JP4439286B2 - Wireless synchronization method and base station apparatus using the same - Google Patents

Description

  The present invention relates to a wireless synchronization technique. In particular, the present invention relates to a radio synchronization method for maintaining synchronization between base station apparatuses and a base station apparatus using the same.

  Mobile phone systems and simplified mobile phone systems have become widespread and are used by many users. In these systems, a terminal device communicates predetermined data using a radio channel assigned by a base station device. One base station apparatus assigns a plurality of radio channels to terminal apparatuses, and multiplexes these terminal apparatuses. In particular, a cellular phone system and a simple cellular phone system generally employ a TDMA (Time Division Multiple Access) system as a multiplexing technique. For example, in the case of a simple mobile phone system, one frame is composed of 8 time slots, of which 4 time slots are set for downlink communication and the remaining 4 time slots are set for uplink. In this TDMA system, it is important to establish frame synchronization between the base station devices constituting the service area. That is, when frame synchronization is not established between adjacent base station devices, if these base station devices select the same frequency band as a radio frequency band for communication, interference occurs in overlapping portions of the slots, and communication Incurs quality degradation.

  Therefore, for example, as a method of establishing radio synchronization between base station apparatuses, the basic operation clock of all base station apparatuses is unified with the network synchronization clock, and when the base station apparatus is initially activated, A technique for adjusting the synchronization position so that the wireless signal is captured and transmitted and received at the same timing is employed.

  However, in the base station apparatus once established with the radio synchronization with the other base station apparatus, when a failure occurs in the basic operation clock extracted from the network, the base station apparatus cannot maintain the synchronization of the radio signal. Radio signals are transmitted and received at a timing different from that of the base station apparatus.

For such a problem, a technique has been proposed in which an error in radio synchronization with another base station apparatus is monitored and corrected when an allowable value is exceeded (see, for example, Patent Document 1).
JP-A-10-145848

  Under such circumstances, the present inventor has come to recognize the following problems.

  If the error in the frame synchronization of the radio signal between the base station device and other base station devices installed in the vicinity exceeds the allowable value due to the monitoring, the connection service is temporarily suspended during the night when communication traffic is low. The frame synchronization is corrected and the frame synchronization is corrected. However, when a failure occurs in the early morning, correction of frame synchronization cannot be performed until the next midnight, forcing operation in a state where usable frequencies are limited. In addition, when frame synchronization is corrected while maintaining the connection service without waiting for the next midnight, depending on the magnitude of the error to be corrected, the terminal device in communication may be disconnected.

  The inventor has made the present invention by recognizing such a situation, and its purpose is to continue the communication of the connected terminal device when the frame synchronization between the base station devices cannot be maintained. It is another object of the present invention to provide a radio synchronization method for quickly reducing synchronization errors and a base station apparatus using the same.

One embodiment of the present invention is a base station apparatus. This apparatus receives a signal from an external base station apparatus, detects a reference timing discretely from the received signal, and continuously determines the internal timing based on the discretely detected reference timing. A timing generation unit that generates, and a communication unit that communicates with a terminal device that is a communication target at a continuously generated internal timing, and the timing generation unit has an error between the reference timing and the continuously generated internal timing, The internal timing is corrected so as to decrease stepwise, and an internal timing that is synchronized with the reference timing of the external base station apparatus is generated.

  In order to gradually correct the error in timing between the reference timing detected from the external base station apparatus to be used as a correction reference and the internal timing generated in the own station so as to be reduced step by step with the above apparatus. The base station apparatus can correct the timing shift while maintaining the connection with the terminal apparatus, and can improve the operation efficiency.

  The timing generation unit may determine a correction range for correcting the internal timing based on an allowable time of an error in reception timing that is specified and permitted in advance by the terminal device.

  “Allowable error time” indicates the time width of the timing at which the terminal device can follow the fluctuation in the transmission timing of the radio signal transmitted by the base station device, but the connection between the base station device and the terminal device is maintained. Any index may be used as long as it indicates the size to be displayed.

  The timing generation unit may determine a correction width for correcting the internal timing based on the error magnitude between the internal timing and the reference timing.

  The timing generation unit may change the correction width for correcting the internal timing according to the number of connected terminal devices.

  One embodiment of the present invention is a wireless synchronization method. In this method, the internal timing is set so that the error between the reference timing discretely detected from the signal received from the external base station apparatus and the internal timing continuously generated based on the reference timing becomes smaller in steps. The internal timing is corrected to be synchronized with the reference timing.

  With the above method, the base station apparatus gradually corrects the timing error while maintaining the connection with the terminal apparatus, so that the synchronization loss can be reduced without causing a decrease in operation efficiency.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

According to the present invention, even when wireless synchronization between base station apparatuses cannot be maintained, the synchronization error can be quickly reduced without causing service interruption while maintaining the connection of the terminal apparatus. Improvements can be made.

This embodiment detects an error in frame synchronization between base station devices, that is, a phase difference, in a wireless communication system such as a mobile phone system or a simple mobile phone system in which a plurality of base station devices are arranged to form a service area. When the phase difference is equal to or greater than a predetermined value, the present invention relates to a base station apparatus that divides the phase difference according to a predetermined standard and corrects it in stages.

  The details will be described below by taking a simple mobile phone system as an example.

  FIG. 1 shows a communication system 10 according to the present embodiment. The communication system 10 includes a terminal device 100, a base station device 200, a base station device 300, a network 700, and a reference clock 702.

  The base station apparatus 200 includes a base station antenna 202, a radio unit 204, a radio signal processing unit 206, a line control unit 208, a network synchronization unit 210, a timing detection unit 212, a synchronization signal generation unit 214, and a network synchronization abnormality detection unit. 216, a synchronization monitoring unit 218, and a control unit 220, and the base station apparatus 300 includes a GPS antenna 302. In addition, the network synchronization clock 20, other station reception signal 22, other station frame timing 24, and own station frame timing 26 are included as signals.

  The base station antenna 202 transmits and receives radio frequency signals. Note that the base station antenna 202 may be any of an omnidirectional antenna, a predetermined directional antenna, and an adaptive array antenna, and may have a diversity function.

  The wireless unit 204 performs signal amplification, mutual conversion between a radio frequency and a baseband signal, A / D or D / A conversion, and the like.

  The radio signal processing unit 206 modulates and demodulates a radio signal transmitted / received via the radio unit 204 and outputs a signal received from another base station apparatus to a timing detection unit 212 described later.

  The line control unit 208 plays a role of connecting the base station apparatus 200 to the network 700, and performs mutual conversion between the format of information modulated / demodulated by the radio signal processing unit 206 and the format of information communicated via the network 700. The network 700 is a synchronous communication network using the reference clock 702 as a standard clock. The reference clock 702 includes a high-precision oscillation source such as a cesium atomic oscillator or a rubidium atomic oscillator. An example of the network 700 is an ISDN (Integrated Services Digital Network), and the line control unit 208 has a physical shape corresponding to ISDN.

  The network synchronization unit 210 receives the reception signal received by the line control unit 208, and extracts and reproduces a standard clock signal used for data transmission / reception on the network 700. The extracted and regenerated standard clock signal is subjected to stabilization processing such as removal of jitter components and suppression of abrupt changes, and frequency conversion to a high frequency that can be used for frame synchronization timing detection is performed. Output as a synchronous clock 20. The network synchronization unit 210 includes, for example, an analog PLL (Phase Locked Loop) circuit including a loop filter with a moderate response characteristic.

  The timing detection unit 212 uses the network synchronization clock 20 as a detection operation clock, and detects the transmission / reception timing of another base station device from the other station reception signal 22 received via the radio signal processing unit 206. Other base station apparatuses to be detected are determined from instructions of a synchronization monitoring unit 218 described later from among a plurality of base station apparatuses installed around the base station apparatus 200.

  The synchronization signal generation unit 214 uses the network synchronization clock 20 as an operation clock to generate the local station frame timing 26 as internal timing used for transmission / reception of the local station. The local station frame timing 26 is a signal generated continuously, and correction processing is performed so that synchronization is established with the other station frame timing 24 as the reference timing detected by the timing detection unit 212.

  When the network synchronization unit 210 extracts a standard clock signal from the network when the network synchronization unit 210 detects a clock stop or phase shift, the network synchronization abnormality detection unit 216 informs the synchronization monitoring unit 218 described later as an abnormality detection signal. Notice.

  When the network synchronization abnormality detection unit 216 detects an abnormality signal, the synchronization monitoring unit 218 instructs the timing detection unit 212 via a signal line (not shown) to confirm frame synchronization with other base station devices. Note that the base station apparatus to be compared with the frame synchronization is determined based on a predetermined condition from neighboring base station apparatuses capable of receiving radio signals. Specifically, the control channel information periodically transmitted by each base station apparatus is received, and the base station apparatus including the display information of the master station is searched from the information. A master station is a base station device equipped with a GPS (Global Positioning System) antenna, receives time information transmitted from GPS satellites, sets a frame synchronization reference, and transmits and receives signals at that timing. .

  The control unit 220 executes various timing processes of the base station apparatus 200, wireless connection control with the terminal apparatus 100, wired connection control with the network 700, and the like.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of an arbitrary computer, and in terms of software, it is realized in advance by a program stored in a memory (not shown) and read out at the time of execution. Here, functional blocks realized by the cooperation are depicted. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 2 shows a frame configuration of a radio section according to the present embodiment. This frame configuration is that of a simple cellular phone system and shows a 4-channel multiple multi-carrier TDMA / TDD (Time Division Duplex) system. In the figure, a frame every 5 msec is divided into 8 slots by time division, and 4 slots are allocated for downlink (base station apparatus to terminal apparatus) and 4 slots are allocated for uplink (terminal apparatus to base station apparatus). These four slots are assigned to a call channel and the remaining one slot is assigned to a control channel, and each of the three slots, uplink and downlink, is used for a call between the base station apparatus and the terminal apparatus and its control.

  In the figure, slots shown in black indicate downlink control channels transmitted from the base station apparatus to the terminal apparatus, and are arranged in units of 20 frames (every 100 msec). This transmission cycle (20 frames) is called a downlink intermittent transmission cycle (LCCH interval), and is arranged in any one of the 20 frames for each base station apparatus (for each (A), (B), and (C)). . Therefore, if the terminal apparatus enters a standby state in the area of the predetermined base station apparatus, the terminal apparatus receives the control information (for example, incoming signal) from the predetermined base station apparatus by performing a receiving operation in units of 20 frames. be able to. In addition, frame intervals and intermittent downlink transmission periods are determined on the system with respect to the accuracy of time intervals in order to ensure connectivity with terminal devices and avoid interference with other base station devices. Specifically, the time width of the timing at which the terminal device can follow the transmission timing of the signal transmitted by the base station device is shown. For example, the transmission timing of the base station device in the simplified mobile phone system is: As shown in (C), the time interval from the slot transmitted last to the slot transmitted in the next frame is defined to be within 5 msec ± 5 ppm (RCR STD-28).

  FIG. 3 is a diagram illustrating a frame synchronization shift between base station apparatuses according to the present embodiment. As a premise for explanation, the base station apparatus 200 is a base station apparatus that generates a frame synchronization shift and requires correction, and the base station apparatus 300 includes a GPS antenna 302 and is a base station apparatus that should be used as a frame synchronization reference. Assume.

  (A) in the figure shows the transmission / reception timing of the base station apparatus 200. Further, (C) shows a control channel set in the base station apparatus 200 during the downlink intermittent transmission period. That is, the control channel is set every 20 frames. Similarly, (B) and (D) in the figure are the transmission / reception timing and control channel of the base station apparatus 300.

  (E) shows the phase difference between the base station apparatus 200 and the base station apparatus 300. This phase difference occurs when, for example, the transmission / reception timing of the base station apparatus 200 changes due to some failure. In FIG. 3, the transmission / reception timing of the base station apparatus 200 is phase-shifted with respect to the transmission / reception timing of the base station apparatus 300. The difference shows a case of shifting forward (when viewed from the base station apparatus 200, the base station apparatus 300 appears delayed).

  (F) to (J) will be described together with FIG. 4 below.

  FIG. 4 shows the configuration of the synchronization signal generator 214. The synchronization signal generation unit 214 includes a comparison unit 240, a correction control unit 242, a correction calculation unit 244, and a local station transmission / reception timing generation unit 246. Further, the signal includes a phase difference 30, a correction total count value 32, a correction value 34, and a correction instruction 36.

  The comparison unit 240 compares the other-station frame timing 24 (FIG. 3 (F)) detected by the timing detection unit 212 with an own-station frame timing 26 (FIG. 3 (G)), which will be described later, and compares the difference with the phase difference. 30 (FIG. 3H) is output. Here, the other station frame timing 24 is a signal obtained by discretely receiving the control channel (FIG. 3D) of the base station apparatus 300 and extracting the timing from the received signal.

  The correction control unit 242 counts the phase difference 30 received from the comparison unit 240 with the network synchronization clock 20 (the count in FIG. 3J), and whether or not the count value has a magnitude that requires correction. To check. If correction is necessary as a result of the confirmation, the count value is output as the correction total count value 32 to the correction calculation unit 244. Further, the correction control unit 242 outputs a correction count value 34 returned from the correction calculation unit 244 described later to the local station transmission / reception timing generation unit 246 in units of frames, and instructs correction of timing.

  The correction calculation unit 244 divides the correction total count value 32 into predetermined maximum values that can be corrected at one time, and outputs the maximum value to the correction control unit 242. Here, the maximum value that can be corrected at one time is a value determined by the frequency of the clock that counts the phase difference and the transmission timing that can be corrected at one time. For example, the clock frequency is 153.6 MHz (one count). Is 6.51 nsec), and when the transmission timing that can be corrected at one time is 25 nsec, the count is 3 counts.

  The local station transmission / reception timing generation unit 246 continuously generates the local station frame timing 26 according to the correction instruction 36 from the correction control unit 242 using the network synchronization clock 20 as an operation clock. Specifically, when there is no correction instruction 36, the local station transmission / reception timing generation unit 246 repeatedly generates a local frame timing having a change point at a predetermined period by counting the network synchronization clock 20, and the correction instruction 36 In some cases, the position of the change point is moved back and forth in accordance with the correction instruction 36.

  FIG. 5 is a flowchart showing a frame timing correction processing procedure according to the present embodiment.

  In this procedure, after the base station apparatus 200 establishes frame synchronization of radio signals with surrounding base station apparatuses and starts connection with the terminal apparatus, the transmission / reception timing of the base station apparatus 200 changes for some reason, and frame synchronization A correction process in the case where it becomes impossible to maintain the will be described. In the following description, it is assumed that the base station apparatus that is the reference for the base station apparatus 200 to synchronize with the frame is a base station apparatus 300 that includes the GPS antenna 302 and functions as a master station.

  The synchronization monitoring unit 218 instructs the timing detection unit 212 to detect the frame timing at a predetermined time or when the network synchronization clock 20 abnormality is detected by the network synchronization abnormality detection unit 216. The timing detection unit 212 discretely receives the control channel transmitted by the base station apparatus 300 via the wireless signal processing unit 206 for each downlink intermittent transmission period, and detects the frame timing from the signal (S500). The detected frame timing is output to the comparison unit 240 of the synchronization signal generation unit 214 as the other station frame timing 24 to be used as a reference. The comparison unit 240 compares the other station frame timing 24 with the own station frame timing 26 and outputs the phase difference of both signals as the phase difference 30 (S502).

  The correction control unit 242 to which the phase difference 30 is input counts the phase difference 30 using the network synchronization clock 20, and compares the result with a predetermined threshold value (S504). As a result, if the count value of the phase difference 30 is smaller than the threshold value, it is determined that there is no need for correction, and the process is terminated (S504-N). This is excluded from the correction target in order to prevent unnecessary follow-up with respect to a phase difference that appears to be caused by a change in radio wave propagation environment around the base station apparatus or a measurement error.

  When the count value of the phase difference 30 is larger than the threshold value, it is determined that a frame synchronization shift that cannot be ignored has occurred (S504-Y), and it is confirmed whether there is a connected terminal device ( S506). In this confirmation, when there is no connected terminal device (S506-N), the correction control unit 242 stops the transmission of the radio signal (S514) and corrects the phase at a time (S516). Then, the transmission of the radio signal is resumed (S518). On the other hand, when there is a connected terminal device (S506-Y), the corrected total count value 32 is output to the correction calculation unit 244. The correction calculation unit 244 divides the correction total count value 32 into counts equal to or less than the maximum value that can be corrected at one time (S508), and returns the value to the correction control unit 242 as a correction instruction 36. The division may be any division as long as it is divided into counts equal to or less than the maximum value. For example, when the correction total count value 32 is 10 and the maximum value that can be corrected at one time is 3, the correction is terminated early. To prioritize, divide by maximum value (eg, 3, 3, 3, 1), while to give priority to connection stability, divide by less than the maximum value (1, 1, 1, 1, A method such as 1,1,1,1,1,1) is effective.

  The correction control unit 242 that has input the divided correction count value 34 sequentially outputs the correction count value 34 to the local station transmission / reception timing generation unit 246 in units of frames, performs stepwise correction (S510), and confirms completion. (S512).

  Upon completion of the frame synchronization correction processing by the local station transmission / reception timing generation unit 246, the synchronization monitoring unit 218 instructs the timing detection unit 212 to check the corrected frame synchronization, and if the frame synchronization with other stations can be confirmed. (S520-Y), the correction operation is terminated. If frame synchronization cannot be confirmed (SS520-N), the process returns to the detection of a phase difference with another station (S502) and the same operation is continued.

  The operation of base station apparatus 200 having the above configuration will be described.

  The synchronization monitoring unit 218 of the base station apparatus 200 monitors frame synchronization with other base station apparatuses in parallel with the operation operation of the base station apparatus. Specifically, a predetermined time (for example, midnight with few interference waves) is set in units of days or weeks and monitored regularly, or an abnormal signal is detected from the network synchronization abnormality detection unit 216. , Monitor in an interrupted manner.

  The timing detection unit 212 detects a frame synchronization signal of another base station device according to an instruction from the synchronization monitoring unit 218. The base station device to be detected is, for example, a base station device that has a GPS antenna and functions as a frame synchronization master station. The signal received from the detection target base station apparatus is a control channel transmitted by the base station apparatus at a predetermined downlink intermittent transmission period.

  The comparison unit 240 compares the other station frame timing 24 detected by the timing detection unit 212 with the own station frame timing 26 and outputs a phase difference 30.

  The correction control unit 242 counts the phase difference 30 detected by the comparison unit 240 with the network synchronization clock 20, and compares the result with a predetermined threshold value. Here, the accuracy of correction is determined according to the height of the frequency of the clock used for counting. Therefore, the accuracy of correction can be improved by counting with a clock having a higher frequency. Further, if the count value is larger than the threshold value as a result of the comparison, the correction control unit 242 outputs the count value to the correction calculation unit 244, assuming that timing correction is necessary. On the other hand, when the count value is smaller than the threshold value, it is determined that there is no need for correction, and the process ends. This determination is to prevent unnecessary correction processing from being activated due to a change in the radio wave propagation environment around the base station device or a measurement error.

  When the correction calculation unit 244 receives the correction total count value 32 from the correction control unit 242, the correction calculation unit 244 compares the value with a predetermined maximum value that can be corrected at one time, and divides the value into count values equal to or less than the maximum value to perform correction control. To the unit 242.

  Again, the correction control unit 244 outputs the divided count value to the local station transmission / reception timing generation unit 36 in units of frames.

  The local station transmission / reception timing generation unit 36 corrects the change point of the local station frame timing 26 based on the correction instruction 36 input in units of frames.

  According to the present embodiment, the base station apparatus monitors frame synchronization at a predetermined timing or when an abnormality is detected, and determines that there is a phase difference greater than or equal to a predetermined value in the phase of frame synchronization. Is divided into a plurality of phase differences of a predetermined size or less and corrected step by step, so that frame synchronization can be corrected quickly without stopping the communication service while maintaining the connection with the terminal device. Can be realized.

  In the above, it demonstrated based on embodiment of this invention. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the present embodiment, the frame synchronization correction processing procedure switches whether to correct the phase difference at a time or to divide it below a predetermined value and make corrections step by step depending on the presence or absence of a connected terminal device. did. However, the present invention is not limited to this, and for example, the correction process may be further subdivided according to the number of connected terminals. Specifically, as described in FIG. 3, when the maximum value that can be corrected at one time is 3, if the number of connected terminals is 1, the predetermined value is 3, and if the number of terminals is 2, The predetermined value is set to 2, and if the number of terminals is 3, the predetermined value is set to 1. That is, the larger the number of connected terminals, the smaller the phase difference that is corrected at one time. The terminal device is configured to synchronize with the base station device, but when the synchronization position varies due to an increase in the number of terminal devices, according to the present modification, the correction amount at one time is set small, so in any terminal device Also, frame synchronization can be corrected without causing communication failure.

  In the present embodiment, it has been described that the frame synchronization correction processing is performed for each frame. However, the present invention is not limited to this, and may be performed more slowly, for example, every few frames or every downlink intermittent transmission cycle. In addition, the error occurrence status of the terminal device is confirmed during the correction process, and errors increase. In such a case, the correction may be temporarily interrupted. According to this modification, the communication maintenance of the terminal device can be made more stable.

  In the present embodiment, the clock for counting the phase difference has been described using the network synchronization clock 20 extracted from the network 700, but is not limited thereto. For example, the clock may be independent from the network synchronization clock. According to this modification, it is possible to eliminate the influence on the phase difference count when a phase disturbance occurs in the network synchronization clock.

It is a figure which shows the communication system which concerns on this Embodiment. It is a figure which shows the flame | frame structure of the radio area of FIG. It is a figure which shows the shift | offset | difference of the frame synchronization between the base station apparatuses of FIG. It is a figure which shows the structure of the synchronizing signal generation part 214 of FIG. 3 is a flowchart showing a procedure for correcting the frame timing of FIG. 1.

Explanation of symbols

10 communication system, 20 network synchronization clock, 22 other station received signal, 24 other station frame timing, 26 own station frame timing, 30 phase difference, 32 correction total count value, 34 correction value, 36 correction instruction, 100 terminal device, 200 Base station apparatus, 202 base station antenna, 204 radio unit, 206 radio signal processing unit, 208 line control unit, 210 network synchronization unit, 212 timing detection unit, 214 synchronization signal generation unit, 216 network synchronization abnormality detection unit, 218 synchronization Monitoring unit, 220 control unit, 240 comparison unit, 242 correction control unit, 244 correction calculation unit, 246 own station transmission / reception timing generation unit, 300 base station device, 302 GPS antenna, network 700, reference clock 702.

Claims (4)

A detection unit that receives a signal from an external base station device and detects a reference timing from the received signal;
A timing generator that continuously generates internal timing;
A communication unit that communicates with a terminal device to be communicated using the continuously generated internal timing,
The internal timing generation unit corrects the internal timing based on a correction width set based on the number of connected terminal devices when there is an error between the reference timing and the continuously generated internal timing. Thus, the base station apparatus generates internal timing that is synchronized with the reference timing. The base station apparatus according to claim 1, wherein the timing generation unit determines the correction width based on an allowable time of an error in reception timing defined in advance by a terminal apparatus. The base station apparatus according to claim 1, wherein the timing generation unit determines the correction width based on a magnitude of an error between the internal timing and the reference timing. A wireless synchronization method in a base station device,
Reference timing detected from a signal received from an external base station,
  An error from the internal timing continuously generated based on the reference timing is synchronized with the reference timing by correcting the internal timing based on a correction width set based on the number of connected terminal devices. A wireless synchronization method characterized by generating an internal timing.

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