JP6023103B2 - Distributed wireless communication base station system and communication method - Google Patents

Description

  The present invention relates to a distributed radio communication base station system having a configuration in which the functions of a radio communication base station are divided into a signal processing unit and a radio communication unit and physically separated from each other, and a communication method therefor.

  In a cellular system, in order to improve the degree of freedom of cell configuration, the base station function is physically separated by dividing it into a signal processing unit (BBU: Base Band Unit) and an RF unit (RRH: Remote Radio Head). It is considered to do. At this time, the radio signal is transmitted between the BBU and RRH by the RoF (Radio over Fiber) technique. RoF technology can be broadly divided into analog RoF technology and digital RoF technology depending on the optical transmission method. Recently, digital RoF technology with excellent transmission quality has been actively studied, and under the standards organizations such as CPRI (Common Public Radio Interface). Specifications are being developed (see, for example, Non-Patent Document 1). In addition, a coaxial cable, an optical fiber, or the like is used as a connection medium between the BBU and RRH, but the transmission distance can be increased by connecting the optical fiber in particular.

  One BBU can accommodate a plurality of RRHs. As a result, the BBUs required for each RRH can be consolidated into one, and the operation / installation cost can be reduced. As an example of such a configuration, a configuration has been proposed in which BBU and RRH are connected by a PON (Passive Optical Network) system, as shown in FIG. As a signal multiplexing method of the PON, TDM (Time Division Multiplex), WDM (Wavelength Division Multiplex), FDM (Frequency Division Multiplex), or the like can be selected.

  In addition, even when one BBU transmits a signal to one RRH, when the RRH includes a plurality of antennas, a plurality of radio signals are multiplexed and transmitted between the BBU and the RRH. Become. As a signal multiplexing method in this case, TDM, WDM, FDM, or the like can be selected.

  In a cellular system such as LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access), a terminal needs a communication channel (wireless band) unique to the terminal. This allocation of the radio band is performed by the base station. Taking the LTE system as an example, as shown in FIG. 9, the base station performs scheduling with a minimum period of 1 ms and allocates a radio band to each terminal. Radio band allocation is performed in units of resource blocks (RBs), and 1 RB is composed of a frequency region of 180 kHz and a time region of 0.5 ms. When the system bandwidth is 20 MHz, 110 RBs exist on the frequency axis. In addition, 7 symbols are inserted into 1 RB assuming a normal cyclic prefix. On the other hand, the signal transmitted from the base station to the terminal includes not only user data for each terminal but also control information (scheduling information, ACK / NACK, etc.) and a reference signal for the terminal to perform channel estimation (transmitted for all terminals) Cell-specific reference signals, UE-specific reference signals transmitted to individual terminals, and the like, and synchronization signals for each terminal to synchronize with the base station.

  Hereinafter, the digital RoF transmission technology between BBU and RRH is referred to as related technology. Also, a digital signal (IQ data) for each I-axis and Q-axis of a radio signal created by BBU is converted to an optical signal and transmitted to RRH, and an optical signal received by RRH is converted to a radio signal and sent to a terminal. The link to transmit is called a downlink. On the other hand, a link that receives a radio modulated signal transmitted by a terminal by RRH, converts the received radio signal to an optical signal and transmits it to the BBU, converts the optical signal received by the BBU to IQ data, and demodulates the signal Is called uplink.

  FIG. 10 shows an example of the configuration of an RRH apparatus according to related technology. For uplink signal processing, the RRH 120 includes an antenna 11 for transmitting / receiving radio signals, a transmission / reception switching unit 12 for switching transmission / reception, and an amplifier that amplifies the signal power of the received radio signals to a level at which signal processing is possible. 21, a down-conversion unit 22 that down-converts the radio signal, an A / D conversion unit 23 that converts the down-converted analog signal into IQ data, and a baseband filter unit (uplink) that performs a filtering process on the IQ data ) 24, a frame conversion unit 25 that multiplexes IQ data and a control signal between BBU-RRH, and an E / O conversion unit 26 that converts an electrical signal into an optical signal and transmits the optical signal. The transmission / reception switching unit 12 is compatible with both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).

  Further, the RRH 120 performs downlink signal processing, and an O / E conversion unit 31 that converts an optical signal received from a BBU into an electrical signal, and a frame conversion unit 32 that extracts a control signal and IQ data between the BBU and RRH from the received signal. A baseband filter unit (downlink) 33 that performs filtering on IQ data, a D / A conversion unit 34 that converts IQ data into an analog signal, an up-conversion unit 35 that up-converts the analog signal, and power And an amplifier 36, a transmission / reception switching unit 12 and an antenna 11.

  FIG. 11 shows a device configuration example of the related art BBU. The BBU 110 uses a radio band allocation / coding rate / modulation scheme determining unit 90 that determines a radio band allocation / coding rate / modulation scheme for downlink signal processing, and user data and data based on the determined coding rate. An encoding and modulation unit 53-5 that performs FEC encoding / modulation on control information, a mapping unit 53-2 that maps the output of the encoding and modulation unit to a predetermined radio band, and an output of the mapping unit as time A time domain conversion unit 53-6 for converting the signal into a domain signal, a frame conversion unit 51 for multiplexing the control data between the IQ data output from the time domain conversion unit and the BBU-RRH, and an electrical signal for converting the signal into an optical signal. And an E / O conversion unit 52 for transmission. This configuration assumes OFDM communication, modulation refers to symbol mapping such as QPSK, 16QAM, etc., and the time domain conversion unit performs operations of IFFT and IDFT.

  Further, the BBU 110 performs an uplink signal processing, an O / E conversion unit 41 that converts an optical signal into an electrical signal, a frame conversion unit 42 that extracts a control signal and IQ data between BBU and RRH from a received signal, and IQ data. Is converted to a frequency domain signal, a demapping unit 43-2 that extracts each radio band signal from the frequency domain data, and returns each demapped signal to a time domain signal. It has a time domain conversion unit 43-7 and a decoding and demodulation unit 43-8 that performs decoding and demodulation on the time domain signal. This configuration assumes DFT-S-OFDM, the frequency domain transforming unit performs FFT or DFT, the time domain transforming unit operates IFFT or IDFT, and demodulation is performed for hard decision / symbol on symbols such as QPSK and 16QAM. Refers to the process of making a soft decision. A case where the uplink is OFDM communication is also conceivable, in which case there is no time domain conversion unit.

  Taking an example of transmitting a Long Term Evolution (LTE) signal using CPRI, a sampling frequency of 30.72 MHz is used for a system with a system bandwidth of 20 MHz, and digital sampling for each of the I axis and the Q axis. The number of quantization bits of 4 to 20 bits for the upstream signal and 8 to 20 bits for the downstream signal is applied. In the frame conversion unit, a control signal is inserted into 1/16 of the entire frame, and the signal is further transmitted after being 8B / 10B encoded.

  By using processing (compression processing) to reduce the amount of IQ data, the optical band between BBU and RRH can be used effectively. In the downlink, the BBU performs a process (decompression process) for compressing and transmitting IQ data and returning the IQ data compressed by the RRH to the original IQ data. As a result, the required bandwidth of the optical section can be reduced without substantially degrading the quality of the radio signal output from the RRH. Similarly, in the uplink, if the RRH compresses and transmits IQ data and the decompression process is performed on the IQ data in which the BBU is compressed, the quality of the radio signal received by the BBU is hardly degraded. The required bandwidth can be reduced.

CPRI, “CPRI Specification V5.0”, Sep. , 2011, http: // www. cpri. info / spec. html

  The base station allocates a radio band existing in the system bandwidth to each radio terminal and communicates with the radio terminal. Here, a frequency bandwidth that can be used for wireless transmission is defined as a system bandwidth.

  Not all radio bands that exist in the system bandwidth are always used. It is possible that the number of radio terminals belonging to the RRH is small, or the required transmission rate of each radio terminal is small, and radio signals exist only in a part of the radio bandwidth of the system bandwidth. In this case, in the related art, an excessive sampling frequency is used, leading to an increase in the required bandwidth of the optical section.

  Therefore, an object of the present invention is to provide a distributed radio communication base station system and a communication method that can reduce the required bandwidth between BBU and RRU in order to solve such an increase in the required bandwidth of the optical section.

Means to solve the problem

  For the above purpose, the present invention reduces the sampling bandwidth and reduces the required bandwidth of the optical section by reducing the system bandwidth in accordance with the amount of radio traffic between each BBU and RRH.

Specifically, in the distributed radio communication base station system according to the present invention, a base station function for transmitting and receiving radio signals to and from a radio terminal has one signal processing device (BBU: Base Band Unit) and one or more radios. A distributed radio communication base station system divided into devices (RRH: Remote Radio Head),
A PON (Passive Optical Network) system that connects one BBU and one or more RRHs, and transmits RoF (Radio over Fiber) as an optical signal between the BBU and the RRH;
A system bandwidth controller that determines a system bandwidth according to the amount of traffic between the BBU and the RRH;
A RoF transmission unit that samples the transmission signal at a sampling frequency determined by the system bandwidth determined by the system bandwidth control unit and transmits and receives the optical signal;
It is characterized by providing.

In addition, the communication method according to the present invention has a signal processing device (BBU: Base Band Unit) function and one or a plurality of wireless devices (RRH: Remote Radio Head), which function as a base station that transmits and receives radio signals to and from a radio terminal. A communication method of a distributed wireless communication base station system divided into
When one BBU and one or a plurality of RRHs are connected by a PON (Passive Optical Network) system and an optical signal is transmitted between the BBU and the RRH by RoF (Radio over Fiber),
A system bandwidth control procedure for determining a system bandwidth according to the amount of traffic between the BBU and the RRH;
A RoF transmission procedure for transmitting and receiving the optical signal by sampling a transmission signal at a sampling frequency determined by the system bandwidth determined by the system bandwidth control procedure;
It is characterized by performing.

  System bandwidth and sampling frequency are related. For example, in the case of LTE, if the system bandwidth is 20 MHz, the sampling frequency is 30.72 MHz, and if the system bandwidth is 10 MHz, the sampling frequency is 15.36 MHz. As described above, since the sampling frequency is changed by adjusting the system bandwidth, the required bandwidth of the optical section can be reduced. Therefore, the present invention can provide a distributed radio communication base station system and communication method that can reduce the required bandwidth of the optical section.

  In the present invention, the RRH has the following circuit configuration in the downstream.

The RoF transmission unit of the distributed wireless communication base station system according to the present invention, the RRH,
An expansion circuit that returns the sampling frequency of the downlink transmission signal after RoF transmission to a specified value based on the expansion information related to sampling notified from the BBU;
A baseband filter circuit for removing an alias signal generated when the decompression circuit returns the sampling frequency of the downlink transmission signal to a specified value;
A digital / analog conversion circuit for converting the downstream transmission signal output from the baseband filter circuit into an analog signal;
It is characterized by having.

  In the present invention, the upstream RRH has the following circuit configuration.

The RoF transmission unit of the distributed wireless communication base station system according to the present invention, the RRH,
An analog / digital conversion circuit that samples an analog signal at a predetermined sampling frequency to generate an upstream transmission signal;
A baseband filter circuit that determines a system bandwidth determined based on compression information related to sampling notified from the BBU, and passes the upstream transmission signal on the system bandwidth;
A compression circuit that changes a sampling frequency of the upstream signal based on the compression information;
It is characterized by having.

Meanwhile, the RoF transmission unit of the distributed radio communication base station system according to the present invention is:
The sampling frequency determined by the system bandwidth is changed based on radio band allocation information in which the frequency of a radio signal to be used is described,
The sampling frequency of the transmission signal after RoF transmission is returned to the sampling frequency determined by the system bandwidth.

Conversely, the BBU of the distributed wireless communication base station system according to the present invention is:
A wireless bandwidth allocation circuit that performs bandwidth allocation only in a wireless bandwidth existing in the system bandwidth determined by the system bandwidth controller;
The RoF transmission unit is
The sampling frequency determined by the system bandwidth is changed to the sampling frequency so that the radio signal allocated by the radio band allocation circuit can be RoF transmitted,
The sampling frequency of the transmission signal after RoF transmission is returned to the sampling frequency determined by the system bandwidth.

  According to the present invention, the sampling frequency can be changed according to the radio band allocation situation, and therefore the required band in the optical section can be further reduced.

  The system bandwidth control unit of the distributed wireless communication base station system according to the present invention has a first threshold value for an increase amount of traffic between the BBU and the RRH, and the increase amount is the first threshold value. The system bandwidth is increased when the frequency exceeds.

  According to the present invention, the sampling frequency can be adjusted in accordance with an increase in traffic volume.

  The system bandwidth control unit of the distributed radio communication base station system according to the present invention has a second threshold for a decrease amount of traffic between the BBU and the RRH, and the decrease amount is the second threshold value. The system bandwidth is reduced when exceeding.

  The present invention can provide a distributed wireless communication base station system and a communication method that can reduce the required bandwidth of an optical section.

It is a figure explaining RRH of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining BBU of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining the communication method which concerns on this invention. It is a figure explaining operation | movement of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining RRH of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining BBU of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining BBU of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining the structure of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining the radio | wireless band allocation method of a LTE system. It is a figure explaining RRH of the distributed radio | wireless communication base station system relevant to this invention. It is a figure explaining BBU of the distributed radio | wireless communication base station system relevant to this invention. It is a figure explaining operation | movement of the distributed radio | wireless communication base station system which concerns on this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are embodiments of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
The distributed wireless communication base station system of this embodiment is a distributed wireless communication base station system in which the function of a base station that transmits and receives wireless signals to and from a wireless terminal is divided into one BBU and one or more RRHs. And
A PON system that connects one BBU and one or a plurality of RRHs and transmits RoF between the BBUs and the RRHs using optical signals;
A system bandwidth controller that determines a system bandwidth according to the amount of traffic between the BBU and the RRH;
A RoF transmission unit that samples a transmission signal at a sampling frequency determined by a system bandwidth determined by a system bandwidth control unit and transmits and receives the optical signal;
Is provided.

FIG. 1 is an apparatus configuration example illustrating the RRH 120 of the present embodiment. RRH120 is
An analog / digital converter 23 that samples an analog signal at a specified sampling frequency to generate an upstream transmission signal;
A baseband filter unit 24-1 that determines a system bandwidth determined based on compression information related to sampling notified from the BBU, and passes the uplink transmission signal on the system bandwidth;
A compression unit 82 that changes a sampling frequency of the upstream signal based on the compression information;
Have

  Unlike the related art, the RRH 120 in FIG. 1 reduces the sampling frequency of IQ data based on the compression information (uplink) extraction unit 86 that extracts compression information and the notified compression information for uplink signal processing. A compression unit (upstream) 82 is included. Compared to the related art, the filter coefficient of the baseband filter unit (upstream) 24-1 is different, and the filtering process is performed so as to pass only the radio signal existing in the changed system bandwidth. Further, the functions of the baseband filter unit 24-1 and the compression unit 82 may be realized by a decimation filter.

RRH120 is
An expansion unit 81 that returns the sampling frequency of the downlink transmission signal after RoF transmission to a specified value based on the expansion information related to sampling notified from the BBU;
A baseband filter unit 33-1 for removing an alias signal generated when the decompression 81 returns the sampling frequency of the downlink transmission signal to a specified value;
A digital / analog conversion circuit 34 for converting the downstream transmission signal output from the baseband filter unit 33-1 into an analog signal;
Have

  The RRH 120 uses a decompression information (downlink) extraction unit 85 that extracts decompression information for downlink signal processing, and a decompression unit (downlink) that returns the sampling frequency of IQ data to the original sampling frequency based on the extracted decompression information. ) 81. Here, the “original sampling frequency” means a (maximum) system bandwidth preset in the distributed wireless communication system. In addition, the filter coefficient of the baseband filter unit (downlink) 33-1 is different from that of the related art, and the filtering process is performed so as to pass only the radio signal existing in the changed system bandwidth. The functions of the baseband filter unit 33-1 and the extension unit 81 may be realized by an interpolation filter.

  FIG. 2 is an example of a device configuration for explaining the BBU 110 of the present embodiment. The BBU 110 includes a wireless traffic amount calculation unit (up and down) 92 that calculates the amount of wireless traffic between each BBU and RRH, and a system bandwidth that determines a system bandwidth between each BBU and RRH according to the calculated amount of wireless traffic. A width control unit 93 and a compression / decompression control unit 91 that determines compression / decompression control parameters based on the determined system bandwidth.

  The compression / decompression control information determined by the compression / decompression control unit 91 is multiplexed with IQ data by the frame conversion unit 51 and transmitted to the RRH 120. The determined system bandwidth is notified to the wireless terminal as a control signal. For example, in LTE, system bandwidth information is transmitted using PBCH. Further, the changed system bandwidth is notified to a portion of the PHY layer / MAC layer / RLC layer where the information is required.

  In LTE, parameters for modulation signal creation and signal demodulation differ according to the system bandwidth. For example, when the system bandwidth is 20 MHz, a sampling frequency of 30.72 MHz and 2048 point IFFT are used. When the system bandwidth is 10 MHz, a sampling frequency of 15.36 MHz and 1024 point IFFT is used. In the present embodiment, the encoding / modulation unit 53-3 and the decoding / demodulation unit 43-8 change the parameters for modulation signal generation / demodulation according to the value determined by the system bandwidth control unit 93.

  That is, in the distributed radio number new base station system of this embodiment, the sampling frequency with respect to the system bandwidth is determined in advance, and the signal transmitted in the optical section is changed by changing the system bandwidth according to the amount of wireless traffic. Change the sampling frequency and adjust the required bandwidth of the light section. For example, if the current system bandwidth is larger than the amount of wireless traffic, the sampling frequency can be reduced by reducing the system bandwidth, and the required bandwidth in the optical section can be reduced. On the other hand, if the current system bandwidth is small with respect to the amount of radio traffic, the system bandwidth is expanded to increase the sampling frequency. Although the required bandwidth of the optical section increases, the required radio frequency bandwidth can be kept from exceeding the system bandwidth even if the radio traffic increases.

  The change period of the system bandwidth is arbitrary. Since PBCH is sent in a 40 ms cycle, the system bandwidth may be changed in a 40 ms cycle.

  The wireless traffic amount calculation unit 92 may calculate the ratio of the used wireless band to the system bandwidth, or may calculate the number of wireless terminals.

  The method of changing the system bandwidth according to the amount of radio traffic described in the present embodiment can be applied to only the uplink, only the downlink, or both the downlink and the uplink. When the method is applied to both the downlink and the uplink, the system bandwidth of the downlink and the uplink may be set separately.

  In the uplink, the PoF transmission unit includes a compression information extraction unit 86, an analog / digital conversion unit 23, a baseband filter unit 24-1, a compression unit 82, a frame conversion unit 25, an E / O conversion unit 26, and an O / O conversion unit 26. / E conversion unit 41, frame conversion unit 42, and compression / decompression control unit 91. The PoF transmission unit includes a compression / decompression control unit 91, a frame conversion unit 51, an E / O conversion unit 52, an O / E conversion unit 31, a frame conversion unit 32, an expansion unit 81, and a baseband filter unit 33 in the downlink. −1, a digital / analog conversion unit 34, and a decompression information extraction unit 85.

  FIG. 3 is an example of a flowchart for determining the system bandwidth. The system bandwidth control unit 93 has a first threshold value for the increase amount of traffic between the BBU 110 and the RRH 120, and a second threshold value for the decrease amount. When the increase amount exceeds the first threshold value, the system bandwidth control unit 93 Increase and decrease system bandwidth when the amount of decrease exceeds the second threshold.

  First, the wireless traffic amount calculation unit 92 calculates the wireless traffic amount between each BBU and RRH (step S01). Then, the system bandwidth control unit 93 determines the system bandwidth according to the amount of wireless traffic (step S02). The method is as follows: (i) the system bandwidth is increased if the increase in the current wireless traffic amount relative to the past wireless traffic amount is equal to or greater than the threshold Th1, and (ii) the current wireless traffic amount relative to the past wireless traffic amount. If the amount of decrease is equal to or less than the threshold Th2, the system bandwidth is reduced. (Iii) Otherwise, the system bandwidth is not changed. The operation (ii) may be omitted at this point. The past wireless traffic amount may be a traffic amount at an arbitrary point in time before the current state, or may be a wireless traffic amount one cycle before the system bandwidth change period.

  Thereafter, the system bandwidth controller 93 calculates the total value of the required bandwidth between BBU and RRH, and ends the process if the total value is equal to or less than the communication capacity of the optical section (YES in step S03), and determines the determined system. In addition to notifying the compression / decompression control unit 91 and the wireless terminal of the bandwidth, the encoding / modulation unit 53-5 and the decoding / demodulation unit 43-8 change parameters for modulation signal creation / demodulation.

  The system bandwidth control unit 93 calculates the total value of the required bandwidth between BBU and RRH, and if the total value exceeds the communication capacity of the optical section (No in step S03), any BBU is used until the communication capacity becomes equal to or less than the communication capacity. -Reduce system bandwidth between RRHs. At this time, as a selection criterion as to which BBU-RRH system bandwidth is to be reduced, the order in which the amount of radio traffic with respect to the system bandwidth is small or the order in which the priority of signals exchanged with the radio terminal is low may be used. It may be good, the current system bandwidth may be in descending order, the channel quality between the wireless terminal and the base station may be in ascending order, or random.

  The threshold Th1 needs to be set so as not to run out of bandwidth between each BBU-RRH until the next system bandwidth change timing. Therefore, if the system bandwidth is not changed, the probability of bandwidth shortage before the next system bandwidth change timing is calculated for each increase in the amount of radio traffic, and the next system bandwidth change timing The threshold value Th1 is set so that the probability that the band will be insufficient by the time becomes small. Further, the threshold Th1 may be for the amount of wireless traffic, not for the amount of increase in the amount of wireless traffic. In this case, the system bandwidth control unit 93 increases the system bandwidth if the amount of wireless traffic is equal to or greater than the threshold Th1.

  The threshold Th2 needs to be set in a range that does not cause a shortage of bandwidth between each BBU-RRH until the next system bandwidth change timing. Therefore, if the system bandwidth is changed, the probability of bandwidth shortage by the next system bandwidth change timing is calculated for each decrease in the amount of radio traffic, and the time until the next system bandwidth change timing is calculated. The threshold value Th2 is set so that the probability of insufficient bandwidth is reduced. Further, the threshold value Th2 is not for the amount of decrease in the radio traffic amount, but may be for the radio traffic amount. In this case, the system bandwidth control unit 93 reduces the system bandwidth if the amount of wireless traffic is equal to or less than the threshold value Th2.

  FIG. 4 shows an operation example of the first embodiment. There are three RRHs, and at the timing of changing the system bandwidth, RRH # 1 corresponds to (iii) of FIG. 3, RRH # 2 corresponds to (i) of FIG. 3, and RRH # 3 corresponds to FIG. Suppose that it corresponds to (ii). At this time, the system bandwidth of RRH # 1 does not change, the system bandwidth of RRH # 2 increases, and the system bandwidth of RRH # 3 decreases.

(Embodiment 2)
In the first embodiment, the input sampling frequency of the D / A converter 34 of the RRH 120 and the output sampling frequency of the A / D converter 23 are constant. In the present embodiment, it is assumed that the input sampling frequency of the D / A converter 34 of the RRH 120 and the output sampling frequency of the A / D converter 23 are variable.

  The apparatus configuration of the BBU of this embodiment is the same as that shown in FIG.

  FIG. 5 is a device configuration example of the RRH 120 of the present embodiment. Unlike FIG. 1, the decompression unit (downstream) 81 and the compression unit (upstream) 82 do not exist. In the present embodiment, the input sampling frequency of the D / A converter 34 varies according to the decompression control information, and the output sampling frequency of the A / D converter 23 varies according to the compression control information.

  For this reason, the distributed radio communication base station system of the present embodiment can obtain the same effects as the distributed radio communication base station system described in the first embodiment.

(Embodiment 3)
In the first embodiment, the sampling frequency is changed by changing the system bandwidth. In the present embodiment, in addition to the change of the sampling frequency described in the first embodiment, the sampling frequency is further reduced by compression / decompression based on the radio band allocation situation.

  The apparatus configuration of the RRH of this embodiment is the same as that shown in FIG.

  FIG. 6 is a device configuration example of the BBU 110 according to the present embodiment. In the present embodiment, the RoF transmission unit changes the sampling frequency determined by the system bandwidth based on the radio band allocation information in which the frequency of the radio signal to be used is described, and the transmission signal after RoF transmission The sampling frequency is returned to the sampling frequency determined by the system bandwidth.

  Unlike FIG. 2, the BBU 110 of FIG. 6 includes a compression unit 83 that reduces the sampling frequency of IQ data for the downlink and an expansion unit 84 that restores the sampling frequency of IQ data for the uplink. Here, “returning the sampling frequency” means returning to the sampling frequency corresponding to the system bandwidth determined by the system bandwidth control unit 93.

  Not all the radio bands existing in the changed system bandwidth are used. Therefore, the compression / decompression control unit 91 confirms the frequency position of the radio signal used based on the radio band allocation information, and determines the minimum sampling frequency within a range that hardly degrades the radio signal quality.

  In the downlink, the compression unit 83 converts the sampling frequency of the input IQ data into the sampling frequency notified from the compression / decompression control unit 91. In the RRH, the decompression information extraction unit 85 acquires the sampling frequency (compression / decompression control information) notified from the compression / decompression control unit 91, and based on the notification, the sampling frequency of the RoF-transmitted signal is decompressed. Return to the original at 81.

  In the uplink, in RRH, the compression information extraction unit 86 acquires the sampling frequency (compression / decompression control information) notified from the compression / decompression control unit 91, and the IQ data input by the compression unit 82 based on the notification. The sampling frequency is converted into the notified sampling frequency. The decompression unit 84 of the BBU 110 returns the sampling frequency of the RoF-transmitted signal to the sampling frequency corresponding to the current system bandwidth notified from the compression / decompression control unit 91.

  The distributed radio communication base station system of the present embodiment actively reduces the sampling frequency when the radio band does not use all the system bandwidth determined by the system bandwidth control unit 93. For this reason, the distributed radio communication base station system of the present embodiment can reduce the required bandwidth of the optical section more than the effect of the distributed radio communication base station system described in the first embodiment.

(Embodiment 4)
In the first embodiment, parameters for generating a modulation signal and demodulating a signal such as a sampling frequency are changed in accordance with the system bandwidth. In the present embodiment, the radio bandwidth used by the BBU is limited according to the system bandwidth.

  The apparatus configuration of the RRH of this embodiment is the same as that shown in FIG.

FIG. 7 is a device configuration example of the BBU 110 of the present embodiment. In this embodiment, the BBU 110 is
A wireless bandwidth allocation unit 90 that performs bandwidth allocation only in the wireless bandwidth existing in the system bandwidth determined by the system bandwidth control unit 93;
The RoF transmission unit changes the sampling frequency determined by the system bandwidth to the sampling frequency so that the radio signal assigned by the radio band assignment 90 can be RoF-transmitted, and the sampling frequency of the transmission signal after RoF transmission is changed to the system Return to the sampling frequency determined by the bandwidth.

  Unlike FIG. 6, the BBU 110 in FIG. 7 does not change parameters for modulation signal creation / demodulation based on the system bandwidth determined by the system bandwidth controller 93, and the determined system bandwidth has a radio bandwidth. The radio band allocation / coding rate / modulation method determination unit 90 limits the radio band allocation so that it can be settled. A specific example is shown in FIG. Assume that the system bandwidth is Bs in the initial state (FIG. 12A). Here, the system bandwidth controller 93 changes the system bandwidth to Bs / 2 based on the amount of wireless traffic (FIG. 12B). Since a wireless band that cannot be used is generated due to the narrowed system bandwidth, the wireless band allocating unit 90 reallocates the wireless band so as to be within the system bandwidth of Bs / 2 (FIG. 12C).

  Then, in the downlink, the compression / decompression control unit 91 determines the minimum sampling frequency necessary for transmitting the radio signal having the determined system bandwidth, and the compression unit 83 compresses the sampling frequency of the input IQ data. / The sampling frequency notified from the expansion control unit 91 is converted. In the RRH, the decompression information extraction unit 85 acquires the sampling frequency (compression / decompression control information) notified from the compression / decompression control unit 91, and based on the notification, the sampling frequency of the RoF-transmitted signal is decompressed. Return to the original at 81.

  In the uplink, the compression / decompression control unit 91 determines a minimum sampling frequency necessary for transmitting a radio signal having the determined system bandwidth. In RRH, the compression information extraction unit 86 acquires the sampling frequency (compression / decompression control information) notified from the compression / decompression control unit 91, and the sampling frequency of the IQ data input by the compression unit 82 based on the notification is obtained. Convert to the notified sampling frequency. The decompression unit 84 of the BBU 110 returns the sampling frequency of the RoF transmitted signal to the sampling frequency corresponding to the current system bandwidth notified from the compression / decompression control unit 91.

[Appendix]
The following describes the distributed wireless communication base station system of this embodiment.
<Issues>
In the related art, an excessive sampling frequency is used between BBU and RRH, which leads to an increase in required bandwidth in the optical section.
<Solution>
The present invention reduces the sampling bandwidth and reduces the required bandwidth of the optical section by reducing the system bandwidth according to the amount of radio traffic between each BBU and RRH.

(1):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH: Remote Radio Head), and the BBU and the RRH are connected by an optical fiber. A distributed radio communication base station system that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the downlink,
Parameters for radio traffic volume calculation unit for measuring radio traffic volume between each BBU-RRH, for determining a system bandwidth based on the radio traffic volume, and for generating a BBU modulation signal and demodulating the signal including a sampling frequency A system bandwidth control unit for changing the sampling frequency, an expansion unit for returning the changed sampling frequency to the original sampling frequency, and a baseband filter unit for removing aliasing generated when the expansion is performed Distributed wireless communication base station system.

(2):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH: Remote Radio Head), and the BBU and the RRH are connected by an optical fiber. A distributed radio communication base station system that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the uplink,
Parameters for radio traffic volume calculation unit for measuring radio traffic volume between each BBU-RRH, for determining a system bandwidth based on the radio traffic volume, and for generating a BBU modulation signal and demodulating the signal including a sampling frequency A system bandwidth control unit for changing the frequency, a baseband filter unit for passing a radio signal on the changed system bandwidth among the received signals, and a compression unit for changing the sampling frequency of IQ data to the changed sampling frequency And a distributed wireless communication base station system.

(3):
The system bandwidth control unit increases the system bandwidth between the BBU and RRH when the amount of wireless traffic increases and reaches a first threshold value. (1) (2) The system described in.

(4):
The system bandwidth control unit reduces the system bandwidth between the BBU and RRH when the wireless traffic amount decreases and reaches a second threshold value. ) System.

(5):
When the required bandwidth of the optical section becomes equal to or greater than the communication capacity of the optical section, the system bandwidth control unit is configured to connect at least one BBU-RRH so that the required bandwidth of the optical section is equal to or less than the communication capacity of the optical section. The system bandwidth according to (1) to (4) above, wherein the system bandwidth is reduced.

(6):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH), and the BBU and the RRH are connected by an optical fiber A distributed radio communication base station system that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the downlink,
A radio traffic amount calculation unit that measures the amount of radio traffic between each BBU and RRH, a system bandwidth control unit that determines a system bandwidth based on the radio traffic amount, and the changed system bandwidth A radio band allocating unit that performs band allocation using only the radio band, and a compression unit that reduces the sampling frequency of IQ data to a minimum necessary sampling frequency that allows only a radio signal existing in the changed system bandwidth to pass. A distributed radio communication base station system comprising: an expansion unit that returns the changed sampling frequency to the original sampling frequency; and a baseband filter unit that removes aliasing that occurs when the expansion is performed.

(7):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH: Remote Radio Head), and the BBU and the RRH are connected by an optical fiber. A distributed radio communication base station system that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the uplink,
A radio traffic amount calculation unit that measures the amount of radio traffic between each BBU and RRH, a system bandwidth control unit that determines a system bandwidth based on the radio traffic amount, and the changed system bandwidth A radio band allocating unit that performs band allocation using only a radio band, a baseband filter unit that passes a radio signal having a changed system bandwidth among received signals, and a system in which the sampling frequency of IQ data is changed A distributed type comprising: a compression unit that reduces only a radio signal existing in a bandwidth to a necessary minimum sampling frequency; and a decompression unit that restores the changed sampling frequency to the original sampling frequency. Wireless communication base station system.

(8):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH: Remote Radio Head), and the BBU and the RRH are connected by an optical fiber. A communication method of a distributed radio base station that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the downlink,
Measure the amount of radio traffic between each BBU-RRH, determine the system bandwidth based on the amount of radio traffic, change the parameters for BBU modulation signal creation and signal demodulation including the sampling frequency, A communication method for a distributed radio base station, wherein the changed sampling frequency is returned to the original sampling frequency, and aliasing generated when the sampling frequency is expanded is removed.

(9):
The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRH), and the BBU and the RRH are connected by an optical fiber A communication method of a distributed radio base station that transmits a transmission signal between the BBU and the RRH as a digital RoF (Radio over Fiber) using an optical signal,
In the uplink,
Measure the amount of radio traffic between each BBU-RRH, determine the system bandwidth based on the radio traffic amount, change the parameters for BBU modulation signal creation and signal demodulation including the sampling frequency, and receive A communication method for a distributed radio base station, comprising: passing a radio signal having a changed system bandwidth among signals and changing a sampling frequency of IQ data to the changed sampling frequency.

<Effect>
According to the present invention, since the system bandwidth is reduced and the sampling frequency is reduced, the required bandwidth between BBU and RRH can be reduced.

11: Antenna 12: Transmission / reception switching unit 21: Amplifier 22: Down-conversion unit 23: A / D conversion unit 24-1: Baseband filter unit (upstream)
25: Frame conversion unit 26: E / O conversion unit 31: O / E conversion unit 32: Frame conversion unit 33-1: Baseband filter unit (downlink)
34: D / A conversion unit 35: up-conversion unit 36: amplifier 41: O / E conversion unit 42: frame conversion unit 43-2: demapping unit 43-6: frequency domain conversion unit 43-7: time domain conversion unit 43-8: Decoding and demodulating unit 51: Frame converting unit 52: E / O converting unit 53-2: Mapping unit 53-5: Encoding and modulating unit 53-6: Time domain converting unit 81: Decompressing unit (downlink)
82: Compression unit (upstream)
85: Decompression information (downlink) extraction unit 86: Compression information (uplink) extraction unit 90: Radio band allocation / coding rate / modulation method determination unit, Radio band allocation unit 91: Compression / decompression control unit 92: Calculation of radio traffic amount Department (Down, Up)
93: System bandwidth control unit 101: Mobile terminal 110: BBU
120: RRU
130: PON system 301: Distributed wireless communication base station system 140: OLT
150: ONU
301: Distributed wireless communication base station system

Claims (8)

A distributed radio communication base in which the function of a base station that transmits and receives radio signals to and from a radio terminal is divided into one signal processing device (BBU) and one or more radio devices (RRH: Remote Radio Head) A station system,
A PON (Passive Optical Network) system that connects one BBU and one or more RRHs, and transmits RoF (Radio over Fiber) as an optical signal between the BBU and the RRH;
A system bandwidth controller that determines a system bandwidth according to the amount of traffic between the BBU and the RRH;
A RoF transmission unit that samples the transmission signal at a sampling frequency determined by the system bandwidth determined by the system bandwidth control unit and transmits and receives the optical signal;
A distributed wireless communication base station system comprising: The RoF transmitter is connected to the RRH.
An expansion circuit that returns the sampling frequency of the downlink transmission signal after RoF transmission to a specified value based on the expansion information related to sampling notified from the BBU;
A baseband filter circuit for removing an alias signal generated when the decompression circuit returns the sampling frequency of the downlink transmission signal to a specified value;
A digital / analog conversion circuit for converting the downstream transmission signal output from the baseband filter circuit into an analog signal;
The distributed wireless communication base station system according to claim 1, comprising: The RoF transmitter is connected to the RRH.
An analog / digital conversion circuit that samples an analog signal at a predetermined sampling frequency to generate an upstream transmission signal;
A baseband filter circuit that determines a system bandwidth determined based on compression information related to sampling notified from the BBU, and passes the upstream transmission signal on the system bandwidth;
A compression circuit that changes a sampling frequency of the upstream signal based on the compression information;
The distributed wireless communication base station system according to claim 1, comprising: The RoF transmission unit is
The sampling frequency determined by the system bandwidth is changed based on radio band allocation information in which the frequency of a radio signal to be used is described,
The distributed radio communication base station system according to claim 1, wherein the sampling frequency of the transmission signal after RoF transmission is returned to the sampling frequency determined by the system bandwidth. The BBU is
A wireless bandwidth allocation circuit that performs bandwidth allocation only in a wireless bandwidth existing in the system bandwidth determined by the system bandwidth controller;
The RoF transmission unit is
The sampling frequency determined by the system bandwidth is changed to the sampling frequency so that the radio signal allocated by the radio band allocation circuit can be RoF transmitted,
The distributed radio communication base station system according to claim 1, wherein the sampling frequency of the transmission signal after RoF transmission is returned to the sampling frequency determined by the system bandwidth. The system bandwidth controller is
The system bandwidth is increased by having a first threshold for an increase in traffic between the BBU and the RRH, and the system bandwidth is increased when the increase exceeds the first threshold. 6. The distributed wireless communication base station system according to any one of 1 to 5. The system bandwidth controller is
2. The system according to claim 1, further comprising a second threshold value for a decrease amount of traffic between the BBU and the RRH, and the system bandwidth is decreased when the decrease amount exceeds the second threshold value. 7. The distributed radio communication base station system according to any one of items 1 to 6. A distributed radio communication base in which the function of a base station that transmits and receives radio signals to and from a radio terminal is divided into one signal processing device (BBU) and one or more radio devices (RRH: Remote Radio Head) A communication method for a station system,
When one BBU and one or a plurality of RRHs are connected by a PON (Passive Optical Network) system and an optical signal is transmitted between the BBU and the RRH by RoF (Radio over Fiber),
A system bandwidth control procedure for determining a system bandwidth according to the amount of traffic between the BBU and the RRH;
A RoF transmission procedure for transmitting and receiving the optical signal by sampling a transmission signal at a sampling frequency determined by the system bandwidth determined by the system bandwidth control procedure;
A communication method characterized by:

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