JP2010258935A - Apparatus and method for detection of moving speed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a moving speed from a received signal, in a digital broadcast receiver. <P>SOLUTION: With respect to an estimate of transmission line characteristics exerted upon a pilot carrier obtained from a received signal, on the basis of results of discrete Fourier transform, that a transformer 1 performs on a plurality of transmission line characteristic estimates obtained within the same frequency in a time direction, a detector 3 detects a first maximum Doppler frequency and on the basis of results of discrete Fourier inverse transform that a transformer 2 performs on a plurality of transmission line characteristic estimates obtained within the same time in a frequency direction, a detector 4 detects a second maximum Doppler frequency. If the detector 4 determines a line-of-sight radio wave environment in which a direct wave is present, a decision unit 5 determines the second maximum Doppler frequency as a maximum Doppler frequency estimate and if the detector 4 determines a non-line-of-sight radio wave environment, the decision unit 5 determines an average value of the first and second maximum Doppler frequencies as a maximum Doppler frequency estimate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to speed detection of a mobile body (for example, a train such as an automobile or a bullet train) in which a receiving apparatus that receives an OFDM signal is mounted or used.

  In terrestrial digital broadcasting, a radio signal output from a transmitter is reflected, diffracted, or scattered by an obstacle such as a building, so that a received signal (OFDM signal) is distorted. Therefore, a receiver that receives the received signal estimates transmission path characteristics from the received signal, and corrects distortion of the received signal using this estimation result. In general, as a method for estimating transmission path characteristics, a method using a known signal inserted on the transmitter side is known.

  In the Japanese terrestrial digital broadcasting system, as shown in FIG. 12, SP (Scattered Pilot) and CP (Continual Pilot) are inserted at predetermined intervals as pilot carriers in many carriers (carrier waves) for transmitting broadcast data. Adopted signal structure. The receiver estimates the channel characteristics based on the pilot carrier, and corrects the distortion of the received signal using the estimated channel characteristics. Here, the estimated value of the transmission path characteristic indicates the attenuation amount of the amplitude and the rotation amount of the phase of each carrier.

  Patent Document 1 describes a method of estimating transmission path characteristics using SP in terrestrial digital broadcasting. The prior art described in Patent Document 1 estimates the transmission path characteristics acting on the SP, and then interpolates the estimated values of the transmission path characteristics in each of the symbol direction (time direction) and the carrier direction (frequency direction). The estimated values of the channel characteristics for all carriers are obtained. The prior art of Patent Document 1 controls the coefficient of the filter used when performing interpolation in the symbol direction according to the moving speed of the moving body on which the receiver is mounted.

  Below, the control method of the interpolation filter of the symbol direction according to the moving speed described in patent document 1 is described simply. When the receiver is moving with the moving body, the transmission path characteristics change with time. At this time, the frequency characteristic (Fourier transform result) of the estimated value of the transmission path characteristic acting on the pilot carriers for a plurality of symbols in the same carrier has a spread in the frequency direction. Here, the maximum value of the frequency spread in the frequency characteristic is called the maximum Doppler frequency Fd, and the maximum Doppler frequency Fd becomes larger as the moving speed of the receiver is faster. The prior art of Patent Document 1 performs interpolation in the symbol direction by performing band limitation of a frequency band from −Fd to Fd for pilot carriers for a plurality of symbols in the same carrier obtained from a received signal. By controlling the coefficient of the filter, noise components existing in other bands are suppressed.

  As described above, it is necessary to estimate the maximum Doppler frequency in order to control the filter coefficient for performing interpolation in the symbol direction. When this estimated value is larger than the true maximum Doppler frequency Fd, noise components existing outside the frequency band from −Fd to Fd (for example, a portion surrounded by a dotted line in FIG. 13A) are suppressed. Can not do it. Conversely, when the estimated value of the maximum Doppler frequency is smaller than the true maximum Doppler frequency Fd, a component having a higher frequency among the frequency components of the estimated value of the transmission path characteristics (as indicated by a dotted line in FIG. 13B). Since the enclosed portion is suppressed, an error occurs in the estimated channel characteristic value after interpolation. That is, in order to interpolate the estimated value of the channel characteristic acting on the SP in the symbol direction, an accurate estimated value of the maximum Doppler frequency is required.

  As a prior art of moving speed detection (maximum Doppler frequency detection) in terrestrial digital broadcasting, there is Patent Document 2. In the prior art of Patent Document 2, a pilot carrier is extracted from an OFDM received signal, and the maximum Doppler frequency is detected based on the amount of change in the phase of the pilot carrier between adjacent symbols.

Japanese Patent Laying-Open No. 2006-203613 (FIG. 6) JP 2008-271302 A (FIG. 7)

  When the receiver is moving in a line-of-sight radio wave environment where the direct wave that the radio wave output from the transmitter reaches directly exists, the pilot carrier is affected by the direct wave whose phase is constant regardless of time. As a result, there is a problem that the maximum Doppler frequency estimated by the prior art of Patent Document 2 is much smaller than the true maximum Doppler frequency Fd.

  On the other hand, even in an unforeseen radio wave environment where no direct wave exists, the prior art of Patent Document 2 that detects the maximum Doppler frequency Fd using the phase fluctuation amount of the pilot carrier in the time direction is included in the pilot carrier. There is a problem that it is easily affected by noise components.

  The present invention has been made in view of such a technical situation, and an object of the present invention is to mount a receiver from a received signal of an OFDM signal in both a radio wave environment within a line of sight and a radio wave environment outside the line of sight. This makes it possible to accurately detect the moving speed of the moving body.

  The subject of the present invention is a moving speed detecting device for determining a moving speed of a receiving apparatus that receives a frequency-multiplexed OFDM signal by allocating known pilot carriers to a plurality of predetermined carriers among carriers used for transmission of transmission data. A discrete time-domain discrete Fourier transform of an estimated value of channel characteristics for a plurality of symbols existing in the same carrier with respect to an estimated value of channel characteristics acting on the pilot carrier obtained from the OFDM signal A Fourier transform unit and an inverse discrete Fourier transform of an estimated value of channel characteristics for a plurality of carriers existing in the same symbol with respect to an estimated value of channel characteristics acting on the pilot carrier obtained from the OFDM signal Frequency direction inverse discrete Fourier transform unit outputting estimated delay profile, and time direction discrete Fourier transform unit The first maximum Doppler frequency is detected based on the signal output from the first maximum Doppler frequency, and the first maximum Doppler frequency detection unit that outputs a signal that gives the first maximum Doppler frequency is output from the frequency-direction inverse discrete Fourier transform unit. A second maximum Doppler frequency detecting unit that detects a second maximum Doppler frequency based on the estimated delay profile and outputs a signal that gives the second maximum Doppler frequency; the first maximum Doppler frequency; and the second maximum Doppler frequency. A maximum Doppler frequency determining unit that estimates a maximum Doppler frequency based on the maximum Doppler frequency, and a moving speed calculating unit that calculates a moving speed of the receiving device from the maximum Doppler frequency estimated by the maximum Doppler frequency determining unit. And

  According to the subject matter of the present invention, the maximum Doppler frequency can be detected with high accuracy in both the case of the radio wave environment within the line of sight and the case of the radio wave environment outside the line of sight.

  In other words, in the case of a line-of-sight radio environment, the effect of direct waves in the line-of-sight radio environment is estimated by estimating the maximum Doppler frequency based on the estimated delay profile output from the frequency-direction inverse discrete Fourier transform unit. The maximum Doppler frequency can be detected with high accuracy.

  Further, in the case of an unrecognized radio wave environment, by averaging the first maximum Doppler frequency output from the time direction discrete Fourier transform unit and the second maximum Doppler frequency output from the frequency direction inverse discrete Fourier transform unit. The noise component contained in the pilot carrier can be suppressed and the maximum Doppler frequency can be detected with high accuracy.

  Hereinafter, various embodiments of the present invention will be described in detail together with effects and advantages based on the attached drawings.

1 is a block diagram illustrating a configuration of a moving speed detection device according to a first embodiment. FIG. 3 is a diagram illustrating a state of time-wise discrete Fourier transform and frequency-direction inverse discrete Fourier transform in the first exemplary embodiment. FIG. 3 is a diagram showing a state of edge detection in the first embodiment. 4 is a block diagram showing a configuration of a first maximum Doppler frequency detection unit in the first embodiment. FIG. 6 is a diagram showing the frequency characteristics of a pilot carrier in a radio wave environment within the line of sight in the first embodiment. FIG. FIG. 6 is a diagram illustrating a variation amount of an estimated delay profile in the first embodiment. FIG. 4 is a block diagram showing a configuration of a second maximum Doppler frequency detection unit in the first embodiment. FIG. 6 is a block diagram showing a configuration of a modification of the second maximum Doppler frequency detection unit in the first embodiment. FIG. 10 is a block diagram showing a configuration of a second maximum Doppler frequency detection unit in the second embodiment. FIG. 10 is a diagram related to discrete Fourier transform in the second embodiment. FIG. 10 is a block diagram showing a configuration of a modification of the second maximum Doppler frequency detection unit in the second embodiment. It is a figure which shows the structure of the OFDM signal in this invention. It is a figure which shows the relationship between the frequency characteristic of the transmission-line estimated value which acts on a pilot carrier, and the frequency characteristic of a symbol direction interpolation filter.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a moving speed detection apparatus for detecting the maximum Doppler frequency Fd and calculating the moving speed of the receiving apparatus according to this embodiment. The moving speed detection apparatus in FIG. 1 is an apparatus provided in an OFDM signal receiving apparatus, and may be configured as hardware, or may be realized as software by using a microcomputer or the like. Also good. FIG. 1 is also used in a second embodiment to be described later.

  In FIG. 1, on the other hand, the time direction discrete Fourier transform unit 1 includes pilot carriers for a plurality of symbols existing in the same carrier among the estimated values of transmission path characteristics acting on the pilot carrier obtained from the received signal. A discrete Fourier transform is performed on the estimated value of the transmission path characteristic acting on The first maximum Doppler frequency detector 3 obtains the first maximum Doppler frequency based on the signal output from the time direction discrete Fourier transform unit 1. On the other hand, the frequency-direction inverse discrete Fourier transform unit 2 has a transmission path acting on pilot carriers for a plurality of carriers existing in the same symbol, among the estimated values of transmission path characteristics acting on the pilot carrier obtained from the received signal. An estimated delay profile is obtained by performing inverse discrete Fourier transform on the estimated value of the characteristic. The second maximum Doppler frequency detection unit 4 obtains the second maximum Doppler frequency based on the signal output from the frequency direction inverse discrete Fourier transform unit 2, and the radio wave propagation environment is in the out-of-sight or in-line described later. Determine if the radio wave environment. Then, the maximum Doppler frequency determination unit 5 estimates the maximum Doppler frequency based on the first maximum Doppler frequency and the second maximum Doppler frequency based on the determination result as to whether the radio wave environment is out of sight or within sight. Further, the maximum Doppler frequency and the moving speed of the moving body or the receiver are in a proportional relationship, and the moving speed calculation unit 6 uses a maximum Doppler frequency estimated by the maximum Doppler frequency determination unit 5 to use a predetermined arithmetic expression ( The speed is uniquely calculated and determined from (known).

  In the present embodiment, an OFDM signal including pilot signals (known signals) such as SP and CP is received, and a signal obtained by estimating transmission path characteristics acting on a pilot carrier from this received signal is shown in FIG. It is assumed that it is input to the moving speed detection device. The method of estimating the transmission line characteristics acting on the pilot carrier is a known method described in Patent Document 1.

  Here, FIG. 2 is a diagram schematically showing a state of discrete Fourier transform in the time direction and inverse discrete Fourier transform in the frequency direction in the present embodiment. Hereinafter, the discrete Fourier transform in the time direction and the inverse discrete Fourier transform in the frequency direction with respect to the estimated value of the channel characteristic acting on the pilot carrier will be described with reference to FIG.

  The vertical axis in FIG. 2 indicates the symbol direction (time direction), the horizontal axis indicates the carrier direction (frequency direction), and each black circle in FIG. 2 indicates an estimated value of the channel characteristics acting on the pilot carrier. is there. The time direction discrete Fourier transform unit 1 performs discrete Fourier transform on the estimated values of the transmission path characteristics acting on the pilot carriers for a plurality of symbols existing in the same carrier indicated by A1, A2, A3... In FIG. . On the other hand, the frequency direction inverse discrete Fourier transform unit 2 reverses the estimated value of the channel characteristics acting on the pilot carriers for a plurality of carriers existing in the same symbol indicated by B1, B2, B3... In FIG. Discrete Fourier transform.

  In the above example, the time direction discrete Fourier transform unit 1 calculates the discrete Fourier transform for the estimated channel characteristics obtained continuously in the same carrier. A discrete Fourier transform may be calculated for the estimated value of the transmission path characteristics thinned out at a predetermined period. The time direction discrete Fourier transform unit 1 performs time direction discrete Fourier transform on one carrier, but may perform time direction discrete Fourier transform on a plurality of carriers.

  The present invention estimates the maximum Doppler frequency using the result of the discrete Fourier transform in the time direction and the result of the inverse discrete Fourier transform in the frequency direction, thereby calculating the moving speed of the receiving apparatus.

  First, a method for estimating the maximum Doppler frequency from the result of discrete Fourier transform in the time direction will be described. As shown in FIG. 2, the frequency characteristic obtained by the discrete Fourier transform in the time direction has a frequency spread in a range from -Fd to Fd. In the case of an ideal non-line-of-sight radio wave environment where there is no noise or interference, sharp edges exist at the frequencies of -Fd and Fd, as shown by the dotted lines in FIG. However, as indicated by the solid line in FIG. 3A, the edges at the frequencies of −Fd and Fd are dull due to the influence of noise or the like.

  The first maximum Doppler frequency detector 3 in FIG. 1 detects an edge from frequency characteristics obtained by discrete Fourier transform in the time direction, and outputs the detected edge as a first maximum Doppler frequency. FIG. 4 is a block diagram showing a configuration of the first maximum Doppler frequency detection unit 3. In FIG. 4, a differentiating unit 31 is an edge detecting unit that performs differentiation (difference) processing on the signal output from the time-direction discrete Fourier transform unit 1 of FIG. Subsequently, the peak detection unit 32 is a first maximum Doppler frequency calculation unit that detects a peak from the differentiation result output from the differentiation unit 31.

  First, the differentiating unit 31 calculates and outputs a difference between adjacent samples with respect to the signal output from the time direction discrete Fourier transform unit 1. The result is as shown in FIG. 3B, and a peak is output at a position where an edge exists. Next, the peak detection unit 32 detects the position where the peak exists from the differentiation result by comparing the threshold value determined in advance with the differentiation result. Here, as shown in FIG. 3B, peaks are detected in the negative and positive frequency regions. In the present embodiment, the peak detection unit 32 outputs, as the first maximum Doppler frequency, the larger peak position among the two peak positions. For example, in FIG. 3B, when Fd_A> Fd_B, the peak detector 32 outputs Fd_A as the first maximum Doppler frequency.

  The peak detector 32 may calculate an average value of absolute values of peak positions (edge detection positions) and detect the calculation result as the first maximum Doppler frequency.

  The above description regarding the estimation of the first maximum Doppler frequency assumes an unforeseen radio wave environment. However, in the case of a line-of-sight radio wave environment, the frequency characteristic of the estimated value of the transmission path characteristic acting on the pilot carrier is as shown in FIG. 5, and the elements in the vicinity of the DC component become large, and −Fd and Fd The edge existing in the frequency of is dull. This is the influence of a direct wave having a constant amplitude and phase independent of time. As can be seen from FIG. 5, since it becomes difficult to detect an edge in the frequency characteristic, the estimation accuracy of the first maximum Doppler frequency is deteriorated.

  As described above, the first maximum Doppler frequency obtained by the first maximum Doppler frequency detection unit 3 in FIG. 1 can be used in a radio wave environment outside the line of sight, but is not accurate in the radio wave environment within the line of sight. Not available. Therefore, as shown in FIG. 1, the moving speed detection apparatus according to the present invention includes a frequency direction inverse discrete Fourier transform unit 2 and a second maximum Doppler frequency detection unit 4 in order to cope with the radio wave environment within the line of sight. I have.

  Next, a method for estimating the maximum Doppler frequency from the frequency direction inverse discrete Fourier transform result will be described.

  The frequency direction inverse discrete Fourier transform result is a delay profile estimation result. For example, in the case of a two-wave model transmission line (a transmission line in which there is a delayed wave that arrives with a delay of time T with respect to the main wave), the estimated delay profile is as shown in FIG. Here, since each value of the estimated delay profile is a complex value, FIG. 6 shows the instantaneous power of each sample of the delay profile. In FIG. 6, there is a peak corresponding to the main wave at time 0 and a peak corresponding to the delayed wave at time T. The amplitude of the estimated delay profile at the position where this peak exists (time 0 and time T) is the amount of attenuation of the reception level of the main wave and delay wave, and the phase is the rotation of the phase of the main wave and delay wave. Amount.

  The second maximum Doppler frequency detector 4 in FIG. 1 estimates the second maximum Doppler frequency from the estimated delay profile. Here, FIG. 7 is a block diagram showing a configuration of the second maximum Doppler frequency detector 4. In FIG. 7, the instantaneous power calculation unit 41 calculates the instantaneous power of the estimated delay profile for each sample. The first threshold value unit 42 detects a peak by comparing the instantaneous power with a predetermined first threshold value. The delay unit 43 delays the estimated delay profile by one symbol interval. The fluctuation amount calculator 44 calculates the fluctuation amount of the estimated delay profile value at the position where the peak is detected. When a plurality of peaks are detected, the maximum value selection unit 45 selects and outputs the maximum variation amount among the plurality of variation amounts. The maximum Doppler frequency calculation unit 46 calculates the second maximum Doppler frequency from the maximum value of the fluctuation amount. The second threshold value unit 47 compares the plurality of fluctuation amounts with a predetermined second threshold value. The line-of-sight determination unit 48 determines whether the radio wave environment is out of line of sight or within the line of sight.

  In the second maximum Doppler frequency detection unit 4, first, the instantaneous power calculation unit 41 calculates the instantaneous power of the estimated delay profile for each sample, and the first threshold value unit 42 is determined in advance as the calculated instantaneous power. The peak corresponding to the incoming wave is detected by comparing with the first threshold. Then, the fluctuation amount calculation unit 44 calculates the fluctuation amount of the estimated delay profile at the position where the peak is detected between adjacent symbols. For example, the estimated delay profile W1 at time 0 in the (i-1) th symbol shown in FIG. 6A and the estimated delay profile W2 at time 0 in the i-th symbol shown in FIG. 6B. Is expressed by a vector as shown in FIG. 6C, the fluctuation amount calculation unit 44 calculates the phase difference between the vector W1 and the vector W2 in the estimated delay profile at the position where the peak is detected. Change amount. This fluctuation amount becomes a large value as the moving speed of the receiver increases.

  In the above example, the fluctuation amount calculation unit 44 calculates the fluctuation amount of the estimated delay profile between adjacent symbols, but the estimated delay profile is calculated between symbols thinned out in a predetermined cycle. The amount of variation may be calculated.

  When the receiving apparatus is moving in a radio environment other than the line of sight, the value of the estimated delay profile corresponding to all incoming waves varies for each symbol. On the other hand, in the case of a line-of-sight radio environment where a direct wave exists, the value of the estimated delay profile corresponding to the incoming wave other than the direct wave changes for each symbol, but the estimated delay profile corresponding to the direct wave The value is constant. Therefore, the maximum value selection unit 45 outputs the largest value among the fluctuation amounts of the estimated delay profile corresponding to each incoming wave. By doing so, in the radio wave environment within the line of sight, the fluctuation amount of the estimated delay profile according to the direct wave is not selected, but the fluctuation amount of the estimated delay profile according to the other incoming waves is selected.

  As described above, the fluctuation amount of the estimated delay profile increases as the moving speed of the receiving apparatus increases. That is, the maximum Doppler frequency and the fluctuation amount of the estimated delay profile are in a proportional relationship. Therefore, the second maximum Doppler frequency calculation unit 46 in FIG. 7 calculates the second maximum Doppler frequency from the amount of fluctuation of the estimated delay profile using a predetermined expression, using this proportional relationship.

  Further, the second threshold value unit 47 compares the variation amount of the estimated delay profile corresponding to each incoming wave with a predetermined second threshold value, and the line-of-sight determination unit 48 determines that 1) the variation amount below the second threshold value is If there is no single wave, it is determined that the radio wave environment is out of line with no direct wave. On the other hand, 2) When there is even one fluctuation amount that does not exceed the second threshold, the line-of-sight determination unit 48 determines that the radio wave environment is within line-of-sight where direct waves exist. The determination result of the line-of-sight determination unit 48 is used in the maximum Doppler frequency determination unit 5 shown in FIG.

  The operation of the maximum Doppler frequency determination unit 5 in FIG. 1 is performed when the second maximum Doppler frequency detection unit 4 determines that the radio wave environment is out of line of sight and when the radio wave environment is within line of sight. Different.

  That is, when it is determined that the radio wave environment is within the line-of-sight, the estimation accuracy of the first maximum Doppler frequency output from the first maximum Doppler frequency detection unit 3 is poor as described above. Outputs the second maximum Doppler frequency as an estimation result of the maximum Doppler frequency. On the other hand, when it is determined that the radio wave environment is out of line of sight, the maximum Doppler frequency determination unit 5 outputs an average value of the first maximum Doppler frequency and the second maximum Doppler frequency as an estimated value of the maximum Doppler frequency.

  Here, FIG. 8 is a block diagram showing a circuit configuration corresponding to a modification of the second maximum Doppler frequency detection unit 4 of FIG. The configuration of FIG. 8 differs from the configuration of FIG. 7 in that an average value calculation unit 45A is provided instead of the maximum value selection unit 45 of FIG. There are no changes to other components. The average value calculating unit 45A determines each estimated delay in which the value of the variation amount is determined to be larger than the second threshold value in the second threshold value unit 47 among the variation amounts of the estimated delay profile corresponding to each incoming wave. The average value of the profile fluctuation amount is calculated, and based on the average value, the second maximum Doppler frequency calculation unit 46 calculates the second maximum Doppler frequency from a predetermined formula. Thus, by using the average value of the fluctuation amount of the estimated delay profile, the pass band of the signal is narrowed, and the second maximum Doppler frequency can be calculated from a signal that does not further contain noise, and the pass band is ideal. It will be closer to the typical passband.

  As described above, in the estimated delay profile obtained by performing the inverse discrete Fourier transform in the frequency direction, the largest variation amount or the second threshold value among the variation amounts of the estimated delay profile value corresponding to each incoming wave. By estimating the maximum Doppler frequency using the average value of the fluctuation amount of each estimated delay profile that is determined to be large, the influence of direct waves in the line-of-sight radio wave environment can be eliminated. In comparison, the estimation accuracy of the maximum Doppler frequency in the radio wave environment within the line of sight can be remarkably improved.

  Further, even in an unsighted radio wave environment, the average of the first maximum Doppler frequency estimated from the time direction discrete Fourier transform result and the second maximum Doppler frequency estimated based on the frequency direction inverse discrete Fourier transform result Since the value is output as the estimated value of the maximum Doppler frequency, the noise component contained in the pilot carrier can be suppressed, and as a result, the estimation accuracy of the maximum Doppler frequency can be significantly improved compared to the conventional technology. Can do.

(Embodiment 2)
In the present embodiment, the second maximum Doppler frequency detector 4 in FIG. 1 detects the second maximum Doppler frequency based on the result of discrete Fourier transform of the peak value of the estimated delay profile. However, the effect obtained by applying the present embodiment is the same as the effect already described obtained in the first embodiment.

  FIG. 9 is a block diagram showing an internal configuration of the second maximum Doppler frequency detection unit 4 according to the present embodiment. In FIG. 9, the instantaneous power calculation unit 51 calculates the instantaneous power of the estimated delay profile for each sample, and the first threshold value unit 52 compares the instantaneous power with a predetermined first threshold value to obtain a peak. Is detected. Also, the discrete Fourier transform unit 53 performs discrete Fourier transform on the estimated delay profile values for a plurality of symbols at the position where the peak is detected. Further, the edge detection unit 54 detects the edge of the signal output from the discrete Fourier transform unit 53. The maximum value selection unit 55 selects and outputs the maximum value among the plurality of edge detection positions. The second threshold value unit 56 compares a plurality of edge detection positions with a predetermined second threshold value, and the line-of-sight determination unit 57 determines that the radio wave environment of the transmission path from the transmitter to the receiver is out of line of sight. It is determined whether the radio wave environment or the radio wave environment within the line of sight.

  Note that the instantaneous power calculation unit 51 and the first threshold value unit 52 in FIG. 9 have the same operation principle as the corresponding components 41 and 42 in FIG. 7 of the first embodiment, respectively. Are omitted in the following.

  The operation of the discrete Fourier transform unit 53 in FIG. 9 will be described with reference to FIG. As described in the first embodiment, when the receiving apparatus is moving, the estimated delay profile that is the result of frequency-wise inverse discrete Fourier transform corresponding to the incoming wave included in the estimated delay profile changes with time. . For example, as shown in FIG. 10A, when the amplitude of the estimated delay profile at time 0 is arranged in the symbol direction between a plurality of symbols, the result is as shown in FIG. The discrete Fourier transform unit 53 in FIG. 9 performs a discrete Fourier transform on the peak value detected at time 0 between the plurality of symbols. The frequency characteristic obtained by the discrete Fourier transform has a frequency spread, and the maximum value is the maximum Doppler frequency Fd. Similarly, the discrete Fourier transform unit 53 performs discrete Fourier transform between the values of the estimated delay profile detected at another time (for example, time T in FIG. 10A) between a plurality of symbols.

  Note that the discrete Fourier transform unit 53 in FIG. 9 performs discrete Fourier transform on the peak value of consecutive symbols, but may perform discrete Fourier transform on the peak value of the symbol thinned out in a predetermined cycle. .

  Next, the edge detection unit 54 in FIG. 9 performs edge detection on each of a plurality of discrete Fourier transform results corresponding to each incoming wave, and outputs an edge detection position. There are as many edge detection positions as the number of incoming waves. Since this edge detection method is the same as that in the first embodiment, description thereof is omitted.

  In the case of an out-of-sight radio wave environment, the result of the discrete Fourier transform in the symbol direction of the estimated delay profile values for all incoming waves has edges near -Fd and Fd. However, in the case of a line-of-sight radio wave environment in which direct waves are present, the discrete Fourier transform in the symbol direction of the estimated delay profile value for incoming waves other than direct waves has edges near -Fd and Fd. However, since the value of the estimated delay profile for the direct wave is constant without depending on time, the discrete Fourier transform result in the symbol direction has a large value in the DC component, and the edges near −Fd and Fd Is dull.

  Therefore, the maximum value selection unit 55 in FIG. 9 selects the maximum value from the plurality of edge detection positions and outputs it as the second maximum Doppler frequency. By so doing, it is possible to estimate the second maximum Doppler frequency without being affected by direct waves even in a radio wave environment within the line of sight.

  9 compares the plurality of edge detection positions with a predetermined second threshold value, and the line-of-sight determination unit 57 does not have any edge detection positions below the second threshold value. Is determined to be an unforeseen radio wave environment in which no direct wave exists. On the other hand, when there is even one edge detection position below the second threshold, the line-of-sight determination unit 57 determines that the radio wave environment is within line-of-sight where direct waves exist. The determination result of the line-of-sight determination unit 57 is used in the maximum Doppler frequency determination unit 5 of FIG.

  Here, FIG. 11 is a block diagram showing a modification of FIG. In FIG. 11, instead of the maximum value selection unit 55 of FIG. 9, an average value calculation unit 55A is provided. There are no changes to the other components. The average value calculation unit 55A calculates the average value of the edge detection results determined by the second threshold unit 56 to be larger than the second threshold value among the edge detection results of the edge detection unit 54, as the second maximum Doppler frequency. Output as. With this configuration, the second maximum Doppler frequency can be calculated from a signal that does not contain noise as a result of the passband approaching an ideal passband.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  1 time direction discrete Fourier transform unit, 2 frequency direction inverse discrete Fourier transform unit, 1st maximum Doppler frequency detection unit, 4 second maximum Doppler frequency detection unit, 5 maximum Doppler frequency determination unit, 6 moving speed calculation unit, 31 differential Unit, 32 peak detection unit, 41 instantaneous power calculation unit, 42 first threshold value unit, 43 delay unit, 44 fluctuation amount calculation unit, 45 maximum value selection unit, 45A average value calculation unit, 46 second maximum Doppler frequency calculation unit, 47 second threshold value unit, 48 line-of-sight determination unit, 51 instantaneous power calculation unit, 52 first threshold value unit, 53 discrete Fourier transform unit, 54 edge detection unit, 55 maximum value selection unit, 55A average value calculation unit, 56 second Threshold part, 57 Line-of-sight determination part.

Claims (8)

A moving speed detection device that determines a moving speed of a receiving apparatus that receives a frequency-multiplexed OFDM signal by allocating known pilot carriers to a plurality of predetermined carriers among carriers used for transmission of transmission data,
A time-direction discrete Fourier transform unit for performing discrete Fourier transform on the estimated values of the channel characteristics for a plurality of symbols existing in the same carrier with respect to the estimated values of the channel characteristics acting on the pilot carrier obtained from the OFDM signal; ,
The estimated delay profile is output by performing inverse discrete Fourier transform on the estimated values of the channel characteristics acting on the pilot carrier obtained from the OFDM signal for the multiple carriers existing in the same symbol. A frequency direction inverse discrete Fourier transform unit,
A first maximum Doppler frequency detector for detecting a first maximum Doppler frequency based on a signal output from the time direction discrete Fourier transform unit and outputting a signal for giving the first maximum Doppler frequency;
A second maximum Doppler frequency detector that detects a second maximum Doppler frequency based on the estimated delay profile output from the frequency direction inverse discrete Fourier transform unit, and outputs a signal that gives the second maximum Doppler frequency;
A maximum Doppler frequency determining unit that estimates a maximum Doppler frequency based on the first maximum Doppler frequency and the second maximum Doppler frequency;
A moving speed calculation unit that calculates a moving speed of the receiving device from the maximum Doppler frequency estimated by the maximum Doppler frequency determination unit;
Characterized by comprising,
Moving speed detection device. The moving speed detection device according to claim 1,
The time-direction discrete Fourier transform unit is characterized by performing discrete Fourier transform on the estimated values of the channel characteristics for a plurality of symbols continuously present in the same carrier,
Moving speed detection device. The moving speed detection device according to claim 1,
The time direction discrete Fourier transform unit is characterized by performing a discrete Fourier transform on the estimated value of the transmission path characteristics thinned out in a predetermined cycle within the same carrier,
Moving speed detection device. The moving speed detection device according to any one of claims 1 to 3,
The first maximum Doppler frequency detector is
An edge detection unit for detecting an edge of a signal output from the time direction discrete Fourier transform unit;
A first maximum Doppler frequency calculation unit that detects and outputs the first maximum Doppler frequency based on a detection position of the edge;
Moving speed detection device. The moving speed detection device according to any one of claims 1 to 4,
The second maximum Doppler frequency detector is
An instantaneous power calculator for calculating the instantaneous power of the estimated delay profile;
A first threshold unit for detecting a peak in the instantaneous power corresponding to each incoming wave by comparing the instantaneous power with a predetermined first threshold;
A fluctuation amount calculation unit for calculating a fluctuation amount of the estimated delay profile at a position where a peak of instantaneous power corresponding to each incoming wave is detected between adjacent symbols or symbols thinned at a predetermined period. When,
A second threshold value unit for comparing the variation amount of the estimated delay profile with a predetermined second threshold value;
The maximum value of the fluctuation amount of the estimated delay profile corresponding to each incoming wave, or the estimated delay profile corresponding to each incoming wave determined to be larger than the second threshold value by the second threshold unit. A second maximum Doppler frequency calculation unit for calculating the second maximum Doppler frequency based on an average value of fluctuation amount;
When there is no fluctuation amount of the estimated delay profile below the second threshold value, it is determined that the radio wave environment is an unforeseen radio wave environment in which no direct wave exists, while the fluctuation of the estimated delay profile does not exceed the second threshold value. When there is even one quantity, it is determined that the radio wave environment is within line-of-sight where the direct wave exists, and a line-of-sight determination unit that outputs the determination result to the maximum Doppler frequency determination unit is provided. Characterized by the
Moving speed detection device. The moving speed detection device according to any one of claims 1 to 4,
The second maximum Doppler frequency detector is
An instantaneous power calculator for calculating the instantaneous power of the estimated delay profile;
A first threshold unit for detecting a peak in the instantaneous power corresponding to each incoming wave by comparing the instantaneous power with a predetermined first threshold;
A discrete Fourier transform unit that discrete Fourier transforms the values of the estimated delay profiles at the plurality of peak detection positions detected by the first threshold unit corresponding to each incoming wave between a plurality of symbols;
Edge detection is performed for each of a plurality of signals corresponding to each incoming wave output from the discrete Fourier transform unit, and a plurality of edge detection positions corresponding to the number of incoming waves are output;
A second threshold value unit for performing a comparison process between the plurality of edge detection positions and a predetermined second threshold value;
A second maximum that outputs a maximum value among the plurality of edge detection positions or an average value of edge detection positions determined to be larger than the second threshold by the second threshold value unit as the second maximum Doppler frequency. A Doppler frequency calculator,
If there is no edge detection position below the second threshold value, it is determined that the radio wave environment is not a line-of-sight where there is no direct wave, while at least one edge detection position is below the second threshold value. In this case, it is determined that the direct wave is in a line-of-sight radio wave environment, and includes a line-of-sight determination unit that outputs the determination result to the maximum Doppler frequency determination unit.
Moving speed detection device. The moving speed detection device according to claim 5 or 6,
The maximum Doppler frequency determination unit outputs the second maximum Doppler frequency as an estimation result of the maximum Doppler frequency when the radio wave environment is within the line-of-sight, whereas when the radio wave environment is outside the line-of-sight The average value of the first maximum Doppler frequency and the second maximum Doppler frequency is output as an estimation result of the maximum Doppler frequency.
Moving speed detection device. A method of determining a moving speed of a receiving apparatus that receives an OFDM signal frequency-multiplexed by allocating known pilot carriers to a plurality of predetermined carriers among carriers used for transmission of transmission data,
A time-direction discrete Fourier transform step of performing discrete Fourier transform on the estimated values of the channel characteristics for a plurality of symbols existing in the same carrier with respect to the estimated values of the channel characteristics acting on the pilot carrier obtained from the OFDM signal; ,
The estimated delay profile is obtained by performing inverse discrete Fourier transform on the estimated values of the channel characteristics for a plurality of carriers existing in the same symbol with respect to the estimated values of the channel characteristics acting on the pilot carrier obtained from the OFDM signal. A frequency direction inverse discrete Fourier transform step;
A first maximum Doppler frequency detection step for detecting a first maximum Doppler frequency based on a signal obtained by the time direction discrete Fourier transform step;
A second maximum Doppler frequency detection step for detecting a second maximum Doppler frequency based on the estimated delay profile obtained from the frequency direction inverse discrete Fourier transform step;
Determining a maximum Doppler frequency based on the first maximum Doppler frequency and the second maximum Doppler frequency; and
A moving speed calculating step of calculating a moving speed of the receiving device from the maximum Doppler frequency estimated by the maximum Doppler frequency determining step;
Characterized by comprising,
Movement speed detection method.

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