Wireless communications device and control method for wireless communications device

A wireless communications device is constituted from a control station and a slave station that perform encryption communication using an encryption key and changes the encryption key in a predetermined procedure, during a call, and the device includes a controller that operates in such a manner that audio is reduced, if the procedure in which the encryption key is changed is not correctly executed, in a case where a change of the encryption key is made.

TECHNICAL FIELD

The present invention relates to a wireless communications device that is capable of being used as a cordless telephone or the like, and a control method for the wireless communications device.

BACKGROUND ART

In order to improve security performance, a technology in which encryption is performed for transmission and reception of control data for negotiation for establishing a communication path or of audio data that is to be transmitted and received during a call and thus communication is performed is used in wireless communication that is used for a cordless telephone or the like. In the wireless communication such as in the cordless telephone, a common key encryption schemes that use the same key for encryption and decoding are widely employed. In order to improve convenience, a key that is used in the common key encryption scheme is automatically generated using wireless communication, and the generated key is stored in a non-volatile memory of each of the master and slave devices, such as an EEPROM and is used for encryption communication, in the wireless communications device, such as a cordless telephone, that is used by an ordinary person. For example, encryption specifications, which are used for wireless communication in compliance with Digital Enhanced Cordless Telecommunications (DECT) schemes that are in wide use around the world as communication schemes for a digital cordless telephone, are stipulated in NPL 1, NPL 2, NPL 3, and NPL 4, and NPL 5. In NPL 5, a procedure and the like in a case where audio communication such as a cordless telephone is performed using a master device and a slave device that perform communication with the DECT scheme is stipulated, and an early-encryption method in which the encryption communication is activated immediately after a wireless link is established between the master device and the slave device and a Re-keying during a call method in which the encryption communication continues while changing a key for the encryption communication at suitable intervals are stipulated.

CITATION LIST

SUMMARY OF THE INVENTION

Solution to Problem

According to an aspect of the present invention, there is provided a wireless communications device that is constituted from a control station and a slave station that perform encryption communication using an encryption key and that changes the encryption key in a predetermined procedure, during a call, the device being constituted to include a controller that operates in such a manner that audio is reduced, if the procedure in which the encryption key is changed is not correctly executed, in a case where a change of the encryption key is made.

DESCRIPTION OF EMBODIMENTS

[Constitution of a Cordless Telephone]

An example of a constitution of a wireless communications device according to a first exemplary embodiment is described.FIG. 1is a diagram illustrating an example of a cordless telephone for which the wireless communications device according to the present exemplary embodiment is used.

The cordless telephone for which the wireless communications device according to the present invention is used, which is illustrated inFIG. 1, is an example of a cordless telephone that is constituted from master device1and slave devices2and3. Master device1is connected to a telephone line. Master device1as a control station and slave devices2and3as slave stations, for example, may be able to perform wireless communication in compliance with a DECT scheme, and slave devices2and3may be able to carry out an external-line call or an internal-line call through master device1.

[Constitution of a Master Device]

An example of a constitution of a master device is described.FIG. 2is a block diagram illustrating an example of the constitution of master device1.

Wireless communicator10performs transmission and reception of control data or audio data for establishment of a wireless link or the external-line call, using a prescribed scheme, and in the case of encryption communication, performs encryption of transmission data and decoding of reception data. In the present specification, the “wireless communication” is assumed to include wireless transmission and wireless reception.

Audio processor12converts into a digital signal an audio signal that is input from a telephone line or a microphone (not illustrated), generates audio data for transmission, converts the received audio data into an analog signal, and outputs the resulting analog signal to the telephone line or a speaker (not illustrated). When a reception error occurs, and when a sequence error is detected at the time of changing an encryption key, an amount of audio output is reduced and the frequency of occurrence of noise is decreased.

Information reporting unit13receives an incoming call from the external line or is called up from slave devices2and3through an internal line, and outputs information reporting sound. An example of the information reporting sound, ringer sound is given.

Operation unit14is a button for receiving a user operation. Examples of the user operation, an operation (an outgoing-call operation) of placing a call, an operation of receiving a call (an incoming-call operation), an operation (slave device registration operation) of performing registration of a slave device, and the like are given.

Information on a user is displayed on display unit15. As example of the information, a telephone number, registration information, an operation menu for slave devices2and3, and the like are given.

An identification code (which is hereinafter referred to as an ID of the master device) of master device1and information on the slave device that is registered with master device1are stored in information storage16. Information storage16is constituted as a non-volatile memory such as an EEPROM. Pieces of information on the slave device that is stored in information storage16are an identification code (which is hereinafter referred to as an ID of the slave device) and an authentication key for identifying and authenticating the registered slave device, and an encryption key that is used for the encryption communication.

Timer unit18measures an interval at which the encryption key changes, and a time, such as an interval for retrying changing the encryption key.

Control unit19controls operation of entire master device1in cooperation with each unit described above. Control by control unit19will be described below. Master device1, for example, has a Central Processing Unit (CPU), a storage medium, such as a Read Only Memory (ROM) in which a control program is stored, and a memory for operation, such as a Random Access Memory (RAM). In this case, a function of control unit19is realized by the CPU executing the control program.

Next, an example of a constitution of a reception processor of audio processor12of master device1is described.FIG. 3is a block diagram illustrating an example of a constitution of the reception processor of audio processor12of master device1.

InFIG. 3, the reception processor of audio processor12of master device1has decoder121, first audio reduction means122, and second audio reduction means123.

Decoder121performs decoding of audio data that is sent in a state of being compressed, and outputs data in compliance with linear PCM. For example, in the case of the wireless communication in compliance with the DECT scheme, the G.726 audio coding scheme is employed as an audio coding scheme, pieces of audio data that are sampled at 8 kHz are compressed into 4 bit data, and the resulting 4-bit data is transmitted and received. A G.726 decoder that is provided to the reception side restores the 4-bit compressed data to the 8-bit data in compliance with the linear PCM.

First audio reduction means122performs audio data reduction according to a control signal from controller19, which notifies a state of occurrence of a reception error. When the occurrence of the reception error is notified by controller19, first audio reduction means122operates in such a manner that an audio output level is lowered to the degree to which the audio is gradually faded out. For example, in the case of the wireless communication in compliance with the DECT scheme, communication that uses a time division multiplexing scheme in which a frame periodicity is 10 msec is performed, and an audio signal with a periodicity of 10 msec is transmitted and received in a state where a code for detection of the reception error is attached to the audio signal itself. In this case, whenever the reception error is detected, first audio reduction means122operates in such a manner that the audio is faded out by 3 db at a time with the periodicity of 10 msec, and when the reception error does not occur, operates in such a manner that the audio is faded in at the periodicity of 10 msec to a stipulated value (maximum value).

Second audio reduction means123performs the audio data reduction according to a control signal from controller19, which notifies a state of occurrence of a sequence error. When the occurrence of the sequence error is notified by controller19, second audio reduction means123performs control in such a manner that the audio output level is lowered to the degree to which the audio is muted, and when the sequence error does not occur, operates in such a manner that the muting is cancelled or the audio is faded out at the periodicity of 10 msec to the stipulated vale (maximum value).

Functional units that are included in master device1is not limited to the functional units whose reference numbers are 10 to 19 and which are illustrated inFIG. 2and the functional units whose reference numbers are 121 to 123 and which are illustrated inFIG. 3, and other functional units may be included. Other functional units may be functional units that realize main functions of master device1, and may be functional units that realize auxiliary functions that assist the main functions.

[Constitution of the Slave Device]

An example of a constitution of the slave device is described.FIG. 4is a block diagram illustrating an example of the constitution of slave device2. Because a constitution of slave device3is the same as that of slave device2, a description relating to slave device3is omitted.

Wireless communication unit20performs transmission and reception of control data or audio data for establishment of a wireless link or the external-line call, using a prescribed scheme, and in the case of encryption communication, performs encryption of transmission data and decoding of reception data.

Audio processing unit22converts into a digital signal an audio signal that is input from a microphone (not illustrated), generates audio data for transmission, converts the received audio data into an analog signal, and outputs the resulting analog signal to a speaker (not illustrated). When a reception error occurs, and when a sequence error occurs at the time of changing an encryption key, an amount of reception audio output is reduced and the frequency of occurrence of noise is decreased.

Information reporting unit23receives the incoming call from the external line or is called up from master device1and slave device3through the internal line, and outputs the information reporting sound. An example of the information reporting sound, the ringer sound is given.

Operation unit24is a button for receiving the user operation.

Examples of the user operation, the operation (an outgoing-call operation) of placing a call, the operation of receiving a call (an incoming-call operation), the operation (slave device registration operation) of performing registration of a slave device, and the like are given.

Information on the user is displayed on display unit25. As example of the information, a telephone number, an operation menu for slave device2, and the like are given.

Included in information storage26are a slave ID of slave device2, a master ID and an authentication key of the registered master device, that is, master device1, and an encryption key that is used for the encryption communication. Information storage16is constituted as a non-volatile memory such as an EEPROM.

Control unit27controls operation of entire slave device2in cooperation with each unit described above. Control by control unit27will be described below. Slave device2, for example, has a CPU, a storage medium, such as a ROM in which the control program is stored, and a memory for operation, such as a RAM. In this case, a function of control unit27is realized by the CPU executing the control program.

Next, an example of a constitution of a reception processor of audio processor22of slave device2is described.FIG. 5is a block diagram illustrating an example of a constitution of the reception processor of audio processor22of slave device2.

InFIG. 5, the reception processor of audio processor22of slave device2has decoder221, first audio reduction means222, and second audio reduction means223.

Decoder221performs decoding of audio data that is sent in a state of being compressed, and outputs data in compliance with the linear PCM. For example, in the case of the wireless communication in compliance with the DECT scheme, the G.726 audio coding scheme is employed as an audio coding scheme, pieces of audio data that are sampled at 8 kHz are compressed into 4 bit data, and the resulting 4-bit data is transmitted and received. The G.726 decoder that is provided to the reception side restores the 4-bit compressed data to the 8-bit data in compliance with the linear PCM.

First audio reduction means222performs the audio data reduction according to a control signal from controller27, which notifies a state of occurrence of a reception error. When the occurrence of the reception error is notified by controller19, first audio reduction means222operates in such a manner that an audio output level is lowered to the degree to which the audio is gradually faded out. For example, in the case of the wireless communication in compliance with the DECT scheme, communication that uses a time division multiplexing scheme in which a frame periodicity is 10 msec is performed, and an audio signal with a periodicity of 10 msec is transmitted and received in a state where a code for detection of the reception error is attached to the audio signal itself. In this case, whenever the reception error is detected, first audio reduction means122operates in such a manner that the audio is faded out by 3 db at a time with the periodicity of 10 msec, and when the reception error does not occur, operates in such a manner that the audio is faded in at the periodicity of 10 msec to a stipulated value (maximum value).

Second audio reduction means223performs the audio data reduction according to a control signal from controller27, which notifies a state of occurrence of a sequence error. When the occurrence of the sequence error is notified by controller19, second audio reduction means223performs control in such a manner that the audio output level is lowered to the degree to which the audio is muted or in such a manner that the audio is steeply faded out, and when the sequence error does not occur, operates in such a manner that the muting is cancelled or the audio is faded in at the periodicity of 10 msec to the stipulated value (maximum value).

Functional units that are included in slave device2is not limited to the functional units whose reference numbers are 20 to 27 and which are illustrated inFIG. 4and the functional units whose reference numbers are 221 to 223 and which are illustrated inFIG. 5, and other functional units may be included. Other functional units may be functional units that realize main functions of slave device2, and may be functional units that realize auxiliary functions that assist the main functions.

[Operation of Each of Master Device1and Slave Device2]

An example of operation of the cordless telephone that uses the wireless communications device according to the present invention, which is described above, will be described below.

FIG. 6is a diagram illustrating an example of a signal that is transmitted and received in wireless communication and an operation between the master device and the slave device from when placing a call to when the call is in progress. InFIG. 6, a call activation phase is a phase for establishing a wireless link between master device1and slave device2, notifying telephone number information and the like of a connection destination, and establishing a path for communication with the other party that is a call destination. When the call activation phase is completed, a telephone line that is connected to audio processor12of master device1and a microphone and a speaker (which are not illustrated) that are connected to audio processor22of slave device2are connected to each other through the wireless communication, and are in a state where the communication is in progress. The other communication party sends a reply, a state in which it is possible to place a call is attained. The encryption key change phase is a phase in which an encryption key is reissued during the communication to change the existing encryption key.

First, the call activation phase will be described in detail below. When an operation in which a telephone number of the other party is designated and an outgoing call is requested is performed in operator24in slave device2, controller27starts an outgoing call operation, and the call activation phase is started. In the call activation phase, a wireless link establishment request (for example, access_request that is a control message of a MAC layer, in the case of the wireless communication in compliance with the DECT scheme) is transmitted by slave device2, master device1replies with a wireless link establishment confirmation (for example, bearer_confirm that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme), and thus the wireless link between the master device and the slave device is established.

Subsequently, slave device2transmits a call request (for example, CC-SETUP that is a control message of an NWK layer, in the case of the wireless communication in compliance with the DECT scheme) that includes the slave device ID for identifying slave device2, information of the telephone number of the other communication party, and the like.

Master device1that receives the call request transmits a message (for example, {AUTHENTICATION-REQUEST} that is a message of the NWK layer, in the case of the wireless communication in compliance with the DECT scheme) for an encryption key generation authentication request, and slave device2transmits an encryption key generation authentication reply (for example, {AUTHENTICATION-REPLY}) that is a message of the NWK layer, in the case of the wireless communication in compliance with the DECT scheme. With the encryption key generation authentication request, random numbers (for example, RS and RAND, in the case of the wireless communication in compliance with the DECT scheme) that are generated by master device1are transmitted, and with the encryption key generation authentication reply, an authentication reply value (for example, RES in the case of the wireless communication in compliance with the DECT scheme) that is generated in the slave device is transmitted. With the transmission and reception of the encryption key generation authentication request and the encryption key generation authentication reply, master device1performs authentication of whether or not the slave device that is the other communication party is slave device2that is registered with master device1itself, and at the same time, encryption key CK1for encryption communication is generated in both of master device1and slave device2. The authentication and the generation of the encryption key are performed by carrying out an arithmetic operation (which is hereinafter expressed as an authentication encryption key generation arithmetic operation) that is determined in advance by using the random numbers that are transmitted and received with the encryption key generation authentication request, the authentication reply value that is transmitted and received with the encryption key generation authentication reply, and the authentication keys that are stored in information storage16of master device1and information storage26of slave device2. That is, the random numbers that are transmitted and received with the encryption key generation authentication request and the authentication keys that have the same value, which are stored in advance in the master device and the slave device respectively, are set to be inputs, and thus the authentication encryption key generation arithmetic operation is carried out and an authentication reply value and an encryption key are calculated in each of master device and slave device. With the encryption key generation authentication reply, slave device2transmits only the obtained authentication reply value. If the result of comparing the value of the authentication reply that is received with the encryption key generation authentication reply and the value of the authentication reply that is obtained by master device1itself performing the calculation is that the two values are the same, master device1, as illustrated inFIG. 6, continues to perform communication and starts to activate the encryption communication. If the result is that the two values are different from each other, the communication is discontinued (this is not illustrated).

When the authentication ends and the generation of encryption key CK1is completed, the activation of the encryption communication starts. In a case where an encryption request (for example, {CIPHER-REQUEST} that is a message of the NWK layer, in the case of the wireless communication in compliance with the DECT scheme) from master device1, an encryption start request (for example, start encryption: request that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from slave device2, an encryption start confirmation (for example, start encryption: confirm that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from the master device, an encryption start grant (for example, start encryption: grant that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from slave device2are sequentially transmitted and received, and the activation of the encryption communication is completed. On the slave device2side, the encryption start request is transmitted, decoding processing of the reception signal is started in the next frame, and when the encryption start confirmation is received, encryption of a transmission signal is started. In master device1, when the encryption start request is received, the encryption of the transmission signal is started in the next frame, and the decoding processing of the reception signal is started with reception of the next frame in which the encryption start confirmation is transmitted. Master device1activates encryption key change timer T1that measures a time at which timer unit18activates the encryption key change phase.

When the activation of the encryption communication is completed, master device1transmits connection notification (for example, {CC-CONNECT} that is a message of the NWK layer, in the case of the wireless communication in compliance with the DECT scheme), transmits to slave device2a signal that is input from a telephone line, and outputs to the telephone line a signal that is received from slave device2. Furthermore, when receiving a connection notification, slave device2outputs the speaker the signal that is received from master device1, starts to transmit to master device1a signal that is input from the microphone, and proceeds to a state where the call is in progress.

Next, the encryption key change phase is described in detail. When encryption key change timer T1of timer unit18of master device1expires, the encryption key change phase is started. When encryption key change timer T1of timer unit18of master device1expires, transmission and reception of a message for changing an encryption key are started.

The change of the encryption key is made by transmitting and receiving the encryption key generation authentication request and the encryption key generation authentication reply as is the case with the generation of the encryption key in the call activation phase. Master device1transmits to the slave device random numbers that are newly generated with the encryption key generation authentication request. The master device and slave device2generate new encryption key CK2by carrying out an operation (which is hereinafter expressed as an authentication encryption key generation arithmetic operation) that is determined in advance by using these random numbers and the authentication keys that are stored in information storage16of master device1and information storage26of slave device2.

When the generation of new encryption key CK2is completed, the encryption communication temporarily stops, and control for changing the encryption key to the new encryption key and resuming the encryption communication is started.

First, the encryption request is transmitted from master device1, in the same manner as when the encryption communication is activated in the call activation phase.

When receiving the encryption request, slave device2transmits an encryption stop request (for example, stop encryption: request that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) for temporarily stopping the encryption communication, stops the decoding for the reception from the next frame, and proceeds to an unencrypted-text reception state (a state where a signal that is not encrypted is received).

When receiving the encryption stop request, master device1stops the encryption for the transmission and transmits an encryption stop confirmation (for example, stop encryption: confirm that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme), and stops the decoding for the reception from the next frame.

When receiving the encryption stop confirmation, slave device2stops the encryption for the transmission, and proceeds to an unencrypted-text transmission and reception state (state in which a signal that is not encrypted is transmitted and received).

When the stopping of the encryption communication is completed, in the same manner as when the encryption communication is activated in the call activation phase, the encryption start request (for example, start encryption: request that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from slave device2, the encryption start confirmation (for example, start encryption: confirm that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from the master device, the encryption start grant (for example, start encryption: grant that is a control message of the MAC layer, in the case of the wireless communication in compliance with the DECT scheme) from slave device2are sequentially transmitted and received, the activation of the encryption communication is completed, and the encryption communication is started using new encryption key CK2.

Master device1activates encryption key change timer T1that measures the time at which timer unit18activates the encryption key change phase, and master device1and slave device2return to the state where the call is in progress.

Subsequently, whenever encryption key change timer T1expires, master device1activates a wireless encryption key change phase, and makes a change of the encryption key.

Next, timings of the stopping of the encryption, the activation and stopping of the encryption of the message for the activation and the transmission signal, and the activation and stopping of the decoding of the reception signal in the reception processing, in the wireless encryption key change phase, are described in detail referring toFIG. 7.FIG. 7is a diagram illustrating an example of the timings of the stopping of the encryption, the activation and stopping of the encryption of the message for the activation and the transmission signal, and the activation and stopping of the decoding of the reception signal in the reception processing.

FIG. 7illustrates the timings of the stopping of the encryption from when slave device2in the encryption key change phase receives the encryption request to when the encryption key is changed and the encryption communication is resumed, and the activation and stopping of the encryption of the message for the activation and the transmission signal, and the activation and stopping of the decoding of the reception signal in the reception processing, which take place inFIG. 6. InFIG. 7, a signal (which is hereinafter expressed as encrypted text) that results from encrypting audio data that is transmitted along with the control message is expressed with a solid-line arrow, and a signal (which is hereinafter expressed as unencrypted text) that is not encrypted is indicated with a dotted-line arrow. Every pair of transmission (a left-headed arrow) from master device1to slave device2and transmission (a right-headed arrow) from slave device2to master device1is given a number (which is hereinafter expressed as a frame number) according to a time sequence.

InFIG. 7, in an initial state, that is, a state of being frame number1, both of master device1and slave device2transmit encrypted-text audio data, and performs the decoding processing.

In a timing of next frame number2, slave device2transmits the encryption stop request, stops the decoding processing of reception audio data, and proceeds to an unencrypted-text reception state. The transmission by slave device2still remains in an encrypted-text transmission state in which the encryption of transmission audio data is performed.

On the other hand, when the encryption stop request is received at the timing of frame number2, master device1stops the encryption of transmission audio data, proceeds to the unencrypted-text transmission state in which the transmission audio data is transmitted without being encrypted, transmits the encryption stop confirmation in the next frame (frame number3), stops the decoding processing of the reception audio data in the next frame (frame number4), and proceeds to the unencrypted-text reception state.

When receiving the encryption stop confirmation at the timing of frame number3, slave device2stops the encryption of the transmission audio data at the timing of the next frame (frame number4), proceeds to the unencrypted-text transmission state in which the transmission audio data is transmitted without being encrypted, and transmits the encryption start request.

When the encryption start request is received at the timing of frame number4, master device1activates the encryption of transmission audio data, proceeds to the encrypted-text transmission state in which the transmission audio data is transmitted being encrypted, transmits the encryption start confirmation in the next frame (frame number5), starts the decoding processing of the reception audio data in the next frame (frame number6), and proceeds to the encrypted-text reception state.

When receiving the encryption start confirmation at the timing of frame number5, slave device2activates the encryption of the transmission audio data at the timing of the next frame (frame number6), proceeds to the encrypted-text transmission state in which the transmission audio data is transmitted being encrypted, and transmits the encryption start grant.

Next, an operation when transition from placing a call to the call being in progress takes place and the change of the encryption key is made is described referring toFIG. 8.FIG. 8is a flowchart illustrating an example of operations in which the transition from placing the call to the call being in progress takes place and the change of the encryption key is made, which are performed by the master device and the slave device.

First, in the call start, wireless link between master device1and slave device2is established (Step:101), and a message for the call request is transmitted and received (Step:102). Slave device authentication is performed, the encryption key for the encryption communication is generated at the same time that the slave device authentication is performed (Step:103), and the connection notification is transmitted and received (Step:104).

After the transmission and reception of the connection notification (Step: S104), an encryption key change timer is activated in master device1(Step:105), the communication is in progress, and the transmission and reception of the audio data is performed (Step:106).

When the transmission and reception of the audio data are performed during the communication (Step:106), it is determined whether or not a reception error occurs in the audio data (Step:107). In a case where the reception error does not occur in the received audio data (No in Step:107), if audio reduction processing for the reception error is stopped, that is, if audio reduction is in progress, fade-in processing is performed (Step:108). In a case where the reception error occurs in the received audio data (Yes in Step:107), the audio reduction processing for the reception error is activated and the fade-out processing is performed (Step:109).

The audio reduction processing in accordance with the reception error is activated (Step:109) and stopped (Step:108), and subsequently, a determination of whether or not the encryption key change timer expires (Step:110) is made in master device1. In a case where the encryption key change timer does not expire (No in Step:110), returning to the performing of the transmission and reception of the audio data (Step:106) takes place, and the processing described above is reiterated.

In a case where the result of determining whether or not the encryption key change timer expires is that the encryption key change timer expires (Yes in Step:110), proceeding to performing of the transmission and reception of an encryption key change message and the audio data (Step:111) takes place.

It is determined whether or not, after the transmission and reception of the encryption key change message, an error occurs in a sequence of encryption key change messages, that is, whether or not, after the stopping of the encryption or a message for requesting the activation is transmitted, a response message responding to that message can be received (Step:112). In a case where it is determined that there is a likelihood that the expected response message will not be able to be received and the stopping of the encryption or a shift from the timing of the activation will occur (Yes in Step:112), the audio reduction for a sequence error, that is, muting processing is performed, is performed. In a case where the response message can be correctly received and the sequence error does not occur (No in Step:112), the audio reduction processing for the sequence error, that is, if the muting is in progress, muting cancellation processing, is performed (Step:114).

The audio reduction processing in accordance with a state of the sequence error is activated (Step:113) and stopped (Step:114), and subsequently a determination of whether or not the encryption key change is completed is made (Step:115). In a case where the encryption key change is not completed (No in Step:115), returning to the performing of the transmission and reception of the encryption key change message and the transmission and reception of the audio data are performed (Step:111) takes place, and processing for the encryption key change is reiterated. In a case where the encryption key change is completed (Yes in Step:115), returning to the (re)activating of the encryption key change timer (Step:105) takes place, the encryption key change timer is reactivated, returning to the state where the call is in progress, and the operation described above is reiterated.

Because slave device2does not have the encryption key change timer, slave device2does not perform the (re)activation of the encryption key change timer (Step:105), does not make the determination of the encryption key change timer (Step:110) and does not make the determination of the encryption key change (Step:115). Instead of the determination of the encryption key change timer (Step:110), in (Step:110), slave device2makes a determination of whether or not a sequence for the encryption key change is activated, that is, of whether or not the encryption key authentication request is received. In a case where the sequence for the encryption key change is activated (Yes in Step:110), slave device2proceeds to performing of the transmission and reception of the encryption key change message and the audio data (Step:111). In a case where the sequence for the encryption key change is not activated (No in Step:110), slave device2performs an operation of returning to the transmission and reception of the audio data (Step:106).

The determination of whether or not the reception error occurs in the audio data (Step:107) or the determination of the occurrence of the sequence error (Step:112) may be performed with a code for detection of the reception error, which is attached to the audio signal that is received from slave device2(or master device1), except for the determination of occurrence of an error in master device1(or slave device2).

Next, operations when making a determination of the sequence error that occurs at the time of changing the encryption key and when stopping the activation of the audio reduction that is based on the determination of the sequence error, which are performed by the slave device, are described referring toFIG. 9.FIG. 9is a flowchart illustrating an example of the operations of making the determination of the sequence error at the time of changing the encryption key and stopping the activation of the audio reduction that is based on the determination of the sequence error, which are performed by the slave device which receives the encryption request from the master device and in which a sequence for an encryption key change is activated.

FIG. 9illustrates the example of the operations of making the determination of the sequence error at the time of changing the encryption key and stopping the activation of the audio reduction that is based on the determination of the sequence error, which subsequently continue to be performed by slave device2in which an encryption key change timer of master device1expires, generation of a new encryption key is ended, and receives a message for the encryption request from master device1. InFIG. 9, when the message for the encryption request is received from master device1, the decoding of the reception signal is stopped (Step:201) and the encryption stop request is transmitted (Step:202).

Slave device2receives a signal (a message) from master device1(Step:203) and makes the determination of whether or not the received signal is the message for the encryption stop confirmation (Step:204).

In a case where the received signal is not the message for the encryption stop confirmation, and in a case where the reception error occurs (No in Step:204), the audio reduction processing (the muting processing) for the sequence error is activated (Step:205), returning to (Step:202) takes place, the encryption stop request is transmitted, and an operation of waiting for the encryption stop confirmation is reiterated.

In a case where the received signal is the message for the encryption stop confirmation (Yes in Step:204), the audio reduction processing for the sequence error is stopped (the muting cancellation processing is performed) (Step:206), the reception of the audio data and the message (Step:207) is performed, and the encryption of the transmission signal is stopped (Step:208).

Subsequently, in order to start the encryption communication with a new encryption key, a decoding operation that uses the new encryption key is started (Step:209), and the encryption key start request is transmitted (Step:210).

After the transmission of the encryption key start request, slave device2receives a signal (a message) from master device1(Step:211), and makes a determination of whether or not the received signal is the message for the encryption start confirmation (Step:212).

In a case where the received signal is not the message for the encryption start confirmation, and in a case where the reception error occurs (No in Step:212), the audio reduction processing (the muting processing) for the sequence error is activated (Step:213), returning to (Step:210) takes place, the encryption start request is transmitted, and an operation of waiting for the encryption start confirmation is reiterated.

In the case where the received signal is the message for the encryption stop confirmation (Yes in Step:212), the audio reduction processing for the sequence error is stopped (the muting cancellation processing is performed) (Step:214), the reception of the audio data and the message (Step:215) is performed, and the encryption of the transmission signal is activated (Step:216).

After activating the encryption of the transmission signal, slave device2transmits the encryption start grant (Step:217), receives the signal (the message) from master device1(Step:218), and makes a determination of whether or not the received signal is the message for the encryption start confirmation (Step:219).

In a case where the received signal is the message for the encryption start confirmation, and in a case where the reception error occurs (No in Step:219), returning to Step:217takes place, the encryption start grant is transmitted, and an operation of waiting to stop (to receive a message other than the encryption start confirmation) the encryption start confirmation is reiterated.

In a case where the received signal is a message other than the encryption start confirmation (Yes in Step:219), it is determined that the encryption start grant is correctly received in the master device, and the sequence for the encryption key change is ended.

Next, operations when making a determination of the sequence error that occurs at the time of changing the encryption key and when stopping the activation of the audio reduction that is based on the determination of the sequence error, which are performed by the master device, are described referring toFIG. 10.FIG. 10illustrates an example of an operation that is performed by master device1in which the encryption key change timer expires and which newly generates the encryption key and transmits the message for the encryption request to slave device2.FIG. 10is a flowchart illustrating an example of an operation in which the determination of the sequence error at the time of changing the encryption key is made and the activation of the audio reduction that is based on the determination of the sequence error is stopped, which is performed by the master device in which the sequence for the encryption key change is activated.

When transmitting a message for the encryption request to slave device2, and receiving a message from slave device2(Step:301), master device1determines whether or not the message is an encryption stop request (Step:302).

In a case where the received signal is not the message for the encryption stop request, and in a case where the reception error occurs (No in Step:302), returning to Step:301takes place, and an operation of waiting to receiving the message for the encryption stop request is reiterated.

In a case where the received signal is the encryption stop request (Yes in Step:302), it is determined that the encryption start grant is correctly received in the master device, and the sequence for the encryption key change is ended. The encryption of the transmission signal is stopped (Step:303), the encryption stop confirmation is transmitted (Step:304), and after a message is received (Step:305), the decoding of the reception signal is stopped (Step:306).

After the decoding of the reception signal is stopped (Step:306), a signal (a message) is received from slave device2(Step:307), and it is determined whether or not the received signal is the message for the encryption start request (Step:308).

In a case where the received signal is not the message for the encryption start request, and in a case where the reception error occurs (No in Step:308), the audio reduction processing (the muting processing) for the sequence error is activated (Step:309), the encryption stop confirmation is transmitted (Step:310), returning to the reception of the message (Step:307) takes place, and an operation of waiting for the encryption start request is reiterated.

In a case where the received signal is the message for the encryption start request (Yes in Step:308), the audio reduction processing for the sequence error is stopped (the muting cancellation processing is performed) (Step:311), the encryption of the transmission signal is activated in such a manner that the encryption is performed with a new encryption key (Step:312), the encryption start confirmation is transmitted (Step:313), and after the message is received (Step:314), the decoding processing that uses a new encryption key for the reception signal is activated (Step:315).

After the decoding of the reception signal is started (Step:315), a signal (a message) is received from slave device2(Step:316), and it is determined whether or not the received signal is the message for the encryption start grant (Step:317).

In a case where the received signal is not the message for the encryption start grant, and in a case where the reception error occurs (No in Step:317), the audio reduction processing (the muting processing) for the sequence error is activated (Step:318), the encryption start confirmation is transmitted (Step:319), returning to the reception of the message (Step:316) takes place, and an operation of waiting for the encryption start grant is reiterated.

In a case where the received signal is the encryption start grant (Yes in Step:317), it is determined that the encryption start grant is correctly received in the master device, the audio reduction processing for the sequence error is stopped (the muting cancellation processing is performed) (Step:320), and the sequence for the encryption key change is ended.

The embodiment of the present invention is described above. As described above, the wireless communications device according to the present invention has an effect in which, in changing the encryption key, at the time of stopping the encryption, in a case where a message that is expected cannot be received in transmitting and receiving a sequence when the encryption is started with a new encryption key, because control is performed in such a manner that audio is reduced, the frequency of occurrence of noise due to the shift from the timings of the stopping of the encryption and the starting of the encryption between the master device and the slave device can be reduced.

The muting processing is performed when the sequence error occurs at the time of changing the encryption key, control is performed when the reception error occurs during the communication in progress in such a manner that the gradual fading-out is performed, and thus it is possible to decrease the frequency of audio interruption due to the sporadically-occurring reception error in a call state other than at the time of changing the encryption key while reducing the frequency of the occurrence of noise at the time of changing the encryption key. As a result, an effect that improves call quality is achieved.

INDUSTRIAL APPLICABILITY

The wireless communications device according to the present invention is useful as a wireless communications device, such as a cordless telephone.

REFERENCE MARKS IN THE DRAWINGS

13,23INFORMATION REPORTING UNIT

122,222FIRST AUDIO REDUCTION MEANS

123,223SECOND AUDIO REDUCTION MEANS