Wireless terminal device

Abstract

To make a wireless terminal device using one time slot for communication among a plurality of time slots appropriately switch a time slot to be received and demodulated.SOLUTION: Demodulation units 21, 27, 29, 30 receive a transmission signal of a time slot among a plurality of time slots and demodulate a sound signal from the transmission signal. Sound output units 25, 30 output a sound of the demodulated sound signal. A signal detection unit 30 sequentially switches the time slots for receiving the transmission signal during operation of a transmission switch 71 for switching from a reception state of the transmission signal to a transmission state thereof, and detects, for each time slot, an empty time slot in which the transmission signal is not present. A switch control unit 30 suspends the switching from the reception state to the transmission state when an empty time slot is not present among the plurality of time slots. The switch control unit 30 restores the time slot for receiving the transmission signal to a time slot before the operation of the transmission switch 71.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wireless terminal device.

Background Art

[0002] Patent Document 1 describes a wireless communication system in which a wireless terminal device communicates with another wireless terminal device via a repeater on an idle channel. In this system, each repeater shares information of other repeaters, and transmits a downlink signal including information of other repeaters to a wireless terminal device that takes the repeater as its home repeater, using the channel of the home repeater.

[0003] When another wireless terminal device is calling the wireless terminal device, the wireless terminal device receives a downlink signal including information on another repeater that has received the call from the home repeater. After receiving the downlink signal including information of another repeater, the wireless terminal device switches the channel for receiving the downlink signal and demodulating the audio signal from the channel of the home repeater to the channel of the another repeater.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] As a digital communication system between wireless terminal devices, there is the DMR (Digital Mobile Radio) digital communication system established by ETSI (European Telecommunications Standards Institute). In this communication system, one channel is time-divisionally divided into two time slots, and each time slot is allocated to separate communication.

[0006] A DMR digital communication system wireless terminal receives one of the time slots, demodulates the audio signal, and outputs the demodulated audio signal through a speaker. When a wireless terminal communicates with a different wireless terminal than the one currently using the time slot it is receiving, it checks the availability of time slots. If another time slot is available instead of the one it is currently receiving, the wireless terminal switches the time slot it is receiving to the available time slot.

[0007] Even with DMR digital communication wireless terminal devices, a procedure is required to switch the receiving time slot, similar to the receiving channel switching procedure in the wireless terminal device described in Patent Document 1.

[0008] The object of the present invention is to enable a wireless terminal device that uses one of several time slots obtained by time-division of a single channel for communication to suitably switch the time slot for receiving and demodulating. [Means for solving the problem]

[0009] To achieve the above objective, a wireless terminal device according to one aspect of the present invention is provided. A demodulation unit receives a transmission signal from one of several time slots obtained by time-dividing a single channel, and demodulates an audio signal from the transmission signal. The demodulation unit has an audio output unit that outputs the audio of the demodulated audio signal, A transmit switch that is operated when switching from the receiving state to the transmitting state of the aforementioned transmit signal, When the transmit switch is operated, the demodulation unit sequentially switches the time slots in which it receives the transmit signal, and the signal detection unit detects for each time slot whether there are any empty time slots in which the transmit signal does not exist. When the signal detection unit detects that the aforementioned empty time slot does not exist among the plurality of time slots, the switching control unit postpones the switching from the receiving state to the transmitting state and returns the time slot in which the demodulation unit receives the transmission signal to the time slot before the operation of the transmit switch, It is equipped with. [Effects of the Invention]

[0010] According to the present invention, a wireless terminal device that uses one time slot out of a plurality of time slots obtained by time-division of a single channel for communication can suitably switch the time slot to be received and demodulated. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows an example of the configuration of a wireless terminal device according to one embodiment of the present invention. [Figure 2] Figure 2 shows an example of using multiple wireless terminal devices as shown in Figure 1 to perform DMR digital communication in repeater mode. [Figure 3] Figure 3 shows the various parts of the main controller section of Figure 1, which are composed of multiple information processing circuits that are virtually constructed within the main controller section. [Figure 4] Figure 4 is a flowchart showing an example of the processing steps performed by the CPU of the main controller unit in Figure 1. [Figure 5] Figure 5 is a timing chart illustrating, as an example, the operation flow of a wireless terminal device when communicating between the terminals shown in Figure 2. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. The same or equivalent parts or components are denoted by the same reference numerals throughout the drawings.

[0013] The embodiments described below exemplify an apparatus and the like for embodying the technical idea of the present invention. The technical idea of the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below.

[0014] Figure 1 is an explanatory diagram showing an example of the configuration of a wireless terminal device according to an embodiment of the present invention. The wireless terminal device 10 of the present embodiment shown in Figure 1 communicates with another wireless terminal device (not shown) using the DMR digital communication scheme.

[0015] In the DMR digital communication scheme, one channel is time-divided into two time slots, and each time slot is allocated to separate communications. In the DMR digital communication scheme, the source wireless terminal device 10 calls the wireless terminal device of the call partner using an idle time slot.

[0016] Calls for wireless terminal devices are categorized into those for group calls and those for individual calls. Group calls are also referred to as group calling. In a group call, all wireless terminal devices belonging to a group are collectively called as call partners. Individual calls are also referred to as two-party calls. In an individual call, an individual wireless terminal device is called as the call partner. An individual call targeting an individual wireless terminal device as the call partner can be treated as a call having a higher priority than a group call targeting a large number of wireless terminal devices belonging to a group as call partners. The transmitting-side wireless terminal device 10 uses an idle time slot to transmit a signal addressed to the call partner's wireless terminal device, thereby calling the call partner's wireless terminal device.

[0017] When the receiving-side wireless terminal device 10 is included as the destination of a signal in any time slot, it receives and demodulates the signal, and outputs the demodulated audio from a speaker. If the receiving-side wireless terminal device 10 is included as the destination in the signals of both time slots, for example, it receives and demodulates the higher priority call signal, and outputs the demodulated audio from the speaker.

[0018] FIG. 2 shows an example of a case where a plurality of wireless terminal devices 10 are used to perform communication according to the DMR digital communication system. In this example, four wireless terminal devices 10, namely terminal A to terminal D, communicate on a channel of the same frequency in a repeater mode via a repeater 100 serving as a relay device.

[0019] First, assume that in a state where both time slots of a channel used for communication by terminals A to D are idle, the wireless terminal device 10 of terminal A makes a call to one or more wireless terminal devices 10 other than terminal B as call partners. In this case, a signal to the call partner is transmitted from terminal A using one of the two idle time slots. FIG. 2 shows a case where time slot 1 is used.

[0020] Assume that in a state where terminal A has started a call using one of the time slots, the wireless terminal device 10 of terminal B makes a call to one or more wireless terminal devices 10 other than terminal A as call partners. In this case, a signal to the call partner is transmitted from terminal B using the remaining one idle time slot. FIG. 2 shows a case where time slot 2 is used.

[0021] When the signals in time slots 1 and 2 include themselves as destinations, the wireless terminal devices 10 of terminal C and terminal D receive and demodulate the signals including themselves as destinations from time slots 1 and 2, and output the demodulated audio from a speaker. When both the signals in time slots 1 and 2 include themselves as destinations, the wireless terminal devices 10 of terminal C and terminal D receive and demodulate the signal of the high-priority call from one of time slots 1 and 2, and output the demodulated audio of the high-priority call from the speaker.

[0022] When the wireless terminal devices 10 of terminal C and terminal D are not included as destinations in any of the signals of time slots 1 and 2, they do not receive or demodulate any of the signals of time slots 1 and 2. In this case, no audio is output from the speaker of the wireless terminal device 10.

[0023] As shown in Figure 1, the wireless terminal device 10 includes an antenna 11, a radio frequency switch (RFSW) 13, and a transmitting / receiving unit 15. The transmitting / receiving unit 15 includes a transmitting unit 17 and a receiving unit 19. Either the transmitting unit 17 or the receiving unit 19 is selectively connected to the antenna 11 via the radio frequency switch 13.

[0024] The wireless terminal device 10 further includes an audio codec unit 21, a microphone 23, a speaker 25, a baseband signal processing unit 27, a vocoder 29, and a main controller unit 30.

[0025] The signal received by the receiver 19 from the air via the antenna 11 is encoded into a digital signal by the audio codec unit 21. The digital signal is a signal obtained by modulating a carrier wave with a baseband signal. In the case of the wireless terminal device 10, the baseband signal is an audio signal. If the digital signal includes itself as the destination, the baseband signal processing unit 27 demodulates the baseband signal from the digital signal.

[0026] In the main controller unit 30, an audio signal is extracted from the demodulated baseband signal. The extracted audio signal is processed by the vocoder 29. The processed audio signal is decoded into an analog signal by the audio codec unit 21 and output from the speaker 25.

[0027] The sound picked up by the microphone 23 is encoded into a digital signal by the audio codec unit 21, and then compressed and encoded by the vocoder 29. In the main controller unit 30, a baseband signal is generated from the encoded digital signal. The generated baseband signal is used for carrier wave modulation in the baseband signal processing unit 27. The digital signal modulated by the baseband signal is decoded into an analog signal by the audio codec unit 21 with destination information added, and transmitted into the air from the transmitter unit 17 through the antenna 11.

[0028] The wireless terminal device 10 further includes a display unit 60, an operation unit 70, and a peripheral element unit 80.

[0029] The display unit 60 has a display 61 as shown in Figure 3. The display 61 displays the status of the wireless terminal device 10, etc.

[0030] The operating unit 70 in Figure 1 has a PTT (Push To Talk) switch 71 as shown in Figure 3. The PTT switch 71 is pressed when calling and transmitting from the wireless terminal device 10 to the wireless terminal device of the other party. The PTT switch 71 enters a pressed state when pressed and returns to a released state when the pressing operation is released.

[0031] The peripheral element section 80 in Figure 1 has a non-volatile memory 81 in Figure 3. The non-volatile memory 81 can store, for example, a list of wireless terminal devices 10 of the call partners for individual calls and group calls as a list of partner stations.

[0032] The main controller unit 30 in Figure 1 controls the operation of each part from the antenna 11 to the vocoder 29 described above so that it can transmit and receive signals with other wireless terminal devices 10 using the DMR digital communication method.

[0033] The main controller unit 30 has a general-purpose microcontroller (not shown). The microcontroller includes a CPU (Central Processing Unit) and memory (not shown). The memory includes ROM (Read Only Memory) and RAM (Random Access Memory).

[0034] A microcontroller can virtually construct multiple information processing circuits by having the CPU execute a program stored in memory. These multiple information processing circuits can be used to configure parts 31 to 53 of the main controller unit 30, as described later in Figure 3.

[0035] This embodiment shows an example in which multiple information processing circuits built on the microcontroller of the main controller unit 30 are implemented by software. Of course, it is also possible to configure the information processing circuits by preparing dedicated hardware to perform each of the information processing operations described below. Alternatively, multiple information processing circuits may be configured with individual hardware. Dedicated hardware includes application-specific integrated circuits (ASICs) arranged to perform the functions of each of the parts 31 to 53 of the main controller unit 30 described later, as well as devices such as conventional circuit components.

[0036] The multiple information processing circuits of the main controller unit 30 constitute a digital signal detection unit 31, a detection data analysis unit 33 having an empty slot detection unit 35, a received voice conversion unit 37, and a reception control unit 39, as shown in Figure 3. The multiple information processing circuits also include a BCL (Busy Channel Lockout) control unit 41, a voice signal extraction unit 43, a voice output control unit 45, a PTT operation detection unit 47, a later notification control unit 49, an additional information extraction unit 51, and a display control unit 53.

[0037] The digital signal detection unit 31 receives the digital signal of the channel used by the wireless terminal device 10, which has been encoded by the audio codec unit 21. The detection data analysis unit 33 analyzes the digital signal input to the digital signal detection unit 31. The analysis performed by the detection data analysis unit 33 includes detecting the destination of the signals present on the two time slots of the channel used by the wireless terminal device 10.

[0038] The available slot detection unit 35 of the detection data analysis unit 33 detects whether or not there is an available time slot on the channel used by the wireless terminal device 10. The analysis results of the detection data analysis unit 33 are output to the BCL control unit 41 by the reception control unit 39. The analysis results of the detection data analysis unit 33 include the detection results of the available slot detection unit 35.

[0039] The receiving audio conversion unit 37 receives a baseband signal demodulated by the baseband signal processing unit 27 from a signal on a time slot that includes itself as its destination. If both signals on two time slots include themselves as their destination, the receiving audio conversion unit 37 receives the baseband signals demodulated by the baseband signal processing unit 27 from the signals on each time slot, at the timing of each time slot.

[0040] The BCL control unit 41 can perform processing related to the busy channel lockout function installed in the wireless terminal device 10. The busy channel lockout function is a function that, when transmitting by pressing the PTT switch 71, prohibits the transmission of a signal and locks the call if it is not possible to start a call. For example, if you try to call someone who is currently speaking on another call, and both time slots on the channel are in use for other calls, the busy channel lockout function will lock the call.

[0041] The BCL control unit 41 outputs to the voice signal extraction unit 43 the baseband signal demodulated from the signal that includes itself as the destination, which is input from the received voice conversion unit 37 by the received control unit 39, with respect to the signal received by the receiving unit 19. At the timing of each time slot, if a baseband signal demodulated from the signal on each time slot is input to the received voice conversion unit 37, the BCL control unit 41 outputs to the voice signal extraction unit 43 the baseband signal demodulated from the signal of the call with the higher priority.

[0042] The audio signal extraction unit 43 extracts an audio signal from the baseband signal, and the audio output control unit 45 decodes the extracted audio signal into an analog signal using the audio codec unit 21, which then outputs it from the speaker 25.

[0043] The BCL control unit 41 refers to the analysis results of the detection data analysis unit 33, which is input from the receiving control unit 39, in order to determine whether it is necessary to lock the call of the wireless terminal device 10 using the busy channel lockout function.

[0044] The BCL control unit 41 determines that transmission is impossible if the analysis result referenced when the PTT operation detection unit 47 detects the pressing operation of the PTT switch 71 includes the detection result of the empty slot detection unit 35, which indicates that there are no empty time slots in the channel. The BCL control unit 41 also determines that transmission is impossible if the analysis result referenced when the pressing operation of the PTT switch 71 is detected includes the information that the person to be called specified before the operation of the PTT switch 71 is currently speaking in a communication on an empty time slot that is in use.

[0045] If the BCL control unit 41 determines that transmission is not possible, it locks the call of the wireless terminal device 10, which was triggered by the pressing operation of the PTT switch 71 detected by the PTT operation detection unit 47, using the busy channel lockout function. When the call is locked, the BCL control unit 41 later requests the notification control unit 49 to notify the user of the wireless terminal device 10 when a time slot becomes available.

[0046] The additional information extraction unit 51 extracts additional information from the analysis results of the detection data analysis unit 33 to be used to display on the display 61 that transmission is impossible when the BCL control unit 41 determines that transmission is impossible. The display control unit 53 uses the additional information extracted by the additional information extraction unit 51 to display on the display 61 that transmission is impossible.

[0047] The BCL control unit 41 starts transmitting using an empty time slot if the analysis result of the detection data analysis unit 33, which was referenced when the operation of the PTT switch 71 was detected, includes the detection result of the empty slot detection unit 35, which indicates that an empty time slot exists in the channel. After the start of transmission, a digital signal modulated with a baseband signal including the voice collected by the microphone 23 in Figure 1 is transmitted into the air from the transmitting unit 17 of the transmitting / receiving unit 15 through the antenna 11.

[0048] When the PTT operation detection unit 47 has not detected any operation of the PTT switch 71, the BCL control unit 41, upon referring to the detection result of the empty slot detection unit 35 indicating the existence of an empty time slot, later queries the notification control unit 49. The notification control unit 49 then replies to the BCL control unit 41 whether or not it has been requested to be notified when an empty time slot occurs.

[0049] If the notification control unit 49 later responds that a notification has been requested, the BCL control unit 41, via the audio signal extraction unit 43 and the audio output control unit 45, causes a beep sound to be output from the speaker 25. The beep sound is a warning sound that informs the user that a time slot has become available. The BCL control unit 41 may also display the fact that a time slot has become available on the display 61.

[0050] Incidentally, in the wireless terminal device 10, when the PTT switch 71 is pressed, the BCL control unit 41 determines whether or not to lock the call using the busy channel lockout function. In making this determination, the BCL control unit 41 switches the digital signal demodulated by the baseband signal processing unit 27 to individually check whether or not two time slots are available.

[0051] The audio codec unit 21, baseband signal processing unit 27, and vocoder 29 of the wireless terminal device 10 are shared for receiving and demodulating the signals of each time slot. When the busy channel lockout function is used for determination, the audio that the speaker 25 can output is limited to the audio demodulated from the signal of the time slot that is being checked to see if it is available or not.

[0052] If, after checking the availability of time slots, neither time slot is available, the audio output by speaker 25 will be demodulated from the signal of the time slot that was checked for availability last.

[0053] For example, when the PTT switch 71 is pressed while the wireless terminal device 10 is demodulating a signal that includes itself as the destination and outputting the demodulated audio from the speaker 25, the BCL control unit 41 first checks for availability of the time slot of the signal that is currently outputting audio from the speaker 25. Since this time slot is being used to transmit a signal that includes itself as the destination, the BCL control unit 41 switches its target to another time slot and checks for availability. If the other time slot is also being used, for example, to transmit a signal that does not include itself as the destination, the call is locked by the busy channel lockout function.

[0054] After a call is locked, the BCL control unit 41 does not check for available time slots. As a result, the signal used to demodulate the audio that the speaker 25 can output will be held in a time slot that was checked for availability later, but does not include itself as the destination.

[0055] In this case, the detection data analysis unit 33 detects a signal that includes itself as the destination, and the audio signal extraction unit 43 extracts the audio signal by demodulating the detected signal, allowing the audio of the signal that includes itself as the destination to be output again from the speaker 25. However, during these processes, the output of the audio of the signal that includes itself as the destination from the speaker 25 is interrupted at least. This interruption makes it difficult to understand the content of the call of the signal that includes itself as the destination.

[0056] For the reasons described above, when the wireless terminal device 10 performs communication using the DMR digital communication method, it is preferable to suitably switch the time slot for receiving and demodulating the signal when detecting an available time slot to be used for a call with another wireless terminal device 10.

[0057] In the wireless terminal device 10 of this embodiment, when an available time slot is detected based on the pressing operation of the PTT switch 71, the time slot for receiving and demodulating the signal is suitably switched.

[0058] In order to efficiently switch time slots, the wireless terminal device 10 of this embodiment has a microcontroller in the main controller unit 30 that performs the processing steps shown in the flowchart of Figure 4 as an example.

[0059] The microcontroller in the main controller unit 30 checks whether the PTT switch 71 is in the pressed state (step S1). If it is not in the pressed state but in the released state (NO in step S1), the process proceeds to step S11, which will be described later. If the PTT switch 71 is in the pressed state (YES in step S1), the microcontroller checks whether the current slot is being used for communication and is busy (step S3).

[0060] The current slot refers to one of the two time slots that the main controller unit 30 has currently designated as the time slot from which the signal is received. The speaker 25 outputs the audio signal extracted from the baseband signal demodulated from the signal in the current slot.

[0061] If the current slot is not busy (Not Busy in step S3), the microcontroller sends a call signal to call the communication partner in one of the time slots currently designated by the main controller unit 30 (step S5). After sending the call signal, the system returns to step S1.

[0062] If the current slot is busy (Busy in step S3), the time slot designated by the main controller unit 30 as the time slot of the signal reception source is changed from one time slot to the other time slot. The microcontroller then checks whether the other time slot, Other Slot, is busy or not (step S7).

[0063] If the other slot is not busy (Not Busy in step S7), the microcontroller sends a call signal to the communication partner in the other time slot currently designated by the main controller unit 30 (step S5). After sending the call signal, the system returns to step S1.

[0064] If the other slot is busy (Busy in step S7), the microcontroller changes the time slot designated by the main controller unit 30 as the time slot for receiving the signal from the other time slot to the other time slot. After changing the time slot designated by the main controller unit 30, the process returns to step S1.

[0065] In step S1, if the PTT switch 71 is in the released state and not in the pressed state (NO), the microcontroller determines in step S11 that the PTT switch 71 has changed from the pressed state to the released state. Based on this determination, the microcontroller checks the communication state of the wireless terminal device 10 before the change.

[0066] If, in the pressed state of the PTT switch 71 before the change, the communication state of the wireless terminal device 10 was in the state of transmitting a call signal (transmitting in step S11), then after performing a transmission termination process to terminate the transmission of the call signal (step S13), the series of processes is terminated.

[0067] If, in the pressed state of the PTT switch 71 before the change, the communication state of the wireless terminal device 10 was in the state of receiving a call signal (receiving in step S11), then the notification control unit 49 is later requested to be notified when a time slot becomes available in the future (step S15).

[0068] The microcontroller checks whether the current slot is busy (step S17). If the current slot is busy (Busy in step S17), the microcontroller notifies that a time slot has become available (step S19). After notifying of the availability, the series of processes ends.

[0069] The notification in step S19 may, for example, involve outputting a beep sound from speaker 25, which is a warning sound indicating that a time slot has become available. In addition to outputting a beep sound, the notification in step S19 may also include, for example, displaying on display 61 that a time slot has become available. The display on display 61 may include, for example, flashing or lighting of an LED (Light Emitting Diode), or displaying characters on a liquid crystal display (LCD).

[0070] If the current slot is not busy (Not Busy in step S17), the microcontroller checks whether the other slot is busy (step S21). If the other slot is busy (Busy in step S21), it returns to step S17.

[0071] If the other slot is not busy (Not Busy in step S21), the microcontroller notifies that a time slot has become available (step S19). After notifying of the availability, the series of processes ends.

[0072] By having the microcontroller of the main controller unit 30 perform the processing described above, the wireless terminal device 10 of this embodiment can be equipped with a demodulation unit, an audio output unit, a transmission switch, a signal detection unit, a switching control unit, a hold control unit, and a notification unit.

[0073] Of these, the demodulation unit receives the transmission signal from one of the multiple time slots obtained by time-dividing a single channel, and demodulates the audio signal from the transmission signal. The demodulation unit can be implemented using an audio codec unit 21, a baseband signal processing unit 27, a vocoder 29, and a main controller unit 30.

[0074] The audio output unit outputs the audio signal demodulated by the demodulation unit. The audio output unit can be implemented using a speaker 25 and a main controller unit 30.

[0075] The transmit switch is operated when switching from the receiving state to the transmitting state of the transmit signal. The transmit switch can be a PTT switch 71.

[0076] The signal detection unit, when the transmit switch is operated, sequentially switches the time slots in which the demodulation unit receives the transmit signal, and detects for each time slot whether there are any empty time slots where no transmit signal exists. The signal detection unit can be implemented using the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the signal detection unit by performing the processing from step S1 to step S3 and step S7 in Figure 4.

[0077] The switching control unit suspends the switch from the receiving state to the transmitting state when the signal detection unit detects that there are no available time slots among the multiple time slots. The switching control unit also restores the time slot in which the demodulation unit receives the transmit signal to the time slot before the transmit switch was operated. The switching control unit can be implemented using the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the switching control unit by performing the processing from step S7 to step S9 in Figure 4.

[0078] Furthermore, the switching control unit may continue to hold the switch from the receiving state to the transmitting state while the transmit switch is being operated. This switching control unit can also be implemented using the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the switching control unit that continues to hold the switch from the receiving state to the transmitting state while the transmit switch is being operated by performing the process of returning from step S9 to step S1 in Figure 4.

[0079] The hold control unit intermittently causes the signal detection unit to detect available time slots for each time slot when the operation of the transmit switch is released while the switching control unit is holding the switch from the receive state to the transmit state. The hold control unit can be implemented using the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the hold control unit by performing the processing from the release of step S1, which returns from step S9 in Figure 4, through the receiving state in step S11, to steps S17 and S19.

[0080] The notification unit, when the signal detection unit detects that an empty time slot exists among multiple time slots during the intermittent detection of empty time slots performed by the signal detection unit, notifies the user of the device of the occurrence of an empty time slot. The notification unit can be implemented using at least one of the speaker 25 and the display 61 and the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the notification unit by performing the processing shown in Figure 4, from step S15 through step S17 or step S19 to step S21.

[0081] Next, the operations that occur in the wireless terminal device 10 during communication using multiple wireless terminal devices 10 of this embodiment will be explained with reference to the time chart in Figure 5. The time chart in Figure 5 shows, as an example, the flow of operations of the wireless terminal device 10 when communicating between terminals A to D in Figure 2.

[0082] First, the wireless terminal device 10 of terminal A uses an available time slot 1 to call the wireless terminal devices 10 of terminals C and D, which belong to the group, in a group call (step S31). The wireless terminal devices 10 of terminals C and D receive a signal that includes themselves as the destination from time slot 1 and output the voice of terminal A, demodulated from the received signal, from the speaker 25 (steps S33 and S35).

[0083] After terminal A initiates a group call, terminal B's wireless terminal device 10 uses an available time slot 2 to call terminal C in an individual call (step S37). Terminal C's wireless terminal device 10 receives a signal from terminal B in an individual call that includes itself as the destination and has a higher priority than the signal from terminal A, from time slot 2, and outputs the voice of terminal B demodulated from the received signal through speaker 25 (step S39).

[0084] While terminals A and B are in the middle of a call, the PTT switch 71 on terminal D's wireless terminal device 10 is pressed to initiate a call to another terminal other than terminals A and B, which are currently in the middle of a call (step S41). In this case, terminal D's wireless terminal device 10 detects available time slots in the following order: time slot 1, which is receiving the original signal demodulated from the audio output of terminal A from speaker 25, and time slot 2.

[0085] Since both time slots 1 and 2 are in use for calls by terminals A and B, the wireless terminal device 10 of terminal D locks the call using the busy channel lockout function. After locking the call, the wireless terminal device 10 of terminal D resets the time slot of the signal receiving source from time slot 2, which was the last time slot free to be detected, back to time slot 1, and continues to output the audio from terminal A through speaker 25 (step S41).

[0086] In the wireless terminal device 10 of terminal D, the PTT switch 71 is assumed to have switched from the pressed state to the released state when the pressing operation is released after the call is locked. Due to this switch, the wireless terminal device 10 of terminal D requests notification from the notification control unit 49 in the future when time slots 1 and 2 become available.

[0087] After the PTT switch 71 of terminal D's wireless terminal device 10 is released, when terminal B ends an individual call with terminal C as the other party (step S43), terminal C's wireless terminal device 10 switches the time slot for receiving signals to time slot 1. This switch causes terminal C's wireless terminal device 10 to switch the audio output from speaker 25 from terminal B's audio to terminal A's audio (step S45).

[0088] When terminal B ends an individual call with terminal C as its calling party (step S43), terminal D's wireless terminal device 10 notifies that time slot 2 has become available. Upon receiving this notification, terminal D's wireless terminal device 10 switches the PTT switch 71 back to the pressed state, and terminal D's wireless terminal device 10 starts transmitting a call using time slot 2, after receiving a signal from terminal A has finished (step S47). This call can be used to call other terminals, excluding terminal B which is currently on a call.

[0089] When the wireless terminal device 10 of terminal D initiates a private call with terminal C as the caller (step S49), the wireless terminal device 10 of terminal D terminates the reception and demodulation of the signal in time slot 1 and terminates the output of terminal A's voice from speaker 25.

[0090] When terminal D's wireless terminal device 10 initiates a private call with terminal C as the caller, terminal C's wireless terminal device 10 detects signals that include itself as the destination in time slots 1 and 2, respectively. Terminal C's wireless terminal device 10 receives the signal from terminal D's private call, which has a higher priority than the signal from terminal A, from time slot 2. Terminal C's wireless terminal device 10 outputs the voice of terminal D, demodulated from the signal received from time slot 2, from speaker 25 (step S51).

[0091] Furthermore, when terminal D's wireless terminal device 10 initiates an individual call with terminal C as its calling partner, it finishes receiving and demodulating the signal in time slot 1 and outputs terminal A's voice from speaker 25. After terminal D's wireless terminal device 10 initiates an individual call with terminal C as its calling partner, when terminal A ends the group call with terminals C and D as calling partners (step S61), the transmission of signals from terminal A using time slot 1 ends. Even after terminal A's group call ends, the transmission and reception status of terminals C and D's wireless terminal devices 10 does not change.

[0092] In this embodiment, when the PTT switch 71 is pressed while the audio of a call with itself as the destination is being output from the speaker 25, if there is no available time slot, the audio of the same call will continue to be output from the speaker 25. Therefore, when there is no available time slot when the PTT switch 71 is pressed, the period during which the audio that was being output from the speaker 25 before the PTT switch 71 was pressed is temporarily not output can be minimized. Thus, it is possible to suppress the difficulty in understanding the content of a call with itself as the destination.

[0093] Furthermore, in this embodiment, even after the PTT switch 71 is released from being pressed when no available time slots exist, the detection of available time slots continues. If an available time slot is detected during this period, the user can be notified that an available time slot has become available by notification from at least one of the speaker 25 and the display 61.

[0094] Furthermore, the hold control unit provided in the wireless terminal device 10 may intermittently cause the signal detection unit to detect available time slots for each time slot, even if the operation of the transmit switch is not released while the switching control unit is holding the switch from the receive state to the transmit state. This hold control unit can also be realized using the main controller unit 30. The microcontroller of the main controller unit 30 can realize the operation of the hold control unit in this case by performing a process that proceeds to step S11 after step S9 in Figure 4 without returning to step S1.

[0095] Furthermore, the switching control unit may switch its device to the transmission state if, during the pending state of switching to the transmission state, the hold control unit intermittently has the signal detection unit perform detections that detect the existence of an empty time slot among multiple time slots. In this case, the switching control unit can be implemented using the main controller unit 30. The microcontroller of the main controller unit 30 can implement the operation of the switching control unit in this case by executing the processing performed during the operation of step S47 in Figure 5.

[0096] While embodiments of the present invention have been described above, modifications or variations of the embodiments are possible based on the above disclosure. All components of the above embodiments, and all features described in the claims, may be individually selected and combined, provided that they do not conflict with each other. [Explanation of symbols]

[0097] 10 Wireless terminal device 21 Audio Codec Section (Demodulation Section) 25 Speakers (News Department) 27 Baseband signal processing unit (demodulation unit) 29. Vocoder (Demodulation Unit) 30 Main controller unit (demodulation unit, audio output unit, signal detection unit, switching control unit, hold control unit, notification unit) 61 Display (News Department) 71 PTT switch (transmitter switch)

Claims

1. A demodulation unit receives a transmission signal from one of several time slots obtained by time-dividing a single channel, and demodulates an audio signal from the transmission signal. The demodulation unit has an audio output unit that outputs the audio of the demodulated audio signal, A transmit switch that is operated when switching from the receiving state to the transmitting state of the aforementioned transmit signal, When the transmit switch is operated, the demodulation unit sequentially switches the time slots in which it receives the transmit signal, and the signal detection unit detects for each time slot whether there are any empty time slots in which the transmit signal does not exist. When the signal detection unit detects that the aforementioned empty time slot does not exist among the plurality of time slots, the switching control unit postpones the switching from the receiving state to the transmitting state and returns the time slot in which the demodulation unit receives the transmission signal to the time slot before the operation of the transmit switch, A wireless terminal device equipped with the following features.

2. The wireless terminal device according to claim 1, further comprising: a hold control unit that causes the signal detection unit to intermittently perform the detection while the switching control unit is holding the switching; and a notification unit that, in the intermittently performed detection, the signal detection unit detects that an available time slot exists among the plurality of time slots, and notifies the user of the device of the occurrence of the available time slot.

3. The wireless terminal device according to claim 2, wherein the hold control unit intermittently performs the detection by the signal detection unit when the operation of the transmit switch is released while the switching control unit is holding the switch.

4. The wireless terminal device according to claim 1, wherein the switching control unit continues to hold the switching while the transmission switch is being operated.

5. The wireless terminal device according to claim 1, further comprising a hold control unit that intermittently performs the detection by the signal detection unit while the switching control unit is holding the switching, wherein the switching control unit switches itself from the receiving state to the transmitting state when the signal detection unit detects in the intermittently performed detection that an empty time slot exists among the plurality of time slots.

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