JP2004304384A - Method and device for discriminating unique word - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate a first unique word composed of the prescribed number of symbols from a second unique word, wherein the first half has the same code as that of the first unique word and the latter half has a code opposite from that of the first unique word. <P>SOLUTION: An inverse modulation processing part 26 inversely modulates an input signal Si inserted with a unique word UW by the first unique word UW1. An FFT (fast Fourier transformation) processing part 28 applies FFT processing to the inversely modulated signal f (UW). The number of peaks detecting part 30 discriminates the first unique work UW1 when the number of peaks of a spectrum S (UW) is one, and the second unique word UW2 when the number of peaks is two. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a unique word discriminating method and apparatus, for example, a unique word suitable for use in a demodulator for demodulating a radio frame relayed by Inmarsat satellite and modulated by offset QPSK (OQPSK: Offset Quadrature Phase Shift Keying). And a device therefor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in communication devices, a unique word has been frequently used as a means for establishing synchronization.
[0003]
This unique word is a data pattern determined identically on the transmitting side and the receiving side.
[0004]
When the transmitting side adds a unique word to the beginning of the data and sends it as a signal (also referred to as a frame), on the receiving side, the complex between the input signal (input signal) and the unique word of the reference stored in the receiving side in advance. Calculate the correlation value. Then, by detecting the peak of the correlation value, synchronization with the transmission side is established in a short time, and by reproducing the carrier, for example, PSK or QAM (Quadrature Amplitude Modulation) data included in the signal is demodulated. be able to.
[0005]
By the way, when the synchronization is established by the unique word, if a frequency offset exists in the input signal, the correlation output decreases due to the frequency offset, so that it cannot be used as it is.
[0006]
A technique for solving this problem has been published as a unique word detector (see Patent Document 1). This unique word detector delay-detects the input signal containing the unique word, removes the frequency offset, correlates the reference unique word with a correlator, and detects the peak to detect the unique word from the input signal. Detected.
[0007]
A technique for reproducing a carrier after detecting a unique word is disclosed as a demodulation device (see Patent Document 2).
[0008]
[Patent Document 1]
JP-A-5-167630 (FIG. 1, paragraphs [0010] to [0012])
[Patent Document 2]
Japanese Patent No. 3185716 (FIG. 1)
[0009]
[Problems to be solved by the invention]
Incidentally, for example, in a communication device using an Inmarsat satellite as a relay station, a first unique word having a predetermined even number of symbols, a first half having the same sign as the first unique word, and a second half having the first unique word. The second unique word having the opposite sign is used as another unique word.
[0010]
However, two sets of correlators are required to determine the first and second unique words having such a configuration by applying the conventional techniques according to Patent Document 1 and Patent Document 2, and the cost increases. The problem arises.
[0011]
The present invention has been made in view of such a problem, and one correlator detects one unique word and the other unique word in the above-described fixed relationship, and then discriminates them. It is an object of the present invention to provide a unique word discriminating method and a unique word discriminating device that make it possible to do so.
[0012]
[Means for Solving the Problems]
The method for determining a unique word according to the present invention is a method for determining a unique word in which one of the unique words or the other half of which has the opposite sign to the one of the unique words is unknown. Inversely modulating the unknown unique word with the one or the other unique word, FFT (Fast Fourier Transform) processing the inversely modulated unknown unique word, Determining an unknown unique word from the number of peaks (the invention according to claim 1).
[0013]
In addition, the unique word discriminating apparatus of the present invention is a unique word discriminating device that determines whether a unique word is unknown, or whether one half of the unique word has the opposite sign to the one unique word. In the apparatus, an inverse modulator that inversely modulates the unknown unique word by the one or the other unique word, an FFT processor that performs an FFT process on the inversely modulated unknown unique word, and a spectrum detected by the FFT process And a discriminator for discriminating an unknown unique word from the number of peaks of (1) (the invention according to claim 2).
[0014]
According to the method and the apparatus for determining a unique word of the present invention, an unknown unique word is inversely modulated by one or the other unique word as a reference signal, and then FFT processing is performed. Since one or two peaks appear on the spectrum obtained by the FFT processing according to the relationship between the unknown unique word and the selected reference signal, the unknown unique word can be determined.
[0015]
For example, when the unique word used as a reference when performing reverse modulation is one of the unique words, and the unknown unique word is the one unique word, the unknown unique word is unmodulated. The spectrum becomes a single peak. On the other hand, when the unknown unique word is the other unique word, the unmodulated signal is modulated by the sign change, and two peaks appear in the spectrum. Using this principle, the one or the other unique word can be determined.
[0016]
As described in the embodiment of the present invention, for example, the first unique word used in the communication using the Inmarsat satellite is the first unique word used in the unique word determination method and the unique apparatus according to the present invention. This is a concept including UW1 or third unique word UW3, and the other unique word of the present invention is a fourth unique word UW4 corresponding to the second unique word UW2 and third unique word UW3 corresponding to the first unique word UW1. It is a concept including
[0017]
It is preferable that one unique word and the other unique word have the same number of codes. In addition, it is preferable that the first half or the second half of the other unique word has the same sign and the other half has the opposite sign with respect to one unique word. Further, the number of codes of the unique word is preferably an even number.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 shows a configuration of a carrier reproducing apparatus 10 including a unique word discriminating apparatus 12 to which the unique word discriminating method of this embodiment is applied. The carrier reproducing apparatus 10 is created using, for example, a digital signal processor, a so-called DSP.
[0020]
In FIG. 1, a frame (an unknown unique word) in which a first unique word (one unique word) UW1 or a second unique word (thus considered as the other unique word) UW2 is inserted at the head of the data portion An input signal Si having a (frame into which is inserted) configuration is stored in the buffer 14 as storage means.
[0021]
In this embodiment, the first unique word UW1 is data of 42 even symbols (codes), and the second unique word UW2 has the same sign as the first unique word UW1 up to the 21st symbol. Thus, from the 22nd symbol to the 42nd symbol, the data has the same length as the number of 42 even-numbered symbols that have the opposite sign to the first unique word UW1.
[0022]
Such a code pair has the same code except for the symbol at the moment when the code is inverted when the differential detection is performed by the differential detection unit 16, so that one unique correlator 18 converts both unique words UW (UW 1 and UW 2). The number of correlators 18 that can be detected and require a lot of calculation is reduced by half, and the cost can be reduced.
[0023]
The technology described in this embodiment is not limited to a code pair of a unique word having a predetermined number of symbols and a unique word having a half code reverse to that of the unique word. This can be applied to the determination of all of the unique words that are partly inverted.
[0024]
Actually, in a communication device using an Inmarsat satellite as a transponder, in addition to the above-described first unique word UW1 and second unique word UW2, a third unique word and a fourth unique word having the same fixed relationship as those described above. Since it is composed of a unique word and an independent fifth unique word, three correlators 18 are required. In this embodiment, however, in order to facilitate understanding of the invention, the first unique word UW1 and the The second unique word UW2 will be described as an example, and only one correlator 18 will be described. That is, the third unique word and the fourth unique word can be determined by using two correlators 18 with the same configuration.
[0025]
Here, the input signal Si is an OQPSK digital modulation signal having a frame configuration in which a unique word can be delayed detected. However, the present invention is not limited to this. It can also be applied to signals.
[0026]
The delay detection section 16 multiplies the input signal Si by the input signal Si delayed by one symbol to obtain a demodulated signal after the delay detection, and sends the demodulated signal to one input terminal of the correlator 18.
[0027]
On the other hand, the first unique word UW1 output from the first unique word table 20, which is a storage means, is similarly delayed detected by the delay detection unit 22, and the delayed detection output is supplied to the other input terminal of the correlator 18.
[0028]
At this time, the peak that occurs in the output of the correlator 18 is detected by the peak detection unit 24, so that the timing for performing the inverse modulation is extracted.
[0029]
When the signal having the frequency offset f0 is subjected to delay detection by the delay detection unit 16, the demodulated signal is ^{subjected to} a phase rotation of ej ^{· 2π · fo · t0} (t0 is a time corresponding to one symbol). However, by calculating the power of the complex correlation output in the correlator 18, this phase rotation is ignored. Therefore, the frequency offset fo is substantially removed by performing the delay detection.
[0030]
Next, the configuration and operation of the unique word discrimination device 12 will be described with reference to the schematic operation conceptual diagram of FIG. In this embodiment, the unique word discriminating device 12 includes a first unique word table 20, an inverse modulation processing unit 26, an FFT processing unit (FFT processing unit) 28, and a peak number detection unit 30. I have.
[0031]
First, the inverse modulation processing section 26 uses the first unique word table 20 to generate a first unique word as a reference signal from the first unique word table 20 as shown in FIG. At the same time as reading out UW1, the input signal Si is read out from the buffer 14, and an inverse modulation process is performed as shown in FIG.
[0032]
In this case, the unknown unique word included in the input signal Si is one of the first unique word UW1 and the second unique word UW2 schematically shown in (a) of FIG. 2 or (b) of FIG. .
[0033]
The first unique word UW1 and the second unique word UW2 have the same sign on the time axis up to the middle first half (21 symbols as a specific example), and the second half from the middle to the second half (21 as a specific example). (Symbols), the sign is inverted.
[0034]
By having such a relationship, that is, a constant relationship in which half of the second unique word UW2 has an opposite sign with respect to the first unique word UW1, in the first unique word UW1 and the second unique word UW2, Except for the symbol at the moment when the signal after differential detection has the opposite sign, the symbols are the same, and the correlator 18 uses the first unique word UW1 after differential detection and the second unique word UW2 after differential detection. In this case, the timing at which the reverse modulation is detected by the peak detection unit 24 is the same. Therefore, the unique word UW as a reference used in the correlator 18 is replaced with the second unique word table (unused) storing the second unique word UW2 instead of the first unique word table 20 storing the first unique word UW1. (Shown) can also be used.
[0035]
When the inverse modulation process is performed by the inverse modulation processing unit 26, the inversely modulated signal f (UW1) corresponding to the unmodulated first unique word UW1 shown in (e) of FIG. 2 and (f) in FIG. ), An inverse modulation signal f (UW2) corresponding to the second unique word UW2 is obtained.
[0036]
Here, the inverse modulation signal f (UW1) shown in (e) of FIG. 2 is a signal of a single spectrum with a frequency offset fo, and the inverse modulation signal f (UW2) shown in (f) of FIG. The frequency spectrum of the signal obtained by multiplying the unmodulated wave of the frequency f1 and the frequency fo (frequency offset) with one cycle of the length (time) of the two unique words UW2 is (fo−f1) · (fo + f1).
[0037]
Therefore, as shown schematically in FIG. 2 (g), the inversely modulated signal f () corresponding to the first unique word UW1 shown in FIG. UW1) is converted into a spectrum S (UW1) shown in FIG. 2H, and an inverse modulation signal f (UW2) corresponding to the second unique word UW2 shown in FIG. It is converted to the spectrum S (UW2) shown in i).
[0038]
As can be seen from FIG. 2H, the spectrum S (UW1) corresponding to the first unique word UW1 has a single peak at the frequency of the frequency offset fo because it is a signal of the same code. .
[0039]
As can be seen from FIG. 2 (i), the spectrum S (UW2) corresponding to the second unique word UW2 has a length of the second unique word UW2 (same as the length of the first unique word UW1) for one cycle. The spectrum of the signal obtained by multiplying the frequency f1 and the frequency fo, that is, two peaks fo-f1 and fo + f1.
[0040]
The frequency offset fo of the processing result of the FFT processing unit 28 is supplied to the carrier reproducing unit 32, and the spectrum S is supplied to the peak number detecting unit 30. The frequency offset fo can be obtained from the position (frequency) of the detected peak when the number of peaks is one. However, when the number of peaks is two, ｛(fo−f1) ) + (Fo + f1)｝ / 2 to determine the frequency offset fo.
[0041]
Here, the peak number detection unit 30 determines whether the unique word UW of which the input signal Si is unknown is the first unique word UW1 or the second unique word UW2 from the number of peaks in the spectrum S (UW). If the number of peaks is one, it can be determined to be the first unique word UW1, and if the number of peaks is two, it can be determined to be the second unique word UW2.
[0042]
That is, the peak number detection unit 30 functions as a discriminator that discriminates an unknown unique word from the number of peaks of the spectrum S detected by the FFT processing.
[0043]
Briefly describing the process of determining the unique word UW, when determining the unique word UW, the inverse modulation processing unit 26 reverse modulates the input signal Si into which the unique word UW has been inserted, using the first unique word UW1. Then, the FFT processing unit 28 performs FFT processing on the inverse modulation signal f (UW). Further, if the number of peaks in the spectrum S (UW) after the FFT processing is one, the peak number detecting unit 30 determines that the spectrum S (UW) is the first unique word UW1 and if the number of peaks is two, the second unique word UW2.
[0044]
When the determination result obtained in this way is supplied to the unique word table 34 storing the first unique word UW1 and the second unique word UW2, the identified unique word UW (UW1 or UW2) is converted to the inverse modulation processing unit. 36, the input signal Si is read out from the buffer 14 and supplied to the other input terminal, so that the true unmodulated input signal Si Is obtained.
[0045]
Next, the carrier reproducing unit 32 reproduces the carrier from which the frequency offset fo has been removed from the true non-modulated input signal Si. This carrier is for knowing a reference phase for a signal in a complex space for demodulating PSK (QAM), and is the same carrier as that used at the time of modulation.
[0046]
As described above, according to the above-described embodiment, the first unique word UW1 consisting of a predetermined number of symbols, for example, 42, and the first half of the first unique word UW1 have the same sign as the first unique word UW1, and the second half of the first unique word UW1 have the same number. When determining the first unique word UW1 and the second unique word UW2 having the opposite sign (of course, the first unique word UW1 consisting of a predetermined number of symbols, and the first half being the first unique word UW2). The same applies when discriminating between the first unique word and the second unique word having the same sign in the second half, which is an inverse code). The signal Si is converted to a first unique word UW1 (a unique word stored in the first unique word table 20) or a second unique word. To reverse modulated by W2. Next, the FFT processing unit 28 performs FFT processing on the inversely modulated signal f (UW) having the unknown unique word that has been inversely modulated.
[0047]
Further, an unknown unique word UW is determined by the peak number detection unit 30 from the number of peaks of the spectrum S (UW) detected by the FFT processing.
[0048]
Then, when the unique word UW is determined by the peak number detection unit 30, if the number of peaks of the spectrum S (UW) when inversely modulated by the first unique word UW1 is one, it is determined to be the first unique word UW1. If the number is two, it is determined that the word is the second unique word UW2.
[0049]
On the other hand, when the number of peaks of the spectrum S (UW) when inversely modulated by the second unique word UW2 is one instead of the first unique word table 20, it is determined as the second unique word UW2, and If so, it is determined that the word is the first unique word UW1.
[0050]
By performing the determination in this way, the unique word UW can be determined with high accuracy even if there is a frequency offset fo or under the influence of noise.
[0051]
Note that the present invention is not limited to the above-described embodiment, and may adopt various configurations based on the description in this specification.
[0052]
【The invention's effect】
As described above, according to the present invention, even if there is one correlator, an effect that two unique words having a fixed relationship can be determined is achieved. Then, the unique word can be determined with high accuracy even under the influence of frequency offset and noise.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a carrier reproducing apparatus to which an embodiment of the present invention has been applied.
FIG. 2 is an explanatory diagram provided for describing the operation of a unique word determination process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Carrier reproducing apparatus 12 ... Unique word discriminating apparatus 14 ... Buffer 16,22 ... Delay detection part 18 ... Correlator 20 ... First unique word table 24 ... Peak detecting part 26,36 ... Inverse modulation processing part 28 ... FFT processing part (FFT processor) 30 ... Peak number detector (discriminator)
32: Carrier playback unit 34: Unique word table

Claims (2)

One of the unique words, or the other unique word half of which is the opposite sign of the one unique word, in the unique word determination method of determining the unknown unique word,
Inverse modulating the unknown unique word with the one or the other unique word;
FFT processing the unknown back-modulated unique word;
Determining an unknown unique word from the number of peaks in the spectrum detected by the FFT processing. One unique word, or the other unique word half of which is the opposite sign to the one unique word, in a unique word discriminating device for discriminating the unknown unique word,
An inverse modulator that inversely modulates the unknown unique word with the one or the other unique word,
An FFT processor for performing FFT processing on the unknown unique word subjected to the inverse modulation;
A discriminator for discriminating an unknown unique word from the number of peaks in the spectrum detected by the FFT processing.

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