KR100209659B1 - Digital Phase-Frequency Sensor for Carrier Recovery - Google Patents

Abstract

A digital phase-frequency sensing device for carrier recovery, comprising: a symbol position determiner for determining which region a currently received symbol belongs to; and a phase value of a current symbol output from the symbol position determiner; Stores the phase detection unit and the phase value of each region of the previous symbol, and when the region of the current symbol determined by the symbol positioning unit is input, outputs the phase value of the corresponding region and stores it again as the previous symbol phase value of the corresponding region. A phase difference of adjusting the local carrier frequency by detecting a phase difference between the two symbols by receiving the potential phase storage unit, the phase value of the previous symbol output from the potential phase storage unit, and the phase value of the current symbol output from the phase detection unit. It is composed of a detection unit, the configuration of the system is simple, and there is an economic effect.

Description

Digital Phase-Frequency Sensor for Carrier Recovery

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a carrier recovery apparatus such as Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Keying (QPSK), and more particularly, to a digital phase-frequency sensing device for carrier recovery to correct carrier frequency offset.

In general, in a passband pulse amplitude modulation (PAM) such as a cable modem, a general telephone line modem, or satellite communication, a carrier recovery that matches the frequency and phase of a carrier on a receiver with the local carrier oscillation frequency and phase on a receiver The device is essential.

In particular, the carrier frequency offset of the transmitting and receiving sides should be corrected. A general modulation and demodulation device for correcting the carrier frequency offset will now be described with reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating a configuration of a QPSK (PAM) modulation apparatus in general digital communication. The first and second transmission filters 11 and 14, the first and second mixers 13 and 15, It consists of an oscillator (OSC) 12 and an adder 16.

Referring to the operation of the modulation device configured as described above, first, the data string of the I signal is filtered through the first transmission filter 11 and then the carrier frequency (cos (fc)) and the first mixer ( 13 is mixed and output to the adder 16.

Also, the data sequence of the Q signal is filtered through the second transmission filter 14 and then mixed in the second mixer 15 with the carrier frequency sin (fc) output from the OSC 12 to the adder 16. Output

The adder 16 adds the signals input from the first and second mixers 13 and 15 and transmits them to the communication channel.

That is, the data sequence of the I and Q signals is transferred from the base band to the band centered on the carrier frequency by carrier mixing and sent to the communication channel.

The following describes a demodulation device for receiving and demodulating a signal modulated to a communication channel as described above.

FIG. 2 is a block diagram illustrating a configuration of a QPSK (PAM) demodulation device in general digital communication, and FIG. 3 is a block diagram illustrating a detailed configuration of a carrier recovery unit of FIG. 2, and an oscillator (OSC) 21. ), Carrier recovery section 26 comprising first and second mixers 22 and 23, first and second reception filters 24 and 25, frequency / phase detector 261 and loop filter 262. It is composed of

In the demodulator configured as described above, the received signal inputted through the channel and the local oscillating carrier cos (f) outputted from the OSC 21 are multiplied by the first mixer 22, and the original signal is transmitted through the first receive filter 24. Restores to the I signal data stream.

Then, the received signal and the local oscillating carrier sin (f) output from the OSC 21 are multiplied by the second mixer 23 and restored to the original Q signal data string through the second receiving filter 25.

In this demodulation process, since the frequency and phase of the transmitting carrier must exactly match the receiving local carrier, the carrier is recovered by the carrier recovery unit 26.

The frequency / phase detector 261 of the carrier recovery unit 26 receives the output of the I, Q signals or the equalizer (not shown) restored by the first and second reception filters 24 and 25. B Detect the difference in phase.

The loop filter 262 of the carrier recovery unit 26 adjusts the local oscillation frequency by filtering the difference in frequency or phase sensed by the frequency / phase detector 261 and outputting the result to the OSC 21 again.

Looking at the phase-frequency detection device according to the prior art in the above QPSK (PAM) demodulation device in more detail as follows.

FIG. 4 is a block diagram illustrating a detailed configuration of the frequency / phase detection unit of FIG. 3. The downcone input from the first and second reception filters 24 and 25 receives the oscillation signal of the OSC 21. Phase shifter for shifting the oscillation signal of the first phase detector 41 which detects the phase difference with the butt I or Q signal and the oscillation signal of the OSC 21 oscillating in accordance with the output of the loop filter 262. (42) and a second phase for detecting a phase difference between the signal shifted by the phase shifter 42 and the down-converted I or Q signal input from the first and second receive filters 24 and 25. A first comparator 44 which compares the signal sinφ (t) output from the detector 43, the first phase detector 41 with a predetermined reference value, and outputs a control signal according to the result; and a second phase detector A second comparator 45 for comparing the signal cosφ (t) output at 43 with a predetermined reference value and outputting a control signal according to the result; 44 and the second comparator 45 perform an AND gate 46 for ANDing the output signal, and perform a track or hold according to the result output from the AND gate 46 to output to the loop filter 262. Consisting of a track / hold section 47.

The operation of the phase-frequency sensing device according to the prior art configured as described above will be described.

5A and 5B are waveform diagrams of the outputs of the first and second phase detectors of FIG. 4, and FIG. 6A is a waveform diagram of the positive frequency offsets of FIG. 4, and FIG. b) is a waveform diagram for the negative frequency offset of FIG.

First, the first phase detector 41 detects the phase difference between the down-converted I or Q signal input from the first and second reception filters 24 and 25 and the output signal of the OSC 21, and FIG. The same sinφ (t) as in (a) is output to the first comparator 44.

In addition, the second phase detector 43 has a down-converted I or Q signal inputted from the first and second reception filters 24 and 25 and an output signal of the OSC 21 from the phase shifter 42. The phase difference of the 90 ° phase shifted signal is detected and cosφ (t) as shown in FIG. 5B is output to the second comparator 45.

Here, the horizontal axis in FIG. 5 represents the phase difference φ (t) as a function of time, and the vertical axis represents the output of the first and second phase detectors 41 and 43.

When the phase difference output from the first phase detector 41 is input, the first comparator 44 outputs 1 when the input phase difference is greater than or equal to a predetermined value θ and less than a predetermined value θ. Output 0.

The second comparator 45 inputs a phase difference output from the second phase detector 43 to output 1 when the input phase difference is greater than or equal to 0, and outputs 0 when less than zero.

The AND gate 46, which receives the outputs of the first and second comparators 44 and 45, logically multiplies to output a control signal to the track / hold unit 47.

The track / hold unit 47 tracks or holds the output signal to the loop filter 262 according to a control signal output from the AND gate 46.

이면 위상 오프셋의 트래킹되는 범위이다.That is, when the phase difference between the received signal and the local carrier is smaller than a predetermined value θ as shown in FIG. If the difference is greater than the constant value θ, the track / hold section 47 holds the output of the first phase detector 41 at the constant value θ, and the range of the constant value θ is

This is the tracked range of the phase offset.

Here, the held direct current component has a positive nonzero value or a negative nonzero value.

As a result, the first phase detector 41 increases or decreases the frequency of the OSC 21 according to the sign of the DC component, and the second phase detector 43 performs phase sensing and tracking of the first phase detector 41. To change holding and holding

The phase-frequency sensing device according to the prior art is composed of two phase detectors and a track / hold part, and outputs the direction of increase and decrease of the local oscillation frequency by switching the phase sensing device to tracking and holding according to a predetermined predetermined value. The configuration is complicated and economical problems arise.

Disclosure of Invention The present invention has been made to solve the problems of the prior art, and the object of the present invention is to provide a digital phase-frequency sensing device for carrier recovery by directly calculating the frequency offset by digital signal processing to adjust the frequency of the local oscillator. have.

1 is a block diagram for explaining the configuration of a QPSK (PAM) modulation device in a general digital communication

2 is a block diagram for explaining a configuration of a QPSK (PAM) demodulation device in general digital communication;

3 is a block diagram illustrating a detailed configuration of a carrier recovery unit of FIG. 2.

4 is a block diagram illustrating a detailed configuration of the frequency / phase detection unit of FIG. 3.

5A and 5B are waveform diagrams of outputs of the first and second phase detectors of FIG. 4.

FIG. 6A is a waveform diagram of the positive frequency offset of FIG.

6B is a waveform diagram of the negative frequency offset of FIG. 4.

7 is a view for explaining a relationship between a phase difference and an offset between two consecutive symbols according to the present invention;

8 is a block diagram illustrating a configuration of a digital phase-frequency sensing device for carrier recovery in the case of QPSK according to an embodiment of the present invention.

9 is a view for explaining the operation of the digital phase-frequency detection device of FIG.

* Explanation of symbols for main parts of the drawings

81: symbol position determining unit 82: phase detection unit

83: full phase storage unit 84: phase difference detection unit

A feature of the digital phase-frequency sensing device for carrier recovery according to the present invention is that the potential storage unit stores the phase value for each region of the previous symbol, and when the region data for the current symbol is input, Output and store it again as the previous symbol phase value of the corresponding area, and the phase difference detector detects the difference between the phase value of the transmitted current symbol and the phase value of the previous symbol outputted from the potential phase storage unit to detect the frequency of the local carrier oscillator. Is in control.

First, the basic operation principle will be described before entering the description of the digital phase-frequency sensing device for carrier recovery according to the present invention.

FIG. 7 is a view for explaining a relationship between a phase difference and an offset between two consecutive symbols according to the present invention. When a frequency offset of a carrier exists between a transmitting side and a receiving side, a transmission symbol is a sign of an offset (+, Rotate clockwise or counterclockwise according to-).

At this time, the phase difference θ between two consecutive symbols is proportional to the offset.

If the frequency offset is large, the absolute value of θ is large. On the contrary, if the absolute value of θ is small, the frequency offset is small.

Here, the symbols for calculating the phase difference θ do not necessarily have to be continuous, but only have a temporal interval. The calculation of the phase difference [theta] between two consecutive symbols can be any number of two or more symbols.

Hereinafter, a digital phase-frequency sensing device for carrier recovery according to the present invention will be described with reference to the accompanying drawings.

FIG. 8 is a block diagram illustrating a configuration of a digital phase-frequency sensing device for carrier recovery in the case of QPSK according to an embodiment of the present invention. A symbol position determining unit 81 for determining whether the symbol belongs, a phase detector 82 calculating a phase value of a current symbol output from the symbol position determining unit 81, and a symbol determining unit 81 for a previous symbol A phase storage unit 83 for storing and outputting the quadrant data output from the phase signal and the phase value of the previous symbol output from the phase detector 82, and a phase value and phase of all symbols output from the potential phase storage unit 83 The phase difference detector 84 receives a phase value of the current symbol output from the detector 82, detects a phase difference between the two symbols, and outputs the detected phase difference to the loop filter 262.

Referring to the operation of the digital phase-frequency sensing device for carrier recovery according to the present invention configured as described above, since the QPSK symbols are irregularly transmitted, I and Q signal regions are divided into four quadrants to calculate the correct phase difference.

In addition, the pre-phase storage unit 83 stores the position of a previously input symbol among the quadrants determined by the symbol position determining unit 81, and stores the position of the previously input symbol among the quadrants determined by the phase detection unit 82. Save the phase value.

Thereafter, when the currently received symbol is input, the symbol position determiner 81 determines a quadrant located among the four quadrants and outputs the quadrants to the phase detector 82 and the full phase storage unit 83.

The phase detector 82 calculates the phase of the quadrant to which the currently received symbol belongs and outputs the phase difference to the phase difference detector 84 and the all phase storage 83.

When the phase of the currently received symbol is input, the previous phase storage unit 83 stores the phase of the quadrant data and the phase to which the previous symbol belongs to the phase difference detection unit 84.

The phase difference detector 84 calculates a difference between a phase value of a currently received symbol and a phase value of a symbol belonging to the same quadrant previously received, and obtains a gain suitable for the difference between the calculated phase values and the loop filter 262. Adjust the appropriate local oscillation frequency by outputting

An embodiment of a digital phase-frequency sensing device for carrier recovery according to the present invention as described above will be described with reference to FIG.

If all phase values and quadrant data for the previous symbols A ', B', C ', and D' are stored in the all phase storage unit 83, and the symbol S belonging to one quadrant is currently received, the symbol positioning unit 81 determines which quadrant the current symbol S belongs to.

The phase detector 82 detects a phase value of the currently input symbol S and outputs the phase value to the phase difference detector 84.

In this case, the previous phase storage unit 83 outputs the phase value of the previous symbol A 'located in the same quadrant as the quadrant to which the currently input symbol S belongs, to the phase difference detector 84.

Then, the phase difference detector 84 calculates a phase difference θ between the previous symbol A 'and the current symbol S and outputs the phase difference θ to the loop filter 262.

The calculated phase value of the current symbol S is stored in the previous phase storage unit 83 as the next previous phase value of the quadrant.

In the case of QAM, in particular, in the case of 16-QAM, the I-Q region may be divided into 16, each previous symbol may be stored, and the phase difference from the current symbol may be calculated and output to the loop filter 262.

The digital phase-frequency sensing device for carrier recovery according to the present invention adjusts the frequency of the local carrier oscillator by calculating the phase difference between the currently transmitted symbol and the previously transmitted symbol, so that the configuration of the system is simple and economical effect. There is.

Claims (3)

A symbol position determiner which determines which region the currently received symbol belongs to, a phase detector which calculates a phase value of the current symbol output from the symbol position determiner, and a phase value of each region of the previous symbol. A potential phase storage unit for storing a current symbol region determined by the symbol position determiner and outputting a phase value of the corresponding region and storing it again as a previous symbol phase value of the corresponding region; Digital phase for carrier recovery, characterized in that the phase difference detection unit for adjusting the local carrier frequency by detecting the phase difference between the two symbols by receiving the phase value of the previous symbol and the current symbol output from the phase detection unit Frequency sensing device. The method of claim 1, wherein when the received symbol is QPSK, the I and Q signal regions are divided into four quadrants to determine which of the four quadrants the currently received symbol belongs to. Digital phase-frequency sensing device. The method of claim 1, wherein when the received symbol is a QAM, the I and Q signal regions are divided into sixteen quadrants to determine which one of the sixteen quadrants the currently received symbol belongs to. Digital phase-frequency sensing device.

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