Receiving device and channel determination method

Abstract

To prevent a receiving device for terrestrial digital broadcasting from input detection reacting and malfunctioning even if the receiving device receives a signal of an interfering channel separated by a predetermined number of channels from a receiving channel set as a processing target.SOLUTION: A receiving device performs a process of detecting signal power by, after frequency-shifting a signal input to an FPGA 15 by an amount obtained by subtracting a first adjustment shift amount related to a first interference channel from a frequency shift amount for main line processing, passing the signal through a LPF 34, which limits it to a band for main line processing, and a process of detecting signal power by, after frequency-shifting the input signal by an amount obtained by adding a second frequency shift amount related to a second interference channel to an adjustment shift amount for main line processing, passing the signal through a LPF 44 which limits it to the band for main line processing band. The receiving device determines that the signal is from a receiving channel if the signal power is detected in both of those processes, and determines that the signal is from an interfering channel if not.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a receiving device for receiving a terrestrial digital broadcast signal. [Background technology]

[0002] In a system that provides terrestrial digital broadcasting, a relay station is installed to relay broadcast signals. The relay station converts a broadcast signal received on, for example, a receiving channel A into a transmitting channel B different from the receiving channel A and retransmits it. An overview of signal processing in a receiving device provided in such a relay station will be explained with reference to FIG. 1. Here, explanations of amplifiers, AGC (Automatic Gain Control), attenuators, and other components that adjust the signal level will be omitted because their insertion positions and number vary depending on the components used in the receiving circuit. In the following explanation, the modulated signal is assumed to be OFDM (Orthogonal Frequency Division Multiplexing) that is used in terrestrial digital broadcasting, and the band is approximately 5.57 MHz (6 MHz x 13 / 14 to be precise).

[0003] Fig. 1 shows an example of the configuration of a portion of a receiving device provided in a conventional relay station. The receiving device in the figure inputs an input receiving signal (R) to a mixer 11, and mixes it with a local signal generated by a local signal generating circuit 12 to obtain an IF (Intermediate Frequency) signal (Ire). To explain this using a specific numerical example in terrestrial digital broadcasting, if the receiving channel is channel 13, the center frequency of channel 13 is (473+1 / 7) [MHz]. In this case, the frequency of the local signal generated by the local signal generating circuit 12 is (510.15+1 / 7) [MHz], which is higher than the center frequency of channel 13 by 37.15 [MHz], which is the frequency of the IF signal. Therefore, the output of mixer 11 is modulated signals centered at 37.15 MHz and 983.44 MHz by multiplying the received signal (473+1 / 7) MHz by the local signal (510.15+1 / 7) MHz.

[0004] By passing the output signal of the mixer 11 through a SAW (Surface Acoustic Wave) filter 13, an IF signal (irk') that is a modulated signal centered on the desired 37.15 [MHz] can be extracted. The SAW filter is designed to limit the band of the IF signal corresponding to the receiving channel (channel 13 in this case). The IF signal (irk') that has passed through the SAW filter 13 is converted from an analog signal to a digital signal by an A / D converter 14, and then input to an FPGA (Field Programmable Gate Array) 15. Here, a clock reproduced from the received signal is used as the clock for the A / D converter 14. Since the clock for performing FFT (Fast Fourier Transform) processing specified in terrestrial digital television is (512 / 63) [MHz], here, a clock 16 times the FFT clock (512 / 63 x 16) [MHz] (hereinafter referred to as the "130 MHz clock") is reproduced from the received signal and used as the sampling clock for the A / D converter 14.

[0005] The FPGA 15 inputs the captured signal to an orthogonal demodulation circuit 20. Fig. 2 shows an example of the configuration of the orthogonal demodulation circuit 20 in a conventional receiving device. The signal input to the orthogonal demodulation circuit 20 is input to an IQ separation circuit 21 that separates the signal into an I (In-phase) signal and a Q (Quadrature-phase) signal, and is converted into an I signal and a Q signal. In Fig. 2, the I signal and Q signal are collectively represented as a complex signal by a thick black arrow.

[0006] The output signal of the IQ separation circuit 21 is input to a DDS (Direct Digital Synthesizer) 22. The DDS 22 converts the input signal into a baseband signal by shifting the frequency by -37.15 [MHz]. The output signal of the DDS 22 is clock-converted to a 32 MHz clock, which is ¼ of the 130 MHz clock, through an LPF (Low Pass Filter) 23 and a 4-sample decimation circuit 24, and is further clock-converted to an 8 MHz clock, which is ¼ of the 32 MHz clock, through an LPF 25 and a 4-sample decimation circuit 26.

[0007] In this way, by converting the input signal into an 8 MHz clock signal, it is possible to convert it into an FFT clock signal specified for terrestrial digital television. The FFT clock signal is output from the orthogonal demodulation circuit 20 and transmitted to a digital processing circuit such as an equalizer in the subsequent stage. The digital processing circuit is not the essence of the present invention described below, so a description thereof will be omitted. Conversely, the present invention can be combined with any kind of digital processing circuit.

[0008] The following are examples of conventional techniques in the technical field of the present invention. For example, Patent Document 1 discloses a technique for removing a loopback wave (loopback signal) that causes a transmission signal to interfere with a receiving antenna in a relay device for terrestrial digital broadcasting. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2012-039300 A Summary of the Invention [Problem to be solved by the invention]

[0010] Here, consider the case where the receiving channel set as the processing target of the receiving device is channel 13, and a channel 13 channels away from the receiving channel (channel 13), that is, a signal of channel 26, is received as the receiving signal (R). Since the center frequency of channel 26 is (551+1 / 7) [MHz], this signal is input to the mixer 11. Meanwhile, since the receiving device is operated to receive a signal of channel 13, a local signal of (510.15+1 / 7) [MHz] is output from the local signal generating circuit 12 as described above. In this case, the mixer 11 multiplies the receiving signal (551+1 / 7) [MHz] by the local signal (510.15+1 / 7) [MHz] to output modulated signals centered on 40.85 [MHz] and 1061.44 [MHz], respectively, and these modulated signals are input to the SAW filter 13.

[0011] The SAW filter 13 is usually designed to pass only the desired frequency band as much as possible. If a filter with nearly ideal characteristics were used, the characteristics of the SAW filter 13 would pass only the IF signal band of 37.15 MHz ±3 MHz. When the output signal of the mixer 11 described above is passed through the SAW filter 13 with these characteristics, the spectrum shown in Figure 3 is obtained.

[0012] In Fig. 3, the horizontal axis indicates frequency and the vertical axis indicates signal level. The dashed line in Fig. 3 indicates the passband of the SAW filter 13, that is, the area that passes the signal to be received. Meanwhile, the hatched area in the figure indicates the spectrum of the signal output from the mixer 11. As can be seen from Fig. 3, when the receiving device receives a signal that is 13 channels away from the receiving channel, a part of the received signal is captured even though it is a channel that is not actually used. As a result, the receiving device erroneously determines that the received signal is the one it wants to receive, causing the input detection of the receiving device to react and malfunction.

[0013] The above explanation is about a signal 13 channels away from the receiving channel, but the same problem of malfunction occurs with a signal 12 channels away from the receiving channel. Specifically, assume that the receiving channel of the receiving device is channel 13 and a signal of channel 25, 12 channels away from that channel, is received. In this case, the center frequency of the received channel 25 (545+1 / 7) and the local frequency for receiving channel 13 (510.15+1 / 7) [MHz] are input to the mixer 11. The mixer 11 multiplies these signals to output modulated signals centered on 34.85 [MHz] and 1055.44 [MHz]. The relationship between this output signal and the spectrum of the SAW filter 13 is shown in Figure 4. In Figure 4, the hatched signal (the output signal of the mixer 11) overlaps with the dashed area (the passband of the SAW filter 13), so the input detection of the receiving device reacts and malfunctions.

[0014] The present invention has been made in consideration of the above-mentioned conventional circumstances, and aims to prevent a terrestrial digital broadcast receiving device from malfunctioning due to a reaction of the input detection even when the device receives a signal from an interfering channel that is a predetermined number of channels away from the receiving channel set to be processed. [Means for solving the problem]

[0015] In order to achieve the above object, a receiving device according to one aspect of the present invention is configured as follows: That is, as an example, a receiving device that receives a signal of terrestrial digital broadcasting includes a signal processing unit to which a signal that is mixed with a local signal for a receiving channel, frequency converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target, the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel, the interference channel signal is a signal of a channel whose partial band passes through the filter when the signal is mixed with the local signal and frequency converted, the channel determination unit has an adjustment shift amount set in advance that is larger than the width of the partial band and smaller than the width of the pass band of the filter, the signal input to the signal processing unit is frequency shifted by an amount obtained by adding or subtracting the adjustment shift amount to or from the frequency shift amount for main line processing, and then passes the signal through a filter that limits the signal to a band for main line processing to detect signal power, and if signal power is detected in the processing, the signal is determined to be a signal of the receiving channel, and if not, the signal is determined to be a signal of the interference channel.

[0016] As another example, a receiving device for receiving a terrestrial digital broadcasting signal includes a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target, the signal processing unit including a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interfering channel different from the receiving channel, the signal of the interfering channel being a signal of a first interfering channel, part of whose band passes through the low-frequency side of the filter when the signal of the interfering channel is mixed with the local signal and frequency converted, or a signal of a second interfering channel, part of whose band passes through the high-frequency side of the filter, and the channel determination unit is configured to determine whether the signal of the first interfering channel is a signal of a first interfering channel, part of whose band passes through the low-frequency side of the filter when the signal of the interfering channel is mixed with the local signal and frequency converted, a first adjustment shift amount that is greater than or equal to the width of the passband of the filter and smaller than the width of the passband of the filter, and a second adjustment shift amount that is greater than the width of the part of the band related to the second interference channel and smaller than the width of the passband of the filter are set in advance; a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by subtracting the first adjustment shift amount from the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power, and a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by adding the second adjustment shift amount to the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power, and if signal power is detected in both of these processes, the signal is determined to be of the receiving channel, and if not, the signal is determined to be of the first interference channel or the second interference channel.

[0017] A channel determination method according to another aspect of the present invention is configured as follows: That is, in a channel determination method implemented by a receiving device receiving a signal of a terrestrial digital broadcasting, the receiving device includes a signal processing unit to which a signal, which is obtained by mixing a received signal with a local signal for a receiving channel and performing frequency conversion, and then passing through a filter that limits the signal to a band of intermediate frequencies, is input as a processing target, the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interfering channel different from the receiving channel, the signal of the interfering channel is a signal of a channel whose part of the band passes through the filter when the signal of the interfering channel is mixed with the local signal and frequency converted, the channel determination unit has an adjustment shift amount set in advance that is larger than the width of the part of the band and smaller than the width of the passband of the filter, the signal input to the signal processing unit is frequency-shifted by an amount obtained by adding or subtracting the adjustment shift amount to or from the frequency shift amount for main line processing, and then passes the signal through a filter that limits the signal to a band for main line processing to detect signal power, and if signal power is detected in the processing, the signal is determined to be a signal of the receiving channel, and if not, the signal is determined to be a signal of the interfering channel.

[0018] As another example, in a channel determination method implemented by a receiving device receiving a signal of terrestrial digital broadcasting, the receiving device includes a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target, the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interfering channel different from the receiving channel, the signal of the interfering channel being a signal of a first interfering channel, part of whose band passes through the low-frequency side of the filter when the signal of the interfering channel is mixed with the local signal and frequency converted, or a signal of a second interfering channel, the part of whose band passes through the high-frequency side of the filter, and the channel determination unit determines whether the part of whose band passes through the high-frequency side of the filter is larger than the width of the part of whose band is related to the first interfering channel. a first adjustment shift amount that is greater than or equal to the width of the passband of the filter and smaller than the width of the passband of the filter, and a second adjustment shift amount that is greater than the width of the part of the band related to the second interference channel and smaller than the width of the passband of the filter are set in advance; a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by subtracting the first adjustment shift amount from the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power, and a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by adding the second adjustment shift amount to the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power, and if signal power is detected in both of these processes, the signal is determined to be of the receiving channel, and if not, the signal is determined to be of the first interference channel or the second interference channel. Effect of the Invention

[0019] According to the present invention, even if a terrestrial digital broadcast receiving device receives a signal of an interfering channel that is a predetermined number of channels away from the receiving channel set to be processed, it is possible to prevent the input detection from reacting and malfunctioning. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a portion of a receiving device provided in a conventional relay station. [Diagram 2] FIG. 1 is a diagram illustrating an example of the configuration of a quadrature demodulation circuit in a conventional receiving device. [Diagram 3] FIG. 13 is a diagram showing a spectrum when signals are received 13 channels apart. [Figure 4] FIG. 13 is a diagram showing a spectrum when signals are received that are 12 channels apart. [Diagram 5] 1 is a diagram illustrating an example of the configuration of a quadrature demodulation circuit in a receiving device according to an embodiment of the present invention. [Figure 6] 1A shows the spectrum when a signal of the receiving channel is received, FIG. 1B shows the spectrum when the signal is shifted by −4.0 [MHz], and FIG. 1C shows the spectrum when the signal is shifted by +3.0 [MHz]. [Figure 7] (a) shows the spectrum when a signal is received that is 12 channels away from the receiving channel, (b) shows the spectrum when the signal is shifted by -4.0 [MHz], and (c) shows the spectrum when the signal is shifted by +3.0 [MHz]. [Figure 8] (a) shows the spectrum when a signal is received that is 13 channels away from the receiving channel, (b) shows the spectrum when the signal is shifted by -4.0 [MHz], and (c) shows the spectrum when the signal is shifted by +3.0 [MHz]. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of the present invention will be described with reference to the drawings. Fig. 5 shows an example of the configuration of an orthogonal demodulation circuit 30 in a receiving device according to an embodiment of the present invention. The orthogonal demodulation circuit 30 of this example includes an IQ separation circuit 21, a DDS 22, an LPF 23, a 4-sample decimation circuit 24, an LPF 25, a 4-sample decimation circuit 26, a DDS 31, an LPF 32, a 4-sample decimation circuit 33, an LPF 34, a signal power calculation circuit 35, a DDS 41, an LPF 42, a 4-sample decimation circuit 43, an LPF 44, a signal power calculation circuit 45, a determination circuit 51, and an output ON / OFF circuit 52.

[0022] The IQ separation circuit 21 to the 4 sample-decimation circuit 26 are circuit parts constituting a main line processing section for processing the reception channel set as the processing target of the receiving device. The IQ separation circuit 21 to the 4 sample-decimation circuit 26 are the same as the configuration of the conventional example shown in FIG. 2 except that the output of the 4 sample-decimation circuit 24 is distributed into three, so detailed description will be omitted. The DDS 31 to the signal power calculation circuit 35 are a first detection circuit part for detecting the signal power of a first interference channel that is 13 channels away from the reception channel. The DDS 41 to the signal power calculation circuit 45 are a second detection circuit part for detecting the signal power of a second interference channel that is 12 channels away from the reception channel.

[0023] The operation of the orthogonal demodulation circuit 30 of this embodiment will now be described. The output of the 4-sample-decimation circuit 24 is distributed into three, and one of them (the main line signal) is passed through an LPF 25 and a 4-sample-decimation circuit 26, as in the conventional method, to generate a signal to be used in a downstream digital signal processing circuit.

[0024] One of the remaining two divided into three is input to the DDS31, where the frequency of the signal is shifted by -4.0 [MHz]. The output signal of the DDS31 is input to the LPF34 via the LPF32 and the 4-sample-decimation circuit 33, which have the same functions as the LPF25 and the 4-sample-decimation circuit 26 on the main line side. As the LPF34, a filter with a frequency characteristic that can only capture the signal of the receiving channel set as the processing target of the receiving device, that is, a filter that limits the band for main line processing, is used. The output signal of the LPF34 is input to the signal power calculation circuit 35, where the signal power is calculated. The calculation result by the signal power calculation circuit 35 is input to the decision circuit 51.

[0025] The other of the remaining two divided into three is input to the DDS 41, where the signal frequency is shifted by +3.0 [MHz]. The output signal of the DDS 41 is input to the LPF 44 via the LPF 42 and the 4-sample-decimation circuit 43, which have the same functions as the LPF 25 and the 4-sample-decimation circuit 26 on the main line side. A filter similar to the LPF 34 is used as the LPF 44. The output signal of the LPF 44 is input to the signal power calculation circuit 45, where the signal power is calculated. The calculation result by the signal power calculation circuit 45 is input to the decision circuit 51.

[0026] The determination circuit 51 determines the received signal of the receiving device based on the calculation results of the signal power calculation circuits 35 and 45. Specifically, it determines whether the received signal is a signal of a receiving channel set as a processing target of the receiving device, a signal of a first interference channel that is 13 channels away from the receiving channel, or a signal of a second interference channel that is 12 channels away from the receiving channel.

[0027] Here, the signal of the first interference channel, which is 13 channels away from the receiving channel, has a spectrum as shown in Figure 3. Since the DDS22 performs a frequency shift of -37.15 [MHz], when the signal is input to the DDS31 or DDS41, the central frequency of 37.15 [MHz] related to the receiving channel is shifted to 0 [MHz]. Since the DDS31 shifts the frequency by -4.0 [MHz], the hatched area shifts by 4.0 [MHz] to the left, but it still overlaps greatly with the band for processing the receiving channel, so a lot of the receiving signal is captured. On the other hand, the DDS41 shifts the frequency by +3.0 [MHz], so the receiving signal is lost away from the band of the receiving channel.

[0028] Fig. 8 shows a spectrum relating to a signal of the first interfering channel, which is 13 channels away from the receiving channel. In Fig. 8, (a) is the spectrum when the signal of the first interfering channel is received, (b) is the spectrum when the signal of the first interfering channel is shifted by -4.0 [MHz], and (c) is the spectrum when the signal of the first interfering channel is shifted by +3.0 [MHz]. As is clear from Fig. 8, when a signal of the first interfering channel, which is 13 channels away from the receiving channel, is received, the signal power is observed by the signal power calculation circuit 35, but the signal power is not observed by the signal power calculation circuit 45.

[0029] Similarly, the signal of the second interfering channel, which is 12 channels away from the receiving channel, has a spectrum as shown in Figure 4. With DDS31, the frequency is shifted by -4.0 MHz, so it is out of the band of the receiving channel and the received signal disappears. On the other hand, with DDS41, the frequency is shifted by +3.0 MHz, so the hatched area shifts by 3.0 MHz to the right, but it still overlaps largely with the band for processing the receiving channel, so a lot of the received signal is captured.

[0030] Fig. 7 shows a spectrum relating to a signal of a second interfering channel 12 channels away from the receiving channel. In Fig. 7, (a) is a spectrum when a signal of the second interfering channel is received, (b) is a spectrum when the signal of the second interfering channel is shifted by -4.0 [MHz], and (c) is a spectrum when the signal of the second interfering channel is shifted by +3.0 [MHz]. As is clear from Fig. 7, when a signal of the second interfering channel 12 channels away from the receiving channel is received, the signal power is observed by the signal power calculation circuit 45, but the signal power is not observed by the signal power calculation circuit 35.

[0031] On the other hand, in the case of a signal from a receiving channel set as the processing target of the receiving device, a signal in a band of ±2.785 [MHz] centered on 0 [MHz] is input to the DDS 31, 41. In this case, whether a frequency shift of -4.0 [MHz] or a frequency shift of +3.0 [MHz] is performed, the signal largely overlaps with the band of the receiving channel, so a large amount of the received signal is captured.

[0032] Figure 6 shows the spectrum of the signal of the receiving channel. In Figure 6, (a) is the spectrum when the signal of the receiving channel is received, (b) is the spectrum when the signal of the receiving channel is shifted by -4.0 [MHz], and (c) is the spectrum when the signal of the receiving channel is shifted by +3.0 [MHz]. As is clear from Figure 6, when a signal of the receiving channel is received, the signal power is observed by both the signal power calculation circuits 35 and 45.

[0033] The decision circuit 51 uses the above characteristics to make a decision about the received signal of the receiving device. Specifically, when the signal power can be detected by both of the two signal power calculation circuits 35, 45, the decision circuit 51 decides that a signal of the receiving channel has been received. In this case, the decision circuit 51 outputs a High level signal to the output ON / OFF circuit 52. When a High level signal is input, the output ON / OFF circuit 52 outputs the main line signal input via the LPF 25 and the 4-sample decimation circuit 26 from the orthogonal demodulation circuit 30.

[0034] On the other hand, when the signal power cannot be detected by either one of the two signal power calculation circuits 35, 45, the determination circuit 51 determines that a signal of a first interference channel that is 13 channels away from the receiving channel or a signal of a second interference channel that is 12 channels away has been received. In this case, the determination circuit 51 outputs a Low level signal to the output ON / OFF circuit 52. When a Low level signal is input, the output ON / OFF circuit 52 cuts off the output of the orthogonal demodulation circuit 30 (i.e., does not output a main line signal).

[0035] Furthermore, when the signal power cannot be detected by both of the two signal power calculation circuits 35, 45, the determination circuit 51 determines that the signal is not being received from the receiving channel, nor from the first or second interfering channel. In this case, too, the determination circuit 51 outputs a Low-level signal to the output ON / OFF circuit 52. When a Low-level signal is input, the output ON / OFF circuit 52 cuts off the output of the orthogonal demodulation circuit 30 (i.e., does not output a main line signal).

[0036] Here, in the determination circuit 51 of this example, when the calculation result by the signal power calculation circuits 35, 45 is greater than 0, it is determined that the signal power is detected, but this is not limited to this. For example, a threshold value greater than 0 may be set in advance in consideration of noise, etc., and when the calculation result by the signal power calculation circuits 35, 45 is greater than the threshold value, it may be determined that the signal power is detected.

[0037] As described above, the receiving device of this embodiment includes an FPGA 15 (an example of a signal processing unit according to the present invention) to which a signal that has passed through the SAW filter 13, which limits the signal to an intermediate frequency band after mixing the received signal with a local signal for the receiving channel and performing frequency conversion, is input as a processing target. The FPGA 15 includes an orthogonal demodulation circuit 30 (an example of a circuit including a channel determination unit according to the present invention) that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel. Here, the signal of the interference channel is a signal of a first interference channel, part of whose band passes through the low-pass side of the SAW filter 13 when the signal is mixed with a local signal and frequency converted, or a signal of a second interference channel, part of whose band passes through the high-pass side of the SAW filter 13. The orthogonal demodulation circuit 30 is preset with a first adjustment shift amount (4.0 [MHz]) that is larger than the width of a portion of the band related to the first interference channel and smaller than the width of the passband of the SAW filter 13, and a second adjustment shift amount (3.0 [MHz]) that is larger than the width of a portion of the band related to the second interference channel and smaller than the width of the passband of the SAW filter 13. The orthogonal demodulation circuit 30 performs the following processes: shifting the frequency of the signal input to FPGA 15 by an amount obtained by subtracting the first adjustment shift amount from the frequency shift amount for main line processing (-4.0 [MHz]), passing the signal through LPF 34 which limits the signal to the band for main line processing to detect signal power; shifting the frequency of the signal input to FPGA 15 by an amount obtained by adding the second adjustment shift amount to the frequency shift amount for main line processing (+3.0 [MHz]), passing the signal through LPF 44 which limits the signal to the band for main line processing to detect signal power; if signal power is detected by both of these processes, it is determined to be a signal of the receiving channel; if not, it is determined to be a signal of the first or second interference channel.

[0038] With this configuration, even if the receiving device receives a signal other than the receiving channel set as the processing target (in this example, a signal from the first interfering channel 13 channels away from the receiving channel or a signal from the second interfering channel 12 channels away), it is possible to prevent the input detection from reacting and malfunctioning.

[0039] The above description is based on the assumption that the receiving device is installed in an environment where there is a possibility of receiving signals of two types of interference channels, but when the receiving device is installed in an environment where there is only a possibility of receiving signals of one type of interference channel, some of the above configurations may be omitted. That is, if there is no possibility of receiving signals of a first interference channel that is 13 channels away from the receiving channel, the DDS31 through the signal power calculation circuit 35 constituting the first detection circuit unit can be omitted. Also, if there is no possibility of receiving signals of a second interference channel that is 12 channels away from the receiving channel, the DDS41 through the signal power calculation circuit 45 constituting the second detection circuit unit can be omitted.

[0040] In addition, the location of the output ON / OFF circuit 52 is not limited to the location shown in Fig. 5. For example, by feeding the High / Low signal of the determination result of the determination circuit 51 to a portion of a downstream digital processing circuit, it is possible to turn the output ON / OFF in another location.

[0041] In addition, the arrangement of the DDS31, 41 is not limited to the position shown in Fig. 5. For example, the output of the IQ separation circuit 21 may be distributed to three: the DDS22, which shifts the signal by -37.15 [Mhz] for the main line signal; the DDS31', which shifts the signal by -41.15 (=-37.15-4) [MHz]; and the DDS41', which shifts the signal by -34.15 (=37.15+3) [MHz]. In this case, however, it is necessary to add an LPF and a 4-sample decimation circuit having the same functions as the LPF23 and the 4-sample decimation circuit 24 to the rear stages of the DDS31', 41'.

[0042] Also, the adjustment shift amount of -4.0 [MHz] for DDS31 is merely an example, and may be further shifted by about -2 MHz. Similarly, the adjustment shift amount of +4.0 [MHz] for DDS41 is merely an example, and may be further shifted by about +2 MHz. The adjustment shift amounts of DDS31 and 41 may be shift amounts that are larger than the width of the band that passes through SAW filter 13 when the interference channel is mixed with the local signal for the receiving channel and frequency converted, and smaller than the width of the passband of SAW filter 13.

[0043] Although the embodiments of the present invention have been described above, the above embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the gist of the present invention. These embodiments and modifications are included in the scope and gist of the invention described in this specification, etc., and are included in the scope of the invention described in the claims and their equivalents.

[0044] Furthermore, the present invention can be provided not only as devices such as those described above or as a system composed of these devices, but also as methods executed by these devices, programs for causing a processor to realize the functions of these devices, and storage media for storing such programs in a computer-readable format. [Industrial Applicability]

[0045] The present invention can be used in a receiving device that receives a terrestrial digital broadcast signal. [Explanation of symbols]

[0046] 11: mixer, 12: local signal generation circuit, 13: SAW filter, 14: A / D converter, 15: FPGA, 20: quadrature demodulation circuit, 21: IQ separation circuit, 22: DDS, 23: LPF, 24: 4 sample-decimation circuit, 25: LPF, 26: 4 sample-decimation circuit, 30: quadrature demodulation circuit, 31: DDS, 32: LPF, 33: 4 sample-decimation circuit, 34: LPF, 35: signal power calculation circuit, 41: DDS, 42: LPF, 43: 4 sample-decimation circuit, 44: LPF, 45: signal power calculation circuit, 51: decision circuit, 52: output ON / OFF circuit

Claims

1. In a receiving device for receiving a terrestrial digital broadcast signal, a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency-converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target; the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel; the interference channel signal is a channel signal whose band is partially passed through the filter when the interference channel signal is mixed with the local signal and frequency converted; The channel determination unit is preset with an adjustment shift amount that is larger than the width of the part of the band and smaller than the width of the passband of the filter, and after frequency shifting the signal input to the signal processing unit by an amount obtained by adding or subtracting the adjustment shift amount to the frequency shift amount for main line processing, the signal is passed through a filter that limits the signal to the band for main line processing, and if signal power is detected by this process, it is determined to be a signal of the receiving channel, and if not, it is determined to be a signal of the interference channel.

2. In a receiving device for receiving a terrestrial digital broadcast signal, a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency-converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target; the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel; the interference channel signal is a first interference channel signal, a part of whose band passes through the low-pass side of the filter when mixed with the local signal and frequency-converted, or a second interference channel signal, a part of whose band passes through the high-pass side of the filter; The channel determination unit is preset with a first adjustment shift amount that is larger than the width of the portion of the band related to the first interference channel and smaller than the width of the passband of the filter, and a second adjustment shift amount that is larger than the width of the portion of the band related to the second interference channel and smaller than the width of the passband of the filter, and performs a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by subtracting the first adjustment shift amount from the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to the band for main line processing to detect signal power, and a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by adding the second adjustment shift amount to the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to the band for main line processing to detect signal power, and if signal power is detected in both of these processes, the signal is determined to be of the receiving channel, and if not, the signal is determined to be of the first interference channel or the second interference channel.

3. A channel determination method implemented by a receiving device for receiving a terrestrial digital broadcast signal, comprising: the receiving device includes a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency-converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target; the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel; the interference channel signal is a channel signal whose band is partially passed through the filter when the interference channel signal is mixed with the local signal and frequency converted; The channel determination unit has a preset adjustment shift amount that is larger than the width of the part of the band and smaller than the width of the passband of the filter, and after frequency shifting the signal input to the signal processing unit by an amount obtained by adding or subtracting the adjustment shift amount to the frequency shift amount for main line processing, the signal is passed through a filter that limits the signal to the band for main line processing, and a channel determination method characterized in that if signal power is detected by this process, the signal is determined to be of the receiving channel, and if not, the signal is determined to be of the interference channel.

4. A channel determination method implemented by a receiving device for receiving a terrestrial digital broadcast signal, comprising: the receiving device includes a signal processing unit to which a signal that has been mixed with a local signal for a receiving channel, frequency-converted, and then passed through a filter that limits the signal to an intermediate frequency band is input as a processing target; the signal processing unit includes a channel determination unit that determines whether the received signal is a signal of the receiving channel or a signal of an interference channel different from the receiving channel; the interference channel signal is a first interference channel signal, a part of whose band passes through the low-pass side of the filter when mixed with the local signal and frequency-converted, or a second interference channel signal, a part of whose band passes through the high-pass side of the filter; a first adjustment shift amount that is greater than a width of the portion of the band related to the first interference channel and smaller than a width of the passband of the filter, and a second adjustment shift amount that is greater than a width of the portion of the band related to the second interference channel and smaller than the width of the passband of the filter are preset in the channel determination unit; and the channel determination unit performs a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by subtracting the first adjustment shift amount from a frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power; and a process of frequency-shifting a signal input to the signal processing unit by an amount obtained by adding the second adjustment shift amount to the frequency shift amount for main line processing, and then passing the signal through a filter that limits the signal to a band for main line processing to detect signal power. If signal power is detected in both of these processes, the signal is determined to be of the receiving channel, and if not, the signal is determined to be of the first interference channel or the second interference channel.

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