JP2010093425A - Base station device and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive a transmission signal from another base station apparatus to be synchronized with an appropriate reception gain.
The present invention relates to base station apparatuses 2 and 3 that perform wireless communication with a terminal apparatus 4 that can execute transmission power control. The base station apparatuses 2 and 3 suspend the wireless communication with the terminal apparatus 4 that performs transmission power control, and send transmission signals from the other base station apparatuses in order to synchronize with the other base station apparatuses. A synchronous mode executing means 18 for executing the receiving synchronous mode, a switching means 19 for switching the receiving gain when executing the synchronous mode to a receiving gain different from that in the normal mode for performing wireless communication with the terminal device 4; It has.
[Selection] Figure 2

Description

  The present invention relates to a base station apparatus serving as a terminal of a wireless communication network including a plurality of terminal devices and a wireless communication system constituting the wireless communication network.

For example, in a wireless communication system in which mobile terminal devices (mobile terminals) such as mobile WiMAX (Worldwide Interoperability for Microwave Access) communicate wirelessly, a large number of base station devices are installed in various places.
The WiMAX employs a TDD (Time Division Duplex) duplex communication system that switches between transmission and reception at high speed as a wireless communication system with a mobile terminal.

Specifically, as shown in FIG. 8, one basic frame composed of a downlink subframe (transmission frame of the base station apparatus) DL and an uplink subframe (transmission frame of the mobile terminal) UL is arranged in the time direction. In addition, a preamble (Preamble) is provided at the head portion of the downlink subframe DL.
In FIG. 8, the transmission timing and the reception timing are the same among a plurality of base station apparatuses, and frame synchronization between base stations (hereinafter, “synchronization” means frame timing synchronization) is achieved. Is shown. Such synchronization processing is normally performed when one of the base station apparatuses is activated, and communication with the mobile terminal is performed after synchronization with the other apparatus.

On the other hand, a mobile terminal in a communication area (cell) covered by each base station apparatus can perform wireless communication with the base station apparatus corresponding to the cell.
For this reason, when the mobile terminal moves to a different cell, the base station apparatus with which the mobile terminal communicates is changed. At this time, the mobile terminal simultaneously receives two base station apparatuses (serving base station and target base station). Will be received.

In order for such mobile terminals to move smoothly between cells, it is necessary to ensure a state (state shown in FIG. 8) in which transmission timings between base station apparatuses adjacent to the cell are aligned. When this inter-base station synchronization is established, when a mobile terminal moves between cells, it is possible to reliably receive transmission signals from the two base station devices, and to smoothly move between cells.
Further, if the frame timing is not synchronized, the transmission timing of the first base station apparatus overlaps with the reception timing of the other second base station apparatus, and the first base station apparatus uses the first base station apparatus. The transmission signal from the station apparatus becomes an obstacle. However, if the base station apparatuses are synchronized, such an interference between the base station apparatuses does not occur.
As a technique for performing synchronization between the base stations, for example, a technique using a GPS signal from a GPS satellite described in Patent Document 1 is known.
JP 59-6642 A

One method of synchronization between base stations is that each base station apparatus receives a GPS signal from a GPS satellite and operates all base station apparatuses with a common synchronization signal as in Patent Document 1 above. Conceivable.
However, in synchronization between base stations using GPS signals, it is necessary to provide a GPS receiver in the base station apparatus, which leads to an increase in size and cost of the base station apparatus. In addition, in the case of this synchronization, there is a drawback that the base station apparatus installed in an environment where GPS signals cannot be received cannot be synchronized.

Therefore, a transmission signal (downlink subframe DL) from another base station apparatus adjacent to the cell is received (intercepted), and the transmission timing of the other base station apparatus is extracted and extracted based on this transmission signal. A synchronization method (air synchronization) that synchronizes with other base station apparatuses using the transmitted timing can be considered.
In this case, since it is possible to synchronize with other radio base stations by radio communication using the same frequency as the radio communication frequency with the mobile terminal, a special reception system for synchronization such as a GPS receiver is used. There is no need to provide it. For this reason, the air synchronization can reduce the size and cost of the base station device, and is suitable as a small indoor base station device.

By the way, in the above-described WiMAX, in a normal communication state in which radio communication by time division duplex is performed between the base station apparatus and each terminal apparatus, the uplink signal (uplink subframe UL) to the base station apparatus has a large level. In order to prevent the fluctuation from occurring, each terminal apparatus performs transmission power control for adjusting its own transmission power.
Note that the transmission power control performed by the terminal device is a method of instructing the transmission power from the base station device to the terminal device (closed loop method) and the transmission power based on the reception level of the downlink signal (downlink subframe DL). There is a method of determining autonomously (open loop method).

Thus, in WiMAX, since each terminal apparatus performs transmission power control, the reception gain of the receiver mounted on the base station apparatus is set to a substantially constant fixed value.
For this reason, when a base station apparatus intercepts a transmission signal transmitted from another base station apparatus to a terminal apparatus in order to perform air synchronization, the distance to the other base station apparatus and other transmission path states Depending on the case, the received signal level intercepted by the receiver of the base station apparatus that performs air synchronization may be too high or too low.

Therefore, the base station apparatus that performs air synchronization may not be able to extract the transmission timing based on a transmission signal from another base station apparatus, and may not be able to appropriately execute air synchronization with another base station apparatus.
In view of such a conventional problem, the present invention can receive a transmission signal from another base station apparatus to be synchronized with an appropriate reception gain to ensure air synchronization with respect to the other base station apparatus. An object of the present invention is to provide a base station apparatus or the like that can be executed.

  A base station apparatus according to the present invention (Claim 1) is a base station apparatus that performs wireless communication with a terminal apparatus that can perform transmission power control, and is wireless with the terminal apparatus that performs transmission power control. Synchronous mode execution means for executing a synchronous mode for receiving a transmission signal from the other base station apparatus in order to pause communication and synchronize with the other base station apparatus, and reception when executing the synchronous mode And a switching means for switching the gain to a reception gain different from that in the normal mode in which radio communication with the terminal device is performed.

  According to the base station apparatus of the present invention, the synchronization mode execution means pauses the wireless communication with the terminal apparatus that performs transmission power control, and synchronizes with the other base station apparatus. Since the synchronous mode for receiving the transmission signal from the mobile station is executed, and the switching means switches the reception gain when executing the synchronous mode to a reception gain different from that in the normal mode for performing wireless communication with the terminal device. A transmission signal from another target base station apparatus can be received with an appropriate reception gain different from the fixed value for the normal mode.

In the base station apparatus of the present invention, a reception gain (specifically, a gain parameter corresponding to this reception gain) when executing the synchronization mode is set in advance as that for a specific other base station apparatus, for example. The set set value can be adopted (claim 7).
In this case, since the reception gain for the synchronization mode can be acquired simply by storing the set value in the storage area in the base station apparatus, there is no need to provide a level detection section and a gain calculation section described later, and the base station apparatus There is an advantage that the manufacturing cost can be reduced.

However, in the base station device of the present invention, based on the level detection unit that detects the reception level of the transmission signal from the other base station device, and the reception level detected by the level detection unit when the own device is activated, A gain calculation unit that calculates a gain parameter corresponding to the reception gain for the synchronous mode may be provided.
In this case, the gain calculation unit calculates the gain parameter corresponding to the reception gain for the synchronization mode based on the reception level received from the other base station apparatus when the own apparatus is started up. The reception gain can be automatically acquired from the time when the own apparatus is activated. This eliminates the need to set the reception gain for the synchronous mode, and simplifies the work of newly installing the base station apparatus.

Further, in the base station apparatus of the present invention, the level detection unit for detecting the reception level of the transmission signal from the other base station apparatus and the synchronization mode executed by the synchronization mode execution means periodically and repeatedly A gain calculation unit that calculates a gain parameter corresponding to the reception gain for the synchronous mode based on the reception level detected by the level detection unit may be provided.
In this case, the gain calculation unit calculates a gain parameter corresponding to the reception gain for the synchronization mode based on the reception level received from another base station device during the periodically repeated synchronization mode. Can automatically update the receiving gain. For this reason, it is possible to flexibly cope with fluctuations in signal level due to environmental changes such as transmission lines.

In the base station apparatus of the present invention, the gain calculation unit calculates a gain parameter corresponding to the reception gain for the synchronization mode only when reception quality of a transmission signal from the other base station apparatus is deteriorated. (Claim 4).
In this case, the gain calculation unit calculates the gain parameter only when it is the minimum necessary to execute the synchronous mode, so the calculation load and power consumption in the gain calculation unit can be reduced.

Also, in the base station apparatus of the present invention, the gain calculation unit is configured to receive the synchronization mode reception gain based on reception levels of a plurality of transmission frames from the other base station apparatus detected by the level detection unit. The gain parameter corresponding to can be calculated (claim 5).
In this case, the synchronization mode execution means is more effective than the case where the calculation is not performed while the gain calculation unit calculates the gain parameter corresponding to the reception gain based on the plurality of transmission frames. If the execution period is set to be short (Claim 6), the gain parameter for the synchronization mode can be calculated in a shorter time by the gain calculation unit, and the total time required for air synchronization can be reduced. it can.

  A radio communication system (Claim 8) of the present invention is a system including a plurality of terminal devices capable of performing transmission power control and the base station apparatus (Claim 1) of the present invention. The same effects as the device (claim 1) are achieved.

  As described above, according to the present invention, a base station apparatus that performs air synchronization receives a transmission signal from another base station apparatus to be synchronized with an appropriate reception gain different from the fixed value for the normal mode. Therefore, air synchronization with respect to other base station devices can be executed reliably.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
[Overall configuration of wireless communication system]
FIG. 1 shows the overall configuration of a wireless communication system having a base station apparatus of the present invention.
This wireless communication system includes a plurality of base station devices (BS: Base Station) 1 to 3 and a large number of mobile terminal devices (MS: Mobile Station) 4 that perform wireless communication with each of the base station devices 1 to 3. I have. In the radio communication system, a scheme based on “WiMAX” defined in IEEE 802.16, which supports an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, is employed to realize broadband radio communication.

As shown in FIG. 8, in the WiMAX, basic frames including downlink subframes (transmission frames of the base station apparatuses 1 to 3) DL and uplink subframes (transmission frames of the terminal apparatus 4) UL are arranged in the time direction. The communication system is arranged and repeats transmission and reception by time division duplex (TDD). Note that the length of one basic frame is 5 ms.
The downlink subframe DL is a time zone in which the base station apparatuses 1 to 3 transmit signals to the terminal apparatuses 4 in its communication area (cell), and the uplink subframe UL is transmitted from the base station apparatuses 1 to 3 itself. This is a time zone for receiving a signal from the terminal device 4 in the communication area, and a preamble of a known signal is provided at the head portion of the downlink subframe DL.

Returning to FIG. 1, each of the base station devices 1 to 3 can wirelessly communicate with the terminal devices 4 in the cells of the own devices 1 to 3. Further, the base station apparatuses 1 to 3 constituting the wireless communication system include at least one master base station apparatus BSm and slave base station apparatus BSs.
Among these, the master base station device BSm is a base station device that does not need to detect the timing of synchronization between base stations from the transmission signal (downlink subframe DL) of another base station device. For example, the master base station apparatus BSm is configured as a self-running master base station apparatus that determines transmission timing based on an accurate self-running clock, or a base station apparatus with a GPS reception function that determines transmission timing using a GPS signal. be able to.

On the other hand, the slave base station device BSs intercepts a transmission signal (downlink subframe DL) transmitted from another base station device toward the terminal device 4, and acquires a synchronization signal based on the intercepted received signal. It is a base station apparatus that performs air synchronization.
Note that the slave base station device BSs can also acquire a synchronization signal by intercepting not only the transmission signal of the master base station device BSm but also the transmission signals of other slave base station devices BSs. In the wireless communication system shown in FIG. 1, the base station device 1 is a master base station device BSm, and the base station device 2 and the base station device 3 are slave base station devices BSs, respectively.

The slave base station apparatuses 2 and 3 select one of the other base station apparatuses (master BSm or slave BSs) as a source base station apparatus for air synchronization when starting up the own apparatus, Timing (transmission timing) for synchronization between base stations is acquired based on a preamble that is a known signal included in a transmission signal from the base station apparatus.
The processing operation in the synchronization mode performed by the slave base station device at the time of activation is referred to as “initial synchronization processing”. Specifically, this initial synchronization processing is performed between the time when the device itself is activated and the time when wireless communication with the terminal device 4 is started.

The slave base station apparatuses 2 and 3 perform wireless communication with the terminal apparatus 4 in the own cell while synchronizing with the transmission timing of the source base station apparatus by the initial synchronization process. For this reason, the wireless communication performed by the slave base station apparatuses 2 and 3 with the terminal apparatus 4 after the initial synchronization processing has the same transmission timing and reception timing as in the case of the source base station apparatus.
However, if the accuracy of the local clock generator of the slave base station devices 2 and 3 is not sufficient, or if the clock accuracy varies between the base station devices, a synchronization error occurs over time, and gradually There is a time lag with the transmission / reception timing of the base station apparatus.

That is, since an error in the clock frequency of the clock generator included in each base station device exists between the base station devices, the time length of one basic frame generated based on the clock frequency (reference signal) ( (5 ms in the standard) is slightly different between base station apparatuses.
Further, even if the error of the time length of one basic frame is slight, if the frame transmission to the terminal device 4 is repeated, the error may be accumulated and a relatively large synchronization shift (for example, about several tens of μsec) may occur. is there. As described above, even if the initial synchronization processing is executed to align the communication timing between the base station apparatuses 1 to 3, the synchronization deviation may gradually increase during the wireless communication with the terminal apparatus 4.

Therefore, the slave base station apparatuses 2 and 3 according to the present embodiment perform normal wireless communication (hereinafter referred to as “normal mode”) with the terminal apparatus 4 even after the initial synchronization process is performed, for a predetermined period. And a “synchronization mode” is executed to eliminate a synchronization shift by receiving a transmission signal from another base station apparatus.
The processing operation in the synchronous mode performed by the slave base station apparatuses 2 and 3 with the normal mode suspended at a predetermined cycle is referred to as “intermediate synchronous processing”. The slave base station apparatuses 2 and 3 can variably set the execution cycle of the intermediate synchronization process.

On the other hand, since the wireless communication system according to the present embodiment conforms to WiMAX, a normal communication state in which wireless communication by time division duplex is performed between the base station apparatuses 1 to 3 and each terminal apparatus 4 (normally) In the mode), each terminal apparatus 4 performs transmission power control for adjusting its own transmission power in order to prevent large reception level fluctuations from occurring in the base station apparatuses 1 to 3.
The transmission power control performed by the terminal device 4 may be a method of instructing the transmission power from the base station devices 1 to 3 to the terminal device 4 (closed loop method), or the terminal device 4 may be based on the reception level of the downlink signal. A method of determining transmission power autonomously (open loop method) may be used.

[Receiver of slave base station device]
FIG. 2 is a functional block diagram illustrating the receiving units of the slave base station apparatuses 2 and 3.
As shown in FIG. 2, the receiver 6 of the slave base station apparatuses 2 and 3 of this embodiment includes a variable gain amplifier 7, a mixer 8, an amplifier 9, an orthogonal demodulator 10, an AD converter 11, an FFT (Fast Fourier Transformer). ) 12 and a demodulator 13.

Among these, the variable gain amplifier 7 is a kind of low noise amplifier which is provided at the front end of the receiver 6 and amplifies a high frequency received signal (OFDM signal).
The variable gain amplifier 7 is composed of, for example, a variable gain amplifier (VGA) that changes the gain by changing the transconductance of a multi-stage MOS transistor with a bias current. The own amplification gain can be variably set by the control signal.
By changing this gain, the reception gain, that is, the gain from the antenna input to the AD converter 11 input can be changed, and the input level of the AD converter 11 can be set to an appropriate value. The position of the variable gain amplifier 7 may be a place where the reception gain can be changed other than the front end section, that is, between the antenna input and the AD converter 11 input.

The mixer 8 constitutes a frequency converter together with a local oscillator 14A composed of a PLL circuit or the like, and converts the received signal from the variable gain amplifier 7 to a constant low intermediate frequency (heterodyne detection) regardless of the frequency. It is.
The amplifier 9 subsequent to the mixer 8 is an intermediate frequency amplifier that amplifies the reception signal frequency-converted by the mixer 8 to a level that can be demodulated by the quadrature demodulator 10. The intermediate amplified signal amplified by the amplifier 9 is quadrature demodulated by the quadrature demodulator 10 at the subsequent stage.

Specifically, the quadrature demodulator 10 generates signals orthogonal to each other from the local frequency signal generated by the local oscillator 14B, and mixes this signal with the input intermediate amplified signal, thereby generating a base orthogonal to a predetermined frequency. Outputs a band signal.
This baseband signal is digitally converted by the A / D converter 11 at the subsequent stage and given to the FTT 12, and Fourier-transformed by the FFT 12, thereby extracting a symbol group included in a large number of subcarriers spread over a wide band.

Then, the parallel digital signal composed of the symbol group is demodulated by the demodulator 13 subsequent to the FTT 12, and the received data composed of the serial digital signal is extracted.
Further, in the receiver 6 of the present embodiment, a synchronization detection unit 15 that extracts a synchronization signal for the source base station apparatus from the output signal of the FFT 12 is provided. The synchronization detector 15 detects, for example, a preamble at the beginning of the downlink subframe DL as a synchronization detection point with the source base station apparatus from the symbol group output by the FFT 12.

As shown in FIG. 2, in addition to the receiver 6, the slave base station devices 2 and 3 of the present embodiment switch the communication mode of the devices 2 and 3 to either the normal mode or the synchronous mode. A portion 17 is provided.
The communication control unit 17 is composed of a programmable microcomputer composed of a plurality of control chips, and includes a synchronous mode execution unit (synchronous mode execution unit) 18 and a selector (switching unit) 19 as functional parts executed by the program. Have.

Among these, the synchronization mode execution unit 18 can execute both the initial synchronization process, which is a synchronization mode performed at startup, and the intermediate synchronization process, which is a synchronization mode performed thereafter at a predetermined execution cycle.
The synchronization mode execution unit 18 stores an execution cycle for performing the intermediate synchronization process in the storage device in advance. When the intermediate synchronization process is not performed, a normal wireless communication with the terminal device 4 that performs transmission power control is performed. Continue communication (normal mode).

Further, when performing the intermediate synchronization process, the synchronization mode execution unit 18 transmits a pause signal to the transmitter side to pause data transmission to the terminal device 4 and to synchronize with the source base station device A synchronous mode for receiving a transmission signal from the station apparatus is executed.
The synchronous mode execution unit 18 transmits a mode type signal indicating whether the current communication mode is the normal mode or the synchronous mode to the selector 19. The selector 19 has a switching function for switching a gain parameter input to the variable gain amplifier 7 of the receiver 5 based on the mode type signal.

That is, the selector 19 stores both the first gain parameter 21 for the normal mode and the second gain parameter 22 for the synchronous mode in the storage area, and is variable when the mode type signal is the normal mode. An external control signal to the gain amplifier 7 is set to the first gain parameter 21.
Further, the selector 19 sets an external control signal to the variable gain amplifier 7 in the second gain parameter 22 when the mode type signal is the synchronous mode. Each gain parameter 21 and 22 stored in the selector 19 is the same physical quantity (control voltage or digital signal) as the external control signal to the variable gain amplifier 7.

Among the gain parameters 21 and 22, the first gain parameter 21 is received by the receiver 6 when the receiver 6 receives a transmission signal from the terminal device 4 that performs transmission power control (in the normal mode). This is a set value set to fix the gain to a predetermined value.
Therefore, the reception gain of the receiver 6 during execution of the normal mode is suitable for reception of a transmission signal from the terminal device 4 when the selector 19 switches the external control signal to the variable gain amplifier 7 to the first gain parameter 21. Receiving gain.

On the other hand, the second gain parameter 22 is a signal transmitted from a specific source base station apparatus when the receiver 6 receives (intercepts) a transmission signal from a specific source base station apparatus (in a synchronous mode). Is a set value that is set to fix the reception gain of the receiver 6 to be a predetermined value.
Therefore, the reception gain of the receiver 6 in the synchronous mode is such that the selector 19 switches the external control signal to the variable gain amplifier 7 to the first gain parameter 21 to receive the transmission signal from the specific source base station apparatus. The receiving gain is suitable for.

[Processing content of synchronous mode execution unit]
FIG. 3 shows a flowchart of the switching operation from the communication mode to the synchronous mode performed by the synchronous mode executing unit 18 of the communication control unit 17.
As shown in FIG. 3, first, the synchronization mode execution unit 18 determines whether or not it is a timing for shifting to the synchronization mode (step S1). As described above, this transition timing is set as a synchronization mode execution cycle (every predetermined time or every predetermined number of frames). When this execution cycle is set in time, it can be set to about 5 minutes, for example, but it can also be set variably.

In FIG. 3, when it is determined that the transition timing from the normal mode to the synchronous mode is reached (YES in step S2), the synchronous mode execution unit 18 changes the communication mode of the own devices 2 and 3 from the normal mode to the synchronous mode. (Step S3). When the synchronization mode ends, the synchronization mode execution unit 18 returns the communication mode to the normal mode again (step S4).
As described above, the synchronization mode execution unit 18 executes the normal mode for performing normal wireless communication with the terminal device 4 and executes the synchronization mode periodically or as needed, so that after the initial synchronization processing, Even if a synchronization error with the source base station apparatus occurs, this can be eliminated.
In this embodiment, the time required for the synchronization mode execution unit 18 to perform one synchronization mode is set to 5 ms, which is the same as the period of one basic frame (see FIG. 5).

FIG. 4 is a flowchart showing the contents of the intermediate synchronization process performed by the synchronization mode execution unit 18.
As shown in FIG. 4, when the synchronization mode is executed by the intermediate synchronization process, the synchronization mode execution unit 18 first starts all the terminals in the own cell before starting the intermediate synchronization process (steps S11 to S15). A notification for setting the terminal device 4 to the sleep mode or the idle mode (power saving mode) is broadcasted to the device 4 (step S10).

When receiving the notification of the sleep mode or the idle mode from the slave base station devices 2 and 3, the terminal device 4 shifts its operation mode to the mode according to the notification. Since the sleep mode and the idle mode are management modes when the terminal device 4 does not execute communication, power consumption can be suppressed.
The terminal device 4 is set to time so that the sleep mode and the idle mode are continued at least while the base station devices 2 and 3 are in the synchronization mode and performing the air synchronization.

As described above, since the terminal device 4 is in the sleep mode or the like while the slave base station devices 2 and 3 are in the synchronous mode, the period during which the transmission signals from the slave base station devices 2 and 3 cannot be received continues. However, the terminal device 4 does not determine that communication is abnormal.
On the other hand, after the slave base station apparatuses 2 and 3 notify the terminal apparatus 4 of the sleep mode or the like, the slave base station apparatuses 2 and 3 shift to the synchronization mode by the intermediate synchronization process. When performing this intermediate synchronization processing, the synchronization mode execution unit 18 sends a pause signal to the transmitters of the own devices 2 and 3 and pauses the downlink subframe DL into the own cell. As a result, the transmission signal of the other base station apparatus can be received even in the time zone where the downlink subframe DL is originally set.

As shown in FIG. 4, in the intermediate synchronization process, the synchronization mode execution unit 18 first switches the mode type signal to the synchronization mode (step S11).
At this time, the external control signal for the variable gain amplifier 7 is switched to the second gain parameter 22 by the selector 19, whereby the reception gain of the receiver 6 is suitable for reception of a transmission signal from a specific source base station apparatus. In this state, a transmission signal is received from the source base station apparatus (step S12). Therefore, when performing air synchronization in the synchronization mode, the base station apparatuses 2 and 3 according to the present embodiment have a reception system suitable for receiving a transmission signal from a specific source base station apparatus assumed in advance. .

In the present embodiment, the preamble at the beginning of the downlink subframe DL transmitted by the source base station apparatus is used as the synchronization signal.
For this reason, the synchronization mode execution unit 18 of the slave base station devices 2 and 3 uses the source base station device based on the preamble at the beginning of the downlink subframe DL of the received signal detected by the synchronization detection unit 15 of the receiver 6. Detect synchronization detection point to synchronize with. However, the synchronization detection point may be a midamble or a pilot signal.

On the other hand, if the synchronization detection unit 15 cannot detect the preamble even after scanning the transmission signal from another source base station device (NO in step S13), the synchronization mode execution unit 18 re-executes the preamble. In order to detect, a preamble detection process using the next transmission frame is performed (step S14).
When the preamble detection is successful in the synchronization detection unit 15 (YES in step S13), the synchronization mode execution unit 18 corrects the synchronization deviation (step S15).

This synchronization shift is corrected by setting the synchronization detection point based on the detected preamble so as to coincide with the transmission timing of the downlink subframe DL of the own devices 2 and 3.
That is, the synchronization mode execution unit 18 corrects the transmission timing of the own devices 2 and 3 based on the detected synchronization detection point, thereby setting the transmission timing of the own devices 2 and 3 of the source base station device. Match the transmission timing.

Note that if the transmission timings of the own devices 2 and 3 are made to coincide with the transmission timings of the source base station device, the reception timings naturally coincide with each other, so that the frame synchronization with the source base station device is established.
As described above, in this embodiment, the normal mode in which normal wireless communication is performed with the terminal device 4 is suspended, and transmission signals from other source base station devices are intercepted and synchronized. Even without this control channel, air synchronization with other base station apparatuses can be performed.

When the correction of the synchronization deviation by the above intermediate synchronization processing is completed, the synchronization mode execution unit 18 notifies the terminal device 4 of the cancellation of the sleep mode (step S16) and ends the synchronization mode (step S17). At this time, the communication mode is switched from the synchronous mode to the normal mode, and the mode type signal to the selector 19 returns to the normal mode.
At this time, the external control signal for the variable gain amplifier 7 is switched to the first gain parameter 21 by the selector 19, whereby the reception gain of the receiver 6 is in a state suitable for reception of the transmission signal from the terminal device 4. For this reason, the reception system of the receiver 6 becomes suitable for reception of transmission signals from each terminal device 4 that performs transmission power control.

On the other hand, the terminal device 4 in the sleep mode or the like automatically receives the sleep mode release notification from the slave base station devices 2 or 3 or automatically becomes a slave when the set sleep time (or idle time) elapses. The normal operation mode for communicating with the base station apparatuses 2 and 3 is restored.
Accordingly, both the slave base station apparatuses 2 and 3 and the terminal apparatus 4 return to the normal mode in which radio communication is performed by time division duplex, and radio communication in the normal mode is resumed between the two.

[Time chart for intermediate synchronization processing]
FIG. 5 shows a time chart when the synchronization mode execution unit 18 performs the intermediate synchronization process.
In FIG. 5, a symbol T indicates a transmission frame (downlink subframe) included in a basic frame, and a symbol R indicates a reception frame (uplink subframe). Also, the black part included in the basic frame indicates the preamble at the beginning of the transmission frame, and the hatched part with horizontal stripes indicates the guard time from transmission to reception (the blank period during which neither transmission nor reception is performed). The hatched portion of hatching indicates the guard time from reception to transmission.

Further, the time chart in the upper part of FIG. 5 shows a temporal change of the frame in the source base station apparatus (BSm or BSs) serving as a reference when air synchronization is established, and the time chart in the middle part of FIG. 6 shows temporal changes of frames in the slave base station apparatus BSs that performs the above.
Furthermore, the time chart in the lower part of FIG. 5 shows an example of a change in reception gain in the slave base station apparatus BSs that performs intermediate synchronization processing.

As can be seen by comparing the time charts in the upper and lower stages of FIG. 5, there is initially a synchronization shift in the transmission / reception timing of the basic frame between the source base station apparatus and the slave base station apparatus.
However, when the slave base station device executes the synchronization mode, the transmission / reception timings thereafter match. Specifically, as described above, when the slave base station device performs the intermediate synchronization process, the synchronization detection point for the source base station device is acquired in the time zone of the synchronization mode, and the slave base station device based on the synchronization detection point The synchronization shift is corrected by changing the timing to match the own transmission timing.

Also, as shown in FIG. 5, while the slave base station device is executing the normal mode, the reception gain of its own receiver 6 is a transmission signal from the terminal device 4 in its own cell that performs transmission power control. On the contrary, while the slave base station apparatus is executing the synchronous mode, the reception gain of its own receiver 6 is the reception gain of the transmission signal from the source base station apparatus. Is set to a reception gain B suitable for the above.
When the slave base station apparatus performs the initial synchronization process, the time zone of the synchronization mode shown in FIG. 5 only comes first. Even in the case of this initial synchronization process, the receiver 6 of the slave base station apparatus The reception gain is set to a reception gain B suitable for reception of a transmission signal from the source base station apparatus.

Thus, according to the base station devices (slave) 2 and 3 of the first embodiment, the synchronization mode execution unit 18 pauses the wireless communication with the terminal device 4 that performs transmission power control, and the source base device A synchronization mode for receiving a transmission signal from the base station apparatus is executed in order to synchronize with the station apparatus, and the selector 19 determines the reception gain of its own receiver 6 when executing the synchronization mode as the source base station. Switching is made to a reception gain B suitable for reception of a transmission signal from the apparatus.
Therefore, when the slave base station apparatuses 2 and 3 execute the air synchronization, the signal level received by the receiver 6 of the own apparatuses 2 and 3 is not too high, or conversely, the source level is not too low. Air synchronization with respect to the base station apparatus can be reliably executed.

Further, according to the base station apparatuses 2 and 3 of the present embodiment, the reception gain (specifically, the first gain parameter 22) when executing the synchronization mode is set in advance as for a specific source base station apparatus. Therefore, the reception gain for the synchronous mode can be acquired only by storing this setting value in the storage area.
Therefore, unlike the second embodiment to be described later, there is no need to provide the level detection unit 24 and the gain calculation unit 25, and there is an advantage that the manufacturing cost of the slave base station devices 2 and 3 can be reduced.

[Second Embodiment]
[Receiver of slave base station device]
FIG. 6 is a functional block diagram illustrating the receiving units of the slave base station apparatuses 2 and 3 according to the second embodiment.

The base station apparatuses 2 and 3 of the second embodiment are different from those of the first embodiment in that the second gain parameter 22 for the synchronization mode is not fixed to a predetermined set value, The other points are the same as in the case of the first embodiment.
Therefore, in the following, the configuration and functions different from those of the first embodiment will be described mainly.

As shown in FIG. 6, the receiver 6 of the base station devices 2 and 3 of the present embodiment includes a level detection unit 24 that detects the reception level of the transmission signal from the source base station device. The communication control unit 17 includes a gain calculation unit 25 that dynamically calculates a gain parameter corresponding to the reception gain for the synchronization mode based on the reception level detected by the level detection unit 24.
Among these, the level detection unit 24 includes a detector or the like that specifies the signal level of the received signal based on the output signal of the amplifier 9.

Further, the gain calculation unit 25 calculates an optimum gain parameter for enabling the receiver 6 to appropriately receive the received signal based on the detection value of the level detection unit 24.
Specifically, the gain calculation unit 25 compares the optimal reception level (threshold value) set in advance with the detection value, and when the reception level is higher than the predetermined threshold value, decreases the gain of the variable gain amplifier 7; When the reception level is lower than the predetermined threshold, an operation for adjusting the gain parameter is performed so as to lower the gain of the variable gain amplifier 7.

The gain parameter calculated by the gain calculation unit 25 is the same physical quantity (control voltage or digital signal) as the external control signal for the variable gain amplifier 7.
As a gain parameter calculation method by the gain calculation unit 25, a reference table (LUT) that defines the relationship between the reception level and the external control signal for the variable gain amplifier 7 that achieves the optimum reception gain is used in advance. The gain parameter may be determined by storing the data in 17 storage areas and applying the detection value of the level detection unit 24 to the reference table.

The gain calculation unit 25 receives the mode type signal from the synchronization mode execution unit 18, and the gain calculation unit 25 determines that the type of the mode type signal determined by the synchronization mode execution unit 18 is the synchronization mode. Only perform gain parameter calculations.
As described above, the synchronization mode execution unit 18 performs the initial synchronization process that is air synchronization at the time of startup of the devices 2 and 3 and the intermediate synchronization process that is air synchronization that is periodically repeated. In both the synchronization process and the intermediate synchronization process, the gain calculator 25 calculates a gain parameter corresponding to the reception gain for the synchronization mode.

Thus, according to the slave base station apparatuses 2 and 3 of the present embodiment, the gain calculation unit 25 is based on the reception level received from the source base station apparatus during the initial synchronization process performed when the own apparatuses 2 and 3 are activated. Since the gain parameter corresponding to the reception gain for the synchronous mode is calculated, the reception gain of the receiver 6 when executing the synchronous mode can be automatically acquired from the time when the own devices 2 and 3 are activated.
This eliminates the need for setting the reception gain for the synchronous mode, and simplifies the work of newly installing the slave base station apparatuses 2 and 3.

In addition, according to the slave base station apparatuses 2 and 3 of the present embodiment, the reception gain for the synchronization mode is based on the reception level received from the source base station apparatus during the intermediate synchronization process that is a periodically repeated synchronization mode. Since the gain parameter corresponding to is calculated, the reception gain for the synchronous mode can be automatically updated.
For this reason, even if the environment such as the transmission path between the slave base station apparatuses 2 and 3 and the source base station apparatus changes, air synchronization with an appropriate reception gain reflecting the latest reception level becomes possible. There is an advantage that it is possible to flexibly cope with fluctuations of

On the other hand, in the gain calculation unit 25 of the present embodiment, when the level detection unit 24 cannot detect the reception level of the transmission signal from the source base station device, or when the preamble cannot be continuously detected, or The gain parameter corresponding to the reception gain for the synchronous mode may be calculated only when it can be determined that the reception quality has deteriorated, such as when a reception error is detected.
In this case, the gain calculation unit 25 calculates the gain parameter only when it is the minimum necessary to execute the synchronous mode, so that the calculation load and power consumption in the gain calculation unit 25 can be reduced. it can.

[Gain parameter setting timing]
FIG. 7 is a time chart for illustrating the gain parameter setting timing by the gain calculation unit 25.
The upper time chart of FIG. 7 shows temporal changes of frames when the slave base station apparatuses 2 and 3 periodically perform the synchronization mode a plurality of times, and the lower time chart of FIG. 7 shows one synchronization mode. The amplitude change of the reception level in the reception period is shown.

  As shown in the time chart at the bottom, the transmission frame from the source base station apparatus received during the synchronous mode reception period (5 ms in the present embodiment) includes a preamble at the beginning. Unlike the subsequent data portion, the amplitude in the preamble is substantially constant, and the average power is also substantially constant.

Therefore, the gain calculation unit 25 of the present embodiment calculates the gain parameter based on the reception level detected by the level detector 24 in the first time zone ta that is the front end portion of the preamble, and uses the remaining portion of the preamble. The calculated gain parameter is input to the selector 19 in a certain second time zone tb.
In this way, it is possible to complete the setting of the reception gain suitable for receiving the transmission signal from the source base station apparatus within the reception period of the single synchronization mode.

[Modification of gain parameter setting timing]
However, since the synchronization mode execution unit 18 of the present embodiment performs an intermediate synchronization process that repeats the synchronization mode at a predetermined cycle, there are multiple reception periods in the synchronization mode as shown in the upper time chart of FIG. .
Therefore, the reception level is detected and the gain parameter is calculated using the frame (first transmission frame) received in the preceding synchronous mode reception period, and the calculation result is used as the frame (first frame) in the subsequent synchronous mode reception period. (2 transmission frames) may be used as a gain parameter when receiving.

In this case, the gain parameter used in each synchronization mode is specified in the reception period of the previous synchronization mode.
In addition, the gain calculation unit 25 detects the reception level of the transmission frame received in the reception periods of the plurality of synchronization modes as well as the reception period of the previous synchronization mode, and calculates the average value obtained from each detection value. Based on this, the gain parameter may be calculated.
In this case, since the gain parameter is calculated using the average value of the reception levels obtained from a plurality of transmission frames, there is an advantage that the calculation accuracy of the gain parameter is improved.

However, in this case, since a plurality of synchronization mode reception periods are required to obtain detection values of a plurality of reception levels, it corresponds to a reception gain suitable for reception of a transmission signal from the source base station apparatus. The time required to determine the gain parameter is increased.
Therefore, when the gain parameter is calculated based on a plurality of transmission frames as described above, the synchronization mode execution unit 18 sets the synchronization mode execution cycle to be shorter than normal, thereby obtaining the synchronization mode gain parameter. It is preferable to reduce the computation time of

For example, when the normal execution period of the synchronous mode is 5 minutes, a method for executing the synchronous mode as many times as necessary for calculating the average value of the reception level within 5 minutes at the latest, or a plurality of synchronization modes A method of continuously executing a plurality of synchronous modes without interposing the normal mode between the modes can be employed.
For the same reason, in the case of initial synchronization processing performed when the own devices 2 and 3 are started, the synchronization mode is continuously executed until a predetermined gain parameter is obtained, or the execution cycle of the synchronization mode is set to about several seconds. Thus, it is preferable to increase the frequency of execution of the synchronous mode.

The above embodiments are all illustrative and not restrictive. That is, the technical scope of the present invention is shown not by the above embodiment but by the scope of claims for patent, and includes all modifications within the scope equivalent to the configurations described in the scope of claims for patent.
For example, in the said embodiment, although the base station apparatuses 1-3 and the terminal device 4 illustrated the radio | wireless communications system which communicates by TDD (Time Division Duplex: Time division duplex), this invention is the base station apparatus 1. 3 and the terminal device 4 can also be applied to a wireless communication system in which communication is performed by FDD (Frequency Division Duplex).

It is the schematic which shows the whole structure of a radio | wireless communications system. It is a functional block diagram which shows the receiving part of the slave base station apparatus which concerns on 1st Embodiment. It is a flowchart of the switching operation from a communication mode to a synchronous mode. It is a flowchart which shows the processing content of an intermediate | middle synchronous process. It is a time chart at the time of performing an intermediate | middle synchronous process. It is a functional block diagram which shows the receiving part of the slave base station apparatus which concerns on 2nd Embodiment. It is a time chart for showing the setting timing of a gain parameter. FIG. 6 is a state diagram of a WiMAX frame when synchronization between base stations is matched.

Explanation of symbols

1: Base station apparatus (BSm) 2: Base station apparatus (BSs) 3: Base station apparatus (BSs)
4: Terminal equipment (MS)
6: Receiver 7: Variable gain amplifier 8: Mixer 9: Amplifier 10: Quadrature demodulator 11: AD converter 12: FFT (Fast Fourier transformer) 13: Demodulator 14A: Local oscillator 14B: Local oscillator 15: Synchronization detector 17: Communication control unit 18: Synchronization mode execution unit (synchronization mode execution unit) 19: Selector (switching unit)
21: First gain parameter 22: Second gain parameter 24: Level detection unit 25: Gain calculation unit

Claims (8)

A base station device that performs wireless communication with a terminal device capable of performing transmission power control,
Synchronous mode for executing a synchronous mode for receiving a transmission signal from another base station apparatus in order to suspend radio communication with the terminal apparatus performing transmission power control and synchronize with the other base station apparatus Execution means;
Switching means for switching the reception gain when executing the synchronization mode to a reception gain different from that in the normal mode in which wireless communication with the terminal device is performed;
A base station apparatus comprising: A level detection unit for detecting a reception level of a transmission signal from the other base station device;
The base station according to claim 1, further comprising: a gain calculation unit that calculates a gain parameter corresponding to the reception gain for the synchronization mode based on the reception level detected by the level detection unit when the own device is activated. apparatus.   The gain calculation unit further includes a gain corresponding to the reception gain for the synchronization mode based on the reception level detected by the level detection unit during the synchronization mode periodically and repeatedly executed by the synchronization mode execution unit. The base station apparatus of Claim 2 which calculates a parameter.   The base station according to claim 3, wherein the gain calculation unit calculates a gain parameter corresponding to the reception gain for the synchronization mode only when reception quality of a transmission signal from the other base station apparatus is deteriorated. apparatus.   The gain calculation unit can calculate a gain parameter corresponding to the reception gain for the synchronization mode based on reception levels of a plurality of transmission frames from the other base station devices detected by the level detection unit. The base station apparatus according to claim 3 or 4.   The synchronization mode execution means sets the execution period of the synchronization mode while the gain calculation unit calculates the gain parameter corresponding to the reception gain based on the plurality of transmission frames as compared with the case where the calculation is not performed. The base station apparatus of Claim 5 set short.   The base station apparatus according to claim 1, wherein the reception gain when executing the synchronization mode is a setting value preset for a specific other base station apparatus. A wireless communication system comprising a plurality of terminal devices capable of executing transmission power control and a plurality of base station devices performing wireless communication with the terminal devices,
At least one of the plurality of base station devices is
Synchronous mode for executing a synchronous mode for receiving a transmission signal from another base station apparatus in order to suspend radio communication with the terminal apparatus performing transmission power control and synchronize with the other base station apparatus Execution means;
Switching means for switching the reception gain when executing the synchronization mode to a reception gain different from that in the normal mode in which wireless communication with the terminal device is performed;
A wireless communication system comprising:

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