JPH04309024A - Time division communication secrecy method for mobile body communication - Google Patents

Abstract

PURPOSE:To prevent fading of mobile body communication in which a signal subjected to time compression is superimposed on a time slot of frame structure. CONSTITUTION:A time length of a time slot used for communication between a mobile radio equipment 100 and a radio base station 30, a time compression rate of the signal superimposed thereon, and a time axis inversion of a time piece signal are revised according to a predetermined sequence for each frame and the content of one time piece signal is sent at least twice. Thus, since a 3rd party not knowing the time length of the time slot for each frame, the time compression rate of the signal, its revision sequence and the inversion of time axis cannot receive a signal, high ciphering performance is attained, and since one signal is sent twice or over, effect of fading is relieved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a confidential communication method in time-division mobile communications. More specifically, given a radio channel, one of the many mobile radios in the service area is communicating with the opposing radio base station by setting up a radio link. The aim is to eliminate the possibility that a wireless device that does not belong to the system tunes to the same radio channel and the same time slot and intercepts the communication content, thereby improving the privacy of communication. be.

0002

[Prior Art] In mobile communication using voice using a small zone method, a method that employs time division time compression multiplexed signals and a small zone configuration that is closely related to the present invention are described in the following documents. .

[0003] Literature 1. Ito “Studying mobile phone systems-
Proposal of time-division time compression FM modulation method -” IEICE technical report
RCS89-11 July 1989

[0004] Literature 2. Ito “Studying mobile phone systems-
Theoretical study of time-division time compression FM modulation method” IEICE technical report RCS89-39 October 1989

[0005] That is, in Document 1, the transmission signal (
baseband signal) is divided into predetermined time intervals and stored in a storage circuit, and when read out, it is read out at a predetermined time slot at a speed n times faster than the speed at which it is stored in the storage circuit. Radio reception having reception mixers that communicate with each other and are built into mobile radios and radio base stations to angle-modulate or amplitude-modulate carrier waves with accommodated signals and transmit and receive them intermittently over time. A switch circuit is provided for the circuit, a wireless transmitting circuit having a transmitting mixer, a synthesizer applying voltage to the receiving mixer of the wireless receiving circuit, and a synthesizer applying voltage to the transmitting mixer of the wireless transmitting circuit, and intermittent the output of the synthesizer applied to each. , this intermittent state is synchronized with transmission and reception, and the same intermittent transmission and reception as described above is synchronized with that of the mobile radio device for the wireless base station communicating with the opposite side, and on the receiving side, in the predetermined time slot. In order to extract only the stored signal, the wireless reception circuit is opened and closed to receive the signal, and the signal obtained by demodulation is stored in a storage circuit, and when it is read out, it is read out at 1/n of the speed at which it is stored in this storage circuit. An example of a system has been reported in which the baseband signal, which is the original transmitted signal, can be reproduced by reading it out at a low speed. However, regarding signal transmission in this system, no explanation is given regarding measures to eliminate the adverse effects of fading that occur when transmitting through a transmission medium, particularly in space, such as transmission diversity.

[0006] Furthermore, in Document 2, a study is conducted on adjacent channel interference and co-channel interference, which are problems when applying the TCM (time division time compression multiplexing)-FM system as described above to a small zone. , the possibility of realizing the system is shown by appropriately selecting the system parameters. However, there is a possibility that a radio device that does not belong to the system may tune to the same radio channel, same time slot, and intercept the communication content, and it is necessary to prevent this from the viewpoint of privacy protection. , no explanation is given regarding this type of technology.

[0007]

[Problem to be solved by the invention] Documents 1 and 2 mentioned above
In this system construction example, a method for transmitting TCM (time division time compression multiplexing) signals transmitted from a wireless base station to a large number of mobile wireless devices, and a method for transmitting TCM (time division time compression multiplexing) signals from the mobile wireless devices to the wireless base station in accordance with the transmission method are explained. Although a TCM signal transmission method is disclosed, depending on the disclosed transmission method, it is possible to tune to the radio channel and time slot in use by other radios that do not belong to the system and listen in on the communication content. There remained a problem to be solved, which is relatively easy.

[0008]

[Means for Solving the Problem] When transmitting a TCM signal, a wireless base station transmits a compressed signal included in a time slot so that the original signal is transmitted at least twice at different times. A mobile radio that generates a code, extracts a code from a code storage unit, temporally compresses the transmitted signal according to the code, encrypts the divided time length and time compression rate for each frame, and communicates with the other side. The machine is given the ability to instruct the machine on the type of code, encryption, and decoding method.

[0009]

[Effect] Since the length of the temporally divided time accommodated in the time slot used and the time compression rate are changed for each frame, the TCM signal has a high cryptographic function equivalent to that of a digital signal. This makes it extremely difficult for a third party's radio equipment that does not belong to the system to listen in on the signal, which does not know the time length of the signal accommodated in the time slot or the order in which the time compression ratio is assigned. It is now possible to ensure the privacy of communications. Also,
When transmitting the TCM signal, the temporally compressed signal is transmitted at least twice at different times, resulting in a transmit diversity effect, which improves the signal's ability to transmit through space. It has become possible to significantly reduce the negative effects of fading that occurs when

0010

Embodiment FIGS. 1, 2 and 3 show a system configuration for explaining an embodiment of the present invention.

In FIG. 1, 10 is a general telephone network, and 20 is a gateway exchange for connecting the telephone network 10 and a wireless system. 30 is a wireless base station, which includes an interface with the gateway exchange 20, a circuit for converting signal speeds, a circuit for allocating and selecting time slots, a control unit, etc., and is responsible for setting and canceling wireless lines. , has a wireless transmitting/receiving circuit for exchanging wireless signals with the mobile wireless devices 100 (100-1 to 100-n).

[0012] Here, the barrier switch 20 and the wireless base station 30
There is a transmission line between them for transmitting communication signals 22-1 to 22-n including communication signals of communication channels CH1 to CHn and control signals.

FIG. 2 shows a circuit configuration of a mobile radio device 100 that communicates with a radio base station 30. Received signals such as control signals and call signals received by the antenna section are sent to the wireless receiving circuit 13 including a receiving mixer 136 and a receiving section 137.
5, and the output communication signal is sent to the speed restoration circuit 1.
38, a decryptor 175, and a clock regenerator 141.

Further, a part of the output of the receiving section 137 is applied to the decryptor 175 to decrypt the code sent from the wireless base station 30, and the decrypted output of the decryptor 175 is applied to the decryptor 175. and is input to the speed restoration circuit 138 and the encrypted time piece signal decoding circuit 179. Clock regenerator 1
41 reproduces a clock from the received signal and applies it to the speed restoration circuit 138, the control section 140, the timing generator 142, and the speed conversion circuit 131.

The speed recovery circuit 138 converts the speed (pitch in the case of an analog signal) of the divided control signals or compressed and divided communication signals in the received signal into instructions from the decryptor 175 for each time piece signal. restore at the same speed as
It is sent to the encrypted time piece signal decoding circuit 179. The encrypted time piece signal decoding circuit 179 has the same function as the encrypted time piece signal decoding circuit group 79 of the radio base station 30, which will be described later, and has the same functions as the decryption circuit 175 and the timing generator 142.
The output signal is input to the telephone section 101 and the control section 140 as a continuous signal.

[0016] In addition to the frame synchronization signal, the signal in the time slot, which is usually placed at the beginning of one frame, includes an uncompressed control signal, and this control signal includes cryptographic information, etc. This is processed by the code decryptor 175.
The data is decoded and input to the control unit 140. Regarding cryptographic information, there is a cryptographic storage unit 177 that stores, for example, a random number table, and this and the control unit 140 exchange information with each other. Furthermore, in order for the mobile radio device 100 to take the lead in encrypting communications, the code storage unit 177 and the code adder 176 are used.

The communication signal output from the telephone section 101 is input to the encrypted time piece signal forming circuit 178. This circuit has the same function as the encrypted time piece signal forming circuit group 78 of the wireless base station 30, which will be described later.
6 is in operation, the telephone signal is transmitted at the time interval according to the instruction, and if it is not in operation, the telephone signal is transmitted at the time interval instructed by the control unit 140 according to the code transmitted from the wireless base station 30. After performing time segmentation, it is sent to the speed conversion circuit 131.

The speed conversion circuit 131 increases (compresses) the speed of the communication signal (the pitch in the case of an analog signal) at a speed instructed by the coder 176 or the control unit 140 for each time piece signal. Transmission mixer 133 and transmission section 1
34. In addition,
The encrypted time piece signal forming circuit 178 receives the cipher from the cipher 176 operated by the control signal given from the control unit 140, and encrypts the signal transmitted to the wireless base station 30. Here, the cipher 176 operates only when it is desired to create a cipher different from the encryption process instructed by the wireless base station 30. Wireless base station 30
If the same content as the cryptanalysis method instructed by is applied to transmission in reverse, the operation described above will occur.

In addition, the timing generator 142 uses the clock from the clock regenerator 141 and the control signal from the control section 140 to control the transmission/reception intermittent controller 123, the speed conversion circuit 131, the encrypted time piece signal forming circuit 178, and the encrypted time piece signal forming circuit 178. It supplies necessary timing to the time piece signal decoding circuit 179 and the speed restoration circuit 138.

The mobile radio 100 further includes synthesizers 121-1 and 121-2, and a changeover switch 122.
-1, 122-2 and selector switch 122-1, 122
-2, the transmitter/receiver intermittent controller 123 and timing generator 142 are included, and the synthesizer 121-1, 121-2, the transmitter/receiver intermittent controller 123, and the timing generator 142 are the control unit. 140. Each synthesizer 121
-1 and 121-2 are supplied with a reference frequency from the reference crystal oscillator 120.

A radio base station 30 is shown in FIG. N-channel communication signal 22-1 with gateway switch 20
22-n are connected to the signal processing unit 31, which forms an interface, by a transmission path.

Now, the communication signals 22-1 to 22-n sent from the barrier exchange 20 are input to the signal processing section 31 of the radio base station 30. The signal processing section 31 is equipped with an amplifier for compensating for transmission loss, and also performs so-called 2-wire to 4-wire conversion. That is, the input signal and the output signal are mixed and separated, and the input signal from the barrier switch 20 is encrypted by the encrypted time piece signal forming circuit group 78 including the encrypted time piece signal forming circuits 78-1 to 78-n. After the signal is converted into a signal, it is sent to the signal speed conversion circuit group 51.

The output signal from the signal speed restoration circuit group 38 is decoded by an encrypted time piece signal decoding circuit group 79 including encrypted time piece signal decoding circuits 79-1 to 79-n, and then subjected to signal processing. 31, and further transmitted to the barrier exchange 20 using the same transmission path as the input signal. Of the above, the input signal from the gateway exchange 20 is input to the encrypted time piece signal forming circuit group 78 and divided into time intervals according to instructions from the encryptor 76.

Next, this output is input to a signal speed converting circuit group 51 including many signal speed converting circuits 51-1 to 51-n, and undergoes speed (pitch) conversion to the speed instructed by the coder 76. . In addition, the signal transmitted from the wireless base station 30 to the gateway exchange 20 has the output of the wireless receiving circuit 35.
The signal is inputted to the signal speed restoration circuit group 38 via the signal selection circuit 39, and after being subjected to speed (pitch) conversion to reduce the speed at the speed instructed by the decryptor 75, the encrypted time piece signal is input to the signal decoding circuit group 38. 79. In this circuit, telephone signals are reproduced at time intervals according to instructions from the decryptor 75 and input to the signal processing section 31 .

[0025] The encryption used in the present invention will be explained below. The encryption method used for TCM signals is the following basic encryption combination. 1) Randomize the temporal order of the arrangement of time piece signals. 2) Change the time length of the time piece signal (randomize). 3) The time piece signals delayed by a certain period of time are combined into a single signal by making them contact each other so that they do not overlap with other time piece signals. 4) Reverse the time characteristics of the time piece signal (reverse the time axis) (like reverse reading on a tape recorder). 5) After creating multiplexed signals, the position of each signal within the frame is randomized for each frame.

By combining 1) to 5) above, a wide variety of encryption will become possible and will be put to practical use. These can be realized with the circuits shown in FIGS. 2 and 3. Therefore, the encrypted time piece signal forming circuit group 78 and the signal speed converting circuit group 5
1 will be explained in detail using FIGS. 4 and 5.

FIG. 4 shows an encrypted time piece signal forming circuit 78- for communication channel number 1 among the encrypted time piece signal forming circuit group 78 and signal speed converting circuit group 51 in FIG.
Only communication channel number 1 and signal speed conversion circuit 51-1 are selected, and similar operations are performed for communication channel numbers 2 to n, so communication channel number 1 is used as a representative.

FIG. 5 is a time chart showing the signal processing state of each part of the circuit shown in FIG. Now, in FIG. 4, a series of telephone signals from the signal processing section 31 of FIG. 5(a) enters the encrypted time piece signal forming circuit 78-1 from the left side.

Hereinafter, the encrypted time piece signal forming circuit group 78-
1 will be explained. As shown in FIG. 4, this circuit is composed of two circuits: encrypted time piece signal forming sections 78-1-1 and 78-1-2. Also, its internal configuration is shown in Figure 4.
As shown, the switch circuit SW1-1 and the memory circuit M1
~M4, and includes a delay circuit φ. Now, the telephone signal 31 in FIG. 5(a) that comes in from the left is divided into two equal parts,
They are applied to switch circuits SW1-1 and SW1-2, respectively. The telephone signal is further divided into two equal parts by the switch circuit SW1-1, and time piece signals A1, A3, A5 in FIG. 5(b) are obtained.
, . . . and A2, A4, A6, . . . and are stored in the storage circuits M1 and M2, respectively. Next, the signal to the switch circuit SW1-2 passes through the delay circuit φ in advance to have a delay time equivalent to one time piece signal. The subsequent processing is further divided into two by the switch circuit SW1-2, and B1, B3, B5... and B2, B in FIG. 5(b).
4, B6, etc., and are stored in the memory circuits M3 and M4, respectively. The time piece signals stored in the memory circuits M1 to M4 are combined by wiring, and the state is schematically shown in FIG. 5(c).

Next, the time piece signals stored in the memory circuits M1 to M4 are read out and sent to the signal speed converter 51-1-1.
Alternatively, it is input to 51-1-2. In this signal speed converter 51-1, the time is compressed at the compression rate instructed by the coder 76 based on the instruction from the control unit 40, and the time length is controlled by the output signal of the coder 76, as shown in FIG. The signal shown in (d) is output. The outputs are mixed to form one series of time-compressed signals shown in FIG. 5(e), which is input to the signal allocation circuit 52-1.

The signal allocation circuit group 52 has the function of arranging the above telephone signals and other telephone signals in a line in time, converting them into a frame structure, and converting them into a form suitable for spatial transmission. However, on the other hand, this circuit also polarizes the signal. This effect will be described later. Further, the signal selection circuit group 39 has a function completely opposite to that of the signal assignment circuit group 52 described above. This effect will also be described later.

Next, the operations of the signal speed restoration circuit group 38 and the encrypted time piece signal decoding circuit group 79 to which the output of the signal selection circuit group 39 is applied will be explained in detail with reference to FIGS. 6 and 7.

FIG. 6 shows the signal speed restoration circuit group 3 in FIG.
8 and the encrypted time piece signal decoding circuit group 79, only the signal speed restoration circuit 38-1 and the encrypted time piece signal decoding circuit 79-1 for the communication channel number 1 are selected. .about.n is also represented by the communication channel number 1 since the same operation is performed. FIG. 7 is a schematic diagram showing the signal processing state of each part of the circuit shown in FIG. 6.

Now, in FIGS. 6 and 7, FIG.
) The output of the signal selection circuit 39-1 shown in FIG. 6 is input to the signal speed restoration circuit 38-1 from the right side of FIG.
-1 and memory circuits 38-1-1 and 38-1-2, and the switch 48-1 installed on the input side is switched to the 48-1-1 side or to the 48-1-2 side. Whether it is switched or not, the timing signal is sent to the timing generation circuit 42.
, and is performed cyclically in synchronization with the time slots within the frame.

FIG. 7 (
As shown in b), the time-compressed time segment signal divided into two is processed by signal speed restorers 38-1-1 and 38-1, respectively.
8-1-2, where time expansion is applied to each signal, and the state before the signal is restored is reached as shown in FIG. 7(c). However, if this continues, the original signal will not be restored. This is because the temporal arrangement of the time piece signals of the original signal is encoded. This state is shown in FIG. 7(c).

In order to restore the actual voice signal from among the above signals, a decryption signal from the decryptor 75 is required, and in accordance with this signal, the decryptor 7 decrypts the encrypted time-piece signal.
At 9-1-1 and 79-1-2, it is necessary to cut the signal time piece into the same length as that at the time of transmission. Therefore, by taking the sum of these signals, a time piece signal as shown in FIG. 7(d) is faithfully reproduced and sent to the signal processing section 31 as a series of telephone signals.

Here, the sum of the signals in FIG. 7(c) is calculated as (d
), the signals with better signal-to-noise ratios (S/N) are made larger and those with worse signal-to-noise ratios are made smaller in proportion to the S/N and are synthesized. This is possible by using the information obtained by the reception quality monitoring section 59 shown in FIG.

Now, the control of the radio reception circuit 35 or the output of the call signal is performed by the signal selection circuit group 3 including signal selection circuits 39-1 to 39-n that select signals for each time slot.
9, where the speech signals are separated corresponding to each speech channel CH1 to CHn. This output undergoes signal speed (pitch) restoration in a signal speed restoration circuit group 38 including signal speed restoration circuits 38-1 to 38-n provided for each channel, and then is input to the signal processing section 31. , 4 line-2
After undergoing line conversion, the output is sent to the barrier switch 20 as communication signals 22-1 to 22-n.

[0039] The encryption processing in the system example to which the present invention is applied as described above is a simple one. In practice, even more complex encryption may be applied. Various types of encryption will be explained below using FIG. 8 while referring to FIG. 4.

Case 1 in FIG. 8 randomizes the temporal order of the time piece signal arrangement, and the cipher time piece signal forming units 78-1-1 and 78-1-2 as shown in FIG. The configuration of the two circuits becomes quite complex. That is, in order to improve encryption, for example, the switch circuit SW1-1
, the number of contacts of SW1-2 is eight, and eight memory circuits are also required. In this case, the encryption is 1
It has a period eight times as long as one time piece signal. Furthermore, the output of the readout section from the storage circuit is not only simply combined by wiring as shown in FIG.
The outputs of a total of 16 memory circuits, 8 of each, must be synthesized. Also, the transmitted signal has 1
This results in a signal delay eight times that of a single time piece signal.

In case 2 of FIG. 8, the time length of the time piece signal is changed, and as shown in the time chart, the randomization within one cycle of encryption is considerably increased.

Case 3 is a case in which a delay time is given to one of the signal sequences in cases 1 and 2 above. In this encryption, the signal delay time given to the transmitted signal is further added by the given delay time.

Furthermore, the time axis inversion of the time piece signal shown in case 4 of FIG. 8 clearly expresses the characteristics of the TCM signal, and is an unprecedented encryption method. That is, for example, reversing the time axis of signal A5 and reading it is as shown in FIG.
When reading time piece signals from the memory circuits M1 to M4, the last signal inputted is read out first, and the first inputted signal is read out last to obtain the time axis inverted signal A5R.

Each case shown in FIG. 8 is a basic encryption method, and combining these cases provides a high degree of encryption.

[0045] The signal encrypted by the above-described encryption method is transmitted from a wireless transmitter, received by a receiver, and then decrypted. It will be obvious that this decryption method can be achieved by completely reversing the encryption process as described above.

Next, the functions of the signal speed conversion circuit group 51 will be explained.

For example, it is 15 times faster than when input signals such as audio signals and control signals divided into a certain length of time are stored in a storage circuit, and when read out, the speed is changed depending on the signal from the coder 76. By reading at a speed of , it is possible to compress the time length of the signal. The principle of the signal speed conversion circuit group 51 is the same as when playing back audio recorded by a tape recorder at high speed, and in reality, for example, a CCD (Charge Coupled
Device ), BBD (Bucket Brig
ade Device) can be used, and the memory used in television receivers and tape recorders that compress or expand the time axis of conversation can be used (References: Kosaka et al. ``Compressing the time axis of conversation /Extending Tape Recorder” Nikkei Electronics, July 26, 1976, pp. 92-133)
.

CCD exemplified in signal speed conversion circuit group 51
As described in the above-mentioned document, a circuit using a BBD can also be used as it is for the signal speed restoration circuit group 38, and in this case, the clock from the clock generator 41 and the control signal from the control section 40 can be used as is. Upon receiving a timing signal from a timing generator 42 that generates timing,
This can be achieved by making the reading speed slower than the writing speed.

The control or audio signal output from the barrier switch 20 via the signal processing section 31 is input to the signal speed conversion circuit group 51, and after speed (pitch) conversion processing is performed, the signal is converted into a time slot. It is applied to a signal allocation circuit 52 that allocates signals separately.

The details of this signal allocation circuit 52 are shown in FIG. 9, as shown in FIG.
, n and a switch matrix TSW. With the information, the signals in the buffer memory BM1 are read out and sent to the switch matrix TSW of the latter. Opening and closing of the switches in the switch matrices TSW1-1 to nn are performed using control signals output from the encryption device 76. And this switch matrix T
When looking at communication signals in terms of channels, the opening and closing of SWs are arranged in series with no overlap in time.
When all of the speech signals or control signals described below are implemented, they appear as if they were continuous signal waves.

The above-mentioned signals are sent to the wireless transmission circuit 32. The state of this compressed signal is shown in FIG. 10 and will be explained.

The output signal of the signal rate conversion circuit group 51 is input to the signal allocation circuit 52, and the time slots for each frame F1, F2, F3, . It will be done. S in FIG. 10(a)
D0, SD1, SD2, ..., SDn are speed-converted communication signals that are assigned different numbered time slots for each frame, such as time slot SD1 of frame F1, SD2 of F2, and SD3 of F3. This indicates that the

Note that the first time slot SD0 of each frame in FIG. Control signals and/or speech signals in response to calls from 100 are accommodated. If call signaling is not implemented,
An empty slot signal is added to the speech signal portion, or in some systems, no signal is transmitted at all, including the carrier wave. In this way, as shown in FIG. 10(a), in the radio transmitting circuit 32, signals forming one frame in time slots SD0, SD1 to SDn are applied to the modulation circuit. The time-series multiplexed signal to be transmitted is angularly modulated in the radio transmission circuit 32, and then sent out into space from the antenna section.

[0054] As described above, the control signal transmission between the radio base station 30 and the mobile radio device 100 prior to the telephone call is carried out using the time slot SD0. Depending on the system, it is possible to use either in-band or out-of-band telephone signals. FIG. 11 shows these frequency relationships. In other words, in (a) of the same figure, there is an example of an out-of-band signal, and as shown in the figure, there is a low frequency side (250Hz) and a high frequency side (3850Hz).
Hz) can be used. This signal is also used, for example, when it is desired to send a control signal during a call, or when a signal is being encrypted, which will be described later. (b) in Figure 11
) shows an example of an in-band signal, which is used when making and receiving calls.

[0055] Although the above examples were all tone signals, it is possible to transmit many types of signals at high speed by increasing the number of tone signals or modulating the tone to create a subcarrier signal. becomes.

[0056] The above was a case of an analog signal, but if a digital data signal is used as a control signal, it is also possible to digitally encode the audio signal and time-division multiplex the two for transmission. , the circuit configuration in this case is shown in FIG. FIG. 12 shows an example of a case where an audio signal is digitized by a digital encoding circuit 91, and a data signal is multiplex-converted by a multiplex conversion circuit 92, and then applied to a modulation circuit included in the wireless transmission circuit 32. The audio signal and the control signal can be extracted separately by receiving the signal with the opposing receiver and performing the operation opposite to that shown in FIG. 12 in the demodulation circuit.

On the other hand, the signal sent from the mobile radio device 100 is received by the antenna section of the radio base station 30 and input to the radio reception circuit 35. FIG. 10(b) schematically shows this upstream input signal. That is,
Time slot S for each frame F1, F2, F3,...
U1, SU2, ..., SUn are mobile radio devices 100-1,
100-2, . . . , 100-n show transmission signals addressed to the wireless base station 30. Also, each time slot SU1, SU
2,..., SUn is shown in detail in Figure 10(b).
As shown in the lower left corner of , it consists of speech signals and/or control signals. However, when it is desired to make a call or emergency communication from the mobile radio device 100 to the radio base station 30, the time slot SU0, which is always placed at the beginning of each frame, is used.

Now, among the input signals that have arrived at the radio base station 30, the control signal is immediately applied to the control section 40 from the radio reception circuit 35. However, depending on the magnitude of the speed conversion rate, it is also possible to apply the signal to the control unit 40 from the output of the signal speed restoration circuit group 38 after performing the same processing as the call signal. Further, the call signal is applied to a signal selection circuit group 39 whose details are shown in FIG. The output from the radio receiving circuit 35 is first stored in the buffer memory BM2, and then, in response to a control signal instruction from the control section 40, a timing signal from a timing generation circuit 42 that generates a predetermined timing is applied. Since the switch matrix RSW is opened and closed by the control signal from the decryptor 75, each time slot S
A call signal or a control signal is separately output for each of U1 to SUn. As a result, when viewed from the perspective of communication channels, the signal becomes a pulse train of signals before encryption is performed in units of time slots on the transmitting side. Each of these signals is input to a signal speed restoration circuit group 38. This circuit is a speed conversion circuit 131 (FIG. 2) in the mobile radio device 100 on the transmitting side.
This function allows the original signal to be faithfully reproduced and transmitted to the gateway exchange 20.

[0059] The secrets of the present invention will be explained below.

The code storage unit 77 in FIG. 3 stores information necessary for the secret story, such as a number sequence that follows a certain rule, such as a random number table, and the same type of function is also stored in the code storage unit 177 of the mobile radio device 100. Equipped. Now, wireless base station 3
The control section 40 of No. 0 extracts the encryption information from the encryption storage section 77 and provides it to the encryption device 76. Encryption device 76
Now, the switch matrix TSW of the signal assignment circuit 52
(Fig. 9) into a signal suitable for operation, opens and closes the switch matrix TSW, and the signal speed conversion circuit group 5
After temporarily storing the compressed pulsed signal input from BM1 in the buffer memory BM1 (FIG. 9), the time slot number within the frame to be accommodated can be changed by reading out the signal sequentially in time. is performed for each frame and then sent to the wireless transmission circuit 32.

FIG. 14 shows the operation of the switch matrix TSW based on the output from the coder 76 for n sets of signal strings output from the signal speed conversion circuit group 51. In the figure, the pulse-like signal of communication channel number 1 (CH1) is accommodated in time slot 1 of frame number 1 (F1), and then is transferred to time slot 2 of F2, and thereafter, as the frames progress, the pulse signal is accommodated in time slot 1 of frame number 1 (F1). - The slot number is sequentially decreased to time slot n of Fn, and then returns to time slot 1 of F1. Below, time slot 2 of F2 and time slot 2 of F3 are shown again.
The operation of moving down to slot 3, etc. is repeated. Similarly, the pulse-like signal of speech channel number 2 (CH2) is delayed one by one from CH1, and the time slot is 2 in the first frame F1, 3 in the second frame F2, and so on, which is 1 time slot compared to CH1.
This indicates that the value is moved down step by step.

Although FIG. 14 is a simple example of encryption, in reality, the time slot number is not simply decremented by one, but the time slot number is, for example, 5. , 7, 13, 2, . . . are completely randomly assigned. The transmission signal to which such a time slot has been assigned is transmitted to the mobile radio device 100, but the mobile radio device 100 uses cryptographic information specified in the time slot SD0 including a control signal in advance to transmit the transmission signal to the mobile radio device 100. It will wait at the time slot number assigned to 100. In other words, the transmission/reception intermittent controller 123 is turned on and off by a process explained in the section on making a call from the mobile radio 100, which will be described later, so that the telephone unit 101 reproduces only the signal transmitted to itself. become.

On the other hand, when the signal transmitted from the mobile radio device 100 uses the cipher assigned by the radio base station 30, the signal transmitted from the mobile radio device 100 is transmitted through the time slots indicated by the communication channel and frame numbers shown in FIG. Use the same time slot number sequence for both sending and receiving. If the mobile radio device 100 independently assigns a password, it is necessary to follow the procedure described below. Confidentialized TC explained above
The M signal is sent into space from a transmitting antenna.

As shown in FIG. 3, the control signal from the control section 40 is applied to the wireless transmission circuit 32 in parallel with the output of the signal allocation circuit group 52. However, depending on the magnitude of the speed conversion rate, it is also possible to apply the signal to the wireless transmission circuit 32 from the output of the signal allocation circuit group 52 after performing the same processing as the call signal. As shown in FIG. 2, the mobile radio device 100 also has a circuit configuration required when one channel is used as a communication path among the functions of the radio base station 30.

In this case, the control signal input from the mobile radio device 100 to the radio base station 30 is input to the radio reception circuit 35, but a part of its output is input to the control section 40,
The others are connected to the signal speed restoration circuit group 38 via the signal selection circuit 39.
sent to. After the latter control signal undergoes speed conversion (conversion to a low-speed signal) that is completely opposite to that at the time of transmission, it becomes the same signal speed as that used in the general telephone network 10, and is transmitted via the signal processing section 31. and is sent to the barrier exchange 20.

Next, the call originating/receiving operation of the system according to the present invention will be explained using a voice signal as an example.

(1) Call origination from mobile radio device 100 FIG. 15
This will be explained using the flowchart shown in FIG.

When the power of the mobile radio device 100 is turned on, the radio reception circuit 135 in FIG. Start capturing control signals. If the system is provided with multiple radio channels, i) the radio channel exhibiting the highest received input field ii)
(iii) A wireless channel instructed by a control signal included in the wireless channel (iii) A channel with an empty time slot among the time slots in the wireless channel, etc. CH1) is in the receiving state. This is possible by capturing the synchronization signal within time slot SD0 shown in FIG. 10(a). In the control unit 140, the synthesizer 121-
A control signal is sent to the synthesizer 122-1 to generate a local frequency that enables reception of the radio channel CH1, and the switch 122-1 is also fixed in the position of the synthesizer 121-1.

Therefore, the handset of the telephone section 101 is turned off.
When hooking (starting calling) (S201, Figure 15), Figure 2
The synthesizer 121-2 receives from the control unit 140 a control signal that generates a local frequency that enables transmission of the wireless channel CH1. Further, the switch 122-2 is also turned toward the synthesizer 121-2 side and becomes fixed. Next, the calling control signal output from the telephone unit 101 is sent out using the radio channel CH1. This control signal is transmitted using time slot SU0 of the uplink radio channel shown in FIG. 10(b). This time slot is always placed at the beginning of each frame and is unrelated to the time slot encryption described below.

This control signal is sent in time slot S.
Since the signal is limited to U0 and is sent in bursts and no signals are sent during other time periods, it does not adversely affect other communications. However, if the speed of the control signal is relatively slow or the amount of information in the signal is large and cannot be accommodated in one time slot, the time slot of one frame later or the next frame will be used. Sent using SU0.

On the other hand, in the control section 40 of the radio base station 30,
Detects the ID (identification signal) of the mobile radio device 100 (S20
2) Since the ID is confirmed, the communication channel designation signal and encryption information necessary for making a call to the mobile radio device 100 are transmitted to the mobile radio device 100 using the downlink time slot SD0 (S203). ).

The following operation will be explained assuming that transmit diversity is not implemented.

Mobile radio device 100, which has received the control information sent from radio base station 30, searches code storage unit 177 based on the code information, frame number, and communication channel, and determines the time slot number assigned to the mobile radio device 100. Assuming that the time slot is SU1 at the designated frame number 1 (F1), the time slot is switched to the designated time slot SU1 (S204), and using this, the slot switching completion signal is sent to the radio base. It is transmitted to station 30 (S205) and waits for a dial tone to be sent (S206).

Naturally, the radio base station 30 expects this and turns on the switch matrix RSW 1-1 (FIG. 13) to wait for reception, and when it receives the slot switching completion report (S207), it sends a message to the gateway exchange 20. mobile radio 1
A calling signal is sent together with ID 00 (S208). On the other hand, the barrier switch 20 turns on the necessary switches among the switch groups included in the barrier switch 20,
Send dial tone to wireless base station 30 (S21
0, Figure 16).

[0075] This dial tone is the radio base station 30
a time slot specified by the encryptor 76 in
For example, the switch matrix TSW1-4 is turned on to transmit in SD4, and the message is transferred to the mobile radio device 100 (S211), and the mobile radio device 100 confirms that the communication path has been set (S212). When this state is reached, a dial tone is heard from the handset of the telephone section 101 of the mobile radio 100, and the transmission of a dial signal begins. This dial signal is speed-converted by a speed conversion circuit 131, sent to a transmitting section 134, and sent to a transmitting mixer 133.
from the wireless transmission circuit 132 including the downlink time slot using the uplink time slot SU4 having the same number as the downlink time slot (S213). This signal is received by the radio receiving circuit 35 of the radio base station 30.

[0076] In the radio base station 30, the mobile radio device 1
In response to the call signal from 00, the wireless base station 3
0, the switch matrix RS of the signal selection circuit 39 is activated by the corresponding control signal from the decryptor 75.
Switch matrix TSW1 of signal assignment circuit group 52 is activated by turning on W1-4 and controlling the control signal of coder 76.
-7 is turned on, the uplink time slot SU4 is received, and the state is shifted to transmitting the downlink time slot SD7 signal. Therefore, the dial signal transmitted from the mobile radio 100 passes through the switch matrix RSW of the signal selection circuit group 39, and then passes through the signal speed restoration circuit group 38 to the encrypted time piece signal decoding circuit group 79.
Here, the original transmission signal is restored and transferred to the gateway exchange 20 as a call signal 22-1 via the signal processing unit 31 (S214), and a call path to the telephone network 10 is set (S215). .

On the other hand, the input signal from the barrier switch 20 (initial control signal, call signal when a call is started) is sent to the encrypted time piece signal forming circuit group 78 via the signal processing section 31 in the radio base station 30. After the polarized signal undergoes speed conversion in the signal speed conversion circuit group 51, it is sent to the switch matrices TSW1-7 of the signal allocation circuit 52 (Fig. 9)
gives time slot SD7. Then, the time signal of the wireless channel downstream from the wireless transmission circuit 32 is
It is transmitted to mobile radio device 100 using slot SD7.

In the mobile radio device 100, the radio channel CH
1 time slot SD7, the switch 122-1 is turned on and off using the output of the transmission/reception intermittent controller 123 to wait for reception, and the radio reception circuit 135
and its output is input to the speed recovery circuit 138. In this circuit, the original signal on the transmitting side is restored and input to the handset of the telephone section 101. Thus, a call is started between the mobile radio device 100 and a regular telephone within the regular telephone network 10 (S216).

[0079] Even after the call has started, the wireless base station 30
The time slot numbers used for transmission from or from the mobile radio device 100 are different for each frame, and their control follows instructions from the encryption devices 76 and 176 provided in each frame.

[0080] The call is terminated by the telephone section 101 of the mobile radio device 100.
By putting the receiver on the hook (S217),
The end of call signal and the on-hook signal from the control unit 140 are
The data is transmitted from the radio transmission circuit 132 to the radio base station 30 via the speed conversion circuit 131 (S218), and the control unit 140 stops the operation of the transmission/reception intermittent controller 123, and switches 122-1 and 122- 2 are fixed to the output ends of synthesizers 121-1 and 121-2, respectively.

On the other hand, in the control section 40 of the radio base station 30,
When the call termination signal is received from the mobile radio device 100, the call termination signal is transferred to the barrier switch 20 (S219), and the switch group (not shown) is turned off to terminate the call (S219).
220). At the same time, signal selection circuit group 3 in wireless base station 30
9 and signal assignment circuit group 52 are opened.

[0082] In the above explanation, the time and
Although slots (other than SD0 and SU0) do not display the ID of the radio base station 30 or mobile radio device 100 that uses them, in some cases an ID signal may be included in each time slot to facilitate communications. It is also possible to improve reliability.

[0083] To explain the method for this purpose, first, there is a method of assigning an ID to the beginning part of a signal within a time slot. However, since this reduces the usage time of the communication signal, it is advantageous to use an out-of-band control signal as shown in FIG. 17 to avoid this. That is, this is a method of displaying the ID using a digital signal or tone signal in the lower frequency band of the communication signal included in each time slot.

By using this method, even if interference occurs due to interference, the mobile radio 100 will transmit signals other than the own ID signal to the telephone section 101 and the radio base station. 30, by not outputting the signal to the signal processing unit 31, it is possible to prevent privacy problems due to interference.

[0085] The above explanation assumes that transmit diversity is not implemented, but if transmit diversity is implemented, the communication channel and encryption information necessary for making a call are transmitted to mobile radio 100 in step 203 (FIG. 15).
You can give one or more.

[0086] In the above explanation, the mobile radio 100 makes a call, but when a call is received, a similar confidential communication method is used. That is, to explain using FIG. 15, when incoming call information addressed to the mobile radio device 100 is sent from the barrier interrogator 20 to the radio base station 30, step S2
It is sufficient to add an incoming call indication to the encrypted information of 03 and transmit it to the mobile radio device 100. Thereafter, the mobile radio device 100 performs a process similar to that shown in step S204, and the call receiving operation proceeds.

[0087] The encryption information explained above was developed under the initiative of the wireless base station 30. The process proceeds in the same manner when the mobile radio device 100 takes the initiative. However, in this case, when a call occurs from another mobile radio, it is necessary to send the encrypted information to the radio base station 30 to avoid interference, which is somewhat inconvenient in practice. Further, the downlink signal may be encrypted information led by the radio base station 30, and the uplink signal may be encrypted information led by the mobile radio device 100, but in this case as well, the uplink signal is delivered to the radio base station 30, Other mobile radios will need to comply with this.

[0088] To summarize the above, it is considered that the wireless base station 30-led type is practical regarding encryption. Delay time of a signal in the communication system using a confidential message according to the present invention, that is, when the wireless base station 30 transmits and the mobile wireless device 100 receives, or when the mobile wireless device 100 transmits and the wireless base station 30 receives. from transmission to reception (listening to the original signal)
The time required to do this will be explained.

The following signal delays exist: (a) Signal delay occurring on the transmitting side i) In the case of randomizing the temporal order of the arrangement of time piece signals, there is a delay of one period of randomization. ii) When the time axis of the time piece signal is reversed, there is a delay of one time piece signal. iii) The effect of signal delay due to transmit diversity is T × p, where the frame time for transmit diversity is T, and the time interval of diversity is p. (b) Signal delay occurring on the receiving side i) Randomized time piece There is a delay of one period to restore the signal arrangement. ii) There is a delay of one time piece signal in restoring the time piece signal whose time axis has been reversed. iii) Diversity As the signal delay due to restoration of the transmitted signal, if the signal frame time is T and the diversity time interval is p, then T×p Therefore, the total transmission and reception signal delay is at most 2×(1 period + 1 time period) One side signal +T×p).

For calculating the delay time above, it is assumed that the time length of the control signal time slot is equal to that of the communication time slot, and the time required during spatial propagation of the signal and circuits such as mixers and amplifiers are The time required to pass through is ignored. Note that the specific circuit of the signal delay amount adjuster (not shown) included in the above-mentioned speed restoration circuit 138 may be a type of memory circuit, and the timing at the time of memory reading may be received from the timing generator 142. Become.

Next, the transmission diversity effect applied to the present invention will be explained. To do so, it is necessary to explain radio wave propagation characteristics.

[0092] In land mobile communications such as car telephones and train telephones, the antenna of the moving body (automobile, train, etc.) is installed at a low position of several meters above the ground.
There are many cases where there is no line of sight between the radio base station 30 and the mobile radio 100 due to interference from buildings, trees (referred to as terrestrial features), or uneven terrain around the mobile radio 100, so propagation loss is free. This is significantly larger than the spatial propagation loss. Further, as the mobile radio device 100 travels, the condition of the obstruction changes from moment to moment, and deep instantaneous fluctuations with fast cycles are observed. Car telephones are a typical example of mobile communication. The propagation characteristics in urban areas where there is a high demand for car phones will be explained based on propagation test data. Below, pages 15 and 16 of Document 3
Explain by citing the page.

Reference 3. Supervised by Kuwahara “Car Telephone” Institute of Electronics and Communication Engineers Published in 1985

FIG. 18 shows the instantaneous fluctuation characteristics of the reception level received using a horizontal omnidirectional antenna while driving a car over a short distance of about 10 meters in a city area. The reception level fluctuates in a range of 20 to 30 dB. Deep reception level attenuation (fading) is observed once every time the car travels a distance equivalent to half the wavelength of the received radio waves, when the rate of change is the fastest. This severe fading always exists as long as the automobile is running, and is therefore a factor that significantly deteriorates the transmission quality of audio signals and control signals.

Instantaneous fluctuations occur through the following propagation mechanism. Radio waves transmitted from wireless base stations are
After being diffracted and reflected by buildings near the car, it is received by the car's antenna. On roads with relatively good visibility, radio waves reflected from a distance can also be received. Therefore, it is thought that many radio waves (referred to as multiplex waves) with different propagation paths interfere with each other, resulting in standing waves on the road. When a car runs through this standing wave, the received voltage will fluctuate with a period proportional to the reciprocal of the wavelength of the standing wave and the speed of the car. Deep fading is called multipath fading because it is caused by the combination of radio waves that have passed through various propagation paths.

Now, as mentioned above, the fading pitch is determined by the speed of the moving object and the wavelength of the radio waves. A familiar example of the Doppler effect, in which the received frequency changes as a moving object moves, is the same as when a fire engine passes by with its siren blaring, the siren can be heard at a higher pitch, then at a lower pitch. It is a phenomenon. The angular frequency of each multiplex radio wave received by a car traveling at speed V is ωi = βV cos θi, where i = 1 to n, β = 2π/λ (λ: wavelength) 0≦θi ≦2π only changes. These frequency-shifted radio waves are received and combined by the receiver, resulting in
It can also be considered that fading occurs. The maximum Doppler frequency fD is V/λ. For example, 800
When MHz radio waves are received by a car traveling at 50 km/h, fading will be observed at a maximum pitch of about 40 Hz.

The above explanation was about general radio wave propagation characteristics. Hereinafter, it will be explained how effective TCM signals are when applying transmit diversity according to the present invention.

[0098] When the applied system is a car phone and the system is traveling at a speed of 50 km/h, fading is said to occur at a maximum pitch of about 40 Hz. This means that in a TCM signal with a frame period of 5 ms, there is a compressed time piece signal affected by severe fading every five frame periods.

By the way, if transmission diversity is to be implemented, if the diversity interval of the same transmission signal is selected to be about 10 to 15 msec, that is, if it is transmitted with a 1 to 3 frame time difference in terms of frame period, Even if the signal-to-noise ratio (S/N) of one signal deteriorates due to fading, there is a high probability that the other signal will not be adversely affected by fading. It can be seen that if selective reception is performed, the reception quality does not deteriorate much.

[0100] Analyzing the above phenomenon in more detail, we find that a single time piece signal that is adversely affected by fading does not deteriorate uniformly, but only partially, such as at the beginning, center, and end. In some cases. Of course, if the fading valley is deep, the entire time-piece signal may be destroyed. Therefore, the time piece signals A1, B1, A2 shown in FIG.
, B2, etc. should separately investigate the S/N of the time piece signals A1, B1, A2, and B2 to determine which time piece signal should be extracted.

[0101] It has become clear that the use of the secret communication method including transmission diversity according to the present invention has the effects described above, and it will be explained below that the effective use of frequencies is also achieved.

Generally, when transmitting a TCM signal, a guard time is provided between time slot signals that accommodate different signals in order to avoid the effects of multipath fading described above. The percentage of time in a frame occupied by guard time is usually about 5 to 10%, and the effective use of frequency is also decreasing at this percentage. However, as is clear from the time piece signals A1, B1, A2, B2, etc. shown in FIG.
There is no guard time in between. This is because this is one signal. Therefore, time piece signals A1, B1;
Compared to sending A2 and B2 separately, the guard
Effective use of frequency will be measured for the time period.

[0103]

[Effects of the Invention] As is clear from the above explanation, a secret method for TCM signals, which has not been disclosed in the past, has become practical, and the quality of signal transmission can be expected to improve by applying transmit diversity, so communication The reliability of TCM communication is also high, and it is difficult for a third party's wireless device not belonging to the system to overhear, and privacy in TCM communication can be ensured, which has a great effect.

[Brief explanation of drawings]

FIG. 1 is a conceptual configuration diagram showing the concept of a system of the present invention.

FIG. 2 is a circuit diagram of a mobile radio used in the system of the present invention.

FIG. 3 is a circuit configuration diagram of a wireless base station used in the system of the present invention.

4 is a detailed circuit configuration diagram of an encrypted time piece signal forming circuit and a signal speed converting circuit, which are the components of FIG. 3; FIG.

[Figure 5] Time diagram showing the signals of each part of the circuit shown in Figure 4.
It is a chart.

6 is a detailed circuit configuration diagram of a signal rate restoration circuit and an encrypted time piece signal decoding circuit, which are the components of FIG. 3; FIG.

[Figure 7] Time diagram showing the signals of each part of the circuit shown in Figure 6.
It is a chart.

FIG. 8 is a time chart of various encrypted time piece signals used in the present invention.

9 is a detailed circuit configuration diagram of a signal allocation circuit that is a component of FIG. 3; FIG.

FIG. 10 is a time slot structure diagram for explaining time slots used in the system of the present invention.

FIG. 11 is a spectrum diagram showing spectra of one embodiment of a speech signal and a control signal.

FIG. 12 is a circuit configuration diagram for multiplexing audio signals and data signals.

13 is a detailed circuit configuration diagram of a signal selection circuit which is a component of FIG. 3; FIG.

FIG. 14 is a diagram showing the relationship between speech channel numbers, frame numbers, and time slot numbers used in the system of the present invention.

FIG. 15 is a flow chart showing the flow of operation of the system according to the present invention.

FIG. 16 is a flow chart showing the operation flow of the system according to the present invention in conjunction with FIG. 15;

FIG. 17 is a spectrum diagram showing spectra of another example of a speech signal and a control signal.

FIG. 18 is a reception level fluctuation diagram in a short section of an urban area.

[Explanation of symbols]

10 Telephone network 20 Gateway exchanges 22-1 to 22-n Communication signal 30 Radio base station 31 Signal processing section 32 Radio transmission circuit 35 Radio reception circuit 38 Signal speed restoration circuit group 39 Signal selection circuit group 39-1 to 39-n Signal Selection circuit 40 Control section 41 Clock generator 42 Timing generation circuit 51 Signal speed conversion circuit group 51-1 to 51-n Signal speed conversion circuit 52 Signal allocation circuit 59 Reception quality monitoring section 75 Code decoder 76 Code adder 77 Code memory Section 78 Encrypted time piece signal forming circuit group 79 Encrypted time piece signal decoding circuit group 91 Digital encoding circuit 92 Multiplex conversion circuit 100, 100-1 to 100-n Mobile radio device 101
Telephone unit 120 Reference crystal oscillator 121-1, 121-2 Synthesizer 122-1,
122-2 Switch 123 Transmission/reception intermittent controller 131 Speed converter circuit 132 Wireless transmitter circuit 133 Transmit mixer 134 Transmitter 135 Wireless receiver circuit 136 Receive mixer 137 Receiver 138 Speed recovery circuit 141 Clock regenerator 175 Decryptor 176 Encryptor 177 Code storage unit 178 Encrypted time piece signal forming circuit 179 Encrypted time piece signal decoding circuit

Claims (1)

[Claims] 1. Each wireless base means (30) each covering a plurality of zones to form a service area;
each mobile radio means (100) using a radio channel carrying temporally compressed delimited signals in time slots of a frame structure for moving across said plurality of zones and communicating with said radio base means; In the mobile communication method using barrier exchange means (20) for exchanging communications between Time-division communication for mobile communication that is created to be transmitted at different times and in which the transmission timing of each frame is changed according to a predetermined order in at least one of the radio base means and the mobile radio means. Secret method.