JP2019054479A - Base station device, radio communication system, and frequency correction method - Google Patents

Abstract

To provide a base station device, a radio communication system, and a frequency correction method capable of correcting oscillation frequency easily and accurately, for frequency drift due to long-term deterioration of an oscillator.SOLUTION: A base station device includes an oscillator 1621 generating a clock signal of first oscillation frequency, a frequency measurement part 1640 for receiving first and second frequency measurement signals transmitted from other base station device, measuring the frequency difference of oscillation frequencies of clock signals of the base station device and other base station device, on the basis of the difference of transmission times of the first and second frequency measurement signals in other base station device, and the difference of first and second reception times, extracting the operation period of other base station device from the first frequency measurement signal, and measuring the operation period of the base station device, a clock correction value calculation part 1641 for calculating a correction value on the basis of the frequency difference and the operation period of other base station device, and a clock correction part 165 for correcting the first oscillation frequency on the basis of the correction value.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a base station apparatus, a radio communication system, and a frequency correction method.

  In LTE (Long Term Evolution), for example, a TDD (Time Division Duplex) method (hereinafter sometimes referred to as “TD-LTE”) and an FDD (Frequency Division Duplex) method (hereinafter referred to as “FDD-LTE”). There are two communication methods.

  TD-LTE is a communication method that uses radio resources in a time-division manner, for example, in the communication direction from the base station apparatus to the terminal apparatus (downlink direction) and the communication direction from the terminal apparatus to the base station apparatus (uplink direction). In TD-LTE, the ratio between the uplink direction and the downlink direction can be changed, so that radio resources can be efficiently used in areas where use is concentrated. However, in the base station apparatus using TD-LTE, the output timing of the radio frame at the antenna end may be matched among a plurality of base station apparatuses. Therefore, the base station apparatus may perform synchronization control by PTP (Precision Time Protocol).

  PTP is a time synchronization protocol standardized as IEEE (The Institute of Electrical and Electronics Engineers) 1588. In PTP, it is possible to synchronize the time of the PTP slave with the time of the PTP master by exchanging messages between the PTP master (for example, PTP grand master) and the PTP slave (for example, base station apparatus).

  FIG. 19 is a diagram illustrating an example of a time synchronization method using PTP. The PTP master periodically sends an announcement message to the PTP slave. Further, the PTP master transmits a Sync message to the PTP slave at the transmission time T1, and the PTP slave receives the Sync message at the reception time T2. The PTP master transmits information (or time stamp information) of the transmission time T1 using the Sync follow up message. On the other hand, the PTP slave transmits a Delay Request message to the PTP master at transmission time T3, and the PTP master receives the Delay Request message at reception time T4. The PTP master transmits information on the reception time T4 to the PTP slave using the Delay Response message.

  The PTP slave calculates an average transmission line delay (= ((T4-T1)-(T3-T2)) / 2) using times T1 to T4. Then, the PTP slave calculates a correction value (= T2−T1−average transmission line delay) using the times T1 and T2 and the average transmission line delay. The PTP slave can obtain a time synchronized with the time of the PTP master by adding a correction value to the time of the local station.

  FIG. 20 is a diagram illustrating an example of PTP synchronization by a BC (Boundary Clock) method. The BC method is a method in which synchronization control is performed in order from the upper layer, for example. In the example of FIG. 20, synchronization control is first performed on the switch 1, and then synchronization control is performed on the switch 2 and finally on the PTP slave. By the BC method, for example, concentration on the PTP master can be avoided.

  Thus, in synchronous control using PTP, a PTP master, a switch, or the like may be hierarchically connected to each base station device, and a large-scale PTP network may be constructed.

  On the other hand, FDD-LTE is a communication method in which, for example, a base station apparatus and a terminal apparatus perform downlink and uplink wireless communication using different frequencies. FDD-LTE, for example, can cover a wide area continuously compared to the TD-LTE system, for example, while it is said that frequency interference occurs and communication failure is likely to occur in areas where use is concentrated. .

  Examples of the technique related to the synchronization control include the following. That is, there is a method of time-synchronizing non-synchronized base stations based on cell timing signal measurement values measured by a base station with better time-synchronization quality than non-synchronized base stations.

  This technology allows high speed, efficient and inexpensive synchronization between operating base stations without consuming additional physical resources, and also provides high precision synchronization. It can be done.

  Further, the external master clock is connected to the first and second devices that generate the clock signal, switches the clock signal of the first or second device based on an instruction from the control unit, and uses the clock signal after the switching. There is a clock generator that outputs a clock signal synchronized with the clock.

  According to this technique, the number of highly stable reference frequency oscillators can be reduced without deteriorating accuracy.

JP 2005-517340 A JP 2014-222857 A

  However, some base station devices are not connected to the PTP network and may not be able to perform synchronization control using PTP. For example, this may be the case when a base station apparatus is installed in an area where the traffic volume is smaller than in an urban area. In such a case, since the base station apparatus cannot perform synchronization control by PTP, time synchronization is performed in a self-running state.

  On the other hand, the base station apparatus includes a highly stable oscillator such as an OCXO (Oven Controlled Crystal Oscillator), and generates a clock signal having a high accuracy of the transmission frequency.

  However, the frequency stability of the highly stable oscillator gradually deteriorates due to long-term aging, although individual differences vary. Therefore, when the base station apparatus is in a free-running state, the frequency accuracy of the clock signal gradually deteriorates due to aging. For this reason, the base station apparatus may correct the changed frequency. However, when such correction is performed manually, it takes time for preparation and work. In addition, when such correction is performed manually, it may be impossible to obtain a clock signal having an accurate frequency.

  Based on the cell timing signal measurement value measured at the base station with good time synchronization quality described above, the technology for time synchronization of the base station that is not synchronized is concerned with the deterioration of frequency accuracy due to aging of the highly stable oscillator. There is no discussion at all. Therefore, in a base station having good time synchronization quality, if there is a frequency fluctuation due to aging deterioration of the highly stable oscillator, even if the base station that is not synchronized is time synchronized, the time synchronization accuracy of the base station is It may get worse.

  Further, the above-described technique for outputting a clock signal synchronized with an external master clock using the clock signal after switching is not discussed at all when the external master clock cannot be used and is in a free-running state. Therefore, in this technique, there is no discussion on how to deal with deterioration of frequency accuracy due to aging of the oscillator in a base station operating in a free-running state.

  Therefore, one disclosure is to provide a base station device, a radio communication system, and a frequency correction method that can easily correct an oscillation frequency against a frequency variation caused by an aging deterioration of an oscillator.

  Another object of the present invention is to provide a base station apparatus, a radio communication system, and a frequency correction method capable of accurately correcting an oscillation frequency with respect to a frequency variation due to an aging change of an oscillator.

  According to one disclosure, in a base station apparatus that performs radio communication with a terminal apparatus without receiving synchronization control from the synchronization control apparatus, an oscillator that generates a clock signal having a first transmission frequency, and receiving synchronization control from the synchronization control apparatus. First and second frequency measurement signals transmitted from other base station apparatuses not receiving the first and second frequency measurement signals transmitted from the other base station apparatus, respectively. When a second transmission time is extracted from the first and second frequency measurement signals, respectively, and the difference between the first and second transmission times and the first and second frequency measurement signals are received, respectively. Based on the difference between the first reception time and the second reception time, a frequency difference between oscillation frequencies of clock signals generated between the base station apparatus and the other base station apparatus is measured, and the first frequency measurement is performed. Signal A frequency measuring unit that extracts an operation period of the other base station apparatus and measures an operation period of the base station apparatus; an operation period of the frequency difference and the other base station apparatus; and an operation period of the base station apparatus And a clock correction value calculating unit for correcting the first transmission frequency based on the correction value.

  According to one disclosure, it is possible to easily correct the oscillation frequency with respect to frequency fluctuation due to aging of the oscillator. Further, according to one disclosure, it is possible to accurately correct the oscillation frequency with respect to the frequency fluctuation due to the secular change of the oscillator.

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system. FIG. 2 is a diagram illustrating an example of a cell range. FIG. 3 is a diagram illustrating a configuration example of the base station apparatus. FIG. 4 is a diagram illustrating a configuration example of the CLK card. FIG. 5 is a diagram illustrating an installation example of the base station apparatus. FIG. 6 (A) is a diagram illustrating an example of displacement of the frequency fluctuation amount of each BBU, and FIGS. 6 (B) to 6 (G) are diagrams illustrating examples of an operation period of each BBU. FIGS. 7A and 7C show examples of displacements of the frequency fluctuation amounts of BBB-A and BBU-F, and FIG. 7B shows an example of the operation period of BBU-F. FIG. 8A and FIG. 8B are diagrams showing examples of displacement of the frequency fluctuation amount of BBU-F with reference to BBU-A. FIG. 9 is a diagram illustrating an example of operation periods and correction values of BBU-A and BBU-F. FIG. 10A is a diagram illustrating an example of displacement of the frequency fluctuation amount of BBU-A and BBU-B, and FIG. 10B is a diagram illustrating an example of an operation period, a correction value, and the like. FIG. 11 is a flowchart showing an operation example in the base station apparatus. FIG. 12 is a flowchart showing an operation example in the base station apparatus. FIG. 13 is a sequence diagram illustrating an operation example in the wireless communication system. FIG. 14A shows a configuration example of a control frame, and FIG. 14B shows a configuration example of a response frame. FIG. 15 is a sequence diagram illustrating an example of frequency difference measurement. FIG. 16A shows a transmission request frame, and FIG. 16B shows a configuration example of a frequency measurement frame. FIG. 17 is a flowchart showing an operation example of correction value calculation processing. FIG. 18 is a diagram illustrating a configuration example of a wireless communication system. FIG. 19 is a diagram illustrating an example of message exchange by the PTP protocol. FIG. 20 is a diagram illustrating an example of the BC method.

  Hereinafter, modes for carrying out the present invention will be described. The following examples do not limit the disclosed technology. Each embodiment can be combined as appropriate within a range that does not contradict processing contents. Further, as terms and technical contents described in the present specification, terms and technical contents described in the specification as communication standards such as 3GPP (Third Generation Partnership Project) and IEEE may be used as appropriate.

[First Embodiment]
<Configuration example of wireless communication system>
FIG. 1 is a diagram illustrating a configuration example of a wireless communication system 10 according to the first embodiment. The wireless communication system 10 is a base station apparatus (hereinafter also referred to as “base station”) 100-A1 to 100-AN (N is an integer of 2 or more), 100-B1 to 100-BN, 100-C1. With ~ 100-CN. Hereinafter, the base stations 100-A1 to 100-AN, 100-B1 to 100-BN, and 100-C1 to 100-CN may be referred to as the base station 100.

  The wireless communication system 10 includes terminal devices (hereinafter also referred to as “terminals”) 200-A1 to 200-AN, 200-B1 to 200-BN, and 200-C1 to 200-CN. Hereinafter, the terminals 200-A1 to 200-AN, 200-B1 to 200-BN, and 200-C1 to 200-CN may be referred to as the terminal 200.

  Furthermore, the wireless communication system 10 includes PTP grand master devices (hereinafter also referred to as “grand master”) 300-1 and 300-2.

  Further, the wireless communication system 10 includes an SW (Switch) device (hereinafter also referred to as a “switch”) 400-A1 to 400-AN, 400-B1 to 400-BN, 400-C1 to 400-. CN is provided. Hereinafter, the switches 400-A1 to 400-AN, 400-B1 to 400-BN, and 400-C1 to 400-CN may be referred to as the switch 400.

  For example, the base station 100 is a wireless communication apparatus that performs wireless communication with a terminal 200 located within a communicable range of the local station and provides the terminal 200 with various services such as a call service and a web browsing service. is there.

  The base stations 100-A1 to 100-AN are connected to the grand master 300-1 via the switches 400-A1 to 400-AN. The base stations 100-A1 to 100-AN, the switches 400-A1 to 400-AN, and the grand master 300-1 form one PTP network. Furthermore, the base stations 100-B1 to 100-BN are also connected to the grand master 300-2 via the switches 400-B1 to 400-BN. The base stations 100-B1 to 100-BN, the switches 400-B1 to 400-BN, and the grand master 300-2 form one PTP network. Therefore, the base stations 100-A1 to 100-AN can be synchronized with the grand master 300-1 by the synchronization control by PTP. The base stations 100-B1 to 100-BN can also be synchronized with the grand master 300-2 by synchronization control using PTP.

  In FIG. 1, two PTP networks are formed, for example, the number of layers of the switches 400-A1 to 400-AN and 400-B1 to 400-BN, the base stations 100-A1 to 100-AN, The connection form of 100-B1 to 100-BN is taken into consideration.

  On the other hand, the base stations 100-C1 to 100-CN are not connected to the grand masters 300-1 and 300-2. The base stations 100-C1 to 100-CN generate an internal clock signal within the local station without performing PTP synchronization control with the grand masters 300-1 and 300-2, and based on the generated internal clock signal, Each block is operating. As described above, a state in which an internal clock signal is generated in the own station without performing PTP synchronization control and each process is performed in the own station using the internal clock signal may be referred to as a free-running state, for example. . Base stations 100-C1 to 100-CN are in a free-running state.

  In the first embodiment, the base stations 100-C1 to 100-CN are targeted. The base stations 100-C1 to 100-CN are base station apparatuses that perform wireless communication with the terminal 200 without receiving synchronization control from the grand masters 300-1 and 300-2, for example. Accordingly, the base stations 100-C1 to 100-CN perform wireless communication with the terminal 200 using, for example, the FDD scheme instead of the TDD scheme. In this case, if the base stations 100-C1 to 100-CN are connected to the grand masters 300-1 and 300-2 via the switch 400, the base stations 100-C1 to 100-CN can also perform wireless communication using the TDD scheme.

  The terminal 200 is a wireless communication device such as a feature phone, a smartphone, a tablet terminal, a personal computer, or a game device. In the example of FIG. 1, each terminal 200 represents an example in which wireless communication is performed with each base station 100. Within the communicable range (or cell range) of each base station 100, one base station 100 and a plurality of terminals 200 can perform wireless communication.

  The grand masters 300-1 and 300-2 perform, for example, a synchronization process using GPS (Global Positioning System) to acquire highly accurate time information. The grand masters 300-1 and 300-2 can perform synchronization processing by PTP on the switch 400 and the base stations 100-A1 to AN and 100-B1 to 100-BN to synchronize time and frequency. It is. Accordingly, the grand masters 300-1 and 300-2 are, for example, synchronous control devices that synchronize the base stations 100-A1 to AN and 100-B1 to 100-BN.

  The switch 400 has, for example, a hierarchical structure, and performs synchronization processing by PTP with the subordinate switches. For example, the lowest layer switch 400 is connected to the base station 100, and the switch 400 performs synchronization processing with the base station 100 by PTP.

  The switch 400 is connected to the core network 500, and transmits and receives user data and the like between the base station 100 and a server device connected to the core network 500, for example. Note that the switch 400 may be a switch dedicated to PTP, for example. In this case, a gateway device is connected between the core network 500 and the base stations 100-A1 to 100-CN, and user data and the like are transmitted / received via the gateway device.

<Example of cell range>
FIG. 2 is a diagram illustrating an example of a cell range. As illustrated in FIG. 2, a single large cell range in which wireless communication is possible with FDD-LTE may include a plurality of small cell ranges in which wireless communication is possible with TD-LTE.

  For example, in areas such as urban areas where there is a large amount of traffic, wireless communication is performed by TD-LTE, and in other areas, the amount of traffic is small, so that the cell is configured to perform wireless communication by FDD-LTE. May be designed. Thereby, for example, it is possible to suppress the occurrence of a communication failure in an urban area where the traffic volume is large, and it is possible to cover a larger area in an area where the traffic volume is small.

  In FIG. 2, the relationship with FIG. 1 is as follows, for example. That is, the base station 100-C1 capable of wireless communication by FDD-LTE has a large cell range. And the cell range of base station 100-A1-100-A3 in which radio | wireless communication is possible by TD-LTE is arrange | positioned in the cell range.

<Configuration example of base station device>
FIG. 3 is a diagram illustrating a configuration example of the base station 100-C1. Since the base stations 100-C1 to 100-CN are all the same in configuration, the configuration example of the base station 100-C1 is representatively shown.

  The base station 100-C1 includes a BBU (Base Band Unit: baseband processing unit) 101-C1 and an RRH (Remote Radio Head: radio unit) 102-C1.

  The BBU 101-C1 is, for example, a base station device or a part of the base station device, and performs processing related to wireless communication with the terminal 200-C. Examples of processing related to wireless communication include error correction coding processing and modulation processing. In addition, BBU101-C1 may be called base station 100-C1, for example.

  The BBU 101-C1 includes HWY (Highway) cards 110-1 to 110-m (m is an integer of 2 or more), a supervisory control card 120, a SW (Switch) card 130, a baseband processing card 140, a CPRI (Common Public Radio Interface). ) A termination card 150 and a CLK (Clock) card 160 are provided.

  In FIG. 3, “BBU # C1” to “BBU # CN” are indicated, but in the following, “BBU101-C1” to “BBU101-CN” are indicated. In addition, “HWY card # C1-1” to “HWY card # C1-m” are described, but in the following, “HWY card 110-1” to “HWY card 110-m” are described. Furthermore, although described as “monitoring control card # C1”, in the following, it is described as “monitoring control card 120”. The same applies to the other cards 130, 140, 150, 160.

  The HWY cards 110-1 to 110-m are, for example, transmission path interfaces. The HWY cards 110-1 to 110-m convert user data output from the SW card 130 into packet data that can be transmitted to an external network, such as S1, X2, and PTP.

  In the following, packet data and frame data may be used without distinction. Packet data or frame data may be referred to as a packet or a frame, respectively. Furthermore, packet data and frame data may be referred to as signals, for example.

  The HWY cards 110-1 to 110-m transmit the converted packet data to the core network 500 and other base stations 100-C2 to 100-CN via the switch 400. The HWY cards 110-1 to 110-m receive the packet data transmitted from the core network 500 and other base stations 100-C2 to 100-CN via the switch 400, and the user receives the packet data from the received packet data. Extract data. The HWY cards 110-1 to 110-m output the extracted user data to the SW card 130.

  The monitoring control card 120 monitors the entire BBU 101-C1 based on, for example, user data input / output to / from the SW card 130. For example, the monitoring control card 120 monitors whether or not the local station is in a self-running state or is in a state where synchronization control by PTP is performed. The monitoring may be performed as follows, for example. That is, the monitoring control card 120 detects that its own station is performing synchronization control by PTP when a message related to PTP is input to or output from the SW card 130. On the other hand, when the SW card 130 does not input / output a message related to PTP for a certain period of time, the monitoring control card 120 detects that its own station is in a free-running state.

  The monitoring control card 120 controls the switching destination of the SW card 130 with respect to the SW card 130, for example.

  The SW card 130 outputs, for example, user data output from the HWY cards 110-1 to 110-m to the baseband processing card 140 or the CLK card 160 in accordance with a switching instruction from the monitoring control card 120. Further, the SW card 130 outputs user data and the like output from the baseband processing card 140 and the CLK card 160 to the HWY cards 110-1 to 110-m according to the switching instruction. Further, the SW card 130 outputs the baseband signal output from the CPRI terminal card 150 to any one of the RRHs 102-C1 in accordance with the switching instruction. In the example of FIG. 3, one RRH 102 -C 1 is connected to the BBU 101 -C 1, but a plurality of RRHs 102 -C 1 may be connected. In accordance with the switching instruction of the card 120, the connection destinations of the plurality of RRHs 102-C1 are switched.

  The baseband processing card 140 performs error correction coding processing, modulation processing, etc. on the user data output from the SW card 130, converts it to a baseband signal, and converts the converted baseband signal into a CPRI terminal Output to the card 150. Further, the baseband processing card 140 performs demodulation processing, error correction decoding processing, and the like on the baseband signal output from the CPRI terminal card 150, converts the baseband signal into user data, etc., and converts the converted user data, etc. Is output to the SW card 130.

  The baseband processing card 140 performs each process in synchronization with the in-system reference clock signal (or internal clock signal) output from the CLK card 160.

  The CPRI terminal card 150 generates CPRI frame data including a baseband signal for the baseband signal output from the baseband processing card 140, and generates the generated CPRI frame data (or CPRI signal. Hereinafter, “CPRI frame data”). Is transmitted to the RRH 102-C1. Further, the CPRI terminal card 150 receives the CPRI frame data transmitted from the RRH 102-C1, and extracts a baseband signal from the received CPRI frame data. The CPRI terminal card 150 outputs the extracted baseband signal to the baseband processing card 140.

  The CPRI terminal card 150 performs each process in synchronization with the in-system reference clock signal output from the CLK card 160.

  The CLK card 160 generates an internal clock signal and outputs the generated internal clock signal to the baseband processing card 140 and the CPRI end card 150. At that time, the CLK card 160 transmits frequency measurement frame data to and from the other base stations 100-C2 to 100-CN via the SW card 130 or the like in the self-running base station 100-C1. (Or a frequency measurement signal; hereinafter, sometimes referred to as “frequency measurement frame data”) or the like can be used to generate a highly accurate internal clock signal. Details of the CLK card 160 will be described later.

  The RRH 102-C1 extracts a baseband signal from the CPRI frame data transmitted from the BBU 101-C1, and converts the extracted baseband signal into a radio signal in a radio band by performing frequency conversion processing or the like. RRH102-C1 transmits the radio signal after conversion to terminal 200-C1. Moreover, RRH102-C1 receives the radio signal transmitted from terminal 200-C1, and converts the received radio signal into a baseband signal of a baseband band by performing frequency conversion processing or the like. The RRH 102-C1 generates CPRI frame data including the baseband signal for the converted baseband signal, and transmits the generated CPRI frame data to the BBU 101-C1.

  The other base stations 100-C2 to 100-CN also include BBU101-C2 to 101-CN and RRH102-C2 to 102-CN, respectively. In this case, the configuration of each of the BBUs 101-C2 to 101-CN is, for example, the same as that of the BBU 101-C1.

<Example of CLK card configuration>
FIG. 4 is a diagram illustrating a configuration example of the CLK card 160. The CLK card 160 includes a PTP function unit 161, a PLL (Phase Locked Loop) function unit 162, an in-system reference timing generation unit 163, a CLK adjustment control unit 164, and a CLK correction unit 165.

  The PLL function unit 162 includes a phase comparator 1620, a high stability oscillator 1621, a loop filter 1622, a flash (FLASH) memory 1623, a DDS (Direct Digital Synthesizer) 1624, and a VCXO (Voltage-Controlled Crystal Oscillator). 1625.

  Furthermore, the CLK adjustment control unit 164 includes a frequency measurement unit 1640, a CLK (clock) correction value calculation unit 1641, and a memory 1642.

  The HWY card 110-1 includes an NW (Network) termination unit 111. FIG. 4 illustrates an example in which the CLK card 160 is connected to the HWY card 110-1. For example, as shown in FIG. 3, the CLK card 160 may be connected to the HWY card 110-1 via the SW card 130. In FIG. 4, the SW card 130 is omitted.

  The NW termination unit 111 is connected to other base stations 100-C2 to 100-CN via the switch 400. The NW termination unit 111 terminates packet data transmitted / received to / from other base stations 100-C2 to 100-CN. For example, the NW termination unit 111 performs the following processing.

  That is, the NW termination unit 111 receives packets transmitted from other base stations 100-C2 to 100-CN, and extracts a frame from the received packets. The NW termination unit 111 outputs the extracted frame to the frequency measurement unit 1640. Further, the NW termination unit 111 receives the frame output from the frequency measurement unit 1640 and generates packet data including the received frame. The NW termination unit 111 transmits the generated packet data to the other base stations 100-C2 to 100-CN.

  The NW termination unit 111 may transmit / receive a packet including a message related to PTP to / from the switch 400. In this case, the NW termination unit 111 extracts a message related to PTP from the packet received via the switch 400, and outputs the extracted message related to PTP to the PTP function unit 161. Further, the NW termination unit 111 generates a packet including this message for the message related to PTP output from the PTP function unit 161, and transmits the packet to the switch 400. The NW termination unit 111 transmits and receives a message related to PTP, for example, when the base station 100-C1 is connected to the grand masters 300-1 and 300-2 via the switch 400 and performs synchronization control by PTP. is there.

  For example, the PTP function unit 161 transmits / receives a message related to PTP to / from the switches 400-C1 to 400-CN and the grand masters 300-1 and 300-2 via the NW termination unit 111.

  In addition, the PTP function unit 161 performs synchronization processing using PTP based on the received message related to PTP. For example, the PTP function unit 161 acquires time information (T1 to T4) based on an announcement message, a Sync message (for example, FIG. 19), and calculates a correction value for the time information. The PTP function unit 161 outputs the calculated correction value to the in-system reference timing generation unit 163.

  Further, for example, the PTP function unit 161 calculates a transmission interval of a Sync follow up message (for example, FIG. 19), and generates a clock signal based on the calculated transmission interval. This clock signal is a clock signal synchronized with the grand masters 300-1 and 300-2 with high accuracy, for example. The PTP function unit 161 outputs the generated clock signal to the phase comparator 1620.

  The phase comparator 1620 performs phase comparison between the clock signal received from the PTP function unit 161 and the clock signal received from the VCXO 1625, and outputs the comparison result of the phase comparison to the loop filter 1622.

  For example, the high stability oscillator 1621 generates a clock signal having a constant frequency, and outputs the generated clock signal to the loop filter 1622 and the DDS 1624. This clock signal is, for example, a clock signal generated by the base station 100-C1. Note that the high stability oscillator 1621 is, for example, an OCXO. OCXO is called, for example, a crystal oscillator with a thermostatic bath, and generates a clock signal having an oscillation frequency with a frequency accuracy of ± 0.05 ppm defined by 3GPP at a relatively high temperature (70 degrees to 80 degrees). Is possible.

  The loop filter 1622 performs AD (Analogue to Digital) conversion on the comparison result output from the phase comparator 1620 on the basis of the clock signal from the high stability oscillator 1621, and outputs the comparison result after AD conversion to the DDS 1624. .

The flash memory 1623 stores, for example, a DDS value. The flash memory 1623 holds, for example, a frequency shift between the clock signal of the high stability oscillator 1621 and the clock signal extracted by the PTP function unit 161 and a DDS value corresponding to the frequency shift. For example, in the flash memory 1623, when the frequency deviation is “−50 ppb (parts per billion (= 1 × 10 ⁻⁹ ))”, the DDS value is “−5”, and “−40 ppb” is “−4”. ”,“ −30 ppb ”,“ −3 ”or the like is retained.

  The DDS 1624 has, for example, a waveform memory therein, and the data from the waveform memory is based on the phase corresponding to the phase comparison result from the loop filter 1622 and the frequency shift corresponding to the DDS value read from the flash memory 1623. Is read. At that time, the DDS 1624 reads data at the timing of the clock signal output from the high stability oscillator 1621. Thereby, for example, the oscillation frequency of the base station 100-C1 (for example, the frequency of the clock signal output from the high stability oscillator 1621) can be matched with the frequency of the clock signal extracted by the synchronization processing by PTP. . The DDS 1624 outputs a control voltage corresponding to the read data.

  When the base station 100-C1 is in a free-running state, for example, the DDS 1624 uses the DDS value stored in the flash memory 1623 without using the comparison result (or the output of the loop filter 1622) in the phase comparator 1620. To work with.

  For example, the VCXO 1625 generates the in-system reference clock signal CLK whose frequency is controlled by the control voltage output from the DDS 1624. The VCXO 1625 outputs the generated in-system reference clock signal CLK to the in-system reference timing generation unit 163, the in-system function unit 170, the phase comparator 1620, and the PTP function unit 161. The PTP function unit 161 or the like can perform processing in synchronization with the in-system reference clock signal CLK output from the VCXO 1625.

  The in-system reference timing generation unit 163 generates a reference timing signal in the base station 100-C1 based on the correction value received from the PTP function unit 161 and the in-system reference clock signal received from the PLL function unit 162. . For example, the in-system reference timing generation unit 163 includes a timer inside, adds a correction value to the time information counted by the timer, corrects the time information, and generates a reference timing signal corresponding to the corrected time information. Generate. The timer represents the time in the base station 100-C1, for example.

  The in-system function unit 170 is the baseband processing card 140 and the CPRI terminal card 150 in the example of FIG. The in-system function unit 170 may be another block in the base station 100-C1, for example. The in-system functional unit 170 performs each process according to the reference timing signal in synchronization with the reference clock signal CLK.

  Based on the frame received from the NW termination unit 111, the frequency measurement unit 1640 measures the frequency difference between the other base stations 100-C2 to 100-CN and the own station 100-C1. Further, the frequency measurement unit 1640 extracts the operation periods of the other base stations 100-C2 to 100-CN from the frame received from the NW termination unit 111. The operation period indicates, for example, a period from when the base station 100-C1 to 100-CN starts operation or when the correction according to the first embodiment is performed to the current time. The frequency measurement unit 1640 outputs the measured frequency difference and the extracted operation period to the CLK correction value calculation unit 1641.

  The CLK correction value calculation unit 1641 calculates a correction value (clock correction value) based on the frequency difference and the operation period of the other base stations 100-C2 to 100-CN. The CLK correction value calculation unit 1641 outputs the calculated correction value to the CLK correction unit 165 and the memory 1642.

  The memory 1642 holds, for example, correction values. The memory 1642 may be a non-volatile memory, for example.

  The CLK correction unit 165 acquires the oscillation frequency of the high stability oscillator 1621 from the high stability oscillator 1621 and corrects the acquired transmission frequency based on the correction value received from the CLK correction value calculation unit 1641. The CLK correction unit 165 controls the high stability oscillator 1621 so as to operate at the corrected oscillation frequency, for example, by rewriting a set value for the high stability oscillator 1621. Also, the CLK correction unit 165 changes the correspondence relationship between the frequency shift and the DDS value in the flash memory 1623 so as to correspond to the corrected oscillation frequency, and stores the changed correspondence relationship. For example, the CLK correction unit 165 may store the correspondence relationship after the change by setting the numerical value obtained by adding the correction value to “−50 ppb” of the frequency shift as the frequency shift after the change.

  In the base station 100-C1, for example, the PTP function unit 161 may be an FPGA (Field Programmable Gate Array) 1611. For example, the FPGA 1611 can implement each function of the PTP function unit 161 by executing a program stored in the internal memory.

  Further, in the PLL function unit 162, the phase comparator 1620, the loop filter 1622, the DDS 1624, and the VCXO 1625 may be, for example, a DSP (Digital Signal Processor) 1626. Further, the in-system reference timing generation unit 163 may be a CPU (Central Processing Unit) 1631. The CPU 1631 can execute the function of the in-system reference timing generation unit 163 by, for example, reading and executing a program stored in a memory (such as the memory 1642).

  Further, the frequency measurement unit 1640 and the CLK correction value calculation unit 1641 may be, for example, the CPU 1643. Further, the CLK correction unit 165 may be a CPU 1651, for example. For example, the CPUs 1643 and 1651 can execute the functions of the CLK correction value calculation unit 1641 and the CLK correction unit 165 by reading and executing a program stored in a memory (memory 1642 or the like), for example. Note that the CPUs 1631, 1643, and 1651 may be the same CPU, for example.

  Note that the FPGA 1611 may be a processor or controller such as a CPU or DSP. The DSP 1626 may also be a processor or controller such as a CPU or FPGA. Further, the CPUs 1631, 1643, and 1651 may be processors or controllers such as DSPs and FPGAs.

<Operation example>
Next, an operation example of the base station 100 will be described. First, an installation example of the base station 100 will be described. Next, an example of correcting the transmission frequency will be described. Finally, an operation example of the base station 100 will be described.

<Example of installation of base station 100>
FIG. 5 is a diagram illustrating an installation example of the base station 100. As shown in FIG. 5, base stations 100-B to 100-G are installed as adjacent base stations of the base station 100-A.

  For example, the base station 100-A in FIG. 5 corresponds to the base station 100-C1 in FIG. The base stations 100-B to 100-G in FIG. 5 may correspond to, for example, any of the base stations 100-C2 to 100-CN in FIG. It may correspond to any of -B1 to 100-BN.

  That is, base station 100-A is a self-running base station. However, any of the base stations 100-B to 100-G may be a self-running base station, and at least one of the base stations 100-B to 100-G is connected to the grand masters 300-1 and 300-2 via the switch 400 to perform PTP synchronization. May be a base station in which

  In the following, base station 100-A may be referred to as BBU-A. Similarly, the base stations 100-B to 100-G may be referred to as BBU-B to BBU-G, respectively.

<Example of correction of transmission frequency>
Next, an example of correcting the transmission frequency for the high stability oscillator 1621 will be described. Two correction examples will be described.

<1. Correction Example 1>
FIG. 6A is a graph showing an example of the frequency fluctuation amount of each BBU-A to BBU-G. In FIG. 6A, the horizontal axis represents an operation period based on BBU-A. The operation period is expressed in months. On the horizontal axis, “0” is a reference value, for example, when BBU-A starts operation. In FIG. 6A, the vertical axis represents the frequency fluctuation amount.

  Focusing on the displacement of BBU-A, the frequency fluctuation amount increases as the operation period elapses. When the operation period is “36 months”, the frequency fluctuation amount is “+0.05 ppm”.

  Focusing on the displacement of BBU-B, BBU-B has started operation when “12 months” have elapsed since the start of operation of BBU-A. In BBU-B, the frequency fluctuation amount gradually increases in the positive direction from “0”.

  Focusing on the displacement of BBU-F, after the operation of BBU-A is started, the operation starts when “6 months” elapses, and the frequency fluctuation amount gradually increases from “0” in the negative direction. .

  Furthermore, focusing on the displacement of BBU-G, the operation started “6 months” before the start of BBU-A operation, and when “24 months” passed (“18 months from the start of operation of BBU-A” ”), The correction in the first embodiment is performed. Therefore, BBU-G has a frequency variation amount of “0” and an operation period of “0”. Thereafter, the frequency fluctuation amount of BBU-G increases in the negative direction.

  FIG. 6B to FIG. 6G show the operation periods of BBU-B to BBU-G, respectively. In FIG. 6B to FIG. 6G, the operation period “0” represents the month in which each BBU-B to BBU-G started operation or the month in which correction was performed.

  The correction example 1 is an example in which the BBU-A calculates a correction value using the BBU-F.

  FIG. 7A is a graph showing an example of frequency fluctuation amounts of BBU-A and BBU-F. FIG. 7A shows a diagram in which the displacements of BBU-A and BBU-F shown in FIG. 6A are extracted. An example in which the BBU-A calculates a correction value of the oscillation frequency of the high stability oscillator 1621 of the BBU-A using the BBU-F will be described with reference to FIG. Both BBU-A and BBU-F are in a free-running state.

  For example, as shown in FIG. 7A, the frequency accuracy of the highly stable oscillator 1621 of BBU-A becomes “+0.05 ppm” at “36 months” (it is expected). “+0.05 ppm” is, for example, the maximum value of the frequency accuracy of the transmission frequency defined by 3GPP. In BBU-A, a frequency with a frequency accuracy exceeding this is not used. Therefore, in BBU-A, the oscillation frequency is corrected before a predetermined period when “36 months” have elapsed. In the example of FIG. 7A, BBU-A performs correction when “24 months” of “12 months ago” has elapsed.

  As shown in FIG. 7A, it is only necessary for BBU-A to be able to calculate the frequency fluctuation amount ΔE of BBU-A when “24 months” as the correction time has elapsed.

  However, BBU-A is in a free-running state and cannot directly detect that the frequency fluctuation amount is “0”, and the frequency fluctuation amount ΔE (hereinafter referred to as “frequency fluctuation amount” from “0”). It may not be directly detected (sometimes referred to as “absolute frequency variation ΔE”).

  However, it is possible for BBU-A to detect a difference ΔB in the amount of frequency fluctuation relative to BBU-F using BBU-F. Details will be described later with reference to FIG.

  Hereinafter, the “frequency difference” may be referred to as “frequency difference” or “frequency difference”. In some cases, the “frequency difference” and the “frequency difference” are not distinguished.

  Also, BBU-A is the same as BBU-F before “24 months” which is the correction time (when “18 months” before “6 months” in FIG. 7A). It is possible to detect the relative frequency difference between.

  In other words, in BBU-A, for example, at the start of operation, a future frequency fluctuation amount is expected to exceed “+0.05 ppm” in three years from the start of operation, and a predetermined time before that (FIG. 7 (A ) Can be used as the correction time, and a predetermined time before that can be used as the correction value calculation start time (“18 months” in the example of FIG. 7A). In the BBU-A, when the correction value calculation start time comes, for example, the relative frequency difference ΔA with the BBU-F is obtained by exchanging the frame with the BBU-F (FIG. 15), and the correction time is calculated. Then, a relative frequency difference ΔB between BBU-F is calculated.

  The frequency difference ΔA represents, for example, the frequency difference between BBU-A and BBU-F when the operation period of BBU-A is the correction amount calculation start time (or when the start time has elapsed). Further, the frequency difference ΔB represents, for example, a frequency difference between BBU-A and BBU-F when the operation period of BBU-A has reached the correction time (or when the correction time has elapsed).

  Next, BBU-A calculates the difference ΔC = ΔB−ΔA between the two frequency differences ΔA and ΔB. This difference ΔC represents the frequency fluctuation amount of BBU-A with respect to BBU-F in the period “6 months” between the correction value calculation start time and the correction time.

  FIG. 8A is a graph showing an example of the frequency fluctuation amount of BBU-F when BBU-A is used as a reference with respect to FIGS. 6A and 7A. In FIG. 8A, the vertical axis represents the frequency fluctuation amount, and the horizontal axis represents the operation period (number of months) of BBU-A. In FIG. 8A, the graph represented by the alternate long and short dash line represents the absolute difference (“deviation amount”) from the frequency variation amount “0”. FIG. 8B is a graph obtained by enlarging the operation period “6 months” to “24 months” in FIG. 8A.

  BBU-A wants to calculate the absolute frequency fluctuation amount ΔE from the frequency fluctuation amount “0”. On the other hand, BBU-A can calculate relative frequency differences ΔA and ΔB with respect to BBU-F. In addition, BBU-A calculated a frequency variation ΔC with respect to BBU-F of BBU-A when “6 months” of operation period “18 months” to “24 months” was operated.

  When attention is paid to FIG. 8B, when the transmission frequency is shifted by ΔC in the six months from the operation period “18 months” to “24 months” of the BBU-A, from the operation period “6 months” of the BBU-A to “ It is assumed that the transmission frequency is displaced by ΔX in 12 months up to “18 months”. In this case, ΔX can be calculated as follows.

ΔX = ΔC / 6 months × 12 months (1)
In the formula (1), “6 months” represents, for example, the operation period of the BBU-A from the start time of the correction value calculation of the BBU-A to the correction time. “12 months” represents, for example, the operation period of BBU-A (or BBU-F) from the operation period “0” of BBU-F to the start time for calculating the correction value of BBU-A. ΔX represents, for example, the amount of frequency fluctuation of BBU-A with respect to BBU-F when BBU-A is operated for 12 months.

  The operation time “0” of the BBU-F can be calculated by back-calculating the operation period of the BBU-F acquired by the BBU-A from the BBU-F at the correction value calculation start time or correction time. . Also, the BBU-A operation period at the time point “0” of the BBU-F is calculated as the difference between the BBU-A operation period and the BBU-F operation period at the correction value calculation start time or correction time. By doing so, calculation is possible.

  Here, ΔD is a frequency difference with respect to BBU-F of BBU-A at the time point of operation period “0” of BBU-F (the operation period of BBU-A is “6 months”). That is, ΔD represents, for example, the absolute frequency fluctuation amount during the operation period “6 months” of BBU-A. ΔD can be calculated as follows.

ΔD = ΔA−ΔX = ΔA−ΔC / 6 months × 12 months (2)
Accordingly, the absolute frequency fluctuation amount ΔE when the correction time “24 months” of BBU-A has elapsed can be calculated as follows.

ΔE = ΔD / 6 months × 24 months (3)
In Expression (3), “6 months” represents, for example, the BBU-A operation period at the time point “0” of the BBU-F operation period. “24 months” represents, for example, an operation period up to the correction time of BBU-A.

  That is, BBU-A can calculate the absolute frequency fluctuation amount ΔE from the frequency fluctuation amount “0” at the correction timing by using the frequency differences ΔA and ΔB with respect to BBU-F. This ΔE becomes, for example, a correction value for the oscillation frequency of the clock signal generated by the high stability oscillator 1621 of BBU-A.

  FIG. 9 shows frequency differences ΔA and ΔB between BBU-A and BBU-F, frequency fluctuation amount ΔC per 6 months, frequency difference ΔD at the time of operation period “0” of BBU-F, and 24 months after BBU-A The correction values ΔE are summarized in a table.

<2. Correction Example 2>
The correction example 2 is an example in which the BBU-A calculates the correction value ΔE using BBU-B.

  FIG. 10A shows a diagram in which the frequency fluctuation amounts of BBU-A and BBU-B are extracted from the example of the frequency fluctuation amount shown in FIG. In FIG. 10A as well, the vertical axis represents the frequency fluctuation amount, and the horizontal axis represents the operation period (number of months) based on BBU-A. The correction time and correction value calculation start time shown in FIG. 10A are the same as the correction time and correction value calculation start time shown in FIG. 6A, respectively.

  As shown in FIG. 10A, BBU-A calculates a frequency difference ΔB from BBU-B at the correction time (when the operation period “24 months” of BBU-A has elapsed). The calculation method will be described later. Further, BBU-A calculates a frequency difference ΔA from BBU-B at the correction length calculation start time (when the operation period “18 months” of BBU-A has elapsed).

  And BBU-A calculates the difference, and calculates the frequency fluctuation amount (DELTA) C (= (DELTA) B- (DELTA) A) with respect to BBU-F of BBU-A per six months. In this case, since ΔA = ΔB, ΔC = 0. Further, as is apparent from FIG. 10A, ΔD = ΔA. Therefore, BBU-A can calculate the absolute frequency fluctuation amount ΔE of the correction time as follows.

ΔE = ΔD / 12 months × 24 months (4)
In Expression (4), for example, “12 months” represents the BBU-A operation period at the operation start time “0” of BBU-B, and “24 months” represents the BBU-A correction period. ΔE is, for example, a correction value for the oscillation frequency of the BBU-A highly stable oscillator 1621 in this example.

  FIG. 10B shows the frequency differences ΔA and ΔB between BBU-A and BBU-F, the frequency variation ΔC per six months, the frequency difference ΔD at the time point “0” of the BBU-F operation period, and 24 of BBU-A. The correction value ΔE after the lapse of months is summarized in a table.

  The correction example 1 and the correction example 2 have been described above. As described above, the self-running BBU-A calculates the frequency differences ΔA and ΔB using the other BBU-B and BBU-F in the free-running state. And BBU-A calculates frequency difference (DELTA) D in the operation start time "0" of other BBU-B and BBU-F using frequency difference (DELTA) A, (DELTA) B. BBU-A uses the frequency difference ΔD to calculate a correction value ΔE at the correction time of BBU-A.

<Operation example of base station device>
11 and 12 are flowcharts illustrating an operation example of the base station 100-A. This operation example includes a correction calculation process (S18 in FIG. 12). FIG. 13 is a diagram illustrating a sequence example in the wireless communication system 10. FIG. 13 will be described as appropriate while describing FIG. 11 and FIG. 12.

  As shown in FIG. 11, when the base station 100-A starts processing (S10), it determines whether or not the own station is in a free-running state (or free-running operation) (S11). For example, the frequency measurement unit 1640 may detect by inquiring the monitoring control card 120 whether or not the own station is in a self-running state. Or the frequency measurement part 1640 may detect that it is a self-running state by confirming whether the frame regarding PTP is not received for a certain period in the NW termination | terminus part 111, for example.

  On the other hand, when the base station 100-A is in a self-running state (Yes in S11), the base station 100-A obtains the correction time of the high stability oscillator 1621 and the correction value calculation start time (S12).

  In the sequence example shown in FIG. 13, the base station (own station) 100-A determines a correction value calculation start time (S110) and a correction time (S120). That is, in FIG. 13, the base station 100-A determines the correction time and the correction value calculation start time at the time of the operation state (S100) before the correction value calculation start time.

  For example, the frequency measurement unit 1640 performs the following processing. That is, the frequency measurement unit 1640 reads the operation start time (or correction time) of the base station 100-A stored in the memory 1642, and sets the time when three years have elapsed from the operation start time as the correction time. Further, the frequency measuring unit 1640 sets the correction value calculation start time six months before the correction time. In the example of FIG. 13, the correction time is “December 2017”, and the correction value calculation start time is “June 2017”.

  Returning to FIG. 11, next, the base station 100-A determines whether or not the current date and time has reached the start time for calculating the correction value (S13). For example, the frequency measurement unit 1640 checks the current date and time with an internal timer, and determines whether the current date and time is the correction value calculation start time calculated in S12.

  When the current date and time has not reached the correction value calculation start time (No in S13), the base station 100-A waits until the start time is reached.

  On the other hand, when the current date and time reaches the correction value calculation start time (Yes in S13), the base station 100-A sets the synchronization state and correction time of each adjacent base station 100-B to 100-N to each adjacent time. The stations 100-B to 100-N are inquired (S14).

  For example, as illustrated in FIG. 13, the base station 100-A transmits a control frame to the adjacent base stations 100-B to 100-N when the current date and time is the correction value calculation start time (S110). . The base station 100-A inquires about the synchronization state and the correction timing in each of the adjacent base stations 100-B to 100-N using the control frame. The control frame is, for example, an inquiry frame (or an inquiry signal) that inquires about the synchronization state and correction timing of the other base stations 100-B to 100-N. The synchronization state indicates, for example, whether the local station is in a free-running state or in a state where synchronization is performed by PTP. The correction time is, for example, a correction time calculated by each adjacent base station 100-B to 100-N. When each of the adjacent base stations 100-B to 100-N receives the control frame, it generates a response frame (or a response signal, which may be referred to as a “response frame” hereinafter) including the synchronization state and the correction time. To base station 100-A. In the example of FIG. 13, the adjacent base stations 100 -B to 100 -N are all “self-running states”. In addition, the correction time is “October 2020” for the adjacent base station 100-B, “January 2018” for the adjacent base station 100-C, and “November 2017” for the adjacent base station 100-N. Yes.

  For example, the base station 100-A performs the following processing. That is, the frequency measurement unit 1640 generates a control frame when the correction value calculation start time comes, and outputs the generated control frame to the NW termination unit 111. The control frame is transmitted from the NW termination unit 111 to each adjacent base station 100-B to 100-N.

  FIG. 14A is a diagram illustrating a configuration example of a control frame. Specifically, the frequency measurement unit 1640 generates a control frame including a “synchronization state request instruction”, and outputs the control frame to the NW termination unit 111. The NW termination unit 111 generates a TCP packet including the control frame in a TCP (Transmission Control Protocol) payload area, and further generates an IP packet including the TCP packet in the IP payload area. The NW termination unit 111 transmits the generated IP packet to each of the adjacent base stations 100-B to 100-N. This IP packet may be referred to as a control frame, for example. The control frame may be another transport layer protocol such as UDP (User Datagram Protocol) or SCTP (Stream Control Transmission Protocol) instead of TCP.

  On the other hand, the base station 100-B that has received the control frame performs, for example, the following processing. That is, the NW termination unit 111 extracts a control frame including a “synchronization state request instruction” from the received IP packet, and outputs the extracted control frame to the frequency measurement unit 1640. When receiving the control frame, the frequency measuring unit 1640 confirms the synchronization state and the correction time according to the “synchronization state request”. The frequency measurement unit 1640 checks the synchronization state of the base station 100-B by making an inquiry to the monitoring control card 120, for example. In addition, the frequency measurement unit 1640 confirms the correction time by reading the correction time from the memory 1642. The frequency measurement unit 1640 generates a response frame including the synchronization state and the correction time. The frequency measurement unit 1640 outputs the generated response frame to the NW termination unit 111, and the NW termination unit 111 transmits an IP packet including the response frame to the base station 100-A.

  FIG. 14B is a diagram illustrating a configuration example of a response frame. Similarly to the control frame, the response frame is also included in the TCP payload area or the IP payload area. This IP packet may be referred to as a response frame, for example. In the response frame, other transport layer protocols such as UDP and SCTP may be used instead of TCP.

  Returning to FIG. 11, next, the base station 100-A determines whether or not all the adjacent base stations 100-B to 100-N are in a free-running state (S15). For example, the base station 100-A performs the following process. That is, the NW termination unit 111 extracts a response frame from the received IP packet and outputs the extracted response frame to the frequency measurement unit 1640. The frequency measurement unit 1640 receives the response frames transmitted from the adjacent base stations 100-B to 100-N, and determines whether or not all the synchronization states included in the response frames are in a free-running state.

  When all the adjacent base stations 100-B to 100-N are in a free-running state (Yes in S15), the base station 100-A has a frequency between the base station 100-A and each adjacent base station 100-B to 100-N. The difference is measured, and the operation period of the adjacent base station is acquired (S16). In the example of FIG. 7A, the frequency difference is the frequency difference ΔA between the own station 100-A and the adjacent base station 100-F at the correction value calculation start time (“18 months”).

  FIG. 15 is a sequence diagram illustrating a measurement example of the frequency difference. The base station 100-A transmits a transmission request frame (or a transmission request signal; hereinafter referred to as “transmission request frame”) to the adjacent base station 100-B (S160). When the adjacent base station 100-B receives the transmission request frame, the base station 100-A transmits a frequency measurement frame (or a frequency measurement signal, hereinafter may be referred to as a “frequency measurement frame”) at a predetermined cycle. (S161-1, S161-2,..., S161-N). At this time, the adjacent base station 100-B measures the transmission times T11, T12,..., T1N of the frequency measurement frame, and transmits them by including them in the frequency measurement frame. The base station 100-A measures the reception times T21, T22, ..., T2N of the frequency measurement frame. Therefore, the base station 100-A can acquire the transmission times T11, T12,..., T1N and the reception times T21, T22,.

Here, when the oscillation frequency of the base station 100-A and the oscillation frequency of the adjacent base station 100-B are synchronized, the transmission interval ΔT1 = T1N-T11 of the frequency measurement frame and the reception interval ΔT2 = T2N-T21 are equal. Become. However, when not synchronized, the difference between the transmission interval ΔT1 and the reception interval ΔT2 appears as the difference between the transmission frequencies of the two base stations 100-A and 100-B. That is, the frequency difference ΔA between the base station 100-A and the adjacent base station 100-B is
ΔA = ΔT1−ΔT2 = (T1N−T11) − (T2N−T21) (5)
It becomes.

  Thus, the base station 100-A can calculate the frequency difference ΔA based on the frequency measurement frame transmitted periodically.

  For example, the base station 100-A and the adjacent base station 100-B perform the following processing. That is, when the frequency measurement unit 1640 of the base station 100-A confirms that all the adjacent base stations 100-B to 100-N are in the automatic state based on the response frame, it generates a transmission request frame. The frequency measurement unit 1640 transmits the generated transmission request frame to the adjacent base stations 100-B to 100-N via the NW termination unit 111.

  FIG. 16A is a diagram illustrating an example of a transmission request frame. Specifically, the frequency measurement unit 1640 generates a transmission request frame including a “frequency measurement frame transmission request” and outputs the transmission request frame to the NW termination unit 111. Similar to the control frame, the NW termination unit 111 generates an IP packet including a transmission request frame and transmits the IP packet to the adjacent base stations 100-B to 100-N. This IP packet may be referred to as a transmission request frame, for example.

  The NW termination unit 111 of the adjacent base station 100-B extracts a transmission request frame from the received IP packet and outputs it to the frequency measurement unit 1640. The frequency measurement unit 1640 generates a frequency measurement frame according to the “frequency measurement frame transmission request” included in the frequency measurement frame, and transmits the frequency measurement frame to the base station 100-A via the NW termination unit 111.

  FIG. 16B is a diagram illustrating an example of a frequency measurement frame. Specifically, the frequency measurement unit 1640 of the adjacent base station 100-B reads the operation start time (or correction time) from the memory 1642 in accordance with the “frequency measurement frame transmission request”, and uses the timer to start the operation. Measure the operation period from the time. The frequency measurement unit 1640 reads the transmission time of the frequency measurement frame from the timer. The frequency measurement unit 1640 generates a frequency measurement frame including the operation period and the transmission time, and outputs the frequency measurement frame to the NW termination unit 111. Similar to the response frame, the NW termination unit 111 generates an IP packet including a frequency measurement frame and transmits the IP packet to the base station 100-A. This IP packet may be referred to as a frequency measurement frame, for example. In the operation period of the base station 100-A, the frequency measurement unit 1640 reads the operation disclosure time (or correction time) from the memory 1642 and uses the timer to measure the operation period from the operation start time. It is possible to get.

  Further, when receiving the IP packet, the NW termination unit 111 of the base station 100-A extracts a frequency measurement frame from the IP packet. The NW termination unit 111 outputs the extracted frequency measurement frame to the frequency measurement unit 1640. The frequency measurement unit 1640 sequentially acquires frequency measurement frames (“transmission time” and “operation period”). Further, the frequency measurement unit 1640 measures the reception times of the sequentially acquired frequency measurement frames using a timer. The frequency measurement unit 1640 calculates the frequency difference ΔA between the base station 100-A and the adjacent base station 100-B by substituting the acquired transmission time and the measured reception time into Equation (5). In the example of FIG. 7A, the base station 100-A measures the frequency difference ΔA at the start time of the correction value calculation, and acquires the operation period “12 months” of the adjacent base station 100-F. The frequency measurement unit 1640 stores in the memory 1642 the frequency difference ΔA measured based on the frequency measurement frame and the operation period of the adjacent base station 100-B extracted from the frequency measurement frame.

  The above is an example of the process of S16 in the base station 100-A and the adjacent base station 100-B.

  Note that the process of S16 is performed again immediately before the correction time or immediately before the correction time (hereinafter may be referred to as “correction time”). In the example shown in FIG. 13, immediately before the correction time (S120), the base station 100-A measures the frequency difference again and extracts the operation period again. In the example of FIG. 7A, the base station 100-A measures the frequency difference ΔB at the correction time, and extracts the operation period “18 months” of the adjacent base station 100-F. The frequency measurement unit 1640 stores the frequency difference ΔB and the operation period of the adjacent base station 100-B in the memory 642.

  For this operation period, the base station 100-A has acquired the operation period of the adjacent base station 100-B, for example, at the correction value calculation start time and correction time. For example, the base station 100-A may acquire the operation period of the adjacent base station 100-B at any one of the correction value calculation start time and the correction time. In calculating the correction value ΔE, for example, the base station 100-A calculates the operation start time of the adjacent base station 100-B. However, the base station 100-A does not acquire the operation period at two opportunities, but at one opportunity. This is because the operation start time can be calculated even if acquired. Therefore, even if the frequency measurement unit 1640 of the adjacent base station 100-A receives the transmission request frame, it inserts the “operation period” into the frequency measurement frame at any one opportunity and transmits it to the base station 100-A. You may make it do.

  In the example illustrated in FIG. 13, the base station 100-A does not perform the frequency measurement process (S16) with the adjacent base station 100-N immediately before the correction time (S120). That is, the correction time of the adjacent base station 100-N is “November 2017”, the correction value calculation start time (June 2017) of the base station 100-A and the correction time (December 2017). It is between. Due to the correction of the base station 100-N, the transmission frequency of the adjacent base station 100-N largely fluctuates before and after the correction time “November 2017”. Even if the base station 100-A performs frequency measurement (FIG. 15) with such an adjacent base station 100-N, it cannot calculate an accurate frequency difference ΔA. Therefore, if there is a correction time of the adjacent base station 100-N between the correction value calculation start time (S110) and the correction time (S120) of the base station 100-A, the base station 100-A The frequency measurement process (S16) is not performed with 100-N.

  In the example shown in FIG. 13, when the adjacent base station 100-C fails (S100), the base station 100-A does not perform frequency measurement processing (S16) with the adjacent base station 100-C. . Also in this case, the frequency fluctuation amount of the failed adjacent base station 100-C is largely different before and after the failure. Therefore, when the adjacent base station 100-C fails during the correction time (S120) after the correction value calculation start time (S110), the base station 100-A has a frequency with the adjacent base station 100-C. The measurement process (S16) is not performed.

  Accordingly, the base station 100-A, for example, assumes that the frequency measurement cannot be performed due to a future failure at the correction value calculation start time (S110). A transmission request frame is transmitted to -N (S16). As for the failure, for example, a confirmation frame (or confirmation signal) for confirming whether another base station is activated is transmitted / received between the base stations 100-A to 100-N. If it does not receive even after a certain period of time, it is possible to confirm that another base station has failed.

  In the example of FIG. 13, the base station 100-A performs frequency measurement processing with the base station 100-B, and calculates the frequency difference ΔA, ΔB.

  Returning to FIG. 11, next, the base station 100-A determines whether or not the current date and time has reached the correction time (S17). For example, the frequency measurement unit 1640 uses a timer to determine whether the current date and time has reached the correction time.

  When the current date does not reach the correction time (No in S17), the base station 100-A waits until the correction time is reached.

  On the other hand, when the current date and time has reached the correction time (Yes in S17), the base station 100-A performs correction value calculation processing (S18 in FIG. 12).

  FIG. 17 is a flowchart illustrating an example of correction value calculation processing.

  When the base station 100-A starts the correction value calculation process (S180), the base station 100-A calculates the frequency fluctuation amount ΔC from the measured frequency differences ΔA and ΔB (S181). For example, the base station 100-A performs the following processing. That is, the frequency measurement unit 1640 outputs the measured frequency difference ΔA, ΔB to the CLK correction value calculation unit 1641 at the correction time. The CLK correction value calculation unit 1641 calculates the difference between the frequency differences ΔA and ΔB, and calculates the frequency fluctuation amount ΔC = ΔB−ΔA per predetermined period.

  Next, the base station 100-A calculates a frequency difference ΔD at the time point “0” of the operation period of the adjacent base station 100-B from the frequency fluctuation amount ΔC (S182). For example, the CLK correction value calculation unit 1641 calculates the frequency difference ΔD using Expression (1) and Expression (2). However, “6 months” in Equation (1) and Equation (2) is, for example, an operation period of the base station 100-A from the correction value calculation start time to the correction time of the base station 100-A. Further, “12 months” is, for example, an operation period of the base station 100-A from the time point “0” of the operation period of the base station 100-B to the start of correction value calculation of the base station 100-A.

  For example, the CLK correction value calculation unit 1641 determines the base station 100-B based on the difference between the operation period of the adjacent base station 100-B extracted from the frequency measurement frame and the correction value calculation start time at the correction value calculation start time. The operation period of the base station 100-A at the operation period “0” can be acquired. Alternatively, the CLK correction value calculation unit 1641 calculates the difference between the operation period of the adjacent base station 100-B extracted from the frequency measurement frame and the correction time at the time of the operation period “0” of the base station 100-B. The operation period of the base station 100-A can be acquired.

  Next, the base station 100-A calculates a correction value ΔE from the frequency difference ΔD (S183). For example, the CLK correction value calculation unit 1641 calculates the correction value ΔE using Expression (3). However, in Equation (3), “6 months” is the operation period of the base station 100-A at the operation period “0” of the adjacent base station 100-B, and “24 months” is the correction of the base station 100-A. The operation period until the time (calculated in S12). The CLK correction value calculation unit 1641 may substitute each operation period into Equation (3).

  Expressions (1) to (4) are stored in the memory 1642, for example. The CLK correction value calculation unit 1641 reads the expressions (1) to (4) from the memory 1642 and substitutes the operation period and the calculated value to calculate the frequency differences ΔX and ΔD, the correction value ΔE, and the like.

  Then, the base station 100-A ends the correction value calculation process (S184). The above is an example of the correction calculation process.

  Returning to FIG. 12, next, the base station 100-A performs correction of the high stability oscillator 1621 (S20). For example, the CLK correction value calculation unit 1641 outputs the calculated correction value ΔE to the CLK correction unit 165, and the CLK correction unit 165 corrects the transmission frequency of the high stability oscillator 1621 based on the correction value ΔE. The CLK correction unit 165 rewrites the frequency deviation or DDS value stored in the flash memory 1623 so as to correspond to the correction value ΔE.

  Next, the base station 100-A stores the correction date and time in the memory 1642 (S21). For example, the CLK correction value calculation unit 1641 acquires the date and time when the correction value ΔE was calculated using a timer, and stores the acquired date and time in the memory 1642. Thereby, for example, the correction time in the base station 100-A is stored in the memory 1642.

  And base station 100-A complete | finishes a series of processes (S22).

  On the other hand, when all the adjacent base stations are not in a free-running state (No in S15), the base station 100-A may be referred to as an adjacent base station (hereinafter referred to as a “PTP synchronous station”) performing synchronization processing by PTP. )) Is performed (S23). For example, when the adjacent base station 100-B is a PTP synchronization station, the base station 100-A performs the process of S16 with the adjacent base station 100-B. For example, as illustrated in FIG. 15, the base station 100-A transmits and receives a transmission request frame and a frequency measurement frame to and from the PTP synchronization station 100-B, and calculates a frequency difference with respect to the PTP synchronization station 100-B. be able to.

  Next, the base station 100-A corrects the transmission frequency of the high stability oscillator 1621 of the own station 100-A so as to match the frequency in the PTP synchronization station 100-B (S24). For example, the frequency measurement unit 1640 measures the frequency difference and outputs it to the CLK correction value calculation unit 1641, and the CLK correction value calculation unit 1641 outputs the frequency difference to the CLK correction unit 165 as the correction value ΔE. The CLK correction unit 165 corrects the oscillation frequency of the high stability oscillator 1621 based on the correction value ΔE, and rewrites the numerical value stored in the flash memory 1623.

  Then, the base station 100-A stores the correction date and time in the memory 1642 (S21), and ends a series of processing (S22).

  As described above, in the first embodiment, the base station 100-A that is in the free-running state is free of other base stations 100- that are in the free-running state with respect to the frequency fluctuation of the oscillation frequency of the high stability oscillator 1621. It is possible to perform correction by calculating a correction value using B to 100-N.

  Therefore, the base station 100-A can easily correct the frequency fluctuation due to the aging deterioration of the highly stable oscillator 1621 as compared with the case where the highly stable oscillator 1621 is manually corrected. Is possible.

  In addition, the base station 100-A calculates an absolute frequency fluctuation amount ΔE of the base station 100-A at the correction time from the relative frequency differences ΔA and ΔB with the adjacent base stations 100-B to 100-N. The correction is performed based on the difference ΔE. Accordingly, since the base station 100-A can calculate the absolute frequency fluctuation amount ΔE as compared with the case where it is performed manually, the base station 100-A can oscillate the oscillation frequency with respect to the frequency fluctuation due to the aging degradation of the highly stable oscillator 1621. Can be corrected with high accuracy.

  In the first embodiment described above, an example has been described in which the correction time is set to three years from the start of operation, and the correction value calculation start time is set to six months before that. The correction time and the correction value calculation start time are examples. For example, the correction time may be two years from the start of operation, the correction value start time may be three months before that, and the like.

  In the first embodiment described above, PTP is described as an example of the time synchronization protocol. For example, SNTP (Simple Network Time Protocol) or NTP (Network Time Protocol) may be used. In these time synchronization protocols, time synchronization and frequency synchronization are possible by exchanging packets and messages as in the case of PTP. Therefore, the base station 100-A and the adjacent base stations 100-B to 100-N can be implemented in the same manner as the above-described embodiment by using such packets and messages.

[Other embodiments]
FIG. 18 illustrates a configuration example of the wireless communication system 10. The radio communication system 10 includes a base station device 100-A, another base station device 100-B, and a terminal device 200. The base station device 100-A performs wireless communication with the terminal device 200 without receiving synchronization control from the synchronization control device 300. Further, the other base station device 100 -B has not received synchronization control from the synchronization control device 300.

  The base station apparatus 100-A includes an oscillator 1621, a frequency measurement unit 1640, a clock correction value calculation unit 1641, and a clock correction unit 165.

  The oscillator 1621 corresponds to, for example, the high stability oscillator 1621 described in the first embodiment. The clock correction value calculation unit 1641 corresponds to, for example, the CLK correction value calculation unit 1641 described in the first embodiment. Furthermore, the clock correction unit 165 corresponds to, for example, the CLK correction unit 165 described in the first embodiment. Furthermore, the synchronization control device 300 corresponds to, for example, the grand masters 300-1 and 300-2 described in the first embodiment.

  The oscillator 1621 generates a clock signal having a first oscillation frequency.

  The frequency measurement unit 1640 receives the first and second frequency measurement signals transmitted from the other base station device 100-B. Also, the frequency measurement unit 1640 uses the first and second frequency measurements as the first and second transmission times when the first and second frequency measurement signals are transmitted in the other base station apparatus 100-B, respectively. Extract from signal. Furthermore, the frequency measurement unit 1640 is based on the difference between the first and second transmission times and the difference between the first and second reception times when the first and second frequency measurement signals are received, respectively. The frequency difference between the oscillation frequencies of the clock signals generated by the base station device 100-A and the other base station device 100-B is measured. Furthermore, the frequency measurement unit 1640 extracts the operation period of the other base station device 100-B from the first frequency measurement signal. Furthermore, the frequency measurement unit 1640 measures the operation period of the base station device 100-A.

  The clock correction value calculation unit 1641 calculates the correction value based on the frequency difference, the operation period of the other base station apparatus 100-B, and the operation period of the base station apparatus 100-A.

  The clock correction unit 165 corrects the first transmission frequency based on the correction value.

  As described above, in the base station apparatus 100-A, even when the synchronization control from the synchronization control apparatus 300 is not received, the first base station apparatus 100-B that has not received the synchronization control similarly transmits the first The first transmission frequency can be corrected based on the second frequency measurement signal. Therefore, it is possible to easily correct the frequency fluctuation due to the aging deterioration of the oscillator 1621 as compared with the case of manually correcting the oscillation frequency of the oscillator 1621 with respect to the clock correction unit 165 or the like. In addition, since the base station apparatus 100-A calculates the correction value from the first and second frequency measurement signals, it can accurately correct the oscillation frequency of the clock signal as compared with the case where correction is performed manually. Is possible.

  The above is summarized as an appendix.

(Appendix 1)
In the base station device that performs wireless communication with the terminal device without receiving synchronization control from the synchronization control device,
An oscillator for generating a clock signal having a first oscillation frequency;
The first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus are received, and the first and second frequency measurement signals are received by the other base station apparatus. Are extracted from the first and second frequency measurement signals, respectively, and a difference between the first and second transmission times and the first and second transmission times are respectively extracted. The difference in the oscillation frequency of the clock signal generated between the base station apparatus and the other base station apparatus is determined based on the difference between the first and second reception times when the frequency measurement signal is received. Measuring, extracting an operation period of the other base station device from the first frequency measurement signal, and measuring an operation period of the base station device;
A clock correction value calculation unit that calculates a correction value based on the frequency difference and an operation period of the other base station apparatus, and an operation period of the base station apparatus;
A base station apparatus comprising: a clock correction unit that corrects the first transmission frequency based on the correction value.

(Appendix 2)
The clock correction value calculation unit, based on the frequency difference, the operation period of the other base station apparatus, and the operation period of the base station apparatus, the frequency fluctuation amount in the base station apparatus from a reference value Is calculated as a correction value. The base station apparatus according to appendix 1, wherein

(Appendix 3)
The frequency measurement unit includes a first frequency difference representing a frequency difference between the base station apparatus and the other base station apparatus when an operation period of the base station apparatus has passed a first operation period, and the base Measuring a second frequency difference representing a frequency difference between the base station apparatus and the other base station apparatus when the operation period of the station apparatus has passed the second operation period;
The clock correction value calculation unit includes the difference between the second frequency difference and the first frequency difference, the first and second operation periods, and the time when the other base station apparatus starts operation. The base station apparatus according to appendix 1, wherein the correction value is calculated based on a third operation period representing an operation period of the base station apparatus.

(Appendix 4)
The clock correction value calculation unit, when the first operation period has elapsed, the difference between the operation period of the other base station device and the first operation period, or the second operation period has elapsed 4. The base station apparatus according to appendix 3, wherein the third operation period is calculated from a difference between an operation period of the other base station apparatus and the second operation period.

(Appendix 5)
The clock correction value calculation unit divides the difference between the second frequency difference and the first frequency difference by the difference between the second operation period and the first operation period, Multiplying by the difference between the first operation period and the third operation period, and subtracting the multiplied value from the first frequency difference, at the time when the other base station apparatus starts operation The frequency correction amount is calculated, the frequency variation amount is divided by the third operation period, and the correction value is calculated by multiplying the divided value by the second operation period. The base station apparatus as described.

(Appendix 6)
The frequency measurement unit includes a synchronization state indicating whether or not the other base station device is receiving synchronization control from the synchronization control device, and a correction indicating a timing for correcting the oscillation frequency of the oscillator of the other base station device. An inquiry signal for inquiring about the time to the other base station apparatus, and the synchronization state and the correction time of the other base station apparatus transmitted from the other base station apparatus in response to the inquiry signal, The base station apparatus according to supplementary note 1, wherein a response signal including: is received.

(Appendix 7)
The frequency measurement unit, after the elapse of the correction time, when there is a correction time of the other base station device after the first operation period of measuring the frequency difference between the base station device and the other base station device The base station apparatus according to appendix 6, wherein a frequency difference between the base station apparatus and the other base station apparatus is not measured when the second operation period elapses.

(Appendix 8)
The frequency measurement unit is configured to perform a measurement after the correction time has elapsed when the other base station device fails after the first operation period in which the frequency difference between the base station device and the other base station device has been measured. 7. The base station apparatus according to appendix 6, wherein a frequency difference between the base station apparatus and the other base station apparatus is not measured when two operation periods have elapsed.

(Appendix 9)
The frequency measurement unit transmits a transmission request signal indicating a transmission request for a frequency measurement signal to the other base station apparatus, and the frequency measurement transmitted from the other base station apparatus in response to the transmission request signal. The base station apparatus according to appendix 1, wherein the base station apparatus receives a signal.

(Appendix 10)
In a wireless communication system comprising a base station device that performs wireless communication with the terminal device without receiving synchronization control from the terminal device and the synchronization control device,
The base station device
An oscillator for generating a clock signal having a first oscillation frequency;
The first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus are received, and the first and second frequency measurement signals are received by the other base station apparatus. Are extracted from the first and second frequency measurement signals, respectively, and a difference between the first and second transmission times and the first and second transmission times are respectively extracted. The difference in the oscillation frequency of the clock signal generated between the base station apparatus and the other base station apparatus is determined based on the difference between the first and second reception times when the frequency measurement signal is received. Measuring, extracting an operation period of the other base station device from the first frequency measurement signal, and measuring an operation period of the base station device;
A clock correction value calculation unit that calculates a correction value based on the frequency difference and an operation period of the other base station apparatus, and an operation period of the base station apparatus;
A wireless communication system, comprising: a clock correction unit that corrects the first transmission frequency based on the correction value.

(Appendix 11)
An oscillator that generates a clock signal having a first transmission frequency, a frequency measurement unit, a clock correction value calculation unit, and a clock correction unit, and wireless communication with a terminal device without receiving synchronization control from the synchronization control device A frequency correction method in a base station apparatus that performs
The frequency measurement unit receives first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus, and the first base station apparatus receives the first and second frequency measurement signals. First and second transmission times when the second frequency measurement signal is transmitted respectively are extracted from the first and second frequency measurement signals, respectively, and the difference between the first and second transmission times; Based on the difference between the first and second reception times when receiving the first and second frequency measurement signals, respectively, the clock signal generated by the base station apparatus and the other base station apparatus Measure the frequency difference of the oscillation frequency, extract the operation period of the other base station device from the first frequency measurement signal, measure the operation period of the base station device,
The clock correction value calculation unit calculates a correction value based on the frequency difference and the operation period of the other base station apparatus, and the operation period of the base station apparatus,
The frequency correction method, wherein the clock correction unit corrects the first transmission frequency based on the correction value.

10: Wireless communication system
100, 100-A1 to 100-AN, 100-B1 to 100-BN, 100-C1 to 100-CN, 100-A to 100-G: Base station apparatus (BBU)
101-C1-101-CN: BBU 102-C1-102-CN: RRH
110-1 to 110-m: HWY card 120: Supervisory control card
130: SW card 140: Baseband processing card 150: CPRI terminal card 160: CLK card 161: PTP function unit 162: PLL function unit 163: In-system reference timing generation unit 164: CLK adjustment control unit 165: CLK correction unit 1621: Highly stable oscillator 1623: Flash memory 1640: Frequency measurement unit 1641: CLK correction value calculation unit 1642: Memory
200, 200-A1 to 200-AN, 200-B1 to 200-BN, 200-C1 to 200-CN: terminal device 300-1, 300-2: PTP grand master device 400-A1 to 400-AN, 400- B1-400-BN, 400-C1-400-CN: SW device

Claims (6)

In the base station device that performs wireless communication with the terminal device without receiving synchronization control from the synchronization control device,
An oscillator for generating a clock signal having a first oscillation frequency;
The first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus are received, and the first and second frequency measurement signals are received by the other base station apparatus. Are extracted from the first and second frequency measurement signals, respectively, and a difference between the first and second transmission times and the first and second transmission times are respectively extracted. The difference in the oscillation frequency of the clock signal generated between the base station apparatus and the other base station apparatus is determined based on the difference between the first and second reception times when the frequency measurement signal is received. Measuring, extracting an operation period of the other base station device from the first frequency measurement signal, and measuring an operation period of the base station device;
A clock correction value calculation unit that calculates a correction value based on the frequency difference and an operation period of the other base station apparatus, and an operation period of the base station apparatus;
A base station apparatus comprising: a clock correction unit that corrects the first transmission frequency based on the correction value.   The clock correction value calculation unit, based on the frequency difference, the operation period of the other base station apparatus, and the operation period of the base station apparatus, the frequency fluctuation amount in the base station apparatus from a reference value The base station apparatus according to claim 1, wherein is calculated as a correction value. The frequency measurement unit includes a first frequency difference representing a frequency difference between the base station apparatus and the other base station apparatus when an operation period of the base station apparatus has passed a first operation period, and the base Measuring a second frequency difference representing a frequency difference between the base station apparatus and the other base station apparatus when the operation period of the station apparatus has passed the second operation period;
The clock correction value calculation unit includes the difference between the second frequency difference and the first frequency difference, the first and second operation periods, and the time when the other base station apparatus starts operation. The base station apparatus according to claim 1, wherein the correction value is calculated based on a third operation period representing an operation period of the base station apparatus.   The clock correction value calculation unit divides the difference between the second frequency difference and the first frequency difference by the difference between the second operation period and the first operation period, Multiplying by the difference between the first operation period and the third operation period, and subtracting the multiplied value from the first frequency difference, at the time when the other base station apparatus starts operation The frequency fluctuation amount is calculated, the frequency fluctuation amount is divided by the third operation period, and the correction value is calculated by multiplying the divided value by the second operation period. 3. The base station apparatus according to 3. In a wireless communication system comprising a base station device that performs wireless communication with the terminal device without receiving synchronization control from the terminal device and the synchronization control device,
The base station device
An oscillator for generating a clock signal having a first oscillation frequency;
The first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus are received, and the first and second frequency measurement signals are received by the other base station apparatus. Are extracted from the first and second frequency measurement signals, respectively, and a difference between the first and second transmission times and the first and second transmission times are respectively extracted. The difference in the oscillation frequency of the clock signal generated between the base station apparatus and the other base station apparatus is determined based on the difference between the first and second reception times when the frequency measurement signal is received. Measuring, extracting an operation period of the other base station device from the first frequency measurement signal, and measuring an operation period of the base station device;
A clock correction value calculation unit that calculates a correction value based on the frequency difference and an operation period of the other base station apparatus, and an operation period of the base station apparatus;
A wireless communication system, comprising: a clock correction unit that corrects the first transmission frequency based on the correction value. An oscillator that generates a clock signal having a first transmission frequency, a frequency measurement unit, a clock correction value calculation unit, and a clock correction unit, and wireless communication with a terminal device without receiving synchronization control from the synchronization control device A frequency correction method in a base station apparatus that performs
The frequency measurement unit receives first and second frequency measurement signals transmitted from other base station apparatuses not receiving synchronization control from the synchronization control apparatus, and the first base station apparatus receives the first and second frequency measurement signals. First and second transmission times when the second frequency measurement signal is transmitted respectively are extracted from the first and second frequency measurement signals, respectively, and the difference between the first and second transmission times; Based on the difference between the first and second reception times when receiving the first and second frequency measurement signals, respectively, the clock signal generated by the base station apparatus and the other base station apparatus Measure the frequency difference of the oscillation frequency, extract the operation period of the other base station device from the first frequency measurement signal, measure the operation period of the base station device,
The clock correction value calculation unit calculates a correction value based on the frequency difference and the operation period of the other base station apparatus, and the operation period of the base station apparatus,
The frequency correction method, wherein the clock correction unit corrects the first transmission frequency based on the correction value.

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