JP2002176411A - Ofdm burst signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OFDM(Orthogonal Frequency Division Multiplex) burst signal receiver that can attain gain control at high-speed with high accuracy so as to establish synchronization with high accuracy. SOLUTION: The OFDM burst signal receiver is provided with an amplifier control section 13 that sets a control variable in response to an output of an integrator 4 to a gain control amplifier 15 on the opportunity of detection of a burst signal to a gain control amplifier 15, a power calculator 24 that detects an output power of an OFDM demodulator 21, a comparator 27 that detects an error between the detected power and a preset reference value, and an amplifier control correction table 18 that corrects the control variable of the gain control amplifier 15 on the basis of the detected error output, and the OFDM burst signal receiver realize gain control at high-speed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an OFDM (Orthogon) used for a digital radio communication system or the like.
al Frequency Division Mul
The present invention relates to a device for receiving a burst signal.

[0002]

2. Description of the Related Art Recently, orthogonal frequency division multiplexing (OF) has been used in mobile digital audio broadcasting and terrestrial digital television broadcasting.
A transmission system using a DM (DM) technique is used. OFD
M is one of the multi-carrier modulation schemes in which a plurality of digitally modulated waves are added. Since data is distributed and transmitted over many carriers, the duration of one symbol is long, and the guard interval is set on the time axis. Addition causes less deterioration in characteristics even in a multipath environment. Combination of appropriate error correction code and interleaving on the frequency axis is resistant to frequency-selective fading. This service has characteristics that the service is not easily disturbed and hardly received, and the band use efficiency is relatively good. Wireless LAN utilizing these features
Etc. are also being used for data transmission.

[0003]

SUMMARY OF THE INVENTION Wireless LAN
In such data transmission, transmission / reception is performed by a burst signal. In order to receive an OFDM burst signal,
It is necessary to establish gain control and OFDM symbol synchronization in a preamble section including a gain control symbol and a symbol synchronization symbol added to the head of a burst signal. As a method of establishing OFDM symbol synchronization,
When the repetition of the synchronization symbol is detected by the self-delay correlation, the received signal must converge to a certain level before the synchronization symbol.

However, in the gain control based on only the signal intensity in the preamble section, high-speed gain control can be realized, but stable gain control cannot be obtained due to variations in components and temperature conditions. Further, when performing gain control by a closed loop, stable control cannot be performed in a synchronization symbol section, and thus there is a problem in the accuracy of synchronization establishment. In such a case, high-speed and high-precision gain control within the gain control symbol section is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an OFDM capable of performing high-speed and high-accuracy gain control and achieving synchronization with high accuracy.
An object of the present invention is to provide a burst signal receiving device.

[0006]

In order to achieve the above object, the present invention provides a gain control amplifier for amplifying a received signal, an OFDM demodulator for demodulating an output signal of the gain control amplifier, and a reception of the received signal. RSSI for detecting the level,
An integrator for integrating the output of the RSSI; a means for detecting a burst signal based on the output of the integrator; and a gain control amplifier for controlling a control value corresponding to the output of the integrator upon detection of the burst signal. Means for detecting the power value of the output of the OFDM demodulator, means for detecting an error between the detected power value and a preset reference value, and based on the detected error. And a correcting means for correcting the control value of the gain control amplifier.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIGS. 1 and 2 are block diagrams showing the configuration of an embodiment of an OFDM burst signal receiving apparatus according to the present invention. The OFDM burst signal receiving apparatus according to the present embodiment mainly includes an amplifier control unit 30 and a reception level error measuring unit 31, and FIG.
0 and FIG. 2 show the reception level error measuring section 31, respectively. First, the configuration of the amplifier control unit will be described with reference to FIG.

In FIG. 1, an amplifier control unit 30 outputs an RSSI (Rec) for outputting a reception level detection signal of an IF band signal.
ieved Signal Strength Ind
icator) 1, an AD converter 2 for performing analog-to-digital conversion of a received signal level detection signal output by the RSSI 1, a sampling clock oscillator 3 for supplying a sampling clock to the AD converter 2, and an output of the AD converter 2 integrated for a certain time An integrator 4 is provided. The integrator 4 is used as a signal level measuring unit that measures the level of the received signal.

The amplifier control section 30 compares the output of the integrator 4 with the output of the noise level measuring section to determine whether or not a signal has been detected. The delay section 6 delays the output of the determination section 5 for a predetermined time. A gate 7 that opens and closes depending on the presence or absence of a signal, a counter 8 that counts the noise level measurement time,
Flip-flop 9 for temporarily holding the output of 0, integrator 4
, An integrator 10 for accumulating the signal level for further averaging, a table ROM 11 for storing a control value of a gain control amplifier 15 corresponding to a reception level, and an initial value for storing an initial value of a control value of the gain control amplifier. Value table 12, an amplifier control unit 13 for controlling a gain control amplifier, I
Step attenuator 14 for attenuating F-band reception signal, gain control amplifier 15 whose gain is controlled by a control value, quasi-synchronous detector 16 for quasi-synchronous detection of the received signal, and converting the quasi-synchronously detected received signal to a digital value And an amplifier control correction table generation unit 18 that generates a correction value for correcting the gain control value stored in the table ROM 11 from the amplifier control correction value input from the reception level error measurement unit 31. .

Next, the configuration of the reception level error measuring section 31 will be described with reference to FIG. In FIG. 2, a reception level error measuring unit 31 includes an OFDM demodulator 21 for demodulating a digitally converted OFDM reception signal, a symbol rate clock oscillator 22 for supplying a symbol rate clock,
A counter 23 for counting the number of symbols for monitoring a data section, a power value calculator 24 for calculating a power value of demodulated data of the OFDM demodulator 21, an integrator 25 for averaging the power value, an averaged power value 26, a reference value table 28 for storing the set optimum reception level, and a comparator 27 for comparing the temporarily held power average value with the reference value to generate an amplifier control correction value.

Here, the amplifier controller 30 controls the step attenuator 14 and the gain control amplifier 15 simultaneously.
When high-speed gain control is required, RSS of IF band signal
An open loop gain control using the I signal level value is employed, but the step attenuator 14 and the gain control amplifier 15
Since there are individual differences and temperature fluctuations, highly accurate gain control cannot be expected.

Therefore, in this embodiment, OFDM
The error of the received power in the demodulator 21 is measured, and the demodulator 2
By correcting the control value of the gain control amplifier 15 so that the received power at 1 becomes constant, high-precision gain control is realized. Step attenuator 14 and gain control amplifier 1
Although there is an individual difference of 5, the gain of the control value of the gain control amplifier 15 needs to be updated at a high speed because the gain fluctuation due to temperature fluctuation is temporally gradual in a steady state in a unique device. Is not effective.

Next, the specific operation of this embodiment will be described with reference to FIG.
This will be described with reference to FIG. First, the amplifier control unit 30 controls the step attenuator 14 and the gain control amplifier 15 to perform high-speed gain control. IF band received signal is a step attenuator 1
4 and input to the RSSI 1 and the gain control amplifier 15. The RSSI 1 detects the reception level of the IF band reception signal, and outputs a voltage signal corresponding to the reception level intensity to the AD converter 2. At this time, the sampling clock is supplied from the sampling clock oscillator 3 to the AD converter 2, and the AD converter 2 samples the voltage signal in synchronization with the sampling clock and converts it into a digital signal. A
The RSSI signal converted into a digital signal by the D converter 2 is integrated for a certain period of time by an integrator (signal level measuring unit) 4 and output as a moving average value.

The decision unit 5 compares the moving average value with a signal detection threshold value obtained by adding a predetermined level to the output level of the noise level measuring unit in advance, and when the moving average value exceeds the signal detection threshold value, the signal is detected. The status signal indicating the state is output to the delay unit 6 and the gate 7. That is, the decision unit 5 functions as a burst signal detection unit, and closes the gate 7 of the noise level measurement unit to interrupt the measurement of the noise level in the signal detection state. The gate 7, the counter 8, the F / F 9, and the integrator 10 are provided as a noise level measuring unit that measures the noise level of the received signal. When the signal is being detected, the gate 7 is turned off to measure the noise level. Absent.

When no signal is detected in the burst signal detecting section, the gate 7 of the noise level measuring section is opened and the output of the integrator 4 which is a signal level measuring section is supplied to the integrator 10. At the same time, a sampling clock is supplied from the sampling clock oscillator 3 to the counter 8,
When the counter 8 counts a predetermined integration time, the value of the flip-flop 9 is updated to the value of the output of the integrator 10. A signal detection threshold obtained by adding a certain level to the signal is output to the decision unit 5, and the decision unit 5 compares the output of the integrator 4 with the signal detection threshold to detect a burst signal. In this case, by setting the initial value of the flip-flop 9 to the maximum value, erroneous detection of the burst signal due to the initial state can be prevented.

When the determiner 5 in the burst signal detector detects a burst signal, a status signal indicating a burst signal detection state is output to the delay unit 6. The delay unit 6 delays the status signal by the signal level measurement time and outputs the status signal to the table ROM 11 and the amplifier control unit 13. The status signal is delayed after the burst signal is detected.
This is to wait until the burst signal level is stabilized.
The control value of the gain control amplifier 15 corresponding to the signal level of the integrator 4 is stored in the table ROM 11, and the amplifier control section 13 detects the burst signal from the table ROM 11 (when the status signal of the delay unit 6 is output). The control value corresponding to the signal level of the integrator 4 is read and output to the gain control amplifier 15. Further, the amplifier control unit 13 generates a control value of the step attenuator 14 corresponding to the signal level, and outputs the control value to the step attenuator 14.

Here, the amplifier control correction table generator 1
Reference numeral 8 samples a signal level averaged by the integrator 4 for a preset error measurement time and an amplifier control correction value from a reception level measurement unit 31 described later, and stores them in association with each other. When the error measurement time elapses, the amplifier control correction table generator 18 corrects the control value of the gain control amplifier 15 using the output of the integrator 4 and the amplifier control correction value obtained earlier. For example, it is assumed that the output of the integrator 4 and the output of the comparator 27 of the reception level error measuring unit 31 are obtained as follows.

[0018] FIG. 3 is a diagram showing this in a graph. The amplifier control correction table generator 18 divides the output of the integrator 4 into sections of 10, 11, 20, 21, 30 and 31 as shown in FIG. 3 and averages the output values of the comparator 27 in each section. And take it as the correction value. Although the number of samples is not small in FIG. 3 for convenience of explanation, it is desirable to increase the number of samples as much as possible because the accuracy increases as the number of samples increases. Assuming that a sample has been taken in this way, for example, if a signal of “15” is next input from the output of the integrator 4, the amplifier control correction table generator 18 uses the correction value of the section corresponding to the signal. The control value of the gain control amplifier 15 is corrected.

In this case, since the signal of the integrator 4 is "15", the correction values in the sections 11 to 20 in FIG.
Correction is made using -2 + 0 + 4) /4=1.25. As described above, the amplifier control correction table generation unit 18 uses the correction value according to the reception level of the integrator 4 to
Is corrected by the gain control amplifier 15, and the signal is amplified by the corrected control value and output to the quasi-synchronous detector 16. The quasi-synchronous detector 16 performs quasi-synchronous detection on the amplifier output, converts the output to a baseband signal, and samples the digital signal by the AD converter 17. This digital signal is demodulated by the OFDM demodulator 21 in FIG. 2, and demodulated data is output.

Next, the operation of the reception level error measuring section 31 shown in FIG. First, since the gain control amplifier 15 in FIG. 1 has not been corrected, it is assumed that the gain control amplifier 15 is controlled by the control value from the amplifier control unit 13 as described above. In this state, the IF band received signal is transmitted through the step attenuator 14 and the gain control amplifier 15 to the quasi-synchronous detection circuit 1.
6 and converted into a baseband signal by the quasi-synchronous detection circuit 16 as described above, then sampled by the AD converter 17 into a digital signal, and the reception level error measurement unit 31
Is supplied to the OFDM demodulator 21 in the above. An amplifier control value error measurement unit is provided in the reception level error measurement unit 31,
Using the demodulated data output from the OFDM demodulator 21, the reception power level of the demodulator 21 is calculated, and the demodulator 21 and an error correction unit (not shown) at the subsequent stage measure an error from the optimum reference level, and Outputs the control correction value.

More specifically, the digitized received signal is demodulated by an OFDM demodulator 21. At this time, the symbol clock is turned off by the symbol clock oscillator 22.
It is supplied to the DM demodulator 21 and the counter 23,
The valid data section of the burst signal is monitored by counting the symbol clock at 3. In this valid data section, the power value calculator 24 calculates the power value of the demodulated data output from the OFDM demodulator 21 and the integrator 25 averages the power values. When the end of the valid data section is detected by the counter 23, the power value of the demodulated data averaged by the integrator 25 is held in the flip-flop 26.
The comparator 27 detects a difference between the power value of the flip-flop 26 and the optimum reference level set in the reference value table 28, converts the difference into an amplifier control correction value, and outputs the result to the amplifier control correction table generator 18. The optimum reference level in the reference value table 28 is set to a value such that the output of the OFDM demodulator 21 becomes the optimum level.

The amplifier control correction table generator 18 corrects the control value of the gain control amplifier 15 using the amplifier control correction value from the reception level error measuring unit 31 and the reception level from the integrator 4 as described above. . In the present embodiment, OF
An error between the received power of the demodulated data of the DM demodulator 21 and the optimum reference level is detected, and the detected error is used for the OFDM demodulator 21.
Since the control value of the gain control amplifier 15 is corrected so that the received power becomes constant, high-precision gain control can be realized. When the burst signal ends, a burst end signal is output from the OFDM demodulator 21 and supplied to the amplifier control unit 13. Upon receiving the burst end signal, the amplifier control unit 13 sets the initial value of the control value stored in the initial value table 12 to the gain control amplifier 15 and sets a state in which no signal is output.

[0023]

As described above, according to the present invention, an error between the received power of demodulated data and a reference value is detected, and the control value of the gain control amplifier is corrected based on the obtained error. Feedback is applied for the error, and the received power in the demodulator can be controlled to be constant.It can follow errors due to individual differences with little change in time and fluctuations due to temperature characteristics that change slowly in time. Gain control can be performed. Further, since the gain is controlled in response to the reception level detected by the RSSI triggered by the detection of the burst signal, high-speed gain control is performed at the head of the OFDM modulated wave burst signal for a reception signal having a large dynamic range. It can be carried out. Therefore,
High-speed and high-accuracy gain control can be performed within the gain control symbol section, and synchronization can be established with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of an amplifier control unit of an OFDM burst signal receiving device according to the present invention.

FIG. 2 is a block diagram illustrating a reception level error measuring unit of the OFDM burst signal receiving apparatus of FIG. 1;

FIG. 3 is a diagram for explaining a correction operation of an amplifier control correction table generation unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 RSSI 2 AD converter 3 Sampling clock generator 4 Integrator 5 Judge 6 Delayer 7 Gate 8 Counter 9 Flip-flop 10 Integrator 11 Table ROM 12 Initial value table 13 Amplifier control unit 14 Step attenuator 15 Gain control amplifier 16 Quasi-synchronous detector 17 AD converter 18 Amplifier control correction table generator 21 OFDM demodulator 22 Symbol clock oscillator 23 Counter 24 Power calculator 25 Integrator 26 Flip-flop 27 Comparator 28 Reference value table 30 Amplifier controller 31 Receive level Error measurement section

Claims (6)

[Claims] A gain control amplifier for amplifying a received signal;
An OFDM demodulator for demodulating an output signal of the gain control amplifier, and an RSSI for detecting a reception level of the reception signal
An integrator for integrating the output of the RSSI, a means for detecting a burst signal based on the output of the integrator, and a control value corresponding to the output of the integrator triggered by the detection of the burst signal. Means for setting the control amplifier;
Means for detecting the power value of the output of the OFDM demodulator;
An OFDM comprising: means for detecting an error between a detected power value and a preset reference value; and correction means for correcting a control value of the gain control amplifier based on the detected error. Burst signal receiving device. 2. The correction means samples the output of the integrator and the output of the error detection means in correspondence with a predetermined measurement time, divides the output of the integrator into a plurality of sections, and calculates an error in each section. The average value of the output of the detection means is used as a correction value,
2. The OFDM burst signal receiving apparatus according to claim 1, wherein the control value of the gain control amplifier is corrected using a correction value in a section corresponding to an output of the integrator. 3. The control circuit according to claim 1, wherein said control value setting means sets a control value in said gain control amplifier a predetermined time after said burst signal is detected.
FDM burst signal receiving device. 4. The control value setting means refers to a table in which the output of the integrator and the control value of the gain control amplifier are stored in association with each other, and controls the control value corresponding to the output of the integrator by the gain control. The OFDM burst signal receiving device according to claim 1, wherein the OFDM burst signal receiving device is set in an amplifier. 5. The burst signal detecting means compares the output of the integrator with a signal detection threshold, and detects a burst signal when the output of the integrator exceeds a signal detection threshold. The OFDM burst signal receiving device according to claim 1, wherein: 6. A step attenuator in series with the gain control amplifier, wherein the control value setting means sets a control value corresponding to an output of the integrator in the step attenuator. The OFDM burst signal receiving device according to claim 1.