JP6449707B2 - Baseband signal converter - Google Patents

Description

  The present disclosure relates to a communication technique between a base station that transmits / receives a radio signal and a baseband processing device that transmits / receives a baseband signal to / from the base station in a wireless communication network.

  At present, for flexible deployment of a radio communication network, a baseband signal is not generated and converted into a radio signal at a base station, but a base installed at a location different from the base station (RRH: Remote Radio Head). A configuration for generating a baseband signal in a band processing unit (BBU: BaseBand Unit) has been proposed. In this configuration, the baseband processing device generates a baseband signal by performing modulation based on transmission data, and transmits the generated baseband signal to a base station using a transmission path such as an optical fiber. The baseband signal is usually an analog signal, but in this configuration, the analog baseband signal is converted into a digital signal of a predetermined format so that it can be transmitted using a transmission line such as an optical fiber. The The base station converts a digital baseband signal received from the transmission path into an analog format, and then performs frequency conversion (up-conversion) and amplification processing and transmits the result as a radio signal to the mobile terminal. On the other hand, the base station performs amplification and frequency conversion (down conversion) of the radio signal received from the mobile terminal, and finally converts it into a digital baseband signal. The baseband signal is transmitted through a transmission line such as an optical fiber. Is transmitted to the baseband processing device, and the baseband processing device demodulates the received baseband signal.

  CPRI (registered trademark) (Common Public Radio Interface) and ORI (Open Radio Interface) are defined as standards for a transmission method between the baseband processing apparatus and the base station. However, these standards are based on the assumption that the baseband processing device and the base station are connected by a pair of optical fibers. In a mobile communication network including many base stations, each base station is used as a baseband processing device. The cost of laying the optical fiber to accommodate becomes a problem. For this reason, Patent Document 1 discloses a configuration in which one baseband processing device and a plurality of base stations are connected by a passive optical network (hereinafter referred to as PON: Passive Optical Network). In Patent Document 1, each base station accommodated in a PON occupies a pair of wavelengths using wavelength multiplexing. Non-Patent Document 1 discloses a configuration in which one baseband processing device and a plurality of base stations are connected by an Ethernet (registered trademark) network such as EPON (Ethernet PON). Further, Patent Document 2 discloses controlling the size of a jitter buffer in a configuration in which jitter generated in an asynchronous transmission network such as an Ethernet network is reduced by a jitter buffer.

JP, 2014-110574, A JP 2009-278212 A

Naoyashi Shibata, et al., “Examination of CPRI-Ethernet conversion transmission for TDM-PON accommodation in mobile optical network”, 2014 IEICE Communication Society Conference, B-8-15

  In the configuration of Patent Document 1, it is necessary to provide an optical transmission / reception unit corresponding to the number of base stations to be accommodated in the baseband processing apparatus, which increases costs. In the configuration of Non-Patent Document 1, it is only necessary to provide one optical transmission / reception unit in the baseband processing device. However, Non-Patent Document 1 describes the jitter generated in the asynchronous transmission network, and between the baseband processing device and the base station. No measures are disclosed about the maximum delay allowed.

  The present invention provides a conversion apparatus for transmitting a baseband signal through an asynchronous transmission network.

According to one aspect of the present invention, a converter for transmitting a baseband signal through an asynchronous transmission network includes buffer means for buffering data received from the asynchronous transmission network, and control for controlling a buffer size of the buffer means. And when the underflow occurs in any of the buffer means and the buffer means of the conversion device facing each other via the asynchronous transmission network , the control means includes a buffer size of the buffer means and as the total value of the buffer size of the buffer means before Symbol pair direction converting device is equal to or less than a predetermined value, and controlling the buffer size of said buffer means.

  The baseband signal can be transmitted through the asynchronous transmission network.

The block diagram of the base station side converter by one Embodiment. The block diagram of the processing apparatus side converter by one Embodiment. 6 is a timing chart of link establishment processing via an asynchronous transmission network according to an embodiment. The flowchart of the buffer size control process in the processor side converter by one Embodiment. The flowchart of the buffer size control process in the processor side converter by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for describing the embodiment are omitted from the drawings. Moreover, the following embodiment is an illustration and does not limit this invention to the content of embodiment.

  FIG. 1 is a configuration diagram of a conversion apparatus (hereinafter referred to as a base station side conversion apparatus) 1 according to the present embodiment installed on the base station (RRH) side, and FIG. 2 is on the baseband processing apparatus (BBU) side. It is a block diagram of the conversion apparatus (henceforth a processing apparatus side conversion apparatus) 2 by which this embodiment is installed. As shown in FIGS. 1 and 2, the base station side conversion device 1 and the processing device side conversion device 2 face each other via an asynchronous transmission network 3 and communicate with each other. The asynchronous transmission network 3 is a packet network such as Ethernet, for example. The base station side conversion device 1 is connected to the RRH 4, and the processing device side conversion device 2 is connected to the BBU 5. In the present embodiment, the BBU 5 and the RRH 4 transmit and receive baseband signals according to the CPRI standard, but may be baseband signals according to other standards. From BBU5 and RRH4, the presence of base station side conversion device 1, processing device side conversion device 2 and asynchronous transmission network 3 is not recognized, and it appears that BBU5 and RRH4 are connected by a baseband signal according to the CPRI standard. .

  The CPRI-R 21 of the processing device side conversion device 2 receives a baseband signal in accordance with the CPRI standard from the BBU 5, and the conversion unit 22 packetizes the baseband signal into a packet that is transmitted and received in the asynchronous transmission network 3, and packet-T 23 is The packet is transmitted to the asynchronous transmission network 3. The packet-R 27 receives a packet from the asynchronous transmission network 3 and stores it in the buffer unit 26. The conversion unit 25 takes out the packet stored in the buffer unit 26 and converts it into a baseband signal, and the CPRI-T 24 transmits the baseband signal to the BBU 5. The buffer unit 26 is provided to reduce jitter generated in the asynchronous transmission network 3. The control unit 28 controls each unit of the processing device side conversion device 2 such as control of the buffer size of the buffer unit 26. In addition, the control unit 28 generates a clock used in the processing device side conversion device 2 and distributes it to each unit. When the underflow occurs in the buffer unit 26 and the signal to be transmitted to the BBU 5 cannot be acquired, the idle generation unit 29 outputs the idle signal to the CPRI-T 24 and transmits it to the BBU 5.

  The CPRI-R11 of the base station side conversion device 1 receives a baseband signal in accordance with the CPRI standard from the RRH 4, and the conversion unit 12 packetizes the baseband signal into a packet to be transmitted / received in the asynchronous transmission network 3, and packet-T13 is The packet is transmitted to the asynchronous transmission network 3. The packet-R 17 receives the packet from the asynchronous transmission network 3 and stores it in the buffer unit 16. The conversion unit 15 takes out the packet stored in the buffer unit 16 and converts it into a baseband signal, and the CPRI-T 14 transmits the baseband signal to the RRH 4. The buffer unit 16 is provided to reduce jitter generated in the asynchronous transmission network 3. The control unit 18 controls each unit of the base station side conversion device 1 such as control of the buffer size of the buffer unit 16. In addition, the control unit 18 generates a clock used in the base station side conversion device 1 and distributes it to each unit. When the underflow occurs in the buffer unit 16 and the signal to be transmitted to the RRH 4 cannot be acquired, the idle generation unit 19 outputs the idle signal to the CPRI-T 14 and transmits it to the RRH 4.

  FIG. 3 is a timing chart of a procedure in which the processing device side conversion device 2 and the base station side conversion device 1 establish a link via the asynchronous transmission network 3. The control unit 28 transmits a link establishment request signal with the address of the base station side conversion device 1 set in advance as a destination. The link establishment request signal includes a time stamp that is the transmission time of the link establishment request in the control unit 28. The control unit 18 adjusts the time in the control unit 18 according to the time stamp included in the link establishment request signal, and transmits a response signal to the processing device side conversion device 2. The response signal also includes a time stamp that is the transmission time of the response signal. The control unit 28 calculates a round trip time (RTT) between the processing device side conversion device 2 and the base station side conversion device 1 based on the time until reception of the response signal.

  Further, the control unit 28 sets the initial sizes Tm and Ts of the buffer unit 26 and the buffer unit 16 based on the upper limit value of the RTT allowed between the BBU 5 and the RRH 4 and the RTT value measured by the processing of FIG. Ask. For example, if the upper limit value of RTT allowed between BBU5 and RRH4 is RTTmax, and the RTT value measured by the processing of FIG. 3 is RTTa, Tm = Ts = (RTTmax−RTTa) / 2. it can. Furthermore, considering the time required for other processing in the processing device side conversion device 2 and the base station side conversion device 1, the values of Tm and Ts are changed from (RTTmax−RTTa) / 2 to the processing device side conversion device 2 and the base. The value can also be reduced by the time required for other processing in the station side conversion device 1. The control unit 28 performs control so that the buffer size of the buffer unit 26 becomes Tm. Further, the control unit 28 transmits a response signal including information indicating the value of Ts and the transmission rate of the baseband signal to the base station side conversion device 1. The control unit 18 performs control so that the buffer size of the buffer unit 16 becomes Ts. Further, the interval between packets to be transmitted / received via the asynchronous transmission network 3 is determined based on the transmission rate of the baseband signal.

  For example, in an asynchronous transmission network using PON such as EPON, the processing is performed in the downstream direction, that is, in the upstream direction, that is, in the base station side conversion device 1 as compared with the conversion device 1 in the processing device side conversion device 2. The fluctuation of the transmission delay in the packet transmitted to the device side conversion device 2 is large. That is, an underflow is likely to occur in the buffer unit 26. If the size of the buffer unit 26 is increased in order to prevent underflow in the buffer unit 26, the round-trip propagation delay between the BBU 5 and the RRH 4 may not satisfy the necessary condition. In the present embodiment, the buffer sizes of the buffer unit 16 and the buffer unit 26 are changed based on the number of packets stored in the buffer unit 16 (hereinafter referred to as the queue size), and thereby, in the upstream direction. The buffer underflow is prevented, and the round-trip propagation delay between BBU5 and RRH4 is kept within the necessary condition.

  FIG. 4 is a flowchart of the buffer size control process executed by the control unit 28 in the present embodiment. Note that the control unit 28 repeatedly acquires, for example, periodically, queue size information indicating the queue size in the buffer unit 16 of the base station side conversion device 1 from the base station side conversion device 1. The acquisition of the queue size information is performed even when the base station side conversion device 1 autonomously notifies the processing device side conversion device 2 of transmission of the queue size information. The base station side conversion apparatus 1 may request the station side conversion apparatus 1 and notify the processing apparatus side conversion apparatus 2 as a response to the request. The control unit 28 stores the queue size of the buffer unit 16 in the past M times, and determines the minimum value among them. For example, assuming that the queue size of the buffer unit 16 at time t is Q (t), the control unit 28 performs the past M queue sizes Q (t), Q (t−1), and Q (t−2). ,..., Q (t−M + 1) is held, and the minimum value is Qmin.

  In S10, the control unit 28 determines whether an underflow has occurred in the buffer unit 26, and waits until an underflow occurs. When an underflow occurs in the buffer unit 26, that is, when the buffer unit 26 becomes empty, the control unit 28, in S11, performs buffering based on the minimum value Qmin of the past M queue sizes currently held. -The size change amount αQmin is obtained. Here, α is a coefficient greater than 0 and less than 1, and is set in the control unit 28 in advance. Then, in S12, the control unit 28 transmits a change request signal including information indicating αQmin, which is a reduction amount of the buffer size, to the base station side conversion device 1. When the control unit 18 reduces the size of the buffer unit 16 by the amount specified by the change request signal and changes the size, the control unit 18 notifies the processing device side conversion device 2 of the change response signal. When receiving the change response signal in S13, the control unit 28 increases the size of the buffer unit 26 by αQmin, which is an increase amount. In addition, the control part 28 resends a change request signal, when a change response signal is not received even if fixed time passes after transmission of a change request signal. Furthermore, if the control unit 28 does not receive the change response signal even if it transmits the change request signal a predetermined number of times, the control unit 28 stops the size change (S13 and S14).

  When the size of the buffer unit 26 is changed, the control unit 28 controls the idle generation unit 29 to transmit an idle signal toward the BBU 5 until a sufficient number of packets are stored in the buffer unit 26. For example, the transmission time of the idle signal can be Tm + αQ (t) × Tf. Here, Tf is a time corresponding to the packet transmission interval in the asynchronous transmission network necessary for securing the transmission rate of the baseband signal. That is, Tm + αQ (t) × Tf is a time for making the buffer unit 26 full. However, the transmission time of the idle signal may be a time equal to or less than Tm + αQ (t) × Tf, for example, a time that fills the buffer unit 26 by 2/3 or 1/2.

  In this embodiment, since the buffer unit 26 and the buffer unit 16 are changed while keeping the total size of the buffer unit 26 and the buffer unit 16 constant, the round-trip propagation delay between the BBU 5 and the RRH 4 satisfies the necessary condition. It will not disappear. Then, the sizes of the buffer unit 26 and the buffer unit 16 are determined on the basis of the number of packets stored in the buffer unit 16 for removing the jitter in the downstream direction with little fluctuation in propagation delay. With this configuration, underflow of the buffer unit 26 that removes jitter in the upstream direction can be suppressed.

  FIG. 5 is a flowchart of the buffer size control process executed by the control unit 28 in the present embodiment. Unlike FIG. 4, FIG. 5 is a process for dealing with an underflow generated in the buffer unit 16 of the base station side conversion device 1. When an underflow occurs in the buffer unit 16, the control unit 18 of the base station side conversion device 1 transmits a change request signal to the processing device side conversion device 2. The control unit 28 waits until a change request signal is received in S20. When the change request signal is received, the control unit 28 obtains a buffer size change amount βRmin based on the minimum value Rmin of the past M queue sizes currently held in S21. Here, the queue size is the queue size of the buffer unit 26. Β is a coefficient greater than 0 and less than 1, and is set in the control unit 28 in advance. In step S22, the control unit 28 transmits a change request signal including information indicating βRmin, which is a buffer size to be increased, to the base station side conversion device 1. The control unit 18 increases the size of the buffer unit 16 by the amount specified by the change request signal, and when the size is changed, notifies the change response signal to the processing device side conversion device 2. When receiving the change response signal in S23, the control unit 28 decreases the size of the buffer unit 26 by βRmin. In addition, the control part 28 resends a change request signal, when a change response signal is not received even if fixed time passes after transmission of a change request signal. Further, if the control unit 28 does not receive the change response signal even if the change request signal is transmitted a predetermined number of times, the control unit 28 stops the size change (S23 and S24).

  When the size of the buffer unit 16 is changed, the control unit 18 controls the idle generation unit 19 to transmit an idle signal to the RRH 4 until a sufficient number of packets are stored in the buffer unit 16. The concept of the idle signal transmission time is the same as that of the processing device side conversion device 2.

  In the present embodiment, the RTT is measured when the processing device side conversion device 2 and the base station side conversion device 1 establish a link, and the initial sizes of the buffer unit 16 and the buffer unit 26 are determined based on the measured RTT. However, the present invention is not limited to such a configuration. For example, the user measures the RTT between the processing device side conversion device 2 and the base station side conversion device 1, determines the initial sizes of the buffer unit 16 and the buffer unit 26 based on the measurement values, and determines the processing device side conversion device 2 and the base unit. It may be configured to be set in the station side conversion device 1. In any case, the total value of the buffer sizes of the buffer unit 16 and the buffer unit 26 is maintained at the total value of the initial size. Further, the total buffer size of the buffer unit 16 and the buffer unit 26 may be controlled to be equal to or less than the total value of the initial sizes, that is, a predetermined value or less. For example, in this embodiment, since the control unit 28 determines the amount of change in the buffer unit 16 and the buffer unit 26, the total buffer size of the buffer unit 16 and the buffer unit 26 is equal to or less than the total initial size. Similarly, the change amount of the buffer unit 16 and the buffer unit 26 can be determined.

  Furthermore, in the present embodiment, the amount of change in the buffer size is determined based on the minimum value of the queue size of the buffer unit 16 or the buffer unit 26 in the past predetermined period, in the embodiment, but not the minimum value. A configuration may be used in which the amount of change in the buffer size is determined based on the average value, the maximum value, or the like. Further, in the present embodiment, the queue size is the number of packets stored in the buffer unit 16 or the buffer unit 26. However, the queue size is not the number of packets but the data stored in the buffer unit 16 or the buffer unit 26. The buffer size change amount may be determined based on the amount.

Claims (9)

A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control means for controlling the buffer size of the buffer means;
With
Wherein, in the the buffer means and the under flow in one of the buffer means converting apparatus of the counterpart via the asynchronous transmission network occurs, converter for countercurrent before Symbol pair and buffer size of said buffer means A conversion apparatus characterized in that the buffer size of the buffer means is controlled so that the total value of the buffer means and the buffer size is not more than a predetermined value. When an underflow occurs in the buffer means, the control means increases the buffer size of the buffer means, and notifies the opposite conversion device that the underflow has occurred in the buffer means of the opposite conversion device. Upon receiving from the device, the conversion device according to claim 1, characterized in that to reduce the buffer size of said buffer means. A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control means for controlling the buffer size of the buffer means;
With
If the control means decides to increase the buffer size of the buffer means by a first value, the control means decreases the buffer size by the first value to the conversion device facing through the asynchronous transmission network. And determining that the buffer size of the buffer means is to be decreased by a first value, the opposite conversion device is notified that the buffer size is to be increased by the first value. It is that conversion apparatus. 4. The conversion apparatus according to claim 3 , wherein the control unit changes a buffer size of the buffer unit by the first value when receiving a response signal to the notification. A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control for controlling the buffer size of the buffer means so that the total value of the buffer size of the buffer means and the buffer size of the buffer means in the conversion device opposed via the asynchronous transmission network is not more than a predetermined value. Means,
With
The control means receives the amount of data stored in the buffer means of the opposing conversion device from the opposing conversion apparatus, and increases the buffer size of the buffer means based on the data amount in the past predetermined period conversion device shall be the determining means determines the. A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control for controlling the buffer size of the buffer means so that the total value of the buffer size of the buffer means and the buffer size of the buffer means in the conversion device opposed via the asynchronous transmission network is not more than a predetermined value. Means,
With
Wherein, based on the amount of data the stored in the buffer means in the past predetermined period, conversion device shall be the determining means determines a decrease amount of the buffer size of said buffer means. A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control means for controlling the buffer size of the buffer means;
With
The control means changes the buffer size of the buffer means by a value notified by a change request signal received from the opposite conversion device via the asynchronous transmission network, and when an underflow occurs in the buffer means, Notifying the occurrence of the underflow to the opposite conversion device via the asynchronous transmission network,
A conversion apparatus characterized in that the total value of the buffer size of the buffer means and the buffer size of the buffer means in the conversion apparatus opposed via the asynchronous transmission network is equal to or less than a predetermined value. When underflow occurs in the buffer means, the buffer size of the buffer means is increased, and when underflow occurs in the buffer means of the opposing converter, the buffer size of the buffer means is decreased. The conversion device according to claim 7 . A conversion device for transmitting a baseband signal through an asynchronous transmission network,
Buffer means for buffering data received from the asynchronous transmission network;
Control means for controlling the buffer size of the buffer means;
With
The control means changes the buffer size of the buffer means by a value notified by a change request signal received from the opposite conversion device via the asynchronous transmission network, and sets the amount of data stored in the buffer means. Repeatedly notify the opposing conversion device,
The opposing conversion device determines a reduction amount of the buffer size of the buffer means based on the data amount in the past predetermined period ,
Conversion device you wherein the total value of the buffer size of the buffer means in the conversion apparatus of the counterpart through the buffer size and the asynchronous transmission network of said buffer means is less than a predetermined value.

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