JP2010245817A - Receiving apparatus and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiving apparatus and receiving method which accurately estimate a receiving status. <P>SOLUTION: A receiving status estimation unit selects and obtains a signal of which transmission line characteristics become equal to or higher than a threshold. A signal which is not selected by the present method but is excluded becomes a signal embedded in noise by considerably reducing its strength during transmission. Meanwhile, a signal which is selected and obtained becomes a signal that is not embedded in noise. The receiving status estimation unit estimates a receiving status using the selected and obtained signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a receiving apparatus and a receiving method for receiving a signal and estimating a reception situation.

  In recent years, digital communication technology has been used in various fields of wireless communication such as television broadcasting and mobile communication. Among such receiving apparatuses, there is a receiving apparatus that estimates a reception situation from a received signal and uses it for various controls.

  For example, Patent Document 1 proposes a receiving apparatus that can quickly estimate a reception situation by estimating a reception situation using a baseband signal obtained upstream of reception processing.

JP 2007-208748 A

  However, the conventional receiving apparatus has a problem that the estimation accuracy of the reception state deteriorates. In particular, the distortion received by the receiving device in the transmission path with respect to the received signal (for example, the transmitted signal is reflected and diffracted by a building or the like so that the signal is transmitted through a plurality of transmission paths (multipath). When a process (equalization process) for correcting (distortion) is performed and a reception state is estimated using a signal subjected to the process, there is a problem that noise is greatly amplified by the process and the estimation accuracy deteriorates. This problem will be described with reference to FIG. FIG. 8 is a graph showing a conventional method of estimating the reception status.

  The graph shown in FIG. 8 shows the frequency of the received signal on the horizontal axis and the intensity on the vertical axis, and shows the state of the signal before and after the equalization processing is performed. As shown in FIG. 8, in the signal before the equalization processing, the portion where the strength becomes extremely small due to the influence of multipath or the like (the broken line area in the figure) is greatly increased in strength by performing the equalization processing. Is amplified. However, since this part is a part where the signal is buried in noise (a part where the ratio of the noise component is large), if the reception situation is estimated using the signal of the part after the equalization processing, it is more than the actual reception situation. It is more likely to be inferior. Therefore, the estimation accuracy of the reception situation may be deteriorated.

  Furthermore, when the multipath state varies with time, such as when applied to mobile communication, the estimation result of the reception status varies accordingly, but the estimation result obtained when the estimation accuracy is poor varies greatly. When the reception process is controlled according to the reception state estimation result, it is difficult to perform appropriate control.

  Therefore, an object of the present invention is to provide a receiving apparatus and a receiving method capable of accurately estimating a reception state.

  In order to achieve the above object, a receiving apparatus according to the present invention, in a receiving apparatus that receives a signal to be transmitted, performs a selection based on an influence received by the signal from the received signal, and selects a selection signal. A signal acquisition unit to be acquired and a reception status estimation processing unit that estimates a reception status using the selection signal.

  In the following embodiments, an average MER estimator and an average C / N estimator are described as examples of the reception status estimation processor.

  The receiving apparatus having the above-described configuration further includes an equalization processing unit that estimates a transmission path characteristic indicating the influence of the signal on the transmission and corrects the signal based on the transmission path characteristic, The unit may perform selection based on the transmission path characteristic from the signal corrected by the equalization processing unit, and acquire the selection signal.

  If comprised in this way, a signal acquisition part will acquire a selection signal by performing selection based on a transmission-line characteristic from the signal correct | amended by the equalization process part. For this reason, it is possible to exclude a signal that has been corrected by the equalization processing unit to be a signal that is not suitable for estimation of the reception situation, and to acquire another signal as a selection signal.

  In the receiving device having the above-described configuration, the signal acquisition unit may acquire the signal having the transmission path characteristic strength equal to or higher than a threshold as the selection signal.

  If comprised in this way, it will become possible for a signal acquisition part to acquire as a selection signal a signal with the low intensity | strength of a transmission-line characteristic and a low possibility that it will be buried in a noise component. For this reason, the estimated reception status is not easily affected by the noise component. Therefore, it is possible to improve the estimation accuracy of the reception status.

  In the receiving device having the above-described configuration, the threshold value may be a value based on an average value of the intensity of the transmission path characteristics.

  If comprised in this way, it will become possible to set the threshold value according to the state of the received signal. Accordingly, it is possible to further improve the estimation accuracy of the reception status.

  Further, in the receiving apparatus having the above-described configuration, the reception status estimation processing unit may select the selection signal from the signal value of the selection signal and a reference value that is a signal value that can be taken by a modulation scheme used for modulation of the signal. The reception status may be estimated based on the magnitude of deviation from the signal value closest to the signal value.

  The receiving method according to the present invention includes a first step of receiving a signal to be transmitted, and selecting the signal received in the first step based on an influence of the signal upon transmission. A second step of acquiring as a signal; and a third step of estimating a reception state using the selection signal acquired in the second step.

  With the configuration of the present invention, it becomes possible to exclude signals that are no longer suitable for estimation of reception status due to the influence of transmission, and select and acquire appropriate signals. Therefore, it is possible to improve the estimation accuracy of the reception status.

These are block diagrams which show the structural example of the receiver in embodiment of this invention. These are the schematic diagrams of the modulation signal shown about an example of an equalization process. Is a constellation showing an example of a demodulation method. These are block diagrams which show the structural example of a reception condition estimation part. These are the graphs shown about an example of the selection method of a signal. These are graphs showing simulation results of reception situations estimated by various methods. These are the constellations shown about another example of the selection method of a signal. These are the graphs which show the estimation method of the conventional reception condition.

  Hereinafter, a configuration example and an operation example of a receiving apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the following, a receiving apparatus that receives a signal that is modulated and transmitted by an orthogonal frequency division multiplexing (OFDM) method will be described as an example. However, the receiving apparatus of this example is only an example, and may be a receiving apparatus that receives other signals.

<Receiving device>
First, a configuration example and an operation example of a receiving apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration example of a receiving device according to an embodiment of the present invention.

  A receiving apparatus 1 shown in FIG. 1 includes an antenna 2 that receives a transmitted signal, and a tuner that selects a signal in a desired band from the signal received by the antenna 2 and converts the signal into a baseband signal and performs amplification and outputs the signal. 3, a synchronization unit 4 that synchronizes the baseband signal output from the tuner unit 3, and an FFT (Fast Fourier Transform) unit that outputs a modulation signal by performing fast Fourier transform on the baseband signal synchronized by the synchronization unit 4 5, an equalization processing unit 6 that performs an equalization process on the modulation signal output from the FFT unit 5 to correct and output distortion received during transmission, and an equalization process output from the equalization processing unit 6 Are provided with a demodulator 7 that demodulates the modulated signal and outputs an encoded signal, and a decoder 8 that decodes the encoded signal that is demodulated and output by the demodulator 7.

  Further, the demodulator 7 includes a reception status estimation unit 70 that estimates the reception status based on the modulated signal to be demodulated, generates reception status information, and outputs the reception status information. The reception status estimation unit 70 generates reception status information by estimating C / N (Carrier to Noise ratio) of the modulated signal, for example. Details of the configuration of the reception status estimation unit 70 will be described later.

  The operation of the receiving apparatus 1 will be described with reference to FIG. In the receiving apparatus 1, first, a signal to be transmitted is received by the antenna 2. Then, the tuner unit 3 selects and acquires a signal having a desired frequency from the signal received by the antenna 2, and converts (down-converts) the frequency of the acquired signal to obtain a baseband signal. The tuner unit 3 also performs amplification of baseband signals.

  The baseband signal output from the tuner unit 3 is input to the synchronization unit 4 and subjected to synchronization processing. For example, symbol synchronization (synchronization performed in the time direction of the signal), carrier synchronization (synchronization performed in the frequency direction of the signal), and frame synchronization (synchronization performed by detecting the start point of the signal frame) are performed. Is called.

  The baseband signal output from the synchronization unit 4 is input to the FFT unit 5 and subjected to FFT processing. Thereby, the signal on the time axis is converted to the signal on the frequency axis, and a signal with a plurality of frequencies (hereinafter referred to as subcarriers) is obtained. In a signal modulated by the OFDM method, the frequencies of these subcarriers are orthogonal. These signals are input to the equalization processing unit 6 and subjected to equalization processing.

  The equalization processing is performed using, for example, pilot symbols that are signals of a known size regularly arranged in the frequency direction and the time direction. In the case of the ISDB-T (Integrated Services Digital Broadcasting for Terrestrial) system adopted in Japanese terrestrial digital television broadcasting, scattered pilot symbols (hereinafter referred to as SP symbols) are used as the pilot symbols. An example of equalization processing using the SP symbol will be described with reference to FIG. FIG. 2 is a schematic diagram of a modulation signal shown as an example of equalization processing.

  For each symbol of the modulated signal shown in FIG. 2, the time number (symbol number) corresponding to the time direction (symbol direction) is represented by t (integer of t ≧ 0), and the carrier number corresponding to the frequency direction (carrier direction) is It is represented by l (integer of l ≧ 0). The position of each symbol is represented by (t, l). In this example, the SP symbol is arranged at a carrier position satisfying l = 3 × (t mod 4) + 12p (p is an integer of 0 or more, and t mod 4 indicates a remainder obtained by dividing t by 4). As shown in this equation, SP symbols are provided in specific subcarriers where l = 3k (k ≧ 0), and every 4 symbols in the time direction and every 12 symbols in the frequency direction. Be placed.

  The equalization processing unit 5 first performs interpolation in the time direction for the SP symbols arranged on a specific subcarrier. Thereby, the transmission path characteristic of a specific subcarrier is estimated. Further, interpolation in the frequency direction is performed using the SP symbol and the interpolation result. Thereby, the channel characteristics in the frequency direction are estimated, and the channel characteristics of all symbols are estimated. The equalization processing unit 5 performs equalization processing by complex-dividing each symbol with this transmission path characteristic. By this equalization processing, the amplitude and phase of the modulated signal distorted by the influence of the transmission path are corrected.

  Each modulation signal output from the equalization processing unit 5 is input to the demodulation unit 7 and demodulated by a demodulation method corresponding to each modulation method for each subcarrier. For example, 16QAM (Quadrature Amplitude Modulation), 64QAM, QPSK (Quadrature Phase Shift Keying), DQPSK (Differential Quadrature Phase Shift Keying), or the like is used as a modulation method.

  An example of the demodulation method of the demodulator 7 will be described with reference to FIG. FIG. 3 is a constellation showing an example of a demodulation method. In the constellation, the in-phase component (In-Phase component, hereinafter referred to as I component), which is the real component of the signal, is used in the horizontal direction, and the quadrature component (Quadrature-Phase component, hereinafter referred to as Q component), which is the imaginary component of the signal. Each is shown in the vertical direction. FIG. 3 shows a case where the modulation signal is modulated by QPSK. In addition to the signal value T of the symbol to be demodulated, the constellation of FIG. 3 also shows reference values S00 to S11 that are signal values that can be taken by the symbol according to the modulation scheme used for the modulation signal.

  In the example illustrated in FIG. 3, the reference value S00 in which both the I component and the Q component are positive indicates a signal value obtained by modulating the data “00”, and the I component is positive and the Q component is negative. Is a signal value obtained by modulating the data “01”, and a reference value S01 obtained by modulating the data “01” where the I component is negative and the Q component is positive. The reference value S11 in which both the I component and the Q component are negative indicates the signal value obtained by modulating the data “11”. Here, as shown in FIG. 3, when the signal value T of the symbol to be demodulated is closest to the reference value S00 among the reference values S00 to S11, the data obtained by demodulating this symbol is “00”. It becomes.

  If the reception condition is good, the signal value obtained by modulating the data on the transmission side (that is, the reference value) and the signal value T of the received symbol are substantially equal. On the other hand, when the reception situation deteriorates, the signal value of the symbol deviates from the reference value. The reception status estimation unit 70 estimates the reception status based on the magnitude of the deviation and generates reception status information. Details of the operation of the reception status estimation unit 70 will be described later.

  The reception status information output from the reception status estimation unit 70 can be used to control the operation of each unit of the reception device 1. For example, when the reception status is good, a high-resolution broadcast signal (for example, a 12-segment broadcast signal) is received, and when the reception status is poor, the low-resolution broadcast signal (for example, 1) This reception status information can be used for the control for switching to receive the segment broadcast signal.

  In addition, the receiving device 1 includes a plurality of receiving units (for example, a part constituted by an antenna 2, a tuner unit 3, a synchronizing unit 4, an FFT unit 5, and an equalization processing unit 6), and the demodulating unit 7 This reception status information can also be used when synthesizing and demodulating the modulated signal obtained from the receiving unit. In this case, for example, control of the composite ratio of the modulation signal (for example, control to reduce the composite ratio of the modulation signal obtained from the reception section having a poor reception condition and increase the composite ratio of the modulation signal obtained from the reception section having a good reception condition) ) And control of the number of receivers to be used (for example, control to increase the number of receivers to be used if the reception status is poor as a whole, and control to reduce the number of receivers to be used if it is good). It does not matter.

  The encoded signal output from the demodulator 7 is input to the decoder 8 and decoded to generate an output signal. The decoding unit 8 decodes the encoded signal by a method corresponding to a compression encoding method (for example, MPEG (Moving Picture Experts Group)) used for the encoded signal. The output signal obtained by decoding is given to an output device (not shown) such as a display, and an output operation such as display is performed. Note that the encoded signal may be subjected to error correction encoding as well as compression encoding, or the decoding unit 8 may perform error correction decoding.

<Reception status estimation unit>
Next, the configuration and operation of the reception status estimation unit 70 shown in FIG. 1 will be described with reference to the drawings. FIG. 4 is a block diagram illustrating a configuration example of the reception status estimation unit.

  As illustrated in FIG. 4, the reception situation estimation unit 70 selects and acquires a signal used for estimation of the reception situation, and an average modulation error rate using the signal acquired by the signal acquisition unit 71. The average C / N is estimated by using an average MER estimating unit 72 that estimates average MER (hereinafter referred to as average MER (Modulation Error Ratio)) and the average MER estimated by the average MER estimating unit 72, and is output as reception status information. An average C / N estimation unit 73.

  The signal acquisition unit 71 selectively acquires a signal (symbol) that satisfies a predetermined condition from the input modulation signal. A specific example of this selection method will be described with reference to FIG. FIG. 5 is a graph showing an example of a signal selection method and corresponds to FIG. 8 showing a conventional estimation method.

  The graph of the signal before equalization processing shown in FIG. 5 shows the state of the modulation signal output from the FFT unit 5 and input to the equalization processing unit 6. This graph also shows the transmission path characteristics (thick line in the figure) in the frequency direction obtained by the equalization processing unit 6. This transmission path characteristic can be obtained by interpolating SP symbols as described above, for example.

  The graph after the equalization processing shown in FIG. 5 shows the state of the modulation signal output from the equalization processing unit 6 and input to the demodulation unit 7. The signal acquisition unit 71 selects and acquires a predetermined symbol from the modulated signal after the equalization processing.

  The signal acquisition unit 71 according to the present embodiment selects a symbol to be acquired based on the strength of the transmission path characteristic estimated by the equalization processing unit 6. In particular, a symbol having a transmission path characteristic strength equal to or higher than a predetermined threshold is selected and acquired. When the modulation signal shown in FIG. 5 is selected by this method, a symbol of a frequency (subcarrier) indicated by an arrow in the figure is selected and acquired.

Next, the average MER estimation unit 72 estimates the average MER using the symbol acquired by the signal acquisition unit 71. The average MER can be estimated by the method shown in the following formula (1). In the following formula (1), I _T (i) and Q _T (i) are the values of the I component and Q component of the i th symbol, and I _S (i) and Q _S (i) are the i th symbol. Are the values of the I component and Q component of the reference value closest to the signal value of the symbol. The denominator in the following formula (1) is the sum of the noise amounts of N symbols from 1 to Nth (the magnitude of the deviation between the signal value of the symbol and the reference value closest to the signal value). is there. On the other hand, the numerator is the sum of the powers of N symbols from the 1st to the Nth (the power of the reference value closest to the signal value of the symbol).

The average MER (M _AVE ) estimated as in the above equation (1) is input to the average C / N estimation unit 72 and used for estimation of the average C / N. For example, as shown in the following equation (2), the average C / N (C _AVE ) is estimated by subtracting the offset amount F from the average MER (M _AVE ). The offset amount F is a value for converting the average MER (M _AVE ) to the average C / N (C _AVE ) and can be obtained experimentally. Then, the average C / N (C _AVE ) obtained by the average C / N estimation unit 72 is output as reception status information.

The average MER (M _AVE ) and average C / N (C _AVE ) obtained by the above formulas (1) and (2) indicate that the larger the value, the better the reception status.

  When the reception status is estimated as described above, symbols excluded by the signal acquisition unit 71 are subjected to equalization processing on symbols whose strength is extremely weakened due to the influence of transmission such as multipath, and are greatly amplified. Symbol. In other words, a symbol that is buried in noise and whose signal value is mostly a noise component is a symbol that has been greatly amplified.

  On the other hand, the symbol that is selected and acquired by the signal acquisition unit 71 is a symbol that has been subjected to equalization processing on a symbol whose intensity has not been extremely weakened and adjusted to an appropriate intensity. In other words, a symbol having a signal value derived from the original signal without being buried in noise is a symbol adjusted to an appropriate signal value.

  With this configuration, it is possible to exclude symbols that are highly likely to be erroneously estimated to have a large noise amount due to the amplified noise component. In addition, it is possible to select and acquire a symbol that is less affected by noise and has a high possibility that the amount of noise is correctly estimated in order to estimate the reception status. Therefore, it is possible to accurately estimate the reception state while suppressing misidentification of the noise amount.

A specific example of the effect of improving the estimation accuracy of the reception status by adopting the configuration of the present embodiment will be described with reference to the drawings. FIG. 6 is a graph showing simulation results of reception conditions estimated by various methods. In the following description, the average C / N (C _AVE ) is simply referred to as C / N.

  FIG. 6 shows C / N (no signal selection, black four strokes and broken lines) estimated by a conventional method for a signal in which C / N is set to various values, and estimation by the method of this embodiment. C / N (signal selection, white-painted four strokes and thick solid line) are displayed together. In addition, the closer the C / N is estimated, the closer to the set value (ideal value, thin solid line).

  As shown in FIG. 6, when C / N estimation is performed by a conventional method that does not perform signal selection, it is greatly deviated from the set value due to the influence of the amplified symbol of the symbol buried in the noise as described above. C / N is obtained. In particular, a C / N smaller than the set value (indicating that the reception status is poor) is obtained.

  On the other hand, when the reception state is estimated by the signal selection method of the present embodiment, a C / N closer to the set value can be obtained than in the conventional method in which signal selection is not performed. That is, it is possible to improve the estimation accuracy of the reception status.

  In addition, by using the reception state estimated with high accuracy in this way, it is possible to appropriately switch broadcast signals to be received (for example, broadcast signals of 12 segments and 1 segment). Further, since modulation signals can be effectively combined, the receivable range can be widened.

  Note that the threshold shown in FIG. 5 may be set in advance as a fixed value. Further, it may be a variable value that changes according to the state of the modulation signal. When the threshold value is a variable value, for example, the threshold value may be calculated by using an average value obtained by averaging the strengths of all the transmission path characteristics (for example, 5617 for ISDB-T MODE3). It is preferable to calculate the threshold value using this average value because it is possible to set the threshold value according to the state of the modulation signal and to improve the estimation accuracy of the reception status.

  In the above-described embodiment, the case where the modulation scheme used for the modulation signal is QPSK has been mainly described. However, even if a modulation scheme other than QPSK (for example, QAM, DQPSK, etc.) is used. I do not care.

<Modification>
The signal acquisition unit 71 may further exclude symbols having a large number of reference values around the constellation. This selection method is shown in FIG. FIG. 7 is a constellation showing another example of the selection method of the signal acquisition unit. FIG. 7 corresponds to the constellation shown in FIG. However, in this example, the modulation method used for the modulation signal is 64QAM. Specifically, the possible values of the I component and Q component of the reference value S are ± 1, ± 3, ± 5, and ± 7, and 64 pieces are arranged in a lattice pattern at equal intervals on the constellation. Is.

As shown in FIG. 7, in this example, the signal acquisition unit 71 excludes a symbol located inside the area surrounded by the outermost reference value S (broken line area E in the figure). Specifically, for example, symbols T _in that satisfy 3 <X <5 and 5 <Y <7 are excluded, and symbols T _out that satisfy 5 <X <7 and 7 <Y are not excluded. The symbols T _in excluded by this method have a large number of reference values (3, 7), (3, 5), (5, 5) and (5, 7) around them. On the other hand, the symbols T _{out that} are not excluded have only a small number of reference values (5, 7) and (7, 7) around them.

The symbol T _in excluded by the method of this example is a symbol that is highly likely to be recognized as corresponding to an incorrect reference value when the reception situation deteriorates and deviates from the original position. Therefore, by excluding such symbol T _in the signal selected by the above method, it is possible to further improve the estimation accuracy of the reception status.

  In addition, the operation of each unit of the reception device 1 and the reception status estimation unit 70 in the embodiment of the present invention may be performed by a control device such as a microcomputer. Further, all or part of the functions realized by such a control device are described as a program, and the program is executed on a program execution device (for example, a computer) to realize all or part of the functions. It doesn't matter if you do.

  In addition to the above-described case, the receiving device 1 in FIG. 1 and the reception status estimation unit 70 in FIG. 4 can be realized by hardware or a combination of hardware and software. Further, when the reception device 1 and the reception status estimation unit 70 are configured using software, a block diagram of a part realized by software represents a functional block diagram of the part.

  As mentioned above, although embodiment in this invention was described, the range of this invention is not limited to this, It can add and implement various changes in the range which does not deviate from the main point of invention.

The present invention relates to a receiving apparatus that receives a signal and estimates a reception state. In particular, the present invention is preferably applied to a receiving apparatus mounted on a moving body such as a car, in which a change in the reception situation is large.

DESCRIPTION OF SYMBOLS 1 Receiver 2 Antenna 3 Tuner part 4 Synchronizing part 5 FFT part 6 Equalization process part 7 Demodulation part 70 Reception condition estimation part 71 Signal selection part 72 Average MER estimation part 73 Average C / N estimation part 8 Decoding part

Claims (6)

In a receiving device that receives a transmitted signal,
From the received signal, a signal acquisition unit that performs selection based on the influence of the signal on transmission and acquires the selection signal;
A reception situation estimation processing unit that estimates a reception situation using the selection signal;
A receiving apparatus comprising: Estimating a transmission path characteristic indicating the influence of the signal due to transmission, and further comprising an equalization processing unit for correcting the signal based on the transmission path characteristic,
The receiving apparatus according to claim 1, wherein the signal acquisition unit performs selection based on the transmission path characteristic from the signal corrected by the equalization processing unit, and acquires the selection signal.   The receiving apparatus according to claim 2, wherein the signal acquisition unit acquires the signal having an intensity of the transmission path characteristic equal to or higher than a threshold as the selection signal.   The receiving apparatus according to claim 3, wherein the threshold is a value based on an average value of the intensity of the transmission path characteristics.   The reception status estimation processing unit is closest to the signal value of the selection signal among the signal value of the selection signal and a reference value that is a signal value that can be taken by the modulation scheme used for modulation of the signal; The receiving apparatus according to claim 1, wherein the reception status is estimated on the basis of a size at which the divergence is different. A first step of receiving a transmitted signal;
A second step of performing selection based on the influence of the signal received from the signal received in the first step and obtaining a selection signal;
A third step of estimating a reception situation using the selection signal acquired in the second step;
A receiving method comprising:

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