Long-distance signal transmission system

Abstract

When using flooding for long-distance signal transmission, synchronization can be easily achieved at each wireless base station. [Solution] A long-distance signal transmission system that transmits signals via a communication network constructed by multiple wireless base stations, wherein the multiple wireless base stations consist of a group of wireless base stations that use flooding as a signal transfer protocol and can transmit information including the data to be transmitted and its own slot number in synchronization with the time slot assigned to it, and a group of wireless base stations that are dedicated to transmission and can transmit data to be transmitted at any time, regardless of the time slot, and each wireless base station included in the group of wireless base stations has a function to correct its own timer time to match the time of the timer of the other wireless base station that is the source of the information, based on information received from other wireless base stations included in the group of wireless base stations.

Description

Technical Field

[0001] The present disclosure relates to a long-distance signal transmission system that performs signal transmission using flooding as a signal transfer protocol via a communication network constructed by a plurality of radio base stations.

Background Art

[0002] When performing signal transmission in a communication network where a plurality of radio base stations are arranged, a broadcast method called flooding using simultaneous transmission has been proposed. In the flooding method using simultaneous transmission, when one radio base station performs data transmission, one or more radio base stations that have received the data broadcast the same data, thereby realizing simultaneous transmission of radio signals.

[0003] By each of a plurality of radio base stations repeating such simultaneous transmission a plurality of times, it becomes possible to transmit data to the entire signal transmission system. By adopting such a communication method, there is an advantage that prior setting for routing regarding the communication path can be made unnecessary.

[0004] In addition, by allocating time slots to each of a plurality of radio base stations, each radio base station performs wireless signal transmission only within the time slot allocated to itself, thereby preventing interference of signal transmission among a plurality of radio stations.

[0005] In a signal transmission system that performs communication using time slots, it is necessary to synchronize among a plurality of radio base stations. As a method for synchronization, there is a conventional technique using synchronization packets (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] However, conventional technologies have the following problems: In the prior art described in Patent Document 1, it is necessary to implement in each wireless base station that communicates using time slots a process for generating and transmitting a specific synchronization packet, and a synchronization recovery process when a synchronization packet is received.

[0008] Consequently, the configuration required to achieve synchronization is complex, and implementing the necessary functions incurs time and expense. In other words, the complexity of the configuration required to achieve synchronization has been one of the bottlenecks in the introduction of signal transmission systems using flooding.

[0009] This disclosure was made to solve the aforementioned problems and aims to provide a long-distance signal transmission system that enables easy synchronization at each wireless base station when performing long-distance signal transmission using flooding. [Means for solving the problem]

[0010] The long-distance signal transmission system according to this disclosure is a long-distance signal transmission system that transmits signals via a communication network constructed by multiple radio base stations, wherein the multiple radio base stations consist of a group of radio base stations that use flooding as a signal transfer protocol and are capable of transmitting information including the data to be transmitted and the slot number assigned to them in synchronization with the time slot assigned to them, and one or more radio base stations that are dedicated to transmission and are capable of transmitting data at any time, regardless of the time slot, and each radio base station included in the group of radio base stations has a function to correct its own timer time to match the time of the timer of the other radio base station that is the source of the information, based on information received from other radio base stations included in the group of radio base stations. [Effects of the Invention]

[0011] According to this disclosure, a long-distance signal transmission system can be obtained that allows for easy synchronization at each wireless base station when performing long-distance signal transmission using flooding. [Brief explanation of the drawing]

[0012] [Figure 1] This is an overall configuration diagram of the long-distance signal transmission system in Embodiment 1 of the present disclosure. [Figure 2] This diagram illustrates the case in which signal transmission is performed using flooding in accordance with Rules 1 and 2 in the long-distance signal transmission system according to Embodiment 1 of this disclosure. [Figure 3] This is an explanatory diagram of signal transmission using flooding implemented in the long-distance signal transmission system according to Embodiment 1 of this disclosure. [Figure 4] This is a functional block diagram of each wireless base station in the long-distance signal transmission system according to Embodiment 1 of the present disclosure. [Figure 5] This is a flowchart illustrating a series of signal transmission processes using flooding implemented at each wireless base station according to Embodiment 1 of this disclosure. [Figure 6] This is an overall configuration diagram of the long-distance signal transmission system in Embodiment 2 of the present disclosure. [Modes for carrying out the invention]

[0013] Hereinafter, preferred embodiments of the long-distance signal transmission system of this disclosure will be described with reference to the drawings. The long-distance signal transmission system according to this disclosure is technically characterized in that each radio base station has a function to correct the time of its own timer when it receives information from other radio base stations. As a result, when performing long-distance signal transmission using flooding, it is possible to obtain the effect of synchronizing at each radio base station with a simple configuration.

[0014] Embodiment 1. There is a demand to use a LoRa-compliant wireless module, which is one of the representative standards for LPWA (Low Power Wide Area) wireless, for information transmission of remote abnormality detection (for example, monitoring of fallen bridges in the mountains). For this purpose, it is necessary to add a wireless mesh network function to enable long-distance transmission to cover a wide area.

[0015] The expansion of the wide area of the wireless mesh network can be achieved by strengthening two functions: an increase in the number of relay wireless stations and an expansion of the distance between wireless stations. From this perspective, when transmitting information such as a fire detection system or a fallen bridge monitoring system in the mountains, adopting a long-distance signal transmission system that applies flooding as a signal transfer protocol through a communication network constructed by a plurality of wireless base stations is one solution.

[0016] When adopting such a long-distance signal transmission system using flooding, it is important to construct a technology for synchronization with an easy configuration in each wireless base station in the communication network to solve the problems of the prior art.

[0017] Therefore, in the following description, taking the case of detecting a fallen bridge in the mountains or the like using a long-distance signal transmission system that performs signal transmission using flooding as a specific example, it will be described in detail. Note that the long-distance signal transmission system of the present disclosure is applicable to various applications using a wireless mesh network.

[0018] FIG. 1 is an overall configuration diagram of the long-distance signal transmission system according to Embodiment 1 of the present disclosure. In FIG. 1, a case where a communication network is constructed by a monitoring center 1 provided in the city hall, three sensor networks 2, 3, 4, and an in-city network 5 is illustrated.

[0019] The monitoring center 1 is configured to include one wireless base station 10 and a monitoring PC (Personal Computer) 40. The operator can centrally monitor the information in the communication network by monitoring the monitoring PC 40 within the monitoring center 1.

[0020] Each of the sensor networks 2 and 3 includes one wireless base station 10 and two dedicated transmission wireless base stations 20.

[0021] The sensor network 4 includes one wireless base station 10, five dedicated transmission wireless base stations 20, and a plurality of sensors 30 installed on a bridge to be monitored for bridge collapse. Also, the city network 5 includes five wireless base stations 10 arranged to form a wireless mesh network.

[0022] Note that the overall configuration shown in FIG. 1 is merely an example, and according to the environment to which the long-distance signal transmission system of the present disclosure is applied, the number, arrangement, and connection relationship of the network, wireless base stations, and sensors can be changed to a desired configuration. In the following description, the wireless base station 10 that performs data transmission and reception is simply referred to as the wireless base station 10, and the dedicated transmission wireless base station 20 is simply referred to as the wireless base station 20.

[0023] In the communication network constructed by a plurality of wireless base stations 10 and a plurality of wireless base stations 20, in the plurality of wireless base stations 10, signal transmission is performed using flooding as a signal transfer protocol. Flooding is a protocol that performs signal transfer based on only the following two simple rules.

[0024] Rule 1: When the wireless base station 10 receives a signal transmitted from another wireless base station 10 or wireless base station 20, it transfers the received signal to all wireless base stations 10 within the range where its radio wave reaches. Rule 2: When the same signal is received again at different timings in the wireless base station 10, the second transfer is not executed.

[0025] FIG. 2 is an explanatory diagram of signal transmission according to Rules 1 and 2 using flooding in the long-distance signal transmission system according to Embodiment 1 of the present disclosure. In FIG. 2, an example is shown in which signal transmission is performed using flooding by three wireless base stations 10(1) to 10(3).

[0026] More specifically, Figure 2 illustrates a case where radio base station 10(1) is the source base station, radio base station 10(2) is the relay base station, and radio base station 10(3) is the destination base station, and a signal transmitted from radio base station 10(1) is eventually reached by flooding to radio base station 10(3).

[0027] In Figure 2, [1] to [4] represent the steps in which signal transmission is performed using flooding. In each step, the following processes are performed sequentially. Step [1]: Radio base station 10(1) transmits a signal to all radio base stations 10 within its radio wave range in accordance with Rule 1. As a result, a signal is transmitted from radio base station 10(1) to radio base station 10(2).

[0028] Step [2]: Radio base station 10(2) transmits a signal to all radio base stations 10 within its radio wave range, in accordance with Rule 1. As a result, a signal is transmitted from radio base station 10(2) to radio base stations 10(1) and radio base station 10(3). Thus, after steps [1] and [2], the signal transmitted from radio base station 10(1) reaches radio base station 10(3), and the original objective is achieved.

[0029] Step [3]: Radio base station 10(1) does not forward the same signal in accordance with Rule 2. On the other hand, radio base station 10(3) forwards the signal to all radio base stations 10 within its radio wave range in accordance with Rule 1. If Rule 3 is established, which states that "if the destination of the signal is itself, the received data is accepted and not forwarded," then radio base station 10(3) can be prevented from forwarding the signal in accordance with Rule 3.

[0030] Step [4]: ​​The wireless base station 10(2) does not perform any further transmission because it has received the same signal as in step [1] in step [3], in accordance with rule 2. As a result, no further transmission occurs, and signal transmission within the network is terminated.

[0031] In the communication network shown in Figure 1, as explained in Figure 2, by performing signal transmission by flooding in accordance with rules 1 and 2, the wireless base station 10 in monitoring center 1 can receive signals transmitted from the wireless base stations 10 in sensor networks 2 to 4 to the wireless base station 10 in monitoring center 1 via the city network 5.

[0032] The advantages of using flooding for signal transmission include the following: Benefit 1: By following Rule 2, the signal will no longer run back and forth indefinitely. Advantage 2: Since there is no need to maintain a routing table that indicates the forwarding destination for each recipient, it becomes easier to operate a long-distance signal transmission system using multiple wireless base stations 10.

[0033] However, the following points should be noted when transmitting signals using flooding. Note 1: Due to redundant transmission, radio collisions and interference are likely to occur, requiring control over the timing of radio wave transmission.

[0034] As part of addressing this point of concern, the system described in Patent Document 1 employs a method of assigning time slots to each of the multiple wireless base stations 10 and synchronizing them. However, the method described in Patent Document 1 aims for high-precision synchronization to achieve general-purpose and highly efficient transmission, which is beyond what is needed to solve the problem shown in Figure 1. As a result, the configuration is complex, and the effort and cost required to implement the function become unnecessarily high.

[0035] Therefore, the long-distance signal transmission system described herein implements a method that allows each wireless base station 10 to easily synchronize when performing long-distance signal transmission using flooding. The specific details will be described in detail using Figures 3 to 5.

[0036] Figure 3 is an explanatory diagram of signal transmission using flooding implemented in the long-distance signal transmission system according to Embodiment 1 of this disclosure. Figure 4 is a functional block diagram of each wireless base station 10 in the long-distance signal transmission system according to Embodiment 1 of this disclosure. Figure 5 is a flowchart showing a series of processes for signal transmission using flooding implemented in each wireless base station 10 according to Embodiment 1 of this disclosure.

[0037] In Figure 3, for the sake of simplicity, an example is shown where a communication network is constructed using three wireless base stations 10(1) to 10(3) and signal transmission is performed using flooding. However, in reality, there are also fourth and subsequent wireless base stations 10, and a wireless mesh network is constructed.

[0038] Figure 3(A) shows a state in which ID1 is assigned to wireless base station 10(1), ID2 is assigned to wireless base station 10(2), and ID3 is assigned to wireless base station 10(3), and signals are transmitted between them.

[0039] In Figure 3(A), the signal transmitted from the radio base station 10(1) assigned ID1 is shown as SG1, the signal transmitted from the radio base station 10(2) assigned ID2 is shown as SG2, and the signal transmitted from the radio base station 10(3) assigned ID3 is shown as SG3.

[0040] Here, we assume that the radio base station 10(1) with ID1 is assigned slot number SNo1, the radio base station 10(2) with ID2 is assigned slot number SNo2, and the radio base station 10(3) with ID3 is assigned slot number SNo3.

[0041] The ID is a unique identifier used to identify each radio base station 10 within the long-distance signal transmission system, and it is not assigned to any other radio base station. On the other hand, the SNo is a slot number assigned to each radio base station to define the time slot for transmission, and it may be assigned to any other radio base station. However, Figure 3(A) illustrates a case where each of the three radio base stations is assigned one of three slot numbers in a way that does not result in overlap.

[0042] Figure 3(B) schematically shows a state in which each of slot numbers SNo1 to SNo3 is assigned one time slot with a time width ΔT for each period T. In other words, each radio base station 10(1) to 10(3) is assigned a slot number SNo to identify one of the time-divided time slots, and the timing of data transmission is defined.

[0043] Specifically, each wireless base station 10(1) to 10(3), when it has data to transmit, transmits information including the data to be transmitted and the slot number SNo assigned to it, at a timing when the period calculated by its own timer matches the period of the time slot corresponding to the slot number SNo assigned to it.

[0044] Next, based on the functional block diagram in Figure 4 and the flowchart in Figure 5, a series of signal transmission processes using flooding performed at each of the radio base stations 10(1) to 10(3) will be described. Note that each radio base station 10(1) to 10(3) has the same configuration and will be described as radio base station 10 unless there is a need to distinguish between them.

[0045] As shown in Figure 4, the wireless base station 10 is configured to include a receiving signal processing unit 11, a synchronization adjustment unit 12, and a transmitting signal processing unit 13. The receiving signal processing unit 11 has the function of receiving information transmitted from other wireless base stations 10 located in the vicinity. The receiving signal processing unit 11 receives the information transmitted from other wireless base stations 10 at the timing of the time slot corresponding to the slot number SNo assigned to the other wireless base station 10 that is the source.

[0046] The synchronization adjustment unit 12 has a function to correct the timer indicating the current position in the time slot period based on the slot number SNo contained in the received signal processing unit 11 when it receives information from another radio base station 10. As a result, the synchronization adjustment unit 12 can synchronize its own timer with the timer of the other radio base station 10, which is the source of the information, and correct the transmission timing by correcting its own timer to match the time of the timer of the other radio base station 10.

[0047] When the transmitting signal processing unit 13 receives information from another radio base station 10 by the receiving signal processing unit 11, it determines whether the transfer conditions based on rules 1 and 2 are met. If the transfer conditions are met, the transmitting signal processing unit 13 determines that there is data to be transmitted.

[0048] Furthermore, the transmission signal processing unit 13 will transfer information including the data to be transmitted and the slot number SNo assigned to it, when the time of its own timer falls within the time slot corresponding to the slot number SNo assigned to it.

[0049] In this transfer process, the transmission signal processing unit 13 can transfer information using its own timer, which has been corrected by the synchronization adjustment unit 12, at the timing when it receives information from another radio base station 10. Therefore, a radio base station 10 with the configuration shown in Figure 4 can correct the time of its own timer by receiving information from another radio base station 10, and as a result, can synchronize with other surrounding radio base stations 10.

[0050] The time correction process performed by the synchronization adjustment unit 12 may be performed at any time when the received signal processing unit 11 receives information from another radio base station 10, but it is also possible to set conditions for initiating the time correction process, such as performing the time correction process only during a predetermined time period, or only when information with a specific slot number SNo is received.

[0051] Next, using Figure 5, the series of signal transmission processes using flooding performed at each wireless base station 10 according to this embodiment 1 can be summarized as follows. First, in step 501, the received signal processing unit 11 within the wireless base station 10 receives information transmitted from other surrounding wireless base stations 10 by performing reception processing.

[0052] Next, in step S502, if the synchronization adjustment unit 12 receives the information transmitted in step 501, it corrects the time of its own timer based on the slot number SNo of the other radio base station 10 and the timing at which the information was received.

[0053] Next, in step S503, the transmission signal processing unit 13 determines whether the transfer conditions based on rules 1 and 2 are met. That is, the transmission signal processing unit 13 determines that the transfer conditions are met if rule 1 is met and rule 2 is not met, and determines that the transfer conditions are not met in all other cases. If the transmission signal processing unit 13 determines in step S503 that the transfer conditions are not met, it does not perform the transfer process and terminates the series of processes.

[0054] Meanwhile, if the transmission signal processing unit 13 determines in step S503 that the transfer conditions have been met, it proceeds to step S504 and waits for the time slot corresponding to the slot number SNo assigned to it, based on its own timer which was corrected in step S502. Then, when the time slot assigned to it arrives, it executes the transmission process of a signal that includes the data received in step S501 (i.e., the data to be transmitted) and the slot number SNo assigned to it.

[0055] In this way, each time a transmission process is performed by flooding, the slot number SNo assigned to the transmitting radio base station 10 is added. Therefore, the radio base station 10 that receives information including the slot number SNo can identify which time slot the information was transmitted from, and can easily correct the timer's time.

[0056] As described above, according to Embodiment 1, each wireless base station can easily correct the time of its own timer used when performing transfer processing using time slots, thanks to the function of the synchronization adjustment unit. As a result, when performing long-distance signal transmission using flooding, a long-distance signal transmission system can be realized in which each wireless base station in the wireless network can easily synchronize.

[0057] Embodiment 2. In this second embodiment, a method for assigning a slot number SNo to each wireless base station 10 in the long-distance signal transmission system according to the present disclosure, taking into consideration communication efficiency, will be described.

[0058] Figure 6 is an overall configuration diagram of the long-distance signal transmission system in Embodiment 2 of this disclosure. The overall configuration shown in Figure 6 is the same as the overall configuration shown in Figure 1 of Embodiment 1. However, the following information is added to Figure 6 compared to Figure 1.

[0059] The nine wireless base stations 10 are identifiable by codes 10(1) to 10(9). Although not shown in Figure 6, each of the nine wireless base stations 10(1) to 10(9) is assigned a unique identifier, ID1 to ID9, and can be identified by ID. This indicates that each of the wireless base stations 10(1) to 10(9) has been assigned one of four slot numbers, Sno1 to SNo4. • The desired communication routes, from Route 1 to Route 3, can be identified using thick arrows.

[0060] This second embodiment describes a case in which a first route is designated as the preferred communication route among multiple wireless base stations 10. The first route is shown as a thick white arrow in Figure 6 and is set as the preferred route for quickly transmitting information from sensors 30 within the sensor network 4 to the monitoring center 1.

[0061] Specifically, the first route is defined as a route passing through radio base station 10(4) → radio base station 10(6) → radio base station 10(9) → radio base station 10(1). In order to sequentially and quickly transfer information along this first route using time slots according to slot number SNo, it is appropriate to assign the order of slot numbers SNo according to the order of radio base stations 10 from the information source to the destination.

[0062] Therefore, in Figure 6, it is conceivable to assign the following slot numbers SNo to the four wireless base stations 10 on the first route, according to the transmission order of the information on the first route. Wireless base station 10(4):SNo1 Wireless base station 10(6):SNo2 Wireless base station 10(9):SNo3 Wireless base station 10(1):SNo4

[0063] By assigning slot numbers SNo in this manner, the radio base station 10(6) can receive information from the radio base station 10(4) at the timing of the time slot SNo1, and then immediately transmit information at the timing of the time slot SNo2 assigned to it.

[0064] Similarly, the wireless base station 10(9) can receive information from the wireless base station 10(6) at the timing of the time slot with slot number SNo2, and then immediately transmit the information at the timing of the time slot with slot number SNo3 assigned to it.

[0065] Finally, the wireless base station 10(1) can receive information from wireless base station 10(9) at the timing of the time slot with slot number SNo3. As a result, the monitoring PC in the monitoring center 1 can quickly acquire the information sent from the source wireless base station 10(4) after three time slots have elapsed.

[0066] In Figure 6, the communication path from sensor network 4 to monitoring center 1 is set as the first route with the highest priority. Then, the second route, indicated by a thick vertical striped arrow in Figure 6, and the third route, indicated by a thick checkerboard arrow in Figure 6, are further set.

[0067] Here, the second route corresponds to the communication path from sensor network 2 to monitoring center 1, and is defined as a route passing through wireless base station 10(2) → wireless base station 10(7) → wireless base station 10(1).

[0068] Then, it is conceivable to assign the following slot numbers SNo to the three wireless base stations 10 on the second route. Wireless base station 10(2):SNo2 Wireless base station 10(7):SNo3 Wireless base station 10(1):SNo4 Furthermore, regarding the wireless base station 10(1), slot number SNo4 was already assigned when the first route was established.

[0069] By setting up this second route, the monitoring PC in monitoring center 1 can quickly acquire the information sent from the source wireless base station 10(2) after two time slots have elapsed.

[0070] Similarly, the third route corresponds to the communication path from the sensor network 3 to the monitoring center 1, and is defined as a route passing through wireless base station 10(3) → wireless base station 10(9) → wireless base station 10(1).

[0071] Then, it is conceivable to assign the following slot numbers SNo to the three wireless base stations 10 on the third route. Wireless base station 10(3):SNo2 Wireless base station 10(9):SNo3 Wireless base station 10(1):SNo4 Furthermore, when the first route was established, the wireless base stations 10(9) and 10(1) were already assigned slot numbers SNo3 and SNo4, respectively.

[0072] By setting up this third route, the monitoring PC in monitoring center 1 can quickly acquire the information sent from the source wireless base station 10(3) after two time slots have elapsed.

[0073] Furthermore, if slot numbers SNo are assigned as shown in Figure 6, for example, when information is transmitted simultaneously from both radio base station 10(2) and radio base station 10(6), both of which are assigned slot number SNo2, the transmitted signals from each may interfere with each other.

[0074] However, wireless base stations 10(2) and 10(6) do not constantly transmit information at the timing of the time slot assigned to slot number SNo2, and the data to be transmitted is not frequent. Furthermore, even if interference occurs, the interference problem can be resolved by receiving information via other routes constructed in a mesh pattern, or by retransmitting the information.

[0075] As described above, according to Embodiment 2, sequential slot numbers SNo are assigned along the desired communication route to each of the multiple wireless base stations located along the desired communication route, so that signal transmission can be performed sequentially using flooding in the order of the slot numbers SNo. As a result, information can be transferred quickly via the desired route.

[0076] As mentioned above, slot numbers SNo can be assigned sequentially along a desired communication route, but it is also possible for each radio base station 10 to automatically assign a slot number SNo based on its own uniquely assigned ID. For example, if each of the nine radio base stations 10(1) to 10(9) shown in Figure 6 is assigned an ID from 1 to 9, and four types of slot numbers Sno1 to SNo4 are used as time slots, it is possible to automatically assign a slot number SNo to each radio base station 10 based on the remainder when the ID number is divided by 4.

[0077] Furthermore, since the transmission timing for the transmission-only wireless base station 20 was not specifically explained in Embodiments 1 and 2, a supplementary explanation will be provided. The transmission-only wireless base station 20 corresponds to a wireless base station that does not need to perform signal transmission using flooding. Also, the transmission-only wireless base station 20 can receive detection results from, for example, the sensor 30 as information to be transmitted at any time. Therefore, if there is information to be transmitted, it is appropriate for the transmission-only wireless base station 20 to transmit that information immediately from the viewpoint of rapid transmission.

[0078] Therefore, for a wireless base station 20 dedicated to transmission, it is conceivable to set the transmission timing so that, when there is data to be transmitted, the data to be transmitted can be made available at any time, independent of the time slot. [Explanation of symbols]

[0079] 1 monitoring center, 2-4 sensor network, 5 city network, 10 wireless base stations, 20 wireless base stations for transmission only, 30 sensors, 40 monitoring PCs.

Claims

1. A long-distance signal transmission system that transmits signals via a communication network constructed by multiple wireless base stations, The aforementioned multiple wireless base stations, A group of radio base stations that use flooding as a signal transfer protocol and are capable of transmitting information including the data to be transmitted and the slot number assigned to them, in synchronization with the time slot assigned to them, One or more dedicated wireless base stations capable of transmitting data at any time, regardless of the aforementioned time slot, Composed of, Each radio base station included in the aforementioned group of radio base stations has a function to adjust its own timer to match the time of the timer of the other radio base station that is the source of the information, based on the information received from the other radio base station included in the group of radio base stations. Long-distance signal transmission system.

2. The aforementioned wireless base station, which is dedicated to transmission, can transmit the detection results from the sensor as data to be transmitted at any arbitrary timing, enabling rapid transmission of the detection results. The long-distance signal transmission system according to claim 1.

3. When a radio base station included in the aforementioned group of radio base stations receives data transmitted from the radio base station dedicated to transmission, it forwards the received data using the flooding method. The long-distance signal transmission system according to claim 1 or 2.

4. The aforementioned communication network is configured to include a sensor network comprising wireless base stations included in the group of wireless base stations and one or more wireless base stations dedicated to transmission. The long-distance signal transmission system according to claim 1 or 2.

5. The aforementioned slot number may be assigned to each radio base station included in the group of radio base stations, and may overlap with other radio base stations. The long-distance signal transmission system according to claim 1 or 2.

6. Each wireless base station included in the aforementioned group of wireless base stations is automatically assigned a slot number based on its own uniquely assigned ID. The long-distance signal transmission system according to claim 1 or 2.

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