JP5434462B2 - Base station equipment - Google Patents

Description

  The present invention relates to a base station apparatus that performs wireless communication with a terminal apparatus.

Many base station apparatuses that communicate with terminal apparatuses are installed to cover a wide area. At this time, synchronization between base stations that synchronizes the timing of communication frames and the like may be performed between a plurality of base station apparatuses.
For example, Patent Literature 1 discloses that a base station apparatus performs synchronization between base stations using a transmission signal from another base station apparatus that is a synchronization source.

JP 2009-177532 A

  The above Patent Document 1 discloses a case where communication between a base station apparatus and a terminal apparatus is performed by time division duplex (TDD). However, it is assumed that communication with a terminal apparatus is performed. When a base station apparatus that performs frequency division duplex (FDD) is to perform the above-described inter-base station synchronization, it may be performed in the following manner.

  That is, as shown in FIG. 13, the terminal device performs scanning of the base station device, identification of the base station device, synchronization with the base station device, and the like in a downlink signal communication frame by the frequency division duplex method, as shown in FIG. For this purpose, a first synchronization signal and a second synchronization signal are arranged. Since these two synchronization signals are known signals, the downlink signal transmitted by the other base station apparatus to the base station apparatus that intends to synchronize with another base station apparatus that is the synchronization source. It is conceivable to perform synchronization between base stations using both synchronization signals included in the base station.

  As shown in FIG. 13, the downlink signal of the base station apparatus adopting FDD is configured by arranging a plurality of subframes in the time axis direction, and the transmission timing between itself and other base station apparatuses is Inter-base station synchronization is realized by detecting a synchronization error between the transmission timings of both subframes, eliminating the synchronization error, and matching the transmission timings of both subframes.

In order to synchronize its own downlink signal with the downlink signal of another base station apparatus, the transmission timing of one of the subframes constituting the downlink signal of the other base station apparatus is It is necessary to correct so as to coincide with the timing of the subframe in the downlink signal.
Here, when the transmission timing of the own downlink signal is earlier than the transmission timing of other base station apparatuses, synchronization can be achieved by delaying the transmission timing of the subframe to be corrected.
On the other hand, when the transmission timing of the own downlink signal is delayed from the transmission timing of other base station apparatuses, it is necessary to advance the transmission timing of the correction target subframe in order to eliminate the synchronization error. .

Since the subframes in the downlink signal by FDD are arranged in the time axis direction as described above, if correction is made so as to advance the transmission timing of the correction target subframe, the subframe is corrected before the correction target subframe. There may be an overlap between the arranged subframes, causing inter-symbol interference, and an effect such as an increase in the error rate during demodulation on the terminal device side.
Between subframes adjacent to each other, areas such as guard intervals and cyclic prefixes are provided so as to withstand intersymbol interference caused by delayed waves such as multipaths. However, if the amount of correction of the transmission timing is small because the amount of synchronization error is relatively small, the influence caused by intersymbol interference due to these regions can be avoided.
However, for example, when it is necessary to correct the transmission timing to such an extent that the synchronization error with the transmission timing of another base station apparatus is relatively large and cannot be handled by the above area, the influence of intersymbol interference is avoided. The possibility that it cannot be increased.

  Also, the case of synchronizing the carrier frequency error between itself and other base station devices is the same as described above, and when correcting the carrier frequency, depending on the magnitude of the error amount of the synchronization error, In some cases, the effects of interference could not be avoided.

  Thus, depending on the error amount of the synchronization error, there is a possibility that the inter-base station synchronization cannot be performed appropriately.

  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 capable of appropriately performing synchronization between base stations according to the amount of synchronization error.

(1) The present invention uses a downlink signal configured by arranging a plurality of communication unit areas having a certain time length on a time axis, and performs communication with a terminal device by frequency division duplexing A receiving unit that receives a downlink signal from another base station device, and a downlink signal of the other base station device based on a downlink signal received by the receiving unit from the other base station device. A synchronization error detecting unit for detecting a synchronization error between the communication unit area of the mobile station and a communication unit area of the own downlink signal, and correcting the downlink signal based on the synchronization error, thereby correcting the other base station. A correction unit that synchronizes with a downlink signal of the apparatus; and a correction control unit that selects a correction method performed by the correction unit from a plurality of types of correction methods according to an error amount of the synchronization error. It is characterized by that.

According to the base station apparatus configured as described above, the correction unit corrects the downlink signal on the basis of the synchronization error detected by the synchronization error detection unit to synchronize with the downlink signal of the other base station apparatus. Thus, inter-base station synchronization can be performed with other base station apparatuses.
Also, according to this base station apparatus, the correction control unit selects a correction method performed by the correction unit according to the error amount of the synchronization error, so that the communication of its own downlink signal is performed by a suitable correction method according to the situation. The unit area can be corrected. For this reason, for example, due to the large amount of error, depending on a certain correction method, even when adjacent communication unit areas are greatly overlapped, there is a risk of being affected by intersymbol interference. Other possible correction methods can be selected. As a result, the influence of intersymbol interference can be avoided regardless of the amount of synchronization error, and inter-base station synchronization can be suitably performed.
Thus, according to the base station apparatus of the present invention, synchronization between base stations can be appropriately performed according to the amount of synchronization error.

(2) Preferably, the plurality of types of correction methods include a first method in which the error amount of the synchronization error is corrected in a plurality of times. In this case, one error amount is set to a plurality of times. Since the correction is performed separately, the correction amount at the time of each correction can be reduced, and the communication unit areas adjacent to each other can be prevented from greatly overlapping.
(3) Specifically, when the downlink signal has a basic frame composed of a plurality of subframes, and the communication unit area is the subframe, the first method includes the synchronization It is preferable to correct the error amount for each of the plurality of subframes.

(4) In addition, a resource allocation control unit that controls resource allocation to the terminal device in the communication unit region is further provided, and the plurality of types of correction methods include a corrected communication unit that is subject to correction by the resource allocation unit. It may include a second method of correcting the corrected communication unit area after limiting resource allocation in the communication unit area arranged in front of the area.
In this case, since the second method restricts resource allocation to the communication unit area arranged before the corrected communication unit area, for example, the corrected communication unit area and the communication unit area arranged before that are large. Even if intersymbol interference occurs due to the overlap, it is possible to avoid the appearance of the effect.

(5) Further, in the second method, transmission of the own downlink signal in the communication unit area arranged before the corrected communication unit area may be suspended.
In this case, even if the corrected communication unit region is corrected in the range of the time length of the communication unit region before the corrected communication unit region, the transmission of the downlink signal is suspended in the range of the interval, so intersymbol interference Does not occur.

(6) In the second method, since the communication unit area can be corrected within the range of the communication unit area where resource allocation is limited and arranged before the corrected communication unit area, the correction is performed. In doing so, a relatively large correction width can be secured. For this reason, it is preferable that the said correction control part selects said 2nd method, when the error amount of the said synchronous error is larger than the predetermined threshold value.

(7) It is preferable that the threshold value is set according to a time length of a guard interval section inserted between adjacent communication unit areas.
In this case, for example, the threshold value can be set to an error amount that can be determined to be corrected beyond the time length of the guard interval section, and the correction needs to be performed more than the time length of the guard interval section. When it is determined that there is, it is possible to select the second method that can ensure a relatively large correction width. Thus, a suitable correction method according to the error amount can be selected.

(8) For example, even if the amount of synchronization error is relatively large, even if intersymbol interference occurs when the amount of data is relatively small, the influence on the terminal device is small. For this reason, the base station device further includes a detection unit that detects the amount of data to be transmitted to the terminal device using its own downlink signal, and the correction control unit includes the error amount of the synchronization error and the detection unit. Depending on the detection result, it may be determined whether to select the second method.
In this case, for example, when the error amount of the synchronization error is relatively large and the data amount is relatively large, the correction control unit selects the second method and restricts resource allocation, whereby the terminal device Can be prevented from being affected by intersymbol interference. On the other hand, even when the error amount of the synchronization error is relatively large, if the data amount is relatively small, even if intersymbol interference occurs, the influence on the terminal device is small, so the correction control unit Other methods than the above method can also be selected.
In this way, the correction control unit determines whether to select the second method according to the amount of data to be transmitted to the terminal device, which is the detection result of the detection unit, in addition to the error amount of the synchronization error. Thus, the inter-base station synchronization can be performed more appropriately while considering the influence on the terminal device due to inter-symbol interference.

(9) Specifically, when the downlink signal has a basic frame composed of a plurality of subframes, and the communication unit area is the subframe, the second method includes the subframe It is preferable to limit resource allocation for each frame.

  According to the base station apparatus of the present invention, synchronization between base stations can be appropriately performed according to the amount of synchronization error.

It is the schematic which shows the structure of the radio | wireless communications system which concerns on one Embodiment of this invention. It is a figure which shows the structure of each uplink and downlink communication frame in LTE. It is a figure which shows the detailed structure of DL frame. It is a figure for demonstrating the detailed structure of the slot which comprises a sub-frame. It is a block diagram which shows the structure of a femto base station apparatus. It is a block diagram which shows the detail of RF part. It is a block diagram which shows the structure of the synchronous process part for performing the synchronous process which takes the synchronization between base stations between other base station apparatuses. It is a figure for demonstrating an example of the aspect of the synchronous process which a synchronous process part performs, and the aspect of the correction method 1 is shown. It is a figure for demonstrating the aspect of the correction method. It is a figure for demonstrating the aspect of the correction method. It is a flowchart which shows the aspect of the process which a correction control part selects the method of correction | amendment. It is a figure which shows the timing when a synchronous process and a measurement process are performed. It is a figure for demonstrating the aspect of the synchronous process which can be taken in the conventional base station apparatus.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[1. Configuration of communication system]
FIG. 1 is a schematic diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.
The wireless communication system includes a plurality of base station devices 1 and a plurality of terminal devices 2 (mobile terminals) that can perform wireless communication with the base station device 1.
The plurality of base station apparatuses 1 are, for example, a plurality of macro base station apparatuses (Macro Base Stations) 1a that form a communication area (macro cell) MC having a size of several kilometers, and are installed in each macro cell MC. And a plurality of femto base station apparatuses (Femto Base Stations) 1b forming a relatively small femtocell FC.

Each macro base station apparatus 1a (hereinafter also referred to as macro BS 1a) can perform radio communication with the terminal apparatus 2 in its own macro cell MC.
Further, the femto base station apparatus 1b (hereinafter also referred to as a femto BS 1b) is arranged, for example, in a place where it is difficult to receive the radio wave of the macro BS 1a, such as indoors, and forms the femto cell FC. The femto BS 1b can wirelessly communicate with the terminal device 2 (hereinafter also referred to as MS2) in the femto cell FC formed by the femto BS 1b. In this system, a place where the radio wave of the macro BS 1a is difficult to receive, etc. However, by installing a femto BS 1b that forms a relatively small femto cell FC at that location, it is possible to provide services to the MS 2 with sufficient throughput.

In the wireless communication system, the femto BS 1b is installed in the macro cell MC formed by the macro BS 1a after the macro BS 1a is installed, and the femto cell FC is formed in the macro cell MC. For this reason, the femto BS 1b may cause interference between the macro BS 1a and the MS 2 that communicates with the macro BS 1a.
For this reason, the femto BS 1b is based on the function of monitoring (measurement processing) the transmission status such as transmission power and frequency used in other base station apparatuses, such as the macro BS 1a and other femto BSs 1b other than itself, and the result thereof. It has a function of adjusting transmission conditions such as transmission power and use frequency so as not to affect communication in the macro cell MC. With this function, the femto BS 1b can form the femto cell FC in the macro cell MC without affecting the communication of other base station apparatuses.

In the communication system of the present embodiment, inter-base station synchronization is performed to synchronize the timing of communication frames between a plurality of base station apparatuses including the macro BS 1a and the femto BS 1b.
Inter-base station synchronization is performed by “air synchronization” in which another base station apparatus receives a signal transmitted from the base station apparatus serving as a parent (synchronization source) to the MS 2 in its own cell. Executed.
The base station device that is the parent (synchronization source) may be one that takes air synchronization with another base station device, or other than air synchronization, such as autonomously determining the frame timing with a GPS signal. The frame timing may be determined by this method.
However, the macro BS 1a can have another macro BS 1a as a parent, but cannot have a femto BS 1b as a parent. The femto BS 1b can have a macro BS 1a as a parent, and can also have another femto BS 1b as a parent.

  The radio communication system according to the present embodiment is a system for mobile phones to which, for example, LTE (Long Term Evolution) is applied, and communication based on LTE is performed between each base station device and a terminal device. . In LTE, a frequency division duplex (FDD) scheme can be adopted. In the present embodiment, the communication system will be described as adopting an FDD scheme. Note that the communication system is not limited to the LTE and is not limited to the FDD system, and may be a TDD (Time Division Duplex) system, for example.

[2. LTE frame structure]
In the FDD scheme that can be adopted in LTE that the communication system according to the present embodiment complies with, an uplink signal (a transmission signal from the terminal device to the base station device) and a downlink signal (a transmission signal from the base station device to the terminal device) By assigning different use frequencies to each other, uplink communication and downlink communication are simultaneously performed.

  FIG. 2 is a diagram illustrating the structure of uplink and downlink radio frames in LTE. The radio frame (DL frame) and the uplink radio frame (UL frame), which are downlink basic frames in LTE, each have a time length of 10 milliseconds, from # 0 to # 9. It is composed of 10 subframes (communication unit area having a certain length of time). These DL frames and UL frames are arranged in the time axis direction with their timings aligned.

FIG. 3 is a diagram illustrating a detailed structure of a DL frame. In the figure, the vertical axis direction represents frequency, and the horizontal axis direction represents time.
Each subframe constituting the DL frame is composed of two slots (for example, slots # 0 and # 1). One slot is composed of seven (# 0 to # 6) OFDM symbols (in the case of normal cyclic prefix: Normal Cyclic Prefix).
In the figure, a resource block (RB: Resource Block), which is a basic unit (minimum unit) in data transmission, is defined by 12 subcarriers in the frequency axis direction and 7 OFDM symbols (1 slot) in the time axis direction. . Therefore, for example, when the frequency bandwidth of the DL frame is set to 5 MHz, 300 subcarriers are arranged, so that 25 resource blocks are arranged in the frequency axis direction.

  As shown in FIG. 3, a control channel for transmitting information necessary for downlink communication from the base station apparatus to the terminal apparatus is assigned to the head of each subframe. The control channel is allocated with symbols # 0 to # 2 (three symbols at the maximum) of slots located on the head side in each subframe. In this control channel, DL control information, resource allocation information of the subframe, a reception success notification (ACK: Acknowledgement) by a hybrid automatic repeat request (HARQ: Hybrid Automatic Repeat Request), a reception failure notification (NACK: Negative Acknowledgment) Etc. are stored.

Also, in the DL frame, a broadcast channel (PBCH: Physical Broadcast Channel) for notifying the terminal device of the system bandwidth and the like by broadcast transmission is assigned to the first subframe # 0. The broadcast channel is arranged with four symbol widths at the positions of symbols # 0 to # 3 in the slot on the rear side in the first subframe # 0 in the time axis direction, and the bandwidth of the DL frame in the frequency axis direction Are allocated by the width of 6 resource blocks (72 subcarriers). This broadcast channel is configured to be updated every 40 milliseconds by transmitting the same information over four frames.
The broadcast channel stores main system information such as the communication bandwidth, the number of transmission antennas, and the structure of control information.

  Of the 10 subframes constituting the DL frame, each of the first (# 0) and sixth (# 5) subframes is a signal for identifying a base station apparatus or a cell. One synchronization signal and second synchronization signal (P-SCH: Primary Synchronization Channel, S-SCH: Secondary Synchronization Channel) are assigned.

The first synchronization signal is arranged with a single symbol width at the position of symbol # 6 which is the last OFDM symbol of the leading slot in each of subframe # 0 and subframe # 5 in the time axis direction, and is in the frequency axis direction In FIG. 5, 6 resource block widths (72 subcarriers) are arranged at the center of the DL frame bandwidth. The first synchronization signal is information for the terminal device to identify each of a plurality (three) sectors obtained by dividing the cell of the base station device, and three patterns are defined.
The second synchronization signal is arranged with one symbol width at the position of symbol # 5 which is the second OFDM symbol from the end of the first slot in each of subframe # 0 and subframe # 5 in the time axis direction, In the frequency axis direction, 6 resource block widths (72 subcarriers) are arranged at the center of the DL frame bandwidth. This second synchronization signal is information for the terminal device to identify each of the communication areas (cells) of the plurality of base station devices, and 168 patterns are defined.

The first synchronization signal and the second synchronization signal are combined with each other to define 504 types (168 × 3) patterns. The terminal device can recognize in which sector of which base station device the terminal is present by acquiring the first synchronization signal and the second synchronization signal transmitted from the base station device.
A plurality of patterns that can be taken by the first synchronization signal and the second synchronization signal are predetermined in the communication standard and are known in each base station device and each terminal device. That is, each of the first synchronization signal and the second synchronization signal is a known signal that can take a plurality of patterns.

  The first synchronization signal and the second synchronization signal are signals for synchronization between base stations that synchronize communication timing and / or frequency between the base station devices in addition to the case where the terminal device synchronizes with the base station device. This point will be described later.

Resource blocks in other areas to which the above-described channels are not assigned (areas without hatching in the figure) are used as DL shared channels (PDSCH: Physical Downlink Shared Channels) for storing user data and the like. The DL shared channel is an area shared for communication by a plurality of terminal devices, and stores user data and control information for each terminal device.
The allocation of user data stored in the DL shared channel is defined by the resource allocation information in the control channel allocated at the head of each subframe. It can be determined whether or not data for itself is stored in the frame.

FIG. 4 is a diagram for explaining a detailed configuration of slots constituting a subframe. FIG. 4 shows the slot configuration when the normal cyclic prefix is adopted.
As described above, the slot is composed of seven (# 0 to # 6) OFDM symbols. A cyclic prefix (hereinafter also referred to as CP) having the same function as the guard interval is arranged on the head side of each symbol, and this CP is inserted between adjacent symbols. .

As shown in FIG. 4, the CP is generated by copying a part of the latter half part of each symbol, and is arranged on the head side of the symbol. By inserting a CP, even if inter-symbol interference occurs due to reception of a multipath delayed wave with a time length T _cp or less of this CP, orthogonality between subcarriers can be maintained, and the terminal device side can perform demodulation. It is possible to prevent an influence such as an increase in the error rate.
In the case of the normal cyclic prefix, the CP has a time length T _cp of about 5.21 microseconds (CP related to the symbol # 0) or about 4.69 microseconds (CP of other symbols). Is set to
Accordingly, a CP having a time length of about 5.21 microseconds is inserted between adjacent subframes.

[3. Configuration of femto base station apparatus]
FIG. 5 is a block diagram showing the configuration of the femto base station apparatus in FIG. Although the configuration of the femto BS 1b will be described here, the configuration of the macro BS 1a is almost the same as that of the femto BS 1b.
The femto BS 1b1 performs processing related to synchronization between base stations in addition to signal processing of transmission / reception signals transmitted and received between the antenna 3, the transmission / reception unit (RF unit) 4 to which the antenna 3 is connected, and the RF unit 4. And a signal processing unit 5 for performing measurement and the like.

[3.1 RF section]
FIG. 6 is a block diagram showing details of the RF unit 4. The RF unit 4 includes an upstream signal reception unit 11, a downstream signal reception unit 12, and a transmission unit 13. The uplink signal receiving unit 11 is for receiving an uplink signal from the terminal device 2, and the downlink signal receiving unit 12 is for receiving a downlink signal from another macro BS 1a or another femto BS 1b. is there. The transmission unit 13 is for transmitting a downlink signal to the terminal device 2.

  In addition, the RF unit 4 includes a circulator 14. The circulator 14 is for giving a reception signal from the antenna 3 to the upstream signal reception unit 11 and the downstream signal reception unit 12 side, and giving a transmission signal output from the transmission unit 13 to the antenna 3 side. The circulator 14 and the fourth filter 135 of the transmission unit 13 prevent the reception signal from the antenna 3 from being transmitted to the transmission unit 13 side.

  Further, the circulator 14 and the first filter 111 of the upstream signal receiving unit prevent the transmission signal output from the transmitting unit 13 from being transmitted to the upstream receiving unit 11. Further, the circulator 14 and the fifth filter 121 prevent the transmission signal output from the transmission unit 13 from being transmitted to the upstream signal reception unit 12.

  The uplink signal receiving unit 11 is configured as a superheterodyne receiver and configured to perform IF (intermediate frequency) sampling. More specifically, the upstream signal reception unit 11 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 A / A D conversion unit 117 is provided.

The first filter 111 is for allowing only the upstream signal from the terminal device 2 to pass, and is configured by a band-pass filter that allows only the frequency f _{u of the} upstream signal to pass. 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 11) is given to the signal processing unit 5 having a function as a demodulation circuit, and the demodulation processing of the reception signal from the terminal device 2 is performed.
Thus, uplink signal reception unit 11, a receiving unit configured to conform to the uplink signal frequency f _u to receive an uplink signal from the terminal device, inherently required received as the base station apparatus Part.

  The transmitter 13 receives the in-phase signal I and the quadrature signal Q output from the signal processor 5 and transmits signals from the antenna 3, and is configured as a direct conversion transmitter. The transmission unit 13 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 each of the in-phase signal I and the quadrature signal Q supplied from the signal processing unit 5. 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 f _d (downlink signal frequency).
The output of the quadrature modulator 132 passes through the third filter 133 that passes only the frequency f _d , is amplified by the third amplifier 134, further obtains the fourth filter 135 that passes only the frequency f _d , and is transmitted from the antenna 3. And becomes a downlink signal to the terminal device.

  The uplink signal reception unit 11 and the transmission unit 13 described above are functions necessary for performing intrinsic communication with the terminal device. However, the base station device 1 of the present embodiment further includes the downlink signal reception unit 12. It has. The downlink signal receiving unit 12 is for receiving a downlink signal transmitted by another base station apparatus.

  In this embodiment, the downlink signal of the other base station apparatus received by the downlink signal reception unit 12 is used for inter-base station synchronization processing and measurement of transmission status such as transmission power of the other base station apparatus.

Here, the frequency of the downlink signal transmitted by another base station apparatus is f _d , which is different from the frequency f _u of the uplink signal. Therefore, in a normal base station apparatus having only the uplink signal processing unit 11, The downlink signal transmitted by the base station apparatus cannot be received.

That is, in the FDD scheme, different from the TDD system, since there uplink and downlink signals simultaneously in a transmission path, the uplink signal reception unit 11, is passed through only the signal of the uplink signal frequency f _u, downlink signal frequency f _d It is designed not to pass the signal. Specifically, the uplink signal reception unit 11, and the first filter 111 for passing only the signal of the uplink signal frequency f _u, the second filter 114 for passing only the first intermediate frequency converted from the frequency f _u is Therefore, even if a signal having a frequency other than the frequency f _u (frequency f _{d of the} downlink signal) is given to the first reception unit 11, it cannot pass through the uplink signal reception unit 11.

That is, the uplink signal receiving unit 11, by the filter 111, 114 which provided in the uplink signal receiving section 11, has become one fit for receiving a signal of the uplink signal frequency f _u, other frequencies of the signals (in particular, (Downlink signal) cannot be received.

Therefore, the RF unit 4 of the present embodiment includes a downlink signal receiving unit 12 for receiving the downlink signal of the frequency f _d transmitted by another base station apparatus, in addition to the uplink signal receiving unit 11. .
The downstream signal receiver 12 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 for passing only downlink signals from other base station apparatuses, and is configured by a band-pass filter that passes only the frequency f _{d 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 f _d to the first intermediate frequency by the third frequency converter 123. Conversion is done. 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 a synchronization processing unit 5b and a measurement processing unit 5c, which will be described later, included in the signal processing unit 5.

  The upstream signal receiver 11 and the downstream signal receiver 11 may be configured as a direct conversion receiver.

  Further, it is preferable that the downlink signal reception unit 11 and the transmission unit 13 ensure the uplink and downlink symmetry in the downlink signal reception unit 11 and the transmission unit 13 by antenna calibration. Antenna calibration can be performed by providing the downstream signal receiving unit 11 and / or the transmitting unit 13 with a gain / phase adjuster (not shown).

[3.2 Signal Processing Unit]
The signal processing unit 5 has a function for performing signal processing of transmission / reception signals transmitted / received to / from the RF unit 4, and transmits various transmission data given from an upper layer of the signal processing unit 5 as a transmission signal And a modulation / demodulation unit 5a that performs a process of demodulating a reception signal given from the RF unit 4 into reception data. In the modem unit 5a, modulation / demodulation processing is performed with the synchronization error corrected based on the synchronization error (timing offset, frequency offset) calculated by the synchronization processing unit 5b described later.
Further, the signal processing unit 5 includes a frame counter (not shown) for determining the transmission timing for each radio frame for the transmission signal supplied to the RF unit 4.
The signal processing unit 5 includes a resource allocation control unit in addition to a synchronization processing unit 5b for performing synchronization processing for synchronization between base stations with another base station device, a measurement processing unit 5c for performing measurement, and the like. 5d and a detection unit 5e for detecting the communication status of terminal devices connected to itself and other base station devices.
Hereinafter, the configuration of the synchronization processing unit 5b will be described.

[3.2.1 Synchronization processing unit]
FIG. 7 is a block diagram illustrating a configuration of a synchronization processing unit 5b for performing a synchronization process for achieving synchronization between base stations with another base station apparatus.
In the base station synchronization, each base station device includes a GPS receiver and may be synchronized by GPS signals, or may be synchronized by connecting the base stations by wire. Inter-base station synchronization by “air synchronization” that performs synchronization by (downlink signal) is adopted.

  That is, the synchronization processing unit 5b acquires a downlink signal of another base station apparatus received by the downlink signal receiving unit 12, and a first synchronization signal (P-SCH) that is a known signal included in the radio frame of the downlink signal. Then, based on the second synchronization signal (S-SCH), a synchronization process for synchronizing the communication timing and communication frequency of the own base station apparatus 1 with other base station apparatuses is performed.

  The synchronization processing unit 5b sets the timing for acquiring the downlink signal of the other base station apparatus given from the downlink signal receiving unit 12 in units of subframes so that the synchronization process is performed in a predetermined cycle. Further, the synchronization processing unit 5b has a function of adjusting the timing of performing the synchronization processing by adjusting the period of the timing for acquiring the downlink signal for the synchronization processing according to the detection result of the detection unit 5e. Yes.

The synchronization processing unit 5b starts the synchronization process by pausing transmission of the transmission signal by the transmission unit 13 in the subframe section corresponding to the timing (synchronization processing start timing) at which the downlink signal set by the synchronization processing unit 5b is acquired. To do. While the transmission of the transmission signal is suspended, the synchronization processing unit 5b causes the downlink signal receiving unit 12 to receive the downlink signal of another base station apparatus, and acquires the received downlink signal. Thereafter, the downlink signal is used to correct its own frame timing (subframe transmission timing) and communication frequency, and the synchronization processing ends. Note that the interval during which transmission of the transmission signal is paused can be set to a subframe corresponding to the timing for acquiring a downlink signal for synchronization processing and one or more subframes subsequent thereto.
In addition to the suspension of transmission of the transmission signal, the reception of uplink signals from the terminal device may be suspended.

  In addition, the synchronization processing unit 5b outputs synchronization timing information, which is information for specifying a subframe corresponding to a section in which transmission of a transmission signal is suspended, to the resource allocation control unit 5d and the measurement processing unit 5c.

  The synchronization processing unit 5b includes a synchronization error detection unit 14, a frame counter correction unit 15, a frequency offset estimation unit 16, a frequency correction unit 17, a storage unit 18, and a correction control unit 19, and performs frame transmission timing synchronization. In addition, it has a function of correcting the carrier frequency.

The synchronization error detection unit 14 detects a frame transmission timing of another base station apparatus using a known signal included in the downlink signal, and also detects an error (frame synchronization error; Communication timing offset) is detected.
The transmission timing can be detected by detecting the timing of the first synchronization signal and the second synchronization signal, which are known signals (waveforms are also known) at a predetermined position in the received downlink signal frame.
The synchronization error detection unit 14 provides the detected frame synchronization error to the correction control unit 19 and also to the storage unit 18 every time it is detected. The storage unit 18 accumulates these detected frame synchronization errors.

  When the correction control unit 19 acquires the frame synchronization error from the synchronization error detection unit 14 and the amount of data (to be described later) to be transmitted to the MS 2 connected to itself from the detection unit 5e, the correction control unit 19 corrects the frame synchronization error. Control information relating to the frame timing to be generated is provided to the frame counter correction unit 15. The frame counter correction unit 15 adjusts the value of the frame counter in accordance with the control information regarding the frame timing given from the correction control unit 19, and corrects the frame timing according to the synchronization error.

  When the correction control unit 19 acquires the frame synchronization error and the amount of data to be transmitted to the MS 2 connected to the correction control unit 19, a plurality of types of frame timing correction methods performed by the frame counter correction unit 15 according to these are obtained. One correction method is selected from the correction methods. Then, the correction control unit 19 controls the frame counter correction unit 15 to correct the frame timing so as to eliminate the synchronization error by the selected correction method.

  The frame counter correction unit 15 corrects the transmission timing of the subframe in its own downlink signal so as to match the transmission timing of the subframe in the downlink signal of another base station device, according to the control information of the correction control unit 19. The correction method will be described in detail later.

  Based on the synchronization error detected by the detector 14, the frequency offset estimator 16 includes a clock frequency of a built-in clock generator (not shown) built in the base station apparatus itself on the receiving side, and others on the transmitting side. The difference (clock frequency error) from the clock frequency of the built-in clock generator of the base station apparatus is estimated, and the carrier frequency error (carrier frequency offset) is estimated from the clock frequency error.

  The frequency offset estimation unit 16 is based on the frame synchronization error t1 detected in the previous air synchronization and the frame synchronization error t2 detected in the current air synchronization in a situation where the air synchronization is periodically executed. To estimate the clock error. The previous frame synchronization error t1 can be acquired from the storage unit 18.

  For example, when the carrier frequency is 2.6 [GHz], T1 is detected as a frame synchronization error at the previous air synchronization timing (synchronization timing = t1), and the timing is corrected by T1. To do. The corrected synchronization error (timing offset) is 0 [msec]. The synchronization error (timing offset) is detected again at the current air synchronization timing (synchronization timing = t2) after T = 10 seconds, and the synchronization error (timing offset) is T2 = 0.1 [msec]. Suppose that

At this time, a synchronization error (timing offset) of 0.1 [msec] generated during 10 seconds is an accumulated value of an error between the clock period of the other base station apparatus and the clock period of the own base station apparatus.
That is, the following equation holds between the synchronization error (timing offset) and the clock period.
Synchronization source base station clock cycle: Synchronization destination base station clock cycle = T: (T + T2) = 10: (10 + 0.0001)

And since the clock frequency is the reciprocal of the clock period,
(Synchronization source base station clock frequency-synchronization destination base station clock frequency)
= Synchronization source base station clock frequency × T2 / (T + T2)
≒ Synchronization source base station clock frequency x 0.00001
It becomes.

  Therefore, in this case, there is an error of 0.00001 = 10 [ppm] between the clock frequency of the other base station apparatus on the transmission side and the clock frequency of the own base station apparatus on the reception side. The frequency offset estimation unit 16 estimates the clock frequency error as described above.

Since the carrier frequency and the synchronization error (timing offset) are similarly shifted, the carrier frequency is also shifted by 10 [ppm], that is, 2.6 [GHz] × 1 × 10 ⁻⁵ = 26 [kHz]. Deviation occurs. In this way, the frequency offset estimation unit 16 can also estimate the carrier frequency error (carrier frequency offset) from the clock frequency error.

The carrier frequency error estimated by the frequency offset estimation unit 16 is given to the frequency correction unit 17.
The frequency correction unit 17 corrects the carrier frequency based on the carrier frequency error. The correction of the carrier frequency can be performed not only for the carrier frequency of the upstream signal but also for the carrier frequency of the downstream signal.
Next, the function of the measurement processing unit 5c will be described.

[3.2.2 About Measurement Processing Unit]
The measurement processing unit 5c has a function for performing measurement (measurement processing) of a downlink signal transmission state such as transmission power and use frequency in other base station apparatuses. The downlink signal of the base station apparatus is acquired, and the received power of the downlink signal is obtained.

  The measurement processing unit 5c sets the timing for acquiring the downlink signal in units of subframes in order to perform the measurement process. Furthermore, the measurement processing unit 5c has a function of adjusting the timing for performing the measurement processing by setting and adjusting the timing for acquiring the downlink signal for the measurement processing according to the detection result of the detection unit 5e. Yes.

Note that the measurement process is preferably performed immediately after the synchronization process is performed, as will be described later. Therefore, the measurement processing unit 5c sets the timing for performing the measurement process in accordance with the synchronization timing information given from the synchronization processing unit 5b.
For example, the measurement processing unit 5c identifies a subframe in which synchronization processing is started based on the received synchronization timing information, and performs measurement processing on a subframe belonging to a radio frame next to the radio frame to which the identified subframe belongs. Set to do.

The measurement processing unit 5c pauses transmission of the transmission signal by the transmission unit 13 in the subframe section corresponding to the timing (measurement processing start timing) at which the downlink signal for measurement processing set by itself is acquired. The measurement process is started. The measurement processing unit 5c causes the downlink signal receiving unit 12 to receive downlink signals from other base station apparatuses while acquiring transmission signals, and acquires the received downlink signals. Thereafter, the received power of the downlink signal is measured, and the measurement process is finished. Note that the interval during which transmission of the transmission signal is paused can be set to a subframe corresponding to the timing at which acquisition of the downlink signal is started, and one or more subframes subsequent thereto.
In addition to the suspension of transmission of the transmission signal, the reception of uplink signals from the terminal device may be suspended.

  In addition, the measurement processing unit 5c outputs measurement timing information, which is information for specifying a subframe corresponding to a section in which transmission of transmission signals is suspended, to the resource allocation control unit 5d.

The measurement processing unit 5c calculates an average value (power average value) of received power for each resource block from the downlink signal acquired from the downlink signal receiving unit 12.
The measurement processing unit 5c extracts, from the acquired downlink signal, a part estimated to be a resource block unit in the time axis direction. Further, a part for each frequency width of the resource block is extracted from each extracted part, and the power of the part for each frequency is obtained as an average power value of the resource block.
When the measurement processing unit 5c determines the power average value, the measurement processing unit 5c outputs measurement result information indicating the power average value to the resource allocation control unit 5d, the detection unit 5e, and the output control unit 5f.

The measurement processing unit 5c acquires a downlink signal that is a quadrature-modulated (pre-demodulation) signal acquired from the downlink signal reception unit 12, and obtains an average power value for each resource block from this signal. A portion estimated to be a resource block unit is extracted in the time axis direction. For this reason, it is necessary to recognize the frame timing of another base station apparatus that is the transmission source of the downlink signal.
Here, if the frame timing is synchronized between the other base station device and itself, the frame timing of the other base station device can be grasped from its own frame timing, so the measurement processing unit 5c The unit of the resource block in the axial direction can be estimated with high accuracy, and the power average value can be obtained with high accuracy. For this reason, the measurement process is preferably performed immediately after the synchronization process is performed.

[3.2.3 Detection unit]
The detection unit 5e has a function of detecting a communication state between itself and another MS 2 connected to another base station device.
More specifically, the detection unit 5e detects the number of MSs 2 connected to itself and other base station devices as the communication status. In addition, MS2 connected to the other base station apparatus used as the detection object of the detection part 5e here is MS2 to which the own downlink signal may arrive.

The detection unit 5e acquires information on the number of MSs 2 connected to itself from the upper layer of the signal processing unit 5 and the amount of data to be transmitted to these MSs 2.
On the other hand, the number of MSs 2 connected to another base station apparatus is estimated based on measurement result information from the measurement processing unit 5c.
The measurement process is performed by receiving a downlink signal from another base station apparatus, and the other base station apparatus is located in a range where both downlink signals are reachable by being located in the vicinity of itself. It is a base station device. Therefore, there is a possibility that the own downlink signal reaches MS2 connected to the other base station apparatus.
Therefore, the detection unit 5e can detect the MS 2 to which the own downlink signal may reach from the measurement result information about the downlink signal of the other base station device as described above.

  The detection unit 5e determines whether or not the MS 2 is connected to another base station apparatus based on the average power value for each resource block included in the measurement result information, and connects to the other base station apparatus. Estimate the number of MS2. That is, if another base station apparatus is communicating with MS2 in its own cell, user data directed to the MS2 is assigned to the transmission signal, and the power of the portion to which the data is assigned is Relative increase compared to unallocated data. Thereby, the detection unit 5e can determine whether the MS 2 is connected to the other base station apparatus based on the reception power of the transmission signal.

  Further, when it can be determined that the MS 2 is connected, it can be determined whether or not user data is allocated to each resource block. Therefore, the detection unit 5e can estimate the number of MSs 2 connected to another base station apparatus from the allocation status.

  The detection unit 5e outputs the detected information related to the number of MSs 2 connected to itself and other base station devices, and the information related to the amount of data to be transmitted to the MS 2 connected to itself to the synchronization processing unit 5b.

[3.2.4 Resource allocation control unit and output control unit]
The resource allocation control unit 5d has a function of allocating user data to be transmitted to each terminal device 2 to the DL shared channel in the radio frame.
Further, the resource allocation control unit 5d receives the synchronization timing information, the measurement timing information, and resource allocation restriction information from the correction control unit 19 to be described later from the synchronization processing unit 5b and the measurement control unit 5f. The allocation of user data is limited to the subframe specified by Furthermore, when the measurement result information is given from the measurement processing unit 5c, the resource allocation control unit 5d determines the user data allocation based on this information.

  The output control unit 5 f has a function of controlling transmission power by the transmission unit 13 of the RF unit 4. The output control unit 5f, when given the average power value of the other base station apparatus obtained by the measurement processing unit 5c, connects to the other base station apparatus and the other base station apparatus based on the average power value. The MS 2 adjusts its own transmission power so that its own transmission signal does not interfere.

[4. About synchronous processing]
FIG. 8 is a diagram for explaining an example of a mode of synchronization processing performed by the synchronization processing unit. In FIG. 8, the frames transmitted by the macro BS 1a as another base station device and the femto BS 1b as its base station device are shown on the same time axis, and the macro BS 1a that is the synchronization source is indicated by the femto BS 1b. The mode which synchronizes with respect to the downstream signal of is shown.
In FIG. 8, in the section before the timing T4, the start of each subframe of the femto BS1b is shifted in timing from the start of the corresponding subframe of the macro BS1a. A state in which a synchronization error is generated with the error amount ΔD is shown.

  Here, when the synchronization processing unit 5b of the femto BS 1b sets the timing for acquiring the downlink signal for the synchronization processing as the subframe SF1 corresponding to the fifth subframe # 4, the synchronization processing unit 5b Synchronization timing information including information for specifying the subframe SF1 is output to the resource allocation control unit 5d and the measurement processing unit 5c. In the example shown in the figure, the section in which transmission of transmission signals is suspended is only the section of subframe SF1 corresponding to the timing of starting the synchronization process.

When this radio frame is transmitted, the synchronization processing unit 5b pauses transmission of the transmission signal by the transmission unit 13 at the transmission timing of the subframe SF1, and causes the downlink signal reception unit 12 to receive the downlink signal of the macro BS 1a. The received downlink signal is acquired.
Then, the synchronization processing unit 5b detects the frame transmission timing of the macro BS 1a using the first synchronization signal and the second synchronization signal included in the acquired downlink signal of the macro BS 1a and An error amount ΔD of the frame synchronization error is detected.

  The synchronization processing unit 5b obtains the first synchronization signal and the second synchronization signal in the downlink signal of the macro BS 1a which is another base station device from the synchronization error in the past synchronization process accumulated in the storage unit 18. Since the transmission timing of the included subframe (# 0 or # 5) can be grasped, the transmission signal can be set to pause in the section of its own subframe corresponding to the transmission timing.

  On the other hand, the resource allocation control unit 5d to which the synchronization timing information is given restricts user data allocation of the terminal device 2 to the section of the subframe SF1, and therefore pauses transmission of transmission signals in this section. Thus, even if the terminal device 2 connected to the femto BS 1b cannot communicate with the femto BS 1b, it does not wastefully scan the base station or recognize that some abnormality has occurred, and can maintain smooth communication.

  After acquiring the downlink signal of the macro BS 1a as described above, the synchronization processing unit 5b detects the error amount ΔD based on the synchronization signal included in the downlink signal, and then corrects the frame timing of the subframe.

Here, the correction control unit 19 of the synchronization processing unit 5b selects a correction method when correcting the frame timing of the subframe.
The correction control unit 19 stores three correction methods 1 to 3 as a plurality of correction methods, and selects any one of these three correction methods and performs frame timing using the selected correction method. The frame counter correction unit 15 is controlled so as to correct the above.
Hereinafter, three correction methods will be described.

[4.1 Correction method 1]
In the correction method 1, as shown in FIG. 8, the detected error amount ΔD is corrected in one subframe. That is, when the correction control unit 19 selects the correction method 1, first, the correction control unit 19 specifies a subframe to be corrected subframe to be subjected to frame timing correction. FIG. 8 shows a case where the subframe # 0 located at the head of the radio frame arranged next to the radio frame that received the downlink signal is specified as the corrected subframe.
Next, the correction control unit 19 causes the frame counter correction unit 15 to correct the frame timing in the corrected subframe.

Assuming that the beginning of the subframe # 0 before correction is the timing T3, the frame counter correction unit 15 determines that the beginning of the subframe # 0 is shifted to a timing T4 that is shifted from the timing T3 by an error amount ΔD. The value of the frame counter is adjusted so that As a result, the transmission timing of subframe # 0 in its own downlink signal is corrected to match the transmission timing of subframe # 1 in the downlink signal of macro BS 1a.
Next, subframes (radio frames) arranged subsequent to the corrected subframe # 0 are sequentially arranged by adjusting the position in the time axis direction according to the timing of the corrected subframe # 0.
As described above, when the correction control unit 19 selects the correction method 1, the synchronization processing unit 5 b corrects the detected error amount ΔD in one subframe, and sets the frame timing of the femto BS 1 b as its own to the macro BS 1 a. The synchronization processing is finished in conformity with the frame timing.
Next, the correction method 2 (first method) will be described.

[4.2 Correction method 2]
FIG. 9 is a diagram for explaining an aspect of the correction method 2. The manner in which the downlink signal of the macro BS 1a is received and the error amount ΔD of the synchronization error is obtained is the same in both the correction methods 1 and 2, as shown in FIG. FIG. 9 shows a timing after timing T4, which is a mode different from the correction method 1.
In the correction method 2, as shown in FIG. 9, the detected error amount ΔD is corrected in a plurality of times. That is, when the correction method 2 is selected, the correction control unit 19 specifies a subframe where correction is to be started, and causes the frame counter correction unit 15 to correct the frame timing from the specified subframe. FIG. 9 shows a case where the subframe # 0 located at the head of the radio frame arranged next to the radio frame that received the downlink signal is specified as the subframe for starting correction.

Assuming that the head before correction of subframe # 0 to start correction is at timing T3, the frame counter correction unit 15 starts the correction of the correction amount Δd (correction amount Δd = error amount ΔD) from the timing T3. / 10) The value of the frame counter is adjusted so that the timing T4 is shifted in the direction of the earlier timing.
Next, the frame counter correction unit 15 performs a timing T6 in which the head of the subframe # 1 is shifted by a correction amount Δd from the head timing T5 of the subframe # 1 when the subframe # 1 is arranged according to the corrected subframe # 0. The value of the frame counter is adjusted so that

Thereafter, each subframe is similarly corrected, and the frame counter correction unit 15 corrects the frame timing for one radio frame from subframes # 0 to # 9.
In other words, the frame counter correction unit 15 corrects the error amount ΔD by 10 correction amounts by Δd, and thereby the downlink signal of the macro BS 1a at the timing T7, which is the start timing of the next radio frame. To match the transmission timing of subframe # 1.
As described above, when the correction control unit 19 selects the correction method 2, the synchronization processing unit 5b corrects the detected error amount ΔD in 10 steps, and sets the frame timing of the femto BS 1b that is the self to the macro BS 1a. The synchronization processing is finished in accordance with the frame timing.

In the correction method 2, since one error amount ΔD is corrected in 10 steps, the correction amount at the time of each correction can be reduced, and the subframes adjacent to each other greatly overlap by the correction of the frame timing. Can be prevented.
Next, the correction method 3 (second method) will be described.

[4.3 Correction method 3]
FIG. 10 is a diagram for explaining an aspect of the correction method 3. The correction method 3 is the same as the correction method 1 until the correction method is selected and the corrected subframe that is the subframe for which the frame timing should be corrected is specified. In FIG. The case where subframe # 0 located at the head of the radio frame arranged next to the radio frame receiving the downlink signal is specified as the frame is shown.
As shown in FIG. 10, the correction method 3 corrects the detected error amount ΔD in one subframe as in the correction method 1, but before the subframe # 0 that is the subframe to be corrected. This is different in that the frame timing is corrected in the subframe to be corrected after the resource allocation in the subframe # 9 arranged in is limited.

  When the correction control unit 19 specifies the corrected subframe # 0, the correction control unit 19 further specifies the subframe # 9 arranged in front of the corrected subframe # 0, and information for specifying the subframe # 9. The resource allocation control unit 5d is notified as resource allocation restriction information. Thereby, resource allocation in subframe # 9 is limited.

  Next, the frame counter correction unit 15 corrects the error amount ΔD in the subframe # 0, which is the corrected subframe, in the same manner as in the correction method 1, and sets the frame timing of the femto BS1b that is itself as the frame of the macro BS1a. The synchronization process is finished in accordance with the timing.

  In the correction method 3 described above, the resource allocation to the subframe arranged before the corrected subframe is limited. Therefore, inter-symbol interference occurs when the corrected subframe and the subframe arranged before the subframe are greatly overlapped. Even if it happens, it can be avoided that the effect appears.

In the description of each of the correction methods 1 to 3, only the frame timing synchronization has been described. However, the carrier frequency correction is also performed in association with the frame timing synchronization. The frequency correction unit 17 performs the same correction as the correction methods 1 to 3 on the error amount of the carrier frequency error estimated by the frequency offset estimation unit 16.
Next, a process performed by the correction control unit 19 for selecting each of the correction methods will be described.

[4.4 Selection of correction method]
FIG. 11 is a flowchart illustrating an aspect of processing in which the correction control unit selects a correction method.
As shown in FIG. 11, first, the correction control unit 19 acquires the error amount ΔD of the synchronization error detected by the synchronization error detection unit 14, and the amount of data to be transmitted from the detection unit 5e to the MS 2 connected to itself. Is acquired (step S101), it is determined whether or not the acquired error amount ΔD is equal to or less than a preset threshold value D _th1 (step S102).
If it is determined in step S102 that the error amount ΔD is equal to or less than the threshold value D _th1 , the correction control unit 19 selects the correction method 1 that is a method for correcting the error amount ΔD in one subframe (step S103), and the process Finish.

Here, the threshold value D _th1 is set to the time length of the CP (see FIG. 4) inserted between each subframe. In the correction method 1, the error amount ΔD is corrected in one subframe. Therefore, when the error amount ΔD becomes larger than the CP time length _Tcp , the corrected subframe is placed before the CP beyond the CP. This is because there is a possibility of causing inter-symbol interference. That is, the threshold value D _th1 is set to a value with which it can be determined whether or not it is necessary to perform correction for the time length T _cp of the CP for one subframe when the correction method 1 is selected.

When it is determined in step S102 that it is not less than or equal to the threshold value D _th1 , the correction control unit 19 further determines whether or not the error amount ΔD is less than or equal to a preset threshold value D _th2 (step S104).
In step S104, when it is determined that the error amount ΔD is equal to or less than the threshold value D _th2 , the correction control unit 19 selects the correction method 2 that is a method of correcting in multiple times (step S105), and ends the process.

Here, the threshold value D _th2 is set to a time length of 10 times the time length of the CP (see FIG. 4) inserted between the subframes. In the correction method 2, since the error amount ΔD is corrected in 10 steps, when the error amount ΔD is larger than the time length 10 times the CP time length _Tcp , each corrected subframe is This is because it overlaps with a subframe arranged before and beyond the CP, which may cause intersymbol interference. That is, the threshold value D _th2 is set to a value with which it can be determined whether or not it is necessary to perform correction for the time length T _cp of the CP for one subframe when the correction method 2 is selected.

When it is determined in step S104 that the threshold value D _th2 is not less than or equal to the threshold value D _th2 , the correction control unit 19 determines whether or not the amount of data to be transmitted to the MS 2 connected to itself is larger than a preset threshold value R ( Step S106).

When it is determined in step S106 that the data amount is not larger than the threshold value R, the correction control unit 19 proceeds to step S105, selects the correction method 2 (step S105), and ends the process.
In this case, when correction by the correction method 2 is performed, each corrected subframe overlaps with a subframe arranged in front of it beyond the CP, which may cause intersymbol interference.
Here, the threshold value R is set to a data amount that does not cause a problem even if there is some overlap between adjacent subframes and interference between symbols occurs. Can be tolerated.

  On the other hand, when it is determined in step S106 that the amount of data is larger than the threshold value R, the correction control unit 19 selects the correction method 3 (step S107) and ends the process.

When the frame timing is corrected by this correction method 3, the transmission timing of its own subframe can be corrected within the range of the subframe that is arranged before the corrected subframe and in which resource allocation is limited. When correcting transmission timing, a relatively large correction width can be secured. For this reason, the correction control unit 19 can select the correction method 3 when the error amount ΔD is larger than the threshold value D _th2 .

The threshold value D _th2 is set according to the time length T _cp of the CP having a function as a guard interval inserted between adjacent subframes. That is, the threshold value D _th2 is set to an error amount that can be determined that it is necessary to correct the CP time length T _cp or more for one subframe when the correction method 2 is selected. When it is determined that it is necessary to correct the frame to the CP time length _Tcp or more, the correction method 3 that can ensure a relatively large correction width is selected. Accordingly, the correction control unit 19 can select a suitable correction method according to the error amount ΔD.

In selecting the correction method 3, in addition to the error amount ΔD being considered in step S102, the data amount to be transmitted to the MS 2 is also considered in step S106. That is, when the error amount ΔD of the synchronization error can be determined to be relatively large because it is larger than the threshold value D _th2 and can be determined to be relatively large because the data amount is larger than the threshold value R, the correction control unit By selecting the correction method 3 and restricting resource allocation, it is possible to avoid the influence of intersymbol interference on the MS 2.
On the other hand, even if the error amount ΔD of the synchronization error is larger than the threshold value D _th2 , if it can be determined that the amount of data is relatively small because the data amount is equal to or less than the threshold value R, even if intersymbol interference occurs, the terminal device Therefore, the correction control unit 19 can select the correction method 2 which is a method other than the correction method 3.

  Thus, in the present embodiment, whether or not the correction control unit 19 selects the correction method 3 according to the amount of data to be transmitted to the MS 2 that is the detection result of the detection unit in addition to the error amount ΔD of the synchronization error. Therefore, it is possible to perform synchronization between base stations more preferably while considering the influence on the MS 2 due to inter-symbol interference.

As described above in detail, according to the base station apparatus configured as described above, the frame counter correction unit 15 corrects the frame timing of its own downlink signal based on the synchronization error detected by the synchronization error detection unit 14. Thus, by synchronizing with the frame timing of the downlink signal of the macro BS 1a, inter-base station synchronization can be performed with other base station apparatuses.
Further, since the correction control unit 19 selects the correction method performed by the frame counter correction unit 15 according to the error amount ΔD of the synchronization error, the frame timing of the own downlink signal is corrected by a suitable correction method according to the situation. be able to. For this reason, depending on a certain correction method, even if adjacent subframes are greatly overlapped, there is a possibility of being affected by intersymbol interference, and another correction method that can avoid the effect of intersymbol interference is selected. be able to. As a result, regardless of the error amount ΔD of the synchronization error, the influence of inter-symbol interference can be avoided and the synchronization between base stations can be preferably performed.
As described above, according to the base station apparatus of the present embodiment, it is possible to appropriately perform inter-base station synchronization according to the amount of synchronization error.

[5. Timing of synchronous processing and measurement processing]
FIG. 12 is a diagram illustrating the timing at which the synchronization process and the measurement process are performed. FIG. 10 shows an arrangement of a radio frame F1 including a subframe on which synchronization processing is performed and a radio frame F2 including a subframe on which measurement processing is performed among a plurality of radio frames arranged in the time axis direction.

  In the present embodiment, the synchronization processing unit 5b sets the timing for performing the synchronization processing so that the synchronization processing is performed at a constant cycle. In addition, the measurement processing unit 5c sets so that the measurement processing is performed in the subframe included in the radio frame F2 following the radio frame F1 for which the synchronization processing unit 5b performs the synchronization processing.

FIG. 12 shows a case where the synchronization processing is set to be performed with 5 radio frames as one cycle.
Here, the synchronization processing unit 5b adjusts the timing of performing the synchronization process by adjusting the period of the start timing of the synchronization process according to the detection result of the detection unit 5e.

The detection unit 5e estimates the number of MSs 2 connected to other base station apparatuses from the measurement result information obtained by the measurement process performed in the radio frame F2 before the synchronization process is performed. In addition, after the measurement process, the detection unit 5e acquires information about the number of MSs 2 connected to itself from the upper layer until the frame in which the next synchronization process is performed.
The detection unit 5e gives information on the estimated number of MSs 2 connected to other base station apparatuses and the number of MSs 2 connected to the base unit as a detection result to the synchronization processing unit 5b.
The synchronization processing unit 5b to which these pieces of information are given adjusts the period of the synchronization processing start timing in accordance with the estimated number of MSs 2 connected to other base station apparatuses and the number of MSs 2 connected to itself. In addition, after the synchronization processing unit 5b adjusts the cycle of the synchronization process, the measurement processing unit 5c sets the cycle of the measurement process according to the cycle of the synchronization process.

  In the present embodiment, the measurement processing unit 5c exemplifies a case where the measurement processing cycle is set according to the synchronization processing cycle adjusted by the synchronization processing unit 5b. It is also possible to set the timing for performing the measurement process independently. In this case, the measurement processing unit 5c sets the timing for performing the measurement process based on the detection result of the detection unit 5e, similarly to the synchronization processing unit 5b.

The present invention is not limited to the above embodiments.
In the above embodiment, the case where the normal cyclic prefix is adopted for the CP inserted between the slots constituting the radio frame of the downlink signal of the base station apparatus is exemplified, but the extended cyclic prefix is adopted. Even in this case, the present invention can be applied. In this case, the throughput slightly decreases as the number of symbols constituting the slot decreases, but the CP time length T _cp is set longer, so that the frame timing correction amount in each correction method is set larger. And correction can be performed for larger synchronization errors.

Further, in the correction method 2 of the above-described embodiment, the case where the correction amount ΔD of the synchronization error is corrected 10 times is illustrated, but the number of corrections may be plural, for example, 2 times. However, it can be set to a larger number of times. Further, the number of corrections need not be a fixed value, and the number of corrections can be set adaptively according to the error amount ΔD.
However, if the number of corrections increases, the subframe transmission timing will be corrected according to the number of corrections, so the time from detection of the synchronization error to completion of correction will be long, and synchronization accuracy will decrease. There is a risk. For this reason, it is preferable that the upper limit value of the number of corrections is within a range of one radio frame (about 10 times when correction is performed in units of subframes).

In the correction method 3 of the above embodiment, the resource allocation is limited for the subframe arranged before the corrected subframe, but the transmission of the downlink signal is suspended at the timing of the subframe in which the resource allocation is limited. May be.
In this case, even if the corrected subframe is corrected in the range of the subframe time length before the corrected subframe, the transmission of the downlink signal is paused in the range of the subframe, so intersymbol interference does not occur. . Further, since resource allocation is limited in this section, it is possible to suppress the influence on the MS 2 by stopping transmission.

  In the above embodiment, in each correction method, the case where the frame timing is corrected or the correction is started in the first subframe # 0 located at the head of the radio frame is exemplified. However, in other subframes, the correction is started. Frame timing correction may be performed or initiated.

  In the above embodiment, the subframe # 0 or the subframe # 5 including the first and second synchronization signals in the own downlink signal matches the transmission timing of the subframe # 1 in the downlink signal of the macro BS 1a. In the example of performing synchronization between base stations, subframe # 0 or subframe # 5 in its own downlink signal is transmitted at the transmission timing of other subframes # 0 and # 2 to 9 in the downlink signal of macro BS1a. The base stations may be synchronized so that they match.

  Further, in the above embodiment, the case where the communication unit area having a certain length of time, which is a target of the synchronization process, is a subframe is exemplified, but other units constituting the downlink signal, for example, a radio frame, A slot can be used as the communication unit area to be synchronized, and a section defined by a symbol can be used as the communication unit area.

  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 Base station apparatus 5b Synchronization processing part 5d Resource allocation control part 5e Detection part 12 Downstream signal reception part 14 Synchronization error detection part 15 Frame counter correction part 17 Frequency correction part 19 Correction control part

Claims (9)

A base station device that communicates with a terminal device by frequency division duplex using a downlink signal configured by arranging a plurality of communication unit areas having a certain time length on a time axis,
A receiving unit for receiving a downlink signal from another base station device;
Based on the downlink signal received from the other base station apparatus received by the receiving unit, a synchronization error between the downlink signal communication unit area of the other base station apparatus and the own downlink signal communication unit area is detected. A synchronization error detecting unit,
Based on the synchronization error, a correction unit for synchronizing the downlink signal of the other base station device by correcting the own downlink signal;
A base station apparatus comprising: a correction control unit that selects a correction method performed by the correction unit from a plurality of types of correction methods according to an error amount of the synchronization error.   2. The base station apparatus according to claim 1, wherein the plurality of types of correction methods include a first method in which the error amount of the synchronization error is corrected in a plurality of times. The downlink signal has a basic frame composed of a plurality of subframes;
The communication unit area is the subframe;
The base station apparatus according to claim 2, wherein the first method corrects the error amount of the synchronization error for each of the plurality of subframes. A resource allocation control unit for controlling resource allocation to the terminal device in the communication unit area;
In the plurality of types of correction methods, the resource allocation unit limits resource allocation in a communication unit area arranged in front of a corrected communication unit area to be corrected, and then corrects the corrected communication unit area. The base station apparatus as described in any one of Claims 1-3 including the 2nd method of performing.   The base station apparatus according to claim 4, wherein the second method pauses transmission of its own downlink signal in a communication unit area arranged before the corrected communication unit area.   The base station apparatus according to claim 4 or 5, wherein the correction control unit selects the second method when an error amount of the synchronization error is larger than a predetermined threshold.   The base station apparatus according to claim 6, wherein the threshold is set according to a time length of a guard interval section inserted between adjacent communication unit areas. It further comprises a detector that detects the amount of data to be transmitted to the terminal device by its own downlink signal,
The base station apparatus according to claim 4 or 5, wherein the correction control unit determines whether to select the second method according to an error amount of the synchronization error and a detection result of the detection unit. The downlink signal has a basic frame composed of a plurality of subframes;
The communication unit area is the subframe;
The base station apparatus according to any one of claims 4 to 8, wherein the second method limits resource allocation for each subframe.

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