Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1999-04-20
2003-02-18
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Angle modulation
C375S316000, C375S229000
Reexamination Certificate
active
06522702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The conventional radio data communication terminal shown in
FIG. 5
includes A/D converters
41
and
42
for A/D-converting I (in-phase), Q (quadrature) signals which have been orthogonally demodulated in an RF unit (not shown). The terminal further includes a phase rotator
43
for rotating the phase of the received signals by a desired phase detection circuit
44
for detecting phase difference between the present angle and an angle before one period. The terminal further includes a average value calculating circuit
45
for calculating an average value by summing the phase differences detected by phase difference detection circuit
44
by a predetermined number of times and dividing the summation by the predetermined number and the number of symbols in the period. The terminal further includes a integration circuit
46
for integrating the average detected by average value calculating circuit
45
every symbol time. The terminal further includes a vector resolving circuit
47
for resolving the integrated value supplied from integration circuit
46
to a real part and an imaginary part and outputting them to phase rotator
43
. The terminal further includes a transmission path distortion estimator
48
for estimating the transmission path distortion during the preamble period by using a pair of signals whose phase has been rotated by phase rotator
43
. The terminal further includes a tap coefficients setter
49
for calculating tap coefficients necessary for equalizer
50
on the basis of the transmission path distortion determined by transmission path distortion estimator
48
and setting the coefficients to equalizer
50
. The terminal further includes a equalizer
50
for equalizing the pair of signals from phase rotator
43
on the basis of the tap coefficient set by tap coefficient setter
49
to perform a demodulation.
2. Description of the Prior Art:
Among radio data communication terminals which operate in accordance with the narrow-band modulation system such as GMSK modulation system, there are such terminals that detect a frequency offset and execute training for estimating a transmission path distortion during a preamble period.
FIG. 5
shows the construction of a conventional radio data communication terminal.
The conventional radio data communication terminal shown in
FIG. 5
includes A/D converters
41
and
42
for A/D-converting I (in-phase), Q (quadrature) signals which have been orthogonally demodulated in an RF unit (not shown), phase rotator
43
for rotating the phase of the received signals by a desired phase, phase difference detection circuit
44
for detecting phase difference between the present angle and an angle before one period, average value calculating circuit
45
for calculating an average value by summing the phase differences detected by phase difference detection circuit
44
by a predetermined number of times and dividing the summation by the predetermined number and the number of symbols in the period, integration circuit
46
for integrating the average detected by average value calculating circuit
45
every symbol time, vector resolving circuit
47
for resolving the integrated value supplied from integration circuit
46
to a real part and an imaginary part and outputting them to phase rotator
43
, a transmission path distortion estimator
48
for estimating the transmission path distortion during the preamble period by using a pair of signals whose phase has been rotated by phase rotator
43
, tap coefficients setter
49
for calculating tap coefficients necessary for equalizer
50
on the basis of the transmission path distortion determined by transmission path distortion estimator
48
and setting the coefficients to equalizer
50
, and equalizer
50
for equalizing the pair of signals from phase rotator
43
on the basis of the tap coefficients set by tap coefficient setter
49
to perform a demodulation.
At a transmission side, the same PN sequence (pseudo noise sequence) is repetitively transmitted during a preamble period inserted before an information data period. At a radio data communication terminal, phase difference detection circuit
44
detects the phase difference between samples which are apart from each other by the period of the PN sequence during a predetermined period within the preamble period. Average value calculating circuit
45
divides the phase difference between the samples which are apart from each other by the period of the PN sequence by the number of symbols during one period of the PN sequence to calculate a symbol-based phase difference &Dgr;&thgr; (frequency offset value), and hold this phase difference &Dgr;&thgr; during one frame period comprising the preamble period and the information data period. Integration circuit
46
integrates the phase difference &Dgr;&thgr; on a symbol basis, and vector resolving circuit
47
resolves the output of integration circuit
46
to vector components. Phase rotator
43
corrects the phase at the receiver side by using the output of vector resolving circuit
47
. After the phase difference &Dgr;&thgr; is calculated, transmission path distortion estimator
48
estimates the transmission path distortion, and tap coefficient setter
49
calculates the tap coefficients necessary for equalizer
50
on the basis of the transmission path distortion thus determined and sets the tap coefficients to equalizer
50
.
Furthermore, according to another prior art disclosed in JPA-6-252698, an automatic adaptive equalizing means repetitively reads a training signal from storage means until tap coefficients or an impulse response converges to the transfer function of a transmission path, whereby the training sequence can be shortened. Therefore, the training signal to be added before the data signal in the same frame of the signal transmitted from the transmission side can be shortened to enhance the information transfer efficiency.
In the prior art shown in
FIG. 5
, it is necessary to successively perform the detection of the frequency offset value, the estimation of the transmission path distortion, the setting of the tap coefficients to the equalizer, etc. in this order within the preamble period before the equalizer is actuated, and thus the preamble period is lengthened. Therefore, this technique has a disadvantage that the information transfer efficiency is reduced.
Further, in the prior art disclosed in JPA-6-252698, when the same training signal is repetitively read out from the storage means in the process of converging the tap coefficients or the impulse response to the transfer function of the transmission path, there is a disadvantage that the processing time of the operation become increased.
SUMMARY OF THE INVENTION
In order to overcome the aforementioned disadvantages, the present invention has been made and accordingly has an object to provide radio data communication terminal of a narrow-band modulation type which can determine a frequency offset value used for phase rotation means and set tap coefficients used in an equalizer by using the shortest preamble.
According to the present invention, there is provided a radio data communication terminal, which includes a phase rotating means for correcting a phase error of a frame signal which conforms to a narrow-band modulation system. The terminal further includes an equalizer for correcting a transmission path distortion of the frame signal corrected in phase. The terminal further includes a calculating means for calculating the phase error by using a preamble in the frame signal, wherein the phase error is used for the phase error correction in the phase rotating means. The terminal further includes a transmission path distortion estimating means for estimating the transmission path distortion by using the preamble in the frame signal corrected in phase and calculating tap coefficients necessary for the equalizer. The terminal further includes a setting means for setting the tap coefficients to the equalizer. The terminal further includes a first del
Burd Kevin M
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
Pham Chi
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