JP3955463B2 - Orthogonal frequency division multiplexing communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an orthogonal frequency division multiplexing communication system, and is particularly suitable for application to a multipath environment such as mobile communication.
[0002]
[Prior art]
In recent years, an Orthogonal Frequency Division Multiplexing (OFDM) method has attracted attention as a high-speed, high-quality transmission method, and its application to a mobile communication system has been studied.
An OFDM signal propagated through a multipath environment such as mobile communication is affected by frequency selective fading, and the amount of phase rotation and received power for each subcarrier fluctuate. The fluctuation characteristics vary depending on the propagation path environment. Change. For this reason, in order to maintain a constant reception quality, a so-called channel estimation is performed in which a known pilot symbol is inserted into all subcarriers on the transmission side, and a fading complex envelope due to a propagation path is estimated on the reception side. It is possible to do it.
In addition, it is also considered to use frequency correlation to insert a pilot symbol for each subcarrier at regular intervals, and to perform channel estimation using interpolation for subcarriers in which no pilot symbol is inserted (ARIB STD- B31 (version 1.1)).
[0003]
[Problems to be solved by the invention]
However, when pilot symbols are inserted into all subcarriers, data transmission efficiency is lowered because data cannot be transmitted by the amount corresponding to the pilot symbols.
In addition, even when pilot symbols are inserted for each subcarrier at regular intervals, if the frequency selective fading fluctuation is moderate, excessive pilot symbols are inserted, resulting in a decrease in data transmission efficiency. It becomes. On the other hand, when frequency selective fading fluctuation is severe, when pilot symbols are inserted at a constant interval (frequency interval), the frequency correlation is low, so the accuracy of channel estimation by interpolation is reduced, and bit errors are reduced. It tends to occur. In particular, in the case of mobile communications, the propagation path environment varies depending on the movement of the user, and the variation characteristics of frequency selective fading also vary. Therefore, the interval between subcarriers where pilot symbols are inserted is fixed. If this is the case, the data transmission efficiency may be reduced.
Furthermore, when the received power of the subcarrier is low, the phase rotation amount changes rapidly, so that the modulation method using phase information decreases the accuracy of channel estimation by interpolation and tends to cause bit errors. In addition, when the pilot symbol insertion interval increases, the phase rotation amount fluctuates greatly when the subcarrier interval is large or the delay spread is large, and the accuracy of channel estimation decreases in the modulation scheme using phase information, and the bit There is a problem that errors are likely to occur.
[0004]
Accordingly, the present invention provides an orthogonal frequency division multiplex communication system capable of improving data transmission efficiency and bit error rate by adaptively controlling the insertion position of a pilot symbol according to a change in propagation path environment. It is an object.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, an orthogonal frequency division multiplexing communication system of the present invention is an orthogonal frequency division multiplexing communication system in which a plurality of subcarriers transmitted from a transmission side apparatus are received by a reception side apparatus, The apparatus includes: a measuring unit that measures a received power of each of the received subcarriers and a variation in received power between subcarriers on the frequency axis; and a subcarrier on the measured received power and frequency axis of each subcarrier. Subcarrier selecting means for determining a subcarrier into which a pilot symbol is inserted based on fluctuations in received power between the information, and means for notifying the transmitting side apparatus of information regarding the subcarrier into which the determined pilot symbol is inserted. The transmitting side apparatus inserts a pilot symbol notified from the receiving side apparatus. To subcarriers corresponding based on information about the A and has a means for transmitting by inserting pilot symbols.
[0006]
Further, the subcarrier selecting means includes one or a plurality of subcarriers including one or a plurality of continuous subcarriers on the condition that the measured difference in received power is within a predetermined threshold. The subcarriers into which the pilot symbols are inserted are determined for each of the divided blocks.
Alternatively, the subcarrier selection means may determine the difference between the measured received powers within a predetermined threshold for the plurality of subcarriers, and the measured received power of each subcarrier may be subcarriers before and after the subcarrier. Are subdivided into one or a plurality of blocks including one or a plurality of continuous subcarriers on condition that the maximum value or the minimum value is not compared with It is supposed to be decided.
Furthermore, an upper limit is set for the number of subcarriers included in one block.
Furthermore, a subcarrier whose measured received power is a predetermined value or less is determined as a subcarrier into which the pilot symbol is inserted.
[0007]
Furthermore, the subcarrier selecting means includes the plurality of subcarriers including one or a plurality of consecutive subcarriers on condition that the measured difference in received power is within a predetermined threshold value. A block obtained by dividing the block into a plurality of blocks, obtaining the number of subcarriers in the block based on the number of subcarriers included in each block, and again dividing all the subcarriers at regular intervals for each obtained number of subcarriers in the block. A subcarrier into which the pilot symbol is inserted is determined every time.
Furthermore, the minimum value of the number of subcarriers included in the one or a plurality of blocks is set as the number of subcarriers in the block.
Alternatively, the number of subcarriers in the block is determined based on a cumulative distribution function of the number of subcarriers included in the one or more blocks.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a main configuration of an embodiment of an orthogonal frequency division multiplexing communication system according to the present invention. Here, a case where base station 1 and one mobile station 2 are shown and an OFDM signal is transmitted from base station 1 to mobile station 2 will be described as an example.
As shown in FIG. 1, the base station 1 includes an OFDM modulator 10, an OFDM demodulator 17, and a control unit 16. The transmission data is subjected to error correction coding and the like in the modulation unit 11 in the OFDM modulator 10 and then modulated. As this modulation method, BPSK, QPSK, 16QAM, 64QAM, or the like is selected according to the transmission rate or the required transmission quality. The pilot insertion unit 12 inserts a pilot symbol into the modulation symbol output from the modulation unit 11 based on the control information indicating the pilot symbol insertion position supplied from the control unit 15, and the serial-parallel conversion unit (S / P conversion). Part) 13 is converted into a number of parallel modulation symbols corresponding to the number of subcarriers.
The parallel modulation symbols output as the number of subcarriers output from the S / P conversion unit 13 are subjected to inverse Fourier transform in an inverse Fourier transform unit (IFFT) 14 to be an OFDM signal. The IFFT 14 may be an inverse discrete Fourier transform unit (IDFT). This OFDM signal is transmitted from the base station 1 on a carrier wave having a predetermined frequency.
[0009]
The mobile station 2 that can receive the OFDM signal includes an OFDM demodulator 20, an OFDM modulator 28, and a control unit 26. The OFDM modulator 28 is configured such that the pilot insertion unit 12 of the OFDM modulator 10 in the base station 1 is omitted.
The OFDM signal received by the mobile station 2 is subjected to Fourier transform in a Fourier transform unit (FFT) 21 and decomposed for each subcarrier. The FFT 21 may be a discrete Fourier transform unit (DFT).
The received power of each subcarrier output in parallel from the FFT unit 21 is measured by the received power measuring unit 22, and the received power value of each subcarrier is supplied to the control unit 26. The subcarriers output in parallel from the FFT unit 21 are supplied to the channel estimation unit 23. Channel estimation unit 23 obtains propagation path information (phase rotation amount and phase rotation amount) from the reception signal of the pilot symbol included in the reception signal of the subcarrier designated by the number of the subcarrier in which the pilot symbol notified from control unit 26 is inserted. Attenuation amount) is estimated, and the phase rotation of the received signal of each subcarrier from the FFT unit 21 is compensated. The reception signal of each subcarrier corrected by the channel estimation unit 23 is supplied to a parallel-serial conversion unit (P / S conversion unit) 24, and the modulation symbols of the parallel subcarriers are converted into serial modulation symbols. The The modulation symbol of the subcarrier output from the P / S conversion unit 24 is demodulated by the symbol demodulation unit 25 to be demodulated data. The symbol demodulator 25 performs demodulation according to modulation such as BPSK, QPSK, 16QAM, or 64QAM performed on the transmission side, and then performs error correction processing and the like and outputs the received data.
[0010]
Here, in the present invention, the control unit 26 adaptively determines the position of the subcarrier into which the pilot symbol is inserted based on the reception power of each subcarrier measured by the reception power measurement unit 22. . Then, information indicating the position of the subcarrier into which the determined pilot symbol is inserted is stored in the information management table 27, and the position information of the subcarrier into which the pilot symbol is inserted is input to the OFDM modulator 28, and the mobile station It transmits to the said base station 1 with transmission data. Further, based on the information in the information management table 27, the channel estimation unit 23 performs channel estimation.
In the base station 1, information indicating the position of the subcarrier into which the pilot symbol decoded by the OFDM demodulator 17 is inserted is written in the information management table 16 of the control unit 15, and this information is stored in the pilot symbol insertion unit 12. I am trying to supply.
[0011]
FIG. 2 is a diagram illustrating an example of a frame configuration of a multicarrier signal transmitted from the base station 1, and here, a part of subcarrier signals (16 from SC1 to SC16) among a plurality of subcarriers. Only shows.
As shown in this figure, in the present invention, only the subcarriers (SC1, SC6, SC9, SC13, SC16,... In the example shown) selected by the control unit 26 among all subcarriers are framed. A pilot symbol indicated by hatching is inserted for each transmission.
The channel estimator 23 compares the received signal of pilot symbols of subcarriers (in the example shown, SC1, SC6, SC9, SC13, SC16,...) Into which pilot symbols are inserted with known symbol data and propagates them. The phase rotation amount and attenuation amount due to the path are calculated, and interpolation on the time axis is performed to obtain the propagation path information of those channels. For subcarriers in which pilot symbols are not transmitted, interpolation on the frequency axis is performed from the pilot symbols received by the selected subcarriers to obtain propagation path information of the subcarriers. Then, the propagation path information of each subcarrier is obtained by performing interpolation on the time axis as described above. Then, based on the propagation path information (channel estimation value) obtained in this way, the phase variation of the reception information of each subcarrier output from the FFT unit 21 is compensated.
[0012]
Next, how to select a subcarrier into which a pilot symbol is inserted as described above will be described. Here, it is assumed that a modulation method (BPSK, QPSK) or the like that changes the phase is adopted as a modulation method of transmission data.
FIG. 3A shows an example of an OFDM signal transmitted from the base station 1. As shown in this figure, signals are transmitted with the same transmission power for all subcarriers, but due to frequency selective fading, the received signal power varies depending on the subcarriers as shown in (b).
Therefore, in the present invention, first, continuous subcarriers whose received power difference is within a predetermined value (here, ΔE) are collectively set as one block, and all subchannels are set as one or a plurality of subchannels. Divide into blocks. In the example shown in FIG. 3 (b), the first subcarrier SC5 up to a subcarrier SC5 in which the difference in received power from the received power of SC1 does not exceed a predetermined value ΔE is based on the subcarrier SC1 having the smallest subcarrier number. Block # 1 is set as the next block # 2 up to subcarrier SC8 where the difference in received power is within the predetermined value ΔE with the subcarrier SC6 exceeding the predetermined value ΔE as a new reference. Similarly, SC9 to SC12 are divided into blocks such as block # 3, and SC13 to SC16 are divided into blocks # 4. Then, a subcarrier selected from each block is set as a subcarrier to which a pilot symbol is inserted and transmitted. In the example shown in the figure, the subcarrier located at the head of each block is selected and is shown by hatching.
As described above, in the present invention, adjacent subcarriers have high frequency correlation, and the phase rotation amount and the variation in received power due to the influence of frequency selective fading in subcarriers within a certain correlation bandwidth are considered to be substantially equal. Therefore, consecutive subcarriers whose received power difference is within a predetermined value are set as one block, pilot symbols are inserted in units of the block, and channel estimation is performed using the inserted pilot symbols. In addition, when the fluctuation of the received power on the frequency axis is sudden, only one subcarrier may be included in one block. This makes it possible to overcome the above-mentioned problems.
[0013]
As shown in FIG. 3B, when subcarriers are divided into blocks based on the difference in received power being within a predetermined value (ΔE), the subcarriers included in each block The number of carriers varies. Therefore, the optimum value of the number of subcarriers included in each block (the number of subcarriers in the block) is calculated based on the result of division into blocks based on the difference in received power as described above, and the subcarriers included in each block are calculated. All the subcarriers may be divided again so that the number of carriers becomes the calculated number of subcarriers in the block, and pilot symbols may be inserted for each block that is subdivided at regular intervals. As a result, only the number of subcarriers in the block needs to be notified as information indicating the position of the subcarrier into which the pilot symbol is inserted from the receiving side (mobile station 2) to the transmitting side (base station 1). The amount can be reduced.
FIG. 4A is a diagram showing this state, and shows a case where the number of subcarriers in a block is 3, and block division is performed again every 3 subcarriers.
Here, as a calculation method of the number of subcarriers in a block, (1) a method in which a minimum value of subcarriers included in each block divided by ΔE is set as the number of subcarriers in a block, (2) by ΔE A method of obtaining the probability of occurrence for each number of subcarriers included in each divided block and setting the number of subcarriers whose cumulative distribution function value is a predetermined value (for example, 60%) as the optimum value of the number of subcarriers, And (3) a method in which the maximum value or average value of the number of subcarriers included in each block divided by ΔE is used as the number of subcarriers in the block.
[0014]
Also, when the received power value is small, the amount of phase rotation will fluctuate abruptly due to fluctuations in received power, and when a modulation method using phase information is adopted, the accuracy of channel estimation by interpolation decreases, and the bit Errors are likely to occur. Therefore, pilot symbols are inserted for subcarriers whose received power value is lower than a predetermined value (ΔPL). FIG. 4B is a diagram showing a case of an embodiment in which pilot symbols are inserted for subcarriers with low received power as described above. As shown in this figure, subcarriers whose received power values are smaller than a predetermined value ΔPL (SC8, SC9, SC10, SC11 in the illustrated example) are subcarriers into which pilot symbols are unconditionally inserted. Accordingly, the remaining subcarriers SC1 to SC7 and SC12 to SC16,... Are referred to as areas. Then, for each area, continuous subcarriers in the range of a predetermined value ΔE determined in the same manner as described above are blocked. Also, pilot symbols are inserted for subcarriers belonging to the edge of the area. As a result, subcarriers indicated by diagonal lines in the figure are selected as subcarriers into which pilot symbols are inserted.
According to this embodiment, since pilot symbols are inserted into subcarriers with low received power, accurate channel estimation is possible even for subcarriers with low received power, and bit errors can be prevented from occurring. Become.
[0015]
Further, as described above, when the received power difference ΔE is divided into blocks, the received power differences of many consecutive subchannels are within the range of ΔE as shown in FIG. 4C. Sometimes, the number of subcarriers included in one block increases. In such a case, if the phase fluctuation in one block exceeds 180 °, erroneous interpolation is performed. Therefore, a maximum value (ΔMB) of the number of subcarriers included in one block is determined in advance, and a pilot symbol is inserted for each ΔMB. The example shown in (c) of FIG. 4 shows a case where ΔMB = 8, and a pilot symbol is inserted in subcarrier SC9.
According to this embodiment, it is possible to prevent bit errors from occurring even when the received power fluctuation is small and the phase rotation amount fluctuation is abrupt.
[0016]
Next, another embodiment suitable for a case where a modulation scheme (16QAM or 64QAM) that also uses amplitude information is employed will be described. In this case, since the received signal power varies depending on the transmission data, more accurate interpolation is required.
As described above, when block division is performed on the condition that the received power value is within the range of the predetermined value ΔE, the received power may be a maximum value or a minimum value on the frequency axis in one block. is there. For example, in FIG. 3B, the received power of the subcarrier SC11 has a minimum value in the block # 3. In such a case, when channel estimation of SC10 to SC12 is performed by interpolating the channel estimation results of subcarriers SC9 and SC13 in which pilot symbols are inserted, the received signal by the modulation scheme using amplitude information is received. A bit error may occur.
Therefore, in this embodiment, a subcarrier whose reception power of a subcarrier has a maximum value or a minimum value on the frequency axis is selected as a subcarrier into which a pilot symbol is inserted. For example, in the example shown in FIG. 5 (a), the subcarrier SC1 located at the end and the subcarrier SC11 having a minimum received power are selected as subcarriers into which pilot symbols are inserted.
That is, in this embodiment, the difference in received power does not exceed a predetermined threshold ΔE, and the received power value has a maximum value or a minimum value compared with the subcarriers before and after the subcarrier. On the condition that it is not taken, it is divided into one or a plurality of blocks including one or a plurality of continuous subcarriers, and a subcarrier into which a pilot symbol is inserted is selected for each block.
In the example shown in FIG. 5B, first, the received power value between the subcarrier SC5 where the difference in received power does not exceed the predetermined threshold ΔE with the subcarrier SC1 having the smallest subcarrier number as a reference. Since there is no subcarrier having a maximum value or a minimum value, SC1 to SC5 are designated as block # 1. Next, with reference to subcarrier SC6, similarly to subcarrier SC8 where the difference in received power is within ΔE is block # 2. Next, subcarrier SC9 serves as a reference, and subcarriers whose received power difference is within ΔE is up to SC12. However, since the received power value of subcarrier SC11 is a minimum value, the received power value is a maximum. Blocks # 3 are subcarriers SC10 that do not take a value or a minimum value. Next, on the basis of the subcarrier SC11, the subcarriers SC11 to SC12 are set to block # 4 and the subcarrier SC13 to block # 5 in the same manner. Then, a subcarrier to be transmitted by inserting a pilot symbol from each block divided in this way is selected. Here, the method shown in FIGS. 4A to 4C may be used.
As described above, according to this embodiment, since pilot symbols are inserted into subcarriers where the received power of subcarriers is an extreme value, it is possible to approximate at least with a broken line and use amplitude information. It is possible to prevent a bit error from occurring when the modulation scheme is adopted.
[0017]
Next, the flow of processing for determining a subcarrier into which such a pilot symbol is inserted will be described with reference to FIG. 6 and FIG.
In the control unit 26, a threshold value ΔE for the difference in received power, a threshold value ΔPL for the received power, and a maximum value ΔMB for the number of subcarriers in the block are set in advance.
First, the reception power measurement unit 22 measures reception power P [x] (x is a subcarrier number) of all subcarriers (S1). Then, the subcarrier x whose received power is smaller than ΔPL (P [x] <ΔPL) is selected as a subcarrier into which a pilot symbol is inserted, and the number x is written in the control information management table 27 (S2). As a result, the areas shown in FIG. 4B (first and last subcarrier numbers of each area) are determined (S3), and for each area, a subcarrier into which a pilot symbol is inserted is determined for each area. (S4, S5).
[0018]
FIG. 7 is a diagram showing a flow of subcarrier selection processing for inserting pilot symbols performed for each area.
First, the subcarrier number x to be processed is set as the number of the first subcarrier in the area (S11), the subcarrier is selected as a subcarrier into which a pilot symbol is inserted, and the number is stored in the control information management table 27. Write (S12).
Next, the reception power value P [x] of the first subcarrier is set as a reference subcarrier power value Pc, and 1 is set to a counter CB that counts the number of subcarriers included in one block (S13).
Then, the subcarrier number x is incremented by 1, the subsequent subcarrier is set as a processing target, and the counter CB is incremented by 1 (S14). Then, it is determined whether or not the subcarrier is the last subcarrier of the area currently being processed (S15). If it is the last subcarrier, the subcarrier into which the pilot symbol is inserted is determined. The carrier is selected and written in the information management table 27 (S18), and the processing of this area is finished.
If it is not the last subcarrier, the process proceeds to step S16, and it is determined whether or not the count value of the counter CB for counting the number of subcarriers included in the block exceeds the maximum value ΔMB of the number of subcarriers in the block. To do.
When it exceeds, the process returns to step S12, and the subcarrier is selected as the subcarrier into which the pilot symbol is inserted, and the processing after S13 is continued.
If not, the process proceeds to step S17, where the absolute value of the difference between the received power value P [x] of the subcarrier currently being processed and the reference subcarrier received power value Pc is the reference threshold value. Whether ΔE is exceeded and whether P [x] is a maximum value or a minimum value, that is, P [x] is the received power values P [x−1] and P [x + 1] before and after that. If it is greater or smaller, the process returns to step S12, and the subcarrier is selected as a subcarrier into which a pilot symbol is inserted, and the processes after step S13 are performed. If neither of the above conditions is satisfied, the process returns to step S14 to process the next subcarrier.
[0019]
As described above, the numbers of subcarriers into which pilot symbols are to be inserted are stored in the information management table 27 as described above, and the stored contents are transmitted from the mobile station 2 to the base station 1 via a control channel or the like. Sent. Information in the information management table 27 demodulated by the OFDM demodulator 17 in the base station 1 (information for specifying a subcarrier into which a pilot symbol is inserted) is written in the control information management table 16 of the base station control unit 15 and is piloted. The signal is supplied to the symbol insertion unit 12, and a pilot symbol is inserted into the designated subcarrier and transmitted.
[0020]
Note that the above-described processing of the mobile station control unit 26 may be performed for each frame, or may be performed for each predetermined period (for each predetermined number of frames).
In the above description, processing such as block division is performed in ascending order of subcarrier numbers. However, the present invention is not limited to this, and processing may be performed in descending order.
Furthermore, in the above, the subcarrier located at the head in the divided block is selected as the subcarrier into which the pilot symbol is inserted. However, the present invention is not limited to this, and which subcarrier is selected in the block. It can be determined as appropriate.
Furthermore, in the example shown in FIGS. 6 and 7, the block is not redivided according to the number of subcarriers in the block shown in FIG. It is easy to change to.
Furthermore, in the above description, the case where the base station 1 is a transmission side device and the mobile station 2 is a reception side device has been described as an example. However, the present invention is not limited to this, and the opposite case may be used. .
[0021]
【The invention's effect】
As described above, according to the orthogonal frequency division multiplexing communication system of the present invention, the pilot symbol insertion position can be determined flexibly according to changes in the propagation path environment, and the pilot symbol is inserted in a fixed manner. Compared to the above, it is possible to improve the data transmission efficiency and the bit error rate. In particular, more effects can be expected in mobile communication in which the propagation path environment changes variously due to the movement of the user. That is, when the fluctuation of frequency selective fading is moderate, it is possible to increase the pilot symbol insertion interval by utilizing the fact that the frequency correlation is high, and to increase the data transmission efficiency. On the other hand, when the frequency selective fading fluctuation is severe, the frequency correlation is low, so that the pilot symbol insertion interval is reduced, and the bit error rate can be reduced.
Further, when the received power of a subcarrier is an extreme value on the frequency axis, according to the present invention in which a pilot symbol is inserted into the subcarrier, even in the case of a modulation scheme using amplitude, The accuracy of channel estimation can be improved.
Furthermore, according to the present invention in which the maximum value of the number of subcarriers included in the block is determined, it is possible to prevent a decrease in channel estimation accuracy due to interpolation even when the phase rotation is abrupt.
Furthermore, according to the present invention in which a subcarrier with low received power is selected as a subcarrier into which a pilot symbol is inserted, the accuracy of channel estimation is reduced by interpolation even when a sudden phase rotation variation occurs due to low received power. It becomes possible to prevent.
Furthermore, the present invention determines a subcarrier into which a pilot symbol is inserted for each block divided again at regular intervals based on the number of subcarriers in the block determined based on the number of subcarriers included in the block divided by the difference in received power. According to this, it is possible to reduce the amount of information related to the position of the subcarrier into which the pilot symbol to be notified from the reception side device to the transmission side device is inserted.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main configuration of an embodiment in an orthogonal frequency division multiplexing communication system according to the present invention.
FIG. 2 shows an example of an OFDM signal according to the present invention.
FIG. 3 is a diagram for explaining a method of selecting a subcarrier into which a pilot symbol is inserted according to the present invention.
FIG. 4 is a diagram for explaining a method for selecting a subcarrier into which a pilot symbol is inserted according to the present invention.
FIG. 5 is a diagram for explaining a subcarrier selection method for inserting a pilot symbol suitable for a modulation scheme using amplitude information;
FIG. 6 is a flowchart showing a flow of processing for selecting a subcarrier into which a pilot symbol is inserted according to the present invention.
FIG. 7 is a flowchart showing a flow of processing executed for each area in order to select a subcarrier into which a pilot symbol is inserted according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Base station 10 OFDM modulator 11 Modulation part 12 Pilot symbol insertion part 13 Serial / parallel converter 14 IFFT part 15 Control part 16 Information management table 17 OFDM demodulator 2 Mobile station 20 OFDM demodulator 21 FFT part 22 Received power measurement part 23 Channel estimation unit 24 Parallel / serial converter 25 Demodulation unit 26 Control unit 27 Information management table 28 OFDM modulator

Claims (8)

An orthogonal frequency division multiplexing communication system in which a plurality of subcarriers transmitted from a transmission side device are received by a reception side device, wherein the reception side device receives the received power and frequency on each of the plurality of subcarriers received Measuring means for measuring fluctuations in received power between subcarriers , and determining subcarriers into which pilot symbols are inserted based on the measured received power of each subcarrier and fluctuations in received power between subcarriers on the frequency axis Subcarrier selecting means, and means for notifying the transmitting side apparatus of information relating to the subcarrier into which the determined pilot symbol is inserted, wherein the transmitting side apparatus inserts the pilot symbol notified from the receiving side apparatus Pilot symbols for the corresponding subcarriers based on the information on the subcarriers to be Orthogonal frequency division multiplexing communication system, characterized in that it comprises means for transmitting the input. The subcarrier selecting means includes one or a plurality of blocks including one or a plurality of consecutive subcarriers, on the condition that the difference between the measured received powers is within a predetermined threshold. The orthogonal frequency division multiplexing communication system according to claim 1, wherein a subcarrier into which the pilot symbol is inserted is determined for each of the divided blocks. The subcarrier selection means compares the measured reception power of the plurality of subcarriers within a predetermined threshold, and compares the measured reception power of each subcarrier with the preceding and succeeding subcarriers. Then, on condition that the maximum value or the minimum value is not reached, it is divided into one or a plurality of blocks including one or a plurality of continuous subcarriers, and a subcarrier into which the pilot symbol is inserted is determined for each of the divided blocks. The orthogonal frequency division multiplexing communication system according to claim 1. 4. The orthogonal frequency division multiplexing communication system according to claim 2, wherein an upper limit is set for the number of subcarriers included in one block. 4. The orthogonal frequency division multiplexing communication system according to claim 2, wherein a subcarrier whose measured received power is equal to or less than a predetermined value is determined as a subcarrier into which the pilot symbol is inserted. The subcarrier selecting means includes one or a plurality of blocks including one or a plurality of consecutive subcarriers, on the condition that the difference between the measured received powers is within a predetermined threshold. The number of subcarriers in a block is calculated based on the number of subcarriers included in each block, and all the subcarriers are again divided at regular intervals for each number of subcarriers in the block. 2. The orthogonal frequency division multiplexing communication system according to claim 1, wherein subcarriers into which pilot symbols are inserted are determined. 7. The orthogonal frequency division multiplexing communication system according to claim 6, wherein a minimum value of the number of subcarriers included in the one or a plurality of blocks is set as the number of subcarriers in the block. 7. The orthogonal frequency division multiplexing communication system according to claim 6, wherein the number of subcarriers in the block is determined based on a cumulative distribution function of the number of subcarriers included in the one or a plurality of blocks.

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