method according to claim I or 2, 3 and 4 and according to claim 5, characterized in that that together with the synchronization of the The recipient of the called station also automatically sends its sender to the received address is set so that when sending from this station the received address is reproduced will.