JP6009983B2 - Distributed wireless communication base station system and communication method of distributed wireless communication base station system - 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 the cellular system, in order to improve the degree of freedom of the cell configuration, the base station function is divided physically into a signal processing unit (BBU: Base Band Unit) and an RF unit (RRU: Remote Radio Unit), and physically separated It is considered to do. At this time, the radio signal is transmitted between the BBU and the RRU by a 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 standardization such as CPRI (Common Public Radio Interface) [1]. The specification is being developed under the organization. As a connection medium between BBU and RRU, a coaxial cable, an optical fiber, or the like is used. In particular, the transmission distance can be increased by connecting with an optical fiber.

  One BBU can accommodate a plurality of RRUs. As a result, the BBUs required for each RRU can be consolidated into one, and the operation / installation cost can be reduced. As an example of such a form, as shown in FIG. 6, a form in which BBU-RRU is connected by a PON (Passive Optical Network) system has been proposed. As a PON signal multiplexing method, TDM (Time Division Multiplex), WDM (Wavelength Division Multiplex), FDM (Frequency Division Multiplex), or the like can be selected.

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

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

  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. 8, 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 (1 symbol including a cyclic prefix, 71.4 μs) 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 determination results, etc.), and a reference signal for the terminal to perform channel estimation (for all terminals) Cell-specific reference signals transmitted to the terminal, UE-specific reference signals transmitted to individual terminals, and the like, and synchronization signals for each terminal to synchronize with the base station.

  Channel quality information between the base station and the terminal estimated using a reference signal or the like is collected in the base station. The base station uses this channel quality information to perform scheduling for allocating a radio band with good channel quality to each terminal and to determine a modulation scheme / coding rate so that each terminal satisfies the required reception quality.

  The digital RoF transmission technology between BBU and RRU is a technology related to the present invention, and this type is hereinafter referred to as a related technology. Also, a digital signal (IQ data) for each I-axis and Q-axis of the radio signal created by BBU is converted into an optical signal and transmitted to the RRU, and the optical signal received by the RRU is converted into a radio signal and sent to the terminal. The link to transmit is called a downlink. On the other hand, a link that receives a radio modulated signal transmitted from a terminal by RRU, 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. 9 shows an example of an RRU apparatus configuration of related technology. For uplink signal processing, the RRU 120 includes an antenna 11 that transmits / receives a radio signal, a transmission / reception switching unit 12 that switches between transmission / reception, and an amplifier that amplifies the signal power of the received radio signal to a level that allows signal processing. 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-RRU, and an E / O conversion unit 26 that converts an electrical signal into an optical signal and transmits it. The transmission / reception switching unit 12 is compatible with both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).

  Further, the RRU 120 performs downlink signal processing, and an O / E converter 31 that converts an optical signal received from the BBU 110 into an electric signal, and a frame converter 32 that extracts a control signal and IQ data between the BBU and RRU 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 that amplifies the signal to a predetermined transmission power.

  The RRU 120 is divided into an RRU function unit 120a and an ONU function unit 150. The RRU function unit 120a includes a transmission / reception switching unit 12, an amplifier 21, a down-conversion unit 22, an A / D conversion unit 23, a baseband filter unit 24, a baseband filter unit 33, a D / A conversion unit 34, an up-conversion unit 35, And an amplifier 36. The ONU function unit 150 includes a frame conversion unit 25, an E / O conversion unit 26, an O / E conversion unit 31, and a frame conversion unit 32.

  An apparatus configuration example of the related art BBU 110 is shown in FIG. The BBU 110 includes a radio band allocation / coding rate / modulation scheme determining unit 90 that determines a radio band allocation / coding rate / modulation scheme based on channel quality information for downlink signal processing, and the determined coding FEC encoding unit 53-4 that performs error correction (FEC) encoding on user data and control information based on the rate, and a bit sequence of user data and control information based on the determined modulation scheme A primary modulation unit 53-3 for modulating the output, a mapping unit 53-2 for mapping the output of the primary modulation unit to a predetermined radio band, a secondary modulation unit 53-1 for secondary modulation of the primary modulation signal, and a secondary A frame conversion unit 51 that multiplexes IQ data output from the modulation unit and a control signal between BBU and RRU, and an E / O conversion that converts an electrical signal into an optical signal and transmits the optical signal Part 52. Here, the primary modulation which is processing from the FEC encoding unit 53-4 to the mapping unit 53-2 is symbol mapping such as QPSK or 16QAM. The secondary modulation, which is the process of the secondary modulation unit 53-1, can be considered as spreading for CDMA modulation and IFFT for OFDM modulation. Further, there may be a case where only the primary modulation exists without the secondary modulation.

  The BBU 110 also includes an O / E converter 41 that converts an optical signal into an electrical signal for uplink signal processing, a frame converter 42 that extracts a control signal and IQ data between the BBU and RRU from the received signal, and an IQ. A secondary demodulator 43-1 that performs secondary demodulation on the data, a demapping unit 43-2 that extracts a signal from a predetermined radio band of the secondary demodulated signal, and performs primary demodulation on the demapped signal Primary demodulator 43-3 for performing, FEC decoder 43-4 for performing FEC decoding on the primary demodulated signal, and channel quality information extracting unit for extracting channel quality information from a part of the demapped signal 43-5. Here, secondary demodulation refers to FFT processing when the secondary modulation unit 43-1 performs IFFT processing, and despreading processing when the secondary modulation unit 43-1 performs spreading processing. The primary demodulation, which is a process from the demapping unit 43-2 to the FEC decoding unit 43-4, refers to a process of performing a hard decision / soft decision on a symbol such as QPSK or 16QAM subjected to the primary modulation. Further, when there is no secondary modulation unit, there is no secondary demodulation unit.

  The BBU 110 is divided into a BBU function unit 110 a and an OLT function unit 140. The BBU function unit 110a secondarily modulates the primary modulation signal with the radio band allocation / coding rate / modulation method determination unit 90, the FEC encoding unit 53-4, the primary modulation unit 53-3, the mapping unit 53-2. A secondary modulation unit 53-1, a secondary demodulation unit 43-1, a demapping unit 43-2, a primary demodulation unit 43-3, an FEC decoding unit 43-4, and a channel quality information extraction unit 43-5 are included. The OLT function unit 140 includes a frame conversion unit 51, an E / O conversion unit 52, an O / E conversion unit 41, and a frame conversion unit 42.

  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. 8B / 10B encoding is an encoding process for converting 8 bits into 10 bits.

  In order to effectively use the bandwidth between BBU and RRU, a case of using processing (compression processing) for reducing the amount of information to be transmitted may be considered. For example, depending on the allocation status of the radio band, there may be no radio terminal belonging to the RRU. In this case, there is no need to transmit information between BBU and RRU. Therefore, the band between BBU and RRU can be effectively used by performing compression processing to stop signal transmission between BBU and RRU according to the allocation situation of the radio band. Also, radio signals are not always present over the system bandwidth. Depending on the allocation status of the radio band, a radio signal may exist only in a part of the system bandwidth. At this time, there is a possibility that the amount of transmission information can be reduced by reducing the sampling frequency so that the aliasing signal component hardly degrades the signal quality of the desired signal component. Therefore, the band between the BBU and the RRU can be effectively used by performing a compression process that reduces the value of the sampling frequency used between the BBU and the RRU in accordance with the allocation state of the radio band.

  By using DBA (Dynamic Bandwidth Allocation), an uplink band in the PON section can be dynamically allocated to each RRU. In the DBA, each ONU transmits the transmission buffer amount to the OLT, the data transmission time and time of each ONU is calculated from the buffer amount collected by the OLT, the calculated information is notified to each ONU, and each ONU is designated. Data is transmitted using the time zone specified for the time. As a result, the bandwidth allocated between BBU and RRU with little communication traffic can be reduced, the bandwidth allocated between BBU and RRU with much communication traffic can be increased, and the bandwidth of the optical access section can be used effectively. In such a system, even if the bandwidth of the PON section is set to be smaller than the total value of the maximum required bandwidth between each BBU-RRU, the bandwidth does not run out in most time.

  This is the same when the BBU performs digital RoF transmission to one RRU equipped with multiple antennas. When IQ data addressed to each antenna is individually compressed, the total required bandwidth between BBU and RRU is Since the average value is lowered, even if the bandwidth of the BBU-RRU section is set smaller than the total value of the maximum required bandwidth between each BBU-antenna, the bandwidth does not run out in most time.

  In BBU-RRU transmission assuming compression processing, traffic between BBU-RRU increases instantaneously, and the total required bandwidth between BBU-RRU is the maximum value (communication capacity) between BBU-RRU. May be exceeded. At this time, a part of the IQ data of the modulation signal cannot be transmitted. That is, as shown in FIG. 11, a signal in a certain time interval of the radio modulation signal cannot be transmitted. There are a plurality of wireless terminal signals on the frequency axis, and if there is a time during which signals cannot be transmitted as shown in FIG. 11, the related technology may not be able to correctly demodulate all wireless terminal signals. There is. In addition, there is another problem that the radio band is widened due to a sudden decrease in the amplitude value of a signal in a certain time section of the radio modulation signal, and spurious may occur.

  Therefore, in order to solve the above-described problem, the present invention is a distributed radio that can correctly demodulate a signal of an arbitrary radio terminal and prevent spurious generation even when the required bandwidth exceeds the communication capacity between BBU and RRU. It is an object of the present invention to provide a communication method for a communication base station system and a distributed radio communication base station system.

  In order to achieve the above object, the present invention suppresses the power of a radio signal in an arbitrary frequency band (applies frequency axis band limitation) to a signal transmitted between BBU and RRU, and reduces the sampling frequency. Thus, the required bandwidth is set to be equal to or less than the communication capacity between BBU and RRU.

Specifically, in the distributed radio communication base station system according to the present invention, the functions of the base station that transmits and receives radio signals to and from the radio terminal are a signal processing device (BBU: Base Band Unit) and a radio device (RRU: Remote Radio Unit). ), The BBU and the RRU are connected by an optical fiber, and a transmission signal between the BBU and the RRU is transmitted as an optical signal by RoF (Radio over Fiber). And
When the transmission amount of the transmission signal increases to reach a preset first threshold, a band limiting function that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases to reach a preset first threshold value, a sampling frequency changing function for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration function for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
It is characterized by providing.

Specifically, in the communication method of the distributed radio communication base station according to the present invention, the function of the base station that transmits and receives radio signals to and from a radio terminal is a signal processing device (BBU: Base Band Unit) and a radio device (RRU: Remote). Of a distributed radio communication base station that is divided into Radio Units and connects the BBU and the RRU with an optical fiber and transmits a transmission signal between the BBU and the RRU as an optical signal by RoF (Radio over Fiber). A communication method,
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a band limiting procedure that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a sampling frequency changing procedure for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration procedure for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
It is characterized by performing.

  The present invention reduces the sampling frequency after applying a band limitation on the frequency axis to a signal transmitted between BBU and RRU when the required bandwidth is likely to exceed the communication capacity between BBU and RRU. To do. Thereby, this invention can keep the required zone | band between BBU-RRU below communication capacity. When the present invention is applied to a wireless system in which the system bandwidth is divided into a plurality of parts on the frequency axis and the bandwidth is allocated to each terminal, as in an OFDM-based system, the signal of some wireless terminals is limited to limit the frequency band. Although the power is suppressed and transmission is not possible, it is possible to avoid the phenomenon that signals from other wireless terminals can be transmitted and all signals in a certain time interval as shown in FIG. 11 cannot be transmitted.

  Therefore, the present invention provides a distributed radio communication base station system and a distributed radio that can correctly demodulate a signal of an arbitrary radio terminal and prevent spurious even if the required bandwidth exceeds the communication capacity between BBU and RRU. A communication method for a communication base station system can be provided.

  The band limiting function and the sampling frequency changing function of the distributed wireless communication base station system according to the present invention are configured to transmit only a part of the frequency band of the transmission signal and reduce the sampling frequency from a predetermined value. When the transmission amount of the transmission signal decreases and reaches a preset second threshold, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value.

  In the communication method of the distributed radio communication base station system according to the present invention, the sampling frequency is lowered from a predetermined value by transmitting only a signal in a partial frequency band of the transmission signal in the band limiting procedure and the sampling frequency changing procedure. Then, when the transmission amount of the transmission signal decreases and reaches a preset second threshold, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value. .

  The present invention cancels the frequency band limitation and the sampling frequency reduction when the required band decreases and falls below the communication capacity between BBU and RRU. When there is a margin in the communication capacity between BBU and RRU, the frequency band limitation and the sampling frequency reduction are immediately released, and the signals of all wireless terminals can be transmitted.

  The sampling frequency changing function of the distributed radio communication base station system according to the present invention can grasp the transmission amount of the transmission signal based on radio band assignment information for assigning a radio band to the radio terminal.

  The communication method of the distributed radio communication base station system according to the present invention can grasp the transmission amount of the transmission signal based on radio band assignment information for assigning a radio band to the radio terminal in the sampling frequency changing procedure.

The sampling frequency changing function of a distributed wireless communication base station system according to the present invention can grasp the transmission amount of the transmission signal based on the cumulative value of the sampling frequency of each pre-Symbol remote RF unit.

Communication method for a distributed wireless communication base station system according to the present invention, at the sampling frequency change procedure, it is possible to grasp the transmission amount of the transmission signal based on the cumulative value of the sampling frequency of each pre-Symbol remote RF unit.

  The present invention provides a distributed wireless communication base station system and a distributed wireless communication base that can correctly demodulate a signal of an arbitrary wireless terminal and prevent spurious generation even when the required bandwidth exceeds the communication capacity between BBU and RRU. A station system communication method can be provided.

It is a figure explaining RRU with which the distributed radio | wireless communication base station system which concerns on this invention is provided. It is a figure explaining BBU with which the distributed radio | wireless communication base station system which concerns on this invention is provided. It is a figure explaining the operation example of the distributed radio | wireless communication base station system which concerns on this invention. It is a figure explaining the RRU side adapter with which the distributed radio | wireless communication base station system which concerns on this invention is provided. It is a figure explaining the BBU side adapter with which the distributed radio | wireless communication base station system which concerns on this invention is provided. 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 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 RRU with which a distributed radio communication base station system of related technology is provided. It is a figure explaining BBU with which the distributed radio | wireless communication base station system of related technology is provided. It is a figure explaining the subject of this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples 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)
In the distributed radio communication base station system according to the present embodiment, 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 (RRU: Remote Radio Unit). A distributed wireless communication base station system that connects the BBU and the RRU with an optical fiber and transmits a transmission signal between the BBU and the RRU as an optical signal by RoF (Radio over Fiber),
When the transmission amount of the transmission signal increases to reach a preset first threshold, a band limiting function that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases to reach a preset first threshold value, a sampling frequency changing function for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration function for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
It is characterized by providing.

In the communication method of the distributed radio communication base station system of the present embodiment, the function of the base station that transmits and receives radio signals to and from the radio terminal is changed to a signal processing device (BBU: Base Band Unit) and a radio device (RRU: Remote Radio Unit). A communication method of a distributed wireless communication base station that is divided and connects the BBU and the RRU with an optical fiber and transmits a transmission signal between the BBU and the RRU as an optical signal by RoF (Radio over Fiber). And
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a band limiting procedure that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a sampling frequency changing procedure for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration procedure for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
It is characterized by performing.

  FIG. 6 is a diagram for explaining the configuration of the distributed radio communication base station system 301 of the present embodiment. The distributed radio communication base station system 301 connects the BBU 110 and a plurality of RRUs 120 with a PON system 130.

Specifically, the distributed wireless communication base station system 301 connects one BBU 110 and a plurality of RRUs 120, and a PON system 130 that performs RoF transmission between the BBUs 110 and the RRU 120 using an optical signal;
An OLT (Optical) that is on the BBU side of the PON system 130 and converts the signal format handled by the BBU 110 and the signal format that can be transmitted by the PON system 130 to control transmission timing to avoid collision of optical signals in the PON system 130 Line Terminal) function unit 140;
An ONU (Optical) that is on the RRU side of the PON system 130, converts the signal format handled by the RRU 120 and the signal format that can be transmitted by the PON system 130, and transmits an upstream optical signal at a timing instructed by the OLT function unit 140. (Network Unit) function unit 150,
Is provided.

  For example, considering the case where a TDM-PON system such as GE-PON (IEEE802.3ah), 10G-EPON (IEEE802.3av), etc. is applied as the PON system 130, the BLT 110 is output from the OLT function unit 140 in the downlink. A function of mapping IQ data to an Ethernet (registered trademark) frame and transmitting it at a predetermined timing, and a function of extracting IQ data from an Ethernet (registered trademark) frame received in the uplink. On the other hand, the ONU function unit 150 is a function that extracts IQ data from an Ethernet (registered trademark) frame received in the downlink and maps IQ data output from the RRU 120 in the uplink to an Ethernet (registered trademark) frame. The function to transmit at the timing of.

  A device configuration example of the RRU 120 is shown in FIG. The RRU 120 is divided into an RRU function unit 120a and an ONU function unit 150. The RRU function unit 120a has the same configuration as that of the RRU 120a in FIG. 9; the decompression information (downstream) extraction unit 85, the compression information (upstream) extraction unit 86, the baseband filter unit (upstream) 24-1, the compression unit 82, and the decompression unit 81. , And a baseband filter unit 33-1. The decompression information (downlink) extraction unit 85 and the compression information (uplink) extraction unit 86 take out the compression / decompression information transmitted by the BBU 110 at the frame conversion unit 32. The baseband filter unit (upstream) 24-1 applies a frequency band limitation to the uplink signal based on the compression information. The compression unit 82 reduces the sampling frequency for the output signal of the baseband filter unit (upstream) 24-1 based on the compression information. The decompression unit 81 returns the sampling frequency of the IQ data converted on the BBU 110 side based on the decompression information to the original sampling frequency. The baseband filter unit 33-1 suppresses an alias signal (folding signal) component for the signal output from the expansion unit 81 based on the expansion information.

  The RRU function unit 120a of the related art also has a baseband filter unit (24, 33). The baseband filter unit 24-1 of the present embodiment has a function of limiting the frequency band to the function of the baseband filter unit 24. Further, the baseband filter unit 33-1 of the present embodiment has a function of suppressing the alias signal component added to the function of the baseband filter unit 33.

  The baseband filter unit 24-1 corresponds to the band limiting function for the uplink. The compression unit 82 corresponds to the sampling frequency changing function for the uplink. The decompression unit 81 and the baseband filter unit 33-1 correspond to the sampling frequency restoration function for the downlink.

  A device configuration example of the BBU 110 is shown in FIG. The BBU 110 is divided into a BBU function unit 110 a and an OLT function unit 140. The BBU function unit 110a further includes an expansion unit 84, a baseband filter unit 80-1, a compression unit 83, a required band calculation unit 92, and a compression / decompression control unit 91 in the configuration of the BBU function unit 110a of FIG.

  The required band calculation unit 92 performs downlink and uplink between BBU and RRU based on the radio band allocation information determined by the radio band allocation / coding rate / modulation scheme determination unit 90 for uplink and downlink signal processing. Calculate the required bandwidth for both. In addition, the compression / decompression control unit 91 has a first threshold based on the communication capacity between the BBU 110 and the RRU 120. The first threshold is set below the communication capacity. The compression / decompression control unit 91 compares the required bandwidth calculated by the required bandwidth calculation unit 92 with the first threshold value. When the required bandwidth reaches the first threshold value, the compression / decompression control unit 91 gives an instruction to limit the bandwidth and reduce the sampling frequency. Do. Specifically, the compression / decompression control unit 91 determines the sampling frequency to be reduced by the compression unit 83 based on the downlink required band calculated by the required band calculation unit 92 and the band limitation performed by the baseband filter unit 80-1. The sampling frequency to be reduced by the RRU 120 is determined based on the range and the required bandwidth of the uplink calculated by the required bandwidth calculation unit 92. The decompression unit 84 restores the sampling frequency based on the sampling frequency reduced by the RRU 120 determined by the compression / decompression control unit 91. The baseband filter unit 80-1 performs frequency band limitation on the signal output from the secondary modulation unit 53-1, based on the band limitation range determined by the compression / decompression control unit 91. The compression unit 83 reduces the sampling frequency of the output signal of the baseband filter unit 80-1 based on the sampling frequency determined by the compression / decompression control unit 91.

  The baseband filter unit 80-1 corresponds to the band limiting function for the downlink. The compression unit 83 corresponds to the sampling frequency changing function for the downlink. The decompression unit 84 corresponds to the sampling frequency restoration function for the uplink.

  The sampling frequency information determined by the compression / decompression control unit 91 is multiplexed by the frame conversion unit 51 and transmitted to the RRU function unit 120a. By receiving this sampling frequency information, the RRU 120 can determine whether or not the downlink sampling frequency is reduced and whether or not the uplink sampling frequency is reduced.

  Note that the band limitation and the sampling frequency reduction may be dynamically changed according to the required band. Further, the band limitation and the sampling frequency reduction may be determined for each symbol (in the example of FIG. 8, every 71.4 μs) or may be determined every integer multiple of the scheduling period.

  FIG. 3 is a diagram for explaining an operation example of the distributed radio communication base station system 301. The BBU 110 applies a frequency band limitation to the output signal (FIG. 3A) of the secondary modulation unit 53-1 by the baseband filter unit 80-1 (FIG. 3B). Similarly, the RRU 120 applies a frequency band limitation to the output signal of the A / D conversion unit 23 by the baseband filter unit 24-1. As a result, the signal power to some of the radio terminals and the signal power from the radio terminals are suppressed. However, since the used frequency bandwidth is reduced, the sampling frequency can be reduced by the compression units (82, 83). Further, the signal of the wireless terminal existing in the pass band of the filter can be correctly demodulated, and the quality is hardly deteriorated. Note that the signal to the wireless terminal and the signal from the wireless terminal whose power is suppressed by the frequency band restriction are subjected to retransmission processing later.

  Further, since the signal power in a part of the band on the frequency axis is suppressed as shown in FIG. 3, the transmission amount between the BBU 110 and the RRU 120 can be within the communication capacity, and a certain time interval as shown in FIG. It is possible to avoid that the IQ data cannot be transmitted. Therefore, the distributed radio communication base station system 301 can suppress spurious noises that are generated when the amplitude value is rapidly reduced without transmitting a part of the signal as in the related art.

  When there is a radio signal to which priority is added, the compression / decompression control unit 91 minimizes the influence on the signal with high priority (it is included in the frequency band through which the signal with high priority passes). To determine the bandwidth limit range. For example, it may be determined that a signal having a higher QoS (Quality of Service) order is included in the transmission band, or a modulation method signal that requires high throughput may be included in the transmission band. .

  In the distributed radio communication base station system according to the present embodiment, after the band limiting function and the sampling frequency changing function transmit only signals in a partial frequency band of the transmission signal and reduce the sampling frequency from a predetermined value, When the transmission amount of the transmission signal decreases and reaches a preset second threshold value, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value.

  In the communication method of the distributed wireless communication base station system of the present embodiment, the sampling frequency is reduced from a predetermined value by transmitting only a signal in a partial frequency band of the transmission signal in the band limiting procedure and the sampling frequency changing procedure. Then, when the transmission amount of the transmission signal decreases and reaches a preset second threshold, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value. .

  The required bandwidth for both downlink and uplink between BBU and RRU exceeds the communication capacity, and after the bandwidth restriction and sampling frequency reduction, the required bandwidth for both downlink and uplink between BBU and RRU decreases and falls below the communication capacity. In this case, it is necessary to recover the sampling frequency by releasing the band limitation. For this reason, the compression / decompression control unit 91 has a second threshold value based on the communication capacity between the BBU 110 and the RRU 120. The second threshold is set below the communication capacity and below the first threshold. Then, the compression / decompression control unit 91 compares the required bandwidth calculated by the required bandwidth calculation unit 92 with the second threshold value, and when the required bandwidth falls below the second threshold value, the band limitation and the sampling frequency reduction are performed. Instruct to cancel. Specifically, the compression / decompression control unit 91 issues an instruction to release the band restriction to the baseband filter unit 80-1 and issues an instruction to stop the reduction of the sampling frequency to the compression unit 83. Also, sampling frequency information indicating that the reduction of the sampling frequency is stopped is transmitted to the RRU function unit 120a. Further, the compression / decompression control unit 91 instructs the decompression unit 84 to stop restoring the sampling frequency.

(Embodiment 2)
In FIG. 6, the distributed radio communication base station system 301 in which the BBU 110 has the OLT function unit 140 and the RRU 120 has the ONU function unit 150 has been described, but the existing BBU / RRU / OLT / ONU may be used. Good. FIG. 7 is a diagram for explaining a distributed radio communication base station system 302 using existing BBU / RRU / OLT / ONU. The distributed wireless communication base station system 302 connects the existing BBU 111 and the existing OLT 220 and the existing RRU 121 and the existing ONU 240 by adapters (210, 230), respectively, and the OLT-ONU is connected by the PON system 130. Will be connected.

  The adapter function between the BBU and the OLT is a function that converts the downstream optical signal output from the BBU 111 into a signal that can be recognized by the input interface of the OLT, and a function that allows the input interface of the BBU 111 to recognize the upstream signal output from the OLT. It includes a function of converting into an optical signal and a function of compressing / decompressing a transmission signal between BBU and OLT.

  On the other hand, the adapter function between the ONU and RRU has the function of converting the downstream signal output from the ONU into an optical signal in a format that can be recognized by the input interface of the RRU 121, and the upstream optical signal output from the RRU 121 is recognized by the ONU input interface. It includes a function of converting the signal into a signal of a possible format and a function of compressing / decompressing a transmission signal between BBU-OLT.

  FIG. 4 is a diagram illustrating the RRU side adapter 230 of the present embodiment. The RRU side adapter 230 includes an expansion unit 81, a baseband filter unit 33-1, a baseband filter unit 24-1, a compression unit 82, a compression / decompression control unit 91a, and a required band calculation unit (upstream) 92a. Further, the RRU 121 has the same configuration as the RRU function unit 120a of FIG. 9, and the ONU 240 has the same configuration as the ONU function unit 150 of FIG.

  FIG. 5 is a diagram illustrating the BBU side adapter 210 of the present embodiment. The BBU side adapter 210 includes an expansion unit 84, a baseband filter unit 24, a baseband filter unit 80-1, a compression unit 83, a compression / decompression control unit 91b, and a required band calculation unit (downstream) 92b. Further, the BBU 111 has the same configuration as the BBU function unit 110a in FIG. 10, and the OLT 220 has the same configuration as the OLT function unit 140 in FIG.

In the first embodiment, the sampling frequency is determined based on the radio band allocation information, but there are other determination methods. The used frequency band information may be extracted from the IQ data of the radio signal to determine the sampling frequency.
Further, since the transmission amount is substantially proportional to the sampling frequency and the number of quantization bits (fixed value), the transmission amount can be estimated from the sampling frequency. For this reason, if the cumulative value of the sampling frequency of each RRU is controlled so as not to exceed a certain value, the total value of the required bandwidth between BBU and RRU can be kept below the communication capacity. For example, the BBU-side adapter 210 may be used as a central control station, and sampling frequency information between each BBU-RRU may be aggregated in the adapter 210 and the adapter 210 may instruct the RRU-side adapter 230 to reduce the sampling frequency.

  This embodiment employs the above method. The compression / decompression control units (91a, 91b) are configured to extract the frequency band information from the IQ data output from the RRU 121 and the BBU 111, respectively, and determine the sampling frequency. The compression / decompression control unit (91a, 91b) extracts the frequency band information from the IQ data as a method of checking the frequency bandwidth by performing an FFT process or the like, or demodulating the control signal to obtain the radio band allocation information. There is a way to extract. Further, in the case of the BBU side adapter 210, the wireless band allocation information is notified from the BBU 111 to the compression / decompression control unit 91b, the frequency band information is obtained from the information, and the compression / decompression process is performed. it can. When the control information is demodulated by the BBU side adapter and uplink and downlink radio band allocation information is extracted, compression / decompression parameters are determined and the required bandwidth is calculated based on the information, and the RRU side adapter reduces parameters and sampling frequency. It is good also as composition which notifies a command. In this case, it is not necessary to place a required bandwidth calculation unit on the RRU side.

  When the required bandwidth exceeds the communication capacity between BBU and RRU, the baseband filter unit (24-1, 80-1) is used for arbitrary IQ data between BBU and RRU as in the description of the first embodiment. The frequency band is limited by and the sampling frequency is reduced.

[Modification 1 of Embodiment 2]
When the BBU 111 and the RRU 121 exchange signals with an optical interface, O / E conversion and E / O conversion are separately required between the BBU 111 and the adapter 210 and between the adapter 230 and the RRU 121.

[Modification 2 of Embodiment 2]
When the signals input to and output from the BBU 111 and the RRU 121 are in a format in which the control signal and IQ data are time-multiplexed, such as a CPRI frame, compression processing may be performed by extracting only IQ data. As a method for extracting IQ data, synchronization between the BBU 111 and the adapter 210 and between the adapter 230 and the RRU 121 may be synchronized so that the position of the IQ data in the frame can be known.

The following describes the distributed wireless communication base station system of this embodiment.
<Issues>
In the related art, when the traffic between BBU and RRU increases instantaneously, the required bandwidth between BBU and RRU exceeds the communication capacity, and there is a possibility that the signals of all the wireless terminals cannot be demodulated correctly.

<Solution>
After limiting the band on the frequency axis for the signal transmitted between BBU and RRU, by reducing the sampling frequency, the required band between BBU and RRU is reduced below the communication capacity, and a part of the frequency band Wireless signals can be transmitted without quality degradation.

<Effect>
In the present embodiment, by limiting the frequency band to a radio signal and reducing the required band between BBU and RRU, it is possible to transmit a radio signal in a partial frequency band without quality degradation.

11: Antenna 12: Transmission / reception switching unit 21: Amplifier 22: Down-conversion unit 23: A / D conversion unit 24, 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, 33-1: Baseband filter unit (downlink)
34: D / A converter 35: Up-converter 36: Amplifier 41: O / E converter 42: Frame converter 43: Modulator / demodulator 43-1: Secondary demodulator 43-2: Demapper 43-3: Primary demodulation unit 43-4: FEC decoding unit 43-5: Channel quality information extraction unit 51: Frame conversion unit 53-1, secondary modulation unit 53-2: mapping unit 53-3: primary modulation unit 53-4: FEC encoding unit 52: E / O conversion unit 80-1: baseband filter unit 81: expansion unit 82: compression unit 83: compression unit 84: expansion unit 85: expansion information (downstream) extraction unit 86: compression information (upstream) ) Extraction unit 90: radio band allocation / coding rate / modulation method determination unit 91: compression / decompression control unit 91a: compression / decompression control unit 91b: compression / decompression control unit 92: required band calculation unit (downlink, uplink)
92a: Required bandwidth calculation unit (upstream)
92b: Required bandwidth calculation unit (downlink)
110, 111: BBU
110a: BBU function unit 120, 121: RRU
120a: RRU function unit 130: PON system 140: OLT function unit 150: ONU function unit 210: adapter 220: OLT
230: Adapter 240: ONU
301, 302: Distributed wireless communication base station system

Claims (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 unit (BBU: Base Band Unit) and a radio unit (RRU: Remote Radio Unit), and the BBU and the RRU are connected by an optical fiber. A distributed wireless communication base station system that transmits a transmission signal between the BBU and the RRU as an optical signal using RoF (Radio over Fiber),
When the transmission amount of the transmission signal increases to reach a preset first threshold, a band limiting function that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases to reach a preset first threshold value, a sampling frequency changing function for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration function for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
A distributed wireless communication base station system comprising:   The band limiting function and the sampling frequency changing function are set in advance by transmitting only a signal in a partial frequency band of the transmission signal and reducing the sampling frequency from a predetermined value, and then reducing the transmission amount of the transmission signal. 2. The distributed radio communication base station system according to claim 1, wherein when the second threshold value is reached, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value.   3. The distributed radio communication base station according to claim 1, wherein the sampling frequency changing function grasps a transmission amount of the transmission signal based on radio band allocation information for allocating a radio band to the radio terminal. system. Distributed wireless communication base station system according to claim 1 or 2, wherein the sampling frequency changing function is characterized by grasping the transmission amount of the transmission signal based on the cumulative value of the sampling frequency of each pre-Symbol remote RF unit. The function of a base station that transmits and receives radio signals to and from a radio terminal is divided into a signal processing unit (BBU: Base Band Unit) and a radio unit (RRU: Remote Radio Unit), and the BBU and the RRU are connected by an optical fiber. A communication method of a distributed radio communication base station that transmits a transmission signal between the BBU and the RRU as an optical signal using RoF (Radio over Fiber),
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a band limiting procedure that transmits only a part of the frequency band of the transmission signal; and
When the transmission amount of the transmission signal increases and reaches a preset first threshold, a sampling frequency changing procedure for reducing the sampling frequency of the transmission signal transmitted by the band limiting function from a predetermined value;
A sampling frequency restoration procedure for restoring the sampling frequency of the transmission signal to a predetermined value when the sampling frequency is reduced from the predetermined value when the transmission signal is received;
A communication method for a distributed radio communication base station, characterized in that:   In the band limiting procedure and the sampling frequency changing procedure, after passing only a part of the frequency band of the transmission signal and reducing the sampling frequency from a predetermined value, the transmission amount of the transmission signal is reduced and preset. 6. The distributed radio communication base station communication method according to claim 5, wherein when the second threshold value is reached, the band limitation of the transmission signal is released and the sampling frequency is restored to a predetermined value.   The distributed radio communication base station according to claim 5 or 6, wherein in the sampling frequency changing procedure, the transmission amount of the transmission signal is grasped based on radio band allocation information for allocating a radio band to the radio terminal. Communication method. In the sampling frequency change procedure, the communication of the distributed wireless communication base station according to claim 5 or 6, characterized in that to grasp the transmission amount of the transmission signal based on the cumulative value of the sampling frequency of each pre Symbol RRU Method.

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