JP2007150789A - Ofdm communication measuring system, receiver, measuring method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM communication measuring system or the like in an environment where a plurality of transmitting stations is mixed. <P>SOLUTION: A receiving unit 201 of a receiver receives signals which a plurality of transmitting devices broadcasting the same program has transmitted with a reference transmitting frequency displaced from one another within the allowable range. An OFDM Fourier transformer 203 separates the received signals into subcarriers, and a discrete Fourier transformer 207 implements the Fourier transform of a transfer function of each subcarrier obtained by a propagation property obtaining unit 205. An extraction unit 208 extracts a frequency component corresponding to the reference transmitting frequency of a desired transmitting device from intensity of the frequency component obtained, while an output unit 209 adopts the frequency component extracted as a transfer function of each subcarrier from the desired transmitting device and obtains a communication property to output the property. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a measurement system, a receiving apparatus, a measurement method, and a program for realizing these using a computer in an environment where a plurality of transmission stations coexist.

Conventionally, various techniques related to OFDM (Orthogonal Frequency Division Multiplex) communication have been proposed. Such a technique is disclosed in the following document.
Japanese Patent No. 3598371 Japanese Patent No. 3605638

  Here, in [Patent Document 1], in the signal processing of OFDM communication, a plurality of signal points of the signal space diagram obtained by demodulation and a plurality of signal points of the signal space diagram plotted by the relative phase difference of the demodulated signal Is used to extract fluctuations in the signal space diagram, classify multiple signal points, determine areas in the signal space diagram where there is a high probability of information error, and the signals contained in those areas Techniques have been proposed for excluding points from statistical processing.

  On the other hand, in [Patent Document 2], the entire band is divided into a plurality of segments, and a plurality of pieces of information having different transmission qualities are distributed to some of the plurality of segments and transmitted simultaneously, thereby providing a digital modulation having a hierarchical structure. The signal is separated for each layer, the characteristics of the transmission line are extracted from the signal of at least one layer, the equalization control information is generated using the extracted characteristic, and the signal of each signal separated into the layer by using this is generated. Techniques for equalization have been proposed.

  Here, when trying to measure frequency, frequency stability, received electric field strength, delay profile, etc. in the service area of terrestrial digital broadcasting, signals arriving from a plurality of transmitting stations may be mixed.

  In general, in OFDM communication of terrestrial digital broadcasting, the allowable range when delay signals are multiplexed is designed so that there is no obstacle to demodulation. Therefore, even in a mixed reception environment, if the combined electric field strength is sufficiently strong, the desired electric field strength is satisfied.

  On the other hand, if you want to measure each frequency, frequency stability, received electric field strength, delay profile, etc. separately for signals from multiple transmitting stations, all transmissions from transmitting stations other than the transmitting station you want to measure are usually performed. It was necessary to stop and transmit to the desired transmitting station for measurement.

  However, since it is difficult to suspend broadcasting for measurement, it is only possible to use the time zone of signal midnight at night, but such measurement is difficult nowadays when 24-hour operation is increasing. It is becoming.

  Also, the delay profile of the transmission signal is measured, the arrival time difference is obtained from the path difference between each of the plurality of transmitting stations and the receiving station, and the profile of each transmitting station is identified by collating with the observation result of the delay profile, There is also a method for calculating the received electric field strength by calculating the DU ratio (Desired to Undesired signal Ratio) based on the strength of the profile, but this method is difficult to measure when the arrival time difference is small or complex multiple propagation paths. It is.

  In addition, there is a method to measure the frequency by measuring the frequency of the center carrier of OFDM communication subcarriers, or measuring the frequency of the outermost carrier, but these are used when there are multiple transmitting stations. I can not cope.

  Therefore, in OFDM communication, the frequency, frequency stability, electric field strength, and delay profile of each transmitting station are appropriately measured in an environment where multiple transmitting stations transmit the same signal and the receiving station receives the same signal simultaneously. Technology is highly desired.

  The present invention has been made in order to solve the above-described problems, and uses an OFDM communication measurement system, reception apparatus, measurement method, and computer in an environment in which a plurality of transmission stations coexist. The purpose is to provide a program to be realized.

  In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.

  A measurement system according to a first aspect of the present invention is a measurement system for measuring communication characteristics of orthogonal frequency division multiplex communication, and includes a plurality of transmitters and a plurality of transmitters that perform orthogonal frequency division multiplex on the same transmission signal. A receiving device is provided for receiving the transmitted signal.

  Here, the plurality of transmission apparatuses employ transmission frequencies that are different from each other and that fall within the allowable range of the reception frequency that is adopted by the reception apparatus.

  On the other hand, the receiving device includes a receiving unit, a dividing unit, a converting unit, an extracting unit, and an output unit, and is configured as follows.

  First, the reception unit receives signals transmitted from a plurality of transmission devices within an allowable range of the reception frequency.

  On the other hand, the dividing unit divides the received signal into complex sequences of transfer functions in time order for each subcarrier.

  Further, the transform unit performs a discrete Fourier transform on each of the divided subcarriers for a complex sequence in time order included in the subcarrier.

  Then, the extraction unit extracts a peak frequency component in the vicinity of the transmission frequency of the desired transmission device from among the plurality of transmission devices, from the frequency components obtained by performing discrete Fourier transform on each of the divided subcarriers.

  On the other hand, the output unit outputs a communication characteristic between the desired transmission device and the reception device from the peak frequency component extracted for at least one of the divided subcarriers.

  As described above, the plurality of transmission apparatuses transmit the same source at baseband frequencies different from each other within an allowable range, and the existing transmission equipment can be used as it is. On the other hand, the receiving device functions as a measurement device for generating and outputting the measurement result of the measurement system. To obtain various communication characteristics, when signals are arranged in the time direction and subcarrier frequency direction, there are a method that uses all the transmitted symbols as a known symbol by completely estimating all transmitted symbols, and pilot symbols. There is a method of using SP (Scattered Pilot) arranged so as to be distributed.

  In the technique using SP, for example, i, m, and n are integers, and for the mi + n-th subcarrier, a pilot is employed for the i-th symbol in time order.

  In the measurement system of the present invention, the output unit can be configured to output a peak frequency extracted for at least one of the divided subcarriers as the communication characteristic.

  In the measurement system of the present invention, the output unit obtains the frequency stability by performing an Allan variance analysis on the time-order complex sequence of the peak frequency component extracted for at least one of the divided subcarriers. The obtained frequency stability can be output as the communication characteristic.

  In the measurement system of the present invention, the output unit obtains the electric field strength by averaging the received intensities of the peak frequency components extracted for each of the divided subcarriers, and obtains the obtained electric field strength for the communication. It can be configured to output as a characteristic.

  Further, in the measurement system of the present invention, the output unit obtains a delay profile by performing a discrete Fourier transform on a sequence in which the frequency components of the peaks extracted for each of the divided subcarriers are arranged in the order of subcarriers. The delay profile can be configured to be output as the communication characteristic.

  A receiving apparatus according to another aspect of the present invention is configured as a receiving apparatus in the above measurement system.

  A measurement method according to another aspect of the present invention is a measurement method for measuring communication characteristics of orthogonal frequency division multiplex communication, wherein the same transmission signal is transmitted from a plurality of transmission devices and a plurality of transmission devices that perform orthogonal frequency division multiplexing. A plurality of transmission devices that use transmission frequencies that are different from each other and that fall within the allowable range of the reception frequency that is adopted by the reception device. A process, a division process, a conversion process, an extraction process, and an output process are executed.

  Here, in the reception step, signals transmitted from a plurality of transmission devices are received within an allowable range of the reception frequency.

  On the other hand, in the dividing step, the received signal is divided into complex sequences of transfer functions in time order for each subcarrier.

  Further, in the converting step, for each of the divided subcarriers, a time-order complex sequence included in the subcarrier is subjected to discrete Fourier transform.

  Then, in the extraction step, a peak frequency component in the vicinity of the transmission frequency of the desired transmission device is extracted from the plurality of transmission devices from the frequency components obtained by discrete Fourier transform for each of the divided subcarriers.

  On the other hand, in the output step, communication characteristics between the desired transmission device and the reception device are output from the peak frequency component extracted for at least one of the divided subcarriers.

  In the measurement method of the present invention, in the output step, the peak frequency extracted for at least one of the divided subcarriers may be output as the communication characteristic.

  In the measurement method of the present invention, in the output step, frequency stability is obtained by performing an Allan variance analysis on a time-order complex sequence of peak frequency components extracted for at least one of the divided subcarriers. The obtained frequency stability can be output as the communication characteristic.

  In the measurement method of the present invention, in the output step, the reception intensity of the peak frequency component extracted for each of the divided subcarriers is averaged to obtain the electric field intensity, and the obtained electric field intensity is calculated as the communication field. It can be configured to output as a characteristic.

  In the measurement method of the present invention, in the output step, a delay profile is obtained by performing discrete Fourier transform on a sequence in which the frequency components of the peaks extracted for each of the divided subcarriers are arranged in the order of subcarriers, and the obtained delay profile is obtained. The delay profile can be configured to be output as the communication characteristic.

  A program according to another aspect of the present invention causes various types of computers, for example, software radios that function as various types of wireless devices corresponding to the software by downloading the software, to function as each unit of the reception device. Constitute.

  In addition, an information recording medium in which the program of the present invention is recorded can be distributed and sold independently from the computer such as the software radio. Further, the program of the present invention can be transmitted, distributed and sold via a computer communication network such as the Internet.

  In particular, when a computer such as the software radio has a programmable electronic circuit such as a DSP (Digital Signal Processor) or FPGA (Field Programmable Gate Array), the program recorded on the information recording medium of the present invention is wirelessly provided. Can be transmitted to the computer, and the DSP or FPGA in the computer can execute this to provide the wireless communication terminal of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the program which implement | achieves these using the measurement system of a OFDM communication in the environment where a some transmitting station coexists, a receiver, a measuring method, and a computer can be provided.

  An embodiment of the present invention will be described below. In addition, embodiment described below is for description and does not limit the scope of the present invention. Accordingly, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.

  FIG. 1 is an explanatory diagram showing a schematic configuration of a measurement system according to an embodiment of the present invention. Hereinafter, a description will be given with reference to FIG.

  As shown in the figure, the measurement system 101 includes one receiving device 131 and a plurality of transmitting devices 151.

  This embodiment assumes an SFN (Single Frequency Network) environment in which the same program is broadcast in the same frequency band in adjacent service areas. One transmission device 151 is assigned to each service area.

  As described above, the plurality of transmitting apparatuses 151 embed pilot symbols in the same arrangement in the same subcarrier (frequency) and symbol (time) in the same source, perform OFDM modulation, and generate baseband complex data. Convert and send. At this time, the reference transmission frequencies are shifted from each other within an allowable range for each transmission device 151.

  In the case of terrestrial digital broadcasting, since the frequency tolerance is ± 1 Hz, the difference in reference transmission frequency for each transmission device 151 is suitably about several hundred mHz to 1 Hz. This tolerance varies from system to system, and may be a value such as ± 2 Hz.

  Depending on the content of the signal transmitted by the transmitter 151, it may not be possible to provide a sufficient frequency difference. In this case, for each symbol of OFDM communication, a phase rotation of a fixed minute angle (this value is different for each transmission device 151) is added to generate a signal whose phase changes in a stepped manner. If the transmission method is employed, the same effect as that obtained when the transmission frequency is different is obtained.

  The receiving device 131 simultaneously receives signals transmitted from the plurality of transmitting devices 151. Since the reference transmission frequency of each transmission device 151 is within the allowable range of the reference reception frequency of the reception device, it is possible to receive any signal.

(Receiver)
FIG. 2 is an explanatory diagram showing a schematic configuration of the receiving apparatus according to the present embodiment. Hereinafter, a description will be given with reference to FIG.

  In the reception device 131, a reception unit 201 including an antenna collectively receives signals within the allowable range of the reference reception frequency. Therefore, signals transmitted by the plurality of transmission devices 151 are also accepted here.

  Next, the baseband conversion unit 202 converts the received signal into baseband complex data, and acquires a complex data sequence in symbol units in synchronization.

  Next, the OFDM Fourier transform unit 203 serializes the acquired complex data series and performs direct Fourier transform on these complex data without correcting the phase, frequency, and amplitude. A time-series complex sequence of received vector values is obtained.

  Demodulation section 204 then estimates a symbol value for each subcarrier, and obtains an ideal vector value of the ideal symbol normalized for each subcarrier.

  Next, the propagation characteristic acquisition unit 205 obtains a transfer function by dividing the received vector value of the complex series by the ideal vector value normalized with respect to each subcarrier.

  Note that the demodulation unit 204 may be omitted, and the propagation characteristic acquisition unit 205 may process only the portion in which the pilot signal (known signal) is embedded. In this case, the transfer function can be obtained by dividing the received vector value of the portion by the vector value of the known signal.

  In this case, in order to synchronize the orthogonal coordinate axes of the symbols, it is possible to apply a technique of arranging known data at a predetermined position with respect to the frequency and time data arrangement. Such known data is called SP (Scattered Pilot symbol).

  FIG. 3 is an explanatory diagram showing how SPs are arranged with respect to a frequency and time data array. Hereinafter, a description will be given with reference to FIG.

  In this figure, the frequency (Frequency, what number subcarrier) is arranged on the horizontal axis, and the time (Time, what number symbol) is arranged on the vertical axis. Each symbol is represented by a circle, a normal data symbol is represented by a white circle, and SP is represented by a black circle.

  In the arrangement shown in the figure, for the first symbol, SPs are arranged on the 1, 13, 25,... Sub-carriers, and for the second symbol, SPs are placed on the 4, 16, 28,. Is arranged, and so on. Here, the n-th SP of the k-th symbol is arranged at a symbol position obtained by 3 (k−1) + 1 + 12 (n−1).

  FIG. 4 is an explanatory diagram showing a state in which a transfer function of a certain subcarrier at a certain time is interpolated from previous and subsequent times. Hereinafter, a description will be given with reference to FIG.

  In the above example, for i = 1, 2, 3,..., SPs are arranged only on the 3 (i−1) + 1-th subcarrier. This figure shows a method for obtaining the transfer function at a certain time (fifth symbol) as a reference for such 3 (i-1) + 1-th subcarrier.

  As shown in this figure, when the fifth symbol is SP (1, 13, 25,... Sub-carriers), the obtained transfer function is used as it is.

  If it is not an SP, interpolation is performed from the values of the SP transfer functions arranged before and after in the time direction (Interpolated).

  For example, the 4, 16, 28,... Subcarriers are interpolated so as to be interpolated from the transfer function of the second symbol and the transfer function of the fifth symbol.

  The seventh, 19, 31,... Subcarriers are interpolated so as to be interpolated from the transfer function of the third symbol and the transfer function of the sixth symbol.

  The 10, 22, 34,... Subcarriers are interpolated so as to be interpolated from the transfer function of the fourth symbol and the transfer function of the seventh symbol.

  However, transfer function interpolation is based on the assumption that the sampling theorem holds. Therefore, it is necessary that the periodic component of the transfer function does not exceed one half of the reciprocal of the four-times symbol interval. In the case of this embodiment, it is assumed that the rate of change of the transfer function does not exceed it.

  In addition, the complex transfer function at each time of each subcarrier can be obtained by various methods. That is, for the processing performed in the propagation characteristic acquisition unit 205 from the reception unit 201, a known technique or a technique having the same function can be applied, and these aspects are also included in the scope of the present invention.

  Now, the accumulation unit 206 sequentially stores and accumulates the obtained transfer functions for each subcarrier at a predetermined time symbol interval. Here, it is assumed that the storage unit 206 stores the value of the transfer function for each subcarrier by L symbols. Here, the value of the complex transfer function corresponding to the kth symbol in the time order of the mth subcarrier in the frequency order is assumed to be g (m, k).

The discrete Fourier transform unit 207 uses the transfer function g (m, k) accumulated in the accumulation unit 206 as time-series data for each of m = 1, 2,.
G (m, n) = (1 / L) Σ _{k = 1} ^L g (m, k) exp (-2π (k-1) nj / L)
The discrete Fourier transform is performed as follows.

  That is, G (m, n) is the intensity of the frequency component in the nth frequency band for the mth subcarrier.

  When the parameter n is changed, several peaks appear in G (m, n). Each peak corresponds to one of the transmission devices 151.

  As described above, the transmission device 151 transmits the same program at a slightly different reference transmission frequency, and the reception device 131 receives the reference program at the reference reception frequency with a certain allowable range. Therefore, a peak existing in the vicinity of n corresponding to the reference transmission frequency (and the difference between the reference reception frequencies) of the transmission device 151 to be measured is the m-th sub-signal of the signal transmitted from the transmission device 151. That is, the component strength of the carrier.

  On the receiving device 131 side, it is assumed that the reference transmission frequencies of the plurality of transmitting devices 151 are known. The reference transmission frequency is not a frequency actually received, but a reference of a frequency used when the transmission device 151 transmits, and when there is no noise or various errors in operation, This is the frequency that is assumed to be used for transmission.

  Therefore, the frequency actually used for transmission / reception generally deviates slightly from this reference transmission frequency due to, for example, the influence of the Doppler effect or the change in the device characteristics of the transmission device 151 due to the influence of temperature change / humidity change. It is.

  Therefore, for each of m = 1, 2,..., The extraction unit 208 calculates the result of the discrete Fourier transform corresponding to the difference between the reference transmission frequency of the desired transmission device 151 and the reference reception frequency of the reception device 131. Check the subscript in the frequency direction. If this value is a, then the peak in the vicinity of a (G (m, a−Δ) to G (m, a + Δ)) corresponding to the difference is the m-th peak of the desired transmitter 151. Extracted as the component strength of the subcarrier. Since G (m, n) is a complex number, “peak” means the maximum value of the absolute value of the complex number.

  Δ is set to a value that does not overlap with an adjacent reference transmission frequency. In the above example, the interval between the reference frequencies is set to several hundred mHz to 1 Hz. Therefore, it is desirable that the interval corresponds to less than half of the minimum value of the interval.

  A transmission radio wave propagates between the desired transmission device 151 and the reception device 131 by spatial propagation. During this time, radio waves radiated from the transmitting antenna and diffused in all directions cause reflection, diffusion, diffraction, and attenuation by all objects in the space. Under such circumstances, signals propagated through various paths arrive at the receiving antenna. As a result, there may be a multiple propagation state (multipath) in which signals of a plurality of paths overlap.

  The influence of multiple propagation appears in the frequency characteristics within the band in the OFDM signal. FIG. 5 is an explanatory diagram showing the influence of an OFDM signal due to multiple propagation. Hereinafter, a description will be given with reference to FIG.

  As shown in this figure, when there is one delayed wave in addition to the direct wave, the power in the band fluctuates due to the difference between the phase and amplitude, and the arrival time difference (delay time).

  The influence of the delayed wave appears as an amplitude frequency characteristic within the band. The situation is that, when the arrival time of the main wave is used as a reference, a period fluctuation of the reciprocal of the delay time of the incoming wave is generated in the frequency band. The amplitude fluctuation range is determined by the DU ratio.

  Therefore, if G (m, n) is also affected by multiple propagation, the peak values of G (m, a-Δ) to G (m, a + Δ) near a corresponding to the difference are multiplexed. It is extracted as the component intensity of the m-th subcarrier of the desired transmission device 151 according to the frequency characteristic of propagation.

For example, when the deviation of the reference frequency between the desired transmitter 151 and receiver 131 corresponds to the index a in the frequency direction as a result of discrete Fourier transform, the peak H (m) for the mth subcarrier is discrete. If it is the q _m- th component among the Fourier transformed components,
H (m) = G (m , q m);
q _m = argmax _{n, a-Δ ≦ n ≦ a + Δ} | G (m, n) |
It can be expressed as H (m) is the frequency characteristic itself that is a transfer function from the desired transmission device 151.

  Finally, the output unit 209 performs processing as described later on the extracted component intensity, obtains communication characteristics such as the frequency, frequency stability, electric field strength, and delay profile of the desired transmission device 151, and outputs it. To do.

  In the above example, G (m, n) and H (m) are obtained for all subcarriers, but only for subcarriers selected at predetermined intervals in consideration of the calculation amount and measurement accuracy. These processes may be executed. The same applies to the following, but in order to facilitate understanding, a case where G (m, n) and H (m) are obtained for all subcarriers will be described as an example.

  Hereinafter, a technique for obtaining communication characteristics performed in the output unit 209 will be described in more detail.

(Acquisition of communication characteristics)
As described above, the extraction unit 208, the peak of the subcarriers extracted to the transmitter 151 to be _{measured, q 1, q 2, q} 3, ... with respect to H (1), H (2 ), In the case of H (3),..., How the output unit 209 processes this data will be described.

(1) Frequency

First, when the reference transmission frequency of the transmission device 151 is to be confirmed and measured by the reception device 131,
q ₁ , q ₂ , q ₃ , ...
Are output as they are, or these are converted into units of frequency as numerical values representing the difference from the reference reception frequency, and the measured value of “transmission frequency for each subcarrier” of the signal transmitted from the transmitter 151 is obtained. Obtainable.

Also,
q ₁ , q ₂ , q ₃ , ...
The weights for each
| H (1) |, | H (2) |, | H (3) |, ...
The measured value of the transmission frequency of the signal transmitted from the transmission device 151 may be obtained by taking the weighted average.

  In addition, when the frequency characteristics are flat, the measured value of the representative value of the transmission frequency from the peak index for any one subcarrier (typically the one corresponding to the center, minimum frequency, or maximum frequency). You may get.

(2) Frequency stability

  Since G (m, n) is a value of a discrete Fourier transform having a window width corresponding to a certain time width τ (L symbol length), it represents an average value of the time width τ.

When measuring the frequency stability, the following processing is performed. For each subcarrier, the extraction unit 208 described above has a certain time t (typically, a discrete value counted in symbol length units and a time that represents a time width τ interval).
H (1), H (2), H (3), ...
Output this,
Hτ (1, t), Hτ (2, t), Hτ (3, t),…
I will write. That is, a complex sequence in the time direction for each time width τ is obtained for each subcarrier.

As described above, the accumulation unit 206 accumulates information for the L symbol length. Therefore, assuming that information for each L symbol length is also accumulated here, the desired transmission apparatus 151 performs transmission for the m-th subcarrier. The complex time series received by the receiving device 131 is
Hτ (m, 1), Hτ (m, 2), ..., Hτ (m, L)
It becomes.

Now, to find the frequency stability for the mth subcarrier, use this complex time series.
Hτ (m, 1), Hτ (m, 2), ..., Hτ (m, L)
An Allan Variance analysis is performed on. Allan dispersion is a widely used technique for determining frequency stability.

  As subcarriers to be subjected to the Allan variance analysis, if the frequency characteristics are flat, those corresponding to the center, the minimum frequency, and the maximum frequency can be considered. On the other hand, under the influence of multiple propagation paths, it may be performed for all subcarriers, or analysis results obtained for a plurality of subcarriers may be appropriately averaged.

(3) Electric field strength

Further, when it is desired to measure the electric field strength, the following processing is performed. That is,
H (1), H (2), H (3), ...
Is a frequency characteristic from the desired transmission device 151 to the reception device 131 obtained from the transfer function g (m, k) actually stored in the storage unit 206. That is, the power of the signal transmitted from the desired transmission device 151 to the reception device 131 can be obtained from the frequency characteristics.

  Therefore, the root mean square of | H (m) | is obtained, and this is output as the electric field strength of the transmitter 151.

  Note that the method of obtaining the electric field strength using only information of some known subcarriers is particularly effective when the reception state is poor and an error occurs in the estimation of the symbol value of the data, but the reception state is good. In order to improve the measurement accuracy in this case, it is desirable to process all subcarriers.

(4) Delay profile

To determine the delay profile, a complex time series of transfer functions from the desired transmitter 151
H (1), H (2), H (3), ..., H (M)
May be subjected to complex discrete Fourier transform. That is,
D (t) = (1 / M) Σ _{m = 1} ^M H (m) exp (-2π (m-1) tj / M)
And

  In a multipath environment, multiple | D (t) | peaks appear. These are associated with each propagation path. D (t) indicates the characteristics of the propagation path of the delay time t, and it can be determined from this information how much the original signal has reached and how much the phase has changed.

  In the following, a description will be given of delay profile conditions that can be analyzed when SPs are arranged only in some subcarriers.

  As shown in FIG. 4, when only SPs interpolated with SP data and used at the same time are used to extract transfer functions, they are simply arranged and subjected to discrete Fourier transform (DFT). In this way, a complex delay profile indicating a delay time and a phase change can be obtained.

  In this case, based on the sampling theorem, the maximum delay time of the delay wave that can be analyzed is less than the inverse of the SP interval.

  In the above example, the SP-only data string is one-third of the total (SP is arranged only in the 3 (k-1) + 1-th subcarrier) and can be analyzed. The maximum delay time is also one third of the reciprocal of the SP interval.

  If there is a delayed wave with a longer delay time than this, it will be folded back as a virtual image component in the delay profile of the analysis result.

For example,
The effective symbol length is 1 ms and 13 segments of mode 3 are used.
The subcarrier spacing is 1 kHz,
The guard interval length is 125 μs, that is, 1/8 of the effective symbol length,
The number of subcarriers is 5617, the bandwidth is 5.617 MHz,
Consider a case where the number of SPs is 1872 and the bandwidth is 5.617 MHz.

  In this case, the maximum delay time that can be analyzed is 1 / (1 kHz) × (1/3) = 333.3 μs.

The resolution of the delay time is 333.3 μs / 1872 = 0.178 μs. This is 0.178 μs × 3.0 × 10 ⁸ m / s = 53.4 m in terms of distance resolution.

  In addition, a transfer function for all subcarriers can be obtained, and a discrete Fourier transform can be performed on the columns in the frequency direction. The subsequent processing is the same as in the above case.

  As described above, according to the present invention, it is possible to provide a measurement system, a reception apparatus, a measurement method, and a program that realizes these using a computer in an environment where a plurality of transmission stations coexist. Can do.

It is explanatory drawing which shows schematic structure of the measurement system which concerns on embodiment of this invention. It is explanatory drawing which shows schematic structure of the receiver which concerns on this embodiment. It is explanatory drawing which shows a mode that SP is arrange | positioned with respect to the data arrangement | sequence of a frequency and time. It is explanatory drawing which shows a mode that the transfer function of a certain subcarrier in a certain time is interpolated from the time before and behind. It is explanatory drawing which shows the influence of the OFDM signal by multiple propagation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Measurement system 131 Reception apparatus 151 Transmission apparatus 201 Reception part 202 Baseband conversion part 203 OFDM Fourier transform part 204 Demodulation part 205 Propagation characteristic acquisition part 206 Accumulation part 207 Discrete Fourier transform part 208 Extraction part 209 Output part

Claims (12)

A measurement system for measuring communication characteristics of orthogonal frequency division multiplex communication, comprising a plurality of transmission devices for orthogonal frequency division multiplexing of the same transmission signal, and a reception device for receiving signals transmitted from the plurality of transmission devices, The plurality of transmission devices employ transmission frequencies that are different from each other and that are included in an allowable range of reception frequencies that the reception device employs,
The receiving device is:
A receiver that receives signals transmitted from the plurality of transmitters within an allowable range of the reception frequency;
A dividing unit that divides the received signal into complex sequences of transfer functions in time order for each subcarrier;
For each of the divided subcarriers, a transform unit that performs a discrete Fourier transform on a complex sequence in time order included in the subcarriers,
An extraction unit that extracts a frequency component of a peak in the vicinity of a transmission frequency of a desired transmission device among the plurality of transmission devices, from the frequency components obtained by performing the discrete Fourier transform on each of the divided subcarriers,
A measurement system comprising: an output unit that outputs a communication characteristic between the desired transmission device and the reception device from the extracted peak frequency component for at least one of the divided subcarriers. . The measurement system according to claim 1,
The output unit outputs the extracted peak frequency for at least one of the divided subcarriers as the communication characteristic. The measurement system according to claim 1,
The output unit obtains a frequency stability by performing an Allan variance analysis on a time-sequence complex sequence of the extracted peak frequency components for at least one of the divided subcarriers, and obtains the frequency stability. A measurement system that outputs the stability as the communication characteristic. The measurement system according to claim 1,
The output unit obtains an electric field strength by averaging the received intensities of the extracted peak frequency components for each of the divided subcarriers, and outputs the obtained electric field strength as the communication characteristic. Characteristic measurement system. The measurement system according to claim 1,
The output unit obtains a delay profile by performing a discrete Fourier transform on a sequence in which the extracted peak frequency components are arranged in subcarrier order for each of the divided subcarriers, and obtains the obtained delay profile for the communication A measurement system characterized by output as a characteristic.   The receiving apparatus in the measuring system of any one of Claim 1 to 5. A measurement method for measuring communication characteristics of orthogonal frequency division multiplex communication, using a plurality of transmission devices that perform orthogonal frequency division multiplexing on the same transmission signal, and a reception device that receives signals transmitted from the plurality of transmission devices, The plurality of transmission devices employ transmission frequencies that are different from each other and that are included in an allowable range of reception frequencies that the reception device employs,
In the receiving device,
A reception step of receiving signals transmitted from the plurality of transmission devices within an allowable range of the reception frequency;
A dividing step of dividing the received signal into complex sequences of transfer functions in time order for each subcarrier;
For each of the divided subcarriers, a transforming step for performing a discrete Fourier transform on a time-order complex sequence included in the subcarriers;
An extraction step of extracting a frequency component of a peak in the vicinity of a transmission frequency of a desired transmission device from among the plurality of transmission devices, from the frequency components obtained by the discrete Fourier transform for each of the divided subcarriers,
A measurement method comprising: outputting a communication characteristic between the desired transmission device and the reception device from the extracted peak frequency component for at least one of the divided subcarriers. . It is the measuring method of Claim 7, Comprising:
In the output step, the extracted peak frequency for at least one of the divided subcarriers is output as the communication characteristic. It is the measuring method of Claim 7, Comprising:
In the output step, an Allan variance analysis is performed on the time-ordered complex sequence of the extracted peak frequency component for at least one of the divided subcarriers to obtain a frequency stability, and the obtained frequency A measurement method characterized by outputting the stability as the communication characteristic. It is the measuring method of Claim 7, Comprising:
In the output step, for each of the divided subcarriers, the reception intensity of the extracted peak frequency component is averaged to obtain an electric field strength, and the obtained electric field strength is output as the communication characteristic. Characteristic measuring method. It is the measuring method of Claim 7, Comprising:
In the output step, a delay profile is obtained by performing a discrete Fourier transform on a sequence in which the frequency components of the extracted peaks are arranged in the order of subcarriers for each of the divided subcarriers, and the obtained delay profile is obtained from the communication A measurement method characterized by outputting as a characteristic.   A program causing a computer to function as each unit of the receiving device according to claim 6.

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