JP2011041060A - Receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiving device which demodulates a received signal with high accuracy. <P>SOLUTION: The receiving device of a radio communication system includes: an AD conversion unit (A/D) 3 which converts an analog received signal into a digital signal; a filter A4 which generates a signal to be used in demodulation processing after completion of acquisition of frequency synchronization and timing synchronization by filtering the digital signal; and a filter B6 with a band narrower than that of the filter A4, which generates a signal to be used in at least either of frequency synchronization acquisition processing or timing synchronization acquisition processing by performing the filtering to the digital signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a desired signal by removing the influence of adjacent interference signals.

  In communication systems such as M-WiMAX (Mobile-Worldwide Interoperability for Microwave Access) and WLAN (Wireless Local Area Network), adjacent channels are close to a desired channel (the carrier interval is set narrow). Since the adjacent channel causes interference for the desired channel, the demodulation characteristic deteriorates when the adjacent channel component (adjacent channel interference component) is input to the demodulator in the receiving apparatus. Therefore, it is necessary for the receiving apparatus to suppress adjacent channel interference. Usually, a receiving apparatus suppresses adjacent channel interference using an analog filter or a digital filter in a demodulator. Here, ideally, it is desirable that the analog filter and the digital filter completely pass the component of the desired channel while suppressing the adjacent channel interference completely. However, since the adjacent channel is actually close to the desired channel, it is difficult to completely suppress the adjacent channel interference, and the adjacent channel interference component remains.

  In an OFDM communication system, FFT (Fast Fourier Transform) is used for demodulation, but if the FFT band (window) is set so as to include adjacent channels (for example, at least twice the desired wave band). Since the signal in the adjacent channel band and the signal in the desired channel band can be separated, the influence of adjacent channel interference can be reduced. However, the timing synchronization and frequency synchronization acquisition processing performed before the FFT is greatly affected by the adjacent channel interference, so that the reception performance eventually deteriorates.

  Normally, when acquiring timing synchronization or frequency synchronization, correlation calculation processing between a received signal and a known OFDM signal sequence is used. However, if adjacent channel interference is large, that is, residual adjacent channel interference that cannot be suppressed by a filter. When many components are included in the received signal, there is a problem that an error occurs in the correlation calculation result and the demodulation accuracy is greatly deteriorated.

  As an example of a conventional apparatus that performs demodulation processing while suppressing interference from adjacent channels as described above, there is a radio reception apparatus described in Patent Document 1 below. The wireless receiver described in Patent Document 1 includes filtering means (adaptive filter unit) including a plurality of filters each having different characteristics, and according to the detection result of the noise level and adjacent interference wave component included in the received signal. Thus, a specific filter in the filtering means is selected and used. As a result, the reception performance is improved.

  However, since the wireless reception device described in Patent Document 1 performs filtering on the entire received signal, there is a problem that a desired signal component is removed more than necessary.

  For example, if FFT is performed in the demodulation process, as described above, the influence of adjacent channel interference can be reduced by setting the window wider. That is, when realizing performance improvement in an apparatus configured to perform FFT, it is possible to remove an interference component from a received signal used in acquisition processing of timing synchronization and frequency synchronization that affects FFT performance. It becomes important. In other words, if timing synchronization and frequency synchronization can be performed with high accuracy, the demodulation accuracy improves if the signal to be demodulated contains more desired signal components. How much the adjacent channel interference component remains is not a big problem in improving the demodulation accuracy.

JP 2008-199209 A

  An object of this invention is to provide the receiver which demodulates a received signal with high precision.

  According to one aspect of the present invention, there is provided a reception device of a wireless communication system, wherein an AD conversion unit that converts an analog reception signal into a digital signal, and filtering the digital signal, thereby performing frequency synchronization and timing synchronization. A first filter that generates a signal to be used in demodulation processing after acquisition of the signal is completed, and at least one of frequency synchronization acquisition processing and timing synchronization acquisition processing by filtering the digital signal A receiving device is provided that includes a second filter having a narrower band than the first filter, which generates a signal.

  Further, according to one aspect of the present invention, there is provided a reception device of a wireless communication system, wherein an AD conversion unit that converts an analog reception signal into a digital signal, and filtering the digital signal allows frequency synchronization and A first filter that generates a signal used in demodulation processing after acquisition of timing synchronization is completed, and an adjacent channel interference component in the digital signal based on the digital signal and the signal generated by the first filter A signal used in at least one of a frequency synchronization acquisition process and a timing synchronization acquisition process when an adjacent channel interference component is included in the digital signal, The first filter generated by filtering the digital signal. Receiving device is provided which also comprises a second filter of a narrow band.

  According to the present invention, since frequency synchronization and timing synchronization can be performed with high accuracy, the received signal can be demodulated with high accuracy.

  In addition, according to the present invention, since filtering is adaptively performed according to the use state of adjacent channels, there is an effect that frequency synchronization and timing synchronization can be performed with higher accuracy.

FIG. 1 is a block diagram showing a configuration example of a receiving apparatus according to the first embodiment of the present invention. FIG. 2 is a diagram illustrating an operation when an adjacent channel is used. FIG. 3 is a block diagram showing a configuration example of a receiving apparatus according to the second embodiment of the present invention.

  Hereinafter, a receiving apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment.

(First embodiment)
FIG. 1 is a block diagram showing a configuration example of a receiving apparatus according to the first embodiment of the present invention. This receiving apparatus includes a frequency conversion unit 1, an analog filter 2, an A / D (AD conversion unit) 3, a filter A4, a CI ratio detection unit 5, a filter B6, a threshold determination unit 7, a selector 8, a frequency error detection unit 9, A frequency error correction unit 10, a timing detection unit 11, an FFT (FFT processing unit) 12, and a channel estimation unit 13 are provided. FIG. 1 shows only the characteristic operation of the receiving apparatus according to the present embodiment and the components that execute the operation related thereto, and executes the same processing (general processing) as before. The components to be omitted are omitted.

  In the receiving apparatus shown in FIG. 1, the frequency converter 1 down-converts the input signal. The analog filter 2 performs filtering in the analog domain on the input signal. The AD conversion unit 3 converts an analog input signal into a digital signal. The filter A4 filters the input signal in the digital domain. The CI ratio detection unit 5 calculates the ratio (CI ratio) between the carrier wave (desired wave) and the interference wave. The filter B6 filters the input signal in the digital domain with a frequency characteristic different from that of the filter A4. Here, the filter A4 and the filter B6 are low pass filters or band pass filters, and the pass band of the filter B6 is set narrower than the pass band of the filter A4.

  The threshold determination unit 7 compares the input signal with a preset threshold and outputs a comparison result. The selector 8 receives the output signal from the filter A4 and the output signal from the filter B6, and outputs one of them according to the determination result (comparison result) in the threshold determination unit 7. The frequency error detector 9 detects a frequency error based on the output signal from the selector 8. The frequency error correction unit 10 corrects the frequency error of the input signal based on the detection result in the frequency error detection unit 9. The timing detection unit 11 determines the FFT execution timing in the FFT processing unit 12. The FFT processing unit 12 performs FFT on the input signal at the timing determined by the timing detection unit 11. The channel estimation unit 13 performs channel estimation based on the output signal from the FFT processing unit 12.

  The reception operation of the reception apparatus according to the present embodiment having the above configuration will be described with reference to FIG.

  A high-frequency analog signal transmitted from the opposing communication device (transmission device) is received by the illustrated antenna and input to the frequency conversion unit 1. When a high-frequency analog signal is input, the frequency converter 1 down-converts the input signal and outputs it to the analog filter 2. The analog filter 2 performs filtering in the analog domain on the input signal from the frequency converter 1 and outputs the filtered analog signal to the AD converter 3. The AD conversion unit 3 converts an input signal (analog reception signal) from the analog filter 2 into a digital signal, and outputs the digital signal to the filter A4, the CI ratio detection unit 5, and the filter B6.

  The filter A4 performs filtering in the digital domain on the digital reception signal input from the AD conversion unit 3, and outputs the filtered digital reception signal to the frequency error correction unit 10. In the receiving apparatus according to the present embodiment, a predetermined demodulation process is performed on the signal output from the filter A4 to restore the data series transmitted from the opposing communication apparatus. Further, the filtered digital reception signal is also output to the CI ratio detection unit 5 and the timing detection unit 11. The frequency characteristic (pass band) of the filter A4 is narrower than the frequency characteristic of the analog filter 2 arranged in the preceding stage.

  The CI ratio detection unit 5 calculates the respective powers of the digital reception signal input from the AD conversion unit 3 and the filtered digital reception signal input from the filter A4, and further calculates the CI ratio. Further, the calculated CI ratio is output to the threshold value determination unit 7. Since the CI ratio is used in the adjacent channel usage status determination process in the threshold determination unit 7, it can be any information that can determine the adjacent channel usage status (information that changes according to the adjacent channel usage status). Any information other than the CI ratio may be calculated. For example, the difference between the received signal powers may be calculated.

  The filter B 6 performs filtering in the digital domain on the digital reception signal input from the AD conversion unit 3, and outputs the filtered digital reception signal to the selector 8. As already described, the frequency characteristic of the filter B6 is narrower than that of the filter A4.

  The threshold determination unit 7 includes the adjacent channel interference component in the received signal (digital received signal output from the AD conversion unit 3) by comparing the CI ratio input from the CI ratio detection unit 5 with a predetermined threshold. Whether or not communication using the adjacent channel is being performed (whether or not the adjacent channel is in use). The determination result is output to the selector 8. The threshold value is set in advance according to the filter characteristics of the filter A4.

  The selector 8 selects one of the signal input from the filter A4 and the signal input from the filter B6 according to the determination result in the threshold determination unit 7, and outputs the selected signal to the frequency error detection unit 9. Specifically, when the determination result in the threshold determination unit 7 indicates that the adjacent channel is being used, the input signal from the filter B6 is selected and output to the frequency error detection unit 9, and the determination result is not determined for the adjacent channel. When indicating in use, the input signal from the filter A4 is selected and output to the frequency error detector 9.

  The frequency error detector 9 detects a frequency error based on the input signal from the selector 8. Specifically, when the adjacent channel is in use, the digital reception signal output from the AD conversion unit 3 includes an interference component (adjacent channel interference component) from the adjacent channel. A frequency error is detected based on the output signal of the filter B6, which is a signal in which the interference component is sufficiently suppressed. On the other hand, when the adjacent channel is not used, the digital reception signal output from the AD conversion unit 3 does not include the adjacent channel interference component, so that the filter A4 which is a signal including more desired wave components is included. A frequency error is detected based on the output signal. The detection result is output to the frequency error correction unit 10.

  The frequency error correction unit 10 corrects the frequency error of the digital reception signal input from the filter A4 based on the frequency error detection result in the frequency error detection unit 9, and acquires frequency synchronization. The digital received signal after the frequency error is corrected is output to the FFT processing unit 12.

  The timing detection unit 11 determines the timing at which the FFT processing unit 12 performs FFT on the input signal based on the digital reception signal input from the filter A4 (acquires timing synchronization). The determination result is output to the FFT processing unit 12.

  The FFT processing unit 12 performs FFT on the digital reception signal input from the frequency error correction unit 10 in accordance with the timing determined by the timing detection unit 11. The frequency domain received signal obtained by performing the FFT is output to the channel estimation unit 13.

  The channel estimation unit 13 performs channel estimation based on the frequency domain received signal input from the FFT processing unit 12. The channel estimation result is used in processing executed later, such as deinterleaving, derandomization, and error correction.

  Here, the reason why the receiving apparatus according to this embodiment performs the above-described operation will be described. In the state where the adjacent channel is used, the accuracy of detecting the frequency error is improved by increasing the reduction amount of the adjacent channel interference component even if the amount of passage of the desired signal component is sacrificed. On the other hand, in the state where the adjacent channel is not used, there is no adjacent channel interference component. Therefore, the frequency signal detection accuracy is improved by passing more desired signal components. Further, in demodulation processing after channel estimation (demodulation processing other than acquisition processing of frequency synchronization and timing synchronization), it is possible to improve demodulation accuracy by using a signal including more desired wave components. For this reason, the receiving apparatus according to the present embodiment performs the control as described above (see FIG. 2). FIG. 2 is a diagram illustrating an operation when an adjacent channel is used. As shown in the figure, the receiving apparatus according to the present embodiment detects a frequency error based on a signal that has passed through filter B (filter B6) when an adjacent channel is used.

  As described above, in the receiving apparatus according to the present embodiment, CI ratio detection unit 5 and threshold determination unit 7 determine whether an adjacent channel component (adjacent channel interference component) is included in the received signal, and an adjacent channel interference component. When the selector 8 determines that the frequency error is included, the selector 8 sends the signal output from the narrower band filter B6, that is, the signal on the side where the residual amount of the adjacent channel interference component is small, to the frequency error detector 9. I decided to output it. As a result, when there is no adjacent wave (when the adjacent channel is not used), the frequency error detection unit 9 uses the received signal filtered by the filter A4 having a wide pass bandwidth. On the other hand, when an adjacent wave exists, a frequency error is detected using the received signal that has been filtered by the filter B6 having a narrow passband width. Thereby, adaptive filtering according to the use state of the adjacent channel can be realized, and the detection accuracy of the frequency error can be improved, so that the demodulation accuracy is improved.

  In addition, the channel estimation process and the subsequent processes are always performed using the received signal that has been filtered by the filter A4 having a wide pass bandwidth regardless of the use status of the adjacent channel. The demodulation process can be performed with high accuracy.

  In the present embodiment, a receiving apparatus that includes CI ratio detection unit 5, threshold determination unit 7 and selector 8 and detects a frequency error using a signal that has passed through filter B6 only when an adjacent channel is in use. As described above, the frequency error may always be detected using a signal that has passed through the filter B6. In this case, since the CI ratio detection unit 5, the threshold determination unit 7, and the selector 8 are not required, the accuracy of detection of the frequency error and the processing accuracy after channel estimation can be improved while minimizing the complexity of the device configuration. Improvements can be realized.

(Second Embodiment)
FIG. 3 is a block diagram showing a configuration example of a receiving apparatus according to the second embodiment of the present invention. This receiving apparatus is obtained by replacing the timing detection unit 11 provided in the receiving apparatus (see FIG. 1) described in the first embodiment with a timing detection unit 11a. Regarding operations other than the timing detection unit 11a, This is the same as the receiving apparatus described in the first embodiment. In the present embodiment, only portions different from the first embodiment will be described.

  In the receiving apparatus according to the present embodiment, as shown in FIG. 3, the output signal from the selector 8 is also input to the timing detection unit 11 a, and the timing detection unit 11 a receives the input signal from the selector 8. Based on this, the FFT processing unit 12 determines the timing for performing FFT on the input signal. That is, when the adjacent channel is used, the timing detection unit 11a determines the FFT execution timing using the received digital signal after being filtered by the filter B6, while the adjacent channel is not used. In this case, the FFT execution timing is determined using the received digital signal after being filtered by the filter A4.

  As described above, in the receiving apparatus according to the present embodiment, it is confirmed whether or not an adjacent channel interference component is included in the received signal, and when the adjacent channel interference component is included (the adjacent channel is used). The frequency error detection and the FFT execution timing detection are performed using a signal obtained by filtering with the filter B6 having a narrow pass band (a signal in which the adjacent channel interference component is sufficiently suppressed). Thereby, the detection accuracy of the frequency error and the FFT execution timing can be improved, and the demodulation accuracy is improved.

  In addition, in demodulation processing other than frequency error detection and FFT execution timing detection, a signal (desired wave component is suppressed) always obtained by filtering with the filter A4 having a wide passband regardless of the use status of adjacent channels. Therefore, demodulation processing other than frequency error detection and FFT execution timing detection can be performed with high accuracy.

  It is also possible to delete the CI ratio detection unit 5, the threshold determination unit 7, and the selector 8 and to always determine the FFT timing and the frequency error using the signal that has passed through the filter B6. .

  In the first embodiment, only the signal used in the frequency error detection process is filtered by the filter B (narrow band filter), and the signal used in the timing detection process is filtered. Although the case where it is configured to perform filtering with A (a filter wider than filter B) has been described, on the contrary, only the signal used in the timing detection process is filtered with filter B, The signal used in the frequency error detection process may be configured to be filtered by the filter A. Even in this case, the demodulation accuracy can be improved as compared with the conventional case.

  In other words, interference components from adjacent channels are sufficiently used as at least one of the signal used for frequency error detection and frequency error correction (frequency synchronization acquisition processing) and the signal used for timing detection (timing synchronization acquisition processing). Demodulation accuracy can be improved by using a received signal filtered with a filter that is narrow enough to be suppressed.

  In each of the above-described embodiments, an example in which the present invention is applied to a multicarrier modulation communication system has been described. However, the present invention is not limited to this, and the present invention can also be applied to a single carrier modulation communication system.

  3 AD conversion unit (A / D), 4 filter A, 5 CI ratio detection unit, 6 filter B, 7 threshold determination unit, 8 selector, 9 frequency error detection unit, 10 frequency error correction unit, 11, 11a timing detection unit .

Claims (5)

A receiving device for a wireless communication system,
An AD converter for converting an analog received signal into a digital signal;
A first filter that generates a signal to be used in demodulation processing after acquisition of frequency synchronization and timing synchronization is completed by filtering the digital signal;
A second filter having a narrower band than the first filter, which generates a signal to be used in at least one of a frequency synchronization acquisition process and a timing synchronization acquisition process by filtering the digital signal;
A receiving apparatus comprising: A receiving device for a wireless communication system,
An AD converter for converting an analog received signal into a digital signal;
A first filter that generates a signal to be used in demodulation processing after acquisition of frequency synchronization and timing synchronization is completed by filtering the digital signal;
Determination means for determining whether the digital signal contains an adjacent channel interference component based on the digital signal and the signal generated by the first filter;
When the digital signal includes an adjacent channel interference component, a signal to be used in at least one of frequency synchronization acquisition processing and timing synchronization acquisition processing is generated by filtering the digital signal. A second filter having a narrower band than the first filter;
A receiving apparatus comprising: The signal generated by the first filter is used in a frequency synchronization acquisition process and a timing synchronization acquisition process when an adjacent channel interference component is not included in the digital signal. 2. The receiving device according to 2. 4. The receiving apparatus according to claim 1, wherein the pass band of the second filter is a pass band that does not pass a signal component of an adjacent channel. When using the signal generated by the second filter in either one of the frequency synchronization acquisition process and the timing synchronization acquisition process,
In the other processing, the signal generated by the first filter is used. The receiving device according to any one of claims 1 to 4, wherein the signal is generated by the first filter.

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