Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1997-10-20
2001-01-30
Pham, Chi H. (Department: 2731)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S325000
Reexamination Certificate
active
06181751
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multi-stage detection system in a digital demodulator for demodulating a received signal by differential detection.
Digital demodulators are widely used in the telecommunication field. A digital modulator which demodulates a received signal by differential detection can be efficiently used in a mobile communication system. The signal to be received by the digital demodulator is transmitted as a transmitted signal from a transmitter. For example, this transmitted signal is produced by differential phase shift keying in the transmitter. That is, the transmitted signal has phase information.
The coherent detection methods obtain the phase information by reproducing the carrier frequency and phase correctly (see, for example, Y. Matsumoto, S. Kubota and S. Kato, “A New Burst Coherent Demodulator for Microcellular TDMA/TDD Systems”, IEICE Trans. Commun. Vol. E77-B, No. 7, pp. 927-933, July, 1994). If the carrier frequency and phase can be reproduced correctly, the demodulation characteristics are superior to that of the other kind of demodulators. However, it is complicated to realize the carrier synchronization and since the modulated signal is always transmitted under a fading environment in mobile communication, it is also quite difficult to reproduce the carrier frequency and phase exactly.
The conventional differential detection methods calculate the phase difference between the two adjacent symbols of the received signal (see, for example, C. Liu and K. Feher, “Proposed &pgr;/4-QPSK with Increased Capacity in Digital Cellular Systems”, ICC'92, pp. 316-318, 1992, and H. Tomita, Y. Yokoyama, T. Matsuki, “DIGITAL INTERMEDIATE FREQUENCY DEMODULATION TECHNIQUE FOR CELLULAR COMMUNICATION SYSTEMS”, IEEE GLOBECOM'90, San Diego, Calif., pp. 1827-1831, December 1990), and a decision rule is used to obtain the transmitted information. Although the differential detection methods are effective under the fading environment, the static characteristics are inferior to those of the coherent detector.
The multiple-symbol method uses more than two symbols for improving the static characteristics of the above differential detectors (see, for example, D. Divsalar and M. Simon, “Multiple-Symbol Differential Detection of MPSK”, IEEE Trans. Commun. Vol. 38, No. 3, pp. 300-308, March 1990). However, it becomes very complicated to realize the multiple-symbols detector.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a multi-stage detection system in a digital modulator which has almost the same static characteristics as the multiple-symbols method and can be realized easily.
It is another object of the present invention to provide a multi-stage detection system in a digital modulator which has a fading characteristic at least as good as that of the conventional differential detector.
In order to achieve the above objects, according to the present invention, there is provided a multi-stage detection system in a digital modulator, comprising first-stage detection means for detecting an input signal, second-stage detection means for receiving outputs from the first-stage detection means, and third-stage detection means for receiving outputs from the second-stage detection means, the first-stage detection means including a first delay for delaying the input signal by one sampling period, a first adder for adding the input signal to an output from the first delay, a first detector for detecting an output from the first adder, a second delay for delaying the output from the first delay by one sampling period, a second adder for adding the input signal to an output from the second delay, a second detector for detecting an output from the second adder, a third delay for delaying the output from the second delay by one sampling period, a third adder for adding the input signal to an output from the third delay, and a third detector for detecting an output from the third adder.
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Y. Matsumoto, S. Kubota and S. Kato, “A New Burst Coherent Demodulator for Microcellular TDMA/TDD Systems”, IEICE Trans. Commun. vol. E77-B, No. 7, pp. 927-933, Jul., 1994.
C. Liu and K. Feher, “Proposed &pgr;/4-QPSK with Increased Capacity in Digital Cellular Systems”, ICC '92, pp. 316-318, 1992.
H. Tomita, Y. Yokoyama, T. Matsuki, “Digital Intermediate Frequency Demodulation Technique for Cellular Communication Systems”, IEEE GLOBECOM '90, San Diego, Ca, pp. 1827-1831, Dec. 1990.
D. Divsalar and M. Simon, “Multiple-Symbol Differential Detection of MPSK”, IEEE Trans. Commun, vol. 38, No. 3, pp. 300-308, Mar. 1990.
Japanese Office Action received May 26, 1999 in corresponding Japanese Application.
English translation of selected portion of May 26, 1999 Japanese Office Action.
Corrielus Jean B.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Pham Chi H.
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