JP2015056736A - Communication system and optical signal transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep transmission efficiency intact in reducing a quantization bit number of a digital RoF signal transmitted between a BBU and an RRU, by the use of predictive coding.SOLUTION: A communication system according to the present invention includes: an error prediction section 47 for generating an error signal of data to be transmitted, by the use of a prediction coefficient stored in a prediction coefficient storage section 46; an error signal transmission section for compressively transmitting the error signal through an optical transmission path; an expansion section 41 for expanding the error signal transmitted by the error signal transmission section; and a signal recovery section 42 for recovering the error signal expanded by the expansion section 41, by the use of a prediction coefficient stored in a prediction coefficient storage section 44.

Description

  The present invention relates to a technique for compressing a digital RoF signal transmitted between BBU and RRU.

  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 between the BBU and the RRU by the RoF technology. The RoF technology can be broadly classified into an analog RoF technology and a digital RoF technology according to an optical transmission method. Recently, studies on a digital RoF technology having excellent transmission quality have been actively conducted, and CPRI (Common Public Radio Interface) (for example, non-patent literature). The use is being developed under a standardization organization such as 1). As a connection medium between BBU and RRU, a coaxial cable, an optical fiber, or the like is used. In particular, the transmission distance can be increased by connecting with an optical fiber.

  One BBU can accommodate a plurality of RRUs. Thereby, BBU required for each RRU can be collected into one, and it becomes possible to reduce an operation cost and an installation cost. As an example of such a form, a form in which BBU-RRU is connected by a PON (Passive Optical Network) system has been proposed. As a signal multiplexing method of the PON, TDM (Time Division Multiplex), WDM (Wavelength Division Multiplex), FDM (Frequency Division Multiplex), or the like can be selected.

  Hereinafter, the digital RoF transmission technology between BBU and RRU is referred to as 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 is converted to an optical signal and transmitted to the RRU, and the optical signal received by the RRU is converted to a radio signal and transmitted to the radio terminal. The link to transmit is called a downlink. On the other hand, a link that receives a radio signal transmitted by a radio terminal by RRU, converts the received radio signal to an optical signal and transmits it to the BBU, converts the optical signal received by the BBU to IQ data, and demodulates the signal Is called uplink.

  FIG. 7 shows an apparatus configuration example of the RRU related to the present invention. For uplink signal processing, the RRU 91 includes an antenna 11 that transmits / receives a radio signal, a transmission / reception switching unit 12 that switches transmission / reception, and an amplifier that amplifies the signal power of the received radio signal to a level that allows signal processing. 13, a down-conversion unit 14 that down-converts a radio signal to baseband, an A / D conversion unit 15 that converts the down-converted analog signal into IQ data, and a baseband filter that performs filtering processing on the IQ data Unit (upstream) 16, a frame conversion unit 17 that multiplexes IQ data and a control signal between BBU 93 and RRU 91, and an electro-optical (E / O) conversion unit 18 that converts an electrical signal into an optical signal and transmits it. . The transmission / reception switching unit 12 is compatible with both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).

  Further, the RRU 91 performs an optical-electrical (O / E) conversion unit 28 for converting an optical signal received from the BBU 93 into an electric signal for downlink signal processing, and a control signal and IQ data between the BBU 93 and the RRU 91 from the received signal. A frame conversion unit 27 to be extracted, a baseband filter unit (downlink) 26 that performs filtering processing on IQ data, a D / A conversion unit 25 that converts IQ data into an analog signal, and an up-conversion that upconverts the analog signal Unit 24, amplifier 23 that amplifies the power to a predetermined transmission power, transmission / reception switching unit 12, and antenna 11.

  FIG. 8 shows an example of a BBU apparatus configuration related to the present invention. For uplink signal processing, the BBU 93 demodulates the IQ data, an O / E converter 31 that converts an optical signal into an electrical signal, a frame converter 32 that extracts a control signal and IQ data from a received signal, and the IQ data. A modem unit 33 is included. Further, for downlink signal processing, the BBU 93 is a modem 33 that outputs IQ data of a radio signal, a frame converter 34 that multiplexes IQ data and a control signal, and an electrical signal that is converted into an optical signal and transmitted. / O converter 35 is provided.

  Taking an example of transmitting a Long Term Evolution (LTE) signal using CPRI, a sampling frequency of 30.72 MHz is used for a system with a system bandwidth of 20 MHz, and digital sampling for each of the I axis and the Q axis. The number of quantization bits of 4 to 20 bits for the upstream signal and 8 to 20 bits for the downstream signal is applied. The frame converter 34 inserts a control signal into 1/16 of the entire frame, and further transmits the signal after 8B / 10B encoding. Therefore, a very wide bandwidth is required in the optical fiber section for digital RoF transmission.

  As a technique for reducing the required bandwidth for digital RoF transmission, there is a technique for reducing the number of quantization bits using predictive coding. In this method, the amplitude value of the next sample point is predicted from several sample points of the radio signal. FIG. 9 shows an example of prediction operation. In FIG. 9, the next sample point is predicted from the past three sample points. In the linear prediction method which is one of the prediction methods, a value obtained by multiplying several past sample points by a coefficient and adding them is used as a predicted value. The coefficient at this time is hereinafter referred to as a prediction coefficient. The prediction coefficient is set so that an error signal, which is the difference between the actual sample point value and the prediction value, becomes small. The higher the prediction accuracy, the closer the amplitude value of the error signal is to zero.

  FIG. 10 shows an example of the probability density function of the error signal. In FIG. 10, the next sample value is predicted at the past 32 sample points for the OFDM radio signal based on the parameters of the LTE PHY layer. The prediction coefficient was determined so that the Euclidean norm of the error signal was minimized every 512 sample points. From FIG. 10, it can be seen that the probability density of the error signal amplitude value is higher near zero. Therefore, if this error signal is encoded by entropy encoding such as Huffman encoding, an amplitude value having a higher appearance probability can be transmitted with a smaller number of bits, thereby reducing the required bandwidth for digital RoF transmission.

  The prediction coefficient is calculated so that an error becomes small with respect to a sample point having a certain length. Hereinafter, a group of the sample points is referred to as a prediction block.

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

  In the method of predicting related error signals, it is necessary to transmit a prediction coefficient from the transmission side to the reception side for each prediction block, which leads to a decrease in transmission efficiency. In addition, for IQ data to be transmitted, a prediction coefficient is generated so that the average amplitude value or average power value of the error signal of the IQ data becomes small, an error signal is calculated, and the error signal is compressed and transmitted. . For this reason, the buffering time until the prediction block is accumulated and the time required to calculate the prediction coefficient are delays in transmission between the BBU 93 and the RRU 91. Although the delay time can be reduced by reducing the length of the prediction block, it is necessary to transmit the prediction coefficient from the transmission side to the reception side for each prediction block, leading to a decrease in transmission efficiency.

  An object of the present invention is to suppress a decrease in transmission efficiency when reducing the number of quantization bits of a digital RoF signal transmitted between BBU and RRU using predictive coding.

  In order to achieve the above object, the present invention calculates a prediction coefficient using data different from IQ data to be transmitted, and uses the IQ data as a prediction coefficient in error prediction.

Specifically, the communication system according to the present invention is:
A communication system in which an antenna unit that transmits and receives radio signals and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
The antenna unit and the signal processing unit are
A prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on the prediction coefficient calculation data;
An error prediction unit that generates an error signal of data to be transmitted using the prediction coefficient stored in the prediction coefficient storage unit;
An error signal transmission unit that compresses the error signal generated by the error prediction unit and transmits the optical transmission path;
An expansion unit for expanding the error signal transmitted by the error signal transmission unit;
Using a prediction coefficient stored in the prediction coefficient storage unit, a signal restoration unit for restoring the error signal expanded by the expansion unit;
Is provided.

  In the communication system according to the present invention, the error signal transmission unit may compress the error signal using entropy coding.

  In the communication system according to the present invention, the prediction coefficient storage unit stores a prediction coefficient corresponding to an average power and variance of a radio signal, and the prediction coefficient output control unit is input every change period of radio band allocation. A prediction coefficient to be output from the prediction coefficient storage unit may be determined by calculating the average power and variance of the radio signal based on the radio band allocation information.

  In the communication system according to the present invention, the signal processing unit includes a prediction coefficient calculation unit that calculates a prediction coefficient using the prediction coefficient calculation data, and the prediction coefficient storage unit of the signal processing unit includes the prediction coefficient The prediction coefficient calculated by the calculation unit is stored, and when the prediction coefficient is notified from the signal processing unit, the prediction coefficient storage unit of the antenna unit deletes the prediction coefficient stored so far and notifies the prediction coefficient. The predicted coefficient may be stored.

In the communication system according to the present invention, the antenna unit and the signal processing unit include a prediction coefficient determination unit that calculates the prediction coefficient using data transmitted in the system in the past as the prediction coefficient calculation data,
The prediction coefficient storage unit may store the prediction coefficient calculated by the prediction coefficient determination unit.

Specifically, the optical signal transmission method according to the present invention includes:
An optical signal transmission method of a communication system in which an antenna unit that transmits and receives a radio signal and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
In the antenna unit and the signal processing unit,
A prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on prediction coefficient calculation data is referred to, and is transmitted using the prediction coefficient stored in the prediction coefficient storage unit. An error prediction procedure for generating an error signal of the data;
An error signal transmission procedure for compressing the error signal generated in the error prediction procedure and transmitting the optical transmission path;
Have

Specifically, the optical signal transmission method according to the present invention includes:
An optical signal transmission method of a communication system in which an antenna unit that transmits and receives a radio signal and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
In the antenna unit and the signal processing unit,
A decompression procedure for decompressing an error signal transmitted through the optical transmission path;
With reference to a prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on the prediction coefficient calculation data, the expansion is performed using the prediction coefficient stored in the prediction coefficient storage unit. A signal restoration procedure for restoring the error signal expanded in the procedure;
Have

  The above inventions can be combined as much as possible.

  According to the present invention, a prediction coefficient is calculated using data different from the IQ data to be transmitted, and the IQ data is used as a prediction coefficient for error prediction. As a result, when transmitting IQ data, the present invention can reduce the delay time by omitting the buffering time for storing the prediction block and the time required for calculating the prediction coefficient.

2 shows an example of a device configuration of an RRU according to the first embodiment. 2 shows an example of a device configuration of a BBU according to the first embodiment. The apparatus structural example of RRU of Embodiment 2 is shown. The apparatus structural example of BBU of Embodiment 2 is shown. 10 illustrates an example of a device configuration of an RRU according to a third embodiment. The apparatus structural example of BBU of Embodiment 3 is shown. The example of apparatus structure of RRU of related invention is shown. The apparatus structural example of BBU of related invention is shown. An example of prediction operation is shown. An example of the probability density function of an error signal is shown.

  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)
A device configuration example of the RRU 91 of the first embodiment is shown in FIG. The RRU 91 is different from the related art for downlink signal processing, the decompression unit 41 that restores the compressed signal, the signal restoration unit 42 that restores the original signal from the error signal, and the prediction that stores the prediction coefficient A coefficient storage unit (downlink) 44 and a prediction coefficient output control unit (downlink) 43 that specifies a prediction coefficient output from the prediction coefficient storage unit 44 are included. Unlike uplink technology, the RRU 91 stores an error prediction unit 47 that generates an error signal of a signal, a compression unit 48 that compresses an error signal output from the error prediction unit 47, and a prediction coefficient. And a prediction coefficient output control unit (upstream) 45 for designating a prediction coefficient output from the prediction coefficient storage unit 46. The compression unit 48 reduces the number of bits by an operation such as entropy encoding, and reduces the required bandwidth for digital RoF transmission. Entropy coding is a process that processes input bit sequences in symbol units that combine multiple bits, examines the appearance probability of each symbol, and converts the output bit sequence so that symbols with higher appearance probability become shorter bit sequences. Is an encoding method in which the length of is shorter than the length of the input bit sequence. In order to perform entropy encoding, it is necessary to measure the distribution function of the amplitude value of the error signal in advance.

  An example of the apparatus configuration of the BBU 93 of the first embodiment is shown in FIG. For downlink signal processing, the BBU 93 stores an error prediction unit 57 that generates an error signal of a signal, a compression unit 58 that compresses an error signal output from the error prediction unit 57, and a prediction coefficient, unlike the related art. And a prediction coefficient output control unit (downlink) 55 that specifies a prediction coefficient output from the prediction coefficient storage unit 56. The BBU 93 is different from the related art for uplink signal processing, the decompression unit 53 that restores the compressed signal, the signal restoration unit 54 that restores the original signal from the error signal, and the prediction that stores the prediction coefficient A coefficient storage unit (upstream) 51 and a prediction coefficient output control unit (upstream) 52 that specifies a prediction coefficient output from the prediction coefficient storage unit 51 are included.

  The RRU 91 functions as an antenna unit, and the BBU 93 functions as a signal processing unit. The prediction coefficient storage units 44 and 46 function as a prediction coefficient storage unit in the RRU 91. The prediction coefficient storage units 56 and 51 function as a prediction coefficient storage unit in the BBU 93. In the downlink, the compression unit 58, the frame conversion unit 34, the E / O conversion unit 35, the O / E conversion unit 28, and the frame conversion unit 27 function as an error signal transmission unit. In the uplink, the compression unit 48, the frame conversion unit 17, the E / O conversion unit 18, the O / E conversion unit 31, and the frame conversion unit 32 function as an error signal transmission unit.

In the optical signal transmission method according to the present embodiment, during downlink signal processing, after the BBU 93 executes the error prediction procedure and the error signal transmission procedure, the RRU 91 executes the extension procedure and the signal restoration procedure.
In the error prediction procedure, the error prediction unit 57 uses the prediction coefficient stored in the prediction coefficient storage unit 56 to generate an error signal of IQ data to be transmitted.
In the error signal transmission procedure, the error signal generated by the error prediction unit 57 is compressed by the compression unit 58 and transmitted to the optical fiber by the E / O conversion unit 35.
In the extension procedure, the extension unit 41 extends the error signal transmitted through the optical fiber.
In the signal restoration procedure, the signal restoration unit 42 restores the error signal expanded by the extension unit 41 using the prediction coefficient stored in the prediction coefficient storage unit 44.

In the optical signal transmission method according to the present embodiment, during uplink signal processing, after the RRU 91 executes the error prediction procedure and the error signal transmission procedure, the BBU 93 executes the extension procedure and the signal restoration procedure.
In the error prediction procedure, the error prediction unit 47 refers to the prediction coefficient storage unit 46 and uses the prediction coefficient stored in the prediction coefficient storage unit 46 to generate an error signal of IQ data to be transmitted.
In the error signal transmission procedure, the error signal generated by the error prediction unit 47 is compressed by the compression unit 48, and the E / O conversion unit 18 transmits it to the optical fiber.
In the extension procedure, the extension unit 53 extends the error signal transmitted through the optical fiber.
In the signal restoration procedure, the signal restoration unit 54 restores the error signal expanded by the extension unit 53 using the prediction coefficient stored in the prediction coefficient storage unit 51.

  The values of the prediction coefficients stored in the prediction coefficient storage units 44, 46, 51 and 56 may be given in advance. Moreover, you may change regularly. When changing periodically, the prediction coefficient may be transmitted from the BBU 93 side. In this case, the BBU 93 includes a prediction coefficient calculation unit that calculates a prediction coefficient. Further, not only one but a plurality of prediction coefficients may be stored. The prediction coefficients designated by the prediction coefficient output control units 43, 45, 52, and 55 may always be the same or may be changed periodically. In order to change periodically, it is necessary to notify the change timing from the BBU 93 to the RRU 91 or to synchronize between the BBU 93 and the RRU 91 so that the respective change timings are aligned.

  External information may be input to the prediction coefficient output control units 43, 45, 52 and 55. For example, radio band allocation information is input. The frequency position and frequency bandwidth used in the radio signal change every change period of the radio band assignment, and the characteristics such as the average power and dispersion of the radio signal change. For this reason, it is considered that the amplitude value of the error signal can be reduced by changing the prediction coefficient according to the allocated frequency position and frequency bandwidth for each period of radio band allocation.

  The prediction coefficient is created using data different from the IQ data to be transmitted. The longer the data length of the other data used at this time, the longer the predicted block length, and thus the prediction accuracy improves.

  In the invention according to the present embodiment, a prediction coefficient is calculated using data different from the IQ data to be transmitted, and the IQ data is used as a prediction coefficient when error prediction is performed. Thereby, when IQ data is transmitted, the buffering time for storing the prediction block and the time required to calculate the prediction coefficient are omitted, and the delay time is reduced. The invention according to the present embodiment uses one prediction coefficient in a fixed manner. Thereby, the exchange of the prediction coefficient between BBU93-RRU91 can be omitted, and a transmission efficiency fall can be suppressed.

(Embodiment 2)
In Embodiment 1, it is necessary to memorize | store a prediction coefficient beforehand by BBU93 and RRU91. In the second embodiment, the prediction coefficient is calculated and used based on the past IQ data transmitted / received between the BBU 93 and the RRU 91, thereby eliminating the need to previously store the prediction coefficient in the BBU 93 and the RRU 91.

  A device configuration example of the RRU 91 of the second embodiment is shown in FIG. The RRU 91 is different from the related art because of downlink signal processing, and an expansion unit 41 that restores a compressed signal, a signal restoration unit 42 that restores the original signal from an error signal, and a signal obtained so far A prediction coefficient determination unit (downlink) 62 that calculates a prediction coefficient based on IQ data is included. The RRU 91 is different from the related art for uplink signal processing, an error prediction unit 47 that generates a signal error signal, a compression unit 48 that compresses an error signal output from the error prediction unit 47, and a baseband filter unit (Uplink) A prediction coefficient determination unit (uplink) 61 that calculates a prediction coefficient based on IQ data output by 16 is provided. The IQ data used by the prediction coefficient determination unit (upstream) 61 at an arbitrary time point is IQ data of a past time point than the IQ data input to the error prediction unit 47 at the same time point.

  FIG. 4 shows a device configuration example of the BBU 93 of the second embodiment. Unlike the related art, the BBU 93 is based on IQ data based on the IQ data based on the IQ data, the error prediction unit 57 that generates an error signal of the signal, the compression unit 58 that compresses the error signal output from the error prediction unit 57, and the related art. Has a prediction coefficient determination unit (downlink) 64 for calculating a prediction coefficient. The IQ data used by the prediction coefficient determination unit (downlink) 64 at an arbitrary time point is IQ data at a past time point than the IQ data input to the error prediction unit 57 at the same time point. The BBU 93 is different from the related art because of uplink signal processing, and an expansion unit 53 that restores a compressed signal, a signal restoration unit 54 that restores the original signal from an error signal, and a signal obtained so far A prediction coefficient determination unit (upstream) 63 that calculates a prediction coefficient based on IQ data is included.

  The prediction coefficient determination unit (upstream) 61 and the prediction coefficient determination unit (downstream) 62 store the calculated prediction coefficients and function as a prediction coefficient storage unit in the RRU 91. The prediction coefficient determination unit (upstream) 63 and the prediction coefficient determination unit (downstream) 64 store the calculated prediction coefficients and function as a prediction coefficient storage unit in the BBU 93.

  As described above, the invention according to the present embodiment calculates the prediction coefficient on the receiving side. For this reason, the exchange of the prediction coefficient between BBU93-RRU91 can be omitted, and a transmission efficiency fall can be suppressed.

(Embodiment 3)
In the third embodiment, the calculation coefficient required for calculating the prediction coefficient is reduced by storing and using the prediction coefficient calculated in the second embodiment in a fixed manner.

  FIG. 5 shows a device configuration example of the RRU 91 of the third embodiment. Unlike the second embodiment, the RRU 91 includes a prediction coefficient storage unit (downlink) 72 that stores the prediction coefficient calculated by the prediction coefficient determination unit (downlink) 62 for downlink signal processing. Unlike the second embodiment, the RRU 91 includes a prediction coefficient storage unit (uplink) 71 that stores the prediction coefficient calculated by the prediction coefficient determination unit (uplink) 61 for uplink signal processing.

  FIG. 6 shows a device configuration example of the BBU 93 of the third embodiment. Unlike the second embodiment, the BBU 93 includes a prediction coefficient storage unit (downlink) 74 that stores the prediction coefficient calculated by the prediction coefficient determination unit (downlink) 64 for downlink signal processing. Unlike the second embodiment, the BBU 93 includes a prediction coefficient storage unit (uplink) 73 that stores the prediction coefficient calculated by the prediction coefficient determination unit (uplink) 63 for uplink signal processing.

  The frequency with which the prediction coefficient determination units 61, 62, 63, and 64 calculate the prediction coefficient can be set to an arbitrary value. The frequency may be set for each period of radio band allocation.

  As described above, the invention according to this embodiment calculates a prediction coefficient on the receiving side, and uses the calculated prediction coefficient. For this reason, the exchange of the prediction coefficient between BBU93-RRU91 can be omitted, and a transmission efficiency fall can be suppressed.

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

11: Antenna 12: Transmission / reception switching unit 13: Amplification unit 14: Down-conversion unit 15: A / D conversion unit 16: Baseband filter unit (upstream)
17: Frame conversion unit 18: Electro-optical (E / O) conversion unit 23: Amplifier 24: Up-conversion unit 25: D / A conversion unit 26: Baseband filter unit (downlink)
27: Frame converter 28: Optical-electrical (O / E) converter 31: O / E converter 32: Frame converter 33: Modulator / demodulator 34: Frame converter 35: E / O converter 41: Decompressor 42 : Signal restoration unit 43: prediction coefficient output control unit (downlink)
44: Prediction coefficient storage unit (downlink)
45: Prediction coefficient output control unit (upstream)
46: Prediction coefficient storage unit 47: Error prediction unit 48: Compression unit 51: Prediction coefficient storage unit (upstream)
52: Prediction coefficient output control unit (upstream)
53: Expansion unit 54: Signal restoration unit 55: Prediction coefficient output control unit (downlink)
56: Prediction coefficient storage unit (downlink)
57: Error prediction unit 58: Compression unit 61: Prediction coefficient determination unit (upstream)
62: Prediction coefficient determination unit (downlink)
63: Prediction coefficient determination unit (upstream)
64: Prediction coefficient determination unit (downlink)
71: Prediction coefficient storage unit (upstream)
72: Prediction coefficient storage unit (downlink)
73: Prediction coefficient storage unit (upstream)
74: Prediction coefficient storage unit (downlink)
91: RRU
93: BBU

Claims (7)

A communication system in which an antenna unit that transmits and receives radio signals and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
The antenna unit and the signal processing unit are
A prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on the prediction coefficient calculation data;
An error prediction unit that generates an error signal of data to be transmitted using the prediction coefficient stored in the prediction coefficient storage unit;
An error signal transmission unit that compresses the error signal generated by the error prediction unit and transmits the optical transmission path;
An expansion unit for expanding the error signal transmitted by the error signal transmission unit;
Using a prediction coefficient stored in the prediction coefficient storage unit, a signal restoration unit for restoring the error signal expanded by the expansion unit;
A communication system comprising:   The communication system according to claim 1, wherein the error signal transmission unit compresses the error signal using entropy coding. The prediction coefficient storage unit stores a prediction coefficient according to the average power and variance of the radio signal,
The prediction coefficient output control unit calculates an average power and variance of a radio signal based on radio band allocation information input at each radio band allocation change period, and determines a prediction coefficient to be output from the prediction coefficient storage unit The communication system according to claim 1 or 2, characterized by: The signal processing unit includes a prediction coefficient calculation unit that calculates a prediction coefficient using the prediction coefficient calculation data,
The prediction coefficient storage unit of the signal processing unit stores the prediction coefficient calculated by the prediction coefficient calculation unit,
When the prediction coefficient is notified from the signal processing unit, the prediction coefficient storage unit of the antenna unit erases the prediction coefficient stored so far and stores the notified prediction coefficient. The communication system according to any one of claims 1 to 3. The antenna unit and the signal processing unit include a prediction coefficient determination unit that calculates the prediction coefficient using data transmitted in the system in the past as the prediction coefficient calculation data,
The communication system according to claim 1, wherein the prediction coefficient storage unit stores the prediction coefficient calculated by the prediction coefficient determination unit. An optical signal transmission method of a communication system in which an antenna unit that transmits and receives a radio signal and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
In the antenna unit and the signal processing unit,
A prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on prediction coefficient calculation data is referred to, and is transmitted using the prediction coefficient stored in the prediction coefficient storage unit. An error prediction procedure for generating an error signal of the data;
An error signal transmission procedure for compressing the error signal generated in the error prediction procedure and transmitting the optical transmission path;
An optical signal transmission method comprising: An optical signal transmission method of a communication system in which an antenna unit that transmits and receives a radio signal and a signal processing unit that controls the antenna unit are connected using an optical transmission line,
In the antenna unit and the signal processing unit,
A decompression procedure for decompressing an error signal transmitted through the optical transmission path;
With reference to a prediction coefficient storage unit that stores a prediction coefficient that predicts an error in reducing the number of quantization bits based on the prediction coefficient calculation data, the expansion is performed using the prediction coefficient stored in the prediction coefficient storage unit. A signal restoration procedure for restoring the error signal expanded in the procedure;
An optical signal transmission method comprising:

Images