JP2005086548A - Digital demodulator and digital demodulating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain digital demodulation having improved process efficiency by reducing an arithmetic operation quantity at the time of determination of a symbol of a QAM signal. <P>SOLUTION: A digital demodulator for demodulating a QAM signal has a quasi-synchronous detector for applying quadrature detection to the QAM signal, and a symbol determination section for determining the symbol of a signal having an I component and a Q component acquired in the quasi-synchronous detector. The symbol determination section solves the above problem by specifying a specific symbol on the basis of a rectangular region set for each of a plurality of symbols and a symbol adjacent to the specific symbol, and performing region determination on the basis of a polygonal region corresponding to each of the specific symbol and the adjacent symbol. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital demodulator and a digital demodulating method, and more particularly to a digital demodulator and a digital demodulating method for performing digital demodulation with reduced calculation amount and improved processing efficiency when determining symbols of a QAM signal.

  Conventionally, a QAM (Quadrature Amplitude Modulation) method, which is one of digital signal methods, is a transmission method that has been used in the field of microwave radio communication for a long time. In recent years, it is also used in the field of cable transmission for digital broadcast retransmission, cable modems, and the like, and square-arranged 64QAM and 256QAM have been put into practical use for ease of modulation processing and demodulation processing. Here, a block configuration of a digital demodulator used for the above-described QAM demodulation will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a block configuration of a conventional digital demodulator. The digital demodulator 10 of FIG. 1 includes a tuner 11, an A / D converter 12, a quasi-synchronous detector 13, a timing recovery unit 14, a roll-off filter 15, a carrier recovery unit 16, and a decision feedback equalization. The unit 17 and the symbol determination unit 18 are configured.

  First, the tuner 11 receives a transmission signal, selects one RF signal from a large number of frequency-multiplexed RF (Radio Frequency) signals included in the received transmission signal, and has a low frequency IF (Intermediate Frequency). Convert to signal. Further, the tuner 11 outputs the signal converted into the IF signal to the A / D conversion unit 12.

  The A / D converter 12 samples the received IF signal and converts it from an analog signal to a digital signal. In addition, the A / D conversion unit 12 outputs the converted digital signal to the quasi-synchronous detection unit 13. The quasi-synchronous detection unit 13 performs quadrature detection on the input digital signal at a fixed frequency, and divides it into an in-phase component (I component) and a quadrature component (Q component). That is, quasi-synchronous detection is performed to extract the I component and Q component from the baseband signal. In addition, the quasi-synchronous detection unit 13 outputs a signal having the extracted I component and Q component to the timing reproduction unit 14.

  The timing reproduction unit 14 recovers symbol timing. Here, since the A / D conversion unit 12 asynchronously samples the digital signal, the timing reproduction unit 14 performs resampling to extract the closest portion of the symbol timing. The timing regenerated signal is output to the roll-off filter 15.

  The roll-off filter 15 performs waveform shaping by removing noise from the signal orthogonally detected by the quasi-synchronous detection unit 13 using a filter or the like, and outputs the waveform-shaped signal to the carrier wave reproduction unit 16. The carrier wave reproducing unit 16 reproduces the carrier wave using the shaped waveform signal and outputs the carrier wave to the decision feedback equalizing unit 17.

  Further, the decision feedback equalization unit 17 performs waveform equalization processing to adaptively control the coefficient of the mathematical expression used in the FIR (Finite Impulse Response) filter to remove reflection interference. The signal subjected to waveform equalization processing by the determination feedback equalization unit 17 is output to the symbol determination unit 18. The symbol determination unit 18 determines which symbol the input signal belongs to, and outputs a demodulated signal based on the determination result symbol.

  Here, when there is isotropic noise on the IQ plane, such as thermal noise, a symbol determination circuit that determines which symbol is transmitted from the received signal (output after equalization (soft-output)) It is optimal to output the symbol closest to the received signal in the constellation pattern in the IQ plane. Here, when the determination threshold region to which symbol belongs is a square arrangement QAM, it can be determined independently in the I direction and the Q direction, and digital demodulation processing becomes easy.

  Note that the constellation pattern on the IQ plane is a signal expressed on the xy plane with respect to quadrature modulation with the in-phase component as the x-axis and the quadrature component as the y-axis.

  Further, when one RF signal is selected by the tuner 11 from a large number of frequency-multiplexed RF signals as described above, it is converted to an IF signal having a lower frequency. At this time, phase noise in the tuner 11 is reduced. It can be a problem. Due to the influence of the phase noise, the symbol error rate in the symbol determination unit increases.

  Here, the influence of the phase noise in the tuner appears more greatly with respect to the symbols away from the origin on the IQ plane. As a countermeasure for this, a QAM signal arrangement method has been disclosed in which a determination threshold region in which a symbol interval is separated at the outer periphery is provided as an arrangement of a QAM signal resistant to phase noise (for example, patents). Reference 1).

  Note that Patent Document 1 proposes a simplified 64QAM signal arrangement with low decoding complexity, and is a decision boundary at the time of decoding given by a perpendicular bisector of lines connecting adjacent symbols? The boundary is set by approximating the line to a rectangular shape.

  However, there may be a case where a symbol arrangement or a determination region that does not consider simplification as described above is desirable. Therefore, a method has been proposed in which when a determination is made on an arbitrary polygonal determination region, the region is quantized and mapped to a memory and compared with the mapped region at the time of symbol determination of a received signal ( For example, see Patent Document 2.)

As another method, only the vertex coordinates of the polygon determination area are stored in the memory, and an operation for determining whether or not the reception point is inside the polygon is performed for all symbols. A method is also conceivable.
JP-T 9-507373 JP 2000-224250 A

  However, any of the above-described methods has a problem that the amount of memory or the amount of calculation increases when the number of QAM multivalues increases. For example, in the case of 1024QAM, in the method of mapping to the memory, even if each quantization of the I component and the Q component is expressed by 10 bits, a memory of about 10M bits is required. In addition, when performing the inside / outside determination of the received signal using the polygonal region set for each symbol, it is necessary to perform the inside / outside determination calculation for 1024 symbols.

  As described above, the method of quantizing the region and mapping it to the memory, or the method of performing the operation for determining whether or not the received signal is inside the polygonal region for all symbols, When it increases, there is a problem that the memory amount or the calculation amount increases.

  The present invention has been made in view of the above-described problems, and provides a digital demodulator and a digital demodulation method for performing digital demodulation with reduced calculation amount at the time of symbol determination of a QAM signal and improved processing efficiency. The purpose is to provide.

  In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.

  The invention described in claim 1 is a digital demodulator for demodulating a QAM signal, a quasi-synchronous detector for quadrature detection of the QAM signal, and an I component and a Q obtained by the quasi-synchronous detector. A symbol determination unit that determines a symbol of a signal having a component, and the symbol determination unit includes a specific symbol and an adjacent symbol adjacent to the specific symbol based on a rectangular area set for each of a plurality of symbols. The region determination is performed based on a polygonal region corresponding to each of the specific symbol and the adjacent symbol.

  According to the first aspect of the present invention, region determination is performed by selecting one candidate specific symbol from a rectangular region and performing symbol determination using regions corresponding to the specific symbol and an adjacent symbol adjacent to the specific symbol. It is no longer necessary to perform the calculation in the region corresponding to all symbols, and the amount of calculation can be reduced. This makes it possible to perform digital demodulation with improved processing efficiency.

  According to a second aspect of the present invention, when the symbol determination unit has a plurality of polygon regions in a rectangular region corresponding to the specific symbol, the specific symbol among symbols corresponding to the plurality of polygon regions. The other symbols are selected as adjacent symbols.

  According to the second aspect of the present invention, it is not necessary to perform the calculation by the inside / outside determination for all the symbols adjacent to the specific symbol, and the amount of calculation can be further reduced. This makes it possible to perform digital demodulation with improved processing efficiency.

  According to a third aspect of the present invention, the symbol determination unit divides a rectangular region corresponding to the specific symbol into a plurality of regions, selects a region including the signal among the divided regions, and based on the selected region. And selecting an adjacent symbol.

  According to the third aspect of the present invention, it is possible to select a region including a signal from the divided regions and further limit adjacent symbols based on the selected divided region. Thereby, the calculation amount can be further reduced, and digital demodulation with improved processing efficiency can be performed.

  The invention described in claim 4 is characterized in that the symbol determination unit determines the specific symbol when a signal to be determined is not included in a polygonal region of the adjacent symbol.

  According to the fourth aspect of the present invention, it is possible to perform symbol determination with a reduced amount of calculation. Further, it is possible to quickly perform symbol determination for a gap region that may occur when setting a polygon determination region.

  According to a fifth aspect of the present invention, there is provided a digital demodulation method for demodulating a QAM signal, a quasi-synchronous detection stage for quadrature detection of the QAM signal, and an I component and a Q obtained in the quasi-synchronous detection stage. A symbol determination step of determining a symbol of a signal having a component, wherein the symbol determination step includes a specific symbol and an adjacent symbol adjacent to the specific symbol based on a rectangular area set for each of a plurality of symbols. The region determination is performed based on a polygonal region corresponding to each of the specific symbol and the adjacent symbol.

  According to the fifth aspect of the present invention, region determination is performed by selecting one candidate specific symbol from a rectangular region and performing symbol determination using regions corresponding to the specific symbol and an adjacent symbol adjacent to the specific symbol. It is no longer necessary to perform the calculation in the region corresponding to all symbols, and the amount of calculation can be reduced. This makes it possible to perform digital demodulation with improved processing efficiency.

  ADVANTAGE OF THE INVENTION According to this invention, the amount of calculations at the time of symbol determination of a received signal can be reduced, and the digital demodulation which improved the processing efficiency can be implement | achieved.

<Outline of the present invention>
The present invention sets one candidate specific symbol (candidate symbol) among a plurality of symbols set in advance to determine which symbol the input signal corresponds to, and the candidate symbol, For the symbols adjacent to the candidate symbols, it is determined whether or not the received signal is included in the polygon determination region corresponding to each symbol. As a result of the determination, if the received signal is included in any of the polygonal regions corresponding to the symbol, the symbol is output as a symbol of the received signal, and is not included in any symbol Outputs candidate symbols as received signal symbols.

  Thereby, the amount of calculation can be reduced as compared with the case where the calculation is performed for all symbols. In the present invention, when determining the region, the polygon region corresponding to the candidate symbol is determined first, and if it is within the region of the candidate symbol, the symbol determination ends at that point.

  Hereinafter, embodiments in which a digital demodulator and a digital demodulation method according to the present invention having the above-described features are suitably implemented will be described in detail with reference to the drawings.

<Embodiment>
The configuration of the digital demodulator in the present invention will be described with reference to the drawings. FIG. 2 is a diagram illustrating an example of a block configuration of the digital demodulator. A digital demodulator 20 shown in FIG. 2 includes a tuner 11, an A / D converter 12, a quasi-synchronous detector 13, a timing recovery unit 14, a roll-off filter 15, a carrier recovery unit 16, a determination feedback, and the like. And a symbol determination unit 28. The operations of the constituent elements other than the symbol determination unit 28 are the same as the contents shown in FIG.

  Here, the configuration of the symbol determination unit 28 will be described with reference to the drawings. FIG. 3 is a diagram illustrating an example of a block configuration of the symbol determination unit in the present invention. The symbol determination unit 28 illustrated in FIG. 3 is configured to include a symbol selection unit 31, a polygon vertex coordinate acquisition unit 32, a region determination unit 33, and a storage unit 34.

  The symbol selection unit 31 selects a candidate symbol based on a rectangular area assigned to each symbol stored in advance in a storage unit 34 such as a memory for an input signal. Further, the symbol selection unit 31 outputs a polygonal area corresponding to each symbol stored in the storage unit 34 to the vertex coordinate acquisition unit 32. Further, the symbol selection unit 31 stores in the storage unit 34 which symbol is a candidate symbol. In the storage unit 34, information on a rectangular area and a polygon area for symbol determination corresponding to each symbol is set in advance.

  Further, when the received signal is outside the polygonal region corresponding to the candidate symbol in the region determination unit 33 described later, the symbol selection unit 31 sends information indicating that fact from the region determination unit 33. At this time, the symbol selection unit 31 acquires the candidate symbols stored in the storage unit 34 and selects a symbol (adjacent symbol) adjacent to the candidate symbol. Further, the symbol selection unit 31 acquires a polygon area corresponding to the adjacent symbol from the storage unit 34 and outputs it to the polygon vertex coordinate acquisition unit 32. Here, the adjacent symbols are four symbols adjacent in the axial direction of the IQ plane and 45 degrees with respect to the axial direction of the IQ plane with respect to a certain symbol positioned on the IQ plane. It consists of a total of 8 symbols consisting of 4 adjacent symbols. Of the symbols positioned on the IQ plane, the number of adjacent symbols decreases for the outermost symbols.

  In the storage unit 34, adjacent symbols corresponding to the symbols are stored in association with each other, so that the adjacent symbols can be easily acquired. Further, as will be described later, an area obtained by further dividing a rectangular area corresponding to a symbol can be set and accumulated.

  The polygon vertex coordinate acquisition unit 32 acquires the vertex coordinates of the polygon region corresponding to the symbol selected from the symbol selection unit 31. In addition, the polygon vertex coordinate acquisition means 32 acquires each vertex coordinate about one polygon area | region, when a candidate symbol is input from the symbol selection means 31. FIG. Further, when adjacent symbols are input from the symbol selection unit 31, the vertex coordinates of the polygonal region corresponding to each symbol are acquired. The polygon vertex coordinate acquisition unit 32 outputs the acquired polygon vertex coordinate to the region determination unit 33.

  The area determination unit 33 determines which symbol the received signal corresponds to based on the polygon vertex coordinates input from the polygon vertex coordinate acquisition unit 32. Here, an area determination method will be described.

  The area determination means 33 sequentially performs an outer product operation of vectors of adjacent vertices clockwise or counterclockwise with respect to a vector connecting the output signal from the determination feedback equalization unit 17 and the vertex of the determination area. The inside / outside determination of the polygonal area is performed depending on whether or not all the directions (signs) of the polygons coincide.

  Next, the symbol determination area in the present invention will be specifically described with reference to FIGS. In FIGS. 4 and 5, 64QAM is used as an example. However, the present invention is not limited to this, and can be applied to multi-level QAM such as 256QAM.

  FIG. 4 is a diagram illustrating an example of a symbol arrangement of 64QAM and a polygon determination area. FIG. 5 is a diagram illustrating an example in which a rectangular region is added to FIG. Here, in FIGS. 4 and 5, the dots indicate symbol positions, the solid lines indicate preset polygon areas for symbol determination, and the dotted lines in FIG. 5 indicate rectangular areas.

  Here, for example, when the received signal is the position X indicated by “+” in FIG. 5, conventionally, the inside / outside determination calculation is performed for all of the polygonal regions shown in FIG. 4. In this case, since it is necessary to calculate based on each side constituting the polygon, the calculation amount becomes enormous.

  Therefore, in the present invention, first, one candidate symbol is selected using a rectangular area. Here, when the preset QAM is a square arrangement, the region determination may be performed for each of the I component and the Q component. In addition, in the case of QAM that is not squarely arranged, the IQ plane is divided into rectangular areas including one symbol inside the area, and the divided areas are stored in a memory or the like and compared with the received signal. Thus, candidate symbols can be selected.

  Further, by having the storage means 34, a polygonal region corresponding to the symbol can be easily acquired. Furthermore, an adjacent symbol corresponding to a certain symbol and a polygonal region corresponding to each adjacent symbol can be easily output.

  Next, a calculation method for determining whether or not the received signal is included in the polygonal region corresponding to the symbol will be described.

  FIG. 6 is an enlarged view in the vicinity of the reception signal X for explaining the inside / outside determination of the polygonal region. In FIG. 6, the coordinates of the polygonal vertex ABCDEF which is the determination region are acquired by the polygonal vertex coordinate acquisition unit 32. Whether or not the received signal X is included in the determination area ABCDEF is determined by using adjacent vertex vectors (for example, XA and XB) for a vector connecting the output from the determination feedback equalization unit 17 and the vertex ABCDEF in the determination area. ) Are sequentially performed clockwise or counterclockwise (XB and XC, XC and XD,...), And the inside / outside determination is made depending on whether or not the vector directions (determined by the signs) all match. Do. Here, when all the codes match, the received signal X is inside the polygon ABCDEF, so that the received signal X can be determined to be a symbol in this determination region.

  Therefore, if the output from the decision feedback equalization unit 17 is within the region as a result of region determination with the polygonal region corresponding to the candidate symbol, the region determination means 33 performs demodulation output corresponding to the candidate symbol. In addition, when it is not within the polygonal area corresponding to the candidate symbol, it is determined whether each of the polygonal areas of the adjacent symbols is within the determination area.

  As a result of the determination, when the output from the determination feedback equalization unit 17 is in the polygonal region corresponding to any adjacent symbol, the demodulation output corresponding to the corresponding adjacent symbol is performed. If it is not included in the polygonal region corresponding to any adjacent symbol, it is determined as a candidate symbol, and demodulation output corresponding to the candidate symbol is performed. Thereby, the symbol determination which reduced the amount of calculations can be performed.

  Here, the above-described symbol determination procedure will be described using a flowchart. FIG. 7 is a flowchart showing an example of a symbol determination procedure in the present invention. First, candidate symbols are selected based on the input received signal (S01). Here, a symbol at a point where a received signal is included based on a rectangular area set in advance for each symbol is set as a candidate symbol.

  Next, a preset polygon region corresponding to the selected candidate symbol is acquired, and the coordinates of the vertexes of the acquired polygon region are acquired (S02). At this time, coordinates are set in advance on the IQ plane, and vertices are acquired corresponding to the coordinates.

  Next, it is determined whether the received signal is included in the polygonal region corresponding to the candidate symbol (S03). In the inside / outside determination, as described above, with respect to the vector connecting the received signal and the vertex of the polygon determination region, the outer product calculation of adjacent vectors is sequentially performed, and the inside / outside determination is performed based on the direction of the vector.

  As a result of the inside / outside determination, it is determined whether it is within the polygonal region corresponding to the candidate symbol (S04). If it is within the region (YES in S04), since the received signal is a candidate symbol, a value corresponding to the candidate symbol is output (S05). If not in the area (NO in S04), an adjacent symbol is selected (S06). Next, a polygonal area corresponding to each adjacent symbol is acquired, and the vertex coordinates for each acquired polygonal area are acquired (S07). After acquisition, the inside / outside determination of the received signal is performed based on the polygonal region corresponding to each adjacent symbol (S08).

  Here, as a result of S08, it is determined whether it is within any adjacent symbol area (S09). If within the area of any adjacent symbol (YES in S09), a value corresponding to the corresponding adjacent symbol is output (S10). If it is not in the area of any adjacent symbol (NO in S09), the value of the received signal is a value corresponding to the candidate symbol (S11).

  According to the above-described symbol determination procedure, it is not necessary to perform the calculation for determining the region of the received signal for all symbols, and the amount of calculation can be reduced. This makes it possible to perform digital demodulation with improved processing efficiency.

  Further, by using the above-described determination procedure, for example, even when a gap area is generated in a polygon area set for each symbol and the received signal is in the gap area, complicated calculation processing is not required. Can be output as candidate symbol values. This makes it possible to perform complex processing that enables digital demodulation with improved processing efficiency.

  In addition, a symbol including a plurality of polygonal regions in a rectangular region corresponding to a symbol is stored in advance in a storage unit such as a memory, and an inner product calculation is performed by performing an outer product operation on only a predetermined symbol from adjacent symbols. The number of symbols to be determined can be reduced.

  Here, the above-mentioned content is demonstrated using figures. FIG. 8 is a diagram for explaining symbols in which a rectangular determination region and a polygon determination region are different. 8 has a polygonal area (solid line) and a rectangular area (dotted line) similar to those shown in FIG.

  In FIG. 8, a symbol P1 is a symbol in which a rectangular determination area and a polygonal determination area are different. That is, in the rectangular area, the symbol P1 is used, but in the polygonal determination area, the symbol P1 may be any one of the symbols P2 to P5. Here, an enlarged view of the vicinity of the symbol P1 is shown in FIG.

  As described above, in order to perform symbol determination while reducing the amount of calculation for the symbol P1 having a rectangular determination region and a polygonal determination region different from each other, for example, the determination region of each symbol in the square QAM is illustrated in FIG. As shown in FIG. 9, in the case of a polygonal region surrounded by a straight line passing through the vertices a, c, f, and h of the quadrangle that is a rectangular region and the midpoints b, d, e, and g of each side, The portion where the region protrudes outward from the rectangular region is only four symbols adjacent in the I-axis direction and the Q-axis direction on the IQ plane.

  In other words, among the polygonal areas corresponding to the adjacent symbols, there is a part that overlaps the rectangular area because of the four adjacent symbols in the I-axis direction and the Q-axis direction with respect to the polygonal area of the symbol P1. It becomes a polygonal area.

  Therefore, the adjacent symbols to be determined inside and outside need only be the symbols in the I-axis direction and Q-axis direction of the candidate symbol corresponding to the polygonal region where there is a portion overlapping the rectangular region. As described above, by selecting adjacent symbols based on the positional relationship between the polygonal area and the rectangular area, it is possible to reduce the amount of calculation in the symbol area determination. Also, digital demodulation with improved processing efficiency can be realized.

  In the inside / outside determination using a polygonal area, there may be an area that is not included in any polygonal area. One example will be described with reference to FIG. FIG. 10 shows an enlarged view near the boundary between the symbols P1, P2, and P5.

  For example, as shown in FIG. 10, depending on the shape of the polygonal area, it is included in any polygonal area by outer product calculation, such as a triangular part surrounded by the polygonal areas corresponding to the symbols P1, P2, and P5. There may be no areas. In the present invention, if the signal for symbol determination is within such a region (region within a triangle), it is determined as P1. This determination corresponds to the procedure of outputting the candidate symbol of S11 as NO in the determination of S09 in FIG.

  Furthermore, as another method for reducing the amount of calculation, the rectangular area is divided into a plurality of areas, it is determined whether the received signal is included in any of the divided areas, and the divided area obtained as a result of the determination is determined. A symbol is selected based on this.

  Here, the above-mentioned content is demonstrated using figures. FIG. 11 is a diagram for explaining selection of adjacent symbols using divided areas. FIG. 11 is a diagram corresponding to FIGS. 8 and 9, and shows an example of division in which a rectangular region is divided into two parts by dividing it vertically with a line de.

  First, an area determination is performed as to whether the received signal is included in a polygon area corresponding to the candidate symbol. Next, an adjacent symbol is selected when it is not included in the polygonal area, but it is first determined which of the two divided rectangular areas shown in FIG. Here, for example, when the received signal is included in the hatched area (divided rectangular area acde) shown in FIG. 11, only two symbols P2 and P5 shown in FIG. 8 need to be selected as adjacent symbols. become. This is because, as described above, the portion where the rectangular area protrudes outside the polygonal area is only the four symbols adjacent in the I-axis direction and the Q-axis direction on the IQ plane, and the hatched area shown in FIG. This is because only two symbols P2 and P5 shown in FIG. 8 have adjacent polygonal regions.

  In this way, it is determined whether the received signal is included in one of the divided determination areas, and by selecting an adjacent symbol based on the determination result, the number of area determination calculations by outer product calculation can be reduced. Can do. Note that the number of divisions for dividing the rectangular area is not limited to two, but is set according to the setting contents of the rectangular area and the polygon area in the symbol.

  As described above, according to the present invention, it is possible to reduce the amount of calculation at the time of symbol determination of a QAM signal and perform digital demodulation with improved processing efficiency. Specifically, one candidate symbol is selected from the rectangular area, and only the candidate symbol and an adjacent symbol adjacent to the candidate symbol are subjected to inside / outside determination of the polygonal area corresponding to the symbol, thereby performing calculation in the determination. Need not be performed for all symbols, and the amount of calculation can be reduced. As a result, digital demodulation with improved processing efficiency can be realized.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

It is a figure which shows an example of the block configuration of the conventional digital demodulator. It is a figure which shows an example of the block configuration of a digital demodulator. It is a figure which shows an example of the block configuration of the symbol determination part 28 in this invention. It is a figure which shows an example of 64QAM symbol arrangement | positioning and a polygon determination area | region. FIG. 5 is a diagram illustrating an example of a determination region of FIG. 4 and a rectangular determination region for a symbol. It is an enlarged view near the received signal X for explaining the inside / outside determination of a polygonal region. It is a flowchart which shows an example of the symbol determination procedure in this invention. It is a figure for demonstrating the symbol from which the rectangular determination area | region and a polygon determination area | region differ. It is an enlarged view near symbol P1. It is a figure which shows the example which is not contained in any polygon area | region. It is a figure for demonstrating selection of the adjacent symbol using the divided | segmented area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Digital demodulator 11 Tuner 12 A / D conversion part 13 Quasi-synchronous detection part 14 Timing reproduction | regeneration part 15 Roll-off filter 16 Carrier wave reproduction | regeneration part 17 Judgment feedback equalization part 18, 28 Symbol judgment part 31 Symbol selection means 32 Polygon Vertex coordinate acquisition means 33 Area determination means 34 Storage means

Claims (5)

In a digital demodulator for demodulating a QAM signal,
A quasi-synchronous detector for quadrature detection of the QAM signal;
A symbol determination unit that determines a symbol of a signal having an I component and a Q component obtained by the quasi-synchronous detection unit,
The symbol determination unit selects a specific symbol and an adjacent symbol adjacent to the specific symbol based on a rectangular area set for each of a plurality of symbols, and a polygon corresponding to each of the specific symbol and the adjacent symbol A digital demodulator which performs region determination based on a region. The symbol determination unit
2. When a plurality of polygonal regions are included in a rectangular region corresponding to the specific symbol, symbols other than the specific symbol are selected as adjacent symbols among symbols corresponding to the plurality of polygonal regions. The digital demodulator according to 1. The symbol determination unit
The rectangular area corresponding to the specific symbol is divided into a plurality of areas, an area including the signal is selected from the divided areas, and an adjacent symbol is selected based on the selected area. A digital demodulator as described in 1. The symbol determination unit
The digital demodulator according to any one of claims 1 to 3, wherein when the signal to be determined is not included in the polygonal area of the adjacent symbol, the specific symbol is used. In a digital demodulation method for demodulating a QAM signal,
A quasi-synchronous detection stage for quadrature detection of the QAM signal;
A symbol determination step of determining a symbol of a signal having an I component and a Q component obtained in the quasi-synchronous detection step;
The symbol determination step selects a specific symbol and an adjacent symbol adjacent to the specific symbol based on a rectangular area set for each of a plurality of symbols, and a polygon corresponding to each of the specific symbol and the adjacent symbol A digital demodulation method characterized by performing region determination based on a region.

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