Patent Description:
Japanese Unexamined Patent Application Publication <CIT> discloses a relaying device that enables verbal communication to be conducted between a wireless apparatus, such as a transceiver, and a telephone set over an IP telephone system having a network or over a wired phone line. The relaying device of this document operates in the following manner. First, the relaying device makes a SIP response in response to a call from a device at the other end, and continuously receives audio packets which the device at the other end has continuously sent over a network. Then, the relaying device determines whether or not an audio signal in the received audio packets has a higher level than a threshold at which an audio signal is regarded as a speech sound (VOX processing). If the level of the audio signal is higher than the threshold, the relaying device causes a repeater as a wireless relaying apparatus to enter a transmission state (VOX-ON), and transfers this audio signal to the repeater. In response, the repeater wirelessly sends the audio signal to a terminal.

Upon receiving a VOX-ON signal or a PTT-ON signal from the relaying device, the repeater first reserves a channel (wireless communication channel), and then starts sending the audio signal. In this case, specifically, the repeater cannot send the audio signal promptly upon receiving the PTT-ON signal, because it requires time to reserve a channel. If an idle channel is present, the repeater spends time of <NUM> or so to perform a processing of reserving a channel. Otherwise, if no idle channel is present, the repeater needs to wait for any idle channel to be made available.

However, a typical relaying device is configured to send an audio signal simultaneously with a VOX-ON signal, and thus a part of the audio signal which the repeater receives in the course of reserving a channel is discarded without being sent to a transceiver. As a result, there are cases where the beginning of the received audio signal is clipped off, and only the remaining part thereof is heard from the transceiver.

Document <CIT> describes a system and a technique for enabling voice activation of an audio transmission system.

Document <CIT> describes a voice communication apparatus. Document <CIT> describes a system for setting up a call for a Push-to-Talk service in a cellular mobile communication system.

An object of the present invention is to provide a relaying device that is capable of mediating communication between a telephone set and a wireless apparatus without clipping off the beginning of verbal communication.

According to a first aspect of the present invention, a relaying device includes the features of patent claim <NUM>.

According to a second aspect of the present invention, a relaying device includes the features of patent claim <NUM>.

In the above-described invention, the predetermined time may correspond to an attack time in the VOX processing.

In the above-described invention, in the case where the control unit has not received a reply from the repeater over a predetermined period or longer since requesting the repeater to reserve a channel, the control unit may abort the transfer of the buffered audio signal.

According to the present invention, the relaying device buffers an audio signal that has been received via the uplink interface, until the repeater connected to the wireless apparatus interface reserves a channel. Consequently, even when it takes time to reserve a channel, the beginning of the audio signal sent from the repeater is not clipped off.

Hereinafter, a description will be given of a relaying device according to an embodiment of the present invention, with reference to the accompanying drawings. <FIG> shows a configuration of a communication system including relaying devices according to an embodiment of the present invention. The relaying device <NUM> is configured to relay outgoing and incoming calls between a transceiver <NUM> and an IP telephone set <NUM> or a telephone set <NUM> and to mediate verbal communication therebetween. In addition, the relaying device <NUM> is configured to control timing of PTT-ON (or VOX-ON) for the repeater <NUM> and timing of transferring an audio signal from the telephone set <NUM> or <NUM>, in such a way that the beginning of a voice sound from the telephone set <NUM> or <NUM> is not clipped off on the transceiver <NUM>.

A network <NUM> may employ Ethernet(TM) LAN or the Internet. The one or more relaying devices <NUM> (the two relaying devices <NUM> in <FIG>) are connected to the network <NUM>. The relaying devices <NUM> (2A and 2B) cover different communication areas A and B, respectively. The relaying device <NUM> is connected to the repeater <NUM> (3A or 3B) acting as a relay transceiver. The repeater <NUM> is a push-to-talk (PTT) and half-duplex type of stationary transceiver. In the communication area of the repeater <NUM>, the one or more transceivers <NUM> (4A-<NUM> and 4A-<NUM> or 4B-<NUM> and 4B-<NUM>) (the two transceivers <NUM> in <FIG>) are present.

The IP telephone set <NUM> and a Voice over Internet Protocol (VoIP) gateway <NUM> are connected to the network <NUM>. The telephone set <NUM> is connected to the VoIP gateway <NUM>. The VoIP gateway <NUM> is a gateway device that mediates between a VoIP procedure through which an audio signal is transmitted via the network <NUM> and the telephone set <NUM> as a verbal communication device.

The relaying device <NUM> is equipped with a SIP server function. The SIP server function is a function of utilizing a SIP protocol to: relate a telephone number (URI) to an IP address; execute calling control by calling and connecting to a telephone set for a communication partner; and perform a processing of responding to a call from a telephone set.

The transceiver <NUM> and the repeater <NUM> are so-called digital transceivers. The digital transceiver sends or receives data in parallel to an audio signal converted in a digital format. The digital transceiver sends or receives control information such as a destination code, as the above data. The repeater <NUM> packetizes a digital signal received from the corresponding transceiver <NUM>, and enters the packetized signal into the corresponding relaying device <NUM>. Then, the repeater <NUM> extracts an audio signal and control information from packets received from the corresponding relaying device <NUM>, and converts the audio signal and the control information into respective serial digital signals to send them out.

The transceiver <NUM> stores an ID <NUM> and a group number <NUM>, as illustrated in <FIG>. The ID <NUM> is transceiver ID information to be used to identify a local station. The group number <NUM> is a number to be used to identify a transceiver group to which the local station pertains. If the ID <NUM> of its local station or the group number <NUM> thereof is embedded in a received digital signal, as a destination code, the transceiver <NUM> demodulates this digital signal into an audio signal, and outputs it from, for example, a speaker. Otherwise, if neither the ID <NUM> of its local station nor the group number <NUM> thereof is embedded in a received digital signal, as a destination code, the transceiver <NUM> discards this digital signal. Here, the ID <NUM> of a local station and the group number <NUM> thereof may be embedded in a received digital signal, for example, as a squelch code.

<FIG> is a block diagram of the relaying device <NUM>. The relaying device <NUM> includes a control unit <NUM>, a wireless apparatus interface <NUM>, and a network interface <NUM>. The wireless apparatus interface <NUM> is provided at a downstream end of the relaying device <NUM> (or at an end of the relaying device <NUM> on the side of the repeater <NUM>). The network interface <NUM> is provided at an upstream end of the relaying device <NUM> (or at an end of the relaying device <NUM> on the side of the network <NUM>). The network interface <NUM> corresponds to an uplink interface according to the present invention. A voice buffer <NUM> is connected to the control unit <NUM>. As the wireless apparatus interface <NUM> and the network interface <NUM>, for example, a connector that conforms to a physical layer of Ethernet (TM) may be used. The wireless apparatus interface <NUM> and the network interface <NUM> together serve the purpose of physical and data link layers in digital communication.

The wireless apparatus interface <NUM> is configured to enter packets received from the repeater <NUM> into the control unit <NUM>, and to send packets received from the control unit <NUM> to the repeater <NUM>.

The network interface <NUM> is configured to enter packets from a device at the other end into the control unit <NUM> via the network <NUM>, and to send packets received from the control unit <NUM> to the network <NUM>.

As the control unit <NUM>, a processor such as a microcontroller may be used. The control unit <NUM> includes, as functional units, a SIP processing unit <NUM>, a storage unit <NUM>, an upstream packet processing unit <NUM>, and a downstream packet processing unit <NUM>. The storage unit <NUM> is provided with a local station IP address storage area <NUM>, a local station telephone number storage area <NUM>, a outgoing telephone number conversion table <NUM>, and a reception transceiver number conversion table <NUM>, as illustrated in <FIG>.

The SIP processing unit <NUM> is configured to, for example, make a call, receive a call, and disconnect a call, in telephone communication. The SIP processing unit <NUM> is equipped with a SIP server function, and relates a telephone number to an IP address and calls a device at the other end.

The upstream packet processing unit <NUM> is configured to: read an audio signal from upstream audio packets received from the repeater <NUM> via the wireless apparatus interface <NUM>; convert the audio signal into RTP packets; and transfer the RTP packets to the network interface <NUM>. In addition, the upstream packet processing unit <NUM> is configured to read a control signal from the upstream audio packets, and to cause the SIP processing unit <NUM> to perform predetermined processing in accordance with the control signal. For example, when receiving packets containing a transmission destination code, the upstream packet processing unit <NUM> causes the SIP processing unit <NUM> to perform calling processing by using a telephone number of this transmission destination.

The downstream packet processing unit <NUM> is configured to receive RTP packets from a communication partner (or the telephone set <NUM> or <NUM>) via the network interface <NUM>, and to transfer an audio signal contained in the RTP packets to the repeater <NUM> through the wireless apparatus interface <NUM>. The downstream packet processing unit <NUM> is not configured to entirely transfer, to the repeater <NUM>, an audio signal continuously received in the verbal communication mode. Instead, the downstream packet processing unit <NUM> is configured to transfer, to the repeater <NUM>, only a time zone of the continuously received audio signal which contains a voice sound. The downstream packet processing unit <NUM> is equipped with a voice operated relay (VOX) function, and is configured to monitor a level and duration of an audio signal contained in RTP packets that have been received from the network interface <NUM>, thereby detecting a voice sound. When the level of the received audio signal is equal to or higher than a preset threshold and the duration of the received audio signal is equal to or longer than an attack time, the downstream packet processing unit <NUM> presumes that a voice sound is detected from the audio signal in the RTP packets, and transfers this audio signal to the repeater <NUM>.

The downstream packet processing unit <NUM> does not promptly transferring, to the repeater <NUM>, an audio signal that would be transferred thereto, but delays the audio signal by buffering it in the voice buffer <NUM> and then transfers it. The repeater <NUM> needs to reserve a channel (wireless communication channel) before it starts sending an audio signal. This channel reservation processing requires time of several hundreds of milliseconds if an idle channel is present. If all channels are in a busy state, the required time is further extended, because the repeater <NUM> needs to wait for any of the channels to be made available. When the downstream packet processing unit <NUM> determines that a zone of a voice sound starts, it requests the repeater <NUM> to reserve a channel. Since then, the downstream packet processing unit <NUM> buffers an audio signal of this voice sound in the voice buffer <NUM>. When the downstream packet processing unit <NUM> receives a reply indicating that a channel has been reserved, from the repeater <NUM>, the downstream packet processing unit <NUM> converts the audio signal buffered in the voice buffer <NUM> into audio packets, and transfers the audio packets to the repeater <NUM> via the wireless apparatus interface <NUM>. Call information is embedded in these audio packets. When the repeater <NUM> receives the audio packets from the relaying device <NUM>, it activates the PTT function, and sends the audio signal contained in the audio packets. Consequently, the audio signal of the voice sound is sent while being delayed by a time interval between when the downstream packet processing unit <NUM> detects the voice sound and when it receives the replay indicating that a channel has been reserved, from the repeater <NUM>.

In this way, the relaying device <NUM> waits for the repeater <NUM> to reserve a channel, and then starts transferring a voice sound to the repeater <NUM>. Therefore, when the transceiver <NUM> receives a voice sound through communication with the repeater <NUM> and reproduces it, the beginning of the voice sound is not clipped off.

The outgoing telephone number conversion table <NUM> provided in the storage unit <NUM> is used to convert a destination code contained in audio packets which the relaying device <NUM> has received from the transceiver <NUM> through the repeater <NUM> into a telephone number. The outgoing telephone number conversion table <NUM> stores call_types (groups/individuals), destination IDs (identifiers), and telephone numbers while relating them to one another. These telephone numbers correspond to those of the IP telephone set <NUM> and the telephone set <NUM> to which the relaying device <NUM> is connected through the SIP procedure via the network <NUM>.

Since a typical digital transceiver has only a few buttons, it is difficult to input a telephone number thereto directly. Therefore, a destination code to be input in the transceiver <NUM> is set to a simple numeral sequence, in order to input the destination code with a small number of buttons. The telephone number is composed of a numeral sequence having many more digits, such as eight to ten digits (eight digits in <FIG>).

When a user selects a group/individual and a destination ID and turns on a PTT button through a button operation, the transceiver <NUM> sends audio packets containing this destination code (call_type and destination ID). The audio packets are received by the repeater <NUM> and transferred to the relaying device <NUM>. The relaying device <NUM> converts the destination code contained in these audio packets into a telephone number by using the outgoing telephone number conversion table <NUM>.

The reception transceiver number conversion table <NUM> provided in the storage unit <NUM> is used to convert a telephone number that the relaying device <NUM> has received from the telephone set <NUM> or <NUM> into a destination code (call_type and destination ID). The reception transceiver number conversion table <NUM> stores transceiver numbers, call_types (groups/individuals), and destination IDs while relating them to one another. Each transceiver number is composed of a simple numeral sequence having, for example, two digits that can be input on a dial. The destination code is composed of a combination of a call_type (group/individual) and a destination ID, and is a code that designates one of the transceivers <NUM> or some of them in group, with which the repeater <NUM> connected to the relaying device <NUM> can communicate. Herein, the destination code corresponds to transceiver ID information to be embedded, and the transceiver number corresponds to transceiver ID information to be designated.

When the telephone set <NUM> or <NUM> communicates with the transceiver <NUM>, a user for the telephone set <NUM> or <NUM> dials the telephone number of the relaying device <NUM>, and subsequently dials the transceiver number. When the relaying device <NUM> is called by using the telephone number, it responds to this call and receives an audio signal. In addition, the relaying device <NUM> searches the reception transceiver number conversion table <NUM> by using the transceiver number that has been received from the telephone set <NUM> or <NUM>, and reads a corresponding destination code. When the relaying device <NUM> detects a voice sound from the received audio signal, it embeds a destination code in this voice sound, and sends it to the repeater <NUM>. Here, the relaying device <NUM> delays the audio signal until the repeater <NUM> reserves a channel, as described above. When the repeater <NUM> reserves the channel and wirelessly sends the audio signal to only one of the transceivers <NUM> which is designated by the destination code. Then, this transceiver demodulates and reproduces the audio signal.

In a digital signal sent/received between digital transceivers, a control information frame on which control information, such as a destination code, is to be written is allocated between audio signals. The destination code may be written on this control information frame. Alternatively, the destination code may be written as a squelch code. The digital signal on which the destination code has been written is demodulated and reproduced by only one of the transceivers <NUM> which is designated by this destination code. Utilizing this function achieves individual verbal communications in the selective calling manner as described above.

<FIG> is a flowchart of an operation in which the relaying device <NUM> sends and receives a call. The control unit <NUM> of the relaying device <NUM> determines whether to have received upstream audio packets from the wireless apparatus interface <NUM> at Step S10 (hereinafter, the word "Step" is omitted). Here, these upstream audio packets have been sent from the transceiver <NUM>, and have been received by the repeater <NUM>. If receiving the upstream audio packets (YES at S10), the control unit <NUM> determines whether a calling flag is presently set or not (S11). When the calling flag is set, the relaying device <NUM> is in the course of the performance of the call sending or receiving processing or the conduction of the verbal communication. If the calling flag is set (YES at S11), the control unit <NUM> does not perform the processing of the flowchart of <FIG>. Otherwise, if the calling flag is not set (NO at S11), the control unit <NUM> performs the following processing. The control unit <NUM> sets a calling flag (S12). The control unit <NUM> reads an outgoing destination code from the received audio packets (S13), and reads a telephone number corresponding to the outgoing destination code from the outgoing telephone number conversion table <NUM> by searching it by using the outgoing destination code (S14). The control unit <NUM> creates an INVITE message by using this telephone number as a SIP address, and sends it to the network <NUM> via the network interface <NUM> (S15).

After that, the control unit <NUM> receives a provisional response from the telephone set <NUM> or <NUM> that is a calling destination (S16). In response, the control unit <NUM> generates audio packets composed of a ring-back tone (RBT), and outputs them from the wireless apparatus interface <NUM> (S17). As a result, the RBT is reproduced on the transceiver <NUM>. Here, the provisional response refers to a response indicating that the INVITE request is received and is being processed. Once the control unit <NUM> receives a formal response from the telephone set <NUM> or <NUM> (S18), it halts the RBT (S19), and causes the transceiver <NUM> and the calling destination to enter a verbal communication state. Processing performed during the verbal communication will be described later.

Since then, if the control unit <NUM> receives a BYE message from the telephone set <NUM> or <NUM>, or if an audio signal in downstream packets has a level lower than a threshold over a preset period or longer and the control unit <NUM> has not received upstream packets over a predetermined period or longer, the control unit <NUM> disconnects the call, or resets the calling flag, and returns to a standby state.

Through the above processing, the relaying device <NUM> determines a telephone number, on the basis of a destination code contained in audio packets received from the transceiver <NUM>, and sends an INVITE message to a telephone set to which this telephone number is assigned. This destination code is composed of a simpler numeral sequence than that of a telephone number. Therefore, even if a digital transceiver has only a few buttons, a user for the digital transceiver can call a target telephone number through a simple operation.

Meanwhile, the control unit <NUM> determines whether to have received an INVITE message via the network interface <NUM>, at S20. This INVITE message is sent from the telephone set <NUM> or <NUM> in order to call the relaying device <NUM>. If the control unit <NUM> receives the INVITE message (YES at S20), it determines whether a calling flag is presently set or not (S21). If the calling flag is set (YES at S21), the control unit <NUM> sends back an error response to a transmission source of the INVITE message (S29), and terminates the operation. This is because the relaying device <NUM> is presently in the course of the performance of a call sending or receiving processing or the conduction of the verbal communication, and cannot accept a new call. Otherwise, if the calling flag is not set (NO at S21), the control unit <NUM> performs the following processing. The control unit <NUM> sets a calling flag (S22), and responds to this INVITE message through the SIP procedure (S23). The control unit <NUM> sends a second dial instruction tone to a device at the other end that is a transmission source of the INVITE message (S24). Here, the second dial instruction tone is a voice that encourages the input of a transceiver number.

Once the control unit <NUM> receives a transceiver number from the device at the other end, in response to the second dial instruction tone (S25), the control unit <NUM> reads a destination code corresponding to the transceiver number from the reception transceiver number conversion table <NUM> by searching it by using the transceiver number (S26). Then, the control unit <NUM> instructs the repeater <NUM> to send audio packets containing a destination code to the device at the other end, in order to call it (S27). When the transceiver <NUM> responds to this instruction (S28), the control unit <NUM> sets the transceiver <NUM> and the telephone set <NUM> or <NUM>, which is the device at the other end, to enter a verbal communication state.

Through the above processing, even when the repeater <NUM> is in a state of being able to communicate with the plurality of transceivers <NUM>, the relaying device <NUM> enables one or more of the transceivers <NUM> and the telephone set <NUM> or <NUM> to enter a verbal communication state by causing the repeater <NUM> to send audio packets in which a transceiver number of a destination is embedded.

Next, a description will be given of processing performed during the verbal communication state. During the verbal communication state, the relaying device <NUM> prioritizes upstream packets received from the repeater <NUM>. Here, the upstream packets correspond to an audio signal from the transceiver <NUM>. While receiving upstream packets, the relaying device <NUM> transfers them to the telephone set <NUM> or <NUM>, regardless of the content of the downstream packets. Meanwhile, while the relaying device <NUM> is not receiving no upstream packets, when downstream packets which the relaying device receives from the telephone set <NUM> or <NUM> via the network <NUM> contain a voice sound, the relaying device <NUM> transfers this voice sound to the repeater <NUM>.

<FIG> and <FIG> are flowcharts of steps of processing a downstream audio signal in the verbal communication state. <FIG> is a flowchart of a processing of receiving downstream packets. Once the control unit <NUM> receives RTP packets, or downstream packets, from the network interface <NUM> (S120), the control unit <NUM> (downstream packet processing unit <NUM>) extracts an audio signal from the RTP packets, and decodes it (S121). The control unit <NUM> subjects the decoded audio signal to the VOX processing (S123).

The VOX processing is a processing of detecting a voice sound from the received audio signal. The control unit <NUM> monitors the level and duration of the received audio signal. When the level of the audio signal continues to be equal to or higher than a threshold over the attack time or longer, the control unit <NUM> determines that a voice sound is present, and then turns on a VOX signal. Meanwhile, when the level of the audio signal continues to be less than the threshold over a predetermined period or longer while the VOX signal is in an ON state, the control unit <NUM> determines that the voice sound is no longer present, and then turns off the VOX signal.

<FIG> is a flowchart of processing performed in relation to ON/OFF of the VOX signal in the control unit <NUM>. When the VOX signal is turned on (YES at S130), the control unit <NUM> activates a transfer processing as in <FIG> (S131). Simultaneously, the control unit <NUM> starts buffering an audio signal (S132). In this case, the control unit <NUM> stores a write address of the voice buffer <NUM> at this time as a starting address (S133).

Meanwhile, when the VOX signal is turned off (YES at S140), the control unit <NUM> stops buffering the audio signal (S141). In this case, the control unit <NUM> stores a write address of the voice buffer <NUM> at this time as an ending address (S142).

If the verbal communication ends between the transceiver <NUM> and the telephone set <NUM> or <NUM> (YES at S150), the control unit <NUM> stops the processing of receiving the packets as in <FIG> (S151). If the VOX signal is in the ON state, or the audio signal is being buffered, at present (YES at S152), the control unit <NUM> stops buffering the audio signal (S141), and stores a write address of the voice buffer <NUM> at this time as an ending address (S142).

<FIG> is a flowchart of a processing of transferring a voice sound. When the VOX signal is turned on, this processing is performed. In this processing, the control unit <NUM> (downstream packet processing unit <NUM>) sends the repeater <NUM> a message of a channel reservation request (S200). Then, the control unit <NUM> stands by until it receives a channel reservation response from the repeater <NUM> (S210) or until a timeout occurs as a result of the repeater <NUM> not to respond to the message of the channel reservation request (S220).

If the control unit <NUM> receives the channel reservation response which the repeater <NUM> has sent in response to the message of the channel reservation request (YES at S210), the control unit <NUM> performs the following processing. The control unit <NUM> sets the repeater <NUM> to a transmission state (PTT-ON) (S230). The control unit <NUM> sets a readout pointer for the voice buffer <NUM> to the starting address stored at S133 (S240). Then, the control unit <NUM> sequentially reads the audio signal buffered in the voice buffer <NUM>, and transfers it to the repeater <NUM> via the wireless apparatus interface <NUM> (S250). The audio signal is packetized, and individual calling data is added to each header of the packets. The control unit <NUM> continues transferring the audio signal until the readout pointer reaches the ending address. If the readout pointer reaches the ending address (YES at S260), the control unit <NUM> releases the transmission state of the repeater <NUM> (PTT OFF) (S270), and terminates the processing.

If a timeout occurs as a result of the repeater <NUM> not to respond to the message of the channel reservation request (YES at S220), the control unit <NUM> stops buffering the audio signal (S280), and terminates the processing without transferring the buffered audio signal to the repeater <NUM>.

In the processing described with reference to <FIG> or <FIG>, the control unit <NUM> buffers the audio signal only during a time interval between when the control unit <NUM> detects the voice sound (VOX-ON) and when it does not detect the voice sound (VOX-OFF). However, in the verbal communication state, the control unit <NUM> may continuously buffer the audio signal, and read only a zone of this audio signal in which a voice sound is detected and transfer it to the repeater <NUM>.

A description will be given of steps of processing an audio signal in the verbal communication state, at which the control unit <NUM> continuously buffers the audio signal, with reference to flowcharts of <FIG> and <FIG>. In the flowcharts of <FIG> and <FIG>, the same step numbers are assigned to the same processing steps as those in the flowcharts of <FIG> and <FIG>.

<FIG> is a flowchart of a processing of receiving downstream packets in the verbal communication state. Once the control unit <NUM> receives RTP packets, or downstream packets, from the network interface <NUM> (S120), the control unit <NUM> (downstream packet processing unit <NUM>) extracts an audio signal from the RTP packets, and decodes it (S121). The control unit <NUM> stores this audio signal in the voice buffer <NUM> (S122). In parallel, the control unit <NUM> subjects this audio signal to the VOX processing (S123). The VOX processing is performed in the above manner.

<FIG> is a flowchart of processing performed in relation to ON/OFF of the VOX signal in the control unit <NUM>. If the VOX signal is turned on (YES at S130), the control unit <NUM> activates a transfer processing as in <FIG> (S131), and stores a write address of the voice buffer <NUM> at which the audio signal is stored at this time, as a starting address (S133).

If the VOX signal is turned off (YES at S140), the control unit <NUM> stores a write address of the voice buffer <NUM> at this time, as an ending address (S142).

Meanwhile, if the verbal communication ends between the transceiver <NUM> and the telephone set <NUM> or <NUM> (YES at S150), the control unit <NUM> stops the processing of receiving the audio packets as in <FIG> (S151). If the VOX signal is in an ON state (YES at S152), the control unit <NUM> stores a write address of the voice buffer <NUM> at this time, as an ending address (S142).

If the control unit <NUM> receives the channel reservation response which the repeater <NUM> has sent in response to the message of the channel reservation request (YES at S210), the control unit <NUM> performs the following processing. The control unit <NUM> sets the repeater <NUM> to a transmission state (PTT-ON) (S230). The control unit <NUM> sets a readout pointer for the voice buffer <NUM> to an address located ahead of the starting address stored at S133 at a distance corresponding to the attack time of the VOX signal (S241). Then, the control unit <NUM> sequentially reads the audio signal buffered in the voice buffer <NUM>, and transfers the audio signal to the repeater <NUM> via the wireless apparatus interface <NUM> (S250). The audio signal is packetized, and individual calling data is added to each header of the packets. The control unit <NUM> continues transferring the audio signal until the readout pointer reaches the ending address. If the readout pointer reaches the ending address (YES at S260), the control unit <NUM> releases the transmission state of the repeater <NUM> (PTT OFF) (S270), and terminates the processing.

If a timeout occurs as a result of the repeater <NUM> not to respond to the message of the channel reservation request (YES at S220), the control unit <NUM> terminates the processing without transferring the buffered audio signal to the repeater <NUM>.

As described above, the control unit <NUM> starts reading the audio signal at the address that is located ahead of the starting address at the distance corresponding to the attack time, at S241. Therefore, during the VOX processing, the control unit <NUM> can transfer the voice sound to the repeater <NUM>, without causing part of the voice sound to be clipped off which has been received before the VOX signal used to determine the voice sound is turned on.

It should be noted that the time length corresponding to the distance at which the readout pointer is located ahead of the starting address at S241 is not limited to the attack time. This time length may be adjusted in accordance with a time interval between when the control unit <NUM> sends a message of a channel reservation request and when it receives a channel reservation response. If the time interval between when the control unit <NUM> sends a message of a channel reservation request and when it receives a channel reservation response considerably extends, the control unit <NUM> may decrease the above time interval or may set it to zero, so that the delay of the voice sound can be suppressed from extending.

In the above embodiments, an audio signal in a packet form is sent or received between the repeater <NUM> and the relaying device <NUM>. However, an audio signal in a digital time-based form or in an analog form is sent or received therebetween. Thus, there is no limitation on the format of an audio signal, as long as any given calling information is superposed on the audio signal.

Claim 1:
A relaying device (<NUM>, 2A, 2B) comprising:
an uplink interface (<NUM>) which is configured to continuously receive an audio signal in communication;
a wireless apparatus interface (<NUM>) to which a half-duplex type of repeater (<NUM>, 3A, 3B) acting as a wireless relaying apparatus is connected, the repeater (<NUM>, 3A, 3B) being configured to reserve a wireless communication channel to send and receive the audio signal and configured to send and receive the audio signal between the repeater (<NUM>, 3A, 3B) and a wireless apparatus;
a voice buffer (<NUM>) which is configured to buffer the audio signal; and
a control unit (<NUM>) which is configured to receive the continuously received audio signal, transfer the continuously received audio signal to the repeater (<NUM>, 3A, 3B) via the wireless apparatus interface (<NUM>), and perform a VOX processing of detecting whether a level of the audio signal is equal to or higher than a preset threshold or not, wherein
only a zone of a voice sound is transferred to the repeater (<NUM>, 3A, 3B) among the continuously received audio signal, wherein when the level of the audio signal is detected as being equal to or higher than the preset threshold in the VOX processing, the control unit (<NUM>) is configured to determine the audio signal as the voice sound and start buffering, in the voice buffer (<NUM>), an audio signal of the voice sound to be transferred to the repeater (<NUM>, 3A, 3B), and when the level of the audio signal is detected as being lower than the preset threshold in the VOX processing, the control unit (<NUM>) is configured to stop buffering the audio signal, when a zone of the voice sound is started, the control unit (<NUM>) is configured to request the repeater (<NUM>, 3A, 3B) to reserve a wireless communication channel, and
after receiving, from the repeater (<NUM>, 3A, 3B), a reply indicating that the wireless communication channel has been reserved, the control unit (<NUM>) is configured to read the audio signal buffered in the voice buffer (<NUM>) and transfer this audio signal to the repeater (<NUM>, 3A, 3B) to set the repeater (<NUM>, 3A, 3B) to turn on a transmission state.