JP2963895B1 - Orthogonal frequency division multiplex receiver - Google Patents

Abstract

A discrete Fourier transform time window is set at an optimum position in accordance with the state of occurrence of a ghost signal observed at a reception point. SOLUTION: An impulse response detection circuit detects an impulse response of a transmission line from a received signal, thereby detecting a state of occurrence of a delayed wave in the transmission line. next,
The position of the time window for performing the discrete Fourier transform for demodulating the OFDM by the time window position control signal generation circuit 15 is represented by
A control signal for controlling according to the content of the impulse response is generated. The discrete Fourier transformer 13 performs a discrete Fourier transform at a time window position on a time axis controlled by the control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiving apparatus, and more particularly, to an orthogonal frequency division multiplexing / modulating / demodulating system (O / O).
(FDM system).

[0002]

2. Description of the Related Art At present, a system using orthogonal frequency division multiplexing (OFDM) technology is being studied as a transmission system for digital terrestrial broadcasting. OFDM is a type of multi-carrier modulation scheme, and transmits digital information using a number of carriers that are orthogonal to each other for each symbol. In OFDM, since digital information is transmitted by dispersing it into a large number of carriers, the symbol length is longer than in the single carrier system, and is less susceptible to delayed waves (ghost in broadcasting) such as multipath. There is.

[0003] As shown in FIG. 7, a transmission symbol of OFDM includes an effective symbol period and a period called a guard interval. An effective symbol period is a signal period substantially required for data transmission. The guard interval is a redundant signal period for reducing the influence of multipath, and is a cyclically repeated signal waveform in an effective symbol period.

FIG. 8 shows a schematic configuration of an OFDM modem. The modulation and demodulation processing of OFDM is performed by a discrete Fourier transform (Di
This can be performed by using a Fourier Transform (FFT) or a Fast Fourier Transform (FFT).

[0005] First, in the transmitting apparatus A, binary transmission data is divided into data blocks each having a certain number of bits, and each data block is input after being converted into one complex value. Then, in the serial / parallel converter A1, one complex value Ci (i = 1) for each carrier frequency.
.. N), and the inverse discrete Fourier transform circuit A2 performs inverse discrete Fourier transform on the time axis. Thus, a sample value of the time axis waveform is generated, and a temporally continuous baseband analog signal waveform is obtained from the sample value sequence.
The baseband analog signal waveform is converted to a transmission frequency by the frequency converter A3 and transmitted.

In the receiving apparatus B, the received signal is frequency-converted by the frequency converter B1 to obtain a baseband signal waveform, and then sampled at the same sample rate as the transmitting side. Then, this sample value sequence is converted to a discrete Fourier transform circuit unit B.
2, a discrete Fourier transform is performed on the frequency axis, the phase and the amplitude of each carrier frequency component are calculated to obtain the value of the received data, and the parallel-to-serial converter B3 converts the data into serial and outputs it.

Here, in receiving apparatus B, a time window (FFT windo) having the same length as the effective symbol period is included in the entire symbol period including the effective symbol period and the guard interval.
w), and the signal contained in this time window is set to 2
ⁿ (n is a positive integer) by discrete Fourier transform by sampling times, performs OFDM demodulation processing.

[0008] The position of the above-mentioned time window is usually set to a position which is least affected by the delay wave in consideration of the delay time distribution of the delay wave generated on the transmission path. For example, considering a terrestrial digital broadcasting system, the delay time of most ghost signals generated in a service area is -5.
In the case of taking a value in the range from μs to 20 μs, as shown in FIG. 9, the guard interval length is set to 25 μs, and a time window is allocated at a position where 20 μs is allocated before the time window and 5 μs is allocated after the time window. If set, the influence of inter-symbol interference due to a delayed wave can be minimized. Here, the inter-symbol interference is a phenomenon in which a signal component of an adjacent symbol enters a discrete Fourier transform time window of a receiving device by adding a delayed wave to a desired wave.

As described above, conventionally, the delay time distribution of the delay wave generated on the transmission line is estimated, the range of the delay time including most of the delay waves is determined, and the delay time within the range is determined. The position of the time window is fixedly set at a fixed position such that the intersymbol interference does not occur depending on the delayed wave having.

[0010]

In the case of terrestrial broadcasting, when the entire service area is covered only by the radio wave of one transmitting station as in the prior art, the signal received by most of the receivers in the service area is not sufficient. Is the sum of the direct wave and the delayed wave (so-called natural ghost) that arrives after the transmitted wave is reflected on a building or a mountain. In this case, there is no received wave (so-called pre-ghost) arriving earlier than the desired wave (arriving wave with the highest level), or
Or, if present, it will be a small percentage of all incoming waves. When a previous ghost exists, the absolute value of the delay time (negative value) is, for example, 2 to 3 μs in an urban area.
It is a small value such as degree.

Therefore, when such a conventional station setting method is employed, as shown in FIG. 9, a guard of about several μs corresponding to the absolute value of the delay time of the previous ghost is provided at the rear end of the entire symbol length. By allocating the interval period and allocating the remaining guard interval period before the time window and setting the position of the time window for the discrete Fourier transform of the receiver fixedly, the effect of the guard interval can be sufficiently achieved. I got it.

On the other hand, in terrestrial digital broadcasting using OFDM, as shown in FIG. 10, a single frequency network (Single Frequency Network) that covers a service area using a plurality of transmission stations having the same transmission frequency. N
etwork: hereinafter abbreviated as SFN). SFN
In, broadcast waves having the same contents are transmitted at the same frequency from each transmitting station, and a receiver in the service area receives the sum of broadcast waves transmitted from a plurality of transmitting stations. Therefore, the received signal includes an incoming wave from a transmitting station other than the desired wave transmitting station, in addition to a reflected wave and a desired wave from a building or a mountain. Therefore, as compared with the case where the entire service area is covered by only the radio wave of one transmitting station using the conventional station setting method, the number of arriving waves having a long delay time increases.

Further, in order to receive the sum of arriving waves from a plurality of transmitting stations, the radio wave from the transmitting station closest to the receiving point in terms of distance is affected by the influence of the terrain and buildings, and the desired wave (having the highest level) is obtained. (Arriving wave) in many cases. In this case, a part of the arriving wave from a transmitting station other than the desired wave transmitting station becomes a pre-ghost having a relatively large level and a long delay time (the absolute value of the delay time is large). Therefore, a pre-ghost with a long delay time is more likely to occur in the service area than in the conventional station setting method.

FIG. 11 shows an example of a typical delay profile for each of the conventional station setting method and SFN.
11A shows an example of a typical delay profile in a conventional station setting method, and FIG.
N shows a case where an incoming wave A is detected as a desired wave as a typical delay profile example 1 in N, and FIG.
As a typical delay profile example 2 for N, a case where an incoming wave B is detected as a desired wave is shown.

Referring to FIGS. 11B and 11C, when the sum of a plurality of arriving waves is received in the SFN service area,
Received wave with a negative delay time (pre-ghost) depending on which incoming wave is detected as the desired wave by the receiver
It can be seen that the ratio of the received wave (post-ghost) having a positive value greatly changes.

That is, in SFN, as compared with the conventional station setting method, the distribution range of the delay time of the received wave (minimum delay time) depends on the surrounding terrain and the condition of the building for each reception point in the service area. Value and the maximum value) are considered to change greatly. Therefore, using the above-described method of setting the guard interval in the conventional station setting method, several μs of the guard interval is fixedly allocated to alleviate the influence of the front ghost, and the remaining part of the guard interval is set later. If allocation is fixedly performed to mitigate the effect of ghost, it is considered that the ratio of reception points that are greatly affected by inter-symbol interference in SFN is greatly increased as compared with the case of the conventional station setting method.

Therefore, the present invention solves the above problems,
Depending on the state of occurrence of the ghost signal observed at the receiving point,
It is an object of the present invention to provide an OFDM receiver capable of setting a time window for discrete Fourier transform at an optimal position, thereby improving reception quality.

[0018]

Means for Solving the Problems To solve the above problems, an OFDM receiving apparatus according to the present invention is configured as follows.

(1) An orthogonal frequency division multiplexing system receiving apparatus for receiving a signal including a transmission symbol modulated by the OFDM system and demodulating the OFDM reception signal.
Discrete Fourier transform means for performing OFDM demodulation by performing a discrete Fourier transform on a DM reception signal in accordance with a position of a time window defining a range on a time axis, and a delay for detecting a generation state of a delay wave included in the OFDM reception signal Wave generation state detection means, and time window position control means for controlling a position of a time window of the discrete Fourier transform means based on the delay wave generation state detected by this means , wherein the delay wave generation state
The detecting means detects the transmission path impulse from the OFDM reception signal.
The delay contained in the received signal by detecting the
Equipped with an impulse response detection circuit to detect the wave generation situation
The time window position control means is configured to detect the impulse response.
The discrete signal according to the impulse response detected by the output circuit.
The position of the time window of the
OFDM determined by the symbol synchronization reproduced on the receiving side
Transmission symbol switching position and transmission path impulse response
The position of the peak point that gives the maximum level matches on the time axis
So that the OFDM transmission symbol sequence and the transmission path
When the impulse response is drawn,
A decibel (A is a certain one) from the maximum level of the impulse response.
Threshold) and set the threshold to a smaller level
The impulse response component of a level higher than the
Set the time window at a position that does not enter the time window where the
Shall be set. (2) Including transmission symbols modulated by OFDM
Orthogonal signal for receiving a received signal and demodulating the OFDM received signal.
In the wave number division multiplex receiver, the OFDM reception is performed.
Depending on the position of the time window that defines the range on the time axis, the signal
Discrete OFDM demodulation by discrete Fourier transform
Fourier transform means, included in the OFDM reception signal
Delay wave generation status detection means for detecting the generation status of delay waves
And based on the delayed wave generation situation detected by this means,
Time to control the position of the time window of the discrete Fourier transform means
Window position control means;
The stage responds to the impulse response of the transmission path from the OFDM reception signal.
Answer, the generation of the delayed wave included in the received signal is detected.
An impulse response detection circuit for detecting a raw situation,
The time window position control means is an impulse response detection circuit.
The discrete Fourier transform according to the detected impulse response
The position of the time window of the switching means shall be controlled, and
OFDM transmission thin determined by generated symbol synchronization
The maximum level of the impulse response of the transmission line
Position on the time axis
The OFDM transmission symbol sequence and transmission path impulse
Time to perform the discrete Fourier transform when drawing a response
The energy of the impulse response penetrating into the window is minimal
A time window is set at a certain position.

According to the configuration of (1) or (2) , the time window for the discrete Fourier transform is set at an optimum position according to the state of generation of the delayed wave observed at the receiving point (impulse response of the transmission path). Since setting can be performed, reception quality can be improved as compared with the case where a fixed time window setting is used in the related art.

Specifically, this is realized by the following configuration.

[0022]

[0023]

[0024]

[0025]

[0026]

(3) In the configuration of (1) , the time window position control means starts setting the position of the time window with a sufficiently small threshold value as an initial value, and then gradually sets the value of the threshold value in steps. The position setting of the time window is repeated while increasing the time window position, and the time window position corresponding to the minimum threshold value that can be set is determined as the final time window position.

(4) In the configuration of (1) , the time window position control means starts setting the position of the time window with a sufficiently large threshold value as an initial value, and then gradually sets the threshold value in a stepwise manner. The position setting of the time window is repeated while decreasing the time window position, and the time window position corresponding to the minimum threshold value that can be set is determined as the final time window position.

(5) In the configuration of (3) or (4) , the time window position control means includes a threshold value setting circuit for setting a threshold value, and an impulse response signal from the impulse response detection circuit. An impulse response level judging circuit for judging the magnitude relation between each component of the response and the threshold value set by the threshold value setting circuit; and a position of a time window based on the impulse response level judgment result of this circuit. A time window position determination circuit; and a time window position control signal output circuit for generating a control signal for controlling the position of the time window at the position determined by the circuit and outputting the control signal to the discrete Fourier transform circuit.

(6) In the configuration of (2) , the time window position control means sets a fixed position on the left or right in a transmission symbol of the OFDM reception signal as an initial position of the time window, By shifting the time window stepwise by a certain value in a certain direction from a certain time, setting the time window at a different position by a certain number of times, and finding the position where the energy of the impulse response penetrating into the time window becomes minimum , Determine the optimal time window position.

(7) In the configuration of (2) , the time window position control means sets the time window at a random position for a certain number of times in a transmission symbol of the OFDM reception signal, and sets the time window in the time window. The optimal time window position is determined by finding the position where the energy of the impulse response that penetrates into is minimized.

(8) In the configuration of (6), the time window position control means sets a fixed position on the left or right in a transmission symbol of the OFDM reception signal as an initial position of the time window, A time window shift control circuit that shifts the time window stepwise by a certain value in a certain direction and sets a time window at a different position by a certain number of times; and the time window shift control based on the detection result of the impulse response detection circuit. A time window impulse response energy calculation circuit for calculating the total energy of the impulse response penetrating into a time window set by the circuit, and a time window position for determining the position of the time window based on the calculation result of the circuit A decision circuit, and a control signal for controlling the position of the time window of the discrete Fourier transform means to the position of the time window determined by the time window position decision circuit. It generates and and a time window position control signal output circuit for outputting to the discrete Fourier transform means.

(9) In the configuration of (7) , the time window position control means includes a time window shift control circuit for setting a time window at a random position for a certain number of times in a transmission symbol of the OFDM reception signal. A time window impulse response energy calculation circuit for calculating the total energy of the impulse response penetrating into the time window set by the time window shift control circuit from the detection result of the impulse response detection circuit; A time window position determining circuit for determining the position of the time window based on the result, and control for controlling the position of the time window of the discrete Fourier transform means to the position of the time window determined by the time window position determining circuit. A time window position control signal output circuit for generating a signal and outputting the signal to the discrete Fourier transform means.

(10) In any one of the constitutions (6) to (9) , the time window shift control circuit of the time window position control circuit sets a range in which the time window is shifted to be constant at both ends of the entire symbol period. Limited to the period excluding the period.

(11) In any one of the constitutions (1) to (10), the time window position control means averages a plurality of impulse response detection results, and responds to the averaged impulse response detection results. , The position of the time window for performing the discrete Fourier transform is adaptively set.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 shows the configuration of an OFDM receiver according to a first embodiment of the present invention. The OFDM receiver according to this embodiment comprises a frequency converter 11 and an A / D converter. / D converter 12, discrete Fourier transformer 13, carrier demodulator 14, time window position control signal generation circuit 15, fixed signal waveform memory 16, cross-correlation value calculation circuit 17, impulse response detection circuit 18
And

The radio frequency or intermediate frequency OFDM reception signal is frequency-converted by the frequency converter 11 into a lower intermediate frequency or baseband OFDM signal. The frequency-converted OFDM signal is sampled (sampled) by the A / D converter 12 and further converted to a digital signal. As the sampling clock frequency, a value for sampling the effective symbol period exactly 2 ⁿ times (n is a positive integer) is usually used.

The A / D-converted sample value sequence is input to the discrete Fourier transformer 13 and the cross-correlation value calculation circuit 17. The cross-correlation value calculation circuit 17 calculates a cross-correlation value between the A / D converted sample value sequence and the fixed signal waveform sample value sequence stored in the fixed signal waveform memory 16. The calculation result of the cross-correlation value is input to the impulse response detection circuit 18. The impulse response detection circuit 18 detects the position on the time axis of the fixed signal waveform component included in the received signal by detecting the peak of the cross-correlation value.

A received signal is usually composed of a plurality of arriving waves (a desired wave and a plurality of delayed waves), and a peak of a cross-correlation value appears at a position of a fixed signal waveform included in each arriving wave. Therefore, the profile of the delayed wave (impulse response of the transmission path) can be detected from the position of the peak of the cross-correlation value.

The time window position control signal generation circuit 15 determines the position of the time window for performing the discrete Fourier transform from the impulse response of the transmission path detected by the impulse response detection circuit 18 and controls the position of the time window. And outputs the signal to the discrete Fourier transformer 13. The discrete Fourier transformer 13 uses the time window set by the time window position control signal generation circuit 15 to convert the sampled value sequence after A / D conversion into a spectrum component on the frequency axis, and obtains a spectrum at each carrier frequency. Are passed to the carrier demodulator 14. The carrier demodulator 14 estimates the value of the data transmitted on the carrier from the amplitude and phase values of each carrier frequency spectrum, and outputs the estimation result as received data.

FIG. 2 shows a time window position control signal generation circuit 15.
1 shows a first example of a time window position setting method in FIG. In this method, an incoming wave having the highest reception level is set as a desired wave, and a threshold is set to a level lower than the desired wave by a fixed value (A decibel). Then, as shown in FIG. 2, when the position of the desired wave in the impulse response coincides with the switching position of the transmission symbol on the time axis, the impulse response component having a level higher than the threshold value becomes discrete Fourier transform. The time window is set at a position that does not enter the time window for performing the operation.

Depending on the value of the threshold value, no matter where the time window is set, an impulse response component having a level larger than the threshold value may enter the time window. Therefore, the position setting of the time window is first started by using a sufficiently small threshold value, and then the position setting of the time window is repeated while gradually increasing the threshold value, thereby obtaining the minimum position setting possible. A method is conceivable in which the time window position corresponding to the threshold is set as the final time window position.

As another method, first, the position setting of the time window is started by using a sufficiently large threshold value, and then the position setting of the time window is performed while the threshold value is gradually reduced. It is also conceivable that the time window position corresponding to the minimum threshold value that can be repeatedly set as the final time window position is used.

FIG. 3 shows a specific configuration of the time window position control signal generating circuit 15 when the time window position setting method shown in FIG. 2 is used. Time window position control signal generation circuit 15 in FIG.
Includes an impulse response level determination circuit 151, a threshold value setting circuit 152, a time window position determination circuit 153, and a time window position control signal output circuit 154.

The impulse response level determination circuit 151
In addition to receiving the impulse response detection result from the impulse response detection circuit 18 and the threshold value from the threshold value setting circuit 152, an impulse response component having a level higher than the threshold value exists at any position on the time axis. This information is passed to the time window position determination circuit 153. The time window position determining circuit 153 sets the position of the time window in accordance with the method shown in FIG. 2, and outputs information as to whether or not the time window position can be set at the current threshold value. Feedback to

The threshold setting circuit 152 decreases the threshold value by a certain value, for example, when it receives information that the time window position can be set, and receives the information that the time window position cannot be set. , The threshold value is increased by a certain value. In this way, the setting of the time window position is repeated while changing the threshold value stepwise.

When a sufficiently small value is used as the initial value of the threshold value, the time window position determining circuit 153 sets the time window position corresponding to the threshold value at which the time window position can be set first to the final time window position. Determined as the time window position. On the other hand, when a sufficiently large value is used as the initial value of the threshold value, the time window position determining circuit 153 corresponds to the threshold value one step larger than the threshold value at which the time window position cannot be set first. Is determined as the final time window position.

The time window position determination circuit 153 passes the finally determined time window position to the time window position control signal output circuit 154 as position information on the time axis. The time window position control signal output circuit 154 converts this position information into, for example, the number of sampling clocks and passes it to the discrete Fourier transformer 13. The discrete Fourier transformer 13 sets, for example, a position counted from the position of the end of each transmission symbol by the number of received clocks as a start position of the time window for discrete Fourier transform.

FIG. 4 shows a time window position control signal generation circuit 15.
2 shows a second example of the time window position setting method in FIG. In this method, the energy of the impulse response penetrating into the time window is calculated while shifting the set position of the time window as shown by a, b, and c as shown in FIG. Then, when the position of the desired wave in the impulse response and the switching position of the transmission symbol are matched on the time axis, a time window is set at a position where the energy of the impulse response entering the time window becomes minimum. I do.

The time window is shifted from a fixed position on the left or right in the transmission symbol in a fixed direction in a stepwise manner by a certain value. A method of setting a time window at a random position by the number of times can be considered. In either method, the time window is set at a different position by a certain number of times, and the position where the energy of the impulse response penetrating into the time window is determined to be the optimum position of the time window. it can.

FIG. 5 shows a specific configuration of the time window position control signal generating circuit 15 when the time window position setting method shown in FIG. 4 is used. Time window position control signal generation circuit 15 in FIG.
Is a time window impulse response energy calculation circuit 155
, A time window shift control circuit 156, a time window position determination circuit 157, and a time window position control signal output circuit 158.

The time window impulse response energy calculation circuit 155 receives the impulse response detection result from the impulse response detection circuit 18, and receives the time window shift control circuit 1.
The sum of the energies of the impulse response components entering the time window designated by 56 is calculated, and the calculation result is passed to the time window position determination circuit 157. The time window shift control circuit 156 shifts the time window to a different position by a certain number of times. Therefore, the calculation results for the set number of times are passed to the time window position determination circuit 157.

The time window position determining circuit 157 determines a time window position at which the energy of the impulse response penetrating into the time window becomes minimum in a fixed number of trials, and determines the position of the finally determined time window. Is passed to the time window position control signal output circuit 158 as position information on the time axis, and the time window position control signal output circuit 158 converts this position information into, for example, the number of clocks of a sampling clock and sends it to the discrete Fourier transformer 13. hand over. The discrete Fourier transformer 13 sets, for example, a position counted from the position of the end of each transmission symbol by the number of received clocks as a start position of the time window for discrete Fourier transform.

In the second example of the time window position setting method, the range of shifting the time window is limited to a period excluding a fixed period at both ends of the entire symbol period in consideration of the accuracy of symbol synchronization. There is a way to do it.

As is apparent from the above description, it is possible to set the time window for the discrete Fourier transform at an optimum position in accordance with the state of occurrence of the ghost signal (impulse response of the transmission path) observed at the receiving point. As a result, the reception quality can be improved as compared with the case where the conventional fixed time window setting is used.

In particular, when the receiving apparatus according to the present invention is used in a service area of a single frequency network (SFN), stable reception is possible even when a high-level pre-ghost exists. In addition, it is possible to flexibly cope with various delay profiles and always receive signals at an optimal time window position. For this reason, a significant increase in coverage can be expected as compared with the case where a conventional fixed time window setting is used.

Further, in mobile reception and portable reception, it is possible to set a time window for discrete Fourier transform at an optimum position in accordance with a ghost occurrence situation which changes every moment, thereby improving reception quality. be able to.

(Second Embodiment) FIG. 6 shows the configuration of an OFDM receiver according to a second embodiment of the present invention. The OFDM receiving apparatus according to the present embodiment includes a frequency converter 21, an A / D converter 22, a discrete Fourier transformer 23, a carrier demodulator 24, a time window position control signal generation circuit 25, an effective symbol length Delay circuit 2
6, a cross-correlation value calculation circuit 27, and an impulse response detection circuit 28. However, the receiver of FIG. 6 includes an effective symbol length delay circuit 26, a cross-correlation value calculation circuit 27,
Except for the impulse response detection circuit 28, the configuration and operation are the same as those of the receiving apparatus of FIG.

In the receiving apparatus shown in FIG. 6, the A / D-converted sample value sequence is input to a discrete Fourier transformer 23, an effective symbol length delay circuit 26, and a cross-correlation value calculation circuit 27. The effective symbol length delay circuit 26 generates a time sample value sequence delayed by a time corresponding to the effective symbol length on the time axis from the input time sample value sequence, and passes the generated time sample value sequence to the cross-correlation value calculation circuit 27. The cross-correlation value calculation circuit 27 calculates a cross-correlation value between the time sample value sequence received from the A / D converter 22 and the time sample value sequence received from the effective symbol length delay circuit 26. The calculation result of the cross-correlation value is input to the impulse response detection circuit 28.

As shown in FIG. 7, each transmission symbol of OFDM includes a guard interval, and the signal waveform of the guard interval is a cyclically repeated signal waveform in the effective symbol period. Therefore, when the cross-correlation value is calculated in the configuration of FIG. 6, a correlation peak appears at a position where the two time sample value sequences input to the cross-correlation value calculation circuit 27 coincide (a position of the guard interval). That is, as in the case of FIG. 1, a peak appears at the position of the guard interval included in each of the plurality of incoming waves (the desired wave and the plurality of delayed waves). Accordingly, the impulse response detection circuit 28 can detect the profile of the delayed wave (impulse response of the transmission line) by detecting the peak of the cross-correlation value.

The time window position control signal generation circuit 25 determines the position of the time window for performing the discrete Fourier transform from the impulse response of the transmission path detected by the impulse response detection circuit 28, and controls the position of the time window. And outputs the signal to the discrete Fourier transformer 23. The configuration and operation of the time window position control signal generation circuit 25 are the same as those described in the first embodiment.
In the description of the first embodiment, the configuration and operation are exactly the same as those described with reference to FIGS. 2 to 5, and the same effects as those of the first embodiment can be obtained in this embodiment.

In both the first embodiment and the second embodiment,
In the case of fixed reception, the impulse response detection circuits 18 and 28 average a plurality of impulse response detection results in order to improve the accuracy of the impulse response detection results,
It can be output as a final impulse response detection result. In the case of mobile reception, the number of times of averaging is reduced or averaging is not performed.
The speed of the impulse response detection can be increased. In other words, as an assumed receiving mode, the number of times of the averaging is adjusted depending on the specific gravity of each of the fixed reception and the mobile reception, so that the optimum impulse response detection can be performed.

[0064]

By using the orthogonal frequency division multiplexing receiving apparatus according to the present invention, the discrete Fourier transform can be set to an optimum position in accordance with the state of occurrence of a ghost signal (impulse response of a transmission line) observed at a receiving point. Can be set, so that the reception quality can be improved as compared with the case where the conventional fixed time window setting is used.

In particular, when the receiving apparatus according to the present invention is used in a service area of a single frequency network (SFN), stable reception is possible even when a high-level pre-ghost exists. In addition, it is possible to flexibly cope with various delay profiles and always receive signals at an optimal time window position. For this reason, a significant increase in coverage can be expected as compared with the case where a conventional fixed time window setting is used.

Furthermore, in mobile reception and portable reception, a time window for discrete Fourier transform can be set at an optimum position in accordance with a ghost occurrence situation that changes every moment, thereby improving reception quality. be able to.

Therefore, according to the present invention, it is possible to set a time window for the discrete Fourier transform at an optimum position according to the state of occurrence of a ghost signal observed at a receiving point,
OFD that can improve reception quality by this
An M-system receiver can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an OFDM receiver according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing a first method of setting a time window position according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a specific configuration of a time window position control signal generation circuit in a first method of setting a time window position according to the first embodiment of the present invention.

FIG. 4 is a timing chart showing a second method of setting a time window position according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a specific configuration of a time window position control signal generation circuit in a second method of setting a time window position according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an OFDM receiver according to a second embodiment of the present invention.

FIG. 7 is a view showing an example of OFDM transmission signal waveforms and transmission symbols.

FIG. 8 is a diagram showing a schematic configuration of an OFDM modem.

FIG. 9 is a diagram showing an example of a setting position of a time window for discrete Fourier transform.

FIG. 10 is a diagram showing a configuration example of a single frequency network (SFN).

FIG. 11 is a diagram showing an example of a typical delay profile in each of the conventional station placement method and SFN.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Frequency converter 12 ... A / D converter 13 ... Discrete Fourier converter 14 ... Carrier demodulator 15 ... Time window position control signal generation circuit 151 ... Impulse response level judgment circuit 152 ... Threshold value setting circuit 153 ... Time window Position determination circuit 154 ... Time window position control signal output circuit 155 ... Time window impulse response energy calculation circuit 156 ... Time window shift control circuit 157 ... Time window position determination circuit 158 ... Time window position control signal output circuit 16 ... Fixed signal waveform Memory 17 Cross-correlation value calculation circuit 18 Impulse response detection circuit 21 Frequency converter 22 A / D converter 23 Discrete Fourier transformer 24 Carrier demodulator 25 Time window position control signal generation circuit 26 Effective symbol Long delay circuit 27 Cross-correlation value calculation circuit 28 Impulse response detection circuit A Transmission device A 1 ... Serial-parallel converter A2 ... Inverse discrete Fourier transform circuit A3 ... Frequency converter B ... Receiving device B1 ... Frequency converter B2 ... Discrete Fourier transform circuit B3 ... Parallel-serial converter

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Jiro Hirono 5-28-8 Akasaka, Minato-ku, Tokyo Inside the Next Generation Digital Television Broadcasting System Laboratory (56) References JP-A-10-126288 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04J 11/00

Claims (11)

(57) [Claims] 1. An orthogonal frequency division multiplexing receiver for receiving a signal including a transmission symbol modulated by an orthogonal frequency division multiplexing (hereinafter abbreviated as OFDM) digital modulation method and demodulating the OFDM reception signal. Is subjected to a discrete Fourier transform in accordance with the position of a time window that defines a range on the time axis, whereby OF
Discrete Fourier transform means for DM demodulation; Delay wave occurrence state detection means for detecting the occurrence state of a delay wave included in the OFDM reception signal; Discrete Fourier transform means based on the delay wave occurrence state detected by this means ; and a time window position control means for controlling the position of the time window, the delayed wave generating condition detecting unit, the OFDM received signal
The reception by detecting the impulse response of the transmission line from
Impulse for detecting the occurrence of delayed waves in a signal
A response detection circuit, wherein the time window position control means is configured to detect the impulse response.
The discrete Fourier according to the impulse response detected on the road.
D) Control the position of the time window of the conversion means, and
OFDM transmission determined by symbol synchronization reproduced in
Maximum symbol switching position and transmission path impulse response
The position of the peak point giving the level matches on the time axis
Thus, the transmission symbol sequence of OFDM and the
When the pulse response is drawn, the impact at the peak point is
A decibel (A is a certain
Value) and set the threshold to a smaller level
The impulse response components at levels higher than
D) Set a time window at a position where it does not
Orthogonal frequency-division multiplexing receiving apparatus, characterized by a constant. 2. An orthogonal frequency division multiplexing (hereinafter, abbreviated as OFDM).
Includes transmission symbols modulated by digital modulation
A quadrature frequency for receiving a signal and demodulating the OFDM reception signal
In the number division multiplex receiving apparatus, a time for defining the range on the time axis of the OFDM reception signal
By performing discrete Fourier transform according to the position of the window, OF
Discrete Fourier transform means for performing DM demodulation, and detecting occurrence of a delay wave included in the OFDM reception signal.
A delay wave generating condition detecting means for output, the release based on the detected delay wave generating availability this means
Time window position for controlling the position of the time window of the scattered Fourier transform means
Control means, and the delay wave generation state detecting means comprises:
The reception by detecting the impulse response of the transmission line from
Impulse for detecting the occurrence of delayed waves in a signal
A response detection circuit, wherein the time window position control means is configured to detect the impulse response.
The discrete Fourier according to the impulse response detected on the road.
D) Control the position of the time window of the conversion means, and
OFDM transmission determined by symbol synchronization reproduced in
Maximum symbol switching position and transmission path impulse response
The position of the peak point giving the level matches on the time axis
Thus, the transmission symbol sequence of OFDM and the
Performs the discrete Fourier transform when drawing a Luth response
The energy of the impulse response penetrating the time window
An orthogonal frequency division multiplexing type receiving apparatus , wherein a time window is set at a position where the time becomes small . 3. The time window position control means starts setting the position of the time window with a sufficiently small threshold value as an initial value,
Thereafter, the position setting of the time window is repeated while gradually increasing the value of the threshold value, and the time window position corresponding to the minimum threshold value that can be set is set as the final time window position. The orthogonal frequency division multiplexing system receiving apparatus according to claim 1 . 4. The time window position control means starts setting a time window position with a sufficiently large threshold value as an initial value,
Thereafter, the position setting of the time window is repeated while gradually decreasing the value of the threshold value, and the time window position corresponding to the minimum threshold value that can be set is set as the final time window position. The orthogonal frequency division multiplexing system receiving apparatus according to claim 1 . 5. The time window position control means comprises: a threshold setting circuit for setting a threshold value; and each component of an impulse response from the impulse response detection circuit and the threshold setting circuit. An impulse response level judging circuit for judging a magnitude relation with a set threshold value; a time window position determining circuit for deciding a time window position based on an impulse response level judgment result of the circuit; position to generate a control signal for controlling the position of the time window according to claim 3, 4, characterized in that it comprises a time window position control signal output circuit for outputting to the discrete Fourier transform circuit Orthogonal frequency division multiplex receiver. 6. The time window position control means, wherein the OFD
A fixed position on the left or right in the transmission symbol of the M received signal is set as an initial position of the time window, and the time window is shifted stepwise by a certain value in a certain direction from this initial position, and the time window is different by a certain number of times. The orthogonal frequency according to claim 2 , wherein an optimal time window position is determined by setting a time window at the position and determining a position where energy of an impulse response penetrating into the time window is minimized. Division multiplex receiver. 7. The time window position control means, wherein
The time window is set at a random position by a certain number of times in the transmission symbol of the M received signal, and the position where the energy of the impulse response penetrating into the time window is minimized to obtain the optimum time window position. The orthogonal frequency division multiplexing receiving apparatus according to claim 2 , wherein: 8. The time window position control means sets a fixed position on the left or right in a transmission symbol of the OFDM reception signal as an initial position of the time window, and a fixed value in a certain direction from the initial position. A time window shift control circuit that shifts the time window step by step, and sets a time window at a different position by a certain number of times; and a time window set by the time window shift control circuit from a detection result of the impulse response detection circuit. A time window impulse response energy calculation circuit for calculating the total energy of the impulse response penetrating into the inside; a time window position determination circuit for determining the position of the time window based on a calculation result of the circuit; and the discrete Fourier transform Generating a control signal for controlling the position of the time window of the means to the position of the time window determined by the time window position determining circuit; Orthogonal frequency-division multiplexing receiving apparatus according to claim 6, characterized in that it comprises a time window position control signal output circuit which outputs to the converter. 9. A time window shift control circuit for setting a time window at a random position for a certain number of times in a transmission symbol of the OFDM reception signal, wherein the time window position control means detects the time window position. A time window impulse response energy calculation circuit for calculating the total energy of the impulse response penetrating into the time window set by the time window shift control circuit from the result; and A time window position determining circuit for determining a position; and a control signal for controlling a position of the time window of the discrete Fourier transforming means to a position of the time window determined by the time window position determining circuit. 8. The orthogonal frequency division multiplexing system receiving apparatus according to claim 7 , further comprising a time window position control signal output circuit for outputting to said converting means. 10. The time window shift control circuit of the time window position control circuit, wherein a range in which the time window is shifted is limited to a period excluding a predetermined period at both ends of all symbol periods. Item 10. The orthogonal frequency division multiplexing receiving device according to any one of Items 6 , 7 , 8 , and 9 . 11. The time window position control means averages a plurality of impulse response detection results, and adaptively sets a position of a time window for performing a discrete Fourier transform according to the averaged impulse response detection results. The orthogonal frequency division multiplexing receiving apparatus according to any one of claims 1 to 10 , wherein: