Methods of and Apparatus for the Encoded Transmission of Information

This invention concerns methods of and apparatus for the encoded transmissions of information in which message elements of equal length are interchanged in time at the transmitter by storage and delay and are re-interchanged at the receiver. In known methods of this kind the storage times are chosen so that no element of the original message (clear message) is omitted from the encoded message and also so that no two or more elements appear simultaneously.

In accordance with a known proposal in British Patent No. 1,353693 several stores are employed, the capacity of each corresponding to one message element. At equal time intervals, corresponding to the length of one message element, there is determined by a quasi-random control signal the number of that one of the stores from which an element of the encoded message is to be withdrawn and into which at the same time an element of the clear message is to introduced. In this method excessive storage times can be avoided by automatic withdrawal of a message element from any store when a predetermined maximum storage time has been reached. In this method of coding, the delay times of the message elements are not uniformly distributed: the probability decreases with increasing delay, while the extreme delay does not appear very frequently. It is true that a certain equalisation of this cryptologically undesirable distribution is possible by operating the individual storeswith unequal maximum delay times. The cost of carrying out this operation automatically is however considerable and in addition it is undesirable for reasons of cryptological security that the storage times shall be determined to an increased extent by the individual storage capacity and not in the first place by the quasi-random control signal.

According to other proposals, given British Patent No. 1,356,970, the message elements are stored in shifting registers, in which the input and withdrawal locations are determined by quasi-random control signals. After the withdrawal of an element the respective storage location thus remains temporarily empty. This leads to inefficient utilization of the available storage capacity and thus to relatively high cost.

According to the present invention, disadvantages of known proposals are reduced or overcome by the provision of a method for the encoded transmission of data, in which data elements of equal length are, by storage and delay for different times, interchanged in timing at the transmitting station and are re-interchanged at the receiving station, wherein there is allotted to each element introduced into a store for delay an age number which, after the lapse of each one element length of storage time at the two stations, is altered in the corresponding sense by one step; there are generated at both stations corresponding age signals changing irregularly within certain limits; at one station the age number allotted to an applied element has at first a definite first extreme value and alters stepwise until it corresponds with a simultaneously appearing age signal, whereupon the element is withdrawn from the store and is replaced in the store by a new element of the input signal; at the other station the age number allotted to a newly applied element is as large as the age signal appearing at the same instant; it is thereafter altered stepwise in the same sense as at the one station until it corresponds with a second extreme value, whereupon the element is withdrawn from the store and is replaced in the store by a new element of the input signal.

The invention also provides apparatus for encoded transmission of data including means whereby data elements of equal length are, by storage and delay for different times, interchanged in time at a transmitting station and are re-interchanged at a receiving station, said apparatus including an age generator for generating a series of quasi-random varying age signals which determine the storage times of individual elements, and age/location converter wherein there are derived from the age signals store control signals which actuate change-over switches, by way of which the individual data elements are applied to or withdrawn from the stores of a delay device.

It is thus possible for the clear message to comprise a train of impulses, as is the case in the transmission of digital data; however it is also possible to transmit an analog signal (e.g. an audio signal) or a train of impulses of changing amplitude (e.g. sampling values of an audio signal). For simpler storage the latter may advantageously be replaced by a corresponding train of digital impulses derived by binary coding or by some other method of coding. The elements to be interchanged to produce the coded signal consist of sections of the clear signal of predetermined length; that is, they comprise one or more amplitude modulated impulses or one or more bits of a train of digital impulses.

Reference will now be made to the drawings in order to describe known arrangements and characteristics of the invention, as well as some embodiments and details of the invention. The drawings comprise FIGS. 1-29, of which:

FIGS. 1 and 2 are block diagrams which illustrate known arrangements;

FIG. 3 is a block diagram which illustrates the method of the invention including age determination by random counting and determination of the storage location from the predetermined age for optimum storage utilization;

FIGS. 4 and 5 are block diagrams which illustrate the transmitter and receiver age/position converters respectively;

FIGS. 4a and 4b are block diagrams showing the switch connections capable of being established by the switching of FIG. 4;

FIGS. 6 and 7 are block diagrams which illustrate apparatus respectively employed at the transmitter and at the receiver for age correction which avoids storage for delay times which are unsuitable and lead to the limiting age being exceeded;

FIG. 8 is a graphical representation of the ageing with mutually independently operated stores (parallel store) shown in simplified fashion as to the manner of relationship between the stores and the waveforms;

FIGS. 9 and 10 are block diagrams which illustrate respectively the conversion of the age control with series and with parallel storage;

FIGS. 9a-9c are block diagrams of the switch connections of the permuting unit of FIG. 9;

FIGS. 10a-10c are block diagrams of the switch connections of the permuting unit of FIG. 10;

FIG. 11 is a graphical representation of the ageing with a series store shown in simplified fashion to explain the relationship between the waveforms and the stores;

FIG. 12 is a graphical representation of the ageing at the transmitter and receiver (both shown in simplified fashion), as a basis for explaining ageing correction;

FIGS. 13-16 are block diagrams which illustrate arrangements for age determination with quasi-random coding signals and for ageing correction;

FIGS. 17 and 19 respectively show block diagrams which illustrate encoding arrangements with age storage for transmitter and receiver operation and FIG. 18 shows the appropriate auxiliary signals helpful in explaining the operation thereof;

FIGS. 20 and 21 are block diagrams which illustrate serial storage without random access with clock generator and FIG. 22 shows a representation of the auxiliary signals derived therefrom;

FIGS. 23 and 25 are block diagrams which illustrate serial storage with smoothed sampling values, and FIGS. 24 and 26 show the appropriate timing signals and control signals developed thereby;

FIGS. 27-29 are block diagrams which illustrate a modification of the transmitter.

FIGS. 30 and 31 are graphs which illustrate the operation of program transformers which are typified in FIGS. 32 through 34.

FIGS. 32 through 34 are block diagrams illustrating several program transformers.

FIG. 35 is a table illustrating several alternative programs which may be utilized in connection with the program transformer of FIG 34.

In the known arrangement shown in FIG. 1 elements of uniform length of the clear signal x are each entered by way of switches U.sub.1, U.sub.2 . . . U.sub.M into a store R.sub.1, R.sub.2, R.sub.M of the delay device VE, and after varying times are withdrawn again as elements of the encoded signal y. Entry and withdrawal takes place simultaneously, so that the store always remains occupied. The switches are actuated by control signals n.sub.1, n.sub.2, . . . n.sub.M (number signals) which are generated in number generator NG and appear quasi-randomly with equal probality. The disadvantages of such arrangements have already been explained.

In the arrangement of FIG. 2 a uniform age-distribution of the stored elements is avoided by developing in age generator AG age numbers of equal probability, which as age signals d.sub.0, d.sub.1, . . . d.sub.M actuate the switches U.sub.0, U.sub.1 . . . U.sub.M for withdrawal of elements of the encoded signal y from selected individual stages Q.sub.1, Q.sub.2 . . . Q.sub.M of a delay chain in delay device VE. These stages are thus only occupied from time to time, so that the cost for long delay times becomes relatively high.

In accordance with the invention, as shown in FIG. 3, an element of the clear signal x is applied to the individual stages of the signal store SP by way of one of the switches U.sub.k and an element of the encoded signal y is simultaneously withdrawn from the same store R.sub.k, so that all stages remain occupied by signals. These switches U.sub.k are however actuated by control impulses i, which are developed in an age/location converter AP from the age signals d, so that all delays appear with the desired mean frequency, while the limiting age value is not exceeded and repetition or omission of individual elements is avoided. Optimum utilization of the store can thus be ensured while non-uniform age distribution is avoided.

The construction and operation of an age/location converter AP will now be described with reference to FIG. 4. A delay device VE again contains individual stores R.sub.1 . . . R.sub.M with the respective switches U.sub.1 . . . U.sub.M. A further switch U.sub.0 allows the undelayed passage of individual message elements. During entry and withdrawal of a message element from a store R.sub.k or for direct passage of an element the respective switch U establishes the connections shown in FIG. 4a, while the connection shown in FIG. 4b is present in all the other switches. The connection of FIG. 4a is established in a switch U.sub.k by an appropriate control signal i.sub.k. These storage control signals are developed in an age/location converter AP from age signals d.sub.B which are obtained in binary coded form from an age generator AG. Each age control impulse i.sub.k starts a counter Z.sub.k so that the instantaneous counter condition (age count) corresponds to the storage time of the element since the entry of a message element, expressed in element lengths. If, for example, an element delayed or "aged" by 4 element lengths is to be taken from the delay device VE, then through the application of an age signal d.sub.B = 100 (which is the binary coded form of the decimal number 4) to the age/location converter AP, the counter which is now set at 100 is selected. This can be effected for example by means of a coincidence circuit K.sub.k, which responds to coincidence between the instantaneous counter signal (age signal) z.sub.k and the age signal d.sub.B. Upon coincidence there appears at the output of coincidence circuit K.sub.k an impulse i.sub.k which is applied to switch U.sub.k to effect withdrawal of the element of desired age and the entry of a new element into the store R.sub.k. It must naturally be assumed that the age signals are of such a nature that the age limit is not exceeded and that no omission or repetition of individual elements occurs. This is ensured by a special age corrector AK which frees the preliminary age signals a.sub.B developed in AV from defects which may occur. The preliminary age signals are derived for example from quasi-randomly occurring encoding signals w by the use of logic circuits, as described below with reference to FIGS. 14 and 16. The encoding signals may be generated by a known arrangement (see Swiss Patent Specification No. 361,839). This arrangement is described in some detail in the appendix hereto. For decoding at the receiver the elements of the received encoded signal are brought again into the original sequential order of the clear signal by repeated individual delays. Each element receives, through the delay at the transmitter and the additional delay at the receiver, the same total delay, e.g. by N elements, so that the decoded signal x* is always displaced by N elements with respect to the original clear signal x. The decoding apparatus shown in FIG. 5 again contains an arrangement AG* for deriving coded age signals d.sub.B * , which correspond with the age signals d.sub.B at the transmitter, and an arrangement VE* for delaying the signal elements. An element already delayed at the transmitter by h element lengths must be delayed by a further N-h element lengths. To monitor this additional ageing there are provided in age/location converter AP* the counters Z.sub.1 * . . . Z.sub.M *, which like the counters at the transmitter are advanced by clock pulses in rhythm with the element changes. At the receiver the age counting begins each time with the age number of the respective element which was reached at the transmitter. During the storage of the element at the receiver the count is advanced until it reaches the limiting age of N elements, i.e. until a count of N is reached. At this instant there appears at the counter an age limit impulse i.sub.k, which by actuation of the switch U.sub.k effects the withdrawal of the element from the store R.sub.k and its advance as the clear signal x* . At the same time there is applied to the same store the just arriving element of the received signal y*. There is also supplied to the age store V.sub.k the individual store control impulse i.sub.k agreeing with v.sub.k, by means of which the age signal associated with the new element received is conducted to the counter Z.sub.k * as a starting signal z.sub.k *. The counter is thus advanced again until the number N is reached, that is, upon attaining a total ageing of the element by N element lengths, whereupon this element also is introduced into the clear signal x*.

If the ageing at the transmitter already amounts to N element lengths, then additional storage at the receiver must not occur. The age signal d.sub.B * is then responded to only by a decoder V.sub.O sensitive to this signal, which yields a switching impulse i.sub.O * for direct transmission of the element by way of the switch U.sub.O.

The count M of the individual stores contained in the delay device VE or VE* is less than the number N, which corresponds to the maximum delay in element lengths and thus also to the sum of all possible delays. In general, M= N/2. For this reason elements of all possible ages are not present in the delay device at any one time. Despite this satisfactory operation is ensured since by means of the age corrector AK or AK* the ages not available in VE, or already occupied in VE*, are automatically avoided.

The preliminary age signals a.sub.B derived from the quasi-randomly occurring train of encoding signals w have a random character and for this reason are not always suitable for proper control of the age/location converter AP and the delay device VE. The following conditions must always be maintained at the transmitter:

(1) Only those age signals d.sub.B should be developed that correspond to the age of one of the elements available in the delay device VE;

(2) whenever an element of maximum age (limiting age) appears in the delay device, than in all cases this element must be called up.

An arrangement which fulfills these requirements is shown in FIG. 6. The age/location converter AP corresponds to the circuit of FIG. 4, the number of storage locations to be controlled being restricted to three for the sake of simplicity in illustration. When they reach the maximum age number, the age counters Z.sub.k provide an age limit pulse v.sub.k which notifies the respective store R.sub.k in VE (FIG. 4) that the age limit is reached. The age generator AG contains, in addition to the preliminary age selector AV, which yields preliminary age signals A.sub.B, an age corrector AK for replacing these preliminary signals when one of the conditions mentioned as items (1) and (2) above is not fulfilled. If the age signal D.sub.B next applied simultaneously to all of the coincidence circuits K of the age/location converter is not appropriate, then a corresponding age number does not appear on any one of age counters Z.sub.k ; that is, an output signal does not result from any one of the coincidence circuits K.sub.k. At OR gate G.sub.61 with negated output there thus results a repetition impulse u, which causes the preliminary age selector AV to provide a further preliminary age signal a.sub.B. If necessary this process is repeated until, when condition (1) is fulfilled further repetitions are suppressed. Instead of developing a completely new preliminary age signal, the unsuitable preliminary signal could be altered once or more often by the addition of a particular binary number until condition (1) is fulfilled. When a limiting age is attained an age limit impulse V.sub.k appears even before the application of the next preliminary age signal a.sub.B, which is applied by way of OR gate G62 to gate T as an inhibiting pulse, so that the preliminary signal path remains interrupted. The age limit impulse v.sub.k is also applied to one of the stores of the delay device VE as a control impulse i.sub.h for an individual store, so that removal of the element stored up to the age limit takes place by way of the switch U.sub.k (FIG. 4). Fulfillment of condition (2) is thus likewise ensured.

The age signals at the receiver also have to fulfill definite conditions:

(1) Only those age signals should be developed which do not correspond to the instantaneous age of an element already stored in the delay device VE*;

(2) if no element of maximum age (limiting age) is present in the delay device, then the element received at that time must be transferred undelayed into the decoded signal.

If condition (1) is not fulfilled, two elements of the same age appear in the delay device and will be simultaneously withdrawn upon reaching the maximum age. As for the arrangement at the transmitter, a new age signal must therefore be found, until condition (1) is fulfilled. Because of the similar construction and programming of the preliminary age selectors AV and AV* at the transmitter and receiver the age signals finally found at the transmitter and receiver again correspond. The maintenance of conditions (1) and (2) at the transmitter makes it certain that all elements of the clear signal reach the receiver, and that the age limit is never exceeded. Because of condition (1) at the receiver an element of limiting age must thus finally be available at the receiver output at every moment of time. If such a signal is not present in the delay device, than the element received at that time must already have the maximum age and it should not therefore be further delayed. This results in receiver condition (2).

A device in accordance with FIG. 7 serves to maintain these conditions (1) and (2) at the receiver. The age/location converter AP* again contains the age counters Z.sub.k * which, on reaching the age limit number yield an age limit impulse i.sub.k *, which is passed on to the delay device VE* (FIG. 5) as the individual store control signal i.sub.k * and at the same time controls the age-gate V.sub.k, so that a new age signal D.sub.B * is passed to the counter through this gate and sets this to the corresponding initial position: z.sub.k *= d.sub.B *. For monitoring in relation to condition (1) there are also provided in AP* the coincidence circuits K.sub.k *, which provide an output pulse u.sub.k * when the age number counted agrees with the binary coded age signal d.sub.B. Since the storage of elements with equal age numbers is prohibited, u.sub.k * is conducted through the OR gate G.sub.71 * to age preselector AV*, where the input signal u* results. The age corrector AK* also contains an OR G.sub.72 * with negated output, which yields an impulse v* when no age limit impulse V.sub.k * occurs. The impulse v* is applied to the switch V.sub.0 (FIG. 5), so that the message element then received passes undelayed directly to the output of the decoding device as a component of the clear signal x*, corresponding to receiver condition (2). Since age correctors AK and AK* shown in FIGS. 6 and 7 derive their criteria from the age/location selectors AP and AP*, coupled age correction is provided.

The transmitter and receiver aging operations in the mutually independent stores R.sub.k and R.sub.k *, on the assumption of three stores, are graphically illustrated by way of example in FIG. 8. The time scale t is calibrated in element lengths. The elements E (input) are numbered by indices in the original sequence. It is seen, for example, that at the transmitter the message element E.sub.6 is applied to the store R.sub.1 at the instant 6 and after one element length is again withdrawn from the store, while at the same time elements E.sub.2 and E.sub.4 which were entered in the stores R.sub.2 and R.sub.3 at times t.sub.2 and t.sub.4 respectively are still stored. In accordance with the switching diagram seen above, applicable to instant 6, the input and output of R.sub.1 are connected with the input signal x and with the output signal y respectively, while the outputs of the two further stores are connected with their own inputs, so that the elements stored therein circulate. The element withdrawn at instant 7 is already delayed by one element length and is therefore designated E.sub.6.sup.1. After transmission to the receiver in the encoded signal y* it is further delayed by 5 elements, so that it finally appears in the reproduced clear signal x* as element E.sub.6.sup.1+5 with the total age of 6 element lengths. On the assumption that the apparatus at the transmitter is first switched on at the time t.sub.s following instant O, while the apparatus at the receiver was in operation even before that, then for example at instant 1 a still `empty` element E.sub.0.sup.1 of age 1 is withdrawn from the store R.sub.1 (shown in broken line), that is called up by an age signal d' = 1, after a first age signal d did not meet the previously discussed transmitter condition (1). A further "empty" element E.sub.0.sup.2 of age 2 follows at instant 2 being called up by the age signal d"/.sup.=2 which was preceded by two age signals unsuitable because of the same condition. At the output of the receiver apparatus ` empty` elements appear first of all, until the clear signal elements appear in the original sequence with individual total delays of 6 elements. At instant 7 is shown the first transmitter age signal, designated (d= 2). Because of unavailability in the age store, in accordance with condition (1) it is called up again, so that the usable age signal d' = 1 appears, which effects withdrawal of the element E.sub.6 delayed by one element length. At time 5 the age signal d= 0 appears, that effects a direct transmission of the element E.sub.5. At time 8 there appears the age signal d= 1, that would otherwise be satisfied by the element E.sub.7. Because of transmitter condition (2), however, the element E.sub.2.sup.6 already delayed by 6 elements (age limit) is transmitted. At the same time the age limit number appears in none of the receiver age counters, that is, no element of limiting age is present in the store R*, so that in accordance with receiver condition (2) the received element E.sub.2.sup.6 is conducted to the output as element E.sub.2.sup.6+0. The receiver age signal d*= 1 is not taken into account, since no age counter and also no store is free. It should be noted that the transmitter and receiver preliminary age selectors AV and AV* always supply corresponding age signals and that also because of condition (1) at both ends the additional age signals provided for age correction are alike.

In the delay devices shown in FIGS. 4 and 5 the elements are aged in independent individual stores R.sub.k and R.sub.k *, return from the output to the input of these stores being provided for greater delay times. This is a parallel storage arrangement, since no element passes through different stores in succession. However, a series connection of the stores may alternatively be used, as shown in FIG. 9, longer delay times being this attained, since one element passes through several individual stores Q.sub.k in succession. The change-over switches U.sub.k lying between these stores are here switched in accordance with FIG. 4b, while the switch settings of FIG. 4a apply for the entry of the elements into this chain and their withdrawal from it. In controlling the switches, care must be taken that an element entered at time 1 by way of switch U.sub.1 passes after one element length through switch U.sub.2, after two element lengths through switch U.sub.3, after three element lengths through switch U.sub.1 again, and so on, while in parallel operation as in FIG. 4 the corresponding element continuously passes through the switch U.sub.1. When the control impulse i.sub.k from an age/location converter AP as in FIG. 4 is used, an additional permutation of this impulse in accordance with time is necessary as shown in FIGS. 9b and 9c, while direct signal transfer is permissible only at times 1, 4, . . . , as shown in FIG. 9a. When using an age/location converter AP.sub.i suitable for parallel operation, as shown in FIG. 9, when series storage is employed, an additional permuting device RQ is thus necessary for deriving the new control impulses j.sub.k for the series store.

By similar reasoning the requirement developed, that the control pulses j.sub.k taken from an age/location converter AP.sub.j, which are suitable for controlling the switches U.sub.k of a series store, are to undergo an additional permutation if they are to serve for controlling the switches of a delay device VE.sub.i, the individual stores in which are provided for independent parallel operation as shown in FIG. 10. The permutation then take place as shown in FIGS. 10a, 10b, 10c and are controlled by permutating unit QR. The control impulse i.sub.O or the corresponding j.sub.O for direct transfer of an element is not involved in a permutation in either store (FIGS. 9 and 10) since this element is not delayed.

The transmitter and receiver aging processes for serial storage are graphically represented by way of example in FIG. 11; on the assumption of the same aging program as for the parallel storage of FIG. 8. The control impulses are thus derived from the impulses effective in accordance with FIG. 8 by permutation in accordance with the rules illustrated by FIGS. 9a, 9b and 9c. The representation shows the movement of the element beginnings through the individual delay stages and their passage to the input and output of the store.

The illustrated switching and storage diagrams for parallel and serial storage are only provided as examples of the aging of the data elements in the use of the invention. Other exampls may be seen from FIGS. 20 and 23, and other embodiments may be provided without difficulty by making use of techniques presently available.

Measures for correcting the aging control are dealt with with reference to FIGS. 6 and 7, which meet the transmitter and receiver requirements for proper interchange of the elements by arrangements with optimum storage utilization. Equally valuable results are also obtained by deriving the age signals with a model which does not initially correspond to optimum utilization. In FIG. 12 there are shown on the model of the known arrangement of FIG. 2, shifting registers to be placed at the transmitter and the receiver, with the respective individual stages Q.sub.k and Q.sub.k * respectively, from the tappings of which the data elements are selectively withdrawn at the transmitter and to the tappings of which the elements are correspondingly applied at the receiver. When transmitted signals y or y* appear, the elements of the clear signal x appear in different sequences, and for the receiver output signal x.sup.* the sequence of the clear signal is reinstated, if the tappings selected at any time at the transmitter and receiver always correspond, as can be seen in the diagram given therebelow. Thus in this case the total aging of all elements up to the receiver output is always of the same magnitude. It is easily seen from the transmitter diagram that each element is to be withdrawn from the store only once, and that the withdrawal must take place at the latest after the element has passed completely through the store. From this there result the transmitter conditions:

(1) in place of each withdrawn signal there passes through the store an "empty" or replacement signal, the subsequent withdrawal of which is inhibited;

(2) when an element reaches the last store then in every case it must be withdrawn.

From the receiver diagram, on the other hand, it can be seen that for the entry of received elements only those stages of the store can be considered which are still free, and that a received element must be taken directly to the output in all cases when the last stage of the store is still free. There thus result the receiver conditions:

(1) Stages of the store already occupied by elements are inhibited from further entry of an element;

(2) If the last stage of the store does not contain an element, then the element next received is to be taken to the output of this stage.

In the example of FIG. 12 the same preliminary age signals are assumed as in FIG. 11. If transmitter or receiver requirement (1) is not fulfilled, further preliminary signals are called up in the same manner. A comparison of the two diagrams shows that equal storage times always result in the two cases. It is thus also possible to attain the same encoding results if the store of FIG. 12 is subsequently replaced by a store with optimum storage utilization, when FIG. 12 may be retained as the model for the dimensioning of the storage times. Such an example is shown later in FIG. 17.

FIG. 13 shows a device which automatically supplies the age signals d.sub.k for determining the register tappings as in FIG. 12, taking account of the relevant conditions. To do so, a model register having stages P.sub.1 . . . P.sub.6 is used, the input stage of which is first occupied at each step of the clock signal e.sub.0. If the last stage is already occupied then, in accordance with condition (2) an output pulse d.sub.6 must be supplied by the control stage S.sub.6, since the occupying signal b.sub.6 then present in the stage sets the switch in S.sub.6 into the actuated position (the opposite position to that shown in FIG. 13), so that the periodically applied clock signal C.sub.C can be passed on. If the last register stage is already free, then all the switches S.sub.k are in the unactuated condition (as shown) until a preliminary age impulse a.sub.k is applied from the preliminary age selector AV. If the preliminary impulse (e.g. a.sub.1) is applied to the respective register (e.g. P.sub.1) at the same time as the address impulse (e.g. b.sub.1), then the respective switch (e.g. S.sub.1) is set to the actuated position, so that the auxiliary pulse C.sub.1 from the following switch is passed on as an age pulse d.sub.1 and at the same time inhibits the transfer of the register contents from P.sub.1 to P.sub.2.

The "empty" signal then travels through the register and inhibits a repeated provision of an age impulse in violation of condition (1). If a register stage (e.g. P.sub.1) should be already emptied, then the respective occupation signal (e.g. b.sub.1) is absent and the respective control switch (e.g. S.sub.1) is itself not actuated when the called-up preliminary impulse (e.g. a.sub.1) is applied to its. When for this reason no age impulse d.sub.k is developed, then all the switches remain in the unactuated condition, so that owing to the passage of the clock signal C.sub.6 through all the switches a repetition impulse u is produced, which gives rise to the repeated provision of a preliminary age impulse by AV. After a brief delay in auxiliary delay unit ZV, the repetition impulse u passes through the switch chain as a new trigger impulse C, until finally, upon coincidence of a new preliminary age impulse with an occupation impulse, a usable age impulse d.sub.k results, which fulfills the transmitter condition (1). An arrangement in accordance with FIG. 13 may also be used to find the receiver age impulses d.sub.k.sup.*, since these must always correspond to the transmitter impulses d.sub.k. As is shown by a comparison of the diagrams of FIGS. 8, 11 and 12, and the respective conditions, the operation of the age controls of FIGS. 6 and 13 is alike by additional means it is sought to ensure that in FIG. 13 also, by suitable age/location conversion, operation with optimum storage utilization is produced.

An important characteristic of the proposed arrangement is that all element displacements occur in the encoded signal with the same frequency, or with a specified frequency distribution. Starting from FIG. 13 the following relations apply, which may however be transferred unchanged to another age control of like performance, such as that of FIG. 6, for example. The switches S.sub.k are actuated in response to the simultaneous application of a.sub.k and b.sub.k ; i.e.

On the assumption that the signals a, b, c, d, occur with the respective probabilities A, B, C, D, and that for successful selection of an age impulse d, W age selections are necessary on average, the following is approximately true for large numbers of stages:

if all delays appear with equal probability, then for a number H of stages P in the storage register used in AV, i.e. for H + 1 different possible ages,

and the probability B that a particular stage is occupied diminishes by D with each stage: ##EQU1##

In accordance with requirement (2), d.sub.H must appear in all cases when the last register stage is still occupied; i.e. it is necessary that C.sub.H = 1. After the age impulse d.sub.H has appeared at any time the condition for the switch S.sub.k to be actuated by a.sub.k is: ##EQU2## and by substituting from (2) and (3) in equation (1) ##EQU3##

On the assumption of six register stages (H = 6) we have: ##EQU4## this being of course only an approximation because of the small number of stages. Because ##EQU5## would therefore give W = 1.86, from which the probabilities A.sub.k may be determined in accordance with equation (4):

The age selection can be effected with an arrangement AV as shown in FIG. 14, in which a coding signal generator SG yields on each occasion a code word consisting of five binary digits W.sub.1 -W.sub.5 in quasi-random distribution. From this code word there is developed in a code converter CW.sub.1 an individual impulse at one of 32 outputs, the locations of these impulses being again interchanged in accordance with the laws of chance. By the combination of three outputs in OR gate G.sub.0 the preliminary age impulse a.sub.0 appears with the probability 3/32, while the preliminary impulses A.sub.1 -A.sub.5 appear at the outputs of the gates G.sub.1 -G.sub.5 with the approximate probabilities given in the table above. By the use of logic circuits in accordance with known techniques, other devices for obtaining age impulses with the desired probability distribution can of course be built.

In FIG. 15 there is shown an age generator consisting of an age preselector AV' and an age corrector AK', which again provides age impulses d.sub.k with uniform probability distribution. For each age selection, however, the age preselector AV' yields several impulses a.sub.k ', of specified probability distribution. A storage register with the individual stages, P.sub.1, P.sub.2, . . . P.sub.6 is again fed with input impulses in rhythm with the clock signal e.sub.0, which in the course of their passage through the register are withdrawn upon the appearance of an age signal d.sub.k. The switches S.sub.k are again actuated upon the simultaneous appearance of a preliminary impulse or release impulse a.sub.k ' and an address impulse b.sub.k,

And since no repetition occurs in the age selection (W = 1), the probability of the negative signals is given by:

Again, for the desired uniform distribution of the age impulses:

and ##EQU6## Because C.sub.H = 1, we get from (6): ##EQU7## and substitution from (7), (8) and (9) in equation (5) yields ##EQU8## Thus on the assumption of 6 storage stages (H = 6) there is obtained:

an advantage of this method is that each age selection leads reliably to the goal at little cost in time, while with the arrangement of FIG. 13 in a few cases frequency repetition of the age selection may be necessary before a useful solution is obtained.

In FIG. 16 there is shown an arrangement AV' for age selection, i.e. for obtaining the preliminary age pulses a.sub.k ', which are suitable as input signals for the age selector of FIG. 15. From the coding signal generator SG there are taken the six coding signals W.sub.1 . . . W.sub.6 which consist of binary signals of quasi-random distribution. Thus there appear each time pulses of probability 1/2 from which there are derived in a system of logic AND gates contained in a signal converter SW a set of three further coding signals consisting of impulses having the probabilities set out in the right-hand column of the table given above. These further coding signals are used as control impulses a.sub.1 ' . . . a.sub.5 ' for coincidence circuits KK and their probabilities A.sub.1 ' . . . A.sub.5 ' will be seen from the table to correspond well enough with the theoretically determined desired values. If the preliminary age pulses are required to follow each other in a particular sequence, then the arrangement AV' of FIG. 16 may be supplemented by a shifting register S'R', through which a drive pulse e.sub.01 is driven by a clock pulse e.sub.1. At the output of the coincidence circuit KK a preliminary age impulse a' thus appears each time the drive impulse coincides with one of the impulses a'.sub.1 . . . a'.sub.5.

Equations (4) and (10) show how the probabilities A.sub.k or A.sub.k ' of the preliminary age impulses or of the age release pulses are to be chosen in order that all element delays shall appear with the same probability. Certain deviations from this requirement may be desired for cryptological reasons, e.g. a preference for large and small displacements as compared with medium values of displacement. Such requirements are naturally easily satisfied by modification of the probabilities A.sub.k or A.sub.k ' and corresponding arrangement of the age selector.

Since the age correctors AK and AK' of FIGS. 13 and 15 form their criteria self-containedly, independent of the age/location selector AP, the operation may be termed independent age control.

It is shown in FIG. 12, that the age selection obtained by a shifting register model (independent age corrector) results in the same aging results as the age corrector with optimum storage utilization shown in FIGS. 6 and 7 (coupled age corrector), and that the requirements laid down for the two methods lead to the same result.

There will now be described with reference to FIG. 17 an arrangement with which the age signal found with an addressable register model (independent age corrector) may be evaluated for age/location conversion with optimum storage utilization without further correction. For the age corrector AK, the circuit of FIG. 15 is modified so that several stages S.sub.k are distributed along the addressable register. The content of the register stages P of SR.sub.1 is on the contrary transferred at a faster sequence to a single switch S, by which, in the end, the same results are obtained. The stages P.sub.11 . . . P.sub.16 (FIG. 17) are next charged with the same load impulses and/or idle impulses as the stages P.sub.1 . . . P.sub.6 (FIG. 15). With the switch S the next stage P.sub.16 is examined and no impulse d=d.sub.6 is yielded with an idle stage. On this the register contents is shifted by the clock pulse e.sub.1.sup.1 in one stage, and, with the same switch the original content of stage 15 will be examined. An exit impulse d=d.sub.5 comes about only if, b.sub.5 (originally in step P.sub.15) and as a.sub.5.sup.40 occur in time synchronism. In the same way and in sequential fashion, the contents of steps P.sub.14, P.sub.13, P.sub.12, P.sub.11 will also be examined until the correct age impulse d results. After the response of the switch S, that is according to the information of an age impulse d, the further conductance of the impulse C to the protracted step TV.sub.1 is interrupted, in which case C is recirculated during clock impulse e.sub.1 when there is no switch response. According to this technique employed during a control cycle, the register contents returns to the original location. During e.sub.01 in slow base time measure of active switch RS, a new imposed impulse will be generated because of this, which, by simultaneous forward switching of the register contents is placed in the first register stage. By the timely location of the characterized age impulse d, the three impulse stages are reset in the code variable CW.sub.2 to change one of the positions of the said three-bit binary code. The variable age/location AP, according to FIG. 17 is as appropriate for use at the transmission side as it is for the reception side of a communications system. In accordance with the arrangements for transmission the switches RW.sub.1 and RW.sub.2 are set either to position A (transmission) or to position B (reception). The arrangement includes an age register sR.sub.2 which in each three successive stages (in the circuit embodiment shown) contains a three-place binary word (age number) giving the ages of the stored elements. The three stages of the interchange register SR.sub.21 and the summing stage SU are also to be considered as stages of this register. The whole register thus comprises 12 stages corresponding to the 2.sup.3 = 8 possible delays of 4 elements conducted through VE, including the zero delay obtained when switch U.sub.0 is closed.

At each step of the basic clock, the contents of the register SR.sub.2 circulate under the control of a fast clock pulse e.sub.2. Thus each binary number entered in the register is increased by one in the summing stage SU with the delay device TV.sub.2, corresponding to the increase of one element length in the time of storage in delay unit VE. This increase is avoided only with age values remaining continuously at 0, to which the switch U.sub.0 is always appropriate. The respective age number 000 arrives in due sequence in the three register stages of SR.sub.21. During transmission the register stages P.sub.21, P.sub.22, P.sub.23 contain the number which corresponds to the age of the element stored in R.sub.3, while the succeeding stages contain the age numbers appropriate to the age stores R.sub.2 and R.sub.1 and already expired. An age signal d.sub.B (e.g. 5) provided by the age corrector AK denotes that an element of corresponding age is to be called up from the delay device VE. For this purpose the three bits of d.sub.B are applied by way of switch RW.sub.2 to a correlator KO, which now compares this binary word with the age numbers contained in register SR.sub.2, which are taken through the register stage SR.sub.21 as an impulse train s.sub.m. Upon agreement a coincidence signal k.sub.0 results, which is taken through a gate T.sub.2 in order to inhibit apparent coincidences of incorrect phase and in order to retain a coincidence impulse k which occurs at the correct time. This impulse travels through the register SR.sub.3 at the slower clock rate of e.sub.3 and is withdrawn at the time of the impulse e.sub.05 through the switch UV.sub.k. If now the age word stored in stages P.sub.21, P.sub.22, P.sub.23 of the age register (and increased by 1 in SU) leads to coincidence, then the coincidence impulse occurs very late and at the instant of withdrawal by e.sub.05 it will be in stage P.sub.33 of register SR.sub.3, so that the contents of the store R.sub.3 are withdrawn by way of switches UV.sub.3 and u.sub.3. For the age words stored only in subsequent stages of SR.sub.2 the respective coincidence impulses occur correspondingly earlier, so that at withdrawal they lie in stage P.sub.32 or P.sub.31 and effect a withdrawal of the element from R.sub.2 or R.sub.1.

A timing diagram for the auxiliary impulses appearing in the circuit of FIG. 17 is shown in FIG. 18. The age control in AK (FIG. 17) begins with the starting impulse e.sub.011, which is followed by the clock pulses e.sub.1 for the register SR.sub.1 and for the delay stage TV.sub.1. The latter clock pulse causes a new occupation pulse to be applied by way of the feedback switch RS actuated by e.sub.01. The timings of the possible age impulses d.sub.k are shown in broken line, while the impulse d.sub.3 which in fact appears is shown in solid line fashion. The duration of the binary coded age word d.sub.B is also shown. The clock pulses e.sub.2 for the age register SR.sub.2 and the timing pulses e.sub.21 for the adding stage SU, suppressed by the age word S.sub.O, are also shown. The times at which the age numbers S.sub.0, S.sub.1, S.sub.2, S.sub.3 circulating in the store SR.sub.2 are in a position in register section SR.sub.21 suitable for a coincidence comparison are designated by S.sub.0 ', S.sub.1 ', S.sub.2 ' and S.sub.3 '. In addition to a coincidence signal k.sub.0 which does appear, further possible coincidence signals are shown in broken line fashion. From this there is derived in gate T.sub.2 the shortened coincidence impulse k which is advanced in register SR.sub.3 as signal P.sub.3 - P.sub.2 - P.sub.1 - P.sub.0. Upon the occurrence of e.sub.05 the register SR.sub.3 is called upon by the switch UV.sub.k ; i.e. at instant 1 (see time scale at bottom) UV.sub.3 is energized by P.sub.3, and at instant 2UV.sub.1 is energized by P.sub.1. Through UV.sub.3 and UV.sub.1 there are provided the control signals i.sub.3 and i.sub.1 respectively, which, by way of the respective store switches U.sub.3 and U.sub.1, effect the withdrawal of the stored element and the introduction of a new element into the store.

It may be seen from FIG. 17 that the coincidence impulse k also opens a gate T.sub.3 through which a three-digit null signal g.sub.1 taken from a fixed value store FS.sub.1 is fed in as the new contents for the interchange register SR.sub.21. This arrangement corresponds to a simple resetting of the age number to zero, to which one age unit is then added at each circulation of the age number, i.e. after each element length has elapsed.

In the operation of the arrangement of FIG. 17 for decoding at a receiver, the switches RW.sub.1 and RW.sub.2 are set to position B. From the fixed value store FS.sub.2 issues the three-digit binary signal which corresponds to the maximum age of 6 element lengths. This signal is fed to coincidence device KO. A coincidence impulse k now results as soon as an age signal s.sub.m reaches a limiting age. This impulse is again applied by way of the register SR.sub.1, at the time of the release impulse e.sub.05 to energize a preliminary switch UV.sub.k which effects the discharge of the respective register R.sub.k and the reception of a new element into this register. The coincidence impulse k also briefly opens a gate T.sub.3, through which the new age signal associated with the new element passes. The age limit signal associated with the withdrawn element is replaced by this new age signal, which gives the age that the new element has already attained at the transmitter. After further aging at the receiver until this element reaches the age limit, a coincidence impulse then causes this element to be passed on into the decoded signal x.sup.*. If the age signal d.sub.B given by the age corrector AK already corresponds to the age limit, then further aging of the received element is unnecessary. This element must therefore be forthwith passed to the output by way of the switch U.sub.0. The age limit signal is determined by an age store V.sub.0 responsive to the pulse sequence 110, which yields a recognition impulse k.sup.*. This impulse is applied directly to the shifting register SR.sub.3, so that when the new release impulse e.sub.05 occurs it is already in the register stage P.sub.30 and energizes the preliminary switch UV.sub.0, so that store switch U.sub.0 is actuated.

A comparison of this process with that of FIG. 12 shows that the requirements of the age control with a storage model or occupation register are perfectly fulfilled, and it has already been shown that compliance with these requirements suffices for fulfilling the conditions (1) and (2) for a direct coupled age corrector as shown in FIGS. 6 and 7. For this reason it is definitely ensured that, in normal operation of an arrangement in accordance with FIG. 17, elements will always be available in the delay device VE at the transmitter of which the ages correspond to the age signals d.sub.B, while in the delay device VE.sup.* at the receiver a storage location will always be free when a new element is to be stored.

In the arrangement of FIG. 19 the age/location converter AP is again equipped with age register SR.sub.2, adder circuit SU, coincidence circuit KO and additional register SR.sub.3, similarly to FIG. 17, and the functions of these parts of the circuit likewise correspond to FIG. 17. Instead of the age control AK with its addressable register there is however provied a control system Ak that has to fulfil the conditions explained with reference to FIGS. 6 and 7 (coupled correction). For this purpose there is provided first of all a control circuit KS.sub.1, the operation of which will be explained below, and an intermediate store ZS coupled with change-over switches F.sub.4 and F.sub.5 for interrupting and storing the preliminary age signals a.sub.B from the age preselector AV. During the operation of this arrangement the following phases may be distinguished, which may in part also be carried out in modified sequences:

Phase 1:

Preselection of the age signal (F.sub.1 in position 1). A single circulation of the age numbers s.sub.m in register SR.sub.2 with simultaneous increase by one age step of the signals s.sub.1, s.sub.2, s.sub.3. Respective clock pulses e.sub.2 and adding impulses e.sub.21 are provided by the control circuit KS.sub.1 .

Coincidence (k = 1):

Control signal r.sub.4 from KS goes briefly to 1, so that a.sub.B is passed through switch F.sub.4 into the intermediate store ZS; at the same time the control signal r.sub.5 produces a changeover of switch F.sub.5, so that the stored preliminary age signal a.sub.B remains available as age signal d.sub.B. The circulation of s.sub.m is then completed.

Non-coincidence (k = 0):

Circulation of the age numbers s.sub.m is repeated after the preliminary age signal a.sub.B has been changed, without further increase of the age values, until a circulation with coincidence occurs.

Phase 2: Interchange of an element when the age limit is reached (F.sub.1 in position 2)

A single circulatin of the age numbers s.sub.m in register SR.sub.2 without increase of the age values. Appropriate clock pulses from KS.sub.1.

Coincidence (k = 1):

The circulating age numbers s.sub.m correspond with the age limit signal g.sub.2 provided by way of switch F.sub.1 from the fixed store FS.sub.2. An input pulse r.sub.1 corresponding with k is applied from the control circuit KS.sub.1 to the register SR.sub.3, in which it is advanced from stage to stage in the direction of the arrow by the clock pulses e.sub.3. In accordance with the timing of k the impulse will be situated in stage P.sub.33, P.sub.32 or P.sub.31 when the auxiliary impulse e.sub.05 appears. The preliminary store switch UV.sub.3, UV.sub.2 or UV.sub.1 will accordingly be actuated by the impulse P.sub.3 or P.sub.2 or P.sub.1 respectively, so that finally a store control impulse i.sub.3, i.sub.2 or i.sub.1 effects the withdrawl of the element that has reached the age limit and the entry of a new element. From the control circuit KS.sub.1 there is also provided a control impulse r.sub.2 coincident with k, that opens the gate T.sub. 3 and effects a transfer of the zero age signal g.sub.1 into the interchange register where it replaces the age signal that has increased to the age limit. The interchange is thus effected without a following Phase 3.

Phase 3: Interchange of an element without reaching the limiting age (F.sub.1 in position 1)

Single circulation of the age numbers s.sub.m in register SR.sub.2 without increase of the age values. Appropriate clock impulse e.sub.2 from KS.sub.1.

On coincidence (k = 1):

The circulating age number s.sub.m corresponds with the age signal d.sub.B transferred from the store ZS. In the same manner as for a coincidence in Phase 2, the element of age d.sub.B now stored is interchanged with a newly received element and the corresponding circulating age signal is replaced by a zero age signal.

No coincidence (k = 0)

This case does not occur, since an age signal d.sub.B was already found in Phase 1, which corresponds with the stored element.

Phase 1: Preselection of the age signal (F.sub.1 to position 1)

In contrast to transmission Phase 1, an age signal d.sub.B must be found that is not represented among the circulating age numbers s.sub.m, in order that two elements of the same age shall not later be called up simultaneously from the delay device VE. The procedure is thus to be carried out as in Phase 1 of the transmitter operation; though the "Coincidence" and "Non-coincidence" criteria must be interchanged.

Phase 2: Interchange of an element upon reaching the age limit (F.sub.1 in position 2)

A single circulation of the age numbers s.sub.m in register SR.sub.2 without increase of the age values. Appropriate clock pulses e.sub.2 from KS.sub.1 .

Coincidence (k = 1):

The circulating age number s.sub.m corresponds with the age limit signal g.sub.2 supplied from the fixed stores FS.sub.2 by way of switch F.sub.1 (at first in position 2). A coincidence impulse k results and as in Phase 2 of the transmitter operation, a control impulse r.sub.1 from the control circuit KS.sub.1 coincident in time with k effects the withdrawal of an element which has reached the limiting age from the delay device VE, as well as the replacement of this element by an element of the received signal. Directly after coincidence, i.e. before the next step in the circulation of s.sub.m the gate T.sub.3 is opened by the control signal r.sub.2 provided from KS.sub.1, so that the new age signal d.sub.B already present in the intermediate store ZS replaces the age number in interchange SR.sub.21 which has reached the limiting value. The element interchange is thus terminated without a succeeding Phase 3.

Phase 3: Transfer of an element without its reaching the age limit (F.sub.1 in position 1)

An input impulse r.sub.1 is provided from KS.sub.1 to register SR.sub.3, further clock pulses e.sub.3 are also provided, through which the input pulse is transported to stage P.sub.30. On the occurrence of the auxiliary signal e.sub.05 the preliminary store switch UV.sub.0 is actuated by the impulse P.sub.0 taken from P.sub.30, so that a control impulse .sup.i.sub.o is provided to the delay device VE, which effects the undelayed transmission of the next-received element. The circulating age number s.sub.m remains unaltered.

Since the described functions satisfy the transmitter and receiver conditions treated with reference to FIGS. 6 and 7, there again results an interchange program for the message elements corresponding for example to the graphic representation of FIG. 8, so that perfect encoding and decoding without omission or repetition or superposition of individual elements is still ensured.

In the arrangement of FIG. 19 it is from time to time tested whether the age signal d.sub.B taken as a test from the age corrector AK agrees with the age number of a stored element. If agreement is not found a repetition of the comparison with a new age signal is effected. This process thus corresponds to that used in the coupled age corrector of FIG. 6. In use at the receiver, on the other hand, an age signal is sought that does not agree with the age number of any stored element, corresponding to the coupled age corrector of FIG. 7.

Analogous results are obtained when controlling the age/location converter AP of FIG. 19 with age signals d.sub.B, which are obtained by independent age correction with an arrangement as in FIG. 13, since the same criteria apply for this independent age corrector as for the coupled age correctors already mentioned.

In the arrangement of FIG. 19 with coupled age corrector, (i.e. without addressable register SR.sub.1 in AK) the same results may be obtained by modification of the circuit, as in the arrangement of FIG. 17 which is operated with independent age correction as in FIG. 15. For this purpose each circulation of the age numbers in register SR.sub.2 must be further repeated several times without alteration of the age numbers while simultaneously changing the age signals d.sub.B taken from AK. To develop these age signals, binary numbers are generated in AK by means of a counter, which increase by one unit after each circulation of the age numbers in SR.sub.2 and are from time to time passed on to AP as age numbers d.sub.B, if there appears at the same time a preliminary age impulse a' from age preselector AV, the function of which corresponds to that of the device AV' in FIG. 16. In the age corrector of FIG. 17, impulses circulating in SR.sub.1 with ages advancing stepwise, from which the age signal d.sub.B is produced on the simultaneous appearance of a preliminary age impulse a' in CW.sub.2. In the arrangement produced by modification from FIG. 19, on the other hand, there is provided after each preliminary age impulse a' an age signal d.sub.B, which is converted into binary form through the counter already mentioned. This age signal is only effective when it corresponds with an age signal appearing in an additional circulation of SR.sub.2. The operation of the register SR.sub.1 of the independent age corrector (see FIG. 17) is thus replaced by repeated circulation of the age numbers in SR.sub.3. The simplification produced through this coupled age correction loses its importance especially in arrangements with greater numbers of stores in the delay device VE and correspondingly high numbers of stages in the additional register.

With parallel-operated individual data stores R.sub.k, as in the delay device of FIGS. 4 and 5 and also with the series connection of the store Q.sub.k of FIG. 9, there results with larger numbers of stores correspondingly numerous connections and switches. A reduction of this expense is possible, for example, with a circuit in accordance with FIG. 20, in which a first store contains the storage locations Q.sub.1-4 for an element consisting of four bits, while a further store contains storage locatons Q.sub.5-12 for two further elements each consisting of four bits. For storage of a larger number of elements the two stores could be further extended without additional connections. The clock signals e.sub.62, e.sub.63 and also the control signals e.sub.60 and e.sub.61 for the switches F.sub.21 and F.sub.22 are taken from a timer TG.sub.1 to which as shown in FIG. 21 there are applied the store age-control signals i.sub.0, i.sub.1, i.sub.2, i.sub.3, as in the arrangements already described. A timing diagram of output signals dependent upon these input signals of the timer is shown in FIG. 22. It is seen that the control signal i.sub.0 effects the change-over of switch F.sub.21, so that the four bits of the next data element, coinciding with the clock pulses e.sub.62 are passed directly from the input X to the output Y of the delay device VE. A control signal i.sub.1, on the other hand, causes the actuation of switch F.sub.22, so that the four bits are stored in the store stages Q.sub.1-4. At the same time an element previously stored in these stages is taken by way of switch F.sub.23 to the output. A control signal i.sub.2 again first produces the generation of 8 clock pulses e.sub.62 and e.sub.63 in rapid succession, so that the contents of all the stores are advanced 8 steps. Thus the element initially entered in stages Q.sub.5-8 is transferred into stages Q.sub.1-4, and from thence is interchanged in the manner already described with a new element which is finally shifted into the stages Q.sub.5-8 again by 4 rapid impulses in e.sub.62. In a similar manner, an i.sub.3 control impulse effects the interchange of the element entered in stages Q.sub.9-12. The result is thus the same as in the operation of three individual stores, each with four stages.

The circuit shown in FIG. 20 certainly causes difficulties if a large number of elements which include numerous values are to be stored. In this particular case a large number of individual values must be transferred through all the store stages in the time between two individual values, or in the very brief interval between two elements, which is not technically possible in all cases. A certain relief may then be obtained by time compression of each element before storage, which results in a prolongation of the intervals. Such time compression can be effected by storing each element in an auxiliary register, from which they are withdrawn by an accelerated clock.

Special transfer of the store contents which are to be interchanged into the stages Q.sub.1-4 may be avoided by dividing the whole data store into several stages (Q.sub.1, Q.sub.2 . . . in FIG. 9), the capacity of each section corresponding to an integral number of elements, additional switches (U.sub.1, U.sub.2, . . . in FIG. 9), each connecting two successive stages to one another when in the unactuated condition. These connections may be broken at any selected position if the respective switch is set to its actuated condition and are thus replaced by connection of one section with the output lead and connection of the following section with the input lead. Thus an element may be forthwith withdrawn at any storage section and at the same time a new element entered into the following section. The particular permutation of the control signals in RQ shown in FIG. 9 may then be omitted if the age numbers are circulated in a register similarly to the data elements, as takes place for example in register SR.sub.2 in the apparatus of FIGS. 17 and 19. In this case the sections Q.sub.1, Q.sub.2 of the data store containing a data element and the sections P.sub.21 -P.sub.23, P.sub.24 -P.sub.26 of the register SR.sub.2 are always mutually associated, so that upon coincidence of an age number it is immediately known at which position of the information store an element is to be interchanged; i.e. which switch of the delay device must be actuated.

The difficulties mentioned as resulting from storage with a reduced number of switches and connections are largely avoided with interdigitated storage with an arrangement as in FIG. 23, which is operated by clock pulses and control signals in accordance with the timing diagram of FIG. 24. It is here assumed that the clear signal x is a speech signal, which is divided into elements of equal length to form the data elements. Each element comprises some 200 analog sampling values, which in the analog/digital converter AD at the input of the delay device are converted into binary words of 6 bits each. Recovery of the analog signal is possible with the digital/analog converter DA at the output of the arrangement. Thus 1200 bits are required to be stored in the delay device for each element. If maximum delay times of 6 element lengths are required, then the simultaneous storage of 3 elements or 3600 bits is necessary. In the arrangement of FIG. 20 approximately this quantity of impulses 9, be transported through the register in each interval. With interdigitated storage as in FIG. 23 on the contrary a complete element length is available for this transport. The bits of the three elements are distributed in the 3600 stages of a shifting register so that the 1200 bits of the first element are placed in stages 1, 4, 7, . . . 3598, the 1200 bits of the second element in stages 2, 5, 8, . . . 3599, and the 1200 bits of the third element in stages 3, 6, 89, . . . 3600. Upon the second element being called up and for simultaneous replacement of this element by a new element, a circulation of the register contents is now effected by the clock pulses e.sub.72, the switches F.sub.25 and F.sub.26 being actuated by the control signal e.sub.71 (i.sub.2) so that the bits belonging to the second element are taken to the output DA converter to obtan the sampling values of the second element. These sampling values finally form an element of the encoded signal y. At the same time the bits withdrawn are replaced by bits of a new clear signal element formed in the converter AD. The register stages of which the content has changed are shown as shaded in FIG. 23, while after the termination of the interchange, that is, when circulation is ended, arrive again in the same locations. Direct transfer of an element, without storage, on the other hand, is effected by actuation of the switch F.sub.24 at the time determined by the timer pulse e.sub.70 (i.sub.0), while at the same time the contents of the store circulates once.

In the encoding device of FIG. 25 the condensed storage mentioned is used. For simplicity the analog/digital converter and the digital/analog converter are omitted on the assumption that the clear signals x (at the transmitter) and x* (at the receiver) are supplied and passed on respectively in digital form. The store SR.sub.6 and the further stages of an adder stage SU and of an interchange register SR.sub.7 connected in cascade with it together comprise 3600 stages, corresponding to 3 store portions each with 1200 bits for 200 sampling values, each coded in 6 bits, of a data element. The age signals d.sub.B are obtained for example in an age corrector AK arranged as in FIG. 17 (independent age corrector) including an addressable register, from the age trigger impulses a' of the age preselector AV and they are applied as in FIG. 17 by way of the transmit/receive changeover switches RW.sub.1 and RW.sub.2 to the interchange register SR.sub.7 or to the coincidence circuit KO. The age register SR.sub.2 shown in FIG. 7 is omitted, since the circulating age numbers are now stored with the coded data elements, for which, by omission of one sampling value of the three elements, 18 free storage locations are obtained. These free locations are situated at the front of each element, i.e. they are positioned in the interchange register SR.sub.6, in the adding stage SU and in the last five stages of the shifting register SR.sub.7. Even the age numbers circulating with the data elements are interdigitated. While the bits of the three data elements follow one after another in three phases, as indicated by shading in store SR.sub.7, four age numbers are accommodated by likewise interdigitated bits, that is three bits associated with the element, which again are correspondingly shaded, and three unshaded bits which designate zero age for cases where storage of the element is to be dispensed with.

The control and clock signals necessary for proper operation of the arrangement are taken from a control circuit KS.sub.2, which as shown in FIG. 26 responds to an applied coincidence impulse k.sub.2 ', for example, or to the likewise possible coincidence impulses k.sub.1 ', k.sub.3 ', k.sub.0 ' shown in broken line. The coincidence impulse k.sub.2 ' immediately effects the provision of a control signal r.sub.6, that opens the gate T.sub.3, so that the zero-age signal g.sub.1 replaces the three bits of the age number s.sub.m in the interchange register SR.sub.7. At the same time and in the same phase a control signal e.sub.81 (k.sub.2 ') is initiated that appears in phase 2, the timing of the pulses being as indicated between the impules of the clock signal e.sub.82. This control signal is in fact interrupted during the time interval t.sub.0. . . t.sub.1, which corresponds to the suppressed first sampling value of the three data elements and it has the effect that each of the bits corresponding to the second element is taken from the store by way of switch F.sub.36 and is replaced by the corresponding bit of the new element to be stored by way of switch F.sub.35. The bits of the two other elements stored during the first or third phase may be withdrawn and replaced in a similar manner. If on the other hand the age signal d.sub.B is expressed by the zero age-value 000, then an undelayed element must be passed on, which is not taken from the store but directly from the applied signal x. Upon coincidence with the circulating zero age signal s.sub.0, which is indicated unshaded in the store SR.sub.7, the coincidence signal k.sub.0 ' results which, as shown in FIG. 26, has as a consequence a periodic direct passage of the applied bits by way of switch F.sub.34. The brief actuation of the switch suffices for the development of these input impulses, since these always have the duration between two elements of the basic clock e.sub.0.

When the arrangement is installed at the receiver, the switches RW.sub.1 and RW.sub.2 are set to position B, i.e. a coincidence signal results in response to each agreement of a circulating age number s.sub.m with an age limit signal g.sub.2 taken from FS.sub.2. The bits of the element that has attained the age limit are then again, in the manner already described, replaced by the bits of an element received at that time. After coincidence has occurred the bits of the zero age signal g.sub.1 are no longer applied to the interchange register SR.sub.7, but the age signal d.sub.B appearing at this instant, which corresponds to the aging already carried out at the transmitter. This age signal now increased by one age step at each circulation of the receiver store. At the same time the age of the stored elements also increases until the age limit is reached, whereat a new interchange results. At the receiver an age signal d.sub.B may already represent the age limit. This signifies that the then received element has already reached the age limit at the transmitter. Such an element must not be further stored, but transferred directly to the output; i.e. a coincidence signal k.sub.0 ' must appear, that effects a direct signal transfer. The ciculating age signals s.sub.m therefore contain in addition to the age numbers increasing at each circulation, which are appropriate to the three stored data elements, an additional age number s.sub.0 always remaining the same, that corresponds to the age limit of 6 units. Upon coincidence of this age number in KO with the limiting age g.sub.2 taken from FS.sub.2, likewise of 6 units, a coincidence signal k' results, which however is effective if no other coincidence impulse originating from the circulating age numbers appears. The effect of this impulse is again to result in the production of a periodically repetitive control signal e.sub.80, that effects each time the direct transfer of the bits belonging to a newly received element by way of the switch F.sub.34. It is thus possible also to omit the always constant age signals at the transmitter and receiver serving for direct transfer of individual elements, and to arrange the control circuit KS.sub.2 so that a direct transfer is effected at any time when the three stepwise increasing circulating age numbers do not yield a coincidence, so that no data element is taken from the store.

In FIG. 26 there are also represented in time interval t.sub.-1 to t.sub.0 the clock and control signals that are included in the operation during the later sampling values, that is, during the last 6 bits of the preceding element. It is assumed that the bits appearing in phase 3 are withdrawn from the store and replaced by actuation of the switches F.sub.35 and F.sub.36 with the control signals e.sub.81 (k.sub.3 '). There are also shown the three control impulses e.sub.83 which increase the circulating age numbers (with the exception of the constant zero or age limit numbers) in the adding stage S0 by one unit at each circulation.

It should be noted that the suppression of one sampling value in each data element during speech encoding, which is effected in order to introduce the age numbers into the data store is without any substantial disadvantageous consequence, since this omission is not in practice noted when listening to the speech signal and brief interruptions between the elements are also introduced because of unavoidable deviations of synchronization and because in most transmission channels the transmission time is dependent upon frequency.

To avoid undesired suppression of individual portions of the data, the age numbers stored in the arrangement of FIG. 25 instead of sampling values, may be shifted into a register operating in parallel with the data store. Instead of the serial storage of, for example, six bits for each data sample value, there may be provided in all the embodiments described, parallel storage in, for example, six shifting registers with a correspondingly reduced number of stages. By the use of known techniques it is however also possible to replace the shifting registers used for storage of the elements by addressable memories known as random access memories (RAM). The construction or conversion of such circuits does not present any particular difficulties in view of the described examples and the relevant explanations.

In the examples discussed, to simplify the explanation, delay devices with only a few individual stores were provided. In practical embodiments, in order to obtain the necessary secrecy, at least a larger number of stores or a larger number of different possible ages is necessary. This is clearly possible without deviating from the principles of the described embodiments.

In FIG. 27 there is once again represented the basic principal of transmission formerly explained. The transmitting station A and also the receiving station B effect aging of the applied elements by e.g. 6 element lengths by the use of delay devices. The delay devices may be replaced by delay lines or by shifting registers with 7 tappings, the withdrawal of the signal at the transmitter and the entry of the signal at the receiver always taking place correspondingly. It is easily seen that the data elements must always pass through the same total number of delay stages, as indicated by the arrows in the drawing. Accordingly the total delay between the clear signal x at the transmitter and the reconstructed clear signal x* at the receiver is also constant (6 element lengths, for example).

However, as shown in FIG. 28, interchange of the types of station described is also possible, so that in the equivalent circuit diagram the message elements are applied at the transmitter to different tappings of the delay device B and at the receiver are withdrawn again from different tappings of the delay device A, while the interchanged elements are taken from the end of arrangement B and are applied, after transmission, to the input of arrangement A. In FIGS. 27 and 28 the arrangements are operated in accordance with the same program. There is thus no danger that an element will be suppressed or that any superposition of elements will occur, even with the transposed arrangements. On the other hand, care must be taken that a constant number (e.g. 6) of delay stages always exists between the varying tappings of B and the varying tappings of A. For this reason the control of the delay at A must always be time-displaced as compared with that at B by this constant number of element lengths. This is conveniently effected by a corresponding time-difference between the synchronizing at the transmitting and the receiving apparatus.

Thus in certain cases an apparatus arranged for encoding may be used unchanged for decoding, if the arrangements of FIG. 29 are changed over for transmitter and receiver operation. During the transmission of the clear signal x.sub.1 (switches in position shown) the age signals at the two stations are developed synchronously, for transmission of the clear signal x.sub.2 (switch positions reversed) a constant delay of the age signal development at the arrangement A as compared with that at arrangement B is provided. No other change-over or alteration of the type of station is necessary, however.

It may be seen from FIG. 12 that even without optimum storage utilization the number of stored elements always remains constant. With optimum utilization this number naturally cannot in any case be exceeded. It would however be possible to start an arrangement in accordance with FIG. 12 with more or less stages occupied, and it would then be found that if the conditions discussed were maintained this number of stages would likewise remain constant. It is true that a preference for particularly large or particularly small storage times would then result. If the transmitter and receiver arrangements were started with unequal numbers of stages occupied, then in an arrangement in accordance with FIG. 12 correct encoding would not be possible without special measures being taken, and naturally the same applies also to the arrangements with addressable registers shown in FIGS. 13, 15 and 17. A means for ensuring the correct number of occupied stages can be to count all the age signals d, the signals greater than the mean number being considered as positive and those less than the mean as negative. If the mean value so determined exceeds certain upper and lower limits, then correction is effected by, for example, automatically withdrawing an additional address impulse from the register or inhibiting an impules withdrawal. It is however also possible to add the age signals taken from the age corrector AK by means of a binary counter, with simultaneous subtraction of the desired mean age. Deviation of the sum towards lower values indicates incorrect store occupation and may again be made use of by automatic additional occupation or withdrawal. Such control is advantageous even in arrangement without addressable registers for producing synchronization as rapidly as possible between the transmitter and receiver stores, for example, in the arrangements of FIGS. 6, 7 and 19. Here also the signals to be additionally introduced or withdrawn may serve for correction, e.g. the injection or withdrawal of age limit signals.

The quasi-randomly occurring encoding signal w can be derived from a randomly occurring control signal u which, for example, can originate with a noise voltage, the specifically timed transient values of which affect a parameter of the control signals u. The encoding signal w comprises a series of pulses which are derived in accordance with a predetermined set of rules from some parameter (e.g. pulse polarity or pulse edge timed position) of a plurality of previously generated pulses comprising control signals u.

The manner in which the encoding signal w may be derived from control signal u can be better understood with reference to FIGS. 30 and 31. A typical control signal u is illustrated in FIGS. 30a and 31a and comprises a plurality of equally spaced pulses having an equal height and either a positive or negative polarity. In the example shown, the output pulse train v (see FIGS. 30 and 31) generated by the program transformer is also composed of a series of equally spaced pulses whose polarity is determined by the polarity of several preceding control signal pulses u.

According to FIG. 30, the polarity of the pulse v.sub.n is determined by the polarity of m directly consecutive preceding pulses of pulse train u. In the particular example shown, m has been selected as being equal to 17. The 17 dominant pulses of pulse train u which determine the polarity of output pulse v.sub.n are emphasized by thick solid lines.

According to the example illustrated in FIG. 31, the polarity of each pulse v is determined by the polarities of several preceding pulses of pulse train u. However, the pulses of pulse train u which determine the polarity of the output pulse v are not in direct-consecutive sequence. Additionally, the number of pulses u which determine each pulse v need not be the same. In the example shown, the polarity of pulse v.sub.n is given by the product of the polarities of the series of 14 pulses u emphasized by thick lines in FIG. 31b. Similarly, the polarity of pulse v.sub.n-1 is determined by the product of the polarities of the 13 pulses u emphasized in FIG. 31c. As is apparent, the number and sequence of pulses u which are used to determine the polarity of pulses v.sub.n and v.sub.n+1, respectively, are not the same.

To ensure encoding safety, the number of pulses u which are utilized to determine the polarity of the pulse v should be sufficiently high. If the number of pulses u determining the polarity of the pulse v is m, then, e.g., with the process illustrated in FIG. 31 the largest possible variation is 2.sup.m potential distributions for this group of m pulses.

To make any unauthorized decoding difficult, an attempt must be made to reduce the probability that consecutive groups of m pulses u are identical. The probability of such repeats decreases with the number of potential distributions of the pulses u. Particularly, the probability decreases exponentially with increasing values m.

FIGS. 32 through 34 illustrate block diagrams of several program transformers which may be utilized to generate the type of output pulses illustrated in FIGS. 30 and 31.

The embodiment illustrated in FIG. 32 operates according to the process illustrated in FIG. 30. The control signal u is applied to a delay line VE having a plurality of outputs A.sub.I -A.sub.1. The delay line VE stores a plurality of previously generated control pulses u such that such pulses can selectively be picked off by multiplier KA. The signals stored in delay line VE represent the dominant pulse group which will determine the polarity of the output pulse w. The multiplieri KA generates signals v.sub.1 through v.sub.n from each applicable number of pulses selected from the group a.sub.1 to a.sub.i. A second circuit component ZE produces the signal w from pulses v.sub.1 to v.sub.n.

FIGS. 33 and 34 illustrate an embodiment of the invention which operates in accordance with FIG. 31. In this embodiment, the number of pulses u and their position within the dominant group is not constant. Accordingly, switching means are provided which are respective to the control signal u and which permutate the connections between the delay line outputs and the multiplier KA according to any predetermined program. In this case, the number of outputs can exceed that of the number of multiplier inputs.

Generally, the foregoing operation can be explained with reference to FIG. 33. The program transformer RG2 actually generates the output signal v which, after further conversion, (i.e. through ZE in FIG. 32) serves as the control signal u. The particular program which will be utilized to generate the output signal v is changed at specified times by unit RG1 which is also controlled by control signal u.

FIG. 34 illustrates a detailed example of a program transformer operating in the foregoing manner. Control signal u passes through delay line VE.sub.1 of unit RG1. After passing through delay VE.sub.1, control signal u is applied to the second delay line VE.sub.2. Multiplier KA.sub.2 generates an output signal in accordance with one of the plurality of predetermined programs stored therein. Each program will generate an output pulse in accordance with the polarity of predetermined ones of previously generated control pulses u as illustrated in FIG. 31. The particular program which is utilized by multiplier KA.sub.2 is intermittently changed by a signal s.sub.2 applied thereto. The signals s.sub.1 and s.sub.2 are produced by a multiplying unit KA.sub.1 which is responsive to the outputs of first time delay circuit VE.sub.1 and therefore also responsive to the control signal u. Multiplier KA.sub.1 further produces a third signal s.sub.3 which affects the program of memory SE such that the sequence of outgoing pulses v do not agree with the sequence of read in pulses b.

On designing the circuit components designated in FIG. 34, numerous known, technologically feasible logic circuit and electronic computer units may be utilized. Some feasibilities which can be realized by simple switching means, and whereby the output magnitudes b can be produced from only two input magnitudes a.sub.1, a.sub.2 is shown in FIG. 35. Particularly, this figure illustrates five possible programs A through E which may be utilized to produce the output pulses b. According to the program A, the sign of the output signal b is determined by the multiplication of the input pulses a.sub.1, a.sub.2. According to the program B, the sign of the output pulse b is determined by the sum of the input pulses a.sub.1, a.sub.2. According to the program C, an output pulse of equivalent polarity is produced only if both input pulses are of the same polarity. According to program D, the output pulse b has the sign of the sum of the input pulses, however, if the sum is 0, than the output magnitude retains the level which it occupied at the immediately preceding pulse time. Finally, according to program E, the magnitude of the output signal b is changed only when the polarity of both input signals are identical. With all of the combinations, the output of both polarities remain at the same level as the previous pulse time.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.