JP2000286819A - Demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve deterioration in the characteristics of a carrier added by a local signal used by a frequency conversion circuit of an OFDM demodulator onto a phase noise. SOLUTION: The demodulator is provided with a phase error detection circuit 11, which uses the phase error information for each sub carrier from a sub carrier demodulation circuit 10 and the amplitude distortion information of each sub carrier from a propagation path distortion estimate circuit 8 to generate phase error information so as to correct a propagation path distortion compensation coefficient, thereby compensating the phase noise. Furthermore, a moving mean circuit applies moving mean processing to the mean results in an OFDM symbol over a required number of symbols so as to increase the detection accuracy of the phase error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an OFDM (Orthogonal Frequency Division Multiplex).
The present invention relates to a demodulation device for a burst signal transmission system using a modulation method (hereinafter, abbreviated as OFDM), which relates to a demodulation device that realizes highly accurate correction of phase rotation caused by carrier frequency error and phase noise.

[0002]

2. Description of the Related Art FIG. 3 shows a format of an OFDM burst signal. As shown in FIG. 3, at the head of each burst, a preamble for synchronization and a preamble for channel estimation are arranged.

FIG. 4 shows a 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 for converting the intermediate frequency band signal output from
Converters 4, 5 as sample quantization means for sample-quantizing the analog complex baseband signal output from
And a timing synchronizing means for synchronizing the baseband signals sample-quantized by the A / D converters 4 and 5 and a carrier frequency synchronizing means for synchronizing the carrier frequency, and outputting a signal after the synchronizing processing. A circuit 6;
A Fourier transform circuit for performing Fourier transform on the signal after the synchronization processing output from the synchronization circuit 6 to separate the burst OFDM modulated signal into signals for each subcarrier, and a propagation path distortion from the signal output from the Fourier transform circuit 7. And a channel distortion estimating circuit 8 that outputs channel distortion information and subcarrier amplitude distortion information, and a signal output from the Fourier transform circuit 7 is subjected to distortion compensation using the channel distortion information. And a phase error correction circuit 14 for correcting the phase error of the carrier after the distortion compensation, and demodulating the signal after the distortion compensation and the phase error correction for each subcarrier, A subcarrier demodulation circuit 10 that outputs demodulated data.

In the conventional demodulator shown in FIG. 1, a 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]

The orthogonal frequency division multiplexing (OFDM) modulation method is a multicarrier modulation method 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 is excellent in multipath fading resistance. On the other hand, there is a problem that the characteristic deterioration 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
There is a problem that precise operation cannot be performed due to the influence of the detection phase error increasing in subcarriers having a low reception level.

The present invention solves such a problem, and can perform a highly accurate phase error detection, thereby realizing a highly accurate correction of a phase rotation caused by a carrier frequency error and phase noise. It is an object to provide a demodulation device. It is another object of the present invention to provide a demodulator with a small increase in circuit scale.

[0007]

SUMMARY OF THE INVENTION 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.

Here, the demodulator of the present invention is characterized in that a frequency conversion circuit for converting a received burst orthogonal frequency division multiplex modulation signal into an intermediate frequency band signal, and an intermediate frequency band signal output from this frequency conversion circuit. A quadrature detection circuit for converting to a baseband signal, sample quantization means for sample-quantizing the baseband signal output from the quadrature detection circuit, and timing synchronization of the baseband signal sample-quantized by the sample quantization means A synchronization circuit that performs processing and carrier frequency synchronization processing, and a Fourier transform circuit that performs Fourier transform on the signal after the synchronization processing output from the synchronization circuit and separates 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, and outputs a signal after distortion compensation output from the channel distortion compensation circuit for each subcarrier. A subcarrier demodulation circuit for demodulating and outputting demodulated data and soft decision data; and a soft decision data output from the subcarrier demodulation circuit and each subcarrier amplitude distortion information output from the propagation path distortion estimation circuit. A phase error detection circuit that generates phase error information common to the subcarriers and outputs the information to the propagation path distortion estimation circuit.

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 determine the error component of each subcarrier. An orthogonal frequency division multiplexing intra-symbol averaging circuit that performs weighted averaging according to the reception level of the subcarrier, and a moving average that outputs a moving average of the weighted averaging result output from the orthogonal frequency division multiplexing intra-symbol averaging circuit and outputs the phase error information And an averaging circuit.

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 detecting circuit.

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 uses the subcarrier amplitude distortion information at this time. By taking a weighted average according to the reception level of each subcarrier, 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]

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

FIG. 1 shows an example of an embodiment of the present invention.
1 shows a configuration of an FDM demodulator.

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, at the head of each burst, a preamble for synchronization and a preamble for channel estimation are arranged.

The demodulator shown in FIG. 1 uses OFDM on the transmitting side.
An antenna 1 for receiving a modulated 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 Convert the output intermediate frequency band signal to an analog complex baseband signal,
A quadrature detection circuit 3 for outputting, A / D converters 4 and 5 as sample quantization means for sample-quantizing the analog complex baseband signal output from the quadrature detection circuit 3,
A synchronization circuit 6 for performing timing synchronization processing and carrier frequency synchronization processing of the baseband signal sample-quantized by the D converters 4 and 5 and outputting a signal after the synchronization processing; and a synchronization processing output from the synchronization circuit 6 Fourier transform of the subsequent signal, and a Fourier transform circuit 7 for separating the burst OFDM-modulated signal into signals for each subcarrier; and estimating propagation path distortion from the signal output from the Fourier transformation circuit 7; And a propagation path distortion estimating circuit 8 for outputting each subcarrier amplitude distortion information, and a signal output from the Fourier transform circuit 7 for distortion compensation using the propagation path distortion information and outputting a signal after distortion compensation. A path distortion compensation circuit 9, a subcarrier demodulation circuit 10 for demodulating the signal after the distortion compensation for each subcarrier, and outputting demodulated data and soft decision data;
Phase error information is generated using the soft decision data output from the subcarrier demodulation circuit 10 and each subcarrier amplitude distortion information output from the channel distortion estimating circuit 8, and the phase output to the channel distortion estimating circuit 8 An error detection circuit 11 is provided.

Next, the operation of the OFDM demodulator of FIG. 1 will be described.

In FIG. 1, a reception OFDM is
A burst modulation signal is input. 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 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 signal after distortion compensation and performs demodulation for each subcarrier. The phase error detection circuit 11 is a subcarrier demodulation circuit 1
The phase error information for each subcarrier from 0 and each subcarrier amplitude distortion information from the propagation path distortion estimating circuit 8 are input, and phase error information is generated and output.

FIG. 2 shows a configuration example of the phase error detection circuit 11. First, when detecting a phase error for each subcarrier in the subcarrier demodulation circuit 10, a method of arranging a known pilot signal on a specific subcarrier and 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 DM symbol averaging circuit 12 is a subcarrier demodulation circuit 1
The phase error for each subcarrier from 0 is averaged for each OFDM symbol. 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 of setting a certain threshold value and averaging the phase errors of only the subcarriers having a higher reception level can be used.

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.

The propagation path distortion estimating circuit 8 uses the phase error information from the phase error detecting circuit 11 to propagate the signal 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. Correct the road distortion compensation coefficient.

[0021]

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 uses the subcarrier amplitude distortion information to receive each subcarrier. High-precision phase error detection can be performed by taking a weighted average according to the level, and high-precision correction of phase rotation caused by a carrier frequency error and phase noise can be realized by the phase error detection. 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.

Since the compensation of the phase noise is performed by correcting the channel distortion compensation coefficient, the circuit of the channel 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]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Frequency conversion circuit 3 Quadrature detection circuit 4, 5 A / D converter 6 Synchronization circuit 7 Fourier transformation 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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuhiro Okanoue 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Tomoki Osawa 5-7-1 Shiba, Minato-ku, Tokyo Japan Within the Electric Company (72) Inventor Tomoaki Kumagai 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Nippon Telegraph and Telephone Corporation F-term (reference) 5K022 DD01 DD13 DD17 DD19 DD33 DD34 DD43 DD44 5K046 AA05 EE55 EF46 EF52 5K052 AA01 BB02 CC00 DD16 EE26

Claims (3)

[Claims] 1. A frequency conversion circuit for converting a received burst orthogonal frequency division multiplex modulation signal into an intermediate frequency band signal, and a quadrature detection circuit for converting the intermediate frequency band signal output from the frequency conversion circuit into a baseband signal Sample quantization means for sample-quantizing the baseband signal output from the quadrature detection circuit; and synchronization for performing timing synchronization processing and carrier frequency synchronization processing of the baseband signal sample-quantized by the sample quantization means. Circuit, a Fourier transform circuit for performing a Fourier transform on the signal after the synchronization process output from the synchronous circuit, and separating the burst orthogonal frequency division multiplex modulation signal into a signal for each subcarrier, a signal output from the Fourier transform circuit A channel distortion estimating circuit that estimates channel distortion from and outputs channel distortion information; and A channel distortion compensation circuit for compensating the output signal for distortion using the channel distortion information; a signal after distortion compensation output from the channel distortion compensation circuit for each subcarrier; A subcarrier demodulation circuit that outputs decision data; and a phase common to each subcarrier using soft decision data outputted from the subcarrier demodulation circuit and each subcarrier amplitude distortion information outputted from the channel distortion estimation circuit. A demodulation device comprising: a phase error detection circuit that generates error information and outputs the error information to the propagation path distortion estimation circuit. 2. The method according to claim 1, wherein 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 an error component of each subcarrier. An average circuit in an orthogonal frequency division multiplex symbol for weighting and averaging according to the reception level of each subcarrier, and a moving average of the weighted average result output from the average circuit in the orthogonal frequency division multiplex symbol to output the phase error information The demodulator according to claim 1, further comprising a moving average circuit. 3. The channel distortion estimating circuit includes means for correcting the channel distortion information so as to compensate for a phase error using the phase error information output from the phase error detecting circuit. The demodulator according to any of the preceding claims.