JP2008053892A - Measurement system, measurement method, transmitter, repeater, receiver, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measurement system or the like suitable for measuring communication characteristics under the environment of providing a GF repeater in OFDM communication. <P>SOLUTION: In the measurement system 101, the transmitter 171 performs orthogonal frequency division multiplex demodulation of transmission signals and relays them to each of the plurality of repeaters 151, and each of the plurality of repeaters 151 receives the modulated signals and wirelessly transmits them by transmission frequencies allocated so as to be different from each other. The receiver 131 receives the signals wirelessly transmitted from the repeaters 151, divides them into the complex sequences of the transmission functions of a time order for each subcarrier, performs discrete Fourier transformation, extracts the frequency component of a peak near the transmission frequency of a desired repeater 151 from the frequency components, and acquires and outputs the communication characteristics. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a measurement system, a measurement method, a transmission device, a relay device, a communication system for measuring communication characteristics in an environment in which a GF (Gap Filler) relay device is provided in OFDM (Orthogonal Frequency Division Multiplex) communication. The present invention relates to a receiving apparatus and a program for realizing these by a computer.

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 signal processing of OFDM communication, a plurality of signal points of a signal space diagram obtained by demodulation and a plurality of signal points of a 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 errors, 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.

  Also, in the terrestrial digital broadcasting service, so-called one-segment broadcasting that is assumed to be received by a mobile terminal or a portable terminal has been started. In 1Seg broadcasting, the receiving side always moves, the gain of the receiving antenna is low, the antenna height is low, and even within the service area, it is affected by the electric field drop in buildings shadows, indoors, underground malls, etc. Failure can occur. Therefore, a technique using a GF relay device has been proposed.

  The GF relay device relays broadcast waves in a limited manner on the same principle as SFN (Single Frequency Network) toward an area where reception failure occurs.

  Therefore, in order to properly arrange the GF relay devices and eliminate the reception failure, each GF relay device (one of which corresponds to the original transmitting station and the other corresponds to the relay station). There is a great demand for measuring communication characteristics appropriately.

  The present invention has been made to solve the above-described problems, and is a measurement system, a measurement method, a transmission device, and a relay device that are suitable for measuring communication characteristics in an environment where a GF relay device is provided in OFDM communication. It is an object of the present invention to provide a receiving apparatus and a program for realizing these by a computer.

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

  A communication characteristic measurement system for orthogonal frequency division multiplex communication according to a first aspect of the present invention includes a transmission device, a plurality of relay devices, and a reception device, and is configured as follows.

  That is, the transmission device includes a modulation unit that performs orthogonal frequency division multiplexing modulation on a transmission signal, and a relay unit that relays the modulated signal to each of a plurality of relay devices.

  On the other hand, each of the plurality of relay apparatuses receives the modulated signal relayed from the transmission apparatus, and receives the modulated signal received by radio at a transmission frequency assigned to the relay apparatus. A part.

  Furthermore, the transmission frequencies assigned to each of the plurality of relay apparatuses are different from each other, and all are included within the allowable range of the reception frequency adopted by the reception apparatus.

  Then, the receiving device receives a signal wirelessly transmitted from the relay device within the allowable range of the reception frequency, and divides the received signal into a complex sequence of transfer functions in time order for each subcarrier. A transform unit that performs discrete Fourier transform on a time-sequence complex sequence included in the subcarrier for each of the divided subcarriers, and a desired relay device from a frequency component obtained by performing discrete Fourier transform on each of the divided subcarriers. An extraction unit that extracts a frequency component of a peak in the vicinity of the transmission frequency, and an output unit that acquires and outputs a communication characteristic between the desired relay device and the reception device from the extracted frequency component.

  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 a reception electric field strength that is a sum of reception strengths of peak frequency components extracted for each of the divided subcarriers, and determines the reception electric field strength as the communication characteristic. Can be configured to output as

  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 communication characteristic measurement method for orthogonal frequency division multiplex communication according to another aspect of the present invention uses a transmission device, a plurality of relay devices, and a reception device, and the transmission device includes a modulation unit and a relay unit. Each of the plurality of relay devices includes a reception unit and a transmission unit, and the reception device includes a reception unit, a division unit, a conversion unit, an extraction unit, and an output unit, and is configured as follows.

  That is, in the transmission device, the modulation unit includes a modulation step of performing orthogonal frequency division multiplexing modulation on the transmission signal, and the relay unit includes a relay step of relaying the modulated signal to each of the plurality of relay devices.

  On the other hand, in each of the plurality of relay devices, the reception unit receives the modulated signal relayed from the transmission device, and the transmission unit allocates the received modulated signal to the relay device. A transmission step of wirelessly transmitting at a transmission frequency to be transmitted.

  Furthermore, the transmission frequencies assigned to each of the plurality of relay apparatuses are different from each other, and all are included within the allowable range of the reception frequency adopted by the reception apparatus.

  In the receiving device, the receiving unit receives a signal wirelessly transmitted from the relay device within the allowable range of the reception frequency, and the dividing unit transmits the received signal for each subcarrier in time order. A dividing step and a converting unit for dividing the complex sequence of functions into discrete Fourier transforms of the time-ordered complex sequences included in the subcarrier for each of the divided subcarriers. An extraction step for extracting a peak frequency component in the vicinity of the transmission frequency of the desired relay device from the frequency component obtained by performing discrete Fourier transform on each of the carriers, and receiving the desired relay device and the reception from the frequency component from which the output unit has been extracted. It further includes an output step of acquiring and outputting communication characteristics with the device.

  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, a reception electric field strength that is a sum of reception strengths of the peak frequency components extracted for each of the divided subcarriers is obtained, and the reception electric field strength is calculated as the communication characteristic. Can be configured to output as

  In the measurement method of the present invention, 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 peaks extracted for each of the divided subcarriers are arranged in the subcarrier order, and the obtained delay profile is obtained. The delay profile can be configured to be output as the communication characteristic.

  A transmission device according to another aspect of the present invention is a transmission device in the above measurement system.

  A relay device according to another aspect of the present invention is a relay device in the above measurement system.

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

  A program according to another aspect of the present invention includes various types of computers, for example, software radios that function as various types of wireless devices corresponding to the software by downloading software, each unit of the transmission device, and each unit of the relay device. Alternatively, it is configured to function as each unit of the receiving device.

  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. In addition, 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. The transmission device, the relay device, and the reception device of the present invention can be obtained by transmitting the data to the computer and causing the DSP or FPGA in the computer to execute this.

  According to the present invention, a measurement system, a measurement method, a transmission device, a relay device, a reception device suitable for measuring communication characteristics in an environment in which an GF relay device is provided in OFDM communication, and the realization of these by a computer Programs 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. Therefore, 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.

  In the following, first, a basic technique for measuring communication characteristics will be described, and then a technique using a GF relay device will be described in detail.

(Measurement system, transmitter, relay device)
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, a plurality of relay devices 151, and one transmitting device 171.

  When this embodiment is applied to the situation of one-segment broadcasting, a combination of one transmission device 171 and one relay device 151 functions as a “broadcast transmitter”, and the other relay device 151 functions as a “gap filler relay”. Will do. This is similar to an SFN (Single Frequency Network) environment in which the same program is broadcast in the same frequency band in adjacent service areas. One transmitter 171 is assigned.

  In transmission apparatus 171, modulation section 172 embeds pilot symbols in a predetermined arrangement in each subcarrier (frequency) and each symbol (time) for one source and performs OFDM modulation. Then, relay section 173 relays the OFDM modulated result to relay apparatus 151.

  On the other hand, in each relay device 151, the reception unit 152 receives the relayed OFDM modulated result, and the transmission unit 153 converts it into baseband complex data and transmits it. At this time, for each relay device 151, the reference transmission frequencies are shifted from each other within an allowable range.

  In the case of terrestrial digital broadcasting, since the frequency tolerance is ± 1 Hz, the difference in the reference transmission frequency for each relay device 151 is suitably about several hundred milliHz 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 relay device 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 relay device 151) is added to generate a signal whose phase changes stepwise. 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 relay devices 151. Since the reference transmission frequency of each relay device 151 is within the allowable range of the reference reception frequency of the receiving device, it is possible to receive signals from any of them.

(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 from a plurality of relay apparatuses 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,... Sub-carriers 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 4-fold symbol interval. In the case of the present 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 relay devices 151.

  As described above, the relay apparatus 151 transmits the same program at a slightly different reference transmission frequency, and the reception apparatus 131 receives the reference program at the reference reception frequency with a certain allowable range. Therefore, the peak existing in the vicinity of n corresponding to the reference transmission frequency (and the difference between the reference reception frequencies) of the relay device 151 to be measured is the m-th sub-signal of the signal transmitted from the relay 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 relay devices 151 are known. The reference transmission frequency is not a frequency actually received, but a reference of a frequency used when the relay 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 the reference transmission frequency due to, for example, the Doppler effect or the change in the device characteristics of the relay device 151 due to the influence of temperature change / humidity change. It is.

  Therefore, for each of m = 1, 2,..., The extraction unit 208 obtains the result of the discrete Fourier transform corresponding to the difference between the reference transmission frequency of the desired relay device 151 and the reference reception frequency of the reception device 131. Check the subscript in the frequency direction. If this value is a, a peak in the vicinity of a (G (m, a−Δ) to G (m, a + Δ)) corresponding to the difference is represented by the m-th peak of the desired relay device 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, since the interval between the reference frequencies is several hundred mHz to 1 Hz, it is desirable that the width corresponds to less than one half of the minimum value of this interval.

  A transmission radio wave propagates between the desired relay device 151 and the receiving 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 such that, when the arrival time of the main wave is used as a reference, a periodic fluctuation in 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 relay device 151 and the receiving device 131 corresponds to the index a in the frequency direction as a result of the 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 relay device 151.

  Finally, the output unit 209 performs processing as described later on the extracted component strength, obtains communication characteristics such as frequency, frequency stability, electric field strength, and delay profile of the desired relay 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 peak of subcarriers extracted by the extracting unit 208 for the relay device 151 to be measured is H (1), H (2), q ₁ , q ₂ , q ₃ ,. 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 relay 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 as numerical values representing the difference from the reference reception frequency and converted into frequency units, the measured value of “transmission frequency for each subcarrier” of the signal transmitted from the relay device 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 relay 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, since the storage unit 206 stores information for the L symbol length, if the information for each L symbol length is also stored here, the desired relay device 151 applies to 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 the electric field strength is to be measured, the following processing is performed. That is,
H (1), H (2), H (3), ...
Is a frequency characteristic from the desired relay device 151 to the receiving device 131, which is 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 relay apparatus 151 to the receiving apparatus 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 relay device 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 obtain a delay profile, a complex time series of a transfer function from a desired repeater 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 reciprocal 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, it is possible to obtain transfer functions for all subcarriers and perform a discrete Fourier transform on the columns in the frequency direction. The subsequent processing is the same as in the above case.

(Embodiments using GF repeaters and details of experimental results)
Based on the above basic technology, the embodiment using the GF repeater and the details of the experimental results will be described in more detail below. In addition, in order to make an understanding easy, the symbol of various formulas may utilize the thing different from the said basic technique.

  In the measurement of the spatial profile of a building obstacle or weak electric field area, when multiple propagation paths are formed, the level of the incoming wave from each station (relay device 151) varies depending on the measurement position. For this reason, it is expected that the station of the incoming wave (relay device 151) with which the receiving device 131 is synchronized as the main wave will change depending on the measurement position. Therefore, in a system in which the absolute arrival time cannot be measured, it may not be possible to capture the incoming wave from the target station (relay device 151).

  Therefore, a GF relay station is temporarily set up for measurement, and this is made to function as the relay device 151 so that wireless transmission is performed toward the space to be measured. There can be a technique to measure.

  In this case, separation can be achieved by making the transmission frequency of the pilot (reference) GF relay station (relay device 151) slightly different from the transmission frequency of the relay device 151 to be measured, as in the above embodiment. Even if the pilot signal itself is multiple-reflected in the space, the effect thereof is about the error of analysis and can be minimized.

FIG. 6 is an explanatory diagram showing an outline of a processing flow of measurement executed by the receiving device 131. Hereinafter, a description will be given with reference to FIG. This processing flow is basically the same as the above basic technology. That is,
(1) A transfer function for each symbol is obtained from a received signal at a desired symbol interval and accumulated for a necessary time.
(2) The accumulated transfer function performs frequency analysis (DFT) in the time direction for each subcarrier, and estimates the carrier frequency of each station of the relay device 151 from the power distribution on the frequency axis.
(3) When a data string for all carriers at the estimated frequency is extracted for each station from the DFT result, a station-specific transfer function is obtained.
(4) If the transfer function can be separated for each station, the field strength for each station can be obtained from the sum of the power.
(5) By performing DFT on this, a station-specific complex delay profile is obtained.

  If this method is used, the received signal can be demodulated at the measurement point, so that the characteristics of all the stations that transmit the arriving broadcast wave can be measured, and the measurement effort can be reduced. Hereinafter, details of numerical analysis of communication characteristics will be described in more detail.

In the following, the symbol number is m, the subcarrier number is l, the transmission symbol is d, the reception symbol is y, the number of relay stations is S, the transfer function is h (transfer function h _u from the u-th relay station), and the noise is N, the number of incoming waves is P, the amplitude is r, the symbol length is τ _s , the delay time is τ _i , the carrier frequency is fc, the carrier interval is fo, and the initial phase is β.

Then, the received symbol obtained by demodulating the received signal in the multiple propagation path is as follows.
y (m, l) = d (m, l) Σ _{u = 1} ^S h _u (m, l)
+ Σ _{v = 0, v ≠ m} ^S-1 [d (v, l) Σ _{u = 1} ^S h _u (v, l)]
+ N (m, l)

  The first term is a desired symbol component, the second term is an intersubcarrier interference component, and the third term is noise. In the SFN environment, there are areas where signals from a plurality of transmitting stations are received simultaneously, and the transfer function h overlaps by the number S of transmitting stations.

Then, the transfer function g of the entire propagation can be calculated as follows.
g (m, l) = y (m, l) / d (m, l)
= (Σ _{i = 1} ^P w _i (m) φ _i (m)) Σ _{u = 1} ^S exp (j ・ 2π ・ Δf _Tu・ lτ _s )
+ Σ _{v = 0, v ≠ m} ^S-1 [d (v, l) / d (m, l) Σ _{u = 1} ^S h _u (v, l)]
+ N (m, l) / d (m, l)

Here, w _i is the amplitude component of the i-th incoming wave, and φ _i is the phase component of the i-th incoming wave.

Δf _Tu · lτ _{s in} the first term is a frequency variation and is a frequency component itself to be obtained. The second and third terms can be regarded as terms that do not directly depend on the carrier frequency of the transmitting station, such as transfer function, interference noise, and external noise. Therefore, it can be seen that the carrier wave frequency (difference from the analysis side) of the transmitting station can be analyzed.

(1) Analysis of frequency components Frequency components can be calculated as follows by performing DFT of the transfer function in a time series in the time direction for each subcarrier.
G (m, n) = (1 / L) Σ _{k = 0} ^L-1 g (m, k) exp (-j ・ 2π ・ k ・ n / L)
Here, L is the number of subcarriers. Since the frequency resolution and the analysis accuracy are determined by the symbol interval and the total number of data, the symbol data may be accumulated and analyzed so as to obtain a desired accuracy.

  By seeing the peak of n of G (m, n), it becomes possible to perform separation for each carrier frequency of the relay device 151. If n is fixed and G (m, n) is seen, there is An incoming wave from the station (relay device 151) can be analyzed.

(2) Received electric field strength If it is found that the peak near the transmission frequency of a certain relay device 151 is the n-th peak in G (m, n), the received electric field strength X (n) from the relay device 151 is The calculation is performed by obtaining the total power as follows.
X (n) = (1 / M) Σ _{m = 0} ^M-1 | G (m, n) | ²
Here, M is the number of symbols in the time direction.

  (3) Complex delay profile

When the frequency component for each station is DFTed, a complex delay profile C (n) can be obtained.
C (n) = (1 / M) Σ _{m = 0} ^M-1 G (m, n) exp (-j ・ 2π ・ k ・ n / M)

  With these techniques, various communication characteristics can be measured for an incoming wave from a desired relay device 151 in the measured space.

(Measurement experiment)
Measurement experiments were conducted using a NICT terrestrial digital broadcasting testbed experimental station. FIG. 7 is an explanatory diagram showing a plan view of the experimental site. 8 and 9 are tables showing various measurement conditions.

  The main station of the experiment station (one of the relay devices 151) is on the roof of the YRP building No. 1 shown in the figure, and the height is about 40 m from the ground.

  The pilot GF station (other relay device 151) was placed on the 2nd floor terrace of the experimental building on the north side of the YRP No. 1 building, about 4 m above the ground.

  The YRP No. 2 building, which is the main wave shield, is about 30 m high, similar to the YRP No. 1 building.

  The measurement vehicle (reception device 131) performs measurement by stopping at each measurement point while moving on a road parallel to the ITS research center on the north side of the YRP No. 2 building.

  FIG. 10 is a graph showing the received electric field strength at each measurement point measured by this method. According to this figure, it can be seen that the measured wave and the pilot wave interfere as multiple propagation.

  FIG. 11 is a graph showing the result of analysis performed by operating only the main station without using the pilot GF station. The horizontal axis represents the delay time, and the vertical axis represents the received power. This corresponds to point 4 in FIG. 7 and item A in FIG. That is, the electric field strength is insufficient due to the influence of the device performance, the synchronization is unstable, the spectrum is broadened, and no delayed wave is seen.

  On the other hand, FIG. 12 is a graph showing the results of analysis by this method, where the horizontal axis represents delay time and the vertical axis represents received power. This corresponds to point 4 in FIG. 7 and item E in FIG. As shown in the figure, it can be seen that the signal from the main station and the pilot signal are clearly separated, and the respective communication characteristics can be analyzed.

  FIG. 13 is a graph displaying only the signal of the incoming wave from the main station in this method, and this graph is a part of FIG.

  As shown in the figure, in this method, two peaks are observed and a delayed wave can be captured. This is a result significantly different from that in FIG. 11 according to the conventional method.

  FIG. 14 is an explanatory diagram showing delay profiles of incoming waves from the main station at point 4 in FIG. 7 and item E in FIG. It can be seen that the presence of the delay wave and its delay time coincide with the result of FIG.

  As described above, according to the present invention, a measurement system, a measurement method, a transmission device, a relay device, a reception device, and these suitable for measuring communication characteristics in an environment where a GF relay device is provided in OFDM communication Can be provided by a computer.

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. It is explanatory drawing which shows the outline | summary of the processing flow of the measurement performed with a receiver. It is explanatory drawing which shows the top view of an experiment place. It is a figure which shows the various conditions table | surface of a measurement. It is a figure which shows the various conditions table | surfaces of a measurement. It is a graph which shows the received power in each measurement point measured by this method. It is a graph which shows the result of having operated by only a main station, without using GF station for pilots. It is a graph which shows the result analyzed by this method. It is a graph which displays the signal of the incoming wave from a main station. It is explanatory drawing which shows the delay profile of the incoming wave from a main station.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Measurement system 131 Reception apparatus 151 Relay apparatus 152 Reception part 153 Transmission part 171 Transmission apparatus 172 Modulation part 173 Relay part 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 unit 208 Extraction unit 209 Output unit

Claims (14)

A communication characteristic measurement system for orthogonal frequency division multiplex communication comprising a transmission device, a plurality of relay devices, and a reception device,
(A) The transmission device includes:
A modulation unit for orthogonal frequency division multiplexing modulation of a transmission signal;
A relay unit that relays the modulated signal to each of the plurality of relay devices;
(B) Each of the plurality of relay devices is
A reception unit that receives the modulated signal relayed from the transmission device;
A transmitter that wirelessly transmits the received modulated signal received at a transmission frequency assigned to the relay device;
(C) Transmission frequencies assigned to each of the plurality of relay devices are different from each other, and both are included in an allowable range of reception frequencies adopted by the reception device,
(D) The receiving device includes:
A receiver that receives a signal wirelessly transmitted from the relay device within an allowable range of the reception frequency,
A divider for dividing 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 relay device from the frequency component obtained by performing the discrete Fourier transform on each of the divided subcarriers;
A measurement system comprising: an output unit that acquires and outputs communication characteristics between the desired relay device and the receiving device from the extracted frequency component. 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 reception electric field strength that is a sum of reception strengths of the extracted peak frequency components for each of the divided subcarriers, and outputs the reception electric field strength as the communication characteristics. Measuring 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. A method of measuring communication characteristics of orthogonal frequency division multiplex communication using a transmission device, a plurality of relay devices, and a reception device, wherein the transmission device includes a modulation unit and a relay unit, and the plurality of relay devices Each includes a reception unit and a transmission unit, and the reception device includes a reception unit, a division unit, a conversion unit, an extraction unit, and an output unit,
(A) In the transmitter,
A modulation step in which the modulation unit performs orthogonal frequency division multiplexing modulation of the transmission signal;
The relay unit includes a relay step of relaying the modulated signal to each of the plurality of relay devices;
(B) In each of the plurality of relay devices,
A receiving step in which the receiving unit receives the modulated signal relayed from the transmission device;
The transmitter further includes a transmission step of wirelessly transmitting the received modulated signal at a transmission frequency assigned to the relay device;
(C) Transmission frequencies assigned to each of the plurality of relay devices are different from each other, and both are included in an allowable range of reception frequencies adopted by the reception device,
(D) In the receiving device,
A receiving step in which the receiving unit receives a signal wirelessly transmitted from the relay device within an allowable range of the reception frequency;
A dividing step in which the dividing unit divides the received signal into complex sequences of transfer functions in time order for each subcarrier;
A transforming step in which the transforming unit performs a discrete Fourier transform on each of the divided subcarriers for a complex sequence in time order included in the subcarriers;
An extraction step in which the extraction unit extracts a frequency component of a peak in the vicinity of a transmission frequency of a desired relay device from a frequency component obtained by performing the discrete Fourier transform on each of the divided subcarriers;
A measurement method comprising: an output step in which the output unit acquires and outputs a communication characteristic between the desired relay device and the receiving device from the extracted frequency component. The measurement method according to claim 5, wherein
In the output step, the extracted peak frequency for at least one of the divided subcarriers is output as the communication characteristic. The measurement method according to claim 5, wherein
In the output step, a reception electric field strength that is a sum of reception strengths of the extracted peak frequency components is obtained for each of the divided subcarriers, and the reception electric field strength is output as the communication characteristics. Measuring method. The measurement method according to claim 5, wherein
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.   The transmission apparatus in the measurement system of any one of Claim 1 to 4.   The relay apparatus in the measurement system of any one of Claim 1 to 4.   The receiving apparatus in the measuring system of any one of Claim 1 to 4.   A program causing a computer to function as the transmission device according to claim 9.   A program causing a computer to function as the relay device according to claim 10.   A program for causing a computer to function as the receiving device according to claim 11.

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