JP2011229068A - Receiver and reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver and a reception method with high tolerance for dynamic CW disturbance.SOLUTION: The receiver includes: a disturbance removal section 3 for removing CW disturbance waves of a specified disturbance frequency which is initially inputted from complex basis signals and outputting as removed complex basis signals as well as outputting a removed disturbance level regarding the removed CW disturbance waves; a disturbance detection section 7 for detecting the CW disturbance wave based on the signals on which FFT processing is carried out by an FFT processing section 6 and outputting detected disturbance frequency and the detected disturbance level; and an integrated control section 8 for outputting the specified disturbance frequency of the CW frequency wave to be removed for the disturbance removal section 7 based on the detected disturbance frequency and the detected disturbance level outputted from the disturbance detection section 7 and the removed disturbance level outputted from the disturbance removal section 3.

Description

  The present invention relates to a receiving apparatus and a receiving method for receiving and demodulating a digital modulation signal compliant with the OFDM system.

  OFDM modulation is known as a modulation scheme having high resistance against multipath interference, and is adopted in terrestrial digital broadcasting standards such as DVB-T in Europe and ISDB-T in Japan.

  An OFDM modulated wave transmitted from a broadcast station is received in a form in which various interference waves such as impulse noise, CW interference, and co-channel NTSC interference are superimposed on the transmission path. In the configuration of the OFDM receiver, it is an important issue to improve resistance to such various interferences. In particular, in-vehicle receivers and portable receivers that are assumed to be used in various reception environments, high resistance to these various interferences is required. The present invention relates to a technique for improving resistance to CW interference, among these interferences. The CW interference referred to here refers to interference caused by a sine wave that is not modulated or modulated with a very narrow band.

  In OFDM modulation, transmission data is distributed and transmitted over a plurality of carriers, so that countermeasures against CW interference are easier than other modulation schemes. The most common and simple countermeasure is to reduce the influence of the interference by treating the carrier that is significantly affected by the erasure after the FFT of the receiver. In particular, when the frequency of the jamming wave matches a specific carrier frequency, only the carrier is affected by the jamming. Therefore, the influence of the jamming wave can be almost eliminated by treating the carrier as an erasure. However, if the frequency of the jamming wave does not match any carrier frequency, the influence of the jamming wave is spread to a large number of surrounding carriers by FFT, so that the above measures may not provide a sufficient effect. .

  On the other hand, Patent Document 1 discloses a method of performing interference wave suppression before FFT of a receiver. In this method, a disturbing wave is detected after FFT, and a component near the frequency of the disturbing wave is suppressed by a notch filter before FFT. Then, by performing synchronization processing based on the signal after suppression, the interference resistance of the synchronization processing is improved.

JP 2006-174218 A

  However, the above method improves only the interference tolerance of the synchronization processing, and does not improve the interference tolerance of the main demodulation processing. Therefore, those skilled in the art can easily devise a configuration for performing FFT on the signal after interference suppression. It is clear that this configuration can be expected to improve the interference resistance in the main demodulation process. Further, since the FFT is performed after the interference is suppressed, the influence of the interference wave does not spread to the peripheral carriers. However, this configuration causes the following problems.

  First, there is a problem that the desired wave component included in the received signal is deteriorated by the removal of the interference wave. The notch filter suppresses not only the interference wave but also the surrounding frequency components. The above-described configuration in which the signal after interference suppression by the notch filter is FFT is greatly affected because all processes after the FFT are performed based on the output of the notch filter. In order to reduce the degradation of the desired wave, the stop band of the notch filter may be set very narrow. However, in this case, when the frequency of the interference wave changes, the interference wave easily deviates from the stop band of the notch filter, which is not preferable.

  Next, there is a problem when the frequency of the interference wave varies. The source of CW interference is often an oscillator built in the receiver or in a peripheral electronic device. In general, such an oscillator has temperature dependence, and its oscillation frequency fluctuates slowly. The method of Patent Document 1 does not cause a problem even when the interference frequency varies in this way. The interference detection unit can continuously detect the frequency of the fluctuating interference wave, and the interference wave can be continuously suppressed by moving the stop band of the notch filter following this frequency change. However, the same method cannot be applied to the configuration in which the signal after interference suppression by the notch filter described above is FFTed. In this configuration, the interference detection unit cannot detect the interference wave suppressed by the notch filter. When the frequency of the jamming wave being suppressed changes, the jamming detection unit discovers that the frequency fluctuates only when the jamming wave deviates from the stop band of the notch filter. However, the suppression of the interference wave is already insufficient at this point, and it is inevitable to deteriorate the reception performance.

  It can also be pointed out that efficient jamming suppression is difficult in a dynamic jamming environment. The number of notch filters that can be installed in the receiver is limited from a cost standpoint. On the other hand, the number of jamming waves included in the received signal varies depending on the reception environment, and this often exceeds the number of notch filters. In mobile reception or the like, it is normal that the power of the disturbing wave changes dynamically. In reception under such an environment, a mechanism for assigning a notch filter in preference to an interference wave having high power at that time is required. However, it is difficult to construct such a mechanism in the configuration in which the signal after the interference suppression is simply performed by the notch filter as described above is performed.

  A specific example will be described. Here, a case is considered in which there are two interference waves A and B while the number of notch filters is one. First, in the initial reception stage, the interference detection unit detects both the interference wave A and the interference wave B. And a notch filter is set so that the interference wave with high electric power among these, for example, interference wave A, may be suppressed. Thereafter, the interference wave A is suppressed by the notch filter, and the interference detector cannot detect its presence. Here, no problem occurs when the state of the interference wave does not change. The receiver will continue to remove the high power jammer A, and efficient jamming will be achieved. However, inconvenience occurs when the power of the interference wave changes. As an example, let us consider a case where the interference wave A completely disappears from a certain point in time. In this case, as a matter of course, it is desirable to stop the suppression of the interference wave A and start the suppression of the interference wave B. However, in practice, such an operation is difficult. As described above, once the suppression of the jamming wave A is started, the jamming detection unit cannot detect the jamming wave A. Therefore, the receiver cannot compare the power of the jamming wave A and the power of the jamming wave B, and cannot determine which jamming wave should be applied to suppress the notch filter.

  The present invention has been devised in view of these problems, and an object of the present invention is to provide a receiving apparatus and a receiving method having high resistance against dynamic CW interference.

  In order to solve the above-described problem, the receiving apparatus according to the first aspect of the present invention includes a time domain processing unit that demodulates a received OFDM signal and outputs a complex baseband signal, and an initially input designated interference frequency. And removing a CW interference wave from the complex baseband signal and outputting it as a removed complex baseband signal, outputting a removed interference level related to the removed CW interference wave, A symbol synchronization means for outputting a symbol synchronization signal based on the symbol synchronization signal; a window extraction means for performing window extraction on the removed complex baseband signal based on the symbol synchronization signal; and the removed signal subjected to window extraction by the window extraction means. FFT processing means for performing FFT processing on a complex baseband signal, and detecting a CW interference wave based on the FFT processed signal by the FFT processing means, and detecting the detected Based on the interference detection means for outputting a harmful frequency and a detected interference level, the detected interference frequency and the detected interference level output from the interference detection means, and the removal interference level output from the interference removal means, Control means for outputting a specified interference frequency of the CW interference wave to be removed to the interference removal means.

  In order to solve the above problem, the invention described in claim 6 is a time domain processing step of demodulating a received OFDM signal and outputting a complex baseband signal, and a CW interference wave having an inputted specified interference frequency. Is removed from the complex baseband signal and output as a removed complex baseband signal, and a disturbance removal step for outputting a removed interference level related to the removed CW interference wave, and symbol synchronization based on the removed complex baseband signal A symbol synchronization step for outputting a signal, a window extraction step for performing window extraction on the removed complex baseband signal based on the symbol synchronization signal, and the removed complex baseband signal window-extracted by the window extraction step FFT processing step for performing FFT processing on the CW interference wave based on the signal FFT processed by the FFT processing step An interference detection step for outputting the detected interference frequency and the detected interference level, the detected interference frequency and the detected interference level output in the interference detection step, and the removed interference level output in the interference removal step. And a control step of outputting a specified interference frequency of the CW interference wave to be removed.

It is a block diagram which shows the structural example of the receiver in embodiment of this invention. It is a block diagram which shows the structural example of an interference remover. It is a block diagram which shows the example of a different structure of a disturbance remover. It is a block diagram which shows the example of a different structure of a disturbance removal part. It is a figure showing the processing content of a disturbance detection part.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example of a main part of a receiving apparatus according to an embodiment of the present invention. The receiving apparatus 100 includes a time domain processing unit 2, an interference removal unit 3, a symbol synchronization unit 4, a window extraction unit 5, an FFT processing unit 6, a frequency domain processing unit 11, an interference detection unit 7, and an integrated control unit 8. ing.

  First, the configuration of the receiving apparatus will be schematically described. The time domain processing unit performs processing such as RF filtering, frequency conversion, IF filtering, A / D conversion, sampling frequency conversion, and quadrature detection, and converts the input RF signal into a complex baseband signal. The interference removal unit removes the interference wave included in the complex baseband signal and outputs it to the window extraction unit and the symbol synchronization unit under the control of the integrated control unit. Further, the interference removal unit outputs the estimated power and the estimated frequency of the interference wave being removed (hereinafter referred to as a removal interference wave) to the integrated control unit. The window extraction unit extracts a window having an effective symbol length from the input signal. The symbol synchronization unit controls the window extraction unit so that window extraction at an appropriate window position is performed. The FFT processing unit performs an FFT process on the window-extracted section signal and converts it into a received symbol composed of a predetermined number of received carriers. The frequency domain processing unit performs processing such as channel estimation, equalization, and error correction on the received symbols, and restores and outputs the transmitted information data. The interference detection unit detects an interference wave based on the received reception symbol, and outputs an estimated power and an estimated frequency of the detected interference wave (hereinafter referred to as a detected interference wave) to the integrated control unit. The integrated control unit controls the interference removal unit so that efficient interference removal is performed based on the estimated power and estimated frequency of the removed jamming wave, and the estimated power and estimated frequency of the detected jamming wave.

  First, the interference removal unit that is one of the features of the present invention will be described. As shown in FIG. 1, the disturbance eliminator comprises a series connection of one or more disturbance eliminators. The number of CW interference waves that can be removed by each interference canceller is one, and by connecting them in series, removal of a plurality of CW interference waves is achieved. In the following, it is assumed that the number of disturbance removers, that is, the number of disturbances that can be removed by the disturbance removal unit is N.

  Each disturbance remover included in the disturbance removal unit has a PLL oscillator, and generates a replica signal of a disturbance wave to be removed by using the PLL oscillator, and subtracts it from the input signal to eliminate the disturbance. Achieve. Each disturbance remover starts removing the interference wave in response to an instruction from the integrated control unit. At this time, each disturbance remover sets the frequency specified by the integrated control unit to the initial oscillation frequency of the PLL oscillator. When the designated frequency is close to the frequency of the jamming wave, the PLL can be phase-synchronized with the jamming wave. Once the phase synchronization is established, the PLL oscillator can follow the frequency fluctuation of the interference wave autonomously, that is, without receiving external control, and stable and continuous interference removal is achieved. . The interference removal process once started is continued until a stop is instructed from the integrated control unit.

  A specific configuration example of the interference eliminator is shown in FIG. In the figure, a portion 50 indicated by a dotted line box generates a replica signal, and a part 40 indicated by a dotted line box in the inside constitutes a PLL oscillator.

  The input signal of the interference canceller is frequency-converted by being multiplied by the complex conjugate value of the complex exponential sequence output from the NCO (Numerically Controlled Oscillator) 27. Here, the oscillation frequency of the NCO is given by the added value of the initial frequency specified by the integrated control unit and the output of the loop filter 26. This oscillation frequency is output to the integrated control unit as the estimated frequency of the interference wave being removed.

  As a result of the PLL control, the oscillation frequency of the NCO is controlled in the vicinity of the frequency of the removed jamming wave, so that the component of the removed jamming wave exists in the vicinity of DC in the output of the multiplier 21. The first low-pass filter 24 extracts this interference wave component. The phase detector 25 detects the phase of the extracted interference wave component and outputs it as a phase error. The loop filter 26 controls the NCO so that the phase error becomes zero. At the start of interference removal, the output of the loop filter is reset to zero, and the NCO starts oscillating at the initial frequency specified by the integrated control unit.

  The output of the multiplier 21, that is, the signal after frequency conversion, is also used for replica signal generation and estimation of interference wave power. When the PLL is phase-synchronized, the interference wave component included in the signal after frequency conversion is observed as a low-frequency signal, and the imaginary part is expected to be zero. The second low-pass filter 30 is provided for the purpose of extracting this interference wave component. The real part extractor 29 is provided for the purpose of extracting only the real part of the interference wave component, and has an effect of suppressing the amount of calculation of the subsequent processing. In addition, the structure which does not provide a real part extraction part is also possible. The interference wave component extracted as described above is multiplied by the NCO output to generate a replica signal of the interference wave to be removed and subtracted from the input signal to achieve interference removal.

  The interference wave component extracted by the second low-pass filter is also input to the power estimation unit. The power estimation unit averages the instantaneous power (norm value) of the interference wave component, thereby estimating the power of the interference wave being removed, and outputs the obtained estimated power to the integrated control unit.

  Unlike the conventional notch filter, the degradation of the desired wave component by the interference canceller can be made very small. As described above, the output signal of the interference canceller is obtained by subtracting the replica signal from the input signal. Here, since the bandwidth of the replica signal is determined by the second low-pass filter, it is possible to reduce the signal degradation caused by the interference remover as much as possible by setting this filter to a narrow band. Although it is not a realistic assumption, when the disturbing wave is a completely unmodulated sine wave, only the disturbing component is removed by bringing the bandwidth of the second low-pass filter as close to zero as possible, and the desired wave component It is possible to eliminate the deterioration of the film. Actually, the bandwidth of the second low-pass filter is set to about 0.01 to 1 times the carrier frequency interval in consideration of the followability to the modulation of the interference wave.

  The configuration shown in FIG. 3 is also possible as the configuration of the interference remover. In this configuration, the interference wave component is removed in a frequency-converted state. The interference eliminator having the configuration of FIG. 3 is completely equivalent to the interference eliminator having the configuration of FIG. 2, and there is no difference in the effect of the present invention regardless of which configuration is used.

  Further, the configuration shown in FIG. 4 is also possible as the configuration of the interference removing unit. The disturbing regenerator shown in the figure is the same as the portion 50 indicated by the dotted line in FIG. 2, and generates a replica signal. In the configuration of FIG. 4, the removal of the interference is achieved by subtracting the replica signal output from each interference regenerator from the input signal in parallel using the subtractor 222. Even when this configuration is used, there is no difference in the main effects of the present invention. However, in this configuration, it is pointed out that the series configuration of FIG. 1 is preferable because different interference regenerators may generate replica signals of the same interference wave.

  Heretofore, the interference removal unit in the present embodiment has been described. As described above, the disturbance removing unit in the present embodiment has a function of autonomously following the disturbance wave and removing it. For this reason, even if the frequency of the interference wave varies, stable and continuous interference removal is achieved. Further, by limiting the band of the replica signal, it is possible to suppress degradation of the desired wave component due to interference removal.

  Next, the interference detection unit will be described. The interference detection unit calculates the reception power for each carrier by averaging the instantaneous power (norm value) of the input reception carrier in the symbol time direction. Further, the average received power is calculated by averaging the received power for each carrier for all carriers. As shown in FIG. 5, the interference detection unit detects the presence of an interference wave when the reception power for each carrier is higher than the average reception power by a predetermined power ratio (for example, 12 dB), and the carrier frequency Is output as the estimated frequency of the detected jamming wave, and a value obtained by subtracting the average received power from the received power of the carrier is output as the estimated power of the detected jamming wave.

  In addition to the above-described method based on the received carrier power distribution, the interference detection method estimates the noise power for each carrier by a so-called decision-directed method, and based on this noise power distribution, A method for detecting an interference wave is also applicable. Note that the decision-oriented technique refers to a general method of estimating which of the prescribed constellation points is transmitted for each received carrier and performing processing based on the estimation result.

  Next, the integrated control unit will be described. First, the role of the integrated control unit in the present invention is clarified. As described above, the interference detection unit placed after the FFT cannot detect the interference suppressed before the FFT, and as a result, efficient interference removal cannot be achieved. On the other hand, in the receiving apparatus according to the present embodiment, the interference removal unit outputs information on the interference wave being removed. The integrated control unit comprehensively determines the status of the jamming signal by referring to both the information on the rejected jamming signal and the information output by the jamming detection unit, that is, the information on the jamming signal remaining after the removal. I can grasp it. Based on these pieces of information, the integrated control unit efficiently operates the interference eliminator so that the influence of the interference wave is minimized.

  In the present embodiment, the integrated control unit removes N interference waves having high power from all the interference waves removed by the interference removal unit and all the interference waves detected by the interference detection unit. Control the interference removal unit.

  Specifically, the integrated control unit performs control according to the following procedure. First, the estimated power is acquired for all detected interference waves and all removed interference waves. Then, these estimated powers are compared, and N interference waves are selected in descending order of power. If the total number of detected jamming waves and removed jamming waves is less than N, all jamming waves are selected. Next, the interference remover that removes each of the removed interference waves included in the unselected interference waves is stopped. Finally, with respect to all the detected jamming waves included in the selected jamming wave, the respective estimated frequencies are designated, and the jamming canceller in the stopped state is instructed to start removal. By performing the control according to the above procedure at an appropriate frequency, for example, every predetermined number of symbols, it is possible to adaptively remove N interference waves having high power at that time.

  As described above, the integrated control unit controls the state of the interference wave by referring to both the estimated power of the interference wave removed by the interference removal unit and the estimated power of the interference wave detected by the interference detection unit. It is possible to grasp the target and operate the interference remover efficiently and adaptively. As a result, the receiving apparatus according to the present embodiment can realize transmission data decoding with few errors even in a reception environment in which a large number of jamming waves exist and the power of the jamming waves fluctuates.

  The best mode for carrying out the present invention has been described above, but the present invention is not limited to this embodiment. Various modifications can be made without departing from the scope of the present invention. In particular, various controls can be applied to the integrated control unit depending on the environment in which the receiver is placed. Below, the example of control of such an integrated control part is demonstrated.

  First, an example of control that autonomously stops the removal process when the interference wave disappears will be described. As described above, the interference removal process involves deterioration of the desired wave. Therefore, it is desirable not to perform interference removal in an environment where there is no interference wave. However, in the above control example, once the interference wave removal that has been started is not stopped, a disturbance wave having a higher power does not appear. Therefore, even if the interference wave disappears, the interference removal process is continued. In order to solve this problem, the integrated control unit continuously monitors the estimated power of the removed jamming wave, and when this becomes smaller than a predetermined power, the jamming removal unit may be instructed to stop removing the jamming wave. .

  The second example is an example considering the correspondence to the modulation component of the interference wave. In the discussion so far, it has been assumed that the interference removal unit can sufficiently remove the instructed interference wave. However, in practice, the interference wave may not be sufficiently removed. For example, when the PLL of the interference remover cannot follow the FM component of the interference wave, the interference wave partially remains. Further, even when the AM component of the interference wave is wider than the bandwidth of the second low-pass filter in the interference remover, the interference wave partially remains. When the interference detection unit detects such a residual component, the integrated control unit may assign an interference canceller to the interference wave that has already been removed. This is not preferable from the viewpoint of effective use of the interference eliminator.

  The above problem can be solved by the integrated control unit performing control based on the estimated frequency of the removed interference wave. Specifically, when the estimated frequency of the detected jamming wave is in the vicinity of the estimated frequency of the removed jamming wave, it is not necessary to newly give an instruction to remove the jamming for the detected jamming wave. Alternatively, in such a case, in order to improve the followability to the modulation component of the interference wave, it is also possible to perform control to widen the loop filter and the second low-pass filter of the interference canceler that removes the interference wave. It is.

2 Time domain processing unit (equivalent to time domain processing means)
3 Interference remover (equivalent to means for obstructing interference)
4 Symbol synchronization unit (equivalent to symbol synchronization means)
5 Window extraction part (equivalent to window extraction means)
6 FFT processing unit (equivalent to FFT processing means)
7 Interference detection unit (equivalent to interference detection means)
8 Integrated control unit (equivalent to control means)
9 Interference remover 40 PLL circuit 100, 200 Receiving device 209, 210 Interference regenerator

Claims (7)

Time domain processing means for demodulating the received OFDM signal and outputting a complex baseband signal;
Interference removing means for removing a CW jamming wave having a designated jamming frequency initially input from the complex baseband signal and outputting it as a removed complex baseband signal, and outputting a removed jamming level related to the removed CW jamming wave; ,
Symbol synchronization means for outputting a symbol synchronization signal based on the removed complex baseband signal;
Window extraction means for performing window extraction on the removed complex baseband signal based on the symbol synchronization signal;
FFT processing means for performing FFT processing on the removed complex baseband signal window-extracted by the window extraction means;
Interference detection means for detecting a CW interference wave based on the signal FFT-processed by the FFT processing means and outputting the detected interference frequency and detection interference level;
Based on the detected jamming frequency and the detected jamming level output from the jamming detection unit, and the cancellation jamming level output from the jamming removal unit, the CW jamming wave to be removed to the jamming removal unit. Control means for outputting the specified interference frequency;
A receiving apparatus comprising:   2. A receiving apparatus according to claim 1, wherein said interference removing means removes a plurality of interferences, and said control means controls an interference wave having a higher level among said detected interference level and said cancellation interference level.   3. The receiving apparatus according to claim 1, wherein the interference removing unit includes an interference regenerator and removes an interference wave by subtracting the output thereof.   The receiving apparatus according to claim 3, wherein the jamming regenerator is configured by a PLL.   5. The receiving apparatus according to claim 3, wherein a plurality of the jamming regenerators are subtracted in series.   5. The receiving apparatus according to claim 3, wherein the plurality of jamming regenerators perform subtraction in parallel. A time domain processing step of demodulating the received OFDM signal and outputting a complex baseband signal;
An interference removal step of removing the inputted CW interference wave of the designated interference frequency from the complex baseband signal and outputting it as a removed complex baseband signal, and outputting a removed interference level related to the removed CW interference wave;
A symbol synchronization step of outputting a symbol synchronization signal based on the removed complex baseband signal;
A window extraction step for performing window extraction on the removed complex baseband signal based on the symbol synchronization signal;
An FFT processing step for performing FFT processing on the removed complex baseband signal window-extracted by the window extraction step;
A jamming detection step of detecting a CW jamming wave based on the signal subjected to the FFT processing in the FFT processing step and outputting the detected jamming frequency and the detected jamming level;
Based on the detected jamming frequency and the detected jamming level output in the jamming detection step and the removed jamming level output in the jamming removal step, the CW jamming wave to be removed is determined for the jamming removal step. A control step for outputting a specified disturbance frequency;
A receiving method comprising:

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