KR20040021085A - Digital optical repeater applied peak power reduction and digital pre-distortion algorithm - Google Patents

Abstract

PURPOSE: A digital optical repeater employing a peak power reduction and digital free distortion algorithm is provided to obtain relatively high output power compared to use of a power amplifier by reducing instantly generated peak power, increase power efficiency of the power amplifier, and considerably reduce the amount of heat releasing of a transmitter. CONSTITUTION: A doner unit(100) includes a digital signal processor(110) and an E/O(Electronic/Optical) converter(120). A remote unit(200) includes an O/E converter(210), a digital signal processor(230) and an RF unit(250). A base station transmits signals which have been modulated to QPS signals usually as an output of 20W. The digital signal processor(110) converts the signal inputted from the base station into a digital signal and reduces peak power of the digital signal. After the digital signal passes through a PPR(Peak Power Reducing) processor(111), a DPD(Digital Pre-Distortion) unit(113) applies a certain distortion signal to the digital signal. The digital signal, which has passed through the digital signal processor(110) having the PPR processor(111) and the DPD unit(113), is converted into an optical signal in the E/O converter(120) and then transmitted to the remote unit(200) connected to an optical cable.

Description

DIGITAL OPTICAL REPEATER APPLIED PEAK POWER REDUCTION AND DIGITAL PRE-DISTORTION ALGORITHM}

The present invention relates to a digital optical repeater, and more particularly, to an apparatus for applying a peak power reduction and digital predistortion algorithm using a digital signal processing function of a digital optical repeater.

In general, base station signals of spread spectrum mobile communication, for example, CDMA, CDMA-2000, and WCDMA systems, are composed of multi-channel modulated signals such as a user channel and a multi-carrier channel, and thus, phase information between the channels. As a result, it is possible to have a peak to average ratio (Crest Factor). For this reason, power amplifiers used in base stations and repeaters should be designed with sufficient margin for maximum output power to withstand the peak power, which occurs probabilistically instantaneously. It is basic to adopt a linearized power amplifier (LPA). As a result, power amplifiers of base stations and repeaters of a spread spectrum mobile communication system have relatively low output power efficiency, are expensive, have a high probability of failure due to a complicated structure, and have various problems of shortened lifetime due to heat dissipation.

In addition, conventional power amplifiers generally apply a complex feed forward method to solve preconditions such as multi-user channel, multi-carrier, peak power handling, and the like. It is common to implement The feed forward method amplifies only the IM (InterModulation) component of the input signal separately, combines it with the IMD (InterModulation Distortion) component of the amplified output signal in phase, and ultimately removes only the IMD component of the final stage and only the desired amplified signal. This is how you get it. However, the feed-forward power amplifier is excellent in performance but relatively difficult to implement, and thus has low productivity, high price, and low power efficiency. An analog pre-distortion amplifier was used. However, the analog predistortion method has the disadvantage that the characteristics of the analog predistortion is less than the feed forward method due to the performance limitation of the analog device itself.

The present invention has been invented to solve the above problems, and an object of the present invention is to reduce peak power and apply digital predistortion in a digital signal processing function of a digital optical repeater, thereby improving and improving output power efficiency by minimizing structural changes. To get the device to maximize.

In order to achieve the above object, the present invention provides a digital signal processing unit for converting an input signal input from a base station into a digital signal to perform a predetermined process on the digital signal and an electrical signal output from the digital signal processing unit as an optical signal. A donor unit including an electric / optical signal converting unit for converting the electric signal; And a remote unit connected to the donor unit through an optical cable and converting an optical signal transmitted through the optical cable into an electrical signal, and then converting the optical signal through an digital signal processing unit into an RF signal and radiating the same. The predetermined processing for the digital signal in Equipped with a peak power reduction unit for reducing the peak power of the digital signal; And a digital predistortion unit for applying a predetermined distortion signal to the digital signal having the reduced peak power.

The present invention also provides a donor unit for converting an input signal input from a base station into a digital signal, performing a predetermined process on the digital signal, and then converting the input signal into an optical signal for transmission. And at least one remote unit connected to the donor unit via an optical cable to receive a digital signal input from the donor unit, and at least one of the digital signal processing units included in the remote unit may include a digital signal. A peak power reduction unit for reducing peak power; And a digital predistortion unit for applying a predetermined distortion signal to the digital signal having the reduced peak power.

Therefore, according to the present invention, the efficiency of the power output from the digital signal processor in the digital optical repeater can be improved.

1 is a schematic block diagram of a digital optical repeater according to a first embodiment of the present invention.

2 is a schematic block diagram of a digital optical repeater according to a second embodiment of the present invention.

3A and 4A are graphs showing characteristics of signals output from a conventional digital signal processor.

3B and 4B are graphs showing characteristics of signals output from the digital signal processor according to the present invention.

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

100: donor

110, 230: digital signal processing unit (DSP processing unit)

111: peak power reduction processing unit (PPR processing unit)

113: digital pre-distortion unit (DPD processing unit)

120: E / O converter

200: remote

210: O / E converter

250: RF section

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

1 is a schematic block diagram of a digital optical repeater according to a first embodiment of the present invention. 2 is a schematic block diagram of a digital optical repeater according to a second embodiment of the present invention. 3A and 4A are graphs showing characteristics of signals output from a conventional digital signal processor. 3B and 4B are graphs showing characteristics of signals output from the digital signal processor according to the present invention.

Referring to FIG. 1, a digital signal processor designed to execute a peak power reduction and digital pre-distortion algorithm in a donor according to an embodiment of the present invention. (Digital Signal Processing) is included.

The donor unit 100 of the digital optical repeater includes a digital signal processing unit 110 and an E / O conversion unit 100 (Electronic / Optical Conversion). At least one remote connected to the donor 100 in parallel with an optical cable includes an O / E converter 210, a digital signal processor 230, and an RF unit 250.

The base station transmits signals modulated with QPS signals to an output of usually 20W. At this time, if the phase of each signal has the same maximum amplitude on the time axis, peak power is generated by the summation. At the worst case, the amplified peak power value is about 10 dB (about 200 W). For this case, the digital signal processing unit 110 converts the input signal input from the base station into a digital signal, and then reduces the peak power of the digital signal. This is implemented by a peak power reduction algorithm in the peak power reduction processor 111. Signal characteristics before and after implementing the peak power reduction algorithm are illustrated in FIGS. 3A and 3B, respectively.

The digital signal passing through the peak power reduction processor 111 may apply a predetermined distortion signal to the digital pre-distortion unit 113. This is to make the output signal have linearity by applying a predetermined distortion to the input signal with respect to a signal characteristic that is saturated when the output signal with respect to the input signal is equal to or greater than a specific input signal.

The digital signal that has passed through the digital signal processor 110 including the peak power reduction processor 111 and the digital predistortion processor 113 is converted into an optical signal by the electrical / optical signal converter 120 (E / O converter). And transmitted to one or more remotes 200 that are connected by optical cables.

The remote can be connected in series or in parallel to the donor 100, and reference numeral 300 denotes a remote connected in parallel.

Since the peak power reduction processing unit 111 and the digital predistortion processing unit 113 are included in the digital signal processing unit 110 of the donor 100, the digital signal processing unit 230 of the one or more remotes includes a peak power reduction processing unit and There is no digital predistortion processing section.

FIG. 2 is a digital optical repeater according to an embodiment of the present invention, and a digital signal processor designed to execute a peak power reduction and digital pre-distortion algorithm in a remote unit. Digital Signal Processing).

A remote unit connected to a donor unit and an optical cable may be connected in series or in parallel, and the peak power reduction and digital predistortion may be performed in at least one or more remote units of a plurality of remote units. It is designed to run the distortion algorithm. Designed to run Peak Power Reduction and Digital Pre-Distortion algorithms on the remote, peak power reduction and digital predistortion may be applied to the donor connected to the remote by optical cable. (Digital Pre-Distortion) algorithm is designed to not exist.

3A is a graph illustrating signal characteristics before implementing a peak power reduction algorithm in a digital signal processor, and FIG. 3B is a signal output after implementing a peak power reduction algorithm in a digital signal processor. Graph showing characteristics.

Crest factor is an important factor that affects signal quality and is also called Peak to Average Power Ratio. Comparing FIG. 3A and FIG. 3B, it can be seen that the peak power of the signal is significantly reduced after implementing the peak power reduction algorithm rather than the signal characteristic before implementing the peak power reduction algorithm.

4A is a graph illustrating a PSD according to a frequency index when no digital predistortion is applied, and FIG. 4B illustrates a PSD according to a frequency index when digital predistortion is applied according to an embodiment of the present invention. It is a graph shown.

4A and 4B, it can be seen that when the digital predistortion is applied (FIG. 4B), the IM (InterModulation) portion is significantly reduced than when the digital predistortion is not applied (FIG. 4A).

Embodiment of the present invention is only one embodiment, of course, many modifications and variations of the components of the present invention without departing from the gist of the present invention, of course, the present invention is not limited to the embodiment. .

As described in detail above, according to the digital optical repeater to which the peak power reduction and the digital predistortion algorithm of the present invention are applied, the output power that is generated instantaneously is reduced to obtain a larger output power than when using the same power amplifier. Similarly, it is possible to use a power amplifier with a lower grade, ie, lower margin, than a conventional power amplifier to obtain the same output power. Through this, there is an advantage to increase the power efficiency of the power amplifier, a key component of the RF unit, and the efficiency is also increased, thereby reducing the amount of heat generated, and at the same time, the effect of dramatically reducing the heat dissipation amount of the transmitter can be obtained. Therefore, the digital optical repeater can be miniaturized and simplified, and the lifespan and failure rate of the equipment can be reduced, and ultimately the price can be reduced.

Claims (2)

A digital signal processor for converting an input signal input from a base station into a digital signal to perform a predetermined process on the digital signal, and an electrical / optical signal converter for converting an electrical signal output from the digital signal processor into an optical signal Donor part to be; And And a remote unit connected to the donor unit by an optical cable and converting an optical signal transmitted through the optical cable into an electrical signal, and then converting the optical signal through an digital signal processing unit into an RF signal and radiating the same. The predetermined processing of the digital signal in the digital signal processing unit includes: a peak power reduction unit for reducing the peak power of the digital signal; And And a digital predistortion unit for applying a predetermined distortion signal to the digital signal having the reduced peak power. A donor unit for converting an input signal input from a base station into a digital signal, performing a predetermined process on the digital signal, and then converting the input signal into an optical signal for transmission And And at least one remote unit connected to the donor unit by an optical cable to receive a digital signal input from the donor unit, At least one of the digital signal processing unit included in the remote unit includes a peak power reduction unit for reducing the peak power of the digital signal; And And a digital predistortion unit for applying a predetermined distortion signal to the digital signal having the reduced peak power.