JP2016130692A - Mobile station speed estimation method in mobile communication system using doppler spectrum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a maximum Doppler frequency estimation method using a Doppler spectrum, taking into account a frequency offset or a line-of-sight propagation environment.SOLUTION: The maximum Doppler frequency estimation method includes: a step for receiving a reference signal; a step for creating time fluctuation data of a propagation path from the received reference signal; a step for performing FFT of the time fluctuation data of the propagation path; a step for calculating a Doppler spectrum from an output of the FFT; a step for detecting a first frequency of a component having the highest power among the components of the Doppler spectrum; a step for detecting a second frequency of a component having the second highest power among the components of the Doppler spectrum; a step for obtaining the maximum Doppler frequency by halving an absolute value of a difference between the first frequency and the second frequency; and a step for determining a moving speed of a mobile station from the maximum Doppler frequency.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a mobile station speed estimation method, and more particularly to a mobile station speed estimation method using a Doppler spectrum.

  Currently, wireless communication systems provide various types of wireless communication services assuming various uses of wireless communication. For example, low data rate text communication and voice call communication, high data rate data communication and video streaming transmission, use in a stationary state or walking state, in a high-speed movement state such as in a vehicle, or indoor use to outdoor use For example, in use.

  In addition to these types of usage, wireless communication systems are systems that take into account various conditions, such as locations that provide services, such as urban and rural areas, the population of users who use services, and the amount of data (traffic density). Need to build. Operators that provide wireless communication systems can change usage patterns and traffic density so that users can connect to wireless communication systems without delay and receive satisfactory services at any location and time. The arrangement design of the cell of the size and shape that is taken into consideration is performed.

  However, with further diversification of usage forms and increase in traffic volume, it is difficult to provide sufficient services with a planar cell arrangement. For this reason, a hierarchical cell configuration that provides services that match various usage forms and traffic characteristics by combining a plurality of types of cells is being studied. As an example of such a cell configuration method, there is a hierarchical cell configuration in which a minimal cell having a small cell size is superimposed (overlaid) in a macro cell having a large cell size. The micro cell is a micro cell, a pico cell, a femto cell, or the like. Such a micro cell is installed in a place where the traffic density in the macro cell is high, a place where high data rate communication is assumed, a place where radio wave reception from the macro cell base station is difficult, and the like.

  A handover between base stations of a mobile station is usually performed by measuring a reference signal from the base station and connecting to a base station having the strongest reference signal power. For this reason, even when a high-speed mobile station passes through the minimal cell in the hierarchical cell configuration, the mobile station may be handed over to the minimal cell. When such a mobile station is handed over to a very small cell, the staying time in the cell is very short. Therefore, handover control frequently occurs, and there is a problem that communication of user data is frequently interrupted due to handover signaling. .

  For this reason, it has been studied to apply hierarchical selection control in a hierarchical cell configuration. In the hierarchy selection control, control is performed so that the mobile station is connected to an appropriate cell according to the service usage form. For example, a base station of a macro cell is connected to a mobile station that moves at a high speed, and a micro cell is connected to a mobile station that is stationary or moves at a low speed.

  In order to appropriately execute the hierarchy selection control, it is important to accurately measure the moving speed of the mobile station and connect it to the macro cell or the minimal cell based on the moving speed. A mobile station having a high moving speed is connected only to a macro cell and not connected to a very small cell. On the other hand, a mobile station having a low moving speed is connected to a minimal cell when in a minimal cell, and is connected to a macro cell at a location where the minimal cell is not superimposed. By such hierarchical selection control, it is possible to prevent a mobile station moving at high speed from frequently handing over to a very small cell, and to improve frequency utilization efficiency by reducing communication interruption accompanying handover control signaling.

  One method for estimating the moving speed is to use a Doppler spectrum (Non-Patent Document 1). Here, the Doppler spectrum is a power waveform on the frequency axis (Doppler frequency shift) obtained as a result of Fourier transform of the time variation of the amplitude value of the propagation path response. When the radio propagation environment between the mobile station and the base station can be regarded as an all-around scattering model in which the distribution of arrival directions of radio waves is uniform, the Doppler spectrum shows a peak at the maximum Doppler frequency. For this reason, the maximum Doppler frequency can be measured by detecting the peak of the spectrum.

G-H. Park, D. Hong and C-E. Kang, `` A New Doppler Spread Estimation Using FFT '' IEICE Trans.Commun., Vol.E86-B, No.9, pp.2799-2803, Sept. 2003. Owatari et al., “Examination of reference signal configuration for downlink channel quality measurement in LTE-Advanced,” IEICE Technical Report, RCS2009-279, March 2014.

  However, the radio propagation environment is usually affected by the surrounding buildings that do not necessarily exist uniformly, and cannot be regarded as an all-around scattering model, and it is difficult to detect the maximum Doppler frequency from the Doppler spectrum. become.

  For example, in the case of a line-of-sight propagation environment where there is no main obstacle between the base station and the mobile station, or in a propagation environment where a strong signal arrives from a specific direction due to reflection from a specific building, etc. In addition, a component of a specific reflected wave may occur in the Doppler spectrum, and a peak may occur in a frequency component other than the maximum Doppler frequency.

  Moreover, the frequency accuracy of the reference oscillator used in the apparatus differs between the base station and the mobile station. This is because base stations can use high-precision reference oscillators provided by rubidium, GPS, etc., while mobile stations consider TCXO (Temperature Compensated) with lower frequency accuracy than base stations in consideration of costs. By using a reference oscillator such as Crystal Oscillator. For this reason, since reference oscillators having different frequency accuracy are used between the base station and the mobile station, a carrier frequency offset between the base station and the mobile station (hereinafter simply referred to as a frequency offset) occurs. Such a frequency offset affects the Doppler spectrum and shifts the Doppler spectrum on the frequency axis.

  The present invention provides a moving speed estimation method for estimating a moving speed by calculating a highly accurate maximum Doppler frequency in consideration of a frequency offset and a line-of-sight propagation environment in estimating a moving speed using a Doppler spectrum. With the goal.

  Furthermore, an object of the present invention is to provide an apparatus that calculates a maximum Doppler frequency with high accuracy and estimates a moving speed in consideration of a frequency offset and a line-of-sight propagation environment.

  The present invention is a method for estimating a moving speed of a mobile station, the step of receiving a reference signal, the step of creating time fluctuation data of a propagation path from the received reference signal, and the time fluctuation of the propagation path Multiplying data by FFT, calculating a Doppler spectrum from the output of the FFT, detecting a first frequency of a component having the highest power among the components of the Doppler spectrum, Detecting a second frequency of a component having the next highest power among the components; setting a half of an absolute value of a difference between the first frequency and the second frequency as a maximum Doppler frequency; and Determining the moving speed of the mobile station from the maximum Doppler frequency.

  The present invention is also a method for estimating a moving speed of a mobile station, the step of receiving a reference signal, the step of creating time variation data of a propagation path from the received reference signal, A step of multiplying time-varying data by FFT, a step of calculating a Doppler spectrum from the output of the FFT, a threshold value for the Doppler spectrum is set, and among the components of the Doppler spectrum, an effective value that is not less than the threshold Selecting a component; detecting a first frequency of the highest frequency component of the effective components; detecting a second frequency of the lowest frequency component of the effective components; The absolute value of the first frequency is compared with the absolute value of the second frequency, and the larger one is set as the maximum Doppler frequency. When, and a step of determining a moving speed of the mobile station from the maximum Doppler frequency.

  Further, the present invention is a method for estimating a moving speed of a mobile station, the step of receiving a reference signal, the step of creating time variation data of a propagation path from the received reference signal, A step of multiplying time-varying data by FFT, a step of calculating a Doppler spectrum from the output of the FFT, a threshold value for the Doppler spectrum is set, and among the components of the Doppler spectrum, an effective value that is not less than the threshold Selecting a component; detecting a first frequency of the highest frequency component of the effective components; detecting a second frequency of the lowest frequency component of the effective components; A half of the absolute value of the difference between the first frequency and the second frequency as a maximum Doppler frequency, and the maximum A determining the moving speed of the mobile station from Ppura frequency, the.

  Furthermore, the present invention provides a signal receiving unit that receives a reference signal, a received signal power measuring unit that measures received power of the received reference signal and creates time variation data of the propagation path, and time variation of the propagation path Using an FFT for Fourier transforming data, a signal selection unit for calculating a Doppler spectrum from the output of the FFT, and detecting a first frequency and a second frequency, the first frequency and the second frequency A maximum Doppler frequency calculating unit that calculates a maximum Doppler frequency; and a mobile station speed estimating unit that determines a moving speed of the mobile station from the maximum Doppler frequency.

  With the moving speed estimation method and apparatus according to the present invention, it is possible to estimate the moving speed by calculating a highly accurate maximum Doppler frequency in a frequency offset or line-of-sight propagation environment.

It is a figure which shows the flowchart of the estimation method of the maximum Doppler frequency. It is a figure which shows the example of a Doppler spectrum. It is a figure explaining the detection method of the maximum Doppler frequency. It is a figure explaining the influence of a frequency offset. It is a figure which shows the flowchart of the estimation method of the maximum Doppler frequency in consideration of the frequency offset. It is a figure explaining the influence of a direct wave. It is a figure explaining application of the threshold value to a Doppler spectrum. It is a figure which shows the flowchart of the estimation method of the maximum Doppler frequency which considered the direct wave. It is a figure which shows the flowchart of the estimation method of the maximum Doppler frequency in consideration of the direct wave and the frequency offset. It is a figure which shows the example of the apparatus of this invention.

  A mobile station speed estimation method using a Doppler spectrum will be described below with reference to the drawings. However, it should be understood that the invention is not limited to the drawings or the embodiments described below.

  FIG. 1 is a flowchart illustrating a method for estimating a maximum Doppler frequency using a Doppler spectrum. In S10, a reference signal is received from a base station or mobile station that is wirelessly connected. Although the reference signal is used here, it is also known as a pilot signal or a beacon depending on the system, and is a known signal used for propagation path estimation. In addition, a data signal can be used in a state where propagation path estimation is performed. In S11, the received reference signal is converted into a baseband signal, demodulated, and then received power is measured to create time variation data of the propagation path of the received signal. The time variation data of the propagation path is stored in the buffer for every fixed section.

  Since the received signal varies in proportion to the moving speed of the mobile station, a Doppler spectrum can be obtained by Fourier transforming the propagation path variation of the received signal. In S12, fast time Fourier transform (FFT) is applied to the time variation data of the propagation path stored for each fixed section. Here, the fixed interval corresponds to the number of points in the FFT. In S13, a Doppler spectrum is calculated from the output of the FFT.

  FIG. 2 shows an example of a Doppler spectrum. This example represents an ideal case where the radio propagation environment can be regarded as an all around scattering model. In the figure, the horizontal axis represents frequency, and the vertical axis represents relative power. However, since FIG. 2 shows the processing result after conversion to the baseband, it should be noted that the frequency 0 Hz on the horizontal axis actually corresponds to the carrier frequency. In the subsequent Doppler spectrum diagrams, the definition of the frequency on the horizontal axis is the same as in FIG. In this example, the maximum Doppler frequency is 100 Hz, and high power components occur at frequencies of 100 Hz and -100 Hz in the Doppler spectrum. In such an ideal wireless propagation environment, the maximum Doppler frequency can be estimated by detecting the frequency of the component with high power from the Doppler spectrum calculated using the propagation path fluctuation of the received signal.

In S14 of FIG. 1, a component having the maximum power in a region where the frequency of the Doppler spectrum is positive is found, and the frequency f (P _{max +} ) is detected. As a search method for the maximum power component, for example, the power P (f = 0) at the frequency 0 Hz is compared with the power P (f = Δf) at the next frequency Δf Hz, and the high power component is selected. Further, the power P (f = 2 × Δf) at the next frequency 2 × Δf Hz is compared, and a higher power component is selected. In this way, the power of each component in the positive frequency region is compared in order, the component with the highest power is finally selected, and the frequency is defined as f (P _{max +} ).

In S15, the frequency f (P _max− ) at which the maximum power is obtained in the region where the frequency of the Doppler spectrum is negative is detected by the same method as in S14.

In S16, the maximum Doppler frequency is calculated using the two detected frequencies. Here, of the frequency f (P _{max +} ) detected on the positive side of the frequency and the frequency f (P _max− ) detected on the negative side, the larger absolute value is set as the maximum Doppler frequency f _D. That is, f _D = max (| f (P _{max +} ) |, | f (P _max− ) |).

  When a radio wave having strong received power comes from a specific direction at the time of signal reception, a strong power component may be generated between the positive and negative maximum Doppler frequencies, that is, both peaks of the Doppler spectrum. For this reason, the case where the frequency which shows maximum electric power does not correspond with the maximum Doppler frequency can be considered. By selecting the larger absolute value of the positive and negative maximum power frequencies detected in S14 and S15, it is possible to determine a more accurate maximum Doppler frequency.

When the maximum Doppler frequency f _D is obtained, the moving speed ν of the mobile station can be calculated by f _D × λ. Here, λ is the wavelength of the carrier frequency.

  FIG. 3 is a diagram simply illustrating a method for calculating the maximum Doppler frequency from the Doppler spectrum. On the negative side of the frequency, f (1) is the frequency at which the maximum power is obtained, and on the positive side, the frequency at which the maximum power is obtained is f (2). Under an ideal fading environment, a U-shaped spectrum is shown between f (1) and f (2), and f (1) and f (2) show the same absolute frequency value. This absolute frequency value is the maximum Doppler frequency. Here, the ideal fading environment is an environment in which the radio propagation environment can be regarded as an all around scattering model.

  However, in an actual wireless propagation environment, the arrival direction distribution around the mobile station is not necessarily uniform, and the received power is not uniform in all directions. In addition, due to the influence of noise, the Doppler spectrum is not a smooth U-shape. Furthermore, since the FFT performs Fourier transformation with a finite number of points, both ends of the original time variation data become discontinuous, resulting in distortion in the spectrum obtained by the FFT. The occurrence of this distortion means that a component that does not originally exist appears in the Doppler spectrum obtained by the FFT, which causes an error in determining the maximum Doppler frequency. For example, there are the following methods as countermeasures against such error factors. Apply a window function such as Hanning window before applying FFT to the time-varying data of the propagation path. By applying the window function, spectrum distortion can be suppressed, and a steeper spectrum can be obtained. In addition, by averaging the spectrum signal after FFT within a certain interval, the influence of noise and the like can be suppressed and a smoother spectrum can be obtained. Here, the fixed interval is a time interval in which the shadowing fluctuation is sufficiently small. Hereinafter, in the description of the embodiments of the present invention, it is not described that these methods are applied, but of course, they can also be applied.

  Considering the influence of frequency offset and line-of-sight propagation that make it difficult to calculate the maximum Doppler frequency, a method for calculating the maximum Doppler frequency with high accuracy in those environments will be described.

  First, the influence of frequency offset and countermeasures will be described. In a radio communication system, generally, the frequency accuracy of a reference oscillator inside the apparatus differs between a base station and a mobile station. Usually, a more elaborate reference oscillator is used on the base station side, and a less accurate reference oscillator is used on the mobile station side. Such a difference in the frequency accuracy of the reference oscillator between the transmitting and receiving stations causes a frequency offset between the base station and the mobile station, which affects the Doppler frequency estimation accuracy.

FIG. 4 is a diagram showing an example of the influence of the frequency offset in the Doppler spectrum. The frequency offset spectrum is shifted by the frequency f _offset of offset. As a result, the maximum Doppler frequency is also f _offset shifted, so that the peak of the spectrum occurs in the f _offset + f _D and f _offset -f _D. In the state where the spectrum is shifted in this way, as shown by S14 to S16 in FIG. 1, the method of selecting the absolute value of the frequency indicating the maximum power cannot obtain the correct maximum Doppler frequency.

  In one embodiment of the present invention, the spectrum width is calculated using the frequencies of the high power components generated at both ends of the Doppler spectrum, and the maximum Doppler frequency is calculated from the spectrum width.

FIG. 5 is a flowchart illustrating a method for calculating the maximum Doppler frequency in an environment where a frequency offset exists. In FIG. 5, the processing (S10 to S13) until the Doppler spectrum is calculated is the same as the method shown in FIG. In S24, the frequency f (P _max1 ) of the component having the first highest power is detected. This frequency f (P _max1 ) is one of f _offset + f _D or f _offset −f _D shown in FIG. 4 in an ideal propagation environment. Subsequently, in S25, the frequency f (P _max2 ) of the component having the second highest power is detected. This frequency f (P _max2 ) is similarly the other of f _offset + f _D or f _offset −f _D. In S26, the maximum Doppler frequency is calculated. Here, the spectrum width is calculated from f (P _max1 ) and f (P _max2 ), and half of the spectrum width is set as the maximum Doppler frequency. That is, let | f (P _max1 ) −f (P _max2 ) | / 2 be the maximum Doppler frequency.

  As described above, by calculating the maximum Doppler frequency from the width of the Doppler spectrum, even if the center of the spectrum does not correspond to the carrier frequency on the transmitting side in an environment where a frequency offset exists, the maximum value with high accuracy is obtained. Allows calculation of Doppler frequency.

  Next, the effects of line-of-sight propagation and countermeasures will be described. In the case of a typical non-line-of-sight propagation environment, it can be modeled by an all-around scattering model in which the arrival direction distribution of radio waves is uniform, and the Doppler spectrum becomes a U-shaped spectrum with the highest power at the maximum Doppler frequency. However, in a line-of-sight propagation environment, a direct wave comes from a signal transmission source. Such a direct wave usually has a higher signal intensity than the scattered wave path, and has a great influence on the spectrum shape. Further, even in environments other than line-of-sight propagation, radio waves with strong signal intensity may arrive from a specific direction due to reflection from a specific building, etc., affecting the spectrum shape.

FIG. 6 shows an example of the influence of the direct wave on the Doppler spectrum. As shown in the figure, in addition to the components of 100 Hz and -100 Hz indicating the maximum Doppler frequency (f _D = 100 Hz), a component with strong power appears. In particular, a component with the maximum power is generated near 0 Hz. The frequency at which such a direct wave component appears is related to the direction of arrival of the direct wave. When a high-power direct wave component occurs in the Doppler spectrum, it is difficult to calculate the maximum Doppler frequency from the frequency indicating the maximum power.

  In another embodiment of the present invention, a threshold is set for the Doppler spectrum, and the maximum Doppler frequency is calculated from the maximum frequency component and the minimum frequency component of the active components that are equal to or greater than the threshold.

FIG. 7 is a diagram showing an example of threshold setting in the Doppler spectrum. Here, the noise power N ₀ [dBm] is calculated, and a value obtained by adding ΔN [dB] calculated from the noise variance is used as a threshold value. As shown in FIG. 7, by using N ₀ + ΔN [dBm] as a threshold, a noise component outside the Doppler spectrum can be excluded. And the effective component which becomes more than a threshold value becomes a component with some high electric power containing a direct wave component. Among these active components, the component having the maximum frequency (ie, the 100 Hz component indicated by “A” in FIG. 7) and the component having the minimum frequency (ie, indicated by “B” in FIG. 7) By selecting (100 Hz component), the influence of the direct wave component can be excluded. There are various methods for estimating the noise power from the actual received signal. For example, there is a method for estimating based on the received signal of the pilot signal or reference signal periodically inserted for channel estimation ( Non-patent document 2).

FIG. 8 is a flowchart showing a method of calculating the maximum Doppler frequency in the line-of-sight propagation environment. The processing (S10 to S13) until the Doppler spectrum is calculated is the same as the method shown in FIG. In S34, a threshold value of the spectrum is set, and an active component that is equal to or higher than the threshold value is detected. In S35, the effective component E _{f_max} having the maximum frequency is selected from the effective components, and the frequency f (E _{f_max} ) is detected. In S36, the effective component E _{f_min} having the minimum frequency is selected from the effective components, and the frequency f (E _{f_min} ) is detected.

In S37, the maximum Doppler frequency is calculated using the two detected frequencies. Here, of the frequency f (E _{f_max} ) and the frequency f (E _{f_min} ), the larger absolute value is set as the maximum Doppler frequency f _D. That is, f _D = max (| f (E _{f_max} ) |, | f (E _{f_min} ) |).

  In this way, by setting a threshold value and extracting an effective component that is equal to or higher than the threshold value, it is possible to exclude only the spectrum due to the noise component and select only the spectrum due to the received signal. Furthermore, by detecting the maximum frequency and the minimum frequency from the active components, it is possible to exclude the spectrum due to the direct wave other than the spectrum due to the scattered wave, and the maximum Doppler frequency with high accuracy can be obtained even in the line-of-sight propagation environment. Enable to calculate.

In the above embodiment, the threshold value is set to a value obtained by adding ΔN to the noise power N ₀ , but is not limited to this. For example, the threshold value can be made variable according to the radio propagation status such as the measured SNR.

  As still another embodiment of the present invention, it is assumed that there is a line-of-sight propagation environment and a frequency offset exists. As described in the above two embodiments, a strong component due to a direct wave is generated in the line-of-sight propagation environment. Then, the Doppler spectrum shifts due to the frequency offset.

FIG. 9 is a flowchart showing a method of calculating the maximum Doppler frequency in a line-of-sight propagation environment where a frequency offset exists. The processing (S10 to S13) until the Doppler spectrum is calculated is the same as the method shown in FIG. In S44, a threshold value of the spectrum is set, and an active component exceeding the threshold value is detected in the spectrum. In S45, the effective component E _{f_max} having the maximum frequency is selected from the effective components, and the frequency f (E _{f_max} ) is detected. In S46, the effective component E _{f_min} having the minimum frequency is selected from the effective components, and the frequency f (E _{f_min} ) is detected.

In S47, the maximum Doppler frequency is calculated using the two detected frequencies. Here, the spectrum width is calculated from f (E _{f_max} ) and f (E _{f_min} ), and half of the spectrum width is set as the maximum Doppler frequency. That is, let | f (E _{f_max} ) −f (E _{f_min} ) | / 2 be the maximum Doppler frequency.

  By calculating the maximum Doppler frequency from the width of the Doppler spectrum, it is possible to calculate the maximum Doppler frequency even when the center of the spectrum does not correspond to the carrier frequency on the transmission side in a frequency offset environment. In addition, by setting an appropriate threshold, it is possible to reduce false detection due to noise components, and to detect scattered wave components with lower received power compared to direct wave components in a line-of-sight propagation environment. Maximum Doppler frequency can be estimated.

  FIG. 10 is a block diagram for briefly explaining the apparatus configuration of the present invention. Such a configuration can be installed on either the base station side or the mobile station side, and enables measurement of the maximum Doppler frequency in both stations.

  In FIG. 10, 50 is a signal receiving unit, 51 is a received signal power measuring unit, 52 is an FFT, 53 is a signal selecting unit, 54 is a maximum Doppler frequency calculating unit, and 55 is a mobile station speed estimating unit. The signal receiving unit 50 receives a signal from a transmitting station that performs wireless communication, and extracts a reference signal from the received signal. The method of inserting the reference signal is defined by the system. The received signal power measurement unit 51 converts the received reference signal into a baseband signal, demodulates it, measures the received power, and generates time variation data of the propagation path of the received signal. The generated time variation data of the propagation path is stored in the buffer. The received signal power measurement unit 51 can also be implemented as part of propagation path estimation. The FFT 53 multiplies the time variation data of the propagation path by FFT to calculate a Doppler spectrum. The signal selection unit 53 selects a component to be used for calculating the maximum Doppler frequency from the Doppler spectrum. In the example of FIG. 5, the signal selection unit 53 selects the first highest power component and the second highest power component. 8 and 9, the signal selection unit 53 sets a threshold value, and selects a maximum frequency component and a minimum frequency component in the effective components. The maximum Doppler frequency calculation unit 54 calculates the maximum Doppler frequency from the frequency of the component selected by the signal selection unit 53. 5 and 9, the maximum Doppler frequency calculation unit 54 calculates the width of the spectrum, and ½ thereof is set as the maximum Doppler frequency. In the example of FIG. 8, the larger absolute value is the maximum Doppler frequency. The mobile station speed estimation unit 55 estimates the mobile station speed from the calculated maximum Doppler frequency.

50 Signal receiver
51 Received signal power measurement section
52 FFT
53 Signal selector
54 Maximum Doppler frequency calculator
55 Mobile station speed estimator

Claims (6)

A method for estimating a moving speed of a mobile station,
Receiving a reference signal; and
Creating propagation time variation data from the received reference signal;
Multiplying the time variation data of the propagation path by FFT;
Calculating a Doppler spectrum from the output of the FFT;
Detecting a first frequency of a component having the highest power among the components of the Doppler spectrum;
Detecting a second frequency of a component having the next highest power among the components of the Doppler spectrum;
Setting half the absolute value of the difference between the first frequency and the second frequency as a maximum Doppler frequency;
Determining a moving speed of the mobile station from the maximum Doppler frequency;
A method for estimating a moving speed. A method for estimating a moving speed of a mobile station,
Receiving a reference signal; and
Creating propagation time variation data from the received reference signal;
Multiplying the time variation data of the propagation path by FFT;
Calculating a Doppler spectrum from the output of the FFT;
Setting a threshold for the Doppler spectrum, and selecting an effective component that is equal to or greater than the threshold among the components of the Doppler spectrum;
Detecting the first frequency of the highest frequency component of the active components;
Detecting a second frequency of the lowest frequency component of the active components;
Comparing the absolute value of the first frequency with the absolute value of the second frequency, and setting the larger one as the maximum Doppler frequency;
Determining a moving speed of the mobile station from the maximum Doppler frequency;
A method for estimating a moving speed.   The method according to claim 2, wherein the threshold is set based on noise power. A method for estimating a moving speed of a mobile station,
Receiving a reference signal; and
Creating propagation time variation data from the received reference signal;
Multiplying the time variation data of the propagation path by FFT;
Calculating a Doppler spectrum from the output of the FFT;
Setting a threshold for the Doppler spectrum, and selecting an effective component that is equal to or greater than the threshold among the components of the Doppler spectrum;
Detecting the first frequency of the highest frequency component of the active components;
Detecting a second frequency of the lowest frequency component of the active components;
Setting half the absolute value of the difference between the first frequency and the second frequency as a maximum Doppler frequency;
Determining a moving speed of the mobile station from the maximum Doppler frequency;
A method for estimating a moving speed.   The method according to claim 4, wherein the threshold is set based on noise power. A signal receiver for receiving a reference signal;
A received signal power measuring unit that measures the received power of the received reference signal and creates time variation data of a propagation path;
FFT for Fourier transforming the time variation data of the propagation path;
A signal selection unit for calculating a Doppler spectrum from the output of the FFT and detecting a first frequency and a second frequency;
A maximum Doppler frequency calculation unit for calculating a maximum Doppler frequency using the first frequency and the second frequency;
A mobile station speed estimator for determining a mobile station's moving speed from the maximum Doppler frequency;
An apparatus for estimating a moving speed.

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