Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1999-05-24
2003-05-27
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Angle modulation
C375S340000, C375S366000, C370S324000, C370S511000, C370S513000, C370S514000, C455S059000, C455S059000
Reexamination Certificate
active
06570935
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and a system for demodulating receive signal including pilot signal, and more particularly to, a method and a system for demodulating receive signal including pilot signal while suppressing BER (bit error rate) on the basis of unique word as pilot signal in mobile satellite communication incurring a fast fading on transmission path.
BACKGROUND OF THE INVENTION
FIG. 1
shows a mobile terminal for mobile satellite communication. This mobile terminal, for example, a portable telephone, is composed of an antenna
81
to receive a transmit signal with a pilot signal in multiple blocks through a satellite, a signal converter
82
to convert the received signal from analogue to digital, a demodulation circuit
10
to demodulate the converted signal, a voice signal generator to convert the demodulated signal from digital to analogue, and a speaker
84
to output a voice signal.
In
FIG.1
, a receive signal including a pilot signal received by the antenna
81
is converted into a digital signal. The converted digital signal is demodulated by the demodulation circuit
10
, and then converted into an analogue voice signal by the voice signal generator
83
. The analogue voice signal converted by the voice signal generator
83
is output as voice sound from the speaker
84
.
In the above satellite communication system, for the purpose of reducing required power or miniaturizing the antenna, further for the purpose of keeping BER low even under the condition with a low signal-to-noise power ratio, an error correction code with large encoding gain or a high-efficiency encoding technique is used.
FIG.2
shows a demodulation system for continuous wave, which is described in Meyr, “Digital Communication Receiver”, John Wiley &Sons, pp.744-747, 1997, that can be used as the demodulation circuit
10
in FIG.
1
. In this system, for a multipath fading including frequency-selective fading and flat fading with no frequency characteristic, receive signals are demodulated compensating a distortion in receive signal on flat fading (hereinafter simply referred to as ‘fading distortion’).
In
FIG. 2
, a continuous-wave receive signal with unique words as pilot signal inserted at given intervals is input to an input terminal IN, and then supplied to a delay circuit
91
and a unique word demodulator
93
. A unique word in the receive signal is demodulated by the unique word demodulator
93
, input to a data distortion estimator
94
composed of a Wiener filter. The data distortion estimator
94
estimates the fading distortion of data in the receive signal based on the fading distortion of unique word calculated from known values (e.g., 0 that +1 is phase-modulated, and &pgr; that −1 is phase-modulated) and the value of the demodulated unique word, then outputting it to a data demodulator
92
. The data demodulator
92
demodulates data delayed a given time by the delay circuit
91
while compensating it with the estimation quantity of fading distortion, then outputting a demodulated signal from an output terminal OUT. Thus, data transmitted on continuous wave can be demodulated with the fading distortion compensated.
FIG. 3
shows another demodulation system, which is described in M. Sanpei, “16QAM Fading Distortion Compensation Method for Land Mobile communication”, IEICE Paper Publication B-11, Vol. J72-B-11, No. 1, pp. 7-15, 1989, that can be used as the demodulation circuit
10
in FIG.
1
. This system demodulates compensating the fading distortion of a continuous receive signal with one unique word symbol inserted for every (N−1) information symbols. In
FIG.3
, when a receive signal is input to an input terminal IN, fading distortion estimators
111
,
112
and
113
calculate the fading distortion estimate values c(k−1), c(k) and c(k+1) of (k−1)th, k-th and (k+1)th unique words in the receive signal that are delayed in the sequence. The estimate values are multiplied with 0
th
-order or 1
st
-order interpolation coefficients by multipliers
114
,
115
and
116
, and added by an adder
117
. The adder
117
outputs c{k+(m/N)} as the fading distortion of m-th information symbol in k-th information symbol sequence, as the addition result. The fading distortion of this information symbol is transformed into 1/c{k+(m/N)} by a reciprocal transformer
118
, then output to a multiplier
120
. The multiplier
120
multiplies information symbol in the receive signal delayed by a delay circuit
119
by 1/c{k+(m/N)} output from the reciprocal transformer
118
to demodulate its information, which is output from a output terminal OUT. Thus, the receive signal is demodulated compensating the envelope curve and phase of the receive signal distorted by fading distortion.
However, the demodulation system in
FIG. 12
has a problem described below. It can demodulate the receive signal at a desired BER for continuous wave that unique words are inserted at given intervals to continuous data. But, for example, when receiving a burst signal with frame format that unique words are inserted to the several parts of a 100 to 150 symbol data sequence, since the fading distortion of data sequence at both ends is estimated from the fading distortion of unique word at one side, the estimation precision of fading distortion of data located at the opposite side of the unique word is reduced. Therefore, under the condition with fast fading or low C/N ratio, a desired BER, e.g., such a BER that corresponds to a deterioration 0.5 dB of from theoretical value when the Rician fading intensity is 0 dB and the Doppler frequency is 0.01%, cannot be obtained. If instead of the Wiener filter, a Kalman filter or MAP estimation with a higher estimation precision is used, since it is such a matrix-like technique that requires a large amount of operation, the amount of operation increases.
For the demodulation system in
FIG. 3
, when it uses a 0
th
-order interpolation coefficient, one unique word value is retained over the corresponding (N−1) information symbols. Also, when it uses a 1
th
-order interpolation coefficient, the fading distortion of information symbol is estimated by connecting between adjacent unique words with a straight line. Therefore, under the condition with fast fading or low C/N ratio, a desired BER cannot be obtained.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method and a system for demodulating receive signal including pilot signal that even when fast fading occurs on the channel, the fading distortion can be estimated at a high precision and a low BER can be obtained, without increasing the amount of operation.
It is a further object of the invention to provide a method and a system for demodulating receive signal including pilot signal that in receiving a burst signal, a low BER can be obtained compensating the fast fading.
According to the invention, a method for demodulating receive signal including pilot signal that a receive signal is demodulated estimating the fading distortion of data by detecting the fading distortion of unique word as pilot signal inserted into multiple sections of the receive signal, comprises the steps of:
comparing a unique word in the multiple sections of receive signal and a known unique word and thereby detecting the fading distortion of unique word in the multiple sections;
calculating a spline interpolation curve based on the fading distortion of unique word in the multiple sections;
estimating the fading distortion of data in the receive signal from the spline interpolation curve; and
demodulating the data in the receive signal based on the fading distortion of the data.
According to another aspect of the invention, a method for demodulating receive signal including pilot signal that a receive signal is demodulated estimating the fading distortion of data by detecting the fading distortion of unique word as pilot signal inserted into multiple sections of the receive signal, comprises the st
Ha Dac V.
NEC Corporation
Sughrue & Mion, PLLC
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