Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
2000-02-01
2003-11-04
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S226000, C375S231000, C375S316000, C375S346000, C375S355000, C375S371000, C370S206000, C455S139000
Reexamination Certificate
active
06643339
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a receiver capable of adaptively taking phase synchronization with high accuracy for a modulated signal in which sub-carriers are multiplexed, such as an OFDM (Orthogonal Frequency Division Multiplexing) system.
One example of this kind of conventional receiver is described in JP-A-95174/1995.
FIG. 13
is a block diagram of its apparatus for demodulating an OFDM signal. This apparatus detects a phase difference from a modulation result of an arbitrary carrier in order to conduct phase synchronization for a modulated signal in which sub-carriers are multiplexed.
In
FIG. 13
,
1000
-
1
-
1000
-n are input terminals,
1001
is a fast Fourier transform (FFT) circuit of n points,
1002
is a parallel/serial transform circuit,
1003
is a selector,
1004
is a phase difference detector, and
1005
and
1006
are output terminals.
Serial/parallel transformed n received signals are input to the FFT circuit
1001
of n points through the input terminals
1000
-
1
-
1000
-n. The FFT circuit
1001
applies Fourier transformation to the input signals and de-multiplexes sub-carriers therefrom, and inputs the sub-carriers to the parallel/serial transform circuit
1002
.
The parallel/serial transform circuit
1002
applies parallel/serial transform to each of the input sub-carrier components and outputs it to the output terminal
1005
, and also, outputs it to the selector
1004
. Furthermore, the parallel/serial transform circuit
1002
outputs to the selector
1003
a pulse for indicating time when each subcarrier component is output.
The selector
1003
selects a sub-carrier component to be input, based on the input pulse, and outputs it to the phase difference detecting circuit
1004
.
In the phase difference detecting circuit
1004
, assuming that a phase of a symbol under ideal condition in which phase synchronization is established is a reference phase, a difference between the input sub-carrier component and the reference phase is detected as a phase error, and it is output to the output terminal
1006
. The phase error output to the output terminal
1006
is integrated by a loop filter and so forth, and is fed back to a local oscillator.
However, in the above-mentioned conventional OFDM signal demodulating apparatus, there is a task that it becomes to be difficult to detect a correct phase difference when distortion occurs in the selected sub-carrier component due to disturbance such as a noise in a communication line.
Also, in JP-A-95174/1995, although it is suggested to adaptively select a sub-carrier based on a noise and distortion, a method and an arrangement therefor are not disclosed.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-mentioned problems.
Moreover, the objective of the invention is to provide a receiver for receiving a modulated wave in which a plurality of sub-carriers are multiplexed, to provide the receiver for conducting phase tracking with high accuracy, and capable of obtaining high reception characteristic.
In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the first present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and also, outputting a distortion correction coefficient for each of the above-described plurality of sub-carrier components, and a value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for outputting a phase error.
For example, the phase estimating circuit of the first present invention has k phase comparison circuits for receiving the determination result of each of the above-described plurality of sub-carrier components and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for detecting a phase difference between the above-described corresponding demodulation result and the value corrected based on the above-described distortion correction coefficient, and outputting it as a phase difference of each sub-carrier, k electric power detecting circuits for receiving the distortion correction coefficient for each of the above-described plurality of sub-carrier components, detecting electric power of the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and outputting it as distortion correction coefficient electric power of each sub-carrier, k weight setting circuits for receiving each distortion correction coefficient electric power of the above-described each sub-carrier, and based on the distortion correction coefficient electric power of the above-described each sub-carrier, for obtaining a weight for the above-described each sub-carrier for weighting a phase difference of the above-described each sub-carrier and conducting synthesis thereof, and outputting the weight, and a weighting and synthesizing circuit for outputting a result of weighting and synthesizing a phase difference of the above-described each sub-carrier based on the weight for the above-described each sub-carrier as a phase error.
For example, the above-described weight setting circuits of the first present invention make a weight for weighting to be large if the distortion correction coefficient electric power of the above-described each sub-carrier is small, and make a weight for weighting to be small if the distortion correction coefficient electric power of the above-described each sub-carrier is large.
For example, the above-described weight setting circuits of the first present invention set a weight to be 1 if the distortion correction coefficient electric power of the above-described each sub-carrier is smaller than a determined threshold value, and set a weight to be 0 if the distortion correction coefficient electric power of the above-described each sub-carrier is larger than a determined threshold value.
In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the second present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and outputting a value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and the above-described plurality of sub-carrier components which are multiplexed and de-multiplexed, and for outputting a phase error.
For example, the pha
Okanoue Kazuhiro
Osawa Tomoki
Yamamoto Takeshi
Ahn Sam K.
Chin Stephen
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
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