JP5409165B2 - Clock correction period correction method and radio base station apparatus - Google Patents

Description

  The present invention relates to a method for correcting a clock correction period when an internal clock is corrected by accessing an NTP (Network Time Protocol) server.

  Conventionally, the 3G wireless base station uses a reference timing using its own internal clock to establish phase synchronization and radio frequency synchronization, but this reference timing has a narrow error and allowable range, An error may occur and be accumulated, which may exceed the allowable range. In order to avoid this, the conventional apparatus is provided with a high-accuracy clock source that is highly accurate and less likely to cause errors, or corrects the timing as needed using a GPS (Global Positioning System) or the like. .

  However, there is a possibility that an inexpensive low-accuracy clock source may be mounted on a small base station used for dead zone countermeasures, for example, in order to reduce the price. Alternatively, such a small base station may be operated in a place where GPS radio waves do not reach such as underground. For this reason, a method of correcting the internal clock by obtaining information such as a time stamp from an external high-accuracy clock source (for example, NTP) connected to the network is considered.

  For example, Patent Document 1 below discloses a technique in which a slave time server acquires a reference clock from a master time server connected via a dedicated line, sends time information to the base station, and corrects the time of the base station. Has been.

JP 2008-182385 A

  However, according to the above conventional technique, when the internal clock is corrected by NTP, if the delay amount greatly exceeds the measured delay distribution average, it is determined that there is a high possibility that a network failure has occurred. However, the time packet is not transmitted and the time is not corrected. Accordingly, there is a problem that the system cannot be used until the next correction timing when the network delay state changes due to a temporary abnormality in the time stamp transmission path or a semi-stationary routing path change.

  The present invention has been made in view of the above, and an object of the present invention is to provide a clock correction cycle correction method that enables correction of an internal clock correction cycle even when a delay fluctuates.

  In order to solve the above-described problems and achieve the object, the present invention provides a clock correction period correction method in a radio base station apparatus that corrects an internal clock of its own apparatus by periodically accessing an NTP server, An NTP access step for executing an NTP access for transmitting an NTP packet to the NTP server and receiving a response to the transmission of the NTP packet over the first number of times, and the most reliable among the execution results of the NTP access step An NTP server delay determination step of extracting a high access result and determining the extraction result as a transmission path delay to the NTP server, and in the NTP access cycle that is shorter than the correction cycle of the internal clock, Repeatedly execute NTP access step and NTP server delay determination step Furthermore, it is determined that the difference between the transmission path delay determined in the NTP server delay determination step and the transmission path delay at the previous correction period has become equal to or greater than a predetermined threshold over the second consecutive number of times. In this case, a correction cycle adjustment step for correcting the shift of the correction cycle is included.

  According to the present invention, there is an effect that the correction cycle can be kept constant.

FIG. 1 is a diagram illustrating a configuration example of an embodiment of a radio base station apparatus according to the present invention. FIG. 2 is a diagram for explaining clock correction in the NTP correction method. FIG. 3 is a diagram illustrating a method for obtaining a residual error. FIG. 4 is a diagram for explaining the NTP access in the present embodiment. FIG. 5 is a diagram illustrating a state in which the current delay measurement result is evaluated based on the delay measurement result in the previous correction cycle. FIG. 6 is a diagram illustrating an example of the relationship between the retry period and the correction period in the embodiment.

  Embodiments of a clock correction period correction method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of the present embodiment of a radio base station apparatus according to the present invention. The radio base station apparatus of FIG. 1 includes an IP (Internet Protocol) I / F unit 1, a clock correction unit 2, a reference clock source 3, and an RF (Radio Frequency) unit 4.

  The IP I / F unit 1 is an interface with an external NTP server (not shown). The clock correction unit 2 adjusts the clock correction cycle. The reference clock source 3 is a crystal oscillator that oscillates the reference clock of the radio base station apparatus of FIG. The RF unit 4 is configured by a digital circuit or the like, and processes a radio signal inside the radio base station apparatus using a clock generated by the reference clock source 3.

  The source oscillation counter unit 11 counts the number of clocks received from the reference clock source 3. The counter value timestamp acquisition unit 12 calculates a time corresponding to the number of clocks based on the number of clocks notified from the source oscillation counter unit 11. Then, for each “number of clocks corresponding to the correction period (time)” managed by itself, the NTP packet processing unit 13 is instructed to acquire time, and the calculation time is notified to the clock adjustment amount calculating unit 14. . The “correction period” is a time stamp interval necessary for maintaining clock accuracy. The time stamp interval may be at least as long as it is necessary to continue observation.

  The counter value time stamp acquisition unit 12 is a period independent of the correction period, and transmits an NTP packet in an NTP access period (details will be described later) for detecting a transmission line delay with the NTP server. The NTP packet processing unit 13 is controlled to execute.

  The NTP packet processing unit 13 transmits / receives an NTP packet to / from an NTP server via the IP I / F unit 1, acquires a reference time stamp (server transmission time: Transmit Timestamp) included in the NTP packet, and adjusts a clock. The amount calculation unit 14 is notified. The clock adjustment amount calculation unit 14 calculates these differences using the calculation time notified from the counter value time stamp acquisition unit 12 and the server transmission time notified from the NTP packet processing unit 13, and calculates the time from the difference. A clock shift at is detected. Further, delay measurement by NTP access is executed, and the correction period is corrected based on the result.

  Next, operations in the radio base station apparatus configured as described above will be described. First, the operation of clock correction using NTP packets will be described.

  The NTP packet received from the NTP server includes a reference time stamp (hereinafter also simply referred to as “time stamp”). The counter value timestamp acquisition unit 12 of the radio base station apparatus calculates the time by counting the number of clocks notified from the source oscillation counter unit 11, and instructs the NTP packet processing unit 13 to acquire the time at regular intervals. The clock adjustment amount calculation unit 14 is notified of the calculation time. The NTP packet processing unit 13 transmits an NTP packet when receiving a time acquisition instruction from the counter value time stamp acquisition unit 12, and receives the NTP packet returned from the NTP server. The NTP packet processing unit 13 acquires a time stamp from the received NTP packet and notifies the clock adjustment amount calculation unit 14 of the time stamp. The clock adjustment amount calculation unit 14 obtains the calculation time from the counter value time stamp acquisition unit 12 and the time stamp from the NTP packet processing unit 13. In the radio base station apparatus, such processing as clock number counting, time calculation, and time acquisition is continuously performed.

  FIG. 2 is a diagram for explaining clock correction in the NTP correction method. As shown in FIG. 2, by comparing the difference between the time stamp (n) (n is a natural number) and the time stamp (n + 1) with the time calculated from the clock count number therebetween, the clock between the time stamps is compared. Deviation can be detected. In order to observe this, NTP packets are transmitted and received at a correction period.

  In the radio base station apparatus, a correction amount is determined according to the amount of clock deviation detected at each correction period, and clock correction is performed. The correction amount at this time is a value that makes the clock shift detected by comparing the server transmission interval of the NTP packet received for each correction period and the clock count number zero. For example, when the time corresponding to the counter value “X” of the clock generated by the reference clock source 3 is “x”, the clock correction amount at this time is calculated by the following equation (1).

[{TS (n + 1) −TS (n)} − x] / [TS (n + 1) −TS (n)] (ppm)
... (1)

  The clock adjustment amount calculation unit 14 corrects a time corresponding to one clock by using the clock correction amount obtained by Expression (1).

  Incidentally, even if correction is performed, an error in the correction amount (hereinafter also referred to as “residual error”) exists. The residual error is determined by the ratio between the maximum delay fluctuation (substantially maximum delay fluctuation) assumed for the network in which the NTP packet is transmitted and the correction period. FIG. 3 is a diagram illustrating a method for obtaining a residual error. For example, assuming that a delay fluctuation of ± Zms is included when the time stamp arrives, the actual clock count time is between MIN represented by the following expression (2) and MAX represented by the expression (3). Will take the value of

MIN = (TS (n + 1) −Zms) − (TS (n) + Zms) (2)
MAX = (TS (n + 1) + Zms) − (TS (n) −Zms) (3)

Therefore, in the above case, since the maximum error of delay fluctuation with respect to the correction period is ± 2Z, the maximum correction residual error at this time is expressed by the following equation (4).
Maximum residual error = ± {2Z / correction period} (ppm) (4)

  Next, an operation for correcting the clock correction period by monitoring the delay state will be described. In the present embodiment, NTP access for accessing the NTP server is performed in a short cycle different from the correction cycle. Hereinafter, this short cycle is referred to as “NTP access cycle”. The NTP access cycle is a cycle in which NTP access is executed in order to detect a transmission path delay with the NTP server. FIG. 4 is a diagram for explaining the NTP access in the present embodiment. The radio base station apparatus obtains a sample by performing, for example, 100 or more NTP accesses every 1 NTP access period. The radio base station apparatus monitors the delay state of the transmission path with the NTP server by the NTP access.

  As described above, the counter value time stamp acquisition unit 12 of the radio base station apparatus calculates the time based on the counter value from the source oscillation counter unit 11, and indicates that the delay monitoring is performed every time the NTP access cycle is reached. The transmission / reception processing unit 13 is instructed. When the NTP packet transmission / reception processing unit 13 transmits an NTP packet and receives a reply of the NTP packet from the NTP server, the NTP packet transmission / reception processing unit 13 notifies the counter value time stamp acquisition unit 12 to that effect. Receiving this, the counter value time stamp acquisition unit 12 calculates the time using the counter value from the source oscillation counter unit 11, and obtains the base station reception time (clock counter value) of the NTP packet. The counter value time stamp acquisition unit 12 notifies the clock adjustment amount calculation unit 14 of the base station reception time. Further, the NTP packet transmission / reception processing unit 13 notifies the clock adjustment amount calculation unit 14 of the server transmission time acquired from the NTP packet. The NTP packet transmission / reception processing unit 13 performs the above processing over a predetermined number of NTP accesses (here, 100 accesses).

  The clock adjustment amount calculation unit 14 performs delay measurement using the samples (sample number: 100) obtained in this way. Specifically, first, a sample with the smallest difference between the server transmission time and the base station reception time (clock counter value) is extracted as the most reliable sample from all the samples. Then, in order to obtain a round trip delay, an access result (round trip transmission line delay) obtained by doubling the delay of the sample is used as a delay measurement result of the current NTP access cycle. Note that the delay measurement result may be determined by another extraction method.

  By the way, the number of samples is the total number when packet loss in the network, discard due to abnormal delay countermeasures, etc. are not considered. Therefore, the number of valid samples acquired varies depending on the delay and packet loss in the network. The value of the number of samples can be changed by tuning parameters.

  In addition, during the reception of NTP packets of the same packet group (same NTP access cycle) so that the time axis of the base station reception time does not fluctuate in comparison between a plurality of NTP packets acquired as samples, normal NTP It is assumed that processing corresponding to time correction in the own apparatus performed by the client (clock counter correction) is not performed.

  Subsequently, the clock adjustment amount calculation unit 14 compares the delay measurement result (last delay measurement result before the correction cycle) measured during the previous correction cycle with the current delay measurement result. Then, when “the difference in the delay measurement result is continuously greater than or equal to the predetermined threshold” for a predetermined number of times, it is determined that a steady delay variation due to a change in the routing path has occurred, and the correction cycle Control to correct the deviation is performed. At this time, the start timing of the next correction cycle is corrected so that the correction cycle does not change. Specifically, for example, the “number of clocks corresponding to the correction period” held by the counter value time stamp acquisition unit 12 is increased or decreased by the number of clocks corresponding to the amount of delay variation. For example, when the transmission delay of 1 second in the round trip changes to 2 seconds, the number of clocks corresponding to 1 second as a difference is subtracted from the number of clocks corresponding to the current correction period. For example, when the transmission delay that was 2 seconds in the round trip changes to 1 second, the number of clocks corresponding to 1 second as a difference is added to the number of clocks corresponding to the current correction period. As described above, the correction cycle can be maintained at a constant cycle by adjusting the start timing of the correction cycle in accordance with the delay variation.

  FIG. 5 is a diagram illustrating a state in which the current delay measurement result is evaluated based on the delay measurement result in the previous correction cycle. FIG. 5 shows a case where the difference from the delay measurement result of the previous correction period is equal to or more than the threshold value shown in the figure three consecutive times.

  FIG. 5 shows an example in which the difference is positive, that is, an example in which the delay measurement result has increased, but the difference may be negative as indicated by the dotted line indicating the threshold value. When the difference is negative, the current delay measurement result is reduced compared to the delay measurement result at the previous correction period. Also in this case, similarly to the above, the deviation of the correction cycle is corrected, and the start timing of the next correction cycle is corrected.

  As a result, even when a network delay situation or a change in the routing path occurs, the change can be detected and the correction period deviation of the clock can be corrected.

  By the way, in order to determine a steady delay, it is a condition that a delay equal to or greater than a threshold value continues for a predetermined number of times. Therefore, the delay is detected. There may not be. In this case, although there is a possibility that a steady delay has occurred, it cannot be determined that it is necessary to correct the shift of the correction period. For this reason, the clock adjustment amount calculation unit 14 detects a delay that is equal to or greater than the threshold by delay measurement when the correction period is reached. The counter value time stamp acquisition unit 12 is instructed to continue the retry with a period for the purpose (hereinafter referred to as a retry period).

  When receiving the instruction, the counter value time stamp acquisition unit 12 instructs the NTP packet processing unit 13 to retry the NTP access. As described above, the NTP packet processing unit 13 transmits an NTP packet and, when receiving a reply of the NTP packet from the NTP server, notifies the counter value time stamp acquisition unit 12 to that effect. Receiving this, the counter value timestamp acquisition unit 12 calculates the time as described above, obtains the base station reception time (clock counter value) of the NTP packet, and notifies the clock adjustment amount calculation unit 14 of it. Further, the NTP packet transmission / reception processing unit 13 notifies the clock adjustment amount calculation unit 14 of the server transmission time acquired from the NTP packet. The NTP packet transmission / reception processing unit 13 performs the above processing over a predetermined number of NTP accesses (here, 100 accesses).

  The clock adjustment amount calculation unit 14 performs delay measurement in the same manner as described above using the samples (sample number: 100) obtained in this way. That is, the sample with the highest reliability is extracted, and the access result obtained by doubling the delay is used as the delay measurement result of the current NTP access cycle.

  Then, the clock adjustment amount calculation unit 14 compares the delay measurement result (last delay measurement result before the correction cycle) measured during the previous correction cycle with the current delay measurement result. The clock adjustment amount calculation unit 14 indicates that when the delay measurement result difference is equal to or greater than a predetermined threshold continuously for a predetermined number of times, a steady delay variation due to a change in the routing path or the like has occurred. Judge. In this case, as described above, the clock adjustment amount calculation unit 14 performs a process of correcting the shift of the correction period, and newly sets the time as the starting point of the correction period. Specifically, for example, the counter value held by the counter value timestamp acquisition unit 12 and used for detection of the correction cycle is cleared. Thereafter, each unit of the radio base station apparatus continues the clock monitoring operation as usual.

  On the other hand, if the clock adjustment amount calculation unit 14 cannot determine that “the difference between the delay measurement results has been continuously greater than or equal to a predetermined threshold value for a predetermined number of times”, the clock adjustment amount calculation unit 14 counts the counter value time stamp so as to continue the retry. The acquisition unit 12 is instructed. Upon reception of this, the counter value time stamp acquisition unit 12 instructs the NTP packet processing unit 13 to execute NTP access retry as described above. The subsequent processing is the same as described above.

  FIG. 6 is a diagram illustrating an example of the relationship between the retry period and the correction period in the present embodiment. FIG. 6 shows a case where the starting point of the correction cycle is changed by performing a retry and obtaining an effective sample.

  The counter value time stamp acquisition unit 12 calculates a time based on the counter value from the source oscillation counter unit 11, and performs timer management of the retry period. When the counter value time stamp acquisition unit 12 recognizes that the retry period has expired, the counter value time stamp acquisition unit 12 notifies the clock adjustment amount calculation unit 14 to that effect. If a valid sample cannot be acquired before the retry period expires, the clock adjustment amount calculation unit 14 controls the RF unit 4 to stop wireless transmission, for example. The retry period is, for example, about 1 hour, and can be changed by tuning parameters.

  As described above, in the present embodiment, the delay of the transmission path with the NTP server is monitored in the NTP access period that is a shorter period than the correction period that is the period for correcting the internal clock, and as a result, Is used to correct the shift of the correction cycle. As a result, even when a delay variation (increase or decrease) occurs in the communication section, it is possible to detect the variation and correct the start timing of the correction cycle to keep the correction cycle constant. Thereby, the selection criteria for the correction data to be acquired can be dynamically changed.

  Further, in the present embodiment, it is assumed that the correction period corresponding to the delay is corrected, so that it is possible to cope with a network delay and a change in the routing route.

  In addition, when it is not possible to determine that the fluctuation is a steady delay by the correction period, the delay measurement (retry) is further performed by increasing the NTP access frequency, and the status of the network delay is grasped in the same manner as described above. It is possible to correct the shift of the correction cycle according to the delay variation. Therefore, it is possible to correct the shift of the correction cycle regardless of the network delay state or the timing of occurrence of the change of the routing path.

  As described above, the clock correction period correction method according to the present invention is useful for a base station that corrects an internal clock, and is particularly suitable for a base station that performs correction using an NTP server.

DESCRIPTION OF SYMBOLS 1 IP I / F part 2 Clock correction part 3 Reference clock source 4 RF part 11 Source oscillation counter part 12 Counter value time stamp acquisition part 13 NTP packet processing part 14 Clock adjustment amount calculation part

Claims (4)

A clock correction period correction method in a radio base station apparatus that corrects the internal clock of its own apparatus by periodically accessing an NTP server,
An NTP access step for performing an NTP access for transmitting an NTP packet to the NTP server and receiving a response to the transmission of the NTP packet over a first number of times;
An NTP server delay determining step of extracting an access result having the highest reliability from the execution results of the NTP access step and determining the extracted result as a transmission path delay to the NTP server;
Including
The NTP access step and the NTP server delay determination step are repeatedly executed in an NTP access cycle that is shorter than a correction cycle that is a cycle for correcting an internal clock,
further,
When it is determined that the difference between the transmission line delay determined in the NTP server delay determination step and the transmission line delay at the previous correction period is equal to or greater than a predetermined threshold over the second consecutive number of times, the correction is performed. Correction cycle adjustment step for correcting the shift of the cycle,
Including a clock correction period correction method. In the correction cycle adjustment step, the difference is equal to or greater than a predetermined threshold value, but the deviation of the correction cycle is not corrected by determining that the number of times has not reached the second number of consecutive times. A retry step for executing the NTP access step, the NTP server delay determination step and the correction cycle adjustment step over a predetermined retry cycle;
When the retry step is executed, the difference between the transmission line delay determined in the NTP server delay determination step and the transmission line delay in the previous correction period is equal to or greater than a predetermined threshold over the second consecutive number of times. When determined, a correction cycle starting point setting step for setting the time point as the starting point of the correction cycle;
The clock correction period correction method according to claim 1, further comprising: A wireless base station device that corrects the internal clock of its own device by periodically accessing the NTP server,
An NTP access that manages a correction cycle that is a cycle for correcting the internal clock , transmits an NTP packet to the NTP server and receives a response to the transmission of the NTP packet in an NTP access cycle shorter than the correction cycle; Counter value timestamp acquisition means for executing
NTP packet processing means for performing the NTP access over a first number of times;
The access result with the highest reliability is extracted from the execution results of the NTP access, the extraction result is determined as a transmission line delay to the NTP server, and the determined transmission line delay and the previous correction period A clock adjustment amount calculating means for correcting the shift of the correction period when it is determined that the difference from the transmission line delay is equal to or greater than a predetermined threshold over a second consecutive number of times;
A radio base station apparatus comprising: The clock adjustment amount calculation means further includes:
When the difference is equal to or greater than a predetermined threshold, but the correction period is not corrected by determining that the number of times has not reached the second number of consecutive times, the counter value timestamp acquisition unit Instructing to retry NTP access over a predetermined retry period,
Further, when it is determined that the difference has exceeded the predetermined threshold over the second number of consecutive times due to the retry, the correction period deviation is corrected, and the time point is set as the starting point of the correction period. ,
The radio base station apparatus according to claim 3.

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