Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-01-26
2001-01-09
Ghebretinsae, Temesghen (Department: 2734)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S324000, C714S795000
Reexamination Certificate
active
06173020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a demodulation circuit including error correction for satellite communication, and more particularly to a demodulation circuit which performs error correction for a channel having a low carrier power to noise power ratio in mobile radio communication.
2. Description of the Related Art
For a demodulation circuit including error correction for a received signal in satellite communication, various demodulation algorithms have been investigated to improve the characteristic in error correction because the received radio wave is very weak. Demodulation circuits including error correction which are based on the demodulation algorithms have been developed. Among them, a demodulation circuit including error correction based on convolutional coding and Viterbi decoding is popularly used. The demodulation circuit has a strong error correction function as a demodulation circuit including error correction and improves the bit error ratio of a received signal significantly.
FIG. 1
is a view showing a construction of a conventional modulation-demodulation circuit including error correction based on convolutional coding and Viterbi decoding. Referring to
FIG. 1
, modulation circuit
100
includes convolutional coder
101
, interleaver
102
, reference bit inserter
103
, and modulator (for example, a BPSK modulator)
104
. Demodulation circuit
200
includes demodulator (for example, a BPSK demodulator)
201
, reference bit remover
202
, deinterleaver
203
, and Viterbi decoder
204
.
Now, operation of modulation circuit
100
is described. Convolutional coder
101
convolutionally codes an input burst data signal. Interleaver
102
interleaves the convolutionally coded data in accordance with specifications. Reference bit inserter
103
delimits the interleaved data at predetermined intervals and inserts reference bits in order to assure a high degree of accuracy in demodulation of a received signal. The reference bits are used as reference information to the phase and the amplitude. Modulator
104
, for example, BPSK converts an output of reference bit inserter
103
and outputs a resulting signal as a transmission signal.
Next, operation of demodulation circuit
200
is described. Demodulator
201
demodulates a received burst data signal using the reference bits by, for example, BPSK demodulation. Reference bit remover
202
removes the reference bits from the demodulated burst data. Deinterleaver
203
performs deinterleaving by which the data are re-arranged (deinterleaved) in accordance with specifications corresponding to those of the interleaving of the modulator, and outputs the deinterleaved data to Viterbi decoder
204
. Viterbi decoder
204
performs decoding corresponding to the coding by the convolutional coder and outputs maximum likely data as Viterbi decoded data.
In the conventional modulation-demodulation circuit including error correction, the demodulation circuit therein supplies, in error correction, information of the maximum likelihood from the demodulator to the error correction unit with not only the demodulator but also characteristics of error correction taken into consideration. In short, the demodulation unit and the error correction unit individually perform optimization separately from each other.
However, for conventional modulation-demodulation circuits including error correction based on convolutional coding and Viterbi decoding, various demodulation algorithms have been investigated and developed to improve the characteristics in error correction. For the demodulation circuit for the modulation-demodulation circuits, efforts are directed to improve the performance with not only the demodulator but also the characteristics in error correction take into consideration. Upon maximum likelihood decoding by which a Viterbi algorithm is used to decode maximum likely data from a convolutional signal in error correction, information of the likelihood is transmitted from the demodulator to the Viterbi decoder including error correction.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a demodulation circuit including error correction based on convolution coding and Viterbi decoding by which the characteristic of error correction is further improved.
According to an aspect of the present invention, there is provided a demodulation circuit including error correction which includes means for demodulating a burst data signal received in a satellite communication channel having a low carrier power to noise power ratio using reference bits, means for removing the reference bits from the demodulated burst data, means for deinterleaving the burst data, from which the reference bits have been removed, in accordance with specifications, and means for Viterbi decoding the convolutionally coded burst data, characterized in that it comprises means for weighting each value of the demodulated burst data in accordance with the distance from the reference bits of the burst data.
According to another aspect of the present invention, there is provided a demodulation circuit including error correction for a satellite communication channel having a low carrier power to noise power ratio, comprising a demodulation circuit unit for demodulating a received burst data signal using reference bits, a data extraction unit for removing the reference bits from the demodulated burst data, a weighting unit for weighting each value of the extracted burst data in accordance with the distance from the reference bits of the burst data, a deinterleave unit for deinterleaving the weighted burst data in accordance with specifications, and an error correction unit for Viterbi decoding the convolutionally coded burst data.
According to a further aspect of the present invention, there is provided a demodulation circuit including error correction for a satellite communication channel having a low carrier power to noise power ratio, comprising, a demodulation circuit unit for demodulating a received burst data signal using reference bits, a weighting unit for weighting each value of the demodulated burst data in accordance with the distance from the reference bits of the burst data, a data extraction unit for removing the reference bits from the burst data which have been weighted, a deinterleave unit for deinterleaving the data, from which the reference bits have been removed, in accordance with specifications, and an error correction unit for Viterbi decoding the convolutionally coded deinterleaved burst data.
According to the present invention, a data signal produced by adding reference bits to burst data at suitable intervals in a data format of a fixed length is weighted, after demodulated, with a likelihood of demodulation which varies in proportion to the distance from the reference signal, and as a result, an advantage that improvement in error correction capacity can be achieved is provided.
As an actual example, error correction was performed after weighting burst data with a weight at a fixed rate such that a maximum weight was applied to a burst data just adjacent the reference bits whereas a minimum weight was applied to another burst data farthest from the reference bits. The BER (Bit Error Ratio) then was, when a test was performed for 200 bursts under Rice fading, 1.302 e
−2
whereas the BER prior to the error correction was 8.411 e
−2
, and error was successfully decreased by 92.6% when compared with the BER 1.406 e
−2
obtained without applying any weight.
REFERENCES:
patent: 5412686 (1995-05-01), Ling
patent: 5450453 (1995-09-01), Frank
patent: 5502713 (1996-03-01), Lagerqvist et al.
patent: 5583886 (1996-12-01), Rohani et al.
patent: 2-53330 (1990-02-01), None
patent: 2-159126 (1990-06-01), None
patent: 5-344002 (1993-12-01), None
Ghebretinsae Temesghen
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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