JP2016134705A - Transmission system and transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rightly set up a CPRI link by substituting a K28.5 code with another bit sequence when multiplexing N pieces of CPRI signals or a compressed CPRI signal, and disposing the K28.5 code of the remaining one CPRI signal or the compressed CPRI signal at the head of a hyper frame of the CPRI signal that is constituted by multiplexing.SOLUTION: A transmission system comprises: a transmission-side device by which, when multiplexing a plurality of digital RoF signals, substitution processing is performed for substituting bit sequences as many as a number subtracting 1 from a multiplex number with any other bit sequence than the bit sequence for frame synchronization, and outputting a result as one digital RoF signal; and a reception-side device which performs restoration processing, after the digital RoF signal is demultiplexed into a plurality of digital RoF signals, for restoring the other bit sequence than the bit sequence for frame synchronization that is substituted by the substitution processing of the transmission-side device, into the bit sequence for frame synchronization.SELECTED DRAWING: Figure 12

Description

  The present invention relates to a BBU-RRH transmission system and a CPRI transmission method.

  In a cellular system, in order to improve the degree of freedom of cell configuration, the base station function is divided into a signal processing unit (BBU: Base Band Unit) and an RF unit (RRH: Remote Radio Head) and physically separated. It is considered to do. At this time, the radio signal is transmitted between the BBU and RRH by the RoF technology.

  RoF technology can be broadly divided into analog RoF technology and digital RoF technology depending on the optical transmission method. Recently, digital RoF technology with excellent transmission quality has been actively studied, and standardization such as CPRI (Common Public Radio Interface) [1]. The use is being developed under the organization. As a connection medium between BBU and RRH, 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.

  The CPRI transmission will be described below. Thereafter, the digital signal (IQ data) for each of the I axis and Q axis of the radio signal created by the BBU is converted into an optical signal and transmitted to the RRH, and the optical signal received by the RRH is converted into a radio signal, and the radio terminal A link transmitted to is called a downlink. On the other hand, a link that receives a radio signal transmitted by a radio terminal by RRH, converts the received radio signal into an optical signal and transmits it to the BBU, converts the optical signal received by the BBU into IQ data, and demodulates the signal Is called uplink.

  An example of the RRH apparatus configuration during CPRI transmission is shown in FIG. For uplink signal processing, the RRH 11 amplifies the radio signal transmission / reception antenna 10, the transmission / reception switching unit 12-1 for switching transmission / reception, and the signal power of the received radio signal to a level at which signal processing is possible. An amplifier 13-1, a down-conversion unit 14-1 that down-converts a radio signal to baseband, an A / D conversion unit 15-1 that converts the down-converted analog signal into IQ data, and IQ data A baseband filter unit (upstream) 16-1 that performs filtering processing, a CPRI framing unit 17-1 that multiplexes IQ data and a control signal, and an electro-optical (E / O) It has the conversion part 18-1. The transmission / reception switching unit 12-1 is compatible with both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).

  The RRH 11 also performs an optical signal received from the BBU 21 to an electric signal for downlink signal processing, and an optical-electrical (O / E) converter 19-1, and a CPRI decoder for extracting a control signal and IQ data from the received signal. A framing unit 22-1; a baseband filter unit (downlink) 23-1 that performs filtering on IQ data; a D / A conversion unit 24-1 that converts IQ data into an analog signal; It has an up-conversion unit 25-1 that performs up-conversion, an amplifier 13-2 that amplifies power to a predetermined transmission power, a transmission / reception switching unit 12-1, and an antenna 10.

  An example of the device configuration of the BBU 21 at the time of CPRI transmission is shown in FIG. For uplink signal processing, the BBU 21 is an O / E converter 19-2 that converts an optical signal into an electrical signal, a CPRI deframing unit 22-2 that extracts a control signal and IQ data from a received signal, and IQ data. A modulation / demodulation unit 26-1 for demodulating the signal.

  Further, for downlink signal processing, the BBU 21 converts a modulation / demodulation unit 26-1 that outputs IQ data of a radio signal, a CPRI framing unit 17-2 that multiplexes IQ data and a control signal, and converts an electrical signal into an optical signal. And an E / O conversion unit 18-2 for transmission.

  FIG. 3 shows a configuration of an option3 CPRI frame. The CPRI has a basic frame as a minimum unit, and 256 basic frames are collected to constitute one hyper frame, and 150 hyper frames are gathered to constitute one CPRI 10 ms frame. One basic frame is about 260 ns, one hyperframe is about 66.6 us, and one CPRI 10 ms frame is 10 ms. Within one basic frame, the first 1/16 is used to send control signals, and the remaining 15/16 is used to send IQ data.

  A K28.5 code is transmitted as a control signal at the head of the hyperframe. The K28.5 code is a code that appears only at the head of the hyperframe, and is used to establish frame synchronization between the BBU 21 and the RRH 11 and to establish a CPRI link.

  The CPRI multiplex transmission will be described below. By multiplex transmission of a plurality of CPRI signals, the optical fibers 20 can be aggregated, leading to economy. FIG. 4 shows a connection example of three BBU21 / RRH11. Unlike FIG.1 and FIG.2, both BBU21 / RRH11 are provided with the demultiplexing parts 27-1 and 27-2 which demultiplex and demultiplex several CPRI signals, respectively. Thereby, compared with the case where each CPRI signal is transmitted with a separate fiber, the optical fibers 20 can be collected. Each RRH 11 and each BBU 21 may be physically separated. The demultiplexing unit 27 in FIG. 4 may be realized by a PON (Passive Optical Network) system.

  FIG. 5 shows an example of connection between the RRH 11 and the BBU 21 that include the three antennas 10. Unlike FIG. 4, in FIG. 5, demultiplexing units 27-3 and 27-4 are provided in the BBU 21 and the RRH 11, respectively. The number of CPRI signals to be demultiplexed is not limited to three, and an arbitrary number of signals can be multiplexed. The demultiplexing unit 27 may be any of time multiplexing, frequency multiplexing, and wavelength multiplexing. However, in frequency multiplexing / wavelength multiplexing, it is necessary to increase the frequency / wavelength in accordance with the number of multiplexing. Therefore, time multiplexing is assumed below.

  The CPRI compression / multiplex transmission will be described below. The CPRI transmission requires a very wide band in the optical fiber 20 section. For example, in a Long Term Evolution (LTE) system, a radio signal of 2 × 2 MIMO with a system bandwidth of 20 MHz is a maximum of 150 Mbps in a radio section. However, in order to transmit this with a 15-bit quantization bit number, option 3 (2. (4576 Gbps) or higher is required. For this reason, in order to improve the number of RRHs 11 accommodated during multiplex transmission, a compression method for reducing the required bandwidth of the CPRI signal is required. Examples of the compression method include a reduction in sampling frequency, a reduction in the number of quantization bits, and entropy coding.

  FIG. 6 shows a configuration example when a compression technique is introduced in the multiplex transmission of FIG. The compression unit 28 compresses the CPRI IQ data, and the decompression unit 29 restores the compressed IQ data. The CPRI control signal is not compressed so that the CPRI link is normally established. For this reason, for example, in order for the result of compressing and multiplexing two CPRI signals of option 3 to have a transmission rate lower than that of one CPRI signal of option 3, the transmission amount of compressed IQ data / the original IQ data It is necessary to apply compression so that the transmission amount <0.467.

  FIG. 7 shows a configuration example when a compression technique is introduced in the multiplex transmission of FIG. The compression unit 28 compresses the CPRI IQ data, and the decompression unit 29 restores the compressed IQ data. 8 and 9 show device configuration examples of the compression unit 28 and the expansion unit 29, respectively. In FIG. 8, a compression unit 28 includes a CPRI deframing unit 22 that separates a CPRI frame into a control signal and IQ data, an IQ data compression unit 31 that performs compression processing on the extracted IQ data, and a compressed data A multiplexing unit 32 for multiplexing the IQ data and the control signal is provided. If the compressed IQ data and the control signal are separately output, input to the demultiplexing unit 27, and multiplexed by the demultiplexing unit 27, the multiplexing unit 32 in the compression unit 28 becomes unnecessary.

  In FIG. 9, the decompression unit 29 includes a separation unit 34 that separates the compressed IQ data and the control signal, an IQ data decompression unit 33 that performs decompression processing on the compressed IQ data, and the decompressed IQ data and control. And a CPRI framing unit 17 for multiplexing signals. If the demultiplexing unit 27 outputs the compressed IQ data and the control signal separately and inputs them to the decompressing unit 29, the separating unit 34 in the decompressing unit 29 becomes unnecessary.

  It is assumed that the interface between the demultiplexing unit 27 is CPRI. The transmission speed of the CPRI signal after compression multiplexing is a value smaller than the total value of the original CPRI signal, but the CPRI control signal is not compressed. For this reason, it is necessary to transmit one of the CPRI control signals on the IQ data area of the CPRI frame.

CPRI, “CPRI Specification V6.0,” Aug. 30, 2013, http: // www. cpri. info / spec. html

  In the following, it is assumed that the interface between the demultiplexing unit 27 is CPRI. FIG. 10 shows an example of the operation of the related art when multiplexing 2CPRI signals. At this time, a plurality of K28.5 codes exist in one hyperframe in the multiplexed CPRI signal. For this reason, there is a possibility that the K28.5 code existing at the head of the hyperframe cannot be detected on the receiving side and the CPRI link cannot be established. In other words, in the case of the related technology, since a plurality of K28.5 codes are included in one hyperframe on the receiving side, there is a possibility that the CPRI link cannot be correctly established.

  FIG. 11 shows an example of the operation of the related art when the 2CPRI signal is compressed and multiplexed. At this time, a plurality of K28.5 codes exist within one hyperframe. For this reason, there is a possibility that the K28.5 code existing at the head of the hyperframe cannot be detected on the receiving side and the CPRI link cannot be established.

  In order to solve the above-described problems, the present invention aims to correctly establish a CPRI link by setting the K28.5 code of the CPRI signal to a hyperframe of the CPRI signal in a predetermined arrangement. .

  In order to achieve the above object, according to the present invention, when N CPRI signals or compressed CPRI signals are multiplexed, the K28.5 code of N-1 CPRI signals or compressed CPRI signals is converted into another bit sequence. Replace with. Further, the K28.5 code of the remaining one CPRI signal or the compressed CPRI signal is arranged at the head of the hyperframe of the CPRI signal formed by multiplexing, so that the K28.5 code cannot be detected. By doing so, a technique capable of correctly establishing a CPRI link is provided.

Specifically, the transmission system according to the present invention is:
When multiplexing a plurality of digital RoF signals, a transmission-side apparatus that performs a replacement process of replacing the multiplex number-1 frame synchronization bit sequence with a bit sequence other than the frame synchronization bit sequence and outputs it as one digital RoF signal When,
After separating the digital RoF signal into a plurality of digital RoF signals, a restoration process is performed to restore a bit series other than the frame synchronization bit series replaced by the replacement process of the transmission side device to the frame synchronization bit series. A receiving-side device.

In the transmission system according to the present invention,
The sending device is
In parallel with the replacement process, the IQ data of the digital RoF signal before multiplexing is compressed,
The receiving device
In parallel with the restoration process, the compressed digital RoF signal after separation may be decompressed.

In the transmission system according to the present invention,
The sending device is
New information may be placed at a position where the frame synchronization bit sequence is replaced by the replacement process, and may be used for communication between the demultiplexing units respectively included in the transmission side device and the reception side device.

In the transmission system according to the present invention,
When the digital RoF signal is a CPRI signal, position information for restoring a frame synchronization bit sequence that is a K28.5 code may be transmitted using reserved bits or an IQ data area of the control signal of the CPRI signal.

In the transmission system according to the present invention,
When the digital RoF signal is a CPRI signal, the position where the frame synchronization bit sequence that is the K28.5 code is restored is the relative position from D5.6 or D16.2 of the CPRI signal in which the K28.5 code is replaced. It may be estimated.

Specifically, the transmission method according to the present invention is:
The sending device is
In the case of multiplexing a plurality of digital RoF signals, a multiplex number-1 frame synchronization bit sequence is replaced with a bit sequence other than the frame synchronization bit sequence and output as one digital RoF signal,
The receiving device
After the digital RoF signal is separated into a plurality of digital RoF signals, a restoration process is performed to restore a bit series other than the frame synchronization bit series replaced by the replacement process of the transmission side device to the frame synchronization bit series.

  The above inventions can be combined as much as possible.

  According to the present invention, the CPRI link can be correctly established by setting the K28.5 code of the CPRI signal to the hyperframe of the CPRI signal in a predetermined arrangement.

An example of the block diagram of RRH at the time of CPRI transmission which concerns on related technology is shown. An example of the block diagram of BBU at the time of CPRI transmission which concerns on related technology is shown. An example of the CPRI frame of the Option 3 according to related technology is shown. An example at the time of connection of 3 BBU / RRH which concerns on related technology is shown. An example at the time of connection of BBU / RRH provided with three antennas concerning related technology is shown. An example of a block diagram at the time of introducing a compression technique at the time of multiplex transmission of three BBU / RRH related technologies is shown. An example of a block diagram at the time of introduce | transducing a compression technique at the time of the multiplex transmission of BBU / RRH provided with three antennas which concern on related technology is shown. An example of the block diagram of the compression part which concerns on related technology is shown. An example of the block diagram of the expansion | extension part which concerns on related technology is shown. An example at the time of multiplexing 2CPRI signal which concerns on related technology is shown. An example in the case of compressing and multiplexing 2CPRI signals according to related technology is shown. An example of a lineblock diagram of three BBU / RRH concerning Embodiment 1 is shown. An example of the block diagram of BBU / RRH provided with the three antennas concerning Embodiment 2 is shown. An example of the block diagram of the code conversion part which concerns on this embodiment is shown. An example of the block diagram of the code decompression | restoration part which concerns on this embodiment is shown. An example of the operation example of the structure which concerns on Embodiment 1 or 2 is shown. An example of a block diagram of three BBU / RRH concerning Embodiment 3 is shown. An example of a block diagram of BBU / RRH provided with three antennas concerning Embodiment 4 is shown. An example of the block diagram of the code conversion compression part which concerns on this embodiment is shown. An example of the block diagram of the code decompression | restoration expansion part which concerns on this embodiment is shown. An example of the operation example of the structure which concerns on Embodiment 3 or 4 is shown. An example of the operation example of the structure which concerns on Embodiment 3 or 4 is shown. An example of the block diagram of the code conversion compression part which concerns on Embodiment 5 is shown. An example of the block diagram of the code decompression | restoration expansion part which concerns on Embodiment 5 is shown. An example of the block diagram of the code decompression | restoration expansion part which concerns on Embodiment 6 is shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
In the present embodiment, the transmission system includes a BBU 21 and an RRH 11. The BBU 21 and the RRH 11 connected via the optical fiber 20 may function as a transmission-side device or a reception-side device, respectively, depending on the link configuration during downlink or uplink communication.

  In the first embodiment, the present invention is applied to FIG. FIG. 12 shows a device configuration example of the BBU 21 / RRH 11 according to the first embodiment. Unlike FIG. 4, the code conversion unit 35 that performs a replacement process for replacing the K28.5 code of the multiplexed number-1 CPRI signal with another bit sequence, and the replaced bit sequence of the multiplexed number-1 replaced with K28. A code restoration unit 36 that performs restoration processing to restore to .5 code is included.

  As shown in FIG. 14, the code converting unit 35 has a K28.5 code replacing unit 38, which detects the K28.5 code and replaces it with another bit sequence. As shown in FIG. 15, the code restoration unit 36 has a K28.5 code restoration unit 39, and restores the replaced another bit sequence to a K28.5 code.

(Embodiment 2)
In the second embodiment, the present invention is applied to FIG. FIG. 13 shows a device configuration example of the BBU 21 / RRH 11 of the second embodiment. Unlike FIG. 5, the code conversion unit 35 that performs a replacement process of replacing the K28.5 code of the multiplex number-1 CPRI signal with another bit sequence, and the multiplex number-1 replaced bit sequence is replaced with K28. A code restoration unit 36 that performs restoration processing to restore to .5 code is included.

  As shown in FIG. 14, the code converting unit 35 has a K28.5 code replacing unit 38, which detects the K28.5 code and replaces it with another bit sequence. As shown in FIG. 15, the code restoration unit 36 has a K28.5 code restoration unit 39, and restores the replaced another bit sequence to a K28.5 code. FIG. 16 shows an operation example when the first or second embodiment is applied. In the multiplexed CPRI signal, only one K28.5 code exists, and in each separated CPRI signal, the K28.5 code is restored.

(Embodiment 3)
In the third embodiment, the present invention is applied to FIG. FIG. 17 shows a device configuration example of the BBU 21 / RRH 11 of the third embodiment. Unlike FIG. 6, a code conversion compression unit 41 that performs a replacement process for replacing the K28.5 code of the multiplexed number-1 CPRI signal with another bit sequence, and another replaced bit sequence of the multiplexed number-1 It has a code restoration / decompression unit 42 that performs restoration processing to restore the K28.5 code.

  As shown in FIG. 19, the code conversion compression unit 41 includes a K28.5 code replacement unit 38 in addition to the compression unit 28 of FIG. 8, and detects the K28.5 code and replaces it with another bit sequence. As shown in FIG. 20, the code restoration / decompression unit 42 has a K28.5 code restoration unit 39 in addition to the decompression unit 29 of FIG. 9, and restores the replaced another bit sequence to the K28.5 code. To do.

(Embodiment 4)
In the fourth embodiment, the present invention is applied to FIG. FIG. 18 shows a device configuration example of the BBU 21 / RRH 11 of the fourth embodiment. Unlike FIG. 7, a code conversion compression unit 41 that performs a replacement process for replacing the K28.5 code of the multiplexed number-1 CPRI signal with another bit sequence, and another replaced bit sequence of the multiplexed number-1 It has a code restoration / decompression unit 42 that performs restoration processing to restore the K28.5 code.

  As shown in FIG. 19, the code conversion compression unit 41 includes a K28.5 code replacement unit 38 in addition to the compression unit 28 of FIG. 8, and detects the K28.5 code and replaces it with another bit sequence. As shown in FIG. 20, the code restoration / decompression unit 42 has a K28.5 code restoration unit 39 in addition to the decompression unit 29 of FIG. 9, and restores the replaced another bit sequence to the K28.5 code. To do.

  An operation example when the third or fourth embodiment is applied is shown in FIGS. As shown in FIG. 21, there is only one K28.5 code in the multiplexed CPRI signal, and as shown in FIG. 22, the K28.5 code is restored in each separated CPRI signal.

(Embodiment 5)
In the fifth embodiment, the K28.5 code is replaced with other new information. The new information is used for communication between the demultiplexing units 27, for example, and synchronization establishment and monitoring control information exchange between the demultiplexing units 27 is performed. According to the fifth embodiment, communication between the demultiplexing units 27 is possible without adding new communication resources (time band or wavelength band).

  23 and 24 show device configuration examples of the code conversion compression unit 41 and the code restoration / decompression unit 42 when the fifth embodiment is applied to FIG. 6 or FIG. Information to be communicated between the demultiplexing units 27 is added in the K28.5 code replacing unit 38 that performs the replacement process, and information to be communicated between the demultiplexing units 27 is extracted in the K28.5 restoration unit 39 that performs the restoration process.

(Embodiment 6)
In the embodiments so far, it has been assumed that the position information of the replaced bit sequence is transmitted. For example, this is realized by placing relative position information from the K28.5 code of the replaced bit sequence in the reserved bit or IQ data area of the CPRI control signal.

  In the sixth embodiment, the position information of the bit sequence replaced by the replacement process is estimated from the compressed CPRI signal. For example, except for option 1, D16.2 or D5.6 code is always sent following K28.5 code, and if these are detected, the position of the replaced bit sequence is specified. FIG. 25 shows a device configuration example of the code restoration / decompression unit 42 that performs restoration processing when the sixth embodiment is applied to FIG. 6 or FIG. The position information estimation unit 43 estimates the position of the replaced bit sequence. The code conversion compression unit 41 is the same as in the third to fifth embodiments.

  So far, the invention has been described for the case of the CPRI signal. The present invention is applicable not only to a CPRI signal but also to a digital RoF signal including a frame sequence bit sequence. When multiplexing a digital RoF signal including a plurality of the frame synchronization bit sequences, a plurality of frame synchronization bit sequences are included in the multiplexed signal. By applying the present invention, a frame included in the multiplexed signal is included. One synchronization bit sequence can be provided.

  According to the above-described embodiment, the number of K28.5 codes included in one hyperframe of the CPRI signal becomes one, and the CPRI link can be correctly established. Further, when N CPRI signals or compressed CPRI signals are multiplexed, the K28.5 code of the N−1 CPRI signals or compressed CPRI signals is replaced with another bit sequence. Also, the KPRI code can be correctly established by placing the K18.5 code of the remaining one CPRI signal or the compressed CPRI signal at the head of the hyperframe of the CPRI signal formed by multiplexing.

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

10: Antenna 11: RRH
12, 12-1, 12-2, 12-3, 12-4, 12-5: transmission / reception switching unit 13, 13-1, 13-2, 13-3, 13-4, 13-4, 13-5 , 13-6, 13-7, 13-8, 13-9, 13-10: amplifiers 14, 14-1, 14-2, 14-3, 14-4, 14-5: down-conversion units 15, 15 -1, 15-2, 15-3, 15-4, 15-5: A / D converters 16, 16-1, 16-2, 16-3, 16-4, 16-5: Baseband filter units (Up)
17, 17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7, 17-8, 17-9, 17-10: CPRI framing units 18, 18- 1, 18-2, 18-3, 18-4, 18-5, 18-6, 18-7, 18-8, 18-9, 18-10, 18-11, 18-12, 18-13, 18-14, 18-15, 18-16, 18-17, 18-18, 18-19, 18-20, 18-21, 18-22, 18-23, 18-24: E / O converter 19 19-1, 19-2, 19-3, 19-4, 19-5, 19-6, 19-7, 19-8, 19-9, 19-10, 19-11, 19-12, 19 -13, 19-14, 19-15, 19-16, 19-17, 19-18, 19-19, 19-20, 19-21, 19-22 19-23,19-24: O / E conversion unit 20: optical fiber 21: BBU
22, 22-1, 22-2, 22-3, 22-4, 22-5, 22-6, 22-7, 22-8, 22-9, 22-10: CPRI deframing units 23 and 23 -1, 23-2, 23-3, 23-4, 23-5: Baseband filter section (downlink)
24, 24-1, 24-2, 24-3, 24-4, 24-5: D / A converter 25, 25-1, 25-2, 25-3, 25-4, 25-5: Up Conversion units 26, 26-1, 26-2, 26-3, 26-4, 26-5: modulation / demodulation units 27, 27-1, 27-2, 27-3, 27-4, 27-5, 27- 6, 27-7, 27-8, 27-9, 27-10, 27-11, 27-12, 27-13: Demultiplexing units 28, 28-1, 28-2, 28-3, 28-4 28-5, 28-6, 28-7, 28-8: compression units 29, 29-1, 29-2, 29-3, 29-4, 29-5, 29-6, 29-7, 29 -8: Expansion unit 31: IQ data compression unit 32: Multiplexing unit 33: IQ data expansion unit 34: Separation units 35, 35-1, 35-2, 35-3, 35-4: Code modification Parts 36, 36-1, 36-2, 36-3, 36-4: code restoration part 38: K28.5 code replacement part 39: K28.5 code restoration part 41, 41-1, 41-2, 41- 3, 41-4: Code conversion compression unit 42, 42-1, 42-2, 42-3, 42-4: Code restoration / decompression unit 43: Position information estimation unit

Claims (6)

When multiplexing a plurality of digital RoF signals, a transmission-side apparatus that performs a replacement process of replacing the multiplex number-1 frame synchronization bit sequence with a bit sequence other than the frame synchronization bit sequence and outputs it as one digital RoF signal When,
After separating the digital RoF signal into a plurality of digital RoF signals, a restoration process is performed to restore a bit series other than the frame synchronization bit series replaced by the replacement process of the transmission side device to the frame synchronization bit series. A receiving device;
A transmission system comprising: The sending device is
In parallel with the replacement process, the IQ data of the digital RoF signal before multiplexing is compressed,
The receiving device
The transmission system according to claim 1, wherein the compressed digital RoF signal after separation is expanded in parallel with the restoration processing. The sending device is
The new information is placed at a position where the bit sequence for frame synchronization is replaced by the replacement process and used for communication between demultiplexing units respectively included in the transmission side device and the reception side device. The transmission system described in 1. When the digital RoF signal is a CPRI signal, position information for restoring a frame synchronization bit sequence that is a K28.5 code is transmitted using a reserved bit or an IQ data area of the control signal of the CPRI signal. The transmission system according to claim 1. When the digital RoF signal is a CPRI signal, the position where the frame synchronization bit sequence that is the K28.5 code is restored is the relative position from D5.6 or D16.2 of the CPRI signal in which the K28.5 code is replaced. The transmission system according to claim 1, wherein the transmission system is estimated. The sending device is
In the case of multiplexing a plurality of digital RoF signals, a multiplex number-1 frame synchronization bit sequence is replaced with a bit sequence other than the frame synchronization bit sequence and output as one digital RoF signal,
The receiving device
After the digital RoF signal is separated into a plurality of digital RoF signals, a restoration process is performed to restore a bit series other than the frame synchronization bit series replaced by the replacement process of the transmission side device to the frame synchronization bit series. A transmission method characterized by the above.

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