JP2015115694A - Wireless signal transmission system, remote device, master device, and transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate the non-linear distortion and waveform deterioration of a downlink optical signal generated in optical transmission by digital signal processing in a preliminary compensation circuit disposed in a master device or a compensation circuit disposed in a remote device in a radio signal transmission system.SOLUTION: A radio signal transmission system includes: a remote device 61 for transmitting an uplink optical signal to a master device 51 connected via an optical transmission line 58; and the master device 51 for receiving the uplink optical signal transmitted by the remote device 61. The remote device 61 adds a preliminarily calculated distortion compensation amount to an electric signal, converts the added electric signal into the uplink optical signal, and transmits it to the master device 51, and the master device 51 converts the received uplink optical signal into the electric signal, detects the distortion amount of the electric signal, compensates the detected distortion amount, and converts the compensated electric signal into a radio signal.

Description

  The present invention relates to a technique for transmitting a high-quality, economically wide-band wireless signal in a wireless signal transmission system using ROF (Radio over Fiber).

  The progress of broadband wireless systems using a cellular configuration including LTE (Long Term Evolution) is remarkable. In such cellular broadband wireless systems, there is a tendency to adopt a small cell configuration with a reduced cell size in order to efficiently provide a wider band service to many users in various environments, thus maintaining coverage. This increases the number of cells.

  In order to install many cells, it is necessary to reduce the size of the base station, and a distributed antenna configuration in which the radio base station is divided into a radio modulation / demodulation unit and a radio transmission / reception unit is adopted. In this case, the wireless transmission / reception unit installed in the vicinity of the antenna can be reduced in size, and efficient installation becomes possible.

  In such a distributed antenna configuration, it is necessary to transmit a radio signal between the radio modulation / demodulation unit 11 and the radio transmission / reception unit 21, and it is also necessary to transmit a long distance. Therefore, an optical fiber transmission line 14 is used as a transmission line. An ROF system is used. As means for realizing the ROF system, there are an analog ROF (FIG. 1) for transmitting a wireless signal as it is and a digital ROF (FIG. 2) for transmitting a digitized wireless signal as data.

  In the analog ROF, analog optical modulation / demodulation is performed with a radio modulation signal in the optical interface 13, and the radio signal is transmitted on the optical fiber transmission line 14. In the digital ROF, the radio modulation signal is digitized, the digital data is converted into an optical signal by the optical interface 13, and transmitted through the optical fiber transmission line 14. In the related art, a system (FIG. 3) using a CPRI (Common Public Radio Interface) using a digital ROF (Non-Patent Document 1) has been widely put into practical use because the ROF section can be transmitted at low cost and high quality. .

  For example, a 2.5 Gb / s CPRI line is used to transmit radio signals for two antennas in the 20 MHz band in LTE. Since CPRI uses a unique transmission format, it is necessary to use a dedicated transmission medium such as dark fiber.

CPRI Specification V 5.0, September 2011 (“1. Introduction”, “2.1. Definitions / Nomenclature”).

  LTE-A (LTE advanced), which is an extension of LTE, requires transmission of a wider band (up to 100 MHz) and increases the multiplicity in the space by MIMO (Multi Input Multi Output). Many antennas are required.

  For this reason, the bandwidth required for CPRI also increases, and a bandwidth of 100 Gb / s or more is required per cell, which increases the interface cost and the fiber cost. When a high-speed interface of 40 Gb / s or 100 Gb / s is used, reception sensitivity is lowered, and transmission is difficult unless an error correction code is used.

  However, since the delay time due to the signal processing of the error correction code is longer than the delay time (3.5 us) allowed for the CPRI device, it is difficult to increase the interface speed. In addition, the number of fibers can be reduced by wavelength division multiplexing (WDM). However, in a future wireless system, it is assumed that the band will be further increased, and thus the transmission capacity is limited.

  On the other hand, when an analog ROF is used, the required bandwidth is that of a radio signal, so there is no problem in terms of transmission capacity, but signal quality deteriorates due to noise, nonlinear distortion, etc. due to optical transmission, resulting in multiple channels and multiple channels. It is difficult to apply a modulation method having a large number of values. Also, monitoring control of the remote device becomes an issue.

  In order to solve the above problems, the present invention provides a digital signal processing in a precompensation circuit provided in a remote device and a compensation circuit provided in a master device for nonlinear distortion and waveform degradation of an upstream optical signal caused by optical transmission in a wireless signal transmission system. The purpose is to compensate.

  In order to achieve the above object, in the wireless signal transmission system of the present invention, a remote device performs distortion compensation by adding a distortion compensation amount calculated in advance to an electrical signal, and the distortion compensation transmission signal is corrected by a master device. Detect and compensate for the detected distortion.

Specifically, the radio signal transmission system according to the present invention is:
A remote device that adds a pre-calculated distortion compensation amount to an electrical signal, converts the added electrical signal into an upstream optical signal, and transmits the upstream optical signal to a master device connected via an optical transmission path;
Receiving the upstream optical signal transmitted by the remote device, converting the received upstream optical signal into an electrical signal, detecting a distortion amount of the electrical signal, compensating the detected distortion amount, A master device for converting the signal into a radio signal.

In the wireless signal transmission system according to the present invention,
The remote device is
A remote device-side monitoring control circuit that outputs a pre-generated monitoring control signal to the remote device-side frequency conversion circuit;
A remote device-side frequency conversion circuit that multiplexes the monitoring control signal with the digital electrical signal output by the wireless reception circuit included in the remote device;
The master device is
A master device side frequency conversion circuit that extracts the monitoring control signal multiplexed by the remote device side frequency conversion circuit, and outputs the extracted monitoring control signal to the master device side monitoring control circuit;
The master apparatus side monitoring control circuit which performs the setting change and control of the master apparatus according to the monitoring control signal may be further provided.

In the wireless signal transmission system according to the present invention,
The remote device side frequency conversion circuit is:
The signal level information is multiplexed with the digital electric signal input from the remote device side analog-digital conversion circuit provided in the remote device,
The master device side frequency conversion circuit is:
The signal level information multiplexed by the remote device side frequency conversion circuit may be extracted, and the signal level in the master device may be set according to the signal level information.

Specifically, the remote device according to the present invention is:
A wireless receiving circuit for outputting a wireless signal;
A remote device side analog-digital conversion circuit for converting the radio signal into a digital electric signal;
A remote device side frequency conversion circuit for converting the digital electrical signal into a predetermined intermediate frequency band and converting the sampling rate;
A pre-compensation circuit for adding a pre-calculated distortion compensation amount to the digital electrical signal converted by the remote device side frequency conversion circuit;
A remote-device-side digital-analog conversion circuit that converts the digital electric signal to which the distortion compensation amount is added into an analog electric signal;
An optical transmission circuit that optically modulates the analog electrical signal and transmits the optically modulated upstream optical signal.

In the remote device according to the present invention,
The remote device is
A remote device-side monitoring control circuit that outputs a pre-generated monitoring control signal to the remote device-side frequency conversion circuit;
The remote device-side frequency conversion circuit may multiplex the monitoring control signal with the digital electrical signal output from the wireless reception circuit.

Specifically, the master device according to the present invention is:
An optical receiver circuit that receives the upstream optical signal transmitted by the remote device and converts it into an analog electrical signal;
An analog-digital conversion circuit that converts the analog electrical signal converted by the optical receiver circuit into a digital electrical signal;
Compensation for detecting the distortion compensation amount of the digital electric signal added by the pre-compensation circuit included in the remote device and detecting a distortion amount other than the distortion compensation amount and compensating the detected distortion compensation amount and the distortion amount Circuit,
A master device side frequency conversion circuit for outputting the distortion compensation amount and a digital electric signal compensated for the distortion amount;
A digital radio demodulation circuit for converting the digital electric signal into a radio signal.

In the master device according to the present invention,
The master device is
A master device side monitoring control circuit is further provided,
The master device side frequency conversion circuit extracts the monitoring control signal multiplexed by the remote device side frequency conversion circuit included in the remote device, and outputs the extracted monitoring control signal to the master device side monitoring control circuit,
The master device side monitoring control circuit may change and control the setting of the master device in accordance with the monitoring control signal.

Specifically, the transmission method of the wireless signal transmission system according to the present invention is:
An optical signal transmission procedure for adding a distortion compensation amount calculated in advance to an electrical signal, converting the added electrical signal into an upstream optical signal, and transmitting the upstream optical signal from a remote device to a master device via an optical transmission path When,
The master device receives the upstream optical signal transmitted by the remote device, converts the received upstream optical signal into an electrical signal, detects the distortion amount of the electrical signal, and calculates based on the detected distortion amount A wireless signal conversion procedure for adding the corrected distortion compensation amount to the electrical signal to compensate for the distortion amount and converting the compensated electrical signal into a wireless signal.

  The above inventions can be combined as much as possible.

  According to the present invention, it is possible to transmit a broadband wireless signal with high quality and economically in a wireless signal transmission system using ROF.

An example of analog ROF in related technology is shown. An example of the digital ROF in related technology is shown. An example of the CPRI system in related technology is shown. 1 shows an exemplary configuration of a wireless signal transmission system according to the present embodiment. 2 shows an example of a configuration of a pre-compensation circuit according to the present embodiment. 2 shows an exemplary configuration of a compensation circuit according to the present embodiment. An example of the band pass sampling which concerns on this embodiment is shown. An example of frequency conversion in the remote device according to the present embodiment is shown. An example of frequency conversion in the master device according to the present embodiment is shown. An example of signal level adjustment according to the present embodiment is shown. An example of transfer of an intensity level signal concerning this embodiment 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.

(First embodiment)
The wireless signal transmission system according to this embodiment includes a remote device and a master device connected via an optical transmission path. The remote device transmits an upstream optical signal to the master device, which is received by the master device. Further, the upstream optical signal transmission method in the wireless signal transmission system has an optical signal transmission procedure performed by the remote device and a wireless signal conversion procedure performed by the master device in this order. In the optical signal transmission procedure, the remote device adds the distortion compensation amount to the electrical signal, converts the electrical signal into an upstream optical signal, and transmits it to the master device. In the radio signal conversion procedure in the master device, the received upstream optical signal is converted into an electric signal, the distortion amount of the electric signal is detected, and the distortion compensation amount calculated based on the detected distortion amount is added to the electric signal to generate a waveform. The electric signal compensated for distortion is converted into a radio signal.

  FIG. 4 shows a first embodiment of the present invention. In the present embodiment, a wireless reception circuit 67, an analog-digital conversion circuit 63 that functions as a remote device-side analog-digital conversion circuit, a frequency conversion circuit 65 that functions as a remote-device-side frequency conversion circuit, a precompensation circuit 54, and a digital-analog conversion circuit 55 A remote device 61 composed of an optical transmitter circuit 56 and a supervisory control circuit 68; an optical receiver circuit 62; an analog-digital converter circuit 80 that functions as a master device-side analog-digital converter circuit; a compensation circuit 64; The master device 51 includes a frequency conversion circuit 53 that functions as a circuit, a digital radio demodulation circuit 52, and a monitoring control circuit 57, and an optical transmission path 58 that connects the master device 51 and the remote device 61.

  The radio signal output from the radio reception circuit 67 of the remote device 61 is converted into a digital signal by the analog-digital conversion circuit 63 that functions as a remote device-side analog-digital conversion circuit, and then the frequency conversion that functions as a remote device-side frequency conversion circuit. After the digital frequency conversion and sampling rate conversion to an appropriate intermediate frequency band by the circuit 65, the distortion compensation amount is given by the precompensation circuit 54, and then converted to an analog signal by the digital analog conversion circuit 55. Output as a modulated signal.

  In the master device 51, the upstream optical signal that is the received optical modulation signal is converted into an electric signal by the optical receiving circuit 62, and is converted into a digital electric signal by the analog-digital conversion circuit 80 that functions as an analog-digital conversion circuit on the master device side. The The digital electric signal is corrected for distortion by a compensation circuit 64, then converted to a sampling rate and digital frequency by a frequency conversion circuit 53 functioning as a master device side frequency conversion circuit, and then converted to a digital radio baseband signal or intermediate frequency band signal. As input to the digital radio demodulation circuit 52. The digital radio demodulation circuit 52 converts the digital electric signal input from the digital radio demodulation circuit 52 into a radio signal.

  As described above, in this embodiment, an analog ROF is used as an optical transmission method. However, nonlinear distortion and waveform degradation caused by optical transmission are compensated by digital signal processing in the precompensation circuit 54 or the compensation circuit 64. It becomes possible to transmit a radio signal with high accuracy.

  The precompensation circuit 54 is configured as shown in FIG. 5, and the distortion compensation amount calculated for the input signal by the distortion calculation unit 71 so as to correct the waveform distortion detected by the compensation circuit 64 of the master device 51 is used as a signal. to add. Causes of waveform distortion include non-linear distortion of the digital-analog conversion circuit 55, non-linear distortion of the optical transmission circuit 56, non-linear distortion in the optical transmission path 58, non-linear distortion of the optical reception circuit 62, and analog-to-digital conversion circuit on the master device side. There is a non-linear distortion of the functioning analog-digital conversion circuit 80.

  Further, the pre-compensation circuit 54 is also provided with an equalizer 73 for waveform pre-equalization according to the transfer function between the output of the pre-compensation circuit 54 and the input of the compensation circuit 64. The transfer function is a product of the transfer function of the optical transmission circuit 56, the transfer function of the optical transmission path 58, and the transfer function of the optical reception circuit 62.

  As shown in FIG. 6, the compensation circuit 64 detects distortion and measures a transfer function as well as the precompensation circuit 54, and functions as a digital / analog conversion circuit 55 and a remote device side analog / digital conversion circuit. Compensation for distortion that cannot be compensated by the pre-compensation circuit 54 is performed according to the number of bits of the conversion circuit 63, and waveform equalization is performed.

  Thus, by performing distortion compensation by the precompensation circuit 54 and the compensation circuit 64, most of the distortion amount is compensated by the precompensation circuit 54, and the distortion amount compensated by the compensation circuit 64 is small. The circuit scale of the compensation circuit 64 can be simplified and highly accurate compensation can be performed.

  If the distortion or waveform deterioration detected by the compensation circuit 64 hardly affects the quality of the radio signal, the distortion compensation and waveform equalization functions of either the pre-compensation circuit 54 or the compensation circuit 64 are deleted. However, the circuit can be simplified. Waveform distortion can be detected by detecting higher-order distortion components output outside the signal band or detecting phase rotation of specific frequency components.

  The radio signal input from the radio reception circuit 67 in the remote device 61 to the analog-digital conversion circuit 63 functioning as the remote device-side analog-digital conversion circuit is an intermediate frequency band signal or a radio frequency band signal lower than the sampling frequency. Or an intermediate frequency band or radio frequency band signal higher than the sampling frequency. The former is baseband sampling, and the latter is bandpass sampling.

For bandpass sampling, only the extracted signal of the center frequency f _{C 'by} the band-pass filter, after sampling of the digital signal is an intermediate frequency band signal having a center frequency f _C of the baseband sampling shifting the center frequency by NF _S (FIG. 7).

Where Fs is the sampling frequency, N is the is the maximum integer not exceeding f _{C '/} F _S. The digital frequency conversion in the frequency conversion circuit 65 functioning as the remote device side frequency conversion circuit of the remote device in the present embodiment is performed with the frequency f ₀ as shown in Expression (1) in the intermediate frequency band signal of the center frequency f _C. This is realized by multiplying the carrier wave to obtain an intermediate frequency band signal having a new center frequency f ₁ (FIG. 8).

Here, f ₀ is set so that the intermediate frequency band signal is arranged at a frequency lower than ½ of the sampling frequency F _S1 of the digital-analog conversion circuit 55. In addition, the sampling frequency of the digital radio modulation signal is converted into the sampling frequency of the digital-analog conversion circuit 55.

In the digital frequency conversion to the baseband signal in the frequency conversion circuit 53 functioning as the master device side frequency conversion circuit of the master device of the present embodiment, the intermediate frequency band signal component is extracted from the analog-digital converted signal by a digital filter. after is realized by multiplying the carrier frequency f _a of the formula (2).

Here, the frequency fa is _a frequency for converting the extracted intermediate frequency band signal of the center frequency f _{1 into} a baseband or a predetermined intermediate frequency as an input of the digital radio demodulation circuit 52 (FIG. 9).

The bandwidth of the optical transmission circuit 56 and the optical reception circuit 62 of the present embodiment is sufficient if there is a bandwidth through which the radio signal output from the digital-analog conversion circuit 55 of the remote device 61 can be transmitted. For example, when LTE-A carrier aggregation requires a 100 MHz band, even if f _{C is set} to about 100 MHz, a band of about 200 MHz is sufficient, and transmission is possible by direct modulation using a general-purpose communication semiconductor laser as a light source. It is. Also, the optical receiver circuit 62 can use inexpensive parts in the several hundred MHz band.

  In general, since the reception level of a radio signal varies greatly depending on the radio wave environment such as distance and shielding, the receiver needs a wide dynamic range. In order to transmit signals with a wide dynamic range as they are, a wide dynamic range is required also in optical transmission.

  In order to relax this condition, the frequency conversion circuit 65 functioning as the remote device side frequency conversion circuit of the remote device of this embodiment includes a level detection unit 81, a level conversion unit 82, a modulation unit 83, and an addition unit 84. The frequency conversion circuit 65 adjusts the signal level of the intermediate frequency band signal that has been analog-digital converted to a constant level, multiplexes and transmits the level information as a signal of another frequency, and the master device side frequency conversion circuit of the master device 51 The signal can be restored to the original level signal by the frequency conversion circuit 53 that functions as (FIG. 10).

  For this level adjustment, for example, a block floating point can be used. In the case where the radio signal intensity level is detected in the radio reception circuit 67 of this embodiment and the gain of the amplifier is adjusted in accordance with the level, an analog functioning as a remote device side analog-to-digital conversion circuit of the remote device 61 is provided. The input level to the digital conversion circuit 63 is substantially constant.

  In the above-described case, the detected radio signal intensity level is digitized and multiplexed and transmitted as a signal of another frequency. Here, the frequency conversion circuit 53 that functions as a master device-side frequency conversion circuit of the master device 51 includes a GCA 85, an AD conversion unit # 1, an addition unit 87, a level detection unit 88, an AD conversion unit # 2, and a modulation unit 90. . It is possible to restore the original level signal by the configuration of the frequency conversion circuit 53 (FIG. 11). In this manner, in the present embodiment, it is possible to optically transmit a wide dynamic range radio signal.

  The monitoring control signal of the master device 51 is multiplexed with the wireless modulation signal by the frequency conversion circuit 65 functioning as a remote device side frequency conversion circuit from the monitoring control circuit 68 of the remote device 61 and transmitted through the optical transmission line 58. Is separated from the wireless modulation signal by the frequency conversion circuit 53 functioning as a master device side frequency conversion circuit of the master device and input to the monitoring control circuit 57.

  The monitoring control information transferred in the present embodiment includes information related to the state of the remote device 61, information related to a radio signal, information related to the compensation circuit 64, and the like. A data rate of about 100 kb / s to 1 Mb / s is sufficient. Phase modulation or the like is performed at an appropriate carrier frequency, and the data is transferred from the remote device 61 to the master device 51. Since the speed is low, signal power can be suppressed, and interference with a radio signal can be reduced to a sufficiently low level.

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

11, 31: Radio modulation / demodulation unit 12, 32: Radio modulation / demodulation circuits 13, 15, 33, 35: Optical interface 14, 34: Optical fiber transmission line 16, 36: Radio transmission / reception circuit 21, 41: Radio transmission / reception unit 51: Master device 52: Digital radio demodulation circuit 53, 65: Frequency conversion circuit 54: Precompensation circuit 55: Digital analog conversion circuit 56: Optical transmission circuit 57, 68: Supervisory control circuit 58: Optical transmission line 61: Remote device 62: Optical reception circuit 63, 80: Analog-digital conversion circuit 64: Compensation circuit 67: Radio reception circuit 71, 76: Distortion calculation unit 72, 77: Addition unit 73, 78: Equalizer 81, 88: Level detection unit 82: Level conversion unit 83 90: Modulator 84, 87: Adder 85: GCA
86, 89: AD converter

Claims (8)

A remote device that adds a pre-calculated distortion compensation amount to an electrical signal, converts the added electrical signal into an upstream optical signal, and transmits the upstream optical signal to a master device connected via an optical transmission path;
Receiving the upstream optical signal transmitted by the remote device, converting the received upstream optical signal into an electrical signal, detecting a distortion amount of the electrical signal, compensating the detected distortion amount, A master device for converting a signal into a radio signal;
A wireless signal transmission system comprising: The remote device is
A remote device-side monitoring control circuit that outputs a pre-generated monitoring control signal to the remote device-side frequency conversion circuit;
A remote device-side frequency conversion circuit that multiplexes the monitoring control signal with the digital electrical signal output by the wireless reception circuit included in the remote device;
The master device is
A master device side frequency conversion circuit that extracts the monitoring control signal multiplexed by the remote device side frequency conversion circuit, and outputs the extracted monitoring control signal to the master device side monitoring control circuit;
The wireless signal transmission system according to claim 1, further comprising: a master device side monitoring control circuit that performs setting change and control of the master device in accordance with the monitoring control signal. The remote device side frequency conversion circuit is:
The signal level information is multiplexed with the digital electric signal input from the remote device side analog-digital conversion circuit provided in the remote device,
The master device side frequency conversion circuit is:
3. The radio signal transmission according to claim 2, wherein the signal level information multiplexed by the remote device side frequency conversion circuit is extracted, and a signal level in the master device is set according to the signal level information. system. A wireless receiving circuit for outputting a wireless signal;
A remote device side analog-digital conversion circuit for converting the radio signal into a digital electric signal;
A remote device side frequency conversion circuit for converting the digital electrical signal into a predetermined intermediate frequency band and converting the sampling rate;
A pre-compensation circuit for adding a pre-calculated distortion compensation amount to the digital electrical signal converted by the remote device side frequency conversion circuit;
A remote-device-side digital-analog conversion circuit that converts the digital electric signal to which the distortion compensation amount is added into an analog electric signal;
An optical transmission circuit that optically modulates the analog electrical signal and transmits the optically modulated upstream optical signal;
A remote device comprising: The remote device is
A remote device-side monitoring control circuit that outputs a pre-generated monitoring control signal to the remote device-side frequency conversion circuit;
The remote device according to claim 4, wherein the remote device-side frequency conversion circuit multiplexes the monitoring control signal with the digital electrical signal output from the wireless reception circuit. An optical receiver circuit that receives the upstream optical signal transmitted by the remote device and converts it into an analog electrical signal;
An analog-digital conversion circuit that converts the analog electrical signal converted by the optical receiver circuit into a digital electrical signal;
Compensation for detecting the distortion compensation amount of the digital electric signal added by the pre-compensation circuit included in the remote device and detecting a distortion amount other than the distortion compensation amount and compensating the detected distortion compensation amount and the distortion amount Circuit,
A master device side frequency conversion circuit for outputting the distortion compensation amount and a digital electric signal compensated for the distortion amount;
A digital radio demodulation circuit for converting the digital electrical signal into a radio signal;
A master device comprising: The master device is
A master device side monitoring control circuit is further provided,
The master device side frequency conversion circuit extracts the monitoring control signal multiplexed by the remote device side frequency conversion circuit included in the remote device, and outputs the extracted monitoring control signal to the master device side monitoring control circuit,
The master device according to claim 6, wherein the master device side monitoring control circuit performs setting change and control of the master device in accordance with the monitoring control signal. An optical signal transmission procedure for adding a distortion compensation amount calculated in advance to an electrical signal, converting the added electrical signal into an upstream optical signal, and transmitting the upstream optical signal from a remote device to a master device via an optical transmission path When,
The master device receives the upstream optical signal transmitted by the remote device, converts the received upstream optical signal into an electrical signal, detects the distortion amount of the electrical signal, and calculates based on the detected distortion amount A wireless signal transmission system comprising: a wireless signal conversion procedure for adding a distortion compensation amount to the electrical signal to compensate the distortion amount and converting the compensated electrical signal into a wireless signal in order.

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