JP5402234B2 - Base station equipment - Google Patents

Description

  The present invention relates to a base station apparatus that performs inter-base station synchronization with another base station apparatus.

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

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

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

JP 59-6642 A

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

Therefore, using a known signal wave such as a preamble included in the received wave of the signal transmitted by another adjacent base station, the transmission timing of the other adjacent base station is detected, and synchronization between base stations is performed at the transmission timing. Can be considered.
In this case, since synchronization can be achieved by wireless communication using the same frequency as that used for communication with the mobile terminal, a special receiving system for synchronization is not required unlike a GPS receiver for receiving GPS signals. For this reason, it is possible to reduce the size and cost of the base station, and it is suitable as a small base station installed indoors.

Here, the WiMAX described above employs a communication method that realizes duplex communication by TDD (Time Division Duplex) that switches between transmission and reception at high speed for wireless communication with a mobile terminal.
Specifically, as shown in FIG. 9, in WiMAX, one basic frame is arranged side by side in the time direction, and a downlink subframe DL (base station signal transmission time) and an uplink subframe UL (base station signal) are arranged. Reception time). The downlink subframe has a preamble at the beginning.

FIG. 9 shows a state in which the transmission timing and the reception timing match and are synchronized among a plurality of base stations.
Such synchronization processing for synchronization between base stations is performed when the base station is activated, and normal communication with the mobile terminal is performed after synchronization between base stations is established.

However, depending on the difference in accuracy error between the clock generators of both base stations, a synchronization shift occurs with time.
FIG. 10 is a graph illustrating an example of a change over time in the offset of the clock frequency of another base station apparatus with respect to the clock frequency of one base station apparatus. As shown in the figure, there is a steady offset value that gradually changes over time between the clock frequency of one base station apparatus and the clock frequency of another base station apparatus. This offset value varies depending on external factors such as ambient temperature change, but if there is no external factor, it tends to increase linearly and gradually due to the difference in accuracy between the clock generators. Yes.

  Since the base station apparatus acquires the transmission timing and the carrier frequency based on the oscillation of its own clock generation apparatus, if there is an offset value in each clock frequency as shown in FIG. A synchronization shift occurs between the apparatus and the transmission timing or carrier frequency.

  For this reason, for example, it is conceivable that communication with the terminal device is temporarily stopped, and synchronization synchronization with other base stations is performed to eliminate the above-described synchronization shift. In this case, while the base station apparatus stops communication with the terminal apparatus, the received wave of the other base station apparatus includes the degree of synchronization deviation with the other base station apparatus again. It is possible to detect and synchronize from a known signal wave such as a preamble wave.

However, the offset value of the clock frequency between the base station devices tends to increase linearly and gradually as described above. For this reason, in the base station apparatus, even if communication with the terminal apparatus is stopped and synchronization with another base station apparatus is taken, when communication with the terminal apparatus is started thereafter, the clock having the above-described tendency The frequency offset value gradually increases, causing a synchronization shift between both base station apparatuses.
That is, the synchronization process can temporarily bring the base station apparatuses into synchronization, but after that, a synchronization shift occurs again during communication with the terminal apparatus. Since the synchronization deviation gradually increases with the passage of time, if the communication time during the communication with the terminal device is long, the synchronization deviation during this communication time will increase. In terms of the total elapsed time in the station apparatus, even if synchronization processing is performed periodically, there will still be a synchronization error.

On the other hand, if the cycle for performing the synchronization process is shortened and synchronization is taken before the synchronization deviation becomes large, the synchronization deviation can be prevented from increasing. However, in order to perform the synchronization process, communication with the terminal device must be stopped. Therefore, if the cycle of the synchronization process is shortened, the throughput with the terminal device is reduced.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a base station apparatus that can suppress a synchronization shift between base stations while suppressing a decrease in throughput.

To achieve the above object, the present invention provides a communication mode in which a communication signal is transmitted to communicate with a terminal device, and a communication signal from another base station device that stops communication with the terminal device. A synchronization mode for performing inter-base station synchronization with the other base station apparatus by receiving
Based on the communication signal of the other base station apparatus received in the synchronization mode, an estimation unit for obtaining an estimated value of synchronization deviation between the communication signal of the other base station apparatus and the own communication signal;
A correction unit that performs synchronization correction to synchronize the communication signal transmitted by itself with the communication signal of the other base station device, based on the estimated value of synchronization deviation obtained by the estimation unit;
The correction unit performs the synchronization correction in a plurality of times during the communication mode until the next switching to the synchronization mode.

  According to the base station apparatus configured as described above, the synchronization correction of the communication signal transmitted by itself in the communication mode is performed in multiple times during the communication mode until the next switching to the synchronization mode. A large deviation can be suppressed over the entire communication mode. Therefore, not only the synchronization shift is suppressed by the synchronization between base stations performed in the synchronization mode, but also the synchronization shift can be suppressed even in the communication mode, so that the synchronization shift can be effectively suppressed.

  Further, according to the present invention, since synchronization deviation is suppressed even in the communication mode for performing communication with the terminal apparatus, it is necessary to stop communication with the terminal apparatus in order to suppress synchronization deviation. There is no need to shorten the period of the synchronous mode. For this reason, the synchronization gap between base stations can be suppressed, suppressing the fall of the throughput between terminal devices.

It is preferable that the correction unit performs synchronization correction for each unit time.
In this case, since the synchronization correction is performed uniformly every unit time over the entire communication mode, the synchronization shift that increases with time can be effectively suppressed.

  Further, the estimation unit obtains the communication timing of the other base station device from the communication signal of the other base station device, and based on the communication timing offset between this communication timing and its own communication timing, It is also possible to obtain an estimated value of synchronization loss.

  More specifically, the estimation unit uses the communication timing offset as the estimated value of the synchronization shift, and the correction unit synchronizes the communication timing by adjusting the time length of the communication frame constituting the communication signal. It is preferable to have a communication timing correction unit that performs correction. In this case, a synchronization shift related to communication timing can be suppressed.

  Further, the estimation unit obtains a carrier frequency offset of the communication signal as an estimated value of the synchronization shift based on the communication timing offset, and the correction unit includes a frequency correction unit that performs synchronization correction of the carrier frequency. It may be what you are doing. In this case, a synchronization shift related to the frequency of the carrier wave can be suppressed.

  As described above, according to the base station apparatus of the present invention, it is possible to suppress a synchronization shift between base stations while suppressing a decrease in throughput.

1 is an overall view of a wireless communication system according to a first embodiment of the present invention. It is the block diagram which showed the structure of the 2nd and 3rd base station apparatus. It is a figure which shows the flame | frame in which the communication frame timing offset produced. It is a figure which shows an example of the method of detecting the timing of a preamble. It is explanatory drawing which shows the timing offset amount in the last and this time synchronous mode. It is a figure which shows the flowchart at the time of a 2nd and 3rd base station apparatus switching from a communication mode to a synchronous mode. It is a figure which shows the aspect of a time-dependent change of the communication timing offset with respect to a master base station apparatus when a slave base station apparatus repeatedly performs communication mode and synchronous mode. FIG. 8 is an enlarged view of a synchronous mode portion in FIG. 7. It is a figure which shows the state of a frame when the synchronization between base stations is taken. It is a graph which shows an example of a time-dependent change of the clock frequency offset of the other base station apparatus with respect to the clock frequency of one base station apparatus. It is a figure which shows the whole structure of the radio | wireless communications system which concerns on 2nd embodiment of this invention. It is a frame configuration diagram of LTE. It is a DL frame structure diagram of LTE. It is a block diagram of a base station apparatus (child BS). It is a block diagram of a synchronous process part. It is a block diagram which shows the other example of child BS in this embodiment.

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

Each base station apparatus 1, 2 and 3 can communicate with a terminal apparatus (mobile terminal MS; Mobile Station) in an area (cell) covered by each base station apparatus 1, 2 and 3. .
As shown in FIG. 9, in WiMAX, one basic frame is composed of a downlink subframe DL (base station apparatus signal transmission time) and an uplink subframe UL (base station apparatus signal reception time) arranged side by side in the time direction. ), And a communication system that performs duplexing of transmission and reception by TDD (Time Division Duplexing).

The length of one basic frame is 5 msec. The downlink subframe DL is a time zone in which the base station devices 1, 2, and 3 transmit signals to the terminal devices in its own area, and the uplink subframe UL is transmitted by the base station devices 1, 2, and 3 in its own area. It is a time zone which receives the signal from the terminal device in the inside.
The downlink subframe DL includes a preamble that is a known signal at the head.
Further, one basic frame is switched so that neither the base station apparatus nor the terminal apparatus transmits between the downlink subframe DL and the uplink subframe UL and between the uplink subframe UL and the downlink subframe DL. It includes a gap TTG (Transmit / Receive Transition Gap) and a switching gap RTG (Receive / Transmit Transition Gap).

The plurality of base station apparatuses 1, 2, and 3 include at least one master base station apparatus and slave base station apparatus.
In this wireless communication system, processing for obtaining frame timing synchronization and carrier frequency synchronization is performed between the base station apparatuses 1, 2, and 3. The master base station apparatus is a reference station for frame timing and carrier frequency. On the other hand, the slave base station device performs frame timing directly to the master base station device as another base station device or indirectly via another slave base station device as another base station device. Take synchronization and carrier frequency synchronization.
In the following description, the first base station apparatus 1 shown in FIG. 1 is described as a master base station apparatus, and the second base station apparatus 2 and the third base station apparatus 3 are described as slave base station apparatuses.

  The frame timing synchronization is such that communication frames of the base station devices 1, 2, and 3 are transmitted at the same timing. That is, as shown in FIG. 9, in the time zone in which a certain base station device (first base station) is transmitting to the terminal device (down subframe time zone) by frame timing synchronization, other base station devices (Second base station) also transmits to the terminal device, and in a time zone (time zone of the uplink subframe) in which a certain base station device (first base station) receives from the terminal device, another base station device The communication timings of the base station apparatuses 1, 2, and 3 can be matched so that the (second base station) also receives from the terminal apparatus.

  Since the frame timing synchronization is established between the base station apparatuses, the terminal apparatus smoothly communicates with each base station apparatus even when the terminal apparatus communicates with a plurality of base station apparatuses at the time of handover or the like. Communication can be performed.

The carrier frequency synchronization is a method in which the carrier frequency (carrier frequency) of a signal (OFDM (A) signal) transmitted from each base station apparatus 1, 2, 3 to the terminal apparatus is matched between the base station apparatuses. It is.
Since the carrier frequency synchronization is established between the base station apparatuses, the terminal apparatus can smoothly communicate with each base station apparatus even when the terminal apparatus communicates with a plurality of base station apparatuses at the time of handover or the like. Can communicate with.

Here, each terminal apparatus detects an error in the carrier frequency of the OFDM signal received from the base station apparatus, and corrects the carrier frequency error in the received OFDM signal (the difference in carrier frequency between the transmission side and the reception side). (Automatic frequency control) function.
Therefore, each terminal apparatus can perform OFDM demodulation after correcting the error even if there is an error in the carrier frequency of the OFDM signal received from the base station apparatus.

  However, when the terminal device is in a state of communicating with a plurality of base station devices, such as at the time of handover, when the carrier frequency synchronization is not established between the base stations and a synchronization shift occurs, the terminal device Even if the AFC function is used, it is very difficult to correct the carrier frequency error.

  That is, when carrier frequency synchronization is not established between base stations, the error of the carrier frequency for one base station device is different from the error of the carrier frequency for another base station device as seen from a certain terminal device. Therefore, when communication is performed simultaneously with the plurality of base station apparatuses, the carrier frequency error cannot be corrected.

Now, since the first base station apparatus 1 is a reference station for frame timing and carrier frequency, it is necessary to acquire a signal for achieving frame timing synchronization or carrier frequency synchronization between base stations from other base station apparatuses. There is no.
For example, the first base station apparatus 1 can be configured as a self-running master base station apparatus that determines its own signal transmission timing based on a clock generated by its own built-in clock generator (crystal oscillator). In addition, the 1st base station apparatus 1 may be provided with a GPS receiver, and may determine the transmission timing of a signal using a GPS signal.

  On the other hand, both base station apparatuses 2 and 3 which are slave base station apparatuses send signals for frame timing synchronization or carrier frequency synchronization between base stations to other base station apparatuses (master base station apparatus or other base station apparatuses). From the slave base station device).

FIG. 2 is a block diagram showing the configuration of both base station apparatuses 2 and 3.
Both base station apparatuses 2 and 3 are configured to receive a signal, an amplifier 11 that amplifies the received signal, a quadrature demodulator 12 that performs a quadrature demodulation (orthogonal detection) process on the received signal output from the amplifier 11, and a quadrature demodulator An A / D conversion unit 13 that performs A / D conversion on the received signal output from the demodulator 12 is provided. The received signal converted into the digital signal is given to a DSP (digital signal processor) 20.

  Also, the base station apparatuses 2 and 3 perform orthogonal modulation processing on the transmission signal output from the D / A converter 15 and the D / A converter 15 for D / A conversion of the digital transmission signal for signal transmission. A quadrature modulator 16 to be performed and an amplifier 17 for amplifying a transmission signal output from the quadrature modulator 16 are provided.

The operation clocks of the quadrature demodulator 12, the A / D converter 13, the D / A converter 15, and the quadrature modulator 16 are provided from a built-in clock generator (reference signal generator) 18. . The built-in clock generator 18 includes a crystal resonator and generates an operation clock having a predetermined frequency. Note that the clock of the clock generator 18 is given to the A / D converter 13 and the like via the constant multipliers 19a and 19b.
The operation clock of the built-in clock generator 18 is also supplied to the DSP 20 and becomes an operation clock in the DSP 20.

  Here, the accuracy of the operation clock given to the D / A converter 15 affects the accuracy of the time length of the transmission frame (downlink subframe). Therefore, if the accuracy of the clock generator 18 is different for each base station device, the time length of the generated transmission frame is slightly different for each base station device. When the frame transmission is repeated, the difference in the frame time length is accumulated, and the frame timing between the base station devices is shifted (communication frame timing offset) (see FIG. 3).

The DSP (signal processing unit) 20 performs signal processing on the reception signal and / or transmission signal.
The main functions of the DSP 20 are a function as an OFDM demodulator for a received signal, a function as an OFDM modulator for a transmitted signal, a function for switching between transmission and reception (transmission frame and reception frame), a frame timing synchronization function between base stations, And a carrier frequency synchronization function between base station apparatuses. In FIG. 2, the blocks shown in the DSP 20 indicate these functions.

The carrier frequency correction unit 21 in FIG. 2 corrects the carrier frequency of the received signal. A carrier frequency correction unit 22 that corrects the carrier frequency of the transmission signal is also provided.
The carrier frequency correction units 21 and 22 correct the carrier frequency of the reception signal and / or the transmission signal based on the carrier frequency offset estimated by the estimation unit 23.

The output of the carrier frequency correction unit 21 of the received signal is given to the demodulation unit (DEM) 25 via the changeover switch 24. The demodulation unit 25 performs demodulation (OFDM demodulation) processing on the received signal that has been subjected to carrier frequency correction.
The change-over switch 24 applies the received signal to the demodulator 25 during the communication mode in which the signal from the terminal apparatus can be received, and the received signal is estimated in the synchronous mode in which the communication mode is stopped (paused). It is for giving to. Switching of the switch 24 is performed by the synchronization control unit 26.
The communication mode is a mode in which communication is performed with the terminal device by transmitting a communication signal to the terminal device. The synchronous mode is a mode in which communication with the terminal device is stopped and another base This is a mode for receiving a communication signal transmitted from a station apparatus and performing inter-base station synchronization processing (synchronization processing) with the other base station apparatus. These communication modes and synchronization modes will be described later.

  The DSP 20 also includes a modulation unit (MOD) 27 that performs modulation (OFDM modulation) processing on the transmission signal. In the modulation unit 27, since the carrier frequency is determined based on the clock frequency of the clock generator 18, an error in the clock frequency affects the carrier frequency of the transmission signal. Note that if a deviation occurs in the carrier frequency of the transmission signal, the center frequency of each subcarrier shifts uniformly, although the frequency interval of each subcarrier does not change.

The transmission signal output from the modulation unit 27 is given to the carrier frequency correction unit 22 via the changeover switch 28.
The changeover switch 28 provides a transmission signal to the D / A converter 15 during a communication mode in which a signal can be transmitted to the terminal device, and transmits the transmission signal to a D / A converter in the synchronous mode in which the communication mode is suspended. 15 is not to be given.
The switching of the switch 28 is also performed by the synchronization control unit 26. In other words, the synchronization control unit 26 constitutes a control unit that executes by switching between the communication mode and the synchronization mode.

The estimation unit 23 detects a preamble that is a synchronization signal from a received signal (communication signal), and detects a timing offset of a communication frame with another base station device and between the other base station devices. The carrier frequency offset (carrier frequency offset) is estimated.
Therefore, the estimation unit 23 includes a preamble detection unit 23a that detects a preamble included in the received signal, a clock error estimation unit 23b that estimates a clock error between another base station device and the own device, and another base station. And a calculation unit 23c that calculates a timing offset per unit time between the station apparatus and the own apparatus.

In this embodiment, the preamble at the head of the downlink subframe DL transmitted by another base station apparatus is used as a synchronization signal for synchronization between base stations. Therefore, the detection unit 23a detects the timing of the preamble at the head of the downlink subframe DL transmitted by another base station device.
Note that the synchronization signal may be a midamble, a pilot signal, or the like.

  The base station apparatuses 2 and 3 have a preamble pattern that may be used by other base station apparatuses 1 and 2 in a memory as a known pattern. The detection unit 23a of the base station apparatuses 2 and 3 detects the preamble timing and the like using these known preamble patterns.

  Here, since the preamble is a known signal, the signal waveform of the preamble is also known. If the received signal after sampling is X (t) and the signal in the discrete time domain of the preamble is P (n) (n = 0,..., N−1), the received wave X shown in FIG. For (t), the sliding correlation of P (n) is taken in the time direction based on the following equation.

  Then, as shown in FIG. 4B, the position where the correlation value between the received wave X (t) and the known preamble pattern P (n) takes a peak can be detected as the preamble timing t.

  The detection unit 23a detects the difference between the transmission timings of the devices 2 and 3 and the detected preamble timing t as a communication timing offset (synchronization deviation). The communication timing offset (communication frame timing offset) is provided to the storage unit 29 and accumulated in the storage unit 29 each time it is detected.

The communication timing offset detected by the detection unit 23a is given to the clock error estimation unit 23b and the calculation unit 23c.
The calculation unit 23c calculates the timing offset per unit time by determining how much the timing offset increases per unit time based on the communication timing offset detected by the preamble detection unit 23a.
In the present embodiment, the unit time is set to 5 ms, which is a time width related to one basic frame.

  Also, the clock error estimation unit 23b, based on the communication timing offset detected by the preamble detection unit 23a, the clock frequency of the built-in clock generator 18 of its own device that is the reception side, and another base station device that is the transmission side The difference (clock frequency error) from the clock frequency of the internal clock generator 18 is estimated. Then, a carrier frequency offset as an estimated value of synchronization deviation is obtained from the estimated value of the clock frequency error.

  Based on the communication timing offset detected in the previous synchronization mode and the communication timing offset detected in the current synchronization mode under the situation where the synchronization mode is periodically executed, the clock error estimation unit 23b Estimate the clock error. The previous timing offset can be acquired from the storage unit 29.

For example, when the carrier frequency is 2.6 [GHz], T1 is detected as a timing offset in the previous synchronization mode (synchronization timing = t1) as shown in FIG. Shall be made. In the current synchronization mode (synchronization timing = t2) after 10 seconds, the timing offset is detected again, and the timing offset is T2.
Then, it is assumed that the difference (T2−T1) between the current timing offset T2 and the previous timing offset T1 is 0.1 [msec].

  Here, since the time length of one basic frame is 5 [msec], 5 [msec] = 2π, and between the previous synchronization mode and the current synchronization mode (Δt = t2−t1 = 10 [sec] ]), The phase is shifted by π / 25 [rad]. That is, the phase rotation amount Δφ = π / 25.

Since the relationship of Δφ = 2πfΔt is established, π / 25 = 2πf × 10.
Therefore, the frequency error f = 1/500 = 0.002 [Hz].
Here, since the frame length of one basic frame is 5 [msec], when this frame length is converted into a frequency, 1 / 0.005 = 200 [Hz].
That is, a frequency error of 0.002 [Hz] is generated for a frequency of 200 [Hz] (per basic frame).

Therefore, in this case, there is an error of 1 × 10 ⁻⁵ = 10 [ppm] between the clock frequency of the other base station apparatus on the transmission side and the clock frequency of the base station apparatus on the reception side. The clock error estimation unit 23b estimates the clock frequency error as described above.

Since the carrier frequency and the timing offset are shifted in the same manner, a shift of 10 [ppm], that is, a shift of 2.6 [GHz] × 1 × 10 ⁻⁵ = 26 [kHz] also occurs in the carrier frequency. .
As described above, the clock error estimation unit 23b obtains the clock frequency error based on the communication frame timing offset detected by the preamble detection unit 23a, and uses it as an estimated value of the synchronization deviation that occurred between the previous synchronization mode. Carrier frequency offset and carrier frequency offset per basic frame (per unit time) can be obtained.

  Of the timing offset and the carrier frequency offset obtained by the clock error estimation unit 23b as described above, the carrier frequency offset (the carrier frequency offset generated between the previous synchronization mode and one basic frame Carrier frequency offset) is provided to the carrier frequency correction units 21 and 22.

In the present embodiment, not only the carrier frequency of the reception signal but also the carrier frequency of the transmission signal can be corrected as in a normal AFC (automatic frequency control) function.
That is, the carrier frequency offset between other base station devices is also given to the carrier frequency correction unit 22 on the transmission side, and the carrier frequency of the transmission signal to the terminal device is corrected in this carrier frequency correction unit 22. .
In the synchronization mode, the carrier frequency correction unit 22 performs a process (synchronization process) for adjusting the carrier frequency in order to eliminate the currently occurring carrier frequency offset.
Further, in the communication mode, the carrier frequency correction unit 22 synchronizes the communication signal transmitted to the terminal device with the communication signal of the other base station device in the communication mode, so that the carrier frequency offset per basic frame is described above. Based on the above, processing for adjusting the carrier frequency for each basic frame (synchronization correction processing) is performed.
Specifically, the carrier frequency of each basic frame is adjusted so that the carrier frequency offset per basic frame, which is the amount of synchronization deviation estimated to occur for each basic frame, is eliminated for each basic frame. .
In other words, the carrier frequency correction unit 22 performs the synchronization correction process for each basic frame (every unit time) multiple times during the communication mode until the next switching to the synchronization mode, The carrier frequency is adjusted so as to eliminate the carrier frequency offset generated as an estimated value of the synchronization error.

  As described above, in the present embodiment, by performing the above processing as carrier frequency synchronization, even if a clock frequency error exists between itself and another base station apparatus, a carrier frequency offset occurs. Can be suppressed, and a synchronization shift regarding the carrier frequency of the communication signal between itself and another base station apparatus can be suppressed.

  The communication timing offset detected by the detection unit 23a is given to the frame timing control unit 30 as an estimated value of synchronization deviation. Further, the timing offset per basic frame (per unit time) obtained by the calculation unit 23 c is also given to the frame timing control unit 30. Based on these, the frame timing control unit (TDD control unit) 30 performs control for switching between transmission and reception, and performs processing for adjusting the time length of the communication frame (transmission frame, reception frame).

  In the synchronous mode, the frame timing control unit 30 that has received the communication timing offset shifts its own transmission timing (transmission subframe timing) in the correct direction by the amount of the communication timing offset detected by the detection unit 23a. (Synchronization processing) is performed. Thereby, it is possible to synchronize the frame timing between the base station devices by matching the transmission timing of the own device with the transmission timing of the other base station device.

Further, in the communication mode, the frame timing control unit 30 is requested by the calculation unit 23c to perform synchronization correction for synchronizing the communication signal transmitted to the terminal device with the communication signal of another base station device. Further, the time length for each basic frame is adjusted based on the timing offset per basic frame (synchronous correction processing).
Specifically, the time length of each basic frame is adjusted so that the timing offset per basic frame, which is the amount of synchronization deviation estimated to occur for each basic frame, is eliminated for each basic frame. .
In other words, the frame timing control unit 30 performs synchronization correction processing for each basic frame (per unit time) in multiple times during the communication mode until the next switching to the synchronization mode, The time length of each basic frame is adjusted so as to eliminate the communication timing offset as an estimated value of the synchronization error that occurs in the meantime.
If the transmission timing is matched with the transmission timing of another base station apparatus, the reception timing is also matched naturally. That is, the frame timing is synchronized with other base station apparatuses.

  Thus, in the present embodiment, by performing the above processing as frame timing synchronization, a communication frame timing offset occurs even if a clock frequency error exists between itself and another base station apparatus. Can be suppressed, and a synchronization shift regarding communication timing between itself and another base station apparatus can be suppressed.

As described above, the estimation unit 23 according to the present embodiment acquires the preamble timing t (communication timing) of the other base station device from the communication signal of the other base station device, and this timing t and the own device 2 , 3 is detected as a communication timing offset (synchronization timing error), and based on this communication timing offset, a synchronization shift between a communication signal of another base station apparatus and its own communication signal Are estimated (communication timing offset, carrier frequency offset).
In addition, the carrier frequency correction units 21 and 22 and the frame timing control unit 30 as correction units are configured to synchronize communication signals transmitted by themselves in communication mode with other base station apparatuses (timing offset and carrier frequency). A synchronization correction process (related to the offset) is performed based on the estimated value of the synchronization deviation.
Further, the carrier frequency correction units 21 and 22 and the frame timing control unit 30 divide the synchronization correction processing (related to the timing offset and the carrier frequency offset) into a plurality of times during the communication mode until the next switching to the synchronization mode. Do it.

  Note that the synchronization processing and the synchronization correction processing regarding the frame timing between the base station apparatuses performed by the estimation unit 23 and the frame timing control unit 30 will be described in detail later.

Returning to FIG. 2, as described above, the synchronization control unit 26 controls the timing (synchronization timing) at which the communication mode is paused to execute the synchronization mode.
The synchronous mode is executed as follows.

  First, the slave base station devices 2 and 3 select one base station device as a source base station device among other base station devices (master base station device or other slave base station devices) at the time of startup, A received wave (source received wave) of a signal (preamble; known signal; synchronization signal) transmitted by the source base station apparatus is detected, and frame timing synchronization and carrier frequency synchronization are established between the base station apparatuses.

  A process for synchronization between base stations performed when the base station apparatus is activated is referred to as an initial synchronization mode. The initial synchronization mode is executed at the time of activation as described above, and more specifically, is performed after the base station apparatus is activated until the communication with the terminal apparatus is started.

After the execution of the initial synchronization mode, the base station apparatus can communicate with the terminal apparatus in its own area.
However, since there is a clock frequency offset due to variations in clock accuracy between base station apparatuses, frame timing and carrier frequency are shifted between base station apparatuses over time.

Therefore, the slave base station devices 2 and 3 pause (stop) communication (transmission signal; downlink subframe) with the terminal device at a predetermined timing, and stop the synchronization mode (communication was paused). Synchronized mode).
FIG. 6 shows a synchronization mode in which the base station apparatuses 2 and 3 receive signals from other base station apparatuses (master base station apparatus or slave base station apparatus) from the (normal) communication mode in which communication with the terminal apparatus is performed. The flowchart for switching to is shown.

As illustrated in FIG. 6, the base station devices 2 and 3 determine whether or not it is a synchronization timing that should be in the synchronization mode (step S1). The synchronization timing is set, for example, as a cycle (every predetermined time or every predetermined number of frames) in which the synchronization mode is set. When setting a period by time, it can be set as about 5 minutes, for example.
When it is determined that it is time to shift to the synchronization mode in the normal communication mode in which communication is performed with the terminal device (step S2), the base station devices 2 and 3 are in the synchronization mode (step S3). Migrate to When the synchronization mode ends, the normal communication mode is resumed (step S4).
The base station devices 2 and 3 communicate with the terminal device, but can eliminate the synchronization loss by executing the synchronization mode periodically or whenever necessary. it can.

  When the base station devices 2 and 3 enter the synchronous mode, communication with the terminal device (downlink subframe transmission) is stopped (paused), and a state in which signals are received even during the time when the base station devices are originally in the downlink subframe. It becomes.

  In the synchronous mode, a signal (OFDM signal) transmitted from another base station device 2 to the terminal device is received. In this embodiment, the preamble at the head of the downlink subframe DL transmitted by another base station apparatus 2 is used as a synchronization signal for synchronization between base stations, and frame timing synchronization and carrier frequency synchronization are achieved.

  When the above synchronization mode ends, the base station devices 2 and 3 return from the synchronization mode to the normal communication mode, and can communicate with the terminal device.

Next, the synchronization process and the synchronization correction process performed by the base station apparatuses 2 and 3 in the synchronization mode and the normal communication mode will be described in detail.
FIG. 7 is a diagram illustrating an aspect of a temporal change in communication timing offset with respect to the master base station apparatus when the slave base station apparatus repeatedly performs the communication mode and the synchronization mode. In addition, in FIG. 7, it demonstrates as a communication timing offset between the 1st base station apparatus 1 and the 2nd base station apparatus 2. FIG.

FIG. 7 shows a mode in which the second base station apparatus 2 periodically repeats the synchronization mode after executing the communication mode with a predetermined time width. In FIG. 7, when the communication timing offset is “0”, the frame timing between the first base station apparatus 1 and the second base station apparatus 2 coincides and the frame timing is synchronized. Show.
In FIG. 7, the broken line is a diagram showing the change over time in the communication timing offset when the frame timing synchronization is achieved only by the synchronization process in the synchronization mode, and the solid line indicates the synchronization process in the synchronization mode and the communication mode. FIG. 6 is a diagram showing a change with time of a communication timing offset according to the present embodiment in which frame timing synchronization is achieved by synchronization correction processing in FIG.

In the communication mode, the second base station device 2 communicates with the terminal device, and therefore operates independently and in a free-run state in relation to the first base station device 1. Therefore, as shown by the broken line in FIG. 7, when the synchronization correction process is not performed in the communication mode, the communication timing offset is changed from the state synchronized by performing the synchronization process in the synchronization mode to the communication mode. Due to the clock frequency error between the two base station apparatuses 1 and 2, it increases with time and a synchronization shift occurs. At this time, the communication timing offset value ΔT _n ′ generated as a synchronization shift when switching from the communication mode to the synchronous mode (at the end of the communication mode) is approximately the same as the clock frequency error between the two accumulates over time. As a value of, it appears periodically corresponding to each communication mode.
On the other hand, in the present embodiment, by performing the synchronization correction process in the communication mode, as shown by the solid line in FIG. 7, it is possible to suppress a communication timing offset that appears periodically corresponding to the communication mode from occurring. Has been.

FIG. 8 is an enlarged view of the synchronous mode portion in FIG.
The second base station apparatus 2 according to the present embodiment obtains a timing offset t _n per basic frame by the estimation unit 23b and the frame timing control unit 30, and the communication mode so that the timing offset t _n is eliminated. The synchronization correction is performed for each basic frame constituting the signal transmitted by.

Specifically, the frame timing control unit 30 performs synchronization correction by shifting the transmission start timing of the downlink subframe DL in each basic frame in a direction in which the timing offset t _n is eliminated. That is, the frame timing control unit 30 can perform the synchronization correction by adjusting the time width of the switching gap RTG adjacent to the next basic frame in the basic frame.
Since the frame timing control unit 30 performs synchronization correction for each basic frame, the value of the communication timing offset in the communication mode increases with the time width of each basic frame as shown in FIG. It is repeated that the timing is decreased by the timing offset t _n at the timing between.

As described above, the frame timing control unit 30 performs synchronization correction in a plurality of times for each basic frame during the communication mode until the next switching to the synchronization mode, and occurs between the previous synchronization mode. Then, the time length of each basic frame is adjusted so as to eliminate the communication timing offset as the estimated value of synchronization loss.
When the synchronization correction is performed in this way, the synchronization correction is performed uniformly over the entire communication mode, so that the synchronization shift that increases with time can be effectively suppressed.
A method for obtaining the timing offset t _n per basic frame will be described later.

When the communication mode is switched to the synchronization mode, the preamble detection unit 23a (FIG. 2) of the estimation unit 23 detects the communication timing offset value ΔT _n as the current synchronization deviation.
Next, the calculation unit 23c (FIG. 2) receives the communication timing offset value ΔT _n from the preamble detection unit 23a as an estimated value of synchronization deviation in the next communication mode, and calculates a timing offset t _{n + 1} per basic frame. Calculate and output to the frame timing control unit 30.

Here, the calculation unit 23c calculates the timing offset t _{n + 1} per basic frame in the next communication mode as follows. In other words, the current communication timing offset value ΔT _n is a synchronization shift generated as a result of the sequential synchronization correction by the timing offset t _n for each basic frame. If, when the same value communication timing offset value [Delta] T _n the current is the timing offset t _n, by the synchronization correction and timing offset t _n, at the time of the synchronous mode, and it is precisely synchronized displacement is eliminated Become.
However, the current communication timing offset value ΔT _n usually has a deviation value δT _n as shown in the following equation (2) depending on the state of the clock generators of both base station apparatuses and the change in the communication environment.
ΔT _n = t _n + δT _n (2)

Note that the communication timing offset value ΔT _n ′ generated when synchronization correction is not performed in the entire previous communication mode is included in one communication mode in the timing offset t _n that is eliminated by synchronization correction for each basic frame. It is expressed as a value obtained by multiplying the number of frames and the deviation value δT _n .

The deviation value δT _n is a synchronization deviation that occurs while correcting the synchronization in the entire previous communication mode. Therefore, the arithmetic unit 23c, as shown in the following formula (3), by dividing the number of basic frames included a shift value? T _n to the time width of the communication mode, the value per basic frame shift value? T _n sought, this by adding the timing offset t _n of 1 basic frame per former, obtaining the timing offset t _{n + 1} per basic frame in the next communication mode.
t _{n + 1} = t _n + δT _n / (number of basic frames included in communication mode)
... (3)

Based on the communication timing offset value ΔT _n detected by the preamble detection unit 23a as an estimated value of synchronization shift in the next communication mode, as shown in the above equations (2) and (3), the calculation unit 23c A timing offset t _{n + 1} per frame is obtained.
For the number of basic frames included in one communication mode, the time width of the communication mode is determined in advance by the synchronization control unit 26, and the time width of the basic frame is set to 5 ms as described above. The computing unit 23c can obtain the number of basic frames included in one communication mode from these values.

When the deviation value δT _n is smaller than a predetermined value, the current timing offset t _n is directly used as the timing offset t _{n + 1} in the next communication mode without considering the deviation value δT _n. It can also be. In this case, it is possible to prevent the synchronous correction from being performed based on the minute deviation value δT _n that does not need to be corrected.
Even when the deviation value δT _n appears as an extremely large value, the current timing offset t _n is directly used as the timing offset t _{n + 1} in the next communication mode without considering the deviation value δT _n. You can also In this case, even if the deviation value δT _n appears as a sudden abnormal value due to, for example, multipath, it is possible to avoid performing synchronization correction based on the abnormal value.

When the timing offset t _{n + 1} per basic frame obtained as described above is received from the calculation unit 23c and the communication timing offset value ΔT _n is received from the preamble detection unit 23a, the frame timing control unit 30 The synchronization process is performed by performing a process of shifting its own transmission timing when starting the communication mode in a direction to eliminate the timing offset value ΔT _n .
In addition, when the frame timing control unit 30 switches to the communication mode after the synchronization process, the frame timing control unit 30 performs the above-described synchronization correction for each basic frame in the communication mode based on the timing offset t _{n + 1} per basic frame. Do.

  According to the second and third base station devices 2 and 3 configured as described above, the synchronization correction of the communication signal transmitted by itself in the communication mode is performed between the communication modes until the next switching to the synchronization mode. Since the process is performed separately, it is possible to suppress the occurrence of a large synchronization shift over the entire communication mode. Therefore, not only the synchronization shift is suppressed by the synchronization between base stations performed in the synchronization mode, but also the synchronization shift can be suppressed even in the communication mode, so that the synchronization shift can be effectively suppressed.

  Further, according to the base station devices 2 and 3 of the present embodiment, since synchronization deviation is suppressed even in the communication mode for performing communication with the terminal device, in order to suppress synchronization deviation, There is no need to shorten the period of the synchronous mode in which communication between the two needs to be stopped. For this reason, the synchronization gap between base stations can be suppressed, suppressing the fall of the throughput between terminal devices.

[Second Embodiment]
FIG. 11 is a diagram showing an overall configuration of a wireless communication system according to the third embodiment of the present invention. FIG. 11 illustrates a communication system that performs wireless communication between base station apparatuses 101a and 101b and user terminals (mobile terminals; MSs) 102a and 102b. In this communication system, a plurality of base station apparatuses (BSs) 101a and 101b are installed and can communicate with user terminals 102a and 102b in a cell.

  This communication system is, for example, a system to which LTE (Long Term Evolution) is applied. In LTE, frequency division duplex (FDD) can be employed. In the following, the communication system will be described as employing a frequency division duplex scheme. The communication system may adopt WCDMA or CDMA2000 in addition to LTE.

In the communication system according to the present embodiment, inter-base station synchronization is performed in which a plurality of base station apparatuses 101a and 101b are synchronized. In the present embodiment, inter-base station synchronization is performed by a base station apparatus (hereinafter referred to as “parent BS”) 101a as another parent base station apparatus transmitted toward the terminal apparatus 102a in the cell of the parent BS 101a. The received signal is received by another base station apparatus (hereinafter referred to as “child BS”) 101b, and this is executed by “air synchronization” for synchronization.
In addition, the parent BS may be one that establishes air synchronization with another base station device, or determines frame timing by a method other than air synchronization, such as synchronization by a GPS signal. There may be.

[LTE frame structure]
In frequency division duplex, the frequency fu of the uplink signal (transmission signal from the terminal device to the base station device) and the frequency fd of the downlink signal (transmission signal from the base station device to the terminal device) are made different from each other. Communication and downlink communication are performed simultaneously.
As shown in FIG. 12, the downlink frame (DL frame) and the uplink frame (UL frame) in LTE each have a time length of 10 milliseconds and are configured by 20 slots # 1 to # 19. Yes. In LTE, a combination of two slots is called a subframe. Note that the timings of these downstream frames and upstream frames are aligned.

As shown in FIG. 13, each slot constituting the downlink frame (DL frame) is composed of seven (I = 0 to 6) OFDM symbols (in the case of Normal Cyclic Prefix).
Of the 20 slots # 0 to # 19 constituting the downlink frame, the 0th (# 0) and 10th (# 10) slots have a primary synchronization signal as an identification code as a base station apparatus. And Secondary Synchronization Signal.

The primary synchronization signal is arranged at the last symbol (I = 6) among the seven OFDM symbols constituting the slot. This Signal is information for identifying each of a plurality of (three) sectors obtained by dividing the communication area (cell) of the base station apparatus, and there are three types.
The Secondary Synchronization Signal is arranged in the second (I = 5) symbol from the last among the seven OFDM symbols constituting the slot. This Signal is information for identifying each of the communication areas (cells) of a plurality of base station apparatuses, and there are 168 types.

504 types (168 × 3) of identification codes are constituted by two of Primary Synchronization Signal and Secondary Synchronization Signal. By acquiring these signals transmitted from the base station apparatus, the user terminal can recognize in which sector of which base station apparatus the own terminal exists.
Also, these signals are signals for the user terminal to synchronize with the base station apparatus, and the user terminal acquires these signals to synchronize with the base station apparatus that is the communication partner. Can be taken.

[Configuration of base station equipment]
FIG. 14 shows the configuration of the base station apparatus (child BS) 101b. The child BS 101b includes an antenna 141, a first reception unit 110, a second reception unit 120, and a transmission unit 130. The first receiving unit 110 is for receiving an uplink signal from the user terminal 102b, and the second receiving unit 120 is for receiving a signal from the parent BS 101a that is another base station device. . The transmission unit 130 is for transmitting a downlink signal to the user terminal 102b.

In addition, the child BS 101b includes a circulator 140. The circulator 140 is for giving a reception signal from the antenna 141 to the first reception unit 110 and the second reception unit 120 side, and for giving a transmission signal output from the transmission unit 130 to the antenna 141 side. The circulator 140 and the fourth filter 135 of the transmission unit 130 prevent the reception signal from the antenna 141 from being transmitted to the transmission unit 130 side.
Further, the circulator 140 and the first filter 111 of the first receiving unit prevent the transmission signal output from the transmitting unit 130 from being transmitted to the first receiving unit 110. Further, the circulator 140 and the fifth filter 121 prevent the transmission signal output from the transmission unit 130 from being transmitted to the second reception unit 120.

  The first receiver 110 is configured as a superheterodyne receiver, and is configured to perform IF (intermediate frequency) sampling. More specifically, the first reception unit 110 includes a first filter 111, a first amplifier 112, a first frequency conversion unit 113, a second filter 114, a second amplifier 115, a second frequency conversion unit 116, and an A / A D conversion unit 117 is provided.

  The first filter 111 is used to pass only the uplink signal from the user terminal 2b, and is configured by a band pass filter that passes only the frequency fu of the uplink signal. The received signal that has passed through the first filter 111 is amplified by a first amplifier (high frequency amplifier) 112 and converted from a frequency fu to a first intermediate frequency by a first frequency converter 113. The first frequency conversion unit 113 includes an oscillator 113a and a mixer 113b.

  The output of the first frequency converter 113 is amplified again by the second amplifier (intermediate frequency amplifier) 115 through the second filter 114 that passes only the first intermediate frequency. The output of the second amplifier 115 is converted from the first intermediate frequency to the second intermediate frequency by the second frequency converter 116 and further converted into a digital signal by the A / D converter 117. The second frequency conversion unit 116 is also composed of an oscillator 116a and a mixer 116b.

The output of the A / D conversion unit 117 (the output of the first reception unit 110) is given to the demodulation circuit 150 (digital signal processing device), and the demodulation process of the reception signal from the user terminal 102b is performed.
As described above, the first receiving unit 110 converts the analog upstream signal received by the antenna 141 into a digital signal, and gives the digital upstream signal to the demodulation circuit 150 configured as a digital signal processing device. is there.

  The transmitter 130 receives the modulated signals I and Q output from the modulation circuit 160 (digital signal processing device) and transmits the signals from the antenna 141, and is configured as a direct conversion transmitter. The transmission unit 130 includes D / A converters 131 a and 131 b, a quadrature modulator 132, a third filter 133, a third amplifier (high power amplifier; HPA) 134, and a fourth filter 135.

The D / A converters 131a and 131b perform D / A conversion on the modulation signals I and Q, respectively. The outputs of the D / A converters 131a and 131b are given to the quadrature modulator 132, and the quadrature modulator 132 generates a transmission signal having a carrier frequency of fd (downlink signal frequency).
The output of the quadrature modulator 132 passes through the third filter 133 that passes only the frequency fd, is amplified by the third amplifier 134, further obtains the fourth filter 135 that passes only the frequency fd, and is transmitted from the antenna 141. This is a downlink signal to the user terminal 102b.

  The first receiving unit 110 and the transmitting unit 130 described above are functions necessary for performing intrinsic communication with the user terminal, but the child BS 101b of the present embodiment further includes the second receiving unit 120. ing. The second receiving unit 120 receives a downlink signal transmitted by the parent BS 101a in order to achieve air synchronization.

  Here, in order for the child BS 101b to synchronize with the parent BS 101a by air synchronization, the child BS 101b needs to receive a downlink signal transmitted by the parent BS 101a. However, since the frequency of the downlink signal is fd and is different from the frequency fu of the uplink signal, the first receiving unit 110 cannot receive it.

That is, since the first receiving unit 110 includes the first filter 111 that passes only the signal of the frequency fu and the second filter 114 that passes only the first intermediate frequency converted from the frequency fu, the frequency fu Even if a signal having a frequency other than (frequency fd of the downlink signal) is given to the first receiving unit 110, it cannot pass through the first receiving unit 110.
That is, the first receiving unit 110 is adapted to receive the signal of the upstream signal frequency fu by the filters 111 and 114 provided in the first receiving unit 110, and cannot receive signals of other frequencies. .

Therefore, the child BS 101b according to the present embodiment includes a second receiving unit 120 for receiving a downlink signal of the frequency fd transmitted from the parent BS 101a, in addition to the first receiving unit 110.
The second receiver 120 includes a fifth filter 121, a fourth amplifier (high frequency amplifier) 122, a third frequency converter 123, a sixth filter 124, a fifth amplifier (intermediate frequency amplifier) 125, and a fourth frequency converter 126. , And an A / D converter 127.

  The fifth filter 121 is used to pass only the downlink signal from the parent BS 101a, and is configured by a band pass filter that passes only the frequency fd of the downlink signal. The received signal that has passed through the fifth filter 121 is amplified by a fourth amplifier (high frequency amplifier) 122, and the output of the fourth amplifier 122 is converted from the downstream signal frequency fd to the first intermediate frequency by the third frequency converter 123. Is made. The third frequency conversion unit 123 includes an oscillator 123a and a mixer 123b.

  The output of the third frequency converter 123 is amplified again by the fifth amplifier (intermediate frequency amplifier) 125 through the sixth filter 124 that passes only the first intermediate frequency output from the third frequency converter 123. The output of the fifth amplifier 125 is converted from the first intermediate frequency to the second intermediate frequency by the fourth frequency converter 126 and further converted into a digital signal by the A / D converter 127. The fourth frequency conversion unit 126 is also composed of an oscillator 126a and a mixer 126b.

  The signal output from the A / D conversion unit 127 is given to the synchronization processing unit 170. As a result, the synchronization processing unit 170 can acquire the downlink signal from the parent BS 101a.

  The synchronization processing unit 170 performs processing for synchronizing the communication timing and the communication frequency of the own apparatus 101b based on the Primary Synchronization Signal and the Secondary Synchronization Signal included in the frame of the downlink signal acquired from the parent BS 101a.

The synchronization processing unit 170 is controlled by the air synchronization control unit 180. The air synchronization control unit 180 has the same function as the synchronization control unit 26 in the first embodiment.
That is, the air synchronization control unit 180 pauses the communication mode for transmitting the downlink signal to the user terminal 102b for air synchronization periodically or as necessary at a fixed period, and is transmitted by the parent BS 101a. The air synchronization state (synchronization mode) for receiving the downstream signal. The air synchronization control unit 180 outputs the air synchronization section information, which is information indicating the time zone in which the air synchronization state is set, to the modulation circuit 160 and the synchronization processing unit 170, thereby the modulation circuit 160 and the synchronization processing unit 170. Control.

FIG. 15 is a configuration diagram of the synchronization processing unit. As illustrated in FIG. 15, the synchronization processing unit 170 includes an estimation unit 171, a frame timing control unit 172, a carrier frequency correction unit 173, and a storage unit 174.
The synchronization processing unit 170 recognizes whether the device 101b is in the communication mode or the synchronization mode based on the air synchronization section information given from the air synchronization control unit 180, and determines whether to perform air synchronization.
When it is determined that air synchronization is performed, the estimation unit 171 acquires a downlink signal from the parent BS 101a, and includes a primary synchronization signal and a secondary synchronization signal (hereinafter, both signals are collectively referred to as “synchronization signal”) included in the downlink signal. Is used to detect the frame transmission timing of the parent BS 101a, and the timing offset of the communication frame between the parent BS 101a and the own apparatus 101b and the carrier frequency offset are estimated.

The estimation unit 171 has the same function as that of the estimation unit 23 in the first embodiment, and includes a detection unit 171a that detects a synchronization signal included in the downlink signal, and between the parent BS 101a and the own device 101b. A clock error estimation unit 171b that estimates a clock error and a calculation unit 171c that calculates a timing offset per unit time between the parent BS 101a and the own apparatus 101b are provided. These functional units also have the same functions as those in the first embodiment.
The detection unit 171a detects the timing of the synchronization signal at a predetermined position in the received downlink frame, and detects the frame transmission timing of the parent BS 101a. Then, the detected frame transmission timing of the parent BS 101a is compared with the frame transmission timing of the own apparatus 101b, and the difference is detected as a communication timing offset (synchronization deviation). Each time this communication timing offset is detected, it is given to the storage unit 174 and accumulated in the storage unit 174.

Also, the frame timing control unit 172 and the carrier frequency correction unit 173 in the present embodiment correspond to the frame timing control unit 30 and the carrier frequency correction units 21 and 22 in the first embodiment, respectively. It has the function of
That is, the frame timing control unit 172 and the carrier frequency correction unit 173 perform synchronization processing for eliminating the currently detected timing offset and carrier frequency offset in the synchronization mode, respectively, and perform basic processing in the communication mode. Based on the timing offset per frame and the carrier frequency offset, synchronization correction processing is performed to adjust the time length and carrier frequency for each basic frame. Note that these synchronization processing and synchronization correction processing are performed in the same manner as in the first embodiment.

As a result, according to the present embodiment, synchronization can be established between the parent BS 101a and the child BS 101b, and the synchronization correction of the downlink signal transmitted by itself is performed during the communication mode until the next switching to the synchronization mode. Therefore, it is possible to suppress the occurrence of large synchronization deviation over the entire communication mode.
Note that the synchronization error (synchronization error) detection / correction target is not limited to the frame timing, but may be symbol timing or slot timing.

As described above, when synchronization is established between the parent BS 101a and the child BS 101b, even if the base station apparatuses 101a and 101b perform broadcast transmission that simultaneously transmits information of the same content to a large number of terminal apparatuses, It is possible to prevent interference from signals from both base station apparatuses 101a and 101b.
In addition, since both base station apparatuses 101a and 101b are synchronized, if the signals having the same contents are transmitted from both base station apparatuses 101a and 1b, macro diversity or spatial multiplexing transmission is performed on the terminal apparatuses 101a and 101b side. Can do. Note that selectivity diversity and maximum ratio combining can be adopted as a method for realizing reception diversity.

In the present embodiment, the child BS 101b can also employ the following configuration.
FIG. 16 shows an example of another configuration of the child BS 101b in the present embodiment. In this child BS 101b, similarly to the child BS 101b shown in FIG. 14, the first receiving unit 110 and the second receiving unit 120 are provided independently, and the first receiving unit 110 and the second receiving unit 120 are provided as direct conversion receivers. It is constituted as follows. That is, the first receiving unit 110 and the second receiving unit 120 pass through only the upstream signal or the downstream signal received by the antenna 141 and the band-pass filters 111 and 121 and the amplifier 112 that amplifies the signal that has passed through the filters 111 and 121. , 122. Furthermore, quadrature demodulators 118 and 128 that demodulate the outputs of the amplifiers 112 and 122 into demodulated signals I and Q, and A / D converters 117a, 117b, 127a, and 127b that convert the demodulated signals I and Q into digital signals, respectively. The modulation signals I and Q are provided to the demodulation circuit 150 or the synchronization processing unit 170.
16, the transmission unit 13 is configured by adding a frequency conversion unit 136 and an amplifier 137 between the amplifier 134 and the filter 135 in the transmission unit 13 shown in FIG.
Thus, the types of the first receiving unit 110 and the second receiving unit 120 are not particularly limited.

The present invention is not limited to the above embodiments. In the above embodiment, the synchronization correction in the communication mode is performed based on one communication timing offset value ΔT _n . For example, a plurality of communication timing offset values ΔT detected in the past synchronization mode are stored and the plurality of these are corrected. It is also possible to obtain an average value for the communication timing offset value ΔT and perform synchronization correction based on the average value.
Further, in the above embodiment, the synchronization correction is performed in a plurality of times for each basic frame in the communication mode based on the timing offset t _{n + 1} per basic frame with the time width of one basic frame as a unit time. However, for example, the synchronization correction may be performed using a plurality of basic frames as a unit time, and in this case, the number of times of performing the synchronization correction processing separately can be reduced, and the degree of freedom of the processing is increased.

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

DESCRIPTION OF SYMBOLS 1 1st base station apparatus 2 2nd base station apparatus 3 3rd base station apparatus 22 Carrier frequency correction | amendment part (frequency correction part, correction | amendment part)
23 Estimator 26 Synchronization Control Unit (Control Unit)
30 frame timing control unit (communication timing correction unit, correction unit)
101a, 101b Base station apparatus 171 Estimating unit 172 Frame timing control unit (communication timing correction unit, correction unit)
173 Carrier frequency correction unit (frequency correction unit, correction unit)

Claims (5)

A communication mode for communicating with a terminal device by transmitting a communication signal; and communication with the other base station device by stopping communication with the terminal device and receiving a communication signal from the other base station device A control unit that switches between and executes a synchronization mode for performing synchronization between base stations between,
Based on the communication signal of the other base station apparatus received in the synchronization mode, an estimation unit for obtaining an estimated value of synchronization deviation between the communication signal of the other base station apparatus and the own communication signal;
A correction unit that performs synchronization correction to synchronize the communication signal transmitted by itself with the communication signal of the other base station device, based on the estimated value of synchronization deviation obtained by the estimation unit;
The correction unit performs the synchronization correction in a plurality of times during the communication mode until the next switching to the synchronization mode.   The base station apparatus according to claim 1, wherein the correction unit performs synchronization correction divided into a plurality of times per unit time.   The estimation unit acquires a communication timing of the other base station device from a communication signal of the other base station device, and based on a communication timing offset between the communication timing and its own communication timing, The base station apparatus of Claim 1 which calculates | requires the estimated value of. The estimation unit uses the communication timing offset as an estimation value of the synchronization deviation,
The base station apparatus according to claim 3, wherein the correction unit includes a communication timing correction unit that performs synchronization correction of communication timing by adjusting a time length of a communication frame constituting the communication signal. The estimation unit obtains a carrier frequency offset of the communication signal as an estimation value of the synchronization deviation based on the communication timing offset,
The base station apparatus according to claim 3, wherein the correction unit includes a frequency correction unit that performs synchronization correction of the carrier frequency.

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