JP2008182385A - Mobile communication system, time server and intra-station synchronization method used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system capable of acquiring the GPS time of error accuracy required in intra-station synchronization in a base station. <P>SOLUTION: In the mobile communication system, a master time server 1 for acquiring the GPS time from a GPS satellite 2 and generating a reference clock and a slave time server 4 connected with the master time server 1 by an exclusive line such as an optical fiber are prepared, and the slave time server 4 is provided together in an RNC 3. The slave time server 4 sends out time information to the plurality of base stations 6-1 to 6-4 subordinate to the RNC 3 without depending on the processing delay of the RNC 3, measures the delay time of the route of the respective base stations 6-1 to 6-4 and the RNC 3 and corrects the time on the basis of the measured result. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile communication system, a time server, and an inter-station synchronization method used for them, and more particularly to an inter-station synchronization method for synchronizing base stations in a mobile communication system.

  Conventionally, in the inter-station synchronization method of a mobile communication system, each base station (BTS: Base Transceiver Station) reads UTC (Coordinated Universal Time) information of GPS (Global Positioning System), and PPS (Pulse Per Sed) included in the UTC information. ) And the clock in the own station, it is possible to synchronize with the adjacent base station by generating a reference clock used for inter-station synchronization.

  This is based on the premise that every base station is in a line-of-sight state from a GPS satellite. If the GPS receiver built in the base station cannot receive the PPS signal, a reference clock may be generated. I have a problem that I can't.

  As shown in FIG. 7, a conventional mobile communication system that requires inter-station synchronization includes a GPS satellite 2 and base stations 7-1 and 7-2. Each of the base stations 7-1 and 7-2 obtains GPS time from the paths 201 and 202 using a built-in GPS receiver (not shown), and is a reference clock used for inter-station synchronization based on the GPS time. Is generated.

As an inter-station synchronization method, there are methods described in Patent Documents 1 and 2 below.
JP 2005-318196 A JP 2001-053759 A

  In the conventional inter-station synchronization method described above, the line-of-sight state cannot be maintained in the path 202 between the GPS satellite 2 and the base station 7-2, and the link is disconnected between the GPS satellite 2 and the base station 7-2. If it has occurred (200), the GPS time is obtained from the base station 7-1 that is linked to the GPS satellite 2 through the wireless path 210, and between the base station 7-1 and the base station 7-2. The delay time is measured inside the base station 7-2, the obtained GPS time is corrected, and a reference clock must be generated.

  In order to solve this problem, a method of acquiring time information from NTP (Network Time Protocol) using a wired network and synchronizing base stations can be considered. However, in the currently available Ethernet (registered trademark) network, congestion that tends to occur in repeaters such as routers and other delay fluctuations due to queuing delays occur, and the GPS time of the error accuracy required for inter-station synchronization is acquired at the base station. There is a problem that it cannot be done.

  Accordingly, an object of the present invention is to solve the above-described problems and to obtain a mobile communication system, a time server, and inter-base station synchronization used in the base station, capable of acquiring GPS time with error accuracy required for inter-station synchronization. It is to provide a method.

A mobile communication system according to the present invention is a wireless communication system including a repeater for controlling a plurality of base stations,
In addition to sending a time packet after sending an IP (Internet Protocol) packet together with a time server in the repeater,
The time server includes means for measuring delay fluctuations between each of the base stations and the repeater, predicts a load situation of the network, and periodically transmits a time packet to the base station so that a reference in the base station is obtained. Means for correcting the clock.

A time server according to the present invention is attached to the repeater in a wireless communication system including a repeater that controls a plurality of base stations,
Means for measuring delay fluctuations between each of the base stations and the repeater, and predicting the load situation of the network, periodically transmitting time packets to the base station, and correcting the reference clock in the base station Means.

The inter-base station synchronization method according to the present invention is an inter-station synchronization method used in a radio communication system including a repeater that controls a plurality of base stations,
A time server provided alongside the repeater measures the delay fluctuation between each of the base stations and the repeater, and predicts the load situation of the network and periodically transmits time packets to the base station. And a process of correcting the reference clock in the base station.

  That is, the mobile communication system according to the present invention avoids congestion due to a repeater (here, RNC (Radio Network Controller)) that is one of the synchronization delay factors of the time synchronization method in a system using Ethernet (registered trademark). Therefore, a time server (Time Server) is installed in the repeater, and a time packet is sent after sending an IP (Internet Protocol) packet, and the base station (BTS: Base Transceiver Station) is always used in the time server installed in the repeater. ) And repeater, measure the network load situation, periodically send time packets to the base station, and correct the reference clock (time) in each base station And

  In the mobile communication system according to the present invention, a dedicated server that generates a reference clock such as a master time server (Master Time Server 11) and a slave time server (a master time server) connected by a dedicated line such as an optical fiber ( Slave Time Server), and a slave time server is provided in the repeater.

  The slave time server attached to the repeater does not depend on the processing delay of the repeater, and is configured to send time information to a plurality of base stations under the repeater, which is the largest cause of delay fluctuations. It becomes possible to avoid congestion of the repeater.

  In addition, the slave time server measures the delay time of the path to the base station under the repeater and corrects the time, thereby suppressing fluctuations due to other queuing delays and the accuracy error of the reference clock necessary for inter-station synchronization. Can be kept within the desired range.

  As a result, in the mobile communication system of the present invention, the slave time server is provided in the repeater so as to reduce the delay fluctuation, and the delay correction function not depending on the processing of the repeater is provided. If it is possible to obtain the time, it is possible to distribute the accurate time to all the base stations under the repeater.

  In the mobile communication system of the present invention, a GPS (Global Positioning System) time with little delay fluctuation can be assigned to a base station under a repeater by wire, and an inter-station synchronization clock is generated based on the GPS time. Therefore, even when the base station is not in a line-of-sight state from a GPS satellite, high-accuracy inter-station synchronization is possible.

  By adopting the above-described configuration and operation, the present invention provides an effect that the GPS time with error accuracy required for inter-station synchronization can be acquired by the base station.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a mobile communication system according to an embodiment of the present invention. In FIG. 1, a mobile communication system according to an embodiment of the present invention includes a master time server (Master Time Server) 1 that collects time information from a GPS (Global Positioning System) satellite 2 and an IP (Internet Protocol) network. A core network (CN) 100, a radio network controller (RNC) 3 connected to the core network 100, a slave time server (Slave Time Server) 4 attached to the RNC 3, A database (DB: Data Base) 5 used for data collection of the slave time server 4 and a base station (BTS: Base Transance) connected to the RNC 3 And a ver Station) 6-1~6-4 Metropolitan.

  The master time server 1 periodically transmits a GPS receiver 11 that receives a GPS signal transmitted from the GPS satellite 2 and a GPS time obtained from the signal received by the GPS receiver 11 to the slave time server 4 through a dedicated path 122. Time information transmission means 12.

  The slave time server 4 includes a path delay measuring unit 41 that measures path delays of the base stations 6-1 to 6-4 under the RNC 3, and a delay amount distribution average that measures the distribution average of the measured delay amount and stores it in the database 5. A measuring means 42; a reference clock generating means 43 for generating a reference clock based on information stored in the database 5; and a reference clock transmitting means 44 for transmitting the generated reference clock to the base stations 6-1 to 6-4. It has.

  It is assumed that the master time server 1 and the GPS satellite 2 are wirelessly connected via a route 110. Further, the master time server 1 is installed so as to be in a line-of-sight state from the GPS satellite 2 as much as possible in order to generate a reference clock (time) of all devices under the RNC 3.

  Furthermore, the master time server 1 and the slave unit time server 4 are connected by a dedicated route (122) such as an optical fiber in order to obtain accurate time information from the master time server 1. The other paths 121 and 131 to 134 are assumed to be configured by a commonly used IP network.

  FIG. 2 is a flowchart showing a reference time setting procedure of the master time server 1 of FIG. The reference time setting procedure of the master time server 1 will be described with reference to FIG. 1 and FIG.

  The master time server 1 expects the GPS time from the GPS satellite 2 with high accuracy of the propagation delay amount and the accuracy of the acquisition time in order to obtain the accurate time, and the propagation path 110 with the GPS satellite 2 is first visible. It is confirmed whether it is in a state (step S1 in FIG. 2).

  When the propagation path 110 with the GPS satellite 2 is in the line-of-sight state, the master time server 1 receives the GPS signal transmitted from the GPS satellite 2 with the GPS receiver 11 and correct GPS time with the propagation delay corrected. Is obtained (step S2 in FIG. 2). When the propagation path 110 with the GPS satellite 2 is not in the line-of-sight state, the master time server 1 holds the GPS time acquisition until the propagation path 100 is in the line-of-sight state.

  In FIG. 1, the master time server 1 that has acquired the GPS time periodically transmits a reference clock to the slave time server 4 through a dedicated path (optical fiber network) 122.

  3 and 4 are sequence charts showing the operation of the mobile communication system according to the embodiment of the present invention. A delay correction flow performed by the slave time server 4 will be described with reference to FIG. 1, FIG. 3, and FIG.

  The slave time server 4 sends the path delay detection packet to the base stations # 1, # in order to measure the path delay of the base stations # 1, # 2 (base stations 6-1, 6-2 in FIG. 1) under the RNC3. 2 is sent out (a1 in FIG. 3).

  Receiving the path delay detection packet, the base stations # 1 and # 2 measure the internal delay time taken from receiving the packet to sending it back to the slave time server 4 (a2 and a3 in FIG. 3). It is added to the detection packet and sent to the slave time server 4 (a4, a5 in FIG. 3).

  The slave time server 4 that has received the path delay detection packet from the base stations # 1 and # 2 uses the packet transmission time and the reception time, and the internal delay time in each of the base stations # 1 and # 2 to The delay time required for the round trip of the path 132 is measured by the path delay measuring means 41 (a6 in FIG. 3). The path delay measuring unit 41 stores the measured delay times of the path 131 and the path 132 in the database 5 provided in the slave time server 4 (a7 in FIG. 3).

  Further, in the slave time server 4, the delay amount distribution average measuring means 42 measures the distribution average of the delay amount measured by the path delay measuring means 41 (a 8 in FIG. 3), and the distribution average is stored in the database 5. Save (a9 in FIG. 3).

  Further, the reference clock corrected for each of the base stations # 1 and # 2 using the delay time / 2 of the path 131 and the path 132 (= the amount of the forward path) is supplied to the reference clock generation means 43 only at the time of the first path delay measurement. Is generated (a10 in FIG. 3), and is transmitted as time packets from the reference clock transmission means 44 to the base stations # 1 and # 2 (a11 in FIG. 3).

  Next, a processing flow when the RNC 3 receives an IP packet from the core network 100 will be described with reference to FIG. However, the code | symbol attached | subjected to the process flow of FIG. 4 shall be followed by the code | symbol attached | subjected to the process flow of FIG.

  When the RNC 3 receives an IP packet from the core network 100, the RNC 3 confirms the destination address of the IP header, and then sends the IP packet to the address destination (a12 in FIG. 4). After sending out the IP packet, the RNC 3 notifies the slave time server 4 of the IP packet transmission destination (a13 in FIG. 4).

  Receiving the notification, the slave time server 4 calls the latest delay time of the path 131 from the database 5 based on the transmission destination address (a14 in FIG. 4). Based on the delay time of the called path 131, the arrival time at the base station # 1 when the path delay detection packet is transmitted to the base station # 1 is predicted, and the packet transmission time and the estimated arrival time at the base station # 1 are calculated. In addition, the path delay detection packet is sent to the base station # 1 (a15 in FIG. 4).

  Receiving the path delay detection packet, the base station # 1 adds the transmission / reception time (transmission / reception time stamp) to the packet (a16 in FIG. 4), and sends the packet back to the slave time server 4 (a17 in FIG. 4).

  The slave time server 4 that has received the path delay detection packet from the base station # 1 measures the delay time and the average delay distribution of the forward path and the return path of the path 131 in FIG. 1 (a18 in FIG. 4), and the path delay amount. And the distribution average are registered in the database 5 (a19 in FIG. 4).

  In addition, the slave time server 4 calls the delay time and the average delay distribution of the forward path and the return path of the immediately preceding path 131 from the database 5 (a19 in FIG. 4), and the delay amount measured in the process of a18 is calculated from the database 5. If it is smaller than the called delay amount and is within the range desired for inter-station synchronization, the time of the base station # 1 is not corrected, and it is determined that correction is necessary otherwise (a20 in FIG. 4).

  When the time correction is performed, the slave time server 4 estimates the time when the time packet arrives at the base station # 1 (a21 in FIG. 4), and sends the time packet toward the base station # 1 ( A22) in FIG.

  However, if the delay amount of the path 131 measured in the processing of a18 is much larger than the delay distribution average measured so far, there is a high possibility that a network failure has occurred in the path 131, so the slave time server 4 Does not transmit a time packet for time correction, and continues to measure the delay amount of the path 131.

  FIG. 5 is a flowchart showing a detailed process flow of the process a20 of FIG. With reference to FIG. 6, the detailed processing of the time correction determination flow shown in the processing of a20 in FIG. 4 will be described.

  The slave time server 4 extracts the immediately preceding delay amount and the average delay distribution from the database 5, and then starts comparing the measured delay amounts. When the measured delay amount is extremely large compared to the average delay distribution extracted from the database 5, the slave time server 4 determines that some trouble has occurred on the IP network and normal time correction cannot be performed ( Step S11 in FIG. 5) does not perform the time correction operation on the base station, and continues the path delay detection (step S14 in FIG. 5).

  On the other hand, if the delay amount is smaller than the average delay distribution, the slave time server 4 determines whether the delay amount is within the desired range in the inter-station synchronization (step S12 in FIG. 5). The slave time server 4 shifts to the delay time correction flow when the delay amount does not fall within the desired range of synchronization between stations (step S15 in FIG. 5), and when the delay amount falls, shifts to the comparison with the immediately preceding delay amount. (Step S13 in FIG. 5).

  If the slave time server 4 is smaller than the immediately preceding delay amount in the process of step S13, the slave time server 4 determines that the delay amount tends to decrease, and proceeds to the path delay detection flow (step S14 in FIG. 5). On the other hand, when the slave time server 4 is larger than the previous delay amount, the slave time server 4 proceeds to the delay time correction flow (step S15 in FIG. 5).

  After shifting to the delay time correction flow in step S15, the slave time server 4 sends the corrected time as a time packet to the target base station (step S16 in FIG. 5).

  As described above, in this embodiment, the slave time server 4 is provided in the RNC 3 so as to reduce the delay fluctuation, and the delay correction function independent of the processing of the RNC 3 is provided, so that only the master time server 1 is accurate. If the time can be obtained, the accurate time can be distributed to all the base stations 6-1 to 6-4 under the RNC3. Therefore, in the present embodiment, the GPS time with error accuracy required for inter-station synchronization can be acquired by the base stations 6-1 to 6-4.

  In this embodiment, the GPS time with little delay fluctuation can be distributed to the base stations 6-1 to 6-4 under the RNC 3 by wire, and the inter-station synchronization clock is generated based on the GPS time. Therefore, even when the base stations 6-1 to 6-4 are not in the line-of-sight state from the GPS satellite 2, high-accuracy inter-station synchronization can be realized.

  Next, a mobile communication system according to another embodiment of the present invention will be described. A mobile communication system according to another embodiment of the present invention uses a Japanese standard frequency station (JJY) instead of the GPS satellite 2 shown in FIG. 1 or an NTP (Network Time Protocol) instead of the GPS satellite 2 shown in FIG. ) It uses a server.

  Accordingly, in another embodiment of the present invention, the time acquisition destination is selected from one of the GPS satellite 2, the Japanese standard frequency station (JJY), and the NTP server according to the installation environment of the master time server 1. It becomes possible.

  A configuration example of a mobile communication system according to another embodiment of the present invention is shown in FIG. In FIG. 6, in a mobile communication system according to another embodiment of the present invention, master time servers 1a and 1b having a plurality of RNCs 3a to 3c are connected to each other by a dedicated line 140 such as an optical fiber.

  Thereby, the error correction between the master time servers 1a and 1b can be performed in advance, and even in a wireless system having large-scale service areas 171 to 173, synchronization between stations using a wired connection is possible.

  In FIG. 6, the mobile communication system according to another embodiment of the present invention includes master time servers 1a and 1b, a core network 100, RNCs (repeaters) 3a to 3c, slave time servers 4a to 4c, It consists of databases 5a-5c and base station groups 6a-6c. Master time servers 1a, 1b and slave time servers 4a-4c are connected by dedicated paths 161-163, and RNCs 3a-3c are connected by paths 151-153. It is connected to the core network 100. The master time servers 1a and 1b and the slave time servers 4a to 4c have the same configuration as the master time server 1 and the slave time server 4 shown in FIG.

  The present invention is applicable to a mobile communication system and a wireless network used indoors or underground.

It is a block diagram which shows the structure of the mobile communication system by one Example of this invention. It is a flowchart which shows the reference time setting procedure of the master time server of FIG. 6 is a sequence chart showing an operation of the mobile communication system according to the embodiment of the present invention. 6 is a sequence chart showing an operation of the mobile communication system according to the embodiment of the present invention. It is a flowchart which shows the detailed process flow of the process of a20 of FIG. It is a block diagram which shows the structural example of the mobile communication system by the other Example of this invention. It is a block diagram which shows the structural example of the conventional mobile communication system.

Explanation of symbols

1,1a, 1b Master time server
2 GPS satellites 3, 3a-3c RNC
4, 4a to 4c Slave time server 5, 5a to 5c Database 6-1 to 6-4 Base station 6a to 6c Base station group
11 GPS receiver
12 Time information transmission means
41 Path delay measuring means
42 Means for measuring delay amount distribution
43 Reference clock generation means
44 reference clock transmission means 122,
161-163 Dedicated route

Claims (15)

A wireless communication system including a repeater for controlling a plurality of base stations,
In addition to sending a time packet after sending an IP (Internet Protocol) packet together with a time server in the repeater,
The time server includes means for measuring delay fluctuations between each of the base stations and the repeater, predicts a load situation of the network, and periodically transmits a time packet to the base station so that a reference in the base station is obtained. A wireless communication system comprising: means for correcting a clock.   2. The wireless communication system according to claim 1, wherein the time server is a slave time server connected by a dedicated line to a dedicated server that generates a reference clock.   3. The wireless communication system according to claim 2, wherein the slave time server sends time information to a plurality of base stations under the repeater without depending on a processing delay of the repeater.   4. The wireless communication system according to claim 2, wherein the slave time server performs time correction by measuring a delay time of a route with a base station under the relay.   The dedicated server acquires time information from at least one of a GPS (Global Positioning System) satellite, a Japanese standard frequency station, and an NTP (Network Time Protocol) server, and the time information is acquired by the slave on the dedicated line. The wireless communication system according to claim 2, wherein the wireless communication system is transmitted to a time server. In a wireless communication system including a repeater that controls a plurality of base stations, the repeater is provided,
Means for measuring delay fluctuations between each of the base stations and the repeater, and predicting the load situation of the network, periodically transmitting time packets to the base station, and correcting the reference clock in the base station A time server.   7. The time server according to claim 6, wherein the time server is a slave time server connected to a dedicated server for generating a reference clock through a dedicated line.   8. The time server according to claim 7, wherein time information is transmitted to a plurality of base stations under the repeater without depending on a processing delay of the repeater.   9. The time server according to claim 7, wherein time correction is performed by measuring a delay time of a route with a base station under the repeater.   The dedicated server receives time information acquired from at least one of a GPS (Global Positioning System) satellite, a Japanese standard frequency station, and an NTP (Network Time Protocol) server through the dedicated line. The time server according to any one of claims 7 to 9. An inter-station synchronization method used in a wireless communication system including a repeater that controls a plurality of base stations,
A time server provided alongside the repeater measures the delay fluctuation between each of the base stations and the repeater, and predicts the load situation of the network and periodically transmits time packets to the base station. And a process of correcting a reference clock in the base station.   12. The inter-station synchronization method according to claim 11, wherein the time server is a slave time server connected by a dedicated line to a dedicated server that generates a reference clock.   13. The inter-station synchronization method according to claim 12, wherein the slave time server transmits time information to a plurality of base stations under the repeater without depending on a processing delay of the repeater.   The inter-station synchronization method according to claim 12 or 13, wherein the slave time server performs time correction by measuring a delay time of a route with a base station under the relay.   The dedicated server acquires time information from at least one of a GPS (Global Positioning System) satellite, a Japanese standard frequency station, and an NTP (Network Time Protocol) server, and the time information is acquired by the slave on the dedicated line. 15. The inter-station synchronization method according to claim 12, wherein the synchronization is transmitted to a time server.

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