JP6979934B2 - Processing devices and programs that make up mobile communication systems and base station devices - Google Patents

Description

The present invention relates to a timing synchronization technique in a mobile communication system.

In a mobile communication system using the TDD (Time Division Duplex) system, the base station apparatus and the user apparatus (UE) perform uplink and downlink wireless communication using the same band. In the TDD system, it is necessary to synchronize the timing at which each base station device of the mobile communication system transmits / receives a radio signal. For example, the base station device can receive time information by GPS or the like and synchronize the timing.

Currently, as shown in FIG. 1, the base station device is a device that performs baseband signal processing (hereinafter referred to as BBU (Base Band Unit)) and a device that performs radio frequency signal processing and radio signal transmission / reception processing (hereinafter referred to as BBU). , RRH (referred to as Remote Radio Head)), and a configuration is used in which the BBU and the RRH are arranged at different geographical positions. In the downlink direction, the baseband signal processing means a process including a process of performing modulation with data to generate an analog baseband signal. Further, the radio frequency signal processing means a process including a process of performing frequency conversion of the baseband signal and generating a signal of the radio frequency band in the downlink direction. Further, the radio signal transmission / reception process means a process including a process of transmitting a radio signal based on a signal in the radio frequency band in the downlink direction. In the configuration in which the base station apparatus is divided into BBU and RRH, the BBU converts an analog baseband signal into a digital signal and transmits it to the RRH, and the RRH converts an analog baseband signal from the digital baseband signal. After the generation, the radio signal is transmitted by performing processing such as frequency conversion. In the configuration in which the base station apparatus is divided into BBU and RRH, the BBU and RRH are connected by an optical transmission line and communicate with each other by the CPRI protocol described in Non-Patent Document 1.

Here, when TDD is used, in a configuration in which the base station apparatus is divided into BBU and RRH, it is necessary to synchronize the timing at which each RRH transmits / receives a radio signal. For example, as shown in FIG. 1, the timing at which the RRH starts transmitting the downlink radio signal is set as the reference timing. Further, it is assumed that the signal transmitted by the BBU is transmitted as a radio signal from the RRH at a timing after the delay time k. In this case, the BBU needs to start transmitting the downlink baseband signal from a timing earlier than the reference timing by a delay time k. Therefore, the CPRI protocol implements a function of measuring the delay time k.

CPRI Specification V7.0, Common Public Radio Interface (CPRI); Interface Specification, October 9, 2015

In future mobile communication systems, the use of high frequencies such as millimeter waves is being studied due to the need for large-capacity communication. When using a high frequency such as millimeter wave, the transmission distance becomes short. Therefore, in future mobile communication systems, it is necessary to arrange small cells at high density. This means that the transmission / reception points of radio signals need to be arranged at high density. For example, RRH needs to be equipped with many functions such as a function of converting a digitally transmitted baseband signal into an analog baseband signal and a function of frequency-converting an analog baseband signal into a signal of a radio frequency band. , It is difficult to arrange RRH having such many functions at high density. Since the conventional base station apparatus that performs from the baseband signal processing to the transmission / reception processing of the radio signal has more functions than the RRH, it is difficult to arrange the conventional base station apparatus at a high density. Therefore, a configuration is being studied in which the base station device is divided into a device that performs baseband signal processing and radio frequency signal processing and a device that performs radio signal transmission / reception processing. As shown in FIG. 2, in the following description, a device having a function of performing baseband signal processing and radio frequency signal processing is referred to as a processing device, and a device having a function of transmitting / receiving radio signals is referred to as a radio device. And.

In a configuration in which the function of the base station device is divided into a processing device and a wireless device, a so-called radio overfiber (RoF) method is used for signal transmission between the processing device and the wireless device. FIG. 2 is a configuration diagram of a processing device and a wireless device in the downstream direction. The processing device includes a baseband signal processing unit and a radio frequency signal processing unit that perform baseband signal processing and radio frequency signal processing, and an optical modulation unit. The optical modulation unit modulates an optical carrier wave (continuous light) with a radio frequency signal output by a radio frequency signal processing unit to generate an optical modulation signal, and transmits the generated optical modulation signal to a wireless device. The photoelectric conversion unit of the wireless device extracts the radio frequency signal by photoelectric conversion of the received optical modulation signal, performs necessary processing such as amplification, and then outputs the radio frequency signal to the antenna. Then, the antenna transmits the radio frequency signal as a radio signal. In the upstream direction, the reverse processing is performed.

Even in a configuration in which the function of the base station device is divided into a processing device and a wireless device, when TDD is used, the timing at which the wireless device transmits and receives a wireless signal must be synchronized. Therefore, the processing device must transmit the optical modulation signal at a timing that is delayed by a delay time k earlier than the timing at which the corresponding wireless device transmits the wireless signal. Here, unlike the communication between BBU and RRH, which is digital transmission, RoF is analog transmission, and it is difficult to implement a protocol for measuring propagation delay, such as the CPRI protocol.

The present invention provides a technique for synchronizing the transmission timing of a radio signal in a mobile communication system using RoF.

According to one aspect of the present invention, a first base station apparatus having a processing apparatus, a radio apparatus that communicates with the processing apparatus in a radio overfiber manner, and a first cell provided by the first base station apparatus overlap. A mobile communication system including a second base station apparatus that provides a second cell having an area communicates with the second base station apparatus, and the user apparatus located in the first cell is described as described above. It is provided with a first notification means for notifying the transmission timing of a test signal having a frequency that can be received by the wireless device, and a second notification means for notifying the processing device of the transmission timing of the test signal notified to the user device . The wireless device transmits the test signal transmitted by the user device at the transmission timing to the processing device, and the processing device receives the transmission timing notified from the second notification means and the wireless device. It is characterized in that the reception timing of the test signal and the timing at which the processing device transmits a signal to the radio device are determined based on the reception timing .

According to the present invention, it is possible to synchronize the transmission timing of a radio signal in a mobile communication system using RoF.

It is explanatory drawing of the transmission timing of BBU in the configuration which divides a base station apparatus into BBU and RRH. The block diagram of the processing apparatus and the wireless apparatus by one Embodiment. The block diagram of the mobile communication system by one Embodiment. The sequence diagram of the measurement process of the delay time by one Embodiment.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiments are examples, and the present invention is not limited to the contents of the embodiments. Further, in each of the following figures, components not necessary for the description of the embodiment will be omitted from the drawings.

<First Embodiment>
FIG. 3 is a configuration diagram of a mobile communication system according to the present embodiment. The base station apparatus 4 provides the cell 41. In the present embodiment, the base station device 4 is a conventional base station device that performs all of baseband signal processing, radio frequency signal processing, and radio signal transmission / reception processing. As described above, in the processing device 2, in addition to the baseband signal processing unit and the radio frequency signal processing unit, an optical modulation unit that modulates an optical carrier wave with a signal in the radio frequency band in the downlink direction is provided in the uplink direction. It is equipped with a photoelectric conversion unit. Similarly, in addition to the antenna, the wireless device 3 includes a photoelectric conversion unit in the downlink direction and an optical modulation unit in the uplink direction. As shown in FIG. 3, the processing device 2 is connected to the wireless device 3 by an optical transmission line, and performs so-called RoF communication. The wireless device 3 provides the cell 31. In the present embodiment, a control device 1 is provided which is connected to the processing device 2 and the base station device 4 by a control line and controls the processing device 2 and the base station device 4. The frequency band of the radio signal transmitted / received by the base station device 4 is different from the frequency band of the radio signal transmitted / received by the radio device 3. The user apparatus (UE) 5 is configured to be able to communicate with the base station apparatus 4 and transmit signals in a frequency band that can be received by the wireless apparatus 3.

In the configuration of FIG. 3, it is assumed that the base station device 4 has already been used to provide the mobile communication service. That is, it is assumed that the base station apparatus 4 knows the reference timing for starting the transmission of the downlink radio signal in TDD, and starts transmitting the downlink radio signal at the reference timing. Further, in the present embodiment, the cell 31 provided by the wireless device 3 is included in the cell 41 provided by the base station device 4.

FIG. 4 is a flowchart of the delay time setting process for the processing device 2 according to the present embodiment. By this setting process, the processing device 2 measures the delay time until the optical signal transmitted by the processing device 2 is converted into a wireless signal in the wireless device 3 and transmitted. Then, the processing device 2 determines the timing at which the optical signal is transmitted to the wireless device 3 based on the reference timing and the delay time. It is assumed that the processing device 2 knows the reference timing by using, for example, GPS or the like. Further, the wireless device 3 receives only the wireless signal and does not transmit the wireless signal until the delay time is set in the corresponding processing device 2.

In this embodiment, UE 5 is used in the setting process. The UE 5 is used, for example, by a worker of the mobile communication system operator shown in FIG. 3 in the setting process. First, the processing device 2 notifies the control device 1 of the start in S1. The start notification is a signal requesting the start of the measurement of the delay time. When the control device 1 receives the start notification from the processing device 2, in S2, the control device 1 gives a measurement notification to the base station device 4 of the cell 41 including the cell 31 of the wireless device 3 corresponding to the processing device 2. The measurement notification includes information indicating the area of the cell 31.

On the other hand, the worker carries the UE 5 and moves into the cell 41. As a result, in S3, the UE 5 connects to the base station device 4. In addition, the worker starts the application installed in the UE 5 to perform the setting process. As a result, the UE 5 repeatedly notifies the base station apparatus 4 of the position information in S4. The UE 5 acquires the position information by, for example, GPS. Further, the UE 5 can show on the display that the position information is being transmitted. The worker carries the UE 5 and moves toward the cell 31. The timing for starting the application is arbitrary. That is, even if the application is started after moving into the cell 31 and the position information is transmitted to the base station device 4, the application is started before entering the cell 41 and the base station connected at that time is started. Location information may be transmitted to the device.

The base station apparatus 4 determines whether the UE 5 is in the cell 31 based on the position information repeatedly received from the UE 5 and the information indicating the area of the cell 31 received in S2. Then, when it is determined that the UE 5 is in the cell 31, the frequency and transmission timing of the test signal transmitted by the UE 5 are notified to the UE 5 in S5. This frequency is a frequency that can be received by the wireless device 3. Further, in S6, the base station apparatus 4 also notifies the processing apparatus 2 of the timing notified to the UE 5. The base station device 4 can communicate with the processing device 2 via, for example, the control device 1. Alternatively, the base station device 4 can directly communicate with a communication line connecting the base station device 4 and the processing device 2 (not shown). The UE 5 transmits a test signal of the notified frequency at the transmission timing notified from the base station apparatus 4 in S7. This test signal is received by the wireless device 3 and transmitted to the processing device 2. The processing device 2 determines in S8 the difference between the transmission timing notified in S6 and the reception timing in which the test signal is actually received in S7, and sets this as the delay time k. When the delay time k is determined, the processing device 2 notifies the control device 1 of the end of the measurement process in S9.

With the above configuration, an appropriate delay time can be set for the processing device 2. In the present embodiment, the base station device 4 is a conventional base station device that performs everything from base band signal processing to wireless signal transmission / reception processing, but it has already been used for providing communication services and is subject to delay time setting. As long as a signal having a frequency different from that of the wireless device 3 corresponding to the processing device 2 is transmitted / received, there is no limitation on the mode of the base station device 4. That is, as the base station device 4, the base station device divided into the processing device and the wireless device can be used, or the base station device divided into the BBU and the RRH can be used. Further, in the present embodiment, the cell 31 provided by the wireless device 3 corresponding to the processing device 2 for which the delay time is set is included in the cell 41 provided by the base station device 4, but the cell 31 and the cell 31 It suffices if the cell 41 has an overlapping area.

Further, in the present embodiment, the base station device 4 monitors the position of the UE 5, and when the UE 5 enters the cell 31, the UE 5 is notified of the frequency and transmission timing of the test signal, but the control device 1 may perform this. That is, the base station device 4 transmits the position information repeatedly transmitted by the UE 5 to the control device 1, the control device 1 monitors the position of the UE 5, and when the UE 5 enters the cell 31, the UE 5 via the base station device 4. It is also possible to notify the frequency and transmission timing of the test signal.

Further, in the present embodiment, an application for performing the setting process is installed in the UE 5, and when the worker starts the application, the UE 5 is notified at the time of transmission of the position information and the notified timing. Although it is assumed that the test signal of the frequency is transmitted, the present invention is not limited to such a configuration. For example, the UE is configured to periodically transmit the position information to the base station device 4 or the control device 1, and the base station device 4 or the control device 1 is in the cell 31 when the setting process is started. It is also possible to configure the test signal to be transmitted to any one of the UEs. Further, instead of the UE transmitting the position information, the base station apparatus 4 estimates the UE located in the cell 31 based on, for example, the received signal strength and the direction of the received signal, and the estimated UE of the UE. It is also possible to configure one of them to transmit a test signal.

Although the present embodiment has been described by taking the synchronization of the transmission / reception timing of the wireless signal in the TDD method as an example, the case where the synchronization of the transmission / reception timing of the wireless signal is necessary even in the FDD (Frequency Division Duplex) method. The present invention can be applied to the above.

Further, when the control device 1, the base station device 4 and the UE 5 according to the present invention are executed by the one or more processors of the device (or computer) having one or more processors, the device is referred to as the control device 1. , Can be realized by a computer program that operates as the base station device 4 or the UE 5. These computer programs are stored in a computer-readable storage medium or can be distributed over a network.

1: Control device, 2: Processing device, 3: Wireless device, 4: Base station device, 5: User device

Claims (7)

A first base station apparatus having a processing apparatus and a wireless apparatus communicating with the processing apparatus in a radio overfiber manner and providing a first cell, and a first base station apparatus.
A second base station apparatus that provides a second cell having an overlapping area with the first cell,
Is a mobile communication system with
A first notification means that communicates with the second base station device and notifies a user device in the first cell of the transmission timing of a test signal having a frequency that can be received by the wireless device.
A second notification means for notifying the processing device of the transmission timing of the test signal notified to the user device, and
Equipped with
The wireless device transmits the test signal transmitted by the user device at the transmission timing to the processing device.
The processing device determines the timing at which the processing device transmits a signal to the wireless device based on the transmission timing notified from the second notification means and the reception timing of the test signal received from the wireless device. A mobile communication system characterized by The mobile communication system according to claim 1, wherein the second base station apparatus includes the first notification means and the second notification means. A control device for controlling the first base station device and the second base station device is further provided.
The mobile communication system according to claim 1, wherein the control device includes the first notification means and the second notification means. The first notification means is characterized in that it determines whether or not the user device is in the first cell based on the position information of the user device that the user device repeatedly transmits to the second base station device. The mobile communication system according to any one of claims 1 to 3. The processing device is
The first processing means for baseband signal processing and
A second processing means that performs radio frequency signal processing,
An optical modulation means that modulates an optical carrier wave with a radio frequency signal output by the second processing means to generate an optical modulation signal, and an optical modulation means.
Equipped with
The mobile communication system according to any one of claims 1 to 4 , wherein the wireless device includes a photoelectric conversion means for performing photoelectric conversion of the optical modulation signal received from the processing device. The processing device of the first base station device having a processing device and a wireless device communicating by a radio overfiber method and providing a first cell.
A test signal having a frequency that can be received by the radio device, which is notified to the user device in the area of the first cell by the second base station device that provides the second cell having the overlap area with the first cell. The acquisition method to acquire the transmission timing and
A receiving means for receiving the test signal transmitted by the user device at the transmission timing via the wireless device, and
A determination means for determining the timing at which the processing device transmits a signal to the wireless device based on the transmission timing and the reception timing of the test signal.
A processing device characterized by being equipped with . A program comprising operating the processing apparatus as the processing apparatus according to claim 6, when executed by one or more processors of the processing apparatus .

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