JP2009260881A - Method for synchronization among base stations, and mobile communication system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for synchronization among base stations, which can maintain synchronization among the base stations with a certain accuracy even when such a trouble occurs that a station cannot receive synchronization signals such as GPS signals; and to provide a mobile communication system using the method. <P>SOLUTION: In the method for synchronization among base stations in the mobile communication system including a plurality of base stations BTS(a), BTS(b) and BTS(c), each base station receives synchronization signals from GPS satellites (GPS) acting as signal generating sources, and establishes synchronization among base stations by synchronizing its own reference time with the synchronization signal. At least one base station BTS(a) receives time information from other base stations BTS(b) and BTS(c) through transmission lines (NW) different from the receiving routes of the synchronization signals, and corrects the deviation of its own reference time by using transmission delay time of this time information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a synchronization method between base stations and a mobile communication system using the method, and more particularly, establishes synchronization between base stations based on a synchronization signal such as a GPS signal in a mobile communication system including a plurality of base stations. Related to technology.

With reference to FIG. 8, a method for synchronizing base stations in a conventional mobile communication system will be schematically described. The ground base stations BS (a), BS (b), and BS (c) receive a GPS signal including a reference timing of 1 pps (1 Pulse Per Second) and GPS time information from a GPS satellite in a geostationary orbit. Each base station establishes synchronization between base stations by synchronizing its own reference time with the GPS signal and operating with the absolute time of GPS time as a reference.
As another synchronization method, there is a method in which a higher-level base station controller controls transmission timing in consideration of propagation delay between base stations.

  By the way, there is a technique using a redundant configuration as a conventional technique for recovering synchronization when synchronization between base stations cannot be established due to some trouble. According to this technique, synchronization between base stations can be recovered by avoiding a site where a failure has occurred with a redundant configuration.

Further, as another technique for restoring synchronization between base stations, for example, there is a technique disclosed in Japanese Patent Laid-Open No. 2000-357988. According to this prior art, a base station that has become unable to establish synchronization due to a GPS signal reception failure receives time information from another base station via a transmission path, and sets the reference time of the other base station. Synchronize the reference time of your station.
Japanese Patent Laid-Open No. 2000-357988 JP 2000-023245 A Japanese Patent Laying-Open No. 2005-223772 JP 2005-318196 A

However, the synchronization technique between base stations in the conventional mobile communication system has the following problems.
According to the conventional technique using the above-described redundant configuration, even if the system is synchronized with the absolute time of the GPS time or the system is used to control the transmission timing by the higher-level base station control device, the physical countermeasure can be taken. Therefore, it becomes difficult to guarantee the accuracy of synchronization between base stations when a failure occurs in a portion where a redundant configuration is difficult, for example, when reception of a GPS satellite antenna is interrupted.
Further, according to the prior art disclosed in the aforementioned Japanese Patent Laid-Open No. 2000-357988, when a failure occurs in another base station, there is a possibility that recovery of synchronization is delayed due to the influence.

  The present invention has been made in view of the above circumstances, and receives a synchronization signal such as a GPS signal in a system that establishes synchronization between base stations by matching the reference time of each base station to an absolute time such as GPS time. An object of the present invention is to provide an inter-base station synchronization method and a mobile communication system using the method, which can maintain synchronization between base stations with a certain accuracy even when a failure that cannot be performed occurs.

In order to solve the above problems, the present invention has the following configuration.
That is, according to the inter-base synchronization method of the present invention, in a mobile communication system including a plurality of base stations, each base station receives a synchronization signal from a signal generation source and synchronizes its own reference time with the synchronization signal. The inter-base synchronization method for establishing synchronization between the plurality of base stations according to claim 1, wherein at least one base station of the plurality of base stations is connected to another base via a transmission path different from the synchronization signal reception path. The time information is received from the station, and the deviation of the reference time of the own station with respect to the synchronization signal is calculated using the transmission delay time of the time information received from the other base station. Based on the difference of the reference time, It has the structure of the inter-base synchronization method which correct | amends reference | standard time.
According to this configuration, the base station in an asynchronous state corrects its own reference time based on the deviation of its own reference time with respect to the synchronization signal, thereby synchronizing its own reference time with the synchronization signal. Therefore, it is possible to restore synchronization between base stations.

In the inter-base synchronization method, for example, at least one base station of the plurality of base stations receives from the other base station via the transmission line in a state where synchronization between the plurality of base stations is established. The difference between the transmission delay time of the received time information and the transmission delay time of the time information received from the other base station via the transmission line when the synchronization is not established is calculated as the difference in the reference time. .
According to this configuration, the base station in an asynchronous state grasps how much the reference time of the own station is deviated from the synchronization signal from the difference. Therefore, it becomes possible to correct the reference time of the own station based on the deviation of the reference time of the own station with respect to the synchronization signal.

In the inter-base synchronization method, for example, the other base station receives time information from the at least one base station via the transmission path, acquires a transmission delay time of the time information, and transmits the transmission delay time. To the at least one base station, and the at least one base station uses the transmission delay time acquired at the other base station to establish synchronization between the plurality of base stations. A transmission delay time of time information received by the other base station from the at least one base station via the transmission path and the other base station in the state where the synchronization is not established, The difference from the transmission delay time of the time information received via the transmission path is calculated as the difference in the reference time, and the reference time of the own station at the time of transmission is corrected based on the difference in the reference time.
According to this configuration, the base station that is in the asynchronous state grasps the deviation of the reference time at the time of transmission of the local station with respect to the synchronization signal from the transmission delay time acquired by the other base station. Therefore, the base station that is in an asynchronous state can recover the synchronization at the time of transmission with high accuracy.

In the inter-base synchronization method, for example, the at least one base station statistically processes a transmission delay time of time information received from the other base station, thereby establishing synchronization between the plurality of base stations. The transmission delay time of time information in a state where
According to this configuration, by estimating the transmission delay time in a state in which synchronization is established by statistical processing, it becomes possible to accurately calculate the deviation of the reference time of the local station in the base station in an asynchronous state. .

  A mobile communication system according to the present invention includes a signal generation source that generates a synchronization signal, and a plurality of base stations that receive the synchronization signal from the signal generation source and operate in synchronization with a reference time of the local station. Unlike the reception path of the synchronization signal, the transmission path includes a transmission path that connects the plurality of base stations, and at least one base station of the plurality of base stations is connected to the other base station via the transmission path. The mobile communication system has a configuration in which a difference in the reference time of the local station with respect to the synchronization signal is calculated using a transmission delay time of received time information, and the reference time of the local station is corrected based on the difference in the reference time.

  In the mobile communication system, for example, at least one base station of the plurality of base stations has received the transmission from the other base station via the transmission path in a state where synchronization between the plurality of base stations is established. The difference between the transmission delay time of the time information and the transmission delay time of the time information received from the other base station via the transmission line in a state where the synchronization is not established is calculated as a deviation of the reference time.

  In the mobile communication system, for example, the other base station receives time information from the at least one base station via the transmission path, acquires a transmission delay time of the time information, and sets the transmission delay time. Transmitting to the at least one base station, and the at least one base station uses the transmission delay time acquired by the other base station in a state where synchronization between the plurality of base stations is established. A transmission delay time of time information received by the other base station from the at least one base station via the transmission path and the other base station from the at least one base station in a state where the synchronization is not established. A difference from the transmission delay time of the time information received via the transmission path is calculated as the difference in the reference time, and the reference time of the own station at the time of transmission is corrected based on the difference in the reference time.

  In the mobile communication system, for example, the at least one base station establishes synchronization between the plurality of base stations by statistically processing a transmission delay time of time information received from the other base station. The transmission delay time of the time information in the state is estimated.

  According to the present invention, since the base station that is out of synchronization corrects the reference time of its own station using the transmission delay time of the time information from other base stations, the base station It becomes possible to restore synchronization between stations.

  Therefore, according to the present invention, for example, in a system that establishes synchronization between base stations by matching the reference time of operation of each base station with an absolute time such as GPS time, a synchronization signal such as a GPS signal cannot be received. Even when such a failure occurs, the synchronization between the base stations can be maintained with a certain degree of accuracy, and the synchronization state between the base stations can be stabilized.

(First embodiment)
Hereinafter, a mobile communication system according to a first embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, illustrating a mobile communication system including a radio base station apparatus in the ^{3GPP (3 rd Generation Partnership Project)} ( hereinafter referred to as "base station") as an example. However, the present invention is not limited to this.

  In this mobile communication system, normally, each base station establishes synchronization between base stations by synchronizing its own reference time with a GPS (Global Positioning System) signal. In addition, as will be described below, the mobile communication system is capable of receiving a GPS signal at any base station by exchanging time information between the base stations via the IP transmission path. Even if this occurs, it is possible to ensure synchronization between base stations with a certain degree of accuracy.

  In the present embodiment, the “reference time” means a time serving as a reference for the operation unique to each base station. When the synchronization is established, the base time of each base station is synchronized with the GPS time (UTC). When the synchronization is not established, the base time of each base station is not synchronized with the GPS time (UTC). It becomes.

FIG. 1 schematically shows the overall configuration of the mobile communication system according to the present embodiment.
This mobile communication system includes a GPS satellite in geostationary orbit, three base stations BTS (a), BTS (b), and BTS (c) shown as examples, and an IP transmission line NW that connects the base stations. Consists of Note that the number of base stations is not limited to this, and may be any number.
The GPS satellite is a signal generation source that generates a GPS signal including GPS reference timing and GPS time information, and transmits the GPS signal toward the ground.

  The plurality of base stations BTS (a), BTS (b), BTS (c) are equipped with a GPS receiver (not shown) for receiving GPS signals from the GPS satellites, and if no reception failure has occurred, The reference time of each base station is synchronized with the GPS signal, and is configured to operate in accordance with the GPS time (UTC) of the GPS satellite. The IP transmission path NW is for exchanging time information between the base stations, and is a path different from the GPS signal reception path. Base stations BTS (a), BTS (b), and BTS (c) are connected to each other via an IP transmission line NW.

Next, the synchronization operation between base stations (synchronization method between base stations) in this mobile communication system will be described.
First, with reference to FIG. 2 and FIG. 4, the operation in a state where no GPS signal reception failure has occurred and synchronization between base stations has been established (GPS synchronization state) will be described. FIG. 2 shows an operation flow in a state where no reception failure has occurred, and FIG. 4 shows an operation timing of each base station in a state where no reception failure has occurred.

  In a state where no GPS signal reception failure has occurred, each of the base stations BTS (a), BTS (b), and BTS (c) receives GPS signals from GPS satellites, and sets the reference time of each base station to the GPS signal. Synchronize with. Therefore, as shown in FIG. 4, the operation timing of each base station maintains a state synchronized with the GPS timing defined by the GPS signal, and synchronization between the base stations is established.

In this state where synchronization between base stations is established, each base station receives GPS time stamps as time information from other base stations via the IP transmission line NW, and measures the transmission delay time. Hold.
Referring to FIG. 2, the base station BTS (a) will be described in detail with a focus on the base station BTS (a). The base station BTS (a) is connected to the base station BTS (b) via the IP transmission line NW. A GPS time stamp 205 as information is received (204), and a GPS time stamp 206 as time information related to the reference time of another base station BTS (c) is received (209).

  Then, the base station BTS (a) measures (207) the transmission delay time Tba of the GPS time stamp from the base station BTS (b) and transmits the GPS time timestamp transmission delay from the base station BTS (c). The time Tca is measured (208). The transmission delay time Tba and the transmission delay time Tca are calculated by the following formulas (1) and (2), respectively.

Tba = BTS (a) reference time (t0)-BTS (b) GPS time reception time (1)
Tca = BTS (a) reference time (t0) −BTS (c) GPS time reception time (2)

  In Equation (1), the first term “BTS (a) reference time (t0)” on the right side represents the reference time of the base station BTS (a). In this case, since the reference time of the base station BTS (a) is synchronized with the GPS signal, it matches the absolute time t0 of the GPS time. The second term “BTS (b) GPS time reception time” on the right side of the base station BTS (a) when the base station BTS (a) receives the GPS time stamp 205 from the base station BTS (b). It is time on. Therefore, Formula (1) is the transmission delay of the time information received by the base station BTS (a) from the other base station BTS (b) via the IP transmission line NW in a state where the synchronization between the base stations is established. Represents time. The same applies to Equation (2).

  The transmission delay time (Tba) represented by the equation (1) is obtained from the base station BTS (b) to the base station BTS (a) via the IP transmission line NW in a normal synchronization state where no reception failure has occurred. It means the time required to transmit the GPS time stamp (hereinafter, this is particularly expressed as “Tbas”). Similarly, the transmission delay time (Tca) represented by the equation (2) is the GPS time stamp from the base station BTS (c) to the base station BTS (a) in the normal synchronization state where no reception failure has occurred. Means the time it takes to be transmitted. The base station BTS (a) periodically receives GPS time stamps from other base stations BTS (b) and BTS (c), and acquires and holds the transmission delay time.

Next, referring to FIG. 3 and FIG. 5, when a GPS signal reception failure occurs in the base station BTS (a) and only the reference time of the base station BTS (a) is not synchronized with the GPS signal (GPS asynchronous (Operation) will be described.
FIG. 3 shows a control flow when a reception failure occurs in the base station BTS (a), and FIG. 5 shows an operation timing when a reception failure occurs in the base station BTS (a). In FIG. 5, t0, t1, and t2 represent GPS time, and t1 = t0 + Δt.

  When the base station BTS (a) enters the GPS asynchronous state, the operation timing of the base station BTS (a) deviates from the GPS timing. Then, as shown in FIG. 5, the reference time of the base station BTS (a) moves to the time t1 of the GPS time, and the operation timing of the base station BTS (a) does not coincide with the GPS timing. In this case, as will be described below, the base station BTS (a) uses the transmission delay time of the GPS time stamp received as time information from the other base station BTS (b) via the IP transmission path NW. Then, the deviation of the reference time of the own station relative to the GPS signal (Δt in FIG. 5) is calculated, and the reference time of the own station is corrected based on the deviation of the reference time.

First, the reference time correction principle in the base station BTS (a) will be described with reference to FIG.
In FIG. 5, Tba represents the transmission delay time Tba of the GPS time stamp received by the base station BTS (a) from the other base station BTS (b) in the state where the reception failure has occurred, and Tbas represents the reception failure. It represents the transmission delay time Tba of the GPS time stamp received by the base station BTS (a) from the other base station BTS (b) in the state where it does not occur, and is a value represented by the above-described equation (1). Δt represents a shift in the operation timing of the base station BTS (a) with respect to the GPS timing, that is, a shift in the reference time of the base station BTS (a) with respect to the time t0 of the GPS time.

  Here, Tbas is an existing value represented by the above-described equation (1), Tba is a value observed in a state where a reception failure has occurred, and the difference between Tba and Tbas is equal to Δt. Therefore, if Δt is calculated from the difference between Tba and Tbas and the reference time of the base station BTS (a) is corrected by Δt, the reference time of the base station BTS (a) can be synchronized with the GPS signal. Even in a state where a failure has occurred, the operation timing of the base station BTS (a) can be synchronized with the GPS timing.

Based on the correction principle described above, the operation when the base station BTS (a) is in the GPS asynchronous state will be described with reference to FIG.
As shown in FIG. 3, in the GPS asynchronous state, the base station BTS (a) transmits a GPS time stamp 305 from the base station BTS (b) via the IP transmission line NW, as in the operation flow of FIG. Is received (304), and the GPS time stamp 306 is received (309) from the base station BTS (c).

  The base station BTS (a) measures (307) the transmission delay time Tba of the GPS time stamp 305 and measures (308) the transmission delay time Tca of the GPS time stamp 306. Here, the transmission delay time Tba of the GPS time stamp 305 and the transmission delay time Tca of the GPS time timestamp 306 are expressed by the following equations (3) and (4).

Tba = BTS (a) reference time t1 (= t0 + Δt) −BTS (b) GPS time reception time t2 (3)
Tca = BTS (a) reference time t1 (= t0 + Δt) −BTS (c) GPS time reception time t2 (4)

  In Equation (3), the first term “BTS (a) reference time (t0 + Δt)” on the right side represents the reference time of the base station BTS (a). In this case, the reference time of the base station BTS (a) is the absolute time t1 (= t0 + Δt) of the GPS time and is not synchronized with the GPS signal. The second term “BTS (b) GPS time reception time” on the right side of the base station BTS (a) when the base station BTS (a) receives the GPS time stamp 205 from the base station BTS (b). It is time on. Therefore, Formula (3) is a transmission delay of time information received by the base station BTS (a) from the other base station BTS (b) via the IP transmission line NW in a state where synchronization between the base stations is not established. Represents time. The same applies to Equation (4).

  Next, the base station BTS (a) collates the value represented by the above formula (3) with the value represented by the above formula (1) held when the GPS synchronization state was established, Calculate the value. That is, the base station BTS (a) transmits the transmission delay time represented by Equation (3) (Tba value in FIG. 5) and the transmission delay time represented by Equation (1) (Tbas value in FIG. 5). Is calculated as the difference (Δt in FIG. 5) of the reference time of the base station BTS (a) with respect to the time t0 of the GPS time, and this is held.

  Then, the base station BTS (a) corrects the reference time of the base station using the difference (Δt) of the reference time of the base station BTS (a) with respect to the time t0 of the GPS time. In the example shown in FIG. 5, timing correction is performed to advance the reference time of the base station BTS (a) by Δt. Thereby, the reference time of the base station BTS (a) is synchronized with the GPS time, and the operation timing is synchronized with the GPS timing.

Therefore, by the above timing correction, the operation timing of the base station BTS (a) can be approximated to the operation timing of the base station BTS (b), and the synchronization between the base stations can be recovered.
Similarly, by using timing correction using Δt acquired from the GPS time stamp of the base station BTS (c) together, the accuracy of timing correction can be further improved.

  By the way, in this embodiment, the value of the transmission delay time obtained by using the time stamp received from another base station varies depending on the influence of the transmission path, for example. For this reason, there is a possibility that the transmission delay time in a state where no reception failure has occurred (GPS synchronization state) cannot be specified correctly.

  In order to avoid such a problem, in the present embodiment, for example, statistical processing (for example, transmission delay times Tba of a plurality of time stamps received from the base station BTS (b) including time stamps received in the past (for example, (3 sigma method) is performed to estimate the transmission delay time Tbas in a state where no reception failure has occurred. The base station TBS (a) holds the transmission delay time Tbas obtained by this statistical processing, and uses it as the value of the first term on the right side of the above-described equations (1) and (2). The same applies to the transmission delay time (Tca) of the time stamp received from the base station BTS (c).

  Thus, by taking statistics of the transmission delay time of the time stamp between the base stations when the base station BTS (a) is in the GPS synchronization state, a reception failure of the GPS signal occurs, and the base station BTS (a) Even when the GPS signal becomes asynchronous with respect to the GPS signal, the base time of the base station BTS (a) can be accurately adjusted to the absolute time in the GPS synchronous state. It becomes possible to keep the accuracy of the constant.

As described above, according to the first embodiment, the following effects can be obtained.
Each base station is normally in a GPS synchronization state, and exchanges information regarding the reference time of each base station by performing data communication using the IP transmission path between the base stations. From this information, for example, the data transmission delay time of the information related to the reference time of the base station BTS (b) received by the base station BTS (a) is calculated and stored in the base station BTS (a). Statistics of data transmission delay time between base stations based on absolute time when synchronized with a signal are taken.

As a result, even when the GPS signal cannot be received and the base station reference time is out of sync with the GPS time, the base station reference time can be controlled to match the absolute time in the GPS synchronized state. This makes it possible to keep the accuracy of synchronization between base stations constant.
The first embodiment has been described above.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 6 shows a control flow of the synchronization operation between base stations in the present embodiment, and FIG. 7 shows the operation timing of the base stations BTS (a) and BTS (b).

  The basic system configuration of this embodiment is basically the same as the configuration shown in FIG. 2 according to the first embodiment described above, but the configuration for calculating Δt is different. That is, in this embodiment, in addition to the configuration of the first embodiment described above, the GPS base time stamp received from the base station BTS (a) in the other base station BTS (b) and the base station BTS (c) A configuration is provided in which the transmission delay time Tab and the transmission delay time Tac are transmitted to the base station BTS (a).

  Specifically, in FIG. 6, when the base station BTS (a) transmits the GPS time stamp 607 via the IP transmission line NW, the base station BTS (b) and the base station BTS (c) perform IP transmission. Receive (605) via path NW. Each of the base station BTS (b) and the base station BTS (c) measures and acquires the transmission delay time Tab and the transmission delay time Tac (609, 606), and transmits them to the base station BTS (a). The base station BTS (a) receives (608) the transmission delay time Tab and the transmission delay time Tac from the base station BTS (b) and the base station BTS (c), respectively.

  Here, if there is no reception failure in the base station BTS (a), the transmission delay time Tab is the GPS time stamp from the base station BTS (a) to the base station BTS (b) when synchronization is established. Represents a time required for transmission via the IP transmission line NW (this is expressed in particular as “Tabs”), and is represented by the transmission delay time Tba represented by the equation (1) of the first embodiment. Corresponding to

On the other hand, if a reception failure occurs in the base station BTS (a), the transmission delay time Tab is a GPS time stamp from the base station BTS (a) to the base station BTS (b) in a state where synchronization is not established. This represents the time required for transmission via the IP transmission line NW, and corresponds to the transmission delay time Tba represented by Equation (3) in the first embodiment.
Since the same applies to the transmission delay time Tac acquired by the base station BTS (c), the description regarding the transmission delay time Tac is omitted below.

  FIG. 7 shows the relationship between the transmission delay time Tabs when no reception failure has occurred and the transmission delay time Tab when a reception failure has occurred. In the figure, t0, t1, and t3 are GPS times. As understood from the figure, when the base time of the base station BTS (a) is moved to time t1 due to reception failure, the transmission time delay Tabs of the GPS time stamp of the base station BTS (a) has elapsed from time t1. At time t3, it is received by the base station BTS (b). The base station BTS (b) measures the transmission delay time Tab of the GPS time stamp from the base station BTS (a) from the reception time on the base station BTS (b) at this time. In this case, the transmission delay time Tab is a value obtained by adding the transmission delay time Tabs to the reference time shift Δt of the base station BTS (a) with respect to the GPS timing (time t0).

  Subsequently, the base station BTS (a) calculates a reference time difference Δt of the base station BTS (a) with respect to the GPS signal using the transmission delay times Tab and Tabs acquired by the other base station BTS (b). To do. That is, the base station BTS (a), in a state where synchronization is established, the transmission delay time Tabs of the time information received by the base station BTS (b) from the base station BTS (a) via the IP transmission line NW, In a state where synchronization is not established, the difference between the transmission delay time Tab of the time information received by the other base station BTS (b) from the base station BTS (a) via the IP transmission path NW is determined by the base station for the GPS signal. It is calculated as a reference time difference Δt of BTS (a), and the reference time of the own station at the time of transmission is corrected based on the reference time difference Δt.

According to the second embodiment described above, the base station in which the reception failure has occurred uses the transmission delay times Tab and Tabs acquired by the other base station TBS (b) in which the reception failure has not occurred. Correct the reference time. Accordingly, since it becomes possible to measure the transmission delay time of the time information transmitted / received by the base station BTS (a) via the IP transmission line NW, compared with the effect of the first embodiment described above, it is possible to measure the transmission delay time. There is a new effect that the accuracy of estimation of the transmission delay time of the time information can be improved.
The second embodiment has been described above.

In the first and second embodiments described above, the case where the reference time of each base station is synchronized with the GPS signal is taken as an example. However, the present invention can also be applied to other synchronization formats. The present invention can also be applied to a method of controlling transmission timing by the base station controller.
Further, in the above-described embodiment, the case where the reception failure occurs only in the base station BTS (a) is taken as an example, but the base where the reception failure occurs except for the case where the reception failure occurs simultaneously in all the base stations. The number of stations is arbitrary.

Furthermore, in the above-described embodiment, the time information of each base station is exchanged using the IP transmission path. However, the present invention is not limited to this, and various transmission paths can be used.
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is a diagram schematically showing an overall configuration of a mobile communication system according to a first embodiment of the present invention. It is a figure which shows the control flow (normal time) of the synchronization between base stations which concerns on the 1st Embodiment of this invention. It is a figure which shows the control flow (at the time of failure occurrence) of the synchronization between base stations which concerns on the 1st Embodiment of this invention. It is a figure which shows the timing chart (normal time) of the synchronization between base stations which concerns on the 1st Embodiment of this invention. It is a figure which shows the timing chart (at the time of failure occurrence) of the synchronization between base stations which concerns on the 1st Embodiment of this invention. It is a figure which shows the control flow (at the time of failure occurrence) of the synchronization between base stations which concerns on the 2nd Embodiment of this invention. It is a figure which shows the timing chart (at the time of failure occurrence) of the synchronization between base stations which concerns on the 2nd Embodiment of this invention. It is a figure which shows roughly the whole structure of the conventional mobile communication system.

Explanation of symbols

GPS; GPS satellite BTS (a), BTS (b), BTS (c); base station (wireless base station device)
NW: IP transmission line

Claims (8)

In a mobile communication system including a plurality of base stations, each base station receives a synchronization signal from a signal generation source, and establishes synchronization between the plurality of base stations by synchronizing its own reference time with the synchronization signal. A base-to-base synchronization method,
At least one base station of the plurality of base stations is
Receiving time information from another base station via a transmission path different from the reception path of the synchronization signal;
Using the transmission delay time of the time information received from the other base station to calculate the difference in the reference time of the own station with respect to the synchronization signal,
An inter-base synchronization method for correcting the reference time of the own station based on the difference in reference time. At least one base station of the plurality of base stations is
A transmission delay time of time information received from the other base station via the transmission path in a state where synchronization between the plurality of base stations is established, and the other base in a state where the synchronization is no longer established. The inter-base synchronization method according to claim 1, wherein a difference from a transmission delay time of time information received from a station via the transmission path is calculated as a deviation of the reference time. The other base station is
Receiving time information from the at least one base station via the transmission path, obtaining a transmission delay time of the time information, and transmitting the transmission delay time to the at least one base station;
The at least one base station is
Using the transmission delay time acquired by the other base station, the other base station is connected from the at least one base station via the transmission path in a state where synchronization between the plurality of base stations is established. The difference between the transmission delay time of the received time information and the transmission delay time of the time information received by the other base station from the at least one base station via the transmission path in a state where the synchronization is not established. The inter-base synchronization method according to any one of claims 1 and 2, wherein the base time is calculated as the difference in reference time, and the reference time of the own station at the time of transmission is corrected based on the difference in reference time. The at least one base station is
4. The transmission delay time of time information in a state where synchronization between the plurality of base stations is established by statistically processing the transmission delay time of time information received from the other base station. The inter-base synchronization method according to any one of the above. A signal source for generating a synchronization signal;
A plurality of base stations that receive the synchronization signal from the signal generation source and operate by synchronizing a reference time of the local station with the synchronization signal;
Unlike the reception path of the synchronization signal, comprising a transmission path for connecting the plurality of base stations,
At least one base station of the plurality of base stations is
Using the transmission delay time of the time information received from the other base station via the transmission path, the deviation of the reference time of the own station relative to the synchronization signal is calculated, and the reference time of the own station is calculated based on the deviation of the reference time. Mobile communication system to be corrected. At least one base station of the plurality of base stations is
A transmission delay time of time information received from the other base station via the transmission path in a state where synchronization between the plurality of base stations is established, and the other base in a state where the synchronization is no longer established. 6. The mobile communication system according to claim 5, wherein a difference from a transmission delay time of time information received from a station via the transmission path is calculated as a difference in the reference time. The other base station is
Receiving time information from the at least one base station via the transmission path, obtaining a transmission delay time of the time information, and transmitting the transmission delay time to the at least one base station;
The at least one base station is
Using the transmission delay time acquired by the other base station, the other base station is connected from the at least one base station via the transmission path in a state where synchronization between the plurality of base stations is established. The difference between the transmission delay time of the received time information and the transmission delay time of the time information received by the other base station from the at least one base station via the transmission path in a state where the synchronization is not established. The mobile communication system according to any one of claims 5 and 6, wherein the mobile communication system calculates the difference in reference time and corrects the reference time of the own station at the time of transmission based on the difference in reference time. The at least one base station is
8. A transmission delay time of time information in a state where synchronization between the plurality of base stations is established by statistically processing a transmission delay time of time information received from the other base station. The mobile communication system according to any one of the above.

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