JP2007027879A - Receiver and reception method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent steep suppression characteristics in multi-carrier communication, and to suppress an undesired signal even if using a band limitation filter whose frequency characteristics vary. <P>SOLUTION: A frequency selector 112 selects a control frequency Δf for controlling the frequency of a frequency variation type local signal oscillator 113, so that a noise signal shifts to a suppression band in the band limitation filter. The frequency selector 112 outputs a control signal for shifting the frequency by Δf to the frequency variation type local signal oscillator 113, and outputs information on the control frequency Δf to a decoder 114. The decoder 114 selects a subcarrier to which information data are assigned, based on the information on the control frequency Δf outputted from the frequency selector 112, and performs OFDM decoding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a receiving apparatus and a receiving method, and more particularly to a receiving apparatus and a receiving method in a system to which multicarrier communication is applied.

  In recent years, even in mobile communication systems, studies have been made to increase system capacity in order to provide a throughput of 100 Mbps or higher over a wide range of coverage. For example, a mobile communication system with a radio bandwidth of 100 MHz or higher is used. Has been reported.

  An OFDM (Orthogonal Frequency Division Multiplex) system is known as a transmission system using a wide band with a radio bandwidth of 100 MHz (see Non-Patent Document 1 and Non-Patent Document 2). The OFDM signal is a frequency division multiplexing digital modulation method that transmits digital information using multiple orthogonal subcarriers. It is multipath resistant, is not susceptible to interference in other transmission systems, is not susceptible to interference, and is used in frequency. It has characteristics such as relatively high efficiency.

  By the way, as an OFDM receiver, for example, one disclosed in Patent Document 1 is known. FIG. 17 is a configuration diagram illustrating an example of a wideband signal receiving apparatus using an OFDM decoding algorithm (see Patent Document 1). A receiving apparatus 10 illustrated in FIG. 17 includes an antenna 11, a front end unit 12, a band limiting unit 13, an A / D (Analog to Digital) conversion unit 14, and an OFDM signal processing unit 15.

  The front end unit 12 amplifies the received signal with low noise and converts it to an IF (Intermediate Frequency) frequency.

  The band limiting unit 13 includes a wide band filter 16 and a band suppression filter (notch filter) 17 that gives sharp attenuation to a specific frequency.

  The broadband filter 16 extracts the band of the OFDM signal converted into the IF frequency band. In general, in a mobile communication system, a filter having excellent frequency selectivity, for example, a SAW (Surface Acoustic Wave) filter using a surface vibration wave of a piezoelectric element is often used as a band limiting filter. Further, in a direct conversion receiving IC that converts a received signal to a baseband frequency without converting it to an IF frequency, band limitation is performed using a low-pass filter in the baseband frequency band.

  The band suppression filter 17 removes adjacent interference components that cannot be removed by the wideband filter 16 alone. Normally, the band suppression filter 17 affects the phase in the OFDM band. However, in the case of OFDM, the phase change is compensated by equalization or delay detection demodulation processing, so that the effect of the phase is virtually eliminated. Has characteristics.

  The A / D converter 14 performs A / D conversion on the signal band-limited by the band limiter 13, and outputs the A / D converted signal to the OFDM signal processor 15.

  The OFDM signal processing unit 15 has functions of orthogonal demodulation processing, FFT (Fast Fourier Transform) processing, and channel estimation processing, and performs OFDM decoding processing on the A / D converted signal.

By the way, in the A / D converter 14, it is desirable that the oversampling number is as large as possible. However, it is generally difficult to increase the oversampling number in consideration of the power consumption of the logic components, the device volume, the cost, and the like. Therefore, there is a possibility that the noise signal is folded back and enters the signal band by sampling in the A / D conversion unit 14. Therefore, it is indispensable to provide a band limiting filter having a steep frequency characteristic before the A / D conversion unit 14.
ITU-RS contribution (TG11 / 3) Television Society Research Report Vol.17, No.54, p7-12, BCS 93-33 (Sep.1993) JP 2000-13357 A

  However, when trying to realize a band limiting filter having steep suppression characteristics and no variation in frequency characteristics, there is a problem that the circuit scale increases and the cost increases. Furthermore, when a semiconductor filter is used, there is a problem that power consumption increases due to an increase in the filter order.

  The present invention has been made in view of the above points, and can suppress undesired signals even in the case of using a band-limiting filter whose suppression characteristics are not steep and whose frequency characteristics vary in multicarrier communication. An object of the present invention is to provide a receiving device and a receiving method that can be used.

  In order to solve this problem, a receiving apparatus according to the present invention includes a receiving unit that receives a signal including frequency components corresponding to a plurality of carriers to which information data is assigned, and frequencies of all frequency components included in the received signal. Frequency conversion means for shifting the frequency, a filter for suppressing the frequency after frequency shift of some frequency components included in the received signal, and frequency components corresponding to the plurality of carriers among the frequency components remaining without being suppressed And the frequency converting means adopts a configuration in which the frequency of the undesired frequency component whose reception quality does not satisfy a predetermined criterion is matched with the frequency suppressed by the filter.

  The reception method according to the present invention includes a reception step of receiving a signal including frequency components corresponding to a plurality of carriers to which information data is allocated, and a frequency conversion step of shifting the frequencies of all frequency components included in the reception signal. A suppression step of suppressing a frequency after frequency shift of a part of frequency components included in the received signal, and a decoding step of decoding frequency components corresponding to the plurality of carriers among frequency components remaining without being suppressed The frequency converting step employs a step of matching a frequency of an undesired frequency component whose reception quality does not satisfy a predetermined standard with a frequency suppressed by the filter.

  According to these, by shifting the frequency of all the frequency components included in the signal including the frequency components corresponding to the plurality of carriers to which the information data is allocated, among the frequency components included in the received signal after the frequency shift, Since the frequency of undesired frequency components whose reception quality does not meet a predetermined standard is suppressed by the filter, and the frequency components corresponding to multiple carriers are decoded among the frequency components that remain without being suppressed, the suppression characteristics are steep. Even when a filter with uneven frequency characteristics is used, the frequency of undesired frequency components can be suppressed by reducing the deterioration of the filter characteristics without the need for a circuit that corrects the deterioration of the filter characteristics. The performance can be improved.

  According to the present invention, undesired signals can be suppressed even in the case of using a band limiting filter whose suppression characteristics are not steep and whose frequency characteristics vary in multicarrier communication.

  The gist of the present invention is to shift the frequency of the undesired signal to the suppression band of the filter based on the filter characteristics of the band limiting filter and the frequency of the undesired signal.

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

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of receiving apparatus 100 according to Embodiment 1 of the present invention. A receiving apparatus 100 illustrated in FIG. 1 includes an antenna 101, an antenna sharing unit 102, a low noise amplification unit 103, a frequency conversion unit 104, a band pass filter 105, an AGC (Auto Gain Control) 106, a local signal oscillator 107, and an orthogonal demodulation unit 108. , Low-pass filter 109-1, low-pass filter 109-2, A / D converter 110-1, A / D converter 110-2, FFT unit 111, frequency selector 112, frequency variable local A signal oscillator 113 and a decoding unit 114 are included.

  The antenna sharing unit 102 shares the antenna 101 with a reception system constituted by the above blocks and a transmission system (not shown).

  The low noise amplification unit 103 amplifies the received signal with low noise and outputs the amplified signal to the frequency conversion unit 104.

  The frequency conversion unit 104 multiplies the amplified received signal by the local signal output from the frequency variable local signal oscillator 113 to convert it to an IF frequency, and outputs the converted IF signal to the bandpass filter 105.

  The bandpass filter 105 limits the band of the IF signal and outputs the obtained IF signal to the AGC 106.

  The AGC 106 adjusts the amplitude level of the IF signal to an optimum level in the A / D conversion unit 110-1 and the A / D conversion unit 110-2 in the subsequent process, and outputs the IF signal whose level has been adjusted to the quadrature demodulation unit 108. To do.

Local signal oscillator 107 outputs the local signal of frequency f _if (MHz) to the quadrature demodulator 108.

  The quadrature demodulator 108 converts the level-adjusted IF signal into I and Q baseband signals, and outputs the obtained baseband signals to the low-pass filter 109-1 and the low-pass filter 109-2. To do.

  The low-pass filter 109-1 and the low-pass filter 109-2 remove unnecessary components from the I and Q baseband signals, respectively, and convert the obtained I and Q baseband signals to A / D. The data is output to the conversion unit 110-1 and the A / D conversion unit 110-2.

  The A / D conversion unit 110-1 and the A / D conversion unit 110-2 perform A / D conversion on the I and Q baseband signals, and the A / D converted I and Q baseband signals are FFT units. To 111.

  The FFT unit 111 performs fast Fourier transform on the A / D-converted I and Q baseband signals to convert a time-domain signal into a frequency-domain signal. The FFT unit 111 outputs the obtained frequency domain signal to the decoding unit 114.

  The frequency selection unit 112 sets the filter characteristics of the bandpass filter 105 output from the filter characteristic measurement unit (not shown), the frequency arrangement of the own channel, or the noise signal frequency and level measured by the noise signal frequency measurement unit (not shown). Based on this, the control frequency Δf for controlling the frequency of the frequency variable local signal oscillator 113 is selected so that the noise signal shifts to the suppression band of the bandpass filter 105. For example, when there is a signal of a system other than the OFDM signal constantly in the reception environment, the frequency selection unit 112 selects the control frequency Δf with the frequency of the signal of the other system as the frequency of the noise signal. The frequency selector 112 outputs a control signal for shifting the frequency by Δf to the frequency variable local signal oscillator 113 and outputs information about the control frequency Δf to the decoder 114.

The frequency variable local signal oscillator 113 generates a local signal having a frequency f _c −f _if −Δf (MHz) based on the control signal output from the frequency selection unit 112 and outputs the local signal to the frequency conversion unit 104. Here, the center frequency, Delta] f of _{f c} is OFDM signal indicates a control frequency selected by the frequency selecting unit 112.

  Decoding section 114 performs OFDM decoding on the signal converted to the frequency domain. At this time, based on the information regarding the control frequency Δf output from the frequency selection unit 112, the subcarriers to which the information data is assigned are selected and OFDM decoding is performed. Subcarrier selection will be described in detail later. The decoding unit 114 outputs the obtained reception data to a subsequent process.

  Next, the receiving operation by the receiving apparatus 100 configured as described above will be described.

  The OFDM signal is output to the low noise amplification unit 103 via the antenna 101 and the antenna sharing unit 102. The received signal is amplified by the low noise amplification unit 103 and output to the frequency conversion unit 104.

  The amplified received signal is multiplied by the local signal output from the frequency variable local signal oscillator 113 by the frequency conversion unit 104 and converted to an IF frequency, and the converted IF signal is output to the bandpass filter 105. . At this time, the frequency of the local signal output from the frequency variable local signal oscillator 113 is shifted by the control frequency Δf selected by the frequency selector 112. The selection of the control frequency Δf controlled by the frequency selection unit 112 will be described in detail later.

  A control signal for shifting the frequency by Δf is output to the frequency variable local signal oscillator 113, and information on the control frequency Δf is output to the decoding unit 114.

  The IF signal converted to the IF frequency is band-limited by the bandpass filter 105, and the obtained IF signal is output to the AGC 106. Then, the AGC 106 adjusts the level of the IF signal to an optimum level in the A / D conversion unit 110-1 and the A / D conversion unit 110-2, and outputs the IF signal to the quadrature demodulation unit 108.

  The IF signal whose level has been adjusted is multiplied by the local signal output from the local signal oscillator 107 by the quadrature demodulator 108 and converted into an I and Q baseband signal.

  The baseband signals of I and Q pass through the low-pass filter 109-1 and the low-pass filter 109-2, respectively, and then in the A / D conversion unit 110-1 and the A / D conversion unit 110-2. A / D conversion is performed and output to the FFT unit 111.

  The I and Q baseband signals are converted from the time domain to the frequency domain signal by the FFT unit 111, and the frequency domain signal is output to the decoding unit 114.

  Then, based on the control frequency Δf output from the frequency selection unit 112, the decoding unit 114 selects a subcarrier to which the information data is assigned, and performs OFDM decoding. Received data obtained by OFDM decoding is output to a subsequent process.

  Next, a reception operation when the receiving apparatus 100 receives an OFDM signal as shown in FIG. 2 will be described.

FIG. 2A shows frequency characteristics of an OFDM signal having a center frequency f _c (MHz) and a signal bandwidth of 50 MHz composed of 682 subcarriers (USC). In FIG. 2A, the horizontal axis represents frequency (MHz), the second horizontal axis represents subcarrier (SB) number, and the vertical axis represents power (dBm).

  By the way, in an OFDM transmitter, a time domain signal is generated from a frequency domain signal by IFFT (Inverse Fast Fourier Transform). At this time, a power of 2 subcarriers is used for the function of IFFT processing. Often the number is used to calculate the time domain signal. However, generally, there are many cases where an OFDM signal is not composed of power-of-two subcarriers due to the restriction of the subcarrier interval due to the phase noise of the local frequency. Therefore, the transmission apparatus generates null power subcarriers by assigning null data to subcarriers. Specifically, an OFDM signal having a signal bandwidth of 50 MHz composed of 682 subcarriers as shown in FIG. 2A is assigned information data only to 682 subcarriers out of 1024 subcarriers. The remaining 342 subcarriers are generated by assigning null data as unused subcarriers and setting the power of unused subcarriers to zero. As a result, in the radio frequency band, an OFDM signal composed of 682 subcarriers with a signal bandwidth of 50 MHz is transmitted.

Consider a case where the receiving apparatus 100 receives the OFDM signal shown in FIG. 2 (b), 2 (c), and 2 (d) show f _c −f _if (MHz) and f _c −f _if +12.5 output from the frequency variable local signal oscillator 113, respectively. (MHz), and _f c -f _if -12.5 after being multiplied in the local signal and the frequency conversion section 104 of the (MHz), a local signal and multiplied by the low-range f _if (MHz) at the local signal oscillator 107 The frequency characteristic of the baseband signal input into the pass filter 109-1 and the low-pass filter 109-2 is shown. Here, in FIGS. 2B, 2C, and 2D, the horizontal axis is the frequency (MHz) and the second horizontal axis is the subcarrier (similar to FIG. 2A). (SB) number, the vertical axis indicates power (dBm).

  At this time, as described above, the decoding unit 114 selects and demodulates the used subcarriers to which the information data is allocated, so that the receiving apparatus 100 can perform the operations shown in FIGS. 2 (b), 2 (c), and 2 (2). Any baseband signal having the frequency characteristics shown in d) can be demodulated.

  For example, for the OFDM signal shown in FIG. 2 (b), information can be obtained by selecting subcarrier numbers 172 to 853 as used subcarriers and performing OFDM decoding in the same manner as the OFDM signal shown in FIG. 2 (a). Data can be decrypted. Also, for the OFDM signal shown in FIG. 2C, information data can be decoded by selecting subcarrier numbers 1 to 682 as used subcarriers and performing OFDM decoding. With respect to the OFDM signal shown in FIG. 2D, it is possible to decode information data by selecting subcarrier numbers 342 to 1024 as used subcarriers and performing OFDM decoding.

  That is, the frequency conversion unit 104 performs frequency conversion so that the used subcarrier is included in the frequency band constituted by the power of 2 subcarriers used in the fast Fourier transform, that is, the frequency range that can be decoded by the decoding unit 114. In this case, it is possible to decode information data using all of the used subcarriers by correctly detecting the used subcarriers in the decoding unit 114. For example, for an OFDM signal as shown in FIG. 2A, if the control frequency Δf satisfies −12.5 ≦ Δf ≦ 12.5H (MHz), the subcarrier to which the information data is allocated. It becomes possible to decode the information data using all of the above.

  Hereinafter, a method of performing OFDM decoding by controlling the frequency of the local signal output from the frequency variable local signal oscillator 113 and selecting a subcarrier based on the control frequency Δf will be referred to as “OFDM signal subcarrier offset demodulation”. .

Next, a reception operation when the receiving apparatus 100 receives an OFDM signal and a noise signal as shown in FIG. 3 will be described. In FIG. 3, the horizontal axis represents frequency (MHz), the vertical axis represents power (dBm), the center frequency f _c (MHz), and a noise signal in the vicinity of an OFDM signal having a bandwidth of 50 MHz. . Noise signal, the center frequency _f n (MHz) is higher 57MHz than _{f c,} a signal bandwidth 12 MHz.

Hereinafter, a case where the sampling frequency f _s of the A / D conversion unit 110-1 and the A / D conversion unit 110-2 is 75 MHz is considered. At this time, the frequency characteristic of the received signal in the IF frequency band of the receiving apparatus 100 is as shown in FIG. In FIG. 4A, the horizontal axis indicates the frequency (MHz), the vertical axis indicates the signal level (dBm), and the second vertical axis indicates the filter suppression amount (dB). 4B and 5A to 8B used in the following, the horizontal axis is the frequency (MHz), the vertical axis is the signal level (dBm), The vertical axis represents the filter suppression amount (dB).

  FIG. 4A shows the OFDM signal, the filter characteristics of the band-pass filter 105, the noise signal, and the noise signal after passing through the band-pass filter 105 as a desired signal, a filter characteristic, neighborhood noise, and input noise, respectively. ing.

  FIG. 4B shows the frequency characteristics of the desired signal and input noise in the baseband frequency band output from the orthogonal demodulation unit 108.

  When the sampling frequency in the A / D conversion unit 110-1 and the A / D conversion unit 110-2 is 75 MHz, a frequency component higher than 37.5 (= 75/2) MHz is folded back in the band. Therefore, after the A / D conversion, the aliasing noise shown in FIG. 4B is input into the band.

  FIG. 5A shows the frequency characteristic of the received signal in the IF frequency band when the slope of the suppression characteristic of the band-pass filter 105 is relaxed compared to FIG. FIG. 5A shows that the input noise after passing through the band pass filter 105 is larger than that in FIG. As shown in FIG. 5B, since the noise signal level that is folded back in the band is also large, the quality of the desired signal deteriorates due to the relaxation of the filter characteristics.

Here, a case will be described in which the frequency of the frequency variable local signal oscillator 113 is set to f _c −f _if −6.25 (MHz) and demodulation is performed using “OFDM signal subcarrier offset demodulation”. At this time, as shown in FIG. 6A, the frequency characteristics of the received signal in the IF frequency band shift the desired signal and the noise signal to 6.25 MHz toward the high frequency side. As a result, the noise signal is shifted to a frequency region where the suppression amount is large, and the noise signal level after passing through the band-pass filter 105 becomes lower than that in FIG. 5A, and the characteristics equivalent to those in FIG. 4A are obtained. be able to.

  FIG. 6B shows the frequency characteristics of the received signal in the baseband frequency band. As shown in FIG. 6 (b), it can be seen that the signal level turned back in the band is lower than that in FIG. 5 (b).

  As described above, since the control frequency Δf is in the range of −12.5 ≦ Δf ≦ 12.5H (MHz), the desired signal is OFDM-decoded by appropriately selecting the subcarrier based on the control frequency Δf. It becomes possible to do.

  In other words, using “OFDM signal subcarrier offset demodulation”, the frequency of the frequency variable local signal oscillator 113 is shifted and demodulated, so that the noise signal is removed even when the suppression characteristic of the band limiting filter is relaxed. OFDM decoding can be performed. As a result, a low-order filter can be used as the band limiting filter, and a low-power consumption filter can be used when an inexpensive semiconductor filter is used.

  In the example described above, the case where the suppression characteristic of the bandpass filter 105 is deteriorated has been described. Next, the case where the frequency characteristic of the bandpass filter 105 is asymmetric with respect to the center frequency will be described. Generally, there are variations in analog devices, and the performance of the machine part may be deteriorated depending on the variation. For example, when the band-pass filter 105 having the filter characteristic shown in FIG. 4A as a basic value varies and the center frequency shifts to the high frequency side, the filter characteristic shown in FIG. 7A is obtained. At this time, when the OFDM signal and noise signal as shown in FIG. 3 pass through the band-pass filter 105 having the filter characteristics shown in FIG. 7A, the level of the input noise becomes larger than that in FIG. 4A. . In addition, as shown in FIG. 7B, the level of the noise signal that is folded back within the band also increases, and the quality of the received desired signal deteriorates.

In this case, a case where the frequency of the frequency variable local signal oscillating unit 115 is set to f _c −f _if −6.25 (MHz) and demodulation is performed using “OFDM signal subcarrier offset demodulation” will be described. At this time, the IF frequency characteristic of the received signal after passing through the bandpass filter 105 is such that the desired signal and the noise signal are shifted to 6.25 MHz toward the high frequency side as shown in FIG. As a result, the noise signal shifts to the high frequency side, and the noise signal level after passing through the band-pass filter 105 becomes lower than that in FIG. 7A, and the same characteristics as in FIG. 4A are obtained. Further, as shown in FIG. 8B, the level of the noise signal folded back within the band is also similar to that in FIG. 4B.

  In other words, by using the “OFDM signal subcarrier offset demodulation” to demodulate the frequency variable local signal oscillator 113 by shifting the frequency, when the frequency characteristic of the band limiting filter varies, the variation correction circuit is This is not necessary, and it is possible to reduce the performance deterioration due to the variation in frequency characteristics, and to remove the noise signal and perform OFDM decoding.

  As described above, according to the present embodiment, the frequency of the frequency variable local signal oscillator 113 is controlled using “OFDM signal subcarrier offset demodulation” to shift the undesired signal to the filter suppression band. OFDM decoding. As a result, when the filter characteristics of the band limiting filter are deteriorated, a circuit for correcting the deterioration is not required, the deterioration of the filter characteristics can be reduced, undesired signals can be suppressed, and OFDM decoding can be performed. Can be improved. Further, since the noise components input to the A / D conversion unit 110-1 and the A / D conversion unit 110-2 are reduced, the performance deterioration due to the quantization noise is reduced, and the reception performance is improved.

  In the above-described example, the case where the receiving apparatus 100 uses a bandpass filter has been described. However, even when conversion to the baseband frequency band is performed without direct conversion to the IF frequency band, “OFDM signal subcarrier offset demodulation” By applying “”, even when the filter characteristics of the low-pass filter deteriorate, it is possible to avoid the performance deterioration of the filter characteristics, suppress undesired signals, and perform OFDM decoding.

  Further, instead of using the filter characteristic output from the filter characteristic measurement unit (not shown), the frequency selection unit 112 may predict the filter characteristic using a temperature sensor. In general, the center frequency of a device such as a SAW filter varies depending on the temperature. By predicting the variation of the center frequency according to the temperature and applying the “OFDM signal subcarrier offset demodulation” as described above, it is shown in FIG. The same effect as that of the OFDM receiver can be obtained.

(Embodiment 2)
The feature of Embodiment 2 of the present invention is that the frequency of the undesired signal is estimated and the undesired signal is shifted to the suppression band of the band limiting filter.

  FIG. 9 is a block diagram showing a configuration of receiving apparatus 100 according to Embodiment 2 of the present invention. In the receiving apparatus of the present embodiment in FIG. 9, the same reference numerals as those in FIG. 9 employs a configuration in which a frequency selection unit 202 is provided instead of the frequency selection unit 112 and a noise measurement unit 201 is added to FIG.

  The noise measurement unit 201 measures the signal power to noise power ratio of the noise signal in the vicinity of the desired signal from the frequency domain signal output from the FFT unit 111 for each frequency component, and the measured signal power to noise power ratio is predetermined. Is determined (estimated) as the frequency of the noise signal. Regarding the measurement of the signal power to noise power ratio and the frequency of the noise signal in the noise measurement unit 201, the bandpass filter 105 has a filter characteristic as shown in FIG. 4A and receives a signal as shown in FIG. The case will be described.

If the sampling clock _{f s} similarly the A / D converter 110-1 and an A / D conversion unit 110-2 in the first embodiment is 75 MHz, the desired signal at the baseband frequency band outputted from the quadrature demodulator 108 The frequency characteristics of the input noise are as shown in FIG. When the FFT unit 111 performs fast Fourier transform on the signal shown in FIG. 4B, the frequency characteristic of the output after the fast Fourier transform is shown in FIG. At this time, the noise measurement unit 201 measures the signal power to noise power ratio in each unused subcarrier for each carrier, and determines (estimates) the frequency of the noise signal from the measurement result. For example, when the noise measurement unit 201 detects that the signal power to noise power ratio is greater than or equal to a predetermined threshold from subcarrier numbers 1 to 172 among unused subcarriers as shown in FIG. The frequency of the noise signal is estimated by assuming that the signal is present or that there is a noise signal on the high frequency side with respect to the desired signal and that the level is raised due to the return. The noise measurement unit 201 outputs the estimated frequency of the noise signal and the signal power to noise power ratio to the frequency selection unit 202. Note that the estimation method of the frequency of the noise signal and the signal power to noise power ratio is not limited to this, and other estimation methods may be used.

  The frequency selection unit 202 changes the frequency of the frequency variable local signal oscillator 113 so as to shift a noise signal having a measured signal power to noise power ratio for each carrier equal to or higher than a predetermined threshold to the suppression band of the bandpass filter 105. A control frequency Δf to be controlled is selected. Then, frequency selection section 202 outputs a control signal for shifting the frequency by Δf to frequency variable local signal oscillator 113 and outputs information about control frequency Δf to decoding section 114.

  Next, the receiving operation by the receiving apparatus 100 configured as described above will be described.

  The OFDM signal is output to the low noise amplification unit 103 via the antenna 101 and the antenna sharing unit 102. The received signal is amplified by the low noise amplification unit 103 and output to the frequency conversion unit 104.

  The amplified received signal is multiplied by the local signal output from the frequency variable local signal oscillator 113 by the frequency conversion unit 104 and converted to an IF frequency, and the converted IF signal is output to the bandpass filter 105. . At this time, the frequency of the local signal output from the frequency variable local signal oscillator 113 is shifted by the control frequency Δf selected by the frequency selection unit 202. As described above, the control frequency Δf is selected from the level of the noise signal estimated by the noise measurement unit 201 so that a noise signal having a level equal to or higher than a predetermined threshold is shifted to the suppression band of the bandpass filter 105.

  A control signal for shifting the frequency by Δf is output to the frequency variable local signal oscillator 113, and information on the control frequency Δf is output to the decoding unit 114.

  As in the first embodiment, the IF signal converted into the IF frequency is supplied to the bandpass filter 105, the AGC 106, the quadrature demodulation unit 108, the low-pass filter 109-1 and the low-pass filter 109-2, A / The data is output to the FFT unit 111 via the D conversion unit 110-1 and the A / D conversion unit 110-2.

  Then, the FFT unit 111 converts the I and Q baseband signals from the time domain to the frequency domain signal, and the frequency domain signal is output to the decoding unit 114.

  Thereafter, as in the first embodiment, the decoding unit 114 selects the subcarrier number to which the information data is assigned based on the information regarding the control frequency Δf output from the frequency selection unit 112, and performs OFDM decoding. . The obtained reception data is output to a subsequent process.

  As described above, according to the present embodiment, the frequency of the undesired signal is estimated using “OFDM signal subcarrier offset demodulation”, and the frequency of the frequency variable local signal oscillator 113 is controlled. OFDM decoding is performed by shifting the desired signal to the filter suppression band. Thereby, even in an environment where the level and frequency of the undesired signal fluctuate, the undesired signal can always be suppressed and OFDM decoding can be performed, and reception performance can be improved.

(Embodiment 3)
The feature of Embodiment 3 of the present invention is that the subcarrier with the lowest level is detected and the subcarrier with the lowest level is shifted to the suppression band of the filter characteristics.

  FIG. 11 is a block diagram showing a configuration of a receiving apparatus according to Embodiment 3 of the present invention. In the receiving apparatus of the present embodiment in FIG. 11, the same reference numerals as those in FIG. FIG. 11 shows a receiving apparatus based on direct conversion. Compared to FIG. 1, instead of AGC 106, low-pass filter 109-1, low-pass filter 109-2, and frequency selector 112, AGC 302-1, AGC 302-2, low-pass filter 301-1, low-pass filter 301-2, and frequency selector 304 are deleted, and frequency converter 104, bandpass filter 105, and local signal oscillator 107 are deleted. The configuration in which the level determination unit 303 is added is adopted.

  The low-pass filter 301-1 and the low-pass filter 301-2 remove unnecessary components from the I and Q baseband signals, respectively, and the obtained I and Q baseband signals are converted into AGC 302-1. , Output to AGC 302-2. The low-pass filter 301-1 and the low-pass filter 301-2 have capacitors (C-coupled) arranged in series in the signal transmission path in order to avoid DC offset caused by local signal leakage. The DC component is cut off.

  The level determination unit 303 measures the signal level of each subcarrier from the frequency domain signal after the fast Fourier transform, and determines the subcarrier having the lowest reception level. Level determination section 303 outputs information about the determined subcarrier frequency to frequency selection section 304.

  From the frequency of the subcarrier with the lowest reception level determined by the level determination unit 303, the frequency selection unit 304 determines that this subcarrier is the suppression band of the low-pass filter 301-1 and the low-pass filter 301-2. The control frequency Δf of the variable frequency local signal oscillator 113 is selected so as to match. Then, frequency selection section 304 outputs a control signal for shifting the frequency by Δf to frequency variable local signal oscillator 113 and outputs information about control frequency Δf to decoding section 114.

  Next, the receiving operation by the receiving apparatus 100 configured as described above will be described.

  The OFDM signal is output to the low noise amplification unit 103 via the antenna 101 and the antenna sharing unit 102. Then, the received signal is amplified by the low noise amplification unit 103 and output to the frequency modulation unit 108.

  The amplified received signal is multiplied by the local signal output from the frequency variable local signal oscillator 113 by the frequency demodulator 108 and converted into I and Q baseband signals. The converted baseband signal is output to the low-pass filter 301-1 and the low-pass filter 301-2. At this time, the frequency of the local signal output from the frequency variable local signal oscillator 113 is shifted by the control frequency Δf selected by the frequency selection unit 304. Selection of the control frequency Δf by the frequency selection unit 304 will be described with reference to FIG.

  FIG. 12 is a signal in the frequency domain after the fast Fourier transform output from the FFT unit 111, the horizontal axis indicates the subcarrier number, and the vertical axis indicates the signal level. As shown in FIG. 12, it is generally known that in mobile communication, there is a frequency band in which the reception level drops due to propagation conditions such as fading. FIG. 12 shows a state in which the signal level drops in the frequency band with the subcarrier number 520.

  At this time, the frequency selection unit 304 has a frequency variable type so that the frequency of the subcarrier number 520 having the lowest reception level matches the suppression band of the low-pass filter 301-1 and the low-pass filter 301-2. A control frequency Δf for controlling the frequency of the local signal generator 113 is selected.

  Since the frequency at which the signal level drops varies with time, the frequency at which the reception level is minimized is always detected by the level determination unit 303, and the frequency at which the reception level drops is detected by the band-pass filter 301-1 and the low-pass filter. By selecting the control frequency Δf in the frequency selection unit 304 so as to coincide with the suppression band of the filter 301-2, it is possible to mitigate the degradation of reception performance.

  A control signal for shifting the frequency by Δf is output to the frequency variable local signal oscillator 113, and information on the control frequency Δf is output to the decoding unit 114.

  The baseband signal is output to FFT section 111 via AGC 302-1 and AGC 302-2, A / D conversion section 110-1 and A / D conversion section 110-2.

  Then, the FFT unit 111 converts the I and Q baseband signals from the time domain to the frequency domain signal, and the frequency domain signal is output to the decoding unit 114.

  Thereafter, as in the first embodiment, the decoding unit 114 selects the subcarrier number to which the information data is assigned based on the information regarding the control frequency Δf output from the frequency selection unit 304, and performs OFDM decoding. . The obtained reception data is output to a subsequent process.

  As described above, according to the present embodiment, by using “OFDM signal subcarrier offset demodulation”, the subcarrier having the minimum reception level is detected from the signal after the fast Fourier transform, and the frequency variable local signal oscillator By controlling the frequency of 113, the carrier having the lowest reception level is shifted to the suppression band of the band limiting filter, and OFDM decoding is performed. As a result, the carrier with the lowest reception level is suppressed by the band limiting filter, and the carrier with the higher reception level is used for decoding, thereby reducing the degradation in reception performance.

(Embodiment 4)
The feature of Embodiment 4 of the present invention is that the frequency of the undesired signal is shifted to the suppression band of the band suppression filter.

  FIG. 13 is a block diagram showing a configuration of a receiving apparatus according to Embodiment 4 of the present invention. In the receiving apparatus of the present embodiment in FIG. 13, the same reference numerals as those in FIG. FIG. 13 shows a receiving apparatus that performs undersampling, and replaces band-pass filter 105, AGC 106, A / D converter 110-1, A / D converter 110-2, and frequency selector 112 with respect to FIG. Thus, a configuration in which the AGC 402, the bandpass filter 403, the A / D conversion unit 404, and the frequency selection unit 405 are added and the band suppression filter 401 is added is adopted.

  The band suppression filter 401 suppresses a narrow band undesired signal. The IF signal after passing through the band suppression filter 401 is output to the AGC 402.

  AGC 402 converts the level of the IF signal to an optimum level in A / D conversion section 404 and outputs the IF signal subjected to the level conversion to bandpass filter 403.

  The bandpass filter 403 removes unnecessary components from the IF signal and outputs the obtained IF signal to the A / D conversion unit 404.

  The A / D conversion unit 404 performs undersampling on the IF signal. Undersampling is performed using a frequency lower than the frequency of the IF signal. For this reason, the aliasing component of the desired signal and the aliasing component of the undesired signal included in the IF signal may overlap, and the desired signal may not be reproduced. Hereinafter, this will be specifically described with reference to FIG. In FIG. 14, the horizontal axis indicates the frequency, and the vertical axis indicates the signal level. 14A shows the frequency characteristics of the desired signal and the undesired signal in the radio frequency band, and FIG. 14B shows the frequency characteristics of the desired signal and the undesired signal after undersampling. As shown in FIG. 14B, it can be seen that the undesired signal may be superimposed on the desired signal after undersampling. Therefore, it is effective to exclude the undesired signal by performing band limitation by the band suppression filter 401 before the undersampling is performed.

  The frequency selection unit 405 includes the frequency variable local signal oscillator 113 so that the undesired signal is shifted to the suppression band of the filter based on the characteristics of the band suppression filter 401 measured by a band suppression filter characteristic measurement unit (not shown). A control frequency Δf for controlling the frequency is selected. Thereby, the frequency of the undesired signal is shifted to the suppression band of the band suppression filter 401, and the undesired signal can be efficiently suppressed.

  The frequency selection unit 405 outputs a control signal for shifting the frequency by Δf to the frequency variable local signal oscillator 113 and outputs information about the control frequency Δf to the decoding unit 114.

  Next, the receiving operation by the receiving apparatus 100 configured as described above will be described.

  The OFDM signal is output to the low noise amplification unit 103 via the antenna 101 and the antenna sharing unit 102. The received signal is amplified by the low noise amplification unit 103 and output to the frequency conversion unit 104.

  The amplified received signal is multiplied by the local signal output from the frequency variable local signal oscillator 113 by the frequency conversion unit 104 and converted to an IF frequency, and the converted IF signal is output to the band suppression filter 401. .

  FIG. 15 shows the frequency characteristics of the desired signal and the undesired signal output from the frequency converter 104 and the frequency characteristics of the band suppression filter 401 and the band pass filter 403. FIG. 15 shows a state where the suppression band of the band suppression filter 401 does not match the frequency of the undesired signal. In general, the band suppression filter 401 is a resonance circuit, has a large attenuation, has a narrow band, and varies in frequency characteristics. Therefore, as shown in FIG. 15, the frequency of the undesired signal, the suppression band of the band suppression filter 401, May not match.

  At this time, the frequency selection unit 405 so that the suppression band of the band suppression filter measured by the filter characteristic measurement unit (not shown) matches the frequency of the undesired signal measured by the undesired signal measurement unit (not shown). Thus, the control frequency Δf of the frequency of the local signal output from the frequency variable local signal oscillator 113 is selected. Thereby, the undesired signal is removed before the undersampling, and the deterioration of the reception performance can be reduced without the desired signal and the undesired signal being superimposed after the undersampling.

  A control signal for shifting the frequency by Δf is output to the frequency variable local signal oscillator 113, and information on the control frequency Δf is output to the decoding unit 114.

  Then, the IF signal after passing through the filter suppression filter 401 is output to the A / D conversion unit 404 via the band suppression filter 401, the AGC 402, and the band pass filter 403. Then, the A / D conversion unit 404 performs oversampling on the IF signal, and the quadrature modulator 108 converts the IF signal into I and Q baseband signals.

  The I and Q baseband signals pass through the low-pass filters 109-1 and 109-2 and are output to the FFT unit 111, respectively. Then, the FFT unit 111 converts the I and Q baseband signals from the time domain to the frequency domain signal, and the frequency domain signal is output to the decoding unit 114.

  Thereafter, as in the first embodiment, the decoding unit 114 selects the subcarrier number to which the information data is assigned based on the information regarding the control frequency Δf output from the frequency selection unit 405, and performs OFDM decoding. . Then, the received data obtained by the decoding unit 114 is output to a subsequent process.

  As described above, according to the present embodiment, the frequency of the frequency variable local signal oscillator 113 is controlled using “OFDM signal subcarrier offset demodulation”, and the frequency of the undesired signal is suppressed by the band suppression filter. Shift to the band and perform OFDM decoding. As a result, when there is variation in the frequency characteristics of the band limiting filter, it is possible to eliminate the undesired signal and perform OFDM decoding without reducing the performance degradation due to the variation in frequency characteristics without the need for a variation correction circuit. It becomes.

  In FIG. 13, the receiver using undersampling has been described. However, the present invention is not limited to this, and other sampling methods can be used by performing frequency conversion so that the undesired signal matches the suppression band of the band suppression filter. The same effect can be achieved even if there is.

(Embodiment 5)
The fifth embodiment of the present invention is characterized in that, in a composite receiving apparatus having a function of receiving a modulated signal of another system having a wider signal band than the OFDM signal band, when receiving an OFDM signal, the undesired signal is converted to a wideband signal. Shift to the suppression band of the optimum band limiting filter.

  FIG. 16 is a block diagram showing a configuration of receiving apparatus 500 according to Embodiment 5 of the present invention. The receiving apparatus illustrated in FIG. 16 is a composite receiving apparatus having a function of receiving a modulated signal (for example, a CDMA signal) of another system having a wider signal band than the OFDM signal band. In the receiving apparatus 500 of the present embodiment shown in FIG. 16, the same reference numerals as those in FIG. FIG. 16 is different from FIG. 11 in that a low-pass filter 501-1, a low-pass filter, and a low-pass filter 301-1, a low-pass filter 301-2, and a frequency selection unit 112 are replaced by a low-pass filter 501-1. The filter 501-2 and the frequency selection unit 504 are included, the level determination unit 303 is deleted, and a system selection unit 502 and another system decoding unit 503 are added.

  The low-pass filter 501-1 and the low-pass filter 501-2 perform band limitation on both OFDM signals having different signal bands and modulated signals of other systems. Since receiving apparatus 500 limits the band of both modulation signals having different signal bands, the pass band is optimal for the modulation signal of another system having a wide signal band.

  Based on instruction information (not shown), the system selection unit 502 outputs the I and Q baseband signals output from the A / D conversion unit 110-1 and the A / D conversion unit 110-2, or The data is output to the other system decoding unit 503. The instruction information indicates the modulation scheme of the signal received by the receiving apparatus 500. In the case of an OFDM modulated signal, the system selection unit 502 outputs I and Q baseband signals to the FFT unit 111, and In the case of the modulation signal, the baseband signals of I and Q are output to the other system decoding unit 503. Further, the system selection unit 502 outputs the instruction information to the frequency selection unit 504.

  The other system decoding unit 503 performs a decoding process on the baseband signal using a decoding method applied in the other system, and outputs the obtained reception data to a subsequent process.

  The frequency selection unit 504 selects the control frequency Δf of the frequency variable local signal oscillator 113 based on the instruction information. Specifically, when the indication information indicates an OFDM modulation system, the frequency selection unit 504 causes the frequency of the undesired signal to match the suppression band of the filter characteristic output from the filter characteristic measurement unit (not shown). The control frequency Δf of the frequency variable local signal oscillator 113 is selected. As described above, the pass bands of the low-pass filter 501-1 and the low-pass filter 501-2 are optimum for the modulation signal of another system having a wide signal band. By controlling the frequency of the local signal 113 and shifting the undesired signal to the suppression band of the low-pass filter 501-1 and the low-pass filter 501-2, while sharing the band limiting filter, Undesired signals can be suppressed. As a result, there is no need to prepare a band limiting filter for each system, which can reduce the size and cost.

  Next, the receiving operation by the receiving apparatus 100 configured as described above will be described.

  The OFDM signal is output to the low noise amplification unit 103 via the antenna 101 and the antenna sharing unit 102. Then, the received signal is amplified by the low noise amplification unit 103 and output to the frequency modulation unit 108.

  The amplified received signal is multiplied by the local signal output from the frequency variable local signal oscillator 113 by the frequency demodulator 108 to be converted into an I and Q baseband signal, and the converted baseband signal is converted into a low frequency band. It is output to the pass filter 501-1 and the low-pass filter 501-2. At this time, the frequency of the local signal output from the frequency variable local signal oscillator 113 is shifted by the control frequency Δf selected by the frequency selection unit 504. As described above, the control frequency Δf is selected so that the undesired signal is shifted to the suppression band of the filter characteristic output from the filter characteristic measurement unit (not shown).

  The control frequency Δf selected by the frequency selection unit 504 is output to the frequency variable local signal oscillator 113 and also output to the decoding unit 114.

  The baseband signal is output to system selection unit 502 via AGC 302-1 and AGC 302-2, A / D conversion unit 110-1 and A / D conversion unit 110-2.

  Then, the system selection unit 502 outputs the baseband signal from the instruction information (not shown) to the FFT unit 111 or the other system decoding unit 503.

  The baseband signal output to FFT section 111 is converted from a time domain signal to a frequency domain signal, and the frequency domain signal is output to decoding section 114.

  Thereafter, the decoding unit 114 selects the subcarrier number to which the information data is assigned based on the information about the control frequency Δf output from the frequency selection unit 112, as in Embodiment 1, and performs OFDM decoding. Is called. Then, the received data obtained by the decoding unit 114 is output to a subsequent process.

  On the other hand, the baseband signal output to the other system decoding unit 503 is subjected to the decoding method of the other system, and the obtained received data is output to the subsequent process.

  As described above, according to the present embodiment, “OFDM signal subcarrier offset demodulation” is used to match undesired signals with the suppression characteristics of a band limiting filter suitable for other systems when receiving an OFDM signal. The frequency of the frequency variable local signal oscillator 113 is controlled to perform OFDM decoding. As a result, the band limiting filter can be shared with other systems, and the size can be reduced and the cost can be reduced.

  Note that the OFDM signal after passing through the low-pass filter 501-1 and the low-pass filter 501-2 can be decoded by the FFT unit 111 in the subsequent stage depending on the signal band difference between the OFDM signal and the modulation signal of another system. When not in the frequency domain, a frequency converter that shifts the frequency of the OFDM signal again may be provided downstream of the low-pass filter 501-1 and the low-pass filter 501-2. As a result, the OFDM signal in which the undesired signal is suppressed is shifted again to the decodable frequency range, and as a result, all the carriers to which the information data is assigned can be used for decoding, and deterioration of reception performance is prevented. can do.

  The receiving apparatus according to the first embodiment of the present invention includes a receiving unit that receives a signal including frequency components corresponding to a plurality of carriers to which information data is assigned, and frequencies of all frequency components included in the received signal. Frequency conversion means for shifting the frequency, a filter for suppressing the frequency after frequency shift of some frequency components included in the received signal, and frequency components corresponding to the plurality of carriers among the frequency components remaining without being suppressed And the frequency converting means adopts a configuration in which the frequency of the undesired frequency component whose reception quality does not satisfy a predetermined criterion is matched with the frequency suppressed by the filter.

  According to this configuration, the frequency of all frequency components included in a signal including frequency components corresponding to a plurality of carriers to which information data is assigned is shifted, and among the frequency components included in the received signal after the frequency shift Since the frequency of undesired frequency components whose reception quality does not satisfy a predetermined standard is suppressed by the filter, and the frequency components corresponding to a plurality of carriers are decoded among the frequency components that remain without being suppressed, the suppression characteristics are steep. In addition, when using a filter with variation in frequency characteristics, it is possible to reduce the frequency of undesired frequency components by reducing the deterioration of the filter characteristics without requiring a circuit for correcting the deterioration of the filter characteristics, Reception performance can be improved.

  The receiving apparatus according to the second exemplary embodiment of the present invention is configured such that, in the first aspect, the frequency converting means uses frequency components other than frequency components corresponding to the plurality of carriers as undesired frequency components. take.

  According to this configuration, since the frequency component other than the frequency component corresponding to the plurality of carriers to which the information data is assigned is set as the undesired frequency component, only the frequency other than the frequency component corresponding to the plurality of carriers is suppressed, The frequencies of the frequency components corresponding to a plurality of carriers are decoded without being suppressed, and reception performance can be improved.

  In the receiving apparatus according to the third exemplary embodiment of the present invention, in the first aspect, the frequency conversion unit is a noise measuring unit that measures a signal power to noise power ratio for each frequency component included in the received signal, And a frequency component whose measured signal power to noise power ratio is equal to or higher than a predetermined threshold is used as an undesired frequency component.

  According to this configuration, the level of noise included in the received signal is estimated, and the frequency component corresponding to noise whose estimated level is equal to or higher than a predetermined threshold is set as an undesired frequency component. However, the frequency component corresponding to noise whose estimated level is equal to or higher than a predetermined threshold is always suppressed and removed by the filter, so that reception performance can be improved.

  The receiving apparatus according to a fourth exemplary embodiment of the present invention, in the first aspect, includes the level measuring unit that measures a level for each frequency component corresponding to the plurality of carriers, A configuration is adopted in which the frequency component having the minimum measured level is set as an undesired frequency component.

  According to this configuration, the level for each frequency component corresponding to a plurality of carriers to which information data is assigned is measured, and the frequency component with the smallest measured level is set as an undesired frequency component, so it corresponds to a plurality of carriers. Of the frequency components to be processed, the frequency component having a high level is not suppressed, and only the frequency component having the minimum reception level is suppressed, so that deterioration of reception performance can be reduced.

  In the receiving device according to the fifth exemplary embodiment of the present invention, in the first aspect, the frequency converting unit is capable of decoding frequencies of all frequency components corresponding to the plurality of carriers by the decoding unit. The structure which shifts to the range is adopted.

  According to this configuration, the frequencies of all the frequency components corresponding to the plurality of carriers to which the information data is allocated are shifted to a decodable frequency range, and thus correspond to the plurality of carriers to which the information data is allocated. All frequency components can be used for decoding.

  In the receiving device according to the sixth exemplary embodiment of the present invention, in the first aspect, the decoding unit selects frequency components corresponding to the plurality of carriers based on a frequency shift amount by the frequency converting unit. The selected frequency component is decoded.

  According to this configuration, since the frequency component corresponding to the plurality of carriers to which the information data is allocated is selected based on the frequency shift amount, and the selected frequency component is decoded, the information data is allocated. All frequency components corresponding to a plurality of carriers are appropriately used and decoded.

  In the receiving device according to the seventh exemplary embodiment of the present invention, in the first aspect, the decoding unit re-shifts the frequency component frequency remaining without being suppressed to a frequency range that can be decoded again. And a frequency conversion unit for decoding frequency components corresponding to the plurality of carriers after re-frequency shifting.

  According to this configuration, the frequency components remaining without being suppressed are shifted again to a frequency range that can be decoded, and the frequency components corresponding to the plurality of carriers to which the information data after the re-frequency shift is assigned are obtained. Even when a filter having a wider pass band than the signal bands of a plurality of carriers to which information data is assigned is used for decoding, a plurality of carriers to which information data is assigned by suppressing the frequency of undesired frequency components Can be used for decoding, and deterioration of reception performance can be prevented. Also, in a composite receiver having a function of receiving a modulated signal of another system having a wider signal band than the signal bands of a plurality of carriers to which information data is allocated, a filter can be shared, and the size and Cost can be reduced.

  The reception method according to the eighth embodiment of the present invention includes a reception step of receiving a signal including frequency components corresponding to a plurality of carriers to which information data is assigned, and frequencies of all frequency components included in the reception signal. A frequency conversion step that shifts the frequency, a suppression step that suppresses the frequency after frequency shift of some frequency components included in the received signal, and a frequency corresponding to the plurality of carriers among the frequency components that remain without being suppressed A decoding step of decoding the component, and the frequency conversion step employs a step of matching a frequency of an undesired frequency component whose reception quality does not satisfy a predetermined reference with a frequency suppressed by the filter.

  According to this method, the frequency of all frequency components included in a signal including frequency components corresponding to a plurality of carriers to which information data is allocated is shifted, and among the frequency components included in the received signal after the frequency shift. Since the frequency of undesired frequency components whose reception quality does not satisfy a predetermined standard is suppressed by the filter, and the frequency components corresponding to a plurality of carriers are decoded among the frequency components that remain without being suppressed, the suppression characteristics are steep. In addition, when using a filter with variation in frequency characteristics, it is possible to reduce the frequency of undesired frequency components by reducing the deterioration of the filter characteristics without requiring a circuit for correcting the deterioration of the filter characteristics, Reception performance can be improved.

  The receiving apparatus and the receiving method of the present invention can suppress undesired signals even when a band limiting filter having a steep suppression characteristic and a variation in frequency characteristic is used in multicarrier communication. This is useful for a receiving apparatus and a receiving method in a system to which communication is applied.

The block diagram which shows the structure of the receiver which concerns on Embodiment 1 of this invention. Diagram showing frequency characteristics of OFDM signal Diagram showing frequency characteristics of desired signal and nearby noise The figure which shows the frequency characteristic of the received signal in IF frequency band of the receiver which concerns on Embodiment 1. FIG. The figure which shows the frequency characteristic of the received signal in IF frequency band of the receiver which concerns on Embodiment 1. FIG. The figure which shows the frequency characteristic of the received signal in IF frequency band of the receiver which concerns on Embodiment 1. FIG. The figure which shows the frequency characteristic of the received signal in IF frequency band of the receiver which concerns on Embodiment 1. FIG. The figure which shows the frequency characteristic of the received signal in IF frequency band of the receiver which concerns on Embodiment 1. FIG. The block diagram which shows the structure of the receiver which concerns on Embodiment 2 of this invention. The figure which shows the frequency characteristic of the signal of the frequency domain after the fast Fourier transform of the receiver which concerns on Embodiment 2 The block diagram which shows the structure of the receiver which concerns on Embodiment 3 of this invention. The figure which shows the frequency characteristic of the signal of the frequency domain after the fast Fourier transform of the receiver which concerns on Embodiment 3 The block diagram which shows the structure of the receiver which concerns on Embodiment 4 of this invention. Diagram showing frequency characteristics of desired and undesired signals after undersampling The figure which shows the frequency characteristic of the received signal in the IF frequency band of the receiver which concerns on Embodiment 4, a band suppression filter, and a band pass filter The block diagram which shows the structure of the receiver which concerns on Embodiment 5 of this invention. Block diagram showing the configuration of a conventional receiving apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Antenna 102 Antenna sharing part 103 Low noise amplification part 104 Frequency conversion part 105,403 Band pass filter 106,302-1, 302-2,402 AGC
107 Local Signal Oscillator 108 Quadrature Demodulator 109-1, 109-2, 301-1, 301-2, 501-1, 501-2 Low-Pass Filter 110-1, 110-2, 404 A / D Converter 111 FFT unit 112, 202, 304, 405, 504 Frequency selection unit 113 Frequency variable local signal oscillator 114 Decoding unit 201 Noise measurement unit 303 Level determination unit 401 Band suppression filter 502 System selection unit 503 Other system decoding unit

Claims (8)

Receiving means for receiving a signal including frequency components corresponding to a plurality of carriers to which information data is assigned;
Frequency conversion means for shifting the frequency of all frequency components included in the received signal;
A filter that suppresses the frequency after frequency shift of some frequency components included in the received signal;
Decoding means for decoding frequency components corresponding to the plurality of carriers among frequency components remaining without being suppressed,
The frequency conversion means includes
A receiving apparatus that matches a frequency of an undesired frequency component whose reception quality does not satisfy a predetermined criterion with a frequency suppressed by the filter. The frequency conversion means includes
The receiving apparatus according to claim 1, wherein frequency components other than frequency components corresponding to the plurality of carriers are set as undesired frequency components. The frequency conversion means includes
A noise measuring unit that measures a signal power to noise power ratio for each frequency component included in the received signal,
The receiving apparatus according to claim 1, wherein a frequency component having a measured signal power to noise power ratio equal to or greater than a predetermined threshold is set as an undesired frequency component. The frequency conversion means includes
A level measuring unit for measuring a level for each frequency component corresponding to the plurality of carriers,
The receiving apparatus according to claim 1, wherein a frequency component having a minimum measured level is set as an undesired frequency component. The frequency conversion means includes
The receiving apparatus according to claim 1, wherein the frequency of all frequency components corresponding to the plurality of carriers is shifted to a frequency range that can be decoded by the decoding unit. The decoding means includes
The receiving apparatus according to claim 1, wherein a frequency component corresponding to the plurality of carriers is selected based on a frequency shift amount by the frequency converting means, and the selected frequency component is decoded. The decoding means includes
A re-frequency conversion unit that re-shifts the frequency of the frequency component that remains without being suppressed to a decodable frequency range;
The receiving apparatus according to claim 1, wherein frequency components corresponding to the plurality of carriers after re-frequency shifting are decoded. A receiving step of receiving a signal including frequency components corresponding to a plurality of carriers to which information data is assigned;
A frequency conversion step for shifting the frequency of all frequency components included in the received signal;
A suppression step of suppressing the frequency after frequency shift of some frequency components included in the received signal;
Decoding a frequency component corresponding to the plurality of carriers among frequency components remaining without being suppressed, and
The frequency conversion step includes
A reception method in which a frequency of an undesired frequency component whose reception quality does not satisfy a predetermined criterion matches a frequency suppressed by the filter.

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