JP2015023337A - Base station and synchronization method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base station and its synchronization method that are able to restrain the consumption of resources while maintaining the accuracy of a frame clock even if trouble has occurred in communication with a GPS satellite.SOLUTION: A base station 110 according to the invention is a base station for performing radio communication and frame synchronization with a radio terminal 104. The base station comprises: a GPS signal receiving unit 122 for receiving a GPS signal from a GPS satellite 102 to output an IPPS signal; a hold-over circuit 124 for outputting a pseudo IPPS signal when the IPPS signal is lost; an oscillator 140 for counting the number of clocks of the IPPS signal and the number of clocks of the pseudo IPPS signal; a difference calculation unit 142 for calculating the difference between the number of clocks of the IPPS signal and the number of clocks of the pseudo IPPS signal; and a synchronization determination unit 116 for adding the difference and for making the base station execute frame synchronization if the added difference reaches a predetermined value or more while the IPPS signal is lost.

Description

  The present invention relates to a base station that performs wireless communication with a wireless terminal and frame synchronization with another base station, and a base station synchronization method that performs frame synchronization using a reception timing of a control signal received from another base station. About.

  FIG. 5 is a diagram for explaining synchronization of base stations. As shown in FIG. 5 (a), in the PHS (Personal Handy phone System), a GPS unit is mounted on a base station serving as a synchronization absolute reference, and the base stations 10a and 10b on which the GPS unit is mounted Transmission / reception timing synchronization (GPS synchronization) is performed using the phase of the 1PPS signal received from the satellite 12 as an absolute reference (for example, Patent Document 1).

  On the other hand, a base station not equipped with a GPS unit synchronizes transmission / reception timing by performing inter-base station synchronization (hereinafter referred to as frame synchronization) by receiving a control channel transmitted by a neighboring base station. ing. As shown in FIG. 5 (b), the base stations 11a and 11b not equipped with the GPS unit are optical line terminators for an IP (Internet Protocol) network and have an OLT (Optical Line Terminal) with absolute time accuracy. Synchronization may be performed by using a clock (synchronization source clock) supplied from the OLT 14 of the ONU (Optical Network Unit) as a frame clock.

JP 2001-339373 A

  As described above, the base station can maintain synchronized accuracy by using the clock from the OLT-ONU as a frame clock, but there are some areas where the OLT cannot be installed due to locational reasons. A base station in an area where the OLT is not installed generates a frame clock only from the 1PPS signal from the GPS satellite. In such a base station, if the GPS unit breaks down or the visibility of the GPS satellites deteriorates, the 1PPS signal cannot be received, and it becomes difficult to maintain the accuracy of the frame clock. When the frame clock deteriorates, synchronization cannot be maintained, and there is a possibility that the communication quality of the wireless terminal communicating with the own base station deteriorates or interference with the wireless terminal communicating with another base station occurs. In addition, if the operation of the base station is stopped due to a failure of the GPS unit, an area where communication is impossible occurs in the area.

  In order to prevent the above-described problems, the base station is provided with a holdover circuit that generates a pseudo 1PPS signal when the 1PPS signal from the GPS satellite is lost. However, the frame clock generated with reference to the pseudo 1PPS signal has lower synchronization frequency accuracy than the frame clock generated with reference to the 1PPS signal. For this reason, the phase is gradually shifted from the frame of the neighboring base station, and the synchronization accuracy with the neighboring base station is lowered.

  Therefore, in a situation where it is difficult to communicate with the GPS satellite 12, as shown in FIG. 5C, the base station 10b that cannot receive the 1PPS signal from the GPS satellite is frame-synchronized with the other base stations 10a in the vicinity. It is possible to make it. However, when performing frame synchronization, it is necessary to use a time slot used for communication with a wireless terminal. For this reason, if frame synchronization is frequently performed in order to maintain the accuracy of the frame clock, time slots, that is, resources allocated for communication with the wireless terminal are consumed.

  In view of such a problem, the present invention provides a base station capable of suppressing resource consumption while maintaining the accuracy of a frame clock even when communication with a GPS satellite is hindered. An object is to provide a synchronization method.

  In order to solve the above problems, a typical configuration of a base station according to the present invention is a base station that performs radio communication with a radio terminal and frame synchronization with another base station, and includes a GPS from a GPS satellite. A GPS signal receiving unit that receives a signal and outputs a 1PPS signal, a holdover circuit that outputs a pseudo 1PPS signal when the 1PPS signal is lost, a clock number of the 1PPS signal, and a clock number of the pseudo 1PPS signal are counted And a difference calculating unit for calculating a difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal, and the difference is added while the 1PPS signal is lost, and the added difference becomes equal to or greater than a predetermined value. And a synchronization determination unit that executes frame synchronization.

  In order to solve the above problems, a typical configuration of a base station synchronization method according to the present invention is a base station synchronization method in which frame synchronization is performed using reception timings of control signals received from other base stations. When the 1PPS signal included in the GPS signal from the GPS satellite can be received, the number of clocks of the 1PPS signal included in the GPS signal is counted, and while the 1PPS signal is lost, a pseudo 1PPS is detected by the holdover circuit. Output a signal, count the number of clocks of the pseudo 1PPS signal, calculate the difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal, and execute frame synchronization when the added difference exceeds a predetermined value It is characterized by.

  According to the present invention, it is possible to provide a base station and a synchronization method thereof capable of suppressing resource consumption while maintaining the accuracy of a frame clock even when communication with a GPS satellite is hindered. be able to.

It is a figure explaining the communication system containing the base station concerning this embodiment. It is a functional block diagram which illustrates the composition of the base station concerning this embodiment. It is a flowchart explaining the synchronization method of the base station concerning this embodiment. It is a figure explaining the count of the number of clocks, and its difference. It is a figure explaining the synchronization of a base station.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram for explaining a communication system 100 including a base station 110 according to the present embodiment. FIG. 2 is a functional block diagram illustrating the configuration of the base station 110 according to the present embodiment. Hereinafter, the base station 110 and the synchronization method thereof according to the present embodiment will be described with reference to the communication system 100 shown in FIG.

  As shown in FIG. 1, in the communication system 100, a plurality of base stations 110a, 110b, 110c, 110d, and 110e are installed in an area 100a. The base stations 110a to 110e perform wireless communication with the wireless terminal 104 (see FIG. 2). Further, since the OLT is not installed in this area 100a, the base stations 110a to 110e generate a frame clock from the 1PPS signal included in the GPS signal from the GPS satellite 102 (see FIG. 2). Since base stations 110a to 110e all have the same configuration, unless otherwise specified, base stations 110a to 110e are referred to as base stations 110 in the following description.

  As shown in FIG. 2, the base station 110 includes a control unit 112. The control unit 112 manages and controls the entire base station 110 by a semiconductor integrated circuit including a central processing unit (CPU). As will be described later, in this embodiment, the control unit 112 also functions as a clock control unit 114 and a synchronization determination unit 116.

  The GPS signal receiving unit 122 receives a GPS signal from the GPS satellite 102 via the GPS antenna 122a, and outputs a 1PPS signal included therein. The 1PPS signal included in the GPS signal is transmitted to the clock control unit 114 via the holdover circuit 124. The holdover circuit 124 generates a pseudo 1PPS signal (HO_1PPS signal) when the 1PPS signal (GPS signal) from the GPS satellite 102 is not received, that is, when the 1PPS signal is lost, and the clock control unit 114 The circuit that outputs to

  The clock controller 114 refers to the transmitted 1PPS signal and adjusts the control voltage applied to the voltage controlled oscillator 126 (VCTCXO) that generates the basic clock. Thereby, the clock speed of the voltage controlled oscillator 126 is controlled, and the clock synchronization of the base station 110 is performed. The basic clock generated by the voltage controlled oscillator 126 is transmitted to the frame clock generator 128. The frame clock generation unit 128 generates a frame clock with reference to the basic clock. The frame clock generated by the frame clock generation unit 128 is transmitted to the baseband unit 130.

  The baseband unit 130 performs analog / digital conversion on the baseband signal and performs processing such as frame synchronization and channel decoding. The wireless communication unit 132 performs wireless communication with the wireless terminal 104 such as a PHS terminal via the communication antenna 132a and frame synchronization with other base stations 110 (eg, the base station 110b illustrated in FIG. 2). Do. Further, the control channel of the other base station 110 b acquired by communication by the wireless communication unit 132 is transmitted to the control unit 112 via the baseband unit 130.

  As described above, the base station 110 in the area where the OLT is not installed as in the present embodiment generates a frame clock based on the 1PPS signal from the GPS satellite 102. For this reason, if the 1PPS signal cannot be received due to a malfunction of the GPS signal receiving unit 122, it becomes difficult to maintain the accuracy of the basic clock and thus the frame clock, and various problems such as deterioration of communication quality of the wireless terminal 104 occur. There is a fear. For this reason, in a situation where it is difficult to communicate with the GPS satellite 102, it is necessary to frame-synchronize the base station 110 with other base stations 110 in the vicinity thereof. The time slot used for communication is used. Therefore, if frame synchronization is frequently performed, resources for wireless communication with the wireless terminal 104 are consumed.

  In order to suppress the consumption of resources due to frequent frame synchronization, it is desirable to maintain the holdover state in which the basic clock and thus the frame clock are generated by the pseudo 1PPS signal by the holdover circuit 124 as long as possible. However, the frame clock generated with reference to the pseudo 1PPS signal has lower synchronization frequency accuracy than the frame clock generated with reference to the 1PPS signal. For this reason, if the holdover state is continuously maintained, the consumption of resources can be suppressed, but the phase is gradually shifted from the frame of the neighboring base station, and the synchronization accuracy with the neighboring base station is lowered. Therefore, in the present embodiment, there is provided a base station 110 that can suppress resource consumption while maintaining the accuracy of the frame clock even when there is a problem in communication with the GPS satellite 102.

  As shown in FIG. 2, as a feature of the present embodiment, the base station 110 further includes an oscillator 140, a difference calculation unit 142, and a memory unit 144, and the control unit 112 functions as the synchronization determination unit 116. The oscillator 140 is used to count the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal. The difference calculation unit 142 calculates the difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal.

  The memory unit 144 includes a ROM, a RAM, a flash memory, and the like, and stores a program executed by the control unit 112. In the present embodiment, the memory unit 144 stores the number of clocks of the 1PPS signal counted using the oscillator 140. Further, the control unit 112 functions as the synchronization determination unit 116 and adds the difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal while the 1PPS signal is lost, and the added difference becomes equal to or greater than a predetermined value. Then execute frame synchronization.

  FIG. 3 is a flowchart for explaining a synchronization method of the base station 110 according to the present embodiment. FIG. 4 is a diagram for explaining the counting of the number of clocks and the difference thereof, FIG. 4 (a) is a diagram for explaining the counting of the number of clocks of the 1PPS signal, and FIG. 4 (b) is the number of clocks of the pseudo 1PPS signal. FIG. 4C is a diagram for explaining the calculation of the difference between them.

  As shown in FIG. 3, in the base station synchronization method according to the present embodiment, first, the control unit 112 determines whether or not a GPS signal, that is, a 1PPS signal is received by the GPS signal receiving unit 122 (step S202). . If a GPS signal has been received in step S202 (YES in step S202), the base station 110a performs GPS synchronization (step S204).

  In the present embodiment, when performing GPS synchronization, the difference calculation unit 142 uses the oscillator 140 to count the number of clocks of the 1PPS signal included in the received GPS signal (step S206). Specifically, as shown in FIG. 4A, the number of clocks until the 1PPS signal is counted by the pulse of the oscillator 140 and the next 1PPS signal is received is the number of clocks per second. In FIG. 4A, the clock number A of the 1PPS signal is a (count). The counted number of clocks of the 1PPS signal is stored in the memory unit 144 by the difference calculation unit 142 (step S208).

  On the other hand, if the GPS signal has not been received (NO in step S202), that is, if the 1PPS signal has been lost, the control unit 112 starts holdover in which a pseudo 1PPS signal is output by the holdover circuit 124 (step S210). ). At this time, the difference calculation unit 142 uses the oscillator 140 to count the number of clocks of the pseudo 1PPS signal output by the holdover circuit 124 (step S212).

  Since the pseudo 1PPS signal is not as accurate as the 1PPS signal of a GPS satellite, errors such as α1 and α2 occur as shown in FIG. As described above, 1 / a which is the time per count is calculated by counting the number of clocks of the 1PPS signal in step S206. Thereby, the pseudo 1PPS signal is counted by the pulse of the oscillator 140, and 1 second + α, which is the time until the next pseudo 1PPS signal is output, is divided by 1 / a which is the time per count, The number of clocks B of the pseudo 1PPS signal is calculated as a (1 second + α) (count).

  When the clock number B of the pseudo 1PPS signal is calculated in step S212, the difference calculation unit 142 reads the clock number of the 1PPS signal counted in step S206 and stored in the memory unit 144, and the clock number of the 1PPS signal and the pseudo number of the 1PPS signal are simulated. The difference from the number of clocks of the 1PPS signal is calculated (step S214). The synchronization determination unit 116 determines whether or not the calculated difference is greater than or equal to a predetermined value (step S216). If the difference is less than the predetermined value (NO in step S216), the control unit 112 performs steps S212 to S212. Repeat S216.

  Here, the difference is less than the predetermined value (NO in step S216), and while steps S212 to S216 are repeated, synchronization determination unit 116 continues to add the difference calculated in step S216 (step S218). If the pseudo 1PPS signal output at the time of holdover is continuously counted, as shown in FIG. 4C, the difference between the count number of the 1PPS signal and the pseudo 1PPS signal gradually increases. As a result of continuing to add the difference, when it becomes equal to or greater than a predetermined value (YES in step S216), the synchronization determination unit 116 uses the reception timing of the control signal received from the other base station to determine the frame of the base station 110. Synchronization is executed (step S222).

  According to the above configuration, the holdover state is maintained when the difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal is less than a predetermined value, that is, the clock shift width is within an allowable range. Frame synchronization is performed when the difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal is equal to or greater than a predetermined value, that is, when the clock shift width exceeds the allowable range.

  As described above, according to the base station 110 and its synchronization method of the present embodiment, the holdover state is continued while the clock accuracy of the pseudo 1PPS signal is maintained, and the frame synchronization is performed when the clock accuracy decreases. For example, the synchronization interval of frame synchronization, which has been conventionally performed every 1 hour, can be extended every 2 hours or every 3 hours. Therefore, the free time slots can be allocated for communication with the wireless terminal 104, and resources can be used effectively. Therefore, even when communication with the GPS satellite 102 is hindered, it is possible to suppress resource consumption while maintaining the accuracy of the clock and thus the frame clock.

  In the present embodiment, the configuration in which the number of clocks of the 1PPS signal stored in the memory unit 144 is read and the difference between the number of clocks of the 1PPS signal and the pseudo 1PPS signal is calculated is exemplified. May be added. For example, in a situation where GPS synchronization is possible, the count value (number of clocks) of the oscillator 140 per 1 PPS signal for each predetermined temperature (for example, every 5 ° C.) in the base station 110 is tabulated and stored in the memory unit 144. . As a result, when GPS synchronization becomes impossible, correction corresponding to a temperature change during the holdover operation, that is, temperature correction of the count value can be performed, and more accurate difference (deviation width) can be detected.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention relates to a base station that performs wireless communication with a wireless terminal and frame synchronization with another base station, and a base station synchronization method that performs frame synchronization using a reception timing of a control signal received from another base station. Is available as

10a, 10b, 11a, 11b ... base station, 12 ... GPS satellite, 14 ... OLT, 100 ... communication system, 100a ... area, 102 ... GPS satellite, 104 ... wireless terminal, 110 / 110a / 110b / 110c / 110d / 110e ... base station, 112 ... control unit, 114 ... clock control unit, 116 ... synchronization determination unit, 122 ... GPS signal reception unit, 122a ... GPS antenna, 124 ... holdover circuit, 126 ... voltage controlled oscillator, 128 ... frame clock generation , 130 ... Baseband part, 132 ... Wireless communication part, 132a ... Communication antenna, 140 ... Oscillator, 142 ... Difference calculation part, 144 ... Memory part

Claims (2)

A base station that performs wireless communication with a wireless terminal and frame synchronization with another base station,
A GPS signal receiving unit that receives a GPS signal from a GPS satellite and outputs a 1PPS signal;
A holdover circuit that outputs a pseudo 1PPS signal when the 1PPS signal is lost;
An oscillator for counting the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal;
A difference calculating unit for calculating a difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal;
A synchronization determination unit that adds the difference while losing the 1PPS signal, and executes the frame synchronization when the added difference exceeds a predetermined value;
A base station comprising: A base station synchronization method for performing frame synchronization using a reception timing of a control signal received from another base station,
When the 1PPS signal included in the GPS signal from the GPS satellite can be received, the number of clocks of the 1PPS signal included in the GPS signal is counted,
While losing the 1PPS signal,
A pseudo 1PPS signal is output by the holdover circuit,
Counting the number of clocks of the pseudo 1PPS signal, and calculating a difference between the number of clocks of the 1PPS signal and the number of clocks of the pseudo 1PPS signal;
The base station synchronization method, wherein the frame synchronization is performed when the added difference becomes equal to or greater than a predetermined value.

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