JP2014099679A - Distributed radio communication base station system, signal processing device, radio device, and distributed radio communication base station system operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of required quantization bits although in the prior art, the number of quantization bits increased because a quantization step is set in conformity with a radio signal with a small amplitude value and a dynamic range is set in conformity with a radio signal with a large amplitude value.SOLUTION: A distributed radio communication base station system of the invention divides a radio signal into multiple radio signals, matches required quantization steps and dynamic ranges by adjusting the amplitude of the divided radio signals such that all of it will be the same, or determines a required quantization step and a dynamic range per divided radio signal, and thereby reduces the number of required quantization bits.

Description

  In a cellular system, in order to improve the degree of freedom of cell configuration, a base station function is physically separated by dividing it into a signal processing unit (BBU: Base Band Unit) and an RF unit (RRU: Remote Radio Unit). It is considered to do. At this time, the radio signal is transmitted through the optical fiber between the BBU and the RRU by the RoF (Radio over Fiber) technique. RoF technology can be broadly divided into analog RoF technology and digital RoF technology, but in recent years, digital RoF technology with excellent transmission quality has been actively studied, and the use formulation under the standard organizations such as CPRI (Common Public Radio Interface) (For example, refer nonpatent literature 1).

  One BBU can also 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 configuration, a configuration has been proposed in which the BBU 110 and the RRU 120 are connected by a PON (Passive Optical Network) as shown in FIG. In this system, the band between the OLT (Optical Line Terminal) 140 and the optical splitter is constant, but the band between the optical splitter and the ONU (Optical Network Unit) 150 can be changed according to the required band of the ONU 150. As a PON signal multiplexing method, TDM, WDM, FDM, or the like can be adopted. The application range of the present invention is not limited to FIG. 15, and can be applied when the BBU 110 accommodates one or more RRUs 120.

  The present invention relates to a required bandwidth reduction technique between a signal processing unit (BBU: Base Band Unit) and an RF unit (RRU: Remote Radio Unit).

  Hereinafter, the digital RoF transmission technology between the BBU 110 and the RRU 120 is referred to as a related technology. Also, a digital signal (IQ data) for each of the I axis and Q axis of the radio signal created by the BBU 110 is converted into an optical signal and transmitted to the RRU 120, and the optical signal received by the RRU 120 is converted into a radio signal to be transmitted to the terminal. The link to transmit is called a downlink. On the other hand, the radio modulation signal transmitted by the terminal is received by the RRU 120, the received radio signal is converted into an optical signal and transmitted to the BBU 110, and the optical signal received by the BBU 110 is converted into IQ data to demodulate the signal. Is called uplink.

FIG. 16 shows a device configuration example of the RRU 120 related to the present invention.
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, 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 RRU 120 performs downlink signal processing, an O / E converter 31 that converts an optical signal received from the BBU 110 into an electric signal, a frame converter 32 that extracts a control signal and IQ data from the received signal, and an IQ data A baseband filter unit (downlink) 33 that performs filtering processing on the 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 a transmission whose power is determined It has an amplifier 36 that amplifies power, a transmission / reception switching unit 12, and an antenna 11.

FIG. 17 shows a device configuration example of the BBU 110 related to the present invention.
For uplink signal processing, the BBU 110 demodulates the IQ data, 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 from a received signal, and the IQ data. A modem unit 43 is included.

  Further, for downlink signal processing, the BBU 110 converts a modulation / demodulation unit 43 that outputs IQ data of a radio modulation signal, a frame conversion unit 51 that multiplexes IQ data and a control signal, and converts an electrical signal into an optical signal for transmission. It has an E / O converter 52 and a control signal generator 50 that generates a control signal using a synchronization signal or the like.

  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. 18, the base station performs scheduling with a minimum period of 1 ms and allocates a radio band to each terminal. In FIG. 18, a white part indicates an unused resource block, and a shaded part indicates an allocated resource block.

  Radio band allocation is performed in resource block (RB) units, and 1 RB is 180 kHz and 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.

  Here, the transmission / reception power of the radio signal may be different for each radio band. For example, in the LTE system, fractional transmission power control is adopted as transmission power control in the uplink of a terminal, and a signal is transmitted at a higher power as the terminal is closer to the base station (the propagation loss between the base station and the terminal is smaller). For this reason, the RRU receives an addition of a plurality of radio signals having different powers.

CPRI, “CPRI Specification V4.2,” Sep. 2010, http: // www. cpri. info / spec. html

  As shown in FIG. 19, in digital RoF transmission, it is necessary to transmit an information amount proportional to the sampling frequency and the number of quantization bits. Here, as shown in FIG. 20, the RRU receives an addition of a plurality of radio signals having different powers in the uplink. When quantizing wireless signals with related technologies, it is necessary to increase the dynamic range according to the wireless signal with a large amplitude value, and to set the quantization step finely according to the wireless signal with a small amplitude value. Leads to an increase in the number of bits. For this reason, it leads to the increase of the required band between BBU-RRU.

  In the present invention, by adjusting the amplitude of the radio signal for each terminal equally, the dynamic range and the quantization step size necessary for the quantization of the radio signal of each terminal are made uniform or the required quantization step for each radio signal of the terminal. The purpose is to reduce the number of required quantization bits by determining the dynamic range.

  To achieve the above object, the distributed radio communication base station system of the present invention divides a radio signal into a plurality of radio signals, and adjusts the divided radio signals so that the amplitudes of all the radio signals are equal to each other. The required quantization bit number is reduced by matching the dynamic range or determining the required quantization step and dynamic range for each divided radio signal.

Specifically, in the distributed radio communication base station system, the function of a base station that transmits and receives radio signals to and from a plurality of radio terminals is assigned to a signal processing device (BBU: Base Band Unit) and a radio device (RRU: Remote Radio Unit). A distributed wireless communication base station system that is divided,
An optical fiber that connects the BBU and the RRU and transmits RoF (Radio over Fiber) as an optical signal between the BBU and the RRU;
A quantization bit number changing function for changing a quantization bit number of a digital signal to be RoF transmitted by the optical fiber from a predetermined value according to an amplitude value of the wireless signal of each wireless terminal;
A quantization bit number restoration function for restoring the number of quantization bits to the predetermined value when the optical signal is received from the optical fiber;
Is provided.

The operation method of the distributed radio communication base station system of the present invention is as follows:
An operation method of a distributed radio communication base station system in which a function of a base station that transmits and receives radio signals to and from a plurality of radio terminals is divided into BBU and RRU,
The BBU and the RRU are connected by an optical fiber, and RoF transmission is performed between the BBU and the RRU as an optical signal.
A quantization bit number changing procedure for changing a quantization bit number of a digital signal to be RoF transmitted by the optical fiber from a predetermined value according to an amplitude value of the radio signal;
A quantization bit number restoration procedure for restoring the number of quantization bits to the predetermined value when the optical signal is received from the optical fiber;
I do.

  The optical fiber is a PON (Passive Optical Network) system that connects one BBU and a plurality of RRUs.

  Moreover, the signal processing apparatus and radio apparatus which concern on this invention are BBU and RRU with which the said distributed radio | wireless communication base station system is provided.

  The quantization bit number changing function of the distributed wireless communication base station system according to the present invention amplifies and adds the maximum amplitude of each wireless terminal so that the number of quantization bits of the digital signal is increased. Can be reduced.

  The quantization bit number changing function of the distributed radio communication base station system according to the present invention sets the dynamic range and the quantization step individually according to the maximum amplitude of the radio signal of each radio terminal, so that the optical signal The number of quantization bits can be reduced.

  The quantization bit number changing function of the distributed wireless communication base station system according to the present invention changes a sampling frequency of a digital signal to be RoF-transmitted by the optical fiber from a predetermined value according to an assignment state of the wireless signal. Can do.

  The above inventions can be combined as much as possible.

  According to the present invention, the dynamic range and quantization step size required for the quantization of the radio signal of each terminal are adjusted by adjusting the amplitude of the radio signal of each terminal equally, or the required quantum for each radio signal of the terminal. The required number of quantization bits can be reduced by determining the quantization step and the dynamic range.

1 is a diagram illustrating a wireless device according to Embodiment 1. FIG. It is a figure explaining the signal processing apparatus which concerns on Embodiment 1. FIG. It is a figure explaining the amplitude conversion part which concerns on Embodiment 1. FIG. It is a figure explaining the amplitude decompression | restoration part in the signal processing apparatus which concerns on Embodiment 1. FIG. FIG. 3 is a diagram illustrating an amplitude restoration unit in the wireless device according to the first embodiment. An example of operation | movement of the amplitude conversion part which concerns on Embodiment 1 is shown. 6 is a diagram illustrating a wireless device according to a second embodiment. FIG. It is a figure explaining the signal processing apparatus which concerns on Embodiment 2. FIG. It is a figure explaining the radio | wireless signal division part which concerns on Embodiment 2. FIG. It is a figure explaining the radio | wireless signal synthetic | combination part which concerns on Embodiment 2. FIG. An example of operation | movement of the radio | wireless signal division part which concerns on Embodiment 2 is shown. 6 is a diagram illustrating a wireless device according to a third embodiment. FIG. It is a figure explaining the radio | wireless signal division part which concerns on Embodiment 3. FIG. It is a figure explaining the radio | wireless signal synthetic | combination part which concerns on Embodiment 3. FIG. It is a figure explaining the structure of the radio | wireless apparatus and signal processing apparatus relevant to this invention. It is a figure explaining the radio | wireless apparatus relevant to this invention. It is a figure explaining the signal processing apparatus relevant to this invention. It is a figure explaining the radio | wireless band allocation method of a LTE system. It is a figure explaining operation | movement of the distributed radio | wireless communication base station system relevant to this invention. It is a figure explaining the subject of the related technology relevant to 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)
An example of the configuration of the RRU 120 when the present invention is applied is shown in FIG. For uplink signal processing, the RRU 120 amplifies the antenna 11 that transmits / receives a radio signal, the transmission / reception switching unit 12 that switches between transmission / reception, and the signal power of the received radio signal to a power that can be handled by the signal processing. An amplifier 21, a down-conversion unit 22 that down-converts a radio signal, an A / D conversion unit 23 that converts the down-converted analog signal into IQ data of a digital signal, and an amplitude conversion unit 236 that adjusts the amplitude of the IQ data A quantization bit number conversion unit 237 that converts the number of quantization bits with respect to the output of the amplitude conversion unit 236, a frame conversion unit 25 that multiplexes IQ data, a control signal, and amplitude information, and an electrical signal as an optical signal. It has an E / O conversion unit 26 for converting and transmitting.

  In addition, the RRU 120 has an O / E converter 31 that converts an optical signal received from the BBU 110 into an electrical signal, a frame converter 32 that extracts a control signal and IQ data from the received signal, and a control signal for downlink signal processing. A radio band allocation information (downlink) extraction unit 231 that extracts radio band allocation information from the radio band allocation information (uplink) extraction unit 232, an amplitude information (downlink) extraction unit 235 that extracts amplitude information of IQ data from the control signal, , A quantization bit number restoration unit 233 that returns the quantization bit number of IQ data to the original value, an amplitude restoration unit 234 that restores the amplitude of the IQ data output from the quantization bit number restoration unit 233, and IQ A D / A converter 34 that converts data into an analog signal, an up-converter 35 that up-converts the analog signal, and amplifies the power of the radio signal Having that amplifier 36.

  An example of the apparatus configuration of the BBU 110 when the present invention is applied is shown in FIG. For uplink signal processing, the BBU 110 includes 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, amplitude information, and IQ data from a received signal, and a quantum of IQ data. Quantization bit number restoration unit 243 for returning the number of quantization bits to the original value, amplitude restoration unit 244 for returning the amplitude of the IQ data output from the quantization bit number restoration unit 243 to the original value, and demodulation for the IQ data A modulation / demodulation unit 43 is provided.

  Further, for downlink signal processing, the BBU 110 includes a modulation / demodulation unit 43 that outputs IQ data of a modulation signal, an amplitude conversion unit 241 that adjusts the amplitude of the IQ data, and a quantization bit for the output of the amplitude conversion unit 241. Quantization bit number conversion unit 242 that converts numbers, frame conversion unit 51 that multiplexes IQ data, control signals, amplitude information, and radio band allocation information, and E / O conversion that converts electrical signals into optical signals and transmits them Part 52.

  FIG. 3 shows a configuration example of the amplitude converters 236 and 241. The wireless band allocation information indicates which wireless band is allocated to each terminal. Based on the radio band allocation information, the amplitude converters 236 and 241 calculate filter coefficients that divide the radio signal into radio signals for each terminal by the filter coefficient determination unit 252 and change the filter coefficient of each filter 251. To do. The amplitude detector 253 detects the maximum amplitude of each divided radio signal. The gain determination unit 254 determines a gain for each divided radio signal according to the maximum amplitude detected by the amplitude detection unit 253. The gain at this time is determined so that the maximum amplitudes of the divided radio signals are equal. The divided radio signals amplified by the gain determined by the gain determination unit 254 are added and output.

  Here, the amplitude converters 236 and 241 output the amplitude information to the frame converters 25 and 51. The amplitude information is obtained by multiplexing the amplitude value of each radio signal calculated by the amplitude detector 253. The frame conversion units 25 and 51 multiplex the amplitude information, IQ data, control signal, and radio band allocation information. Also, based on the channel quality information between the base station and the terminal and the transmission power information of the terminal, the base station calculates the amplitude of each divided radio signal and transmits this value from the BBU 110 to the RRU 120 as amplitude information. May be used. At this time, considering that the amplitude information includes an error, the amplitude information may be estimated to be somewhat large.

  FIG. 4 shows a configuration example of the amplitude restoration units 234 and 244. Based on the radio band allocation information, the amplitude restoration units 234 and 244 calculate a filter coefficient that divides the radio signal into radio signals for each terminal by the filter coefficient determination unit 263, and changes the filter coefficient of each filter 264. . The gain determination unit 262 determines a gain for returning the amplitude of each divided radio signal based on the input amplitude information. The divided radio signals amplified by the gain determined by the gain determination unit 262 are added together and output. The data separator 261 separates the amplitude information from the frame converters 32 and 42 into the amplitude information of the divided radio signals and outputs the separated information.

  Note that the frame converters 25 and 51 may multiplex the gain of each radio signal instead of the amplitude information. In this case, the data separation units 261 and 263 of the amplitude restoration units 234 and 244 output the gain of each divided radio signal to each gain determination unit 262.

  FIG. 5 shows a configuration example of the amplitude restoration units 234 and 244. Unlike FIG. 4, a filter coefficient determining unit 263 determines a filter coefficient having a filtering function for dividing a radio signal and an amplification function for restoring the amplitude of each divided radio signal. Perform filtering processing.

  When the present invention is applied, the number of quantization bits when IQ data is output by the A / D conversion unit 23 and the modem unit 43 is set to be sufficiently large. Thereafter, the quantization bit number conversion unit 237 reduces the number of quantization bits. IQ data output from the A / D conversion unit 23 and the modulation unit is a fixed point, the quantization bit conversion unit operates to convert the fixed point to a floating point, and the quantization bit restoration unit 294 converts the floating point to a fixed point. It is also possible to perform the operation of returning to. The radio signal division units 272 and 273 that divide the radio signal into a plurality of radio signals may divide the radio signal on the time axis, or may divide the radio signal on the frequency axis using FFT processing or the like. The operation according to the present invention may be performed for each I component / Q component.

  FIG. 6 shows an operation example of the amplitude converters 236 and 241. Amplitude converters 236 and 241 divide the radio signal into a plurality of radio signals, perform amplification so that the amplitudes of the divided radio signals are equal, add the divided radio signals, and add the number of quantization bits To reduce. As described above, the amplitude of the radio signal for each terminal is equal, and the dynamic range and quantization step size required for the quantization of these radio signals are the same. Compared with the case where the quantization step is set and the dynamic range is set in accordance with the radio signal having a large amplitude value, the required number of quantization bits is reduced, and the required bandwidth between the BBU 110 and the RRU 120 can be reduced. Further, the unit of division is not limited to dividing the signal for each terminal, but radio signals having similar amplitude values may be grouped into one group, and the signal may be divided for each group.

The sampling frequency S _a, N _demod quantization bit number necessary for demodulation _and the number of quantization bits required to extend the dynamic range and N _D, the amount of information sent by the RoF section when using the related method It is proportional to S _a (N _demod + N _D ). On the other hand, in the proposed method, the number of quantization bits for expanding the dynamic range is not required as compared with the related method, and the power is calculated in dB to equalize the amplitudes of k radio signals and add up to about k ^1/2 times. _{Therefore, the} amount of information proportional to S _a N _demod k ^1/2 is transmitted in the RoF section. Therefore, the wireless terminal is at the _{N demod + N D> N demod} k 1/2 to become the number of terminals, the amount of transmission information is reduced by the proposed scheme.

(Embodiment 2)
In the first embodiment, a wireless signal is divided into a plurality of wireless signals, and the divided wireless signals are added and transmitted. In Embodiment 2, a radio signal is divided into a plurality of radio signals, and each divided radio signal is transmitted individually.

  FIG. 7 shows a device configuration example of the RRU 120 when the present invention is applied. For uplink signal processing, the RRU 120 amplifies the antenna 11 that transmits / receives a radio signal, the transmission / reception switching unit 12 that switches between transmission / reception, and the signal power of the received radio signal to a power that can be handled by the signal processing. An amplifier 21, a down-conversion unit 22 that down-converts a radio signal, an A / D conversion unit 23 that converts the down-converted analog signal into IQ data, and a radio signal division unit that divides the IQ data into a plurality of radio signals 272, a frame conversion unit 25 that multiplexes IQ data and a control signal, and an E / O conversion unit 26 that converts an electrical signal into an optical signal and transmits the optical signal.

  In addition, the RRU 120 has an O / E converter 31 that converts an optical signal received from the BBU 110 into an electrical signal, a frame converter 32 that extracts a control signal and IQ data from the received signal, and a control signal for downlink signal processing. A wireless band allocation information (uplink) extraction unit 232 that extracts the wireless band allocation information from the radio signal, a radio signal synthesis unit 271 that combines IQ data divided into a plurality of radio signals and returns it to one radio signal, and IQ data A baseband filter unit (downstream) 33 that performs filtering processing on the D / A converter 34 that converts IQ data into an analog signal, an up-converter 35 that up-converts the analog signal, and amplifies the power of the radio signal An amplifier 36.

  FIG. 8 shows a device configuration example of the BBU 110 when the present invention is applied. The BBU 110 is divided into an O / E converter 41 that converts an optical signal into an electrical signal, a frame converter 42 that extracts a control signal and IQ data from a received signal, and a plurality of radio signals for uplink signal processing. A wireless signal combining unit 274 that combines the IQ data into a single wireless signal, and a modulation / demodulation unit 43 that demodulates the IQ data.

  Further, for downlink signal processing, the BBU 110 includes a modulation / demodulation unit 43 that outputs IQ data of a modulation signal, a radio signal division unit 273 that divides IQ data into a plurality of radio signals, IQ data, a control signal, and a radio band. It has a frame conversion unit 51 that multiplexes the allocation information, and an E / O conversion unit 52 that converts the electrical signal into an optical signal and transmits it.

  9 and 10 show configuration examples of the radio signal dividing units 272 and 273 and the radio signal combining units 271 and 274 when the radio signal is divided / synthesized on the time axis. The wireless band allocation information indicates which wireless band is allocated to each terminal.

  The radio signal dividing units 272 and 273 in FIG. 9 calculate a filter coefficient that divides the radio signal into radio signals for each terminal based on the radio band allocation information, and the filter coefficient determining unit 281 calculates the filter coefficient of each filter. Change the coefficient. Also, the quantization bit conversion unit 283 sets a quantization dynamic range and a quantization step for each divided radio signal, and converts the input signal according to the set parameters. The signals output from the quantized bit conversion unit 283 are multiplexed by the data multiplexing unit 284 and output.

  The radio signal synthesis units 271 and 274 in FIG. 10 separate and output the input signals. The quantized bit restoration unit 286 converts the dynamic range and quantization step of the input signal to the original values, and restores the signal before being input to the quantization bit conversion unit 283 of the wireless signal dividing units 272 and 273. . The adder 287 adds all the outputs of the quantized bit restoration unit 286 and outputs the result.

  When the present invention is applied, the IQ data output from the A / D conversion unit 23 and the modulation / demodulation unit 43 is a fixed point, and the quantization bit conversion unit 283 performs an operation of converting the fixed point to a floating point. The bit restoration unit 286 may perform an operation of returning the floating point to a fixed point. The radio signal division units 272 and 273 that divide the radio signal into a plurality of radio signals may divide the radio signal on the time axis, or may divide the radio signal on the frequency axis using FFT processing or the like. The operation according to the present invention can also be performed for each I component / Q component.

  FIG. 11 shows an operation example of the radio signal division units 272 and 273. The radio signal division units 272 and 273 divide the radio signal for each radio signal of the terminal on the time axis, and set a dynamic range and a quantization step for each of the divided radio signals. For example, the dynamic range is set larger than the amplitude value (power) of each divided radio signal, and the quantization step size is determined so that the quantization error hardly affects the signal quality. If the allowable value of the influence on the signal quality is unified for each divided radio signal, the same number of quantization bits is used for each divided radio signal.

The sampling frequency S _a, N _demod quantization bit number necessary for demodulation _and the number of quantization bits required to extend the dynamic range and N _D, the amount of information sent by the RoF section when using the related method It is proportional to S _a (N _demod + N _D ). On the other hand, in the proposed scheme, the number of quantization bits for expanding the dynamic range is not required compared to the related scheme, and the data needs to be divided and transmitted for each number of terminals k. _{Therefore, the} amount of information proportional to S _a N _demod k Are transmitted in the RoF section. Therefore, the wireless _terminal, when the number of terminals becomes _{N demod + N D> N demod} k, the amount of transmission information is reduced by the proposed scheme.

  The adder 287 adds the output signals from the filter 296. As described above, since the dynamic range and the quantization step can be determined for each wireless signal, the quantization step is set according to the wireless signal having a small amplitude value as in the related art, and the wireless signal having a large amplitude value is used. Compared with the case where the dynamic range is set according to the above, the required number of quantization bits is reduced, and the required bandwidth between the BBU 110 and the RRU 120 can be reduced.

(Embodiment 3)
The amount of transmission information can be reduced by reducing the sampling frequency for each divided radio signal. In the third embodiment, this method and the second embodiment are used in combination.

FIG. 12 shows the apparatus configuration of the RRU 120 of the third embodiment. The difference from the apparatus configuration of the RRU 120 of the second embodiment is that a radio band allocation information (downlink) extraction unit 231 is added, and the function of the baseband filter unit (downlink) 33 is added to the radio signal synthesis unit 271. The baseband filter unit (downstream) 33 is not provided.
The device configuration of the BBU 110 of the third embodiment is the same as the device configuration of the BBU 110 of the second embodiment.

  FIGS. 13 and 14 are configuration examples of the wireless signal dividing units 272 and 273 and the wireless signal combining units 271 and 274 according to the third embodiment. The difference between the radio signal dividing units 272 and 273 and the second embodiment in FIG. 13 is that a sampling frequency determining unit 291 and a sampling frequency converting unit 292 are added. The sampling frequency determination unit 291 determines a required sampling frequency for each radio signal divided based on the radio band allocation information, and the sampling frequency conversion unit 292 obtains the sampling frequency of the divided radio signal by the sampling frequency determination unit 291. Converted to a new value.

  The difference between the wireless signal synthesis units 271 and 274 and the second embodiment in FIG. 14 is that a sampling frequency determination unit 293, a sampling frequency restoration unit 286, a filter coefficient determination unit 295, and a filter 296 are added. Since the sampling frequency of each radio signal divided by the radio signal dividing units 272 and 273 is converted, the sampling frequency determining unit 293 determines the sampling frequency based on the radio band allocation information in the radio signal synthesizing units 271 and 274. The sampling frequency restoration unit 286 returns the sampling frequency of each divided radio signal to the original value. Since the aliasing component is generated by converting the sampling frequency, the filter coefficient determination unit 295 of the wireless signal synthesis units 271 and 274 calculates a filter coefficient that extracts the desired signal component and suppresses the power of the aliasing component. Then, based on the filter coefficient, the filter 296 performs a filtering process on each divided radio signal.

The sampling frequency f _s determined in the BBU 110 and the RRU 120 is arbitrary. The sampling frequency may be determined within a range where the aliasing signal component and the desired signal component do not overlap, for example, the frequency interval between the aliasing signal component and the desired signal component. The sampling frequency may be determined so that is separated by f _th or more. Here, it is assumed that the desired signal component and aliasing signal components exist apart frequency interval f _t. The filter 296 is present passband / transition zone / stopband but when retrieving desired signal components in the filtering process, the frequency band width of the transition zone is less than or equal to f _t, the power of the aliasing signal components in the stopband Can be suppressed. If the frequency bandwidth of the transition region is f _t or more, the desired signal component extracted by the filtering process, the power of the aliasing signal component will be included without being suppressed. Therefore, f _th may be determined in consideration of f _t of the filter 296 so that the desired signal component does not deteriorate.

  The present invention can be applied to the information communication industry.

11: Antenna 12: Transmission / reception switching unit 21, 36: Amplifier 22: Down-conversion unit 23: A / D conversion unit 24: Baseband filter unit (upstream)
25, 32, 42, 51: Frame conversion unit 26, 52: E / O conversion unit 31, 41: O / E conversion unit 33: Baseband filter unit (downlink)
34: D / A converter 43: Modulator / demodulator 50: Control signal generator 110: BBU
120: RRU
130: PON system 140: OLT
150: ONU
231: Radio band allocation information (downlink) extraction unit 232: Radio band allocation information (uplink) extraction units 233, 243, 286, 294: Quantization bit number restoration units 234, 244: Amplitude restoration unit 235: Amplitude information (downlink) Extraction units 236, 241: amplitude conversion units 237, 242, 283: quantization bit number conversion units 251, 264, 282, 296: filters 252, 263, 281, 295: filter coefficient determination unit 253: amplitude detection units 254, 262 : Gain determination units 255, 284: Data multiplexing units 256, 265, 287: Adders 261, 285: Data separation units 271, 274: Radio signal synthesis units 272, 273: Radio signal division unit 292: Sampling frequency conversion unit 291, 293: Sampling frequency determination unit

Claims (8)

A distributed radio communication base station system in which the function of a base station that transmits and receives radio signals to and from a plurality of radio terminals is divided into a signal processing device (BBU: Base Band Unit) and a radio device (RRU: Remote Radio Unit). ,
An optical fiber that connects the BBU and the RRU and transmits RoF (Radio over Fiber) as an optical signal between the BBU and the RRU;
A quantization bit number changing function for changing a quantization bit number of a digital signal to be RoF transmitted by the optical fiber from a predetermined value according to an amplitude value of the wireless signal of each wireless terminal;
A quantization bit number restoration function for restoring the number of quantization bits to the predetermined value when the optical signal is received from the optical fiber;
A distributed wireless communication base station system comprising:   The said quantization bit number change function reduces the quantization bit number of the said digital signal by amplifying and adding so that the maximum amplitude of each radio | wireless terminal may become fixed. Distributed wireless communication base station system.   The quantization bit number changing function reduces the number of quantization bits of the optical signal by individually setting a dynamic range and a quantization step according to the maximum amplitude of the wireless signal of each wireless terminal. The distributed wireless communication base station system according to claim 1.   4. The distributed type according to claim 3, wherein the quantization bit number changing function changes a sampling frequency of a digital signal to be RoF-transmitted through the optical fiber from a predetermined value according to an allocation state of the radio signal. Wireless communication base station system.   5. The distributed wireless communication base station system according to claim 1, wherein the optical fiber is a PON (Passive Optical Network) system that connects one BBU and a plurality of RRUs. 6.   The signal processing apparatus with which the distributed radio | wireless communication base station system in any one of Claim 1 to 5 is provided.   A wireless device provided in the distributed wireless communication base station system according to claim 1. An operation method of a distributed radio communication base station system in which a function of a base station that transmits and receives radio signals to and from a plurality of radio terminals is divided into BBU and RRU,
The BBU and the RRU are connected by an optical fiber, and RoF transmission is performed between the BBU and the RRU as an optical signal.
A quantization bit number changing procedure for changing a quantization bit number of a digital signal to be RoF transmitted by the optical fiber from a predetermined value according to an amplitude value of the radio signal;
A quantization bit number restoration procedure for restoring the number of quantization bits to the predetermined value when the optical signal is received from the optical fiber;
A method for operating a distributed radio communication base station system, characterized in that:

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