Pulse or digital communications – Repeaters – Testing
Patent
1997-02-12
1999-08-17
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375208, 375200, 370515, 370516, H04K 100
Patent
active
059404337
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an acquisition method and system of a spreading code, which is applicable to radio receivers in a CDMA (Code Division Multiple Access) carrying out the multiple access in a mobile communication system using a spread spectrum.
More particularly, the present invention relates to a technique for making decision or confirmation whether the acquisition of a received spreading code is established or not in a radio receiver in a mobile system adopting a direct sequence CDMA (DS-CDMA) performing the multiple access using the spread section technique.
BACKGROUND ART
The CDMA transmission is classified into a direct sequence (DS) method that spreads a conventionally modulated signal with a spreading code at a high rate, and a frequency hopping (FH) method. It is necessary for the FH method to divide each symbol into much smaller units called chips, and to switch the central frequency of each chip at a high rate. Since this makes it difficult to implement a device employing the FH method, the DS method is usually used.
DS-CDMA radio equipment, different from SCPC (Single Channel Per Carrier)/FDMA (Frequency Division Multiple Access) radio equipment or TDMA (Time Division Multiple Access) radio equipment, carries out at a transmitting side secondary modulation with a spreading code after data modulation, thereby transmitting a signal whose bandwidth is spread. On the other hand, at a receiving side, it restores a narrowband signal from the wideband received signal through a process called despreading, and demodulates the despread signal by a conventional method. The despreading at the receiving side requires to detect correlation between the received spreading signal and the spreading code sequence locally generated in the receiver.
Usually, it is necessary for the DS-CDMA receiver to generate a replica of the spreading code, and to synchronize the spreading code replica with the spreading code in the received signal. The synchronization process of the spreading code is divided into acquisition and tracking. Since the spreading code such as a Gold code or the like can obtain the autocorrelation only within a range of plus minus one chip, the acquisition must reduce the phase difference between the spreading code sequence in the received signal and the spreading code replica within a range much smaller than plus minus one chip, and then the tracking keeps the phase difference within this range.
The acquisition method is described, for example, in M. K. Simon, J. K. Omura, R. A. Scholtz, and B. K. Levitt, "Spread Spectrum Communications", Vol. III, Computer Science Press, 1985.
Next, the acquisition method that constitutes a prior art of the present invention will be described with reference to FIG. 1.
FIG. 1 is a block diagram of serial code acquisition process using a sliding correlator. In this figure, the reference numeral 1 designates an input terminal of the spread signal, 2 designates an output terminal for outputting a signal indicating that the acquisition has been established, 3 designates a multiplier, 5 designates an integrator/dump circuit, 6 designates a square-law detector, 7 designates a threshold decision circuit, 8 designates a digital control clock generator, and 9 designates a spreading code replica generator.
The operation of the sliding correlator as shown in FIG. 1 is as follows. To achieve the acquisition of the spreading code, the received signal input to the input terminal 1 is multiplied by the spreading code replica by the multiplier 3, and the output of the multiplier 3 is integrated for a certain time by the integrator/dump circuit 5, thereby obtaining a correlation output. The correlation output undergoes square-law detection by the square-law detector 6, and the detected output is decided whether it exceeds a threshold or not by the threshold decision circuit 7. Thus, a decision is made whether the acquisition of the spreading code has been established or not.
In a single dwell system, in which the integrator/dump circuit 5 has only one
REFERENCES:
patent: 4168398 (1979-09-01), Matsuo et al.
patent: 5638362 (1997-06-01), Dohi et al.
patent: 5729571 (1998-03-01), Park et al.
Higashi Akihiro
Higuchi Kenichi
Sawahashi Mamoru
Chin Stephen
Deppe Betsy L.
NTT Mobile Communications Network Inc.
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