Power spectrum detector, receiving system, and receiving station

Abstract

A digital filter bank (220) separates a baseband signal obtained from a reception signal into a plurality of sub-bands and outputs a plurality of pieces of complex sub-band data. A power converter (208) calculates, for each sub-band of the plurality of sub-bands, the reception power of the reception signal in the sub-band on the basis of the complex sub-band data of the sub-band, and outputs reception power spectrum data. The plurality of sub-bands are arranged consecutively with a frequency interval ΔF in a frequency direction. The digital filter bank (220) has a frequency characteristic in which a single-side occupied bandwidth of each sub-band of the plurality of sub-bands is within the frequency interval ΔF, and a power sum of frequency-to-power characteristics of two sub-bands adjacent to each other in the frequency direction, among the plurality of sub-bands, is constant.

Description

Power spectrum detector, receiving system and receiving station

[0001] FIELD OF THE DISCLOSURE This disclosure relates to detecting the power spectrum of a received signal.

[0002] A method using a digital filter bank is known as a means for detecting the power spectrum of a received signal. Patent Documents 1 and 2 cite FFT (discrete Fourier transform) as a specific method for realizing a digital filter bank. When detecting the power spectrum of a received signal using the FFT cited in Patent Documents 1 and 2, the detection characteristics of the power spectrum depend on the window function used to extract the time waveform during the FFT.

[0003] Digital filter banks (digital demultiplexing, digital multiplexing) for relaying signals as channelizers are known. Patent Document 3 (Patent Document 3) cites a tree circuit composed of multiple half-band filters (HBFs) and multiple channel filters (CFs) as a specific implementation method of a digital filter bank. When the tree circuit (Patent Document 3) is used to detect the power spectrum of a received signal, the band of the subband itself is primarily extracted, and other bands are suppressed by several tens of decibels, resulting in steep frequency characteristics. Therefore, the issues encountered when using FFT do not arise. However, if no constraints are placed on the frequency characteristics of the subbands, detection errors will occur when detecting the power spectrum of the received signal.

[0004] Patent No. 4084269 Patent No. 4812685 Patent No. 5575149

[0005] The present disclosure aims to enable accurate detection of the power spectrum of a received signal.

[0006] The power spectrum detector of the present disclosure comprises: a digital filter bank that demultiplexes a baseband signal obtained from a received signal into a plurality of subbands and outputs a plurality of complex subband data; and a power converter that calculates, for each subband of the plurality of subbands, the received power of the received signal in the subband based on the complex subband data of the subband, and outputs received power spectrum data, wherein the plurality of subbands are arranged consecutively in the frequency direction at frequency intervals ΔF, and the digital filter bank has frequency characteristics such that the one-sided occupied bandwidth of each of the plurality of subbands is within the frequency interval ΔF and the power sum of the frequency-to-power characteristics of two subbands that are adjacent to each other in the frequency direction among the plurality of subbands is constant.

[0007] According to the present disclosure, the power spectrum of a received signal can be accurately detected.

[0008] FIG. 1 is a configuration diagram of a receiving system 100 according to the first embodiment. FIG. 2 is a configuration diagram of a terminal station 200 according to the first embodiment. FIG. 3 is a configuration diagram of a ground station 300 according to the first embodiment. FIG. 4 is a configuration diagram of a digital filter bank 220 according to the first embodiment. FIG. 5 is a diagram showing frequency vs. power characteristics of the digital filter bank 220 according to the first embodiment. FIG. 6 is a diagram showing frequency vs. amplitude characteristics of the digital filter bank 220 according to the first embodiment. FIG. 7 is a diagram showing an example of frequency characteristics of the digital filter bank 220 according to the first embodiment. FIG. 8 is a diagram showing frequency vs. amplitude characteristics after passing through a receiving filter 303 according to the first embodiment. FIG. 9 is a diagram showing an image of demultiplexing processing by the digital filter bank 220 according to the first embodiment. FIG. 10 is a diagram showing an image of multiplexing processing by the multiplexing filter 304 according to the first embodiment. FIG. 11 is a diagram showing an example of conventional normalized frequency vs. power characteristics. FIG. 12 is a diagram showing an example of conventional frequency vs. amplitude characteristics. FIG. 13 is a configuration diagram of a receiving station 101 according to the second embodiment. FIG. 14 is a diagram showing an example of frequency vs. power characteristics of the digital filter bank 220 according to the third embodiment. FIG. 15 is a diagram showing an example of frequency characteristics of the digital filter bank 220 according to the third embodiment. Fig. 10 is a diagram showing an example of a lookup table according to the third embodiment. Fig. 11 is a diagram showing an example of a moving average of a band signal according to the third embodiment. Fig. 12 is a diagram showing an example of an estimation of a center frequency according to the third embodiment.

[0009] In the embodiments and drawings, the same or corresponding elements are denoted by the same reference numerals. The description of elements denoted by the same reference numerals as those already described will be omitted or simplified as appropriate. Arrows in the drawings primarily indicate the flow of signals or the flow of processing.

[0010] First Embodiment A receiving system 100 will be described with reference to FIGS.

[0011] ***Configuration Description***

[0012] The configuration of a receiving system 100 will be described with reference to Fig. 1. The receiving system 100 includes a terminal station 200 and a ground station 300. The terminal station 200 and the ground station 300 communicate with each other wirelessly.

[0013] The configuration of terminal station 200 will be described with reference to Fig. 2. Terminal station 200 includes receiving antenna 201, variable attenuator 202, bandpass filter 203, AD converter 204, oscillator 205, automatic gain controller 206, and downconverter 207. Terminal station 200 also includes digital filter bank 220, power converter 208, modulator 209, and transmitting antenna 210.

[0014] The terminal station 200 includes a power spectrum detector 110. The power spectrum detector 110 is a circuit that includes a digital filter bank 220 and a power converter 208.

[0015] The configuration of the ground station 300 will be described with reference to Fig. 3. The ground station 300 includes a receiving antenna 301, a demodulator 302, a receiving filter 303, and a multiplexing filter 304.

[0016] The configuration of the digital filter bank 220 will be described with reference to Fig. 4. Fig. 4 shows an example of the configuration of the digital filter bank 220 when dividing a baseband signal into four.

[0017] The digital filter bank 220 is composed of one or more stages (preceding stages) and a channel filter 250 (final stage). Each stage is composed of multiple frequency converters (FCs) and multiple 1 / 2 decimation filters. The 1 / 2 decimation filters are composed of half-band filters (HBFs) and 1 / 2 decimators (↓2). The channel filter 250 is composed of multiple channel filters 251. "FC" is an abbreviation for Frequency Converter. "HBF" is an abbreviation for Half Band Filter. "↓2" means the 1 / 2 decimator. "CF" is an abbreviation for Channel Filter.

[0018] The digital filter bank 220 divides the baseband signal into 1 / 2, 1 / 4, 1 / 8, . . . for each stage.

[0019] The configuration other than the channel filter 250 is the same as the configuration of the tree circuit disclosed in Patent Document 3.

[0020] The digital filter bank 220 is realized, for example, by a tree circuit as shown in FIG. 4 . The digital filter bank 220 includes a first stage 230, a second stage 240, and a channel filter 250. The first stage 230 includes two pairs of a frequency converter 231 and a ½ decimation filter 232. The ½ decimation filter 232 is composed of a half-band filter 233 and a ½ decimator 234. The second stage 240 includes two pairs of a frequency converter 241 and a ½ decimation filter 242, one for each pair of the frequency converter 231 and the ½ decimation filter 232. The ½ decimation filter 242 is composed of a half-band filter 243 and a ½ decimator 244. The channel filter 250 includes a channel filter 251 for each pair of the frequency converter 241 and the ½ decimation filter 242. The digital filter bank 220 divides the input baseband signal into four parts and outputs four complex subband data (#1 to #4).

[0021] The digital filter bank 220 may be configured such that the demultiplexing number N is other than 4. The demultiplexing number N has a relationship of "N=2S" with respect to the number of stages S. The demultiplexing number N can be increased by increasing the number of stages S. The digital filter bank 220 demultiplexes the input baseband signal into N signals and outputs N pieces of complex subband data (#1 to #N).

[0022] The frequency characteristics of the digital filter bank 220 will be described with reference to Figures 5 and 6. Figure 5 shows the frequency-power characteristics of the digital filter bank 220. Multiple subbands (#1 to #8) are arranged consecutively in the frequency direction at a frequency interval ΔF. At the point where the frequency-power characteristics of two adjacent subbands in the frequency direction intersect, the power of each subband is 0.5. The one-sided transition bandwidth Fx is narrow. The one-sided transition bandwidth Fx is the region where the frequency-power characteristics of two adjacent subbands overlap.

[0023] The digital filter bank 220 has a frequency characteristic in which the power sum (=1.0) of the frequency-to-power characteristics of two subbands adjacent in the frequency direction is constant. The frequency characteristic of the digital filter bank 220 is provided to the channel filter 250.

[0024] FIG. 6 shows the frequency-amplitude characteristics of the digital filter bank 220. At the point where the frequency-amplitude characteristics of two adjacent subbands intersect, the amplitude is 0.707. "0.707" corresponds to the square root of 0.5 (1 / 2). The unmodulated wave represents the received signal. If an unmodulated wave is present at the frequency where the frequency-amplitude characteristics of subband #3 and subband #4 intersect, the power detected in each of subband #3 and subband #4 will be 1 / 2 times. "1 / 2" corresponds to the square of 0.707. Therefore, the sum of the power detected in each of subband #3 and subband #4 will be 1 times. This means that the sum of the detected powers is the same as the received power of the unmodulated wave. Therefore, no errors occur when detecting the power spectrum of the received signal.

[0025] Although FIGS. 5 and 6 show the case where the baseband signal is demultiplexed into eight subbands, the number of demultiplexing N may be any integer equal to or greater than two.

[0026] The frequency characteristics of the digital filter bank 220 will be described in detail with reference to FIG. 7 . "#m" represents the subband number. "fM" represents the center frequency of the unmodulated wave. "HM(f)" represents the frequency vs. normalized power characteristics. The normalized power is the power of the unmodulated wave normalized by the power of the center frequency fM. "ΔF" represents the frequency interval between two consecutive subbands in the frequency direction. "Fx" represents the bandwidth of the one-sided transition band (one-sided transition bandwidth) of the frequency characteristics. The one-sided transition bandwidth Fx is greater than 0 and is within the frequency interval ΔF. "FB" represents the bandwidth of the one-sided occupied band (one-sided occupied bandwidth) of the frequency characteristics. The one-sided occupied bandwidth FB includes the one-sided transition bandwidth Fx. The one-sided occupied bandwidth FB is greater than 0 and is within the frequency interval ΔF.

[0027] The digital filter bank 220 has frequency characteristics such that the one-sided occupied bandwidth FB of each subband is within a frequency interval ΔF. The frequency characteristics of the digital filter bank 220 are provided to the channel filter 250.

[0028] In the digital filter bank 220, the frequency characteristics of each subband satisfy equation (1).

[0029]

[0030] By satisfying equation (1), a frequency characteristic is realized in which the one-sided occupied bandwidth FB of each subband is within the frequency interval ΔF and the power sum of the frequency-to-power characteristics of two adjacent subbands in the frequency direction is constant.

[0031] By setting the range of the one-sided transition bandwidth Fx to 0<Fx≦ΔF, the range of the one-sided occupied bandwidth FB becomes 0<FB≦ΔF. As a result, the double-sided occupied bandwidth of each subband is limited to within 2×ΔF.

[0032] The digital filter bank 220 may be any type as long as it has frequency characteristics that satisfy equation (1).

[0033] For example, a root roll-off filter can be used to satisfy equation (1). When using a root roll-off filter, ΔF is set as the symbol frequency and Fx / ΔF is set as the roll-off rate. The symbol frequency and the roll-off rate are parameters of the root roll-off filter.

[0034] 8 shows the frequency characteristics of the digital filter bank 220 when a root roll-off filter is used, with a roll-off factor of 0.1.

[0035] For example, the frequency characteristics of a root roll-off filter are applied to the channel filter 250. The channel filter 250 has an FIR filter configuration. Therefore, if the filter coefficient sequence of the channel filter 250 is set to the impulse sequence of the root roll-off filter, the frequency characteristics that satisfy equation (1) are realized.

[0036] The frequency characteristics of the receive filter 303 of the ground station 300 will be described. The receive filter 303 has the same frequency characteristics as the digital filter bank 220. In the receive filter 303, the frequency characteristics of each subband satisfy equation (1). The receive filter 303 is composed of multiple channel filters, just like the channel filter 250, and the same frequency characteristics as the digital filter bank 220 are provided to the receive filter 303.

[0037] 9 shows the frequency versus amplitude characteristics after passing through the receive filter 303. At the point where the frequency versus amplitude characteristics of two subbands adjacent in the frequency direction intersect, the amplitude of each subband is 0.5.

[0038] The frequency characteristics after passing through the receiving filter 303 have a frequency characteristic in which the sum of the amplitudes (=1.0) of the frequency-to-amplitude characteristics of two subbands adjacent in the frequency direction is constant.

[0039] Since the signal after passing through the receiving filter 303 has such frequency characteristics, the subsequent multiplexing filter 304 performs amplitude vector synthesis (multiplexing processing) to restore a normal modulated wave.

[0040] ***Explanation of Operation*** The operation of the terminal station 200 will be described with reference to FIG. 2. The receiving antenna 201 receives radio waves in the observation band. The received radio waves are referred to as the received signal. The variable attenuator 202 attenuates the received signal in accordance with instructions from the automatic gain controller 206. The bandpass filter 203 performs band limiting on the received signal. The bandpass filter 203 acts as an anti-aliasing filter to prevent alias components from overlapping with the observation band during the subsequent AD conversion process. The AD converter 204 samples the received signal that has passed through the bandpass filter 203 using a clock signal supplied from the oscillator 205. The oscillator 205 supplies a clock signal to the AD converter 204 and each functional block that performs digital signal processing after the AD conversion process. The automatic gain controller 206 operates as follows to prevent the input level of the received signal to the AD converter 204 from exceeding full scale. Automatic gain controller 206 detects the reception level from the received signal that has passed through AD converter 204. If the detected reception level exceeds a threshold, automatic gain controller 206 issues a command to variable attenuator 202 to provide attenuation. Downconverter 207 frequency-converts the RF data obtained by sampling in AD converter 204 and outputs a baseband signal (=I, Q data). Digital filter bank 220 demultiplexes the baseband signal output from downconverter 207 into multiple subbands and outputs multiple complex subband data.

[0041] An example of the operation of the digital filter bank 220 will be described with reference to Figure 4. The first stage 230 splits the baseband signal in half. The second stage 240 splits the split baseband signal in quarters. As a result, the baseband signal is split into four subband signals. The channel filter 250 filters the four subband signals and outputs four subband data (#1 to #4).

[0042] 10 shows an image of the demultiplexing process by the digital filter bank 220. The shaded trapezoid represents a modulated wave. The dashed trapezoid represents the frequency characteristics of the digital filter bank 220. The input baseband signal has a bandwidth B and includes three modulated waves (#0 to #2). The bandwidth B has the relationship B = N × ΔF. The input baseband signal is demultiplexed into multiple complex subband data at frequency intervals ΔF.

[0043] Returning to Fig. 2, the explanation will be continued. The power converter 208 calculates the received power of the received signal in each subband based on the complex subband data of each subband, and outputs received power spectrum data. The received power spectrum data indicates a received power sequence of multiple subbands. In other words, the received power spectrum data indicates the received power of multiple subbands.

[0044] Specifically, the power converter 208 operates as follows: The power converter 208 squares N pieces of complex subband data and converts them into power. At this time, the power converter 208 calculates the received power of each subband by calculating equation (2). "iT" represents time (i=1, 2, 3, ...). "T" represents the sample period. "#M" represents the subband number (M=1, 2, 3, ..., N). "P Ｍ (i)" represents the received power of subband #M at time i. Ｍ (i)" represents the power of the I data of subband #M at time i. Ｍ (i)" represents the power of the Q data of subband #M at time i.

[0045] By calculating equation (2) for each time iT, the received power sequence P １ (i) to P Ｎ(i) is obtained. The frequency interval between each subband is ΔF. Therefore, the received power sequence corresponds to the received power spectrum at time iT, its frequency resolution corresponds to the frequency interval ΔF, and the number of subbands N corresponds to the number of points. The frequency span is the bandwidth B of the input baseband signal. Since the bandwidth B has the relationship B = N × ΔF (see FIG. 10), if the bandwidth B is constant and the number of subbands N is increased, the frequency resolution corresponding to the frequency interval ΔF becomes finer as the reciprocal of the number of subbands N. Note that in FIG. 2, when the automatic gain controller 206 provides an attenuation amount L [decibels] to the variable attenuator 202, the received power received by the receiving antenna 201 is L [decibels] higher than the received power spectrum calculated by equation (2). Therefore, to calculate the received power spectrum received by the receiving antenna 201, the received power spectrum calculated by equation (2) is multiplied by L [decibels].

[0046] The operations of the modulator 209 and the transmitting antenna 210 will now be described. The modulator 209 modulates the received power spectrum data and outputs a radio signal. The modulator 209 also modulates two or more complex subband data that are consecutively arranged in the frequency direction among the plurality of complex subband data and outputs a radio signal. The transmitting antenna 210 transmits the radio signal of the received power spectrum data to the ground station 300. The transmitting antenna 210 also transmits the radio signal of the two or more complex subband data to the ground station 300.

[0047] The operation of the ground station 300 will be described with reference to Figure 3. The receiving antenna 301 receives a radio signal containing received power spectrum data. The receiving antenna 301 also receives a radio signal containing two or more complex subband data. The demodulator 302 demodulates the received radio signal to obtain received power spectrum data. The demodulator 302 also demodulates the received radio signal to obtain two or more complex subband data. The receiving filter 303 filters the two or more complex subband data. The multiplexing filter 304 multiplexes the two or more filtered complex subband data to restore modulated wave data of each of the one or more modulated waves contained in the two or more complex subband data among the one or more modulated waves contained in the baseband signal.

[0048] FIG. 11 shows an image of the multiplexing process performed by the multiplexing filter 304. The shaded trapezoid represents a modulated wave. The dashed trapezoid represents the frequency characteristics after passing through the receiving filter 303. The multiplexing filter 304 multiplexes K pieces of complex subband data to restore L pieces of modulated data (1≦L<K). In FIG. 11, two modulated waves (#1, #2) are demultiplexed into 12 subbands. Each of the 12 complex subband data is filtered by the receiving filter 303. The multiplexing filter 304 multiplexes eight pieces of complex subband data that are consecutive on the frequency axis to restore modulated wave #1. At the same time, the multiplexing filter 304 multiplexes four pieces of complex subband data that are consecutive on the frequency axis to restore modulated wave #2.

[0049] ***Effects of First Embodiment*** Figure 12 shows an example of conventional normalized frequency versus power characteristics. The normalized frequency is a frequency normalized by the bandwidth of a subband (bin). When a rectangular window is used to extract a time waveform during FFT power spectrum detection, the frequency characteristics of the subband corresponding to each bin are as shown in Figure 12. This frequency characteristic is a SINC characteristic that is not limited to the subband itself (normalized frequency: -0.5 to +0.5) but spreads to multiple subbands (bins). Therefore, even if an adjacent subband signal is input, its leakage power is detected in the subband itself, resulting in the observed received power spectrum being broadened.

[0050] FIG. 13 shows an example of conventional frequency-amplitude characteristics. When the amplitude at the intersection of the frequency characteristics of two adjacent subbands is 0.5 (= 1 / 2), an error of up to -3 dB occurs in the detection result. When an unmodulated wave is present at the frequency where the frequency characteristics of subband #3 and subband #4 intersect, the power detected in each of subband #3 and subband #4 is 1 / 4 times. 1 / 4 received power corresponds to the square of an amplitude of 1 / 2. Therefore, the total power detected in each of subband #3 and subband #4 is 1 / 2 (= 1 / 4 + 1 / 4). This means that the total detected power is 1 / 2 of the received power of the unmodulated wave. In other words, when detecting the power spectrum of a received signal, an error of -3 dB occurs in the detection result.

[0051] The first embodiment has been made in view of the above-mentioned problems. In the first embodiment, a digital filter bank 220 is used in which the power sum of the frequency characteristics of two adjacent subbands is 1. This makes it possible to accurately detect the received power spectrum while ensuring the amount of suppression outside the subband, similar to the method of Patent Document 3. By using the digital filter bank 220, it is possible to achieve accurate received power spectrum detection without errors, regardless of the frequency of the received signal.

[0052] In the terminal station 200, the digital filter bank 220, which separates the baseband signal into multiple subbands, is given a frequency characteristic such that the power sum of the frequency characteristics of two adjacent subbands is 1. Furthermore, the one-sided occupied bandwidth of each subband is limited to within the frequency interval ΔF between the subbands. This makes it possible to obtain accurate received power spectrum information. Furthermore, in the ground station 300, which receives and analyzes the K pieces of complex subband data separated by the digital filter bank 220, the same frequency characteristic as that given by the digital filter bank 220 is given to the receiving filter 303. As a result, the K pieces of complex subband data filtered by the receiving filter 303 can be combined to obtain a correctly restored modulated wave. This makes it possible to achieve accurate analysis of the modulated wave.

[0053] *** Supplement to First Embodiment *** In the terminal station 200, if the condition that the input level of the AD converter 204 does not exceed the full scale is met, the automatic gain controller 206 and the variable attenuator 202 are not necessary.

[0054] If the bandwidth of the received spectrum to be observed is less than 1 / 4 of the sampling rate of the AD converter 204, the downconverter 207 may output data by lowering the sampling rate using a decimation filter.

[0055] The multiplexing filter 304 can be realized by a tree circuit as disclosed in, for example, Patent Document 3.

[0056] The first embodiment is based on the premise that the center frequency and bandwidth of each modulated wave are known. In the process of selecting K complex subband data from M complex subband data and the process of restoring L modulated wave data from the K complex subband data, the allocation of each complex subband data is performed based on known information. However, in the first embodiment, the center frequency and bandwidth of each modulated wave may be unknown. For example, the terminal station 200 may select the received power spectrum P １ (i) to P Ｎ(i) is compared with the threshold value TH. Then, the terminal station 200 transmits the complex subband data of each subband whose received power spectrum P exceeds the threshold value TH together with the subband number #M to the terrestrial station 300. This allows the terrestrial station 300 to restore the L pieces of modulated wave data, just as in the case where the center frequency and bandwidth of each modulated wave are known.

[0057] Second Embodiment A receiving station 101 corresponding to the receiving system 100 will be described with reference to FIG. 14, focusing mainly on the differences from the first embodiment.

[0058] ***Description of Configuration*** The configuration of the receiving station 101 will be described with reference to Fig. 14. The receiving station 101 comprises a receiving antenna 201, a variable attenuator 202, a bandpass filter 203, an AD converter 204, an oscillator 205, an automatic gain controller 206, a downconverter 207, a digital filter bank 220, and a power converter 208. Furthermore, the receiving station 101 comprises a receiving filter 303 and a multiplexing filter 304.

[0059] The receiving station 101 includes a power spectrum detector 110. The power spectrum detector 110 is a circuit that includes a digital filter bank 220 and a power converter 208.

[0060] ***Description of Operation*** The operation of the receiving station 101 will be described with reference to FIG. 14. The receiving antenna 201 receives radio waves in the observation band. The variable attenuator 202 attenuates the received signal in accordance with a command from the automatic gain controller 206. The bandpass filter 203 performs band limiting on the received signal. The AD converter 204 samples the received signal that has passed through the bandpass filter 203 using a clock signal supplied from the oscillator 205. The downconverter 207 frequency-converts the RF data obtained by sampling in the AD converter 204 and outputs a baseband data signal (=I, Q data). The digital filter bank 220 demultiplexes the baseband signal output from the downconverter 207 into multiple subbands and outputs multiple complex subband data. The power converter 208 calculates the received power of the received signal in each subband based on the complex subband data of each subband, and outputs received power spectrum data. The receiving filter 303 filters two or more pieces of complex subband data that are consecutively arranged in the frequency direction from among the plurality of complex subband data. The multiplexing filter 304 multiplexes the two or more pieces of complex subband data after filtering to restore modulated wave data of each of the one or more modulated waves included in the two or more pieces of complex subband data from among the one or more modulated waves included in the baseband signal.

[0061] ***Effects of Second Embodiment*** When there is no need to transmit the received power spectrum data and the complex subband data wirelessly, the receiving station 101 takes over for the receiving system 100. By having the receiving station 101 take over for the receiving system 100, the hardware scale can be reduced.

[0062] *** Supplementary Note to Second Embodiment *** The receiving system 100 may include a master station and multiple receiving stations 101. Any one of the receiving stations 101 may function as the master station. The master station and each receiving station 101 are connected by wire. Each receiving station 101 is located outdoors or indoors. The master station collects received power spectrum data and complex subband data from each receiving station 101, and monitors or analyzes the received power spectrum data and complex subband data.

[0063] Third Embodiment A third embodiment of estimating the center frequency of a received signal will be described below, focusing mainly on the differences from the first and second embodiments, with reference to Figs.

[0064] ***Description of Configuration*** The configuration of the receiving system 100 is the same as that in the first embodiment. The configuration of the receiving station 101 is the same as that in the second embodiment.

[0065] However, power converter 208 also functions as a frequency estimator, which estimates the center frequency of the received signal based on the relationship between the power magnitudes of the frequency-to-power characteristics of two subbands adjacent in the frequency direction, and outputs the estimated center frequency value.

[0066] The following describes the frequency characteristics of the digital filter bank 220. The frequency characteristics of the digital filter bank 220 are further constrained such that the one-sided transition bandwidth Fx is equal to the frequency interval ΔF (Fx=ΔF).

[0067] 15 shows an example of the frequency vs. power characteristics of the digital filter bank 220. In the graph of the frequency vs. power characteristics, if the frequency characteristics of each subband form a triangle, the frequency vs. power characteristics correspond to the frequency characteristics of the digital filter bank 220.

[0068] FIG. 16 shows the frequency characteristics of the digital filter bank 220 when a root roll-off filter is used. The roll-off ratio is 1.0. The solid waveform represents the frequency characteristics of the own channel. The dotted waveform represents the frequency characteristics of the adjacent channel. Assume that an unmodulated signal with a normalized power of 1 is received at the normalized frequency indicated by the upward arrow (↑). In this case, normalized power A of the own channel's subband and normalized power B of the adjacent channel's subband are detected in the received power spectrum. The adjacent channel is the channel next to the own channel. In this case, the sum of normalized power A and normalized power B is 1. Even if a received signal occurs at a subband boundary, no power loss occurs, and the accuracy of the received power measurement is maintained. Furthermore, the center frequency of the unmodulated signal can be estimated based on the relationship between normalized power A and normalized power B.

[0069] ***Description of Operation*** The power converter 208 detects the normalized power A of the subband of its own channel and the normalized power B of the subband of the adjacent channel, and estimates the center frequency of the received signal based on the relationship between the normalized power A and the normalized power B.

[0070] The center frequency of the received signal is estimated as follows. First, the power converter 208 calculates the arc tangent of normalized power B relative to normalized power A (ATAN(B / A)). Next, the power converter 208 obtains the offset frequency corresponding to the calculated arc tangent value from a lookup table. An example of the lookup table is shown in FIG. 17. The lookup table is data showing the relationship between the arc tangent value and the (normalized) offset frequency. Then, the power converter 208 calculates the offset frequency F ＯＦＦ and the center frequency of the own channel f Ｍ The center frequency Fc of the received signal is calculated using the frequency interval ΔF. The center frequency Fc of the received signal is expressed by the following formula: Fc=f Ｍ + (F ＯＦＦ ) × ΔF

[0071] ***Effects of Third Embodiment*** In the third embodiment, an additional constraint (Fx=ΔF) is imposed on the subband frequency characteristics given to the digital filter bank 220. This makes it possible to estimate the center frequency of the received signal with an accuracy less than the frequency resolution ΔF.

[0072] Conventionally, it was not possible to estimate the center frequency of a received signal with high precision unless the demultiplexing number N was increased to increase the frequency resolution. The resolution corresponds to the subband bandwidth. The third embodiment can estimate the center frequency of a received signal with precision less than the frequency resolution of the received spectrum. In other words, the third embodiment can estimate the center frequency of a received signal with high precision even if the demultiplexing number N is small (even if the frequency resolution is coarse). Furthermore, being able to suppress an increase in the demultiplexing number N leads to a reduction in the circuit size of the digital filter bank 220. In other words, the third embodiment makes it possible to estimate the center frequency of a received signal with high precision while suppressing the hardware size.

[0073] *** Supplementary Note on Third Embodiment *** The third embodiment may be applied to estimating the center frequency of a received signal other than an unmodulated wave. The third embodiment can be applied to a signal having a bandwidth (band signal). When a band signal is received, the received power is not necessarily detected in only two adjacent subbands, but may be detected in three or more consecutive subbands on the frequency axis. In this case, too, the received power P detected in each subband is Ｍ (i) to P Ｍ＋Ｊ－１ The center frequency of the subband signal can be estimated based on the relationship (i), where "J" is an integer equal to or greater than 3. For example, the power converter 208 estimates the received power P Ｍ (i) to P Ｍ＋Ｊ－１ The moving average of (i) is calculated, and the frequency indicating the peak point of the average power characteristic after the moving average is calculated. The calculated frequency is the center frequency of the band signal.

[0074] FIG. 18 shows an example of a moving average of a band signal. The waveform connecting the circles represents the power spectrum of the band signal. The band signal has a bandwidth of approximately five subbands. The waveform connecting the triangles represents the power spectrum after the moving average. When the moving average is performed over a bandwidth (7 subbands) slightly wider than the bandwidth of the band signal, the power spectrum after the moving average has a peak in a subband (M=6) that is approximately the center frequency of the band signal. FIG. 19 shows an example of estimating the center frequency. The power converter 208 calculates an approximation curve (dashed curve) that connects the peak value of the subband having the peak and the values ​​before and after the peak. The power converter 208 then calculates the frequency corresponding to the peak of the approximation curve. The calculated frequency is the center frequency of the band signal.

[0075] The process of estimating the center frequency of the received signal (frequency estimation process) may be performed anywhere after the received power spectrum is obtained. For example, the frequency estimation process may be performed in the terminal station 200, the ground station 300, or the receiving station 101. When the frequency estimation process is performed in the terminal station 200, the estimated center frequency is transmitted wirelessly to the ground station 300 together with the received power spectrum.

[0076] Fourth Embodiment The following describes the configuration for switching the one-sided transition band Fx, mainly in terms of differences from the third embodiment.

[0077] ***Description of Configuration*** The configuration of the receiving system 100 is the same as that in the first embodiment. The configuration of the receiving station 101 is the same as that in the second embodiment.

[0078] When the center frequency of the received signal is estimated, the digital filter bank 220 operates with frequency characteristics in which the one-sided transition bandwidth Fx is equal to the frequency interval ΔF. When the received power of the received signal is calculated for each subband, the digital filter bank 220 operates with frequency characteristics in which the one-sided transition bandwidth Fx is smaller than the frequency interval ΔF.

[0079] ***Description of Operation*** The digital filter bank 220 switches the single-sided transition bandwidth Fx within the range of 0<Fx≦ΔF. When a root roll-off filter is used, the digital filter bank 220 switches the roll-off rate R within the range of 0<R≦1. For example, when estimating the center frequency of a received signal as in the third embodiment, the digital filter bank 220 makes the single-sided transition bandwidth Fx equal to the frequency interval ΔF. This widens the bandwidth of each subband. For example, when observing the signal power of each subband as in the first embodiment, the digital filter bank 220 makes the single-sided transition bandwidth Fx smaller than the frequency interval ΔF (e.g., Fx = 0.1ΔF). This narrows the bandwidth of each subband. Furthermore, when transmitting multiple complex subband data from the terminal station 200 to the ground station 300, the digital filter bank 220 makes the single-sided transition bandwidth Fx smaller than the frequency interval ΔF. This narrows the bandwidth of each subband. Narrowing the subband bandwidth reduces the sampling rate. Therefore, the transmission speed of the complex subband data from the terminal station 200 to the ground station 300 can be reduced.

[0080] ***Effects of the Fourth Embodiment*** According to the fourth embodiment, it is possible to realize the receiving system 100 or the receiving station 101 that can flexibly accommodate various purposes or uses.

[0081] *** Supplementary Notes on the Embodiments *** The embodiments relate to a terminal station 200 and a receiving station 101 that have a function of detecting the power spectrum of a received signal. Examples of applications of the terminal station 200 include artificial satellites and unmanned aerial vehicles. Examples of applications of the receiving station 101 include sensors placed on the ground.

[0082] Each embodiment is an example of a preferred embodiment and is not intended to limit the technical scope of the present disclosure. Each embodiment may be implemented in part or in combination with other embodiments.

[0083] Aspects of the present disclosure are described below as supplementary notes. (Supplementary note 1) A power spectrum detector comprising: a digital filter bank that demultiplexes a baseband signal obtained from a received signal into a plurality of subbands and outputs a plurality of complex subband data; and a power converter that calculates a received power of the received signal in each subband of the plurality of subbands based on the complex subband data of the subband and outputs received power spectrum data, wherein the plurality of subbands are arranged consecutively in a frequency direction at frequency intervals ΔF, and the digital filter bank has frequency characteristics such that a one-sided occupied bandwidth of each of the plurality of subbands is within the frequency interval ΔF and a power sum of frequency-to-power characteristics of two subbands that are adjacent to each other in the frequency direction among the plurality of subbands is constant.

[0084] (Supplementary Note 2) The power spectrum detector according to Supplementary Note 1, wherein the digital filter bank sets a one-sided transition bandwidth of each of the plurality of subbands equal to the frequency interval ΔF, and the power converter estimates a center frequency of the received signal based on a power magnitude relationship in the frequency-to-power characteristics of two subbands adjacent in the frequency direction, and outputs the estimated center frequency value and the received power spectrum data.

[0085] (Supplementary Note 3) The power spectrum detector according to Supplementary Note 2, wherein the digital filter bank operates with frequency characteristics in which the one-sided transition bandwidth is equal to the frequency interval ΔF when the center frequency of the received signal is estimated, and operates with frequency characteristics in which the one-sided transition bandwidth is smaller than the frequency interval ΔF when the received power of the received signal is calculated for each subband.

[0086] (Supplementary Note 4) The power spectrum detector according to any one of Supplementary Note 1 to Supplementary Note 3, wherein a root roll-off filter is used in the digital filter bank, and the frequency characteristics of the digital filter bank are realized by setting parameters of the root roll-off filter.

[0087] (Supplementary Note 5) The power spectrum detector according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the digital filter bank is configured by a tree circuit including a plurality of frequency converters, a plurality of ½ decimation filters, and a plurality of channel filters, the frequency characteristics of the digital filter bank are given to the plurality of channel filters, and the plurality of channel filters are arranged in a final stage of the tree circuit, and filter a plurality of subband signals obtained by demultiplexing the baseband signal into the plurality of subbands using the plurality of frequency converters and the plurality of ½ decimation filters, and output the plurality of complex subband data.

[0088] (Supplementary Note 6) A receiving system comprising: a terminal station equipped with the power spectrum detector according to any one of Supplementary Note 1 to Supplementary Note 5; and a ground station receiving, from the terminal station, a radio signal obtained by modulating the received power spectrum data, and demodulating the received radio signal to obtain the received power spectrum data.

[0089] (Supplementary Note 7) The receiving system described in Supplementary Note 6, wherein the terminal station comprises: a modulator that modulates the received power spectrum data and two or more complex subband data that are consecutively arranged in the frequency direction among the plurality of complex subband data; and a transmitting antenna that transmits the radio signal; and the earth station comprises: a receiving antenna that receives the radio signal; a demodulator that demodulates the radio signal to obtain the received power spectrum data and the two or more complex subband data; a receiving filter that filters the two or more complex subband data; and a multiplexing filter that multiplexes the filtered two or more complex subband data to restore modulated wave data of each of the one or more modulated waves included in the two or more complex subband data among the one or more modulated waves included in the baseband signal, and the receiving filter has the same frequency characteristics as the frequency characteristics of the digital filter bank.

[0090] (Supplementary Note 8) A receiving station comprising: a power spectrum detector according to any one of Supplementary Note 1 to Supplementary Note 5; a receiving filter that filters two or more complex subband data that are consecutively arranged in the frequency direction from among the plurality of complex subband data; and a multiplexing filter that multiplexes the two or more complex subband data after filtering to restore modulated wave data of each of one or more modulated waves included in the two or more complex subband data from among one or more modulated waves included in the baseband signal, wherein the receiving filter has the same frequency characteristics as the frequency characteristics of the digital filter bank.

[0091] 100 Receiving system, 101 Receiving station, 110 Power spectrum detector, 200 Terminal station, 201 Receiving antenna, 202 Variable attenuator, 203 Bandpass filter, 204 AD converter, 205 Oscillator, 206 Automatic gain controller, 207 Downconverter, 208 Power converter, 209 Modulator, 210 Transmitting antenna, 220 Digital filter bank, 230 First stage, 231 Frequency converter, 232 Half-decimation filter, 233 Half-band filter, 234 Half-decimator, 240 Second stage, 241 Frequency converter, 242 Half-decimation filter, 243 Half-band filter, 244 Half-decimator, 250 Channel filter, 251 Channel filter, 300 Earth station, 301 Receiving antenna, 302 Demodulator, 303 Receive filter, 304 multiplexing filter.

Claims

1. A power spectrum detector comprising: a digital filter bank that demultiplexes a baseband signal obtained from a received signal into a plurality of subbands and outputs a plurality of complex subband data; and a power converter that calculates a received power of the received signal in each subband based on the complex subband data of the subband for each of the plurality of subbands and outputs received power spectrum data, wherein the plurality of subbands are arranged continuously in the frequency direction at a frequency interval ΔF, and the digital filter bank has a frequency characteristic that one-sided occupied bandwidth of each subband of the plurality of subbands is within the frequency interval ΔF and a sum of powers of frequency-to-power characteristics of two adjacent subbands in the frequency direction in the plurality of subbands is constant.

2. The power spectrum detector according to claim 1, wherein the digital filter bank makes one-sided transition bandwidth of each subband of the plurality of subbands equal to the frequency interval ΔF, and the power converter estimates a center frequency of the received signal based on a relationship between magnitudes of powers of the frequency-to-power characteristics of two adjacent subbands in the frequency direction and outputs a value of the estimated center frequency and the received power spectrum data.

3. The power spectrum detector according to claim 2, wherein the digital filter bank operates with a frequency characteristic that the one-sided transition bandwidth is equal to the frequency interval ΔF when the center frequency of the received signal is estimated, and operates with a frequency characteristic that the one-sided transition bandwidth is smaller than the frequency interval ΔF when the received power of the received signal is calculated for each subband.

4. The power spectrum detector according to any one of claims 1 to 3, wherein a root raised cosine filter is used in the digital filter bank, and the frequency characteristic of the digital filter bank is realized by setting parameters of the root raised cosine filter.

5. The digital filter bank is composed of a tree circuit including a plurality of frequency converters, a plurality of 1 / 2 decimation filters, and a plurality of channel filters. The frequency characteristics of the digital filter bank are provided to the plurality of channel filters. The plurality of channel filters are arranged at the final stage of the tree circuit, and filter a plurality of subband signals obtained by dividing the baseband signal into the plurality of subbands by the plurality of frequency converters and the plurality of 1 / 2 decimation filters, and output the plurality of complex subband data. The power spectrum detector according to any one of claims 1 to 4.

6. A terminal station including the power spectrum detector according to any one of claims 1 to 5, and a ground station that receives a radio signal obtained by modulating the received power spectrum data from the terminal station, demodulates the received radio signal, and obtains the received power spectrum data. A receiving system comprising:

7. The terminal station includes a modulator that modulates two or more complex subband data arranged continuously in the frequency direction among the received power spectrum data and the plurality of complex subband data, and a transmission antenna that transmits the radio signal. The ground station includes a receiving antenna that receives the radio signal, a demodulator that demodulates the radio signal to obtain the received power spectrum data and the two or more complex subband data, a receiving filter that filters the two or more complex subband data, and a combining filter that combines the filtered two or more complex subband data to restore the modulation wave data of each of the one or more modulation waves included in the two or more complex subband data included in the one or more modulation waves included in the baseband signal. The receiving filter has the same frequency characteristics as the frequency characteristics of the digital filter bank. The receiving system according to claim 6.

8. A power spectrum detector according to any one of claims 1 to 5, a receiving filter that filters two or more complex sub-band data arranged continuously in the frequency direction among the plurality of complex sub-band data, and the two or more complex sub-band data after filtering And a multiplexing filter that restores the modulation wave data of each of the one or more modulation waves included in the two or more complex sub-band data among the one or more modulation waves included in the baseband signal, and the receiving filter has the same frequency characteristics as the frequency characteristics of the digital filter bank. Receiver.

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