JP7648424B2 - Wireless communication method and wireless communication system - Google Patents

Description

The present invention relates to a wireless communication method.

In the railway industry, there is a shift away from the conventional track circuit-based signaling system that realizes fixed blocks, to signaling systems that realize moving blocks by transmitting train control information bidirectionally between the ground and on-board via radio. One example of a signaling system that realizes moving blocks is CBTC (Communication Based Train Control). The CBTC methods provided by different vendors vary, but many of them use 2.4 GHz radio, which does not require a radio station license.

The 2.4 GHz frequency is used by various wireless communication standards such as wireless LAN and Bluetooth (registered trademark), some of which are widely used, and other wireless communication systems can cause interference waves for the CBTC system. If interference disrupts the CBTC system's radio waves and communication becomes difficult, it becomes difficult to continue train control, which can lead to emergency stops of trains. Therefore, in order to achieve availability equal to or greater than that of track circuit-based signaling systems, it is important to take measures against interference.

In addition, CBTC places base stations along the tracks, and radios on trains continue wireless communication related to train control while handing over between base stations as the train moves. One method of achieving handover is to perform handover based on the real-time position of the train, as described in Patent Document 1 (JP Patent Publication No. 2000-229571). As pointed out in Patent Document 2 (JP Patent Publication No. 2009-78734), this method involves complicated database management of train positions for which handovers are performed, so a method of performing handovers based on the radio wave strength of radio signals transmitted from base stations has also been proposed, as shown in Patent Document 2.

Countermeasures against interference with CBTC signals are disclosed in Patent Document 3 (JP Patent Publication No. 2020-191558). Patent Document 3 discloses a method of eliminating interference with both the preamble, which is a channel synchronization signal, and the data portion. The former regards the signal observed in the no-signal section immediately before the preamble as interference, and generates array weights to suppress it to eliminate interference with the preamble, while the latter is a technology that eliminates interference in the data portion based on the principle of MMSE (Minimum Mean Square Error).

JP 2000-229571 A JP 2009-78734 A JP 2020-191558 A

When implementing a train control radio system that realizes handover based on the radio wave reception power from base stations with asynchronous base stations, the issue is how to deal with interference with the synchronization signal for ensuring synchronization of radio frames, i.e., the recognition signal shown in Patent Document 2. In addition, when removing interference with the synchronization signal for radio frame synchronization using the approach shown in Patent Document 3, it is assumed that the receiving side correctly knows the time position of the signal-free section immediately before the synchronization signal, but this approach is difficult when base stations are asynchronous because the radio frame interval is indefinite.

Given the above, the challenge is to implement measures to prevent interference with radio frame synchronization signals when base stations are assumed to be asynchronous.

A representative example of the invention disclosed in the present application is as follows. That is, a wireless communication method in a wireless communication system configured with multiple frequency channels is provided, which includes an information transmission slot for transmitting information bidirectionally between one or multiple terminals and the base station while applying frequency hopping, and a synchronization slot in which the base station transmits a synchronization channel for synchronizing between the base station and the terminal before the information transmission slot, the synchronization slot is configured with the same number of synchronization channels as the number of frequency channels or a large number of synchronization channels, each of the synchronization channels is arranged at a different time or at a different frequency within the synchronization slot, and includes leading time estimation information that allows estimating the leading time of the information transmission slot, and frequency channel information that indicates the frequency used for the information transmission slot.

According to one aspect of the present invention, a mobile terminal can observe the power of the synchronization channels of various base stations, and can realize handover based on radio reception power for each radio frame. Problems, configurations, and effects other than those described above will be made clear by the description of the following embodiment.

FIG. 1 is a diagram showing a wireless communication system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of the configuration of a wireless frame according to the present embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a synchronous slot according to the present embodiment. 2 is a diagram illustrating an example of the configuration of an information transmission slot according to the present embodiment. FIG. FIG. 2 is a diagram illustrating an example of allocation of information transmission channels in this embodiment. FIG. 2 is a diagram illustrating an example of a random access method according to the present embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a ground side device group according to the present embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a vehicle on-board device group according to the present embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a radio resource management table according to the embodiment; FIG. 2 is a diagram illustrating an example of the configuration of a base station group management table according to the embodiment; FIG. 2 is a diagram illustrating an example of an initial connection sequence of a mobile terminal according to the present embodiment. FIG. 4 is a diagram showing an example of a sequence of bidirectional transmission of train control information in the present embodiment.

Figure 1 shows a wireless communication system according to an embodiment of the present invention.

The wireless communication system of this embodiment provides a highly reliable wireless communication path between the train and the ground for controlling the train 14. In the wireless communication system of this embodiment, control information for controlling the train 14 is exchanged between the ground train control device 12 and the onboard train control device 16. That is, the control information is exchanged by wireless communication via the base station 13 and the mobile terminal 15. Each train 14 is equipped with multiple (e.g., two) mobile terminals 15 for communication path redundancy. In addition, as described below, the base stations 13 are grouped, and all base stations 13 in a group transmit the same information in the same time slot.

In this way, when identical information is received at the receiving end due to the redundancy of the wireless transmission path, a sequence number is assigned to the information when it is sent, and if the receiving end confirms multiple pieces of information with the same sequence number, duplications are eliminated.

Each mobile terminal 15 independently establishes a connection to the radio control device 11 via the base station 13. The radio control device 11 allocates radio resources to be used for each mobile terminal 15. On the other hand, in order to transmit the same train control information to two mobile terminals 15, the radio control device 11 instructs the ground-side train control device 12 on the number of radio resources for transmitting train control information to one train, equal to the number of mobile terminals 15 installed on the train.

The ground-side train control device 12 transmits the radio resource information instructed by the radio control device 11 to all base stations 13 together with train control information and a sequence number for eliminating duplicates. Each base station 13 wirelessly transmits the train control information and sequence number for each train 14 using the radio resources instructed by the ground-side train control device 12.

Figure 2 shows an example of the wireless frame configuration in this embodiment.

A radio frame is composed of a synchronization slot 101 and one or more information transmission slots 102, and radio frames of the same composition are transmitted successively thereafter. In this embodiment, there are three information transmission slots 102 per radio frame. The synchronization slot 101 and the information transmission slot 102 each have multiple synchronization channels and time-division information transmission channels. Details will be described later.

All base stations 13 transmit downstream transmissions from the base station 13 to the mobile terminal 15, specifically, the downstream information transmission channels of the synchronization slots 101 and the information transmission slots 102. However, the base station 13 does not output anything on information transmission channels that the radio control device 11 has not assigned to any mobile terminal 15.

When a mobile terminal 15 receives train control information addressed to itself from a base station 13 over a certain information transmission channel, it transmits the train control information to the base station 13 using the upstream information transmission channel (from the mobile terminal 15 to the base station 13) that is paired with the relevant information transmission channel. To determine whether the train control information received by the mobile terminal 15 is addressed to itself, the base station 13 adds information indicating the mobile terminal 15 that is the destination of the train control information to the train control information as header information. By checking this information, the mobile terminal 15 obtains only the train control information addressed to itself and discards other train control information.

A mobile terminal 15 that has not requested a connection from the radio control device 11 and is not recognized by the ground side observes the received power for each information transmission channel used by the base station 13 for downstream transmission, identifies a downstream information transmission channel that can be determined to be unused, and transmits a connection request using an upstream information transmission channel that is paired with the identified information transmission channel.

Figure 3 shows an example of the configuration of a synchronous slot in this embodiment.

Figure 3 shows a grid, with the vertical direction being the frequency channel and the horizontal direction being the time division unit of the synchronization channel. In this embodiment, there are 8 frequency channels and 16 time division units.

In FIG. 3, the colored grids are the synchronization channels 201. The synchronization channels 201 are sparsely arranged within the synchronization slot 101, as in frequency hopping. One or more synchronization channels 201 are arranged within one frequency channel. The radio control information held by each synchronization channel 201 includes information that allows estimation of the time gap from the synchronization channel 201 to the beginning of the first information transmission slot (102-1 in FIG. 2) within the radio frame, and data to be notified by the synchronization channel 201 (for example, the number of the frequency channel used by each information transmission slot 102 within the radio frame).

The information that allows the time gap to be estimated may, for example, specify the time gap in terms of time (e.g., milliseconds) or indicate the time division unit in which the synchronization channel is located on the time axis within the synchronization slot. In the latter case, the time gap from the time division unit to the information transmission slot 102 can be calculated using the time length (Tsch) of the time division unit.

Each synchronization channel 201 includes a preamble 202 for detecting the start time of the synchronization channel 201 on the mobile terminal 15 side, a modulated signal 203 including the radio control information described above, and a guard interval 204 that is a time gap with no signal until the start of the next synchronization channel 201 or information transmission slot 102. Since it is sufficient for the preamble 202 to be able to identify the start time of the modulated signal 203, it may adopt the same method as that used in wireless LAN, for example.

There are various methods for generating the modulated signal 203, but one example is a method in which preprocessing such as adding a CRC code for error detection, convolutional coding for error correction, rate matching, repetition, interleaving, and scrambling is applied to the information bit sequence, and then this bit sequence is modulated using OFDM-QPSK (Orthogonal Frequency Domain Multiplexing - Quadrature Phase Shift Keying).

The placement of the synchronization channels 201 on the frequency axis and on the time axis is randomized, and it is desirable to reduce the time division units that use the same frequency channel between nearby base stations 13 as much as possible, and to place the same number of synchronization channels 201 on all frequency channels within the synchronization slot 101. In the example shown in Figure 3, two synchronization channels 201 are placed on each frequency channel.

The simplest implementation is to store the synchronization channel allocation pattern in the memory of the base station, write the synchronization channel allocation pattern to the memory in advance, and refer to the synchronization channel allocation pattern written in the memory every time the base station 13 outputs a synchronization slot.

Here, by imposing a constraint that the same number of synchronization channels 201 be placed on all frequency channels within the synchronization slot 101, the mobile terminal 15 does not need to recognize the synchronization channel placement pattern of the base station 13. In the mobile terminal 15, if a certain frequency channel is continuously observed within the synchronization slot, in the example shown in FIG. 3, two opportunities to capture the synchronization channel within the synchronization slot are obtained. Even if one of the synchronization channels 201 is subjected to interference from another base station or from outside, the other synchronization channel 201 can be captured.

Since all synchronization channels 201 have the same information, namely the start position of the information transmission slot 102 and information indicating the frequency channel of each information transmission slot 102, if one of the many synchronization channels 201 can be captured, train control information can be transmitted in both directions using the subsequent information transmission slots 102.

Figure 4 shows an example of the configuration of the information transmission slot 102 in this embodiment, and shows a grid of frequency channels and time-division information transmission channels.

Each information transmission slot 102 is placed on a different frequency channel by frequency hopping. The frequency channel used by the information transmission slot 102 in the radio frame is identified by referring to the synchronization channel 201 described in FIG. 3.

Each information transmission slot 102 is composed of multiple (e.g., 10) information transmission channels 301. The information transmission channels are assigned to each mobile terminal 15 by the radio control device 11 as a pair for downstream communication and upstream communication.

In this embodiment, there are downstream information transmission channels 301-1 to 301-5 and upstream information transmission channels 301-6 to 301-10. These are assigned to each mobile terminal 15 in pairs, so for example, downstream information transmission channel 301-1 and upstream information transmission channel 301-6 are assigned to the same mobile terminal 15.

The configuration of each synchronization channel 201 is the same for both uplink and downlink, and includes a preamble 302 that allows the mobile terminal 15 or base station 13 receiving the radio signal to identify the start time of the modulated signal 303, the modulated signal 303 that transmits train control information and associated sequence numbers, etc., and a guard section 304 that is a time gap until the next information transmission channel and is a non-signal section.

For the preamble 302 and the modulated signal 303, the method described above in FIG. 3 can be implemented.

Figure 5 shows an example of the allocation of information transmission channels in this embodiment.

Three information transmission slots 102 are arranged on a grid of frequency channels and information transmission channels. Each information transmission slot 102 has 10 information transmission channels. Of the 10 information transmission channels, the first five are downstream information transmission channels and the last five are upstream information transmission channels.

For a given mobile terminal 15, the second and seventh information transmission channels in the information transmission slot 102 are assigned to the downstream and upstream, respectively. The other information transmission channels are free channels that are not assigned to any mobile terminal 15.

The base station 13 has three opportunities to transmit information transmission channels to the mobile terminal 15 using three information transmission slots 102, and the same train control information is transmitted on all of these transmission opportunities. The receiving mobile terminal 15 extracts the train control information by individually decoding the radio signals containing the three pieces of the same information, or by decoding them in the order they are received and then sequentially combined. Similarly, the same train control information is transmitted three times from the mobile terminal 15 to the base station 13, and the receiving base station 13 extracts the train control information by individually decoding the signals, or by decoding them in the order they are received and then sequentially combined.

Figure 6 is a diagram showing an example of the random access method of this embodiment. Like Figure 5, Figure 6 shows a grid of frequency channels and information transmission channels, and shows a situation in which radio resources are assigned to three pairs of information transmission channels, a pair of information transmission channels for each of three mobile terminals 15.

Since no wireless communication resources are allocated to a mobile terminal 15 that has not been recognized by the ground side, it is first necessary to transmit a connection request to have the mobile terminal 15 recognized by the ground side. The mobile terminal 15 observes the power of the downstream information transmission channel, stores the downstream information transmission channel that is determined to have a low observed power (e.g., threshold judgment) and is not assigned to the mobile terminal 15, and sets the upstream information transmission channel that is paired with the unassigned downstream information transmission channel as the wireless resource for the connection request. When multiple upstream information transmission channels are candidates, it is advisable to select one by uniform random selection, for example, or by comparing the received power of the downstream information transmission channels.

The mobile terminal 15 transmits a connection request to the base station 13 using the uplink information transmission channel selected here. If the uplink information transmission channel for transmitting the connection request is determined by the downlink information transmission channel in the first information transmission slot in the radio frame, the connection request 313 with the same contents may be transmitted multiple times across three information transmission slots 102 from the first information transmission slot 102. If it takes time to determine the uplink information transmission channel for the connection request, the connection request may be transmitted from the second information transmission slot 102 or the third information transmission slot 102.

Figure 7 shows an example of the configuration of the ground side device group in this embodiment.

The ground equipment group includes a radio control device 11, a ground-side train control device 12, and a base station 13.

The radio control device 11 has a message processing unit 403 that transmits, generates, and analyzes messages between the ground-side train control device 12 and the base station 13, an authentication unit 401 that authenticates a mobile terminal 15 whose connection request has been recognized by the message processing unit 403, and a resource management unit 402 that adds and deletes resources to be allocated to the mobile terminal 15. The radio control device 11 manages a radio resource management table 1000 (see FIG. 9) and a base station group management table 1010 (see FIG. 10). The radio control device 11 is composed of a computer equipped with a CPU and storage.

The resource management unit 402 allocates and deletes radio resources to the mobile terminal 15. As will be described in detail later, a certain number of base stations (for example, 10) are grouped together to manage resources. For example, the starting point of the railway line may be defined as base station group 0, and the direction in which the up line train travels may be defined as group 1, group 2, and so on. In this case, for trains on the down line, they move from sections with larger base station group numbers to sections with smaller base station group numbers.

The basic idea behind resource allocation is to assign to the mobile terminal 15 the base station group that covers the train's current location and the adjacent base station group that covers the direction in which the train is traveling. For each base station group in the current area, there are usually candidates for adjacent base station groups in the two directions in which the track extends, and the train control side can determine which adjacent base station group to assign to the mobile terminal 15 by referring to attribute information on whether the train is traveling up or down, which is managed by the train control side.

Based on this concept, it is necessary to release the radio resources of the base station group that covers the section that the train has already passed. There are several ways to determine when to release the radio resources, but one method is for the ground-side train control device 12 to determine that the train has passed through that section and release the radio resources when the upstream information transmission channel of the base station group for the section that has already been passed is completely unreceived for a certain period of time (e.g., 5 seconds). This release can then be used as a trigger to secure the radio resources that cover the next section.

A connection request from a mobile terminal 15 also triggers the reservation of radio resources. A connection request is transmitted upstream using free radio resources from one of the base station groups, so radio resources from that base station group and radio resources from an adjacent base station group are reserved depending on the direction of travel of the train carrying the mobile terminal.

When radio resource allocation is added or deleted as described above, the latest status is notified to the ground-side train control device 12. This is to allow the ground-side train control device 12 to generate additional information on which radio resource to use to transmit downlink train control information, and to recognize information on which base station group the uplink train control information should originally arrive from in order to release the radio resources mentioned above.

There are various possible methods for authentication by the authentication unit 401, but since this authentication is related to train control, it is necessary to avoid impersonation by outsiders in order to avoid accidents resulting in personal injury or property damage. It is advisable to use two-step authentication, which involves device authentication of the mobile terminal 15 mounted on the train, which is difficult for outsiders to take away, and a train operations manager who can compare the device authentication results with the train operation plan and evaluate their validity, or to use more authentication elements.

The ground-side train control device 12 transmits train control information in both directions between each train for which the radio control device 11 has secured radio resources. In addition, the ground-side train control device 12 cooperates with the radio control device 11 to generate additional information on which radio resources to use to transmit the downlink train control information, enabling the base station to transmit radio signals based on this information, and monitors whether the uplink train control information received via the base station 13 can be continuously received using the allocated resources, and releases the radio resources if reception fails for a certain period of time or more.

The base station 13 is composed of a message processing unit 501 that exchanges messages between the radio control unit 11 and the ground-side train control unit 12, a channel allocation unit 502 that instructs the radio signal processing unit 503 on the synchronization channel allocation within the synchronization slot and which radio resource to use to transmit downlink train control information for each train, and notifies the message processing unit 501 of which train the uplink train control information received by the radio signal processing unit 503 belongs to, and a radio signal processing unit 503 that transmits and receives radio signals on each channel of the synchronization slot and information transmission slot.

The message processing unit 501 extracts information to be transmitted by the base station 13 based on information input from the radio control device 11 and the ground-side train control device 12, divides the information into units that can be transmitted by each radio information transmission channel, and sets them in the radio signal processing unit 503. The message processing unit 501 also combines information from information transmission channels that have been successfully received by the radio signal processing unit 503 for each destination, i.e., the destination of the radio control device 11 or the ground-side train control device 12, and transmits the information to each destination by adding information with the identifier of the transmitting base station 13 and the identifier of the transmitting mobile terminal 15 as a header to each piece of information.

The method for extracting downstream information to be transmitted by the base station in question is to refer to additional information (e.g., information included in the header) of the received information, which indicates whether the radio resources to be used belong to the base station in question, or more specifically, which base station group the information will be transmitted from, and to record in advance in the base station 13 the information of the base station group to which the base station 13 itself belongs, and then extract only information for which the base station group matches. For this reason, the header of the information transmitted from the radio control device 11 and the ground-side train control device 12 must include information on the base station group and information transmission channel used to transmit each piece of information. As described above, this information is shared between the radio control device 11 and the ground-side train control device 12.

Whether the destination of the upstream information is the radio control device 11 or the ground-side train control device 12 is based on a judgment of whether the information from the mobile terminal 15 is a connection request or upstream train control information. This is achieved by providing a field in the header of the information transmitted over the information transmission channel in the radio layer that can distinguish between a connection request and train control information, and the mobile terminal 15 adding this information makes it possible for the base station 13 to make the distinction. It is also advisable to add an identifier for the mobile terminal 15, which includes a train identifier, to the header.

The channel allocation unit 502 instructs the wireless signal processing unit 503 on the synchronization channel 201 based on a value previously written in memory. The channel allocation unit 502 also instructs the wireless signal processing unit 503 on which wireless resource of the downlink wireless should be used to transmit information based on the information analyzed by the message processing unit 501. The channel allocation unit 502 also notifies the message processing unit 501 of information indicating the mobile terminal 15 that transmitted the information received by the wireless signal processing unit 503 in the uplink wireless transmission.

The channel arrangement unit 502 manages information regarding the arrangement method of the synchronization channel 201 and the numbers of the radio transmission channels used by each mobile terminal 15 as instructed by the ground-side train control device 12, and can realize the above-mentioned functions based on that information.

The wireless signal processing unit 503 functions as a transmitter that performs error detection code assignment, error correction code assignment, rate matching, repetition, interleaving, scrambling, modulation, and time-frequency channel allocation for the information bit sequence. The wireless signal processing unit 503 also functions as a receiver that synchronizes the timing of each information transmission channel using the preamble 202 included in the received wireless signal, performs interference removal processing, demodulation, descrambling, deinterleaving, repetition synthesis, error correction, error detection, and other processing for the data signal portion as disclosed in Patent Document 3, and allows the message processing unit 501 to refer to the extracted bit sequence and error detection result (OK or NG).

Figure 8 shows an example of the configuration of the on-board device group in this embodiment.

The onboard equipment group includes a mobile terminal 15 and an onboard train control device 16. In this embodiment, two mobile terminals 15 are installed on one train to ensure redundancy in the transmission of train control information.

The mobile terminal 15 has a radio signal processing unit 601 that operates in the same manner as the radio signal processing unit 503 of the base station 13, a channel monitoring unit 603 for monitoring frequency channels with less interference and searching for available information transmission channels at the time of initial connection, a channel selection unit 602 that selects a frequency channel for continuously observing the synchronization channel 201 based on the monitoring results of the channel monitoring unit 603, selects an information transmission channel at the time of initial connection transmission, identifies an uplink transmission channel that is paired with the downlink information transmission channel that received the downlink train control information, and notifies the radio signal processing unit 601 of this, and a message processing unit 604 that exchanges messages with the onboard train control device 16.

The radio signal processing unit 601 is similar to the radio signal processing unit 503 on the base station side, but has the added function of observing the channel reception power level. The channel reception power monitoring function observes the reception power of each downlink information transmission channel, the reception power of each frequency channel utilizing the signal-free intervals between radio frames, and the reception timing and reception power of each synchronization channel 201.

The purpose of observing the received power level is, first, to select an uplink information transmission channel for transmitting a connection request, second, to select a frequency channel to observe for each radio frame, and third, to select the synchronization channel 201 that can be received most strongly. The radio signal processing unit 601 reports only the measurement results to the channel monitoring unit 603. The channel monitoring unit 603 is a storage area that manages the above measurement results.

The channel selection unit 602 selects a frequency channel and an information transmission channel for transmitting the initial connection based on the records of the channel monitoring unit 603, selects a frequency channel for continuously observing the synchronization channel 201 for each radio frame, selects an uplink information transmission channel that pairs with a downlink information transmission channel related to train control information, and notifies the radio signal processing unit 601 of the selection result.

The first uplink information channel is selected by capturing the synchronization channel 201 and determining the frequency at which the subsequent information transmission slot 102 is transmitted, and comparing the received power of the downlink information transmission channel with a threshold value. A downlink information transmission channel with a received power lower than the threshold value is free, and the paired uplink information transmission channel is also determined to be free, and the uplink information transmission channel is selected as the channel for initial connection transmission.

The second selection of the wireless channel to be observed is performed by measuring the received power of all frequency channels during the signal-free intervals between wireless frames, estimating that frequency channels with low received power have less interference and a higher probability of capturing the synchronization channel 201, and selecting them as the frequency channels to be observed in order to detect the synchronization channel 201.

The third selection of the synchronization channel 201 implicitly includes the selection of the base station 13 for each radio frame with respect to the bidirectional transmission of stationary train control information. The mobile terminal 15 continuously searches for the synchronization channel 201 by fixing the frequency channel during the synchronization slot period, but this measurement method makes it possible to capture multiple synchronization channels 201, and each of the captured multiple synchronization channels 201 may have been transmitted from a different base station 13. The channel selection unit 602 selects one synchronization channel 201 based on the synchronization channel 201 with the highest received power, but the base station to which the uplink information transmission channel is transmitted may change depending on the selection. Note that the frequency channel for transmitting the uplink train control information differs depending on the selected base station, but the uplink information transmission channel in the time direction is determined based on the position of the downlink information transmission channel. The position of the downlink information transmission channel may also differ depending on the base station, but since the position of the uplink information transmission channel is determined after observing the position of the downlink information channel, bidirectional transmission of train control information can be continued even if the base station 13 changes for each radio frame.

To determine whether the downlink train control information is addressed to the base station 13, the base station 13 assigns an identifier indicating the destination mobile terminal 15 as header information when transmitting the information.

The message processing unit 604 transmits train control information received on the downlink to the onboard train control device 16. The message processing unit 604 also receives train control information generated by the onboard train control device 16 and sets it in the radio signal processing unit 601. The message processing unit 604 also manages whether a connection with the ground side has been established, and if not, sets an initial connection message to the radio signal processing unit 601.

For this reason, header information is added to distinguish whether the information transmitted by the radio signal is train control information or initial connection information. This is as explained in the explanation of Figure 7.

The onboard train control device 16 has a message processing unit 701 and a train control unit 702. The train control unit 702 transmits train control information bidirectionally between the onboard train control device 12 and the ground-side train control device 12, and actually controls the train based on the train control information from the ground side.

The message processing unit 701 receives downbound train control information received by the mobile terminal 15 and transfers it to the train control unit 702, which then transfers the upbound train control information generated by the train control unit 702 to all mobile terminals 15.

For downstream radio signals, train control information is received via multiple mobile terminals 15, so duplicates of identical information are eliminated based on sequence numbers. For this reason, the ground-side train control device 12 assigns sequence numbers to the train control information.

For upstream radio transmissions, since train control information is transmitted via multiple mobile terminals 15, the ground-side train control device 12 assigns a sequence number to each piece of train control information as header information to eliminate duplicates.

Figure 9 shows an example of the configuration of the radio resource management table 1000 in this embodiment.

The radio resource management table 1000 is managed by the radio control device 11, and includes base station groups 1001, information transmission channels 1002, and mobile terminal identifiers 1003, and indicates which information transmission channel 1002 in each base station group 1001 is assigned to which mobile terminal 15 of which train. Vacant indicates that the mobile terminal 15 is not assigned to a radio resource.

The addition and deletion of radio resource allocations to mobile terminal 15 is explained in detail in Figure 7, so it will not be repeated here.

Figure 10 shows an example of the configuration of the base station group management table 1010 in this embodiment.

The base station group management table 1010 is information manually set by the train operation manager and managed by the radio control device 11, and indicates the base station group to which each base station belongs. As already mentioned in the explanation of Figure 7, the base station 13 itself needs to know the base station group to which it belongs. Specifically, a base station identifier and a base station group identifier 1004 are statically assigned to each base station 13 so as to be consistent with the base station group management table 1000. Also, a dynamic assignment method may be adopted in which a message sequence is defined to inquire about the base station identifier and base station group identifier when the base station 13 starts up and establishes a connection with the radio control device 11, and each base station 13 recognizes the base station group of the mobile terminal 15 in response to this inquiry.

Figure 11 is a diagram showing an example of an initial connection sequence for a mobile terminal 15 in this embodiment. Figure 11 shows the base stations 13 as a target base station 13-1 to which a connection request is sent, and its neighboring base station 13-2.

First, both base stations 13-1 and 13-2 transmit synchronization slots (S2001). The mobile terminal 15 selects a frequency channel as described in FIG. 8 and searches for the synchronization channel 201 (S2002). As a result, the frequency of the information transmission slot 102 of the target base station 13-1 is determined.

Both base stations 13-1 and 13-2 then transmit the information transmission slot 102 three times at three different frequencies according to the frequency hopping pattern of each base station (S2003-1 to S2003-3). The mobile terminal 15 switches the frequency channel of the information transmission slot 102 of the target base station 13-1 identified by the synchronization channel 201, and identifies an available channel among the downlink information transmission channels in the first information transmission slot by the method described in the explanation of Figure 8 (S2004).

If an available downstream information transmission channel is found, a connection request is sent on the upstream information transmission channel that is paired with the found available channel. It is advisable to send the connection request three times in three information transmission slots while switching the frequency (S2005).

The base station 13 always attempts to decode all uplink information transmission channels, observes the headers of information that has been successfully decoded on uplink information transmission channels that are not assigned to the mobile terminal 15, and if the observed header is a connection request, transfers the connection request to the radio control device 11 (S2006).

If the authentication of the mobile terminal 15 is successful, the radio control device 11 allocates radio communication resources to the mobile terminal 15. That is, it updates the radio resource management table 1000 (FIG. 9). After updating the radio resource management table 1000, it shares the radio resource allocation status with the ground-side train control device 12 (S2007).

Then, the radio control device 11 transmits a response to the connection request to the entire base station group assigned to the mobile terminal 15 (S2008), and each base station 13 returns a response to the connection request to the mobile terminal 15 on the newly assigned downlink information transmission channel (S2003-4).

When the mobile terminal 15 receives the connection request response, it changes the connection management state from not connected to a connection established with the ground side (S2009), and thereafter transmits train control information in both directions.

Figure 12 shows an example of a sequence for bidirectional transmission of train control information in this embodiment. This sequence operates with a period equal to the length of the radio frame.

The ground-side train control device 12 transmits the down train control information to the entire base station group indicated in the radio resources assigned to the destination mobile terminal (S3001). The on-board train control device 16 transmits the up train control information to the mobile terminal 15 (S3003).

Each base station 13 transmits a synchronization slot to the mobile terminal 15 (S3002). The mobile terminal 15 searches for synchronization channels 201 for each radio frame and selects the frequency of the base station 13 and the information transmission slot 102 based on one of the synchronization channels 201 (S3004).

This operation is performed for each radio frame, and the base station 13 with which the mobile terminal 15 communicates bidirectionally within that radio frame may change depending on the observed synchronization channel 201. On the other hand, since downstream train control information is transmitted from multiple base stations 13, the mobile terminal 15 can maintain bidirectional transmission of train control information even if it performs handover to switch base stations for each radio frame.

Then, the information transmission slot is transmitted bidirectionally three times at three different frequencies (S3005, S3006).

The mobile terminal 15 receives and decodes the downlink information transmission channel (S3007) and transfers the received train control information to the onboard train control device 16 (S3009). The base station 13-1 receives and decodes the uplink information transmission channel (S3008) and transfers the received train control information to the ground-side train control device (S3010).

The mobile terminal 15 and base station 13 repeat the above sequence for each radio frame. The base station 13 generates a radio signal triggered by the arrival of train control information from the ground-side train control device 12 in S3001. The mobile terminal 15 transmits an upstream radio signal in synchronization with the radio signal timing of the base station 13. For this reason, although the radio frame interval is not necessarily constant, it is guaranteed that the interval between each channel within the radio frame is constant.

As described above, in the wireless communication method of an embodiment of the present invention, an information transmission slot 102 is provided for transmitting information in both directions between one or more terminals and the base station while applying frequency hopping, and a synchronization slot 101 is provided in which the base station 13 transmits a synchronization channel 201 for synchronization between the base station 13 and the mobile terminal 15 before the information transmission slot 102, and the synchronization slot 101 is composed of a number of synchronization channels 201 equal to the number of frequency channels or a large number of synchronization channels 201, and each of the synchronization channels 201 is arranged at a different time or at a different frequency within the synchronization slot 101, and includes leading time estimation information that allows the leading time of the information transmission slot 102 to be estimated, and frequency channel information indicating the frequency used for the information transmission slot 102. Therefore, the synchronization channel 201 for wireless frame synchronization can obtain a synchronization channel with high interference and a synchronization channel with low interference by time and frequency diversity, and the mobile terminal 15 can capture the synchronization channel for wireless frame synchronization with low interference. In addition, because the synchronization channel 201 is transmitted by changing the time and frequency arrangement between base stations 13, the mobile terminal 15 can observe the power of the synchronization channel 201 of various base stations 13, and handover based on radio reception power can be realized for each radio frame.

In addition, one or more synchronization channels 201 corresponding to the frequency channels are arranged in the synchronization slot 101, and are arranged so that the synchronization channel 201 can be captured at least once regardless of which frequency channel the mobile terminal 15 continuously observes in the synchronization slot 101. Therefore, by the mobile terminal 15 continuing to observe a specific frequency channel during radio frame synchronization, it is possible to observe the synchronization channels 201 transmitted by various base stations 13, and handover based on radio wave reception power can be realized for each radio frame. In addition, the effect of interference can be reduced by selecting a frequency channel with less interference as the frequency channel observed by the mobile terminal 15.

In addition, the synchronization channel 201 includes a preamble 202 for the mobile terminal 15 to capture the synchronization channel, and a payload portion which is a modulated signal 203 including information transmitted on the synchronization channel 201. The information transmitted on the synchronization channel 201 includes start time estimation information and frequency channel information. Therefore, no matter which synchronization channel 201 of which base station 13 the mobile terminal 15 captures, it can recognize the start time and frequency channel of the subsequent information transmission slot 102, and train control information can be continuously transmitted in both directions even if a power-based handover is performed for each radio frame.

In addition, the information transmission slot 102 includes a set of one or more time-division bidirectional information transmission channels 301, and the information transmission channel 301 includes a preamble 302 for the mobile terminal 15 or base station 13 to capture the information transmission channel, and a payload portion which is a modulated signal 303 including information transmitted between the mobile terminal 15 and the base station 13, so that train control information can be transmitted in both directions.

In addition, when the mobile terminal 15 has not established a connection with the base station 13, it observes whether each of the information transmission channels 301 used for transmission from the base station 13 to the mobile terminal 15 is in use, selects one of the unused information transmission channels, and requests a connection on the information transmission channel 301 that is paired with the selected information transmission channel 301 and is used for transmission from the mobile terminal 15 to the base station 13. The base station 13 transmits a response to the connection request on the information transmission channel 301 that is paired with the information transmission channel 301 to which the connection request was transmitted and is used for transmission from the base station 13 to the mobile terminal 15, so that the train can connect to the wireless network at any time. In addition, a dedicated channel for establishing a connection is not required, and the wireless resources available for transmitting train control information are increased.

In addition, a radio frame is composed of one synchronization slot 101 and one or more information transmission slots 301 following the synchronization slot 101, and in multiple radio frames, the time interval between the synchronization slot 101 and the information transmission slot 102 is the same, frequency hopping is applied to the information transmission slot 102 for each information transmission slot 102, and the frequency channel used by each information transmission slot 102 in the radio frame is notified from the base station 13 to the mobile terminal 15 in the synchronization slot 101 in the same radio frame. Therefore, if the synchronization channel is provided with minimum information regarding the time positional relationship with the information transmission slot and the frequency channel, train control information can be continuously transmitted in both directions even if the base station 13 changes for each radio frame.

In addition, the base station 13 and mobile terminal 15 transmit the same information in multiple information transmission slots 301 within the radio frame, and the receiving mobile terminal 15 and base station 13 select a receiving slot and combine the radio signals of the selected receiving slots, thereby improving the transmission reliability of train control information.

In addition, the mobile terminal 15 captures the synchronization channel 201 for each radio frame and transmits information on the frequency channel specified by the captured synchronization channel, so that the mobile terminal 15 can change the base station with which it communicates for each radio frame, and can always communicate with the base station 13 with the best radio power conditions.

In addition, multiple base stations 13 that are geographically close to each other are grouped so that they belong to the same group, and base stations 13 that transmit the same information to a mobile terminal 15 belong to the same group. Since a mobile terminal 15 transmits information to one base station 13 that belongs to the same group, different information can be transmitted on the same time-division channel for information transmission when spanning base station groups, thereby expanding the information transmission capacity of the entire wireless system.

In addition, wireless communication resources are secured for communication with the mobile terminal 15 in the group of base stations 13 to which the mobile terminal 15 is transmitting information and in the group of base stations 13 that are geographically adjacent in the direction of travel of the mobile terminal 15. This means that a channel for transmitting information is already secured at the destination of the mobile terminal 15, which crosses the radio coverage boundary of the base station group, and therefore the information transmission capacity of the wired system can be expanded while ensuring stable communication as the mobile terminal 15 moves.

The present invention is not limited to the above-described embodiments, but includes various modified examples and equivalent configurations within the spirit of the appended claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to having all of the configurations described. Furthermore, part of the configuration of one embodiment may be replaced with the configuration of another embodiment. Furthermore, the configuration of another embodiment may be added to the configuration of one embodiment. Furthermore, part of the configuration of each embodiment may be added, deleted, or replaced with other configurations.

Furthermore, each of the configurations, functions, processing units, processing means, etc. described above may be realized in part or in whole in hardware, for example by designing them as integrated circuits, or may be realized in software by a processor interpreting and executing a program that realizes each function.

Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, hard disk, or SSD (Solid State Drive), or in a recording medium such as an IC card, SD card, or DVD.

In addition, the control lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines necessary for implementation. In reality, it is safe to assume that almost all components are interconnected.

11... Radio control device 12... Ground-side train control device 13... Base station 14... Train 15... Mobile terminal 16... On-board train control device 101... Synchronization slot 102... Information transmission slot 201... Synchronization channel 202... Preamble (synchronization channel)
203...modulation signal (synchronization channel)
204...guard interval 301...information transmission channel 302...preamble (information transmission channel)
303...modulation signal (information transmission channel)
304...guard section 401...authentication unit 402...resource management unit 403...message processing unit 501...message processing unit 502...channel arrangement unit 503...radio signal processing unit 601...radio signal processing unit 602...channel selection unit 603...channel monitoring unit 604...message processing unit 701...message processing unit 702...train control unit

Claims (12)

A wireless communication method in a wireless communication system configured with a plurality of frequency channels,
An information transmission slot for transmitting information bidirectionally between a mobile terminal and a base station while applying frequency hopping, and a synchronization slot for transmitting a synchronization channel by the base station for synchronizing between the base station and the mobile terminal before the information transmission slot are provided;
The synchronization slot is composed of a number of synchronization channels equal to or greater than the number of frequency channels,
A wireless communication method, characterized in that each of the synchronization channels is arranged at a different time or frequency within a synchronization slot, and includes start time estimation information that enables estimation of the start time of the information transmission slot, and frequency channel information that indicates the frequency used for the information transmission slot. 2. The wireless communication method according to claim 1,
One or more of the synchronization channels corresponding to the frequency channels are arranged in the synchronization slot;
A wireless communication method, characterized in that the synchronization channel is arranged so that the mobile terminal can capture the synchronization channel at least once even if the mobile terminal continuously observes any frequency channel within the synchronization slot. 2. The wireless communication method according to claim 1,
The synchronization channel includes a preamble for the mobile terminal to capture the synchronization channel, and a payload portion which is a modulated signal including information to be transmitted on the synchronization channel;
A wireless communication method, characterized in that the information transmitted on the synchronization channel includes the leading time estimation information and the frequency channel information. 2. The wireless communication method according to claim 1,
The information transmission slot comprises a set of one or more time-division bidirectional information transmission channels;
A wireless communication method, characterized in that the information transmission channel includes a preamble for the mobile terminal or the base station to capture the information transmission channel, and a payload portion which is a modulated signal including information transmitted between the mobile terminal and the base station. 5. The wireless communication method according to claim 4,
The mobile terminal,
If a connection with the base station is not established, monitoring whether each of the information transmission channels used for transmission from the base station to the mobile terminal is in use;
Selecting one of the unused information transmission channels;
requesting a connection on an information transmission channel paired with the selected information transmission channel and used for transmission in a direction from the mobile terminal to the base station;
A wireless communication method, characterized in that the base station transmits a response to the connection request on an information transmission channel that is paired with the information transmission channel on which the connection request was transmitted and is used for transmission from the base station to the mobile terminal. 2. The wireless communication method according to claim 1,
A radio frame is formed by one of the synchronization slots and one or more information transmission slots following the synchronization slot,
In the plurality of radio frames, the time interval between the synchronization slot and the information transmission slot is the same;
The information transmission slots are subjected to frequency hopping for each of the information transmission slots;
A wireless communication method, characterized in that the frequency channel used by each of the information transmission slots in the wireless frame is notified from the base station to the mobile terminal in the synchronization slot in the same wireless frame. 7. The wireless communication method according to claim 6,
The base station and the mobile terminal transmit the same information in a plurality of the information transmission slots in the radio frame;
A wireless communication method, characterized in that the mobile terminal and the base station on the receiving side select a receiving slot and combine radio signals of the selected receiving slot. 7. The wireless communication method according to claim 6,
The mobile terminal,
capturing the synchronization channel for each of the radio frames;
A wireless communication method comprising: transmitting information on a frequency channel designated by the acquired synchronization channel. 2. The wireless communication method according to claim 1,
A plurality of the base stations that are geographically close to each other are grouped so as to belong to the same group,
base stations transmitting the same information to the mobile terminal belong to the same group;
A wireless communication method, comprising the steps of: transmitting information from the mobile terminal to one base station belonging to the same group; 10. The wireless communication method according to claim 9,
A wireless communication method characterized by reserving wireless communication resources available for communication with the mobile terminal in a group of base stations to which the mobile terminal is transmitting information and in a group of base stations that are geographically adjacent in the direction of travel of the mobile terminal. A wireless communication system configured with a plurality of frequency channels,
An information transmission slot for transmitting information bidirectionally between one or more terminals and a base station while applying frequency hopping, and a synchronization slot for transmitting a synchronization channel by the base station for synchronizing between the base station and the terminal before the information transmission slot are provided;
The synchronization slot is composed of a number of synchronization channels equal to or greater than the number of frequency channels,
A wireless communication system characterized in that each of the synchronization channels is arranged at a different time or frequency within a synchronization slot, and includes start time estimation information that enables estimation of the start time of the information transmission slot, and frequency channel information that indicates the frequency used for the information transmission slot. 12. The wireless communication system according to claim 11,
One or more of the synchronization channels corresponding to the frequency channels are arranged in the synchronization slot;
A wireless communication system according to claim 1, wherein said terminal is given at least one opportunity to capture said synchronization channel even if said terminal continuously observes any frequency channel within said synchronization slot.

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