Pulse or digital communications – Transmitters – Antinoise or distortion
Reexamination Certificate
1999-07-20
2001-06-26
Pham, Chi (Department: 2631)
Pulse or digital communications
Transmitters
Antinoise or distortion
C375S221000, C455S063300
Reexamination Certificate
active
06252914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio communication system, particularly to a radio communication system capable of reducing deterioration of transmission quality due to multipath fading.
2. Description of the Prior Art
As for a conventional radio communication system having at least a terminal and a base station, transmission quality is deteriorated if frequency-selective fading due to a multipath occurs in the propagation path between the terminal and the base station. Therefore, an automatic equalizer is set in a terminal serving as a reception side to thereby reduce deterioration of transmission quality.
In case of an automatic equalizer, however, when the multipath fading of a propagation path greatly acts, it is necessary to increase the size of a circuit in order to conquer the action of the multipath fading. Therefore, problems occur that the size of a terminal to which downsizing and reduction of power consumption are requested is increased and it is difficult to realize a circuit for practical use
BRIEF SUMMARY OF THE INVENTION Object of the Invention
The present invention is made to solve the above problems and its object is to provide a radio communication system capable of reducing deterioration of transmission quality due to multipath fading while downsizing a terminal and reducing the power consumption.
SUMMARY OF THE INVENTION
To attain the above object, the present invention uses a radio communication system having at least a terminal and a base station connected each other through a propagation path and capable of reducing deterioration of transmission quality between the terminal and the base station due to multipath fading in the propagation path, characterized in that the base station comprises:
a frequency converter for frequency-converting the data sent from the terminal through the propagation path into a base band signal and outputting the signal;
sample quantization means for sample-quantizing the base band signal output from the frequency converter;
an automatic equalizer for equalizing distortions of the propagation path about the base band signal sample-quantized by the sample quantization means, estimating the characteristic of the propagation path in accordance with the base band signal sample-quantized by the sample quantization means, and outputting an estimated result;
a demodulator for demodulating the base band signal whose distortions are equalized by the automatic equalizer;
a predistortion section for adding the inverse characteristic of the propagation path to the data to be transmitted to the terminal in accordance with the estimated result in the automatic equalizer; and
a modulator for modulating the data to which the inverse characteristic of the propagation path is added by the predistortion section.
Moreover, the automatic equalizer is characterized by comprising:
a Fourier transform circuit for transforming the base band signal sample-quantized by the sample quantization means into a frequency-region signal;
a propagation-path-characteristic estimation section to which frequency-region signals output from the Fourier transform circuit are input to estimate the transfer function of the propagation path in accordance with a reference signal regularly inserted into the data sent from the terminal and a signal corresponding to the reference signal among the frequency-region signals output from the Fourier transform circuit and moreover, estimate the propagation path characteristic of the propagation path;
a complex divider for computing the inverse characteristic of the propagation path characteristic by applying complex-division to the propagation characteristic estimated by the propagation-path-characteristic estimation section;
a complex multiplier for multiplying the frequency-region signals output from the Fourier transform circuit with the inverse characteristic of the propagation path characteristic computed by the complex divider;
selection means for outputting the multiplication result computed by the complex multiplier when the base station receives data from the terminal and, after the base station receives the data transmitted from the terminal, outputting the computation result computed by the complex divider; and
an inverse Fourier transform circuit for inverse-Fourier-transforming the multiplication result computed by the complex multiplier or the computation result computed by the complex divider, input through the selection means.
Furthermore, the predistortion section is characterized by comprising inverse characteristic addition means for adding the inverse characteristic of the propagation path computed by the complex divider and inverse-Fourier-transformed by the inverse Fourier transform circuit to the data to be transmitted to the terminal at the timing when the base station completes the reception of the data transmitted from the terminal.
Furthermore, the inverse characteristic addition means is characterized by adding the inverse characteristic of the propagation path to the data to be transmitted to the terminal by using the inverse characteristic of the propagation path as a tap coefficient and thereby, performing the convolutional operation between the inverse characteristic of the propagation path and the data to be transmitted to the terminal.
Furthermore, the predistortion section is characterized by comprising storage means for storing the inverse characteristic of the propagation path as a tap coefficient at the timing when the base station completes the reception of the data transmitted from the terminal, and
the inverse characteristic addition means is characterized by performing the convolutional operation between the inverse characteristic of the propagation path stored in the storage means as a tap coefficient and the data to be transmitted to the terminal and by adding the inverse characteristic of the propagation path to the data to be transmitted to the terminal.
Furthermore, the sample quantization means is characterized by comprising an A/D converter.
As for the present invention configured as described above, the propagation characteristic of a propagation path is estimated by an automatic equalizer set in a base station, the inverse characteristic of the propagation path is added to the down-transmission data to be transmitted to a terminal in a predistortion section in accordance with the estimation result, and the data to which the inverse characteristic of the propagation path is added is transmitted to the terminal as transmission data through the propagation path. Therefore, even if a distortion due to a multipath occurs in the propagation path, a down-link signal transmitted from a base station is correctly received by a terminal without setting any function for reducing deterioration of transmission quality due to multipath fading to the terminal and therefore, transmission quality is not deteriorated.
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NEC Corporation
Pham Chi
Phu Phuong
Sughrue Mion Zinn Macpeak & Seas, PLLC
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