JP2009232434A - Base station device, and synchronizing signal acquiring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct out-of-synchronism that occurs during a communication with a mobile terminal. <P>SOLUTION: Regarding a base station device includes a means for periodically halting a communication mode for communicating with a terminal device and a means which implements a synchronization mode for receiving a transmission signal from another base station device and acquiring a synchronizing signal while the communication mode is periodically halted. During the synchronization mode, on the basis of the synchronizing signal, out-of-synchronism that occurs during the communication mode is corrected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a base station apparatus and a synchronization signal acquisition method.

  In a wireless communication system in which mobile terminals can communicate, such as WiMAX (Worldwide Interoperability for Microwave Access), a large number of base stations are installed in various places. A mobile terminal in an area (cell) covered by each base station can communicate with a base station covering the area.

When the mobile terminal moves, the base station with which the mobile terminal communicates is changed. However, when the base station is changed, the mobile terminal simultaneously changes from two base stations (serving base station and target base station). Will receive the signal.
For this reason, in order to smoothly move a mobile terminal between base stations, it is necessary to ensure synchronization between base stations with the same transmission timing between adjacent base stations.

When synchronization between base stations is established, when a mobile terminal moves between base stations, the mobile terminal can simultaneously receive signals from two base stations, and can smoothly move between base stations.
Here, as a technique for synchronization between base stations, for example, there is one described in Patent Document 1.
JP 59-6642 A

In order to achieve synchronization between base stations, it is conceivable that each base station apparatus receives a GPS signal from a GPS satellite and each base station operates with a common synchronization signal as in Patent Document 1.
However, when synchronizing using a GPS signal, each base station needs to have a GPS receiver, resulting in an increase in size and cost. In addition, in the case of a base station installed in an environment that cannot receive GPS signals such as indoors, it becomes impossible to establish synchronization between base stations.

Therefore, it is conceivable to receive a synchronization signal transmitted by another adjacent base station, detect the transmission timing of the other adjacent base station, and synchronize at the transmission timing.
In this case, since synchronization can be achieved by wireless communication using the same frequency as that used for communication with the mobile terminal, a special receiving system for synchronization is not required unlike a GPS receiver for receiving GPS signals.
For this reason, it is possible to reduce the size and cost of the base station, and it is suitable as a small base station installed indoors.

Here, the WiMAX described above employs a communication method that realizes duplex communication by TDD (Time Division Duplex) that switches between transmission and reception at high speed for wireless communication with a mobile terminal.
Specifically, as shown in FIG. 17, in WiMAX, one basic frame is composed of a downlink subframe (base station signal transmission time) and an uplink subframe (base station signal reception time) arranged in the time direction. Has been placed. The downlink subframe has a preamble at the beginning.

FIG. 17 shows a state in which the transmission timing and the reception timing coincide and are synchronized among a plurality of base stations.
Such processing for synchronization between base stations is performed when the base station is activated, and normal communication with a mobile terminal is performed after synchronization between base stations is established.

  However, depending on the difference in the accuracy of the clock generators possessed by the base station, the synchronization may shift due to the passage of time or the like. In other words, even if synchronization with other base stations is established when the base station is started, if communication is subsequently performed with the mobile terminal (terminal device), synchronization deviation gradually occurs due to a difference in accuracy of the clock generator. .

  Therefore, an object of the present invention is to correct a synchronization shift that occurs during communication with a terminal device.

  The present invention relates to a means for periodically suspending a communication mode for performing communication with a terminal device, and a synchronization signal by receiving a transmission signal from another base station device during the periodic suspend of the communication mode. And a means for executing a synchronization mode for obtaining a base station apparatus, wherein, in the synchronization mode, a synchronization shift occurring during the communication mode is corrected based on the synchronization signal. .

  According to the present invention, the communication mode is periodically paused, and the synchronization mode is executed during the pause. Therefore, even if a synchronization shift occurs while the base station apparatus communicates with the terminal apparatus, the synchronization shift is periodically corrected.

  Moreover, it is preferable to provide a means for changing the cycle for suspending the communication mode. It is preferable to provide means for randomly changing the period for pausing the communication mode. It is preferable to provide a means for changing the period of suspending the communication mode based on a past amount of synchronization deviation.

  In order to eliminate the synchronization error, as described above, it is necessary to reestablish synchronization between base stations even during communication with a mobile terminal.

Here, when adopting a synchronization method using a synchronization signal transmitted by another base station, the base station to be synchronized is at a timing when the other base station is transmitting to the mobile terminal, A synchronization signal must be received.
In other words, in order to achieve synchronization between base stations, signal transmission to the mobile terminal must be suspended during the time when the signal should be transmitted to the mobile terminal.

For this reason, the base station (second base station) that is attempting to synchronize with another base station (first base station) is further in the meantime other base stations (third base station). The synchronization signal for the station cannot be transmitted.
As a result, the re-establishment of synchronization between base stations in the third base station is prevented.

  Therefore, it is also desired to reduce the influence on other base station devices even if the communication mode is suspended in order to acquire a synchronization signal from another base station device.

  The present invention from the above viewpoint is a synchronization signal acquisition method for a base station apparatus in a radio communication system having a plurality of base station apparatuses that perform radio communication by time division duplex with a terminal apparatus. Including a step of suspending a communication mode for performing communication with a terminal device and executing a synchronization mode for acquiring a synchronization signal from a transmission signal from another base station device during the suspension, The synchronization signal acquisition method is characterized in that a signal acquisition timing is different for each base station apparatus.

  According to the present invention, since the timing for acquiring the synchronization signal for eliminating the synchronization shift is different for each base station apparatus, even if the communication mode is suspended to acquire the synchronization signal from another base station apparatus. Furthermore, there is little influence on other base station apparatuses.

Further, the present invention related to a base station apparatus is a base station apparatus that performs radio communication by time division duplex with a terminal apparatus, and pauses a communication mode for performing communication with the terminal apparatus. Means for executing a synchronization mode for acquiring a synchronization signal by receiving a transmission signal from another base station apparatus during the suspension, and when the synchronization signal cannot be acquired in the synchronization mode, Means for attempting to acquire the synchronization signal even at the timing of the communication frame.
According to the present invention, the synchronization signal acquisition timing can be shifted even if the synchronization mode for acquiring the synchronization signal is started simultaneously with another base station apparatus.

Another aspect of the present invention related to a base station apparatus is a base station apparatus that performs radio communication by time division duplex with a terminal apparatus, and pauses a communication mode for performing communication with the terminal apparatus. Means for executing a synchronization mode for receiving a transmission signal from another base station apparatus during the suspension and acquiring a synchronization signal; and means for controlling the synchronization mode to be performed at a set cycle And means for randomly changing the set value of the period.
According to the present invention, since the cycle of the synchronization mode is randomly changed, it is unlikely that the synchronization mode for acquiring the synchronization signal is performed simultaneously with other base station apparatuses.

Another aspect of the present invention related to a base station apparatus is a base station apparatus that performs radio communication by time division duplex with a terminal apparatus, and pauses a communication mode for performing communication with the terminal apparatus. A means for executing a synchronization mode for receiving a transmission signal from another base station device during the suspension and acquiring a synchronization signal; and a means for controlling the synchronization mode to be performed at a set timing. The setting timing value of the synchronization mode is a unique value unique to the base station apparatus.
According to the present invention, since the setting timing value of the synchronization mode is a unique value unique to the base station apparatus, the synchronization mode for acquiring the synchronization signal is prevented from being performed simultaneously with other base station apparatuses. it can.

  A frame counter that counts communication frames, means for acquiring frame index information included in a transmission signal from another base station device, and a value of the frame counter based on the acquired frame index information. And a means for matching with the value of the frame counter in the base station device, and the synchronization mode setting timing value is preferably a unique frame counter value unique to the base station device. In this case, the frame counters between the base station devices are matched, and the unique frame counter value unique to the base station device is set as the synchronization mode setting timing value, so the synchronization mode timing is shifted between the base station devices. Easy to do.

  It is preferable to further include means for obtaining a unique frame counter value unique to the base station apparatus from identifier information unique to the base station apparatus. In this case, since a unique frame counter value unique to the base station apparatus itself can be obtained from the identifier information unique to the base station apparatus, the unique frame counter value unique to the base station apparatus can be obtained from each base station. There is no need to set the station device.

Another aspect of the present invention related to a base station apparatus is a base station apparatus that performs radio communication by time division duplex with a terminal apparatus, and receives a transmission signal from another base station apparatus to acquire a synchronization signal Means for executing a synchronous mode for performing, and at a set timing, a means for suspending the communication mode for performing communication with a terminal device and controlling the synchronous mode to be performed. And when the synchronization signal cannot be acquired even after performing the synchronization mode, the communication mode is resumed, and then the communication mode is suspended and the synchronization mode is performed again. Features.
According to the present invention, the synchronization signal acquisition timing can be shifted even if the synchronization mode for acquiring the synchronization signal is started simultaneously with another base station apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, even if a synchronization gap generate | occur | produces during communication with a terminal device, a synchronization gap can be corrected in the synchronization mode performed by pausing the communication mode.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
FIG. 1 shows a wireless communication system having a plurality of base station devices (BS) 1, 2, 3,. In this wireless communication system, for example, in order to realize broadband wireless communication, a method based on “WiMAX” defined in IEEE 802.16 that supports an orthogonal frequency division multiple access (OFDMA) method is adopted.

Each base station apparatus 1, 2 and 3 can communicate with a terminal apparatus (mobile terminal MS; Mobile Station) in an area (cell) covered by each base station apparatus 1, 2 and 3. .
As shown in FIG. 17, in WiMAX, one basic frame is arranged such that a downlink subframe (signal transmission time of the base station apparatus) and an uplink subframe (signal reception time of the base station apparatus) are arranged in the time direction. It is a communication system that performs duplexing of transmission and reception by TDD (Time Division Duplexing).

The length of one basic frame is 5 msec. The downlink subframe is a time zone in which the base station devices 1, 2, and 3 transmit signals to the terminal devices in its own area, and the uplink subframe is the base station devices 1, 2, and 3 in its own area. It is a time zone for receiving a signal from the terminal device.
The downlink subframe includes a preamble that is a known signal at the head.

The plurality of base station apparatuses 1, 2, and 3 include at least one master base station apparatus and slave base station apparatus.
The master base station device is a base station device that does not need to detect and acquire timing for synchronization between base stations from a received wave of a signal transmitted by another base station device. For example, the master base station device can be configured as a self-running master base station device that determines the signal transmission timing based on a synchronization signal (clock) generated by the device. Note that the master base station apparatus may include a GPS receiver and determine the signal transmission timing using a GPS signal.

The slave base station device is a base station device that detects and acquires timing for synchronization between base stations from a received wave of a signal transmitted by another base station device.
In the following, the first base station apparatus 1 shown in FIG. 1 is a master base station apparatus, and the second base station apparatus 2 and the third base station apparatus 3 are slave base station apparatuses.

  Slave base station apparatuses 2 and 3 select one base station apparatus as a source base station apparatus from among other base station apparatuses (master base station apparatus or other slave base station apparatus) at the time of activation, and the source A reception wave (source reception wave) of a signal (preamble; known signal; synchronization signal) transmitted by the base station apparatus is detected, and timing (signal transmission timing) for synchronization between base stations is acquired. Note that processing for synchronization between base stations performed when the base station apparatus is activated is referred to as initial synchronization processing. The initial synchronization process is performed at the time of activation as described above, and more specifically, is performed after the base station apparatus is activated and before communication with the terminal apparatus is started. The specific contents of the initial synchronization process are almost the same as those in the “synchronization mode in which communication is suspended” described later.

And a slave base station apparatus communicates with the terminal device in an own area, synchronizing with the transmission timing (reception timing) of a source base station apparatus. That is, the communication (communication mode) performed by the slave base station device with the terminal device after the initial synchronization processing is the transmission timing and reception timing (communication timing) and timing of the source base station device (other base station device). Will match.
However, if the accuracy of the clock generator of the slave base station device is not sufficient, or if the clock accuracy varies among the base station devices, a synchronization shift occurs over time. That is, when the base station device is communicating with the terminal device, a transmission / reception timing (communication timing) of another base station device and a shift (synchronization shift) gradually occur.
That is, since an error in the clock frequency of the clock generator included in the base station apparatus exists between the base station apparatuses, one communication frame (downlink subframe) generated based on the clock frequency (reference signal) The time length (for example, 5 msec in the standard) is slightly different between the base station apparatuses. Even if the error of the time length of one frame is slight, if the transmission of the frame to the terminal device is repeated, the error accumulates and there is a possibility that a relatively large synchronization shift (for example, about 1 μsec) may occur.
Thus, even if the communication timing between the base station apparatuses is aligned in the initial synchronization process, the synchronization shift gradually increases during the communication with the terminal apparatus.

Therefore, the slave base station devices 2 and 3 pause (stop) communication (transmission signal; downlink subframe) with the terminal device at a predetermined timing, and stop the synchronization mode (communication was paused). Synchronized mode).
FIG. 2 shows a synchronization mode in which the base station apparatuses 2 and 3 receive signals from other base station apparatuses (master base station apparatus or slave base station apparatus) from the (normal) communication mode in which communication with the terminal apparatus is performed. The flowchart for switching to is shown.

As shown in FIG. 2, the base station apparatuses 2 and 3 determine whether or not it is a synchronization timing that should be set to the synchronization mode (step S1). The synchronization timing is set, for example, as a cycle (every predetermined time or every predetermined number of frames) in which the synchronization mode is set. When setting a period by time, it can be set as about 5 minutes, for example.
When it is determined that it is time to shift to the synchronization mode in the normal communication mode in which communication is performed with the terminal device (step S2), the base station devices 2 and 3 are in the synchronization mode (step S3). Migrate to When the synchronization mode ends, the normal communication mode is resumed (step S4).
The base station devices 2 and 3 communicate with the terminal device, but can eliminate the synchronization loss by executing the synchronization mode periodically or whenever necessary. it can.

  As shown in FIG. 3, when the base station devices 2 and 3 are in the synchronization mode, first, before starting the synchronization process (steps S12 to S14), the terminal is broadcast to all the terminal devices in its own area. Notification is made to put the device into sleep mode or idle mode (power saving mode) (step S11).

When receiving the notification such as the sleep mode from the base station devices 2 and 3, the terminal device shifts to the sleep mode. Since the sleep mode or the like is a management mode when the terminal device is not performing communication, power consumption can be suppressed.
The sleep time of the terminal device is set so as to continue at least while the base station devices 2 and 3 perform the synchronization process.

  Since the terminal device is in the sleep mode or the like while the base station devices 2 and 3 are performing the synchronization process, there is a possibility that the terminal device may determine that it is abnormal even if the signal from the base station devices 2 and 3 cannot be received. Absent.

  After notifying the terminal device of the sleep mode or the like, the base station devices 2 and 3 shift to synchronization processing (synchronization processing in which communication is suspended). During this synchronization process, communication with the terminal device (downlink subframe transmission) is suspended, and a signal is originally received even in the time of the downlink subframe.

In the synchronization process (synchronization process in which communication is suspended), first, a signal from another base station apparatus 2 is received (step S12). In this embodiment, the preamble at the head of the downlink subframe DL transmitted by another base station apparatus 2 is used as a synchronization signal for synchronization between base stations. For this reason, the base station apparatus 1 detects the timing of the preamble at the head of the downlink subframe DL transmitted by the other base station apparatus 2.
Note that the synchronization signal may be a midamble, a pilot signal, or the like.

Base station apparatuses 2 and 3 have a function of scanning (receiving signals) received waves from other base station apparatuses adjacent to the base station apparatuses 2 and 3 in order to detect preamble timing.
The base station apparatuses 2 and 3 have a preamble pattern that may be used by other base station apparatuses 1 and 2 in a memory as a known pattern. The base station apparatuses 2 and 3 detect the preamble timing and the like using these known preamble patterns.

そして、図４（ｂ）に示すように、受信波Ｘ（ｔ）と既知プリアンブルパターンＰ（ｎ）の相関値がピークをとった位置を、プリアンブルのタイミングｔとして検出することができる。
このプリアンブルタイミングｔが、自装置２，３が下りサブフレームを送信する際の送信タイミングとなる。 FIG. 4 shows an example of a method for detecting the preamble timing. Since the preamble is a known signal, the signal waveform of the preamble is also known. If the received signal after sampling is X (t) and the signal in the discrete time domain of the preamble is P (n) (n = 0,..., N−1), the received wave X shown in FIG. For (t), the sliding correlation of P (n) is taken in the time direction based on the following equation.

Then, as shown in FIG. 4B, the position where the correlation value between the received wave X (t) and the known preamble pattern P (n) takes a peak can be detected as the preamble timing t.
This preamble timing t is a transmission timing when the own apparatuses 2 and 3 transmit a downlink subframe.

  If the preamble is not detected (timing is acquired) even if the signals from the other base station apparatuses 1 and 2 are scanned (received) (step S13), the process of step S14 is performed to detect the preamble again. (Details will be described later). When the preamble can be detected (step S13), the synchronization shift is corrected (step S15).

The base station apparatuses 2 and 3 correct the synchronization error by setting the acquired preamble timing t to be the transmission start timing of the downlink subframe. That is, the difference between the transmission timings of the devices 2 and 3 and the detected preamble timing t is detected as a synchronization shift (timing offset; synchronization error). Then, by correcting the transmission timing (frame timing) of the own devices 2 and 3 based on the detected synchronization shift, the transmission timing of the own devices 2 and 3 is changed to the transmission timing of the other base station devices 1 and 2. Can match. In other words, synchronization can be reestablished by shifting the transmission timing (frame timing) of the own apparatus in the correct direction by the amount of the detected synchronization error with reference to the timing of the detected synchronization signal.
If the transmission timing is matched with the transmission timing of another base station, the reception timing is also matched naturally. That is, the frame synchronization is established with other base stations.
In this way, the communication mode for performing communication with the terminal device is suspended, and synchronization is performed using a synchronization signal from another base station device, so that even if there is no control channel for synchronization, Can be synchronized.

When the above synchronization processing is completed, the base station devices 2 and 3 return from the synchronization mode to the normal communication mode, and can communicate with the terminal device.
The terminal device in the sleep mode or the like automatically enters the normal communication mode in which communication with the base station devices 2 and 3 is automatically performed when the set sleep time (idle time) has elapsed. That is, when both the base station apparatuses 2 and 3 and the terminal apparatus return to the normal communication mode, communication between the two is resumed.
The synchronization mode is repeatedly performed with the communication mode paused at any time, so that synchronization with other base station apparatuses can be maintained even if a synchronization shift occurs during the communication mode.

Now, the process of step S14 when the preamble cannot be detected in step S13 of FIG. 3 will be described.
Here, it is assumed that the slave base station apparatus 3 (BS3) in FIG. 1 cannot detect the preamble. Moreover, if the preamble is transmitted from the slave base station apparatus 2 (BS2), the slave base station apparatus 3 can receive it.

  Even under the above conditions, the base station apparatus 3 cannot detect the preamble from the base station apparatus 2 as shown in FIG. 5 because the base station apparatus 3 (BS3) scans in the synchronous mode (signal reception). This is because the base station apparatus 2 (BS2) is also performing scanning (reception of signals) in the synchronous mode while the base station apparatus 2 is not transmitting a preamble.

That is, if the base station apparatus 2 (BS2) and the base station apparatus 3 (BS3) are simultaneously set to the synchronous mode and simultaneously perform scanning (signal reception), the base station apparatus 3 cannot detect the preamble.
Also, if the scanning period is set in advance, and if the preamble is not detected and re-scanning is performed in the next period, the scanning (synchronous mode) timing is the same for both base station apparatuses 2 and 3. If it does, naturally, even in the next period, the scanning (synchronous mode) timings of both base station apparatuses coincide with each other, and the rescanning cannot be successful.

  Therefore, in the first embodiment, if preamble detection cannot be performed at the timing of the communication frame corresponding to the set scanning cycle, the rescanning is performed at the timing of the next communication frame regardless of the set scanning cycle. I do.

FIG. 6 illustrates the rescanning process performed by the base station apparatus 3 (BS3). In FIG. 6, the base station apparatus 2 (BS2) performs scanning within the time of the downlink subframe DL of the frame F2 in FIG.
The base station apparatus 2 can acquire a synchronization signal (preamble) from the base station apparatus 1 (BS1) by scanning at the timing of the frame F2. Instead, the base station apparatus 2 cannot transmit a signal within the time corresponding to the downlink subframe DL of the frame F2.

  In this state, even if the base station apparatus 3 (BS3) performs scanning within the time of the downlink subframe DL of the frame F2, the synchronization signal (preamble) from the base station apparatus 2 cannot be acquired.

Therefore, the base station apparatus 3 performs rescanning at a time corresponding to the downlink subframe DL of the next frame F3 (step S14 in FIG. 3). At the timing of this frame F3, since the base station apparatus 2 has finished the synchronization mode and has transmitted the downlink subframe DL, the base station apparatus 3 can acquire the synchronization signal.
Further, if the base station apparatus 3 cannot acquire a synchronization signal even in the next frame F3, it may be rescanned in the next frame.

In the frame F2 of the base station apparatus 2 (BS2), normal communication with the terminal apparatus is performed for the uplink subframe UL. This is because the user (terminal device) allocation in the uplink subframe UL is performed in the UL-MAP (uplink map) included in the downlink subframe DL of the previous frame F1.
Therefore, with respect to the uplink subframe UL, the downlink subframe DL of the frame F2 is paused, so that the uplink frame UL of the next frame F3 is paused.

  Similarly, in the base station apparatus 3 (BS3), the uplink subframe UL is not paused in the frame F2, but is paused in the next frame F3. Further, in the base station apparatus 3, because of the rescanning, the downlink subframe DL of the next frame F3 is also paused, and the uplink subframe UL of the next frame F3 is also paused.

  As described above, in the first embodiment, when a synchronization signal cannot be acquired, re-scanning is performed in the next frame regardless of the scanning period, and thus a plurality of base station apparatuses 2 and 3 are simultaneously set to the synchronization mode. Even in this case, the timing for actually acquiring the synchronization signal can be shifted.

Moreover, if all the slave base station apparatuses 2 and 3 have a function of performing rescanning in the next frame, the synchronization signal acquisition timing can be automatically shifted in the plurality of base station apparatuses.
In other words, in order to shift the synchronization signal acquisition timing in a plurality of base station devices, it may be possible to manually set individual base station devices as such at the time of installation of the base station device, but manual setting at the time of such installation Although it is not preferable because the installation work of the base station apparatus is complicated, each base station apparatus 2 and 3 has a function of automatically shifting the synchronization signal acquisition timing, thereby facilitating the installation work of the base station apparatus. .

[Second Embodiment]
FIG. 7 shows another method for shifting the timing for acquiring the synchronization signal between the base station apparatuses 2 and 3. In the second embodiment shown in FIG. 7, the points that are not particularly described are the same as those in the first embodiment. Further, the method of the second embodiment can be applied in addition to or instead of the method of rescanning in the next frame in the first embodiment.

In the second embodiment, the base station devices 2 and 3 are configured to appropriately change the set value (set synchronization timing cycle) used for the synchronization timing determination performed in step S1 of FIG.
That is, in the base station apparatus of 2nd Embodiment, the change period which changes a synchronization timing period is set, and it has a function which changes a synchronization timing for every this period.

For example, in the base station apparatus 2 (BS2), the synchronization timing period is T1 until a certain point in time, but the synchronization timing period is changed from T1 to T2 in the set change period. In the next change cycle, the synchronization timing cycle is changed from T2 to T3.
The changed synchronization timing cycle is randomly determined using a random number or the like.

  Further, in the base station apparatus 2 (BS3), the synchronization timing period is T1 until a certain point in time, but the synchronization timing period is changed from T1 to T4 in the set change period. In the next change cycle, the synchronization timing cycle is changed from T4 to T5. These changed synchronization timing periods are also determined randomly.

  In this way, by periodically changing the synchronization timing period at random, even if the initial setting value of the synchronization timing period is manufactured at a common value T1 in each base station apparatus, the base station apparatus is operated. By doing so, the synchronization timing period automatically differs in each base station apparatus, and the synchronization signal acquisition timing of each base station apparatus can be shifted.

[Third Embodiment]
8 to 10 show still another method for shifting the timing for acquiring the synchronization signal between the base station apparatuses 2 and 3. In the third embodiment shown in FIGS. 8 to 10, the points not particularly described are the same as those in the first embodiment. Further, the method of the third embodiment can be applied in addition to or instead of the method of rescanning in the next frame in the first embodiment.

  In the third embodiment, each base station apparatus 1, 2, 3 in the system is provided with a frame counter function for counting communication frames, and the values of the respective frame counters are made to coincide between the base station apparatuses. In the third embodiment, the base station apparatuses 2 and 3 perform scanning for acquisition of synchronization signals at different frame timings based on the frame counter value.

Here, the frame counter counts each basic frame, and the counter value ranges from the counter minimum value to the counter maximum value. The frame counter performs a cyclic count that returns to the counter minimum value when the counter value exceeds the maximum value.
The counter value of the frame counter is included as frame index information indicating a frame number in a downlink subframe transmitted to the terminal device. Since the frame index information is broadcasted as a control signal (FCH; frame control header) that can be read by all terminal apparatuses, other base station apparatuses after the synchronization between base stations can read the frame index information. it can.

In the third embodiment, in order to match the frame counter value with the source base station apparatus, the frame index information is acquired after the synchronization processing in the synchronization mode. Specifically, as shown in FIG. 8, after synchronization processing (steps S12 to S15), frame index information is obtained from a frame (downlink subframe DL) transmitted from another base station apparatus (source base station apparatus). Is acquired (step S16). Then, the acquired frame index information is set in the frame counter of the own device. As a result, the frame counter value of the source base station apparatus matches the frame counter value of the own apparatus, and the frame counter synchronization is established between these base station apparatuses.
In FIG. 8, steps S11, S12, S13, and S15 are the same processes as steps S11, S12, S13, and 15 in FIG.

  In addition, here, the frame index information is acquired every time the synchronization mode is used, but if the frame index information is acquired immediately after the synchronization processing between the base stations when the base station apparatus is activated, You may make it not acquire.

In the present embodiment, since the frame counter values of the base station devices match each other, this frame counter value can be used as a reference when determining the timing at which each base station device acquires the synchronization signal.
That is, as in the second embodiment, even if the synchronization signal acquisition timing is simply random, the scanning timing usually shifts between the base station apparatuses, but there is a possibility that the scanning timings coincide with each other. . Therefore, in order to reliably shift the synchronization signal acquisition timing, it is necessary to use the method as in the first embodiment in combination.

  On the other hand, if each base station apparatus 1, 2, 3 has a common reference (frame counter), the synchronization signal acquisition timing is determined by determining the synchronization signal acquisition timing (scanning timing) using the reference. It is possible to reliably shift between devices.

For this reason, the base station apparatus according to the third embodiment, as shown in FIG. 9, determines the synchronization signal acquisition timing (synchronization timing; synchronization signal) from the identifier information (BS ID or cell ID) unique to each base station apparatus. (Acquisition cycle).
The synchronization timing calculation function shown in FIG. 9 is a common function (calculation formula) possessed by each of the base station apparatuses 2 and 3. This function is to determine a frame counter value (frame index) Is that is unique to each base station apparatus from a unique identifier of the base station apparatus (hereinafter referred to as “BS ID”). The value determined by this function takes a value from the minimum value to the maximum value of the frame counter.
Such a function is realized by, for example, a hash function (not necessarily a complete hash function).

  FIG. 10 shows a flowchart for performing the determination in step S1 of FIG. 2 using the synchronization timing Is determined using the function of FIG. First, it is determined whether or not the frame counter value of its own device matches the frame index Is that is the synchronization timing (step S21). If the frame counter value matches Is, it is determined that it is the synchronization timing (step S22). If the frame counter value does not coincide with Is, it is not the synchronization timing, and the process ends.

  The frame counter is also counted when the base station apparatus enters the synchronization mode and does not transmit a frame (downlink subframe). In other words, the time for receiving the synchronization signal from the other base station apparatus does not transmit the downlink subframe, but maintains normal frame counter synchronization with the other base station apparatus. In the case of the mode, the frame counter is counted at every timing of transmitting a frame (downlink subframe).

  As described above, in the third embodiment, since the base station apparatus itself can automatically determine the timing of acquisition of the synchronization signal specific to each base station apparatus from the identifier information specific to the base station apparatus like the ID of the BS, If identifier information unique to the base station apparatus is set like the ID of the BS, it is not necessary to manually set the timing until acquisition of the synchronization signal specific to each base station apparatus.

Further, since the function itself is common to each base station apparatus, it is not necessary to make a special setting for shifting the timing of synchronization signal acquisition in each base station apparatus.
In addition, even if the base station apparatus itself automatically determines the synchronization signal acquisition timing, the timing is surely shifted between the base station apparatuses because it is based on the common frame counter value among the base station apparatuses. .

[Fourth Embodiment]
11 and 12 show still another method for shifting the timing for acquiring the synchronization signal between the base station apparatuses 2 and 3. In the fourth embodiment shown in FIGS. 11 to 12, the points not particularly described are the same as those in the first embodiment. In addition, the method of the fourth embodiment temporarily resumes the normal communication mode instead of performing rescanning in the next frame as in the first embodiment when the synchronization signal cannot be acquired in a certain frame. Then, re-scanning is performed.

Specifically, as shown in FIG. 11, the base station apparatuses 2 and 3 determine whether or not it is a synchronization timing that should be in the synchronization mode (step S1). The synchronization timing is set, for example, as a cycle (every predetermined time or every predetermined number of frames) in which the synchronization mode is set.
When it is determined that it is time to shift to the synchronization mode in the normal communication mode in which communication is performed with the terminal device (step S2), the base station devices 2 and 3 are in the synchronization mode (step S3). Migrate to When the synchronization between base stations is successful and the synchronization mode ends (step S5), the normal communication mode is resumed (step S4).

On the other hand, in the synchronization mode, when the synchronization signal cannot be acquired and the synchronization between base stations fails (step S5), the base station devices 2 and 3 determine whether or not it is a re-synchronization timing to try again to acquire the synchronization signal Make a decision.
The resynchronization timing is set in advance so as to be the timing before the synchronization timing arrives, or is determined at random using a random number. Further, when a preset value is used as the resynchronization timing, it is preferable that the resynchronization timing is different between the base station apparatuses.

  If it is not resynchronization timing (step S7), it will once return to normal communication mode, and base station apparatus 2 and 3 will communicate with a terminal device until it becomes resynchronization timing (step S8). That is, when the synchronization between the base stations fails in the synchronization mode, the base station devices 2 and 3 once return to the normal communication mode (provisional communication mode). In this provisional communication mode, the base station devices 2 and 3 can communicate with the terminal device.

In the provisional communication mode, when the resynchronization timing comes (steps S6 and S7), the synchronization mode (resynchronization mode) is performed again.
The processes in steps S5 to S9 are repeatedly performed until the synchronization between base stations in the synchronization mode in step S9 is successful, but the repetition ends before the synchronization timing determined in step S1 is exceeded.

FIG. 12 shows the processing in the synchronous mode shown in step S3 and step S9 in FIG.
As shown in FIG. 12, when the base station devices 2 and 3 enter the synchronous mode, first, the terminal devices are set to the sleep mode or the idle mode (power saving mode) by broadcasting to all the terminal devices in the own area. Notification is made (step S11).

  Subsequently, the base station apparatus 3 receives a signal from another base station apparatus 2 (step S12). Then, the base station device 3 detects the preamble timing from the other base station device 2.

When the base station apparatus 3 can scan the signals from the other base station apparatuses 1 and 2 to detect the preamble and acquire the preamble timing (step S13), the synchronization error correction is performed using the preamble timing. Is performed (step S15).
If the synchronization between base stations in step S15 is successful, a synchronization success flag is set, and the synchronization mode ends.

On the other hand, in step S13, if a preamble is not detected even if signals from other base station apparatuses 1 and 2 are scanned, scanning is continued until a predetermined time for continuing scanning arrives (step S17). .
If the preamble cannot be detected even after a predetermined time for continuing scanning (step S17), a synchronization failure flag is set, and the synchronization mode is terminated.
Thus, in the fourth embodiment, synchronization may fail and the synchronization mode may end.

  Here, in the synchronization success determination in step S5 of FIG. 11, if the synchronization success flag is set, it is regarded as synchronization success, and if the synchronization failure flag is set, it is regarded as synchronization failure.

[Fifth Embodiment]
FIG. 13 shows the configuration of base station apparatuses 1, 2, and 3 according to the fifth embodiment. The base station apparatus of 5th Embodiment can change the period (timing) which pauses communication with a terminal device for synchronous mode execution. This cycle changing function has already been described in the above-described embodiment, but in the fifth embodiment, this cycle changing function will be described in further detail. Note that points not particularly described in the fifth embodiment can be the same as those in the first to fourth embodiments.

FIG. 13 illustrates a configuration centering on the reception unit 10 and the transmission unit 20 in the base station apparatus. The reception unit 10 includes an amplifier 11 that amplifies the reception signal, an A / D conversion unit 12 that performs A / D conversion on the reception signal, and a demodulation unit (DEM) 13 that demodulates the reception signal converted into a digital signal. .
The transmission unit 20 includes a modulation unit (MOD) 21 that modulates a transmission signal that is a digital signal, a D / A conversion unit 22 that performs D / A conversion on the transmission signal, and an amplifier 23 that amplifies the transmission signal. Yes.
Since the base station apparatus communicates with the terminal apparatus by TDD (Time Division Duplex), a switch (SW) 31 for switching the connection with the antenna 30 between the receiving unit 10 side and the transmitting unit 20 side is provided. I have. That is, at the timing of the transmission frame (downlink subframe), the switch 31 is switched to the transmission unit 20 side, and at the timing of the reception frame (uplink subframe), the switch 31 is switched to the reception unit 10 side.

  The operation clocks of the A / D converter 12 and the D / A converter 22 are supplied from a reference signal generator 40. The reference signal generator 40 includes a clock generator such as a crystal resonator and generates an operation clock having a predetermined frequency. Needless to say, the operation clock also serves as an operation clock for other digital circuits in the base station apparatus such as the frame timing counter 40.

  Here, the accuracy of the operation clock of the D / A converter 22 affects the accuracy of the time length of the transmission frame (downlink subframe). Therefore, if the accuracy of the reference signal generator is different for each base station apparatus, an error occurs in the operation clock between the base station apparatuses, and the time length of the generated transmission frame is slightly different for each base station apparatus. Become.

  Switching between transmission and reception is performed according to the counter value in the frame timing counter 32. That is, the time length of the transmission frame, the time length of the reception frame, and the time interval between these frames are determined in advance, and when the counter value matches a predetermined transmission / reception switching timing, transmission / reception is performed by the changeover switch 31. Switching takes place.

  When a synchronization shift with another base station apparatus occurs, the synchronization shift can be corrected by correcting the counter value of the frame timing counter 32. For example, when it is detected that there is n synchronization values (synchronization errors), the transmission / reception switching timing can be matched with other base station apparatuses by shifting the counter value of the counter 32 in the correct direction by n. it can.

  The synchronization error (synchronization error) is detected by the synchronization error detector 33. As shown in FIG. 4, the synchronization error detector 33 detects a synchronization signal (preamble) from the received signal (received wave), and detects a synchronization error (timing offset). The detected synchronization error is given to the frame timing counter 32, and the synchronization error (synchronization error) is corrected.

  In order to detect a synchronization error using a signal transmitted from another base station apparatus, the reception unit 10 includes a changeover switch 14 for switching the reception signal to the demodulation unit 13 side or the synchronization error detection unit 33 side. . This change-over switch 14 gives the received signal to the demodulator 13 during the communication mode in which the signal from the terminal device can be received, and the received signal is sent to the synchronization error detector 33 in the synchronous mode in which the communication mode is suspended. give.

  The transmission unit 20 also has a changeover switch 24. The changeover switch 24 applies a transmission signal to the D / A converter 22 during a communication mode in which a signal can be transmitted to the terminal device, and transmits the transmission signal to a D / A converter in the synchronous mode in which the communication mode is suspended. 22 is not to be given.

  The period controller 34 switches the selectors 14 and 24 between the receiver 10 and the transmitter. The cycle control unit 34 is for controlling the cycle (synchronization timing) for suspending the communication mode. The cycle control unit 34 performs processing according to the flowchart of FIG. That is, when the cycle control unit 34 determines that it is time to shift to the synchronization mode when it is in the normal communication mode in which communication with the terminal device is performed, the cycle control unit 34 enters the synchronization mode and switches the switches 14 and 24. I do. Then, when the synchronous mode ends, the normal communication mode is restored.

  In addition, the cycle control unit 34 has a function of changing the cycle for suspending the communication mode. That is, the cycle control unit 34 can set the cycle for suspending the communication mode to, for example, 5 minutes in some cases and 6 minutes in other cases. The period (synchronization timing) for suspending the communication mode can be changed for the purpose of shifting the synchronization signal acquisition timing between the base station apparatuses as in the above-described embodiment, but for other purposes. You can go. As another object, specifically, adaptive control of a period (synchronization timing interval) for suspending the communication mode can be mentioned.

  Here, the adaptive control of the cycle for stopping the communication mode (synchronization timing interval) means that in the situation where the synchronization shift (synchronization error) is likely to increase, the cycle for stopping the communication mode is shortened and the synchronization mode is frequently set. In such a situation that the synchronization error deviation does not become large by executing, and the synchronization deviation (synchronization error) does not occur so much, the communication mode is paused, etc., and the frequency of executing the synchronization mode is reduced. It is.

FIG. 14 shows a synchronization shift (timing offset) between the master base station apparatus (master BS) 1 and the slave base station apparatus (slave BS) 2.
As described above, even if the error of each communication frame of the slave base station apparatus is slight, if the frame transmission is repeated, an error of the time length of the frame accumulates, and as shown in FIG. (Offset) increases.

In order to eliminate this synchronization shift, the slave base station apparatuses 2 and 3 execute a synchronization mode in which the communication mode for performing communication (transmission) with the terminal apparatus is periodically paused and the synchronization is resumed.
FIG. 15A shows an offset of the clock frequency of the slave base station device 2 with respect to the clock frequency of the master base station device 1. As illustrated in FIG. 15A, the offset of the clock frequency of the slave base station apparatus 2 becomes larger than the clock frequency of the master base station apparatus 1 as time elapses. The cause of this change in offset is a change in environmental temperature.

  FIG. 15B shows a change in the synchronization shift (timing offset) in the slave base station apparatus 2 when the synchronization mode is executed every 5 minutes. When the synchronization mode is executed at the timing indicated by the arrow in FIG. 15B, the timing offset becomes almost 0, but the timing offset gradually increases between the synchronization mode and the synchronization mode (in communication mode).

As shown in FIG. 16, since the base station apparatuses 2 and 3 in the synchronous mode perform reception in a time zone that should become a transmission frame (downlink subframe), the packet that should have been transmitted in that time zone Packet loss that is not transmitted. In order to correct the synchronization shift, at least one frame may be set to the synchronization mode. However, when the synchronization mode requires several frames, the packet loss is further increased.
Therefore, from the viewpoint of preventing packet loss as much as possible, it is better that the frequency of executing the synchronous mode is low. On the other hand, in a situation where synchronization loss is likely to increase, the frequency at which the synchronization mode is executed should be increased even if there is some packet loss.

  Therefore, the cycle control unit 34 adaptively changes the cycle (frequency) at which the synchronous mode is executed as described above. In the present embodiment, the change is performed based on the past synchronization error. As shown in FIG. 13, in order to change the execution period of the synchronization mode based on the past synchronization error, the base station apparatus includes a synchronization error history storage unit 35 that stores a past history of the synchronization error.

The synchronization error history storage unit 35 can store synchronization errors for the past predetermined period (one or more synchronization errors in the past).
The cycle control unit 34 calculates information (statistics) indicating the past tendency of the synchronization error based on the history information of the synchronization error, and the synchronization mode is executed according to the size of the information (statistic). Change the cycle (frequency). That is, if the past synchronization error is large, the cycle is shortened (increased frequency), and if the past synchronization error is small, the cycle is lengthened (lower frequency).
Here, the clock frequency offset does not change rapidly with the passage of time, but changes gently with respect to the change of time, as shown in FIG. Therefore, the period can be appropriately changed based on the past tendency of the synchronization error.

  Note that the information (statistic) indicating the past trend of the synchronization error may be an average of past synchronization errors, or may be a variance value, standard deviation, or mean square value of past synchronization errors. .

  Note that the change of the period (interval) for entering the synchronization mode may be based on other information that affects the synchronization shift. For example, since the environmental temperature affects the accuracy of the clock frequency, the base station apparatus may be provided with a temperature sensor to acquire temperature information, and the period (interval) of the synchronization mode may be changed based on the temperature information. . Specifically, if the temperature change detected by the temperature sensor is large, the synchronous mode cycle (interval) is reduced, and if the temperature change is small, the synchronous mode cycle (interval) is increased. Can do.

  Further, since the synchronization accuracy is also affected by the number of stages from the master base station apparatus 1, the period of the synchronization mode may be changed according to the number of stages from the master base station apparatus 1. Here, the number of stages from the master base station apparatus 1 is the slave base station apparatus 2 having the master base station apparatus 1 as a source base station, as shown in FIG. Becomes the second stage, and the slave base station apparatus 3 having the second-stage base station apparatus 2 as the source base station becomes the third stage. Since the base station apparatus having a larger number of stages from the master base station apparatus 1 has a lower synchronization accuracy, the period of the synchronization mode can be reduced, and the base station apparatus having a smaller number of stages can increase the period of the synchronization mode.

  Note that the number of stages from the master base station apparatus 1 may be set in advance in each base station apparatus, or in the synchronous mode, obtain the number of stages of other base station apparatuses (source base station apparatuses) A value obtained by adding 1 to the number of stages may be the number of stages of the own device. In order to obtain the number of stages of other base station devices (source base station devices), for example, in the case of WiMAX, since a plurality of types are defined as preamble patterns, this can be used. Specifically, if a predetermined preamble pattern is assigned to each stage in advance, the base station apparatus that performs the synchronization process grasps the number of stages of other base station apparatuses (source base station apparatuses) by identifying the preamble pattern. can do.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is an overall view of a wireless communication system. It is a flowchart which shows switching of normal communication mode and synchronous mode. It is a flowchart in synchronous mode. It is explanatory drawing for detecting the timing of a preamble. It is explanatory drawing when a some base station apparatus becomes synchronous mode simultaneously. It is a time chart which shows the method which concerns on 1st Embodiment. It is a time chart which shows the method which concerns on 2nd Embodiment. It is a flowchart which shows the acquisition method of the frame index in 3rd Embodiment. It is explanatory drawing of a synchronous timing calculation function. It is a determination flowchart of a synchronization timing. It is a flowchart which shows switching of normal communication mode and synchronous mode in 4th Embodiment. It is a flowchart of the synchronous mode in 4th Embodiment. It is a figure which shows the structure of the base station apparatus which concerns on 5th Embodiment. It is a figure which shows a synchronization shift | offset | difference (timing offset produced) flame | frame. FIG. 15A is a graph showing the clock frequency offset, and FIG. 15B is a graph showing the timing offset. It is a figure which shows a mode that a packet loss arises in synchronous mode. It is a figure which shows the state of a WiMAX frame when the synchronization between base stations is taken.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base station apparatus 2 Base station apparatus 3 Base station apparatus 32 Frame timing counter 33 Synchronization error detection part 34 Period control part 35 Synchronization error history storage part

Claims (11)

Means for periodically suspending a communication mode for communicating with a terminal device;
Means for executing a synchronization mode for receiving a transmission signal from another base station device and acquiring a synchronization signal during periodic suspension of the communication mode,
In the synchronization mode, the base station apparatus corrects a synchronization shift occurring during the communication mode based on the synchronization signal.   The base station apparatus according to claim 1, further comprising: a unit that changes a period for suspending the communication mode.   The base station apparatus according to claim 1, further comprising means for randomly changing a period for pausing the communication mode.   The base station apparatus according to claim 2, further comprising: a unit that changes a period for suspending the communication mode based on a past synchronization deviation amount. A method for acquiring a synchronization signal of a base station apparatus in a radio communication system having a plurality of base station apparatuses that perform radio communication by time division duplex with a terminal apparatus,
A step in which a base station apparatus pauses a communication mode for performing communication with a terminal apparatus, and executes a synchronization mode for acquiring a synchronization signal from a transmission signal from another base station apparatus during the suspension. Including
A method for acquiring a synchronization signal, wherein the timing for acquiring the synchronization signal differs for each base station apparatus. A base station device that performs wireless communication by time division duplex with a terminal device,
Means for suspending a communication mode for communicating with a terminal device, executing a synchronization mode for receiving a transmission signal from another base station device and acquiring a synchronization signal during the suspension;
If the synchronization signal could not be acquired in the synchronization mode, means for trying to acquire the synchronization signal also at the timing of the next communication frame;
A base station apparatus comprising: A base station device that performs wireless communication by time division duplex with a terminal device,
Means for suspending a communication mode for communicating with a terminal device, executing a synchronization mode for receiving a transmission signal from another base station device and acquiring a synchronization signal during the suspension;
Means for controlling the synchronization mode to be performed at a set period;
Means for randomly changing the set value of the period;
A base station apparatus comprising: A base station device that performs wireless communication by time division duplex with a terminal device,
Means for suspending a communication mode for communicating with a terminal device, executing a synchronization mode for receiving a transmission signal from another base station device and acquiring a synchronization signal during the suspension;
Means for controlling the synchronization mode to be performed at a set timing;
The base station apparatus, wherein the synchronization mode setting timing value is a unique value unique to the base station apparatus. A frame counter for counting communication frames;
Means for acquiring frame index information included in a transmission signal from another base station device;
Means for matching the value of the frame counter with the value of the frame counter in the other base station apparatus based on the acquired frame index information;
Further comprising
The base station apparatus according to claim 8, wherein the synchronization mode setting timing value is a unique frame counter value unique to the base station apparatus.   The base station apparatus according to claim 9, further comprising means for obtaining a unique frame counter value unique to the base station apparatus from identifier information unique to the base station apparatus. A base station device that performs wireless communication by time division duplex with a terminal device,
Means for receiving a transmission signal from another base station device and executing a synchronization mode for acquiring a synchronization signal;
When the set timing is reached, the communication mode for performing communication with the terminal device is suspended, and the control unit performs control so that the synchronization mode is performed.
With
When the synchronization signal cannot be acquired even after performing the synchronization mode, the communication mode is resumed, and then the communication mode is suspended and the synchronization mode is performed again. Base station equipment.

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