JP7673015B2 - Long distance signal transmission system - Google Patents

Description

This disclosure relates to a long-distance signal transmission system that transmits signals using flooding as a signal transfer protocol via a communication network constructed with multiple wireless base stations.

When transmitting signals in a communication network in which multiple wireless base stations are deployed, a broadcast method called flooding that uses simultaneous transmission has been proposed. In the flooding method that uses simultaneous transmission, when one wireless base station transmits data, one or more wireless base stations that receive the data broadcast the same data, thereby achieving simultaneous transmission of wireless signals.

By having multiple wireless base stations each repeat this type of simultaneous transmission multiple times, it becomes possible to transmit data throughout the entire signal transmission system. The advantage of adopting this type of communication method is that it eliminates the need for pre-configuration of routing for communication paths.

In addition, there is a method to prevent interference between signal transmissions from multiple wireless stations by allocating a time slot to each of the multiple wireless base stations, so that each wireless base station transmits signals wirelessly only within the time slot that has been allocated to it.

In a signal transmission system that uses time slots for communication, it is necessary to achieve synchronization between multiple wireless base stations. One conventional technique for achieving synchronization is to use synchronization packets (see, for example, Patent Document 1).

JP 2021-177616 A

However, the conventional techniques have the following problems.
In the conventional technology described in Patent Document 1, the process of generating and transmitting a specific synchronization packet, as well as the process of recovering synchronization when the synchronization packet is received, must be implemented in each wireless base station that communicates using time slots.

As a result, the configuration required to achieve synchronization is complex, and implementing the necessary functions requires time and expense. In other words, the complexity of the configuration required to achieve synchronization has been one of the bottlenecks in introducing signal transmission systems that use flooding.

The present disclosure has been made to solve the above-mentioned problems, and aims to provide a long-distance signal transmission system that can achieve synchronization with a simple configuration in each wireless base station when performing long-distance signal transmission using flooding.

The long-distance signal transmission system of the present disclosure is a long-distance signal transmission system that transmits signals via a communication network constructed by a plurality of wireless base stations using flooding as a signal transfer protocol, in which each of the plurality of wireless base stations is assigned a slot number for identifying one of the time-divided time slots, and when there is data to be transmitted, the transmission timing is set so that the system can transmit information including the data to be transmitted and the slot number assigned to the system at a timing when the period calculated by the system's own timer matches the period of the time slot corresponding to the slot number assigned to the system, and when information is received from another wireless base station, the system corrects the time of its own timer based on the slot number included in the information , and corrects the transmission timing by synchronizing the time of its own timer with the time held by the timer of the other wireless base station that is the source of the information .

According to the present disclosure, it is possible to obtain a long-distance signal transmission system that can achieve synchronization with a simple configuration at each wireless base station when performing long-distance signal transmission using flooding.

1 is an overall configuration diagram of a long-distance signal transmission system according to a first embodiment of the present disclosure. 1 is an explanatory diagram of a case where signal transmission is performed according to rules 1 and 2 using flooding in a long-distance signal transmission system according to embodiment 1 of the present disclosure. FIG. 1 is an explanatory diagram of signal transmission using flooding implemented in a long-distance signal transmission system according to a first embodiment of the present disclosure. FIG. A functional block diagram of each wireless base station in a long-distance signal transmission system according to a first embodiment of the present disclosure. 1 is a flowchart showing a series of processes of signal transmission using flooding performed in each wireless base station according to the first embodiment of the present disclosure. FIG. 11 is an overall configuration diagram of a long-distance signal transmission system according to a second embodiment of the present disclosure.

Below, a preferred embodiment of the long-distance signal transmission system of the present disclosure will be described with reference to the drawings. The long-distance signal transmission system of the present disclosure has a technical feature in that each wireless base station has a function for correcting the time of its own timer when it receives information from another wireless base station. As a result, when performing long-distance signal transmission using flooding, it is possible to obtain the effect of being able to achieve synchronization with a simple configuration in each wireless base station.

Embodiment 1.
There is a demand for wireless modules that comply with LoRa, one of the representative standards for LPWA (Low Power Wide Area) wireless, to transmit information for detecting abnormalities in remote locations (for example, monitoring for fallen bridges deep in the mountains). To achieve this, it is necessary to add a wireless mesh network function to enable long-distance transmission so that a wide area can be covered.

The expansion of a wireless mesh network can be achieved by strengthening two functions: increasing the number of relay radio stations and increasing the distance between radio stations. From this perspective, when transmitting information for fire detection systems, bridge collapse monitoring systems deep in the mountains, etc., one solution is to adopt a long-distance signal transmission system that applies flooding as a signal transfer protocol via a communication network built with multiple wireless base stations.

When adopting such a long-distance signal transmission system using flooding, it is important to develop technology that can achieve synchronization with a simple configuration at each wireless base station in the communication network and to resolve the issues with conventional technology.

The following detailed explanation will be given of a specific example of detecting fallen bridges deep in the mountains using a long-distance signal transmission system that transmits signals using flooding. The long-distance signal transmission system disclosed herein can be applied to a variety of applications that use wireless mesh networks.

Figure 1 is an overall configuration diagram of a long-distance signal transmission system in embodiment 1 of the present disclosure. Figure 1 illustrates an example in which a communication network is constructed from a monitoring center 1 installed in a city hall, three sensor networks 2, 3, and 4, and a city network 5.

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

Each of the sensor networks 2 and 3 is composed of one wireless base station 10 and two wireless base stations 20 dedicated to transmission.

The sensor network 4 is composed of one wireless base station 10, five wireless base stations 20 dedicated to transmission, and a number of sensors 30 installed on bridges that are the subject of bridge collapse monitoring. The city network 5 is composed of five wireless base stations 10 arranged to form a wireless mesh network.

The overall configuration shown in FIG. 1 is merely an example, and the number, arrangement, and connection relationship of the network, wireless base stations, and sensors can be changed as desired depending on the environment in which the long-distance signal transmission system of the present disclosure is applied. In the following description, the wireless base station 10 that transmits and receives data will be simply referred to as the wireless base station 10, and the wireless base station 20 dedicated to transmission will be simply referred to as the wireless base station 20.

In a communication network constructed by multiple wireless base stations 10 and multiple wireless base stations 20, the multiple wireless base stations 10 transmit signals using flooding as a signal transfer protocol. Flooding is a protocol that transfers signals using only the following two simple rules:

Rule 1: When a radio base station 10 receives a signal transmitted from another radio base station 10 or a radio base station 20, it forwards the received signal to all radio base stations 10 within its radio wave range.
Rule 2: If the wireless base station 10 receives the same signal again at a different timing, it will not forward the signal a second time.

Figure 2 is an explanatory diagram of a case where signal transmission is performed using flooding according to rules 1 and 2 in a long-distance signal transmission system according to embodiment 1 of the present disclosure. Figure 2 illustrates an example where signal transmission is performed using flooding by three wireless base stations 10(1) to 10(3).

More specifically, FIG. 2 illustrates a case in which wireless base station 10(1) is the source base station, wireless base station 10(2) is the relay base station, and wireless base station 10(3) is the destination base station, and a signal transmitted from wireless base station 10(1) ultimately reaches wireless base station 10(3) through flooding.

2, [1] to [4] represent steps in which signal transmission is performed using flooding. In each step, the following processing is performed in sequence.
Step [1]: The wireless base station 10(1) transfers a signal to all wireless base stations 10 within its radio range in accordance with rule 1. As a result, a signal is transmitted from the wireless base station 10(1) to the wireless base station 10(2).

Step [2]: According to rule 1, wireless base station 10(2) transfers the signal to all wireless base stations 10 within its radio range. As a result, the signal is transmitted from wireless base station 10(2) to wireless base station 10(1) and wireless base station 10(3). Therefore, after steps [1] and [2], the signal transmitted from wireless base station 10(1) reaches wireless base station 10(3), and the original purpose is achieved.

Step [3]: Wireless base station 10(1) does not forward the same signal in accordance with rule 2. Meanwhile, wireless base station 10(3) forwards the signal to all wireless base stations 10 within its range in accordance with rule 1. If rule 3 is set, stating that "if the signal is addressed to itself, the received data is accepted but not forwarded," wireless base station 10(3) can be prevented from forwarding in accordance with rule 3.

Step [4]: In accordance with rule 2, the wireless base station 10(2) receives the same signal in step [3] as in step [1], and therefore does not forward the signal any further. As a result, no further forwarding is performed, and signal forwarding within the network is terminated.

In the communication network in FIG. 1, as explained in FIG. 2, signal transmission by flooding according to rules 1 and 2 allows the wireless base station 10 in the monitoring center 1 to receive signals transmitted from the wireless base stations 10 in the sensor networks 2 to 4 via the city network 5 to the wireless base station 10 in the monitoring center 1.

The advantages of signal transmission by flooding include the following:
Advantage 1: By following rule 2, the signal will not travel back and forth indefinitely.
Advantage 2: Since there is no need to prepare a routing table indicating the forwarding party for each destination, operation of a long-distance signal transmission system using multiple wireless base stations 10 becomes easier.

However, the following points should be noted when transmitting signals by flooding:
Point to note 1: Because redundant transmissions are performed, collisions and interference of radio waves are likely to occur, making it necessary to control the timing of radio wave transmissions.

As part of the measures to address this issue, the system disclosed in Patent Document 1 employs a method of allocating time slots to each of the multiple wireless base stations 10 and achieving synchronization. However, a method such as that disclosed in Patent Document 1 aims for highly accurate synchronization to achieve versatile and highly efficient transmission, which is more than is necessary for the problem we are trying to solve, as shown in Figure 1, and as the configuration is complex, the effort and cost required to implement the function is unnecessarily high.

The long-distance signal transmission system according to the present disclosure realizes a method that allows each wireless base station 10 to achieve synchronization with a simple configuration when performing long-distance signal transmission using flooding. The specific contents will be described in detail with reference to Figures 3 to 5.

Figure 3 is an explanatory diagram of signal transmission using flooding implemented in a long-distance signal transmission system according to embodiment 1 of the present 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 the present disclosure. Also, Figure 5 is a flowchart showing a series of processes of signal transmission using flooding implemented in each wireless base station 10 according to embodiment 1 of the present disclosure.

For the sake of simplicity, FIG. 3 illustrates an example in which a communication network is constructed using three wireless base stations 10(1) to 10(3) and signal transmission is performed using flooding. In reality, however, a fourth or subsequent wireless base station 10 will also exist, and a wireless mesh network will be constructed.

In FIG. 3(A), 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 a state in which signals are transmitted between them is shown.

In FIG. 3(A), the signal transmitted from the wireless base station 10(1) to which ID1 is assigned is indicated as SG1, the signal transmitted from the wireless base station 10(2) to which ID2 is assigned is indicated as SG2, and the signal transmitted from the wireless base station 10(3) to which ID3 is assigned is indicated as SG3.

Here, assume that SNo1 is assigned as the slot number to radio base station 10(1) having ID1, SNo2 is assigned as the slot number to radio base station 10(2) having ID2, and SNo3 is assigned as the slot number to radio base station 10(3) having ID3.

The ID is a unique identifier for identifying each wireless base station 10 within the long-distance signal transmission system, and is never assigned in a way that overlaps with other wireless base stations. On the other hand, the SNo is a slot number assigned to each wireless base station to specify the time slot for transmission, and may be assigned in a way that overlaps with other wireless base stations. However, FIG. 3(A) illustrates an example in which three types of slot numbers are assigned to each of the three wireless base stations without overlapping.

Figure 3 (B) shows a schematic diagram of a state in which a time slot of duration ΔT is assigned to each of slot numbers SNo1 to SNo3, one per period T. That is, each of wireless base stations 10(1) to 10(3) is assigned a slot number SNo for identifying one of the time-divided time slots, and the timing of data transmission is specified.

Specifically, when each wireless base station 10(1) to 10(3) has data to transmit, it transmits information including the data to be transmitted and the slot number S No 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 S No assigned to it.

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

As shown in FIG. 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 a function of receiving information transmitted from other wireless base stations 10 located in the vicinity. The receiving signal processing unit 11 receives 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 of the information.

When information is received from another wireless base station 10 by the reception signal processing unit 11, the synchronization adjustment unit 12 has a function of correcting the time of a timer indicating the current position in the time slot period based on the slot number SNo included in the information. As a result, the synchronization adjustment unit 12 can synchronize its own timer with the timer of the other wireless base station 10 that is the source of the information by correcting the time of its own timer to match the time held by the timer of the other wireless base station 10 that is the source of the information, thereby correcting the transmission timing.

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

Furthermore, the transmission signal processing unit 13 will transfer information including the data to be transmitted and the slot number S No assigned to itself at a timing when the time on its timer is within the time slot corresponding to the slot number S No assigned to itself.

In this forwarding process, the transmission signal processing unit 13 can forward information using its own timer, the time of which has been adjusted by the synchronization adjustment unit 12, at the timing when information is received from another wireless base station 10. Therefore, the wireless base station 10 having the configuration of FIG. 4 can adjust the time of its own timer by receiving information from another wireless base station 10, and as a result, can achieve synchronization with other surrounding wireless base stations 10.

The time correction process by the synchronization adjustment unit 12 may always be performed whenever the reception signal processing unit 11 receives information from another wireless base station 10, but it is also possible to set the start conditions for the time correction process, such as performing the time correction process only during a certain period of time, or performing the time correction process only when information is received from a specific slot number SNo.

Next, the series of processes for signal transmission using flooding performed in each wireless base station 10 according to the first embodiment will be summarized as follows, using FIG. 5. First, in step 501, the reception signal processing unit 11 in the wireless base station 10 performs reception processing to receive information transmitted from other surrounding wireless base stations 10.

Next, in step S502, when 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 wireless base station 10 and the timing at which the information was received.

Next, in step S503, the transmission signal processing unit 13 determines whether the forwarding conditions based on rules 1 and 2 are met. That is, if rule 1 is met and rule 2 is not met, the transmission signal processing unit 13 determines that the forwarding conditions are met, and otherwise determines that the forwarding conditions are not met. If the transmission signal processing unit 13 determines in step S503 that the forwarding conditions are not met, it does not perform the forwarding process and ends the series of processes.

On the other hand, if the transmission signal processing unit 13 determines in step S503 that the forwarding condition is met, it proceeds to step S504 and waits for the time slot corresponding to the slot number S No assigned to itself to arrive based on its own timer, which was corrected in step S502. Then, when the time slot assigned to itself arrives, it executes the transmission process of a signal including the data received in step S501 (i.e., the data to be transmitted) and the slot number S No assigned to itself.

In this way, each time a transmission process is performed by flooding, the slot number SNo assigned to the source wireless base station 10 is added. Therefore, the wireless base station 10 that receives information including the slot number SNo can identify which time slot the information was transmitted from and can easily adjust the timer.

As described above, according to the first embodiment, the synchronization adjustment unit in each wireless base station can easily adjust the time of its own timer used when performing forwarding processing using time slots. As a result, it is possible to realize a long-distance signal transmission system that can achieve synchronization with a simple configuration in each wireless base station in the wireless network when performing long-distance signal transmission using flooding.

Embodiment 2.
In the second embodiment, a method of allocating slot numbers SNo to each wireless base station 10 in consideration of communication efficiency in the long-distance signal transmission system according to the present disclosure will be described.

Figure 6 is an overall configuration diagram of a long-distance signal transmission system in embodiment 2 of the present disclosure. The overall configuration shown in Figure 6 is the same as the overall configuration shown in Figure 1 in the previous embodiment 1. However, in Figure 6, the following content has been added to the previous Figure 1.

The nine wireless base stations 10 are identified by symbols 10(1) to 10(9). Although not shown in Fig. 6, each of the nine wireless base stations 10(1) to 10(9) is assigned a unique identifier ID1 to ID9, making it possible to identify the base stations by their IDs.
Each of the wireless base stations 10(1) to 10(9) is assigned one of four slot numbers Sno1 to Sno4.
The first to third routes can be identified as desired communication routes by using thick arrows.

In this second embodiment, a case will be described in which the first route is specified as the desired communication route with the highest priority among multiple wireless base stations 10. The first route is depicted as a bold white arrow in FIG. 6, and is set as the desired route for quickly transmitting information from the sensor 30 in the sensor network 4 to the monitoring center 1.

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 transfer information sequentially and quickly using time slots according to slot number SNo on this first route, it is appropriate to assign the order of slot numbers SNo according to the order of radio base stations 10 from the source of information to the destination.

Therefore, in FIG. 6, it is conceivable to allocate the following slot numbers SNo to the four wireless base stations 10 on the first route in accordance with the transmission order of the information on the first route.
Wireless base station 10 (4): SNo1
Wireless base station 10 (6): SNo.2
Radio base station 10 (9): SNo. 3
Wireless base station 10 (1): SNo. 4

By allocating slot numbers SNo in this manner, wireless base station 10 (6) can receive information from wireless base station 10 (4) in the time slot of SNo1, and then immediately transmit information in the time slot of slot number SNo2 that has been allocated to itself.

Similarly, wireless base station 10 (9) can receive information from wireless base station 10 (6) in the time slot with slot number SNo2, and can then immediately transmit information in the time slot with slot number SNo3 assigned to itself.

Finally, 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 monitoring center 1 can quickly obtain the information sent from wireless base station 10(4), the source, after the elapse of three time slots.

In FIG. 6, the communication path from the sensor network 4 to the monitoring center 1 is set as the first route with the highest priority, and then a second route shown as a thick arrow with vertical stripes in FIG. 6 and a third route shown as a thick arrow with a checker mark in FIG. 6 are further set.

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

Then, it is possible to assign the following slot numbers SNo to the three wireless base stations 10 on the second route.
Wireless base station 10 (2): SNo.2
Wireless base station 10 (7): SNo.3
Wireless base station 10 (1): SNo. 4
Incidentally, the slot number SNo4 has already been assigned to the wireless base station 10(1) when the first route was set.

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

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

Then, it is possible to assign the following slot numbers SNo to the three wireless base stations 10 on the third route.
Radio base station 10 (3): SNo.2
Radio base station 10 (9): SNo. 3
Wireless base station 10 (1): SNo. 4
Incidentally, slot numbers SNo3 and SNo4 have already been assigned to the radio base stations 10(9) and 10(1), respectively, when the first route was set.

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

When slot numbers SNo are assigned as shown in FIG. 6, for example, when information is transmitted simultaneously from radio base station 10(2) and radio base station 10(6), both of which are assigned slot number SNo2, there is a risk that the transmitted signals of radio base station 10(7) may interfere with each other.

However, wireless base station 10(2) and wireless base station 10(6) do not always transmit information at the time slot assigned to slot number SNo2, and data to be transmitted is not frequent. Even if interference occurs, the interference problem can be resolved by receiving information via other routes constructed in a mesh or by retransmitting the information.

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

As described above, the slot numbers SNo can be sequentially assigned along the desired communication route, but each wireless base station 10 can also automatically assign the slot numbers SNo from the ID that is uniquely assigned to it. For example, if ID1 to ID9 are assigned to each of the nine wireless base stations 10(1) to 10(9) shown in FIG. 6, and four slot numbers Sno1 to Sno4 are used as time slots, it is possible to automatically assign the slot numbers SNo to each wireless base station 10 based on the remainder when the ID number is divided by 4.

Furthermore, in the first and second embodiments, no particular explanation was given regarding the transmission timing of the dedicated transmission radio base station 20, so a supplementary explanation will be given below. The dedicated transmission radio base station 20 corresponds to a radio base station that does not need to transmit signals using flooding. Furthermore, the dedicated transmission radio base station 20 may receive, for example, the detection results of the sensor 30 as information to be transmitted at any timing. Therefore, when the dedicated transmission radio base station 20 has information to transmit, it is appropriate for the dedicated transmission radio base station 20 to transmit the information immediately from the viewpoint of rapid transmission.

Therefore, for the wireless base station 20 dedicated to transmission, when there is data to be transmitted, it is conceivable to set the transmission timing so that the data to be transmitted can be transmitted at any timing independent of the time slot.

1 Monitoring center, 2-4 Sensor networks, 5 City network, 10 Wireless base station, 20 Wireless base station for transmission only, 30 Sensor, 40 Monitoring PC.

Claims (3)

A long-distance signal transmission system that transmits signals through a communication network constructed by a plurality of wireless base stations using flooding as a signal transfer protocol,
Each of the plurality of radio base stations
A slot number for specifying one of the time slots allocated to the device is assigned to the device, and when there is data to be transmitted, a transmission timing is set so that the device can transmit information including the data to be transmitted and the slot number allocated to the device at a timing when a period calculated by the device's own timer coincides with the period of the time slot corresponding to the slot number allocated to the device,
A long-distance signal transmission system in which , upon receiving the information from another wireless base station, the station corrects the time of its own timer based on the slot number contained in the information , and corrects the transmission timing by synchronizing the time of its own timer with the time held by the timer of the other wireless base station that is the source of the information. 2. The long-distance signal transmission system according to claim 1, wherein among the plurality of wireless base stations, each wireless base station arranged on a desired communication route is assigned sequential slot numbers along the communication route so that the signal transmission can be performed sequentially using the flooding according to the order of the slot numbers. 3. The long-distance signal transmission system according to claim 1, wherein among the plurality of wireless base stations, a wireless base station dedicated to transmission that does not need to perform the signal transmission using the flooding has its transmission timing set so that, when there is data to be transmitted, the data to be transmitted can be transmitted at any timing independent of the time slot.