JPH11312995A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To periodically and accurately discriminate components such as a noise other than a desired signal by discriminating the reception condition based on the state of a no-signal section during the received broadcast. SOLUTION: A control part 51 fetches the output of an A/D converter 3 and obtains the entire energy quantity in a null part and the energy distribution from the fetched data group to determine the final controlled variables of VCXOs 6 and 11. The control which the control part 51 executes by using the output of the A/D converter 3 is periodically performed by its synchronous control in response to establishment of frequency synchronism of VXCOs 6 and 11. After confirmation of a reference symbol, the control part 51 calculates the entire energy quantity and the energy distribution of a null symbol section from the output of the A/D converter 3 for the held null symbol section. This entire energy quantity is obtained by, for example, calculating an average of the held data and the energy distribution is obtained by obtaining an average of plural sections into which the null symbol section is divided and comparing them with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver, and more particularly to a digital audio broadcast receiver which is already in practical use in Europe.
ng; hereinafter, referred to as DAB).

[0002]

2. Description of the Related Art As a system for transmitting and receiving a broadcast wave having a data signal of a predetermined format including a digital audio signal, a European standard (Eureka 14) is used.
There is a DAB system conforming to 7). In DAB, 1
An ensemble consists of several services, each of which consists of several components, such as English and German.

FIG. 4 shows an example of a service configuration of the DAB system. The services (three in this case) constituting the ensemble 1, each component (six in this case) and the D
FIG. 3 is a diagram illustrating a link with an OFDM signal transmitted from an AB station.

The OFDM signal transmitted from the DAB station is
It is divided into FIC (Fast Information Channel) and MSC (Main Service Channel).

Each sub-channel (Su) constituting the MSC
bCh0 to 63) have a correspondence with the above components, and the FIC includes information on services available in the ensemble and information indicating links between services, components, and subchannels.

[0006] Therefore, in DAB, when a certain ensemble is received, information on a plurality of services and components included in the ensemble can be obtained.
It is possible to switch instantly to different services and components without changing the reception frequency.

Next, a schematic configuration of a DAB receiver for receiving the broadcast is shown in FIG. Note that FIG. 5 mainly describes a configuration for performing frequency synchronization of an IF signal and frequency synchronization of a clock signal, which are particularly relevant to the present invention.

The DAB receiver includes a tuning unit 1, a SAW filter 2, an A / D converter 3, an FFT (fast Fourier transform) unit 4, a control unit 5, and a VCXO (voltage controlled crystal oscillator) 11.
It is composed of

The tuning section 1 includes a phase comparator 7, a VCO 8,
A PLL composed of a divider 9 is arranged, and a VCXO6
Is supplied to the mixer 10, and frequency conversion is performed by the received signal and this reference signal.

The SAW filter 2 extracts an IF (intermediate frequency) signal from the output of the mixer 10 with a predetermined selectivity. The extracted IF signal is supplied to an A / D converter 3 at the subsequent stage.
Is output to

In the A / D converter 3, the IF signal is converted into a digital signal. The digital IF signal converted into a digital value by the A / D converter 3 is input to an FFT unit 4 for demodulating an OFDM signal.

The FFT unit 4 performs a FFT process by providing a predetermined FFT window for an input signal. With this processing, each phase information of the multicarrier can be obtained. The result of the FFT processing is output to a Viterbi decoder (not shown) at the subsequent stage and is also output to the control unit 5.

The control unit 5 calculates the frequency offset amount of the IF signal based on the result of the FFT of the synchronization reference symbol included in the DAB signal and transmitted after the no-signal section (null symbol). , An automatic frequency control signal AFC (Automatic Frequency Control) signal is generated based on the calculation result and is output to the tuning unit.

According to the AFC signal, the VCXO of the tuning unit 1 is
By adjusting the oscillation frequency of No. 6, it becomes possible to establish and maintain the frequency synchronization of the IF signal.

Further, the control unit 5 calculates the correlation (the amount of deviation) between the result of the FFT of the above-mentioned reference symbol included in the DAB signal and the original reference symbol. The result is subjected to IFFT (Inverse Fourier Transform) to determine the impulse response of the transmission path. The impulse response is then analyzed and the receiver clock generator, VCXO
11 to output a control signal.

By adjusting the oscillation frequency of the VCXO 11 with this control signal, it is possible to establish and maintain the frequency synchronization of the clock signal between the transmitter and the receiver. The above is the outline of the receiver.

The contents are also disclosed in "Nikkei Electronics Books, 1995 Edition".

[0018]

One of the application fields of the above-mentioned receiver is an in-vehicle device. However, in mobile reception, since the reception status changes variously, the S / N of the received signal is always changed. It is difficult to keep good. If so, the receiver used for the mobile body needs to be controlled to appropriately reflect the fluctuating reception conditions.

Accordingly, it is an object of the present invention to provide a digital broadcast receiver capable of accurately determining a reception state and appropriately reflecting the determined result in control.

[0020]

According to the first aspect of the present invention, there is provided a digital broadcast receiver capable of receiving a digital broadcast constituting one frame by a non-signal section and a data signal section following the non-signal section. And a receiving state determining unit for determining a receiving state based on the state of the no-signal section during broadcasting.

According to a second aspect of the present invention, in the digital broadcast receiver according to the first aspect, the digital broadcast receiver controls the digital broadcast receiver based on at least the determination result. It is characterized in that one or more control signals are generated.

According to a third aspect of the present invention, in the digital broadcast receiver according to the second aspect, the data signal section includes a reference symbol for synchronizing transmission and reception, and the control signal Includes a synchronization signal generated based on the reference symbol and the determination result.

According to a fourth aspect of the present invention, in the digital broadcast receiver according to the first aspect, the state of the no-signal section is evaluated based on at least an energy distribution of the no-signal section. And

According to a fifth aspect of the present invention, in the digital broadcast receiver according to the first aspect, the state of the no-signal section is evaluated based on at least an energy amount of the no-signal section. And

[0025]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram of a receiver when the present invention is applied to the above-described synchronization control. The control targets here are the VCXOs 6 and 11 as described above. The same parts as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. 5 is different from FIG. 5 in that the output of the A / D converter 3 is fetched by the control unit 51 in order to accurately judge the current reception situation, and the control unit 51 uses the fetched data group to execute the entire energy amount and energy of the null portion. Find the distribution, VCXO
The point is that the final control amounts of 6 and 11 are determined.

FIG. 2 is a specific control flowchart executed by the control unit 51 using the output of the A / D converter 3. It is to be noted that the flowchart described below is described as being executed periodically once the frequency synchronization of the VCXOs 6 and 11 is once determined by the synchronization control of the control unit 51.

The control unit 51 first detects a null symbol section of the received signal, and the A / D converter 3 corresponding to the section.
(Step S1).

As a method of detecting a null symbol section of a received signal, the input signal A / D converted by the A / D converter 3 is sequentially compared with a predetermined threshold, and a section below the threshold is defined as a null symbol section. The A / D converter 3 in this section
Is used as the output of the A / D converter 3 corresponding to the null symbol section, or the start of the null symbol section,
A method can be used in which it is determined that the output is completed, and the output of the A / D converter 3 within the range is determined as the output of the A / D converter 3 corresponding to the null symbol section.

The data of the A / D converter in the null symbol section is held in the control unit 51 for the purpose of judging the reception status described later.

After the null symbol section is detected, the control unit 51 calculates a control amount for maintaining synchronization in the same manner as in the related art, based on the result of the FFT of the received synchronization reference symbol (step S1). S2). By this processing, AF
The basic control amounts of the C signal and the clock control signal are determined.

After confirming the reference symbol, the control unit 51
Evaluate the energy state in the null symbol section. Specifically, the A / A of the null symbol section held in step S1
From the output of the D converter 3, the total energy amount and energy distribution in the null symbol section are calculated (step S
3).

The total energy amount can be obtained, for example, by calculating the average of the held data. The energy distribution can be obtained by dividing the null symbol section into a plurality of sections, calculating the average of each of the divided sections, and comparing the averages with each other.

The reason that the null symbol section is used in the present invention is that, in DAB broadcasting, a null symbol section is periodically present. This is because it is optimal to use this null part.

After analyzing the reception status in step S3,
The control unit 51 determines a final control amount in step S4, and outputs this to each control target. The final control amount is
For example, the control amounts calculated in step S2 are each represented by f
If it is 1, t1, it can be obtained by multiplying the control amounts f1, t1 by a variable n (<1) according to the reception situation.

The obtained final control amount n * f1 is determined by AFC
The signal is fed back to the VCXO 6 as a signal, and n * t1
Is fed back to the VCXO 11 as a clock control signal.

Therefore, with the deterioration of the reception situation, for example,
The variable n is continuously reduced, and the actual control amount is determined in step S
It is possible to perform control such that the control amount calculated in step 2 is corrected to be gradually reduced.

Next, the reason why it is desirable to calculate the energy distribution in the null symbol section in order to determine the reception situation will be described below.

FIG. 3 is a diagram showing the state of the null symbol section of the DAB signal, and FIG. 3A is a diagram showing the state of the null symbol section when the reception condition is good.
FIG. 3B is a diagram illustrating a state of a null symbol section when the reception state is deteriorated over the entire null symbol section due to random noise, and FIG. 3C is a diagram illustrating multipath and SF.
FIG. 7 is a diagram illustrating a state of a null symbol section when two waves (a desired wave and an interfering wave) of the same signal are received with a time difference by N (Single Frequency Network).

Assuming that only the total energy amount in the null symbol section is considered for the determination of the reception situation, only the comparison of the total energy amount and the total energy amount in FIG. 3B and FIG. Since the total amount of energy may be equal, it is difficult to clearly distinguish these two reception situations.

However, both show different reception situations, and judging them as the same reception situation and outputting the same control amount to the control target does not lead to detailed control.

Therefore, in the present embodiment, not only the total energy amount but also the energy distribution in the null symbol section is calculated, so that the reception states shown in FIGS. The optimal control amount can be set according to the conditions.

As a result, even if the total energy amount is the same,
The variable nw at the time of the energy distribution of FIG.
The variable ns at the time of the energy distribution of (c) is made different,
Control for weighting nw <ns is also possible.

In the present embodiment, the constant for determining the AFC signal and the constant for determining the clock control signal are set to the same value n. However, the present invention is not limited to this.
The constant n1 for determining the C signal is different from the constant n2 for determining the clock control signal, and the control amount fed back to the VCXO 6 is calculated by n1 * f1,
The control amount fed back to the VCXO 11 is n2 *
It is also possible to configure to calculate at t1, and A
The control amount of only one of the FC signal and the clock control signal may be corrected.

Furthermore, in the present embodiment, the control targets are VCXOs 6 and 11 for application to frequency synchronization.
However, the present invention is not limited to this, and can be applied to other control targets in which control according to the reception state can be used. Further, in the present embodiment, not only the total energy amount but also the energy distribution in the null symbol section is calculated as the most desirable example. It may be configured to make a determination.

[0045]

As described above, according to the first aspect of the present invention, since there is provided the reception status determining means for determining the reception status based on the status of the no-signal section in the received broadcast, noise is reduced. And other components other than the desired signal can be regularly and accurately determined.

According to the second aspect of the present invention, one or a plurality of control signals for controlling the digital broadcast receiver are generated based on at least the determination result of the reception status determining means. Control that reflects the reception status becomes possible.

According to the third aspect of the invention, the synchronization control between transmission and reception reflects the reception state.

According to the fourth aspect of the present invention, the state of the no-signal section is evaluated based on at least the energy distribution of the no-signal section. It can be evaluated in detail whether the reception situation is deteriorated due to.

According to the fifth aspect of the present invention, since the state of the no-signal section is evaluated based on at least the energy amount of the no-signal section, the degree of deterioration of the reception status can be evaluated in detail.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital broadcast receiver according to the present invention.

FIG. 2 is a flowchart showing a control amount correction process of the present invention.

FIG. 3 is a diagram illustrating a state of a null symbol section when a reception state changes.

FIG. 4 is a service configuration example of a DAB system.

FIG. 5 is a block diagram of a conventional digital broadcast receiver.

[Explanation of symbols]

 1 ··· Tuning unit 2 ··· SAW filter 3 ··· A / D converter 4 ··· FFT 5 ··· Control unit 6 ··· VCXO 7 ··· Phase comparison Unit 8 VCO 9 Divider 10 Mixer 11 VCXO 51 Controller

Claims (5)

[Claims] 1. A digital broadcast receiver capable of receiving a digital broadcast constituting one frame by a non-signal section and a subsequent data signal section, wherein a reception state is determined based on a state of the non-signal section during a received broadcast. A digital broadcast receiver, comprising: a reception status determining unit for determining whether a digital broadcast is received. 2. The digital broadcast according to claim 1, wherein the digital broadcast receiver generates one or a plurality of control signals for controlling the digital broadcast receiver based on at least the determination result. Receiving machine. 3. The data signal section includes a reference symbol for synchronization between transmission and reception, and the control signal includes a synchronization signal generated based on the reference symbol and the determination result. The digital broadcast receiver according to claim 2, wherein: 4. The digital broadcast receiver according to claim 1, wherein the state of the no-signal section is determined based on at least an energy distribution of the no-signal section. 5. The digital broadcast receiver according to claim 1, wherein the state of the no-signal section is determined based on at least an energy amount of the no-signal section.