JPH11331299A - 64qam, 256qam modulation analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain analysis of 64 point QAM modulation. SOLUTION: A maximum amplitude and a minimum amplitude of base band I, Q input signals are retrieved (S5), a gain is decided so that the minimum amplitude is in matching with a minimum amplitude of 1st to 9th amplitudes taken in a 64 point QAM signal space (S6), the gain is multiplied with each symbol point string (S7), the symbol point string is phase-rotated by πi/256 rad each to produce an ideal symbol point string (S10). The correlation between this string and the original input symbol point string is obtained till an angle πi/256 reaches π/4, and the gain is decided so that the minimum amplitude is in matching with a 2nd standard amplitude (S15). Whether or not the product of the gain and the maximum amplitude is larger than a sum of a prescribed value to the standard maximum amplitude is discriminated (S17), and when larger, the phase rotation at that time is given to an input symbol to obtain a frequency error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to 64QAM modulation,
The present invention relates to a method of performing modulation analysis of 256QAM modulation.

[0002]

2. Description of the Related Art FIG. Input terminal 11
Is converted into an intermediate frequency signal in the down converter 12 by the local signal from the local oscillator 13. The intermediate frequency of this intermediate frequency signal is a frequency that can be converted by a subsequent AD converter and has a modulation band of a modulation signal. This intermediate frequency signal is band-limited by a band-pass filter 14 so that aliasing does not occur in an AD converter 15 at the next stage, and is converted into a digital signal by the AD converter 15, and this digital signal is converted into a local signal generator. The digital local signal of the cosine wave and the sine wave from 16 is multiplied by multipliers 17 and 18 and further passed through low-pass filters 21 and 22 to be converted into baseband signals, so-called I and Q signals. The local signal of the sine wave is obtained by phase-shifting the local signal of the cosine wave by 90 degrees by the phase shifter 19. This digital signal processing portion is performed by either software processing or hardware processing.
The baseband I and Q signals performed in this way are D
A modulation analysis unit 23 including an SP (Digital Signal Processor) performs frequency error estimation and modulation analysis such as modulation accuracy. A specific method of the modulation analysis unit 23 is described in, for example, US Pat. No. 5,187,7 issued on Feb. 16, 1993.
No. 19, particularly in the description with reference to FIG.

[0003]

In order to perform the modulation analysis correctly, the local signal of the local signal generator 16 must be
It is necessary to synchronize the phase with the local signal at the time of quadrature modulation in the transmission signal. If the received signal is modulated by a known data pattern such as a sync word, the phase of the local signal on the receiving side can be synchronized with that on the transmitting side by relying on the known data pattern. However, in the case of a measuring instrument, its data pattern may not be generally understood, and it is required that measurement can be performed in such a case.

When performing modulation analysis, it is necessary to demodulate a received signal and create an ideal modulated signal from the demodulated data. In the case of QPSK modulation, the possible phases of the symbol points are 45 °, 135 °, −45 °, as shown in FIG. 4A.
° and -135 °, so that the ideal modulation signal can be created by forcibly adjusting the first received symbol point to one of these four points. Even if the transmission pattern and the demodulation pattern do not match, modulation analysis is possible.

If the phase of the local signal does not match that of the transmitting side, the phase of the symbol point will be shifted, for example, as shown in FIG. 4B. In the case of QPSK modulation, the possible phase of a symbol point is only four phases as shown in FIG. 4A, so that the first received symbol point is adjusted to one of FIG. 4A to obtain the signal shown in FIG. 4A. Because of the point arrangement, an ideal modulation signal can be created. Furthermore, Q
In the case of PSK modulation, demodulation can be performed only with phase information of a symbol point, amplitude information can be ignored, and it is not necessary to perform amplitude information matching.

However, the signal space of 64QAM modulation is shown in FIG.
A is defined as shown in FIG. Even if only the phases of the local signals on the transmitting side and the receiving side are shifted, for example, the result is as shown in FIG. 5B. At this time, on the receiving side, it is unknown whether only the phase is shifted or the amplitude is also shifted, and even if it is assumed that only the phase is shifted, if the shift amount is not known,
However, if only the phase of the first received symbol is adjusted to one of the possible phases at that amplitude, the signal point arrangement shown in FIG. 5A is less likely to occur, and demodulation cannot be performed.

In 64QAM modulation, not only phase information of a symbol point but also amplitude information is required for demodulation. Therefore, it is difficult to perform modulation analysis unless the received signal has a known data pattern.

[0008]

According to the present invention, a maximum value and a minimum value of an amplitude at a symbol point of an input signal are detected, and a gain is determined from the detected minimum value (or maximum value) and a specified value. The gain is multiplied by the amplitude of the symbol point of the input signal, the phase of the symbol point sequence of the input signal multiplied by the gain is rotated by a predetermined amount, and the symbol point sequence of the phase-rotated input signal is demodulated. Then, an ideal symbol point sequence is obtained, a cross-correlation between the ideal symbol point sequence and the symbol point sequence of the phase-rotated input signal is obtained, and the phase of the symbol point is kept until a predetermined amount of phase rotation becomes π / 4 radian. Rotation and
The generation of the ideal symbol point sequence and the calculation of the cross-correlation are repeated.

In the input signal, 64QAM or 256QA
Since the minimum value (or maximum value) in the signal space of M may not be included, the detected minimum value (or maximum value)
And a second specified value from the minimum value (maximum value) of the specified amplitude obtained from the signal space, and a gain is multiplied by the detected maximum value (or minimum value). (Or minimum value) + allowable value), that is, check whether the threshold is exceeded.
The frequency error is estimated using the phase and the gain corresponding to the maximum cross-correlation value.

[0010]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a functional configuration example of the present invention. FIG.
As described above, the input signal is an intermediate frequency signal, and the digital data signal is stored in the memory 31.
The input signal converted to the digital value and set to the intermediate frequency is fetched from the memory 31 (S1 in FIG. 2), and the quadrature detector 3
2 to perform quadrature detection to obtain baseband I and Q signals (S2). The quadrature detector 32 includes the multipliers 17 and 18, the phase shifter 19, the low-pass filters 21 and 22 shown in FIG.
It is composed of

The I and Q signals are supplied to a clock delay detector 33.
, The shift between the sampling point of the digital signal and the symbol point of the modulation signal of the input signal is detected (S3), and the detected clock delay is converted by the clock delay correction unit 34 into I and Q. The signal is corrected, and the sampling point and the symbol point are matched (S4). The respective methods of clock delay detection and clock delay correction are described in, for example, the clock delay estimator 63 and the resampler 64 in FIG.

The amplitude of each symbol point of the I and Q signals subjected to the clock delay correction is checked, and the maximum value and the minimum value are searched by the maximum value / minimum value search unit 35 (S5). The gain is determined by the gain determiner 36 so that the searched minimum value is the smallest value of the amplitude that the standardized 64QAM signal can take (S6). That is, if 0 to π / 2 radians of the signal space of the 64QAM signal is indicated, the result is as shown in FIG. 4C. From this, all the symbols of the 64QAM signal can be any one of the minimum 1st to the maximum 9th shown in FIG. 4C. Will be taken. These nine amplitudes are determined by standards. Therefore, the gain may be determined so that the minimum amplitude of the symbol point of the input signal matches the standardized first (minimum) amplitude.

The determined gain is multiplied by the gain multiplying section 37 with the input symbol sequence whose clock delay has been corrected (S7). The parameter i is initialized to 0 (S8), and the gain-multiplied input symbol point sequence is phase-rotated by πi / 256rad by the phase rotation unit 39 (S9). The input symbol point sequence rotated in phase is converted into an ideal symbol generation unit 41.
And an ideal symbol point sequence is generated based on the demodulated data (S10). The cross-correlation between the ideal symbol point sequence and the input symbol point sequence from the phase rotation unit 39 is calculated by the correlation calculation unit 42 (S11). The relationship between each rotation phase πi / 256 rad, the cross-correlation value, and the gain is stored in the storage unit 44 in the control unit 43.

Next, the phase rotation in step S9 is π / 4r.
It is determined by the determination unit 45 in the control unit 43 whether it has become ad (S12). That is, by rotating any of the signal points by an integral multiple of π / 4 from the signal points in the signal space of FIG. 4C, all other signal points can be represented. Unit of phase rotation π /
256 is appropriately determined by experiment. This value is π / 256
If it is smaller, the amount of calculation increases, and if it is larger than π / 256, the input symbol point sequence may not be correctly demodulated. The designation of the phase rotation πi / 256 is performed by the rotation phase determination unit 46 in the control unit 43.

If it is not determined in step S12 that πi / 256 = π / 4, i is incremented by 1 and the process returns to step S9 (S1).
3). Accordingly, the phase rotation of πi / 256 with respect to the input symbol, the generation of the ideal symbol point sequence, and the calculation of the cross-correlation with the phase rotated input symbol point sequence are repeated. π
When i / 256 = π / 4, the parameter j is incremented by 1 (j is initialized to 1 in advance) (S14). The gain determination unit 36 determines the gain so that the minimum value searched by the maximum / minimum value search unit 35 matches j = 2nd amplitude among the amplitudes that the signal point can take in the signal space (S15).

The determined gain is multiplied by the searched maximum amplitude (S16), and the gain-multiplied maximum amplitude is obtained by adding a margin to the maximum value of the standard amplitude, that is, the j = 9th amplitude, that is, It is determined whether the value is larger than the threshold value (S17). If the search minimum value is the minimum value j of the standard amplitude
= 1, and if the search maximum value corresponds to the value of the maximum value j = 9 of the standard amplitude, step S17 is determined to be larger than the threshold value. The control unit 43 performs the gain determination in step S15, the gain multiplication in step S16, and the determination in step S17.

If the determination in step S17 is equal to or less than the threshold, the process returns to step S7. At this time, the gain used in step S16 is used. In other words, it is determined that there is an input symbol point sequence corresponding to the standard amplitude j = 1, the gain is determined so that the minimum value matches the standard amplitude j = 2, and the gain is determined as the input symbol point. The column is multiplied and a phase rotation of πi / 256 is performed on it, and so on.

If there is no search maximum value corresponding to the standard amplitude maximum value j = 9th, the threshold value is not exceeded in step S17 even if the search minimum value matches the corresponding standard value amplitude. Is incremented by 1 and steps S14 to S17 are repeated, and the gain is determined so as to match the search minimum value and the value larger than the corresponding standard amplitude. That is, the large gain is multiplied by the search maximum value, and step S17 is performed. To exceed the threshold.

When the threshold value is exceeded in step S17, the rotational phase and gain at the time when the obtained cross-correlation value in the storage unit 44 becomes maximum are obtained (S18), and the frequency error estimating unit 47 is obtained from this. (S19), and the frequency error is estimated by the frequency error correction unit 48 with respect to the symbol point sequence whose delay has been corrected by the clock delay correction unit 34.
(S20), the modulation accuracy is calculated by the modulation accuracy calculation unit 49 using the symbol point sequence corrected for the frequency error (S21), and displayed on the display unit 51.

The control unit 43 operates each unit, performs various determination calculations, and stores and reads out required data such as having the first to ninth standard amplitudes in the storage unit 52. In the above description, the gain is determined so that the search minimum value matches the standard minimum amplitude in step S6. However, the search maximum value may match the standard maximum amplitude. In this case, the standard maximum amplitude is set to j = 1 and the minimum amplitude is set to j = 9. In step S15, the gain is determined so that the search maximum value becomes the j-th standard amplitude, and the gain is determined in step S16. The search minimum value is multiplied. In step S17, a value obtained by subtracting a margin from the minimum standard amplitude is set as a threshold. When the amplitude is equal to or smaller than the threshold, the process proceeds to step S18. What should I do?

Instead of performing the phase rotation on the input symbol point sequence in the phase rotation section 39, the phase rotation on the local signal of the local signal generator 16 may be performed. In the input symbol point sequence supplied to the frequency error correction unit 48, the initial phase of the local signal is used as the rotation phase when the cross-correlation is maximum. The configuration shown in FIG. 1 is a functional configuration,
These can be executed by a computer.
In the above description, the present invention is applied to a 64QAM signal.
It can also be applied to 6QAM signals. In this case, there are 32 possible amplitudes of the symbol points in the signal space.

[0022]

As described above, according to the present invention, focusing on the fact that the amplitude value that can be taken in the signal space is a predetermined limited value, the maximum value and the minimum value of the input symbol point sequence are determined. The gain with respect to the standard amplitude is determined with reference to one of them, and the rotation is performed by a unit phase experimentally determined so that each symbol can be correctly demodulated.
4 to obtain the ideal symbol point sequence and the cross-correlation with the original input symbol point sequence to obtain the gain and phase of the input symbol point sequence. Modulation accuracy analysis of a 256QAM signal can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a functional configuration of a modulation analyzer to which an embodiment of the present invention is applied.

FIG. 2 is a flowchart showing a processing procedure in the embodiment of the present invention.

FIG. 3 is a block diagram showing a general functional configuration example of a conventional modulation analysis.

4A and 4B are diagrams showing a signal space of a QPSK signal,
C is a diagram showing a possible amplitude of a symbol point of the 64QAM signal.

5A is a diagram illustrating a signal space of 64QAM modulation, and FIG. 5B is a diagram in which the phase is rotated;

Claims (2)

[Claims] 1. A modulation analysis method for decoding an input signal, estimating an ideal symbol point thereof, generating an ideal symbol point sequence, and estimating a frequency error from the ideal symbol point sequence and the input signal. A first step of detecting a maximum value and a minimum value of the amplitude at a symbol point of the input signal; a second step of determining a gain from the detected maximum or minimum value and a specified value; A third step of multiplying the amplitude of the symbol point of the input signal by a predetermined amount; a fourth step of rotating the phase of the symbol point sequence of the input signal multiplied by the gain by a predetermined amount; A fifth step of demodulating and generating an ideal symbol point sequence, a sixth step of obtaining a cross-correlation between the ideal symbol point sequence and the input signal symbol point sequence whose phase has been rotated, and / A seventh step of repeating the fourth to sixth steps until the current reaches 4 radians; and an eighth step of obtaining the maximum value of the cross-correlation, and using the gain and phase at that time for estimating the frequency error. 64QAM, 256QAM modulation analysis method. 2. After the seventh step, the gain is determined by using the next lower or higher specified value and the maximum value or the minimum value with respect to the specified value used for determining the gain in the second step. A ninth step of determining; a tenth step of multiplying the gain determined in the ninth step by the minimum value or the maximum value; and determining whether a result of the multiplication in the tenth step is greater than a threshold value. If the judgment is small, the process returns to the third process, and the gain obtained in the ninth process is used. If the judgment is large, the process proceeds to the eighth process. The 64QAM and 256QAM modulation analysis method according to claim 1, wherein