WO2016185823A1 - 光通信システム及び光通信方法 - Google Patents
光通信システム及び光通信方法 Download PDFInfo
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- WO2016185823A1 WO2016185823A1 PCT/JP2016/061374 JP2016061374W WO2016185823A1 WO 2016185823 A1 WO2016185823 A1 WO 2016185823A1 JP 2016061374 W JP2016061374 W JP 2016061374W WO 2016185823 A1 WO2016185823 A1 WO 2016185823A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
- H04B10/25752—Optical arrangements for wireless networks
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
- H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
- H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
- H03M7/3068—Precoding preceding compression, e.g. Burrows-Wheeler transformation
- H03M7/3071—Prediction
- H03M7/3073—Time
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
- H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
- H03M7/40—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code
- H03M7/4031—Fixed length to variable length coding
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
- H04L69/04—Protocols for data compression, e.g. ROHC
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/69—Electrical arrangements in the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
- H04L25/40—Transmitting circuits; Receiving circuits
- H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
Definitions
- the present invention relates to digital RoF transmission (Radio over Fiber) technology.
- This application claims priority based on Japanese Patent Application No. 2015-101840 for which it applied to Japan on May 19, 2015, and uses the content here.
- BBU Base Band Unit
- RRH Remote Radio Head
- Non-Patent Document 1 A coaxial cable, an optical fiber, or the like is used as a connection medium between BBU and RRH.
- the transmission distance can be increased by connecting the BBU and RRH with an optical fiber.
- the downlink represents a communication path for radio waves transmitted from the BBU to the wireless terminal connected to the RRH via the RRH.
- the uplink represents a communication path of radio waves transmitted from the wireless terminal connected to the RRH to the BBU via the RRH.
- the BBU creates a digital signal for each I-axis and Q-axis of a radio signal (hereinafter referred to as “IQ data”), converts the created IQ data into an optical signal, and converts the optical signal through an optical fiber.
- IQ data a radio signal
- the RRH converts the received optical signal into a radio signal and transmits the converted radio signal to the radio terminal.
- the RRH receives a radio signal transmitted from a radio terminal, converts the received radio signal into an optical signal, and transmits the converted optical signal to the BBU via an optical fiber.
- the BBU demodulates the signal by converting the received optical signal into IQ data.
- FIG. 15 is a schematic block diagram illustrating a functional configuration of the RRH 500 at the time of digital RoF transmission.
- the RRH 500 includes an antenna 501, a transmission / reception switching unit 502, an amplifier 503, a down-conversion unit 504, an A / D conversion unit (Analog / Digital) 505, a baseband filter unit 506, a framing unit 507, and an E / O (Electric / Optic).
- a conversion unit 508, an O / E (Optic / Electric) conversion unit 509, a deframe unit 510, a baseband filter unit 511, a D / A conversion unit (Digital / Analog) 512, an up-conversion unit 513, and an amplifier 514 are provided.
- the antenna 501 transmits and receives radio signals.
- the transmission / reception switching unit 502 performs transmission / reception switching of the antenna 501.
- the amplifier 503 amplifies the signal power of the received radio signal to a level that allows signal processing.
- the down-conversion unit 504 down-converts the amplified radio signal to baseband.
- the A / D conversion unit 505 converts the down-converted radio signal (analog signal) into IQ data that is a digital signal.
- the baseband filter unit 506 performs a filtering process on the IQ data.
- the framing unit 507 forms a frame by multiplexing the IQ data after the filtering process and the control signal.
- the E / O conversion unit 508 converts a framed signal (hereinafter referred to as “frame signal”) (electrical signal) into an optical signal, and transmits the converted optical signal to the BBU via the optical fiber 550. To do.
- the O / E conversion unit 509 converts the optical signal received via the optical fiber 550 into a frame signal (electric signal).
- the deframing unit 510 extracts a control signal and IQ data from the frame signal.
- the baseband filter unit 511 performs a filtering process on the IQ data.
- the D / A converter 512 converts the IQ data after the filtering process into an analog signal.
- the up-conversion unit 513 up-converts the analog signal.
- the amplifier 514 amplifies the power of the analog signal to a predetermined transmission power.
- FIG. 16 is a schematic block diagram showing a functional configuration of the BBU 600 at the time of digital RoF transmission.
- the BBU 600 includes an O / E converter 601, a deframer 602, a modem unit 603, a framing unit 604, and an E / O converter 605.
- the O / E converter 601 converts an optical signal received via the optical fiber 650 into a frame signal (electric signal).
- the deframing unit 602 extracts a control signal and IQ data from the frame signal.
- the modem unit 603 restores the radio signal by demodulating the IQ data. Further, the modem unit 603 generates IQ data by modulating the radio signal.
- the framing unit 604 forms a frame by multiplexing the IQ data and the control signal.
- the E / O conversion unit 605 converts the frame signal (electric signal) into an optical signal, and transmits the converted optical signal to the RRH 500 via the optical fiber 650.
- Digital RoF transmission requires a very wide bandwidth in the optical fiber section.
- a radio signal of 2 ⁇ 2 MIMO (Multiple-Input and Multiple-Output) with a system bandwidth of 20 MHz is a maximum of 150 Mbps in a radio section.
- a CPRI link of option 3 (2.4576 Gbps) or higher is required. Therefore, in order to effectively use the optical band, application of a compression technique to digital RoF transmission is being studied.
- the compression techniques are roughly classified into lossy compression and lossless compression. Examples of lossy compression include a reduction in sampling frequency and a reduction in the number of quantization bits.
- Lossless compression includes the combined use of linear predictive coding and entropy coding. For example, when the transmission speed of the wireless section is increased, the required transmission band of the optical section increases, but if the required transmission band of the optical section is reduced by compression technology, the wireless section can be increased without changing the optical transceiver. It becomes possible to respond.
- Non-Patent Document 2 describes MPEG-4 ALS (Moving Picture Experts Group-4 Audio Lossless Coding) which is one of lossless compression techniques.
- FIG. 17 is a schematic block diagram showing a functional configuration of the RRH 500a when a compression technique is introduced during multiplex transmission.
- the RRH 500a includes an antenna 501, a transmission / reception switching unit 502, an amplifier 503, a down-conversion unit 504, an A / D conversion unit 505, a baseband filter unit 506, a compression unit 701, a framing unit 507a, an E / O conversion unit 508, an O / O An E conversion unit 509, a deframing unit 510, a decompression unit 702, a baseband filter unit 511a, a D / A conversion unit 512, an up-conversion unit 513, and an amplifier 514 are provided.
- the compression unit 701 compresses the IQ data after the filtering process.
- the framing unit 507a forms a frame by multiplexing the compressed IQ data and the control signal.
- the decompression unit 702 restores the IQ data by decompressing the compressed IQ data.
- the baseband filter unit 511a performs a filtering process on the restored IQ data.
- FIG. 18 is a schematic block diagram showing the functional configuration of the BBU 600a when a compression technique is introduced during multiplex transmission.
- the BBU 600 a includes an O / E converter 601, a deframer 602, a decompressor 801, a modem 603 a, a compressor 802, a framer 604 a, and an E / O converter 605.
- the decompression unit 801 restores IQ data by decompressing the compressed IQ data.
- the modem 603a reconstructs the radio signal by demodulating the reconstructed IQ data. Also, the modem unit 603a generates IQ data by modulating the radio signal.
- the compression unit 802 compresses IQ data.
- the framing unit 604a forms a frame by multiplexing the compressed IQ data and the control signal.
- Some compression techniques perform compression processing and decompression processing for each predetermined number of samples.
- a unit for performing compression processing is described as a frame, and a predetermined number of samples is described as a frame size.
- a value obtained by multiplying several sample points past a certain sample point by a coefficient and adding the multiplication result is used as a predicted value, and an error between the predicted value and a certain sample point. Is output. If the prediction accuracy is high, the amplitude value of the error signal is close to zero. Therefore, if the amplitude value having a higher appearance probability is transmitted with a smaller number of bits by entropy coding, the required bandwidth of the optical section can be reduced.
- the coefficient is determined for each frame, and is calculated so as to reduce the prediction error with respect to the IQ data of each frame.
- the LTE radio signal will be described.
- OFDM Orthogonal Frequency Division Multiplexing
- IFFT Inverse Fast Fourier Transform
- DFT-S-OFDM Discrete Fourier Transform-Spread OFDM
- a signal having a cyclic prefix added to a signal after IFFT having a predetermined size is periodically output as a time waveform.
- a signal after cyclic IFFT added with a cyclic prefix is referred to as an OFDM symbol, and is used without distinction between downlink and uplink.
- FIG. 19 shows the structure of a time slot in LTE.
- the normal cyclic prefix is shorter in size and more efficient in frequency utilization than the extended cyclic prefix. Therefore, since a normal cyclic prefix is normally used, the following description will be made taking a normal cyclic prefix as an example.
- FIG. 19 shows the structure of a time slot in LTE. In the example shown in FIG. 19, seven OFDM symbols are arranged in a 0.5 ms interval.
- the system bandwidth is 20 MHz
- the IFFT size is 2048
- the cyclic prefix (CP1) of the first OFDM symbol is 160 points
- the cyclic prefix (CP2) of the second to seventh OFDM symbols is 144 points.
- the OFDM symbol length is 2208 points for the first OFDM symbol and 2192 points for the second to seventh OFDM symbols.
- Non-Patent Document 3 describes a configuration related to an LTE frame.
- FIG. 20 is a diagram showing a compression rate for each frame when MPEG4-ALS is applied to I component data of a radio signal.
- the frame number represents the order of frames subjected to compression processing.
- the compression rate is a ratio of the data amount after compression to the original data amount.
- the radio signal is OFDM modulation, subcarrier spacing is 15 kHz, the number of subcarriers is 1200, 256QAM (Quadrature Amplitude Modulation) modulation, and the cyclic prefix is 160 samples (first OFDM symbol) or 144 samples (second OFDM symbol to seventh OFDM symbol). . That is, it is assumed that all radio bands are used for data transmission in an LTE downlink system with a system bandwidth of 20 MHz.
- the frame size was 548.
- (a) represents the compression rate when only the first OFDM symbol is included in the frame.
- (B) represents the compression rate when the first OFDM symbol and the second OFDM symbol are included in the frame.
- (C) represents the compression rate when only the second OFDM symbol is included in the frame.
- (D) represents the compression rate when the second OFDM symbol and the third OFDM symbol are included in the frame.
- (E) represents the compression rate when only the third OFDM symbol is included in the frame.
- (F) represents the compression rate when the third OFDM symbol and the fourth OFDM symbol are included in the frame.
- (G) represents the compression rate when only the fourth OFDM symbol is included in the frame.
- (H) represents the compression rate when the fourth OFDM symbol and the fifth OFDM symbol are included in the frame.
- (I) represents the compression rate when only the fifth OFDM symbol is included in the frame.
- (J) represents the compression rate when the fifth OFDM symbol and the sixth OFDM symbol are included in the frame.
- the compression rate when the compression process is performed without including a plurality of types of OFDM symbols is less than 0.7, but the compression process is performed with a plurality of types of OFDM symbols. In all cases, the compression ratio exceeds 0.7. That is, when the compression process is performed including a plurality of types of OFDM symbols, the compression rate is deteriorated as compared with the case where the compression process is performed within one type of OFDM symbol. This is thought to be due to the fact that the frequency accuracy is different for each OFDM symbol and the nature of the signal is different, so that the accuracy of prediction is reduced. As described above, the conventional technique has a problem in that the compression rate is deteriorated by performing compression processing including a plurality of types of OFDM symbols.
- an object of the present invention is to provide a technique capable of reducing deterioration in compression rate.
- One embodiment of the present invention includes a signal processing device having a function of a divided base station and a wireless device, and has a predetermined size by digital RoF (Radio) over Fiber) transmission between the signal processing device and the wireless device.
- An optical communication system that transmits a cyclic symbol sequence in which a cyclic prefix is added to a signal after IFFT (Inverse Fast Fourier Transform), each of the signal processing device and the wireless device including a transmitter and a receiver
- the transmitter is configured to acquire symbol information related to a start position of the symbol series and a length of each symbol constituting the symbol series, and to perform compression processing based on the acquired symbol information
- a compression size determination unit for determining a compression size for each symbol, and the symbol series in units of the determined compression size
- a compression unit that compresses, and the reception unit determines a decompression size for each symbol to be subjected to decompression processing of the symbol series, and a symbol in units of the determined decompression size
- An optical communication system comprising:
- the transmission unit further includes a compression rate measurement unit that measures a compression rate for each symbol, and the compression size determination unit has a predetermined statistical value of the measured compression rate being minimized.
- the position of the symbol may be acquired as the start position, and the compression size may be determined using the acquired start position and information regarding the length of each symbol.
- the transmission unit may further include a symbol information estimation unit that estimates the start position based on downlink or uplink IQ data.
- One embodiment of the present invention includes a signal processing device and a wireless device each having a divided base station function, and each of the signal processing device and the wireless device includes a transmission unit and a reception unit,
- An optical communication system that transmits a cyclic symbol sequence in which a cyclic prefix is added to a signal after IFFT (Inverse Fourier Transform) of a predetermined size by digital RoF (Radio over Fiber) transmission with the wireless device
- the transmitting unit acquires symbol information related to a start position of the symbol series and a length of each symbol constituting the symbol series, and performs compression processing based on the acquired symbol information.
- a compression size determination step for determining a compression size for each symbol to be performed, and the transmitter is determined.
- a compression step of compressing the symbol sequence in units of the compression size an expansion size determination step in which the reception unit determines an expansion size for each symbol to be subjected to the expansion processing of the symbol sequence; and the reception unit And an expansion step of expanding the symbol sequence by the determined expansion size unit.
- the present invention makes it possible to reduce the deterioration of the compression rate.
- an RRH and a BBU in an optical communication system including an RRH (wireless device) having a divided base station function and a BBU (signal processing device) are composed of a plurality of OFDM symbols (symbols).
- OFDM symbol information Information about the start position of each OFDM symbol and the length of each OFDM symbol.
- the RRH and BBU determine the frame size for each OFDM symbol to be subjected to compression processing based on the acquired OFDM symbol information, and perform the compression processing with the determined frame size.
- the RRH and BBU acquire OFDM symbol information (symbol information), determine the frame size for each OFDM symbol to be subjected to compression processing based on the acquired OFDM symbol information, and determine Perform compression processing at the frame size. Moreover, RRH and BBU determine the frame size for each OFDM symbol to be subjected to the decompression process based on the acquired OFDM symbol information, and perform the decompression process with the determined frame size.
- symbol information symbol information
- RRH and BBU determine the frame size for each OFDM symbol to be subjected to the decompression process based on the acquired OFDM symbol information, and perform the decompression process with the determined frame size.
- FIG. 1 is a schematic block diagram illustrating a functional configuration of the RRH 100 according to the first embodiment.
- FIG. 2 is a schematic block diagram showing the functional configuration of the BBU 200 in the first embodiment.
- the RRH 100 includes an antenna 101, a transmission / reception switching unit 102, an amplifier 103, a down-conversion unit 104, an A / D conversion unit 105, a baseband filter unit 106, a compression processing size determination unit 107, a compression unit 108, a framing unit 109, an E / D
- the antenna 101 transmits / receives a radio signal to / from a radio terminal connected to the RRH 100.
- the transmission / reception switching unit 102 performs transmission / reception switching of the antenna 101.
- the transmission / reception switching unit 102 can handle both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).
- FDD Frequency Division Duplex
- TDD Time Division Duplex
- the down-conversion unit 104 down-converts the radio signal to baseband.
- the A / D converter 105 converts the down-converted radio signal (analog signal) into IQ data that is a digital signal.
- the baseband filter unit 106 performs a filtering process on the IQ data. By this process, an OFDM symbol of a radio signal is generated.
- the compression processing size determination unit 107 determines the frame size (hereinafter referred to as “compression size”) of a frame to be subjected to compression processing based on the acquired OFDM symbol information.
- the frame is a unit for performing compression processing, and is configured by arranging IQ data by a predetermined number of samples in a time waveform, for example.
- the compressing unit 108 compresses the OFDM symbol in units of the compression size determined by the compression processing size determining unit 107 for each frame.
- the framing unit 109 generates a frame signal by multiplexing the compressed OFDM symbol and the control signal.
- the E / O conversion unit 110 converts the frame signal (electrical signal) into an optical signal, and transmits the converted optical signal to the BBU 200 via the optical fiber 150.
- the O / E converter 111 converts an optical signal received via the optical fiber 150 into a frame signal (electric signal).
- the deframing unit 112 extracts a control signal and a compressed OFDM symbol from the frame signal.
- the decompression processing size determination unit 113 determines a frame size (hereinafter referred to as “expansion size”) for performing the decompression processing based on the frame size acquired from the BBU 200.
- expansion size a frame size
- the compression unit of the BBU 200 adds the frame size to the beginning of the compressed data as a header and transmits it.
- the frame size is determined based on the header.
- a method of obtaining is conceivable. In the case of the LTE system, at least two frame sizes are sufficient, and at this time, the header may be 1 bit.
- the decompression size and the compression size are the same size.
- the decompression unit 114 decompresses the compressed OFDM symbol in units of the decompression size determined by the decompression processing size determination unit 113. Specifically, the decompression unit 114 decompresses the compressed OFDM symbol in units of the determined decompression size to restore it to an OFDM symbol.
- the baseband filter unit 115 performs a filtering process on the restored OFDM symbol.
- the D / A converter 116 converts the signal after the filtering process into an analog signal.
- the up-conversion unit 117 up-converts the analog signal.
- the amplifier 118 amplifies the power of the analog signal to a predetermined transmission power.
- the BBU 200 includes an O / E conversion unit 201, a deframing unit 202, an expansion processing size determination unit 203, an expansion unit 204, a modulation / demodulation unit 205, a compression processing size determination unit 206, a compression unit 207, a framing unit 208, and an E / O.
- a conversion unit 209 is provided.
- the O / E converter 201 converts an optical signal received via the optical fiber 250 into a frame signal (electric signal).
- the deframing unit 202 extracts a control signal and a multiplexed signal from the frame signal.
- the expansion process size determination unit 203 determines the expansion size based on the frame size acquired from the RRH 100. As a method for the expansion processing size determination unit 203 to acquire the expansion size, a method of acquiring the expansion size by a process similar to that of the expansion processing size determination unit 113 can be considered.
- the expansion unit 204 expands the compressed OFDM symbol in units of the expansion size determined by the expansion processing size determination unit 203. Specifically, the decompression unit 204 decompresses the compressed OFDM symbol in units of the determined decompression size to restore it to an OFDM symbol.
- the modem unit 205 restores the radio signal by demodulating the restored OFDM symbol. Further, the modem unit 205 outputs the IQ data of the radio signal to the compression processing size determination unit 206 and the compression unit 207.
- the compression processing size determination unit 206 determines the compression size based on the acquired OFDM symbol information.
- the relationship between the OFDM symbol length and the frame size may be determined in advance.
- the compression processing size determining unit 206 determines the compression size based on the OFDM symbol length of the acquired OFDM symbol information and the predetermined frame size. For example, the compression processing size determination unit 206 determines the frame size corresponding to the OFDM symbol length as the compression size.
- the compression unit 207 compresses the OFDM symbol in units of compression size determined by the compression processing size determination unit 206 for each frame.
- the framing unit 208 generates a frame signal by multiplexing the compressed OFDM symbol and the control signal.
- the E / O conversion unit 209 converts the frame signal (electrical signal) into an optical signal, and transmits the converted optical signal to the RRH 100 via the optical fiber 250.
- the compression unit 108 and the compression unit 207 are not particularly distinguished, they are simply referred to as a compression unit.
- the expansion unit 114 and the expansion unit 204 are simply referred to as an expansion unit unless otherwise distinguished.
- the compression processing size determination unit 107 and the compression processing size determination unit 206 will be simply referred to as a compression processing size determination unit unless otherwise distinguished.
- the expansion process size determination unit 113 and the expansion process size determination unit 203 are simply referred to as an expansion process size determination unit unless otherwise distinguished.
- the compression unit performs compression processing according to the determined compression size. Further, the decompression unit performs decompression processing according to the determined decompression size. For example, when linear predictive coding is performed in the compression unit, the number of samples used for obtaining the coefficient is changed when the frame size (compression size) is changed.
- the compression unit / decompression unit may be provided with a compression / decompression circuit for each frame size, and which one of them is used may be switched according to the notified frame size.
- the compression processing size determination unit 206 acquires the OFDM symbol information from the modulation / demodulation unit 205 of the BBU 200. In this case, it is necessary to notify the OFDM symbol information to the compression processing size determination unit 107 of the RRH 100. Therefore, when the BBU 200 and the RRH 100 are CPRI interfaces, it is possible to transmit OFDM symbol information using reserved bits of the CPRI control signal.
- the compression processing size determination unit 107 acquires the OFDM symbol information by receiving the OFDM symbol information from the BBU 200.
- the OFDM symbol start position / OFDM symbol length information of the downlink 0.5 ms period is known
- the uplink OFDM symbol start position is known.
- -OFDM symbol length information can also be estimated.
- the OFDM symbol length information may be stored in advance in the compression processing size determination unit. For example, in an LTE radio system, if the start position of an OFDM symbol having a CP (cyclic prefix) length of 160 is known, the start position of the subsequent OFDM symbol and the OFDM symbol length can be known.
- FIG. 3 is a diagram illustrating an operation example of the compression processing size determination unit and the decompression processing size determination unit.
- a plurality of OFDM symbols are shown.
- (A) represents the first OFDM symbol
- (b) represents the second OFDM symbol
- (c) represents the third OFDM symbol.
- the compression processing size determining unit determines the frame size a i, j for each OFDM symbol so as not to include a plurality of OFDM symbols.
- the compression processing size determination units 107 and 206 may determine two frame sizes, one for the first OFDM symbol and one for the second to seventh OFDM symbols.
- the decompression processing size determination units 113 and 203 may similarly determine the frame size (expansion size).
- FIG. 4 is a flowchart illustrating a process flow in the uplink of the RRH 100 according to the first embodiment.
- the antenna 101 receives a radio signal (step S101).
- the antenna 101 outputs the received radio signal to the amplifier 103 via the transmission / reception switching unit 102.
- the amplifier 103 amplifies the signal power of the radio signal to a level that allows signal processing (step S102).
- the down-conversion unit 104 down-converts the radio signal to baseband (step S103). Thereafter, the A / D conversion unit 105 converts the down-converted radio signal into IQ data that is a digital signal (step S104).
- the baseband filter unit 106 performs a filtering process on the IQ data (step S105).
- the compression processing size determination unit 107 determines the compression size based on the OFDM symbol information acquired from the BBU 200 (step S106).
- the compression unit 108 compresses the OFDM symbol in units of the compression size determined by the compression processing size determination unit 107 (step S107).
- the framing unit 109 generates a frame signal by multiplexing the compressed OFDM symbol and the control signal (step S108).
- the E / O conversion unit 110 converts the frame signal into an optical signal (step S109). Then, the E / O conversion unit 110 transmits an optical signal to the BBU 200 via the optical fiber 150 (step S110).
- FIG. 5 is a flowchart showing a processing flow in the uplink of the BBU 200 in the first embodiment.
- the O / E converter 201 converts an optical signal received via the optical fiber 250 into a frame signal (electric signal) (step S201).
- the O / E converter 201 outputs the frame signal to the deframer 202.
- the deframing unit 202 extracts a control signal and a compressed OFDM symbol from the frame signal (step S202).
- the decompression processing size determination unit 203 determines the decompression size based on the frame size notified from the RRH 100 (step S203).
- the decompression unit 204 decompresses the compressed OFDM symbol in units of the decompression size determined by the decompression processing size determination unit 203 and restores it to an OFDM symbol (step S204).
- the modem unit 205 restores the radio signal by demodulating the restored OFDM symbol (step S205).
- the modem unit 205 receives the restored radio signal (step S206). Note that the reception in the process of step S206 means that the modem unit 205 acquires a radio signal to demodulate the OFDM symbol.
- FIG. 6 is a flowchart illustrating a processing flow in the downlink of the RRH 100 according to the first embodiment.
- the O / E converter 111 converts the optical signal received via the optical fiber 150 into a frame signal (electric signal) (step S301).
- the deframing unit 112 extracts the control signal and the compressed OFDM symbol from the frame signal (step S302).
- the expansion processing size determination unit 113 determines the expansion size based on the frame size notified from the BBU 200. (Step S303).
- the decompression unit 114 decompresses the compressed OFDM symbol in units of the frame size determined by the decompression processing size determination unit 113 and restores it to an OFDM symbol (step S304).
- the baseband filter unit 115 performs a filtering process on the restored OFDM symbol (step S305).
- the D / A conversion unit 116 converts the filtered signal into an analog signal (step S306).
- the up-conversion unit 117 up-converts the analog signal (step S307).
- the amplifier 118 amplifies the power of the analog signal to the determined transmission power (step S308).
- the antenna 101 transmits an analog signal to the wireless terminal connected to the RRH 100 (step S309).
- FIG. 7 is a flowchart showing a process flow in the downlink of the BBU 200 in the first embodiment.
- the modem unit 205 outputs the IQ data of the radio signal to the compression processing size determination unit 206 and the compression unit 207 (step S401).
- the compression processing size determination unit 206 determines the compression size based on the acquired OFDM symbol information (step S402).
- the compression unit 207 compresses the OFDM symbol in units of the compression size determined by the compression processing size determination unit 206 (step S403).
- the framing unit 208 generates a frame signal by multiplexing the compressed OFDM symbol and the control signal (step S404).
- the E / O conversion unit 209 converts the frame signal (electric signal) into an optical signal (step S405).
- the E / O conversion unit 209 transmits the optical signal to the RRH 100 via the optical fiber 250 (step S406).
- the RRH 100 and the BBU 200 determine a compression size for compressing the radio signal based on the acquired OFDM symbol information.
- the RRH 100 and the BBU 200 determine the frame size so as not to include OFDM symbols having different frequency characteristics when performing the compression process.
- the RRH 100 and the BBU 200 perform compression processing in units of the determined compression size. Therefore, it becomes possible to reduce deterioration of the compression rate as a whole.
- the transmission band can be used effectively.
- the RRH and BBU acquire information on the start position of the OFDM symbol based on the compression rate for each OFDM symbol. Then, the RRH and BBU determine the frame size in the OFDM symbol to be compressed based on the acquired information on the start position of the OFDM symbol and the information on the OFDM symbol length, and perform the compression processing with the determined frame size. .
- FIG. 8 is a schematic block diagram illustrating a functional configuration of the RRH 100a according to the second embodiment.
- FIG. 9 is a schematic block diagram showing the functional configuration of the BBU 200a in the second embodiment. First, the RRH 100a will be described.
- the RRH 100a includes an antenna 101, a transmission / reception switching unit 102, an amplifier 103, a down-conversion unit 104, an A / D conversion unit 105, a baseband filter unit 106, a compression processing size determination unit 107a, a compression unit 108, a framing unit 109, an E / O converter 110, O / E converter 111, deframer 112, decompression processing size determiner 113, decompressor 114, baseband filter 115, D / A converter 116, upconverter 117, amplifier 118, A compression rate measurement unit 119 is provided.
- the RRH 100a is different from the RRH 100 in that the RRH 100a includes a compression processing size determination unit 107a instead of the compression processing size determination unit 107, and a compression rate measurement unit 119 is newly provided.
- the RRH 100a is the same as the RRH 100 in other configurations. Therefore, description of the entire RRH 100a is omitted, and the compression processing size determination unit 107a and the compression rate measurement unit 119 will be described.
- the compression rate measurement unit 119 measures the compression rate for each OFDM symbol from the output of the compression unit 108.
- the compression processing size determination unit 107a determines the compression size based on the compression rate measured by the compression rate measurement unit 119. Specifically, the compression processing size determination unit 107a acquires a position where the average value or the maximum value of the measured compression rate is minimum as the OFDM symbol start position. Then, the compression processing size determination unit 107a determines the compression size from the acquired OFDM symbol start position information and OFDM symbol length information so as not to span OFDM symbols having different frequency characteristics. In the second embodiment, the compression processing size determination unit 107a needs to acquire the information of the OFDM symbol length by the method of the first embodiment or store it in advance.
- the BBU 200a includes an O / E conversion unit 201, a deframing unit 202, an expansion processing size determination unit 203, an expansion unit 204, a modem unit 205, a compression processing size determination unit 206a, a compression unit 207, a framing unit 208, and an E / O.
- a conversion unit 209 and a compression rate measurement unit 210 are provided.
- the BBU 200a is different from the BBU 200 in that a compression processing size determination unit 206a is provided instead of the compression processing size determination unit 206, and a compression rate measurement unit 210 is newly provided.
- the BBU 200a is the same as the BBU 200 in other configurations.
- the processing of the compression processing size determination unit 206a and the compression rate measurement unit 210 is the same as the processing of the compression processing size determination unit 107a and the compression rate measurement unit 119.
- FIG. 10 is a flowchart illustrating a processing flow in the uplink of the RRH 100a in the second embodiment.
- symbol similar to FIG. 4 is attached
- the RRH 100a performs an OFDM symbol start position information acquisition process (step S501).
- the OFDM symbol start position information acquisition process will be described later.
- the compression processing size determination unit 107a determines the compression size from the OFDM symbol start position information and the OFDM symbol length information acquired in step S501 so as not to straddle OFDM symbols having different frequency characteristics. (Step S502). Thereafter, the processing after step S107 is executed.
- FIG. 11 is a flowchart showing a flow of OFDM symbol start position information acquisition processing.
- LTE Long Term Evolution
- OFDM symbols are transmitted with a period of 0.5 ms (15360 samples).
- i represents the frame number
- i a represents the estimated value of the OFDM symbol start position
- the provisional minimum value represents the minimum value of the compression rate.
- the compression rate measuring unit 119 measures the compression rate (step S602).
- the compression processing size determination unit 107a determines whether or not the measured compression rate is smaller than the provisional minimum value (step S603). If the measured compression rate is smaller than the provisional minimum value (step S603—YES), the compression processing size determination unit 107a sets i a to a value of i, and sets the provisional minimum value to the measured compression rate. (Step S604). Thereafter, the compression processing size determination unit 107a adds 1 to the value of i (step S605). The compression processing size determination unit 107a determines whether or not the value of i is equal to or greater than a preset i max (step S606).
- i max is 15360.
- the best OFDM compression rate characteristic from among the estimated values i a compression processing size determination unit 107a every OFDM symbol start position estimates i a symbol start position is obtained as the start position information of the OFDM symbol (step S607).
- the start position of the OFDM symbol when the compression rate characteristic is the best is the position where the average value or the maximum value of the compression rate becomes the minimum.
- step S606 if the value of i is not equal to or greater than the preset i max (step S606—NO), the RRH 100a repeatedly executes the processes after step S602. In the process of step S603, when the measured compression rate is not smaller than the provisional minimum value (step S603: NO), the compression process size determining unit 107a adds 1 to the value of i (step S605).
- the RRH 100a and the BBU 200a configured as described above, it is possible to obtain the same effect as in the first embodiment. Further, the RRH 100a and the BBU 200a acquire information on the start position of the OFDM symbol from the compression rate of the compression processing performed by the compression unit 108 and the compression unit 207. Then, the RRH 100a and the BBU 200a determine the compression size based on the acquired OFDM symbol start position information and OFDM symbol length information. Therefore, more accurate compression becomes possible. Further, even if the start position of the OFDM symbol deviates from the assumption due to the influence of the radio propagation environment, processing delay of BBU / RRH, fiber delay between BBU 200a and RRH 100a, etc., correction can be performed.
- the compression rate measurement unit 119 and the compression rate measurement unit 210 may reduce the amount of calculation using an analysis result performed in the compression unit instead of the compression rate measurement. Specifically, the compression rate measurement unit 119 and the compression rate measurement unit 210 estimate the information amount for each frame, that is, the compression rate, based on the autocorrelation coefficient and the PARCOR (Partial Auto-Correlation) coefficient obtained during the linear prediction analysis. This processing can reduce the amount of processing required for entropy coding.
- PARCOR Partial Auto-Correlation
- the RRH and the BBU acquire OFDM symbol information from downlink or uplink IQ data. Then, the RRH and the BBU determine the frame size in the OFDM symbol to be compressed based on the acquired OFDM symbol information, and perform the compression process with the determined frame size.
- FIG. 12 is a schematic block diagram illustrating a functional configuration of the RRH 100b according to the third embodiment.
- FIG. 13 is a schematic block diagram showing the functional configuration of the BBU 200b in the third embodiment. First, the RRH 100b will be described.
- the RRH 100b includes an antenna 101, a transmission / reception switching unit 102, an amplifier 103, a down-conversion unit 104, an A / D conversion unit 105, a baseband filter unit 106, a compression processing size determination unit 107b, a compression unit 108, a framing unit 109, an E / D O converter 110, O / E converter 111, deframer 112, decompression processing size determiner 113, decompressor 114, baseband filter 115, D / A converter 116, upconverter 117, amplifier 118, An OFDM symbol information estimation unit 120 is provided.
- the RRH 100b is different from the RRH 100 in that the RRH 100b includes a compression processing size determination unit 107b instead of the compression processing size determination unit 107 and newly includes an OFDM symbol information estimation unit 120.
- the RRH 100b is the same as the RRH 100 in other configurations. Therefore, description of the entire RRH 100b is omitted, and the compression processing size determination unit 107b and the OFDM symbol information estimation unit 120 will be described.
- the OFDM symbol information estimation unit 120 estimates OFDM symbol start position and OFDM symbol length information from the uplink signal.
- the compression processing size determination unit 107b acquires the OFDM symbol information estimated by the OFDM symbol information estimation unit 120. Then, the compression processing size determination unit 107b determines the compression size based on the acquired OFDM symbol information.
- the BBU 200b includes an O / E conversion unit 201, a deframe unit 202, a decompression processing size determination unit 203, a decompression unit 204, a modulation / demodulation unit 205, a compression processing size determination unit 206b, a compression unit 207, a framing unit 208, and an E / O.
- a conversion unit 209 and an OFDM symbol information estimation unit 211 are provided.
- the BBU 200b differs from the BBU 200 in that it includes a compression processing size determination unit 206b instead of the compression processing size determination unit 206, and newly includes an OFDM symbol information estimation unit 211.
- the BBU 200b is the same as the BBU 200 in other configurations. Therefore, description of the entire BBU 200b is omitted, and the compression processing size determination unit 206b and the OFDM symbol information estimation unit 211 will be described.
- the OFDM symbol information estimation unit 211 estimates information on the OFDM symbol start position and OFDM symbol length from the downlink signal.
- the compression processing size determination unit 206b acquires the OFDM symbol information estimated by the OFDM symbol information estimation unit 211. Then, the compression processing size determination unit 206b determines the compression size based on the acquired OFDM symbol information.
- FIG. 14 is a flowchart illustrating a process flow in the uplink of the RRH 100b according to the third embodiment.
- symbol similar to FIG. 4 is attached in FIG. 14, and description is abbreviate
- the OFDM symbol information estimation unit 120 estimates information on the OFDM symbol start position and OFDM symbol length from the uplink signal (step S801).
- EVM Error Vector Magnitude
- the OFDM symbol information estimation unit 120 shifts the FFT window one point at a time, and the OFDM symbol start position and cyclic prefix length (OFDM symbol length) information at the position and period at which the EVM after the FFT is minimized. Is estimated.
- the OFDM symbol information estimation unit 120 may estimate the OFDM symbol start position and cyclic prefix length (OFDM symbol length) information from the autocorrelation of the uplink signal using the cyclic prefix periodicity.
- the OFDM symbol length information may be acquired by the method of the first embodiment, or may be stored in advance in the OFDM symbol information estimation unit 120.
- the RRH 100b and the BBU 200b configured as described above, it is possible to obtain the same effect as that of the first embodiment.
- the RRH 100b and the BBU 200b can perform correction even if the start position of the OFDM symbol is deviated from the expected due to the influence of the radio propagation environment, the processing delay of the BBU / RRH, the fiber delay between the BBU 200b and the RRH 100b, etc. .
- the RRH 100b and the BBU 200b can perform the OFDM symbol start position and the OFDM symbol from the downlink signal and the uplink signal, respectively, without requiring additional information for estimating the OFDM symbol start position and OFDM symbol length information. Long information can be estimated.
- the program for executing each process of RRH100, RRH100a, RRH100b, BBU200, BBU200a, and BBU200b of the present invention is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system.
- the above-described various processes relating to the processes of the RRH 100, the RRH 100a, the RRH 100b, the BBU 200, the BBU 200a, and the BBU 200b may be performed.
- the “computer system” may include hardware such as an OS (Operating System) and peripheral devices.
- the “computer system” includes a homepage providing environment (or display environment) if a WWW (World Wide Web) system is used.
- the “computer-readable recording medium” means a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a writable nonvolatile memory such as a flash memory, and a portable medium such as a CD (Compact Disc) -ROM.
- a storage device such as a hard disk built in a computer system.
- the “computer-readable recording medium” means a volatile memory (for example, DRAM (Dynamic DRAM) in a computer system that becomes a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Random Access Memory)), etc., which hold programs for a certain period of time.
- the program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium.
- the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
- the program may be for realizing a part of the functions described above. Further, the program may be a so-called difference file (difference program) that can realize the above-described functions in combination with a program already recorded in the computer system.
- the present invention is applicable to digital RoF transmission, for example. According to the present invention, it is possible to reduce deterioration of the compression rate.
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Abstract
Description
本願は、2015年5月19日に日本へ出願された特願2015-101840号に基づき優先権を主張し、その内容をここに援用する。
デジタルRoF伝送を説明するにあたり、以下の文言を定義する。
下りリンクは、BBUからRRHを介して、RRHに接続される無線端末に送信される電波の通信経路を表す。
上りリンクは、RRHに接続される無線端末からRRHを介してBBUに送信される電波の通信経路を表す。
また、デジタルRoF伝送の上りリンクでは、以下のような処理が行われる。RRHは、無線端末から送信された無線信号を受信し、受信した無線信号を光信号に変換して、光ファイバを介して変換後の光信号をBBUに伝送する。BBUは、受信した光信号をIQデータに変換して信号を復調する。
RRH500は、アンテナ501、送受切替部502、増幅器503、ダウンコンバート部504、A/D変換部(Analog/Digital)505、ベースバンドフィルタ部506、フレーム化部507、E/O(Electric/Optic)変換部508、O/E(Optic/Electric)変換部509、デフレーム化部510、ベースバンドフィルタ部511、D/A変換部(Digital/Analog)512、アップコンバート部513及び増幅器514を備える。
BBU600は、O/E変換部601、デフレーム化部602、変復調部603、フレーム化部604及びE/O変換部605を備える。
O/E変換部601は、光ファイバ650を介して受信した光信号をフレーム信号(電気信号)に変換する。デフレーム化部602は、フレーム信号から制御信号及びIQデータを取り出す。変復調部603は、IQデータを復調することによって無線信号を復元する。また、変復調部603は、無線信号を変調することによってIQデータを生成する。フレーム化部604は、IQデータと制御信号とを多重化することによってフレーム化する。E/O変換部605は、フレーム信号(電気信号)を光信号に変換して、光ファイバ650を介して変換後の光信号をRRH500に送信する。
RRH500aは、アンテナ501、送受切替部502、増幅器503、ダウンコンバート部504、A/D変換部505、ベースバンドフィルタ部506、圧縮部701、フレーム化部507a、E/O変換部508、O/E変換部509、デフレーム化部510、伸張部702、ベースバンドフィルタ部511a、D/A変換部512、アップコンバート部513及び増幅器514を備える。
圧縮部701は、フィルタリング処理後のIQデータを圧縮する。フレーム化部507aは、圧縮されたIQデータと、制御信号とを多重化することによってフレーム化する。伸張部702は、圧縮されたIQデータを解凍することによってIQデータを復元する。ベースバンドフィルタ部511aは、復元されたIQデータに対してフィルタリング処理を行う。
BBU600aは、O/E変換部601、デフレーム化部602、伸張部801、変復調部603a、圧縮部802、フレーム化部604a及びE/O変換部605を備える。
伸張部801は、圧縮されたIQデータを解凍することによってIQデータを復元する。変復調部603aは、復元されたIQデータを復調することによって無線信号を復元する。また、変復調部603aは、無線信号を変調することによってIQデータを生成する。圧縮部802は、IQデータを圧縮する。フレーム化部604aは、圧縮されたIQデータと、制御信号とを多重化することによってフレーム化する。
LTEにおける下りリンクでは、OFDM(Orthogonal Frequency Division Multiplexing)が用いられる。時間波形としては、所定サイズのIFFT(Inverse Fast Fourier Transform)後の信号に対してサイクリックプレフィックスを付加した信号が周期的に出力される。一方、LTEにおける上りリンクでは、DFT-S-OFDM(Discrete Fourier Transform-Spread OFDM)が用いられる。こちらの場合もOFDMと同様に、時間波形としては所定サイズのIFFT後の信号に対してサイクリックプレフィックスを付加した信号が周期的に出力される。以下の説明では、IFFT後の信号にサイクリックプレフィックスを付加したものをOFDMシンボルと記載し、下りリンクと上りリンクとで区別なく用いることとする。
図20において、フレーム番号は、圧縮処理がなされたフレームの順番を表す。圧縮率は、元々のデータ量に対する圧縮後のデータ量の比である。無線信号は、OFDM変調、サブキャリア間隔15kHz、サブキャリア数1200、256QAM(Quadrature Amplitude Modulation)変調、サイクリックプレフィックスは160サンプル(第1OFDMシンボル)又は144サンプル(第2OFDMシンボル~第7OFDMシンボル)とした。つまり、システム帯域幅20MHzのLTE下りリンクシステムで、全ての無線帯域がデータ伝送に使用されている場合を想定した。フレームサイズは548とした。
[概要]
本発明では、分割された基地局の機能を備えるRRH(無線装置)とBBU(信号処理装置)とを備える光通信システムにおけるRRH及びBBUが、複数のOFDMシンボル(シンボル)で構成されるシンボル系列の開始位置及び各OFDMシンボルの長さに関する情報(以下、「OFDMシンボル情報」という。)を取得する。そして、RRH及びBBUは、取得したOFDMシンボル情報に基づいて圧縮処理を行う対象となるOFDMシンボル毎のフレームサイズを決定し、決定したフレームサイズで圧縮処理を行う。
以下、複数の実施形態(第1実施形態~第3実施形態)を例にして具体的に説明する。
第1実施形態では、RRH及びBBUが、OFDMシンボル情報(シンボル情報)を取得して、取得したOFDMシンボル情報に基づいて圧縮処理を行う対象となるOFDMシンボル毎のフレームサイズを決定し、決定したフレームサイズで圧縮処理を行う。また、RRH及びBBUは、取得したOFDMシンボル情報に基づいて伸張処理を行う対象となるOFDMシンボル毎のフレームサイズを決定し、決定したフレームサイズで伸張処理を行う。
RRH100は、アンテナ101、送受切替部102、増幅器103、ダウンコンバート部104、A/D変換部105、ベースバンドフィルタ部106、圧縮処理サイズ決定部107、圧縮部108、フレーム化部109、E/O変換部110、O/E変換部111、デフレーム化部112、伸張処理サイズ決定部113、伸張部114、ベースバンドフィルタ部115、D/A変換部116、アップコンバート部117及び増幅器118を備える。
増幅器103は、受信された無線信号の信号電力を信号処理ができるレベルまで増幅する。ダウンコンバート部104は、無線信号をベースバンドにダウンコンバートする。A/D変換部105は、ダウンコンバートされた無線信号(アナログ信号)をデジタル信号であるIQデータに変換する。ベースバンドフィルタ部106は、IQデータに対してフィルタリング処理を行う。この処理によって、無線信号のOFDMシンボルが生成される。
圧縮部108は、フレーム毎に、圧縮処理サイズ決定部107によって決定された圧縮サイズ単位でOFDMシンボルを圧縮する。
E/O変換部110は、フレーム信号(電気信号)を光信号に変換して、光ファイバ150を介して変換後の光信号をBBU200に送信する。
O/E変換部111は、光ファイバ150を介して受信された光信号をフレーム信号(電気信号)に変換する。
伸張処理サイズ決定部113は、BBU200から取得したフレームサイズに基づいて、伸張処理を行うフレームサイズ(以下、「伸張サイズ」という。)を決定する。伸張処理サイズ決定部113が伸張サイズの情報を取得する方法としては、BBU200の圧縮部がフレームサイズをヘッダとして圧縮されたデータの先頭に付加して送信する構成とし、ヘッダを基にフレームサイズを取得する方法が考えられる。LTEシステムの場合、最小では2つのフレームサイズで十分であり、この時ヘッダは1bitあればよい。伸張サイズと圧縮サイズとは、同じサイズである。
ベースバンドフィルタ部115は、復元されたOFDMシンボルに対してフィルタリング処理を行う。
D/A変換部116は、フィルタリング処理後の信号をアナログ信号に変換する。
アップコンバート部117は、アナログ信号をアップコンバートする。
増幅器118は、アナログ信号の電力を決められた送信電力まで増幅する。
BBU200は、O/E変換部201、デフレーム化部202、伸張処理サイズ決定部203、伸張部204、変復調部205、圧縮処理サイズ決定部206、圧縮部207、フレーム化部208及びE/O変換部209を備える。
O/E変換部201は、光ファイバ250を介して受信された光信号をフレーム信号(電気信号)に変換する。デフレーム化部202は、フレーム信号から制御信号及び多重化信号を取り出す。
伸張部204は、伸張処理サイズ決定部203によって決定された伸張サイズ単位で、圧縮されたOFDMシンボルを伸張する。具体的には、伸張部204は、決定された伸張サイズ単位で、圧縮されたOFDMシンボルを解凍することによってOFDMシンボルへと復元する。
変復調部205は、復元されたOFDMシンボルに対して復調を行うことによって無線信号を復元する。また、変復調部205は、無線信号のIQデータを圧縮処理サイズ決定部206及び圧縮部207に出力する。
フレーム化部208は、圧縮されたOFDMシンボルと、制御信号とを多重化することによってフレーム信号を生成する。
E/O変換部209は、フレーム信号(電気信号)を光信号に変換して、光ファイバ250を介して変換後の光信号をRRH100に送信する。
図3に示される例では、複数のOFDMシンボルが示されている。(a)は第1OFDMシンボルを表し、(b)は第2OFDMシンボルを表し、(c)は第3OFDMシンボルを表す。ここで、j番目のOFDMシンボル中のフレーム数をAj、各フレームのフレームサイズをai,j(1≦i≦Aj)とすると、(a)~(c)はそれぞれ図3に示すように表すことができる。このように、圧縮処理サイズ決定部は、複数のOFDMシンボルを含まないようにOFDMシンボル毎にフレームサイズai,jを決定する。LTEシステムでは、第2~第7OFDMシンボルのOFDMシンボル長は等しいため、ai,2=ai,3=ai,4=ai,5=ai,6=ai,7としてもよい。この場合、圧縮処理サイズ決定部107及び206は、第1OFDMシンボルで1つ、第2~第7OFDMシンボルで1つのようにフレームサイズを2つ決定すればよい。また、簡単に、a1,j=a2,j=・・・=aAj,jとしてもよい。また、伸張処理サイズ決定部113及び203も同様にフレームサイズ(伸張サイズ)を決定してもよい。
アンテナ101は、無線信号を受信する(ステップS101)。アンテナ101は、受信した無線信号を、送受切替部102を介して増幅器103に出力する。増幅器103は、無線信号の信号電力を信号処理ができるレベルまで増幅する(ステップS102)。ダウンコンバート部104は、無線信号をベースバンドにダウンコンバートする(ステップS103)。その後、A/D変換部105は、ダウンコンバートされた無線信号をデジタル信号であるIQデータに変換する(ステップS104)。ベースバンドフィルタ部106は、IQデータに対してフィルタリング処理を行う(ステップS105)。
O/E変換部201は、光ファイバ250を介して受信された光信号をフレーム信号(電気信号)に変換する(ステップS201)。O/E変換部201は、フレーム信号をデフレーム化部202に出力する。デフレーム化部202は、フレーム信号から制御信号及び圧縮されたOFDMシンボルを取り出す(ステップS202)。伸張処理サイズ決定部203は、RRH100から通知されたフレームサイズに基づいて伸張サイズを決定する(ステップS203)。
O/E変換部111は、光ファイバ150を介して受信された光信号をフレーム信号(電気信号)に変換する(ステップS301)。デフレーム化部112は、フレーム信号から制御信号及び圧縮されたOFDMシンボルを取り出す(ステップS302)。伸張処理サイズ決定部113は、BBU200から通知されたフレームサイズに基づいて伸張サイズを決定する。(ステップS303)。伸張部114は、伸張処理サイズ決定部113によって決定されたフレームサイズ単位で、圧縮されたOFDMシンボルを解凍することによってOFDMシンボルへと復元する(ステップS304)。
変復調部205は、無線信号のIQデータを圧縮処理サイズ決定部206及び圧縮部207に出力する(ステップS401)。圧縮処理サイズ決定部206は、取得したOFDMシンボル情報に基づいて圧縮サイズを決定する(ステップS402)。圧縮部207は、圧縮処理サイズ決定部206によって決定された圧縮サイズ単位でOFDMシンボルを圧縮する(ステップS403)。フレーム化部208は、圧縮されたOFDMシンボルと、制御信号とを多重化することによってフレーム信号を生成する(ステップS404)。E/O変換部209は、フレーム信号(電気信号)を光信号に変換する(ステップS405)。E/O変換部209は、光ファイバ250を介して光信号をRRH100に伝送する(ステップS406)。
RRH100及びBBU200は、取得したOFDMシンボル情報に基づいて、無線信号を圧縮するための圧縮サイズを決定する。この処理によって、RRH100及びBBU200は、圧縮処理を行う際に、周波数特性が異なるOFDMシンボルを含まないようにフレームサイズを決定する。そして、RRH100及びBBU200は、決定した圧縮サイズ単位で圧縮処理を行う。そのため、全体として圧縮率の劣化を低減させることが可能になる。また、圧縮率の劣化が低減されるため、伝送帯域を有効に利用することが可能になる。
第2実施形態では、RRH及びBBUが、OFDMシンボル毎の圧縮率に基づいて、OFDMシンボルの開始位置の情報を取得する。そして、RRH及びBBUは、取得したOFDMシンボルの開始位置の情報と、OFDMシンボル長の情報とに基づいて圧縮処理を行うOFDMシンボル中のフレームサイズを決定し、決定したフレームサイズで圧縮処理を行う。
RRH100aは、アンテナ101、送受切替部102、増幅器103、ダウンコンバート部104、A/D変換部105、ベースバンドフィルタ部106、圧縮処理サイズ決定部107a、圧縮部108、フレーム化部109、E/O変換部110、O/E変換部111、デフレーム化部112、伸張処理サイズ決定部113、伸張部114、ベースバンドフィルタ部115、D/A変換部116、アップコンバート部117、増幅器118及び圧縮率測定部119を備える。
圧縮処理サイズ決定部107aは、圧縮率測定部119によって測定された圧縮率に基づいて圧縮サイズを決定する。具体的には、圧縮処理サイズ決定部107aは、測定された圧縮率の平均値又は最大値等が最小となる位置を、OFDMシンボルの開始位置として取得する。そして、圧縮処理サイズ決定部107aは、取得したOFDMシンボルの開始位置の情報とOFDMシンボル長の情報とから、周波数特性が異なるOFDMシンボルを跨らないように圧縮サイズを決定する。なお、第2実施形態では、圧縮処理サイズ決定部107aは、OFDMシンボル長の情報を、第1実施形態の方法で取得するか、予め記憶しておく必要がある。
BBU200aは、O/E変換部201、デフレーム化部202、伸張処理サイズ決定部203、伸張部204、変復調部205、圧縮処理サイズ決定部206a、圧縮部207、フレーム化部208、E/O変換部209及び圧縮率測定部210を備える。BBU200aは、圧縮処理サイズ決定部206に代えて圧縮処理サイズ決定部206aを備え、圧縮率測定部210を新たに備える点でBBU200と構成が異なる。BBU200aは、他の構成についてはBBU200と同様である。そのため、BBU200a全体の説明は省略し、圧縮処理サイズ決定部206a及び圧縮率測定部210について説明する。圧縮処理サイズ決定部206a及び圧縮率測定部210の処理は、圧縮処理サイズ決定部107a及び圧縮率測定部119の処理と同様である。
RRH100aは、OFDMシンボル開始位置情報取得処理を実行する(ステップS501)。OFDMシンボル開始位置情報取得処理については後述する。そして、圧縮処理サイズ決定部107aは、ステップS501の処理で取得されたOFDMシンボル開始位置の情報と、OFDMシンボル長の情報とから、周波数特性が異なるOFDMシンボルを跨らないように圧縮サイズを決定する(ステップS502)。その後、ステップS107以降の処理が実行される。
まず、圧縮処理サイズ決定部107aは、初期値としてi=0、ia=0、暫定最小値を∞に設定する(ステップS601)。ここで、iはフレーム番号を表し、iaはOFDMシンボル開始位置の推定値を表し、暫定最小値は圧縮率の最小値を表す。圧縮率測定部119は、圧縮率を測定する(ステップS602)。圧縮処理サイズ決定部107aは、測定された圧縮率が暫定最小値よりも小さいか否か判定する(ステップS603)。測定された圧縮率が暫定最小値よりも小さい場合(ステップS603-YES)、圧縮処理サイズ決定部107aはiaをiの値に設定し、暫定最小値を、測定された圧縮率に設定する(ステップS604)。その後、圧縮処理サイズ決定部107aは、iの値に1を加算する(ステップS605)。圧縮処理サイズ決定部107aは、iの値が予め設定されているimax以上であるか否か判定する(ステップS606)。ここで、システム帯域幅20MHzのLTEの場合、imaxは15360である。
また、ステップS603の処理において、測定された圧縮率が暫定最小値よりも小さくない場合(ステップS603-NO)、圧縮処理サイズ決定部107aはiの値に1を加算する(ステップS605)。
また、RRH100a及びBBU200aは、圧縮部108及び圧縮部207によって行われた圧縮処理の圧縮率から、OFDMシンボルの開始位置の情報を取得する。そして、RRH100a及びBBU200aは、取得したOFDMシンボルの開始位置の情報と、OFDMシンボル長の情報とに基づいて圧縮サイズを決定する。そのため、より精度の高い圧縮が可能となる。また、無線伝搬環境・BBU/RRHの処理遅延・BBU200a-RRH100a間のファイバ遅延等の影響で、OFDMシンボルの開始位置が想定とずれていても補正を行うことが可能になる。
第3実施形態では、RRH及びBBUが、下りリンク又は上りリンクのIQデータからOFDMシンボル情報を取得する。そして、RRH及びBBUは、取得したOFDMシンボル情報に基づいて圧縮処理を行うOFDMシンボル中のフレームサイズを決定し、決定したフレームサイズで圧縮処理を行う。
RRH100bは、アンテナ101、送受切替部102、増幅器103、ダウンコンバート部104、A/D変換部105、ベースバンドフィルタ部106、圧縮処理サイズ決定部107b、圧縮部108、フレーム化部109、E/O変換部110、O/E変換部111、デフレーム化部112、伸張処理サイズ決定部113、伸張部114、ベースバンドフィルタ部115、D/A変換部116、アップコンバート部117、増幅器118及びOFDMシンボル情報推定部120を備える。
圧縮処理サイズ決定部107bは、OFDMシンボル情報推定部120によって推定されたOFDMシンボル情報を取得する。そして、圧縮処理サイズ決定部107bは、取得したOFDMシンボル情報に基づいて圧縮サイズを決定する。
BBU200bは、O/E変換部201、デフレーム化部202、伸張処理サイズ決定部203、伸張部204、変復調部205、圧縮処理サイズ決定部206b、圧縮部207、フレーム化部208、E/O変換部209及びOFDMシンボル情報推定部211を備える。BBU200bは、圧縮処理サイズ決定部206に代えて圧縮処理サイズ決定部206bを備え、OFDMシンボル情報推定部211を新たに備える点でBBU200と構成が異なる。BBU200bは、他の構成についてはBBU200と同様である。そのため、BBU200b全体の説明は省略し、圧縮処理サイズ決定部206b及びOFDMシンボル情報推定部211について説明する。
圧縮処理サイズ決定部206bは、OFDMシンボル情報推定部211によって推定されたOFDMシンボル情報を取得する。そして、圧縮処理サイズ決定部206bは、取得したOFDMシンボル情報に基づいて圧縮サイズを決定する。
OFDMシンボル情報推定部120は、上りリンク信号からOFDMシンボルの開始位置及びOFDMシンボル長の情報を推定する(ステップS801)。OFDMシンボルの開始位置及びOFDMシンボル長情報を推定する方法として、IQデータをFFT変換してEVM(Error Vector Magnitude)を測定する方法がある。この時、OFDMシンボル情報推定部120は、FFTウィンドウを1ポイントずつずらしていき、FFT後のEVMが最小となる位置や周期で、OFDMシンボルの開始位置やサイクリックプレフィックス長(OFDMシンボル長)情報を推定する。または、OFDMシンボル情報推定部120は、サイクリックプレフィックスの周期性を利用し、上りリンク信号の自己相関からOFDMシンボルの開始位置やサイクリックプレフィックス長(OFDMシンボル長)情報を推定してもよい。なお、OFDMシンボル長情報は、第1実施形態の方法によって取得してもよいし、予めOFDMシンボル情報推定部120に予め記憶されていてもよい。
また、RRH100b及びBBU200bは、無線伝搬環境・BBU/RRHの処理遅延・BBU200b-RRH100b間のファイバ遅延等の影響で、OFDMシンボルの開始位置が想定とずれていても補正を行うことが可能になる。また、RRH100b及びBBU200bは、OFDMシンボルの開始位置及びOFDMシンボル長情報を推定するための追加の情報を必要とすることなく、それぞれ、下りリンク信号及び上りリンク信号からOFDMシンボルの開始位置及びOFDMシンボル長情報を推定することができる。
200、200a、200b、600、600a…BBU
101、501…アンテナ
102、502…送受切替部
103、503…増幅器
104、504…ダウンコンバート部
105、505…A/D変換部
106、506…ベースバンドフィルタ部(上り)
107、107a、107b…圧縮処理サイズ決定部
108、701…圧縮部
109、507、507a…フレーム化部
110、508…E/O変換部
111、509…O/E変換部
112、510…デフレーム化部
113…伸張処理サイズ決定部
114、702…伸張部
115、511、511a…ベースバンドフィルタ部(下り)
116、512…D/A変換部
117、513…アップコンバート部
118、514…増幅器
119…圧縮率測定部
120…OFDMシンボル情報推定部
150、250、550、650…光ファイバ
201、601…O/E変換部
202、602…デフレーム化部
203…伸張処理サイズ決定部
204、801…伸張部
205、603、603a…変復調部
206、206a、206b…圧縮処理サイズ決定部
207、802…圧縮部
208、604、604a…フレーム化部
209、605…E/O変換部
210…圧縮率測定部
211…OFDMシンボル情報推定部
Claims (4)
- 分割された基地局の機能を備える信号処理装置と無線装置とを備え、前記信号処理装置と前記無線装置との間においてデジタルRoF(Radio over Fiber)伝送により所定サイズのIFFT(Inverse Fast Fourier Transform)後の信号に対してサイクリックプレフィックスが付加された周期的なシンボル系列を伝送する光通信システムであって、
前記信号処理装置及び前記無線装置のそれぞれは送信部及び受信部を備え、
前記送信部は、
前記シンボル系列の開始位置及び前記シンボル系列を構成する各シンボルの長さに関するシンボル情報を取得し、取得した前記シンボル情報に基づいて、圧縮処理を行う対象となる前記シンボル毎の圧縮サイズを決定する圧縮サイズ決定部と、
決定された前記圧縮サイズ単位で前記シンボル系列を圧縮する圧縮部と、
を備え、
前記受信部は、
前記シンボル系列の伸張処理を行う対象となる前記シンボル毎の伸張サイズを決定する伸張サイズ決定部と、
決定された前記伸張サイズ単位で前記シンボル系列を伸張する伸張部と、
を備える光通信システム。 - 前記送信部は、前記シンボル毎に圧縮率を測定する圧縮率測定部をさらに備え、
前記圧縮サイズ決定部は、測定された圧縮率の所定の統計値が最小となる前記シンボルの位置を前記開始位置として取得し、取得した前記開始位置と、前記各シンボルの長さに関する情報とを用いて前記圧縮サイズを決定する、請求項1に記載の光通信システム。 - 前記送信部は、下りリンク又は上りリンクのIQデータに基づいて前記開始位置を推定するシンボル情報推定部をさらに備える、請求項1に記載の光通信システム。
- 分割された基地局の機能を備える信号処理装置と無線装置とを備え、前記信号処理装置及び前記無線装置のそれぞれは送信部及び受信部を備え、前記信号処理装置と前記無線装置との間においてデジタルRoF(Radio over Fiber)伝送により所定サイズのIFFT(Inverse Fast Fourier Transform)後の信号に対してサイクリックプレフィックスが付加された周期的なシンボル系列を伝送する光通信システムにおける光通信方法であって、
前記送信部が、前記シンボル系列の開始位置及び前記シンボル系列を構成する各シンボルの長さに関するシンボル情報を取得し、取得した前記シンボル情報に基づいて、圧縮処理を行う対象となる前記シンボル毎の圧縮サイズを決定する圧縮サイズ決定ステップと、
前記送信部が、決定された前記圧縮サイズ単位で前記シンボル系列を圧縮する圧縮ステップと、
前記受信部が、前記シンボル系列の伸張処理を行う対象となる前記シンボル毎の伸張サイズを決定する伸張サイズ決定ステップと、
前記受信部が、決定された前記伸張サイズ単位で前記シンボル系列を伸張する伸張ステップと、
を有する光通信方法。
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US10469167B2 (en) | 2019-11-05 |
US20180294881A1 (en) | 2018-10-11 |
EP3285417A1 (en) | 2018-02-21 |
JP6340140B2 (ja) | 2018-06-06 |
EP3285417A4 (en) | 2019-01-09 |
CN107534489B (zh) | 2019-12-27 |
CN107534489A (zh) | 2018-01-02 |
EP3285417B1 (en) | 2020-03-11 |
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