JP2008283296A - Reception device and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reception device and a receiving method that suppress misrecognition of a signal due to signal deterioration and unnecessary radiation of a noise component by removing spurious component generated due to unnecessary addition of the noise component. <P>SOLUTION: Broadcast signals of a plurality of channels are received by a receiver 10 and converted into a digital signal of the IF band comprising the plurality of channels through a frequency converter 20 and an analog-to-digital converter 30. The digital signal is input to a channel distributor 40, and quadrature-demodulated by a quadrature demodulator 41 into an I/Q signal, which is multiplied with a weight coefficient multiplier 42 by a weight coefficient based upon a window function in band-pass filter form and then subjected to FFT processing by an FFT unit 43 to be divided into I/Q signals for the each channel. Then the I/Q signals divided by the FFT unit are frequency-converted with mixers 44-1 to 44-N for the channels into base band signals. Thus, the base band signals output from the channel distributor 40 are subjected to signal demodulation processing for the each channel with demodulators 50-1 to 50-N. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a receiving apparatus and a receiving method for simultaneously receiving transmission signals of a plurality of channels, for example, used in a relay apparatus that relays a plurality of terrestrial digital broadcast signals and a monitor apparatus that monitors a plurality of terrestrial digital broadcast signals.

  In a conventional terrestrial digital broadcasting system, a receiving device used as a relay device or a monitoring device for monitoring a digital broadcasting signal of a plurality of channels takes in a digital broadcasting signal received by a receiving antenna and puts it in an intermediate frequency band by a frequency converter. After being converted and digitized by an analog-to-digital conversion unit, the channel dividing unit divides each channel, and then a demodulating unit demodulates the broadcast signal of each channel to extract necessary signal information.

  Here, the channel dividing unit multiplies the broadcast signal converted into a digital signal by a weighting factor based on a window function in a weighting factor multiplication unit, and performs FFT of this signal in an FFT (Fast Fourier Transform) unit for each channel. Branch to signal. Then, by performing frequency conversion or quadrature demodulation on a part of the output from the FFT unit, the signal is converted into a baseband signal or an in-phase (I: In Phase) signal and a quadrature (Q: Quadrature) signal. Signal processing such as distortion compensation and suppression of unwanted waves.

At this time, as a coefficient of the window function, a coefficient of an FIR (Finite Impulse Filter) filter that realizes a low-pass filter (LPF) that extracts a baseband signal of one channel is used (for example, Patent Documents). 1 and 2). By doing this, the FFT output of the m-th (m = 0 to N−1) terminal is

It becomes. Here, I _in (k) is the k-th amplitude component of the input signal, W _LPF (k) is the window function component in the LPF format, f is the frequency, fs is the sampling frequency of the FFT unit, and N is the size of the FFT. . From equation (1), the FFT output of the 0th terminal is

It becomes. This coincides with the frequency characteristic of the FIR filter having the window function W _LPF (k) as a coefficient, so that the high-frequency signal is cut by the LPF by the window function W _LPF (k). On the other hand, the output signal from the m-th terminal is obtained by shifting the frequency characteristic shown in Expression (2) by m / N. That is, the m-th output signal is a signal when it passes through a band pass filter (BPF: Band Pass Filter) in which the reference frequency located at the center of the pass band is shifted by mfs / N. Therefore, by appropriately selecting m and N, it is possible to take out signals of only each channel to the FFT terminal.

However, in the signal processing using the LPF format for the window function, since the reference frequency is regarded as a direct current component (DC component) in a normal FFT, the noise component is power-added to generate a spurious component. Therefore, there is a problem that when a signal is not put on the channel of interest, a signal in which a noise component is added to the reference frequency is generated. In particular, when this receiving apparatus is used for broadcast wave relay, there is a problem that there is a high possibility that noise components will be radiated even though there is no input on the channel. Even when a signal is input, there is a noise component that is increased by adding a noise component to the reference frequency, so that the signal-to-noise ratio of the signal deteriorates, There was a problem of causing misrecognition.
Japanese Patent Application No. 2005-362335 Japanese Patent Application No. 2006-305503

  As described above, in conventional receivers that simultaneously receive a plurality of channels, a signal in which a noise component is added to a reference frequency located at the center of the passband is generated, and the signal is placed on the channel of interest. Even if not, there is a problem that noise components are radiated from the channel. In addition, when a signal is input, the signal-to-noise ratio of the signal is deteriorated due to a noise component present at the center frequency of the band, causing erroneous recognition of the signal.

  The present invention has been made under the circumstances described above, and an object thereof is to eliminate a spurious component generated by unnecessary addition of a noise component, and to suppress a false recognition of a signal due to signal deterioration and an unnecessary emission of a noise component. It is to provide a receiving method.

  In order to achieve the above object, the present invention provides a receiving antenna that receives a radio signal composed of a plurality of channels, and converts the radio signal composed of a plurality of channels received by the receiving antenna into an IF (Intermediate Frequency) signal for a plurality of channels. A frequency conversion unit for conversion, an analog-digital conversion unit for converting the IF signals for the plurality of channels into digital signals for the plurality of channels, and the digital signals for the plurality of channels are divided into digital signals for each channel and distributed. A quadrature demodulating unit for demodulating each digital signal for each channel, wherein the channel distributing unit quadrature demodulates the digital signals for the plurality of channels into an in-phase signal and a quadrature signal; And a band pass filter for each of the in-phase signal and the quadrature signal from the quadrature demodulation unit. A weight coefficient multiplication unit that multiplies the weight coefficient based on the window function of the data format, a fast Fourier transform (FFT) on the in-phase signal and the quadrature signal multiplied by the weight coefficient, and the same for each channel. An FFT unit that divides and distributes a phase signal and an orthogonal signal, and a plurality of digital frequency conversion units that perform frequency conversion on a signal for each channel output from the FFT unit.

  In the receiving apparatus having the above configuration, a radio signal composed of a plurality of channels is received by a receiving antenna and converted into a digital signal composed of a plurality of channels via a frequency converter and an analog-digital converter. In the channel distributor, the digital signal is quadrature demodulated to the in-phase signal and the quadrature signal by the quadrature demodulator, the weight coefficient multiplier multiplies the weight coefficient based on the bandpass filter type window function, and the FFT section performs FFT. Is divided into an in-phase signal and a quadrature signal for each channel. Then, the in-phase signal and the quadrature signal divided by the FFT unit are frequency-converted for each channel by the digital frequency conversion unit, and output to the demodulation unit. The signal output from the channel distributor is demodulated for each channel by the demodulator. This makes it possible to divide the digital signals for a plurality of channels into digital signals for each channel using a bandpass filter type window function.

  In the receiving apparatus and the receiving method according to the present invention, it is possible to suppress signal misrecognition due to signal degradation and unnecessary emission of noise components.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, in the terrestrial digital television broadcasting system, a receiving device used as a monitor device for monitoring digital broadcasting signals of a plurality of channels will be described as an example.

(First embodiment)
FIG. 1 is a block diagram showing a functional configuration of a receiving apparatus according to the first embodiment of the present invention. In FIG. 1, a receiving unit (RX) 10 receives a plurality of channels of broadcast signals transmitted in a frequency band previously assigned for digital terrestrial broadcasting through a receiving antenna and amplifies them to a prescribed level. Is converted to an intermediate frequency (IF) signal by the frequency converter 20 and converted to a digital signal by the analog-digital converter 30. A plurality of channels of digitally converted broadcast signals are divided and distributed into broadcast signals for each channel by the channel distribution unit 40, and each channel is demodulated by the demodulation units 50-1 to 50-N (N is an integer of 2 or more). The broadcast signal is demodulated.

  The channel distribution unit 40 inputs the broadcast signals of a plurality of channels digitized by the analog-digital conversion unit 30 to the orthogonal demodulation unit 41 and performs orthogonal demodulation on the I / Q signal. Then, the weighting factor multiplication unit 42 generates a weighting factor representing a BPF format window function corresponding to the frequency band of one channel on the time axis, and multiplies the time series data (I / Q signal) of each channel. To do. Then, the I / Q signal multiplied by the weighting coefficient is subjected to FFT processing by the FFT unit 43 and divided into signals for each channel, and the mixers 44-1 to 44 -N output from the local oscillators 45-1 to 45 -N. Mix with local signal and convert to baseband signal. Thus, the baseband signal distributed for each channel by the channel distribution unit 40 is demodulated by the demodulation units 50-1 to 50-N, and necessary signal information is extracted.

  In the above configuration, the operation of the channel distributor 40 will be described in detail. FIG. 2 is a conceptual diagram showing distribution of digital signals for each channel by the channel distributor 40 according to the first embodiment of the present invention. 2A is a conceptual diagram showing a digitized IF signal input to the channel distribution unit 40, and FIG. 2B is a conceptual diagram showing an I / Q signal orthogonally demodulated by the orthogonal demodulation unit 41. FIG. 2C is a conceptual diagram showing the I / Q signal distributed for each channel. In addition, Ch. The dotted line in FIG. 3 indicates that no signal component exists.

  The digitized IF signal input to the channel distributor 40 (FIG. 2A) is quadrature demodulated by the orthogonal demodulator 41 to become an I / Q signal (FIG. 2B), and the weight coefficient multiplier 42. Is output.

In the weighting coefficient multiplication unit 42, as a window function coefficient, a coefficient of an FIR filter that realizes a BPF for extracting a signal of one channel is used. Thereby, the output of the m-th (m = 0 to N−1) terminal of the FFT unit 43 is

It becomes. Here, I _in (k) is the k-th amplitude component of the input signal, W _BPF (k) is the window function component in the BPF format, f is the frequency, fs is the sampling frequency of the FFT unit 43, and N is the FFT size. is there. In the formula (3), the difference from the formula (1) is that the window function component is W _BPF (k) in the BPF format. That is, in the LPF format, the reference frequency is the center of the pass band, whereas in the BPF format, it is outside the pass band. At this time, the output signal from the m-th terminal is a signal when passing through the BPF having a reference frequency that is shifted by mfs / N from the reference frequency defined by W _BPF (k). Therefore, as in the equation (1), by selecting m and N appropriately, it becomes possible to take out signals of only the respective channels to the FFT terminal.

Here, the reference frequency f ₀ and the band W ₀ (band equal to the band of one channel) are used as the coefficients of the window function, and the sampling frequency fs, the FFT size N, and the FFT terminal m are appropriately selected, so that the signal of one channel is obtained. Only the signal can be extracted (FIG. 2C). A thick line on the frequency axis in FIG. 2C indicates a spurious component generated by adding power to noise. At this time, since the reference frequency in the BPF format is located f ₀ away from the center of the pass band, the spurious component is generated outside the pass band of the BPF as shown in FIG.

For comparison, FIG. 3 is a conceptual diagram illustrating an example of distribution of digital signals for each channel by the channel distribution unit 40 using W _LPF (k) as a window function component. A thick line on the frequency axis in FIG. 3 indicates a spurious component as in FIG.

Even when W _LPF (k) is used as the window function component, the signal can be divided for each channel as in FIG. However, since the reference frequency in the LPF format is located at the center of the passband, when a spurious component is generated at the reference frequency, a noise component is radiated in a channel having no signal component (Ch. 3 in FIG. 3). Thus, in a channel having a signal component (Ch. 1, 2, 4 in FIG. 3), the signal-to-noise ratio of the signal deteriorates.

On the other hand, in the configuration of the first embodiment, the digital signals of a plurality of channels output from the analog-digital conversion unit 30 are divided into signals for each channel by the channel distribution unit 40 and output. At this time, the channel distribution unit 40 multiplies the quadrature demodulated I / Q signal by the weighting factor multiplication unit 42 by a weighting factor based on the window function W _BPF (k), and performs the FFT by the FFT unit 43 to perform one channel. Divide every signal. As a result, since the reference frequency is located outside the pass band, a spurious component is generated outside the pass band.

  Therefore, the receiving apparatus having the above configuration can automatically remove spurious components, can suppress unnecessary emission of noise components, and can prevent erroneous recognition due to deterioration of the S / N ratio of the signal. Is possible.

(Second Embodiment)
FIG. 4 is a block diagram showing a functional configuration of a receiving apparatus according to the second embodiment of the present invention. In FIG. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted here.

  The configuration of the channel distribution unit 40 differs between the receiving device in FIG. 4 and the receiving device in FIG. In the channel distribution unit 40 of the receiving apparatus of FIG. 1, first, the quadrature demodulation unit 41 quadrature-demodulates the I signal and the Q signal, then the weighting factor multiplication unit 42 multiplies the weighting factor, and the FFT unit 43 divides each channel. However, in the receiving apparatus according to the second embodiment in FIG. 4, the IF band signal is multiplied by the weighting factor by the weighting factor multiplication unit 42 and divided by the FFT unit 43 for each channel. On the other hand, orthogonal demodulation is performed by the orthogonal demodulation units 41-1 to 41-N.

  As described above, in the second embodiment, after the signal is divided for each channel by the FFT unit 43, the quadrature demodulation units 41-1 to 41-N perform quadrature demodulation on each channel signal. . As a result, the frequency conversion can be reduced by one stage.

  Therefore, addition of phase noise due to the local oscillation signals from the local oscillators 45-1 to 45-N to the signal can be prevented, and the circuit scale can be reduced.

  The present invention is not limited to the following embodiment. The present invention can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the structure of 1st Embodiment of the receiver which concerns on this invention. The conceptual diagram which shows the distribution for every channel of the digital signal by the channel distribution part of the said 1st Embodiment. The conceptual diagram which shows an example of the distribution of the digital signal for every channel by the channel distribution part which used the conventional _WLPF (k) for the window function component. The block diagram which shows the structure of 2nd Embodiment of the receiver which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Reception part, 20 ... Frequency conversion part, 30 ... Analog-digital conversion part, 40 ... Channel distribution part, 41, 41-1 to 41-N ... Orthogonal demodulation part, 42 ... Weight coefficient multiplication part, 43 ... FFT part 44-1 to 44-N, mixers, 45-1 to 45-N, local oscillation units, 50-1 to 50-N, demodulation units.

Claims (8)

A reception processing unit that receives transmission signals of a plurality of channels having different frequencies within a predetermined band; and
A frequency conversion unit for simultaneously converting the transmission signals of a plurality of channels received by the reception processing unit into signals of an intermediate frequency band;
An analog-to-digital converter that converts a plurality of channels of transmission signals converted into the intermediate frequency band into digital signals;
The multi-channel transmission signal converted into the digital signal is divided for each channel, and multiplied by a weighting factor based on a window function having a band-pass filter characteristic for extracting the transmission signal, and fast Fourier transform (FFT) And a channel distribution unit that distributes the transmission signal of each channel by performing (Transform). The channel distributor is
A quadrature demodulator that performs quadrature demodulation of an in-phase signal and a quadrature signal from a transmission signal of a plurality of channels converted into the digital signal;
A weight coefficient multiplier that multiplies each of the in-phase signal and the quadrature signal demodulated by the quadrature demodulator by a weight coefficient based on a window function having bandpass filter characteristics of the transmission signals of the plurality of channels;
An FFT unit that performs fast Fourier transform on the in-phase signal and the quadrature signal multiplied by the weighting factor to obtain an in-phase signal and a quadrature signal for each channel;
The receiving apparatus according to claim 1, further comprising: a plurality of digital frequency conversion units that frequency-convert in-phase signals and quadrature signals for each channel output from the FFT unit into baseband. The channel distributor is
A weighting factor multiplier that multiplies the transmission signals of the plurality of channels converted into the digital signal by a weighting factor based on a window function having a bandpass filter characteristic of each of the transmission signals of the plurality of channels;
An FFT unit that performs fast Fourier transform on the transmission signals of the plurality of channels multiplied by the weighting factor to obtain transmission signals for each channel;
The receiving apparatus according to claim 1, further comprising: a plurality of quadrature demodulation units that quadrature demodulate an in-phase signal and a quadrature signal from transmission signals for each channel output from the FFT unit. The receiving apparatus according to claim 1, further comprising a plurality of demodulation means for demodulating a baseband transmission signal from a plurality of channel transmission signals distributed by the channel distribution unit. Receive transmission signals of multiple channels with different frequencies within a predetermined band,
The received transmission signals of a plurality of channels are simultaneously converted into intermediate frequency band signals,
The transmission signal of a plurality of channels converted into the intermediate frequency band is converted into a digital signal,
The multi-channel transmission signal converted into the digital signal is divided for each channel, and multiplied by a weighting factor based on a window function having a band-pass filter characteristic for extracting the transmission signal, and fast Fourier transform (FFT) (Transform) is performed to distribute the transmission signal of each channel. Distribution of the transmission signal for each channel is as follows:
The in-phase signal and the quadrature signal are quadrature demodulated from the transmission signal of the plurality of channels converted into the digital signal,
Multiplying each of the quadrature demodulated in-phase signal and quadrature signal by a weighting factor based on a window function having bandpass filter characteristics of the transmission signals of the plurality of channels,
Performs a fast Fourier transform on the in-phase signal and quadrature signal multiplied by the weighting factor to distribute to the in-phase signal and quadrature signal for each channel,
6. The receiving method according to claim 5, wherein the in-phase signal and the quadrature signal for each channel are frequency-converted to baseband. Distribution of the transmission signal for each channel is as follows:
Multiplying the transmission signal of the plurality of channels converted into the digital signal by a weighting factor based on a window function having a bandpass filter characteristic of each of the transmission signals of the plurality of channels,
Performing a fast Fourier transform on the transmission signals of the plurality of channels multiplied by the weighting factor to distribute the transmission signals for each channel;
6. The reception method according to claim 5, wherein an in-phase signal and a quadrature signal are quadrature demodulated from the transmission signal for each channel. 6. The receiving method according to claim 5, further comprising demodulating a baseband transmission signal from each of the transmission signals distributed for each channel.

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