KR20120114823A - Apparatus for processing beacon signal - Google Patents

Abstract

PURPOSE: An apparatus for processing a modulation beacon signal is provided to synchronize a carrier frequency by using a CW(Continuous Wave) component which is the largest value in the modulation beacon signal. CONSTITUTION: A FFT(Fast Fourier Transform) part(210) changes a modulation beacon signal of a digital form using 2^n(n is a natural number) point FFT. A CW component extraction part(230) extracts the largest FFT point by comparing a size of each point value. A frequency synchronous part(250) synchronizes a carrier frequency of the modulation beacon signal using the extracted FFT point. The CW component extraction part comprises a FFT output position shifting part(231), a point extracting part(233) extracting the largest FFT point through the comparison of each point which is changed in the FFT output position shifting part, and a multiplier(235). [Reference numerals] (110) Amplification part; (120) Digital conversion part; (130) Baseband conversion part; (140) Carrier wave phase synchronization part; (150) Code synchronization part; (160) Code tracking part; (170) Slicer; (180) Gain control part; (200) Carrier wave frequency synchronization part; (210) FFT part; (230) CW component extraction part; (231) FFT output location displacement part; (233) Point extracting part; (235) Multiplier; (250) Frequency synchronization part

Description

Modulated Beacon Signal Processing Equipment {APPARATUS FOR PROCESSING BEACON SIGNAL}

The present invention relates to a modulation beacon signal processing apparatus, and more particularly, to a modulation beacon signal processing apparatus that is robust to a low signal noise ratio operating environment while not using a pilot signal.

In a typical spread spectrum communication system, a transmission signal includes a pilot signal for carrier and despread synchronization, and based on this information, frequency phase lock (FPLL) for simultaneously detecting the frequency and phase of a carrier wave. It has a synchronous structure to which the method is applied. In addition, the despread code synchronization also enables relatively stable despreading with one detection using the pilot signal information. Automatic gain control also enables stable analog-to-digital conversion of RF signals based on despread modulated signal power.

FIG. 1 is a block diagram illustrating a conventional modulated beacon signal processor, and FIG. 2 is a schematic diagram illustrating a configuration of a carrier frequency / phase reconstructor (FPLL) included in the conventional modulated beacon signal processor.

The modulated beacon signal processor shown in FIG. 1 includes a variable amplifier 10 for amplifying a modulated beacon signal received by an antenna, an ADC (analog digital converter) 20 for converting an amplified signal (analog) into a digital signal, and a converted signal. Down conversion to baseband 30 to convert digital signals to baseband, carrier frequency / phase reconstructor (FPLL) 40 to recover carrier frequency and carrier phase, code synchronizer 50 to synchronize codes ), A code tracker 60 for correcting clock error to maintain code synchronization reliability, a slicer 70 for outputting 0 or 1 as a final output value, and a variable amplifier using an output signal of the code tracker 10) and an automatic gain adjuster 80 for adjusting the gain.

2 shows the structure of the carrier frequency / phase reconstructor 40, the branched beacon signal is a phase detector (41), a frequency detector (42), a loop filter ( 43) and NCO (Numerical Controlled Oscillator) 44 to return to the input of each detector to correct the carrier frequency and phase. This correction synchronizes the carrier frequency and phase. The phase detector 41 and the frequency detector 42 calculate a phase difference and a frequency difference using a pilot signal.

However, since pilot signals use separate channels, pilot signals may be excluded to increase communication lines in a limited channel environment such as satellite communication.

In such an environment, the modulated beacon signal is a two-phase pulse-shaped modulated beacon waveform of a power spreading code, and unlike a conventional method, a transmission signal does not include a pilot signal for carrier and inverse conversion synchronization, so that noise exists. In an operating environment, there is a problem in that demodulation is rapidly degraded due to inaccuracy of carrier frequency and phase information prediction.

An object of the present invention is to provide a modulation beacon signal processing apparatus that is robust to a low signal noise ratio operating environment while not using a pilot signal.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise forms disclosed. Other objects, which will be apparent to those skilled in the art, It will be possible.

Modulation beacon signal processing apparatus of the present invention for achieving the above object is an FFT unit for converting a modulated beacon signal of the digital format 2 ⁿ (n is a natural number) point FFT (Fast Fourier Transform), the value of each point The CW component extractor extracts the FFT point having the largest value by comparing the magnitudes of the signals, and the frequency synchronizer synchronizes the carrier frequency of the modulated beacon signal by using the extracted value of the FFT point.

In this case, n may be 10.

In addition, the CW component extraction unit, the FFT output position displacement unit for converting the value of each point from 0 to 2 ⁿ -1 to -2 ⁿ / 2 to 2 ⁿ / 2-1, the conversion in the FFT output position displacement unit It may include a point extractor for extracting the FFT point of the largest value by comparing the value of each point and a multiplier to multiply the value of the extracted FFT point by 1/2 ⁿ .

Here, an amplifying unit for amplifying an analog-type modulated beacon signal received by the antenna, a digital converter for converting the amplified modulated beacon signal to a digital format, after converting the modulated beacon signal converted to the digital format to a baseband The apparatus may further include a baseband converter provided to the FFT unit and a gain adjuster adjusting the gain of the amplifier so that the value of the FFT point extracted by the CW component extractor satisfies a preset range.

The gain adjusting unit may adjust the gain of the amplifier so that the largest value among the values of each point converted by the FFT output position displacement unit satisfies a preset range.

In addition, the clock error is coupled to the frequency synchronization unit to perform code synchronization for despreading and the code synchronization performed in the code synchronization unit to prevent the clock error from being corrupted due to a clock error with the transmitter. The code tracking unit may further include a correcting code tracking unit.

The apparatus may further include a carrier phase synchronizer configured to synchronize a carrier phase of a modulated beacon signal output from the code tracker.

The code synchronizer may further perform code synchronization during a predetermined symbol period after acquiring the code on which the code synchronization has been performed.

As described above, the modulated beacon signal processing apparatus of the present invention enables reliable frequency synchronization in a low signal noise ratio environment by synchronizing a carrier frequency using a largest value, that is, a CW component, in a modulated beacon signal.

Further, by adjusting the gain of the amplifier for amplifying the modulated beacon signal through the CW component used for frequency synchronization, the modulated beacon signal can be easily amplified to a desired level.

In addition, by synchronizing the carrier phase after the code synchronization code tracking, it is possible to perform the carrier phase synchronization, which is conventionally performed on a chip basis, in symbol units, thereby improving the reliability of the carrier phase synchronization.

In addition, in the case of performing code synchronization on some symbols, code synchronization reliability may be improved by additionally performing code synchronization on a symbol subsequent to the symbol on which the code synchronization has been performed.

1 is a block diagram illustrating a conventional modulated beacon signal processor.
2 is a schematic diagram showing the configuration of a carrier frequency / phase reconstructor (FPLL) included in a conventional modulated beacon signal processor.
3 is a block diagram showing an apparatus for processing a modulated beacon signal of the present invention.
Figure 4 is a schematic diagram showing a carrier frequency synchronization unit in the modulated beacon signal processing apparatus of the present invention.
5 is a schematic diagram showing a carrier phase synchronizer.
6 is a schematic diagram showing a code synchronizer 150 in a modulation beacon signal processing apparatus of the present invention.
7 is a schematic diagram showing a modulated beacon signal to be processed by the modulated beacon signal processing apparatus;

EMBODIMENT OF THE INVENTION Hereinafter, the modulation beacon signal processing apparatus of this invention is demonstrated in detail with reference to drawings.

3 is a block diagram illustrating a modulated beacon signal processing apparatus of the present invention, and FIG. 4 is a schematic diagram showing a carrier frequency synchronizer 200 in the modulated beacon signal processing apparatus illustrated in FIG. 3.

The modulation beacon signal processing apparatus shown in FIG. 3 includes an FFT unit 210 for converting a digital modulation modulated beacon signal by 2 ⁿ (n is a natural number) point FFT (Fast Fourier Transform), and the magnitude of the value of each point. And a CW component extractor 230 for extracting the FFT point having the largest value, and a frequency synchronizer 250 for synchronizing a carrier frequency of the modulated beacon signal by using the extracted FFT point value. In this case, the FFT unit, the CW component extractor, and the frequency synchronizer constitute a carrier frequency synchronizer 200 among the modulation beacon signal processing apparatuses, and a more specific configuration thereof is shown in FIG. 4.

7 is a schematic diagram showing a modulated beacon signal that is a processing target of the modulated beacon signal processing apparatus.

7 shows the frequency spectral waveform and the baseband signal trajectory of a two-phase pulse shaped modulated beacon signal of a power spreading code.

The modulation beacon signal shown in FIG. 7 may be represented by Equation 1 below.

Where C is the SHF beacon signal power,

F _c is the SHF beacon signal carrier frequency (stability: 2 kHz),

θ is the carrier modulation index (0.9rad-pk),

D (t) is beacon modulation data,

PN (t) is a beacon spreading signal.

If Equation 1 is analyzed as Equation 2 below, it can be seen that CW (Continuous Wave) component is included in the beacon signal.

The modulation beacon data rate may be 625bps. If the modulation beacon data consists of 250bit frames, the frame format should be as shown in Table 1 below.

Frame header TOD Valid TOD Message TOD Parity Check BM Message BM Squelch 8bit 1 bit 36bit 4 bit 200 bit 1 bit

As shown in FIG. 7, the modulated beacon signal has no separate pilot channel for spreading signal synchronization, and the beacon spreading signal is line-coded to Bi-Phase so that there is no interference between the beacon data and the tone signal for antenna satellite orientation of the terminal. Has become.

Modulation beacon signal processing apparatus of the present invention includes the FFT unit 210, the CW component extraction unit 230, the frequency synchronization unit 250 by using the CW component (CW Beacon Signal) of the modulation beacon signal described above Synchronize the frequency.

The FFT unit 210 converts a digital beaded beacon signal 2 ⁿ (n is a natural number) point FFT (Fast Fourier Transform). n may be, for example, 10, in which case the FFT unit performs a 1024 point FFT transform.

Each sampling in a digital signal is a point, so 2 ⁿ (n is a natural number) point is the resolution of the frequency in the FFT.

When n = 10, a total of 1024 FFT points are output.

The CW component extractor 230 compares the value of each point to extract the FFT point having the largest value. The largest value at each point corresponds to the CW component in the modulated beacon signal.

Specifically, the CW component extraction unit 230, the FFT output position displacement unit 231 for converting the value of each extracted point from 0 to 2 ⁿ -1 to -2 ⁿ / 2 to 2 ⁿ / 2-1, FFT A point extractor 233 for comparing the value of each point converted in the output position displacement unit and extracting the largest FFT point, and a multiplier 235 for multiplying the extracted FFT point by 1/2 ⁿ . Can be.

For example, when n = 10, an FFT point of 1024 output from the FFT unit is converted from 0 to 1023 to -512 to 511 by the FFT output position displacement unit 231. Next, the point extractor 233 extracts the FFT point having the largest value, and the multiplier 235 multiplies the extracted FFT point by 1/1024 to scale a value of -0.5 to 0.499. This scaled value becomes an instantaneous frequency error, that is, a frequency offset value. The frequency synchronizer 250 achieves frequency synchronization by using the frequency offset value at this time.

The frequency synchronizer 250 is an element for synchronizing the carrier frequency of the modulated beacon signal using the value of the FFT point extracted by the CW component extractor 230. The frequency synchronizer 250 is output from the loop filter 236 and the loop filter connected to the multiplier. NCO (Numerical Controlled Oscillator) that generates digital sin wave corresponding to the phase of signal Multiplier 238 may be included.

Since the loop filter, the NCO, and the second multiplier are the same as in the related art, detailed description thereof will be omitted.

Overall, the frequency synchronizer derives the frequency offset value using the CW component and makes the frequency offset value zero through feedback. The CW component used in this process has strong energy and can be reliably extracted even in an environment with low signal noise ratio. As a result, reliable carrier frequency synchronization is possible even in an environment with low signal noise ratio.

On the other hand, the modulation beacon signal processing apparatus of the present invention is an amplifier 110 for amplifying the analog signal modulated beacon signal received by the antenna, the digital conversion unit 120 for converting the amplified modulated beacon signal into a digital format, The baseband converter 130 and the FFT point extracted by the CW component extractor after converting the modulated beacon signal converted into a digital format to the baseband to the FFT unit satisfies a preset range. It may further include a gain adjusting unit 180 to adjust the gain.

In this case, the components of the amplifier 110, the digital converter 120, the baseband converter 130, and the gain adjuster 180 may be the same as in the related art. However, note that there is a difference in the position of the gain adjustment unit 180.

The magnitude of the analog signal input to the digital converter (ADC) 120 may vary for various reasons. In this case, if the signal is too large, distortion due to saturation may occur. On the contrary, if the signal is too small, the quantization noise may be large. For this reason, it is necessary to adjust the magnitude of a signal so that it becomes a fixed magnitude | size signal.

In the present invention, the gain of the amplifier 120 is adjusted to obtain a signal having an appropriate magnitude by using the magnitude of the CW component of the modulated beacon signal. In this case, the gain to be adjusted is determined by the gain adjusting unit 180. Because the beacon signal uses spread spectrum technology, the noise may be louder than the size of the received signal. Therefore, if the gain is adjusted based on the magnitude of the received signal, the desired performance cannot be obtained. In the present invention, a method of setting gains such that the magnitude of the CW component becomes a desired magnitude by using the fact that the magnitude of the CW component is much larger than signals of other bands in the frequency domain is used. The position having the largest value in the 1024 point FFT output from the CW component extraction unit 230 is the CW component position. It can be seen that the absolute value represents the magnitude of the CW component. In other words, if the gain is adjusted so that the largest value in the FFT output represents the magnitude of the CW component and the value becomes the desired value, the gain adjustment that makes the received signal to be demodulated constant can be successfully performed.

To this end, the input signal of the gain adjusting unit 130 is a signal of the CW component extraction unit from the output signal of the conventional code tracking unit.

When the CW component extractor 230 includes the FFT output position shifter 231, the point extractor 233, and the multiplier 235, the gain adjuster inputs an output signal of any one of the above three elements. You can do In FIG. 3, an example in which the output signal of the FFT output position shift unit is used as an input signal is shown. In this case, the gain adjusting unit may adjust the gain of the amplifier so that the largest value among the values of each point converted by the FFT output position shift unit satisfies a preset range. Since the output signal of the FFT output position displacement unit includes a plurality of values having a value in the range of -512 to 511 when n = 10, for example, the gain adjusting unit extracts a maximum value as described in FIG. 4. 'Must contain a block.

Referring to FIG. 4, the gain adjusting unit 180 compares the magnitude information of the CW component from the FFT with a desired threshold level, accumulates the error, and uses the result to obtain an amplifier 110 located in front of the digital converter 120. For example, by adjusting the gain of a variable amplifier, gain adjustment is performed so that a signal of a desired magnitude is obtained.

The gain adjusting unit 180 may perform reliable gain adjustment in a low signal noise ratio environment by using a CW component that is robust to a low signal noise ratio environment as an input signal.

On the other hand, the modulation beacon signal processing apparatus of the present invention is connected to the frequency synchronization unit, the code synchronization unit 150 for performing code synchronization for despreading and the code synchronization performed in the code synchronization unit clock error with the transmitting side The code tracking unit 160 may further include a code tracking unit for correcting the clock error in order to prevent damage caused by the clock.

6 is a schematic diagram showing the code synchronizer 150 in the modulation beacon signal processing apparatus of the present invention.

Code spreading for despreading in spread spectrum communication shows the ability to synchronize the receiver local PN code with the received data. The bandwidth assurance code used for the beacon receiver is a PN code with a period of 2047.

In the code acquisition process, a code synchronization is obtained when a threshold value is exceeded while performing a correlation between the first 250 binary PN codes and a received data in 2047 bits of a cycle. Since the input signal operates at 2.5 MHz and the PN code operates at 156.25 kHz, one is selected for every 16 input signals to obtain the PN code and correlation, and compares this value to the threshold or not. To determine whether or not code synchronization has been achieved.

However, in the case of a beacon signal without a pilot signal for code synchronization, code synchronization targeting only some symbols in one bit of a cycle may make a wrong decision in a noise environment, thereby causing a problem of inconsistent performance and stable operation.

Therefore, the code synchronizer 150 shown in FIG. 6 has an added portion for verifying whether the obtained synchronization is correct. At this time, the verification is performed to determine whether the threshold value is continuously exceeded by performing a correlation operation for several symbol intervals after the code acquisition using the acquired synchronization. This is necessary to prevent the possibility of incorrectly performing code synchronization for reasons such as noise. At this time, the additional symbol interval may be four. In other words, as a result of the experiment, the verification degree of 4 times (5 times of code synchronization combined with the initial code synchronization) was determined to be sufficient. After the code synchronization, PN codes are generated by c ₂₅₀ , c ₂₅₁ , ... in order and are multiplied by one for every 16 received signals. In this way, when the correlation for the 250 chip is completed, the output size is compared with the threshold value to verify that normal code synchronization is achieved.

In summary, the code synchronizer of the present invention may further perform code synchronization during a predetermined symbol period after acquiring a code on which code synchronization has been performed.

The code tracking unit 160 prevents a possibility that the code synchronization made by the code synchronization unit 150 is unwound due to a clock error that may occur between the transceivers. To this end, the code tracking unit tracks code synchronization while correcting clock errors between the transceivers in real time. Since the code tracking unit is the same as the conventional one, detailed description thereof will be omitted.

Meanwhile, the modulated beacon signal processing apparatus of the present invention may further include a carrier phase synchronizer 140 for synchronizing the carrier phase of the modulated beacon signal output from the code tracking unit 160.

The carrier phase synchronizer 140 may be arranged together with the carrier frequency synchronizer 200. However, as located in the rear end of the code tracking unit as in the present invention, the reliability of the carrier phase synchronization can be improved.

5 is a schematic diagram showing a carrier phase synchronizer, which is similar in configuration to a phase detector included in a conventional carrier frequency / phase decompressor as a whole. However, the frequency of the symbol 625Hz output from the code tracking unit is used as the input signal, not the frequency 2.5MHZ of the chip. That is, the carrier phase synchronizer of the present invention is disposed at the rear end of the mode tracker to enable phase synchronization in symbol units instead of phase synchronization in chip units. Therefore, the phase synchronization is performed for a symbol of a larger unit, thereby improving the reliability of the carrier phase synchronization.

The slicer 170 determines (1 or 0) bit data from the output signal of the carrier phase synchronizer or the output signal of the code tracker when the carrier phase synchronizer is arranged together with the carrier frequency synchronizer. Since the slicer is the same as the conventional one, detailed description is omitted.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

It can be applied to an apparatus for receiving and processing a modulated beacon signal.

In particular, it is advantageous to apply it to the apparatus used in the environment which shows low signal noise ratio by ambient noise etc.

110 amplification unit 120 digital conversion unit
130 Baseband converter 140 Carrier phase synchronizer
150 ... Code Synchronizer 160 ... Code Tracer
170 ... Slicer 180 ... Gain Control
200 ... carrier frequency synchronizer 210 ... FFT section
230 ... CW component extraction section 231 ... FFT output position displacement
233 points extraction section 235 multiplier
250 ... frequency sync

Claims (8)

An FFT unit for converting a digitally modulated beacon signal 2 ⁿ (n is a natural number) point FFT (Fast Fourier Transform);
A CW component extraction unit for extracting the FFT point having the largest value by comparing the magnitude of the value of each point; And
A frequency synchronizer for synchronizing a carrier frequency of the modulated beacon signal using the value of the extracted FFT point;
Modulation beacon signal processing apparatus comprising a.
The method of claim 1,
N is 10, characterized in that the modulated beacon signal processing apparatus.
The method of claim 1,
The CW component extraction unit,
An FFT output position displacement unit for converting the value of each point from 0 to 2 ⁿ -1 to -2 ⁿ / 2 to 2 ⁿ / 2-1;
A point extracting unit for extracting the FFT point having the largest value by comparing the value of each point converted by the FFT output position displacement unit; And
And a multiplier multiplying the extracted FFT point value by 1/2 ⁿ .
The method of claim 3, wherein
An amplifier for amplifying an analog modulated beacon signal received by the antenna;
A digital converter converting the amplified modulated beacon signal into a digital format;
A baseband converter for converting the modulated beacon signal converted into the digital format into a baseband and providing the modulated beacon signal to the FFT unit; And
And a gain adjusting unit for adjusting the gain of the amplifier so that the value of the FFT point extracted by the CW component extracting unit satisfies a preset range.
The method of claim 4, wherein
And the gain adjusting unit adjusts the gain of the amplifying unit so that the largest value among the values of each point converted by the FFT output position displacement unit satisfies a preset range.
The method of claim 1,
A code synchronizer connected to the frequency synchronizer and performing code synchronization for despreading; And
And a code tracking unit to correct the clock error in order to prevent the code synchronization performed by the code synchronization unit from being damaged due to a clock error with a transmitter.
The method according to claim 6,
And a carrier phase synchronizer for synchronizing a carrier phase of a modulated beacon signal output from the code tracking unit.
The method according to claim 6 or 7,
And the code synchronizer is further configured to perform code synchronization during a predetermined symbol period after acquiring the code on which the code synchronization has been performed.

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