Pulse or digital communications – Synchronizers
Reexamination Certificate
1999-10-04
2004-05-25
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Synchronizers
C370S335000, C370S342000, C370S503000, C375S343000
Reexamination Certificate
active
06741667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a perch channel reception device and a perch channel reception method of a mobile radio communication terminal which executes radio communication according to CDMA (Code Division Multiple Access).
Description of the Prior Art
Mobile radio communication terminals such as portable cellular phones have become widely available these days. Generally, a mobile radio communication terminal has to search for base stations around the mobile radio communication terminal and obtain base station information (information with regard to a base station, such as present time of the base station, an ID of the base station, transmission power of the base station, etc.) which is transmitted by each of the base stations, when power of the mobile radio communication terminal is turned on or at predetermined time periods.
The base station information which is transmitted by a base station so as to be received by mobile radio .communication terminals in its own base station cell (area) is included in a channel which is called “perch channel”. Therefore, the mobile radio communication terminal has to receive and demodulate the perch channel of each of the base stations first, in order to obtain the base station information of the base stations.
In a mobile radio communication terminal which executes radio communication according to CDMA (Code Division Multiple Access), information transmitted by a desired base station can be demodulated from multiplexed data (that is, a received radio wave which has been modulated according to CDMA and transmitted by base stations) by taking the correlation between the received modulated radio wave and a predetermined scrambling code of the base station in sync with predetermined scrambling timing of the base station.
The modulated radio wave which is received by the mobile radio communication terminal includes frame boundary symbols of the base stations around the mobile radio communication terminal, in which each frame boundary symbol indicates information concerning the scrambling timing of a base station and the type of the scrambling code used by the base station. The mobile radio communication terminal can detect the scrambling timing and the scrambling code of the perch channel of each base station, by detecting the frame boundary symbols included in the received modulated radio wave.
After the perch channel reception of the base stations around the mobile radio communication terminal is completed, the mobile radio communication terminal starts next procedure for establishing communication with the most suitable one of the base station. After the communication between the mobile radio communication terminal and the most suitable base station is started, the mobile radio communication terminal periodically executes the perch channel reception of base stations around the mobile radio communication terminal, while executing the communication with the most suitable base station.
FIG. 1
is a block diagram showing a conventional perch channel reception device of a mobile radio communication terminal according to CDMA, for executing the perch channel reception with respect to base stations around the mobile radio communication terminal.
The perch channel reception device shown in
FIG. 1
includes a delay profile generator
1
, a base station scrambling timing detector
2
, a correlator with time window
4
, and a perch channel demodulator
5
.
The delay profile generator
1
detects frame boundary symbols which are included in a received modulated radio wave, and thereby generates a delay profile of base stations around the mobile radio communication terminal. There are a plurality of base stations around the mobile radio communication terminal, and thus the delay profile generated by the delay profile generator
1
includes a plurality of peaks corresponding to the base stations around the mobile radio communication terminal. The base station scrambling timing detector
2
detects scrambling timing of each of the base stations based on the delay profile which has been generated by the delay profile generator
1
and thereby generates a base station scrambling timing table which indicates the detected scrambling timing of each of the base stations around the mobile radio communication terminal. Thereafter, the base station scrambling timing detector
2
selects a base station from the base stations one by one, and informs the timing corrector
3
about the scrambling timing of the selected base station (i.e. base station scrambling timing). The base station scrambling timing detector
2
also determines the type of the scrambling code used by the selected base station based on the frame boundary symbol corresponding to the selected base station, and informs the correlator with time window
4
A about the type of the scrambling code used by the selected base station (i.e. the type of base station scrambling code). The correlator with time window
4
, which is provided with a time window of a fixed size, takes the correlation between (compares) the received modulated radio wave and the base station scrambling code (i.e. the scrambling code of the selected base station which has been detected by the base station scrambling timing detector
2
), with respect to a plurality of comparison starting times (that is, the time when the comparison between the received modulated radio wave and the base station scrambling code is started) in the fixed time window around the base station scrambling timing, and thereby generates correlation data. The perch channel demodulator
5
demodulates the correlation data which has been generated by the correlator with time window
4
into logic data which indicates the base station information of the selected base station such as present time of the selected base station, an ID of the selected base station, transmission power of the selected base station, etc.
As described above, in the conventional perch channel reception device of a mobile radio communication terminal according to CDMA, the correlator with time window
4
generates correlation data between the received modulated radio wave and the base station scrambling code, with respect to a plurality of comparison starting times in the fixed time window around the base station scrambling timing.
Generally, each base station is provided with a high precision oscillator, while precision of the oscillator of each mobile radio communication terminal is not high enough. The oscillation frequency of the oscillator of a mobile radio communication terminal has an error of the order of PPM due to variations in the environment in which the mobile radio communication terminal is used, limited size and price of the mobile radio communication terminal, etc. Further, in the conventional perch channel reception device of
FIG. 1
, there is a large time difference between the generation of the delay profile and the completion of the perch channel reception of the base stations around the mobile radio communication terminal. The perch channel reception becomes impossible if the scrambling timing used by the mobile radio communication terminal is shifted by 1 chip (chip: a time period corresponding to one scrambled code when logic data is scrambled) in comparison with real scrambling timing of the selected base station. Therefore, the conventional perch channel reception device has to be provided with a time window of a very large size in order to absorb and compensate the shift of the scrambling timing during the perch channel reception of all the base stations.
In the following, the shift of the scrambling timing between the base station and the mobile radio communication terminal will be explained in detail referring to FIG.
2
. Incidentally, the following explanation will be given with respect to a case where the number of base stations around the mobile radio communication terminal is three, the scrambling frequency (chip frequency) is 4 MHz, and reception time necessary for the perch channel reception of one base station is 50 ms, for
Corrielus Jean B.
McGinn & Gibb PLLC
NEC Electronics Corporation
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