KR101257357B1 - Carrier recovery apparatus for qpsk transmission system and method thereof - Google Patents

Abstract

Disclosed is a carrier recovery apparatus and method for a quadrature phase shift keying (QPSK) transmission system according to the present invention.
A carrier recovery apparatus for a QPSK transmission system according to the present invention includes: a data dependency removal module for outputting a signal from which phase information is removed by removing phase information generated by data from a received signal; An averaging module for accumulating a predetermined number of signals from which the phase information has been removed and outputting an average value of the accumulated signals; An angle measuring module for measuring an angle of the received signal using the average value; And a phase unwrapping module estimating a phase error of the received signal based on the measured angle.
Through this, the present invention can not only reduce the complexity of hardware but also improve the operation speed.

Description

Carrier recovery apparatus and method therefor for PPS transmission system {CARRIER RECOVERY APPARATUS FOR QPSK TRANSMISSION SYSTEM AND METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a carrier recovery apparatus, which can remove data dependence and estimate phase error by using a comparator and an adder instead of a multiplier for a quadrature phase shift keying (QPSK) modulation scheme suitable for a high speed optical communication system. The present invention relates to a carrier recovery apparatus and method for a QPSK transmission system.

Phase noise is a major cause of performance degradation in coherent communication systems. In the decoding process of a synchronous system with high data throughput, a phase locked loop (PLL) is used to recover phase noise due to a phase mismatch between a local oscillator (LO) and a transmitter laser. However, analog circuit design requires a lot of time and effort to design a PLL that is sensitive to propagation delay.

Advances in process technology have enabled digital circuits to operate at high speeds, making it possible to replace DSPs with digital signal processing (DSP) algorithms. The phase error caused by the phase mismatch between the LO and the laser of the transmitting end is compensated using a carrier decoder, so the PLL is no longer needed.

The Viterbi and Viterbi (V & V) algorithms enable forward-forward operation, enabling high-speed operation through parallelism. For this reason, the V & V algorithm is often used as a carrier decoder. However, the V & V algorithm requires a multiplier, which is unsuitable for high speed operation due to its high complexity and low operating speed.

In addition, the V & V algorithm eliminates data dependency through multiple square operations, but has a disadvantage of significantly increasing noise power compared to signal power.

Therefore, an object of the present invention is to solve the problems of the prior art, and an object of the present invention is to estimate the phase error by removing the data dependency using a comparator instead of a multiplier for the QPSK modulation scheme to be suitable for a high-speed optical communication system and the estimated phase The present invention provides a carrier recovery apparatus and method for a QPSK transmission system capable of recovering a carrier phase using an error.

However, the objects of the present invention are not limited to those mentioned above, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above objects, a carrier recovery apparatus for a QPSK transmission system according to an aspect of the present invention is to remove the data dependency to remove the phase information generated by the data in the received signal to output the signal from which the phase information is removed module; An averaging module for accumulating a predetermined number of signals from which the phase information has been removed and outputting an average value of the accumulated signals; An angle measuring module for measuring an angle of the received signal using the average value; And a phase unwrapping module estimating a phase error of the received signal based on the measured angle.

Preferably, if the real part of the received signal is less than zero, the data dependency elimination module rotates the received signal 180 degrees clockwise on a constellation, and then the absolute value of the real part of the received signal is greater than the absolute value of the imaginary part. If it is small, it can be rotated 90 degrees clockwise or counterclockwise on the constellation to remove phase information generated by the data from the received signal.

Preferably, when the absolute value of the real part of the received signal is less than the absolute value of the imaginary part but the imaginary part is less than zero, the data dependency elimination module rotates the received signal by 90 degrees counterclockwise on the constellation. Phase information generated by the data can be removed.

Preferably, the data dependency elimination module is configured to rotate the received signal by 90 degrees clockwise on a constellation diagram if the absolute value of the real part of the received signal is less than the absolute value of the imaginary part but greater than zero. It is possible to remove the phase information generated by.

Preferably, the data dependency removal module may be implemented using a comparator for comparing and outputting a real part and an imaginary part of the received signal.

In addition, the carrier recovery apparatus for the QPSK transmission system according to the present invention may further include a multiplier for restoring the carrier phase by multiplying the estimated phase error and the received signal.

According to another aspect of the present invention, a carrier recovery method for a QPSK transmission system includes: a data dependency removal step of outputting a signal from which phase information is removed by removing phase information generated by data from a received signal; An averaging step of accumulating a predetermined number of signals from which the phase information has been removed and outputting an average value of the accumulated signals; An angle measuring step of measuring an angle of the received signal using the average value; And a phase unwrapping step of estimating a phase error of the received signal based on the measured angle.

Preferably, if the real part of the received signal is less than zero, the data dependency removing step rotates the received signal 180 degrees clockwise on a constellation, and then the absolute value of the real part of the received signal is greater than the absolute value of the imaginary part. If it is small, it can be rotated 90 degrees clockwise or counterclockwise on the constellation to remove phase information generated by the data from the received signal.

Preferably, the step of removing the data dependency is that if the absolute value of the real part of the received signal is less than the absolute value of the imaginary part but the imaginary part is less than 0, the received signal is rotated 90 degrees counterclockwise on the constellation to the Phase information generated by the data can be removed.

Preferably, the step of removing the data dependency is that if the absolute value of the real part of the received signal is less than the absolute value of the imaginary part but the imaginary part is greater than zero, the received signal is rotated 90 degrees clockwise on a constellation view to the data in the received signal. It is possible to remove the phase information generated by.

Preferably, the step of removing the data dependency may be implemented using a comparator for comparing and outputting the real part and the imaginary part of the received signal.

In addition, the carrier recovery method for the QPSK transmission system according to the present invention may further include a multiplication step of recovering the carrier phase by multiplying the estimated phase error and the received signal.

Through this, the present invention estimates the phase error by removing the data dependency using a comparator instead of the multiplier for the QPSK modulation scheme, and restores the carrier phase by using the estimated phase error. There is an effect that can reduce the complexity of.

In addition, the present invention estimates the phase error by using a comparator instead of a multiplier for the QPSK modulation scheme to estimate the phase error and to restore the carrier phase by using the estimated phase error for the high speed optical communication system, There is an effect to improve.

1 is an exemplary view showing the structure of a carrier recovery apparatus according to an embodiment of the present invention.
2 is an exemplary view showing a QPSK constellation diagram according to an embodiment of the present invention.
3 is an exemplary view showing an estimated phase according to an embodiment of the present invention.
4 is an exemplary diagram illustrating a detailed configuration of the data dependency removal module 110 shown in FIG. 1.
5 is an exemplary view illustrating a method for restoring a carrier wave according to an embodiment of the present invention.
FIG. 6 is an exemplary diagram illustrating in detail a process of removing data dependency (S510) shown in FIG. 5.
7 is an exemplary view for explaining the rotation of the constellation diagram according to the process of removing data dependency.
8 is an exemplary view showing a result of comparing the performance of the V & V algorithm and the proposed algorithm.

Hereinafter, a carrier recovery apparatus for a quadrature phase shift keying (QPSK) transmission system and a method thereof according to an embodiment of the present invention will be described with reference to FIGS. 1 to 8. The present invention will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present invention. Like reference numerals in the drawings denote like elements throughout the specification.

Particularly, in the present invention, a carrier wave capable of estimating a phase error by removing data dependency using a comparator instead of a multiplier for the QPSK modulation method and reconstructing a carrier phase using the estimated phase error is suitable for a high speed optical communication system. We propose a recovery circuit.

1 is an exemplary view showing the structure of a carrier recovery apparatus according to an embodiment of the present invention.

As shown in FIG. 1, the carrier recovery apparatus or the carrier decoder according to the present invention includes a data dependency elimination module 110, an averaging module 120, an angle measurement module 130, It may be configured to include a phase unwrapping module 140, a multiplier 150, and the like.

First, a signal transmitted by the QPSK modulation scheme may be represented by Equation 1 below.

[Equation 1]

x _m = e ^{j2mπ / 4} , m = 0,1,2,3

Here, m may mean a digital value to be transmitted.

The k-sampled output of the QPSK-modulated symbol from the receiver may be represented by Equation 2 below.

&Quot; (2) "

y _k = x _k e ^jθk + n _k

Here, x _k may mean a k-th transmitted complex-valued symbol, θ _k may mean a phase error, and n _k may mean additive white gaussian noise.

Data-dependent removal module 110 upon receipt of the signal y _k, because it is in a phase in the received signal y _k error θ _k, as well as generated by the symbol or data x _k the phase information from the received signal y _k Only the phase information generated by the data can be removed to output the signal Z _k from which the phase information has been removed. Details will be described below.

In this case, the QPSK signal may determine that the data dependency removal is not necessary when the QPSK constellation is divided into a plurality of regions and is within a range of +45 degrees to -45 degrees among the divided ranges.

2 is an exemplary view showing a QPSK constellation diagram according to an embodiment of the present invention.

As shown in FIG. 2, the QPSK constellation diagram can be divided into a range located for each symbol, which is region0 between +45 degrees and -45 degrees, region1 between +45 degrees and +135 degrees, and +135 degrees and -135 degrees. Region2 between degrees, and region3 between -135 degrees and -45 degrees.

The data dependency elimination module 110 1) rotates π / 2 or 90 degrees to the right on the constellation diagram when the received signal is in region1, and 2) π or 180 rotates to the right on the constellation diagram when the received signal is in region2. 3) If the received signal is in region 3, it rotates 3π / 2 or 270 degrees to the right on the constellation. When the data dependency is removed in this way, signals in all ranges are gathered into region0, which can be expressed as Equation 3 below.

&Quot; (3) "

region0:

y _k = e ^jθk + n _k

Z _k = e ^jθk + n _k

region1:

y _k = e ^{j (π / 2)} e ^jθk + n _k

Z _k = e ^{-j (π / 2)} e ^{j (π / 2)} e ^jθk + n _k

= e ^jθk + n _k

region2:

y _k = e ^{j (2π / 2)} e ^jθk + n _k

Z _k = e ^{-j (2π / 2)} e ^{j (2π / 2)} e ^jθk + n _k

= e ^jθk + n _k

region3:

y _k = e ^{j (3π / 2)} e ^jθk + n _k

Z _k = e ^{-j (3π / 2)} e ^{j (3π / 2)} e ^jθk + n _k

= e ^jθk + n _k

The averaging module 120 may accumulate the signal Z _k from which phase information is removed by a predetermined number and obtain an average value of the accumulated signal as shown in Equation 3 below.

&Quot; (3) "

avg (Z _k ) =

Here, L may mean the observation range, that is, the number to be accumulated.

The angle measuring module 130 may measure an angle of the received signal using an average value. This is to reduce the influence of additive white gaussian noise (AWGN) of the received signal.

For example, if the average value is 1 + i1, the signal is located at (1,1) and the value is π / 4.

를 추정할 수 있다. 이러한 위상 오차

를 추정하는 원리를 도 5를 참조하여 설명한다.
Phase unwrapping module 140 is a phase error of the received signal based on the measured angle

Can be estimated. This phase error

The principle of estimating is explained with reference to FIG.

3 is an exemplary view showing an estimated phase according to an embodiment of the present invention.

As shown in FIG. 3, when the +45 degree or -45 degree is passed, an abnormal jump phenomenon, that is, suddenly crosses from +45 degree to -45 degree or suddenly crosses from -45 degree to +45 degree occurs. have.

를 추정하게 된다. 예컨대, 페이즈 언래핑 모듈(140)은 +45도에서 -45도로 넘어가면 측정된 각도에 π/2를 더하고, -45도에서 +45도로 넘어가면 측정된 각도에 π/2를 빼게 된다.
When such an abnormal jump occurs, the phase unwrapping module 140 adds or subtracts π / 2 from the measured angle to phase error of the received signal.

. For example, the phase unwrapping module 140 adds [pi] / 2 to the measured angle when it is crossed from +45 degrees to -45 degrees, and subtracts [pi] / 2 from the measured angle when it is crossed from -45 degrees to +45 degrees.

와 수신된 신호 y_k를 곱하여 반송파 위상을 복원할 수 있다.
Multiplier 150 estimates the phase error

The carrier phase can be restored by multiplying by and the received signal y _k .

FIG. 4 is an exemplary diagram illustrating a detailed configuration of the data dependency removal module 110 shown in FIG. 1.

As shown in FIG. 4, the data dependency elimination module 110 according to the present invention includes a first comparator 111, a second comparator 112, a third comparator 113, a fourth comparator 114, and a first comparator 114. 5 may include a comparator 115 and the like. The first comparator 111, the second comparator 112, the third comparator 113, the fourth comparator 114, and the fifth comparator 115 may compare and output the real part and the imaginary part of the received signal. have.

The operation principle thereof is as follows. The positive real part Re (y _k ) and the negative real part -Re (y _k ) of the received signal may be input to the first comparator 111. The first comparator 1111 may output any one of a positive real part Re (y _k ) and a negative real part -Re (y _k ) according to a selection condition, that is, Re (y _k ) <0.

In this case, the negative real part -Re (y _k ) is a complement to 2 of the positive real part Re (y _k ).

Similarly, the positive imaginary part Im (y _k ) and the negative imaginary part -Im (y _k ) of the received signal can be input to the second comparator 112. The second comparator 112 may output one of a positive imaginary part Im (y _k ) and a negative imaginary part -Im (y _k ) according to a selection condition, that is, Re (y _k ) <0.

In this case, the negative real part -Im (y _k ) is the complement of 2 of the positive real part Im (y _k ).

When the third comparator 113 receives an absolute value between the value output from the first comparator 111 and the value output from the second comparator 112, the selection condition, that is, abs [Re (y _k )] <abs [Im (y _k )] can respectively output any one of the input values.

When the fourth comparator 114 receives the values output from the first comparator and the second comparator 111 and 112, respectively, the selection condition, that is, abs [Re (y _k )] <abs [Im (y _k )] Accordingly, any one of the input values can be output.

At this time, the value output from the third comparator 113 becomes the real part Re (Z _k ).

When the fifth comparator 115 receives a value output from the fourth comparator 114, that is, a positive value and a negative value, the selection condition, that is, abs [Re (y _k )] <abs [Im (y _k ) ], One of the input values can be output according to Im (y _k ) <0, and the output value becomes the imaginary part Im (Z _k ).

Thus, the present invention eliminates data dependency by using a comparator instead of a multiplier.

5 is an exemplary view illustrating a method for restoring a carrier wave according to an embodiment of the present invention.

As shown in FIG. 5, the carrier recovery apparatus according to the present invention may output a signal from which phase information has been removed by removing phase information generated by data from a received signal (S510).

Next, the carrier recovery apparatus may accumulate a predetermined number of signals from which phase information has been removed in order to reduce the influence of the AWGN of the received signal and obtain an average value of the accumulated signals (S520).

Next, the carrier recovery apparatus may measure the angle on the constellation of the received signal using the obtained average value (S530).

Next, the carrier recovery apparatus may estimate the phase error of the received signal based on the measured angle (S540). That is, if an abnormal jump phenomenon occurs, the phase unwrapping module 140 estimates the phase error of the received signal by adding or subtracting π / 2 from the measured angle.

Next, the carrier recovery apparatus may restore the carrier phase by multiplying the received signal with the phase error estimated from the signal from which the data dependency is removed (S550).

FIG. 6 is an exemplary view illustrating the data dependency removing process S510 shown in FIG. 5 in detail, and FIG. 7 is an exemplary view illustrating the constellation rotation according to the data dependency removing process.

As shown in FIG. 6, the carrier recovery apparatus according to the present invention checks whether the real part of the received signal is smaller than 0 (S511), and if the real part is smaller than 0 as a result of the checking, rotates the received signal by π. It may be (S512). The operation of rotating by π changes the sign of the real part and the imaginary part of the received signal as shown in FIG. That is, the signal in region2 rotates to region0, the negative real part in region1 rotates to the positive real part of region3, and the negative real part in region3 rotates to the positive real part of region1. do. As a result, the signals in the negative real range are rotated to the dark range in which the positive real part is positive.

Through this process, the real part of the received signal may be changed to greater than zero.

Next, the carrier recovery apparatus checks whether the absolute value of the real part of the received signal is smaller than the absolute value of the imaginary part (S513). It may be (S514).

Next, if the absolute value of the real part is smaller than the absolute value of the imaginary part, but the imaginary part is smaller than 0, the carrier recovery device rotates π / 2 or 90 degrees counterclockwise to rotate to region 0 (S515).

On the other hand, when the absolute value of the real part is smaller than the absolute value of the imaginary part, but the imaginary part is larger than 0, the carrier recovery device rotates π / 2 or 90 degrees clockwise to rotate to region 0 (S516).

Hereinafter, the results of simulating the performance of the carrier recovery apparatus in a white noise channel environment will be described.

8 is an exemplary view showing a result of comparing the performance of the V & V algorithm and the proposed algorithm.

As shown in FIG. 8, the performance of the carrier recovery apparatus of the V & V algorithm and the proposed algorithm is compared. The V & V algorithm uses multiple square operations on the received signal to eliminate data dependency, and quadratic operations on the QPSK modulation. In optical communication systems that require high speed operation, speed limiters are introduced by the multipliers.

On the other hand, the proposed algorithm can remove the data dependency without multiplication.

For example, when comparing the total gate count, the proposed algorithm has 2.3 times faster operation speed and 61.5% reduction in hardware complexity than V & V algorithm.

Various modifications and variations may be made by those skilled in the art to which the carrier recovery apparatus and method for the QPSK transmission system according to the present invention belong without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

110: data dependency removal module
111: first comparator
112: second comparator
113: third comparator
114: fourth comparator
115: fifth comparator
120: averaging module
130: angle measurement module
140: phase unwrapping module
150: multiplier

Claims (12)

A data dependency removal module for outputting a signal from which the phase information is removed by removing phase information generated by data from a received signal;
An averaging module for accumulating a predetermined number of signals from which the phase information has been removed and outputting an average value of the accumulated signals;
An angle measuring module for measuring an angle of the received signal using the average value; And
A phase unwrapping module for estimating a phase error of the received signal based on the measured angle;
Carrier recovery apparatus for a QPSK transmission system comprising a. The method according to claim 1,
The data dependency removal module,
If the real part of the received signal is less than zero, rotate the received signal 180 degrees clockwise on the constellation diagram, and if the absolute value of the real part of the received signal is less than the absolute value of the imaginary part, clockwise or counterclockwise on the constellation diagram Rotates 90 degrees in the direction to remove phase information generated by the data from the received signal,
And outputting the received signal if the absolute value of the real part of the received signal is greater than the absolute value of the imaginary part. The method of claim 2,
The data dependency removal module,
If the absolute value of the real part of the received signal is smaller than the absolute value of the imaginary part but the imaginary part is less than zero, the received signal is rotated 90 degrees counterclockwise on a constellation to remove phase information generated by the data from the received signal. Carrier recovery apparatus for a QPSK transmission system, characterized in that. The method of claim 2,
The data dependency removal module,
If the absolute value of the real part of the received signal is smaller than the absolute value of the imaginary part but greater than zero, the received signal is rotated 90 degrees clockwise on a constellation to remove phase information generated by the data from the received signal. A carrier recovery apparatus for a QPSK transmission system, characterized in that. The method according to claim 1,
The data dependency removal module,
And a comparator for comparing and outputting a real part and an imaginary part of the received signal. The method according to claim 1,
A multiplier for restoring a carrier phase by multiplying the estimated phase error by the received signal;
Carrier recovery apparatus for a QPSK transmission system characterized in that it further comprises. A data dependency removal step of outputting a signal from which the phase information is removed by removing phase information generated by data from a received signal;
An averaging step of accumulating a predetermined number of signals from which the phase information has been removed and outputting an average value of the accumulated signals;
An angle measuring step of measuring an angle of the received signal using the average value; And
A phase unwrapping step of estimating a phase error of the received signal based on the measured angle;
Carrier recovery method for a QPSK transmission system comprising a. The method of claim 7, wherein
The data dependency removing step,
If the real part of the received signal is less than zero, rotate the received signal 180 degrees clockwise on the constellation diagram, and if the absolute value of the real part of the received signal is less than the absolute value of the imaginary part, clockwise or counterclockwise on the constellation diagram Rotates 90 degrees in the direction to remove phase information generated by the data from the received signal,
And if the absolute value of the real part of the received signal is greater than the absolute value of the imaginary part, outputting the received signal. The method of claim 8,
The data dependency removing step,
If the absolute value of the real part of the received signal is less than the absolute value of the imaginary part but the imaginary part is less than zero, the received signal is rotated 90 degrees counterclockwise on a constellation to remove phase information generated by the data from the received signal. A carrier recovery method for a QPSK transmission system, characterized in that. The method of claim 8,
The data dependency removing step,
If the absolute value of the real part of the received signal is smaller than the absolute value of the imaginary part but greater than zero, the received signal is rotated 90 degrees clockwise on a constellation to remove phase information generated by the data from the received signal. A carrier recovery method for a QPSK transmission system characterized by the above-mentioned. The method of claim 7, wherein
The data dependency removing step,
And a comparator configured to compare and output the real part and the imaginary part of the received signal. The method of claim 7, wherein
A multiplication step of multiplying the estimated phase error by the received signal to restore a carrier phase;
Carrier recovery method for a QPSK transmission system characterized in that it further comprises.

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