Patent Description:
A fire alarm outputs an alarm when it detects a fire. By building wireless communication functions in the fire alarm and forming a multihop network by a plurality of fire alarms, it is possible, when one fire alarm detects a fire, for another fire alarm to output an alarm (see, for example, <CIT>). <CIT> describes the scheduling of data transfers in a multi-hop packet network. The nodes of the network are adapted to schedule their transmissions according to a common time sequence, recurring in time domain and comprising a control portion for transmission of at least one control packet and a data portion for transmission of data packets. In order to accomplish a simple and controlled way for minimizing delay and delay variation, the network is classified into several levels with respect to a certain node, each level comprising the nodes located at the same distance from said certain node, measured in number of hops along the shortest path in the network. The data portion is further divided into successive reservation periods, each being allocated to transmissions of delay sensitive traffic through the hops between two predetermined neighboring levels so that a data packet can be transferred across the network within a single time sequence. <CIT> describes a sensor network that includes a sink and multiple sensor nodes. The sink is coupled to a substrate and configured to transmit a periodic ultrasonic pulse on the substrate. A first one of the sensor nodes is coupled to the substrate. The first sensor node is configured to (i) receive the periodic ultrasonic pulse from the substrate, (ii) synchronize an internal clock of the first sensor node to the sink based on the periodic ultrasonic pulse, (iii) selectively detect an event in a region surrounding the first sensor node, and (iv) in response to detecting the event, transmit a first ultrasonic pulse toward the sink on the substrate. <CIT> describes a relay device, which can receive communication signals from each of a plurality of fire alarms. A plurality of communication time slots in which each of the plurality of fire alarms can transmit a communication signal and a monitoring time slot in which the fire alarm scheduled to transmit the communication signal should transmit the monitoring signal in the communication time slots are arranged in a time axis. A monitoring unit monitors to receive the monitoring signal in the monitoring time slot. When the monitoring unitdoes not detect receiving the monitoring signal, a control unit stops the communication signal reception processing in the plurality of communication time slots. When the monitoring unit detects receiving the monitoring signal, the control unit executes the communication signal reception processing in one or more of the plurality of communication time slots. [SUMMARY OF.

The fire alarm and the relay device included in a multihop network are required to stand by for a signal constantly unless the timing of a signal is known. By standing by for a signal constantly, the power consumption in the relay device and the fire alarm is increased. Also, formation of a multihop network by a plurality of fire alarms may result in a long delay time in transfer in the multihop network. It is therefore required to reduce the delay time in transfer in a multihop network while at the same time reducing the power consumption.

The present disclosure addresses this issue, and a purpose thereof is to provide a technology of reducing the delay time in transfer in a multihop network, while at the same time reducing the power consumption.

The present invention relates to an alarm according to claim <NUM>, an alarm system according to claim <NUM>, a method according to claim <NUM>, and a program according to claim <NUM>. Claims <NUM> to <NUM> refer to specifically advantageous realizations of the alarm system according to claim <NUM>.

Optional combinations of the aforementioned constituting elements, and implementations of the disclosure in the form of methods, apparatuses, systems, recording mediums, and computer programs may also be practiced as additional modes of the present disclosure.

According to the present disclosure, it is possible to reduce the delay time in transfer in a multihop network, while at the same time reducing the power consumption.

A brief summary will be given before describing the present disclosure in specific details. The embodiment relates to an alarm system provided in a facility such as a multi-unit apartment building, an independent housing, an office, and a hospital. In the alarm system, a relay device is connected to a management device, and a plurality of fire alarms are connected to the relay device in a multihop network. In this network, the management device represents the higher level, and the fire alarm with the largest hop count from the relay device represents the lower level. Upon detecting an outbreak of a fire, the fire alarm transfers a result of detection to the relay device, and the relay device transfers the result of detection to the management device. When the result of detection is received, the management device selects one or more fire alarms that should sound an alarm and transmits an instruction to sound an alarm to the one or more selected fire alarms as the ultimate destinations. The relay device and the fire alarm transfer the instruction to sound an alarm to the fire alarm at the ultimate destination, and the fire alarm at the ultimate destination sounds an alarm upon receiving the instruction to output an alarm.

Given that the line for a signal from the relay device to the fire alarm with the largest hop count from the relay device is referred to as "downlink line", the line for a signal from the fire alarm with the largest hop count to the relay device is referred to as "uplink line". In this embodiment, one frame is formed by arranging a plurality of time slots, and one super frame is formed by arranging a plurality of frames. Further, one fire alarm is allocated to one of time slots for the downlink line (hereinafter, "downlink communication time slot") and is also allocated to one of time slots for the uplink line (hereinafter, "uplink communication time slot"). The downlink communication time slot is used for transfer on the downlink line, and the uplink communication time slot is used for transfer on the uplink line.

In the downlink line, a signal (hereinafter, "synchronization signal") for establishing and maintaining synchronization for mutual transmission and reception by the relay device and the fire alarm in the multihop network using time slots is periodically transferred in addition to the instruction to sound an alarm. On the other hand, the uplink line is used mainly to transfer a detection result so that the traffic on the uplink line is extremely low. However, the fire alarm in a multihop network should monitor whether a detection result is transmitted in uplink communication time slots assigned to other fire alarms on the lower level. In particular, when the number of fire alarm on the lower level is increased, the number of uplink communication time slots that should be monitored is increased so that the power consumption in the fire alarms is increased. In the following description, a synchronization signal, a detection result, an instruction to sound an alarm may generically be referred to as "communication signals".

A monitoring time slot is introduced to suppress an increase in the power consumption in the fire alarm. As described above, a frame includes a plurality of downlink communication time slots and a plurality of uplink communication time slots. A frame also includes a time slot for monitoring (hereinafter, "monitoring time slot") in which the fire alarm scheduled to transmit a communication signal in the assigned uplink communication time slot transmits a signal (hereinafter, "monitoring signal"). Each fire alarm stands by for the reception of a monitoring signal in the monitoring time slot. When a monitoring signal is received in the monitoring time slot, the fire alarm stands by for the reception of a communication signal in the uplink communication time slot assigned to the fire alarm. When a monitoring signal is not received in the monitoring time slot, on the other hand, the fire alarm does not stand by for the reception of a communication signal in the uplink communication time slot assigned to the fire alarm.

By introducing a monitoring time slot, the time slot in which the fire alarm should stand by is limited so that the power consumption in the fire alarm is reduced. When a frame is comprised of only one monitoring time slot, however, transfer of a communication signal in the multihop network will have to extend over a plurality of frames because the number of fire alarms capable of transferring a communication signal in one frame is "<NUM>". Accordingly, reduction in the delay time in transfer is called for. In this embodiment, a plurality of monitoring time slots are included in one frame to reduce the delay time in transfer.

<FIG> shows a configuration of an alarm system <NUM>. The alarm system <NUM> includes a first fire alarm 600a through a ninth fire alarm 600i, which are generically referred to as fire alarms <NUM>, a first relay device 700a through a third relay device 700c, which are generically referred to as relay devices <NUM>, and a management device <NUM>. The number of fire alarms <NUM> is not limited to "<NUM>", and the number of relay devices <NUM> is not limited to "<NUM>".

The alarm system <NUM> is a system applied to facilities such as houses, offices, and commercial facilities to detect a fire and alert that a fire has broken out. The plurality of fire alarm <NUM> are, for example, home fire alarms and are provided with fire detection sensors. The plurality of fire alarm <NUM> are provided on, for example, the ceilings of facilities but may be provided on the walls, etc..

The first fire alarm 600a through the sixth fire alarm 600f form a multihop network extending from the first relay device 700a. For example, a relay route that links the first relay device 700a, the first fire alarm 600a, and the second fire alarm 600b and a relay route that links the first relay device 700a, the fourth fire alarm 600d, the fifth fire alarm 600e, and the third fire alarm 600c are formed. Further, a relay route that links the first relay device 700a, the fourth fire alarm 600d, the fifth fire alarm 600e, and the sixth fire alarm 600f and a relay route that links the first relay device 700a and the seventh fire alarm <NUM> are also formed. These relay routes are determined by the respective fire alarms <NUM> and are shared by the first relay device 700a and the management device <NUM>.

In these relay routes, the first fire alarm 600a, the fourth fire alarm 600d, and the seventh fire alarm <NUM> can communicate with the first relay device 700a in "<NUM>" hop. The second fire alarm 600b and the fifth fire alarm 600e can communicate with the first relay device 700a in "<NUM>" hops. The third fire alarm 600c and the sixth fire alarm 600f can communicate with the first relay device 700a in "<NUM>" hops.

The second relay device 700b, the third relay device 700c, the eighth fire alarm <NUM>, and the ninth fire alarm 600i are configured in a manner similar to that of the first relay device 700a, the first fire alarm 600a, etc. For example, a multihop network starting from the first relay device 700a is provided on the first floor of a facility, a multihop network starting from the second relay device 700b is provided on the second floor of the facility, and a multihop network starting from the third relay device 700c is provided on the third floor of the facility. Different frequencies are used in the multihop network starting from the first relay device 700a, the multihop network starting from the second relay device 700b, and the multihop network starting from the third relay device 700c. Further, the first relay device 700a, the second relay device 700b, and the third relay device 700c communicate with each other wirelessly or by wire.

Thus, the relay device <NUM> communicates with the plurality of fire alarm <NUM> that form the multinetwork wirelessly and also communicates with the other relay devices <NUM> wirelessly or by wire. It can be said that the relay device <NUM> relays communication between the plurality of fire alarm <NUM> included in the multihop network. Further, the first relay device 700a is connected to the management device <NUM> by a cable and communicates with the management device <NUM> by wire. The first relay device 700a and the management device <NUM> may communicated wirelessly.

The management device <NUM> is, for example, a controller of a home energy management system (HEMS) provided in the facility. The management device <NUM> can communicate with a plurality of appliances provided in the facility. The plurality of appliances include, for example, air conditioners, illumination appliances, hot water dispensers, etc. having a communication function. Further, the management device <NUM> can communicate with the first relay device 700a provided in the facility. The management device <NUM> can also communicate with the second relay device 700b, the third relay device 700c, and the fire alarms <NUM> via the first relay device 700a.

<FIG> shows a configuration of the fire alarm <NUM>. The fire alarm <NUM> includes a communication unit <NUM>, a processing unit <NUM>, a control unit <NUM>, a fire detection sensor <NUM>, and a buzzer <NUM>, and the control unit <NUM> includes a monitoring unit <NUM>. The processing unit <NUM> and the control unit <NUM> may be integrated. A publicly known technology may be used in the fire detection sensor <NUM>. For example, the fire detection sensor <NUM> may be an optical smoke detection sensor and may detect a fire by detecting the smoke in a fire by utilizing diffuse reflection of light. For example, the fire detection sensor <NUM> may be a heat detection sensor and may detect a fire by detecting the heat from a fire. For example, the fire detection sensor <NUM> may be a carbon monoxide detection sensor and may detect a fire by detecting the density of carbon monoxide generated by combustion in a fire. For example, the fire detection sensor <NUM> may be an infrared detection sensor and may detect a fire by detecting infrared rays radiated by combustion in a fire.

The communication unit <NUM> communicates with the other fire alarm <NUM> or the relay device <NUM> wirelessly. The communication unit <NUM> may perform communication by wire. The processing unit <NUM> processes a signal received by the communication unit <NUM> or generates a signal that should be transmitted from the communication unit <NUM>. The control unit <NUM> controls the operation of the communication unit <NUM> and the processing unit <NUM>. The detail of the control unit <NUM> will be described later. The buzzer <NUM> can output a buzzer sound. The fire alarm <NUM> may be configured not to include the buzzer <NUM> and include the fire detection sensor <NUM>. In other words, the fire alarm <NUM> may be configured to have the detection function and the communication function. The fire alarm <NUM> configured as described above can be said to be a sensor capable of alerting that a fire is detected.

<FIG> show a configuration of a super frame <NUM> used in the alarm system <NUM>. As shown in <FIG>, a predefined period of time is defined as the super frame <NUM>. The super frame <NUM> is arranged repeatedly. The super frame <NUM> is divided into a plurality of frames <NUM>. As shown in <FIG>, one frame <NUM> is divided into a plurality of time slots <NUM>. <FIG> shows one time slot <NUM>. The communication signal or the monitoring signal is transmitted in the time slot <NUM>. The duration of the communication signal or the monitoring signal is shorter than the duration of one time slot <NUM>.

<FIG> shows the usage of the plurality of time slots <NUM> included in the frame <NUM> shown in <FIG>. Of the plurality of time slots <NUM>, one or more time slots <NUM> in the leading portion are used as "downlink communication time slots". Three time slots <NUM> following the downlink communication time slots are used as "monitoring time slots". One or more time slots <NUM> following the three monitoring time slots are used as "uplink communication time slots". One or more time slots <NUM> following the uplink communication time slots are used as "backup slots". The number of downlink communication time slots and the number of uplink communication time slots are identical and are equal to or larger than the number of fire alarms <NUM> included in the multihop network. The number of monitoring time slots is not limited to "<NUM>". Backup slots may not be provided.

<FIG> shows an exemplary assignment of the time slots <NUM> in the alarm system <NUM> as similarly shown in <FIG>. The figure shows the assignment of a plurality of time slots <NUM> to the first relay device 700a, the first fire alarm 600a through the seventh fire alarm <NUM> of <FIG>. "M" in <FIG> denotes the first relay device 700a, and "S1" through "S7" denote the first fire alarm 600a through the seventh fire alarm <NUM>, respectively. "N1", "N2", and "N3" will be described later.

The first relay device 700a, the first fire alarm 600a, the fourth fire alarm 600d, the seventh fire alarm <NUM>, the second fire alarm 600b, the fifth fire alarm 600e, the third fire alarm 600c, and the sixth fire alarm 600f are sequentially allocated to downlink communication time slots, with the first relay device 700a preceding the rest. As described above, the hop count from the first fire alarm 600a, the fourth fire alarm 600d, and the seventh fire alarm <NUM> to the first relay device 700a is "<NUM>". The hop count from the second fire alarm 600b and the fifth fire alarm 600e to the first relay device 700a is "<NUM>", and the hop count from the third fire alarm 600c and the sixth fire alarm 600f to the first relay device 700a is "<NUM>". In other words, the smaller the hop count to the first relay device 700a, the earlier the downlink communication slot assigned to the fire alarm <NUM>.

The the sixth fire alarm 600f, the third fire alarm 600c, the fifth fire alarm 600e, the second fire alarm 600b, the seventh fire alarm <NUM>, the fourth fire alarm 600d, the first fire alarm 600a, and the first relay device 700a are sequentially allocated to uplink communication time slots, with the sixth fire alarm 600f preceding the rest. In other words, the larger the hop count to the first relay device 700a, the earlier the uplink communication time slot assigned to the fire alarm <NUM>.

To highlight the fifth fire alarm 600e, the fifth fire alarm 600e is allocated to the downlink communication time slot later than the time slot allocated to the fourth fire alarm 600d and earlier than the time slots allocated to the third fire alarm 600c and the sixth fire alarm 600f. The fifth fire alarm 600e is allocated to the uplink communication time slot later than the time slots allocated to the third fire alarm 600c and the sixth fire alarm 600f and earlier than the time slot allocated to the fourth fire alarm 600d.

The monitoring time slots "N1", "N2", and "N3" are arranged earlier than the downlink communication time slot. The monitoring time slot "N1" is the time slot <NUM> in which the fire alarm <NUM> with the hop count "<NUM>" from the first relay device 700a should transmit the monitoring signal for reception by the first relay device 700a. The fire alarms <NUM> with the hop count "<NUM>" from the first relay device 700a correspond to the first fire alarm 600a, the fourth fire alarm 600d, and the seventh fire alarm <NUM> of <FIG>.

The monitoring time slot "N2" is the time slot <NUM> in which the fire alarm <NUM> with the hop count "<NUM>" from the first relay device 700a should transmit the monitoring signal for reception by the fire alarm <NUM> with the hop count "<NUM>" from the first relay device 700a. The fire alarms <NUM> with the hop count "<NUM>" from the first relay device 700a correspond to the second fire alarm 600b and the fifth fire alarm 600e of <FIG>.

The monitoring time slot "N3" is the time slot <NUM> in which the fire alarm <NUM> with the hop count "<NUM>" from the first relay device 700a should transmit the monitoring signal for reception by the the fire alarm <NUM> with the hop count "<NUM>" from the first relay device 700a. The fire alarms <NUM> with the hop count "<NUM>" from the first relay device 700a correspond to the third fire alarm 600c and the sixth fire alarm 700f of <FIG>.

The monitoring time slots are arranged in the order "N3", "N2", and "N1". In other words, the larger the hop count of the fire alarm <NUM> from the first relay device 700a, the earlier the monitoring time slot assigned to the fire alarm <NUM>. Referring to <FIG>, the maximum hop count from the first relay device 700a is "<NUM>" so that the number of monitoring time slots is also configured to be "<NUM>". If the maximum hop count from the first relay device 700a is "<NUM>", the number of monitoring time slots is also configured to be "<NUM>". The number of monitoring time slots is set in accordance with the hop count from the relay device <NUM> in the multihop network, but the embodiment is non-limiting as to this arrangement. When the relay device <NUM> is not driven by a battery, for example, the power consumption need not be reduced, and reception may take place constantly regardless of the time slot <NUM>. In that case, the monitoring time slot "N1" will be unnecessary. Further, one or more fire alarms <NUM> having the same hop count are allocated to the same monitoring time slot.

The assignment of the time slots <NUM> is determined by the first relay device 700a or the management device <NUM>. For example, the first relay device 700a or the management device <NUM> determines the assignment of the time slots <NUM> based on the information on the relay routes. The first relay device 700a or the management device <NUM> notifies the fire alarms <NUM> of the assignment of the time slots <NUM> thus determined. Therefore, the fire alarms <NUM> also have the knowledge of the assignment of the time slots <NUM>. As a result, the fire alarm <NUM> has the knowledge of the time slot <NUM> in which the communication signal should be transmitted and which is assigned to the fire alarm <NUM>. The fire alarm <NUM> also has the knowledge of the time slot <NUM> in which the communication signal from the adjacent fire alarm <NUM> or the relay device <NUM> on the relay route can be received.

In this setup, the communication unit <NUM> of the fire alarm <NUM> may perform an intermittent receiving operation to reduce the power consumption. In the intermittent receiving operation in the communication unit <NUM>, a receiving operation is performed during a predefined period of time in the leading portion of the time slot <NUM>, and a receiving operation is suspended in the remainder of the time slot <NUM> if a signal (communication signal, monitoring signal) is not received during the predefined period of time. When a signal is received during the predefined period of time in the leading portion of the time slot <NUM>, on the other hand, a receiving operation is continued in the remainder of the time slot <NUM>.

<FIG> shows an outline of downlink communication in the alarm system <NUM>. The figure shows downlink communication slots of <FIG>. The first relay device 700a periodically transmits a synchronization signal to the plurality of fire alarms <NUM> that form the multihop network. The synchronization signal is, for example, a beacon signal. The synchronization signal is transmitted in, for example, the leading frame <NUM> of the super frame <NUM> shown in <FIG> and is not transmitted in the remaining frames <NUM>. The first relay device 700a transmits the synchronization signal in the time slot <NUM> "M" in the leading frame <NUM> of the super frame <NUM>. When the fourth fire alarm 600d receives the synchronization signal in the time slot <NUM> "M", the fourth fire alarm 600d transfers the synchronization signal in the time slot <NUM> "S4". Further, the fourth fire alarm 600d transmits a response signal to the first relay device 700a in the time slot <NUM> "S4". The response signal is, for example, Ack (ACKnowledgment). The response signal may be included in a portion of the synchronization signal.

The first relay device 700a receives the response signal in the time slot <NUM> "S4". When the fifth fire alarm 600e receives the synchronization signal in the time slot <NUM> "S4", the fifth fire alarm 600e transfers the synchronization signal and transmits the response signal to the fourth fire alarm 600d in the time slot <NUM> "S5". The fourth fire alarm 600d receives the response signal in the time slot <NUM> "S5". The fourth fire alarm 600d transfers the response signal from the fifth fire alarm 600e to the first relay device 700a in the time slot <NUM> "S4" of the next frame (not shown in <FIG>). The fourth fire alarm 600d may transfer the response signal from the fifth fire alarm 600e to the first relay device 700a in the uplink communication time slot used in the uplink communication. Alternatively, the fourth fire alarm 600d may not transfer the response signal from the fifth fire alarm 600e to the first relay device 700a.

When the third fire alarm 600c receives the synchronization signal in the time slot <NUM> "S5", the third fire alarm 600c transfers the synchronization signal and transmits the response signal to the fifth fire alarm 600e in the time slot <NUM> "S3". When the sixth fire alarm 600f receives the synchronization signal in the time slot <NUM> "S5", the sixth fire alarm 600f transfers the synchronization signal and transmits the response signal to the fifth fire alarm 600e in the time slot <NUM> "S6".

The fifth fire alarm 600e receives the response signal in the time slots <NUM> "S3" and "S6". The fifth fire alarm 600e transfers the response signal from the third fire alarm 600c and the response signal from the sixth fire alarm 600f to the fourth fire alarm 600d in the time slot <NUM> "S5" of the next frame (not shown in <FIG>). The fourth fire alarm 600d transfers the response signal from the fifth fire alarm 600e to the first relay device 700a in the time slot <NUM> "S4" in the frame after next. The uplink communication time slot may be used for transfer of the response signal. The response signal may not be transferred.

Thus, the synchronization signal is transferred in the frame <NUM> in which the first relay device 700a transmitted the synchronization signal. Further, the fire alarm <NUM> that received the synchronization signal from the first relay device 700a establishes and maintains timing synchronization with the first relay device 700a based on the synchronization signal. A publicly known technology may be used for timing synchronization so that a description thereof is omitted.

<FIG> show an outline of uplink communication in the alarm system <NUM>. The figures show monitoring time slots and uplink communication time slots of <FIG>. It is assumed here that the fire detection sensor <NUM> of the sixth fire alarm 600f detects an outbreak of a fire. The processing unit <NUM> of the sixth fire alarm 600f causes the communication unit <NUM> to transmit a detection result. The detection result includes identification information on the sixth fire alarm 600f that has detected the fire and also includes information relating to an abnormality. The communication unit <NUM> of the sixth fire alarm 600f transmits a monitoring signal in the monitoring time slot <NUM> "N3". The fifth fire alarm 600e receives the monitoring signal in monitoring time slot <NUM> "N3".

<FIG> shows a process that follows the process of <FIG>. The fifth fire alarm 600e that received the monitoring signal in the monitoring time slot <NUM> "N3" transmits the monitoring signal in the monitoring time slot <NUM> "N2". The fourth fire alarm 600d receives the monitoring signal in the monitoring time slot <NUM> "N2".

<FIG> shows a process that follows the process of <FIG>. The fourth fire alarm 600d that received the monitoring signal in the monitoring time slot <NUM> "N2" transmits the monitoring signal in the monitoring time slot <NUM> "N1". The first relay device 700a receives the monitoring signal in the monitoring time slot <NUM> "N1".

As a result, the monitoring signal is transferred from the sixth fire alarm 600f on the lowest level in the multihop network to the first relay device 700a within one frame <NUM>. When the fire detection sensor <NUM> of the sixth fire alarm 600f does not detect a fire, on the other hand, the transfer as shown in <FIG> is not performed.

<FIG> show an outline of uplink communication in the alarm system <NUM>. <FIG> shows a process that follows the process of <FIG>. The sixth fire alarm 600f that received the monitoring signal in the monitoring time slot <NUM> "N3" transmits the detection result in the time slot <NUM> "S6". The fifth fire alarm 600e receives the detection result in the time slot <NUM> "S6". The monitoring unit <NUM> of the fifth fire alarm 600e monitors the reception of the monitoring signal in the monitoring time slot "N3". When the reception of the monitoring signal is not detected, the fifth fire alarm 600e suspends the process of receiving the communication signal in the time slots <NUM> "S3" and "S6". When the monitoring unit <NUM> of the fifth fire alarm 600e detects the reception of the monitoring signal, on the other hand, the fifth fire alarm 600e receives the communication signal in the time slot <NUM> "S3" or "S6".

<FIG> shows a process that follows the process of <FIG>. The fifth fire alarm 600e that received the detection result in the time slot <NUM> "S6" transmits the detection result in the time slot <NUM> "S5". Further, the fifth fire alarm 600e transmits the response signal to the sixth fire alarm 600f in the time slot <NUM> "S5". The response signal may be included in a portion of the communication signal. The sixth fire alarm 600f receives the response signal in the time slot <NUM> "S5". The fourth fire alarm 600d receives the detection result in the time slot <NUM> "S5".

<FIG> shows a process that follows the process of <FIG>. The fourth fire alarm 600d that received the detection result in the time slot <NUM> "S5" transfers the detection result and transmits the response signal to the fifth fire alarm 600e in the time slot <NUM> "S4". The fifth fire alarm 600e receives the response signal in the time slot <NUM> "S4". The fifth fire alarm 600e transfers the response signal from the fourth fire alarm 600d to the sixth fire alarm 600f in the time slot <NUM> "S5" of the next frame <NUM> (not shown in <FIG>). The sixth fire alarm 600f performs a receiving process in the time slot <NUM> "S5" of the frame <NUM> following the transmission of the detection result. The uplink communication time slot may be used for transfer of the response signal. The response signal may not be transferred. The first relay device 700a receives the detection result in the time slot <NUM> "S4".

<FIG> shows a process that follows the process of <FIG>. The first relay device 700a that received the detection result in the time slot <NUM> "S4" transmits the response signal in the time slot <NUM> "M". The response signal is transferred by the fourth fire alarm 600d and the fifth fire alarm 600e and received by the sixth fire alarm 600f.

When the first relay device 700a receives a detection result from the fourth fire alarm 600d, the first relay device 700a transfers the detection result to the management device <NUM>. When the management device <NUM> receives the detection result, the management device <NUM> identifies the fire alarm <NUM> that should sound an alarm based on the identification information included in the detection result. The correspondence between the identification information and the information on the fire alarm <NUM> that should sound an alarm is stored in the management device <NUM> in advance. The management device <NUM> transmits an instruction to sound an alarm to the identified fire alarm <NUM> as the ultimate destinations. The instruction to sound an alarm is transferred to the second relay device 700b and the third relay device 700c.

When the fire alarm <NUM> identified by the management device <NUM> are the third fire alarm 600c and the sixth fire alarm 600f, an instruction to sound an alarm is received by the third fire alarm 600c and the sixth fire alarm 600f by transferring signals in the same manner.

In this case, the instruction tc sound an alarm is transmitted instead of the synchronization signal of <FIG>. When the instruction to sound an alarm is received from the management device <NUM> by way of the first relay device 700a, the second relay device 700b and the third relay device 700c transfer the instruction to sound an alarm to the fire alarms <NUM>. When the communication units <NUM> of the third fire alarm 600c and the sixth fire alarm 600f receive the instruction to sound an alarm, the control unit <NUM> causes the buzzer <NUM> to sound an alarm. The control unit <NUM> may cause a light-emitting device to flash.

To highlight the uplink communication in the fifth fire alarm 600e, the fire alarms <NUM> having a hop count larger by "<NUM>" than the fifth fire alarm 600e are the third fire alarm 600c and the sixth fire alarm 600f. The communication unit <NUM> of the fifth fire alarm 600e can communicate with the third fire alarm 600c and the sixth fire alarm 600f.

Of the monitoring time slots "N3", "N2", and "N1" arranged on the time axis, the monitoring unit <NUM> monitors the reception of the monitoring signal in the monitoring time slot "N3". The monitoring time slot "N3" is the monitoring time slot in which the third fire alarm 600c or the sixth fire alarm 600f can transmit the monitoring signal.

When the monitoring unit <NUM> does not detect the reception of the monitoring signal, the control unit <NUM> suspends the process of receiving the communication signal in the communication time slots "S3" and "S6". When the monitoring unit <NUM> detects the reception of the monitoring signal, on the other hand, the control unit <NUM> causes the monitoring signal to be transmitted in the monitoring time slot "N2". Further, the control unit <NUM> causes the communication signal to be received in the communication time slot "S3" or "S6". Still further, the control unit <NUM> causes, when a communication signal is actually received, the communication signal to be transferred in the communication time slot "S5". In that process, the control unit <NUM> also transmits the response signal to the third fire alarm 600c or the sixth fire alarm 600f in the communication time slot "S5".

Unlike the communication signal, the monitoring signal described so far may be an unmodulated signal. In this case, the fire alarm <NUM> or the relay device <NUM> that receives the monitoring signal confirms a long (e.g., <NUM>-<NUM>) signal from the fire alarm <NUM> by repeating an intermittent reception process within the monitoring time slot a plurality of times to determine whether the reception of the monitoring signal is detected.

To illustrate the benefit of a plurality of monitoring time slots included in one frame, a description will be given below of the operation of the alarm system according to a comparative example in which one monitoring time slot is included in one frame. The alarm system according to the comparative example is of the same type as that of <FIG> and <FIG>. The fire alarm, the relay device, and the management device included in the alarm system of the comparative example are also indicated as the fire alarm <NUM>, the relay device <NUM>, and the management device <NUM>. Further, the frame and the time slot in the alarm system of the comparative example are also indicated as the frame <NUM> and the time slot <NUM>.

<FIG> shows an exemplary assignment of the time slots in the alarm system of the comparative example. <FIG> shows the assignment as similarly shown in <FIG> except that one monitoring time slot is arranged between the downlink communication time slot and the uplink communication time slot.

<FIG> shows an outline of uplink communication in the alarm system. The figure shows monitoring time slots and uplink communication time slots of <FIG>. "Monitor" denotes a monitoring time slot. It is also assumed here that the fire detection sensor <NUM> of the sixth fire alarm 600f detects an outbreak of a fire. The sixth fire alarm 600f transmits the monitoring signal in the monitoring time slot of the frame <NUM> "K" and transmits the detection result in the time slot <NUM> "S6".

The fifth fire alarm 600e receives the monitoring signal in the monitoring time slot of the frame <NUM> "K" and receives the detection result in the time slot <NUM> "S6". In other words, the fifth fire alarm 600e monitors the reception of the monitoring signal in the monitoring time slot. When the reception of the monitoring signal is not detected, the fifth fire alarm 600e suspends the process of receiving a communication signal in the time slots <NUM> "S3" and "S6". When the reception of the monitoring signal is detected, on the other hand, the fifth fire alarm 600e receives the communication signal in the time slot <NUM> "S3" or "S6". Subsequently, the fifth fire alarm 600e transmits the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>" and transfers the detection result in the time slot <NUM> "S5". Further, the fifth fire alarm 600e transmits a response signal to the sixth fire alarm 600f in the time slot <NUM> "S5". The response signal may be included in a portion of the synchronization signal.

The sixth fire alarm 600f receives the response signal in the time slot <NUM> "S5" of the frame <NUM> "K+<NUM>". The fourth fire alarm 600d receives the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>" and receives the detection result in the time slot <NUM> "S5". The fourth fire alarm 600d transmits the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>", transfers the detection result in the time slot <NUM> "S4", and transmits the response signal to the fifth fire alarm 600e.

The fifth fire alarm 600e receives the response signal in the time slot <NUM> "S4" of the frame <NUM> "K+<NUM>". The fifth fire alarm 600e transmits the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>" and transfers the response signal from the fourth fire alarm 600d to the sixth fire alarm 600f in the time slot <NUM> "S5" (not shown in Fig. <NUM>).

The first relay device 700a receives the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>" and receives the detection result in the time slot <NUM> "S4". As in the foregoing case, the first relay device 700a transmits the monitoring signal in the monitoring time slot of the frame <NUM> "K+<NUM>" and transmits the response signal in the time slot <NUM> "M". The response signal is transferred by the fourth fire alarm 600d and the fifth fire alarm 600e and is received by the sixth fire alarm 600f.

When the first relay device 700a receives a detection result from the fourth fire alarm 600d, the first relay device 700a transfers the detection result to the management device <NUM>. When the management device <NUM> receives the detection result, the management device <NUM> identifies the fire alarm <NUM> that should sound an alarm based on the identification information included in the detection result. The correspondence between the identification information and the information on the fire alarm <NUM> that should sound an alarm is stored in the management device <NUM> in advance. The management device <NUM> transmits an instruction to sound an alarm to the identified fire alarm <NUM> as the ultimate destination.

In other words, when one monitoring time slot is included in one frame <NUM>, a delay of a plurality of frames <NUM> is incurred for transfer of the detection result. When a plurality of monitoring time slots are included in one frame <NUM> as in the embodiment, on the other hand, the detection result is transferred within one frame.

The device, the system, or the entity that executes the method according to the disclosure is provided with a computer. By causing the computer to run a program, the function of the device, the system, or the entity that executes the method according to the disclosure is realized. The computer is comprised of a processor that operates in accordance with the program as a main hardware feature. The disclosure is non-limiting as to the type of the processor so long as the function is realized by running the program. The processor is comprised of one or a plurality of electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integration (LSI). The plurality of electronic circuits may be integrated in one chip or provided in a plurality of chips. The plurality of chips may be aggregated in one device or provided in a plurality of apparatuses. The program is recorded in a non-transitory recording medium such as a computer-readable ROM, optical disk, and hard disk drive. The program may be stored in a recording medium in advance or supplied to a recording medium via a wide area communication network including the Internet.

According to the embodiment, the monitoring time slot is included in the frame <NUM> of the multihop network. When the monitoring signal is not received in the monitoring time slot, the reception process in the uplink communication time slot is suspended so that the power consumption in the fire alarm <NUM> and the relay device <NUM> is reduced. Further, the power consumption in the fire alarm <NUM> and the relay device <NUM> is reduced so that the frequency of exchanging batteries for driving the fire alarm <NUM> and the relay device <NUM> is reduced. Further, the frequency of battery exchange is reduced so that the convenience for the user is improved. Further, a plurality of monitoring time slots are included in the frame <NUM> of the multihop network so that transfer from the fire alarm <NUM> in the lowest level to the relay device <NUM> is performed within one frame <NUM>. Further, transfer from the fire alarm <NUM> in the lowest level to the relay device <NUM> is performed within one frame <NUM> so that the delay time in transfer is reduced. Further, a plurality of monitoring time slots are included in the frame <NUM> of the multihop network so that the delay time in transfer in the multihop network is reduced, while at the same time the power consumption is reduced.

Further, the response signal is also transmitted in the communication time slot in which the communication signal should be transferred so that transmission of the response signal is performed efficiently. Further, the number of monitoring time slots is set in accordance with the maximum hop count to the relay device <NUM> in the multihop network so that the fire alarm <NUM> with a different hop count is allowed to use a further monitoring time slot. Further, the fire alarm <NUM> with a different hop count is allowed to use a further monitoring time slot so that collision of monitoring signals from fire alarms <NUM> with different hop counts is prevented. Further, one or more fire alarms <NUM> having the same hop count are allocated to the same monitoring time slot so that an increase in the monitoring time slots is suppressed. Further, the communication signal includes information relating to an abnormality so that the relay device <NUM> or the management device <NUM> is notified of the abnormality.

A plurality of time slots <NUM> are included in the frame <NUM> of the multihop network, and each time slot <NUM> is assigned to the fire alarm <NUM> so that collision of signals is inhibited. The fire alarms <NUM> are allocated to the time slots <NUM> in the order determined by the hop count from the relay device <NUM> so that the transfer is performed efficiently. Further, whether the monitoring signal is available is determined by repeating intermittent reception a plurality of times so that a determination error due to the noise that lasts a short period of time (a signal having the same frequency but does not contain desired waves) is eliminated. Further, a determination error due to the noise that lasts a short period of time is eliminated so that further transmission of the monitoring signal or reception operation in the uplink communication time slot is suspended even when the noise that lasts a short period of time is imposed (in error) in the monitoring time slot.

Described above is an explanation based on an exemplary embodiment. The embodiment is intended to be illustrative only and it will be understood by those skilled in the art that various modifications to constituting elements and processes could be developed and that such modifications are also within the scope of the present invention.

In the embodiment, the relay device <NUM> connects the fire alarms <NUM> each provided with the function of detecting a fire and the function of outputting an alarm sound. Alternatively, however, the fire alarm <NUM> may only be provided with the function of detecting a fire. Instead of the fire alarm <NUM> for detecting a fire, sensors for detecting flood damage, earthquakes, gas leakage, or generation of CO (carbon monoxide) due to imperfect combustion may be provided. According to this variation, the flexibility in the configuration is improved.

Claim 1:
A first alarm (<NUM>) of a plurality of alarms (<NUM>) that form a multihop network extending from a relay device (<NUM>), comprising:
a communication unit (<NUM>) capable of communicating with the relay device (<NUM>) with a hop count i (i is an integer equal to or larger than <NUM>) and also capable of communicating with a second alarm (<NUM>) and a third alarm (<NUM>) capable of communicating with the relay device (<NUM>) with a hop count i+<NUM>;
a first communication time slot in which the first alarm (<NUM>) is configured to transmit a communication signal, a second communication time slot in which the second alarm (<NUM>) is configured to transmit a communication signal, and a third communication time slot in which the third alarm (<NUM>) is configured to transmit a communication signal being arranged on a time axis,
a first monitoring time slot in which the first alarm (<NUM>) is configured to transmit a monitoring signal and a second monitoring time slot in which the second alarm (<NUM>) or the third alarm (<NUM>) is configured to transmit a monitoring signal being arranged earlier than the first communication time slot, the second communication time slot, and the third communication time slot, and
the first monitoring time slot being arranged later than the second monitoring time slot,
the first communication time slot being arranged later than the second communication time slot and the third communication time slot,
the alarm further comprising:
a monitoring unit configured to monitor reception of the monitoring signal in the second monitoring time slot;
a control unit (<NUM>) configured to suspend a process of receiving the communication signal in the second communication time slot and the third communication time slot when the monitoring unit (<NUM>) does not detect reception of the monitoring signal,
and the control unit (<NUM>) being further configured, when the monitoring unit (<NUM>) detects reception of the monitoring signal, to cause the monitoring signal to be transmitted in the first monitoring time slot and then cause the communication signal to be received in the second communication time slot or the third communication time slot and then also cause the communication signal which was received in the second communication time slot or the third communication time slot to be transferred in the first communication time slot.