CDMA receiver

Details CDMA receiver CDMA receiver

1998-04-20

2001-05-22

Ngo, Ricky (Department: 2664)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C370S515000, C375S150000, C375S367000

Reexamination Certificate

active

06236648

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a code division multiple access (CDMA) receiver used for a digital portable telephone or the like, or more particularly to a synchronization tracking circuit of a CDMA receiver.
2. Description of the Related Art
A conventional CDMA receiver of this type is disclosed in JP-A-9-18446, for example.
In the conventional CDMA receiver, as shown in
FIG. 1
, an analog reception signal is over-sampled and converted into a digital reception signal by an A/D converter
610
. A correlator
620
obtains a correlation value between the digital reception signal and a spreading code of a pilot channel (pilot spreading code) in accordance with a reception timing of the receiver. In the process, a reception timing correlator
621
obtains a correlation value between the digital reception signal and the pilot spreading code which is synchronous with a present reception timing. An early timing correlator
622
obtains a correlation value between the digital reception signal and the pilot spreading code which is synchronous with an early reception timing having a phase ahead of the present reception timing. A late timing correlator
623
obtains a correlation value between the digital reception signal and the pilot spreading code which is synchronous with a late reception timing signal having a phase lagging behind the present reception timing.
A phase difference detecting unit
630
obtains a phase difference between the reception signal and the present reception timing based on the three correlation values obtained by the correlator
620
. A timing controlling unit
640
synchronizes the reception timing, which is used for obtaining the correlation values in the correlator
620
, with the reception signal by shifting the reception timing in such a direction as to eliminate the phase difference obtained by the phase difference detecting unit
630
. In the case where the reception timing is shifted intentionally, the direction of the phase difference to be shifted and the angle to be shifted are indicated to the timing controlling unit
640
.
With the above-mentioned conventional CDMA receiver, the system configuration is restricted for selection of the sampling frequency of the A/D converter
610
. Nevertheless, any sampling frequency can be selected.
An arbitrary selection of the sampling frequency, however, makes it necessary to perform a dividing operation for calculating, setting and implementing a correction value of the reception timing when the phase difference between the reception signal and the reception timing is detected to correct the reception timing. The result is longer time required for calculating the correction value of the reception timing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a CDMA receiver capable of shortening the time required for calculating a correction value of a reception timing.
According to a first aspect of the present invention, there is provided a CDMA receiver which comprises: an A/D converter for over-sampling an analog reception baseband signal with a sampling clock having a frequency 2
n
times higher than that of a chip clock and for converting the analog reception baseband signal into a digital reception baseband signal; a correlator for obtaining a correlation value between the digital reception baseband signal and a pilot spreading code which is synchronous with a reception timing; a phase difference detecting unit for obtaining a phase difference between the digital reception baseband signal and the reception timing based on the correlation value; and a timing controlling unit for changing the reception timing so as to eliminate the phase difference.
According to a second aspect of the present invention, there is provided a CDMA receiver, wherein the timing controlling unit includes a chip phase shifting unit for changing the reception timing in chips; and a 1/2
n
-chip phase shifting unit for changing the reception timing in 1/2
n
chips.
According to a third aspect of the present invention, there is provided a CDMA receiver, wherein the timing controlling is constituted using a synchronizing circuit.


REFERENCES:
patent: 4665404 (1987-05-01), Christy et al.
patent: 5349606 (1994-09-01), Lovell et al.
patent: 5361276 (1994-11-01), Subramanian
patent: 5844935 (1998-12-01), Shoji
patent: 5914943 (1999-06-01), Higuchi et al.
patent: 0 522975 (1993-07-01), None
patent: 0 698 971 (1996-02-01), None
patent: 0 726 658 (1996-08-01), None
patent: 9-018446 (1997-01-01), None

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