KR19990055487A - False lock detection device in Kewpiesuke system - Google Patents

Abstract

First and second matching filters for receiving and filtering I and Q signals, an up / down filter for receiving and filtering I and Q signals input from the first and second matching filters, and the up / down filters Compares the first and second accumulators accumulating the signal filtered by the filter for a predetermined period (N) with the output value accumulated by the first accumulator and the output value accumulated by the second accumulator and is a true lock. It is composed of a detection unit that detects whether it is a lock, and by determining the sign of the frequency offset when a false lock occurs, it can reduce the time required to lock accurately and improve reliability. have.

Description

False lock detection device in QPSK system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital / satellite broadcast receiver for high-speed transmission, and more particularly, to a QPSK system that detects carrier wave synchronization during quadrature phase shift keying (QPSK) demodulation. False A lock and a device for determining the sign of a frequency offset caused thereby.

In general, when a satellite is used for broadcasting, an efficient modulation method must be adopted because transmission power is not largely taken.

Therefore, in satellite broadcasting, many efficient QPSK modulation methods are employed as digital modulation methods.

That is, the QPSK scheme has a high amplitude modulation because the amplitude is constant and only the phase information needs to be transmitted.

The operation principle of the QPSK method is shift keying of four phases. The data is divided into the I-axis and the Q-axis (1 bit each), and the transmission carriers that are orthogonal to the data, that is, the 90-degree shifted phase are respectively modulated. It is.

Therefore, a satellite broadcasting receiver receiving a QPSK modulated high-speed transmission signal requires a lock detection circuit that detects whether a carrier is synchronized during QPSK demodulation.

Hereinafter, with reference to the accompanying drawings as follows.

1 is a block diagram showing a lock detection circuit according to the prior art.

Referring to FIG. 1, a QPSK demodulator 1 and a preprocessing error correction (FEC) unit 2 which detects an error by receiving a signal modulated and transmitted by the QPSK demodulator 1 and displays a correction or an error; And a microcomputer 3 that receives the signal transmitted from the QPSK demodulator 1 and outputs a lock signal for detecting whether the carrier is synchronized.

The preprocessing error correction (FEC) unit 2 includes a Viterbi decoder 2a for detecting an error of a signal transmitted from the QPSK demodulator 1, and a deinterleaver for transmitting an error corrected at the Viterbi decoder 2a. (2b) and an RS-decoder (2c) for decoding the error signal transmitted from the deinterleaver (2b).

In addition, a bit error rate (BER) output from the Viterbi decoder 2a is input to the lock detection signal and the microcomputer 3 output from the QPSK demodulator 1.

In the process of removing the carrier in the QPSK demodulator 1, symbol rate Even if a frequency offset difference occurs, it outputs a signal that it is locked.

Accordingly, the Viterbi decoder 2a of the preprocessing error correction (FEC) unit 2 generates a large number of error signals and outputs the signals output from the QPSK demodulator 1 and the error signals output from the Viterbi decoder 2a. Output to the microcomputer (3).

The microphone 3 is correctly locked by receiving a myriad of error signals and outputting a false lock signal.

The lock detection circuit according to the prior art Since we cannot detect the sign of the frequency difference It takes a lot of time to lock because it must detect all the frequency difference, and even if the BER (Bit Error Rate) increases due to noise, it is considered as a false lock, so there is a problem that the reliability is degraded. .

The present invention has been made to solve this problem, the symbol rate of the frequency offset (offset) is It is an object of the present invention to provide a lock detection device in a QPSK system that can detect and correct a false lock occurring when there is a difference.

1 is a block diagram showing a lock detection apparatus according to the prior art

2 is a block diagram showing a lock detection apparatus in a QPSK system according to the present invention.

3 is a block diagram illustrating in detail the lock detection unit of FIG. 2;

4A is a diagram showing the configuration of an up filter according to the present invention;

4b is a view showing the configuration of a down filter according to the present invention;

5A to 5B show a false lock detection spectrum according to the present invention.

5C illustrates a true lock detection spectrum in accordance with the present invention.

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

11: QPSK demodulator 12: FEC

13, 27: lock detector 14: microcomputer

21: first matched filter 22: second matched filter

23: up filter 24: down filter

25: first accumulator 26: second accumulator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lock detection device, comprising: a lock detection device including a QPSK demodulator, a preprocessing error correction (FEC) unit, and a microcomputer, for receiving and filtering received signals I and Q, respectively. Each of the first and second matched filters, the up / down filter for receiving and filtering the I and Q signals inputted from the first and second matched filters, and the signal filtered by the up / down filter are respectively a predetermined period ( N and a detector for comparing the first and second accumulators accumulated during N) with the output value accumulated by the first accumulator and the output value accumulated by the second accumulator to detect whether the device is true lock or false lock. It is configured to include a lock (Lock) detection unit is characterized by.

Hereinafter, with reference to the accompanying drawings as follows.

FIG. 2 is a block diagram illustrating a lock detection apparatus according to the present invention, and FIG. 3 is a block diagram showing the lock detection unit in FIG. 2 in detail.

As shown in FIG. 2, the QPSK demodulator 11 receives the demodulated signals I and Q, demodulates the carrier, and outputs the carrier signal. The QPSK demodulator 11 receives an error signal. A preprocessing error correction (FEC) unit 12 for detecting, correcting, and outputting the received signal, and the received signals I and Q demodulated by the QPSK demodulator 11 to receive a true lock or a false lock. A microcomputer that outputs a detected signal by receiving a signal output from a lock detector 13 for determining whether a lock is applied, and a signal output from the lock detector 13 and a preprocessing error correction (FEC) unit 12. It consists of 14.

As shown in FIG. 3, the lock detector 13 receives first and second matching filters 21 and 22 for receiving the received signals I and Q to maximize the output SN ratio, An up filter 23 for receiving an I signal output from the first matched filter 21 and a Q signal output from the second matched filter 22 and up-filtering the output signal from the first matched filter 22; A down filter 24 for receiving the I signal and the Q signal output from the second matching filter 22 and down filtering the first signal; and a first accumulator 25 for calculating the magnitude of the frequency filtered by the up filter 23; The second accumulator 26 calculating the magnitude of the frequency filtered by the down filter 24 is compared with the magnitude calculated by the first accumulator 25 and the magnitude calculated by the second accumulator 26. It is comprised by the detection part 27 which determines whether it is a true lock or a false lock.

4A is a diagram illustrating the configuration of the up filter 23, and FIG. 4B is a diagram illustrating the configuration of the down filter 24.

As shown in FIG. 4A, the process of filtering by the up filter 23 is expressed as an equation.

[Equation 1]

In addition, the process filtered by the down filter 24 is expressed as an equation.

[Equation 2]

The output values filtered by the up filter 23 and the down filter 24 are accumulated for a predetermined period N through the first and second accumulators 25 and 26.

The signal filtered by the up filter 23 is accumulated in the first accumulator 25 for a predetermined period N using the following equation.

[Equation 3]

In addition, the output value filtered by the down filter 24 is accumulated in the second accumulator 26 for a predetermined period (N symbol interval) using the following equation.

[Equation 4]

The lock detection unit 27 compares the accumulated output values u _k and d _k and detects whether they are true lock or false lock.

On the other hand, referring to Figures 5a to 5c is expressed as a spectrum in the characteristics determined by the lock (lock) detection unit 27 as follows.

If u _k accumulated in the first accumulator 25 is greater than or equal to 1.6d _k (u _k > 1.6d _k ), it is a false lock, and the sign of the remaining frequency offset is + 0.25fs, and thus, FIG. As shown, there are many regions overlapping to the right.

In addition, if d _k accumulated in the second accumulator is 1.6u _k or more (d _k > 1.6u _k ), it is a false lock, and the sign of the remaining frequency offset is -0.25fs. As shown, there are many regions overlapping to the left.

In this way, when the lock is false, the frequency The energy difference is 1.6 or more.

On the other hand, if u _k accumulated in the first accumulator and d _k accumulated in the second accumulator coincide, a true lock is formed, and the left and right overlapping portions coincide.

The false lock detector according to the present invention simplifies the conventional false lock determination system, and shortens the time taken to accurately lock by discriminating the sign of the frequency offset. It can improve the reliability.

Claims (4)

First and second matching filters for receiving and filtering I and Q signals, an up / down filter for receiving and filtering I and Q signals input from the first and second matching filters, and the up / down filters Compares the first and second accumulators accumulating the signal filtered by the filter for a predetermined period (N) with the output value accumulated by the first accumulator and the output value accumulated by the second accumulator and is a true lock. Lock detection device in a QPSK system, characterized in that the detection unit for detecting whether the lock (False Lock). The method of claim 1, Lock detection device in the QPSK system characterized in that the true lock (true lock) if the output value of the first accumulator and the second accumulator match. The method of claim 1, If the cumulative value of the first accumulator is equal to or greater than the cumulative value of the second accumulator, the lock is false, and the sign of the frequency offset is positive. The lock is performed in the QPSK system. Detection device. The method of claim 3, If the cumulative value of the first accumulator is less than or equal to the cumulative value of the second accumulator, the lock is false lock, and the sign of the frequency offset is minus (-). ) Detection device.