JP2009206812A - Receiver, and transceiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver which receives-demodulates a transmission signal to be transmitted in a frequency band close to a frequency band used by others while suppressing an influence of a transmitting signal to be transmitted in the frequency band used for others more. <P>SOLUTION: A circuit 17 via OFDM setting and tuner setting dynamically changes a frequency of a local oscillator with which a tuner circuit 2 is provided by an instruction from a CPU 3, as its demodulation result, acquires the maximum values between CN values obtained by every segment from a CN judgment circuit 16 by every frequency, and notifies a CPU 2 of a frequency in which the smaller maximum value is obtained from among the dynamically changed frequencies as a frequency optimal for down convert. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a transmission signal transmitted in a first frequency band, converts the received signal obtained by the reception into a second received signal that is a signal in a lower frequency band, and demodulates the received signal. .

  In a receiving apparatus capable of receiving a transmission signal transmitted in a high frequency band (first frequency band), the reception signal obtained by receiving the transmission signal is usually lower in frequency band (second frequency band). (Down-conversion) and demodulating (Patent Document 1). The conversion is usually performed by multiplying the received signal by a local frequency signal having a frequency lower than the frequency band. Hereinafter, the frequency of the local frequency signal is referred to as “local frequency”.

  As is well known, aliasing occurs when multiplied by a local frequency signal. The folding causes the received signal in the other frequency band to overlap the received signal in the desired frequency band. For this reason, when using a frequency band close to the frequency band used elsewhere, it is important to set the local frequency in consideration of noise caused by aliasing. Hereinafter, this will be specifically described with reference to the explanatory diagrams shown in FIGS. 4 to 6, the horizontal axis indicates the frequency, and the vertical axis indicates the signal level on the transmission side (frequency bands used in other areas (here, the 7 and 9 channel frequency bands)).

  4 and 5 assume that the frequency band between 7 channels (CH) and 9 channels of analog broadcasting, that is, the frequency band of 8 channels is used in terrestrial digital broadcasting of 1 channel and 3 segments. It is a figure explaining the setting method of local frequency. A segment corresponds to a unit band used for transmission of a transmission signal. Here, for convenience, the segments are referred to as “first segment”, “second segment”,.

  As shown in FIG. 4, a total of 8 segments can be used in the frequency band of 8 channels (VHF 8 channels). Of these, the frequency band for three segments is 1.285714 MHz.

  The local frequency is set below or above the desired signal band, which is a frequency band (second frequency band) for frequency conversion of the received signal. Accordingly, “LoL” and “LoH” in FIGS. 4 and 5 indicate the positions of the lower and upper frequencies that can be set as local frequencies on the frequency axis of the received signal (transmission signal), respectively. Yes. For the sake of convenience, a frame with “image” inward indicates a frequency band in which a reception signal (a reception signal that becomes noise, hereinafter referred to as “image”) is superimposed when the frequency LoL or LoH is selected as a local frequency. It is a representation. “LoLIM” and “LoHIM” indicate the lower limit and the upper limit frequency of an image that is folded back within a desired signal band for converting a transmission signal of three segments, respectively. From this, the local frequency is the lower frequency of three segments as shown in FIG. 4, that is, the frequency LoH when the first to third segments are used for broadcasting, and the higher frequency as shown in FIG. When 3 segments, that is, the 6th to 8th segments are used for broadcasting, by selecting and setting the frequency LoL, it is possible to avoid unnecessary images (received signals) being folded in the desired signal band. it can.

  The receiving apparatus usually has a mechanism for removing an image, for example, an image removal filter. However, the amount of image attenuation by the mechanism is finite, and there is a part that cannot be removed. Compared with digital broadcasting, the signal level of analog broadcasting is very high. For this reason, it is essential to select and set an appropriate local frequency when using a channel that is adjacent to the channel being used.

As described above, even when a frequency band (channel) that is used and a frequency band (channel) adjacent to the frequency band (channel) are used, the frequency band actually used in the frequency band (hereinafter referred to as the frequency band of the channel). To avoid the influence of the transmission signal (image) transmitted in the adjacent used frequency band by selecting the “partial frequency band” for distinction) and selecting the local frequency according to the selection. Is possible. However, when trying to use frequency resources more effectively, there is a possibility that a desired partial frequency band cannot always be selected. For example, as shown in FIG. 6, when trying to use three segments from the third lowest frequency, that is, the third to fifth segments for broadcasting, select either the frequency LoL or LoH as the local frequency. Even if it is set, the image of the adjacent frequency band in use is folded back into the desired signal band. For this reason, in order to use the frequency resource more effectively, it is considered important to reduce the influence of the image on the premise that the image that becomes noise is folded.
JP 2005-244481 A

  An object of the present invention is to provide a receiving device that receives and demodulates a transmission signal transmitted in a frequency band close to the frequency band while suppressing the influence of a transmission signal transmitted in a frequency band used elsewhere. There is to do.

  The receiving apparatus of the present invention receives a transmission signal transmitted in a first frequency band, and uses a local frequency signal having a frequency lower than the first frequency band as the first reception signal obtained by the reception. The second reception signal in the second frequency band is converted into a second reception signal and demodulated, and a transmission signal in the designated first frequency band is received and a second reception signal is output. Receiving means capable of changing the frequency of the local frequency signal used for generating the received signal, demodulating means for demodulating using the second received signal output from the receiving means, and receiving means for generating the second received signal Frequency discriminating means for dynamically changing the frequency of the local frequency signal to be used and discriminating an optimum frequency as the frequency of the local frequency signal based on a demodulation result by the demodulating means.

  Note that when there are a plurality of unit bands each used for transmission of a transmission signal in the designated first frequency band, the frequency discriminating unit determines the optimum based on the demodulation result by the demodulating unit for each unit band. It is desirable to determine the frequency.

  The transmission / reception method of the present invention receives a transmission signal transmitted in a first frequency band, and uses a local frequency signal having a frequency lower than the first frequency band as the first reception signal obtained by the reception. A transmission / reception method assuming a receiving apparatus that converts to a second received signal in the second frequency band and demodulates the received signal, wherein the transmitting side of the transmission signal is used as the first frequency band elsewhere. The transmission apparatus transmits the transmission signal using the first frequency band adjacent to the first frequency band, and the reception apparatus generates the second reception signal when receiving the transmission signal of the adjacent first frequency band. The second received signal is generated and demodulated using the local frequency signal having the optimum frequency determined by dynamically changing the frequency of the local frequency signal to be used.

  In the system to which the present invention is applied, the frequency of the local frequency signal used for obtaining the second reception signal from the first reception signal obtained by receiving the transmission signal of the designated first frequency band is dynamically changed. The optimum frequency is discriminated as the frequency of the local frequency signal from the result of changing and demodulating using the obtained second received signal. For this reason, even if another first frequency band that is close to (is near to) the first frequency band is used elsewhere, the influence of the transmission signal transmitted in the other first frequency band is further suppressed. Can be received and demodulated. Thereby, the options of the first frequency band that can be used for the transmission signal can be substantially increased, and the frequency resource can be used more effectively.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating the circuit configuration of the receiving apparatus according to the present embodiment.

  The receiving apparatus is for receiving and demodulating a transmission signal (hereinafter also referred to as “OFDM signal”) transmitted by an OFDM (Orthogonal Frequency Division Multiplexing) method employed in, for example, terrestrial digital broadcasting. As shown in FIG. 1, an antenna 1 for receiving an OFDM signal, a tuner circuit 2 for receiving an OFDM signal of a set channel via the antenna 1, a CPU 3 for controlling the entire apparatus, and a tuner circuit 2, an OFDM baseband circuit (hereinafter abbreviated as “BB circuit”) 4 that demodulates the received OFDM signal and outputs a baseband signal. The baseband signal is reception data finally obtained by demodulation, that is, a TS (transport stream) packet, and at least one of an image and audio obtained by expanding the TS packet is output.

  The tuner circuit 2 converts the received OFDM signal into an intermediate frequency band signal having a lower frequency (hereinafter referred to as an “intermediate OFDM signal” or an “IF (intermediate frequency) signal”) for output. . The conversion is performed by multiplying the local frequency signal by the OFDM signal. In order to perform such conversion, a local oscillator capable of changing the local frequency is provided. At the time of down-conversion for multiplying the local frequency signal, a real part and an imaginary part of the complex OFDM signal are generated and combined to obtain a complex OFDM signal.

  The BB circuit 4 includes an ADC circuit 11, an FFT circuit 12, a transmission line equalization circuit 13, a demodulation circuit 14, an error correction circuit 15, a CN (Carrier to Noise ratio) determination circuit 16, and an OFDM setting / tuner setting via circuit (hereinafter referred to as a circuit). (Abbreviated as “setting via circuit”) 17.

  The ADC circuit 11 converts the analog IF signal (reconstructed OFDM signal) input from the tuner circuit 2 into a digital IF signal and outputs the digital IF signal. The FFT circuit 12 performs an FFT (Fast Fourier Transform) on the IF signal and outputs an IF signal in the frequency domain. The transmission line equalization circuit 13 corrects (compensates) distortion caused by the transmission line in the transmitted OFDM signal by a known technique. In other words, it detects (estimates) the IF signal, that is, the shift or magnitude generated between the actually obtained complex OFDM signal and the ideal signal due to the influence of the ghost wave or the shift of the FFT window. Correct.

  The demodulation circuit 14 demodulates the corrected IF signal, that is, restores data transmitted from the transmission side, cancels various interleaving, and outputs the data in units of TS packets. The error correction circuit 15 performs Viterbi decoding or Reed-Solomon decoding on the data output from the demodulation circuit 14 to correct the generated error. The corrected data is output from the BB circuit 4 in the form of TS packets.

  The CN determination circuit 16 quantifies the deviation or size detected by the transmission line equalization circuit 13 and calculates a CN (Carrier to Noise ratio) value. An OFDM setting and tuner setting via circuit (hereinafter abbreviated as “setting via circuit”) 17 performs setting of the tuner circuit 2 and the BB circuit 4 in accordance with an instruction from the outside (here, the CPU 3).

  As shown in FIG. 6, when trying to use three segments from the third lowest frequency, that is, the third to fifth segments in the channel adjacent to the other channel being used for broadcasting, Regardless of which of the frequencies LoL and LoH is selected and set as the frequency, the image (interference wave signal) of the adjacent frequency band in use is folded back into the desired signal band. In the present embodiment, assuming such a case, an optimum frequency is determined from frequencies (frequency LoL and LoH) that can be selected as local frequencies.

  The optimum frequency is discriminated by sequentially setting the frequencies (frequency LoL and LoH) that can be selected, that is, dynamically changing the frequency (setting), and referring to the demodulation result obtained by the setting. I have to. As a demodulation result, the CN value for each segment is referred to. This is for the following reason. The reason will be specifically described with reference to FIG.

  FIG. 3 is a diagram illustrating an image (jamming wave) that is folded back within a desired signal band by selecting a local frequency. FIG. 3A shows a case where the frequency LoL is selected as the local frequency, and FIG. 3B shows a case where the frequency LoH is selected as the local frequency. The horizontal axis represents frequency, and the vertical axis represents signal level.

  When the frequency LoL is selected, as shown in FIG. 6, the image (interference wave) of the channel (here, 7 channels) adjacent to the lower side (the lower frequency side) is folded back within the desired signal band. The image folded in 7 channels has a frequency band of about 1.5 segments, and the frequency band is in the range of the lower half of the folded image. Therefore, the image of the range (denoted as “lower adjacent channel interference wave” in FIG. 3A) mainly affects the upper half of the three segments as shown in FIG. 3A. Become. That is, about half of the fourth segment affects the whole of the fourth segment, and the image is superimposed on the received signal. This means that there is a large difference in CN value particularly between the third segment and the fifth segment.

  On the other hand, when the frequency LoH is selected, on the contrary, the image (interference wave) of the channel (here, 9 channels) adjacent to the upper side (the higher frequency side) is folded back within the desired signal band. As a result, the 9-channel image (shown as “upper adjacent channel jamming wave” in FIG. 3B) mainly affects the lower half of the three segments as shown in FIG. 3B. Become. That is, about half of the fourth segment affects the whole of the fourth segment, and the image is superimposed on the received signal.

  For this reason, the difference in CN value between segments indicates the degree of influence of an image (interference wave). Thereby, the degree of the influence of the image is estimated using the difference as an index, and the frequency with the smaller difference is discriminated as the optimum local frequency. Note that the demodulation result that can be referred to is not limited to the CN value, but the BER (Bit Error Rate) obtained by comparing the bits before and after correction, or the variation in data symbol coordinates is quantified. MER (Modulation Error Ratio) obtained by the above can be employed.

  FIG. 2 is a flowchart showing the operations performed by the respective units of the CPU 3, the BB circuit 4, and the tuner circuit 2 and the flow thereof when determining the optimum frequency. Next, the operation of each part and the flow in that case will be described in detail with reference to FIG.

  In this embodiment, for each channel (station), a table (channel table) defining local frequencies to be set is created and managed so as to correspond to user tuning. The creation and management of the table is performed by the CPU 3, and the operation for determining the optimum frequency is started by instructing the BB circuit 3 from the CPU 3. The instruction is given at a predetermined timing. The timing is, for example, when a user selects a broadcasting station that does not define a local frequency (a frequency band that is not used by others), when the power is turned on, or when a predetermined date and time is reached. . Here, for convenience, description will be made assuming that the user selects a broadcasting station that does not define a local frequency. In that case, a local frequency for better receiving the transmission signals of the third to fifth segments is defined only for that station.

  When the user selects such a station, the CPU 3 transfers a command for instructing an operation for determining the optimum frequency together with the basic operation setting value to the setting via circuit 17 of the BB circuit 3 (step SC1). . Thereby, the setting via circuit 17 sets each part of the BB circuit 4 and the tuner circuit 2 according to the transferred basic operation setting value (step SO1). As a result, the tuner circuit 2 is set other than the local frequency (step SR1).

  Next, the setting relay circuit 17 selects the frequency LoL from the frequencies LoL and LoH that can be selected as the local frequency, and sets the tuner circuit 2 (step SO2). Thereby, the tuner circuit 2 sets a local oscillator (not shown) to generate a local frequency signal at the frequency LoL (step SR2).

  With this setting, the tuner circuit 2 starts outputting an analog IF signal (reconstructed OFDM signal) generated by down-conversion using a local frequency signal having the frequency LoL. With this start, the transmission line equalization circuit 13 estimates the transmission line characteristics and compensates for distortion of the IF signal for each segment, and the CN determination circuit 16 calculates the CN value for each segment from the estimation result. The maximum value of the CN value difference between segments is calculated and stored as a variable LoLDEF (steps SO3 and SO4).

  When the calculation (storage) of the variable LoLDEF is notified from the CN determination circuit 16, the setting via circuit 17 selects the frequency LoH from among the frequencies LoL and LoH that can be selected as the local frequency next, and sets the tuner circuit 2. Is performed (step SO5). Thereby, the tuner circuit 2 sets the local oscillator (not shown) to generate a local frequency signal at the frequency LoH (step SR3).

  With this setting, the tuner circuit 2 starts outputting an analog IF signal (reconstructed OFDM signal) generated by down-conversion using a local frequency signal having a frequency LoH. By the start, the CN determination circuit 16 similarly calculates the CN value for each segment, calculates the maximum value of the CN value difference between the segments, and stores it as a variable LoHDEF (steps SO6 and SO7).

  When the calculation (storage) of the variable LoHDEF is notified from the CN determination circuit 16, the setting via circuit 17 compares the values of the variables LoLDEF and LoHDEF, and transmits information indicating the smaller value to the CPU 3 (step SO8). . Upon reception of the information, the CPU 3 defines the frequency indicated by the information on the channel table as the optimum frequency to be set at the current target station (step SC2). When the value of the variable LoHDEF is larger, the setting via circuit 17 is instructed to set the frequency LoL as the local frequency. Thereby, the local frequency is changed so that demodulation can be performed better.

  By determining the optimum frequency in this way, even if a frequency band in the vicinity of a frequency band used elsewhere (a frequency band that can be received on the receiving side) is used, the frequency band that has less influence as an interference wave Thus, the local frequency can be set so that the received signal (image) is folded within the desired signal band. In the situation where the frequency band used elsewhere is only one of the two sides (only one of channels 7 and 9 in the example of FIG. 6), the reception of the unused frequency band (the frequency band that cannot be received) is received. The local frequency can be set so that the signal is folded within the desired signal band. For this reason, demodulation of the received signal can be performed in a more desirable form.

  As a result, the receiving side can be demodulated more favorably, so that on the transmitting side (for example, the broadcasting station side), there are more choices of frequency bands used for transmitting transmission signals. Thereby, the frequency resource can be used more effectively.

  In this embodiment, the optimum frequency is discriminated on the BB circuit 4 side, but the discrimination may be made on the CPU 3 side. As the modulation method, the OFDM method is adopted, but a modulation method other than the OFDM method may be used. Since the frequency band (first frequency band) used for transmission of the transmission signal by the transmission side is high, the reception signal (first reception signal) obtained by receiving the transmission signal is set to a lower frequency band (first frequency band). (2 frequency band) received signal (second received signal) need only be converted (down-converted). The conversion may be performed in two or more stages. The first frequency band is for three segments, but the bandwidth is not particularly limited.

It is a figure explaining the circuit structure of the receiver by this embodiment. 6 is a flowchart showing an operation performed by each unit of the CPU 3, the BB circuit 4, and the tuner circuit 2 and the flow thereof when determining the optimum frequency. It is a figure explaining the image (jamming wave) folded in the desired signal band by selection of a local frequency. It is a figure explaining the setting method of the local frequency at the time of assuming using the frequency band of 8 channels between 7 channels (CH) and 9 channels of analog broadcasting by the terrestrial digital broadcasting of 1 channel 3 segments. (Part 1). It is a figure explaining the setting method of the local frequency at the time of assuming using the frequency band of 8 channels between 7 channels (CH) and 9 channels of analog broadcasting by the terrestrial digital broadcasting of 1 channel 3 segments. (Part 2). The figure explaining the malfunction which arises by the segment to be used when assuming that the frequency band of 8 channels between 7 channels (CH) and 9 channels of analog broadcasting is used in terrestrial digital broadcasting of 1 channel 3 segments It is.

Explanation of symbols

1 Antenna 2 Tuner Circuit 3 CPU
4 OFDM Baseband Circuit 11 ADC Circuit 12 FFT Circuit 13 Transmission Line Equalization Circuit 14 Demodulation Circuit 15 Error Correction Circuit 16 CN Determination Circuit 17 OFDM Setting and Tuner Setting Via Circuit

Claims (3)

A transmission signal transmitted in the first frequency band is received, and the first reception signal obtained by the reception is transmitted to the second frequency band using a local frequency signal having a frequency lower than the first frequency band. In a receiving apparatus that converts to a second received signal and demodulates it,
Receiving means capable of changing the frequency of the local frequency signal used for generating the second received signal, which receives the transmission signal of the designated first frequency band and outputs the second received signal;
Demodulating means for demodulating using the second received signal output from the receiving means;
The receiving unit dynamically changes the frequency of the local frequency signal used for generating the second received signal, and determines an optimum frequency as the frequency of the local frequency signal based on a demodulation result by the demodulating unit. Frequency discriminating means,
A receiving apparatus comprising: When there are a plurality of unit bands each used for transmission of a transmission signal in the designated first frequency band, the frequency determination unit is based on a demodulation result by the demodulation unit for each unit band, Determining the optimal frequency;
The receiving apparatus according to claim 1. A transmission signal transmitted in the first frequency band is received, and the first reception signal obtained by the reception is transmitted to the second frequency band using a local frequency signal having a frequency lower than the first frequency band. A transmission / reception method assuming a receiving device that converts to a second received signal and demodulates it,
The transmission side of the transmission signal transmits the transmission signal using the first frequency band adjacent to the first frequency band used elsewhere as the first frequency band,
The receiving device, when receiving a transmission signal in the adjacent first frequency band, the optimum frequency determined by dynamically changing the frequency of the local frequency signal used for generating the second reception signal Generating and demodulating the second received signal using the local frequency signal of
A transmitting / receiving method characterized by the above.