CDMA receiver phase tracking system

Details CDMA receiver phase tracking system CDMA receiver phase tracking system

1998-12-18

2002-12-03

Kizou, Hassan (Department: 2662)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C370S441000, C370S479000, C370S491000, C370S516000, C375S147000

Reexamination Certificate

active

06490265

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a CDMA receiver phase tracking system, and more particularly, to a CDMA receiver phase tracking system which optimally changes the amount of processing operations for calculation of phase tracking according to the receiving environment, as well as to a CDMA receiver.
In code division multiple access (CDMA) spectrum spread digital communication, a pilot signal plays an important role in ensuring and maintaining synchronization between a base station and a mobile station. A CDMA receiver phase tracking system is used for ensuring synchronization with the pilot signal.
FIG. 4
shows the configuration of a conventional CDMA receiver phase tracking system. A signal
1
which is received by the CDMA receiver and converted into a signal of base band range through frequency conversion is input to despreading means
10
, where the signal is despread. In short, voltage-controlled oscillation means
10
a
provided in the despreading means
10
produces a despread code. A despreading device
10
b
despreads a pilot signal contained in the received signal through use of the thus-produced despread code. Phase shift means
10
c
produces from the despread code a despread advance code whose timing is made faster by a given period of time and a despread lag code whose timing is made later by a given period of time. A changeover switch
10
d
permits alternate output of the despread advance code and the despread lag code. The despread timing signal is made earlier by a given period of time through use of the despread advance code, and the pilot signal included in the received signal is despread by the despreading device
10
e
. Further, despread timing is made later by a given period of time through use of the despread lag code, and the pilot signal included in the received signal is despread.
Strength determination means
11
determines the strength of the pilot signal despread by making the despread timing earlier by a given period of time or the strength of the pilot signal despread by making the despread timing later by a given period of time.
A strength difference detection section
12
a
provided in strength difference detection means
12
detects a difference between the strength of the pilot signal despread by making the despread timing earlier (or later) by a given period of time and the strength of the pilot signal despread by making the despread timing later (or earlier) by a given period of time, the strength of the latter pilot signal having been received from the strength determination means
11
and stored in a storage section
12
prior to determination of the strength of the former pilot signal. More specifically, a difference is detected by subtracting the strength of the pilot signal despread by making the despread timing later by a given period of time from the strength of the pilot signal despread by making the despread timing earlier by a given period of time.
Integral means
13
A integrates a difference-between the pilot signal despread by making the despread timing by earlier a given period of time and the pilot signal despread by making the despread timing later by a given period of time-corresponding to the overall received data frame. On the basis of the result of integration, phase tracking control means
14
controls the despread timing of the despreading means
10
.
However, in the foregoing existing CDMA receiver phase tracking system, the integration means
13
integrated the strength difference corresponding to the entire received data frame. It has already been known that an integration interval can be reduced in superior receiving conditions; namely, even if the strength difference corresponding to the entire received data frame is not integrated, there is obtained an accuracy of phase tracking which is identical with that obtained by integrating all the difference corresponding to the entire received data frame. However, the strength difference corresponding to the entire received data frame is integrated every interval on the basis of the assumption that the receiving environments will be deteriorated. For this reason, the tracking system has a problem of the integration means
13
performing excessive processing operations.
SUMMARY OF THE INVENTION
The present invention is aimed at solving the aforementioned problem in the existing system, and the object of the present invention is to provide a superior CDMA receiver phase tracking system in which there can be changed the interval at which the integration means
13
performs an integration operation according to receiving environments and which reduces the load imposed on the integration means by decreasing the amount of processing operations in a superior receiving environment, thus realizing low power consumption.
To solve the problem, the present invention provides a CDMA receiver phase tracking system having the following configuration. Specifically, despreading means despreads a pilot signal included in a received signal, and strength determination means determines the strength of the despread pilot signal. Integration control means decides an integration interval from the strength of the received pilot signal and by means of an ON/OFF switch activates or deactivates the integration means according to the integration time. Strength difference detection means detects differences in strength among received pilot signals having different phases, and the integration means adds together the strength differences, thus producing a received strength difference sum. Phase tracking control means adjusts a despread phase on the basis of the received strength difference sum.
With the foregoing configuration, the integration interval used by the integration means is made changeable according to receiving environments, and the amount of processing operations can be reduced in a superior receiving environment. Accordingly, the load imposed on the integration means can be reduced, thus enabling realization of reduced power consumption.
According to the first aspect of the present invention, a CDMA receiver comprises: despreading means which produces a first despread pilot signal by despreading at a first timing a pilot signal included in a received signal, produces a second despread pilot signal by despreading the pilot signal at a second timing earlier than the first timing by a given period of time, and produces a third despread pilot signal by despreading the pilot signal at third timing later than the first timing by a given period of time; first strength determination means which produces a first received pilot signal strength from the first despread pilot signal; second strength determination means which produces a second received pilot signal strength from the second despread pilot signal and a third received pilot signal strength from the third despread pilot signal; strength difference detection means for detecting a difference between the second received pilot signal strength and the third received pilot signal strength; integration means which adds together the strength differences and outputs a received strength difference sum; integration control means which determines an integration interval for the integration means from the first received pilot signal strength; an ON/OFF switch for activating or deactivating the integration means according to the integration interval; and phase tracking control means for adjusting the phase of the first timing on the basis of the received strength difference sum. The CDMA receiver changes the integration interval according to the strength of the received pilot signal, thus reducing the amount of integrating operations.
According to the second aspect of the present invention, the CDMA-receiver as mentioned above further comprises: demodulation means which demodulates the received data signal despread by the despreading means and outputs demodulated data; re-modulation means which modulates again the demodulated data and outputs re-modulated signal; error rate calculation means which calculates a receiving err

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