JP2008011462A - Demodulator - Google Patents

Abstract

The present invention relates to a demodulator that demodulates a quadrature amplitude modulation signal, and aims to speed up the reception level estimation process and improve the accuracy.
A first average calculator 33 that calculates and averages the power of a known pilot signal, and a second average calculator 34 that calculates and averages the power of a signal other than a known pilot signal, A third average calculator 37 that performs an averaging process on the output signal of the first average calculator 33 by multiplying the output signal of the second average calculator 34 by a coefficient by the multiplier 35; The output signal of the second average calculation unit 34 is multiplied by a coefficient, and the output signal of the first average calculation unit 33 is compared with the threshold value determination unit 36. When the comparison difference is within a predetermined range, the third average calculation is performed. A selection means including a multiplexer control circuit 39 and a multiplexer 38 for selectively outputting the output signal of the unit 37, and otherwise selecting the output signal of the first average calculating unit 33 and outputting it as an estimated value of the reception level. And.
[Selection] Figure 2

Description

  The present invention relates to a demodulation device that receives and demodulates a multilevel quadrature amplitude modulation signal in a wireless communication system.

  As a modulation method in a wireless communication system, a multi-level quadrature amplitude modulation (QAM) method combining quadrature phase modulation and amplitude modulation is known. As the multi-value number, 16 values, 64 values, 256 values, etc. are put into practical use. 4A shows an example of a transmission format of the wireless communication system, and FIG. 4B shows a case of 16-value QAM with 16 multi-values and orthogonal I and Q axes and 16 signal points. An arrangement relationship is shown, and (C) shows an example of a synchronization word SW having a known pattern. The known signal SW next to the Ramp corresponding to the first preamble in the transmission format of FIG. 4A is a known pattern sync word (SW) shown in FIG. 4C, and information after the sync word. A known pilot signal indicated by an arrow is inserted into the field Information Field at a predetermined interval and transmitted.

  As shown in FIG. 4C, the known pattern synchronization word (SW) is assigned signal points 0, 8, and A indicating the maximum amplitude values corresponding to SW1 to SW10, for example, in the case of a 10 symbol configuration. ing. The signal point of the maximum amplitude value corresponds to the intersection of ± 3 on the I and Q axes in FIG. That is, the signal point has the maximum amplitude value on the dotted circle. The pilot signal is also assigned one of signal points 0, 2, 8, and A having the maximum amplitude value. Therefore, the reception level can be estimated by detecting a known synchronization word and pilot signal. Based on the estimated reception level, an amplitude threshold level of 0 level and ± 2 level on the I and Q axes is set, and the amplitude threshold level and the signal level are compared, and the decoded data corresponding to the signal point position Can be obtained. Note that the level calculation threshold range indicated as a circle is an example of a range obtained by power averaging processing of signals other than pilot signals described later.

Further, in a mobile station of a mobile radio communication system to which 16-value QAM is applied, power ratio information between a data channel and a pilot channel is transmitted from a base station through a control channel, and the mobile station uses this power ratio information as a basis. In addition, a configuration for performing signal point identification at the time of demodulation is known, and without transmitting power ratio information by a control channel from the base station, the mobile station receives the power value of the received pilot signal and the data signal. There has been proposed a demodulator that calculates a power value, thereby calculating a power ratio between a pilot signal and a data signal, and performs signal point identification at the time of demodulation based on this power ratio (for example, Patent Documents) 1).
JP 2004-166004 A

  In order to improve the accuracy of QAM signal demodulation processing, it is necessary to increase the estimation accuracy of the reception level and set the amplitude threshold level. In the wireless communication system, the fluctuation of the reception level is relatively large compared to the wired communication system. Therefore, the amplitude threshold level setting for reception decoding is estimated as described above. Conventionally, the reception level is generally estimated using both a known synchronization word and a pilot signal, but either one of them is used to simplify the processing. It is also possible to perform reception level estimation for other signals together with known synchronization words and pilot signals. In either case, an averaging process within a predetermined period is necessary to maintain the reception level estimation accuracy. In that case, in order to estimate the received signal level using all known signals and other signals, it is necessary to lengthen the time required for the averaging process. Therefore, it is difficult to speed up the setting of the amplitude threshold level. In addition, when the reception level estimation is performed using only known signals, there is a problem that the reception level estimation accuracy is lowered.

  The present invention solves the above-described conventional problems, and an object thereof is to improve the accuracy and calculation speed of reception level estimation processing.

  The demodulator of the present invention is a demodulator including means for estimating a reception level of a multi-level quadrature amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point based on the reception level. First average calculating means for calculating and averaging the power of the signal, second average calculating means for calculating and averaging the power of signals other than the known signal, and the second average calculating means A third average calculating means for multiplying the output signal by a coefficient and averaging the output signal of the first average calculating means, and a coefficient for the output signal of the second average calculating means Compared with the output signal of the first average calculation means, the output signal of the third average calculation means is selectively output when the comparison difference is within a predetermined range, and otherwise the first average calculation means Output signal is output as an estimate of the reception level. And a selection means that.

  Also, a demodulator including means for estimating a reception level of a multi-level quadrature amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point based on the reception level is transmitted at a predetermined period. Pilot detection means for detecting a known pilot signal; first average calculation means for performing power calculation of the known pilot signal identified by the pilot detection means to perform an averaging process; and other than the known pilot signal A second average calculating means for performing an averaging process by calculating the power of the signal, and averaging the output signal of the second average calculating means by multiplying the output signal of the first average calculating means with a coefficient; A third average calculating means for performing processing; a multiplying means for multiplying a preset coefficient so as to approximate the output signal of the second average calculating means to the output signal of the first average calculating means; hand And the output signal of the first average calculating means, and when the comparison difference is within the level calculation threshold range, the output signal of the third average calculating means is selected, and otherwise Selecting means for selecting an output signal of the first average calculating means and outputting it as an estimated value of the reception level.

  When the power is turned on or when the channel is switched, it is possible to speed up the setting of the amplitude threshold level for identifying the modulation signal point by estimating the reception level of a known pilot signal transmitted at a predetermined period. By multiplying the reception level estimated by the averaging process for the known pilot signal with the averaging process for the other signals together with a coefficient and approximating the reception level of the known pilot signal for comparison, the power level or channel Based on the result of determining whether or not it is in a normal reception state at the time of switching, when a normal reception state is obtained, the reception level is estimated using a known pilot signal and other signals, thereby The setting system can be improved.

  The demodulator of the present invention will be described with reference to FIG. 2. Means for estimating the reception level of a multilevel quadrature amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point based on this reception level In the demodulator including the first average calculating means 33 such as a first average calculating unit 33 for calculating and averaging the power of a known signal such as a pilot signal, and calculating the power of a signal other than the known signal Second average calculating means such as a second average calculating section 34 for performing averaging, and an output signal of the second average calculating means is multiplied by a coefficient by a multiplier 35 to obtain first average calculating means. Output from the first average calculation means by multiplying the output signal of the third average calculation means by the third average calculation means such as the third average calculation section 37 that performs the averaging process on the output signal of the first average calculation means The third average operation is performed when the comparison difference is within a predetermined range. A selection means including a multiplexer control circuit 39 and a multiplexer 38, which selectively outputs the output signal of the stage and selects the output signal of the first average calculation means at other times and outputs it as an estimated value of the reception level; I have.

  FIG. 1 is an explanatory diagram of a first embodiment of the present invention, where 1 is a bandpass filter (BPF), 2 is an AD converter (ADC), 3 is a quadrature detector, and 4 and 5 are filters (FIR; Finite Impulse). (Response Filter), 6 is a complex correlator, 7 is a frame detector, 8 is an AFC rotation corrector, 9 is a phase error corrector, 10 is a phase error calculator, 11 is a frequency error calculator, 12 is a demapping unit, 13 is a frame synchronization monitoring unit, 14 is an operation enable signal generator, 15 is an enable signal, 16 is a filter table, 17 is a timing corrector, 18 is a zero cross detector, 19 is a pilot detector, and 20 is a threshold and level calculator. , 21 is a clock regenerator, and 22 and 23 are buffer memories (FIFO) for output. The functional blocks denoted by reference numerals 3 to 20 are blocks that can be realized by firmware processing. Note that the front-stage wireless reception unit and the subsequent-stage reception signal processing unit are not shown.

  The preceding radio receiving unit (not shown) shows a case where a radio frequency received signal is converted into an intermediate frequency signal IF and input to the band pass filter 1. The band pass filter 1 removes unnecessary band signals, and AD The signal is converted into a digital signal by the converter 2. Each functional block by the firmware process for inputting and processing the digital signal can be realized by a processing function of a DSP (Digital Signal Processor), but each functional block can also be realized by a digital processing circuit. The above-mentioned IF signal is converted into a digital signal by the AD converter 2 and input to the quadrature detector 3, and the quadrature I and Q signals of the quadrature detection output signal are passed through the filters 4 and 5 to the complex correlator 6. Then, a correlation operation for detecting a synchronization word (SW) of a known pattern is performed, and the result is input to the frame detector 7. The frame detector 7 detects the head of the frame according to the synchronization word detection, and inputs the detection signal to the operation enable signal generator 14 and the clock regenerator 21. The filters 4 and 5 are controlled to have characteristics according to the filter coefficients from the filter table 16.

  The 1 and Q signals of quadrature are input to the AFC rotation corrector 8 through the filters 4 and 5, and the AFC rotation corrector 8 uses the signal indicating the steady frequency error from the frequency error calculator 11. A phase rotation correction process is performed and input to the phase error corrector 9 and the phase error calculator 10, and the phase error corrector 9 receives I based on the signal indicating the phase error from the phase error calculator 10. , Q phase errors are corrected and input to the demapping unit 12, the pilot detector 19, and the threshold & level calculator 20. The zero cross detector 18 receives one of the I and Q signals. In the demapping unit 12, the I and Q signals whose phase error has been corrected by the phase error corrector 9 are subjected to code determination using the amplitude threshold level calculated by the threshold & level calculator 20 to obtain decoded data. The data is input to the buffer memory 23, written by the write enable signal WE, read as a decoded output by the read enable signal RE from the clock generator 21, and transferred to a reception signal processing unit at a subsequent stage (not shown).

  The zero cross detector 18 uses the pattern effect of the I signal. The sign inversion point between the previous symbol and the current symbol is detected, and the timing corrector 17 uses the random walk filter for timing synchronization with the transmission side. The characteristics of the filters 4 and 5 are as follows. Control is performed according to the filter coefficient read from the filter table 16 corresponding to the zero cross point detected by the zero cross detector 18. The pilot detector 19 is inserted into the information field at a predetermined period, detects a pilot signal as a known signal, and inputs the detection signal to the frame detector 7 and the threshold value & level calculator 20. Based on the input I and Q signals, the threshold value & level calculator 20 averages the received levels of the known pilot signal and signals other than the pilot signal, and calculates the threshold value and the level. The calculated threshold value is input to the demapping unit 12 for signal point determination, and an RSSI (Received Signal Strength Indicator) signal is input to the buffer 22 and written by the write enable signal WE. Read by the read enable signal RE and transfer to the next stage (not shown).

  Also, a channel switching signal for switching the radio channel is input to the threshold & level calculator 20, and the received power of a known pilot signal is calculated during the initial period when the power is turned on and when the channel is switched. And a reception level is estimated, and after a predetermined period elapses or when a predetermined reception state is determined, the processing is switched to estimate the reception level using a pilot signal and other signals. The frame synchronization monitoring unit 13 performs frame synchronization monitoring based on the decoded data from the demapping unit 12 and the frame detection signal from the frame detector 7. When the frame synchronization loss is detected, the frame detector 7 A reset signal RES is input to restart the frame detection process. The operation enable signal generation unit 14 generates an enable signal 15 to the complex correlator 6, the phase error calculator 10, the frequency error calculator 11, and the demapping unit 12 based on the frame detection signal. Enter the path without.

  FIG. 2 is an explanatory diagram of the main part of the first embodiment of the present invention, showing the function of the threshold & level calculator 20 in FIG. 1, wherein 31 is a power calculator, 32 is a changeover switch circuit, 33, Reference numeral 34 denotes first and second average calculation units constituting the first average calculation means and the second average calculation means, 35 denotes a multiplier constituting the multiplication means, 36 denotes a threshold determination unit, and 37 denotes a third average. A third average calculation unit constituting the calculation means, 38 is a multiplexer, 39 is a multiplexer control circuit, and the multiplexer 38 and the multiplexer control circuit 39 constitute selection means.

  The I and Q signals from the phase error corrector 9 in FIG. 1 are input to the power calculator 31 to obtain the received power, and the pilot signal 19 is switched from the pilot detector 19 as a pilot signal detector. Input to the switch circuit 32, and based on the detection signal of the pilot signal, the output signal of the power calculation unit 31 is input to the first average calculation unit 33 for pilot signals, and the other input to the second average calculation unit 34 Thus, the changeover switch circuit 32 is controlled.

  As shown in the signal point arrangement of FIG. 4B, the pilot signal is a signal point of maximum amplitude 0, 2, A, or 8, and the power calculation unit 31 uses the pilot signal power. By performing the calculation and performing an averaging process for a predetermined period by the first average calculator 23, a signal indicating a reception level corresponding to the 0 signal point of the coordinates (3, 3) of the signal point arrangement is output. In addition, the signal other than the pilot signal is one of 16 signal points in the steady state, so that the power calculation unit 31 calculates the power and the second averaging calculation unit 34 performs the averaging process for a predetermined period. Thus, a signal indicating the reception level of the coordinates (2, 2) of the signal point arrangement is output. This signal indicates the center position of the circle in the level calculation threshold range. Therefore, when the reception level estimated for signals other than the pilot signal is multiplied by 1.5 by the multiplier 35, in a steady state, a value in a circle shown as the level calculation threshold range is shown.

  The threshold value determination unit 36 compares the output signal of the first average calculation unit 33 with the output signal of the multiplier 35, inputs the comparison determination result signal to the multiplexer control circuit 39, and outputs the output signal of the multiplier 35. Is input to the third average calculator 37. When the comparison determination result signal from the threshold determination unit 36 indicates a predetermined range for the difference between the output signal of the first average calculation unit 33 and the output signal of the multiplier 35, the multiplexer control circuit 39 The multiplexer 38 selects the output signal of the third average calculation unit 37 and controls it to be input to the buffer memory 22 and the demapping unit 12. Otherwise, the multiplexer 38 selects the first average The output signal of the arithmetic unit 33 is selected and controlled to be input to the buffer memory 22 and the demapping unit 12. The multiplexer control circuit 39 selects and outputs the output signal of the first average calculator 33 when the channel switching signal is input and in the initial state of power-on. To control.

  Therefore, when the power is turned on or when the channel is switched, the amplitude threshold level is set based on the reception level estimated using a known pilot signal, so that the reception level can be increased and the normal reception state can be obtained. In this case, the estimation accuracy of the reception level can be improved by setting the amplitude threshold level based on the reception level estimated using the known pilot signal and other signals.

  FIG. 3 shows the RSSI characteristics when the power is turned on or when the channel is switched between the embodiment of the present invention and the conventional example. The conventional example uses a signal other than the pilot signal and the pilot signal to set the reception level. In the case of the configuration for obtaining the RSSI shown, as shown by the curve b, the time to fluctuate and converge becomes longer, but the present invention first obtains the RSSI indicating the reception level using a known pilot signal. As shown in a, it is possible to converge in about the time of receiving a known pilot signal 10 times, and thereafter, the reception level is averaged by including a pilot signal and a signal other than the pilot signal. The estimation accuracy can be improved.

  The present invention is not limited to the above-described embodiments. For example, the multi-value number of QAM can be applied to multi-value numbers such as 64 values, 256 values, etc. It is also possible to estimate the reception level including the synchronization word together with the signal. In addition, when including reception level estimation of signals other than pilot signals, the switching is performed according to the determination result by the threshold determination unit 36 described above. However, the control configuration may be switched according to the passage of time from power-on or channel switching. Is possible.

It is explanatory drawing of Example 1 of this invention. It is principal part explanatory drawing of Example 1 of this invention. It is explanatory drawing of the effect of Example 1 of this invention. It is explanatory drawing of an example of a transmission format, signal point arrangement | positioning, and a synchronous word.

Explanation of symbols

1 Band pass filter (BPF)
2 AD converter (ADC)
3 Quadrature detector 4, 5 filter (FIR)
6 complex correlator 7 frame detector 8 AFC rotation corrector 9 phase error corrector 10 phase error calculator 11 frequency error calculator 12 demapping unit 13 frame synchronization monitoring unit 14 operation enable signal generator 15 enable signal 16 filter table 17 Timing corrector 18 Zero cross detector 19 Pilot detector 20 Threshold & level calculator 31 Power calculator 32 Changeover switch circuit 33, 34, 37 Average calculator 35 Multiplier 36 Threshold determiner 38 Multiplexer 39 Multiplexer control circuit

Claims (2)

In a demodulator including means for estimating a reception level of a multi-level quadrature amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point based on the reception level,
First average calculating means for calculating power of a known signal and averaging the power,
A second average calculating means for calculating and averaging the power of signals other than the known signal;
A third average calculating means for multiplying the output signal of the second average calculating means by a coefficient and averaging the output signal of the first average calculating means;
The output signal of the third average calculation means is multiplied by a coefficient and compared with the output signal of the first average calculation means, and when the comparison difference is within a predetermined range, the output signal of the third average calculation means Selecting means for selecting and outputting the output signal of the first average calculating means at other times and outputting it as an estimated value of the reception level. In a demodulator including means for estimating a reception level of a multi-level quadrature amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point based on the reception level,
Pilot detection means for detecting a known pilot signal transmitted at a predetermined period;
First average calculating means for performing an averaging process by calculating the power of the known pilot signal identified by the pilot detecting means;
Second average calculation means for performing power calculation of signals other than the known pilot signal and performing averaging processing;
A third average calculating means for multiplying the output signal of the second average calculating means by a coefficient and averaging the output signal of the first average calculating means;
Multiplication means for multiplying a preset coefficient so as to approximate the output signal of the second average calculation means to the output signal of the first average calculation means;
The output signal of the multiplication means is compared with the output signal of the first average calculation means, and when the comparison difference is within the level calculation threshold range, the output signal of the third average calculation means is selected, otherwise In this case, a demodulating apparatus comprising: selecting means for selecting an output signal of the first average calculating means and outputting it as an estimated value of the reception level.

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