Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Patent
1996-08-30
1999-04-27
Kizou, Hassan
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
370350, 375208, 375325, 375371, H04J 1304, H04L 700
Patent
active
058986650
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a radio receiver in mobile communications, and more particularly to a coherent tracking apparatus and method for a receiver in a CDMA (Code Division Multiple Access) system using spread spectrum.
BACKGROUND ART
As is well known, it is necessary for a direct sequence receiver to synchronize a replica of a spreading code generated in the receiver with the spreading code in a received spread signal. The synchronization process falls into initial acquisition and tracking.
FIG. 1 is a block diagram showing a conventional DLL (Delay Locked Loop) used for the tracking. A spreading code replica is generated by a spreading code replica generator 1, and spreading codes whose phases are advanced and lagged by one chip with respect to the spreading code replica are fed to multipliers 3 and 4, respectively. The multipliers 3 and 4 take correlation between these spreading codes and the received spread signal. The correlation signals output from the multipliers 3 and 4 are passed through BPFs 5 and 6 which remove spurious high frequency components, and undergo square-law detection by square-law detectors 7 and 8. The outputs of the square-law detectors 7 and 8 are added in opposite phase by an adder 10 so that the phase error components are extracted between the received spreading code and the spreading code replica. The phase error components obtained are passed through a loop filter 11, and fed back to a voltage controlled clock generator 1. Thus, the generating phase of the spreading code replica is controlled so that its phase matches that of the received spreading code.
In this DLL, the signals after the correlation are passed through the square-law detectors to remove the residual frequency components of the carrier after the quadrature detection, or to remove the modulated components of the information data, which are contained in the signals after the correlation. Although this method has an advantage that the phase error can be easily extracted between the received spreading code and the spreading code replica, it has a disadvantage that noise and tracking jitter are increased because the noise components are also squared.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a coherent tracking apparatus and method for a CDMA receiver, which can achieve high accuracy tracking.
In a first aspect of the present invention, there is provided a coherent tracking apparatus for a CDMA receiver for use in a CDMA system that performs multiple access transmission by transmitting and receiving a spread signal, the spread signal being generated by spreading a pilot signal of a known pattern and an information data signal into a wideband signal with a spreading code whose rate is higher than a rate of an information symbol, the pilot signal and the information data signal being alternated at a fixed pilot period, the coherent tracking apparatus comprising: demodulation spreading code replica inphase with a spreading code in a received spread signal; pair of tracking spreading code replicas whose phases are equal to a phase of the demodulation spreading code replica plus and minus a predetermined value, respectively; received spread signal and the demodulation spreading code replica; of the demodulation correlator means, and for detecting phase errors of the pilot signal; data signal in the output of the demodulation correlator means; data signal output from the first delay means by interpolating the phase errors of the pilot signal into a section of the information data signal; signal by deciding an output of the first phase compensator; between the received spread signal and the tracking spreading code replicas; phases to produce a first phase error signal; means and an output of the adder for delaying the first phase error signal by at least the pilot period; signal with an output of the demodulation means to remove modulated components of the information data signal, which are included in the first phase error signal, thereby producing a secon
REFERENCES:
patent: 5477195 (1995-12-01), Spilker
patent: 5638362 (1997-06-01), Dohi et al.
patent: 5640416 (1997-06-01), Chalmers
patent: 5691974 (1997-11-01), Zehavi et al.
patent: 5737362 (1998-04-01), Hyun et al.
Adachi Fumiyuki
Sawahashi Mamoru
Kizou Hassan
NTT Mobile Communications Network Inc.
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