JP6087664B2 - Wireless communication system - Google Patents

Description

  The present invention relates to an MCA (Multi Channel Access) wireless communication system, and more particularly to a method of using a control channel.

An MCA wireless communication system (hereinafter referred to as an MCA wireless system) is a system in which a large number of users jointly use a certain number of frequencies and has high frequency utilization efficiency.
The MCA radio system includes, for example, a control station configured with a line control device or a control console, one or a plurality of base stations, and a plurality of terminal stations. The terminal station is not limited to a movable wireless terminal (mobile station) such as a portable wireless device or an in-vehicle wireless device, and may be a wireless terminal that is fixedly installed.

Various inventions have been proposed for such MCA radio systems.
For example, Patent Document 1 discloses a wireless communication system that can effectively use a plurality of systems that operate independently in normal times in an emergency.

JP 2008-301327 A

Here, an SCPC (Single Channel Per Carrier) method has conventionally existed as a wireless method. For example, when considering an MCA radio system in which the radio system is an SCPC system, it is conceivable that a control channel used for the mobile station to synchronize with the base station or to establish communication is provided separately from the call channel. When there are a plurality of base stations in the system, particularly when there is an area covered by a communication area between the plurality of base stations, different frequencies (channels) are used in the plurality of base stations to prevent the same wave interference. Would have to allocate a control channel.
However, among the limited number of channels that can be obtained from the frequency band assigned to the system, increasing the control channel by one means reducing the communication channel by one. It will be sacrificed.

  The present invention has been made in view of the above-described conventional circumstances, and in a wireless communication system in which a plurality of base stations transmit signals through a common channel, even when base station areas overlap. It is an object to prevent co-wave interference and to make effective use of channel resources.

In order to achieve the above object, the present invention is configured as follows in a wireless communication system in which a plurality of base stations transmit signals using a common channel.
That is, in the radio communication system according to the present invention, a plurality of base stations are synchronized in timing, and signal transmission timings are set in advance for each base station so that signal transmissions between the base stations do not collide. In addition, each base station transmits a signal at its own transmission timing. Here, the signal transmitted by each base station includes a first signal and a second signal whose transmission time is shorter than that of the first signal. The base station has the transmission timing of the first signal, and the other base station has the second transmission timing.

In this way, each base station synchronizes timing and assigns transmission timing so that transmissions do not collide with each other, so that even when multiple base stations use a common channel, they are transmitted from each base station. It is possible to avoid the collision of signals that occur, and to prevent co-wave interference caused by this.
Also, the first signal and the second signal having different transmission times are prepared, and during the cycle of the transmission timing of each base station, one of the base stations has the transmission timing of the first signal, Since the base station has the second transmission timing, the base station that needs to transmit information having a relatively large capacity can transmit the information when the first transmission timing is obtained.
Thereby, it is possible to provide a user-friendly wireless communication system in an environment where a plurality of base stations need to transmit signals using a common channel.

Furthermore, in the radio communication system according to the present invention, every time the transmission timing of each base station makes a round, the base stations having the transmission timing of the first signal are changed in order.
Thereby, the transmission timing of the first signal is not occupied by a specific base station, and each base station can obtain an opportunity to transmit information having a relatively large capacity.

In the radio communication system according to the present invention, the cycle of the transmission timing of the second signal in each base station is shorter than the cycle of the transmission timing of the first signal.
As a result, each base station can quickly obtain an opportunity to transmit information that requires immediacy. In addition, the mobile station existing in the base station zone of each base station is synchronized with the timing based on the first signal, and is transmitted a plurality of times in the meantime until the next first signal is obtained. The timing synchronization can be maintained based on the second signal.

In the wireless communication system according to the present invention, each base station includes a GPS receiver, and transmits a signal based on a reference signal and time information output from the GPS receiver.
As a result, the base stations can be synchronized so as to have a common timing cycle, and it is possible to avoid duplication of signal transmissions by the base stations due to synchronization loss.

In the radio communication system according to the present invention, a series of cycles in which the transmission timing of the first signal is given to all the base stations once is started from the timing synchronized with the reference signal.
This makes it possible to synchronize the timing of each base station simply by synchronizing the start of a series of periods with the reference signal, and it is easy to synchronize the timing of each base station.

Moreover, this invention can also be grasped | ascertained as a base station which comprises the above radio | wireless communications systems.
That is, the base station according to the present invention synchronizes timing with other base stations, and the periodicity of signals set in advance with respect to the own station so that signal transmission does not collide with other base stations. Holds transmission timing information and transmits a signal at the transmission timing of the local station. Here, the signals to be transmitted include a first signal and a second signal whose transmission time is shorter than that of the first signal, and the transmission timing of the first signal during the round of the transmission timing of each base station. Alternatively, it has either of the second transmission timings.

  According to the present invention, in a wireless communication system in which a plurality of base stations transmit signals using a common channel, even when base station areas overlap, it is possible to prevent the same wave interference and effectively use channel resources. It can be used.

It is a figure which shows the example of the system configuration | structure of a MCA radio system. It is a figure which shows the example of the communication procedure of a MCA radio system. It is a figure which shows the example of a frame structure of a super frame and a sub-frame. It is a figure which shows the example of the transmission timing of all the base stations in a super frame. It is a figure which shows the example of the transmission time which paid its attention to one base station in a super frame. It is a figure which shows the example of a structure of the main function parts in connection with the timing synchronization of a base station. It is a figure which shows the example of the relationship between time information, 1PPS signal, and the timing of each flame | frame.

An embodiment of the present invention will be described with reference to the drawings.
Hereinafter, an MCA radio system in which the first to tenth ten base stations transmit control signals using a common control channel will be described as an example. The basic configuration and operation of the MCA radio system of this example will be described with reference to FIGS.

  As shown in FIG. 1, the MCA radio system as an embodiment includes a control station 103 including a communication console 101 and a line control device 102. The line control device 102 of the control station 103 includes a base station 104 and a base station. The station 105 is connected to be communicable. As described above, the present embodiment includes the first to ten ten base stations, but FIG. 1 shows only two base stations 104 and 105 for the sake of simplicity.

The base station 104 and the base station 105 have base station zones (communicable areas) 106 and 107, respectively, and the base station zones 106 and 107 serve as the service areas of the base stations 104 and 105, respectively. The total of the base station zones 106 and 107 is the service area of this MCA radio system.
In addition, there are a plurality of mobile stations 108 to 112 which are a kind of terminal station. The mobile stations 108, 109, and 110 are in the service area (base station zone 106) of the base station 104, and the mobile stations 111 and 112 are in the base station 105. It is in the service area (base station zone 107) and communicates with each of the base stations 104 and 105 by radio.

  Further, in this system, SCPC is adopted as a radio system, and a plurality of channels (upper and lower pair waves) can be used. As an example of the usage situation in FIG. 1, the control channel is CH1 (uplink frequency: f1, downlink frequency). : F2), and CH2 (uplink frequency: f3, downlink frequency: f4) and CH3 (uplink frequency: f5, downlink frequency: f6) are assigned to the communication channel. That is, a plurality of base stations share and use the control channel CH1, and other communication channels CH2, CH3, etc. are assigned to the communication between the communication console 101 and the mobile stations 108-112 and the mobile stations 108-112. use.

FIG. 2 shows an example of the communication procedure of the MCA radio system.
Here, communication between the two mobile stations 108 and 109 will be described as an example.
First, the mobile stations 108 and 109 wait on the control channel when they are not communicating. When the mobile station 108 makes a call, the mobile station 108 transmits a communication start request to the base station 104 through the control channel. When receiving the communication start request from the mobile station 108, the base station 104 notifies the line control apparatus 102 of the communication start request from the mobile station 108. If the communication partner (in this example, the mobile station 109) is not in a communication impossible state such as the busy state, the line control device 102 allocates a free communication channel and sets a communication channel to be used for communication start. The base station 104 is instructed to notify the communication partner. Receiving the instruction from the line control apparatus 102, the base station 104 notifies the mobile station 108 and the mobile station 109, which is the communication partner, of the communication start and the communication channel to be used. The mobile stations 108 and 109 that have received the notification of the communication start and the communication channel to be used change the channel setting to the designated communication channel in accordance with the instruction, and start communication.

  As described above, in the MCA wireless system of this example, control system communication such as a connection request (transmission of control signals) is performed on the control channel, and a communication start request for communication start is available in the line controller. By sequentially assigning channels to the communication, a certain number of frequencies (channels) assigned to the system are efficiently used.

  Next, the details of the control channel transmission method in this system will be described. Here, in this specification, a group of a plurality of radio frames having a frame length of 40 ms is referred to as a subframe, and a group of a plurality of subframes is referred to as a superframe. Each base station has a GPS (Global Positioning System) receiver, and is synchronized so that each base station has a common timing period based on time information and a reference signal output from the GPS receiver. (Details will be described later).

FIG. 3 shows an example of the frame configuration of the superframe and the subframe.
In the example in the figure, the subframes in the superframe are arranged in order from the subframe corresponding to the first base station to the subframe corresponding to the tenth base station. The subframe is composed of 30 radio frames (40 ms), and the superframe is composed of 300 radio frames (40 ms). Each radio frame in the super frame has a frame number of 0 to 299 as identification information. The radio frame of frame numbers 0 to 29 belongs to a subframe corresponding to the first base station, and frame numbers 30 to 59 radio frames belong to the subframe corresponding to the second base station,..., And radio frames of frame numbers 270 to 299 belong to the subframe corresponding to the tenth base station.

  Since the subframe is composed of 30 radio frames, it has a transmission time of 40 ms × 30 frames = 1200 ms (= 1.2 seconds). Also, since the super frame is composed of 300 radio frames, it has a transmission time of 40 ms × 300 frames = 12000 ms (= 12 seconds). With such a configuration, since the super frame is completed in 12 seconds, for example, the super frame starts in units of good intervals such as 0 second, 12 seconds, 24 seconds, 36 seconds, and 48 seconds per minute. In this way, the reference point can be set, and it becomes easier to synchronize the timing at each base station. That is, more accurate timing synchronization between base stations can be achieved by synchronizing each base station using not only the reference signal output from the GPS receiver but also the time information.

The subframe is divided into an occupied section of 10 frames and a shared section of 20 frames following this. That is, the occupied section has a transmission time of 40 ms × 10 frames = 400 ms, and the shared section has a transmission time of 40 ms × 20 frames = 800 ms.
The occupied section is a section occupied by the target base station, and since it is longer than the shared section, it is possible to transmit information having a relatively large capacity.
The shared section is a section shared by all base stations, and two frames are allocated in order for all base stations. This assignment is performed in order from the base station next to the base station for the occupied section, and finally the base station for the occupied section is assigned.
For example, in a subframe in which the first base station is the base station for the occupied section, first, 10 frames are allocated to the first base station, and then the second base station to the tenth base station in order. The frame configuration is such that two frames are allocated and finally two frames are allocated to the first base station.

In the example of FIG. 3, among the 10 frames allocated to the occupied section in the subframe, the first 3 frames are used for the synchronization burst (SB), and the remaining 7 frames are used for the communication information channel (SC). It has become. Note that this communication information channel includes broadcast information and connection information for communication connection, and the transmission period of the communication information channel may be partially or entirely empty depending on circumstances.
Of the two frames allocated to each base station in the shared section in the subframe, the first frame is used for the synchronization burst (SB), and the next one frame is used for the synchronization burst or communication information channel (SB / SC). ).

FIG. 4 shows an example of transmission timings of all base stations in the superframe.
According to the figure, transmission time allocation is performed in a cycle from the first base station to the tenth base station. In addition, while transmission time allocation is completed, a long transmission time (10 frames) is allocated to only one base station, and a short transmission time (2 frames each) is allocated to the other base stations. . Also, every time transmission time allocation is completed, long transmission time allocation base stations are sequentially shifted (changed), and long transmission time allocation is performed once for each base station until one superframe is completed. It is done one by one. That is, one superframe completes a series of cycles in which a long transmission time is given to all base stations once.
On the other hand, focusing on radio frames, each radio frame is assigned exclusively to one of the base stations, so that collision due to simultaneous transmission of signals is avoided. Also, since all radio frames are always assigned to any one base station, one control channel can be used without waste.

In this way, synchronization is performed so that each base station has a common timing cycle, and transmission timings are allocated so that transmissions do not collide with each other (so that transmission times do not overlap) The transmission timings of the base stations are held in advance, so that even when a plurality of base stations use a common channel (for example, one channel), it is possible to avoid collision of signals transmitted from the respective base stations. Wave interference can be prevented.
In addition, while preparing a long transmission time and a short transmission time, while the transmission time allocation is completed, one of the base stations has the transmission timing of the first signal which is a long transmission time, and the other base station Since it has the 2nd transmission timing which is short transmission time, the base station which needs to transmit the information of comparatively big capacity can transmit the information, when the 1st transmission timing is obtained.
Also, every time transmission time allocation is completed, long transmission time allocation base stations are shifted (changed) in order, so that long transmission time allocation is not occupied by a specific base station. The station can have an opportunity to transmit a relatively large amount of information.

FIG. 5 shows an example of transmission time focusing on one base station in the superframe.
In the figure, attention is focused on the first base station, and the first 10 frames (frame numbers 0 to 9) in the superframe are occupied sections, and this occupied section turns around once every superframe. . On the other hand, in the shared section (other than the occupied section), there is a transmission time of 2 frames after placing an 18-frame non-transmission section immediately after the occupied section, and thereafter there is a period of 28 frames (26 frames are not transmitted). The transmission time for two frames turns around.

That is, a long transmission time of 10 frames is assigned to each base station with a relatively long cycle (300 frame cycles), and a short transmission time of 2 frames is assigned with a relatively short cycle (approximately 28 frame cycles).
Since a long transmission time has a long interval until the next allocation, it is used for transmission of a signal carrying information (for example, broadcast information) that does not require relatively immediacy. On the mobile station side that receives signals from the base station, synchronization is facilitated by performing synchronization using a synchronization burst having a long transmission time. However, the mobile station may establish synchronization with a synchronization burst in a short transmission time. Further, when there is call connection information, it may be used for transmission of the signal, and it is not prohibited to use it for transmission of a signal carrying information that requires immediacy.
Since the short transmission time has a short interval until the next allocation, it is used for transmission of a signal carrying information that requires immediacy such as call connection information. If there is no information, an empty line (or synchronization burst) is transmitted. Further, the synchronization burst signal having a short transmission time can be used as a signal for the mobile station to maintain synchronization with the base station.

  In this way, since two types of transmission time allocated to each base station in the superframe, a long transmission time and a short transmission time, are prepared, information that does not require urgent information such as broadcast information or information with a large amount of data is compared. Transmitting using a long transmission time assigned with a long period, and transmitting information such as a connection request from all base stations using a short transmission time assigned with a relatively short period, such as a connection request. It is possible to transmit information by selecting a long transmission time or a short transmission time according to the characteristics of information to be performed (role, immediacy, data amount, etc.). For this reason, even in an environment where each base station needs to transmit a control signal through a common channel, it is possible to provide an MCA radio system that is convenient for the user.

  The frame configuration described with reference to FIGS. 3 to 5 is merely an example, and the number of subframes in the superframe, the number of radio frames, the radio frame length, information to be transmitted in each transmission time, and the like are the MCA radio system. May be determined in accordance with factors such as the environment (for example, the number of channels, the bandwidth of the assigned frequency, and the number of base stations). In addition, a long transmission time may be assigned to a plurality of base stations within one subframe. In addition, the order of the base stations to which the transmission times are assigned is not always fixed as in this example, but the transmission times may be assigned to the base stations in a different order each time the transmission times are made. Good.

Next, a method for timing synchronization at each base station will be described.
As a synchronization method for synchronizing timing so that each base station can handle a super frame at a common timing, there is a method using GPS. That is, each base station has a GPS receiver, and generates (or reproduces) the timing of each frame (superframe, subframe, radio frame) based on time information and a reference output from the GPS receiver. As the reference signal, for example, a 1 PPS (Pulse Per Second) signal is used. The 1PPS signal is a rectangular wave signal with a period of 1 second indicating a timing (second timing) at which the second of time information becomes 0 seconds.

FIG. 6 illustrates an example of a configuration of main functional units related to timing synchronization of the base station (the first to tenth base stations described above).
The base station 201 in the figure includes a memory 202, a GPS receiver 203, a timing control unit 204, and a wireless communication unit 205.
The memory 202 stores and holds frame allocation information (for example, a frame number) indicating a transmission time (timing) allocated to the own station (base station 201) in the super frame.
The GPS receiver 202 generates time information and a 1 PPS signal and outputs the time information and the timing control unit 203.

  The timing control unit 203 generates a timing signal indicating the start timing of a super frame or a radio frame with a predetermined timing (for example, 0 second per minute) as a reference point based on the time information output from the GPS receiver 202 and 1 PPS. (Or playback) and output to the wireless communication unit 204. Note that if the start timing of the superframe can be specified, the start timing of each subframe can also be specified. Therefore, the generation of the timing signal of the subframe is omitted, but the timing signal may also be generated for the subframe.

  Based on the timing signal output from the timing control unit 203 and the frame allocation information stored in the memory 202, the wireless communication unit 204 transmits various types of information at the timing at which the transmission time is allocated to the own station (base station 201). The loaded signal is transmitted wirelessly. Specifically, for example, each radio frame is 40 ms, and the start timing of the super frame is coincident with the start timing of the radio frame of frame number 0. The wireless transmission is performed using the wireless frame having the frame number corresponding to the transmission time allocated to the local station (base station 201).

FIG. 7 shows an example of the relationship between the time information and the 1PPS signal and the timing of each frame.
According to the figure, it can be seen that the timing at which the second of the time information is switched coincides with the rising timing of the pulse of the 1PPS signal. Therefore, with the time point and 0 second per minute specified by the 1PPS signal as a reference point, the start timing of a superframe with a 12 second period starting from the reference point (0 second, 12 seconds, 24 seconds, 36 seconds, 48 minutes) Second). Then, the start timing of the radio frame of frame number 0 is made to coincide with the start timing of the super frame, and the start timing of the radio frame having a period of 40 ms is specified. Further, the start timing of the subframe having a cycle of 1.2 seconds is specified by counting the radio frames in units of 30 from the radio frame of frame number 0.

In this way, each base station can specify the timing of each frame based on the time information and the reference signal given from its own GPS receiver, so that all base stations are synchronized so as to have a common timing period. Therefore, it is possible to avoid duplication of signal transmission by each base station due to synchronization loss. Also, since the start timing of the super frame is synchronized with the 1PPS signal, it is easy to synchronize the timing of each base station.
Note that signals other than the 1PPS signal may be used as the reference signal, and it is easy to synchronize the timing of each base station as long as it is a signal that can accurately specify the timing for counting seconds.

As described above, in this example, in the MCA radio system in which a plurality of base stations share one channel and transmit a control signal, the plurality of base stations are synchronized in timing, and signal transmission between the base stations is performed. Signal transmission timing is set for each base station in advance so as not to collide, and each base station transmits the signal at its own transmission timing. Includes a first signal (10 frames in the occupied section) and a second signal (2 frames in the shared section) whose transmission time is shorter than that of the first signal, and the transmission timing of each base station makes a round. 1, one of the base stations has a first signal transmission timing, and the other base station has a second transmission timing.
Thereby, even when the base station areas overlap, it is possible to prevent the same wave interference and to provide a user-friendly system.

In addition, in an MCA radio system using a plurality of channels, as one method for preventing the occurrence of the same wave interference by using only one control channel, signals are transmitted from a plurality of base stations only when necessary rather than periodically. It is also possible to carry out emergency transmission operations. However, when the base station performs emergency transmission, the mobile station side portable device cannot use the saving function for extending the operation time with the battery. Here, the saving function receives necessary information that is transmitted periodically (at a certain interval) from the base station, and during other times it is in the sleep state (the reception operation is also stopped and only the minimum necessary functions are operated) This is a function to suppress power consumption as If the base station makes an emergency transmission, the mobile station does not know when the base station is transmitting, so the reception operation cannot be stopped and the sleep state cannot be entered.
However, in this example, since a plurality of base stations periodically transmit control signals, the mobile station can be equipped with a saving function.

  Further, in order for the mobile station to establish synchronization with the base station, it is preferable that the base station continuously transmits a control signal (synchronization burst) for a certain period of time, and all the base stations of the first to tenth base stations It is also conceivable to sequentially transmit the first signal having a long transmission time. However, if it does so, since the interval of the transmission timing of each base station will become long, when there is a call connection request | requirement, time until communication will be established will become long. In this example, the base station, which is each subframe in the superframe, transmits the first signal having a long transmission time, and the other base stations transmit the second signal having a short transmission time. The mobile station can reliably establish synchronization with the base station without increasing the time.

Here, in the above description, an example of an MCA radio system in which a plurality of base stations share one control channel and transmit a control signal has been shown, but a plurality of base stations share a plurality of control channels and control. It is good also as a structure which transmits a signal.
In this case, a plurality of base stations may be classified into the same number of groups as the number of control channels, and a control signal may be transmitted by sharing one control channel for each group. Here, grouping so that adjacent base stations belong to different groups is effective in avoiding control signal collision (preventing the same wave interference).

  Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing processing according to the present invention, a program for realizing such a method or method, or a storage medium for storing the program. .

  For example, in a wireless communication system including a control station (line control device), one or more base stations, and one or more mobile stations, and having one control channel and a plurality of communication channels, First, when a communication request is issued using a control channel and a communication channel assigned by the control station is used for communication, a wireless communication system uses a control channel. Has a means for generating (or reproducing) a common timing period in all base stations constituting the system, and each base station transmission does not collide in the timing period, and each base station turns to each base station in turn. A control channel use method characterized in that transmission timing of a control channel of a base station is specified in advance, and each base station intermittently transmits a signal at the specified transmission timing; It is possible to grasp Te.

Also, for example, in the above control channel use method, the transmission timing assigned to each base station can be grasped as a control channel use method characterized by comprising two types of transmission timings, one with a long transmission time and one with a short transmission time. it can.
Also, for example, in the above control channel usage method, the transmission timing is specified so that the transmission timing having a long transmission time is assigned to each base station in a long cycle and the transmission timing having a short transmission time is assigned in a short cycle. It can also be grasped as a control channel usage method characterized by the above.
Also, for example, it can be grasped as a wireless communication system to which the above control channel use method is applied or a base station thereof.

In the above-described embodiment, one base station transmits the first signal in each subframe configuring the superframe. However, a plurality of base stations may transmit the first signal. That is, in one subframe in which the transmission timing of each base station makes a round, at least one base station may transmit the first signal, and the other base station may transmit the second signal. The same effect as that of the embodiment described above can be obtained.
Furthermore, in the above-described embodiment, the MCA wireless system that employs SCPC as a wireless method has been described as an example. However, the present invention is not limited to this, and can be applied to other wireless systems, and can be applied to a wireless communication system in which a plurality of base stations transmit signals using a common channel.

  The present invention can be applied to various types of wireless communication systems in which a plurality of base stations transmit signals using a common channel, and is particularly suitable for an MCA wireless system.

101: Communication console 102: Line control device 103: Control station 104, 105: Base station 106, 107: Base station zone 108-112: Mobile station
201: base station, 202: memory, 203: GPS receiver, 204: timing control unit, 205: wireless communication unit

Claims (5)

In a wireless communication system in which a plurality of base stations transmit signals on a common channel,
Multiple base stations are timing synchronized,
Preset the periodic transmission timing of the signal for each base station so that the transmission of the signal between the base stations does not collide,
Each base station transmits the signal at its own transmission timing,
The signal includes a first signal and a second signal whose transmission time is shorter than the first signal,
Between the transmission timing of each base station takes a round, the one of the base station has a transmission timing of the first signal, the other base stations have a transmission timing of the second signal,
The cycle of the transmission timing of the second signal in each base station is shorter than the cycle of the transmission timing of the first signal,
A wireless communication system. The wireless communication system according to claim 1, wherein
Each time the transmission timing of each base station makes a round, the base stations having the transmission timing of the first signal are changed in order.
A wireless communication system. The wireless communication system according to claim 1 or 2 ,
Each base station includes a GPS receiver, and transmits the signal based on a reference signal and time information output from the GPS receiver.
A wireless communication system. The wireless communication system according to claim 3 ,
A series of cycles in which the transmission timing of the first signal is given to all the base stations once is started from the timing synchronized with the reference signal.
A wireless communication system. In a base station constituting a wireless communication system in which a plurality of base stations transmit signals on a common channel,
Synchronize timing with other base stations,
Holds information on the periodic transmission timing of the signal preset for the own station so that the transmission of the signal does not collide with other base stations,
The signal is transmitted at the transmission timing of the own station,
The signal includes a first signal and a second signal whose transmission time is shorter than the first signal,
Between the transmission timing of each base station takes a round, have a one of transmission timing of the transmission timing or the second signal of the first signal,
The cycle of the transmission timing of the second signal in each base station is shorter than the cycle of the transmission timing of the first signal,
A base station characterized by that.

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