KR100712594B1 - Digital optical repeater using digital predistortion - Google Patents

Abstract

The present invention provides a digital communication system including a main hub unit for performing wireless communication with a base station, and a remote optical unit for connecting to the main hub unit via an optical cable and performing wireless communication with a subscriber station. In the optical relay system, the remote optical unit is composed of a ROU integration module, a duplexer, and an LNA / downconversion module, wherein the ROU integration module converts the forward optical signal received through the optical cable into an electrical signal and the following FPGA unit. Converts the reverse electrical signal from the optical signal into an optical signal and transmits the optical signal to the optical cable; and serially outputs the forward electrical signal from the digital optical converter, and performs signal processing on the reverse signal from the following ADC unit. The FPGA unit for transmitting to the digital light conversion unit and the signal from the FPGA unit are distorted and outputted for excellent linearity. A pre-distortion processing unit, a digital / analog conversion unit for converting the output signal of the pre-distortion processing unit into an analog signal, and outputting the up-converting unit for up-converting the output signal of the digital / analog conversion unit; A digital optical relay system using a digital predistortion comprising a high power amplifier for high power amplification and a module integrating an analog / digital conversion unit for converting a reverse signal from the LNA / downconversion module into a digital signal and outputting the digital signal to the FPGA. to provide.

Description

Digital optical repeater using digital predistortion {Digital optical repeater using digital predistortion}

1 is a block diagram showing a conventional digital optical relay system.

FIG. 2 is a block diagram illustrating concrete components of the signal processing module in the remote optical unit (ROU) shown in FIG.

3 is a block diagram illustrating a digital optical relay system using a digital predistortion (DPD) method according to a preferred embodiment of the present invention.

4 is a block diagram illustrating a detailed block configuration of an ROU integration module in a digital optical relay system according to an exemplary embodiment of the present invention shown in FIG. 3.

FIG. 5 is a diagram illustrating amplification characteristics of a nonlinear device to which predistortion is applied in a digital predistortion (DPD) unit of a digital optical relay system according to an exemplary embodiment of the present invention shown in FIG. 4.

6A to 6C illustrate input signal waveforms of the 1FA (Frequency Allocation) upconversion module 60, output signal waveforms of the 1FA upconversion module 60, and 1FA linear power amplification in the conventional digital optical relay system illustrated in FIG. 1. Each output signal waveform of the module LPA is shown.

7A to 7C are input signal waveforms of the 4FA up-conversion module 60, output signal waveforms of the 4FA up-conversion module 60, and 1FA linear power amplification module (LPA) in the conventional digital optical relay system shown in FIG. Are output signal waveforms respectively.

8A and 8B illustrate output signal waveforms of the 1FA ROU integration module 120 and output signal waveforms of the 4FA ROU integration module 120 in the digital optical relay system according to the preferred embodiment of the present invention shown in FIG. 4, respectively. .

9 is a block diagram of a remote optical unit (ROU) in a digital optical relay system using a digital predistortion method as a comparative example of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: base station 2: main hub unit (MHU)

3,3A: Remote optical unit (ROU) 4: Subscriber terminal

110: duplexer 120: ROU integrated module

121: digital light conversion unit 122: FPGA unit

123: digital predistortion (DPD) unit 124: DAC unit

125: up-conversion unit 126: high power amplification (HAP) unit

127: down converter 128: FPGA

129 DSP section 130 ADC section

140: LNA / down conversion module

The present invention relates to a wireless communication system, and more particularly, a wireless communication frequency between a main hub unit (hereinafter referred to as "MHU") and a remote optical module (hereinafter referred to as "ROU"). The present invention relates to a digital optical relay system that adopts a digital optical transmission method and employs a digital predistortion (DPD) method instead of a linear power amplifier (LPA) to perform high power amplification and transmission.

In the conventional optical relay system, as shown in FIG. 1, the down conversion module 10 in the MHU 2 receiving the signal of the base station 1 converts the intermediate frequency into an intermediate frequency and converts the intermediate frequency into the digital signal processing module 20. The signal is converted into an optical signal through the digital optical module 30 and transmitted to the remote ROU 3. Accordingly, the optical signal received by the digital optical module 40 of the ROU (3) is converted into an electrical signal, the signal processing module 50 is converted to an analog intermediate frequency and then input to the up-conversion module 60. The up-conversion module 60 converts an analog intermediate frequency into an RF signal, amplifies the signal using a linear power amplifier (LPA) module 70 or a high power amplifier (HPA) module, and then through a duplexer 110 and an antenna. It is radiated to the subscriber terminal 4 side at high power.

As shown in FIG. 2, the signal processing module 50 of the ROU 3 includes a field-programmable gate array (FPGA) unit 51, a digital / analog converter (DAC unit) 52, and an analog / digital converter. A part (ADC part) 53 is comprised.

The FPGA unit 50 receives a clock / data signal and a reference frequency signal (for example, a 10 MHz reference frequency signal) from the digital optical module 40 and synchronizes the reference frequency signal with the clock signal and the data signal. After the separation, the digital / analog converter 52 outputs the converted clock signal and the data signal to the analog forward IF signal. The reverse IF signal is input to an analog / digital converter (ADC unit) 53, and the ADC unit 53 synchronizes the reverse analog IF signal with a clock signal from the FPGA unit 50. Converted to and transferred to the FPGA unit (50). The FPGA unit 50 transfers the digital data signal from the ADC unit 53 to the digital optical module 40.

Here, the reverse link from the subscriber station 4 to the base station 1 (that is, the duplexer 110 of the ROU 3, the low noise amplifier (LNA) module 100, the downconversion module 90, and the signal processing module ( 50) and the digital optical module 40, and the digital optical module 30, the signal processing module 20 and the up-conversion module 80 of the MHU 2 are not related to the present invention and thus description thereof will be omitted. Shall be.

In the above-described conventional system, since the up-conversion module 60 of the ROU 3 is expensive and the linear amplifier module 70 has a large amount of heat generation, a large capacity heat sink must be provided. In addition, when the linear power amplifier (LPA) module and the high power amplifier (HPA) module are applied in the forward link of the ROU (3), the output power efficiency is relatively low, the cost is high, the structure is complicated, the probability of failure is high, and the heat generation is high. There is a problem that the life is short and the area of the apparatus must be increased for heat dissipation.

The present invention has been made to solve the problems of the prior art as described above, adopting the digital optical transmission method between the radio communication frequency MHU and ROU, and uses a digital predistortion (DPD) method rather than a linear power amplifier The purpose of the present invention is to provide a digital optical relay system using digital predistortion which can provide high output efficiency, simple structure and low failure rate.

Digital optical relay system using a digital predistortion according to the present invention for achieving the above object is, the main hub unit (Main Hub Unit) for wireless communication with the base station, the main hub unit is connected via an optical cable and the subscriber In the digital optical relay system including a remote optical unit (Remote Optic Unit) for wireless communication with a terminal, the remote optical unit is composed of a ROU integration module, a duplexer and an LNA / down conversion module, the ROU integration module, The digital optical converter converts the forward optical signal received through the optical cable into an electrical signal, converts the reverse electrical signal from the FPGA unit into an optical signal, and transmits the optical signal to the optical cable, and the forward electrical signal from the digital optical converter. Serialize and output the signal, and process the reverse signal from the ADC unit below to the digital light conversion unit. An FPGA unit, a predistortion processor for distorting and outputting the signal from the FPGA unit in order to improve linearity, a digital / analog converter for converting an output signal of the predistortion processor into an analog signal and outputting the analog signal; An up-converter for up-converting the output signal of the digital / analog converter, a high-power amplifier for high-power amplifying the output of the up-converter, and converting a reverse signal from the LNA / down-conversion module into a digital signal and outputting the digital signal to the FPGA; The analog / digital conversion unit is characterized in that consisting of a module integrated.

In this case, the predistortion processing unit performs a non-linear amplification characteristic of the signal converted into a digital signal after down-converting the frequency down-converted with respect to the signal detected at the output of the high power amplifier and performing digital low pass filtering on the down-converted signal. After comparing and analyzing the signals input through the FPGA unit, it is characterized in that the linearity is excellent by randomly distortion.

Hereinafter, a digital optical relay system using digital predistortion according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram illustrating a digital optical relay system using a digital predistortion (DPD) method according to a preferred embodiment of the present invention.

In the conventional digital optical relay system, a linear power amplifier (LPA) module or a high power amplifier (HPA) module is used in the forward link of the ROU. However, in the digital optical relay system according to the present invention, the duplex 110 is reversed from the ROU 3A. There is a fundamental difference in simplifying the configuration of equipment by integrating all components except the LNA / down conversion module 130. In addition, in the digital optical relay system according to the present invention, the use of the digital predistortion (DPD) method in the forward link of the ROU is fundamentally different from the conventional technology.

Hereinafter, a description of the same components as in the conventional digital optical relay system will be omitted.

As shown in FIG. 3, the digital optical relay system according to the present invention includes an MHU 2 and an ROU 3A. The MHU 2 includes a down conversion module 10, an up conversion module 80, and a signal. The processing module 20 and the digital optical module 30, the ROU (3A) is composed of a ROU integration module 120, a duplexer 110, LNA / down conversion module 130.

As shown in FIG. 4, the ROU integration module 120 includes a digital light conversion unit 121, an FPGA unit 122, a predistortion (DPD) unit 123, a DAC unit 124, and an upconversion unit. An integrated module including a 125, a high power amplification (HPA) unit 126, a downconversion unit 127, an FPGA unit 128, a DSP unit 129, and an ADC unit 130 is provided.

Referring to the operation of the present invention, the down conversion module 10 of the MHU (2) receiving the forward signal applied from the base station 1 converts the signal of the RF band to the intermediate frequency signal processing module 20 Apply it at an appropriate level without distortion.

The signal processing module 20 of the MHU 2 converts an analog signal into a digital signal and supplies the digital signal to the digital optical module 30, and the digital optical module 30 converts the input digital signal into an all-optical light beam through an optical path. Send to ROU 3A.

The digital optical signal transmitted to the ROU 3A is converted into a digital electrical signal by the digital optical converter 121 inside the ROU integrated module 120. The process so far is the same as the existing digital optical relay system.

In the conventional digital optical relay system illustrated in FIG. 1, the signal processing module 50 outputs the analog intermediate frequency to the upconversion module 60 in the form of an analog intermediate frequency, and the upconversion module 60 converts the analog intermediate frequency into an RF signal. After converting and outputting to the linear power amplifier (LPA) module 70, and amplified in the linear power amplifier module 70 and radiated toward the subscriber station (4) through the duplexer 110 and the antenna.

However, in the present invention, the digital light conversion unit 121 inside the ROU integrated module 120 converts the electrical signal into a clock / data signal and a reference frequency signal (for example, a reference frequency signal of 10 MHz). The controller 122 separates the clock signal and the data signal in synchronization with the reference frequency signal in the FPGA unit 122, and serializes the data signal to the DPD unit 123. The DPD unit 123 arbitrarily distorts and outputs a signal in order to improve linearity. The output signal of the DPD unit 123 is converted into an analog signal by the DAC unit 124 and then up-converted by the up-conversion unit 125 to perform high output amplification by the HPF unit 126 and then the duplex 110 and the antenna. Via subscribers at the end of the month.

 This process is the biggest difference from the conventional system, and because it is connected in this way, there is no need to use the conventional upconversion module, and the role of the signal processing unit is greatly reduced, the number of modules is simplified, and the cost and heat generation are reduced. have.

Looking at the operation of the ROU integrated management module 120 in more detail as follows.

The FPGA unit 122 processes a clock / data signal and a reference frequency signal (for example, 10 MHz reference frequency signal), which are electrical signals input from the digital light conversion unit 121, and converts the signal into serial data to convert the DPD unit ( 123).

The DPD unit 140 compares and analyzes the nonlinear amplification characteristic detected by the output unit and the signal inputted through the FPGA 122 in the signal processing module 50B, and then arbitrarily distorts the signal to excellent linearity. Let's do it.

Introducing the feedback process, the RF signal detected by the output unit (that is, the output of the HPA unit 126) is down-converted by the down-conversion unit 127, thereby converting the FPGA unit 128 and the DSP (Digital Signal Processor) unit. Feedback is provided to the DPD unit 123 through 129. Here, the FPGA unit 128 is configured to digitally filter the output signal of the down converter 127, and the DSP unit 129 samples the digital low pass filtered signal and converts the digital signal into a digital signal. Is output to the DPD unit 123.

The output signal of the DPD unit 123 is converted into an analog signal by the digital-to-analog converter (DAC) 124 and then adjusted upward by a wireless communication frequency by the up-converter 125 and the high power amplification by the HPA unit 126. After the duplexer 110 and the antenna is transmitted to the subscriber station (4).

In case of applying the conventional linear amplifier (LPA) module and high power amplifier (HPA) module, the output power efficiency is relatively low compared to the DPD method, and the cost is high, the structure is complicated, the probability of failure is high and the heat generation is high. There is a problem of shortening the lifespan and increasing the area of the apparatus for heat dissipation, all of which are compensated by using the DPD method in the present invention.

Linearization techniques that can compensate for the nonlinearity of power amplifiers that are well known to date are Back-Off, Negative Feedback, Envelope Feedback, and PreDistortion. And forward mode.

Among them, the fed forward method has a complicated structure, but the degree of linearization is excellent compared to other methods and has the characteristics of broadband. These fed forward linear power amplifiers require adaptive control and complex cooling schemes to compensate for deterioration of the device and overall performance due to the environment.

Predistortion (PD) is a process intentionally distorting the input signal of the power amplifier in order to compensate for the nonlinearity of the power amplifier as shown in the graph of FIG. Digital Predistortion (DPD) is one of the most promising linearity techniques that is more efficient and cost-effective than power forward.

8A and 8B show an output signal waveform of the ROU integration module 120 in the digital optical relay system according to the present invention configured as described above. FIG. 8A shows a case of 1FA (Frequency Allocation) and FIG. 8B shows a case of 4FA.

6A to 6C illustrate an input signal waveform of the 1FA up-conversion module 60, an output signal waveform of the 1FA up-conversion module 60, and a 1FA linear power amplifier module in the conventional digital optical relay system illustrated in FIG. 1. LPA) output signal waveforms, respectively. 7A to 7C illustrate an input signal waveform of the 4FA upconversion module 60, an output signal waveform of the 4FA upconversion module 60, and a 1FA linear power amplifier module in the conventional digital optical relay system shown in FIG. LPA) output signal waveforms respectively.

The output signal waveform of the DPD module in the digital optical relay system according to the present invention of FIGS. 8A and 8B is inferior to the output signal waveform of the linear power amplifier module (LPA) in the conventional digital optical relay system of FIGS. 6C and 7C. It can be seen.

Accordingly, the digital optical relay system according to the present invention adopts an up-conversion module and a linear power amplifier (LPA) module (or high power amplifier (HPA) module) without deteriorating signal characteristics as compared with the prior art. Can solve the problem.

In addition, the digital optical relay system according to the present invention is composed of all the components except the duplexer, LNA and down-conversion configuration in one ROU configuration as a single integrated module and also the equipment by remarkably configuring the LNA and down-conversion configuration as a single module Will be simplified.

FIG. 9 is a block diagram of a remote optical unit (ROU) in a digital optical relay system applying a digital predistortion method, which is filed by the present applicant.

The remote optical unit ROU of the figure includes a digital optical module 40, a signal processing module 50A, a DPD module 150, a duplexer 110, an LNA module 100, and a down conversion module 90. .

In the signal processing module 50A, a clock / data signal input from the digital optical module 40 is synchronized with a reference frequency signal to separate the clock signal and the data signal and output the clock signal and the data signal to the FPGA unit 54.

The FPGA unit 54 processes the clock signal and the data signal to generate 16-bit parallel baseband I data, 16-bit parallel baseband Q data, and 1-bit clock signal to generate low voltage differential signaling (LVDS). Output to the DPD module 150 in the form.

The digital baseband I / Q signal input to the DPD module 150 is serialized by the input FPGA unit 151 and transmitted to the digital predistortion (DPD) unit 152.

The DPD unit 152 compares and analyzes the nonlinear amplification characteristics detected and outputted by the output unit and the signal input through the input FPGA 151 in the signal processing module 50A, and then arbitrarily distorts to improve linearity. do.

In the feedback process, the RF signal detected at the output of the HPA unit 155 is down-converted by the down converter 156 to feed back to the DPD unit 152 through the FPGA unit 157 and the DSP unit 158. Becomes

The output signal of the DPD unit 152 is converted into an analog signal by the DAC unit 153 and then up-converted by the up-conversion unit 154 to a wireless communication frequency and amplified by high power in the HPA unit 155 and then duplexer 110. And is transmitted to the subscriber station (4) via the antenna.

Compared with the comparative example configured as described above, the digital optical relay system according to the present invention employs the same DPD method in the remote optical unit (ROU), but the conventional digital optical module 40 and the signal processing module 50A And DPD module 150 by integrating a single module to significantly simplify the configuration. That is, in the configuration example, the FPGA unit 54 of the signal processing module 54 and the input FPGA unit 151 of the DPD module 150 could be removed. This is because the integrated modularization eliminates the low voltage differential signaling (LVDS) method used as an interface bus between modules. In addition, the digital optical relay system according to the present invention significantly simplified the configuration by integrating the LNA module 100 and the down conversion module 90 as a single module compared to the comparative example.

On the other hand, the present invention is not limited to the above specific embodiments, but can be modified and modified in various ways without departing from the gist of the present invention. It will be apparent that such variations and modifications are included in the present invention as long as they belong to the appended claims.

As described above, according to the present invention, it is possible to implement a repeater having a simple structure and excellent assemblability by not using an upconversion module as compared to the existing digital optical relay system. In addition, the overall current consumption is significantly reduced compared to the existing relay system, the heat generation is reduced, and the power supply capacity and the size of the power supply can be designed smaller. There is no need for an up-conversion module, and the size of the power supply is small, and the amount of heat generated is small, so that the area of the apparatus for the overall heat generation can be reduced, and the material cost of the apparatus is low, which is a great advantage in terms of cost.

In addition, according to the present invention, in the configuration of the remote optical unit (ROU), all components except the duplexer, the LNA, and the downconversion configuration are configured as one integrated module, and the LNA and the downconversion configuration are configured as a single module, thereby making the equipment remarkable. There is an advantage that can be simplified.

Claims (2)

A digital optical relay system including a main hub unit for wireless communication with a base station and a remote optic unit connected to the main hub unit via an optical cable and for wireless communication with a subscriber station. To The remote optical unit is composed of a ROU integration module, a duplexer and an LNA / downconversion module, The ROU integrated module includes a digital light conversion unit for converting a forward optical signal received through an optical cable into an electrical signal and converting a reverse electrical signal from an FPGA unit into an optical signal and transmitting the optical signal to the optical cable; Serializing and outputting a forward electrical signal from the unit, and processing the reverse signal from the following ADC unit to pass the signal to the digital light conversion unit, and distorting the signal from the FPGA unit for excellent linearity. A pre-distortion processor for outputting, a digital / analog converter for converting the pre-distortion processor output signal into an analog signal, and an up-converter for up-converting the output signal of the digital / analog converter; A high power amplifier for high power amplifying the output and a reverse signal from the LNA / downconversion module Converted by an analog / digital converting part digital optical relay system using a digital predistorter according to claim consisting of an integrated module that outputs to the FPGA arcs. The method of claim 1, The predistortion processor may further include a non-linear amplification characteristic of a signal which is down-converted in frequency with respect to the signal detected at the output of the high power amplifier, and digitally low-pass filtered on the down-converted signal and then converted into a digital signal; And comparing and analyzing the signals inputted through the FPGA unit to arbitrarily distort the signal to improve linearity.

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