Communication system

Abstract

To provide a communication system that can reduce costs and transmit and receive data correctly.SOLUTION: In a firefighting wireless communication system 1, a master station 11 transmits a frame number to base station wireless devices 13A, 13B, 13C when communicating with a mobile station; the base station wireless devices 13A, 13B, 13C that have received the frame number transmit, to the master station 11, notification signals providing notification about receiving of the frame number; the master station 11 determines the transmission timing at which the base station wireless devices 13A, 13B, 13C transmit the communication content received from the master station 11 to mobile stations 15A, 15B, 15C on the basis of the notification signal; and the master station 11 transmits a transmission signal including a synchronous transmission start frame number which is transmission timing information to the base station wireless devices 13A, 13B, and 13C when the master station transmits the transmission signal to the mobile station.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a communication system comprising a plurality of base stations.

Background Art

[0002] In a conventional fire department digital radio system, when a fire department headquarters calls a mobile station such as a fire truck, communication is performed via a line controller and a base station that covers the area where the mobile station is located. Each base station is disposed for each predetermined area, and mediates communication with mobile stations present in the disposed area. Different frequencies are assigned to each base station, and each base station transmits radio waves at the assigned frequency. In order to communicate with a mobile station in such a fire department digital radio system, the fire department headquarters needs to grasp which base station's area the mobile station is located in, and perform communication using the frequency assigned to the base station located in that area. For this reason, the fire department headquarters is required to always keep track of the frequency assigned to each base station and which area the mobile station is located in.

[0003] In such a fire department radio system, as described above, different frequencies need to be assigned to each base station, so a plurality of frequencies need to be prepared for operating one fire department system, which impairs frequency utilization efficiency. Further, as described above, in order to perform communication between the fire department headquarters and the mobile station, it is necessary to grasp the area where the mobile station is located and select a corresponding base station. Therefore, by making the frequencies of radio waves transmitted from all base stations the same, the number of required frequencies can be reduced and frequency utilization efficiency is improved. In addition, since it is no longer necessary to select the frequency for transmission by the base station, the system can be simplified. On the other hand, if radio waves are freely transmitted with the same frequency of radio waves transmitted from all base stations, radio waves of the same frequency are transmitted from each base station at their respective timings, so there is a problem that a large interference area (dead area) occurs. In order to solve this problem, a technique is known in which the frequencies of all base stations are matched and the same data is transmitted at the same time (the same timing) (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-144408 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, realizing such a wireless communication system requires a mechanism to synchronize the transmission timing of each base station. For this reason, for example, Global Positioning System (GPS) receivers are installed in the line control unit and each base station, and the transmission timing of each device is synchronized according to the time notified by the GPS receiver. However, such wireless communication systems have the problem of increased costs because each line control unit and each base station must be equipped with a GPS receiver. In addition, such wireless communication systems have the problem that, during communication between the line control unit and each base station, delays occur in communication between devices due to the influence of line load, resulting in timing not being synchronized and data not being sent and received correctly.

[0006] The objective of this invention is to provide a communication system that is cost-effective and capable of correctly transmitting and receiving data. [Means for solving the problem]

[0007] To achieve the above objective, a communication system according to one aspect of the present invention comprises a master station, a plurality of base stations, and one or more mobile stations that communicate with the master station via the plurality of base stations, wherein the master station transmits a synchronization signal to the base stations when communicating with the mobile stations, the base stations that receive the synchronization signal transmit a notification signal to the master station that indicates that the synchronization signal has been received, including the frame number at the time the synchronization signal was received, and the master station transmits the communication content received by the plurality of base stations from the master station to the mobile stations. synchronization The master station determines the transmission timing to be transmitted based on the notification signal, and when the master station transmits the transmission signal to the mobile station, it transmits the transmission signal, which includes the transmission timing information, to the multiple base stations. [Effects of the Invention]

[0008] According to one aspect of the present invention, costs can be reduced and data can be transmitted and received correctly. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram schematically shows an example of the general configuration of a fire-fighting radio communication system according to one embodiment of the present invention. [Figure 2] This figure shows an example of a schematic configuration of components provided in a fire radio communication system according to one embodiment of the present invention. [Figure 3] This diagram schematically shows, in chronological order, an example of the operation up to the start of synchronous transmission of data in a fire radio communication system according to one embodiment of the present invention. [Figure 4] This is a sequence diagram showing an example of the operation up to the start of synchronous transmission of data in a fire radio communication system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] A communication system according to one embodiment of the present invention will be described with reference to Figures 1 to 3. First, the schematic configuration of the communication system according to this embodiment will be described with reference to Figures 1 and 2. Hereinafter, the communication system according to this embodiment will be described using a fire department radio communication system as an example, but the communication system according to this embodiment can also be applied to communication systems other than fire department radio communication systems.

[0011] (Outline configuration of the fire department's radio communication system) Figure 1 is a schematic diagram showing an example of the general configuration of the fire radio communication system 1 according to this embodiment. Figure 2 is a diagram showing an example of the specific configuration of the line control device 111 and base station radio devices 13A, 13B, and 13C provided in the fire radio communication system 1 according to this embodiment.

[0012] As shown in Figure 1, the fire radio communication system (an example of a communication system) 1 according to this embodiment comprises a master station 11, a plurality (three in this embodiment) of base station radio devices (an example of a base station) 13A, 13B, 13C, and one or more (three in this embodiment) of mobile stations 15A, 15B, 15C that communicate with the fire department equipment 113 via the plurality of base station radio devices 13A, 13B, 13C. The master station 11 includes a fire department equipment 113 having a user interface and a line control device 111 that communicates wirelessly with the fire department equipment 113.

[0013] The base station radio devices 13A, 13B, and 13C are connected to the line control device 111 via a communication network. Specifically, base station radio device 13A is connected to the line control device 111 via a wired local area network (LAN) cable 17A. Base station radio device 13B is connected to the line control device 111 via a wired LAN cable 17B. Base station radio device 13C is connected to the line control device 111 via a wired LAN cable 17C. Thus, in the fire department radio communication system 1, the line control device 111 communicates bidirectionally with the base station radio devices 13A, 13B, and 13C via wired LAN cables 17A, 17B, and 17C. However, the fire department radio communication system 1 may also be configured so that the line control device 111 and the base station radio devices 13A, 13B, and 13C communicate bidirectionally via a wireless LAN.

[0014] Base station radio units 13A, 13B, and 13C receive GNSS signals containing time information transmitted from Global Navigation Satellite System (GNSS) satellite 2. Base station radio units 13A, 13B, and 13C operate in synchronous manner by operating based on the time information contained in the received GNSS signals. Base station radio unit 13A communicates with mobile station 15A located in the communication range ZEA, which is within the range of radio waves transmitted by the unit. Base station radio unit 13B communicates with mobile station 15B located in the communication range ZEB, which is within the range of radio waves transmitted by the unit. Base station radio unit 13C communicates with mobile station 15C located in the communication range ZEC, which is within the range of radio waves transmitted by the unit.

[0015] As shown in Figure 1, within the communication range of base station radio devices 13A, 13B, and 13C, there are interference ranges IZE1 where communication ranges ZEA, ZEB, and ZEC overlap; interference range IZE2 where communication ranges ZEA and ZEB overlap; interference range IZE3 where communication ranges ZEB and ZEC overlap; and interference range IZE4 where communication ranges ZEC and ZEA overlap. Interference range IZE1 is the range where radio waves emitted from each of the base station radio devices 13A, 13B, and 13C interfere. Interference range IZE2 is the range where radio waves emitted from each of the base station radio devices 13A and 13B interfere. Interference range IZE3 is the range where radio waves emitted from each of the base station radio devices 13B and 13C interfere. Interference range IZE4 is the region where radio waves emitted from each of the base station radio devices 13C and 13A interfere. However, in the fire radio communication system 1, the base station radio devices 13A, 13B, and 13C transmit the same information to multiple mobile stations at the same time, thereby narrowing the interference areas IZE1, IZE2, IZE3, and IZE4.

[0016] As shown in Figure 2, the line control device 111 includes a crystal oscillator 111b and a control unit 111a connected to the crystal oscillator 111b. The control unit 111a is connected to the fire department equipment 113. The control unit 111a is connected to the base station radio equipment 13A by LAN cable 17A, to the base station radio equipment 13B by LAN cable 17B, and to the base station radio equipment 13C by LAN cable 17C. The control unit 111a can communicate bidirectionally with the fire department equipment 113. In this embodiment, the control unit 111a and the fire department equipment 113 are connected to each other by wire, but they may also be connected to each other by wireless means.

[0017] The fire department headquarters device 113 has a user interface (not shown) for users of the fire department wireless communication system 1. The fire department headquarters device 113 controls, for example, a control unit 111a provided in a line control device 111, and transmits data related to requests, commands, etc., from the fire department headquarters to fire departments and emergency medical teams to mobile stations 15A, 15B, 15C (e.g., portable terminal devices carried by fire trucks, ambulances, or fire departments and emergency medical teams using the same) via the base station radio devices 13A, 13B, 13C. Furthermore, the fire department headquarters device 113 controls the control unit 111a to receive data related to information such as reports transmitted from the mobile stations 15A, 15B, 15C via the base station radio devices 13A, 13B, 13C and the line control device 111.

[0018] A clock signal output from a crystal oscillator 111b is synchronized with extremely accurate time information transmitted from an NTP (Network Time Protocol) server 3 connected to the line control device 111, and is input to the control unit 111a. The control unit 111a operates in synchronization with the clock signal output from the crystal oscillator 111b. The control unit 111a outputs transmission data, which includes a count value obtained by counting the clock signal as a frame number for specifying a transmission frame number (details will be described later), to the base station radio devices 13A, 13B, 13C (details will be described later). Until the timing for starting synchronization of the base station radio devices 13A, 13B, 13C is determined, the control unit 111a sets a number indicating "immediate" (details will be described later) (e.g., "0") for the transmission frame number specification.

[0019] The control unit 111a includes a synchronization start determination unit 111a-1. The synchronization start determination unit 111a-1 operates in synchronization with the clock signal output from the crystal oscillator 111b. As will be described in detail later, the synchronization start determination unit 111a-1 determines the timing for starting transmission of identical data at the same time (the same timing) from the base station radio devices 13A, 13B, 13C to the mobile stations 15A, 15B, 15C.

[0020] The base station radio apparatus 13A, the base station radio apparatus 13B, and the base station radio apparatus 13C have the same configuration as each other and are configured to exhibit the same functions. Therefore, a specific configuration example of the base station radio apparatus 13A, the base station radio apparatus 13B, and the base station radio apparatus 13C will be described below by taking the base station radio apparatus 13A as an example.

[0021] As shown in FIG. 2, the base station radio apparatus 13A includes: an antenna 136A that receives a GNSS signal transmitted from, for example, a GNSS satellite 2 (not shown in FIG. 2, see FIG. 1); and a GPS receiver 131A that generates a highly accurate 1PPS (PPS: Pulse Per Second) time pulse signal PLS and a clock signal GCK having a highly accurate oscillation frequency (e.g., 10 MHz) based on time information included in the GNSS signal received by the antenna 136A. The base station radio apparatus 13A has a phase locked loop (PLL) 132A that generates a reference clock signal PCK based on the clock signal GCK output from the GPS receiver 131A. The base station radio apparatus 13A has a counter 133A that, when receiving the time pulse signal PLS input from the GPS receiver 131A in synchronization with the reference clock signal PCK output from the PLL circuit 132A, clears the count of frame number A and starts counting the frame number A. The count value output from the counter 133A serves as the frame number A.

[0022] The base station radio device 13A transmits the transmission data sent from the line control device 111 to a mobile station (mobile station 15A in Figure 1) located within the communication range ZEA (not shown in Figure 2, see Figure 1) via the radio unit 135A. The base station radio device 13A has a timing control unit 134A that controls the timing at which the transmission of this transmission data begins. The timing control unit 134A and the control unit 111a provided in the line control device 111 are connected by a LAN cable 17A. As a result, the timing control unit 134A receives the transmission data to be sent to the mobile station (mobile station 15A in Figure 1) located within the communication range ZEA of the base station radio device 13A (see Figure 1) via the LAN cable 17A from the control unit 111a. For the sake of explanation, it will be assumed that only mobile station 15A exists within the communication range ZEA. In addition to controlling the timing, the timing control unit 134A also performs response processing to inquiries from the line control device 111.

[0023] The base station radio device 13A includes a radio unit 135A that outputs transmission data input from the timing control unit 134A in synchronization with the reference clock signal PCK output from the PLL circuit 132A, and an antenna 137A connected to the radio unit 135A. The timing control unit 134A operates in synchronization with the reference clock signal PCK input from the PLL circuit 132A. When the value of frame number A input from the counter 133A matches the value of the transmission frame number specification (details described later) to start synchronous transmission input from the control unit 111a provided in the line control device 111, the timing control unit 134A instructs the radio unit 135A to start outputting transmission data. As a result, the radio unit 135A transmits the transmission data via the antenna 137A to a mobile station (mobile station 15A in Figure 1) located within the communication range ZEA.

[0024] Although a detailed explanation is omitted below, as indicated by the arrows, each component provided in the base station radio device 13B (to the right of the arrow) corresponds to each component provided in the base station radio device 13A (to the left of the arrow). GUID receiver 131A → GPS receiver 131B PLL circuit 132A → PLL circuit 132B Counter 133A → Counter 133B Timing control unit 134A → Timing control unit 134B Radio section 135A → Radio section 135B Antenna 136A → Antenna 136B Antenna 137A → Antenna 137B

[0025] When counter 133B receives a time pulse signal PLS input from GPS receiver 131B in synchronization with the reference clock signal PCK output from PLL circuit 132B, it clears the count for frame number B and starts counting frame number B. Timing control unit 134B is connected to control unit 111a, which is located in line control device 111, by LAN cable 17B. As a result, transmission data to be sent to the mobile station (mobile station 15B in Figure 1) located within the communication range ZEB (see Figure 1) of base station radio device 13B is transmitted to timing control unit 134B from control unit 111a via LAN cable 17B. For the sake of explanation, it will be assumed that only mobile station 15B exists within the communication range ZEB.

[0026] Although a detailed explanation is omitted below, as indicated by the arrows, each component provided in the base station radio device 13C (to the right of the arrow) corresponds to each component provided in the base station radio device 13A (to the left of the arrow). Automatic receiver 131A → GPS receiver 131C PLL circuit 132A → PLL circuit 132C Counter 133A → Counter 133C Timing control unit 134A → Timing control unit 134C Radio section 135A → Radio section 135C Antenna 136A → Antenna 136C Antenna 137A → Antenna 137C

[0027] When counter 133C receives a time pulse signal PLS input from GPS receiver 131C in synchronization with the reference clock signal PCK output from PLL circuit 132C, it clears the count for frame number C and starts counting for frame number C. Timing control unit 134C is connected to control unit 111a, which is located in line control device 111, by LAN cable 17C. As a result, transmission data to be sent to a mobile station (mobile station 15C in Figure 1) located within the communication range ZEC (see Figure 1) of base station radio device 13C is transmitted to timing control unit 134C from control unit 111a via LAN cable 17C. For the sake of explanation, it will be assumed that only mobile station 15C exists within the communication range ZEC.

[0028] Counters 133A, 133B, and 133C operate synchronously with each other because they are driven by a time pulse signal PLS and a clock signal GCK based on time information included in the GNSS signal. As a result, counters 133A, 133B, and 133C synchronously generate frame numbers A, B, and C with the same number and output them to the timing control units 134A, 134B, and 134C. This allows the fire radio communication system 1 to synchronize the timing of when it starts transmitting data A from the base station radio device 13A to the mobile station 15A, when it starts transmitting data B from the base station radio device 13B to the mobile station 15B, and when it starts transmitting data C from the base station radio device 13C to the mobile station 15C, as will be described in detail later.

[0029] (Operation of the fire department's radio communication system) The operation of the fire radio communication system 1 according to this embodiment will be explained with reference to Figures 1 and 2, and with reference to Figures 3 and 4. Figure 3 is a schematic diagram showing in chronological order an example of the operation of the line control device 111 and base station radio devices 13A, 13B, and 13C, which is one of the operations of the fire radio communication system 1, up to the start of synchronous transmission of transmission data.

[0030] In Figure 3, the "transmission data" in the line control device 111 indicates the transmission data transmitted from the synchronization start determination unit 111a-1 to the base station radio devices 13A, 13B, and 13C. Figure 3 shows "D1" through "D13" as "transmission data". Also in Figure 3, the "transmission frame number specification" indicates the frame number that is associated with the "transmission data" and transmitted from the synchronization start determination unit 111a-1 to the base station radio devices 13A, 13B, and 13C. Figure 3 shows "immediate" and "22" through "27" as "transmission frame number specifications". The "immediate" in the "transmission frame number specification" indicates that the base station radio devices 13A, 13B, and 13C are instructed to immediately transmit the received transmission data to the mobile stations 15A, 15B, and 15C. For example, "22" in the "Transmit Frame Number Specification" indicates that when the frame number generated by the base station radio equipment 13A, 13B, 13C is "22", then "D8" of the "Transmit Data" received in association with "22" in the "Transmit Frame Number Specification" will be transmitted to the mobile stations 15A, 15B, 15C.

[0031] In Figure 3, "Input" for base station radio devices 13A, 13B, and 13C indicates the transmission data received from the line control device 111. In Figure 3, "Frame Number A" for base station radio device 13A indicates the frame number formed by counter 133A. In Figure 3, "Transmission Data A" for base station radio device 13A indicates the transmission data that base station radio device 13A transmits to mobile stations located in the communication range ZEA. In Figure 3, "Frame Number B" for base station radio device 13B indicates the frame number formed by counter 133B. In Figure 3, "Transmission Data B" for base station radio device 13B indicates the transmission data that base station radio device 13B transmits to mobile stations located in the communication range ZEB. In Figure 3, "Frame Number C" for base station radio device 13C indicates the frame number formed by counter 133C. In Figure 3, "Transmission Data C" for base station radio device 13C indicates the transmission data that base station radio device 13C transmits to mobile stations located in the communication range ZEC.

[0032] As described above, counters 133A, 133B, and 133C (see Figure 2) clear frame numbers A, B, and C using the high-precision time pulse signal PLS input from GPS receivers 131A, 131B, and 131C (see Figure 2), and then begin counting frame numbers A, B, and C. Therefore, as shown in Figure 3, the frame numbers A, B, and C and the frame timings generated by counters 133A, 133B, and 133C are consistent with each other. In this embodiment, the frame period for which each of frame numbers A, B, and C is generated is, for example, 40 ms.

[0033] As shown in Figure 3, at the start of communication, for example at time t1, the master station 11 (see Figure 2) transmits a frame number (an example of a synchronization signal) to the base station radio devices 13A, 13B, and 13C when communicating with the mobile stations 15A, 15B, and 15C. The frame number that the master station 11 transmits to the base station radio devices 13A, 13B, and 13C at the start of communication is generated by the control unit 111a provided in the line control device 111 and corresponds to the "transmit frame number specification" shown in Figure 3. In the example operation shown in Figure 3, the line control device 111 provided in the master station 11 transmits "immediately" as the frame number for the "transmit frame number specification" to the base station radio devices 13A, 13B, and 13C at time t1. The line control device 111 also transmits the transmission data (an example of a synchronization signal) as "transmit data" associated with "immediately" as the frame number for the "transmit frame number specification" to the base station radio devices 13A, 13B, and 13C at time t1. In the example shown in Figure 3, the line control device 111 installed at the master station 11 transmits the transmission data D1 as "transmission data" to the base station radio devices 13A, 13B, and 13C.

[0034] When communication begins, the line control device 111 transmits frame data (i.e., transmission data) to the base station radio equipment 13A, 13B, and 13C at a predetermined interval. The predetermined interval is the same as the interval (40 ms in this embodiment) for which the counters 133A, 133B, and 133C (see Figure 2) installed in the base station radio equipment 13A, 13B, and 13C generate frame numbers. From time t1 at the start of communication, the line control device 111 transmits the transmission data D1, D2, D3, D4, D5, D6, D6, D8, D9, D10, D11, D12, and D13, along with additional information such as "immediate" for "transmission frame number specification" and frame numbers "22", "23", "24", "25", "26", and "27" to the base station radio equipment 13A, 13B, and 13C at the predetermined interval.

[0035] The base station radio devices 13A, 13B, and 13C receive the "transmission data" and "transmission frame number specification" transmitted from the line control device 111 at different times. Therefore, as shown in Figure 3, the transmission data D1 and transmission frame number specification "immediately" transmitted from the line control device 111 at time t1 reach base station radio device 13A at time t2A, reach base station radio device 13B at time t2B (later than time t2A), and reach base station radio device 13C at time t2C (later than time t2B).

[0036] Next, the base station radio devices 13A, 13B, and 13C take into consideration that the arrival time of the transmission data D1 sent from the line control device 111 will differ depending on the time it takes for the radio waves to reach the station, and begin transmitting the transmission data D1 to the mobile stations 15A, 15B, and 15C in accordance with the timing of the radio frame boundary (i.e., the timing when the frame number changes). Specifically, as shown in Figure 3, base station radio device 13A begins transmitting the transmission data D1 to mobile station 15A at time t3A, for example, when frame number A changes from "10" to "11". Base station radio device 13B begins transmitting the transmission data D1 to mobile station 15C at time t3B, for example, when frame number B changes from "12" to "13". Base station radio device 13C begins transmitting the transmission data D1 to mobile station 15C at time t3C, for example, when frame number C changes from "14" to "15". The period Δt23A between time t2A and time t3A, the period Δt23B between time t2B and time t3B, and the period Δt23C between time t2C and time t3C are, for example, the same length.

[0037] Next, the base station radio devices 13A, 13B, and 13C each store the frame number in which they started transmitting the transmission data D1 to the mobile stations 15A, 15B, and 15C, respectively. Specifically, base station radio device 13A stores the frame number "11," which is the frame number in which it started transmitting the transmission data D1 to the mobile station 15A, in a memory unit (not shown) provided in, for example, the timing control unit 134A (see Figure 2). Similarly, base station radio device 13B stores the frame number "13," which is the frame number in which it started transmitting the transmission data D1 to the mobile station 15B, in a memory unit (not shown) provided in, for example, the timing control unit 134B (see Figure 2). Similarly, base station radio device 13C stores the frame number "15," which is the frame number in which it started transmitting the transmission data D1 to the mobile station 15C, in a memory unit (not shown) provided in, for example, the timing control unit 134C (see Figure 2).

[0038] Next, the base station radio devices 13A, 13B, and 13C, which have received the frame data, transmit a notification signal to the master station 11 indicating that they have received the frame data. Specifically, as shown in Figure 3, almost simultaneously with the start of transmission of transmission data D1 to the mobile station 15A (i.e., immediately after time t3A), the base station radio device 13A includes "11," the frame number A in which transmission of transmission data D1 to the mobile station 15A was initiated, in the notification signal and transmits it to the synchronization start determination unit 111a-1 provided in the master station 11. Similarly, as shown in Figure 3, almost simultaneously with the start of transmission of transmission data D1 to the mobile station 15B (i.e., immediately after time t3B), the base station radio device 13B includes "13," the frame number B in which transmission of transmission data D1 to the mobile station 15B was initiated, in the notification signal and transmits it to the synchronization start determination unit 111a-1. Similarly, as shown in Figure 3, almost simultaneously with the start of transmission of transmission data D1 to the mobile station 15C (i.e., immediately after time t3C), the base station radio equipment 13C transmits to the synchronization start determination unit 111a-1 the frame number C, "15", which indicates the start of transmission of transmission data D1 to the mobile station 15C, in the notification signal.

[0039] Thus, each base station radio device 13A, 13B, and 13C (an example of multiple base stations) is equipped with GPS receivers 131A, 131B, and 131C, respectively. Each device generates a frame number synchronized with the reference clock signal PCK (an example of a reference signal) output from the GPS receivers 131A, 131B, and 131C at regular intervals (40ms in this embodiment), and transmits to the master station 11 the frame number when it receives the frame data with the "transmit frame number specified" in the notification signal. In other words, base station radio device 13A transmits the value of frame number A when it receives the transmit data from the line control device 111, along with the notification signal, to the synchronization start determination unit 111a-1. Base station radio devices 13B and 13C transmit frame numbers B and C to the synchronization start determination unit 111a-1 in the same manner as base station radio device 13A.

[0040] Next, the master station 11 determines, based on the notification signal, the transmission timing for the base station radio devices 13A, 13B, and 13C to transmit the communication content (e.g., transmission data) received from the master station 11 to the mobile stations 15A, 15B, and 15C. Specifically, the synchronization start determination unit 111a-1 provided in the line control device 111 determines the base station radio device with the largest delay from the frame numbers notified by each of the base station radio devices 13A, 13B, and 13C. Furthermore, the synchronization start determination unit 111a-1 uses the frame number of the base station radio device that arrives the latest to determine the frame number at which synchronous transmission of the transmission data will begin. As shown in Figure 3, the notification signal transmitted from base station radio device 13A reaches the line control device 111 at time t4A, for example. The notification signal output from base station radio device 13B reaches the line control device 111 at time t4B, for example. The notification signal output from base station radio device 13C reaches the line control device 111 at time t4C, for example.

[0041] The synchronization start determination unit 111a-1 obtains the frame number contained in the notification signal each time it receives a notification signal, and determines that the base station radio device that transmitted the notification signal containing the largest frame number is the base station radio device with the greatest delay. In this example, the frame number "15" contained in the notification number transmitted from base station radio device 13C is the largest frame number, so the synchronization start determination unit 111a-1 determines that base station radio device 13C is the base station radio device with the greatest delay. The synchronization start determination unit 111a-1 determines the frame number for initiating synchronous transmission (hereinafter sometimes referred to as the "frame number for initiating synchronous transmission") as the sum of the frame number "15" contained in the notification number transmitted from base station radio device 13C and the number of transmission data transmitted to base station radio device 13C from the transmission of "specifying transmission frame number" until the notification number is received. In this example, the synchronization start determination unit 111a-1 has sent seven transmission data (transmission data D1 to D7) to the base station radio device 13C from the transmission of "transmission frame number specification" until it receives the notification number, so it determines the frame number for starting synchronization transmission to be "22" (=15+7).

[0042] In this way, based on the notification signals received from the base station radio devices 13A, 13B, and 13C, the master station 11 calculates the respective delay times that occur between the master station 11 and the base station radio devices 13A, 13B, and 13C when the master station 11 and the base station radio devices 13A, 13B, and 13C communicate, and generates a frame number for initiating synchronous transmission (an example of transmission timing information) based on these delay times.

[0043] When the master station 11 transmits a transmission signal to the mobile stations 15A, 15B, and 15C, it transmits a transmission signal to the base station radio equipment 13A, 13B, and 13C that includes the frame number for starting synchronous transmission, which is information about the transmission timing. The synchronization start determination unit 111a-1 provided in the master station 11 includes the transmission data that the base station radio equipment 13A, 13B, and 13C should transmit to the mobile stations 15A, 15B, and 15C, along with the frame number for starting synchronous transmission, in the transmission signal.

[0044] Specifically, as shown in Figure 3, when the synchronization start determination unit 111a-1 transmits a transmission signal to mobile stations 15A, 15B, and 15C at time t5, for example, it includes the synchronization transmission start frame number "22" and the transmission data D8 to be transmitted synchronously to mobile stations 15A, 15B, and 15C in the transmission signal and transmits it to base station radio equipment 13A, 13B, and 13C. The transmission signal transmitted from the synchronization start determination unit 111a-1 reaches base station radio equipment 13A at time t6A, for example. The transmission signal transmitted from the synchronization start determination unit 111a-1 reaches base station radio equipment 13B at a later time than t6A, for example, at time t6B. Furthermore, the transmission signal transmitted from the synchronization start determination unit 111a-1 reaches base station radio equipment 13C at a later time than t6B, for example, at time t6C.

[0045] Next, when the base station radio devices 13A, 13B, and 13C transmit the communication content (e.g., transmission data) received from the master station 11 to the mobile stations 15A, 15B, and 15C, they determine the transmission timing to be transmitted to the mobile stations 15A, 15B, and 15C based on the synchronization start frame number (an example of transmission timing information) received from the master station 11.

[0046] Specifically, the timing control unit 134A in the base station radio device 13A determines the transmission timing to be when the counter number "22" (i.e., frame number "22"), which is the same number as the synchronization start frame number "22" included in the transmission signal received at time t6A, is input from the counter 133A (see Figure 2). Furthermore, as shown in Figure 3, the base station radio device 13A transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15A until the determined synchronization start frame number ("22" in this example) and frame number A are the same value. In addition, the base station radio device 13A transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15A each time frame number A is changed.

[0047] Similarly, the timing control unit 134B in the base station radio device 13B determines the transmission timing based on the synchronization start frame number "22" included in the transmission signal received at time t6B, and determines the timing at which the same number of counters "22" (i.e., frame number "22") as the synchronization start frame number "22" is input from the counter 133B (see Figure 2). Also, as shown in Figure 3, the base station radio device 13B transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15B until the determined synchronization start frame number ("22" in this example) and frame number B become the same value. Furthermore, the base station radio device 13B transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15B each time frame number B is changed.

[0048] Similarly, the timing control unit 134C in the base station radio device 13C determines the transmission timing based on the synchronization start frame number "22" included in the transmission signal received at time t6C, and determines the timing at which the same number of counters "22" (i.e., frame number "22") as the synchronization start frame number "22" is input from the counter 133C (see Figure 2). Furthermore, as shown in Figure 3, the base station radio device 13C transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15C until the determined synchronization start frame number ("22" in this example) and frame number C are the same value. The base station radio device 13C also transmits the last received transmission data (transmission data D7 in this example) to the mobile station 15C each time frame number C is changed.

[0049] As shown in Figure 3, at time t7, when the frame number switches from "21" to "22," that is, when the period of frame number "22" which is the same as the synchronization start frame number "22" begins, base station radio devices 13A, 13B, and 13C begin synchronous transmission of the transmission data D8, which was included in the transmission signal along with the synchronization start frame number "22," to mobile stations 15A, 15B, and 15C. Base station radio device 13A begins synchronous transmission (in this example, it begins synchronous transmission of transmission data D8) when the determined synchronization start frame number (in this example, "22") and frame number A become the same value. Similarly, base station radio devices 13B and 13C begin synchronous transmission when the determined synchronization start frame number and frame numbers B and C become the same value. Although a detailed explanation is omitted, base station radio devices 13A, 13B, and 13C continue synchronous transmission of transmission data to mobile stations 15A, 15B, and 15C even after frame number "23."

[0050] Next, we will explain one of the operations of the fire radio communication system 1 according to this embodiment, specifically the process up to the start of synchronous transmission of transmission data, using Figure 4. Figure 4 is a sequence diagram showing an example of the process up to the start of synchronous transmission by the fire radio communication system 1. In Figure 4, for ease of understanding, the transmission data transmitted from the line control device 111 is shown on the left side of the figure, and the frame numbers generated by the base station radio devices 13A, 13B, and 13C are shown on the right side of the figure.

[0051] As shown in Figure 4, in step S1, the line control device 111 transmits the transmission data D1 of the "transmission data" and "immediate" of the "transmission frame number specification" as synchronization signals to the base station radio devices 13A, 13B, and 13C.

[0052] In the next step S2 following step S1, the base station radio device 13A receives a synchronization signal transmitted from the line control device 111, which includes the transmission data D1 and the word "immediately".

[0053] In the next step S3 following step S2, the base station radio device 13A transmits the transmission data D1 of the "transmission data A" included in the received synchronization signal to the mobile station 15A, based on the "immediate" "transmission frame number specification" included in the synchronization signal.

[0054] In the next step S4 following step S3, the base station radio device 13A stores the frame number A (in this example, "11") that was transmitted to the mobile station 15A with the transmission data D1, and transmits a notification signal SaA containing frame number A "11" to the line control device 111.

[0055] In the next step S5 following step S4, the base station radio device 13B receives a synchronization signal transmitted from the line control device 111, which includes the transmission data D1 and the word "immediately". In this way, the base station radio device 13B receives the synchronization signal transmitted from the line control device 111 in step S1 at a different timing than the base station radio device 13A.

[0056] In the next step S6 following step S5, the base station radio device 13B transmits the transmission data D1 of the "transmission data B" included in the received synchronization signal to the mobile station 15B based on the "immediate" "transmission frame number specification" included in the synchronization signal.

[0057] In the next step S7 following step S6, the base station radio device 13B stores the frame number B (13 in this example) of the transmitted data D1 to the mobile station 15B, and transmits a notification signal SaB containing frame number B "13" to the line control device 111.

[0058] In the next step S8 following step S7, the base station radio device 13C receives a synchronization signal transmitted from the line control device 111, which includes the transmission data D1 and the word "immediately". In this way, the base station radio device 13C receives the synchronization signal transmitted from the line control device 111 in step S1 at a different timing than the base station radio devices 13A and 13B.

[0059] In the next step S9 following step S8, the base station radio device 13C transmits the transmission data D1 of the "transmission data C" included in the received synchronization signal to the mobile station 15C based on the "immediate" "transmission frame number specification" included in the synchronization signal.

[0060] In the next step S10 following step S9, the base station radio device 13C stores the frame number C (15 in this example) of the transmitted data D1 to the mobile station 15C, and transmits a notification signal SaC containing frame number C "15" to the line control device 111.

[0061] In the next step S11 following step S10, the line control device 111 determines the start timing for synchronously transmitting transmission data to the mobile stations 15A, 15B, and 15C. The line control device 111 adds the number of transmission data transmitted from step S1 to step S11 (7 in this example) to the frame number "15" included in the notification signal SaC among the notification signals SaA, SaB, and SaC transmitted from the base station radio equipment 13A, 13B, and 13C. As a result, the line control device 111 determines the frame number for starting synchronous transmission, which is the frame number for the start timing of synchronously transmitting transmission data to the mobile stations 15A, 15B, and 15C, to be "22".

[0062] In the next step S12 following step S11, the line control device 111 transmits a transmission signal St to the base station radio equipment 13A, 13B, and 13C, which includes the frame number "22" for initiating synchronous transmission and the transmission data D8 to be transmitted synchronously to the mobile stations 15A, 15B, and 15C.

[0063] In the next step S13 following step S12, the base station radio device 13A receives a transmission signal St, which includes transmission data D8, transmitted from the line control device 111.

[0064] In the next step S14 following step S13, the base station radio device 13A transmits the transmission data D7 to the mobile station 15A. Specifically, the base station radio device 13A determines that the synchronous transmission start frame number "22" included in the received transmission signal St does not match the current frame number 16, and at the timing when the period of frame number 17 begins, it transmits to the mobile station 15A the last transmission data (transmission data D7 in this example) that was received before the transmission signal St containing the synchronous transmission start frame number "22" was received.

[0065] In the next step S15 following step S14, the base station radio device 13B receives a transmission signal St, which includes transmission data D8, transmitted from the line control device 111.

[0066] In the next step S16 following step S15, the base station radio device 13B transmits the transmission data D7 to the mobile station 15B. Specifically, the base station radio device 13B determines that the synchronous transmission start frame number "22" included in the received transmission signal St does not match the current frame number 18, and at the timing when the period of frame number 19 begins, it transmits to the mobile station 15B the last transmission data (transmission data D7 in this example) that was received before the transmission signal St containing the synchronous transmission start frame number "22".

[0067] In the next step S17 following step S16, the base station radio device 13C receives a transmission signal St, which includes transmission data D8, transmitted from the line control device 111.

[0068] In the next step S18 following step S17, the base station radio device 13C transmits the transmission data D7 to the mobile station 15C. Specifically, the base station radio device 13C determines that the synchronous transmission start frame number "22" contained in the received transmission signal St does not match the next frame number 20, and at the timing when the period of frame number 21 begins, it transmits to the mobile station 15C the last transmission data (transmission data D7 in this example) that was received before the transmission signal St containing the synchronous transmission start frame number "22".

[0069] In the next steps S19A, S19B, and S19C following step S18, the base station radio devices 13A, 13B, and 13C transmit the transmission data D8 contained in the received transmission signal St to the mobile stations 15A, 15B, and 15C, respectively. Steps S19A, S19B, and S19C are all executed at the timing when the frame number switches from "21" to "22", that is, when the period of frame number "22" begins.

[0070] Since the next frame number "22" matches the frame number "22" for initiating synchronous transmission, the base station radio equipment 13A, 13B, and 13C transmit the transmission data D8 contained in the received transmission signal St to the mobile stations 15A, 15B, and 15C.

[0071] In this way, the fire radio communication system 1 begins synchronous transmission of transmission data to mobile stations 15A, 15B, and 15C. Although not shown in the diagram, even when frame numbers A, B, and C reach "23" or later, the base station radio devices 13A, 13B, and 13C continue to transmit the transmission data sent from the line control device 111 to the mobile stations 15A, 15B, and 15C while maintaining transmission synchronization.

[0072] As described above, the fire radio communication system 1 can initiate synchronous transmission of data to multiple mobile stations located within the communication range of multiple base station radio devices, even if the line control device 111 is not equipped with a GPS receiver. This allows the fire radio communication system 1 to reduce costs. Furthermore, the fire radio communication system 1 can prevent communication failures due to radio interference at these mobile stations, even if one or more mobile stations are located within the interference range where the communication ranges of multiple base station radio devices overlap.

[0073] Furthermore, the line control device 111 can transmit "immediately" as a "transmission frame number specification" to multiple base station radio devices before initiating synchronous transmission of transmission data to mobile stations, that is, during the adjustment period for initiating such synchronous transmission. This allows multiple base station radio devices to transmit transmission data to one or more mobile stations even before initiating synchronous transmission of transmission data to these mobile stations. The line control device 111 may also transmit transmission data to multiple base station radio devices that includes information such as "adjusting for synchronous transmission" along with the "immediately" "transmission frame number specification." One or more mobile stations that receive transmission data containing such information can understand the current status before initiating synchronous transmission.

[0074] As described above, the fire radio communication system 1 according to this embodiment comprises a master station 11, base station radio devices 13A, 13B, 13C, and mobile stations 15A, 15B, 15C that communicate with the fire department headquarters device 113 via the base station radio devices 13A, 13B, 13C. When the master station 11 communicates with the mobile stations 15A, 15B, 15C, it transmits a frame number to the base station radio devices 13A, 13B, 13C as a "transmission frame number specification". The base station radio devices 13A, 13B, 13C that receive the frame number then transmit the frame number A notification signal indicating that a frame number has been received is sent to the master station 11. Based on the notification signal, the master station 11 determines the transmission timing for the base station radio devices 13A, 13B, and 13C to transmit the communication content (e.g., transmission data) received from the master station 11 to the mobile stations 15A, 15B, and 15C. When the master station 11 transmits the transmission signal to the mobile stations 15A, 15B, and 15C, it also transmits a transmission signal to the base station radio devices 13A, 13B, and 13C that includes the frame number for synchronous transmission initiation, which is information about the transmission timing. This allows the fire department radio communication system 1 to be made more cost-effective and to transmit and receive data correctly.

[0075] The present invention is not limited to the embodiments described above, and various modifications are possible. The fire radio communication system 1 according to the above embodiment determines the time required to send and receive data between the line control device 111 and the base station radio devices 13A, 13B, and 13C based on the frame number (i.e., frame duration), but the present invention is not limited thereto. The fire radio communication system 1 may, for example, measure the time required to send and receive data between the line control device 111 and the base station radio devices 13A, 13B, and 13C and determine the time.

[0076] In this case, the line control device 111 stores the transmission time when it sent the synchronization signal to the base station radio devices 13A, 13B, and 13C. The base station radio devices 13A, 13B, and 13C send a notification signal to the line control device 111 that includes the reception time of the synchronization signal sent from the line control device 111. The line control device 111 may calculate the difference between the stored transmission time and the received reception time, and determine the time to start synchronous transmission (i.e., the time corresponding to the frame number for starting synchronous transmission in the above embodiment) based on the largest of these differences.

[0077] Although embodiments of the present invention have been described above, these embodiments are merely illustrative examples of apparatus and methods for realizing the technical concept of the present invention, and the technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims. [Explanation of Symbols]

[0078] 1. Fire Department Radio Communication System 2 GNSS satellites 3 NTP servers 11 Master station 13A,13B,13C Base station radio equipment 15A,15B,15C Mobile station 17A, 17B, 17C LAN cables 111 Line control device 111a Control Unit 111a-1 Synchronization start determination section 111b Crystal Oscillator 113 Fire Department Headquarters Equipment 131A, 131B, 131C GPS receivers 132A,132B,132C PLL circuit 133A, 133B, 133C counters 134A, 134B, 134C Timing Control Unit 135A,135B,135C Radio section 136A, 136B, 136C, 137A, 137B, 137C Antenna D1~D13 Transmission Data GCK clock signal IZE1, IZE2, IZE3, IZE4 Interference Range PCK reference clock signal PLS Time Pulse Signal SaA,SaB,SaC notification signal St transmission signal ZEA, ZEB, ZEC communication range

Claims

1. A communication system comprising a master station, a plurality of base stations, and one or more mobile stations that communicate with the master station via the plurality of base stations, The aforementioned base station transmits a synchronization signal to the base station when communicating with the mobile station. Upon receiving the synchronization signal, the base station transmits a notification signal to the master station, including the frame number at the time the synchronization signal was received, in order to notify that the synchronization signal has been received. The base station determines, based on the notification signal, the transmission timing at which the plurality of base stations synchronously transmit the communication content received from the base station to the mobile station. When the base station transmits a transmission signal to the mobile station, it transmits the transmission signal, including the transmission timing information which is information about the transmission timing, to the multiple base stations. A communication system characterized by the following.

2. Each of the aforementioned multiple base stations is equipped with a GPS receiver, generates the frame number synchronized with the reference signal output from the GPS receiver at regular intervals, and transmits the notification signal to the base station. The communication system according to claim 1, characterized by the following:

3. The master station calculates the respective delay times that occur between the master station and the multiple base stations when the master station and the multiple base stations communicate, based on the notification signal received from the base station, and generates the transmission timing information based on the delay times. A communication system according to claim 1 or 2, characterized by the above.

4. When the plurality of base stations transmit the communication content received from the base station to the mobile station, they determine the transmission timing to transmit to the mobile station based on the transmission timing information received from the base station. The communication system according to claim 3, characterized by the following:

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