JP2000134174A - Ofdm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep optimum reception quality by amplifying only a digital signal component, even when a digital signal with a high level analog signal superimposed thereon is received. SOLUTION: When a signal where a digital multi-carrier signal with a broad band and an analog signal carrier signal with a narrow band are in existence with the duplicate band is received, if an RF-AGC amplifier 6 amplifiers the signal on the basis of the analog signal with a higher level, a desired digital wave signal becomes smaller, and this method is disadvantageous from the standpoint of the S/N ratio or the like. Thus, the allocated frequency for the analog signal is detected and the signal passes through a filter 40, that attenuates a signal of this band only to obtain the signal including only the desired digital wave components, then the resulting signal is amplified by the RF-AGC amplifier 6 to obtain the digital signal with a proper amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environment in which a narrowband analog modulated single carrier signal (hereinafter referred to as an analog wave) and a wideband digitally modulated multicarrier signal (hereinafter referred to as an OFDM wave) are mixed. , And an OFDM wave receiving apparatus that satisfactorily extracts the latter signal.

[0002]

2. Description of the Related Art In recent years, developments aimed at enhancing services such as digitalization of broadcast waves, high sound quality, high image quality, multi-channel, and development to data broadcasting have been actively conducted. As a domestic broadcasting system currently under study, a multicarrier multiplexing system called OFDM (Orthogonal Frequency Division Multiplexing Communication System) is dominant. This system transmits hundreds to thousands of carriers, each modulated by an input digital signal, collectively, and is known as a multiplexing system having high interference rejection capability and high frequency use efficiency. By the way, in the frequency allocation of this broadcast wave, most of the frequencies currently used in Japan are already used up for various purposes such as business use, and there is almost no surplus frequency for new allocation, This is the situation. Therefore, when trying to broadcast such a wideband signal, the signal overlaps with the existing analog broadcast band and interferes with each other.

[0003] However, at present, there are a large number of existing analog television (TV) radio receivers on the market, and they have become a media closely related to daily life. The analog waves cannot be stopped to eliminate mutual interference during the transitional transition. For this reason, during the transition period to digital broadcasting unification, transmission and reception must be continued in a mixed environment of both analog and digital waves. One of the measures is to use OFDM to maintain the same quality as analog broadcasting.
There may be ways to reduce the transmission power of the wave.

[0004]

As described above, during the transition period to digital broadcasting, a mixed environment of analog and digital is unavoidable, and it is necessary to perform normal OFDM wave reception mainly by measures on the receiver side. There is. Moreover, as described above, the OFDM wave has a smaller electric field strength than the analog wave for the purpose of reducing interference, and is disadvantageous for originally normal reception.

In addition, an AGC amplifier is provided at the front stage of the receiver to absorb fluctuations in the received signal level and output a fixed level in order to perform mixing processing and IF amplification at a fixed level. Since the amplifier gain is set in accordance with a high-level analog signal in an environment of a simple signal, the OFDM wave becomes a component whose level is considerably smaller than that of the analog wave.
There is a problem that it is disadvantageous in terms of N ratio.

Accordingly, an object of the present invention is to provide an OFDM receiver which amplifies only digital signal components and maintains optimum reception quality even when receiving a digital signal on which a high-level analog signal is superimposed. The purpose is to:

[0007]

According to the present invention, there is provided an OFDM wave receiving apparatus in which an OFDM wideband multicarrier signal and an analog single carrier signal are mixedly input in the same band. An analog wave detector for detecting the arrangement frequency of the analog single carrier from the input signal, a frequency band variable band-attenuation filter provided in front of the RF amplifier of the OFDM wave detector, and an analog wave detector. Indicating means for instructing the band-attenuating filter the same frequency band as the arrangement frequency of the analog single carrier.

The analog wave detecting section includes a variable frequency local oscillator, an analog signal demodulating device, and detecting means for scanning a carrier frequency of a received signal to detect a frequency arrangement of the analog signal. Can be.

The variable frequency band-attenuating filter includes a plurality of band-attenuating filters having different attenuation bands, and some band-attenuating filters can be selectively and effectively operated according to an instruction from an instruction means.

[0010]

FIG. 1 shows the spectrum of a general OFDM wave. The horizontal axis is the frequency f, and the vertical axis is the amplitude. A plurality of digitally modulated digital signals are dispersed and multiplexed on hundreds to thousands of carriers C1,..., Cn. These carriers C1, ...,
Cn is set at a frequency interval that does not cause mutual interference, and in short-term observation (symbol unit) viewed microscopically, line spectra appear differently for each carrier as shown in FIG. On the other hand, it appears as a broadband rectangular spectrum Sm in macro observation for a long time.

As described above, even if such digital broadcasting is performed, there is no frequency margin, so that existing analog waves Ch1 to Chn are superimposed within the spectrum Sm of the OFDM wave as shown in FIG. It will be mixed. The analog wave is a single carrier and is subjected to analog modulation such as AM. For this reason, analog waves are generally OFD
It has a narrower band than the M wave. Further, as described above, the level of the OFDM wave is lower than that of the analog wave to avoid mutual interference.

FIG. 3 is a block diagram of a general OFDM digital signal receiving apparatus. The broadcast wave received by the antenna 2 passes through a BPF (Band Pass Filter) 4 and is amplified by a next-stage RF-AGC amplifier 6 in a form in which noises other than a desired band are removed. This RF-AGC amplifier 6 is configured with an AGC (automatic gain control) for absorbing a fluctuation of an input signal and outputting a signal of a constant amplitude in order to ensure signal processing in a subsequent stage. The output signal of the RF-AGC amplifier 6 is converted to an intermediate frequency by a mixer 8 having a local oscillator 10 and an IF amplifier 12, and further converted to a BPF 1
4 and digitized by an A / D converter 16. The signal digitized by the AD converter 16 is FF
At T18, the signal is converted to the frequency domain, demodulated at the demodulator 20, corrected for error by the error corrector 22, further converted to a transport stream by the formatter 24,
The PEG decoder 26 performs MPEG processing, decodes the image and audio, and reproduces it as an AV output.

FIG. 4 shows the input / output characteristics of the RF-AGC amplifier 6 described above. The amplitude of the received signal may fluctuate with time due to fading, multipath, or the like. However, the signal processing after the mixer 8 does not operate properly unless a signal having a substantially constant amplitude is input.
Has a characteristic that the output OP becomes constant even if the input voltage Vi fluctuates, as shown in FIG. In the receiving apparatus of FIG. 3, in order to obtain such characteristics, the output signal of the BPF 14 is monitored, and the magnitude of the signal is determined by the RF-AGC of the preceding stage.
The signal is fed back to the amplifier 6 as a gain control signal.

FIG. 5 shows a received signal waveform when an OFDM wave on which analog waves Ch1 to Chn are superimposed as shown in FIG. 2 is received in the receiver having the circuit configuration of FIG. FIG. 5A shows an analog wave envelope EVa and an OFDM wave Sd as input waveforms of the RF-AGC amplifier 6 in FIG. 3, and FIG.
The output of the amplifier 6 is an analog wave envelope EVa
And OFDM wave Sd. As can be seen from FIG. 2, the weak analog OFDM wave Sd is superimposed on the strong analog wave (EVa) on each waveform, and the amplitude is almost constant when viewed from the output of FIG. 5B. The ratio between the two hardly changes. The output of the RF-AGC amplifier 6 is finally adjusted to the maximum input range Ae of the A / D converter 16 so that the maximum input range Ae is used to the maximum to increase the conversion accuracy and the reception quality. I have to.

However, in practice, as can be seen in FIG. 5B, the level of the analog wave which is not finally required is high, so the gain is adjusted to this level, and the required O
Although the FDM wave is small and uses the maximum input range Ae to the maximum, it is the case when viewed from the analog wave. When viewed from the OFDM wave, the maximum input range Ae is used to the maximum. It cannot be said that the reception is performed as it is, and a reception error or the like occurs to deteriorate reception quality.

In order to eliminate such inconvenience, R
Before amplification by the F-AGC amplifier 6, unnecessary analog waves may be removed and amplified. For that purpose, first, it is necessary to detect the band allocation of analog waves, and since analog waves have different frequency allocations in adjacent areas to avoid interference, especially when mobile reception is performed across areas, It is necessary to re-detect the frequency arrangement at any time.

FIG. 6 is a block diagram showing a receiving apparatus according to the present invention. 3. The receiving device shown in FIG.
A variable band attenuation filter (BEF) 40 for attenuating a designated frequency band and an analog wave detection unit 50 are additionally provided to the M wave detection unit 30. Variable BE
F40 has a plurality of BEFs depending on the required attenuation band.
.., 40n. The BEF group 30 is provided between the BPF 4 of the OFDM wave detection unit 30 and the RF-AGC amplifier 6, the input side of each BEF is commonly connected to the output terminal of the BPF 4, and each output terminal is connected to the addition unit 42. The input terminal of the RF-AGC amplifier 6 is connected to the input terminal.

The analog wave detecting section 50 has a circuit portion similar to that of the receiving apparatus shown in FIG.
RF-AGC that operates by receiving an input signal from the output terminal of F4
A mixer (MI) having a local oscillator 60 below the amplifier 56
X) 58, an IF amplifier 62, a BPF 64, and a demodulator (DEC) 66. The output of the DEC 66 is introduced into a microprocessor (μP) 68 where a predetermined operation is performed, and the output controls the variable BEF 40 and is fed back to the local oscillator 60 via a PLL circuit 72. An arrangement RAM 70 for storing the arrangement of the analog wave frequencies is connected to the microcomputer 68.

The operation of the analog wave detecting section 50 is the same as that of a general radio receiving apparatus. That is, first, the signal from the BPF 4 passes through the RF-AGC amplifier 56 and is amplified to a constant amplitude. The signal is mixed with the oscillation signal of the local oscillator 60 by the mixer 58 to become an intermediate frequency. The intermediate frequency signal is amplified by the IF amplifier 62, a peripheral signal is attenuated by the BPF 64, input to the DEC 66, and sends a normally demodulated signal to the microprocessor 68. DEC66 is specifically F
It is of the M demodulation type, and the presence of a signal can be detected in such a manner that a pilot signal can be received normally and the PLL circuit 72 locks it. In the case of a TV signal, the determination can be made in the same manner depending on whether or not the synchronization separation can be normally performed. The microprocessor 68 loads the PLL circuit 72 with the local oscillation frequency value,
The entire analog frequency band is scanned by sequentially increasing the frequency. Then, the normally received frequencies are temporarily stored in the arrangement RAM 70 as a table. Further, the table of the arrangement RAM 70 is read out, and the variable B
The setting is loaded into the EF 40 to attenuate the detected analog waveband.

The dashed line in FIG. 7 shows the attenuation characteristic E40 of the BEF group 30 shown in FIG. The attenuation characteristic E40 is set so as to exhibit a large attenuation rate in a band where the analog wave Ch to be attenuated is located. The BEF group 30 is a variable attenuation filter device for attenuating a signal in a designated frequency band, and is configured so that a parameter such as a frequency band can be programmably set by a microprocessor 68 shown in FIG. The attenuation frequency bandwidth is specifically about 6 MHz for a TV signal and about 75 for an FM radio signal.
kHz. This filter attenuates unnecessary analog waves for the OFDM wave.

FIGS. 8 to 10 show the signal waveforms of the respective parts of the circuit device shown in FIG. 6 in the respective figures (a) and the frequency spectrum in the same figure (b). FIG. 8A shows an output signal S4 of the BPF 4, that is, a received RF signal, and an envelope EV of an analog wave due to fading, multipath, or the like.
The amplitude of “a” fluctuates with time, and as shown in FIG. 3B, the level of the OFDM wave Sm is low in frequency, and the analog wave Ch of a higher level is superimposed on this. Therefore, the required OFDM wave Sd is shown in FIG.
As shown in FIG.

FIG. 9A shows a signal after passing through the variable BEF 40, that is, an input signal S5 of the RF-AGC amplifier 6. Since the analog band is detected by the analog wave detection unit 50 in FIG. 6 and the frequency band is attenuated by the variable BEF 40, there is no unnecessary analog wave component, and only the target OFDM wave Sd (here, noise) is generated. Is appearing. It can be seen that the frequency band shown in FIG. 9B is also comb-shaped because the analog portion is attenuated.

FIG. 10A shows the signal S6 after passing through the RF-AGC amplifier 6, and the output amplitude is constant by absorbing the amplitude fluctuation of the input signal as described above.
Here, most of the signal components are the desired OFDM wave Sd
Since the amplitude is fixed and amplified, the amplitude can be adjusted to the maximum input range Ae of the A / D converter 16, and the conversion accuracy can be increased and the reception quality can be improved.

FIG. 11 is a flowchart showing the operation of the microprocessor 68 shown in FIG. The function of the microprocessor 68 is to give a command to the PLL circuit 72 of the analog wave detection unit 50 to scan the reception frequency,
That is, the frequency arrangement information is given to the variable BEF 40 as an attenuation band parameter. So first, the placement RAM
At the same time, the initial frequency f is set in the PLL circuit 72 (step 101). The initial frequency f is
For example, the frequency is 78 MHz for an FM broadcast frequency. Next, the frequency is increased by a predetermined increment, for example, every 1 kHz based on the frequency f (step 10).
2) It is confirmed whether or not an analog wave signal is detected (step 103). If detected, the frequency at that time is temporarily stored as a table in the arrangement RAM 70 (step 104). Immediately
It is checked whether the frequency f has reached the upper limit, for example, 90 MHz (step 105). If the frequency f has not reached the upper limit, the process returns to the step 102 to repeat the steps following the increase of the frequency f. When the frequency f has reached the upper limit, the scanning is terminated.
The analog wave frequency stored in 70 is read out, and the parameters of the attenuation frequency band are sent to the variable BEF 40 from the frequency arrangement (step 106), and unnecessary analog frequencies are attenuated.

By performing the above routine periodically, even if the receiving apparatus moves to an area where the analog frequency band is arranged differently, the change is detected as needed and updated as a table. A certain necessary frequency band is not attenuated. Therefore, since it is possible to always follow the frequency allocation for each area, the reception quality does not deteriorate.

When an analog wave is attenuated, the carrier of the OFDM wave in the attenuated band is lost at the same time. However, the OFDM wave is originally assigned redundant data due to measures such as fading of frequency selectivity. Time-interleaving, even if some carriers cannot be read, it can be corrected by the data of other carriers that have been read. It does not cause any obstacles.

[0027]

According to the invention described above, even if a wideband digital multicarrier signal and a narrowband analog single carrier signal overlap in band, unnecessary analog wave signals are attenuated. Since only the OFDM wave to be amplified is selectively amplified, the range of the A / D converter can be used to the maximum and a signal can be received with high accuracy.

In the case where the frequency arrangement of the analog wave signal is detected at regular intervals and the intermediate frequency of the band-attenuating filter is updated, the receiver moves together with the moving object to an area where the frequency arrangement of the analog wave is different. However, it is possible to automatically respond to the change and avoid a situation where a reception failure occurs.

[Brief description of the drawings]

FIG. 1 is a diagram showing a spectrum of an OFDM wave.

FIG. 2 is a diagram showing a spectrum of an OFDM wave and an analog wave.

FIG. 3 is a block diagram of an OFDM wave receiving device.

FIG. 4 is a diagram showing input / output characteristics of an AGC.

FIG. 5 is a diagram showing input / output waveforms of AGC.

FIG. 6 is a block diagram of an OFDM wave receiving apparatus according to the present invention.

FIG. 7 is a diagram illustrating frequency characteristics of a BEF.

FIG. 8 is a diagram showing an output waveform and frequency characteristics of a BPF of the OFDM wave receiving apparatus according to the present invention.

FIG. 9 is a diagram showing an input waveform and frequency characteristics of an RF-AGC amplifier of the OFDM wave receiving apparatus according to the present invention.

FIG. 10 shows an RF-AGC of the OFDM wave receiving apparatus of the present invention.
FIG. 3 is a diagram illustrating an output waveform and frequency characteristics of an amplifier.

FIG. 11 is a flowchart showing the operation of the microcomputer of the OFDM wave receiving apparatus according to the present invention.

[Explanation of symbols]

 2 Antenna 4 Bandpass Filter (BPF) 6 RF-AGC Amplifier 8 Mixer (MIX) 10 Local Oscillator (OSC) 12 IF Amplifier 14 BPF 16 A / D Converter 18 FFT 20 Demodulator (DEC) 22 Error Corrector ( FEC) 24 formatter 26 MPEG decoder 30 OFDM wave detector 40 variable band attenuation filter (BEF) 50 analog wave detector 56 RF-AGC amplifier 58 mixer (MIX) 60 local oscillator (OSC) 62 IF amplifier 64 BPF 66 demodulation (DEF) 68 Microprocessor (μP) (instruction means) 70 Placement RAM 72 PLL circuit

Claims (3)

[Claims] 1. An OFDM receiving apparatus in which an OFDM wideband multicarrier signal and an analog single carrier signal are mixedly input in the same band, wherein: an analog wave detecting unit for detecting an arrangement frequency of the analog single carrier from the input signal. A frequency band variable band-attenuation filter provided in front of the RF amplification unit of the OFDM wave detection unit; and a frequency band identical to the arrangement frequency of the analog single carrier detected by the analog wave detection unit. OFDM provided with instruction means for instructing
Receiver. 2. The OFDM receiver according to claim 1, wherein the analog wave detector scans a carrier frequency of the received signal by scanning a frequency-variable local oscillator, an analog signal demodulator, and a frequency of the analog signal. An OFDM receiving apparatus comprising: a detection unit that detects an arrangement. 3. The OFDM receiver according to claim 1, wherein the frequency-variable band-attenuating filter comprises a plurality of band-attenuating filters having different attenuation bands, and a part of the band-attenuating filter is instructed by the instruction means. An OFDM receiver, wherein a filter selectively operates effectively.