JP5155105B2 - Base station equipment - Google Patents

Description

  The present invention relates to a base station apparatus serving as a terminal of a wireless communication network including a plurality of terminal apparatuses. More specifically, the present invention relates to a synchronization method performed between the base station apparatuses and a radio communication system constituting the radio 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. 10, 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. 10, the transmission timing and the reception timing are the same among a plurality of base station apparatuses, and the frame synchronization between the base stations (hereinafter, “synchronization” means the synchronization of the frame timing). 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. 10) 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.
If the frame timing is not synchronized, the transmission timing of the first base station device overlaps with the reception timing of the other second base station device, and the second base station device 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, the wireless communication with the terminal device is temporarily suspended, the transmission signal (downlink subframe DL) from another adjacent base station device is received (intercepted), and the other base station is based on the transmission signal. A synchronization method (air synchronization) that extracts the transmission timing of the station device and synchronizes with other base station devices using the extracted transmission 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 WiMAX described above, a plurality of frequency channels are assigned to each base station apparatus operated by each communication carrier, and this frequency channel is, for example, in increments of 10 MHz within a range of 2600 to 2620 MHz. .
Therefore, a slave base station apparatus that performs air synchronization must perform air synchronization using a transmission signal from a master base station apparatus (a base station apparatus to be synchronized) that has a use frequency different from its own use frequency. It is assumed that this is not possible.

The reason is that, for example, in the conventional PHS and the like, since there was a control channel that all terminals use in common, the slave should have made that channel subject to air synchronization, but in WiMAX there is no common control channel. This is because it is necessary to select an appropriate synchronization target (master) in the base station apparatus (slave) that performs air synchronization.
However, the slave base station device needs to perform frequency switching with respect to a local oscillator (PLL circuit or the like) provided in its own receiver when performing air synchronization with a master base station device having a different use frequency. During this frequency switching, the reception frequency of the receiver is in an unstable state, so there is a possibility that air synchronization cannot be performed.
Therefore, it is conceivable to provide a guard time sufficient to complete frequency switching before and after the execution period of air synchronization. However, this increases the pause time of wireless communication with the terminal device, and communication with the terminal device. There arises a new problem of inconvenience and deterioration of communication efficiency.

  In view of such a conventional problem, the present invention makes it possible to shorten the idle period of wireless communication with a terminal device as much as possible even when performing air synchronization with another base station device that uses a different frequency from that of its own device. An object of the present invention is to provide a base station apparatus and the like that can efficiently execute air synchronization with other base station apparatuses.

  A base station apparatus (Claim 1) of the present invention is a base station apparatus that performs wireless communication with a terminal apparatus, and includes a transmission / reception system including at least one transmission system and a plurality of reception systems, and a used frequency. In order to synchronize with another base station apparatus different from itself, a synchronization mode executing means for executing a synchronization mode for causing a part of the plurality of reception systems to receive a transmission signal from the other base station apparatus Then, a part of the reception system sets a guard time sufficient to complete the switching of the reception frequency before and after the execution period of the synchronous mode, and a part of the reception system overlaps with the guard time setting period. And a time setting unit that causes the remaining transmission / reception system excluding the reception system to perform wireless communication with the terminal device.

  According to the base station apparatus of the present invention, the time setting means sets a guard time sufficient for a part of the reception systems to complete switching of the reception frequency before and after the execution period of the synchronous mode. Because the wireless communication with the terminal device is executed by the remaining transmission / reception systems except for some reception systems so as to overlap with the time setting period, between other base station devices that use different frequencies from the own device Even when air synchronization is performed, the wireless communication pause period with the terminal device can be made as short as possible.

In the base station apparatus of the present invention, the synchronization mode execution means may cause the reception units of the plurality of reception systems that perform reception in the synchronization mode to receive the transmission signals from the other base station apparatuses in a diversity manner. Preferred (claim 2).
In this case, since the reception units of a plurality of reception systems receive diversity transmission signals from other base station devices, the transmission signals are more compared to the case where the transmission signals are received by a single transmission / reception system reception unit. There is an advantage that it can be received reliably.

On the other hand, when the other base station apparatus is composed of a plurality of base station apparatuses having different use frequencies, the synchronization mode execution means is a plurality of types having different frequencies transmitted by the plurality of other base station apparatuses. The transmission signal may be received individually and simultaneously by the reception unit of the reception system (claim 3).
In this case, since the receiving unit of each receiving system receives a plurality of types of transmission signals having different frequencies individually and simultaneously, sampling of the synchronization timing that can be synchronized as compared with the case of receiving the transmission signals in a time division manner. Time can be shortened and air synchronization can be executed in a shorter time.

  And as a base station apparatus of the present invention, search means for searching for the other base station apparatus to be synchronized among a plurality of other base station apparatuses based on a plurality of types of transmission signals having different frequencies (Claim 4), even if there are a plurality of other base station apparatuses having different use frequencies, the other base station apparatuses to be synchronized can be identified in a short time Can do.

  As described above, according to the present invention, even when air synchronization is performed with another base station apparatus having a different frequency from that of the own apparatus, it is possible to shorten the suspension period of wireless communication with the terminal apparatus as much as possible. Air synchronization with the apparatus can be executed efficiently.

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) 5 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. 10, 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 5) 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 apparatus 5 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 5 in the communication area, and a preamble (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 device 5 in the cell of the own device 1 to 3. In addition, the base station devices 1 to 3 constituting the wireless communication system include a slave base station device 1 and master base station devices 2 and 3.
In this specification, “slave base station apparatus (BSs) 1” refers to a base station apparatus that performs air synchronization, and “master base station apparatuses (BSm2, BSm3) 2, 3” It means a base station apparatus that can be a synchronization target of air synchronization performed by the slave base station apparatus 1.

That is, the slave base station device 1 intercepts the transmission signal (downlink subframe DL) transmitted from the other base station devices 2 and 3 to the terminal device 5, and at the beginning of the received signal (downlink frame) intercepted. Transmission base station, that is, a base station apparatus that performs air synchronization that synchronizes the beginning of a downstream frame.
On the other hand, at least one of the master base station apparatuses 2 and 3 does not detect the synchronization timing from the transmission signal (downlink subframe DL) of the other base station apparatus, but it is an accurate self-running clock or GPS signal. The transmission timing must be determined based on the above. Since the other base station devices need only be synchronized with the slave base station device, the transmission timing may be determined by a slave function that performs air synchronization by itself.

In the wireless communication system of FIG. 1, one slave base station apparatus 1 (BSs) that performs air synchronization.
, There are two master base station apparatuses 2 and 3 (BSm2 and BSm3) that can be synchronized.
In the wireless communication system of FIG. 1, the frequency (transmission / reception frequency) used by the slave base station device 1 for wireless communication with the terminal device 5 is f1, and the master base station devices 2 and 3 are wireless with the terminal device 5. The frequencies (transmission / reception frequencies) used in communication are f2 and f3, respectively. Therefore, the use frequency f1 of the slave base station apparatus 1 is different from the use frequencies f2 and f3 of the master base station apparatuses 2 and 3, and specific numerical values of these frequencies are, for example, f1 = 2600 MHz and f2 = 2610 MHz. , F3 = 2620 MHz.

The slave base station apparatus 1 selects one of the other base station apparatuses 2 and 3 as a synchronization target for air synchronization when the own apparatus 1 is activated, and the base station apparatus that is the synchronization target The timing (transmission timing) for synchronization between base stations is acquired based on the preamble that is a known signal included in the transmission signal from the base station.
Note that the processing operation in the synchronization mode that the slave base station device 1 performs at startup 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 5 is started.

The slave base station apparatus 1 performs wireless communication with the terminal apparatus 5 in its own cell while synchronizing with the transmission timing of the master base station apparatuses 2 and 3 by the initial synchronization process. For this reason, the wireless communication performed by the slave base station device 1 with the terminal device 5 after the initial synchronization processing has the same transmission timing and reception timing as those of the master base station devices 2 and 3.
However, if the accuracy of the local clock generator of the slave base station device 1 is not sufficient, or if the clock accuracy among the base station devices 1 to 3 varies, a synchronization shift occurs over time, and gradually. There is a time lag with the transmission / reception timing of the other base station apparatuses 2 and 3.

That is, since an error in the clock frequency of the clock generator included in each of the base station apparatuses 1 to 3 exists between the base station apparatuses 1 to 3, one basic generated based on the clock frequency (reference signal). The frame time length (5 ms in the standard) is slightly different between the base station apparatuses 1 to 3.
Further, even if the error in the time length of one basic frame is slight, if the frame transmission to the terminal device 5 is repeated, the error may accumulate and a relatively large synchronization shift (for example, about 1 μsec) may occur. . 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 shift may gradually increase during the wireless communication with the terminal apparatus 5.

Therefore, the slave base station apparatus 1 according to the present embodiment pauses normal wireless communication (hereinafter referred to as “normal mode”) performed with the terminal apparatus 5 at a predetermined cycle even after the initial synchronization processing is executed. In addition, the “synchronization mode” for receiving the transmission signals from the other base station apparatuses 2 and 3 and eliminating the synchronization shift is periodically executed.
Note that the processing operation in the synchronization mode performed by the slave base station apparatus 1 with the normal mode suspended at a predetermined cycle is referred to as “intermediate synchronization processing”. The slave base station apparatus 1 can variably set the execution cycle of this intermediate synchronization process.

[Internal configuration of slave base station]
FIG. 2 is a functional block diagram showing an internal configuration of the base station apparatus 1 according to the first embodiment.
As shown in FIG. 2, the slave base station apparatus 1 of the present embodiment has two systems capable of executing MIMO (Multiple Input Multiple Output) wireless communication, which is a kind of wireless communication by space division multiplexing, with the terminal apparatus 5. Transmission / reception systems A and B are provided.
That is, the transmitter 26 of the slave base station apparatus 1 includes a modulator 27, a MIMIO encoder 28, and two transmission systems A and B in order from the transmission data side. , Each comprises an IFFT (Inverse Fast Fourier Transform) 29, a DA converter 30, and a transmission unit 31.

The transmission data input to the transmitter 26 is digitally modulated by the modulator 27 by the OFDM method, and distributed and input to the transmission systems A and B by a predetermined determinant in the MIMO encoder 28.
In each of the transmission systems A and B, the distributed modulation data is subjected to inverse Fourier transform in the IFFT 29, then converted into analog data in the DA converter 30, amplified through the transmission unit 31, and transmitted to the outside.

On the other hand, the received signal received by the antenna of the receiver 33 is amplified by the receiving units 38 of the receiving systems A and B, converted into digital data by the AD converter 37, and then Fourier-transformed by the FTT 36, and the MIMO decoder 35. Is input.
The MIMO decoder 35 reproduces digital data by performing a decoding process on the received signal after Fourier transform obtained by the receiving systems A and B using a determinant opposite to the determinant of the MIMO encoder 28. The digital data is demodulated by the OFDM demodulator 34 to extract received data.

The reception units 38 of the reception systems A and B each include a variable gain amplifier, a mixer, a local oscillator (PLL circuit), a quadrature demodulator, and the like, amplify a reception signal of a predetermined frequency, and receive the signal. Has a function of quadrature demodulation.
The local oscillator (PLL circuit) in the reception unit 38 on the reception system B side can variably set the frequency division ratio of the frequency divider. The reception frequency of the receiving unit 38 on the receiving system B side can be variably set by changing the frequency dividing ratio for the frequency divider using an external control signal from the synchronous mode executing unit 16 described later.

On the reception system B side, a synchronization detection unit 15 is provided that extracts a synchronization signal for the master base station apparatuses 2 and 3 from the output signal of the FFT 36. The synchronization detection unit 15 detects, for example, a preamble at the beginning of the downlink subframe DL as a synchronization detection point with the master base station apparatuses 2 and 3 from the symbol group output by the FFT 36.
The MIMO encoder 28 and the MIMO decoder 35 are connected to a synchronization mode execution unit 16 to be described later.

[Function of synchronous mode execution unit]
As shown in FIG. 2, the slave base station device 1 of the present embodiment includes a synchronization mode execution unit 16 that is a communication control unit that switches the communication mode of the device 1 to either the normal mode or the synchronization mode. Yes.
The synchronization mode execution unit 16 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 at a predetermined execution period, and the current communication mode is It manages the mode type indicating whether it is “normal mode” or “synchronous mode”.

In addition, the synchronization mode execution unit 16 stores an execution cycle (for example, 5 minutes) for performing the intermediate synchronization process in the storage device in advance, and when the intermediate synchronization process is not performed, the synchronization mode execution unit 16 is normally connected to the terminal device 5. The wireless communication (normal mode) is continued as it is.
Furthermore, when performing the intermediate synchronization process, the synchronization mode execution unit 16 sends a pause signal to each of the MIMO encoder 28 and the MIMO decoder 35 to stop the MIMO communication with the terminal device 5 and any master base station device. In order to synchronize with the second and third base stations, a synchronization mode for receiving transmission signals (frequency is f2 or f3) from the base station apparatuses 2 and 3 is executed.

The synchronization mode execution unit 16 also uses an external control signal (divided to the frequency divider of the local oscillator corresponding to its own use frequency f1 and use frequencies f2 and f3 of the master base station apparatuses 2 and 3 that can be synchronized. (Circumference ratio) is previously stored in the storage area as a set value.
When the mode type is the normal mode, the synchronous mode execution unit 16 sets the external control signal for the frequency divider of the local oscillator to a value for its own use frequency f1, and sets the reception frequency of the reception system B to its own. Use frequency f1 is set.

On the other hand, when the mode type is the synchronous mode, the synchronous mode execution unit 16 sends an external control signal for the frequency divider of the local oscillator on the reception system B side to the use frequency f1, of any of the master base station apparatuses 2 and 3. Switch to the value for f2.
As a result, when the mode type is the synchronous mode, the transmission signals from the master base station devices 2 and 3 having the usage frequencies f2 and f3 different from the usage frequency f1 of the own device 1 are received by the receiver of the own device 1. 33 (reception system B) can receive.

The synchronization mode execution unit 16 then downloads the downlink subframes of the reception signals (transmission signals from the master base station devices 2 and 3) of the frequencies f2 and f3 detected by the synchronization detection unit 15 on the reception system B side in the synchronization mode. The synchronization timing is detected based on the preamble at the beginning of the DL. However, this synchronization timing can also be detected by a midamble or a pilot signal.
On the other hand, the synchronization mode execution unit 16 manages the mode type of the communication mode performed by the own device 1, but always notifies the MIMO encoder 28 and the MIMO decoder 35 of the mode type.

When the mode type is the normal mode, the synchronous mode execution unit 16 sets the MIMO encoder 28 and the MIMO decoder 35 so that predetermined MIMO wireless communication using the two transmission / reception systems A and B is executed. Control.
On the other hand, when the mode type is the synchronous mode, the synchronous mode execution unit 16 pauses the wireless communication in one transmission / reception system A during the execution period of the synchronous mode, and the master base station apparatus 2, The MIMO encoder 28 and the MIMO decoder 35 are controlled so that the transmission signal (frequency is f2 or f3) from 3 is received by the receiving unit 38 of the other transmission / reception system B.

In addition, the synchronization mode execution unit 16 of the present embodiment sets a guard time sufficient for the reception unit 38 of the transmission / reception system B to complete the switching of the reception frequency in executing the synchronization mode, in the execution period of the synchronization mode. In addition to being set before and after, the transmission / reception system A has a time setting function for executing wireless communication with the terminal device 5 so as to overlap the setting period of the guard time.
The time setting function performed by the synchronous mode execution unit 16 will be discussed again when the time chart shown in FIG. 5 is described.

[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 execution unit 16.
As shown in FIG. 3, first, the synchronization mode execution unit 16 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 S <b> 2), the synchronous mode execution unit 16 shifts the communication mode of the own device 4 from the normal mode to the synchronous mode. (Step S3).
When the synchronization mode ends, the synchronization mode execution unit 16 returns the communication mode to the normal mode again (step S4).

As described above, the synchronization mode execution unit 16 executes the normal mode for performing normal wireless communication with the terminal device 5 while executing the synchronization mode periodically or as needed as necessary. Even if a synchronization error with the master base station apparatuses 2 and 3 occurs, this can be eliminated.
In the present embodiment, the time required for the synchronization mode execution unit 16 to perform one synchronization mode is set to 5 ms, which is the same as the period of one basic frame.

FIG. 4 is a flowchart showing the processing contents of the intermediate synchronization processing.
As shown in FIG. 4, when the synchronization mode is executed in the intermediate synchronization process, the synchronization mode execution unit 16 first starts all the terminals in the own cell before starting the intermediate synchronization process (steps S11 to S15). A notification for switching the terminal device 5 to the sleep mode or the idle mode (power saving mode) is transmitted to the device 5 by broadcasting (step S10).

When receiving the notification of the sleep mode or the idle mode from the slave base station device 1, the terminal device 5 shifts its own operation mode to the mode according to the notification. Since the sleep mode and the idle mode are management modes when the terminal device 5 does not execute communication, power consumption can be suppressed.
The terminal device 5 is time-set so as to continue the sleep mode and the idle mode at least while the base station device 1 is in the synchronization mode and performing air synchronization.

As described above, since the terminal device 5 is in the sleep mode or the like while the slave base station device 1 is in the synchronous mode, the terminal device can be used even if the transmission signal non-reception period from the slave base station device 1 continues. 5 does not determine that communication is abnormal.
On the other hand, after notifying the terminal device 5 of the sleep mode or the like, the slave base station device 1 shifts to the synchronization mode by the intermediate synchronization process. When performing this intermediate synchronization processing, the synchronization mode execution unit 16 transmits a pause signal to the transmitter 26 of the own device 1 and pauses transmission of the downlink subframe DL into the own cell. As a result, the transmission signals of the other master base station apparatuses 2 and 3 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 16 first switches the mode type to the synchronization mode (step S11).
At this time, the synchronization mode execution unit 16 stops the MIMO communication with the terminal device 5 by the transmission / reception systems A and B, and switches the external control signal to the frequency divider of the local oscillator of the reception system B. As a result, the reception system of its own receiver 33 is switched to the reception frequencies f2 and f3 for the master base station devices 2 and 3 (see FIG. 3), and transmission signals from the master base station devices 2 and 3 are received. (Step S12).

After that, the synchronization mode execution unit 16 adopts the preamble at the beginning of the downlink subframe DL transmitted by the master base station apparatuses 2 and 3 as the synchronization detection point (step S13), and the synchronization shift occurs in accordance with the synchronization detection point. Is corrected (step S14).
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 apparatus 1.
In other words, the synchronization mode execution unit 16 corrects the temporal error of the transmission timing of the own device 1 based on the detected synchronization detection point, so that the transmission timing of the own device 1 becomes the synchronization target. The transmission timing is matched with a few.

In addition, if the transmission timing of the own apparatus 1 is matched with the transmission timing of the master base station apparatuses 2 and 3, the reception timing is also matched naturally, so that frame synchronization can be established between the master base station apparatuses 2 and 3. It becomes a state.
As described above, in this embodiment, the normal mode in which normal wireless communication is performed with the terminal device 5 is suspended, and transmission signals from the other master base station devices 2 and 3 are intercepted and synchronized. Even if there is no dedicated control channel for synchronization, air synchronization with the other base station apparatuses 2 and 3 can be performed.

When the correction of the synchronization deviation by the above intermediate synchronization processing is completed, the synchronization mode execution unit 16 notifies the terminal device 5 of the cancellation of the sleep mode (step S15) and ends the synchronization mode (step S16).
At this time, the communication mode is switched from the synchronous mode to the normal mode, and the external control signal to the local oscillator returns to the value for its own use frequency f1. As a result, the reception system on the reception system B side of the receiver 33 is adjusted to a normal state suitable for reception of the transmission signal from the terminal device 5.

Note that the terminal device 5 in the sleep mode or the like automatically returns to the normal operation mode in which communication with the slave base station device 1 is automatically performed when the set sleep time (or idle time) elapses.
Therefore, both the slave base station apparatus 1 and the terminal apparatus 5 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 (in the case of 2 systems)]
FIG. 5 shows a time chart when the synchronization mode execution unit 16 performs intermediate synchronization processing in the base station apparatus 1 of the present embodiment having two transmission / reception systems A and B.
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 gap time from transmission to reception (blank interval in which neither transmission nor reception is performed). The hatched portion of hatching indicates the gap time from reception to transmission.

In FIG. 5, it is assumed that the synchronization target of the slave base station apparatus 1 (BSs: use frequency f1) is the master base station apparatus 2 (BSm2: use frequency f2), and the upper time chart of FIG. FIG. 5 shows temporal changes in the frame of the master base station apparatus 2.
Further, the middle time chart of FIG. 5 shows temporal changes in the frames of the transmission / reception system A of the slave base station apparatus 1, and the lower time chart of FIG. It shows changes over time.

By the way, when the slave base station apparatus 1 executes the synchronization mode for the master base station apparatus 2 having a use frequency f2 different from its own use frequency f1, the slave base station apparatus 1 receives the transmission signal from the master base station apparatus 2 It is necessary to switch frequencies.
In general, in the case of a PLL oscillator that is commonly used as a local oscillator, if this is used for an OFDM receiver, low phase noise and spurious characteristics are required, and therefore the band of the loop filter needs to be narrowed. ing. However, when the loop filter band is narrowed, the time required for switching the frequency of the PLL circuit (the time from setting the frequency until the frequency stabilizes to the desired value) becomes longer, and it is found that it takes several milliseconds. ing.

Therefore, as shown in the lower time chart of FIG. 5, in the present embodiment, the synchronization mode execution unit 16 has a guard time (guard time) sufficient for the reception unit 38 of the reception system B to complete the switching of the reception frequency. ) Are provided before and after the execution period of the synchronous mode.
That is, when the synchronization mode execution unit 16 performs a synchronization mode using a synchronization signal having a frequency f2 different from its own use frequency f1, frequency switching is performed by a local oscillator (PLL circuit) before and after the execution period of the synchronization mode. A guard time longer than the time (5 ms in the illustrated example) is provided.

And the synchronous mode execution part 16 suspends the radio | wireless communication in the normal mode with the terminal device 5 regarding the transmission / reception system B which performs synchronous mode also in the setting period of the said guard time.
Thus, according to the slave base station apparatus 1 of the present embodiment, when the synchronization mode execution unit 16 synchronizes with the master base station apparatus 2 having the use frequency f2 different from itself, the guard time for frequency switching is set. The synchronization mode is executed by setting it before and after, and the normal mode is paused during the period of the synchronization mode and the guard time, so that the synchronization mode is not executed when the reception frequency of the reception unit 38 is unstable. Air synchronization can be performed reliably.

However, as described above, if the guard time for frequency switching is set before and after the synchronous mode, the pause period of the normal mode related to the transmission / reception system B becomes longer (in the example of FIG. 5, approximately three basic frames). Similarly, if communication is stopped for the transmission / reception system A, there is a problem that communication with the terminal device 5 may be disabled.
That is, since the terminal device 5 constantly receives the downlink subframe DL and obtains control information, when the reception failure state from a certain base station device 1 continues, an operation for searching for a new base station device is started. Resulting in. Also, from the viewpoint of communication efficiency, it is desirable that the number of stops of transmission frames from the base station apparatus 1 is small.

Accordingly, it is preferable that the stop frequency of the down signal accompanying the execution period of the synchronous mode is as low as possible.
Therefore, as shown in the middle time chart of FIG. 5, the synchronization mode execution unit 16 of the present embodiment uses that the own apparatus 1 includes two transmission / reception systems A and B for MIMO communication. Thus, in a time zone that overlaps the period of the guard time during which the transmission / reception system B performs frequency switching, communication control is performed to cause the other transmission / reception system A to perform wireless communication with the terminal device 5.

  That is, the synchronization mode execution unit 16 also stops the wireless communication by the other transmission / reception system A during the execution period of the synchronization mode in one transmission / reception system B, but during the guard time setting period in one transmission / reception system B Is configured to cause the other transmission / reception system A to perform wireless communication of only one system using its own use frequency f1 so as to overlap with the set period of the guard time.

As described above, according to the slave base station device 1 of the present embodiment, the synchronization mode execution unit 16 performs wireless communication with the terminal device 5 in the transmission / reception system A (in this case) in a time zone that overlaps the guard time setting period. 1 performs wireless communication instead of MIMO communication), even if the guard time is set to switch the operating frequency of the receiving unit 38, the wireless communication may be continued during the guard time setting period. it can.
For this reason, when performing air synchronization with the master base station devices 2 and 3 having different frequencies from that of the own device 1, the number of stops of the transmission frame of the own device 1 can be reduced as much as possible, and a decrease in communication efficiency can be minimized. Can do.
In the first embodiment (FIG. 2), the case where both the transmission system and the reception system are two systems A and B is illustrated on the assumption that MIMO wireless communication with the terminal device 5 is performed. At least one system is sufficient for the system, and even in this case, communication can be continued during the set guard time.

[Second Embodiment]
[Internal configuration of slave base station]
FIG. 6 is a functional block diagram showing an internal configuration of the base station apparatus 1 according to the second embodiment.
The base station device 1 of the second embodiment is different from that of the first embodiment in that the number of transmission / reception systems corresponding to the MIMO wireless communication with the terminal device 5 is four (A to D). Other configurations and functions are the same as those in 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 slave base station apparatus 1 of the present embodiment includes four transmission / reception systems A to D that can perform MIMO wireless communication with the terminal apparatus 5.
In the present embodiment, of the four transmission / reception systems A to D, two transmission / reception systems C and D are transmission / reception systems that execute the synchronous mode, and the remaining two transmission / reception systems A and B are in a guard time setting period. Is a transmission / reception system in which wireless communication with the terminal device 5 is continued.

A diversity combining unit 17 is connected to the subsequent stage of the FFT 36 of the two receiving systems C and D on the side executing the synchronization mode, and the synchronization detecting unit 15 is connected to the combining unit 17.
Accordingly, the combined signal that is diversity-received by the receiving units 38 of the two receiving systems C and D is input to the synchronization detecting unit 15, and the synchronization timing detected based on the combined signal is input to the synchronous mode executing unit 16. It is like that.

[Time chart for intermediate synchronization processing (for 4 systems)]
FIG. 7 is a time chart of the intermediate synchronization process performed by the synchronization mode execution unit 16 when there are four transmission / reception systems A to D as in the present embodiment.
As shown in FIG. 7, in this embodiment, the synchronization mode execution unit 16 performs a guard time for frequency switching (5 ms in the illustrated example) before and after the execution period of the synchronization mode using the two transmission / reception systems C and D. ).

In this case, the synchronization mode execution unit 16 performs diversity reception of the transmission signal from the master base station apparatus 2 (use frequency f2) using the two reception systems C and D, and uses the synchronization timing detected from the reception signal. Correct the synchronization error.
For this reason, compared with the case where the transmission signal from the master base station apparatus 2 is received by one transmission / reception system, the transmission signal can be received more reliably and the air synchronization can be reliably performed.

  On the other hand, in this embodiment, the synchronization mode execution unit 16 also stops the wireless communication by the remaining transmission / reception systems A and B during the execution period of the synchronization mode in the transmission / reception systems C and D. During the guard time setting period, the remaining transmission / reception systems A and B are caused to execute two systems of MIMO wireless communication at their own use frequency f1 so as to overlap with the guard time setting period. Yes.

In the four-system base station apparatus 1 shown in FIG. 6, the number X (positive integer) of transmission / reception systems that execute the synchronization mode and the number Y (positive integer) of transmission / reception systems that do not execute this are 2 respectively. It is not limited to one, and can be arbitrarily set in a range where the sum of X and Y is equal to or less than the total number of systems (= 4). For example, if X = 3 and Y = 1, transmission signals from the master base station apparatuses 2 and 3 can be received by diversity reception using three reception systems.
In the case of a base station apparatus having N transmission / reception systems, the combination of the numbers of X and Y can be arbitrarily set within a range that satisfies the inequality of X + Y ≦ N.
In the second embodiment (FIG. 6), the case where both the transmission system and the reception system are 4 systems A and B is illustrated on the assumption that MIMO wireless communication with the terminal device 5 is performed. At least one system is sufficient for the system, and even in this case, communication can be continued during the set guard time. This also applies to a third embodiment (FIG. 8) described later.

[Third Embodiment]
[Internal configuration of slave base station]
FIG. 8 is a functional block diagram showing an internal configuration of the base station apparatus 1 according to the third embodiment.
The base station apparatus 1 of the third embodiment is the same as the base station apparatus 1 of the second embodiment in that the number of transmission / reception systems corresponding to MIMO wireless communication is four (A to D). However, the third embodiment is different from the second embodiment in that signals of a plurality of frequencies f2 and f3 different from the use frequency f1 of the device 1 are individually and simultaneously received by the receiving systems C and D. Therefore, in the following, the configuration and functions different from those of the second embodiment will be mainly described.

  In this embodiment, the synchronization mode execution unit 16 can transmit external control signals to local oscillators (PLL circuits) in the reception units 38 of the two reception systems C and D for synchronization mode. Thereby, the reception frequencies of the reception systems C and D can be simultaneously set to different values (for example, the use frequency f2 of the master base station device 2 and the use frequency f3 of the master base station device 3).

In the slave base station apparatus 1 of the present embodiment, the synchronization detectors 15C and 15D are connected to the subsequent stage of the two reception systems C and D on the side that executes the synchronization mode, and are received by the reception systems C and D, respectively. The synchronization timing can be detected individually for each signal. The detection signals of the synchronization detection units 15C and 15D are sent to a search unit (search means) 18 described later.
The search unit (search means) 18 is a master base station to be synchronized based on two types of transmission signals received by the receiving systems C and D and having different frequencies from the master base station devices 2 and 3, respectively. Search for devices 2 and 3.

Specifically, for example, the search unit 18 selects a transmission signal with a good reception state based on a reception level (RSSI: Received Signal Strength Indicator) detected by a level detector such as a detection circuit in the reception unit 38. The master base station apparatuses 2 and 3 corresponding to this transmission signal are selected as synchronization targets.
Note that the search unit 18 can also determine the quality of the reception state in the reception systems C and D based on the value of CINR (Carrier to Interference and Noise Ratio) that is generally detected in a normal receiver.

[Time chart for intermediate synchronization processing (for 4 systems)]
FIG. 9 is a time chart of another intermediate synchronization process performed by the synchronization mode execution unit 16 when there are four transmission / reception systems A to D as in the present embodiment.
As shown in FIG. 9, also in this case, the synchronization mode execution unit 16 performs a guard time for frequency switching (5 ms in the example) before and after the execution period of the synchronization mode using the two transmission / reception systems C and D. Are inserted respectively.

  Also in this embodiment, the synchronization mode execution unit 16 also stops the wireless communication by the remaining two transmission / reception systems A and B during the execution period of the synchronization mode in the two transmission / reception systems C and D. During the setting period of the guard time in the two transmission / reception systems C and D, the two remaining MIMO transmission / reception systems A and B perform the two systems of MIMO radio communication using their own use frequency f1 so as to overlap the setting period of the guard time. Is supposed to be executed.

On the other hand, as shown in the lower two-stage time chart of FIG. 9, in this embodiment, the reception signal of the frequency f2 (transmission signal from the master base station apparatus 2) by one reception system C and the other reception are received. Reception of a transmission signal of frequency f3 (transmission signal from master base station apparatus 3) by system D is simultaneously performed during the execution period of the same synchronization mode.
Then, based on the reception levels of the signals of the frequencies f2 and f3 received by the two receiving systems C and D, the search unit 18 specifies the master base station devices 2 and 3 to be synchronized, respectively. The synchronization mode execution unit 16 is notified of the synchronization timing corresponding to the synchronization target.
Thereafter, the synchronization mode execution unit 16 corrects its own transmission timing based on the notified synchronization timing, and eliminates the synchronization shift.

  As described above, according to the base station apparatus 1 of the present embodiment, transmission signals from a plurality of types of master base station apparatuses 2 and 3 having different use frequencies f2 and f3 are transmitted to some of the transmission / reception systems A to D. Since the receiving systems C and D receive individually and simultaneously, the execution period of the synchronization mode for the search unit 18 to search for the synchronization target is shortened as compared with the case where the reception is performed in a time division manner. There is an advantage that air synchronization can be executed in a shorter time.

In the four-system base station apparatus 1 shown in FIG. 8, the number X (positive integer) of transmission / reception systems that execute the synchronization mode and the number Y (positive integer) of transmission / reception systems that do not execute the synchronization mode are respectively It is not limited to two, and can be arbitrarily set within a range where the sum of X and Y is equal to or less than the total number of systems (= 4). For example, if X = 3 and Y = 1, a synchronization mode for transmission signals of three types of frequencies can be simultaneously performed.
In the case of a base station apparatus having N transmission / reception systems, the combination of the numbers of X and Y can be arbitrarily set within a range that satisfies the inequality X + Y ≦ N.

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 5 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 5 can also be applied to a wireless communication system in which communication is performed by FDD (Frequency Division Duplex). In the case of this FDD, the base station apparatuses 1 to 3 can execute the synchronization mode without suspending communication with the terminal apparatus 5.

It is the schematic which shows the whole structure of a radio | wireless communications system. It is a functional block diagram which shows the internal structure of the base station apparatus of 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 in case a synchronous mode execution part performs an intermediate | middle synchronous process. It is a functional block diagram which shows the internal structure of the base station apparatus of 2nd Embodiment. It is a time chart of the intermediate | middle synchronous process which a synchronous mode execution part performs when there exist four transmission / reception systems. It is a functional block diagram which shows the internal structure of the base station apparatus of 3rd Embodiment. It is a time chart of the intermediate | middle synchronous process which a synchronous mode execution part performs when there exist four transmission / reception systems. FIG. 6 is a state diagram of a WiMAX frame when synchronization between base stations is matched.

Explanation of symbols

1: Slave base station apparatus (BSs) 2: Master base station apparatus (BSm2)
3: Master base station device (BSm3) 5: Terminal device (MS)
15: Synchronization detection unit 16: Synchronization mode execution unit (synchronization mode execution means, time setting means)
17: Diversity combining unit 18: Search unit (search means)
26: Transmitter 27: Modulator 28: MIMO encoder 29: IFFT (Inverse Fast Fourier Transformer) 30: DA converter 31: Transmitter 33: Transmitter 34: Demodulator 35: MIMO decoder 36: FFT (Fast Fourier Transformer) 37: AD converter 38: Receiver A to D: Transmission / reception system

Claims (4)

A base station device that performs wireless communication with a terminal device,
A transmission / reception system including at least one transmission system and a plurality of reception systems;
A synchronization mode for executing a synchronization mode in which a part of the plurality of reception systems receives a transmission signal from the other base station apparatus in order to synchronize with another base station apparatus that uses a different frequency. Execution means;
A part of the reception system is set so that a guard time sufficient to complete the switching of the reception frequency is set before and after the execution period of the synchronous mode, and is overlapped with the setting period of the guard time. Time setting means for causing the remaining transmission / reception system excluding the system to perform wireless communication with the terminal device;
A base station apparatus comprising:   The base station apparatus according to claim 1, wherein the synchronization mode execution unit causes the reception units of the plurality of reception systems that perform reception in the synchronization mode to receive the transmission signal from the other base station apparatus in a diversity manner. The other base station device is composed of a plurality of base station devices each having a different use frequency,
2. The base station according to claim 1, wherein the synchronization mode execution unit causes the reception unit of the reception system to individually and simultaneously receive a plurality of types of the transmission signals having different frequencies transmitted from the plurality of other base station apparatuses. apparatus.   The search unit according to claim 3, further comprising: a search unit configured to search for the other base station apparatus to be synchronized among the plurality of other base station apparatuses based on the plurality of types of transmission signals having different frequencies. Base station equipment.

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