JP3555843B2 - Demodulator - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a demodulation device for a burst signal transmission system using an orthogonal frequency division multiplexing (hereinafter, abbreviated as OFDM) modulation scheme, in a demodulation device of a burst signal transmission system, which performs high-precision correction of phase rotation caused by carrier frequency error and phase noise. The present invention relates to a demodulation device to be realized.
[0002]
[Prior art]
FIG. 3 shows a format of the OFDM burst signal. As shown in FIG. 3, a preamble for synchronization and a preamble for channel estimation are arranged at the head of each burst.
[0003]
FIG. 4 shows the configuration of a conventional OFDM demodulator. The OFDM demodulator includes an antenna 1 for receiving a burst OFDM modulated signal, a frequency conversion circuit 2 for converting a modulated signal received via the antenna 1 into an intermediate frequency band signal, and outputting the signal, and a frequency conversion circuit 2. A quadrature detection circuit 3 that converts the intermediate frequency band signal output from the multiplexed signal into an analog complex baseband signal and outputs the analog complex baseband signal, and a sample quantization unit that samples and quantizes the analog complex baseband signal output from the quadrature detection circuit 3 Synchronization including A / D converters 4 and 5, timing synchronization means for performing timing synchronization processing on the baseband signals sampled and quantized by A / D converters 4 and 5, and carrier frequency synchronization processing means for performing carrier frequency synchronization processing A synchronization circuit 6 for outputting a signal after the processing, and a Fourier transform of the signal after the synchronization processing output from the synchronization circuit 6 to obtain the burst O A Fourier transform circuit 7 for separating the DM modulation signal into signals for each subcarrier, and a propagation path for estimating propagation path distortion from a signal output from the Fourier transformation circuit 7 and outputting propagation path distortion information and each subcarrier amplitude distortion information. A channel distortion estimating circuit 8, a channel distortion compensating circuit 9 for compensating for a signal output from the Fourier transform circuit 7 using the channel distortion information, and outputting a signal after distortion compensation, and a carrier wave after the distortion compensation. And a sub-carrier demodulation circuit 10 that demodulates the signal after the distortion compensation and the phase error correction for each sub-carrier and outputs the demodulated data as demodulated data.
[0004]
In the conventional demodulator shown in FIG. 4, the synchronization circuit 6 establishes carrier frequency synchronization and symbol timing synchronization using a synchronization preamble. The phase error correction circuit 14 is provided as needed, and corrects the phase error of the carrier wave in the phase error correction circuit 14 as necessary.
[0005]
[Problems to be solved by the invention]
The orthogonal frequency division multiplexing (OFDM) modulation scheme is a multicarrier modulation scheme in which data to be transmitted is divided into a plurality of subcarriers and modulated. By using multicarriers, each subcarrier has a narrow band and has excellent multipath fading resistance. On the other hand, there is a problem that the characteristic degradation is large with respect to the phase noise of the carrier added by the local signal used in the frequency conversion circuit. Therefore, it is desired to realize highly accurate carrier phase synchronization even in a multipath fading environment. In the conventional demodulator configuration example of FIG. 4, especially under a multipath fading environment, the phase error correction circuit 14 has a problem that a precise operation cannot be performed due to an influence that a detected phase error becomes large in a subcarrier having a low reception level. .
[0006]
The present invention solves such a problem, and a demodulation device capable of performing high-accuracy phase error detection and thereby achieving high-accuracy correction of phase rotation caused by carrier frequency error and phase noise is provided. The purpose is to provide. Another object of the present invention is to provide a demodulation device with a small increase in circuit scale.
[0007]
[Means for Solving the Problems]
The present invention relates to an OFDM demodulator for receiving and demodulating a burst OFDM modulated signal output from a transmitter via a propagation path.
[0008]
Here, the features of the demodulation device of the present invention include a frequency conversion circuit that converts a received burst orthogonal frequency division multiplexed modulation signal into an intermediate frequency band signal, and a baseband signal that is output from the frequency conversion circuit. A quadrature detection circuit for converting the baseband signal output from the quadrature detection circuit into a sample signal, a sample quantization unit for sample-quantizing the baseband signal output from the quadrature detection circuit, a timing synchronization process for the baseband signal sample-quantized by the sample quantization unit, and a carrier wave. A synchronizing circuit for performing frequency synchronizing processing, a Fourier transform circuit for performing a Fourier transform on the signal after the synchronizing process output from the synchronizing circuit and separating the burst orthogonal frequency division multiplex modulation signal into a signal for each subcarrier, and a Fourier transform A channel distortion estimating circuit for estimating channel distortion from a signal output from the circuit and outputting channel distortion information; D. A channel distortion compensation circuit that performs distortion compensation on a signal output from the conversion circuit using the channel distortion information, and demodulates a signal after distortion compensation output from the channel distortion compensation circuit for each subcarrier. A subcarrier demodulation circuit that outputs demodulated data and soft decision data; and a subcarrier demodulation circuit that outputs soft decision data output from the subcarrier demodulation circuit and subcarrier amplitude distortion information output from the propagation path distortion estimation circuit. And a phase error detecting circuit for generating common phase error information and outputting the same to the propagation path distortion estimating circuit.
[0009]
The phase error detection circuit uses the soft decision data output from the subcarrier demodulation circuit and the subcarrier amplitude distortion information output from the propagation path distortion estimation circuit to calculate the error component of each subcarrier for each subcarrier. An orthogonal frequency division multiplexing intra-symbol averaging circuit that performs weighted averaging according to the reception level, and a moving average circuit that performs a moving average of the weighted average result output from the orthogonal frequency division multiplexing intra-symbol averaging circuit and outputs the phase error information. Can be provided.
[0010]
Further, the propagation path distortion estimating circuit may include means for correcting the propagation path distortion information so as to compensate for the phase error using the phase error information output from the phase error detection circuit.
[0011]
In the present invention configured as described above, the phase error detection circuit averages the phase error of each subcarrier for each OFDM symbol, and at this time, uses the subcarrier amplitude distortion information to calculate each subcarrier. By performing weighted averaging in accordance with the reception level of the above, highly accurate phase error detection can be performed. Further, the moving average circuit performs a moving average of the average result in the OFDM symbol over a required number of symbols, so that the detection accuracy of the phase error can be further improved. Thereby, highly accurate correction of the phase rotation caused by the carrier frequency error and the phase noise can be realized.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 shows a configuration of an OFDM demodulator showing one embodiment of the present invention.
[0014]
FIG. 1 shows a configuration example of an OFDM demodulator according to the present invention. FIG. 3 shows the format of an OFDM burst signal. As shown in FIG. 3, a preamble for synchronization and a preamble for channel estimation are arranged at the head of each burst.
[0015]
The demodulator of FIG. 1 receives an OFDM-modulated burst OFDM-modulated signal on the transmission side, and converts the modulated signal received via the antenna 1 into an intermediate frequency band signal and outputs it. A frequency conversion circuit 2, a quadrature detection circuit 3 that converts the intermediate frequency band signal output from the frequency conversion circuit 2 into an analog complex baseband signal and outputs the analog complex baseband signal, and an analog complex baseband output from the quadrature detection circuit 3 A / D converters 4 and 5 as sample quantization means for sample-quantizing the signal, and a timing synchronization process and a carrier frequency synchronization process of the baseband signal sample-quantized by the A / D converters 4 and 5 are performed. A synchronization circuit 6 for outputting a signal after the synchronization processing, and a Fourier transform of the signal after the synchronization processing output from the synchronization circuit 6 to perform the burst OFDM modulation. Fourier transform circuit 7 for separating the signal into signals for each subcarrier, and a propagation path for estimating propagation path distortion from a signal output from the Fourier transformation circuit 7 and outputting propagation path distortion information and each subcarrier amplitude distortion information A distortion estimating circuit 8, a distortion compensating circuit 9 for compensating the distortion of the signal output from the Fourier transform circuit 7 using the propagation distortion information, and outputting a signal after the distortion compensation; A subcarrier demodulation circuit 10 that demodulates a signal for each subcarrier and outputs demodulated data and soft decision data, and soft decision data outputted from the subcarrier demodulation circuit 10 and outputted from the channel distortion estimating circuit 8 A phase error detection circuit 11 that generates phase error information using each subcarrier amplitude distortion information and outputs the generated phase error information to the propagation path distortion estimation circuit 8 is provided.
[0016]
Next, the operation of the OFDM demodulator of FIG. 1 will be described.
[0017]
In FIG. 1, a received OFDM burst modulation signal is input to an antenna 1. The frequency conversion circuit 2 converts an input received OFDM burst signal into an intermediate frequency band signal. The quadrature detection circuit 3 converts a received signal into an analog complex baseband signal using a local signal that is substantially close to a carrier in the intermediate frequency band. The A / D converters 4 and 5 sample quantize the analog complex baseband signal output from the quadrature detection circuit 3. The synchronization circuit 6 receives the sample-quantized digital complex baseband signal output from the A / D converters 4 and 5 when the synchronization preamble is received, and establishes carrier frequency synchronization and symbol timing synchronization. The Fourier transform circuit 7 performs a fast Fourier transform on the output signal of the synchronization circuit 6, and separates the OFDM modulated signal into signals for each subcarrier. The propagation path distortion estimating circuit 8 estimates the propagation path characteristics using the signal separated for each subcarrier from the Fourier transform circuit 7 when receiving the preamble for propagation path estimation, and outputs a propagation path distortion compensation signal. . The channel distortion compensation circuit 9 performs channel distortion compensation on the data signal after the preamble for channel estimation using the channel distortion compensation signal from the channel distortion estimation circuit 8. The subcarrier demodulation circuit 10 receives the distortion-compensated signal and performs demodulation for each subcarrier. The phase error detection circuit 11 inputs the phase error information for each subcarrier from the subcarrier demodulation circuit 10 and each subcarrier amplitude distortion information from the propagation path distortion estimation circuit 8, and generates and outputs phase error information.
[0018]
FIG. 2 shows a configuration example of the phase error detection circuit 11. First, when the subcarrier demodulation circuit 10 detects a phase error for each subcarrier, a known pilot signal is arranged on a specific subcarrier, and a method of taking a difference between a reference pilot signal and a received signal, or A method of detecting a deviation from a reference signal point corresponding to a subcarrier modulation scheme for all subcarriers can be used. Next, since the phase noise added by the local signal of the frequency conversion circuit 2 is common to all subcarriers, the OFDM intra-symbol averaging circuit 12 averages the phase error of each subcarrier from the subcarrier demodulation circuit 10 for each OFDM symbol. Take. When averaging within an OFDM symbol, weighted averaging according to the reception level of each subcarrier is performed using each subcarrier amplitude distortion information from the channel distortion estimation circuit 8. As a specific example, for example, a method can be adopted in which a certain threshold value is provided, and the average of the phase errors of only the subcarriers having a higher reception level is obtained.
[0019]
Further, the moving average circuit 13 generates phase error information by performing a moving average of the average result in the OFDM symbol over several symbols.
[0020]
The propagation path distortion estimating circuit 8 uses the phase error information from the phase error detecting circuit 11 to compensate the propagation path distortion to the propagation path distortion compensating circuit 9 so as to compensate for the phase noise added by the local signal of the frequency conversion circuit. Modify the coefficient.
[0021]
【The invention's effect】
As described above, according to the present invention, the phase error detection circuit averages the phase error of each subcarrier for each OFDM symbol, and at this time, uses the subcarrier amplitude distortion information to perform weighting according to the reception level of each subcarrier. By taking the average, highly accurate phase error detection can be performed, and this phase error detection can realize highly accurate correction of phase rotation caused by carrier frequency error and phase noise. Further, by performing a moving average of the average result in the OFDM symbol in a required number of symbols in the moving average circuit, the detection accuracy of the phase error can be further improved. Thereby, highly accurate correction of the phase rotation caused by the carrier frequency error and the phase noise can be realized.
[0022]
Further, since the compensation of the phase noise is performed by correcting the propagation path distortion compensation coefficient, the circuit of the propagation path distortion compensation circuit 9 can be used as it is for the compensation operation. Therefore, an increase in circuit scale can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an embodiment of a demodulation device of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a phase error detection circuit.
FIG. 3 is a diagram showing an example of a burst format configuration.
FIG. 4 is a diagram showing a configuration example of a demodulation device of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 antenna 2 frequency conversion circuit 3 quadrature detection circuit 4, 5 A / D converter 6 synchronization circuit 7 Fourier conversion circuit 8 propagation path distortion estimation circuit 9 propagation path distortion compensation circuit 10 subcarrier demodulation circuit 11 phase error detection circuit 12 OFDM symbol Inner average circuit 13 Moving average circuit 14 Phase error correction circuit

Claims (2)

A frequency conversion circuit for converting the received burst orthogonal frequency division multiplex modulation signal into an intermediate frequency band signal,
A quadrature detection circuit that converts the intermediate frequency band signal output from the frequency conversion circuit to a baseband signal,
Sample quantization means for sample-quantizing the baseband signal output from the quadrature detection circuit;
A synchronization circuit for performing timing synchronization processing and carrier frequency synchronization processing of the baseband signal sample-quantized by the sample quantization means,
A Fourier transform circuit for performing a Fourier transform on the signal after the synchronization process output from the synchronization circuit and separating the burst orthogonal frequency division multiplex modulation signal into a signal for each subcarrier;
A channel distortion estimating circuit that estimates channel distortion from a signal output from the Fourier transform circuit and outputs channel distortion information;
A channel distortion compensation circuit that performs distortion compensation on a signal output from the Fourier transform circuit using the channel distortion information,
A subcarrier demodulation circuit that demodulates the signal after distortion compensation output from the propagation path distortion compensation circuit for each subcarrier and outputs demodulated data and soft decision data;
Using the soft decision data output from the subcarrier demodulation circuit and each subcarrier amplitude distortion information output from the channel distortion estimation circuit, generates phase error information common to each subcarrier, and and a phase error detecting circuit to be output to,
The demodulation method, wherein the propagation path distortion estimating circuit includes means for correcting the propagation path distortion information so as to compensate for a phase error by using phase error information output from the phase error detection circuit. apparatus. The phase error detection circuit receives an error component of each subcarrier by using the soft decision data output from the subcarrier demodulation circuit and each subcarrier amplitude distortion information output from the propagation path distortion estimation circuit. An orthogonal frequency division multiplexing intra-symbol averaging circuit that performs weighted averaging according to the level, and a moving average circuit that performs a moving average of the weighted average result output from the orthogonal frequency division multiplexing intra-symbol averaging circuit and outputs the phase error information. The demodulation device according to claim 1, further comprising:

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