JP2019161313A - Frame synchronization system for base station - Google Patents

Abstract

To provide a frame synchronization system capable of reducing installation costs of a system for performing frame synchronization on a base station of a TDD method.SOLUTION: A first synchronization signal transmission device installed at a location in a building at which a radio wave from a GPS satellite can be received receives a radio wave from the GPS satellite and, on the basis of a GPS reception signal, transmits a radio synchronization signal for frame synchronization. A synchronization signal reception device installed at a location in the building at which the radio synchronization signal can be received transmits, on the basis of the radio synchronization signal received from the first synchronization signal transmission device and via wired connection, a wired synchronization signal for frame synchronization. A second synchronization signal transmission device installed in the building receives the wired synchronization signal via the wired connection and, on the basis of the wired synchronization signal, transmits the radio synchronization signal. The synchronization signal reception device transmits via the wired connection the wired synchronization signal to a base station using a TDD method or to both of the base station and the second synchronization signal transmission device.SELECTED DRAWING: Figure 5

Description

  The present invention relates to frame synchronization of a base station that performs radio communication with a mobile station using a TDD (time division duplex) scheme.

  Conventionally, as a communication system that performs radio communication between a mobile station and a base station using the same frequency band, a TD-LTE (Time Division Long Term Evolution) system, a PHS (Personal Handy Phone System) system, DECT (Digital) One using a TDD (time division duplex) method such as an Enhanced Cordless Telecommunications method is known (for example, see Patent Document 1 and Non-Patent Document 1). In the TDD scheme, a radio frame is configured so that the downlink from the base station to the mobile station and the uplink from the mobile station to the base station are divided on the time axis.

  In an area where a TDD base station is installed in a cell of another TDD base station (for example, an area where a plurality of TDD base stations are installed on the same floor of a building), Interference may occur. When interference between base stations occurs, the throughput of communication between the base station and the mobile station decreases or communication with the mobile station becomes impossible. In order to prevent interference between the base stations, frame synchronization is performed in which the timings of the downlink and the uplink are aligned between the base stations.

  As a system that performs frame synchronization of a TDD base station installed in a building, there is a system that uses a GPS reception signal received from a radio wave from a GPS satellite. For example, a GPS receiver that receives radio waves from GPS satellites is installed outdoors on the rooftop of a building, and the GPS receiver and the base station are wired with a coaxial cable. There are systems that perform station frame synchronization. In addition, a GPS receiver and a PTP (Precision Time Protocol) server are connected via a coaxial cable, and the PTP server (master device) and the base station (slave device) provide time information via a LAN cable such as a UTP cable. The base station (slave device) calculates the delay between the devices and the time difference between the devices based on the transmission time and reception time of the PTP packet, and the base station (slave device) time There is a system that synchronizes the frame of the base station by synchronizing the time with the time of the PTP server (master device).

JP 2013-219918 A

3GPP TS 36.211 V13.1.0 (2016-04), Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation, Release 13

  However, in the conventional frame synchronization system of the base station, it is necessary to wire an expensive coaxial cable from the GPS receiver to the base station in the building and pull it into the base station, install an expensive PTP server, etc. There is a problem that the installation cost is high.

In order to solve the above problems, a system according to one aspect of the present invention is a system for performing frame synchronization of a base station that performs radio communication with a mobile station using a TDD (Time Division Duplex) scheme, A GPS receiver installed at a position capable of receiving radio waves from a GPS satellite, and transmitting a radio synchronization signal for frame synchronization based on a GPS reception signal of the GPS receiver and receiving a radio wave from the GPS satellite A first synchronization signal transmission device having a wireless communication unit that performs reception, a wireless communication unit that is installed at a position in the building where the wireless synchronization signal can be received, and that receives the wireless synchronization signal, and is received by the wireless communication unit A synchronization signal receiving device having a wired communication unit that transmits a wired synchronization signal for frame synchronization via a wired connection based on the wireless synchronization signal, and installed in the building, A second synchronization signal transmitting apparatus comprising: a wired communication unit that receives the wired synchronization signal via a line connection; and a wireless communication unit that transmits the wireless synchronization signal based on the wired synchronization signal received by the wired communication unit The synchronization signal receiving apparatus transmits the wired synchronization signal to the base station or to both the base station and the second synchronization signal transmitting apparatus via a wired connection.
The system may further include a branching device that branches and transfers the wired synchronization signal transmitted from the synchronization signal receiving device via a wired connection.
Moreover, the said system WHEREIN: The said 1st synchronizing signal transmission apparatus may be installed in the window of the said building, and may have a built-in battery which supplies a power supply.
Further, in the system, the second synchronization signal transmitting device receives the wired synchronization signal from a synchronization signal receiving device installed on the same floor as the second synchronization signal transmitting device in the building via a wired connection. Receiving and transmitting the wireless synchronization signal to another synchronization signal receiving device installed on the same floor, and the other synchronization signal receiving device has a wired connection to a base station installed on the same floor. The wired synchronization signal may be transmitted through the network.
In the system, the second synchronization signal transmission device is installed on an underground floor of the building, and is installed on a floor higher than the floor on which the second synchronization signal transmission device is installed. From the receiving device, the wired synchronization signal is received via a wired connection, the wireless synchronization signal is transmitted to another synchronization signal receiving device installed on the underground floor, and the other synchronization signal receiving device is The wired synchronization signal may be transmitted via a wired connection to a base station installed on the same floor as the second synchronization signal transmitting device.
In the system, the second synchronization signal transmission device is installed on an underground floor of the building, and is installed on a floor higher than the floor on which the second synchronization signal transmission device is installed. From the receiving device, the wired synchronization signal is received via a wired connection, the wireless synchronization signal is transmitted to another synchronization signal receiving device installed on the same floor as the second synchronization signal transmitting device, and the other The synchronization signal receiving device transmits the wired synchronization signal to the base station installed on the same floor as the own device via a wired connection, and is installed on a floor on a lower floor than the own device. The wired synchronization signal may be transmitted to the second synchronization signal transmitting device via a wired connection.
The system further includes a TDD base station capable of receiving the wired synchronization signal from the synchronization signal receiving device via a wired connection and executing frame synchronization between base stations based on the wired synchronization signal. May be.
In the system, the wired connection may be a connection using a cable for transmitting a digital signal, or a connection using a LAN cable.

  A method according to another aspect of the present invention is a method of transmitting a synchronization signal for performing frame synchronization of a base station that performs radio communication with a mobile station using a TDD (Time Division Duplex) method, wherein the frame synchronization Transmitting a wireless synchronization signal for the first synchronization signal transmission device installed at a position capable of receiving radio waves from GPS satellites in the building to the synchronization signal receiving device installed in the building; The wired synchronization signal for frame synchronization is transmitted from the synchronization signal receiving device to the base station via a wired connection, or to both the base station and the second synchronization signal transmitting device installed in the building. Transmitting.

  ADVANTAGE OF THE INVENTION According to this invention, the installation cost of the system for performing the frame synchronization of the base station of a TDD system can be reduced.

(A) And (b) is explanatory drawing which shows an example of the mobile communication system containing the base station of the TDD system which can apply the frame synchronization system which concerns on embodiment, respectively. Explanatory drawing which shows an example of the radio | wireless frame used for the radio | wireless communication between the base station and mobile station of a TD-LTE system. Explanatory drawing which shows an example of the interference by the shift | offset | difference of the radio frame between the base stations of a TD-LTE system. Explanatory drawing which shows an example of the frame synchronization between the base stations of the TD-LTE system which concerns on embodiment. Explanatory drawing which shows an example of the whole structure of the frame synchronization system which concerns on embodiment. The block diagram which shows an example of the basic composition of each apparatus which comprises the frame synchronization system of FIG. Explanatory drawing which shows an example of the whole structure of the frame synchronization system which concerns on other embodiment. Explanatory drawing which shows schematic structure of the frame synchronization system which concerns on a reference example. Explanatory drawing which shows schematic structure of the frame synchronization system which concerns on another reference example. Furthermore, explanatory drawing which shows schematic structure of the frame synchronization system which concerns on another reference example. The block diagram which shows the basic composition of each apparatus which comprises the frame synchronization system which concerns on the reference example of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A and FIG. 1B are explanatory diagrams illustrating an example of a mobile communication system including a base station to which the frame synchronization system according to the embodiment can be applied.
FIG. 1A shows a base station that forms a wide-area macro cell 25A as a plurality of TDD (time division duplex) base stations (also referred to as “access points (AP)”) used in the same frequency band. A cellular mobile communication system comprising a macro cell base station) 25 and a base station (small cell base station) 20 that forms a small cell (also referred to as “femto cell” or “pico cell”) 20A in the macro cell 25A. An example is shown. FIG. 1B illustrates an example of a cellular mobile communication system including a plurality of base stations 20 forming a small cell 20A as a plurality of TDD base stations used in the same frequency band. . In FIG. 1B, another adjacent base station is located in each small cell.

  Each of the base stations 25 and 20 according to the present embodiment is a mobile station in the same frequency band (for example, a frequency band of 1.9 GHz band (1880 MHz to 1920 MHz)) according to the TD-LTE scheme compliant with the LTE / LTE-Advanced standard. (Also referred to as “user equipment” or “UE”) 10 performs uplink (UL) and downlink (DL) two-way wireless communication.

  Note that the base stations 25 and 20 in FIGS. 1A and 1B are base stations using the TD-LTE scheme (also referred to as “eNodeB”), but other TDD schemes such as the PHS scheme and the DECT scheme are used. It may be a base station of the type. Further, the macro cell base station 25 may be a TD-LTE base station, and the small cell base station 20 may be another TDD base station such as a PHS system or a DECT system.

  The base station 20 forming the small cell 20A is disposed in an area where traffic in a building is concentrated, for example, and can cope with an increase in mobile communication traffic by a large number of mobile stations located in the building.

  FIG. 2 is an explanatory diagram illustrating an example of a radio frame used for radio communication between a TD-LTE base station and a mobile station. As shown in FIG. 2, a radio frame (RF) 150 having a predetermined period (Tf = 10 ms), which is one unit on the time axis in TD-LTE radio communication in the same frequency band, is divided into 10 sub-frames of 1 ms. It consists of a frame (SF). One subframe (SF) can be further divided into two time slots (TS). That is, one radio frame is composed of 10 subframes (20 time slots). Thus, for example, the downlink (DL) from the base station to the mobile station and the uplink (UL) from the mobile station to the base station are alternately assigned to the subframes divided on the time axis.

  FIG. 3 is an explanatory diagram illustrating an example of interference due to a radio frame shift between TD-LTE base stations. When a radio frame shift occurs between a plurality of base stations (AP1, AP2) 20 that are close to each other, interference occurs in DL and UL communication between each base station and the mobile station. For example, as shown in FIG. 3, when a radio frame shift occurs so that a DL subframe corresponds to a UL subframe, the DL transmission signal of the base station (AP1) 20 having a large output is transmitted to the other base station. The (AP2) 20 interferes with the UL of the base station (AP2) 20, and the UL throughput of the base station (AP2) 20 is greatly reduced. In the worst case, the UL communication is disabled.

  In order to prevent interference between the base stations, it is necessary to perform frame synchronization so that DL subframes of radio frames correspond to each other and UL subframes correspond to each other between base stations (see FIG. 4).

  For frame synchronization between the TD-LTE base stations 20 installed in the building, a GPS reception signal received from a radio wave from a GPS satellite can be used. As such a frame synchronization system, as described above, a GPS receiver 910 installed outdoors such as the roof of a building 90 and a base station 920 in the building 90 are wired with a coaxial cable 930 to receive GPS signals. A system (see FIG. 8) that pulls a signal into the base station 920 and performs frame synchronization of the base station 920, a GPS receiver 910 and a PTP server 940 are connected via a coaxial cable 930, and a LAN cable 950 and a HUB 960 are connected. The PTP server 940 and the base station 920 exchange PTP packets with time information, and the base station 920 calculates the delay between devices and the time difference between devices based on the transmission time and reception time of the PTP packet. The frame of the base station 920 is synchronized with the time of the PTP server 940 by adjusting the time of the base station 920. There is a system (see Figure 9) to perform. However, in such a frame synchronization system, it is necessary to draw a synchronization signal as an analog signal from the GPS receiver 910 into the base station 920 or the PTP server 940 in the building via the coaxial cable 930, and the coaxial signal The cable 930 is more expensive than a LAN cable, and an analog signal amplifier that is more expensive than a digital signal amplifier may be required, so that the installation cost is high. Further, the frame synchronization system of FIG. 9 requires expensive PTP server installation, signal branching by a router or HUB, and the installation cost is high.

  Therefore, in this embodiment, as shown below, an expensive coaxial cable for transmitting an analog signal from a GPS receiver to a base station in a building and drawing into the base station, an expensive analog signal amplifier, or a PTP server The installation cost of the frame synchronization system is reduced by eliminating the need for installation and signal branching by a router or HUB.

  FIG. 5 is an explanatory diagram illustrating an example of the overall configuration of the frame synchronization system according to the embodiment. FIG. 6 is a block diagram showing an example of a basic configuration of each device constituting the frame synchronization system of FIG. 5 and 6 show an example in which a base station (AP) 20 that forms a small cell of the TD-LTE system is installed on each floor of a building 90 composed of buildings on the third floor and the third floor on the ground.

  The frame synchronization system of the present embodiment includes a first synchronization signal transmitter 30 having a GPS reception function for receiving radio waves (GPS signals) from GPS satellites 80, and a synchronization signal capable of wireless communication with the first synchronization signal transmitter 30. A receiving device 40 and a second synchronizing signal transmitting device 35 capable of communicating with the synchronizing signal receiving device 40 via a wired connection are provided.

  The first synchronization signal transmitting device 30 is, for example, a small size (e.g., width: 100 mm or less, length: 150 mm or less, thickness: 100 mm or less) that can be placed on the palm, and has a GPS receiving function. It is installed at a position (for example, a position near the window) where the radio wave (GPS signal) from the GPS satellite 80 can be received in the building 90. When installing the 1st synchronizing signal transmitter 30 in a window, it installs in the position where a window is not conspicuous so that the scenery of a window may not be spoiled. Moreover, when installing the 1st synchronizing signal transmitter 30 in windows, such as a high-rise building, an office building, a hotel, a hospital, etc., there are various restrictions about an installation place from a viewpoint different from the viewpoint of the scenery of a window. For example, when the first synchronization signal transmission device 30 is installed in a window of a hospital or the like, there are restrictions on the installation position such that the first synchronization signal transmission device 30 does not affect the medical device. Therefore, it is configured to be driven by the built-in battery 304 so as to cope with the case where the power cable cannot be pulled in due to various restrictions.

  The first synchronization signal transmitter 30 includes a GPS receiver 301 including an antenna that receives radio waves (GPS signals) from the GPS satellite 80 and a GPS receiver, and frame synchronization based on the GPS reception signal of the GPS receiver 301. A wireless communication unit 302 including an antenna for transmitting a wireless synchronization signal, and a control unit 303 that controls the GPS reception unit 301 and the wireless communication unit 302. The control unit 303 includes, for example, a storage unit such as a CPU, a RAM, and a ROM, a clock, and the like, and performs various signal processing and control in the first synchronization signal transmission device 30 by executing a predetermined control program. Function as.

  The synchronization signal reception device 40 has a synchronization signal repeater function, and is installed at a position where the wireless synchronization signal from the first synchronization signal transmission device 30 in the building 90 can be received. The synchronization signal reception device 40 includes a wireless communication unit 401 that receives a wireless synchronization signal from the first synchronization signal transmission device 30, and a LAN cable (for example, a wired connection) based on the wireless synchronization signal received by the wireless communication unit 401. And a control unit 403 for controlling the wireless communication unit 401 and the wired communication unit 402. The wired communication unit 402 transmits a wired synchronization signal for frame synchronization via the UTP cable 50). The wireless communication unit 401 of the synchronization signal receiving device 40 can also receive a wireless synchronization signal from the second synchronization signal transmitting device 35. The wired communication unit 402 may be configured to function as a PTP master that transmits a PTP signal described later as a wired synchronization signal. The control unit 403 includes, for example, a storage unit such as a CPU, RAM, and ROM, a clock, and the like, and functions as a unit that performs various signal processing and control in the synchronization signal receiving device 40 by executing a predetermined control program. To do.

  The second synchronization signal transmitting device 35 has a synchronization signal repeater function and is installed in the building 90. The second synchronization signal transmission device 35 receives a wired synchronization signal from the synchronization signal reception device 40 via a LAN cable (for example, UTP cable) 50, and a wired synchronization signal received by the wired communication unit 351. A wireless communication unit 352 that transmits a wireless synchronization signal based on the wireless communication unit 352, and a control unit 353 that controls the wired communication unit 351 and the wireless communication unit 352. The wired communication unit 351 may be configured to function as a PTP slave that receives a PTP signal described later as a wired synchronization signal. The control unit 353 includes, for example, a storage unit such as a CPU, a RAM, and a ROM, a clock, and the like, and performs various signal processing and control in the second synchronization signal transmission device 35 by executing a predetermined control program. Function as.

  The transmission of the wireless synchronization signal from the first synchronization signal transmission device 30 and the second synchronization signal transmission device 35 to the synchronization signal reception device 40 is performed by, for example, a specific low-power radio station whose license is not required by the Radio Law or the like. A predetermined antenna power (for example, 0.01 W or less) and a radio wave of a predetermined frequency band (for example, 920 MHz) can be used. An area 350 indicated by an alternate long and short dash line in FIG. 5 indicates an area where the radio signal of the radio synchronization signal transmitted from the first synchronization signal transmitter 30 and the second synchronization signal transmitter 35 can be received by the synchronization signal receiver 40. ing.

  The radio synchronization signal transmitted from the first synchronization signal transmission device 30 and the second synchronization signal transmission device 35 is generated based on, for example, a GPS reception signal and has a predetermined period (for example, 1 second) synchronized with the absolute time. This is a PPS (Pulse Per Second) reference signal. The wireless synchronization signal may include a reference clock signal (Time-of-Day reference signal) having a predetermined reference frequency (for example, 1 MHz or 10 MHz).

  The wired synchronization signal transmitted from the synchronization signal receiving device 40 to the base station 20 and the second synchronization signal transmitting device 35 is, for example, a PTP signal for time synchronization conforming to the PTP (Precision Time Protocol) standard defined by IEEE 1588. It is.

  The LAN cable (for example, UTP cable) 50 may be an existing LAN cable already installed in the building 90 for other purposes, and may be arbitrarily branched and wired using the existing HUB. it can. Note that a cable for transmitting a digital signal other than the LAN cable 50 may be used for the wired connection for transmitting the wired synchronization signal. For example, an optical fiber cable may be used for wired connection.

  In FIG. 5, a first synchronization signal transmitting device 30 attached to each window or the like on the ground floor (first to third floors) of a building 90 receives radio waves from an outdoor GPS satellite 80 and receives a predetermined carrier frequency ( For example, a wireless synchronization signal is transmitted indoors at 920 MHz).

  The synchronization signal receiving device 40 installed on the same floor (the first floor to the third floor) as the first synchronization signal transmitting device 30 receives the wireless synchronization signal transmitted from the first synchronization signal transmitting device 30, and is wired (for example, A wired synchronization signal is transmitted to a nearby small cell base station 20 via a LAN cable such as a UTP cable. The base station 20 can perform frame synchronization with a predetermined time accuracy (for example, accuracy of ± 1.5 μs or less) based on the wired synchronization signal received from the synchronization signal receiver 40.

  Furthermore, the synchronization signal receiving device 40 installed on the third floor transmits a wired synchronization signal to the second synchronization signal transmission device 35 installed on the same third floor via a wire (for example, a LAN cable such as a UTP cable). Send. The second synchronization signal transmitter 35 receives the wired synchronization signal from the synchronization signal receiver 40 and transmits a wireless synchronization signal to the synchronization signal receiver 40 installed on the same third floor. The synchronization signal receiver 40 receives the wireless synchronization signal transmitted from the second synchronization signal transmitter 35 and transmits a wired synchronization signal to the base station 20 of the nearby small cell. The base station 20 can perform frame synchronization with a predetermined time accuracy (for example, accuracy of ± 1.5 μs or less) based on the wired synchronization signal received from the synchronization signal receiver 40. By installing the first synchronization signal transmission device 30, the synchronization signal reception device 40, and the second synchronization signal transmission device 35 on the same floor as described above, the synchronization signal can be received on the same floor without additional wiring of a LAN cable. Thus, the base station 20 installed over a wide area on the same floor can receive the synchronization signal and perform frame synchronization.

  The synchronization signal receiving device 40 installed on the first floor is a second synchronization signal transmitting device installed on the next lower floor (the first basement floor) via a wire (for example, a LAN cable such as a UTP cable). A wired synchronization signal is also transmitted to 35. The second synchronization signal transmission device 35 installed on the first basement floor receives a wired synchronization signal from the synchronization signal reception device 40 installed on the first floor above the ground, and receives the synchronization signal reception device 40 installed on the first basement floor. To send a wireless synchronization signal. The base station 20 installed on the first basement floor can receive a wired synchronization signal from the synchronization signal receiving device 40 and perform frame synchronization with a predetermined time accuracy.

  A synchronization signal receiving device 40 installed on the first basement floor receives a wireless synchronization signal from the second synchronization signal transmitting device 35, and a base of a nearby small cell via a wire (for example, a LAN cable such as a UTP cable). In addition to transmitting a wired synchronization signal to the station 20, a wired synchronization signal is also transmitted to the second synchronization signal transmitting device 35 installed on the next lower floor (the second basement floor). By repeating the transmission / reception of the wireless synchronization signal and the wired synchronization signal, the synchronization signal used for frame synchronization can be supplied to the third floor of the building 90.

  As described above, according to the present embodiment, the expensive coaxial cable is connected between the GPS receiver installed outdoors such as the rooftop of the building in the conventional system and the base station in the building, and drawn into the base station. Installation of a server is unnecessary. Therefore, it is possible to reduce the installation cost of a frame synchronization system that distributes a synchronization signal for performing frame synchronization to a plurality of base stations 20 installed on each floor in the building 90.

  In particular, according to the present embodiment, routing of wiring within the same floor can be minimized, and wiring can be made compact. Further, by providing the synchronization signal receiving device 40 with a function as a PTP master, the first synchronization signal transmitting device 30 does not have to have the function of a PTP master, and the devices in the first synchronization signal transmitting device 30 are not provided. The quantity can be reduced. Accordingly, the weight of the first synchronization signal transmitting device 30 can be reduced, and the battery consumption of the built-in battery 304 of the first synchronization signal transmitting device 30 can be reduced. In addition, since the wiring for the distribution of the wired synchronization signal is performed from the synchronization signal receiving device 40, the additional wiring to the first synchronization signal transmitting device 30 installed near the window on the ground floor becomes unnecessary, and the base station ( The existing LAN cable (UTP cable) wired for (AP) 20 can be effectively used for the distribution of the wired synchronization signal.

  Moreover, according to this embodiment, since the LAN cable (UTP cable) is used for the wiring between the synchronization signal receiving device 40 and the second synchronization signal transmitting device 35, an expensive coaxial cable or optical cable is used. Unlike the case where a serial cable or a USB cable is used, an existing LAN cable (UTP cable) in the building 90 can be used, and no additional cable wiring is required. In addition, the synchronization signal delay is smaller than when using infrared communication, Bluetooth (registered trademark), WiFi, or other wireless communication between the synchronization signal receiver 40 and the second synchronization signal transmitter 35. High-accuracy frame synchronization is possible. In addition, since the synchronization signal receiving device 40 and the second synchronization signal transmitting device 35 can be wired separately from each other, compared to the case where the synchronization signal receiving device 40 and the second synchronization signal transmitting device 35 are configured integrally. Thus, the influence of the interference of the radio wave output from the second synchronization signal transmitter 35 can be reduced, and the area where the synchronization signal can be distributed can be easily expanded to the underground area.

  In addition, according to the present embodiment, since an existing LAN cable (UTP cable) can be used, additional wiring of the LAN cable is provided to cover a wide area from the ground floor to the basement floor of the building 90 and distribute a synchronization signal. It is unnecessary. In particular, it is not necessary to perform wiring by the window from the ground floor to the basement. Further, a high-performance HUB (low delay HUB) provided in the case of direct wiring from the first synchronization signal transmission device 30 on the ground floor to the second synchronization signal transmission device 35 in the underground is unnecessary.

  In the embodiment of FIG. 5, when the time accuracy Δt of the synchronization signal per transmission / reception of the wireless synchronization signal is ± 1.5 μs with reference to the first synchronization signal transmission device 30, the basement on the first basement floor Since the station 20 receives the synchronization signal via two transmissions / receptions of the wireless synchronization signal, the time accuracy Δt (B1F) of the synchronization signal becomes ± 3.0 μs. Similarly, since the base station 20 on the second basement floor receives the synchronization signal via transmission / reception of the wireless synchronization signal three times, the time accuracy Δt (B2F) of the synchronization signal becomes ± 4.5 μs, and the third basement floor In the base station 20, the synchronization signal is received via the transmission / reception of the wireless synchronization signal four times, so that the time accuracy Δt (B3F) of the synchronization signal becomes ± 6.0 μs. Thus, the time accuracy of the synchronization signal when the first synchronization signal transmission device 30 is used as a reference deteriorates as it goes underground. However, between a plurality of base stations 20 located in the same underground floor, the time accuracy of the synchronization signal can be made ± 1.5 μs or less, and frame synchronization can be performed with high precision. Interference between base stations can be reliably prevented.

  FIG. 7 is an explanatory diagram showing an example of the overall configuration of a frame synchronization system according to another embodiment. In FIG. 7, the same reference numerals are given to portions common to those in FIG. 5 described above, and description thereof is omitted. FIG. 7 shows that the synchronization signal receiving device 40 on the ground floor, the underground base station 20 and the second synchronization signal transmitting device 35 are not directly connected by the LAN cable 50 but connected via the HUB 55 as a LAN branching device. is doing. The wired synchronization signal transmitted from the synchronization signal receiving device 40 on the ground floor through the LAN cable 50 is branched by the HUB 55 and transferred to the base station 20 and the second synchronization signal transmitting device 35 in the basement.

  In particular, according to the embodiment of FIG. 7, transfer is performed from the synchronization signal receiving device 40 on the ground floor to the plurality of base stations 20 and the second synchronization signal transmitting device 35 via the existing LAN cable 50 and the HUB 55. Therefore, the synchronization signal distribution area (range) can be easily expanded underground.

  In the embodiment of FIG. 7, when the time accuracy Δt of the synchronization signal per transmission / reception of the wireless synchronization signal is ± 1.5 μs with reference to the first synchronization signal transmission device 30, the basement on the first basement floor Since the station 20 receives the synchronization signal without going through the transmission / reception of the wireless synchronization signal, the time accuracy Δt (B1F) of the synchronization signal remains ± 1.5 μs. In addition, since the base station 20 on the second and third basement floors receives the synchronization signal via two transmissions / receptions of the wireless synchronization signal, the time accuracy Δt (B2F) and Δt (B3F) of the synchronization signal is ± 3. 0.0 μs. However, even in the embodiment of FIG. 7, the time accuracy of the synchronization signal can be made ± 1.5 μs or less between the plurality of base stations 20 located in the same underground floor, and the frame synchronization is performed with high accuracy. Therefore, it is possible to reliably prevent interference between base stations on the same underground floor.

  FIG. 10 is an explanatory diagram illustrating an example of a schematic configuration of a frame synchronization system according to another reference example. FIG. 11 is a block diagram showing a basic configuration of each device constituting the frame synchronization system according to the reference example of FIG. In FIGS. 10 and 11, the same reference numerals are given to portions common to FIGS. 5 and 6 described above, and description thereof is omitted.

  In the reference examples of FIGS. 10 and 11, the first synchronization signal transmission device 31 with the GPS reception function installed near the window of the building 90 is different from the first synchronization signal transmission device 30 of the present embodiment in that the PTP signal is transmitted. It further includes a wired communication unit 305 that functions as a PTP master for transmission. The wired communication unit 305 of the first synchronization signal transmission device 31 transmits a wired synchronization signal (PTP signal) for frame synchronization based on the GPS reception signal of the GPS reception unit 301 to the LAN cables (for example, UTP cables) 50 and 51. Send through. The second synchronization signal transmission device 35 receives the wired synchronization signal from the first synchronization signal transmission device 31 via the LAN cables (for example, UTP cables) 50 and 51.

  In the frame synchronization system of the reference example, in order to cover a wide area within the same floor and distribute the synchronization signal to the base station 20, it is necessary to additionally wire a LAN cable (see, for example, the third floor in FIG. 10). Furthermore, since the first synchronization signal transmitter 31 installed near the window of the building 90 needs to further include a wired communication unit 305 that functions as a PTP master, the number of devices in the first synchronization signal transmitter 30 is large. As a result, the weight of the first synchronization signal transmission device 30 increases, and battery consumption when the first synchronization signal transmission device 30 is driven by the built-in battery increases. Further, it is necessary to additionally perform wiring by the window of the LAN cable from the first synchronization signal transmission device 31 on the ground floor (for example, the first floor) to the second synchronization signal transmission device 35 in the basement, and a high performance HUB ( Low delay HUB) is required.

DESCRIPTION OF SYMBOLS 10 Mobile station 20 Small cell base station 20A Small cell 25 Macro cell base station 25A Macro cell 30 1st synchronizing signal transmission apparatus 301 GPS receiving part 302 Wireless communication part 303 Control part 304 Battery 35 2nd synchronizing signal transmission apparatus 351 Wired communication part 352 Wireless communication unit 353 Control unit 40 Synchronization signal receiver 401 Wireless communication unit 402 Wired communication unit 403 Control unit 50 LAN cable 55 HUB
80 GPS satellite 90 building

Claims (10)

A system for performing frame synchronization of a base station that performs radio communication with a mobile station using a TDD (time division duplex) method,
A GPS receiving unit that is installed in a building at a position where radio waves from a GPS satellite can be received and receives radio waves from the GPS satellite, and wireless synchronization for the frame synchronization based on a GPS reception signal of the GPS receiving unit A first synchronization signal transmitting device having a wireless communication unit for transmitting a signal;
Based on the wireless synchronization signal received by the wireless communication unit, the wireless communication unit installed in the building at a position where the wireless synchronization signal can be received, and receiving the wireless synchronization signal, via the wired connection, A synchronization signal receiving device having a wired communication unit that transmits a wired synchronization signal for frame synchronization;
A wired communication unit that is installed in the building and receives the wired synchronization signal via a wired connection, and a wireless communication unit that transmits the wireless synchronization signal based on the wired synchronization signal received by the wired communication unit. A second synchronization signal transmission device having
The synchronization signal receiving apparatus transmits the wired synchronization signal to the base station or to both the base station and the second synchronization signal transmitting apparatus via a wired connection. The system of claim 1, wherein
The system further comprising: a branching device for branching and transferring the wired synchronization signal transmitted from the synchronization signal receiving device via a wired connection. The system of claim 1 or 2,
The system according to claim 1, wherein the first synchronization signal transmitter has a built-in battery that is installed in a window of the building and supplies power. The system according to any one of claims 1 to 3,
The second synchronization signal transmitting device receives the wired synchronization signal via a LAN cable from a synchronization signal receiving device installed on the same floor as the second synchronization signal transmitting device in the building, and Transmitting the wireless synchronization signal to another synchronization signal receiver installed in
The other synchronization signal receiving apparatus transmits the wired synchronization signal to a base station installed on the same floor via a LAN cable. The system according to any one of claims 1 to 4,
The second synchronization signal transmitting device is installed on an underground floor of the building and is connected to a LAN cable from a synchronization signal receiving device installed on a floor higher than the floor on which the second synchronization signal transmitting device is installed. Receiving the wired synchronization signal via, transmitting the wireless synchronization signal to another synchronization signal receiving device installed on the same floor as the second synchronization signal transmitting device,
The other synchronization signal receiving apparatus transmits the wired synchronization signal to a base station installed on the underground floor via a LAN cable. The system according to any one of claims 1 to 3,
The second synchronization signal transmitting device is installed on an underground floor of the building, and is connected by a wired connection from a synchronization signal receiving device installed on a floor higher than the floor on which the second synchronization signal transmitting device is installed. Receiving the wired synchronization signal via, transmitting the wireless synchronization signal to another synchronization signal receiving device installed on the same floor as the second synchronization signal transmitting device,
The other synchronization signal receiving device transmits the wired synchronization signal to a base station installed on the same floor as the own device via a wired connection, and is installed on a floor on a lower floor than the own device. And transmitting the wired synchronization signal to another second synchronization signal transmitting device via a wired connection. The system according to any one of claims 1 to 6,
The system further comprising a TDD base station capable of receiving the wired synchronization signal from the synchronization signal receiving device via a wired connection and executing frame synchronization based on the wired synchronization signal. The system according to any one of claims 1 to 7,
The wired connection is a connection using a cable for transmitting a digital signal. The system according to any one of claims 1 to 7,
The wired connection is a connection using a LAN cable. A method of transmitting a synchronization signal for performing frame synchronization of a base station that performs radio communication with a mobile station using a TDD (time division duplex) method,
The wireless synchronization signal for frame synchronization is transmitted from the first synchronization signal transmitting device installed at a position where the radio wave from the GPS satellite can be received in the building to the synchronization signal receiving device installed in the building. And
The wired synchronization signal for frame synchronization is transmitted from the synchronization signal receiving device to the base station via a wired connection, or to both the base station and the second synchronization signal transmitting device installed in the building. Transmitting. A method comprising: transmitting.

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