KR20020097293A - Apparatus for demodulating blind in a digital communication system - Google Patents

Abstract

The present invention relates to a blind demodulation device for a digital communication system, comprising: a matched filter for converting a baseband signal into a digital signal using an analog / digital converter and filtering only a desired band among digital signals received while being converted; A time recoverer for restoring the time of the digital signal filtered by the matched filter; An interpolator for interpolating a timing error of the digital signal filtered by the matched filter and providing a digital signal visually restored by the visual decompressor; A phase detector / automatic frequency adjuster for detecting and restoring a delayed phase of the digitally restored signal by the interaction of the interpolator and the visually reconstructor, and adjusting and providing a frequency of the phase-restored digital signal; A lock detector for determining and providing a lock of a digital signal adjusted by a phase detector / automatic frequency regulator; A modulation detector for detecting a modulation scheme that is locked by the lock detector when demodulating the digital signal provided by the phase detector / automatic frequency regulator and determined that demodulation is possible; And a normalizer which normalizes the magnitude of the demodulated digital signal from the phase detector / automatic frequency regulator to a constant signal magnitude. Therefore, the conventional transmitter side has to inform the receiver in advance of the information on the modulation scheme, so that the receiver side can solve the inconvenience of demodulating using this information.

Description

Blind demodulation device for digital communication system {APPARATUS FOR DEMODULATING BLIND IN A DIGITAL COMMUNICATION SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blind demodulation device for a digital communication system. In particular, a blind demodulation method suitable for detecting a modulation method corresponding to a received signal is detected, regardless of a modulation method used for a transmission signal in a wireless communication system. The present invention relates to an apparatus for demodulating a received signal by applying.

In general, when a wireless communication system transmits a modulation scheme having various data bit rates according to the communication channel state in order to improve data transmission efficiency, the receiving side modulates the received signal. You must demodulate without knowing any information about.

That is, the amount of information transmitted using the same frequency band in the wireless communication system is determined by the transmission bit rate of the modulation method used when converting the data to be sent to a signal suitable for transmission. For example, a binary phase shift keying (hereinafter, abbreviated as BPSK), a modulation method of transmitting a carrier phase in binary phase in response to a digital signal, provides one bit of information in a signal representing a phase. Quadrature Phase Shift Keying (hereinafter, abbreviated as QPSK) is a two-bit information that is twice as large as BPSK. QPSK has a higher transmission efficiency than BPSK as the signal is transmitted on a signal representing a phase. In other words, in order to increase transmission efficiency, it is desirable to use a bit rate modulation scheme as high as possible.

However, if a high bit rate modulation scheme is used, the transmission bit rate can be obtained according to the state of the communication channel as a high signal-to-noise ratio is required at the receiving side because the discrimination power between the signals representing the respective information is reduced. It is limited by the signal-to-noise ratio present.

In addition, the wireless communication channel system is more affected by the external environment than the wired channel. In other words, as the frequency band is higher, the state of the channel is very different according to the weather. The information on the channel state is collected by the transmitting side and determined by a modulation method of a bit rate that can be transmitted.

For example, when data is transmitted using a Ka or Ku band in a communication using a satellite system, when data is transmitted in bad weather (rainfall), very different channel characteristics are shown. In other words, if the attenuation of the signal due to bad weather is very severe (SNR is about 7 dB), the signal is modulated and transmitted to a low bit rate BPSK, and when the attenuation of the signal is improved (SNR is 10 dB or more), the QPSK 8-phase shift keying (hereinafter referred to as 8PSK), which is a modulation method that modulates and transmits the phase of the carrier in octal phase in response to a digital signal when the weather is very good (SNR is 15dB or more). Transmit data by modulating.

While the data transmission efficiency is increased according to the adaptive modulation scheme, a problem arises in that the reception signal needs to be demodulated without knowing the selection and application time of the modulation scheme to be used.

In other words, when a multiple modulation scheme is used, when the modulation scheme needs to be changed, information is informed to the receiver in advance by using various means, and the receiver performs demodulation suitable for the modified modulation scheme using the information. However, there is a problem that it is difficult to correctly demodulate in the conventional manner when such information is not known from the receiving side.

Accordingly, the received side demodulates the received signal using a demodulator corresponding to each modulation scheme used at the transmitting side with respect to the received signal. However, as a result, when the type of modulation scheme used on the transmitting side increases, the structure of the demodulator becomes complicated and the cost also increases.

Therefore, the present invention has been made to solve the above-described drawbacks, and its object is to provide a modulation scheme by using the relationship between the characteristics of the received signal and the modulation schemes regardless of the modulation scheme used for the transmission signal at the receiving side. The present invention provides a blind demodulation device for a digital communication system for detecting and successfully demodulating a received signal by applying a demodulation method suitable for the detected modulation method.

In the present invention for achieving the above object, the blind demodulation device of the digital communication system converts the baseband signal into a digital signal using an analog-to-digital converter, and filters only a desired band of the digital signals received while being converted. Matched filter; A time recoverer for restoring the time of the digital signal filtered by the matched filter; An interpolator for interpolating a timing error of the digital signal filtered by the matched filter and providing a digital signal visually restored by the visual decompressor; A phase detector / automatic frequency adjuster for detecting and restoring a delayed phase of the digitally restored signal by the interaction of the interpolator and the visually reconstructor, and adjusting and providing a frequency of the phase-restored digital signal; A lock detector for determining and providing a lock of a digital signal adjusted by a phase detector / automatic frequency regulator; A modulation detector for detecting a modulation scheme that is locked by the lock detector when demodulating the digital signal provided by the phase detector / automatic frequency regulator and determined that demodulation is possible; And a normalizer which normalizes the magnitude of the demodulated digital signal from the phase detector / automatic frequency regulator to a constant signal magnitude.

1 is a block diagram of a blind demodulation device of a digital communication system according to the present invention;

2 is a constellation diagram of a modulation scheme used in a digital communication system according to the present invention,

3 is a table showing demodulation of a modulation scheme of a digital communication system according to the present invention.

4A is a signal constellation diagram when demodulating a signal modulated with BPSK with QPSK according to the present invention;

4B is a signal constellation diagram when demodulating a BPSK modulated signal to 8PSK according to the present invention;

4C is a signal constellation diagram when demodulating a signal modulated with QPSK according to the present invention with QPSK.

5 is a detailed flowchart of a blind demodulation device of a digital communication system according to the present invention.

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

100: digital communication system 101: matching filter

103 power detector 104 automatic gain regulator

105: interpolator 107: visual restorer

109: phase detector / automatic frequency regulator

111: lock detector 113: modulation method detector

115: normalizer 200: demodulation determination processor

300: gain control unit (GCU)

Hereinafter, with reference to the accompanying drawings will be described in detail the operation of the preferred embodiment according to the present invention.

1 is a block diagram of a blind demodulation device of a digital communication system according to the present invention, which includes a digital communication system 100, a demodulation determination processor 200, and a gain control unit (GCU) ( 300).

The digital communication system 100 is a block having a blind demodulation function, and includes a matched filter 101, a power detector 103, an automatic gain controller 104, an interpolator 105, and a time recoverer 107. And a phase detector / automatic frequency regulator 109, a lock detector 111, a modulation method detector 113, and a normalizer 115.

The matching filter 101 receives a digital signal obtained by converting a baseband signal, which has been transmitted from the transmitting side, through a high frequency and an intermediate frequency into a digital signal through an analog-to-digital converter (not shown), and then uses only a desired band among the provided digital signals. Filtering is provided to the power detector 103, the auto gain controller 104, and the interpolator 105.

The power detector 103 detects the power of the digital signal filtered by the matching filter 101 and provides a control signal indicating the presence or absence of the digital signal to the demodulation determination processor 200.

The automatic gain controller 104 generates an error signal for adjusting the magnitude of the digital signal filtered by the matched filter 101 to a desired value and provides it to a gain control unit (GCU) 300.

The interpolator 105 interpolates a timing error of the digital signal filtered by the matched filter 101, and receives a digital signal visually restored by the time recoverer 107 to receive a timing error. Is precisely interpolated and provided to the phase detector / automatic frequency regulator 109.

The time reconstructor 107 is filtered by the matched filter 101 and reconstructs the time of the digital signal interpolated by the interpolator 105 to provide the interpolator 105.

The phase detector / automatic frequency regulator 109 detects and restores the delayed phase of the time-restored digital signal by the interaction of the interpolator 105 and the time reconstructor 107, and adjusts the frequency of the restored digital signal. The lock detector 111 and the modulation method detector 113 are provided. The phase detector / automatic frequency regulator 109 also provides to the normalizer 115 a digital signal that is demodulated in accordance with the modulation scheme determined by the modulation scheme detector 113.

As shown in FIG. 3, the lock detector 111 demodulates the digital signals (types 1, 2, 3) controlled by the phase detector / automatic frequency regulator 109 into BPSK only when the modulation scheme is BPSK. The locked control signal is provided to the modulation method detector 113. In addition, the lock detector 111 provides the modulation method 113 with a control signal that is locked when the modulation method is BPSK and QPSK when demodulating the digital signals (types 1, 2, 3) to QPSK. Finally, the lock detector 111 demodulates the digital signals (types 1, 2, 3) to 8PSK and modulates the control signals in which the modulation scheme is locked to both BPSK and QPSK and 8PSK. To provide.

When the modulation method detector 113 demodulates the digital signal provided from the phase detector / automatic frequency regulator 109 to QPSK by using a control signal generated by being locked by the lock detector 111, the modulation method is BPSK. And when it is determined that both demodulation is possible when the QPSK is locked and the demodulation is possible, the modulation scheme is changed to BPSK or QPSK according to whether or not the condition shown in Equation 1 is satisfied for the demodulated signal. And provide it to the phase detector / automatic frequency regulator 109.

Where k is any constant, , ... denotes the number of signals corresponding to each signal point of BPSK, QPSK, and 8PSK, as shown in FIG. 2.

That is, the modulation method detector 113 evaluates whether a sufficient number (for example, about 1000 samples) of input signals satisfies Equation 1 above, and determines that the modulation method is BPSK. If not, the modulation method is QPSK. Is determined. Here, when demodulating a signal modulated with BPSK with QPSK, as shown in FIG. 4A, it appears as a constellation diagram of a signal demodulated with two symmetrical points among four signal points.

In addition, when the demodulation detector 113 demodulates the digital signal provided by the phase detector / automatic frequency regulator 109 to 8PSK, the modulation scheme is locked to both BPSK, QPSK, and 8PSK, and demodulation is possible. If it is determined that Equation 2 is satisfied for the digital signal demodulated to distinguish three modulation schemes, the modulation scheme is determined to be BPSK and is provided to the phase detector / automatic frequency regulator 109.

When the equation 3 is satisfied, the modulation scheme is determined to be QPSK, and the modulating method is provided to the phase detector / automatic frequency regulator 109.

On the other hand, if the equations (2) and (3) are not satisfied, the modulation scheme is determined to be 8PSK, and the phase detector / automatic frequency regulator 109 is provided.

Here, when demodulating a signal modulated with BPSK to 8PSK as shown in FIG. 4B, the signal is modulated with QPSK as shown in FIG. 4C, and is mapped to two symmetric signal points among eight possible signal points. When demodulating to 8PSK, four of eight possible signal points are mapped to symmetric signal points.

The normalizer 115 normalizes that the magnitude of the digital signal demodulated from the phase detector / automatic frequency regulator 109 is attenuated to a constant signal size and provides it to a decompression device (not shown) for data reconstruction.

The demodulation determination processor 200 receives a control signal indicating the presence or absence of a digital signal from the power detector 103 and determines whether or not to demodulate the received digital signal. The demodulation process. If there is no digital signal, the demodulation process is not performed.

The GCU 300 receives the error signal from the automatic gain adjuster 104 and adjusts the baseband signal to a desired size before converting the baseband signal into a digital signal.

Referring to the flowchart of Fig. 5, the blind demodulation device of the digital communication system according to the present invention will be described in detail based on the above-described configuration.

First, the matching filter 100 in the digital communication system 100 receives a digital signal converted from a baseband signal transmitted through a transmitting side through a high frequency and an intermediate frequency through an analog-to-digital converter (not shown). Thereafter, only desired bands of the provided digital signals are filtered and provided to the power detector 103, the automatic gain adjuster 104, and the interpolator 105, respectively (step 501).

The power detector 103 detects the power of the digital signal filtered by the matched filter 101 and provides a control signal indicating the presence or absence of the digital signal to the demodulation determination processor 200 (step 502).

The demodulation determination processor 200 receives a control signal indicating the presence or absence of a digital signal from the power detector 103 and determines whether or not to demodulate the digital signal received from the transmitting side (step 503).

If there is a digital signal in the determination step 503, it is controlled to perform a demodulation process on the received digital signal (step 504). On the other hand, if there is no digital signal in the determination step 503, the demodulation process is not performed (step 505).

On the other hand, the automatic gain controller 104 generates an error signal for adjusting the magnitude of the digital signal filtered by the matching filter 101 to a desired value and provides it to a gain control unit (GCU) 300. (Step 506), the GCU 300 receives the error signal from the automatic gain adjuster 104 and controls to adjust the baseband signal to a desired size before it is converted into a digital signal (step 507).

As described above, when a series of demodulation processes are performed on the digital signal received from the transmitting side, the interpolator 105 interpolates a timing error of the digital signal filtered by the matching filter 101. To the time recoverer 107 (step 508).

The time decompressor 107 restores the time of the digital signal interpolated by the interpolator 105 and provides it to the interpolator 105 (step 509).

The interpolator 105 receives the digital signal visually restored by the time recoverer 107 to interpolate the timing error more precisely, restores the precise time, and provides it to the phase detector / automatic frequency adjuster 109. (Step 510). Here, the interpolator 105 interacts with the time recoverer 107 to more accurately restore the time of the digital signal.

The phase detector / automatic frequency regulator 109 detects and restores the delayed phase of the time-restored digital signal by the interaction of the interpolator 105 and the time reconstructor 107, and adjusts the frequency of the restored digital signal. And the lock detector 111 and the modulation method detector 113, respectively (step 511).

The lock detector 111 checks whether the digital signal frequency adjusted by the phase detector / automatic frequency regulator 109 is demodulated to BPSK, QPSK or 8PSK (step 512).

When demodulating the digital signal to BPSK in the check step 512, the control signal is locked to the modulation method detector 113 only when the modulation method is BPSK (step 513).

When the demodulation detector 113 demodulates the digital signal provided from the phase detector / automatic frequency regulator 109 to BPSK by using a control signal generated by being locked by the lock detector 111, the lock is performed immediately. And provide a modulation scheme to the phase detector / automatic frequency regulator 109 as it is determined that demodulation is possible (step 514).

When demodulating the digital signal to QPSK in the check step 512, a control signal that is locked when the modulation method is BPSK and QPSK is provided to the modulation method detector 113 (step 515).

When the modulation method detector 113 demodulates the digital signal provided from the phase detector / automatic frequency regulator 109 to QPSK by using a control signal generated by being locked by the lock detector 111, the modulation method is BPSK. And when it is determined that both of the QPSKs are locked and demodulated, it is determined whether the demodulated signal satisfies the condition shown in Equation 1 above to distinguish the two modulation schemes (step 516).

If Equation 1 is satisfied for a sufficient number (e.g., about 1000 samples) of digital signals in the determination step 516, the modulation scheme is determined to be BPSK and is provided to the phase detector / automatic frequency regulator 109 (step 517). ).

If the determination step 516 does not satisfy Equation 1, the modulation scheme is determined to be QPSK and is provided to the phase detector / automatic frequency regulator 109 (step 518).

In addition, when the digital signal is demodulated to 8PSK in the check step 512, a modulation signal is provided to the modulation method detector 113 in which the modulation method is locked to both BPSK and QPSK and 8PSK (step 519).

When the modulation method detector 113 demodulates the digital signal provided from the phase detector / automatic frequency regulator 109 to 8PSK, it is determined that the modulation method is locked to both BPSK and QPSK and 8PSK so that demodulation is possible. Therefore, to determine the three modulation schemes, it is determined whether the above-described equation (2), the above-described equation (3), or the above-described equations (2) and (3) are not satisfied. (Step 520).

If the above-described Equation 2 is satisfied in the determination step 520, the modulation scheme is determined to be BPSK and is provided to the phase detector / automatic frequency regulator 109 (step 521).

If the above-described Equation 3 is satisfied in the determination step 520, the modulation scheme is determined to be QPSK and is provided to the phase detector / automatic frequency regulator 109 (step 522).

If both of the equations (2) and (3) are not satisfied in the determination step (520), the modulation scheme is determined to be 8PSK and is provided to the phase detector / automatic frequency regulator 109 (step 523).

Phase detector / automatic frequency regulator 109 provides digital signal demodulated according to the modulation scheme determined by modulation scheme detector 113 to normalizer 115 (step 524).

The normalizer 115 normalizes that the magnitude of the digital signal demodulated from the phase detector / automatic frequency regulator 109 has been attenuated to a constant signal size and provides it to a decompression device (not shown) for data restoration (step 525). ).

Therefore, the digital communication system 100 detects the modulation scheme by applying Equations 1, 2, and 3 while using the relationship between the characteristics of the received digital signal and the modulation schemes regardless of the modulation scheme used for the transmission signal. In this case, demodulation is performed in the same manner as the transmitted signal by applying a demodulation scheme suitable for the detected modulation scheme.

As described above, regardless of the modulation scheme used for the transmission signal in the digital communication system, the modulation scheme is detected using a relationship between the characteristics of the received signal and the modulation schemes, and a demodulation scheme suitable for the detected modulation scheme. By successfully demodulating the received signal by applying, the conventional transmitter side has to inform the receiver in advance of information on the modulation scheme in advance so that the receiver side can solve the inconvenience of demodulating using this information.

Claims (6)

In the demodulation device of a wireless communication system, A matching filter for converting a baseband signal into a digital signal using an analog / digital converter and filtering only a desired band among the digital signals received while being converted; A time recoverer for recovering the time of the digital signal filtered by the matched filter; An interpolator interpolating a timing error of the digital signal filtered by the matched filter and providing a digital signal visually restored by the time recoverer; A phase detector / automatic frequency adjuster for detecting and restoring a delayed phase of the digitally restored signal by the interaction of the interpolator and the visually reconstructor, and adjusting and providing a frequency of the phased digital signal; A lock detector for determining and providing a lock of a digital signal adjusted by the phase detector / automatic frequency regulator; A modulation method detector for detecting a modulation method that is locked by the lock detector and determined that demodulation is possible when demodulating the digital signal provided by the phase detector / automatic frequency regulator; And a normalizer for normalizing the digital signal demodulated from the phase detector / automatic frequency regulator to a predetermined signal magnitude. The method of claim 1, A power detector which detects the power of the digital signal filtered by the matched filter and provides a control signal indicating the presence or absence of the signal; And a automatic gain controller for generating an error signal for adjusting the magnitude of the filtered digital signal to a desired value. The method of claim 1, And a signal normalized to a predetermined signal size by the normalizer is used as an input for restoring data. The method of claim 1, wherein the lock detector, When demodulating the digital signal to BPSK, it is locked only when the modulation scheme is BPSK. When demodulating the digital signal to QPSK, the modulation scheme is locked when the modulation scheme is BPSK and QPSK, and the digital signal is 8PSK. The demodulation system of the digital communication system, characterized in that the modulation scheme is locked to both BPSK and QPSK and 8PSK. The method of claim 1 or 4, wherein the modulation method detector, When demodulating the digital signal to QPSK, it is determined that both modulation modes are locked and demodulated when the modulation schemes are BPSK and QPSK. Equation 1 indicating the number [Equation 1] for k is any constant, Is the number of signals corresponding to the signal point, And if it is determined that the modulation scheme is BPSK, and if the equation (1) is not satisfied, the modulation scheme is determined as QPSK. The method of claim 1 or 4, wherein the modulation method detector, When demodulating the digital signal to 8PSK, it is determined that the modulation scheme is locked to both BPSK and QPSK and 8PSK, so that demodulation is possible. Equation 2 representing the number of signals [Equation 2] If is satisfied, the modulation method is determined as BPSK, and Equation 3 [Equation 3] If it is satisfied that the modulation scheme is QPSK, and if the equations (2) and (3) are not satisfied, it is determined that the modulation scheme is 8PSK.