JP4628977B2 - Transmission path estimation device, transmission path estimation program, and recording medium - Google Patents

Description

  The present invention relates to a transmission path at a position in the frequency direction of a data symbol based on a transmission path characteristic at a position in the frequency direction of the known symbol obtained from the reception result of the known symbol arranged with the data symbol in the frequency direction. The present invention relates to a transmission path estimation apparatus that estimates characteristics. The present invention also relates to a transmission path estimation program for causing a computer to execute processing for realizing the function of the transmission path estimation apparatus, and also to a computer-readable recording medium on which the transmission path estimation program is recorded.

  In wireless communication, a signal output from a transmitter is affected by amplitude fluctuations and phase rotation while propagating in a wireless section, and thus a waveform of a signal received by a receiver is distorted. Therefore, in order to correctly demodulate and decode at the receiver, it is necessary to correctly estimate the influence of these fluctuations and to correct the received signal. The process of estimating the influence of a transmission signal from a transmission path (propagation path) is called transmission path estimation (channel estimation), and the process of correcting a received signal according to the estimated transmission path information is called transmission path correction (channel correction). As a transmission path estimation method, a known method is that a known pilot symbol is transmitted together with a data symbol, amplitude fluctuation and phase rotation of the pilot symbol are measured, and transmission path fluctuation is estimated from the result. However, if the ratio of pilot symbols to data symbols increases, the transmission throughput decreases, so there is a trade-off between improving estimation accuracy and improving throughput.

  In broadband wireless transmission, since the occupied bandwidth is wide, the influence of frequency selective fading due to multipath or the like becomes significant. FIG. 12 shows an example of transmission path fluctuation in the frequency direction. It can be seen that the characteristics of the transmission line greatly change depending on the frequency. In consideration of the influence of frequency selective fading as described above, a multicarrier transmission scheme that performs parallel transmission of information using a plurality of low-speed subcarriers that are orthogonal to each other has been studied. In the multi-carrier transmission method, the occupied bandwidth of each subcarrier is sufficiently narrow, so the transmission path variation seen from each subcarrier can be treated as simple attenuation (flat fading), and the effects of frequency selective fading are compared. Can be corrected easily. However, since the influence of transmission path variation differs for each subcarrier, transmission path estimation needs to be performed for each subcarrier.

  FIG. 13 schematically shows a state where pilot symbols are inserted between data symbols. The pilot symbols are distributed in the frequency direction and the time direction. In FIG. 13A, when viewed in the time direction, pilot symbols are inserted only in the first symbol in the subframe, and in the symbols, pilot symbols are inserted at equal intervals in the frequency direction. Further, in FIG. 13B, the number of pilot symbols inserted in the first symbol in the subframe is smaller than that in FIG. 13A, and the reduced pilot symbols are inserted in other symbols. ing. When the subframe configuration in FIG. 13B is used, the resistance to transmission path fluctuations in the frequency direction is lower than in the case of using the subframe configuration in FIG. It becomes possible to cope with high-speed movement. Data symbol transmission path fluctuations are obtained by performing some interpolation processing in the frequency and time directions on transmission path values (transmission path fluctuation values, channel gains) indicating transmission path characteristics obtained by measuring pilot symbols. Presumed.

As a method of interpolating transmission line values obtained from pilot symbols in the frequency direction, an interpolation method based on the sampling theorem (sampling theorem) has been proposed (see Non-Patent Document 1, for example). Here, this is called sampling interpolation. Assuming that pilot symbols are inserted in the frequency direction at a frequency interval f _s and the transmission path value H (nf _s ) of each pilot symbol is obtained, sampling interpolation uses the following equation (1) to obtain an arbitrary frequency f The transmission line value H (f) in can be interpolated.

However, n is an integer. Also, sinc (x) = sin (x) / x. When the maximum delay time of the multipath is τ, if the pilot symbols are inserted at the frequency interval f _s = 1 / τ according to the sampling theorem, the transmission path fluctuation of each subcarrier can be completely reproduced.
Itami Makoto, “~ OFDM Modulation Technology for Digital Broadcasting / Mobile Communications”, Trikes, Inc., March 6, 2000, p. 102-108

  As shown in equation (1), in the transmission path estimation method using sampling interpolation, it is assumed that pilot symbols are arranged at equal intervals over an infinite frequency band. Further, as a general tendency, the pilot symbol that is located closer to the data symbol for which the transmission path value is estimated has a greater contribution to the calculation of the estimated value.

  In actual transmission, the frequency band that can be used for communication is limited, and the pilot symbols are not necessarily arranged at equal intervals. For example, as shown in FIG. 14, consider a case where pilot symbols are inserted at a rate of one in four symbols. In FIG. 14, it is assumed that the right side is the high frequency side and the left side is the low frequency side. The hatched circle indicates the frequency position (arrangement position in the frequency direction) of the pilot symbol, and the white circle indicates the frequency position of the data symbol. Also, n is the number of subcarriers in the used frequency band, and p is the number of pilot symbols. In the following description, for the sake of convenience, the transmission line value at the pilot symbol frequency position is referred to as the pilot symbol transmission line value, and the transmission line value at the data symbol frequency position is referred to as the data symbol transmission line value.

  At this time, as shown in FIG. 14 (a), for the data symbols arranged on the n-2 and n-1 subcarriers, there is no pilot symbol in the region on the higher frequency side than the position, The transmission path value of the pilot symbol that should have contributed greatly cannot be used. Also, as shown in FIG. 14 (b), when the first pilot symbol cannot be received for some reason, the transmission path value of the data symbol allocated to the 1st to 3rd and 5th to 7th subcarriers is estimated. In this case, it is impossible to use the transmission path value of the first pilot symbol that should have contributed greatly. Therefore, if the sampling interpolation of equation (1) is applied as it is, the estimation accuracy of the transmission path may be deteriorated.

  In addition, when performing communication using a very large number of subcarriers, the number of pilot symbols to be inserted becomes large. Therefore, the number of terms related to addition on the right side of equation (1) is proportional to the number of subcarriers. There is a problem that the amount of computation for estimating the transmission path increases significantly.

  The present invention has been made in view of the above-described problems, and a first object thereof is to improve the estimation accuracy of a transmission path. A second object of the present invention is to reduce the amount of calculation related to transmission path estimation.

  The present invention has been made to solve the above-described problem, and transmission path characteristics at a position in the frequency direction of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In the transmission path estimation apparatus for estimating the transmission path characteristic of the data symbol at the position in the frequency direction based on the first transmission path showing the transmission path characteristic at the position of the known symbol actually received A first transmission path estimation means for calculating a second transmission path value indicating a transmission path characteristic at the position of the virtual known symbol using the value; the first transmission path value; and the second transmission path value. And a second transmission path estimation means for calculating a third transmission path value indicating a transmission path characteristic at the position of the data symbol by sampling interpolation using the transmission path value. Road estimation equipment It is.

  In the transmission path estimation apparatus of the present invention, the second transmission path estimation means selects the first transmission path value and the second transmission path value in the order closer to the position of the data symbol. The third transmission line by sampling interpolation using transmission line values at positions of k (2 or more and an integer less than the sum of the number of the first transmission line value and the second transmission line value) A value is calculated.

  In the transmission path estimation apparatus according to the present invention, the second transmission path estimation means has an influence on the third transmission path value among the first transmission path value and the second transmission path value. The third transmission line value is calculated by sampling interpolation using the transmission line value at the position of the known symbol where the value of the sinc function indicating the value is equal to or greater than a predetermined value.

  Further, the present invention provides the frequency direction of the data symbol based on transmission path characteristics of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In the transmission path estimation apparatus for estimating the transmission path characteristic at the position, the data symbol is obtained by sampling interpolation using the first transmission path value indicating the transmission path characteristic at the position of the actually received symbol. First transmission path estimation means for calculating a second transmission path value indicating a transmission path characteristic at the position, and the other data symbols excluding the position of the data symbol from which the second transmission path value was obtained The third transmission line value indicating the transmission line characteristic at the position of the first transmission line value is the first transmission line value at the position closest to the position of the other data symbol among the positions where the first transmission line value is obtained. A channel estimation device characterized by comprising a second channel estimation section that calculates as the same value as the road value.

  Further, the present invention provides the frequency direction of the data symbol based on transmission path characteristics of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In the transmission path estimation apparatus for estimating the transmission path characteristic at the position, the data symbol is obtained by sampling interpolation using the first transmission path value indicating the transmission path characteristic at the position of the actually received symbol. First transmission path estimation means for calculating a second transmission path value indicating a transmission path characteristic at the position, and the other data symbols excluding the position of the data symbol from which the second transmission path value was obtained And a second transmission path estimation means for calculating a third transmission path value indicating the transmission path characteristics at the position by linearly interpolating the plurality of first transmission path values. A channel estimation device according to.

  Further, in the transmission path estimation apparatus of the present invention, the first transmission path estimation means selects k pieces (k is 2 or more, and selected from the first transmission path values in the order closest to the position of the data symbol). The second transmission line value is calculated by sampling interpolation using transmission line values at a position of an integer less than the total number of the first transmission line values).

  In the transmission path estimation apparatus of the present invention, the first transmission path estimation means has a predetermined value of a sinc function indicating a degree of influence on the second transmission path value among the first transmission path values. The second transmission path value is calculated by sampling interpolation using a transmission path value at the position of the known symbol that is equal to or greater than the value.

  Further, the present invention provides the frequency direction of the data symbol based on transmission path characteristics of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In a transmission path estimation program for causing a computer to execute processing for estimating transmission path characteristics at the position of the first position, the first transmission path value indicating the transmission path characteristics at the position of the known symbol actually received is used. A first process for calculating a second transmission line value indicating a transmission line characteristic at the position of the virtual known symbol, and the first transmission line value and the second transmission line value. And a second process of calculating a third transmission line value indicating a transmission line characteristic at the position of the data symbol by the sampling interpolation used. Is a program.

  Further, in the transmission path estimation program of the present invention, in the second process, of the first and second transmission path values, k pieces (k is 2 or more, selected in the order close to the position of the data symbol). And the third transmission line value is calculated by sampling interpolation using the transmission line value at a position of an integer less than the sum of the number of the first transmission line value and the second transmission line value). And

  In the transmission path estimation program of the present invention, in the second process, the value of a sinc function indicating the degree of influence on the third transmission path value among the first and second transmission path values is calculated. The third transmission line value is calculated by sampling interpolation using the transmission line value at the position of the known symbol that is equal to or greater than a predetermined value.

  Further, the present invention provides the frequency direction of the data symbol based on transmission path characteristics of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In a transmission path estimation program for causing a computer to execute processing for estimating transmission path characteristics at the position of the first position, the first transmission path value indicating the transmission path characteristics at the position of the actually received symbol is used. A first process for calculating a second transmission line value indicating a transmission line characteristic at the position of the data symbol by sampling interpolation, and a position of the data symbol from which the second transmission line value is obtained. The third transmission line value indicating the transmission line characteristic at the position of the other data symbol is set to the position of the other data symbol among the positions where the first transmission line value is obtained. A channel estimation program for causing to execute a second process for calculating the same value as the first transmission channel value at the closest position to the computer.

  Further, the present invention provides the frequency direction of the data symbol based on transmission path characteristics of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction. In a transmission path estimation program for causing a computer to execute processing for estimating transmission path characteristics at the position of the first position, the first transmission path value indicating the transmission path characteristics at the position of the actually received symbol is used. A first process for calculating a second transmission line value indicating a transmission line characteristic at the position of the data symbol by sampling interpolation, and a position of the data symbol from which the second transmission line value is obtained. A second transmission line value indicating a transmission line characteristic at the position of the other data symbol is calculated by linearly interpolating the plurality of first transmission line values. A channel estimation program characterized by executing the management to the computer.

  In the transmission channel estimation program of the present invention, in the first process, k pieces (k is 2 or more, and the first transmission channel value is selected in the order close to the position of the data symbol among the first transmission channel values). And the second transmission path value is calculated by sampling interpolation using transmission path values at a position of an integer less than the total number of the second transmission path values.

  In the transmission path estimation program according to the present invention, in the first process, a value of a sinc function indicating an influence on the second transmission path value among the first transmission path values is a predetermined value or more. The second transmission path value is calculated by sampling interpolation using the transmission path value at the position of the known symbol.

  Further, the present invention is a computer-readable recording medium on which the above transmission path estimation program is recorded.

  According to the present invention, the transmission path value at the position of the virtual known symbol is calculated using the transmission path value at the position in the frequency direction of the known symbol actually received, and the transmission path value is calculated. Since it is used for sampling interpolation, it is possible to improve the estimation accuracy of the transmission path.

  Further, according to the present invention, regarding the transmission line value at the position in the frequency direction of the data symbol, the transmission line value at other positions excluding the position where the transmission line value is calculated by sampling interpolation is actually received. Therefore, when there is no known symbol required for sampling interpolation, the estimation accuracy of the transmission path is improved and the error rate is improved. Can be reduced.

  Further, according to the present invention, the calculation related to the sampling interpolation is performed by performing the sampling interpolation using only some known symbols, instead of using all the known symbols required in the sampling interpolation formula. The amount can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a wireless communication system according to the first embodiment of the present invention. In the present embodiment, the transmitter 1 and the receiver 2 perform communication using a multicarrier communication scheme such as OFDM (Orthogonal Frequency Division Multiplexing) or MC-CDM (Multi-Carrier-Code Division Multiplexing). In the transmitter 1, the modulator 11 performs digital modulation on the information bits to be transmitted. The serial / parallel converter 12 performs serial / parallel conversion on the digitally modulated signal.

  Pilot symbol inserter 13 inserts pilot symbols into the data symbol sequence. The inverse Fourier transformer 14 performs an inverse Fourier transform on the symbol sequence to convert a frequency domain signal into a time domain signal. The converted signal is subjected to parallel / serial conversion by the parallel / serial converter 15 and the cyclic prefix is inserted by the cyclic prefix inserter 16, and then transmitted to the receiver 2. The transmitted signal is affected by frequency selectivity in the transmission line, and additive white Gaussian noise is applied in the receiver.

  In the receiver 2, the received signal is subjected to serial / parallel conversion by the serial / parallel converter 22 after the cyclic prefix is removed by the cyclic prefix remover 21. The Fourier transformer 23 performs a Fourier transform to convert a time domain signal into a frequency domain signal. The data / pilot symbol separator 24 separates the data symbol and the pilot symbol, and outputs the data symbol to the equalizer 26 and the pilot symbol to the transmission path estimator 25.

  The transmission path estimator 25 estimates the transmission path value at the pilot symbol frequency position from the pilot symbol reception result, and further estimates the transmission path value at the data symbol frequency position. Based on the transmission path estimation result from the transmission path estimator 25, the equalizer 26 compensates for transmission path fluctuations for data symbols. The parallel / serial converter 27 performs parallel / serial conversion on the data symbol string. The demodulator 28 demodulates the data symbol sequence and generates information bits.

  FIG. 2 shows the configuration of the transmission path estimator 25. In transmission path estimator 25, pilot symbol transmission path value calculator 251 compares the received value and transmission value (known) of the pilot symbol separated from the data symbol by data / pilot symbol separator 24, and the pilot. A transmission line value (first transmission line value) at the frequency position where the symbol is arranged is calculated. Data symbol transmission path estimator 252 calculates the transmission path value at the frequency position where the data symbol is arranged based on the transmission path value of the pilot symbol. The calculation result is output to the equalizer 26 as a data symbol transmission path estimation value.

  FIG. 3 shows the configuration of the data symbol transmission path estimator 252. In data symbol transmission path estimator 252, pilot symbol transmission path value determiner 252a determines whether or not pilot symbol transmission path values necessary for calculating a transmission path value of data symbols are available. The pilot symbol transmission line value and the determination result are output to pilot symbol transmission line value interpolator 252b (first transmission line estimation means).

  The pilot symbol transmission path value interpolator 252b is not actually received by interpolating the transmission path value of the pilot symbol determined to be insufficient using the transmission path value of the pilot symbol actually received. A virtual pilot symbol transmission line value (second transmission line value) is generated. The data symbol transmission line value calculator 252c (second transmission line estimation means) performs data symbol transmission line value (first transmission) by sampling interpolation using the actually received pilot symbol and virtual pilot symbol transmission line values. 3 transmission line value).

  Next, a method for interpolating pilot symbol transmission line values in the present embodiment will be described. As shown in FIG. 4A, for example, the transmission path value of the p-th pilot symbol that has not been actually received and that greatly contributes to the calculation result of the transmission path values of the n-2 and n-1 data symbols. Are interpolated from the transmission path values of other pilot symbols. FIG. 4A shows a state in which the transmission path value of the p-th pilot symbol is calculated by interpolation such as linear interpolation using the transmission path values of the p-2 and p-1 pilot symbols. The interpolation method of the transmission path value is not limited to this, and for example, the transmission path value of the p-1 pilot symbol may be used as the transmission path value of the pth pilot symbol.

  Also, as shown in FIG. 4B, for example, transmission of the first pilot symbol that is not actually received and that greatly contributes to the calculation result of the transmission path values of the first to third and fifth to seventh data symbols. The path value is interpolated from the transmission path values of other pilot symbols. FIG. 4B shows a state in which the transmission path value of the first pilot symbol is calculated by interpolation such as linear interpolation using the transmission path values of the 0 and 2 pilot symbols. The method for interpolating the transmission path value is not limited to this. For example, the transmission path value of the pilot symbol 0 or 2 may be used as the transmission path value of the first pilot symbol.

  FIG. 5 shows a specific procedure for interpolating pilot symbol transmission line values by the above method and estimating data symbol transmission line values by sampling interpolation. The pilot symbol transmission line value determining unit 252a determines, for each position of each data symbol, whether or not all transmission lines of pilot symbols necessary for estimating the transmission line value of the data symbol are obtained by sampling interpolation. Step S101). At the time of determination, whether or not at least the transmission path value of the latest pilot symbol that should exist on each of the high frequency side and the low frequency side is obtained at the position of the data symbol to be determined is a determination criterion. In the case of the n-2 and n-1 data symbols in FIG. 4A, the p-1 and p-1 pilot symbols are the most recent pilot symbols, and the 1-3 data symbols in FIG. 4B. In the case of, pilot symbols 0 and 1 are the latest pilot symbols.

  When all the necessary pilot symbol transmission line values are available, pilot symbol transmission line value interpolator 252b outputs the required pilot symbol transmission line value to data symbol transmission line value calculator 252c. The data symbol transmission path value calculator 252c calculates the transmission path value of the data symbol by sampling interpolation according to the above-described equation (1) (step S102).

  If the required pilot symbol transmission line values are not available, the pilot symbol transmission line value interpolator 252b interpolates the transmission line values based on the determination result of the pilot symbol transmission line value determiner 252a. Is selected (step S103). Subsequently, the pilot symbol transmission line value interpolator 252b calculates a virtual pilot symbol transmission line value by interpolation using the actually received pilot symbols, and all necessary for estimating the data symbol transmission line value. The pilot symbol transmission line value is output to the data symbol transmission line value calculator 252c (step S104). The data symbol transmission path value calculator 252c calculates the transmission path value of the data symbol by sampling interpolation according to the above-described equation (1) (step S102).

As described above, when communication using a very large number of subcarriers is performed, there is a problem in that the amount of calculation related to sampling interpolation increases significantly. Therefore, sampling interpolation according to equation (1) may be performed using only pilot symbol transmission line values that greatly contribute to estimation of data symbol transmission line values. The degree of contribution (influence degree) of the data symbol to the transmission line value estimation is represented by the value of the sinc function in equation (1). FIG. 6 shows the value of the sinc function at each frequency position. A curve 601 indicates the value of the sinc function at each frequency position by the pilot symbol p ₁ , a curve 602 indicates the value of the sinc function at each frequency position by the pilot symbol p ₂ , and a curve 603 indicates the pilot symbol p _3. shows the value of the sinc function at each frequency position according to the curve 604 represents the value of the sinc function at each frequency position by the pilot symbol p _4.

For example, paying attention to the data symbol 605, the degree of contribution of the pilot symbols p ₁ , p ₂ , p ₃ , and p _{4 to} the transmission line value of the data symbol 605 is K ₁ , K ₂ , K ₃ , and K ₄ , respectively. . Since | K ₁ | <| K ₄ | <| K ₂ | <| K ₃ |, the contributions of pilot symbols p ₂ and p ₃ are relatively large, and the contributions of pilot symbols p ₁ and p ₄ are relatively small. . Therefore, when sampling and interpolating the transmission line value of the data symbol 605 according to equation (1), for example, the terms relating to the pilot symbols p ₁ and p ₄ are omitted, and only the terms relating to the pilot symbols p ₂ and p ₃ are calculated. Good.

  In this embodiment, as shown in FIG. 7, among pilot symbol transmission line values (including transmission line values after interpolation), k pilots selected in order from the closest to the position of the data symbol whose transmission line value is estimated. The symbol transmission line value is used for sampling interpolation. When pilot symbols are arranged at equal intervals, it is possible to use at least the pilot symbols closest to the high frequency side and the pilot symbols closest to the low frequency side for sampling interpolation when viewed from the position of the data symbol for estimating the transmission path value. desirable. Also, in order to reduce the amount of calculation, it is desirable to use only a part of the transmission path values of all pilot symbols that have already been estimated for sampling interpolation. Therefore, k is preferably an integer of 2 or more and less than the total number of pilot symbol transmission path values already estimated. k may be a fixed value or variable depending on the frequency position of the data symbol.

  Further, instead of selecting the transmission path value of the pilot symbol based on the positional relationship between the pilot symbol and the data symbol as described above, k values whose sinc function value is equal to or greater than a predetermined value (the condition of k is the same as above) ) Pilot symbol transmission line values may be selected. Further, m (m is an integer from 2 to k) may be selected from the pilot symbol transmission line values having a sinc function value greater than or equal to a predetermined value, from the larger sinc function value.

  As described above, according to the present embodiment, the transmission path value at the position of the virtual pilot symbol is calculated using the transmission path value at the position in the frequency direction of the pilot symbol actually received, and the transmission is performed. Since the path value is used for sampling interpolation, the estimation accuracy of the transmission path can be improved and the error rate can be reduced. Also, by performing sampling interpolation using only some pilot symbols instead of using all pilot symbols required in equation (1), the amount of calculation related to sampling interpolation is reduced, and the apparatus is saved. Electric power and downsizing can be achieved.

  In addition, since the estimation accuracy of the transmission path can be improved compared to the conventional case, the number of pilot symbols in the frequency direction to be inserted in the subframe can be reduced if the estimation accuracy of the transmission path is comparable to the conventional case. In addition, the number of data frames can be increased correspondingly, so that the throughput can be improved. Furthermore, if it is only necessary to maintain the same estimation accuracy of the transmission path as in the prior art, the arrangement intervals in the frequency direction of the pilot symbols inserted into the subframes are made sparse, and the arrangement intervals in the time direction are made dense accordingly. Therefore, resistance to fluctuations in the transmission path in the time direction is improved, and it is possible to cope with high-speed movement.

  Next, a second embodiment of the present invention will be described. FIG. 8 shows the configuration of the data symbol transmission path estimator 252 according to this embodiment. In the present embodiment, the pilot symbol transmission line value interpolator 252b is removed and the data symbol transmission line value calculator 252d is compared with the data symbol transmission line estimator 252 (see FIG. 3) according to the first embodiment. Have been added. In the present embodiment, when pilot symbol transmission line values necessary for estimating the data symbol transmission line value are obtained by sampling interpolation, the data symbol transmission line value calculator 252c (first transmission line estimation) is obtained. Means) calculates a data symbol transmission line value (second transmission line value) by sampling interpolation using a pilot symbol transmission line value actually received.

  If the pilot symbol transmission line values necessary for estimating the data symbol transmission line values by sampling interpolation are not available, the data symbol transmission line value calculator 252d (second transmission line estimation means) Then, the data symbol transmission line value (third transmission line value) is calculated by another interpolation (linear interpolation) using the actually received pilot symbol transmission line value. That is, in this embodiment, the data symbol transmission line value at the position where the pilot symbol transmission line value necessary for sampling interpolation is obtained is calculated by the data symbol transmission line value calculator 252c, and the other positions are calculated. A data symbol transmission line value calculator 252d calculates the data symbol transmission line value in FIG.

  As shown in FIG. 9 (a), for example, the p-th pilot symbol that greatly contributes to the calculation result of the transmission path values of the n-2 and n-1 data symbols is not received. The transmission path value is interpolated from the transmission path values of other pilot symbols. In FIG. 9A, the transmission channel values of these data symbols are the same values as the transmission channel values of the p-1 pilot symbol at the position closest to each data symbol among the actually received pilot symbols. Is used. As described above, the pilot symbol closest to each data symbol contributes the most to the estimation result of the transmission path value of the data symbol, so out of the obtained transmission path values of the pilot symbol, It is desirable to use the transmission line value at the position of the pilot symbol closest to the position as the transmission line value of the data symbol.

  Further, as shown in FIG. 9 (b), for example, since the first pilot symbol that greatly contributes to the calculation result of the transmission path values of the first to third and fifth to seventh data symbols is not received, these data are not received. The symbol transmission line value is interpolated from the transmission line values of other pilot symbols. In FIG. 9B, the transmission line values of the first to third data symbols are the same as the transmission line values of the pilot symbol 0 of the closest position to each data symbol among the actually received pilot symbols. A value is used. Further, the transmission line value of the 5th to 7th data symbols is the same value as the transmission line value of the 2nd pilot symbol closest to each data symbol among the actually received pilot symbols.

  In FIG. 9A, the transmission path value of the data symbol is interpolated from the transmission path value of a single pilot symbol, but may be interpolated from the transmission path values of a plurality of pilot symbols. As shown in FIG. 10A, for example, the transmission path values of the n-2 and n-1 data symbols are the values of the pilot symbols of the p-2 and p-1 among the actually received pilot symbols. It is obtained by linear interpolation of the transmission line value. Also, as shown in FIG. 10B, for example, the transmission path values of the data symbols 1 to 3 and 5 to 7 are the transmission paths of the pilot symbols 0 and 2 among the pilot symbols actually received. It is obtained by linear interpolation of values.

  As described above, when the data symbol transmission line value is interpolated from k pilot symbol transmission line values (k is an integer of 2 or more), the pilot symbol transmission line value closest to the position of the estimation target data symbol It is desirable to use the pilot symbol transmission line values selected in the order close to the position of the estimation target data symbol for interpolation of the data symbol transmission line values.

  FIG. 11 shows a specific procedure for estimating the transmission path value of the data symbol by the above method. The pilot symbol transmission line value determining unit 252a determines, for each position of each data symbol, whether or not all transmission lines of pilot symbols necessary for estimating the transmission line value of the data symbol are obtained by sampling interpolation. Step S201). At the time of determination, whether or not at least the transmission path value of the latest pilot symbol that should exist on each of the high frequency side and the low frequency side is obtained at the position of the data symbol to be determined is a determination criterion. In the case of the n-2 and n-1 data symbols in FIGS. 9A and 10A, the p-1 and p-1 pilot symbols are the most recent pilot symbols, and FIG. 9B and FIG. In the case of 10 (b) data symbols 1-3 and 5-7, the pilot symbols 0 and 1 are the latest pilot symbols.

  When all the necessary pilot symbol transmission line values are available, pilot symbol transmission line value interpolator 252b outputs the required pilot symbol transmission line value to data symbol transmission line value calculator 252c. The data symbol transmission path value calculator 252c calculates the transmission path value of the data symbol by sampling interpolation according to the above-described equation (1) (step S202).

  Also, if the required pilot symbol transmission line values are not available, the data symbol transmission line value calculator 252d interpolates the data symbol transmission line values based on the determination result of the pilot symbol transmission line value determiner 252a. A pilot symbol to be used is selected (step S203). Subsequently, the data symbol transmission path value calculator 252d estimates the transmission path value of the data symbol by linear interpolation using one or more actually received pilot symbols (step S204).

  As described above, according to the present embodiment, with respect to the transmission line value at the position in the frequency direction of the data symbol, the transmission line value at a position other than the position where the transmission line value is calculated by sampling interpolation is actually received. Interpolated from the transmission path value at the position of the pilot symbol in the frequency direction. As a result, it is possible to improve the estimation accuracy of the transmission path and reduce the error rate, rather than performing sampling interpolation as it is when there is no pilot symbol necessary for sampling interpolation. Also in this embodiment, as in the first embodiment, sampling is not performed by performing sampling interpolation using only a part of pilot symbols instead of using all pilot symbols required in the equation (1). The amount of calculation related to interpolation may be reduced.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and includes design changes and the like without departing from the gist of the present invention. . For example, a program for realizing the operation and function of the transmission path estimator 25 according to the above-described embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read by the computer and executed. May be.

  Here, the “computer” includes a homepage providing environment (or display environment) if the WWW system is used. The “computer-readable recording medium” refers to a storage device such as a portable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a hard disk built in the computer. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program described above may be transmitted from a computer storing the program in a storage device or the like to another computer via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting a program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the above-described program may be for realizing a part of the above-described function. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer, what is called a difference file (difference program) may be sufficient.

It is a block diagram which shows the structure of the communication system by the 1st Embodiment of this invention. It is a block diagram which shows the structure of the transmission-line estimator by the 1st Embodiment of this invention. It is a block diagram which shows the structure of the data symbol transmission path estimator by the 1st Embodiment of this invention. FIG. 5 is a reference diagram for explaining a method of interpolating transmission line values at the frequency positions of pilot symbols in the first embodiment of the present invention. It is a flowchart which shows the procedure which estimates the transmission-line value in the frequency position of the data symbol in the 1st Embodiment of this invention. FIG. 5 is a reference diagram for explaining a method of reducing the amount of calculation related to sampling interpolation in the first embodiment of the present invention. FIG. 5 is a reference diagram for explaining a method of reducing the amount of calculation related to sampling interpolation in the first embodiment of the present invention. It is a block diagram which shows the structure of the data symbol transmission path estimator by the 2nd Embodiment of this invention. It is a reference figure for demonstrating the method of interpolating the transmission line value in the frequency position of the data symbol in the 2nd Embodiment of this invention. It is a reference figure for demonstrating the method of interpolating the transmission line value in the frequency position of the data symbol in the 2nd Embodiment of this invention. It is a flowchart which shows the procedure which estimates the transmission line value in the frequency position of the data symbol in the 2nd Embodiment of this invention. It is a reference figure which shows the transmission line fluctuation | variation by frequency selective fading. It is a reference drawing which shows the mode of arrangement | positioning of the pilot symbol within a sub-frame. It is a reference figure for demonstrating the problem concerning sampling interpolation.

Explanation of symbols

25 ... Transmission path estimator, 251 ... Pilot symbol transmission path value calculator, 252 ... Data symbol transmission path estimator, 252a ... Pilot symbol transmission path value determiner, 252b ... Pilot symbol Transmission path value interpolator, 252c, 252d ... data symbol transmission path value calculator

Claims (3)

A transmission path at the position in the frequency direction of the data symbol based on a transmission path characteristic at the position in the frequency direction of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction In a transmission path estimation device that estimates characteristics,
Using the first transmission path value indicating the transmission path characteristic at the position of the known symbol actually received, the second transmission path value indicating the transmission path characteristic at the position of the virtual known symbol. First transmission path estimation means for calculating
Of the first transmission line value and the second transmission line value, the transmission line at the position of the known symbol where the value of the sinc function indicating the degree of influence on the third transmission line value is a predetermined value or more. Second transmission path estimation means for calculating a third transmission path value indicating a transmission path characteristic at the position of the data symbol by sampling interpolation using a value;
A transmission path estimation apparatus comprising: A transmission path at the position in the frequency direction of the data symbol based on a transmission path characteristic at the position in the frequency direction of the known symbol obtained from the reception result of the known symbol arranged together with the data symbol in the frequency direction In a transmission path estimation program for causing a computer to execute processing for estimating characteristics,
Using the first transmission path value indicating the transmission path characteristic at the position of the known symbol actually received, the second transmission path value indicating the transmission path characteristic at the position of the virtual known symbol. A first process for calculating
Of the first transmission line value and the second transmission line value, the transmission line at the position of the known symbol where the value of the sinc function indicating the degree of influence on the third transmission line value is a predetermined value or more. A second process of calculating a third transmission line value indicating a transmission line characteristic at the position of the data symbol by sampling interpolation using the value;
A transmission path estimation program for causing a computer to execute.   A computer-readable recording medium on which the transmission path estimation program according to claim 2 is recorded.

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