JP2013223177A - Receiver unit, reception method and reception program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver unit, a reception method and a reception program, capable of highly accurate propagation path estimation.SOLUTION: A CIR estimation unit b105-2 calculates a CIR estimation value using a correlation value between a first CFR estimation value input from a first CIR estimation unit b105-1 and a path input from a correlation calculation unit b105-4. The CIR estimation unit b105-2 then outputs the calculated CIR estimation value to a convergence determination unit b105-3. The convergence determination unit b105-3 determines whether the CIR estimation value input from the CIR estimation unit b105-2 converges. On determination of convergence, the convergence determination unit b105-3 outputs the CIR estimation value to a second CFR estimation unit b105-5, whereas otherwise, outputs the CIR estimation value to the correlation calculation unit b105-4.

Description

  The present invention relates to a receiving apparatus, a receiving method, and a receiving program that perform channel estimation and calculate a frequency response of a propagation path for each subcarrier when demodulating a received signal such as an OFDM (Orthogonal Frequency Division Multiplexing) signal.

  In wireless communication, in particular, in the case of broadband transmission, in addition to the path received in advance, there are paths that arrive after a delay, such as through reflections from obstacles such as buildings and mountains. An environment in which the path of arriving is called multipath environment. In recent years, OFDM has attracted attention as a method for realizing high-speed and highly reliable transmission in such a multipath environment. Next-generation mobile communication systems such as LTE (Long Term Evolution) and LTE-A (LTE-Advanced), wireless It is used in various fields such as LAN and broadcasting. When the receiving apparatus demodulates the OFDM signal, it is necessary to perform channel estimation and calculate a channel frequency response (CFR) for each subcarrier. In order to realize this, there is a method in which the receiving apparatus transmits pilot symbols in which the waveform (or the signal sequence) is stored in advance from the transmitting apparatus to the receiving apparatus. Patent Document 1 describes a method for estimating a channel impulse response (CIR) which is a propagation path in a time domain. The method consists of a two-step process of determining a discrete path structure and CIR estimation using the extracted path structure. When this technique is used for OFDM, the estimated CIR is subjected to time-frequency conversion and converted to CFR before use.

Japanese translation of PCT publication No. 2002-527997

  However, since the actual propagation path is a continuous amount, the estimation accuracy decreases when a discrete path structure as in Patent Document 1 is used.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a receiving apparatus, a receiving method, and a receiving program capable of highly accurate propagation path estimation.

The present invention includes a channel impulse response estimation unit that calculates a channel impulse response estimation value based on a correlation between a frequency response estimation value and a path, a convergence determination unit that determines convergence of the channel impulse response estimation value, and the channel impulse response A correlation calculation unit that calculates the correlation of the path based on the estimated value,
The reception apparatus is characterized in that the channel impulse response estimation unit and the correlation calculation unit are repeatedly operated until the convergence determination unit determines convergence.

  In the receiving apparatus of the present invention, the channel impulse response estimation unit further calculates the channel impulse response estimated value by using an average value of channel impulse responses.

  In the reception apparatus of the present invention, the correlation calculation unit further calculates an average value of the channel impulse response based on the channel impulse response estimation value.

Further, the receiving apparatus of the present invention comprises a path extraction unit that extracts a path on which the channel impulse response estimation unit and the correlation calculation unit calculate using the frequency response estimation value,
The channel impulse response estimation unit and the correlation calculation unit perform a calculation process on the extracted path.

  In the receiving apparatus of the present invention, the path extraction unit calculates a temporary channel impulse response estimated value, and extracts a predetermined number of paths in descending order of the power of the paths constituting the temporary channel impulse response estimated value. It is characterized by.

Further, in the receiving apparatus of the present invention, the channel impulse response estimation unit and the correlation calculation unit calculate the channel impulse response estimation value and calculate the correlation by selecting a decision path to be calculated from candidate paths, To a plurality of path structures created by adding a channel path response, and a channel adaptation calculation unit for calculating a plurality of channel adaptations from the plurality of channel impulse response estimation values, and the channel adaptation cannot be improved An unnecessary candidate path removing unit that deletes a path from a candidate path, and an element of the candidate path used to create a path structure that maximizes the propagation path compatibility are selected as the determined path and added to the determined path A path determination unit,
The channel impulse response estimation value calculation, the propagation path fitness calculation, the candidate path element deletion, and the path determination are repeated until the number of candidate path elements becomes 0 or 1.

  Further, in the receiving apparatus of the present invention, the propagation path adaptability is calculated as an error evaluation value between the channel impulse response estimation value and the frequency response estimation value, and a penalty for increasing the number of paths in the path structure. It is characterized by using a sum.

  In the receiving apparatus of the present invention, the penalty is set to a value based on an Akaike information amount.

  In the receiving apparatus of the present invention, the penalty is set to a value based on a Bayes information amount.

  In the receiving apparatus of the present invention, in order to create the path structure, the number of elements of the candidate path added to the determined path is one.

  In the receiving apparatus of the present invention, the number of paths that the path determining unit moves from the candidate path to the determined path is one.

Further, the present invention provides a channel impulse response estimation process for calculating a channel impulse response estimation value based on a correlation between a frequency response estimation value and a path, a convergence determination process for determining convergence of the channel impulse response estimation value, and the channel A correlation calculation step of calculating a correlation of the path based on an impulse response estimation value,
The channel impulse response estimation process and the correlation calculation process are operated until the convergence determination unit determines convergence.

  Further, the present invention is a reception program for causing a computer to execute the reception method.

  According to the present invention, since the channel impulse response estimation unit and the correlation calculation unit are repeatedly operated until the convergence determination unit determines convergence, the channel estimation accuracy can be greatly improved.

It is a figure which shows the outline | summary of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows the structure of the transmitter which concerns on the 1st Embodiment of this invention. It is a figure which shows an example in which a mapping part maps. It is a figure which shows another example which a mapping part maps. It is a schematic block diagram which shows the structure of the receiver which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows the structure of the propagation path estimation part which concerns on the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the receiver which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows the structure of the receiver which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram which shows the structure of the propagation path estimation part which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the receiver which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram which shows the structure of the receiver which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram which shows the structure of the propagation path estimation part which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of the receiver which concerns on the 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a diagram showing an overview of a wireless communication system according to the first embodiment of the present invention.
The wireless communication system includes a transmission device a1 and a reception device b1. The transmission device a1 is, for example, a base station (sometimes referred to as a “base station device”) of a mobile communication system, and the reception device b1 is a terminal (“terminal device”, “mobile station”, or “ Mobile station apparatus ”).

  The transmission device a1 includes a transmission antenna a1-1, and the reception device b1 includes a reception antenna b1-1. The transmission device a1 and the reception device b1 may include a plurality of antennas. For example, the wireless communication system may perform MIMO (Multiple Input Multiple Output) communication.

  FIG. 2 is a schematic block diagram illustrating a configuration of the transmission device a1. In this figure, the transmission device a1 includes a pilot generation unit a101, a coding unit a102, a modulation unit a103, a mapping unit a104, an IFFT unit a105, a GI insertion unit a106, and a transmission unit a107. FIG. 2 also shows the transmission antenna a1-1. The transmission antenna a1-1 transmits an OFDM signal.

  The pilot generation unit a101 generates a pilot symbol in which the reception apparatus stores in advance the amplitude value of the waveform (or the signal sequence), and outputs the pilot symbol to the mapping unit a104. The receiving apparatus b1 performs propagation path estimation using the pilot symbol as a reference signal.

  The encoding unit a102 encodes information bits to be transmitted to the reception device b1 using an error correction code such as a convolutional code, a turbo code, and an LDPC (Low Density Parity Check) code, Is generated. The encoding unit a102 outputs the generated encoded bits to the modulating unit a103.

  The modulation unit a103 modulates the coded bits input from the coding unit a102 using a modulation scheme such as PSK (Phase Shift Keying) or QAM (Quadrature amplitude modulation), and modulates the modulation symbol. Generate. Modulation section a103 outputs the generated modulation symbol to mapping section a104.

  The mapping unit a104 maps the pilot symbol input from the pilot generation unit a101 and the modulation symbol input from the modulation unit a103 to a resource (time-frequency band) based on predetermined mapping information, and performs frequency domain And the generated frequency domain signal is output to the IFFT unit a105. Note that a resource is a unit in which a modulation symbol is arranged, which is composed of one subcarrier and one later-described FFT interval in a frame transmitted by the transmission apparatus a1. Also, the mapping information is determined by the transmission device a1, and is notified in advance from the transmission device a1 to the reception device b1.

  The IFFT unit a105 performs frequency-time conversion on the frequency domain signal input from the mapping unit a104, and generates a time domain signal. Here, a time interval of a unit for performing IFFT is referred to as an FFT interval. The IFFT unit a105 outputs the generated time domain signal to the GI insertion unit a106.

  The GI insertion unit a106 adds a guard interval (GI) for each signal in the FFT interval to the time domain signal input from the IFFT unit a105. Here, the guard interval is a known signal using a cyclic prefix (CP), which is a part of the rear of the signal in the FFT interval, zero padding in which the zero interval continues, a Golay code, or the like. Yes, the GI insertion unit a106 adds such a signal to the front of the signal in the FFT interval.

  The FFT interval and the time interval (referred to as GI interval) of the guard interval added to the signal in the time interval by the GI insertion unit a106 are collectively referred to as an OFDM symbol interval. A signal in the OFDM symbol section is called an OFDM symbol. The GI insertion unit a106 outputs a signal with the guard interval added to the transmission unit a107.

  A guard interval may be inserted behind the FFT interval. For example, when a cyclic prefix is used, a part of the replica in front of the FFT interval is added behind the signal in the FFT interval. In the case of a cyclic prefix, the periodicity may be maintained in the OFDM symbol period, and is not limited to the above.

  The transmission unit a107 performs digital / analog conversion on the signal input from the GI insertion unit a106, and shapes the waveform of the converted analog signal. The transmission unit a107 upconverts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna a1-1 to the reception device b1.

  FIG. 3 is an example in which the mapping unit a104 performs mapping, and shows an example of pilot arrangement in LTE. FIG. 4 is an example in which the mapping unit a104 performs mapping, and is an arrangement example in Japanese terrestrial digital television broadcasting.

  FIG. 5 is a schematic block diagram illustrating a configuration of the receiving device b1 according to the present embodiment. In this figure, the receiving device b1 includes a receiving unit b101, a GI removing unit b102, an FFT unit b103, a demapping unit b104, a propagation path estimating unit b105, a demodulating unit b106, and a decoding unit b107. FIG. 5 also shows the receiving antenna b1-1.

  The reception unit b101 receives the transmission signal transmitted by the transmission device a1 via the reception antenna b1-1. The receiving unit b101 performs frequency conversion and analog-digital conversion on the received signal.

  The GI removal unit b102 removes the guard interval from the reception signal input from the reception unit b101, and outputs the guard interval to the FFT unit b103.

  The FFT unit b103 performs time-frequency conversion on the time-domain signal input from the GI removal unit b102, and outputs the converted frequency-domain signal to the demapping unit b104.

  The demapping unit b104 performs demapping based on the mapping information notified in advance from the transmission device a1, and outputs the received signal of the resource element to which the separated pilot symbol is transmitted to the propagation path estimation unit b105. Further, the reception signal of the resource element to which the data is transmitted is output to the demodulation unit b106.

  The propagation channel estimation unit b105 performs propagation channel estimation using the received signal of the resource element to which the pilot symbol input from the demapping unit b104 is transmitted, and is a first frequency response (CFR) for demodulation. 2 CFR estimate is calculated. The propagation path estimation unit b105 outputs the calculated second CFR estimation value to the demodulation unit b106. This operation will be described later with reference to FIG.

  The demodulation unit b106 calculates filter coefficients such as a ZF (Zero Forcing) standard and an MMSE (Minimum Mean Square Error) standard using the second frequency response estimation value input from the propagation path estimation unit b105. The demodulator b106 compensates for variations in the amplitude and phase of the signal (referred to as propagation path compensation) using the calculated filter coefficient.

  The demodulation unit b106 outputs a bit log likelihood ratio (LLR) as a result of the demodulation process to the decoding unit b107.

  The decoding unit b107 performs, for example, maximum likelihood decoding (MLD), maximum a posteriori probability (MAP), log-MAP, Max- on the demodulated symbols input from the demodulation unit b106. Decoding processing is performed using log-MAP, SOVA (Soft Output Viterbi Algorithm), or the like.

  FIG. 6 is a schematic block diagram illustrating a configuration of the propagation path estimation unit b105. In this figure, a propagation path estimation unit b105 includes a first CFR estimation unit b105-1, a CIR (Channel Impulse Response) estimation unit b105-2, a convergence determination unit b105-3, and a correlation calculation unit b105-4. And a second CFR estimator b105-5.

The propagation path estimation unit b105 repeats the calculation of the CIR estimated value and the correlation value.
First CFR estimator b105-1 calculates a first CFR estimate using the received signal of the resource element to which the pilot symbol is transmitted, which is input from demapping unit b104. The first CFR estimator b105-1 outputs the first CFR estimated value to the CIR estimator b105-2.

  The CIR estimation unit b105-2 uses the first CFR estimation value input from the first CFR estimation unit b105-1 and the correlation value between the paths input from the correlation calculation unit b105-4, to provide a CIR estimation value. Is calculated. However, since the correlation value is not calculated in the first process, it may be set to 0, for example. This will be described in detail later together with the operating principle. The CIR estimation unit b105-2 outputs the calculated CIR estimation value to the convergence determination unit b105-3.

  The convergence determination unit b105-3 determines whether the CIR estimation value input from the CIR estimation unit b105-2 has converged. Specifically, if the difference between the input CIR estimated value and the CIR estimated value in the previous iteration is considered, and if the magnitude of the difference falls below a predetermined threshold, it is determined that the convergence has occurred. Good. Alternatively, the number of repetitions may be determined in advance without using the CIR estimated value, and it may be determined that the convergence has been achieved when the number of repetitions has been performed. The predetermined threshold value and the predetermined number of repetitions may be fixed at the design stage of the receiving device b1, or may be updated when updating the firmware or software of the receiving device b1.

  The convergence determination unit b105-3 outputs the CIR estimation value to the second CFR estimation unit b105-5 when determining that the convergence has occurred, and otherwise outputs the CIR estimation value to the correlation calculation unit b105-4. .

  The correlation calculation unit b105-4 calculates a correlation value between the paths using the CIR estimation value input from the convergence determination unit b105-3. The estimated correlation value is output to the CIR estimation unit b105-2.

  The second CFR estimation unit b105-5 performs time-frequency conversion on the CIR estimation value input from the convergence determination unit b105-3, and converts it to a second CFR estimation value. The second CFR estimated value is output to demodulation section b106.

<About the operating principle>
Hereinafter, the operating principle of the receiving device b1 will be described with reference to FIG.

The received signal R _{i, n} of the i-th symbol n-th subcarrier, which is obtained by receiving by the receiving unit b101, removing the GI by the GI removing unit b102, and performing the FFT by the FFT unit b103, is _expressed by the following equation (1). expressed.

Here, S _{i, n} is the transmission signal of the i-th symbol n-th subcarrier, and Z _{i, n} is the noise of the i-th symbol n-th subcarrier. H _n is the CFR of the n-th subcarrier and can be expressed by the following formula (2).

Here, h (tau) represents the complex amplitude of tau delay, delta _f represents a sub-carrier interval. _TD is the maximum delay time. However, it is assumed that the propagation path is unchanged during communication from the transmission device a1 to the reception device b1.

In the propagation path estimation unit b105, although the estimate of H _n H '' _n calculated in is performed, which will be described later. Here, the remaining functions of the receiving device b1 will be described assuming that an estimated value is obtained.
For example, when the MMSE standard filtering is used, the demodulator b106 calculates the demodulated symbol S ′ _{i, n} using the following equation (3).

Here, Y ^* indicates a complex conjugate of Y. In Equation (3), σ _z ² is an estimated value of the power of Z _{i, n} . The sigma _z ² can be S _i obtained by using the decoding _{result, n} replicas S '' _i, with _n, is calculated as the following formula (4).

Here, N is the number of FFT points. However, if only some of the N frequency positions are used as subcarriers, the number of subcarriers to be averaged is adjusted as appropriate. This processing may be performed on the OFDM symbol that has been decoded. Further, as S ″ _{i, n} , a soft replica created using the output result of the decoding unit b107 may be used, or a hard replica obtained by hard decision thereof may be used. Further, in the case of corresponding to the pilot symbol, the pilot symbol may be used as it is.

The demodulator b106 calculates a bit log likelihood ratio from the demodulated symbol S ′ _{i, n} in Expression (3). An equivalent amplitude gain is used for this calculation process. Specifically, in the case of QPSK, the bit log likelihood ratio λ is expressed by the following equations (6) and (7) with respect to the equivalent amplitude gain μ _n of the n-th subcarrier expressed by the following equation (5). It is. Here, the equations (6) and (7) are respectively _{expressed by} bit log likelihood ratios λ (b _{i, n} ) of the first bit bits b _{i, n, 0} and the second bit bits b _{i, n, 1. , 0} ), λ (b _{i, n, 1} ).

Next, the operation of channel estimation will be described with reference to FIG.
The first CFR estimator b105-1 calculates a first CFR estimated value H ′ _n based on the equation (1). Specifically, it is estimated as the following equation (8).

In order to do this, the signal S _{i, n} of the nth subcarrier needs to be known, but a pilot symbol or the like may be used. In addition, when two pilot symbols are inserted in the same pilot subcarrier as shown in FIG. 3, the CFR estimation values estimated for each OFDM symbol may be averaged before use.

Next, a method for estimating CIR from H ′ _n in CIR estimation section b 105-2 will be described. First, it is assumed that h (tau) is be sampled at τ = dΔ _t. However, Δ _t = 1 / (NΔ _f ). In this case, the complex amplitude h _d of the d path sampled is expressed by the following equation (9).

At this time, the expression (2) is rewritten as the following expression (10).

Here, D = T _D / _Δt , where D represents the maximum sampled delay time.

_Then, n _1, n 2, · · ·, a _{n P} a pilot subcarrier, are defined as the following equation (11) a frequency response estimate vector _{H P.}

However, bold represents a vector or matrix, and Y ^T represents the transpose of Y. For example, considering FIG. 3, n ₁ is the lowest subcarrier, n ₂ is three subcarriers ahead, n ₃ is three further subcarriers, and so on. At this time, the CIR estimation vector h _{MMSE by MMSE} is expressed by the following equations (12) to (14).

Where F is a P × L Fourier transform matrix, _Ch is an L × L correlation matrix, μ is a CIR average vector σ ′ _z ² is noise power on H ′ _n . L is the maximum delay time assumed by the receiving apparatus b1, and is set to a large value so that L ≧ D. This value may be fixed at the design stage of the receiving device b1, or may be updated when the firmware or software of the receiving device b1 is updated. E [x] represents an ensemble average of x.

For example, Patent Document 1, although the non-diagonal elements of C _h is treated as 0, the place where actual channel is represented by formula (2), since the model by the equation (10) If not set to 0, propagation path estimation accuracy can be improved.

However, since the average correlation value in the process for the first time it is not known, following equation μ and C _h (15), the calculation of Equation (12) as (16).

  However, α is a hyper parameter, and a small value such as 0.5 or 0.25 may be set. This value may be fixed at the design stage of the receiving device b1, or may be updated when the firmware or software of the receiving device b1 is updated.

Then, the correlation calculating unit b105-4 uses the CIR estimate of equation (12), the following equation (17), calculates the to μ and _{C h} as (18).

  However, β is a hyper parameter and may be set to a value larger than 0 such as 1 or 2. Further, ν is a hyper parameter, and may be set to a small value of 0 or more such as 0 or 1. β and ν may be fixed at the design stage of the receiving device b1, or may be updated when the firmware or software of the receiving device b1 is updated.

  The CIR estimation unit b105-2 calculates a CIR estimation value in the next iterative process using the average and correlation matrix obtained by the equations (17) and (18).

  It is not necessary to calculate the average. This corresponds to a case where β is increased infinitely. In this case, the term of μ disappears from the equation (12), and the term of β / (β + 1) in the equation (18) is changed to 1.

  The second CFR estimator b105-5 calculates a second CFR estimated value as in the following equations (19) and (20).

<Operation of Receiving Device b1>
FIG. 7 is a flowchart showing the operation of the receiving apparatus according to this embodiment. The operation shown in this figure is processing after the receiving unit b101 in FIG. 5 outputs the received signal to the GI removing unit b102.

  (Step S101) The GI removal unit b102 removes the guard interval from the received signal. Then, it progresses to step S102.

  (Step S102) The FFT unit b103 performs time-frequency conversion on the signal obtained in step S101. The demapping unit b104 separates data and pilot from the obtained frequency domain signal. After the reception signal of the pilot subcarrier is output to the first CFR estimation unit b105-1 of the propagation path estimation unit b105, the process proceeds to step S103.

  (Step S103) The first CFR estimator b 105-1 calculates a first CFR estimated value using the received signal of the pilot subcarrier obtained in step S102. Thereafter, the process proceeds to step S104.

  (Step S104) The CIR estimation unit b 105-2 calculates a CIR estimated value using the first CFR estimated value obtained in step S103 and the correlation value obtained in step S106. Thereafter, the process proceeds to step S105.

  (Step S105) The convergence determination unit b105-3 determines whether or not the convergence is made from the CIR estimated value obtained in Step S104. If it is determined that it has not converged, the process proceeds to step S106. If not, the process proceeds to step S107.

  (Step S106) The correlation calculation unit b105-4 calculates the power of each path and the correlation between the paths using the CIR estimation value obtained in Step S104. Thereafter, the process returns to step S104.

  (Step S107) The second CFR estimator b105-5 performs time-frequency conversion on the CIR estimated value obtained in Step S104 and converts it to a second CFR estimated value. Thereafter, the process proceeds to step S108.

  (Step S108) The demodulation unit b106 performs a demodulation process using the second CFR estimated value obtained in Step S107. Thereafter, the process proceeds to step S109.

  (Step S109) The decoding unit b107 performs decoding using the demodulation result obtained in step S108. Thereafter, the receiving device b1 ends the operation.

  Thus, according to this embodiment, the propagation path estimation part b105 can improve a propagation path estimation precision significantly by repeating CIR estimation and correlation calculation.

  In the first embodiment, the case where the frequency response is estimated using a pilot symbol for each OFDM symbol has been described. However, interpolation may be performed using pilot symbols of neighboring OFDM symbols. For example, in the first OFDM symbol of FIG. 3, the pilot subcarriers are every six from the subcarrier with the lowest frequency, but the locations other than the pilot subcarriers are estimated using the pilot symbols of the OFDM symbols having different times. May be. Also, with respect to subcarriers with pilot symbols, noise and interference may be reduced by using pilot symbols at different times.

  In the first embodiment, a case has been described in which pilot symbols are used as reference signals used for frequency response estimation. However, estimation may be performed using determined data. Specifically, it can be realized by feeding back the output of the demodulator b106 or the decoder b107 to the first CFR estimator b105-1.

  In the first embodiment, the communication system performs communication of multicarrier signals such as OFDM. However, the present invention is not limited to this, and communication of single carrier signals using FFT is performed. Can also be applied.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment, the receiving device b1 repeats the calculation of the CIR estimation value and the correlation calculation to improve the accuracy of the CIR estimation value. In the present embodiment, a method for reducing the amount of calculation by limiting the paths for calculating the CIR estimated value and calculating the correlation will be described.
The transmission apparatus according to the present embodiment has the same configuration as the transmission apparatus a1 (FIG. 2) according to the first embodiment, and thus description thereof is omitted.

  FIG. 8 is a schematic block diagram showing the configuration of the receiving device b2 according to the second embodiment of the present invention. When the receiving apparatus b2 (FIG. 8) according to the present embodiment is compared with the receiving apparatus b1 (FIG. 5) according to the first embodiment, the propagation path estimation unit b205 is different. However, the functions of other components (receiving unit b101, GI removing unit b102, FFT unit b103, demapping unit b104, demodulating unit b106, decoding unit b107) are the same as those in the first embodiment. A description of the same functions as those in the first embodiment is omitted.

  FIG. 9 is a schematic block diagram showing the configuration of the propagation path estimation unit b205. Comparing the propagation path estimation unit b205 (FIG. 9) and the propagation path estimation unit b105 (FIG. 6), the CIR estimation unit b205-2 and the correlation calculation unit b205-4 are different, and a path extraction unit b205-6 is newly provided. . However, the functions of other components (first CFR estimation unit b105-1, convergence determination unit b105-3, and second CFR estimation unit b105-5) are the same as those of the propagation path estimation unit b105. A description of the same functions as those in the first embodiment is omitted.

  In the second embodiment, the first CFR estimation value output from the first CFR estimation unit b105-1 is also input to the path extraction unit b205-6.

The path extraction unit b205-6 performs path extraction using the first CFR estimation value input from the first CFR estimation unit b105-1. Specifically, for example, among temporary CIR estimated values obtained by performing frequency-time conversion on the first CFR estimated value, a predetermined time is determined in descending order of power from the delay time 0 path to the delay time L path. Extract the number of paths. If this number is N _s , N _s may be, for example, the number of points that is half the GI length. N _s may be fixed at the design stage of the receiving device b2, or may be updated when firmware or software of the receiving device b2 is updated.

The path extraction unit b205-6 outputs the extracted path numbers k ₁ , k ₂ ,..., K _Ns to the CIR estimation unit b 205-2.
The CIR estimation unit b205-2 calculates a CIR estimation value using the first CFR estimation value input from the first CFR estimation unit b105-1 and the path information input from the path extraction unit b205-6. . Specifically, the Fourier transform matrix represented by the equation (13) is corrected as the following equation (21).

Here, Φ is a symbol representing the extracted pass number. By using this, the CIR estimation vector of Expression (13) is calculated. At that time, mu and _{C h} are fixed in a matrix of vectors and _{N s} × _{N s} size _{N s.}

Correlation calculating unit b205-4 performs calculation of μ and _{C h.} Equation (17) is used as it is for the μ update equation, and Equation (18) is used as the _Ch update equation after changing I _{L + 1} in the equation to I _Ns .
In addition, when the second CFR estimation value is calculated by the second CFR estimation unit b105-5, the Fourier transform matrix expressed by the equation (20) is changed to the following equation (22).

<Operation of Receiving Device b2>
FIG. 10 is a flowchart showing the operation of the receiving apparatus according to this embodiment. The operation shown in this figure is processing after the reception unit b101 in FIG. 8 outputs the reception signal to the GI removal unit b102.

  (Step S201) The GI removal unit b102 removes the guard interval from the received signal. Thereafter, the process proceeds to step S202.

  (Step S202) The FFT unit b103 performs time-frequency conversion on the signal obtained in step S201. The demapping unit b104 separates data and pilot from the obtained frequency domain signal. After the received signal of the pilot subcarrier is output to the first CFR estimator b105-1 of the propagation path estimator b205, the process proceeds to step S203.

  (Step S203) The first CFR estimator b105-1 calculates a first CFR estimated value using the received signal of the pilot subcarrier obtained in step S202. Thereafter, the process proceeds to step S204.

  (Step S204) The path extraction unit b205-6 performs path extraction using the first CFR estimation value obtained in step S203, and creates path information. Thereafter, the process proceeds to step S205.

  (Step S205) The CIR estimation unit b 205-2 calculates a CIR estimation value using the first CFR estimation value obtained in step S203, the path information obtained in step S204, and the correlation value obtained in step S207. . Thereafter, the process proceeds to step S206.

  (Step S206) The convergence determining unit b105-3 determines whether or not the convergence is made from the CIR estimated value obtained in Step S205. If it is determined that it has not converged, the process proceeds to step S207. If not, the process proceeds to step S208.

  (Step S207) The correlation calculation unit b205-4 calculates the power of each path and the correlation between the paths by using the path information obtained in Step S204 and the CIR estimation value obtained in Step S205. Thereafter, the process returns to step S205.

  (Step S208) The second CFR estimator b105-5 performs time-frequency conversion on the CIR estimated value obtained in Step S205, and converts it into a second CFR estimated value. Thereafter, the process proceeds to step S209.

  (Step S209) The demodulation unit b106 performs a demodulation process using the second CFR estimation value obtained in Step S208. Thereafter, the process proceeds to step S210.

  (Step S210) The decoding unit b107 performs decoding using the demodulation result obtained in step S209. Thereafter, the receiving device b2 ends the operation.

  Thus, according to the present embodiment, the path extraction unit b205-6 performs path extraction and reduces the number of paths for performing CIR estimation and correlation calculation, so that the amount of calculation can be greatly reduced.

(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in detail with reference to the drawings. In the second embodiment, in order to reduce the calculation amount, the number of paths to be estimated is reduced. In the present embodiment, a method for performing propagation path estimation while selecting estimation paths in order of importance in order to improve estimation accuracy, not reduction in calculation amount, will be described.

  Since the transmission apparatus according to the present embodiment has the same configuration as the transmission apparatus a1 (FIG. 2) according to the first embodiment, a description thereof will be omitted.

  FIG. 11 is a schematic block diagram illustrating a configuration of a reception device b3 according to the third embodiment of the present invention. When the receiving apparatus b3 (FIG. 11) according to the present embodiment is compared with the receiving apparatus b1 (FIG. 5) according to the first embodiment, the propagation path estimation unit b305 is different. However, the functions of other components (receiving unit b101, GI removing unit b102, FFT unit b103, demapping unit b104, demodulating unit b106, decoding unit b107) are the same as those in the first embodiment. A description of the same functions as those in the first embodiment is omitted.

  FIG. 12 is a schematic block diagram illustrating the configuration of the propagation path estimation unit b305. When the propagation path estimation unit b305 (FIG. 12) and the propagation path estimation unit b105 (FIG. 6) are compared, the CIR estimation unit b305-2, the convergence determination unit b305-3, and the correlation calculation unit b305-4 are different. A degree calculation unit b305-7, an unnecessary candidate path removal unit b305-8, an end determination unit b305-9, and a path determination unit b305-10. However, the functions of the other components (the first CFR estimation unit b105-1 and the second CFR estimation unit b105-5) are the same as those of the propagation path estimation unit b105. A description of the same functions as those in the first embodiment is omitted.

In the first embodiment, the propagation path estimation unit b105 repeats CIR estimation and correlation calculation for paths with path numbers 0 to L. In the second embodiment, the propagation path estimation unit b205 repeats CIR estimation and correlation calculation after reducing the number of paths to be estimated to N _s among the path numbers 0 to L. In the present embodiment, the propagation path estimation unit b305 uses path numbers 0 to L as candidate paths, and selects one path at a time from paths of high importance. Specifically, it has an internal memory for storing the decision path and the candidate path, and elements of the selected candidate path are added to the decision path.

  The CIR estimation unit b305-2 adds one of the paths stored in the candidate path to the decision path, and the CFR estimation value input from the first CFR estimation unit b105-1 for the path structure The CIR estimated value is calculated using the correlation value input from the correlation calculating unit b305-4. For example, when the determined path is (0, 2) and the candidate path is (1, 3, 4, 5), (0, 1, 2), (0, 2, 3), (0, 2 4), CIR estimation values are calculated for four path structures (0, 2, 5). Thereafter, the CIR estimating unit b305-2 outputs all the calculated CIR estimated values to the convergence determining unit b305-3.

  The convergence determination unit b305-3 determines whether each CIR estimation value input from the CIR estimation unit b305-2 has converged. For the determination, the same method as the convergence determination unit b105-3 of the first embodiment may be used. The convergence determination unit b305-3 outputs each CIR estimation value to the propagation path fitness calculation unit b305-7 when it is determined that all the CIR estimation values have converged. Otherwise, the CIR estimation value is output. It outputs to correlation calculation part b305-4. However, for the path structure determined to have converged, subsequent correlation calculation and CIR estimation processing may be omitted.

  The correlation calculation unit b305-4 calculates a correlation value between paths using each CIR estimation value input from the convergence determination unit b305-3. The estimated correlation value is output to the CIR estimation unit b305-2.

The propagation path adaptability calculation unit b305-7 calculates the propagation path adaptability of each path structure using the CIR estimation value input from the convergence determination unit b305-3. Here, the propagation path adaptability is an amount that quantitatively represents the adaptability between the calculated CIR estimated value and the first CFR estimated value, and specifically, an error between the CIR estimated value and the first CFR estimated value. And the sum of the penalties for the number of paths of the path structure used to calculate the CIR estimation value. Specifically, if the CIR estimated value for a certain path structure Φ is h _Φ , the channel match b (Φ) is expressed by the following equation (23).

  However, | Φ | is the number of paths of the path structure Φ. For example, the above (0, 1, 2), (0, 2, 3), (0, 2, 4), (0, 2, 5) The case is 3. The propagation path adaptability calculation unit b305-7 outputs the propagation path adaptability calculated for all the CIR estimation values to the unnecessary candidate path removal unit b305-8. Note that x is a parameter that determines the size of the penalty, and the larger the number, the smaller the number of final selected paths. Specifically, 2 or log (P) may be used. In addition, the propagation path adaptability when it is set to 2 is called the Akaike information criterion, and the propagation match when log (P) is sometimes called the Bayes information criterion.

  The unnecessary candidate path removing unit b305-8 compares each channel matching level input from the channel matching level calculating unit b305-7 with the channel matching level stored in the previous iteration, and compares the channel matching level stored in the previous iteration. Candidate paths corresponding to propagation path suitability lower than the repeated propagation path suitability are deleted. Also, the corresponding CIR estimated value is discarded. For example, out of the previous (0, 1, 2), (0, 2, 3), (0, 2, 4), (0, 2, 5), (0, 2, 5) propagation path adaptability Is less than the previous repetitive propagation path fitness, the path number 5 is deleted from the candidate path. That is, the candidate path is changed to (1, 3, 4). Thereafter, the unnecessary candidate path removing unit b305-8 outputs the remaining channel IR estimated value and the corresponding channel matching degree to the termination determining unit b305-9.

  When the remaining candidate paths are 0, the end determination unit b305-9 outputs the CIR estimation value in the previous iteration to the second CFR estimation unit b105-5, and ends the iterative process. If the remaining candidate path is 1, the CIR estimation value input from the unnecessary candidate path removal unit b305-8 is output to the second CFR estimation unit b105-5, and the iterative process ends. In other cases, the CIR estimation value and the channel matching degree are output to the path determination unit b305-10.

  The path determination unit b305-10 selects the maximum one of the propagation path matching degrees input from the end determination unit b305-9, and selects the corresponding path. The path number is moved from the candidate path to the determined path. For example, if (0, 1, 2) of (0, 1, 2), (0, 2, 3), (0, 2, 4) has the highest propagation path adaptability, the path number 1 is moved from the candidate path to the decision path. As a result, the determined path is (0, 1, 2), and the candidate path is (3, 4).

<About the operation of the receiving device b3>
FIG. 13 is a flowchart showing the operation of the receiving apparatus according to this embodiment. The operation shown in this figure is processing after the reception unit b101 in FIG. 11 outputs the reception signal to the GI removal unit b102.

  (Step S301) The GI removal unit b102 removes the guard interval from the received signal. Thereafter, the process proceeds to step S302.

  (Step S302) The FFT unit b103 performs time-frequency conversion on the signal obtained in step S301. The demapping unit b104 separates data and pilot from the obtained frequency domain signal. After outputting the received signal of the pilot subcarrier to the first CFR estimator b105-1 of the propagation path estimator b305, the process proceeds to step S303.

  (Step S303) The first CFR estimator b105-1 calculates a first CFR estimated value using the received signal of the pilot subcarrier obtained in step S302. Thereafter, the process proceeds to step S304.

  (Step S304) The CIR estimation unit b305-2 has a path structure in which one candidate path element obtained in Step S310 is added to the first CFR estimation value obtained in Step S303 and the decision path obtained in Step S310. Is used to calculate the CIR estimated value. Thereafter, the process proceeds to step S305.

  (Step S305) The convergence determination unit b305-3 determines whether or not the CIR estimated value obtained in Step S304 has converged. If it cannot be determined that all CIR estimation values have converged, the process proceeds to step S306. If not, the process proceeds to step S307.

  (Step S306) The correlation calculation unit b305-4 calculates the power of each path and the correlation between the paths using the CIR estimation value in Step S304. Thereafter, the process returns to step S304.

  (Step S307) The propagation path adaptability calculation unit b305-7 calculates the propagation path adaptability using the CIR estimation value obtained in step S304. Thereafter, the process proceeds to step S308.

  (Step S308) The unnecessary candidate path removing unit b305-8 detects a channel path matching degree obtained in step S307 that is lower than the channel path matching degree in the previous iteration, and the candidate path corresponding to that is detected. Remove elements from the candidate path. Thereafter, the process proceeds to step S309.

  (Step S309) If the result of step S308 is that the remaining number of candidate paths is 0, the end determination unit b305-9 sets the CIR estimated value in the previous iteration as 1; if it is 1, the CIR obtained in step S304 The estimated value is output and the process proceeds to step S311. Otherwise, the process proceeds to step S310.

  (Step S310) As a result of Step S308, the path determination unit b305-10 selects the maximum one of the propagation path matching degrees corresponding to the remaining candidate paths. The candidate path element corresponding to the selected propagation path fitness is moved from the candidate path to the decision path. Thereafter, the process returns to step S304.

  (Step S311) The second CFR estimator b105-5 performs time-frequency conversion on the CIR estimated value obtained in step S309, and converts it to a second CFR estimated value. Thereafter, the process proceeds to step S312.

  (Step S312) The demodulator b106 performs a demodulation process using the second CFR estimation value obtained in step S311. Thereafter, the process proceeds to step S313.

  (Step S313) The decoding unit b107 performs decoding using the demodulation result obtained in step S312. Thereafter, the receiving device b3 ends the operation.

  As described above, according to the present embodiment, the propagation path estimation unit b305 selects a path in the order of improving the propagation path adaptability, and improves the propagation path estimation accuracy by performing estimation only on the selected path. Can do. In addition, the amount of calculation can be reduced by deleting a path that cannot improve the channel matching degree.

  In the third embodiment, the case where the path determination unit b305-10 determines one path at a time has been described. However, the number of paths determined at one time may be more than 1, for example, 2 or 3 Good.

  In the third embodiment, the CIR estimation unit b 305-2 has been described for adding one candidate path element to the determined path, but the number of paths to be added may be increased. For example, when the previously determined path is (0, 2) and the candidate path is (1, 3, 4, 5), two are added, and the CIR estimated value calculated by the CIR estimating unit b 305-2 is , (0, 1, 2, 3), (0, 2, 4, 5).

  In the third embodiment, the case where the processing is performed for the pass numbers 0 to L has been described. However, the processing may be performed after the number of paths is reduced in advance using the method of the second embodiment.

  Note that part of the transmission device a1 and the reception devices b1 to b3, for example, the propagation path estimation unit b105 and the demodulation unit b106 in the above-described embodiment may be realized by a computer. In that case, the program for realizing the control function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by a computer system and executed.

  Here, the “computer system” is a computer system built in the transmission device a1 or the reception devices b1 to b3, and includes an OS and hardware such as peripheral devices. Further, 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 system. Furthermore, the “computer-readable recording medium” is a medium that dynamically holds a program for a short time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, In such a case, a volatile memory inside a computer system serving as a server or a client may be included and a program that holds a program for a certain period of time. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  Further, part or all of the transmission device a1 and the reception devices b1 to b3 in the above-described embodiment may be realized as an integrated circuit such as an LSI (Large Scale Integration). Each functional block of the transmission device a1 and the reception devices b1 to b3 may be individually made into a processor, or a part or all of them may be integrated into a processor. Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. Further, in the case where an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology may be used.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

a1 Transmitting device a1-1 Transmitting antenna a101 Pilot generating unit a102 Encoding unit a103 Modulating unit a104 Mapping unit a105 IFFT unit a106 GI inserting unit a107 Transmitting signal units b1 to b3 Receiving device b1-1 Receiving antenna b101 Receiving unit b102 GI removing unit b103 FFT unit b104 Demapping unit b105 Propagation path estimation unit b105-1 First CFR estimation unit b105-2 CIR estimation unit b105-3 Convergence determination unit b105-4 Correlation calculation unit b105-5 Second CFR estimation unit b205 Propagation path Estimator b205-2 CIR estimator b205-4 Correlation calculator b205-6 Path extractor b305 Propagation path estimator b305-2 CIR estimator b305-3 Convergence determining part b305-4 Correlation calculator b305-7 Propagation degree of channel Calculation unit b305-8 Unnecessary candidate path removal Part b305-9 end determination part b305-10 path determination part

Claims (13)

A channel impulse response estimator that calculates a channel impulse response estimate based on the correlation between the frequency response estimate and the path;
A convergence determining unit that determines convergence of the channel impulse response estimation value;
A correlation calculation unit for calculating the correlation of the path based on the channel impulse response estimation value;
With
The receiving apparatus, wherein the channel impulse response estimation unit and the correlation calculation unit are repeatedly operated until the convergence determination unit determines convergence.   The receiving apparatus according to claim 1, wherein the channel impulse response estimation unit further calculates the channel impulse response estimation value by using an average value of the channel impulse response.   The receiving apparatus according to claim 2, wherein the correlation calculation unit further calculates an average value of the channel impulse response based on the channel impulse response estimation value. Using the frequency response estimation value, the channel impulse response estimation unit and a path extraction unit for extracting a path to be calculated by the correlation calculation unit,
The receiving apparatus according to claim 1, wherein the channel impulse response estimation unit and the correlation calculation unit perform calculation processing on the extracted path.   The path extraction unit calculates a temporary channel impulse response estimated value, and extracts a predetermined number of paths in descending order of power of the paths constituting the temporary channel impulse response estimated value. Receiver. The channel impulse response estimation unit and the correlation calculation unit are generated by calculating a channel impulse response estimation value and calculating a correlation by selecting a decision path to be calculated from candidate paths and adding the elements thereof. For the path structure of
further,
A channel adaptation calculation unit that calculates a plurality of channel adaptations from the plurality of channel impulse response estimation values;
An unnecessary candidate path removing unit that deletes a path that cannot improve the channel adaptation from a candidate path;
A path determination unit that selects an element of the candidate path used to create a path structure that maximizes the propagation path fitness as the determined path, and adds the determined path to the determined path;
With
The channel impulse response estimation value calculation, the propagation path fitness calculation, the candidate path element deletion, and the path determination are repeated until the number of candidate path elements becomes 0 or 1. Item 6. The receiving device according to any one of Items 1 to 5.   The propagation path adaptability uses a sum of an error evaluation value between the channel impulse response estimation value and the frequency response estimation value, and a penalty for increasing the number of paths in the path structure. Item 7. The receiving device according to Item 6.   The receiving apparatus according to claim 7, wherein the penalty is set to a value based on an Akaike information amount.   The receiving apparatus according to claim 7, wherein the penalty is set to a value based on a Bayes information amount.   10. The receiving apparatus according to claim 6, wherein the number of elements of the candidate path added to the determined path in order to create the path structure is one.   The receiving apparatus according to claim 6, wherein the number of paths that the path determination unit moves from the candidate path to the determined path is one. A channel impulse response estimation process for calculating a channel impulse response estimate based on the correlation between the frequency response estimate and the path;
A convergence determination process for determining convergence of the channel impulse response estimate;
A correlation calculation step of calculating a correlation of the path based on the channel impulse response estimation value;
With
The reception method characterized by operating the channel impulse response estimation process and the correlation calculation process until the convergence determination unit determines convergence.   A receiving program for causing a computer to execute the receiving method according to claim 12.

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