Base station device

Abstract

Provided is a base station device for executing time-division multiplexing wireless communication with a terminal that transmits a time-sequenced uplink radio frame at a transmission timing based on an uplink timing advance value, the base station device comprising: a detection unit that detects an observation period, which is a period in which a time-sequenced downlink radio frame transmitted from a synchronized base station is received within a period in which a time-sequenced uplink radio frame is received from the terminal; a base station control unit that, on the basis of the position and the length of the observation period detected by the detection unit, synchronizes the timing at which the base station device transmits a time-sequenced downlink radio frame with the timing at which the synchronized base station transmits a time-sequenced downlink radio frame; and a base station transmission unit that transmits a downlink radio frame to the terminal on the basis of the timing synchronized by the base station control unit.　

Description

base station equipment

[0001] The present invention relates to a base station device.

[0002] When analog RoF (Radio-over-Fiber) is applied to a communication system, the functions of the communication system's base station may be divided into an aggregation station and a base station (see Non-Patent Document 1). By deploying base stations with simple configurations in wireless areas, a flexible and economical mobile network is realized. Hereinafter, the direction from the terminal to the base station is referred to as "uplink," and the direction from the base station to the terminal is referred to as "downlink."

[0003] Communication systems such as mobile networks often use the Time Division Duplex (TDD) method, which switches between uplink (UL) and downlink (DL) in the same frequency band on a slot-by-slot basis.

[0004] A communication system may be equipped with a Timing Advance (TA) function (see Non-Patent Document 2, 3GPP (registered trademark)). In the Timing Advance, a Timing Advance value (TA value) corresponding to the amount of transmission delay in a wireless section is determined. An uplink radio frame is transmitted at a timing earlier than a downlink radio frame by a time based on this Timing Advance value (see Non-Patent Document 3).

[0005] As a result, for example, when an uplink radio frame is transmitted from a terminal to an asynchronous base station (own station), the reception timing of the uplink radio frame at the antenna of the asynchronous base station is synchronized with the reference timing of time division multiplexing of the synchronous base station (other station).

[0006] Kodai Ito, Mizuki Suga, Hirofumi Shirato, Naoki Kita, and Takeshi Onisawa, "Efficient Accommodation of Diverse High-Frequency Band Wireless Systems Using Analog RoF," NTT Technical Journal, 32(3), 15-17, 2020. 3GPP TS 38.211 version 16.7.0 Release 16 3GPP TS 38.133 version 15.3.0 Release 15

[0007] Hereinafter, the timing advance value for uplink transmission will be referred to as the "uplink timing advance value." Hereinafter, the timing advance value for downlink transmission will be referred to as the "downlink timing advance value."

[0008] When a timing advance function is applied to an analog RoF communication system, the central station estimates a transmission delay amount in the analog RoF section (optical section) from the central station to the base station. The central station determines a downlink timing advance value of the central station based on the estimated transmission delay amount in the optical section so that the transmission timing of the downlink radio frame at the base station is synchronized with the reference timing.

[0009] When a timing advance function is applied to an analog RoF communication system, the central station estimates a transmission delay amount in a wireless section from a terminal to a base station. The central station determines an uplink timing advance value for the terminal based on the estimated transmission delay amount in the wireless section so that the reception timing of an uplink wireless frame at the base station is synchronized with a reference timing. The central station notifies the terminal of the uplink timing advance value.

[0010] When a timing advance function is applied to a digital RoF communication system, the central station estimates the amount of transmission delay in the wireless section from the terminal to the base station. The central station determines an uplink timing advance value for the terminal based on the estimated value of the transmission delay in the wireless section so that the reception timing of the uplink wireless frame at the base station is synchronized with the reference timing. The central station notifies the terminal of the uplink timing advance value.

[0011] However, if the timing of time division multiplexing transmission and reception between a base station and other base stations is not synchronized, it will affect the communications of other base stations. While using the Global Navigation Satellite System (GNSS) is one possible method for synchronizing timing, it requires that all base stations be equipped with a function for time synchronization with the GNSS. Therefore, it is desirable to synchronize the timing of time division multiplexing communications between base stations without time synchronization using the GNSS.

[0012] In view of the above circumstances, an object of the present invention is to provide a technique that can synchronize the timing of time division multiplexing communication with other base stations in a simple manner.

[0013] One aspect of the present invention is a base station device that performs wireless communication using time division multiplexing with a terminal that transmits time-series uplink radio frames at transmission timing based on an uplink timing advance value, and includes: a detection unit that detects an observation period, which is a period during which time-series downlink radio frames transmitted from a synchronized base station are received, within a period during which time-series uplink radio frames are received from the terminal; a base station control unit that synchronizes the timing at which the base station transmits the time-series downlink radio frames with the timing at which the synchronized base station transmits the time-series downlink radio frames based on the position and length of the observation period detected by the detection unit; and a base station transmission unit that transmits the downlink radio frames to the terminal based on the timing synchronized by the base station control unit.

[0014] According to the present invention, it is possible to synchronize the communication timing of time division multiplexing with other base stations using a simple method.

[0015] Fig. 1 is a diagram showing an example of the configuration of a communication system in a first embodiment. Fig. 2 is a diagram showing an example of an observation period in the first embodiment when the transmission timing of a base station (asynchronous base station) is earlier than the reference timing of time division multiplexing of a synchronous base station (other station). Fig. 3 is a diagram showing an example of an observation period in the first embodiment when the transmission timing of a base station (asynchronous base station) is later than the reference timing of time division multiplexing of a synchronous base station (other station). Fig. 4 is a flowchart showing an example of the operation of a communication system in the first embodiment. Fig. 5 is a diagram showing an example of the configuration of a communication system in a second embodiment. Fig. 6 is a diagram showing an example of the hardware configuration of a communication device in each embodiment.

[0016] An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) Fig. 1 is a diagram showing an example of the configuration of a communication system 1a in the first embodiment. The communication system 1a is a system that performs wireless communication between a base station and a terminal. The communication system 1a includes a base station 2a (base station device), a terminal 3, and a synchronized base station 4. The synchronized base station 4 is installed in advance at a location adjacent to the base station 2a. In this embodiment, as an example, a case will be described in which the number of the base station 2a, the terminal 3, and the synchronized base station 4 is one.

[0017] The base station 2a includes a base station antenna 21, a detector 22, a base station controller 23, and a base station transmitter 24. The base station antenna 21 and the base station transmitter 24 (optical section) are connected by an optical fiber. The optical fiber may be a single-mode optical fiber, a multi-mode optical fiber, a single-core optical fiber, or a multi-core optical fiber.

[0018] During a time period when the time division multiplexing timing is not synchronized in the base station 2a (asynchronous base station), there is a possibility that interference between uplink and downlink communications may occur with other base stations (for example, the synchronous base station 4, etc.). Therefore, in this embodiment, a configuration will be described in which the timing of time division multiplexing is adjusted in the base station 2a (asynchronous base station) so as to suppress interference with other stations.

[0019] The base station 2a (asynchronous base station) synchronizes the timing of time division multiplexing by communicating with the synchronous base station 4. Therefore, until timing synchronization is achieved, the base station 2a (asynchronous base station) performs beamforming control in the direction of the synchronous base station 4. Therefore, the base station 2a (asynchronous base station) does not transmit downlink radio frames to the terminal 3 until timing synchronization is achieved.

[0020] In order to perform timing synchronization at the base station 2a (asynchronized base station), it is necessary to receive a signal from the synchronous base station 4. Therefore, the synchronous base station 4 periodically performs beamforming control in the direction in which the base station 2a (asynchronized base station) is located until timing synchronization of the base station 2a (asynchronized base station) is completed. In this way, communication is performed between the base station 2a (asynchronized base station) and the synchronous base station 4.

[0021] The completion of timing synchronization of the base station 2a (asynchronized base station) may be achieved by a synchronization completion notification. The synchronization completion notification is a signal for notifying that timing synchronization of the base station 2a (asynchronized base station) has been completed. When the base station 2a (asynchronized base station) has achieved synchronization with the time division multiplexing timing, it may transmit the synchronization completion notification to the synchronous base station 4. The synchronization completion notification may be notified to the synchronous base station 4 wirelessly, or may be notified to the synchronous base station 4 by wire via an upper core. Upon receiving the synchronization completion notification transmitted from the base station 2a (asynchronized base station), the synchronous base station 4 terminates beamforming control in the direction in which the base station 2a (asynchronized base station) is located.

[0022] The timing synchronization method in base station 2a (asynchronous base station) will be described. By receiving a signal from synchronous base station 4, base station 2a (asynchronous base station) observes the signal level corresponding to the inter-base station interference that should be avoided and synchronizes the timing. Here, inter-base station interference refers to interference that occurs when an error occurs in the timing of time division multiplexing between base stations, for example, when base station #1 is in the period of transmitting an uplink radio frame and base station #2 is in the period of transmitting a downlink radio frame, and base station #1 receives a downlink radio frame from base station #2 that it should not receive.

[0023] Note that until timing synchronization is achieved in the base station 2a (asynchronized base station), beamforming control is not performed in the direction in which the terminal 3 is located. Therefore, the reception level of synchronization signals such as RACH from the terminal 3 is negligibly small and has no effect on this synchronization process. When the base station 2a (asynchronized base station) communicates with a synchronous base station 4, the base station 2a (asynchronized base station) and the synchronous base station 4 need to mutually know in advance the beam ID information corresponding to their respective positions or their respective directions.

[0024] After the base station 2a (asynchronous base station) has been synchronized with the timing of time division multiplexing, it starts communication with the terminal 3. Then, the base station 2a (asynchronous base station) notifies the terminal 3 of the uplink timing advance value. The terminal 3 executes a transmission process (advance transmission process) based on the uplink timing advance value.

[0025] The base station 2a estimates the amount of transmission delay in the wireless section from the terminal 3 to the base station 2a. The base station 2a calculates the estimated value of the amount of transmission delay in the wireless section "t" so that the reception timing of the uplink wireless frame at the base station antenna 21 is synchronized with the reference timing. ＲＦ The base station 2 a determines the uplink timing advance value based on the above. The base station 2 a notifies the terminal 3 of the uplink timing advance value.

[0026] Next, a detailed configuration example of the communication system 1a will be described. The base station antenna 21 may be an antenna with a fixed direction of directivity of wireless frames (radio waves), or an antenna with a variable direction of directivity of wireless frames. An example of an antenna with a variable direction of directivity of wireless frames is a phased array antenna.

[0027] The base station antenna 21 communicates between the synchronized base station 4 and the terminal 3. Here, the case is shown in which the same antenna is used for communication between the synchronized base station 4 and the terminal 3, but different antennas may be used for communication between the synchronized base station 4 and the terminal 3. The base station antenna 21 communicates with the synchronized base station 4 until the timing is synchronized. After the timing is synchronized, the base station antenna 21 communicates with the terminal 3.

[0028] The base station antenna 21 receives the radio frame transmitted from the synchronized base station 4. When the timing is synchronized, the base station antenna 21 transmits a synchronization completion notification to the synchronized base station 4.

[0029] The base station antenna 21 acquires the uplink timing advance value of the terminal 3 from the base station transmitter 24. The base station antenna 21 transmits a downlink radio frame indicating the uplink timing advance value to the terminal antenna 31. The base station antenna 21 receives, from the terminal antenna 31, the uplink radio frames in time series that have been transmitted at timings based on the uplink timing advance value.

[0030] The detector 22 detects a reception level observation period in a time-series radio frame transmitted from a synchronized base station 4. The position of the observation period in the time-series radio frame (observation position) is represented, for example, by a slot number. The length of the observation period is represented, for example, by the number of symbols in Orthogonal Frequency Division Multiplexing (OFDM). The detector 22 outputs the detection result of the observation period to the base station controller 23.

[0031] The base station control unit 23 determines whether the transmission timing of the radio frame of the local station is earlier than the reference timing of time division multiplexing of the synchronized base station (other station) based on the position of the observation period in the time series of radio frames. The base station control unit 23 determines the error (absolute value) from the reference timing of time division multiplexing of the synchronized base station (other station) based on the length of the observation period. Here, the base station control unit 23 may determine the error from the reference timing of time division multiplexing of the synchronized base station (other station) based on the average or median of the lengths of the observation periods detected multiple times.

[0032] The base station control unit 23 corrects the transmission timing so as to reduce the error with respect to the reference timing of time division multiplexing of the synchronized base station (other station). If the base station 2a determines that the transmission timing of the radio frame is early with respect to the reference timing, the base station control unit 23 delays the transmission timing of the downlink radio frame. If the base station 2a determines that the transmission timing of the radio frame is late with respect to the reference timing, the base station control unit 23 advances the transmission timing of the downlink radio frame.

[0033] The base station transmitter 24 starts transmitting the downlink radio frame at the corrected transmission timing. When transmitting the downlink radio frame, the base station transmitter 24 transmits the downlink radio frame including information indicating the uplink timing advance value to the terminal 3 as necessary.

[0034] Next, an example of detecting an observation period will be described. Fig. 2 is a diagram showing an example of an observation period 7 in the first embodiment when the transmission timing of base station 2a (asynchronous base station) is earlier than the reference timing of time division multiplexing of a synchronized base station 4 (other station). In the following, as an example, the slot with slot number "SL2" is a special slot in the time-series radio frame.

[0035] The upper part of Fig. 2 illustrates an example of a time-series radio frame indicating the timing of time division multiplexing in a synchronized base station 4. In the special slot with slot number "SL2" in the time-series radio frame shown in the upper part of Fig. 2, a guard period 5 is inserted at the timing of switching between downlink transmission "DL" and uplink transmission "UL". The length of the guard period 5 is, for example, 2 OFDM symbols. Downlink transmission "DL" represents a period during which a downlink radio frame can be transmitted from the base station to a terminal 3, for example, and uplink transmission "UL" represents a period during which an uplink radio frame can be received from the terminal 3, for example.

[0036] The lower part of Fig. 2 illustrates an example of a time-series radio frame indicating the timing of time division multiplexing in base station 2a (asynchronous base station). In the special slot with slot number "SL2" in the time-series radio frame shown in the lower part of Fig. 2, a guard period 6 is inserted at the timing of switching between downlink transmission "DL" and uplink transmission "UL". The length of the guard period 6 is, for example, 2 OFDM symbols.

[0037] In the special slot with slot number "SL2" shown in FIG. 2 , there is a period during which the base station 2a (asynchronous base station) receives a downlink radio frame transmitted from a synchronous base station 4 to the base station 2a (asynchronous base station) at the transmission timing of the uplink radio frame. The base station 2a (asynchronous base station) detects the period during which the base station 2a (asynchronous base station) receives a downlink radio frame transmitted from a synchronous base station 4 at the transmission timing of its own uplink radio frame as a reception level observation period 7. The base station control unit 23 determines whether the timing of time division multiplexing of the base station 2a is early with respect to the reference timing based on the position of the observation period 7 in the time series radio frames. If the observation period 7 exists immediately after switching from downlink transmission to uplink transmission (if the observation period 7 exists in the first uplink radio frame), the base station control unit 23 determines that the timing of time division multiplexing of the base station 2a is early with respect to the reference timing.

[0038] 2, the base station control unit 23 determines the number of symbols in the observation period 7 as the error (absolute value) from the reference timing of time division multiplexing of the synchronous base station (other station). The base station control unit 23 may also determine the sum of the number of symbols in the observation period 7 and the number of symbols in the guard period as the error (absolute value) from the reference timing of time division multiplexing of the synchronous base station (other station). In this case, the base station control unit 23 corrects the transmission timing of the downlink radio frame so that it is delayed by the error from the reference timing of time division multiplexing of the synchronous base station (other station). This allows the transmission timing of the downlink radio frame of the base station 2a (asynchronous base station) to be synchronized with the transmission timing of the downlink radio frame of the synchronous base station 4.

[0039] FIG. 3 is a diagram showing an example of the observation period 8 in the first embodiment when the transmission timing of the base station 2a (asynchronous base station) is later than the reference timing of time division multiplexing of the synchronized base station 4 (other station).

[0040] The upper part of Fig. 3 illustrates a time series of radio frames indicating the timing of time division multiplexing in the synchronous base station 4. The lower part of Fig. 3 illustrates a time series of radio frames indicating the timing of time division multiplexing in the base station 2a (asynchronous base station).

[0041] 3, there is a period during which a downlink radio frame transmitted from a synchronous base station 4 to the base station 2a (asynchronous base station) is received at the transmission timing of an uplink radio frame from the base station 2a (asynchronous base station). The base station 2a (asynchronous base station) detects the period during which a downlink radio frame transmitted from a synchronous base station 4 is received at the transmission timing of its own uplink radio frame as a reception level observation period 8. In this way, when the observation period 8 exists in the middle of the time-series uplink radio frames, the base station control unit 23 determines that the timing of time division multiplexing of the base station 2a is slower than the reference timing.

[0042] 3, the base station control unit 23 determines the number of symbols in the observation period 8 as the error (absolute value) from the reference timing of time division multiplexing of the synchronous base station (other station). The base station control unit 23 corrects the transmission timing of the radio frame so that it is earlier by the error from the reference timing of time division multiplexing of the synchronous base station (other station). This allows the transmission timing of the downlink radio frame of the base station 2a (asynchronous base station) to be synchronized with the transmission timing of the downlink radio frame of the synchronous base station 4.

[0043] In addition, not only when the uplink radio frame is transmitted by the OFDM method (multi-carrier) but also when the uplink radio frame is transmitted by a single carrier, it is possible to determine whether the reception timing of the uplink radio frame at the base station 2a is earlier than the reference timing based on the position of the observation period. Also, it is possible to determine the error (absolute value) from the reference timing of time division multiplexing of a synchronized base station (other station) based on the length of the observation period (number of samples).

[0044] Next, an operation example of the communication system 1a will be described. Fig. 4 is a flowchart showing an operation example of the communication system 1a in the first embodiment. Note that the processing in Fig. 4 describes processing up to timing synchronization of time division multiplexing in the base station 2a (asynchronous base station).

[0045] The base station 2a (asynchronous base station) executes processing for timing synchronization with the synchronous base station 4 (step S101). Specifically, the detection unit 22 detects the observation period 7 or the observation period 8 by receiving time-series radio frames transmitted from the synchronous base station 4. The base station control unit 23 corrects the timing of time division multiplexing so as to shorten the observation period 7 or the observation period 8 based on the position and length of the detected observation period 7 or the observation period 8. In this way, the base station 2a (asynchronous base station) synchronizes the timing of time division multiplexing of the base station with the timing of the synchronous base station 4.

[0046] The detector 22 determines whether or not the uplink reception level has been observed (step S102). If the detector 22 determines that the uplink reception level has been observed (step S102-YES), this means that the timing of time division multiplexing of the base station 2a (asynchronous base station) is not synchronized. Therefore, the base station 2a (asynchronous base station) executes the process of step S101 again.

[0047] On the other hand, if the detector 22 determines that the uplink reception level has not been observed (step S102-NO), this means that the time division multiplexing timing of the base station 2a (asynchronous base station) has been synchronized. Therefore, the base station antenna 21 transmits a synchronization completion notification to the synchronized base station 4 (step S103). Thereafter, the base station 2a (asynchronous base station) starts transmitting downlink radio frames at the transmission timing of the downlink radio frames (step S104).

[0048] When the base station 2a (asynchronous base station) starts transmitting a downstream radio frame, the base station 2a estimates the amount of transmission delay in the wireless section from the terminal 3 to the base station 2a. The base station 2a calculates the estimated value "t ＲＦ Then, the base station 2a notifies the terminal 3 of the uplink timing advance value. This enables communication between the base station 2a and the terminal 3 taking into account the transmission delay in the wireless section.

[0049] As described above, the base station 2a (asynchronous base station) includes a detection unit 22 that detects an observation period, which is a period during which time-series downlink radio frames transmitted from a synchronized base station 4 are received, within a period (e.g., an uplink transmission "UL" slot) during which time-series uplink radio frames are received from the terminal 3; a base station control unit 23 that synchronizes the timing at which the base station 2a transmits the time-series downlink radio frames with the timing at which the synchronized base station 4 transmits the time-series downlink radio frames, based on the position and length of the observation period detected by the detection unit 22; and a base station transmission unit 24 that transmits the downlink radio frames to the terminal based on the timing synchronized by the base station control unit 23.

[0050] This allows the error between the time division multiplexing timing of the base station 2a (asynchronous base station) and the time division multiplexing timing of the synchronous base station 4 to be detected, and then the time division multiplexing timing of the base station 2a (asynchronous base station) is corrected to reduce the error. Furthermore, this method does not require the time of the base station 2a to be synchronized with the highly accurate time of the global positioning navigation satellite system. Therefore, it is possible to synchronize the communication timing of time division multiplexing with other base stations in a simple manner.

[0051] Furthermore, base station 2a (asynchronous base station) does not communicate with terminal 3 until timing synchronization is completed. Therefore, interference with other base stations does not occur. Therefore, it is possible to suppress the impact on communications of other base stations.

[0052] (Second Embodiment) In the first embodiment, a configuration was described that assumes that the timing of time division multiplexing of base stations other than the own station (e.g., an asynchronous base station) is synchronized. However, this condition is not always met. Therefore, in the second embodiment, a configuration is described in which synchronization of multiple asynchronous base stations installed in a desired area is achieved using one base station that can be trusted to be completely synchronized as a reference. In the second embodiment, the differences from the first embodiment will be mainly described.

[0053] Fig. 5 is a diagram showing an example of the configuration of a communication system 1b in the second embodiment. The communication system 1b is a system that performs wireless communication between a base station and a terminal. The communication system 1b includes a plurality of base stations 2b (asynchronous base stations) and one synchronous base station 4. Although not shown in Fig. 5, a terminal 3 is connected to each base station 2b.

[0054] The synchronous base station 4 is installed in advance at a location adjacent to multiple base stations 2b (asynchronized base stations). For example, the synchronous base station 4 may be installed in a location where it can communicate with multiple base stations 2b (asynchronized base stations), and in the example shown in Fig. 5, it is installed at the center of the multiple base stations 2b (asynchronized base stations). In this embodiment, as an example, a case will be described in which there are five base stations 2b (asynchronized base stations), but it is sufficient if there are multiple base stations 2b (asynchronized base stations).

[0055] Timing synchronization of time division multiplexing by each base station 2b (asynchronous base station) is the same as the method shown in the first embodiment. That is, each base station 2b (asynchronous base station) estimates and corrects the timing deviation based on the reception level observation position observed by communicating with the synchronous base station 4. The configuration of each base station 2b (asynchronous base station) is the same as that of the base station 2a (asynchronous base station) shown in the first embodiment.

[0056] In the second embodiment as well, until timing synchronization is achieved, each base station 2b (asynchronous base station) performs beamforming control in the direction of the synchronous base station 4. Therefore, each base station 2b (asynchronous base station) does not transmit downlink radio frames to the terminal 3 until timing synchronization is achieved.

[0057] In order to perform timing synchronization at each base station 2b (asynchronized base station), it is necessary to receive a signal from the synchronous base station 4. Therefore, the synchronous base station 4 periodically performs beamforming control in the direction in which each base station 2b (asynchronized base station) is located until timing synchronization of each base station 2b (asynchronized base station) is completed. This allows communication to be performed between each base station 2b (asynchronized base station) and the synchronous base station 4.

[0058] The completion of timing synchronization of each base station 2b (asynchronized base station) may be performed by a synchronization completion notification. The synchronized base station 4 terminates beamforming control for the base station 2b (asynchronized base station) that has received the synchronization completion notification, and continues beamforming control for the base station 2b (asynchronized base station) that has not received the synchronization completion notification. Then, the synchronized base station 4 terminates beamforming control when it receives synchronization completion notifications from all the base stations 2b (asynchronized base stations).

[0059] The synchronized base station 4 synchronizes the TDD timing with high precision using PTP (Precision Time Protocol) or other methods. Other methods include, for example, a method using round trip time (RTT). Note that TDD timing refers to a signal synchronized with a reference time such as GNSS (Global Navigation Satellite System).

[0060] The synchronous base station 4 communicates with each base station 2b (asynchronous base station) by transmitting and receiving radio frames to and from each base station 2b (asynchronous base station). The synchronous base station 4 may communicate with each base station 2b (asynchronous base station) by switching connections in a time-division manner, or may form multiple beams to communicate with each base station 2b (asynchronous base station) simultaneously.

[0061] The synchronous base station 4 may have a function of communicating with the terminal 3, or may be a dedicated communication station for achieving timing synchronization with each base station 2b (asynchronous base station). The synchronous base station 4 may use an antenna for communicating with the terminal 3 together with an antenna for achieving timing synchronization with each base station 2b (asynchronous base station), or may be provided with a separate antenna for communicating with the terminal 3 and an antenna for achieving timing synchronization with each base station 2b (asynchronous base station).

[0062] The operation of the communication system 1b in the second embodiment is the same as that in the first embodiment, except that the synchronized base station 4 communicates with each of the plurality of base stations 2b (asynchronized base stations).

[0063] According to the communication system 1b configured as above, even when a plurality of base stations 2b (asynchronous base stations) are provided, it is possible to obtain the same effects as those of the first embodiment.

[0064] (Modification Common to First and Second Embodiments) The communication systems 1a and 1b in each of the above-described embodiments may be communication systems employing digital RoF or analog RoF. The analog RoF may be "BB over Fiber (BBoF)" that transmits baseband (BB) signals over optical fiber, "IF over Fiber (IFoF)" that transmits intermediate frequency (IF) signals over optical fiber, or "RF over Fiber (RFoF)" that transmits RF signals directly over optical fiber. An analog RoF communication system requires not only upstream transmission processing based on an upstream timing advance value, but also downstream transmission processing based on a downstream timing advance value.

[0065] When a timing advance function is applied to a digital RoF communication system, in the digital RoF, a functional unit that performs modulation and demodulation processing is provided in the base station antenna 21. The base station antenna 21 generates downlink radio frames in synchronization with the reference timing of time division multiplexing. Therefore, in the base station antenna 21, the transmission timing of the downlink radio frames is synchronized with the reference timing, and therefore transmission processing based on the timing advance value (downlink timing advance value) is not required for downlink transmission by the base station transmitter 24.

[0066] The base stations 2a and 2b estimate the amount of transmission delay in the wireless section from the terminal 3 to the base stations 2a and 2b. The base stations 2a and 2b calculate the estimated value of the amount of transmission delay in the wireless section "t" so that the reception timing of the uplink wireless frame at the base station antenna 21 is synchronized with the reference timing. ＲＦ The base stations 2 a and 2 b notify the terminal 3 of the uplink timing advance value.

[0067] When a timing advance function is applied to an analog RoF communication system, base stations 2a and 2b are composed of a central station and one or more base stations. The central station has the signal processing function, which is the separated function from the communication function of the base stations 2a and 2b. The base station has the communication function, which is the separated function from the signal processing function of the base stations 2a and 2b. Transmission is performed between the central station and each base station using analog RoF, which transmits radio signals using optical fiber.

[0068] The base stations 2a and 2b notify the terminal 3 of the uplink timing advance value. The terminal 3 executes a transmission process (advance transmission process) based on the uplink timing advance value. The uplink timing advance value notified to the terminal 3 is used as an estimate of the transmission delay amount in the wireless section, "t ＲＦ " is based on the estimated value of the transmission delay in the wireless section, "t ＲＦ " is the total transmission delay "t ＲｏＦ +t ＲＦ ” from the above, the estimated value of the transmission delay amount between the central station and each base station (optical section) “t ＲｏＦ " is obtained by subtracting

[0069] The central station measures the amount of transmission delay in the analog RoF section (optical section) from the central station to each base station. Based on the measurement result of the amount of transmission delay, the central station calculates an estimated value of the amount of transmission delay in the optical section, "t ＲｏＦ The central station determines the estimated value of the transmission delay amount in the optical section, "t ＲｏＦ " determines the downlink timing advance value based on the

[0070] The base station control unit 23 and the terminal control unit 33 included in the device of the present invention can each be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0071] 9 is a diagram illustrating an example of the hardware configuration of the communication device 100 in each embodiment. The example of the hardware configuration of the communication device 100 corresponds to the example of the hardware configuration of the base station (base station device) in each embodiment and the example of the hardware configuration of the terminal in each embodiment.

[0072] The communication device 100 is realized as software by a processor 101, such as a CPU (Central Processing Unit), executing a program stored in a storage device 103 having a non-volatile recording medium (non-transitory recording medium) and a memory 102. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), and a CD-ROM (Compact Disc Read Only Memory), and non-transitory recording media such as a hard disk or a solid-state drive (SSD) built into a computer system. The communication unit 104 executes predetermined communication processing.

[0073] The communication device 100 may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0074] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0075] The present invention is applicable to communication systems.

[0076] 1a, 1b...communication system, 2a, 2b...base station, 3...terminal, 4...synchronized base station, 5...guard interval, 6...guard interval, 7...observation period, 8...observation period, 21...base station antenna, 22...detection unit, 23...base station control unit, 24...base station transmission unit, 100...communication device, 101...processor, 102...memory, 103...storage device, 104...communication unit

Claims

1. A base station device that performs wireless communication using time division multiplexing with a terminal that transmits time-series uplink radio frames at transmission timing based on an uplink timing advance value, comprising: a detection unit that detects an observation period, which is a period during which time-series downlink radio frames transmitted from a synchronized base station are received, within a period during which time-series uplink radio frames are received from the terminal; a base station control unit that synchronizes the timing at which the base station transmits the time-series downlink radio frames with the timing at which the synchronized base station transmits the time-series downlink radio frames based on the position and length of the observation period detected by the detection unit; and a base station transmission unit that transmits downlink radio frames to the terminal based on the timing synchronized by the base station control unit.

2. The base station device according to claim 1, wherein the base station transmitter does not transmit the time-series downlink radio frames to the terminal until synchronization with the synchronized base station is completed.

3. The base station device according to claim 1 or 2, wherein the base station control unit calculates an error between the timing at which the base station transmits a time-series downlink radio frame and the timing at which the synchronized base station transmits a time-series downlink radio frame based on the position and length of the observation period detected by the detection unit, and synchronizes the base station by controlling the communication timing so as to reduce the calculated error.

4. The base station device according to claim 1 or 2, wherein the synchronized base station is a base station device synchronized with the reference timing of the time division multiplexing.

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