JP2005295177A - Frame synchronization system of base station of mobile communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frame synchronization system of a base station for mobile communication that can perform correct frame synchronization even at a base station that can not use a clock signal supplied from a network side as a clock signal to be reference. <P>SOLUTION: Since sufficient accuracy can not be obtained by the following method even though an internal clock 106 is used in order to synchronize the timing of a frame that is transmitted by a self-station 100 with that of another base station 200, a system uses a frame time correction circuit 104 as a means for satisfying the above problem to compare a CCH(control channel) 300 transmitted from the base station 100 to be reference with the timing of the frame 400 transmitted by the self-station and correct transmission timing so as to meet the CCH in timing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a frame synchronization method for a mobile communication base station, and more particularly to a frame synchronization method in a base station in which a clock signal supplied from a network side cannot be used as a reference clock signal.

  In a mobile communication system such as the PHS system, a mobile terminal generally communicates with a plurality of base stations within a radio wave service area of each base station. Since the service areas of the base stations overlap with each other, the transmission / reception frames of the base stations need to be synchronized in order to avoid radio wave interference between the base stations. For this reason, each base station requires a very accurate clock source in order to maintain the accuracy of frames to be transmitted and received. A conventional base station uses a clock signal supplied from an I 'line, an ISDN line or the like in order to obtain this clock source. This signal is very accurate and has little fluctuation, and since it is supplied uniformly throughout the country, there is an advantage that the same clock signal can be obtained no matter where the base station is installed in the country.

  However, in recent years, mobile communication tends to increase the speed and bandwidth of a line connected to a base station in order to increase the communication speed. The base station can be replaced with an Ethernet network instead of an I ′ line or an ISDN line. It is required to connect to the network. However, in this case, there arises a problem that an accurate clock signal cannot be obtained from the network side. Even if the clock is generated based on the signal supplied from the network side, the layer 1 usually terminates at the nearest termination device, etc., so it depends on the clock accuracy of the nearest termination device. The same accuracy cannot be maintained nationwide.

  For this reason, a built-in clock source must be used. However, in order to maintain the same clock accuracy as when the clock signal is obtained from the line side as in the prior art, there is a problem that the cost becomes very high. . As a countermeasure, a method of connecting a circuit capable of supplying a clock signal to the base station in addition to a high-speed and wide-band circuit to obtain an accurate clock is conceivable. For example, a local LAN facility is used. Even when trying to construct a local mobile communication network, it is necessary to draw a line capable of supplying a clock signal, and there is a problem that a mobile communication network cannot be constructed in a place where such a line cannot be used.

  Accordingly, an object of the present invention is to improve such conventional drawbacks, and enables mobile communication that enables accurate frame synchronization even in a base station that cannot use a clock signal supplied from the network side as a reference clock signal. Another object of the present invention is to provide a frame synchronization method for a base station.

  The mobile communication base station frame synchronization method of the present invention receives a radio wave transmitted by a mobile communication reference base station, extracts a transmission frame, and extracts the transmission frame. Means for controlling a built-in reference clock source by means of a frame, and means for controlling the transmission frame of the own station using the built-in reference clock source controlled by this means to synchronize with the transmission frame of the reference base station. It is characterized by this.

  In the mobile communication base station frame synchronization system of the present invention, the frame extraction means receives control channel information transmitted from the reference base station, and uses a timing signal generated from the control channel information. Then, the transmission frame of the reference base station and the own station are synchronized by correcting the timing of the transmission frame.

  In the mobile communication base station frame synchronization system of the present invention, the means for controlling the built-in reference clock source receives the control channel information and generates a transmission frame timing signal; A frame timing signal generation circuit for generating a transmission frame timing signal of a station, a frame timing comparison circuit to which a transmission frame timing signal generated by the frame timing signal generation circuit and a frame timing signal generated by the radio unit are supplied The frame timing signal is changed by controlling the internal clock source when the difference between the two input transmission frame timing signals, which is the output of the frame timing comparison circuit, exceeds a predetermined range. The transmission frame of the local station. It is characterized in that to match the timing to receive the frame from the other base station.

  According to the present invention, accurate frame synchronization is possible even in a base station that cannot use a clock signal supplied from the network side as a reference clock signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

    FIG. 1 is a block diagram showing a configuration of a frame synchronization system in a PHS base station according to an embodiment of the present invention.

(1) System Configuration As shown in FIG. 1, in this system, a PHS base station (hereinafter referred to as a reference PHS base station) 200 connected to an I ′ line that serves as a frame synchronization reference, and an I such as an Ether net are used. 'A base station (hereinafter referred to as another network connection PHS base station or own base station) 100 connected to a network other than a line.

(2) Configuration of PHS Base Station for Other Network Connection The PHS base station for other network connection 100 includes a radio unit 1 (101), a radio unit 2 (102), a frame timing comparison circuit 103, a frame timing correction circuit 104, a frame timing. The generation circuit 105, the built-in clock source 106, the main control unit 107, the network IF unit 108, and software for operating them.

  The built-in clock source 106 includes an oscillator of a type whose oscillation frequency can be changed by an applied voltage and a peripheral control circuit (not shown).

  Next, the operation of the frame synchronization system configured as described above will be described.

(1) Reference PHS Base Station The reference PHS base station 200 transmits a control channel (CCH) frame 300 in synchronization with a clock signal supplied from the I ′ line.

(2) Other network connection PHS base station The other network connection PHS base station 100 performs the correction operation of the transmission frame 400 in the following procedure.

1) Selection of reference PHS base station 2) Determination of timing of CCH frame 400 transmitted by own station 3) Correction of CCH frame 400 transmitted by own station These correction operations will be sequentially described below.

1) Reference PHS base station selection operation In the start-up operation, the other network connection PHS base station 100 searches for the reference PHS base station 100 before the local station starts transmission of the CCH, and the CCH of the base station 100 Start receiving.

The other network connection PHS base station 100 uses the wireless unit 1 (101) for a certain period of time to perform peripheral carrier sensing, and when a reference PHS base station is found in the vicinity, the CHS reception from the base station is performed. To start. Whether or not the partner base station is a reference PHS base station is determined by adding dedicated information to the originating identification code (CS-ID) transmitted by the base station and detecting it.

  FIG. 2 shows an example of a call identification code (CS-ID). The example shown in FIG. 2 is a configuration used in a PHS public network. The CS-ID is information that is always included in the control channel signal transmitted by the base station, and this information is used to specify the transmission source of the control channel. In general, a unique number that can identify the base station is assigned to the additional ID (33-n bit) included in the additional ID for outdoor public (33 bit).

  In order to determine whether the CS-ID received by the other network connection base station 100 is the CS-ID of the reference station 200, the transmitting base station (reference base station) 200 turns on a specific bit of this additional ID. Alternatively, the determination can be made by turning off and detecting whether the specific bit is turned on or off by the other network connection base station 100 which is the receiving base station.

  If the reference PHS base station 100 is not found in the vicinity as a result of the search, the search is retried, but if it cannot be found even after performing a predetermined number of retries, there is no base station in the vicinity and frame synchronization is not performed. Even if the CCH frame is transmitted to the other station, it is determined that the neighboring base station does not interfere with the other network connection base station 100 which is the receiving base station, and the CCH frame transmitted by the own station is transmitted without correction. I do.

  In addition, if there is no reference base station in the vicinity and a base station other than the reference base station, that is, a base station that is not connected to the I ′ line, which is a reference for frame synchronization, is found, frame synchronization is not performed. If the CCH transmission is performed, there is a possibility of serious interference in the vicinity, so that the start-up operation can be stopped.

  In addition, when the other network connection base station 100 is synchronized with the reference base station 200, a specific bit different from the above of the CS-ID is turned ON or OFF to indicate that it is synchronized with the reference base station. When the other base station 100 ′ (not shown) for connecting to the other network cannot find the reference base station 200, the base station 100 for connecting to another network that is in frame synchronization with the reference base station 200 is sent to. By synchronizing, the accuracy of frame synchronization can be maintained.

2) Determination of CCH frame timing transmitted by own station First, transmission and reception timings of the own station and the peripheral station which are base stations for connection to other networks will be described with reference to FIG. In the PHS base station, one signal section for transmission and reception is called a slot, and eight consecutive slots are called one frame. One frame is divided into a transmission frame and a reception frame each including four slots. The transmission frame and the reception frame appear alternately as positive and negative pulse waveforms as shown in the figure.

  Four slots from the first slot to the fourth slot are provided in the order in which they appear in the transmission frame and the reception frame. Normally, communication between a base station and a mobile unit that is a mobile PHS terminal is performed in a pair of slots. For example, when transmission is performed from a base station to a mobile unit using the first slot, The station receives the signal from the slave unit using the same slot (first slot) of the reception frame.

  Next, transmission / reception timing between base stations will be described.

  Assume that a peripheral station (a reference base station or another network connection base station) performs transmission and reception at the timing indicated by 301 in FIG. In this case, since the local station needs to perform transmission and reception at the same timing as the peripheral station, transmission and reception are performed at the timing indicated by 302. This is because if the transmission timing of the local station is different from the timing shown in 302 in the figure, the reception timing of the peripheral station overlaps with the transmission timing of the local station, which causes serious interference to the peripheral station. is there.

  In addition, when it is necessary for the local station to receive a signal transmitted by the peripheral station, it is necessary to perform reception at the timing indicated by 303 in the figure because it is necessary to perform reception at the timing transmitted by the peripheral station. .

  Next, a procedure in which the other network connection PHS base station 100 determines the transmission / reception timing of the own station will be described.

  The own station which is the base station 100 for connecting to the other network first performs reception only for a certain period of time using either the wireless device 1 (101) or the wireless device 2 (102), and the received base The CS-ID and reception level of the station are stored, and it is determined from the CS-ID whether the station is the reference base station 200 or not. Next, the base station 200 that matches the synchronization condition is selected from the stored CS-ID, the reception operation is started again to receive the signal of the selected base station 200, and the transmission timing of the selected base station 200 is set. Originally, the timing of the frame transmitted by the local station 100 is determined. The timing of the frame transmitted by the own station 100 is controlled and determined by the following method according to the procedure shown in the flowchart shown in FIG.

  First, in step START, a base station that matches the conditions as described above is determined, and a signal transmitted from the base station is transmitted by either the wireless device 1 (101) or the wireless device 2 (102) shown in FIG. Receive. Note that it is determined in advance which of the wireless device 1 and the wireless device 2 is used for reception from the base station.

  Next, the wireless device 1 or the wireless device 2 generates a timing signal based on the received signal, and sends the generated signal 401 as shown in FIG. 4 to the frame timing comparison circuit 103.

  Next, in step 501, the frame timing comparison circuit 103 compares the signal 402 shown in FIG. 4 sent from the frame timing generation circuit 105 with the signal 401 generated by the wireless device 1 or the wireless device 2, and the phase difference 403. And the detection result is notified to the main control unit 107.

  In step 502, the main control unit 107 determines whether or not the phase difference 403 shown in FIG. 4 is within a predetermined allowable range. As a result of the determination, if it is within the allowable range, the timing generated by the frame timing generation circuit 103 is determined as the frame timing of the own station, and the process ends at step END. If the result of determination in step 502 is outside the allowable range, in step 503, a value necessary for correction is notified to the frame timing correction circuit 104, and the frame timing correction circuit 104 based on the notified value. The voltage applied to the built-in clock source 106 is adjusted.

  By repeating these operations, the phase difference 403 between the signal 402 generated from the frame timing generation circuit 104 and the frame timing 401 of the neighboring base station is set within an allowable range.

  Next, as shown in FIG. 3, the position of the CCH transmission slot (any one of the first slot to the fourth slot) transmitted by the own station is determined. At this time, transmission is performed in a slot different from the CCH timing of the peripheral station 200. This is because the own station always needs to receive the signal of the neighboring base station 200 in order to correct the frame timing, but as shown in FIG. 3, the own station transmits the transmission timing 311 of the neighboring base station. This is because, if the timing 321 overlaps, if the local station receives the signal at the timing 331 in order to obtain a correction signal, it causes serious interference.

  As a result of the frame synchronization processing, when the timing of CCH transmitted by the local station is determined, transmission of CCH is started.

3) Correction of CCH frame transmitted by own station After starting transmission of CCH, the other network connection base station 100 corrects a frame transmitted by the own station. This frame correction is obtained from the signal obtained by receiving the CCH of the reference base station 200 by the wireless device 2 (102) different from the wireless device transmitting the CCH (wireless device 1 in the above example). The received frame timing is sent to the frame timing correction circuit 104. Note that the wireless device 2 performs only the reception operation without performing transmission. Next, the CCH frame timing transmitted by the local station is corrected in the same manner as when determining the CCH timing transmitted by the local station.

  By controlling with the above method, it becomes possible to keep the gap between the timing of the transmission frame and the timing of the reception frame constant, and the timing of the frame transmitted by the own station and the timing of the frame transmitted by the other station are matched. be able to.

  According to the embodiments of the present invention described above, a built-in clock is used to synchronize the timing of a frame transmitted by the local station with other base stations. However, this method can obtain sufficient accuracy. Since this is not possible, as a means to compensate for this, a method is used in which the CCH transmitted from the base station serving as a reference is compared with the frame timing transmitted by the own station, and the transmission timing is corrected so that the timing matches the CCH. This means maintains the accuracy of frame synchronization.

  Therefore, a high-accuracy clock source with high cost is not required, and since the transmission timing of the frame transmitted by the local station is generated from the built-in clock, the clock signal on the line side as a clock source becomes unnecessary, and the nationwide Can maintain almost uniform frame accuracy.

  Further, in the example of the PHS base station, it is not necessary to incorporate a high-accuracy clock as a clock source, so that the cost can be reduced.

  Furthermore, since it is not necessary to connect a dedicated line to the base station for the purpose of obtaining a clock signal, a local PHS network dedicated to the premises can be constructed using existing LAN equipment or the like. A PHS base station can be installed even in a place where a line capable of supplying signals cannot be drawn.

  Furthermore, even with a base station connected to a line that cannot supply a clock source, it is possible to maintain almost uniform frame accuracy throughout the country by synchronizing with the reference base station, and to prevent interference between PHS base stations. effective.

  In addition, although the said embodiment demonstrated the Example in PHS base station, it can implement | achieve in the same method also in the base station for mobile communication other than PHS which requires frame synchronization.

It is a system configuration | structure figure of the frame synchronization system in the PHS base station for other network connection which is one Embodiment of this invention. It is a figure which shows the example of the option alerting | reporting information message used with the system shown in FIG. FIG. 2 is a transmission / reception timing chart in the system shown in FIG. 1. It is a timing diagram for demonstrating the determination method of the frame timing in the system shown in FIG. FIG. 2 is a timing diagram for explaining a frame timing control method in the system shown in FIG. 1.

Explanation of symbols

100 ... PHS base station 101 for connection to another network ... Radio unit 1 Radio unit 2
DESCRIPTION OF SYMBOLS 102 ... Frame 103 ... Timing comparison circuit 104 ... Frame timing correction circuit 105 ... Frame timing generation circuit 106 ... Built-in clock source 107 ... Main control unit 108 ... Network IF unit 200 ... Reference PHS base station 300 ... Control channel (CCH) frame 400 ... Transmission frame

Claims (3)

    Frame extraction means for receiving radio waves transmitted by a reference base station for mobile communication and extracting the transmission frame; means for controlling a built-in reference clock source by the frame extracted by the frame extraction means; and A frame synchronization method for a base station for mobile communication, comprising: means for controlling a transmission frame of the own station using the built-in reference clock source to be controlled, and synchronizing the transmission frame of the reference base station. .     The frame extraction means receives control channel information transmitted from the reference base station, and corrects the timing of the transmission frame using a timing signal generated from the control channel information, thereby automatically 2. The frame synchronization method for mobile communication base stations according to claim 1, wherein the transmission frames of the stations are synchronized.     The means for controlling the built-in reference clock source receives the control channel information and generates a transmission frame timing signal, a frame timing signal generation circuit for generating the transmission frame timing signal of the own station, and the frame A frame timing comparison circuit to which a transmission frame timing signal generated by a timing signal generation circuit and a frame timing signal generated by the radio unit are supplied, and the two input transmission frames as outputs of the frame timing comparison circuit When the difference between the timing signals exceeds a predetermined range, the frame timing signal is changed by controlling the internal clock source, and the timing of the transmission frame of the local station is received from the other base station. With the feature to match the frame Frame synchronization method of a mobile communication base station according to claim 2, wherein that.

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