JP5764454B2 - Reception device and transmission / reception system - Google Patents

Description

  The present invention relates to a receiving apparatus and a transmission / reception system.

  Patent Document 1 discloses a technique related to an optical fiber transmission device. In this technique, an RF signal is converted into an IF signal by down-conversion in the transmission device, converted into a digital signal by A / D conversion, converted into an optical signal, and transmitted to the reception device. In the receiving apparatus, the received optical signal is converted into an electric signal, then D / A converted to an analog signal, and restored to an RF signal by up-conversion.

  8 and 9 are diagrams for explaining an example of the operation of Patent Document 1. FIG. FIG. 8 shows the operation of the transmission apparatus. In the transmission device, as shown in FIG. 8A, for example, an RF signal (a trapezoidal signal indicated by a solid line) having a bandwidth (BW) of 90 MHz and a center frequency (fc) of 3.55 GHz is used. Down-conversion is performed by a 5 GHz local oscillation signal (arrow signal indicated by a solid line). As a result, as shown in FIG. 8B, a signal (a trapezoidal signal indicated by a solid line) having a bandwidth of 90 MHz and a center frequency of 55 MHz is generated. The signal down-converted in this manner is sampled at the sampling frequency Fs, converted into a digital signal, converted into an optical signal, and transmitted to the receiving device.

  In the receiving device, the received optical signal is converted into an electrical signal, and then converted into an analog signal by D / A conversion. As a result, as shown in FIG. 9A, a signal having a bandwidth of 90 MHz and a center frequency of 55 MHz (a trapezoidal signal indicated by a solid line) is generated. As shown in FIG. 9B, such an analog signal is up-converted by a 3.5 GHz local oscillation signal (an arrow signal indicated by a solid line) to obtain an original RF signal (a trapezoidal signal indicated by a solid line). Is generated.

Japanese Patent Laid-Open No. 08-316908

  In the above-described technique, since it is necessary to attenuate and remove the local oscillation signal included in the RF signal obtained by up-conversion in the receiving device, as shown in FIG. It is necessary to provide a bandpass filter having pass characteristics at the output.

  Incidentally, the bandpass filter having the characteristics shown in FIG. 9B needs to have a very high passband frequency and a very steep cutoff characteristic. Such a bandpass filter is difficult to design and is expensive.

  Therefore, it is conceivable to set a wide interval between the RF signal and the local signal by setting the frequency of the signal after down-conversion to be high. According to such setting, the interval between the RF signal and the local oscillation signal is widened, so that a band-pass filter having a gentle cutoff characteristic can be used. However, in such a setting, there is a problem that the SNR (Signal to Noise Ratio) deteriorates due to the jitter of the sampling clock in the A / D converter. That is, the SNR due to jitter is expressed by the following equation. .

Here, fin is the frequency of the analog signal (IF signal) input to the A / D converter, Jitter _clock is the effective value of the jitter of the external clock supplied to the A / D converter, and Jitter _upper is It is an effective value of jitter due to fluctuation between samplings of the A / D converter. From this equation, it can be seen that as the frequency of the input analog signal increases, the amplitude error due to clock jitter increases and the SNR deteriorates. FIG. 10 is a diagram illustrating the degradation of the SNR due to the frequency fin. As shown in this figure, when there is a temporal jitter Δt of the sampling clock, the voltage error ΔV is larger when the frequency is high than when the frequency is low. Therefore, if the frequency of the signal input to the A / D converter is set to be high, the characteristics of the bandpass filter can be made gentle, but there is a problem that the SNR deteriorates.

  Therefore, an object of the present invention is to provide a receiving apparatus and a transmission / reception system that can use a filter that generates less noise and has a gentle characteristic.

In order to solve the above-mentioned problem, the present invention converts a digitized signal into an analog signal in a receiving apparatus that receives a down-converted and digitized signal using a first frequency signal in a transmitting apparatus. Converting means for extracting, an extracting means for extracting an aliasing signal of a predetermined order contained in the analog signal obtained by the converting means, and the aliasing signal extracted by the extracting means at a frequency higher than the first frequency. And restoring means for restoring to the original signal by up-conversion using the signal of the second frequency having a low frequency.
According to such a configuration, it is possible to provide a receiving apparatus that can use a filter that generates less noise and has moderate characteristics.

In another aspect of the invention, in addition to the above-described invention, the transmission device downconverts the original signal to a signal in the first Nyquist zone using the signal of the first frequency, and oversamples the downconverted signal. The extraction means extracts a third-order aliasing signal.
According to such a configuration, generation of noise can be further reduced.

According to another aspect of the invention, in addition to the above-described aspect, the transmission apparatus down-converts the original signal into a third Nyquist zone signal using the first frequency signal, and performs band-limited sampling on the down-converted signal. The extracting means extracts a fifth-order aliasing signal.
According to such a configuration, a signal can be transmitted without impairing the characteristics of the original signal due to aliasing noise.

In addition, the present invention provides a transmission device that downconverts an original signal using a signal of a first frequency and digitizes and transmits, a conversion unit that converts the digitized signal into an analog signal, and a conversion unit. Extraction means for extracting an aliasing signal of a predetermined order included in the obtained analog signal, and the aliasing signal extracted by the extraction means using a signal of a second frequency lower than the first frequency And a restoration device that restores the original signal by up-conversion.
According to such a configuration, it is possible to provide a transmission / reception system that can use a filter that generates less noise and has moderate characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the receiver which can use a filter with few generation | occurrence | production of noise and a loose characteristic.

It is a figure which shows the structural example of the transmission / reception system which concerns on 1st Embodiment of this invention. It is a figure which shows the structural example of the transmitter shown in FIG. It is a figure which shows the structural example of the receiver shown in FIG. It is a figure for demonstrating operation | movement of the transmitter shown in FIG. It is a figure for demonstrating a Nyquist zone. It is a figure for demonstrating operation | movement of the receiver shown in FIG. It is a figure which shows the structural example of 2nd Embodiment of this invention. It is a figure for demonstrating operation | movement of the transmitter of a prior art. It is a figure for demonstrating operation | movement of the receiver of a prior art. It is a figure which shows the mode of the generation | occurrence | production of the jitter noise by a frequency.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of First Embodiment FIG. 1 is a diagram illustrating a schematic configuration example of a transmission / reception system according to the first embodiment of the present invention. As shown in this figure, the transmission / reception system 1 includes a transmission device 10, an optical fiber 30, and a reception device 20 as main components. The first embodiment shown in FIG. 1 is configured as a system for supplying radio waves to a radio wave insensitive zone where radio waves from a mobile phone base station are difficult to reach.

  Here, the transmission device 10 is arranged at a place where radio waves from a base station (not shown) can be received, and captures radio waves from the base station by the antenna 11. The transmission device 10 down-converts and digitizes the received signal (RF signal), converts the signal into an optical signal, and transmits the optical signal to the reception device 20 via the optical fiber 30. The transmitting device 10 converts the optical signal received from the receiving device 20 through the optical fiber 30 into an electrical signal and converts it to an analog signal, and then up-converts it to restore the original RF signal, and To the base station as radio waves. In the example of FIG. 1, the transmitting apparatus 10 and the base station exchange information wirelessly, but they may exchange information via wire.

  The receiving device 20 is disposed in a radio wave insensitive zone where radio waves from the base station are difficult to reach, and receives an optical signal transmitted from the transmitting device 10 via the optical fiber 30. The receiving device 20 converts the received optical signal into an electrical signal and converts it into an analog signal, and then up-converts it to restore the original RF signal, and transmits the radio wave to the radio wave insensitive zone via the antenna 21. . In addition, the reception device 20 receives radio waves received from the mobile phone by the antenna 21, down-converts the received signal (RF signal), digitizes it, converts it to an optical signal, and transmits it via the optical fiber 30. 10 is supplied. Note that a plurality of receiving apparatuses 20 are actually connected in accordance with the area of the radio wave dead zone, but FIG. 1 shows a state in which only one receiver 20 is connected in order to simplify the drawing.

  With the above configuration, even when a user having a mobile phone is located in a dead band, radio waves are exchanged between the mobile phone and the base station via the transmission / reception system 1 of the first embodiment. It becomes possible to perform a call or communication.

  FIG. 2 is a diagram illustrating a configuration example of the transmission device 10 illustrated in FIG. 1. In the example of FIG. 2, only the block diagram regarding the downlink direction (the direction in which the radio wave received from the base station is transmitted to the receiving device 20) is shown to simplify the drawing. As illustrated in FIG. 2, the transmission apparatus 10 includes a mixer 101, a low-pass filter 102, an amplification unit 103, an ADC (Analog to Digital Converter) 104, a signal processing unit 105, an optical transmission unit 108, an optical distribution unit 109, and a clock unit 110. A distribution unit (DIV) 111, a PLL synthesizer (PLLSYN) 112, and an oscillation unit 113.

  Here, the mixer 101 mixes the RF signal supplied via the antenna 11 and the local oscillation signal supplied from the oscillation unit 113 and outputs an intermediate frequency signal. The signal supplied via the antenna 11 can be, for example, a signal having a center frequency fc of 3.55 GHz and a bandwidth BW of 90 MHz. Further, the local oscillation signal output from the oscillation unit 113 can be a 3.5 GHz signal.

  The low-pass filter 102 is a filter that passes the intermediate frequency signal generated by the mixer 101 and attenuates other band components. The amplifying unit 103 amplifies the intermediate frequency signal that has passed through the low-pass filter 102 with a predetermined gain and outputs the amplified signal. The ADC 104 samples the intermediate frequency signal amplified by the amplification unit 103 in synchronization with the clock signal supplied from the distribution unit 111, converts the sampled signal into a digital signal, and outputs the digital signal.

  The signal processing unit 105 includes a parallel-serial conversion unit (P / S) 106 and a transmission unit (TXD) 107. The signal processing unit 105 includes, for example, an FPGA (Field Programmable Gate Array) and is output from the ADC 104. The digital signal is subjected to parallel-serial conversion or other encoding processing and output. Here, the parallel-serial conversion unit 106 converts the parallel signal output from the ADC 104 into a serial signal based on the clock signal output from the distribution unit 111 and outputs the serial signal. The transmission unit 107 converts the serial signal supplied from the parallel-serial conversion unit 106, for example, by 8b / 10b, generates a transmission signal by superimposing a clock signal, and then outputs the transmission signal.

  The optical transmission unit 108 converts the electrical signal supplied from the transmission unit 107 into a corresponding optical signal and outputs it. In the optical distribution unit 109, the optical signal output from the optical transmission unit 108 is distributed to each optical fiber 30.

  For example, the clock unit 110 generates and outputs a clock signal having a frequency of 250 MHz. The distribution unit 111 distributes the clock signal supplied from the clock unit 110 to the ADC 104, the parallel / serial conversion unit 106, the transmission unit 107, and the PLL synthesizer 112.

  The PLL synthesizer 112 controls the local oscillation signal output from the oscillation unit 113 based on the clock signal supplied from the distribution unit 111 so as to have a predetermined frequency. The oscillation unit 113 is a voltage controlled oscillation circuit (VCO: Voltage Control Oscillator) that generates a sine wave signal having a frequency corresponding to the control voltage supplied from the PLL synthesizer 112. In this example, a 3.5 GHz signal is output as the local signal.

  FIG. 3 is a diagram illustrating a detailed configuration example of the receiving device 20 illustrated in FIG. 1. In the example of FIG. 3, only the block diagram regarding the downlink direction (direction in which the radio wave received from the base station is transmitted to the receiving device 20) is shown in the same manner as in FIG. 2 in order to simplify the drawing. As illustrated in FIG. 3, the reception device 20 includes an optical reception unit (RX) 201, a signal processing unit 202, a DAC (Digital to Analog Converter) 205, a bandpass filter 206, a mixer 207, a bandpass filter 208, and a waveform shaping unit. (Cleaner) 209, PLL synthesizer (PLLSYN) 210, and oscillation unit 211.

  Here, the optical receiving unit 201 converts the optical signal transmitted from the transmission device 10 via the optical fiber 30 into an electrical signal and supplies the electrical signal to the signal processing unit 202.

  The signal processing unit 202 includes a reception unit (RXD) 203 and a serial / parallel conversion unit (S / P) 204. The signal processing unit 202 includes, for example, an FPGA or the like, and converts a serial signal output from the optical reception unit 201 into a parallel signal. And is supplied to the DAC 205, and a clock signal is extracted and supplied to the waveform shaping unit 209. Here, the reception unit 203 extracts a digital signal that is a main signal from the electrical signal supplied from the optical reception unit 201 and supplies the digital signal to the serial / parallel conversion unit 204, and also extracts a clock signal to the waveform shaping unit 209. Supply. The serial / parallel conversion unit 204 converts the serial signal supplied from the receiving unit 203 into a parallel signal based on the clock signal supplied from the waveform shaping unit 209 and supplies the parallel signal to the DAC 205.

  The DAC 205 converts the digital signal supplied from the serial / parallel conversion unit 204 into an analog signal in synchronization with the clock signal supplied from the waveform shaping unit 209 and outputs the analog signal. The band pass filter 206 extracts and outputs a third-order aliasing signal from the analog signal output from the DAC 205.

  The waveform shaping unit 209 shapes the clock signal extracted by the receiving unit 203 and supplies it to the serial / parallel conversion unit 204, the DAC 205, and the PLL synthesizer 210. The PLL synthesizer 210 controls the local oscillation signal output from the oscillation unit 211 based on the clock signal supplied from the waveform shaping unit 209 so as to have a predetermined frequency. The oscillation unit 211 is a voltage controlled oscillation circuit that generates a sine wave signal having a frequency corresponding to the control voltage supplied from the PLL synthesizer 210. In this example, 3.25 GHz having a frequency lower than 3.5 GHz that is the local oscillation signal of the transmission device 10 is output as the local oscillation signal.

  The mixer 207 performs up-conversion by mixing the third-order aliasing signal output from the bandpass filter 206 and the local oscillation signal supplied from the oscillation unit 211, and generates and outputs an RF signal. . Note that the third-order aliasing signal output from the bandpass filter 206 is, for example, a signal having a center frequency fc of 305 MHz and a bandwidth BW of 90 MHz. Further, the local oscillation signal supplied from the oscillating unit 211 is a 3.25 GHz signal as described above. By mixing these signals, an RF signal having a center frequency fc of 3.55 GHz and a bandwidth BW of 90 MHz is generated. The band-pass filter 208 passes the RF signal included in the signal output from the mixer 207, attenuates other frequency components, and outputs the attenuated frequency component.

(B) Description of Operation of First Embodiment Next, the operation of the first embodiment will be described. A radio wave transmitted from a base station (not shown) is captured by the antenna 11 of the transmission device 10 and supplied to the mixer 101 as an RF signal having a center frequency fc of 3.55 GHz and a bandwidth BW of 90 MHz, for example. The mixer 101 mixes and outputs the 3.5 GHz local oscillation signal supplied from the oscillation unit 113 and the RF signal. FIG. 4A is a diagram illustrating a relationship between an RF signal (trapezoidal signal) input to the mixer 101 and a local oscillation signal (arrow-shaped signal). In this figure, the horizontal axis indicates the frequency, and the vertical axis indicates the amplitude. As shown in FIG. 4A, the local oscillation signal is set to a frequency lower by about 50 MHz than the RF signal. By mixing these two signals by the mixer 101, as shown in FIG. 4B, a down-converted IF signal having a center frequency fc 55 MHz corresponding to the difference between these frequencies (indicated by a solid line in the figure). Signal) is obtained.

  The IF signal output from the mixer 101 is supplied to the low-pass filter 102, where frequency components other than the IF signal are attenuated and output to the amplification unit 103. In the amplifying unit 103, the IF signal output from the low-pass filter 102 is amplified with a predetermined gain and output.

  The ADC 104 samples and quantizes the IF signal supplied from the amplification unit 103 in synchronization with the clock signal supplied from the distribution unit 111, and converts the IF signal into a digital signal. As shown in FIG. 4B, since the IF signal has a bandwidth BW of 90 MHz and the sampling frequency Fs of the ADC 104 is 250 MHz, oversampling is executed with a sampling frequency that is twice or more the bandwidth of the IF signal. For example, after being converted into a 12-bit digital signal, it is output to the signal processing unit 105.

  The parallel-serial conversion unit 106 of the signal processing unit 105 converts the digital signal output from the ADC 104 into a serial signal based on the clock signal supplied from the distribution unit 111 and outputs the serial signal to the transmission unit 107. The transmission unit 107 converts the serial signal supplied from the parallel-serial conversion unit 106 by, for example, 8b / 10b and superimposes the clock signal, and then outputs the superimposed signal to the optical transmission unit 108.

  The optical transmission unit 108 converts the electrical signal supplied from the transmission unit 107 into a corresponding optical signal, and transmits the optical signal to the reception device 20 via the optical distribution unit 109 and the optical fiber 30.

  By the above operation, the radio wave from the base station captured by the antenna 11 is digitized after being down-converted by the local signal. The digitized signal is converted into a serial signal, converted into an optical signal, and sent to the optical fiber 30.

  The optical signal transmitted from the transmission device 10 is received by the optical reception unit 201 of the reception device 20, converted into a corresponding electrical signal, and then output to the signal processing unit 202. The receiving unit 203 of the signal processing unit 202 extracts a clock signal included in the signal supplied from the optical receiving unit 201 and supplies the clock signal to the waveform shaping unit 209, and converts the digital signal that is the main signal into a serial / parallel conversion unit. 204. The serial / parallel conversion unit 204 converts the digital signal (serial signal) supplied from the reception unit 203 into a parallel signal based on the clock signal supplied from the waveform shaping unit 209 and outputs the parallel signal to the DAC 205.

  The DAC 205 converts the digital signal output from the serial / parallel conversion unit 204 into an analog signal in synchronization with the clock signal supplied from the waveform shaping unit 209, and outputs the analog signal to the band pass filter 206. The band pass filter 206 extracts a third-order aliasing signal from the signal output from the DAC 205. FIG. 5 is a diagram for explaining an aliasing signal. In FIG. 5, the horizontal axis indicates a normalized frequency obtained by normalizing the signal frequency with the sampling frequency. That is, the normalized frequency “1” indicates that the signal frequency is equal to the sampling frequency. The vertical axis indicates the amplitude, and the numbers attached to the signals in each band indicate the Nyquist zone numbers.

  Here, as known from the sampling theorem, when a signal having a frequency half the sampling frequency (standardized frequency 0 to 0.5) is sampled and restored, as shown in FIG. Signal (aliasing signal) appears. That is, FIG. 5 shows 2nd to 6th order signals in addition to the original signal (the signal whose Nyquist zone number is 1). Note that the frequency relationship is inverted between the odd-order signal and the even-order signal. The band pass filter 206 extracts the third-order aliasing signal (the signal with the Nyquist zone number of 3) shown in FIG. 5 and supplies it to the mixer 207.

  The mixer 207 mixes and outputs the local oscillation signal supplied from the oscillation unit 211 and the signal supplied from the band pass filter 206. FIG. 6 is a diagram for explaining the operation of the bandpass filter 206 and the mixer 207. FIG. 6A shows a signal extracted by the band pass filter 206. As shown in this figure, the band pass filter 206 extracts a third-order aliasing signal (a signal having a center frequency of about 305 MHz (= 250 + 55 MHz)) indicated by a solid line on the right side of the sampling frequency Fs. Next, as shown in FIG. 6B, the mixer 207 mixes the third-order aliasing signal output from the bandpass filter 206 and the 3.25 GHz local oscillation signal supplied from the oscillation unit 211. By performing up-conversion, an original RF signal (signal indicated by a solid line) having a center frequency fc of 3.55 GHz is obtained. The RF signal obtained in this way is transmitted as a radio wave via the antenna 21 after components other than the RF signal are attenuated by the band pass filter 208. The mobile phone that exists in the communication area of the receiving device 20 can receive the same radio waves as those transmitted from the base station.

  The receiving apparatus 20 includes two bandpass filters 206 and 208. Since the bandpass filter 206 has a pass band of about 300 MHz, the 3 GHz band pass in the prior art shown in FIG. Compared with a band-pass filter of a band, since an element having a low frequency characteristic can be used as an active element and a passive element constituting the filter element, the filter element can be configured easily and at low cost. On the other hand, the band-pass filter 208 has a wider interval between the 3.25 GHz local oscillation signal and the 3.55 GHz RF signal than in the prior art of FIG. 9B. A band-pass filter having a gentle cutoff characteristic as indicated by a one-dot chain line can be used. For this reason, while simplifying a design, the cost of an apparatus can be held down.

  As described above, according to the first embodiment of the present invention, the signal that has been down-converted and digitized using the signal of 3.5 GHz that is the first frequency in the transmission device 10 is converted into an optical signal. In the receiving device 20, the signal is converted into an electrical signal, then converted into an analog signal, a third-order aliasing signal included in the analog signal is extracted, and a 3.25 GHz signal that is the second frequency is used. Upconverted to restore the original signal. As a result, the interval on the frequency axis between the local oscillation signal and the RF signal can be widened, so that the band-pass filter 208 having a gentle cutoff characteristic can be used, which simplifies the design and reduces the manufacturing cost. Can be reduced.

  In the first embodiment, the local oscillation signal when down-converting in the transmission device 10 is converted to a signal having a center frequency fc of about 55 MHz using the same 3.5 GHz signal as in FIG. A filter having a gentle cutoff characteristic can be used as the band-pass filter 208 without increasing the generation of jitter noise in the ADC 104. The band-pass filter 206 extracts the third-order aliasing signal. Since the third-order aliasing signal is a harmonic component of the first Nyquist zone signal, the jitter noise of the third-order aliasing signal is It is the same as the signal of about 55 MHz that is the first Nyquist zone signal. Therefore, it is possible to use a filter having a gentle cutoff characteristic as the bandpass filter 208 without increasing jitter noise.

  In the first embodiment, the transmitting device 10 and the receiving device 20 perform down-conversion and up-conversion based on local oscillation signals having different frequencies. However, these are the same frequency generated by the clock unit 110. Since it is generated based on the clock signal, it is possible to suppress the frequency deviation of the restored RF signal even when conversion is performed with different frequencies.

(C) Description of Configuration of Second Embodiment FIG. 7 is a diagram for explaining a second embodiment of the present invention. In the second embodiment, the configuration of the receiving device is different from that of the first embodiment, and the configuration of the system and the configuration of the transmitting device 10 are the same as those of the first embodiment. In FIG. 7, portions corresponding to those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. Compared with FIG. 3, the receiving apparatus 20 </ b> A illustrated in FIG. 7 excludes the PLL synthesizer 210, the oscillation unit 211, the mixer 207, and the bandpass filter 206. In addition, a bandpass filter 220 is newly added to the signal processing unit 202 to form a signal processing unit 202A, and the bandpass filter 208 is replaced with a bandpass filter 221. Other configurations are the same as those in FIG.

  Here, the band pass filter 220 is a digital filter, and extracts a signal (3.5 GHz) signal having a frequency corresponding to the RF signal from the aliasing signal included in the digital signal output from the serial / parallel conversion unit 204. And output. The band pass filter 221 passes the signal corresponding to the RF signal from the signal output from the DAC 205 and attenuates the others.

(D) Description of Operation of Second Embodiment The second embodiment is characterized in that an aliasing signal in a band corresponding to an RF signal is extracted without up-conversion in the receiving apparatus 20A. This will be described in more detail. As in the case of the first embodiment, the transmission device 10 down-converts the RF signal received from the base station, converts it to a digital signal, converts it to an optical signal, and transmits it through the optical fiber 30. In the second embodiment, the frequency of the local oscillation signal at the time of down-conversion in the transmission apparatus 10 is the same as the RF signal frequency of the aliasing signal of a predetermined order output from the DAC 205 in the reception apparatus 20A. Is set to

  The receiving device 20A that has received such an optical signal is converted into a corresponding electrical signal in the optical receiving unit 201 and supplied to the receiving unit 203. In the reception unit 203, the clock signal is extracted and supplied to the waveform shaping unit 209, and the digital signal is supplied to the serial / parallel conversion unit 204. The waveform shaping unit 209 shapes the waveform of the clock signal, and then supplies the waveform to the serial / parallel conversion unit 204, the band pass filter 220, and the DAC 205.

  The serial / parallel converter 204 converts the digital signal (serial signal) supplied from the receiving unit 203 into a parallel signal based on the clock signal supplied from the waveform shaping unit 209. The band pass filter 220 performs filtering processing such as IIR (Infinite Impulse Response) on the digital signal converted into the parallel signal, and outputs a signal in the same frequency band (3.55 GHz in this example) as the RF signal. Pass selectively.

  The DAC 205 converts the digital signal output from the bandpass filter 220 into an analog signal in synchronization with the clock signal supplied from the waveform shaping unit 209 and outputs the analog signal. The bandpass filter 221 passes a signal in a frequency band (3.55 GHz in this example) corresponding to the RF signal among the analog signals output from the DAC 205, and attenuates and outputs the other bands. The RF signal that has passed through the band pass filter 221 is transmitted to the mobile phone via the antenna 21.

  As described above, in the second embodiment of the present invention, since the receiving device 20A extracts the aliasing signal in the band corresponding to the RF signal without performing the up-conversion, it relates to the up-conversion. The apparatus can be simplified by omitting the components.

  In the second embodiment, an aliasing signal in a band corresponding to the RF signal is extracted by the band-pass filter 220 which is a digital filter in the previous stage of the DAC 205. As described above, the digital filter can easily realize a steep characteristic by adjusting the filter constant. Therefore, by executing the processing by the band-pass filter 220 in the previous stage of the DAC 205, a filter having a gentler characteristic than that of FIG. 9 can be used as the band-pass filter 221 that is an analog filter, so that the configuration of the apparatus is simplified. And simplification of the design.

  In the second embodiment described above, the output of the serial / parallel converter 204 is directly input to the bandpass filter 220. For example, an upsampler is inserted between the serial / parallel converter 204 and the bandpass filter 220. You may make it do. Here, the up-sampler is caused by up-sampling the digital signal output from the serial / parallel conversion unit 204 at a frequency (for example, 1 GHz) higher than the original sampling frequency (250 MHz in this example). Execute interpolation and output to suppress aliases. By inserting such an upsampler, aliasing signals in the same Nyquist region can be suppressed, so that the sampling frequency in the transmission apparatus 10 can be set low.

(E) Description of Modified Embodiment The above embodiment is an example, and it is needless to say that the present invention is not limited to the case as described above. For example, in each of the above embodiments, as shown in FIG. 1, the transmission apparatus 10 transmits and receives information wirelessly to and from the base station via the antenna 11. You may make it give and receive. In FIG. 1, only one receiving device 20 is provided, but a plurality of receiving devices 20 may be connected according to the area size of the radio wave dead zone.

  Further, in each of the above embodiments, only the configuration in the downlink direction (direction from the transmission device 10 to the reception device 20) is shown for simplification, but the uplink direction (direction from the reception device 20 to the transmission device 10). The same configuration as that shown in FIGS. 2, 3, and 7 may be added.

  In the first embodiment described above, the third-order aliasing signal is extracted using the band-pass filter 206 that is an analog filter. For example, a digital filter is provided between the DAC 205 and the serial-parallel conversion unit 204. The third-order aliasing signal may be extracted by inserting such a digital filter. Such a digital filter may be used alone or in combination with the bandpass filter 206.

In the first embodiment described above, the third-order aliasing signal is extracted, but it is also possible to use an aliasing signal of other orders. For example, when the order of the aliasing signal is n, the sampling frequency is Fs, the frequency of the local oscillation signal of the oscillation unit 113 is Fd, and the frequency of the local oscillation signal of the oscillation unit 211 is Fu, What is necessary is just to set each parameter so that a relationship may be materialized.
Fu = Fd−Fs × (n−1) / 2 (1)

Further, in each of the above embodiments, the transmitting apparatus 10 is configured to fit the IF signal in the first Nyquist zone, but may be configured to fit in the third or fifth Nyquist zone, for example. For example, if the order of the Nyquist zone of the input signal frequency of the ADC 104 is m and the order of the Nyquist zone of the output signal frequency of the DAC 205 is n, the above-described equation (1) is expanded as the following equation (2). Can do.
Fu = Fd−Fs × (nm) / 2 (2)

  In addition, the numerical values such as frequencies given in the above embodiments are examples, and other numerical values may be adopted.

  In each of the above embodiments, the transmission device and the reception device are connected by an optical fiber. However, it goes without saying that the transmission device and the reception device may be connected by another transmission medium (for example, a transmission cable). .

  In addition, an additional note is described below in relation to the above embodiment.

(Appendix 1)
In the receiving device that receives the down-converted and digitized signal in the transmitting device,
Conversion means for converting the digitized signal into an analog signal;
Extracting means for extracting an aliasing signal of a predetermined order included in the analog signal obtained by the converting means and having a frequency band corresponding to an original signal before being down-converted in the transmission device; ,
A receiving apparatus comprising:

(Appendix 2)
The receiving apparatus according to appendix 1, wherein a digital filter having a pass band of an aliasing signal having a frequency band corresponding to the original signal before down-conversion is provided in a preceding stage of the converting means.

(Appendix 3)
The receiving apparatus according to claim 2, further comprising an upsampler that changes a frequency higher than a sampling frequency in the transmitting apparatus at a preceding stage of the digital filter.

(Supplementary Note 4) A transmission device that down-converts and digitizes the original signal,
Conversion means for converting the digitized signal into an analog signal, and an aliasing signal of a predetermined order included in the analog signal obtained by the conversion means, which is an original before being down-converted in the transmission device An extraction means for extracting an aliasing signal having a frequency band corresponding to the signal;
A transmission / reception system comprising:

DESCRIPTION OF SYMBOLS 10 Transmitter 11 Antenna 20, 20A Receiver 21 Antenna 30 Optical fiber 101 Mixer 102 Low pass filter 103 Amplifying part 104 ADC
DESCRIPTION OF SYMBOLS 105 Signal processing part 106 Parallel serial conversion part 107 Transmission part 108 Optical transmission part 109 Optical distribution part 110 Clock part 111 Distribution part 112 PLL synthesizer 113 Oscillation part 201 Optical reception part 202,202A Signal processing part 203 Reception part 204 Serial parallel conversion part 205 DAC (conversion means)
206 Band pass filter (extraction means)
207 Mixer (restoration means)
208 Band Pass Filter 209 Waveform Shaping Unit 210 PLL Synthesizer 211 Oscillating Unit 220, 221 Band Pass Filter

Claims (4)

In a receiving apparatus that receives a down-converted and digitized signal using a signal of a first frequency in a transmitting apparatus,
Conversion means for converting the digitized signal into an analog signal;
Extracting means for extracting an aliasing signal of a predetermined order included in the analog signal obtained by the converting means;
Restoring means for upconverting the aliasing signal extracted by the extracting means using a signal having a second frequency lower than the first frequency to restore the original signal;
A receiving apparatus comprising: The transmission device down-converts the original signal to a signal in the first Nyquist zone using the signal of the first frequency, oversamples the down-converted signal,
The extracting means extracts a third-order aliasing signal;
The receiving apparatus according to claim 1. The transmission device down-converts the original signal into a signal in the third Nyquist zone using the signal of the first frequency, and performs band-limited sampling on the down-converted signal,
The extraction means extracts a fifth-order aliasing signal;
The receiving apparatus according to claim 1. A transmission device that down-converts and digitizes an original signal using a signal of a first frequency, and
Conversion means for converting the digitized signal into an analog signal, extraction means for extracting an aliasing signal of a predetermined order included in the analog signal obtained by the conversion means, and the extraction means extracted by the extraction means A receiving device comprising: restoration means for up-converting an aliasing signal using a signal of a second frequency lower than the first frequency to restore the original signal;
A transmission / reception system comprising:

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