JPH06237248A - Digital communication method - Google Patents

Abstract

PURPOSE:To change a cipher key during communication without interrupting the communication. CONSTITUTION:A synchronizing signal including a special pattern is transmitted from the transmission side, and a synchronizing signal 2 indicating that frame synchronism is established is received from the reception side, and the number of frames from the current frame to the start of a superframe is transmitted by a synchronizing signal 3, and a synchronizing signal 4 for confirmation which indicates the reception of this signal 3 is received. Thereafter, a cipher key is designated and transmitted, and its reception is confirmed, and a key change timing is transmitted as a preceding frame position in the superframe, and its reception is confirmed, and the cipher is switched to another cipher based on this designated cipher key at this change timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is designed to perform arithmetic processing such as encryption on a digital signal and transmit the digital signal, and to change the arithmetic method, that is, the encryption method and the encryption key during communication. The present invention relates to a digital communication method.

[0002]

2. Description of the Related Art For example, as a mobile communication system, there is a wireless digital communication system in which a frame of a fixed cycle is constructed, and communication channel information and control channel information are multiplexed and transmitted by the bit arrangement in the frame. In some cases, the information contents of both the control channel information and the control channel information are encrypted and transmitted. At that time, a super frame is composed of a plurality of frames and the super frame synchronization timing is used for synchronization of the encryption process. There is a method of making the superframe period extremely long and exchanging information on timing in a frame synchronization procedure at the time of starting communication to establish synchronization of superframe start timings at the same time.

By adopting this method, in the above example, the mobile station exchanges control signals with the base station using the common control channel, receives radio frequency allocation, and establishes synchronization.
After the communication starts, that is, the communication starts with the subscriber number (the mobile station number up to that point), but since multiple subscribers use the same mobile station, the encryption key is used from the viewpoint of communication safety. When changing the key, if the key changes at both communication nodes are inconsistent, it becomes impossible to exchange control signals based on the control channel information during communication, and communication and even control are lost.

Therefore, in order to reliably change the key during communication in this manner, the key to be used next is specified by using the control channel information during communication, and then the reallocation of the wireless channel is requested, that is, , Requesting channel switching during communication, and establishing synchronization by following the procedure for channel switching during communication,
At that time, it is possible to use a new key.

[0005]

When the method of changing the encryption key at the same time as establishing the synchronization in the communication channel switching procedure is adopted as described above, the synchronization is temporarily changed when the encryption key is changed. There is a drawback that communication is interrupted until the synchronization is lost and synchronization is established again. An object of the present invention is to provide a digital communication method in which communication is not interrupted when changing an arithmetic processing method such as encryption during communication.

[0006]

Generally, in arithmetic processing such as encryption, synchronization of a cycle is established with a communication partner, information corresponding to a temporal position in the cycle is applied to information, and the information is transmitted and received. On the side, the inverse operation of the above operation is performed on the received signal at the same temporal position within the cycle to obtain the original information. However, in the present invention, the timing information for changing the operation method is used as the preceding temporal position information within the cycle. Is transmitted to the communication partner, and after confirming that the communication partner has received the information on the timing, the calculation method is changed at the timing based on the information on the timing.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Communication channel information and control channel information are input to an encoding circuit 1 on the transmitting side. The coding circuit 1 divides the input communication channel information and control channel information into fixed lengths defined by the time base 2, multiplexes them, and performs error correction coding, frame synchronization signal addition, and the like. The output of the encoding circuit 1 is subjected to a predetermined arithmetic processing on the information bits in the arithmetic circuit 3 according to the arithmetic key from the arithmetic key setting circuit 4. This arithmetic key is designated and set by the control circuit 5. The arithmetic processing of the arithmetic circuit 3 is not generally the same for each frame, but differs for each frame. That is, the lapse of time is recognized by the number of frames input from the counter 6 that counts the frame timing from the time base 2, and the arithmetic processing according to the number of frames is performed. For example, this calculation is an encryption process, and the process is determined by the frame position in the superframe having a very long cycle. The output of the arithmetic circuit 3 is converted into a radio signal by the transmission circuit 7 and transmitted.

The receiving side first establishes superframe synchronization with the transmitting side, the signal received by the receiving circuit 8 is input to the frame detecting circuit 9, and the frame timing is detected by detecting the frame synchronizing signal or the like. To be done. On the other hand, the received signal is also input to the arithmetic circuit 10 and is subjected to arithmetic processing according to the arithmetic key from the arithmetic key setting circuit 11. The arithmetic key setting circuit 11 is designated and set by the control circuit 12. As this operation key, the same operation key is set in advance by exchanging a control signal with the transmission side, and the operation processing is the inverse operation processing of the processing on the transmission side. Moreover, since the calculation opposite to that on the transmission side is performed on the same frame in the superframe, the counter 1
3, the timing of the frames detected by the frame detection circuit 9 is counted, and the counted number of frames is calculated by the arithmetic circuit 1.
0 and the control circuit 12. As a result, the information restored to the original information on the transmitting side is obtained from the arithmetic circuit 10,
This information is subjected to a decoding process of an error correction code and separation of communication channel information and control channel information by the encoding circuit 14. Although not shown in the figure, it is actually applied to bidirectional communication. In the figure, the transmitting side has the same configuration as the receiving side and the receiving side has the same configuration as the transmitting side. , Exactly the same processing is performed, and bidirectional communication of control channel information is performed.

FIG. 2 shows an example of the structure of a frame signal. The frame position can be recognized by a frame synchronization signal having a specific bit pattern, and the control channel information and the communication channel information are arranged at a predetermined relative position from the frame synchronization signal to perform multiplexing. In general, communication channel information is digitally encoded voice data that is being communicated or data service information, and control channel information is used to maintain communication lines such as re-designation of frequencies for wireless communication. This is information for necessary control.

FIG. 3 shows a procedure for changing the operation key during communication in the embodiment of the present invention. When a wireless channel for communication is set in order to start communication, a signal for synchronization of a specific pattern is exchanged to establish bit synchronization or frame synchronization. Information about the superframe is transmitted and received in the synchronization signal to simultaneously establish the superframe synchronization. This is, for example, when a synchronization signal of a specific pattern is transmitted by the synchronization signal 1, a confirmation in synchronization with this, that is, a frame synchronization confirmation is received by the synchronization signal 2, and a superframe is started from the current frame by the synchronization signal 3. The number of frames up to the position is sent, and the number of frames up to the start position of the superframe calculated from the received frame position of the synchronization signal 3 is sent by the synchronization signal 4 to confirm that the superframe synchronization has been established on the receiving side. after,
This can be realized by transitioning from the state of transmitting / receiving the synchronization signal to the normal communication state. In general, the reception of the synchronization signal may be unsuccessful, and this is dealt with by continuously transmitting the same synchronization signal 3 and synchronization signal 4. However, the number of frames up to the start position of the superframe is different for each transmission frame. Send the counted down value. Sync signal 3 and sync signal 4
And the like are transmitted and received in the state where the arithmetic key is operated on the control channel information.

When the synchronization is established and the communication state is transitioned to as described above, the arithmetic operation based on the arithmetic key set before the communication state and the inverse operation are executed by the arithmetic circuits 3 and 10 in FIG. . Prior to the change of the operation key, a new operation key is sent from one side in the control channel information, and the reception confirmation from the other party is received. Transmission / reception based on the control channel information is performed by arithmetic processing using the arithmetic keys used up to that point. When designating (transmitting) a new operation key, the operation key is not directly transferred, but a certain value is transferred, and a predetermined operation of the secret key and the transferred value set in advance in both communication nodes is performed. The result may be used as a calculation key.

Next, information indicating the change timing of the arithmetic processing is transmitted from one side, and after receiving the confirmation, the arithmetic key is changed to the arithmetic operation at the timing based on the information indicating the change timing. The information indicating the change timing may be indicated by a value indicating the preceding (preceding the current frame) frame position in the superframe of the frame to be changed. Alternatively, a method of indicating the number of frames from the current frame to the change and counting down for each frame to be transmitted may be used. Generally, when receiving and sending these signals, the signal reception may fail, and as a confirmation method to deal with it, there is a method of resending when the confirmation signal does not come within a certain time, or a confirmation signal. There is a method of continuously transmitting the designated signal unconditionally until the arrival of.

When it is detected that the signal transfer is unlikely to succeed by the first change timing, the change timing may be changed during the designated operation. After changing the operation key, if there is a mismatch in the change timing, the control channel information cannot be sent / received. Therefore, if the control channel information or the communication channel information cannot be sent / received even if the frame synchronization signal can be received, it is fixed. After the lapse of time, the certainty of the change can be increased by returning to the original operation key and again specifying the change timing.

When the arithmetic processing is determined only by inputting the arithmetic key and the time (the number of frames elapsed from the superframe start timing), the above embodiment can be easily implemented. When performing sequential processing such as used for frame processing, that is, in the case of processing that cannot be calculated immediately with only the above two inputs, before the change is made between the confirmation of the change timing and the actual change. The present invention can be implemented by preparing for the changed arithmetic processing while continuing the communication by the key.

The present invention is not limited to the case of changing the communication using the mobile station number to the communication using the subscriber number in mobile communication, but is generally applied to the case of changing the calculation method such as changing the key during communication. it can. Further, the superframe may have an infinite cycle that does not return to the initial state due to the arithmetic processing. However, the temporal position on the super-cycle, that is, the frame position in the super-frame in the above example, is set to be synchronized on the transmitting side and the receiving side.

[0016]

As described above, according to the present invention, the change timing is transmitted as the information of the temporal position within the super-cycle, and it is confirmed that the communication partner has received it, and the calculation method is executed at the change timing. Since it is changed, it is possible to change arithmetic processing such as encryption during communication without interrupting communication.
Moreover, its certainty is high.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a communication node that executes an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a frame configuration of a signal.

FIG. 3 is a diagram showing a procedure for changing a calculation key according to the embodiment of the present invention.

Front page continuation (72) Inventor Kiyoshi Imae 2-10-1 Toranomon, Minato-ku, Tokyo NTT Mobile Communication Network Co., Ltd.

Claims (1)

[Claims] 1. A transmission side establishes a cycle synchronization with a communication partner, applies an operation corresponding to a temporal position within the cycle to information, and transmits the information, and a receiving side performs the operation at the same temporal position within the cycle. In a digital communication method in which a received signal is subjected to an inverse operation of an operation to obtain original information, information relating to a timing for changing the operation method is transmitted to the communication partner as preceding temporal position information in the cycle, A digital communication method in which after confirming that the communication partner has received timing information, the calculation method is changed at a timing based on the timing information.