JP2009033380A - Demodulator and demodulating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a demodulator and a demodulating method capable of estimating a receiving level with high accuracy and at a high speed. <P>SOLUTION: The demodulator including means for estimating the receiving level of a multivalued orthogonal amplitude modulation signal and setting an amplitude threshold level for identifying a modulation signal point on the basis of the receiving level is provided with first equalizing means for calculating the power of a known signal to equalize the power; discriminating means for calculating the power about a signal other than the known signal and discriminating a signal in which the calculated power is included in a prescribed range; second equalizing means for selectively equalizing the signal discriminated by the discriminating means; third equalizing means for equalizing an output signal obtained from the first equalizing means and an output signal obtained from the second equalizing means; and selecting means for selecting an output of the third equalizing means as an estimated value of a receiving level when the discriminating means discriminates the signal, and selecting the output of the first equalizing means as an estimated value of the receiving level in other cases. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a demodulation device and a demodulation method for receiving and demodulating a multilevel quadrature amplitude modulation signal in a wireless communication system.

  As a modulation method in a wireless communication system, a multi-level quadrature modulation (QAM) method in which quadrature phase modulation and amplitude modulation are combined is known. 256 values and the like have been put into practical use.

  In an example of the transmission format of the wireless communication system shown in FIG. 4A, a frame is composed of a Ramp corresponding to the first preamble, a known signal SW that follows this, and an information field that follows it. Has been. In 16QAM with 16 multilevel values, 16 signal points are arranged as shown in FIG.

  The above-described known signal SW is a synchronization word having a known pattern as shown in FIG. 4C. For example, each symbol constituting the synchronization word (in the case of 10 symbols, SW1 to SW10). ) Are assigned signal points 0, 8, and A (see FIG. 4B) indicating the maximum amplitude values.

  In FIG. 4B, the signal point indicating the maximum amplitude value obtained by adding signal point 2 to signal points 0, 8 and A described above corresponds to the intersection of I = ± 3 and Q = ± 3. 4 (B) is a point on the circumference indicated by a dotted line. Also, pilot signals (indicated by arrows in FIG. 4 (A)) inserted at predetermined intervals in the information field shown in FIG. 4 (A) are signal points 0, 2, 8 indicating the maximum amplitude values described above. , A is assigned.

  Therefore, the reception level can be estimated by detecting the synchronization word SW and the pilot signal described above. Based on the estimated reception level, amplitude threshold levels (indicated by broken lines in FIG. 4B) corresponding to 0 level and ± 2 levels on the I and Q axes are set, and the amplitude threshold level and signal level are set. And the decoded data corresponding to the signal point position can be obtained.

Also, in the mobile station of the mobile radio communication system to which 16QAM is applied, the power ratio information between the data channel and the pilot channel is transmitted from the base station through the control channel, and the mobile station performs demodulation based on this power ratio information. A configuration for performing signal point identification is known. Also, without transmitting power ratio information by the control channel from the base station, the mobile station calculates the power ratio between the received pilot signal and data signal, and based on this power ratio, identifies the signal point at the time of demodulation. A demodulating device that performs this has also been proposed (see, for example, Patent Document 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. This is because the wireless communication system has a larger reception level fluctuation than the wired communication system, and therefore, the amplitude threshold level setting for reception decoding is obtained by estimating the reception level as described above.

  As a method for estimating the reception level, a method of using both a synchronization word and a pilot signal, which are known signals, is generally used, but in order to simplify the processing, either one of them may be used. Is possible. In addition to the known signals (synchronization word and pilot signal) described above, it is also possible to estimate reception levels for other signals.

  Regardless of which method is used, averaging processing over a predetermined period is necessary to maintain the estimation accuracy of the reception level. In particular, when the received signal level is estimated using all known signals and other signals, it is expected to improve the received level estimation accuracy, but it is necessary to lengthen the period of the averaging process. On the other hand, when the reception level is estimated using only known signals, although the period required for the averaging process is relatively short, the reception level estimation accuracy may be reduced.

  An object of the present invention is to provide a demodulation device and a demodulation method capable of estimating a reception level with high accuracy and high speed.

  A first demodulating device according to the present invention is a demodulating device 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. A first averaging unit that calculates and averages the power of a known signal and a determination that performs power calculation on a signal other than the known signal and discriminates a signal in which the calculated power is included in a predetermined range Means, a second averaging means for selectively averaging the signals discriminated by the discrimination means, an output signal obtained from the first averaging means, and an output obtained from the second averaging means A third averaging unit that performs an averaging process on the signal, and when the signal is discriminated by the discriminating unit, the output of the third averaging unit is selected as an estimated value of the reception level; In addition, The output of the serial first averaging means and selecting means for selecting as an estimate of the received level.

  In the first demodulator configured as described above, the discrimination unit discriminates, for example, a signal having a predetermined range of power including the power value of the known signal, and the second averaging unit selects the power. Averaged. By supplying the average value obtained by the second averaging means together with the average value obtained for the known signal by the first averaging means to the processing of the third averaging means, Both of the power of the signal appropriately selected from signals other than the known signal can be reflected in the estimated value of the reception level, and can be replaced with the estimated value based only on the power of the known signal according to the determination result by the determining means. .

  In this way, a signal other than a known signal whose amplitude value is known in advance is received by narrowing down the signal to be averaged into an appropriate range based on the power in the second averaging means. It is possible to shorten the time required for converging the average value required for use in level estimation. As a result, it is possible to achieve both improvement in estimation accuracy by using a signal other than a known signal for estimation of the reception level and speeding up of the estimation process.

  According to a second demodulating device of the present invention, in the first demodulating device described above, the first averaging means includes a detecting means for detecting a known pilot signal transmitted at a predetermined period as a known signal. And calculating means for calculating power for the pilot signal detected by the detecting means and executing an averaging operation, wherein the determining means is based on the power value of the pilot signal obtained by the calculating means or the average value thereof. And setting means for setting a discrimination range for discriminating a signal to be subjected to the averaging process by the second averaging means.

  In the second demodulator configured as described above, the pilot signal detected by the detection unit is subjected to power calculation processing and averaging calculation processing by the calculation unit, and reception based on the pilot signal is performed by the first averaging unit. An estimate of the level is obtained. Also, the signal point indicating the maximum amplitude value from signals other than the pilot signal by reflecting the power value of the pilot signal obtained in the process of the calculation means or the average value thereof in the discrimination range set by the setting means. Can be determined with high accuracy and used for the processing of the second averaging means.

  A demodulation method according to the present invention is a known demodulation method 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. The signal power is calculated and averaged to obtain the first average value, the power is calculated for signals other than the known signal, and the signal in which the calculated power is included in the predetermined range is determined. A signal is selectively averaged to obtain a second average value, the first average value and the second average value are averaged to obtain a third average value, and the signal is determined according to the determination of the signal The third average value is selected as the estimated value of the reception level, and in other cases, the first average value is selected as the estimated value of the reception level.

  In the demodulation method thus configured, for example, a second average value obtained by discriminating a signal having a predetermined range of power including the power value of a known signal and selectively averaging the power, It is possible to obtain a third average value reflecting signal power other than the known signal by averaging the first average value obtained for the known signal and select this as an estimated value of the reception level. it can.

  When obtaining the above-mentioned second average value, the time required to converge the average value can be shortened by narrowing down the signal to be averaged into an appropriate range based on the power. As a result, it is possible to achieve both improvement in estimation accuracy by using a signal other than a known signal for estimation of the reception level and speeding up of the estimation process.

  According to the demodulating apparatus and the demodulating method according to the present invention, it is possible to achieve both improvement in estimation accuracy by using a signal other than a known signal for estimation of the reception level and speeding up of the estimation process. As a result, it is possible to follow the fluctuation of the reception level due to fading and the like, and to set the amplitude threshold level for identifying the modulation signal point of the multilevel quadrature amplitude modulation signal at high speed and precisely. Accurate autonomous power control can be realized.

  FIG. 1 shows a configuration diagram of a demodulated signal processing apparatus according to the present invention. FIG. 2 shows the detailed configuration of the main part of the demodulator according to the present invention. Further, FIG. 3 shows an explanatory diagram of the reception level estimation processing according to the present invention.

  A radio frequency reception signal is converted into an intermediate frequency signal IF by a radio reception unit (not shown), and is input to an analog / digital converter (ADC) 2 through a band pass filter (BPF) 1. Converted to a signal.

  The I and Q signals obtained by inputting this digital signal to the quadrature detection unit 3 are input to the complex correlator 6 through the filters 4 and 5, respectively, and are used for correlation calculation for detecting the synchronization word (SW). Is done. The frame detection unit 7 shown in FIG. 1 detects the head of the frame based on the correlation calculation result by the complex correlator 6, and uses the detection signal as the clock regenerator 21, the frame synchronization monitoring unit 13, and the operation enable signal generation unit. 14 and send it out.

  Further, the I and Q signals that have passed through the filters 4 and 5 described above are input to the demapping unit 12 through correction processing for frequency and phase errors by the AFC correction unit 8 and used for identification processing of modulation signal points. . For the identification process of the modulation signal point by the demapping unit 12, an amplitude threshold level obtained by the threshold & level calculator 20 as described later is used. The decoded data obtained by the demapping unit 12 is output as a decoded output via the FIFO 23 and used for processing of a received signal processing unit (not shown).

  The write / read processing of the FIFO 23 is performed according to the write enable signal (WE) generated by the demapping unit 12 and the read enable signal (RE) generated by the clock regenerator 21 described above. The operations of the demapping unit 12, the complex correlator 6 and the AFC correction unit 8 described above are controlled according to the operation enable signal generated by the operation enable signal generation unit 14. The decoded data described above is also input to the frame synchronization monitoring unit 13, and a frame synchronization monitoring process based on the detection signal obtained by the frame detector 7 and the decoded data is performed. When frame synchronization loss is detected by this frame synchronization monitoring process, a reset signal is generated by the frame synchronization monitoring unit 13, and the frame detection process by the frame detector 7 is resumed accordingly.

  Further, the zero cross detector 18 shown in FIG. 1 detects the sign inversion point between the previous symbol and the current symbol by using the pattern effect of the I signal subjected to the correction processing by the AFC correction unit 8 described above, The timing corrector 17 uses the random walk filter to achieve timing synchronization with the transmission side. Corresponding to the zero cross point detected by the zero cross detector 18, an appropriate filter coefficient is read from the filter table 16, and the characteristics of the filters 4 and 5 are controlled according to the filter coefficient.

  In FIG. 1, the I and Q signals that have been subjected to the correction processing by the AFC correction unit 8 described above are also input to the pilot detector 19, and the pilot detector 19 provides information as shown in FIG. A known pilot signal inserted in the field at a predetermined period is detected. A pilot detection signal obtained by the pilot detection unit 19 shown in FIG. 1 is input to the frame detector 7 and also input to the threshold & level calculator 20, and the reception level of the threshold & level calculator 20 is determined. It is used for estimation processing and amplitude threshold level calculation processing.

  In addition, RSSI (Received Signal Strength Indicator) obtained by the threshold & level calculator 20 shown in FIG. It is read in accordance with a read enable signal (RE) generated by the regenerator 21 and passed to a received signal processing unit (not shown).

  The quadrature detection unit 3, the filters 4, 5, the complex correlator 6, the frame detector 7, the AFC correction unit 8, the demapping unit 12, the frame synchronization monitoring unit 13, the operation enable signal generator 14, and the filter table shown in FIG. 16, timing corrector 17, zero cross detector 18, pilot detector 19 and threshold & level calculator 20 can be realized by DSP (Digital Signal Processor) firmware. The functions of these units can also be realized by a digital signal processing circuit.

  Hereinafter, the configuration and operation of the main part of the demodulator according to the present invention will be described in detail.

  In the threshold & level calculator 20 shown in FIG. 2, the power calculation unit 31 obtains received power based on the I and Q signals output from the AFC correction unit 8, and averages the pilot signal via the switch circuit 32. The data is sent to either the calculation unit 33 or the average calculation unit 34 for other data signals.

  The switch circuit 32 shown in FIG. 2 connects the power calculation unit 31 and the average calculation unit 33 when the detection signal from the pilot detector 19 indicates that the pilot signal has been detected. In this case, the power calculation unit 31 and the average calculation unit 34 are connected via the threshold value determination unit 35.

  Therefore, the power value calculated by the power calculation unit 31 corresponding to the pilot signal is input to the average calculation unit 33 via the switch circuit 32 and is subjected to an averaging process over a predetermined period. The reception level corresponding to the zero signal point of the coordinates (3, 3) of the signal point arrangement shown is calculated. That is, the switching circuit 32 is switched by the detection signal from the pilot detector 19 corresponding to the detection means, and the output of the power calculation unit 31 obtained corresponding to the pilot signal is averaged by the average calculation unit 33 corresponding to the calculation means. By serving, the function of the first averaging means according to the present invention is fulfilled.

  On the other hand, the power value calculated by the power calculation unit 31 corresponding to a signal other than the pilot signal is input to the threshold value determination unit 35 and corresponds to the range indicated by shading in FIG. 3, that is, the maximum amplitude value. A power value corresponding to a signal included in a range in which the signals of signal points 0, 8, A, and 2 are highly likely to be distributed is determined. The power value discriminated in this way is selectively inputted to the average calculation unit 34 and subjected to the averaging process over a predetermined period, whereby the coordinates (3, 3) of the signal point arrangement shown in FIG. The reception level corresponding to the zero signal point is calculated. That is, the switch circuit 32 is switched by a detection signal from the pilot detector 19 and the output of the power calculation unit 31 obtained in response to a signal other than the pilot signal is subjected to a determination process by the threshold determination unit 35. The function of the discriminating means concerned is fulfilled. In particular, the threshold discriminating unit 35 is set to perform discrimination based on the above-described range (see FIG. 3) with reference to the average value of the pilot signal power values obtained by the average calculating unit 33. The function of the setting means according to the invention is fulfilled, the power value calculated for the signal corresponding to the maximum amplitude value is discriminated with high accuracy, and the average by the average calculating unit 34 corresponding to the second averaging means is selectively used. It can be used for the chemical treatment.

  In FIG. 2, the outputs of the above-described two average calculation units 33 and 34 are input to an average calculation unit 36 corresponding to a third averaging unit, and are averaged over a predetermined period. The average value obtained by the average calculation unit 36 is input to the multiplexer 37 together with the average value for the power value of the pilot signal obtained by the average calculation unit 33 described above, and according to the control signal from the multiplexer control circuit 38. , Either one is selectively output and input to the FIFO 22.

  The multiplexer control circuit 38 shown in FIG. 2 indicates that the multiplexer 37 selects the output of the average calculation unit 36 in response to the determination signal that the threshold value determination unit 35 has determined the power value included in the above-described range. Instructs to select the output of the average calculation unit 33 in other cases. In this way, the multiplexer control circuit 38 controls the switching of the multiplexer 37 in accordance with the determination signal from the threshold determination unit 35, thereby fulfilling the function of the selection means according to the present invention.

  In this way, in response to reception of a data signal having an amplitude value equivalent to that of the pilot signal, a reception level that reflects both the power of the data signal and the power of the pilot signal is calculated to obtain an estimated value of the reception level. By doing so, it is possible to improve the estimation accuracy of the reception level.

  Note that the multiplexer control unit 38 controls the multiplexer 37 so as to select and output the output of the average calculation unit 33 when the channel switching signal is input and in the initial state of power-on.

  Here, the power value corresponding to the signal point corresponding to the maximum amplitude value is selectively input to the above-described average calculation unit 34 by the threshold discrimination unit 35. Therefore, since the variation in the power value input to the average calculation unit 34 is as small as the power value input to the average calculation unit 33 for pilot signals, the averaging processing period performed in the average calculation unit 34 is averaged. By shortening the period to the extent applicable to the arithmetic unit 33, it is possible to speed up the reception level estimation process using a signal other than a known signal such as a pilot signal.

  Accordingly, in the embodiment according to the present invention shown in FIGS. 1 and 2, when the power is turned on or when the channel is switched, the reception level is estimated at high speed based only on the pilot signal, and in the steady state, the data signal other than the pilot signal is estimated. It is possible to achieve high-accuracy reception level estimation using both the power value of the pilot signal and the power value of the pilot signal with the same high speed as the reception level estimation processing based only on the pilot signal.

  Note that the present invention is not limited only to the above-described embodiments, and can be applied to, for example, a QAM demodulator having a multi-value number of 64 values, 256 values, or the like. Further, as a known signal, it is possible to estimate the reception level by including a synchronization word in addition to the pilot signal described above.

  As described above, according to the demodulation device and the demodulation method according to the present invention, the reception level estimation process using a signal other than a known signal such as a pilot signal is accelerated, thereby increasing the reception level estimation process. And high accuracy can be achieved at the same time. As a result, for example, autonomous power control in a mobile station of a mobile radio communication system can be performed more accurately, which greatly contributes to fields such as interference wave suppression technology of a digital communication system.

It is a figure which shows embodiment of the demodulation apparatus concerning this invention. It is a figure which shows the detailed structure of the principal part of the demodulation apparatus concerning this invention. It is explanatory drawing of the reception level estimation process concerning this invention. It is a figure which shows an example of a transmission format, signal point arrangement | positioning, and a synchronization 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 Correction Unit 12 Demapping Unit 13 Frame Synchronization Monitoring Unit 14 Operation Enable Signal Generation Unit 16 Filter Table 17 Timing Corrector 18 Zero Cross Detector 19 Pilot Detector 20 Threshold & Level Calculator 21 Clock Regenerator 22, 23 FIFO
31 Power Calculation Unit 32 Switch Circuits 33, 34, 36 Average Calculation Unit 35 Threshold Determination Unit 37 Multiplexer 38 Multiplexer Control Circuit

Claims (3)

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 averaging means for calculating and averaging the power of known signals;
Determining means for performing power calculation on a signal other than the known signal and determining a signal in which the calculated power is included in a predetermined range;
Second averaging means for selectively averaging signals determined by the determination means;
Third averaging means for performing an averaging process on the output signal obtained from the first averaging means and the output signal obtained from the second averaging means;
When the signal is discriminated by the discriminating means, the output of the third averaging means is selected as an estimated value of the reception level. In other cases, the output of the first averaging means is set to the reception level. A demodulating device comprising: selecting means for selecting an estimated value. The demodulator according to claim 1, wherein
The first averaging means includes
Detecting means for detecting a known pilot signal transmitted at a predetermined period as a known signal;
Computation means for performing power calculation on the pilot signal detected by the detection means and performing an averaging computation,
The discriminating unit is configured to set a discriminating range for discriminating a signal to be subjected to the averaging process by the second averaging unit based on the power value of the pilot signal obtained by the arithmetic unit or the average value thereof. A demodulating device comprising means. In a demodulation method 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,
Calculate and average the power of the known signal to obtain the first average value,
Power calculation is performed for signals other than the known signal, and a signal in which the calculated power is included in a predetermined range is determined.
Selectively averaging the determined signals to obtain a second average value;
Average the first average value and the second average value to obtain a third average value,
The third average value is selected as an estimated value of the reception level in accordance with the discrimination of the signal, and in other cases, the first average value is selected as the estimated value of the reception level. Method.

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