DE2747454C1 - Message transfer system with frequency hopping - Google Patents

Description

The invention relates to a message transmission system for simplex operation in which the carrier frequencies jump changed preprogrammed within short intervals be with adaptive multiple transmission of the message on different Frequencies and a receipt return for optimal Adaptation of the system to the respective disturbances, the both by propagation disturbances (multipath propagation, man- made-noise) as well as caused by targeted disruptive measures could be.

There are known communication systems in which frequency hopping is worked, d. H. the carrier frequencies in continuous change preferably periodically within a very long time short time units are changed. Examples of this form the DE-PS 19 49 351 or DE-PS 19 54 754. In these Systems will each be a jump at short intervals Changing the carrier frequencies made according to a specific scheme. This scheme is for all stations involved in message traffic are known and, for example, via a Period of one day stored in the system computer. This System computer is encrypted with military radio systems Messaging work, in the form of a Cryptology device anyway available.  

As a rule, these frequency-hopping transmission methods work with digital messaging in the Time division duplex mode; this means that the message is in each flow direction initially stored at short notice, and then alternately in compressed form blockwise and is sent out at twice the bitrate. For every block In this case, a changed transmission frequency is selected.

Through this block organization are for each participant between the transmission blocks receive blocks of the same period provided for the simultaneous reception of messages of the partner (duplex mode).

In military intercommunication prevails in general a high speech discipline, this means that almost exclusively only one partner or the other speaks. This means that in duplex mode there is one transmission direction unused and the designated time practically wasted.

The invention is based on the object, a message transmission system of the type described in the introduction to be specified, taking into account the maximum permissible Funkbitratenerhöhung optimal redundancy and thus allowing a maximum of interference immunity.

Starting from a message transmission system with Radio transceivers, in which the carrier frequencies leaps and bounds preprogrammed within short intervals to change a scheme and in which the transfer the message digitized and block by block in each case  a period of fractions of a second or more times preferably at different carrier frequencies (redundancy) takes place and on the sending side the message in a memory compressed and the receiving side in there Memory expands and returns to the original signal is joined together, this object is achieved according to the invention solved by the fact that the transmission of the message each in one direction (simplex operation) made is and between the blocks a versus the total time one block short acknowledgment signal from the receiving station is sent to the transmitting station, if necessary one or more faulty blocks automatically adapted to the current transmission conditions, then to repeat if necessary and for that purpose in the transmit-side memory (SSP) one of the average block repetition rate appropriate compression made is.

In itself, DE-AS 23 61 785 already discloses a simplex Transfer device known in which the blocks transmitted combined signals to the receiving side and there to be examined for errors. Upon detection of Errors are sent via a feedback signal sending the disturbed Blocks repeated. However, this arrangement works on the principle of a half-duplex operation, in which the Waiting time between two sending blocks equal to the transmission time a block is. An optimized redundancy will not achieved in this system, also will not be here made use of a frequency hopping method.

The introduction of simplex operation will therefore increase the transmission redundancy (multiple transmission) used, in order to increase the resistance of the system both against targeted Increase disturbance as well as against fading. The adaptation of the system to the respective transmission conditions Automatically takes place within wide limits automatically adaptive multiple transmission system.  

To the intended multiple transmission frequency hopping with simplex operation to the respective transmission conditions (Interference) automatically and optimally to be able to adjust is a short acknowledgment of receipt required participant to the sending required. The designated acknowledgment block only has a small fraction of the length of the message block and thus changes the messaging available time only minimal.

The implementation of the method is advantageous in that on the transmission side for the signal compression and signal delay a memory is provided and the output signals of this memory to a transmission Receivers are given, that further the acknowledgment signal from the receiving part of the transceiver to the memory acts accordingly, and that the same arrangement on the opposite side is provided for the radio subscriber.

For the feedback, it is useful if for the better Transmission of the acknowledgment signal respectively accordingly briefly switching the transmission-reception directions is made.

In a preferred type of process, it is advantageous if at the occurrence of disturbances a block up to a maximum  specified number is repeated until the acknowledgment signal transmitted for correct reception by the other party and meanwhile the transmission memory has accumulated in the meantime message to be transmitted initially except for one before set the appropriate number of blocks, the maximum Repeatability equals, withholds (temporary memory) and that when overflowing this short term memory (i.e. without acknowledgment entry) the further messages to be transmitted inevitably be transferred and the following good Transfer again a time limit for the multiple transmission is formed in the temporary memory.

The invention will be described below with reference to figures which follow include, explained in more detail.

Fig. 1 shows the radio bit rate increase as a function of the redundancy factor in the frequency hopping,

FIG. 2 shows a time diagram of a interference-free duplex link with time division multiplexing without transmission redundancy with frequency hopping method, FIG.

Fig. 3 shows a timing diagram of a slightly disturbed simplex route without transmission redundancy with frequency hopping,

Fig. 4 shows a timing diagram of a highly disturbed Simplex track with dual emission = 2 for frequency hopping,

Fig. 5 shows a timing diagram of a highly disturbed simplex route with adaptive Six transmission and handshaking = 2 for frequency hopping,

Fig. 6 shows a block diagram of Funkanlge for automatically adapting multiple transmission when frequency hopping.

Before now the invention is explained in more detail, should on the basic Features of frequency hopping with duplex and Simplex transmission and the achievable transmission redundancy depending on the increase in the transmission bit rate  To be received.

The frequency hopping process is the form of system organization essentially determined by the radio-technical considerations permissible increases in the radio bit rate, the organizational form adhere. A basic measure of the radio bit rate is the Usage bit rate of the speech device used (eg vocoder = 1.8 kBd).

The increases of the radio bit rate are given by the following facts caused:

• 1. Time required for switching the radio systems on and off (transmitter, Receiver, synthesizer, transit times, etc.);
• 2. time required for signaling (eg bar code);
• 3. Time required for error detection (message backup);
• 4. Time requirement for the repetition of disturbed intervals (Redundancy);
• 5. System organization principle: alternating or double-talk (Simplex or duplex operation).

Points 1, 2 and 3 result in a total sum time requirement is not significantly involved in the increase of the radio bit rate. For this reason, these points will be for further consideration summarized.

To what extent point 4 contributes to increasing the radio bit rate depends from the redundancy factor R. The redundancy factor R is defined by the ratio of the number of sent intervals to the number of intervals, with their proper reception counted becomes.

Example: R = means that out of 5 sent intervals only 4 to be expected to be receivable, or in other words in statistical terms  Means every 5th interval represents a repetition. The 4 must be receivable as expected intervals thus containing the information amount of 5 intervals. The means an increase in the amount of information per interval of by the factor R = = 1.25. If one generally designates the number the intervals after which a repetition is possible or necessary is, with n, so will

The radio bit rate is thus a function of R.

Point 5. (simplex or duplex operation) represents two very crucial Alternatives: For simplex operation go so far indicated facts proportional to the radio bit rate. In duplex mode, however, in principle with a factor of two.

Regardless of the organizational advantages of duplex operation when moving to other networks using radio concentrators the main disadvantage, which is the increase of the radio bit rate always, if one participant with the other speaks, the flow of information goes only in one direction. By Due to the duplex operation, but are the same time intervals for Sending and receiving provided, the alternatively not used and be given away, because whenever a participant hears, he does not speak like that and vice versa (especially in consideration the military speech, as well as the most provided Interpretation of the cryptology facilities in the vocoder).

A major argument for duplexing in a wireless network is the return of the receipt in the receiving Burst, because of the provided Redundancy R (see point 4) is basically necessary is. The redundancy provides a means by which the system properties digital and especially frequency-hopping radio networks considerably improved.

Since the receipt but is short against the interval duration could this principle, even with a slight reduction of the transmission interval (= slight increase of the radio bit rate) on the  same frequency be retransmitted. The redundancy with their Benefits can thus also be used with simplex systems. It even results in the further advantage that by the Acknowledgment on the same frequency is avoided that the Although the consignment would receive perfect, but the receipt due the disturbance of the next jump frequency is lost. This would lead to a completely unnecessary repetition and used up the transmission reserves provided as redundancy and practically correspond to multiplicative error propagation.

The following is an overview of the Funkbitratenerhöhung in simplex and duplex mode as a function of the redundancy factor R be given.

The following symbols are used for this:

B _f = radio bit rate,
B _n = useful bit rate,
S = simplex increase factor = 1,
D = duplex increase factor = 2, R = = redundancy factor,
x = additional bit requirement for duplex,
y = additional bit requirement for simplex with acknowledgment retransmission,
a = 10 = number of transmission intervals per second for duplex,
b = 20 = number of transmission intervals per second with simplex.

The factors for the additional bit requirements x and y include the beginning Points 1, 2 and 3 mentioned above (switching on and off, signaling and backup). These are for duplex: x = 40 bits, which are composed as follows:

Switching on and off | 8 bits Signaling (Barker code) 11 bits Fuse (EDC) approx. 21 bits total 40 bits

For simplex operation y = 45 bits:

Switching on and off | 8 bits signaling 11 bits Fuse approx. 10 bits directional shift 5 bits receipt 11 bits total 45 bits

For y, the backup bit requirement may be reduced by half, as well as the radio bit rate about a factor of 2 and thus the number of bits per interval is reduced.

The radio bit rate without considering x and y will now for duplex:

_Bf = _Bn * R * D (2)

for simplex:

_Bf = _Bn * R * S = _Bn * R (since S = 1) (3)

The ratio of radio bit rate to useful bit rate of (1), (2) and (3) is for duplex:

for simplex:

The equations of (4) and (5) are shown in FIG

Duplex _min and simplex _min applied.

If, on the other hand, one considers x and y and sets B _n 1800 Bd (vocoder), then:

for duplex:

for simplex:

In Fig. 1, equations (7) and (9) are shown as a function of R labeled Duplex Dx and Simplex Sx over the minimum curves (Dx _min , Sx _min ). The hatched part between the curves indicates the additional increase in the ratio caused by x and y, respectively

Fig. 2 shows schematically the signal distance of a trouble-free time duplex line without repetition possibility (R = 1).

The upper line 1 (the lines are in the figures each with Circles) shows the digital input signal that is in  Time blocks 1, 2, 3, etc. is divided. The individual time blocks were compressed by a factor of 2

and in the alternating transmission blocks S (Line 2) sent out by the user TLN A. Between the transmission blocks Receiving blocks E are provided, in which the subscriber A the transmission of the subscriber TLN B over the radio link FS receives.

In line 3, the subscriber B receives the program of the subscriber A in the reception blocks E and now puts them in line 4 decompressed and gapless as a continuous output signal to disposal. ti is the delay time between the Data signal input (line 1) and the data signal output (line 4).

According to the frequency hopping principle, each transmit and receive block on another preprogrammed frequency f₁, f₂, f₃, etc. (for a simplified representation is the Letter f placed before the whole line concerned) over the Transmitted radio link Fs.

As far as the radio link are regarded as trouble-free can, no interruptions occur in the message flow.

The equivalent ratios for simplex operation (intercommunication) are shown in FIG . However, it is already assumed here that slight disturbances in the radio link already occur, which means for a frequency-hopping system that a low percentage of the transmission frequencies can be totally disturbed (example f in FIG. 3). Are z. B. disturbed on average two out of ten frequencies, then arises according to the laws of error probability, a systematic error rate of 10%.

Line 1 in FIG. 3 shows the block-divided input signal which is transmitted in this block structure without compression, see line 2

The broadcast Each block is also here on each one another Frequency (f₁, f₂, f₃, etc.).  

Line 3 shows the receive blocks E which are the message blocks in line 4.

Due to the disturbance ST in the radio link at f₇ the receive block 7 (lines 3 and 4) is falsified to 50%. This corruption of block 7 corresponds to its maximum error expectation. Based on the entire time period considered from block 1 to block 12 in FIG. 3, this fault thus corresponds to an error expectation of

In earthbound radio fields occur partial and total disturbances of frequencies with increasing distance between transmitter and Receiver as a consequence of multipath propagation always more often. Added to this are the facilities in military systems of targeted disruptive measures. These effects lead to the fact that a high number of frequencies can be disturbed and so that the number of disturbed blocks increases rapidly. As soon as more than a block of 10 blocks is disturbed, the fail most digital language conversion procedures completely. So is the marginal error rate at the vocoder about only 1. , , 2%, for the Δ modulator however, about 10%. This occurs with the simplex method without redundancy even at relatively low levels of breakdown the collapse the communication link.

Basically, the effect of the disturbing influence changes, if a redundant transmission method is used. For example, suppose that on average every second block is disturbed, resulting in a strong interference of 50% of those used Hopping frequencies, so it is a minimum requirement, transfer each block at least twice. The forcible out of it resulting bit rate increase on the radio must be so for simplex operation at least a factor of 2

Increases the demand for immunity and expects that on average only 1/3, 1/4 or 1/5 of the hopping frequencies still readable signals, so must the bitrate increase be expanded accordingly to the factor 3, 4 or 5.  

A general prerequisite for this is that the respective Bitrate for reasons of multipath propagation (bit erasure) can still be increased by a certain factor, because otherwise the route for reasons of Bitauslöschung (critical Detour lengths) and the measure of the redundant Transmission is nullified.

Since from this point of view, the transmission bitrates are not made too high may be, the other invention describing relate Considerations on a bit rate increase = 2, which corresponds to a strong disturbance of 50% of the hopping frequencies.

Fig. 4 shows for these ratios, the basic scheme of the invention: The divided into blocks digital message signal (line 1) is compressed by buffering by a factor of 2 and in each of the transmission blocks S₁ and S₂, which alternate in succession, emitted by the subscriber A (line 2 ). It is generally the case that the transmission block S₂ always represents a repetition of S₁, which basically takes place on a different frequency. This generally applies to all further considerations.

In addition to the interference improvement by dual transmission, the already immunity to transmission on a single frequency Burst disturbance increases, comes with the fundamental two-frequency transmission a frequency diversity effect to bear, the both the system's resistance to multipath interference as also improved against targeted disruptive measures.

The undisturbed blocks are from the receiver of the subscriber B (Line 3) detected and after a repeated buffering decompressed read out (line 4), which in turn is a continuous Message stream is created. Inevitably, it is there but the receive data stream (line 4) compared to the transmit data stream (Line 1) delayed by one signal block length tr. These Delay but does not matter in simplex operation.  

In the interference conditions shown in Fig. 4, an irregular distribution of the disturbed frequencies is assumed. The resulting double interference are typical of the interference occurring in practice: double blocks occur at a mean block disturbance of 50% with a probability W₂ of 12.5%. The probability that the double interferences detect the first transmission block S₁ and likewise the repetition block S₂ of the same message block (eg block 9 in Fig. 4) is 6.25%. This results in a total disturbance of 50% of the hopping frequencies with the inventively proposed system, an error rate of 3.12%.

Under the same disturbance conditions, an error rate of 25% would already arise in the case illustrated in FIG. 3 (no transmission redundancy). The method according to the invention thus leads, under the same disturbance conditions, to an improvement by a factor of 8 already under the organizational possibilities shown in FIG .

However, the spurious distribution shown in FIG. 4 is not exclusively representative of the assumed spurious measurement of 50%: apart from single and double interference blocks, tristimulus, quadruple, quintuple interference blocks, etc. are also becoming less and less likely:

Triple blocks with a probability W₃ of 4.17%;
Quadruple blocks with a probability W₄ of 1.56%;
Fivefold blocks with a probability W₅ of 0.62%;
Six-fold blocks with a probability W₆ of 0.26%.

In a system design of Fig. 4, triple, quad, and fivefold blocks, etc. would clearly result in an increase in the error rate.

This circumstance can be avoided according to the invention (see FIG. 5) if the bit rate increase of = 2 is maintained, but the compressed transmission block (line 2) is adapted automatically more often than twice, if necessary, for example. B. a maximum of six times, repeated. Since this multiple repetition should not be considered as a further bitrate increase for reasons of multipath propagation (bit cancellation), it must inevitably lead to a higher delay of the message flow.

In the case of the ratios of a maximum possible adaptive 6-fold transmission of a block, as shown in FIG. 5, the delay for this reason is three signal block lengths 3 * tv. This means that with a single-frame signal length of 100 ms, a 300 ms voice delay occurs, which is in a range of values that is completely unproblematic for simplex operation.

The design of the automatic adaptive adaptation of the repetition However, to the occurring block disturbances must First of all, the prerequisite here is of course exclusively the bitrate increase = 2 resulting possibility, each Block on average twice to be repeated. So will too in turn, from a 50% error Leaping frequencies are assumed, although for other circumstances other parameters could be assumed.

The design of the automatic adaptation is a criterion which gives information about the momentary disturbance, incessantly necessary. This criterion requires a route check be performed. It will be for this purpose one of participants B perfectly received block with a short acknowledgment sending confirmed back to participant A. For the receipt transfer the transmitting / receiving direction becomes momentary switched.

The additional bit rate increase associated therewith and also with the necessary identification marks is taken into account in FIG. 1 as the upper limit of the hatched area and in the relevant formula (9) for simplex operation.

In the representation of Fig. 5, a double arrow, which bridges the radio link in each case for a block, a successful acknowledgment exchange and thus a perfectly received block.

If a disturbance occurs in the route, a block can not be received and the acknowledgment can therefore not be returned, or there is a fault in the return direction if the block reception is correct, but this is only relative because of the reversibility of the radio links for propagation reasons rarely occurs. In Fig. 5 these two cases are summarized for clarity and uniformly shown as an end in disturbance ST arrow.

The mode of action of automatic adaptation is based on that the A-subscriber increases the number of its repeats up to a predetermined maximum number depends on the receipt exchange makes. If an acknowledgment is received, then the block does not need more to be repeated, and then it can already be the next block will be sent.

As a special feature remains the fact that at completely undisturbed route each block forcibly sent out twice must be, even if the receipt is always the first time could be received. On undisturbed routes occur with it So repetition systematically on. With increasing Circuit disturbance forced repetitions become more and more rare and in case of severe disturbance (50% disturbed) only sporadically correspondingly the statistical probability of occurrence.

In the ratios shown in Fig. 5 is in the transmission of the message block 1 (line 1) already in the transmission block S₁ (line 2), the acknowledgment return instead. However, the message block 1 must now be forcibly repeated in the following transmission block S₂ on a different frequency, because at its transmission time of the message block 2 has not yet fully entered the cache. The second correctly transmitted block E is not read out.

In the next transmission block S₁, where the time condition for the transmission of block 2 is now met, this is also sent and receive the receipt.

The following transmission of block 2 in S₂ represents a compulsory repetition, which is disturbed, but due to the proper transmission of S₁ is also unnecessary.

Reverse conditions prevail in the transmission of block 3 , since this S₁ is disturbed. The transmission can thus take place only at block S₂. Now, since S₁ is disturbed, it is at S₂ but no longer a compulsory repetition, but a necessary repetition, which is read out in the participant B.

In block 4 , the same transmission conditions prevail as in block 2 . Again, the forced repetition is disturbed.

In the transmission of message block 5 S₁, S₂, S₃ and S₄ is disturbed. Thus, this block must necessarily be repeated 4 times on each different frequencies. In S₅ there is no fault, the block 5 can be transmitted here. In this case, block 5 has also been transmitted at five different hopping frequencies, which directly corresponds to a 5-fold frequency diversity.

In the transmission of block 7 and block 8 , no forced repetitions occur because in the transmission memory, caused by the interference in the transmission of block 5 , a block pool has accumulated. Thus, as long as a block stock is present, all immediately transferable blocks are sent only once and so the interference is automatically compensated again.

Although S₁ is disturbed in block 9 and thus S₂ represented a necessary repetition, is already exhausted in the successful transmission S₁ of block 11 of the block supply on the transmitting side again, and thus represents S₂ / block 11 again a compulsory repetition.

In block 12 , where the block supply is also exhausted, it is shown that in the event of a disturbance of five completely different hopping frequencies, a sixfold transmission can take place (sixfold diversity), which finally leads here to the transmission of block 12 .

This is now in the transmission memory again a corresponding block supply available, which is processed again depending on the interference (blocks 13 to 21 ). For the first time in block 22 then a forced repetition is necessary, etc.

Looking now at the line 4 in Fig. 5, it can be seen that despite these massive block disturbances in the radio link no interference in the data signal output take place.

Since longer coherent disorders but relatively rare and contiguous blocks of six (error on 6 completely different frequencies) only with a probability of 0.26% occur, the method shown here is suitable, with a medium distance disturbance of 50% a middle one Disturbance of the data signal output of only 0.13%.

The improvement of the error rate of this arrangement compared to a simplex path according to FIG. 3 (without redundancy, error 25%) thus represents a factor of = 192≈200.

Fig. 6 shows the basic structure of an arrangement according to Fig. 5: The data input DSE runs via the transmission memory SSP to the transceiver S / E, from which the acknowledgment signals Q are also given to the memory. In the transmission memory SSP, the data signal is compressed, stored between and read out as required, depending on the acknowledgment input.

In the receive memory ESP are recognized as correct blocks again correctly joined together and thus arrive at the data signal output DSA. The acknowledgment Q is transferred back to the A-subscriber.

Claims (4)

1. message transmission system with radio transceivers, in which the carrier frequencies are suddenly changed within short intervals preprogrammed according to a scheme in which the transmission of the message digitized and blockwise in a period of fractions of a second or more preferably on different carrier frequencies (redundancy ), and on the transmitting side the message is compressed in a memory and expanded on the receiving side in the local memory and is reassembled in the original signal, characterized in that the transmission of the message in each case in one direction (simplex) is made and between the blocks a to the Total time of a block short feedback signal is sent from the receiving station to the transmitting station to possibly one or more faulty blocks automatically adapted to the current transmission conditions, then repeat if necessary h, and in that for this purpose a compression corresponding to the average block repetition rate is undertaken in the transmission-side memory (SSP). 2. message transmission system according to claim 1, characterized characterized in that the transmitting side (TLN A) for the signal compression and Signal Delay Memory (SSP) is provided and the output signals of this memory on a transmission Receiver (S / E) are given, that further the acknowledgment signal  (Q) from the receiving part of the transceiver to the Memory (SSP) acts accordingly, and that the same Arrangement on the far side for the radio subscriber (TLN B) is provided. 3. Messaging system according to one of the preceding Claims, characterized that for better transmission of the Acknowledgment signal (Q) respectively correspondingly short time a switchover of the transmission-reception directions takes place.   4. message transmission system according to one of the preceding Claims, characterized that at the occurrence of disturbances one block up to a maximum specified number is repeated until the acknowledgment signal transmitted for correct reception by the other party and meanwhile the send memory (SSP) has become the meantime Accumulated message to be transmitted, except for one previously determined corresponding number of blocks that the corresponds to maximum repeatability, withholds (short-term memory) and that when overflowing this short term memory (i.e. without acknowledgment entry) the further messages to be transmitted inevitably be transferred and the following good Transfer again a time limit for the multiple transmission is formed in the temporary memory.