JP2007184662A - Digital receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital receiver capable of eliminating distortion of a received signal with high accuracy even when a reception state is changed. <P>SOLUTION: A pilot signal transmission path response estimate section 25 estimates a transmission path response of a pilot signal. An unknown signal transmission path response estimate section applies-sum operation to a weight in a weight memory 24 and the transmission path response of the pilot signal to estimate the transmission path response of an unknown signal on the basis of a result of the cross-product arithmetic operation. A division section 26 equalizes the unknown signal by dividing the unknown signal by the transmission path response of the unknown signal. A weight update section 41 updates the weight in the weight memory 24. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital receiver, and more particularly to a digital receiver that receives a signal modulated by an orthogonal frequency division multiplexing (OFDM) system transmitted from a terrestrial digital broadcasting station.

  In recent years, the OFDM system has been attracting attention in digital audio broadcasting for mobile terminals or terrestrial digital television broadcasting. The OFDM scheme is a scheme in which a large number of subcarriers (hereinafter also referred to as subcarriers) orthogonal to each other are modulated with digital data to be transmitted, and these modulated waves are multiplexed and transmitted.

By the way, multipath exists in terrestrial transmission, and the frequency characteristic of a received signal may be distorted by this multipath. Equalization is performed to remove this distortion. For example, in Patent Document 1, a known signal (hereinafter also referred to as a pilot signal) scattered in a transmission signal is extracted on the receiving side. The transmission path response of the unknown signal is estimated by estimating the transmission path response of the pilot signal and performing a product-sum operation on the transmission path response of the pilot signal and a predetermined coefficient. The unknown signal is equalized by dividing the unknown signal by the estimated transmission line response.
Japanese Patent Laid-Open No. 11-239115

  However, in Patent Document 1, since the coefficient used when estimating the transmission path response of an unknown signal is fixed, the accuracy of equalization, that is, the distortion removal accuracy when the reception situation changes, such as when the digital receiver moves. Becomes worse.

  Therefore, an object of the present invention is to provide a digital receiver that can remove the distortion of a received signal with high accuracy even when the reception state changes.

  In order to solve the above-mentioned problem, a digital receiver for receiving a digital modulated wave signal of an orthogonal frequency division division transmission system, in which each subcarrier is modulated by a predetermined modulation system, A first extraction unit for extracting a pilot signal inserted according to a predetermined pattern; a second extraction unit for extracting an unknown signal in the digital modulated wave signal; and a first estimation for estimating a transmission path response of the pilot signal Unit, a memory for storing the transmission path response weight of the pilot signal, a product-sum operation of the weight in the memory and the transmission path response of the pilot signal, and based on the product-sum operation result, the transmission path response of the unknown signal A second estimation unit that estimates the signal, a division unit that divides and equalizes the unknown signal by the transmission path response of the unknown signal, and an update unit that updates the weight in the memory.

  Preferably, the update unit demodulates the division result by the division unit using a demodulation method corresponding to the modulation method, generates a demodulated bit data, modulates the demodulated bit data using the modulation method, and generates a transmission signal replica. A modulation unit for generating, a generation unit for generating an unknown signal replica by multiplying the transmission signal response of the transmission signal replica and the unknown signal, an error calculation unit for calculating an error between the unknown signal and the unknown signal replica, and an error And a weight calculation unit that updates the weight based on this.

  Preferably, the weight calculation unit updates the weight in a direction to minimize the mean square of the error according to the LMS algorithm based on the steepest descent method.

  According to the digital receiver of the present invention, it is possible to remove the distortion of the received signal with high accuracy even if the reception situation changes.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
(Configuration of digital receiver)
FIG. 1 is a schematic block diagram of a digital receiver 100 according to an embodiment of the present invention.

  Referring to FIG. 1, a high frequency signal input (RF input) input from an antenna (not shown) is input to tuner 1. In the tuner 1, the RF input signal is down-converted to an intermediate frequency (IF frequency) and converted into an analog OFDM signal under a predetermined band limitation. The analog OFDM signal is input to an analog / digital conversion circuit 2 (also referred to as an A / D circuit), and converts the analog OFDM signal into a digital signal. Here, it is assumed that each subcarrier of the OFDM signal is modulated by a 16QAM (Quadrature Amplitude Modulation) modulation method.

  Next, the OFDM signal converted into the digital signal is converted into an I signal which is an in-phase detection axis signal (real axis component signal) and a Q signal which is a quadrature detection axis signal (imaginary axis component signal) by the Hilbert transform unit 3. A complex OFDM signal is generated. The complex OFDM signal generated by the Hilbert transform unit 3 is sent to the first carrier synchronization unit 4.

  The first carrier synchronization unit 4 corrects a carrier frequency error based on a correlation signal described later output from the symbol synchronization unit 7 and a signal from the second carrier synchronization unit 9.

  The FFT 5 performs a fast Fourier transform process on the complex OFDM signal, and converts the signal from the time axis domain to the frequency axis domain.

  The equalization unit 6 obtains a transmission line response from the pilot signal, estimates the transmission line response of the unknown signal, and adaptively equalizes the unknown signal based on the estimation result.

  The symbol synchronization unit 7 uses the formation of one symbol by copying a part of the effective symbol period, which is a characteristic of the OFDM signal, as a guard interval period. Symbol synchronization is calculated based on the correlation value. Further, the symbol synchronization unit 7 outputs a correlation signal based on the correlation value to the first carrier synchronization unit 4 in order to correct a frequency error within the carrier frequency.

  The second carrier synchronization unit 9 calculates the error of the carrier frequency interval from the arrangement on the frequency axis of the output signal of the FFT 5 and outputs a signal based on the calculation result to the first carrier synchronization unit 4.

  The clock synchronization unit 8 calculates clock synchronization from the symbol synchronization timing shift obtained by the symbol synchronization unit 7 and controls the sampling frequency of the A / D circuit 2.

  The frequency deinterleave 11 performs a process of returning the frequency interleave performed to compensate for the loss of a signal of a specific frequency due to the reflection of radio waves. The output of the frequency deinterleave 11 is given to the time deinterleave 12, and the time deinterleave 12 performs a process for restoring the time interleave applied for anti-fading and the like.

  The real-axis component signal (I signal) and the imaginary-axis component signal (Q signal) subjected to time deinterleaving are each converted into a 4-bit signal in demapping 13.

  Bit deinterleaving 21 cancels bit interleaving performed for the purpose of increasing error correction on the demapped signal. The Viterbi decoding unit 15 performs error correction using the convolutional code performed on the transmission side.

  The byte deinterleave 16 cancels the byte interleave performed for the purpose of increasing error correction in the same manner as the bit interleave for the signal subjected to Viterbi decoding. Then, the TS reproduction unit 17 reconstructs data according to the transport stream format, and the RS decoding unit 18 decodes the Reed-Solomon encoded data on the transmission side. The RS decoding unit 18 outputs a Reed-Solomon decoded result to a TS decoder (not shown).

  The error-corrected signal is output after the compressed signal is expanded in an MPEG decoding unit (not shown), converted into an analog video and an analog audio signal by digital / analog conversion.

(Configuration of equalization unit)
FIG. 2 is a schematic block diagram of the equalization unit 6.

  Referring to FIG. 2, equalization section 6 has reception buffer 32, pilot signal extraction section 21, unknown signal extraction section 22, pilot transmission signal memory 23, weight memory 24, and pilot signal transmission path response estimation. Unit 25, unknown signal transmission line response estimation unit 33, division unit 26, and weight update unit 41. In the figure, the line connecting each component of the equalization unit 6 represents the I component and the Q component integrated, and the calculation of each component in the equalization unit 6 is a complex operation. is there.

  The reception buffer 32 accumulates at least 5 symbols of the OFDM signal output from the FFT 5.

  The pilot signal extraction unit 21 extracts six pilot signals from the reception buffer 32 by six.

The unknown signal extraction unit 22 extracts 11 unknown signals from the reception buffer 32 one by one.
FIG. 3 is a conceptual diagram illustrating an example of an arrangement pattern of pilot signals and unknown signals.

  Referring to FIG. 3, pilot signals are arranged at subcarriers and time (symbol) positions marked with ○, and unknown signals are arranged at other positions. That is, in this example, a pilot signal is inserted at a rate of one for 12 carriers included in one symbol, and the pilot signal insertion position is shifted by 3 carriers for each symbol.

  Referring to FIG. 2 again, pilot transmission signal memory 23 stores the pilot transmission signal.

The weight memory 24 stores the weight of the pilot signal transmission line response estimation value.
The division unit 26 divides the unknown signal by the unknown signal transmission line response estimated value to calculate an equalized signal.

  The pilot signal transmission path response estimation unit 25 reads a pilot transmission signal corresponding to the pilot signal from the pilot transmission signal memory 23, divides the pilot signal by the pilot transmission signal, and calculates a pilot signal transmission path response estimated value. .

  The unknown signal transmission line response estimation unit 33 calculates the sum of the pilot signal transmission line response estimated value and the weight in the weight memory 24 to calculate the unknown signal transmission line response estimated value.

  The weight update unit 41 updates the weight in the weight memory 24, and includes a demapping unit 27, a mapping unit 28, an unknown signal replica generation unit 29, an error signal calculation unit 30, and a weight calculation unit 31. Including.

  The demapping unit 27 demodulates the equalized signal using a demodulation method corresponding to the 16QAM modulation method to generate 4-bit demodulated bit data. That is, the demapping unit 27 selects a reference point closest to the equalized signal from the 16 reference points of the 16QAM modulation scheme, and generates 4-bit data representing the reference point as demodulated bit data.

  The mapping unit 28 modulates the 4-bit demodulated bit data by the 16QAM modulation method to generate a transmission signal replica.

  The unknown signal replica generation unit 29 multiplies the transmission signal replica by the unknown signal transmission line response estimated value to calculate an unknown signal replica.

The error signal calculator 30 calculates an error signal between the unknown signal and the unknown signal replica.
The weight calculation unit 31 updates the weight in a direction that minimizes the mean square error (also referred to as the mean square error) according to an LMS (Least Mean Square) algorithm based on the steepest descent method.

(Operation)
FIG. 4 is a flowchart showing an operation procedure of adaptive equalization of digital receiver 100 according to the embodiment of the present invention.

Referring to FIG. 4, the number of repetitions t = 0 is set (step S101).
Next, the pilot signal extraction unit 21 extracts six pilot signals r _j ^(t) (j = A to F) from the reception buffer 32 (step S102).

Next, the unknown signal extraction unit 22 extracts 11 unknown signals r _k ^(t) (k = 1 to 11) from the reception buffer 32 (step S103).

  FIG. 5A is a diagram illustrating an example of extraction of a pilot signal and an unknown signal at the number of repetitions t = 0.

Referring to FIG. 5A, when the number of repetitions t = 0, the subcarriers denoted by A to F and pilot signals r _j ^(t) (j = A to F) at the time (symbol) positions are extracted. Then, the unknown signals r _k ^(t) (k = 1 to 11) at the positions of the subcarriers and times (symbols) indicated by 1 to 11 are extracted.

Next, the pilot signal transmission path response estimation unit 25 reads the pilot transmission signal s _j ^(t) corresponding to the pilot signal r _j ^(t) from the pilot transmission signal memory 23, and transmits the pilot signal transmission path response estimated value. h _j ^(t) is calculated by the following equation (A1) (step S104).

h _j ^(t) = r _j ^(t) / s _j ^(t) (A1)
Next, the unknown signal transmission line response estimation unit 33 and the pilot signal transmission line response estimation value h _j ^(t) and the weight w _kj ^(t) in the weight memory 24 (k = 1 to 11, j = A to F). ) And the following equation (A2) to calculate a sum of products to calculate an unknown signal transmission line response estimated value h _k ^(t) (step S105).

h _k ^(t) = [w _kA ^(t) , w _kB ^(t) , w _kC ^(t) , w _kD ^(t) , w _kE ^(t) , w _kF ^(t) ]
[H _A ^(t) , h _B ^(t) , h _C ^(t) , h _D ^(t) , h _E ^(t) , h _F ^(t) ] ^T (A2)
Next, based on the unknown signal transmission line response estimated value h _k ^(t) and the unknown signal r _k ^(t) , the divider 26 calculates the equalized signal u _k ^(t) by the following equation (A3). Calculate (step S106).

u _k ^(t) = r _k ^(t) / h _k ^(t) (A3)
Next, the demapping unit 27 demodulates the equalized signal u _k ^(t) by a demodulation method corresponding to the 16QAM modulation method, and generates 4-bit demodulated bit data (b ₁ , b ₂ , b ₃ , b ₄ ). _k ^(t) is generated (step S107).

Next, the mapping unit 28 modulates the 4-bit demodulated bit data (b ₁ , b ₂ , b ₃ , b ₄ ) _k ^(t) by the 16QAM modulation method to generate a transmission signal replica d _k ^(t) . (Step S108).

Next, the unknown signal replica generation unit 29 determines the unknown signal replica r _k ′ ^(t) as follows based on the transmission signal replica d _k ^(t) and the unknown signal transmission path response estimated value h _k ^(t). (A4) is calculated (step S109).

r _k ′ ^(t) = h _k ^(t) × d _k ^(t) (A4)
Next, the error signal calculation unit 30 calculates an error signal e _k ^(t) between the unknown signal r _k ^(t) and the unknown signal replica r _k ′ ^(t) as in the following equation (A5). (Step S110).

e _k ^(t) = r _k ^(t) −r _k ′ ^(t) = r _k ^(t) −h _k ^(t) × d _k ^(t) (A5)
Next, the weight calculator 31 calculates the mean square error ({e ₁ ^{(t) 2} + e ₂ ^(t)) according to the LMS (Least Mean Square) algorithm based on the steepest descent method as in the following equation (A6 ^{). _{2 + ··· + e 11 (t}} ) 2} / 11) to update the weight w _kj in a direction to minimize (step S111).

w _kj ^{(t + 1)} = w _kj ^(t) + μ × d _k ^(t) × e _k ^(t) × h _j ^(t) (A6)
Next, the repeat count t is incremented by one (step S112).

  Next, if there is a new unknown signal in the reception buffer 32 (YES in step S113), the process returns to step S102, and if not (NO in step S113), the process ends.

  The iterative process from step S102 is the same as the process described above, but the pilot signal and unknown signal extraction process in steps S102 and S103 is an extraction process corresponding to the number of repetitions t. Hereinafter, the extraction process of steps S102 and S103 in which the number of repetitions t is 1 or later will be described.

  First, every time the number of repetitions t increases, a pilot signal and an unknown signal at positions moved by 13 in the subcarrier direction are extracted.

  FIG. 5B is a diagram illustrating an example of extraction of a pilot signal and an unknown signal at the number of repetitions t = 1.

Referring to FIG. 5B, when the number of repetitions is t = 1, the pilot signals r _j ^(t) (j = A to F) at the positions of the subcarriers and times (symbols) indicated by A to F are extracted. Then, the unknown signals r _k ^(t) (k = 1 to 11) at the positions of the subcarriers and times (symbols) indicated by 1 to 11 are extracted.

  Next, it is assumed that the movement in the subcarrier direction is completed at the number of repetitions t = 99. When the number of repetitions t = 100, the pilot signal and the unknown signal are extracted by moving one time (one symbol) in the time (symbol) direction.

  FIG. 5C is a diagram illustrating an example of extraction of a pilot signal and an unknown signal at the number of repetitions t = 100.

Referring to FIG. 5C, when the number of repetitions is t = 100, the subcarriers denoted by A to F and the pilot signal r _j ^(t) (j = A to F) at the time (symbol) position are extracted. Then, the unknown signals r _k ^(t) (k = 1 to 11) at the positions of the subcarriers and times (symbols) indicated by 1 to 11 are extracted.

  As described above, according to the digital receiver according to the embodiment of the present invention, the coefficient (weight) used when estimating the transmission path response of the unknown signal can be adaptively changed according to the reception situation. The distortion of the received signal can be removed with high accuracy.

(Modification)
The present invention is not limited to the above-described embodiment, and includes, for example, the following modifications.

(1) Modulation method In the embodiment of the present invention, the case where 16QAM is used as the modulation method has been described as an example. However, the present invention is not limited to this, and other modulation methods can be similarly applied.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a schematic block diagram of a digital receiver 100 according to an embodiment of the present invention. 3 is a schematic block diagram of an equalization unit 6. FIG. It is a conceptual diagram explaining the example of the arrangement pattern of a pilot signal and an unknown signal. It is a flowchart showing the operation | movement procedure of the adaptive equalization of the digital receiver 100 of embodiment of this invention. (A) is a figure showing the example of extraction of the pilot signal and unknown signal in the number of repetitions t = 0, and (b) shows the example of extraction of the pilot signal and unknown signal in the number of repetitions t = 1. (C) is a figure showing the example of extraction of a pilot signal and an unknown signal in repetition frequency t = 100.

Explanation of symbols

  1 tuner, 2 A / D circuit, 3 Hilbert transform unit, 4 first carrier synchronization unit, 5,80 FFT, 6 equalization unit, 7 symbol synchronization unit, 8 clock synchronization unit, 9 second carrier synchronization unit, 11 frequency Deinterleaving, 12-hour deinterleaving, 13 demapping, 14 bit deinterleaving, 15 Viterbi decoding unit, 16 byte deinterleaving, 17 TS playback unit, 18 RS decoding unit, 21 pilot signal extracting unit, 22 unknown signal extracting unit, 23 Pilot transmission signal memory, 24 weight memory, 25 pilot signal transmission line response estimation unit, 26 division unit, 27 demapping unit, 28 mapping unit, 29 unknown signal replica generation unit, 30 error signal calculation unit, 31 weight calculation unit, 32 Reception buffer, 33 unknown signal transmission path response estimation unit, 41 Eight update unit.

Claims (3)

A digital receiver for receiving a digital modulated wave signal of an orthogonal frequency division division transmission system, in which each subcarrier is modulated by a predetermined modulation system,
A first extraction unit for extracting a pilot signal inserted in the digital modulation wave signal according to a predetermined pattern;
A second extraction unit for extracting an unknown signal in the digital modulated wave signal;
A first estimation unit for estimating a transmission line response of the pilot signal;
A memory for storing a weight of a transmission line response of the pilot signal;
A second estimator that performs a product-sum operation on the weight in the memory and the transmission path response of the pilot signal, and estimates a transmission path response of the unknown signal based on the product-sum operation result;
A division unit that divides and equalizes the unknown signal by a transmission line response of the unknown signal;
A digital receiver comprising: an updating unit that updates weights in the memory. The update unit
A demodulator that demodulates the result of the division by the demodulation method corresponding to the modulation method, and generates demodulated bit data;
A modulation unit that modulates the demodulated bit data with the modulation method to generate a transmission signal replica;
A generation unit for generating an unknown signal replica by multiplying the transmission signal replica by the transmission path response of the unknown signal;
An error calculator that calculates an error between the unknown signal and the unknown signal replica;
The digital receiver according to claim 1, further comprising: a weight calculation unit that updates the weight based on the error.   The digital receiver according to claim 2, wherein the weight calculation unit updates the weight in a direction that minimizes a mean square of the error according to an LMS algorithm based on a steepest descent method.

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