Pulse or digital communications – Receivers – Automatic frequency control
Reexamination Certificate
2001-02-27
2003-01-21
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Receivers
Automatic frequency control
C375S147000, C455S234100, C370S342000
Reexamination Certificate
active
06510187
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-261294, filed Aug. 30, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile radio terminal and automatic frequency control circuit for use in a mobile telephone terminal, portable telephone system or wireless LAN system using the CDMA scheme.
2. Description of the Related Art
A receiving system of a conventional mobile radio terminal device in a CDMA-type radio communication system is constituted as shown in FIG.
1
.
A radio signal from a base station (not shown) is downconverted to a baseband signal by a receiving unit (RX)
103
. The baseband signal is output to a searcher
10
and fingers
31
to
3
n.
The searcher
10
detects number n of different passes suitable for reception by despreading the baseband signal at various timings. Then the searcher
10
assigns synchronous positions of slots and frames for reception of the respective passes to the fingers
31
to
3
n
as pass synchronization information.
Each of the fingers
31
to
3
n
generates a scramble code of the timing based on the pass synchronization information assigned by the searcher
10
and despreads the baseband signal by using the scramble code. Thus, n baseband signals despread by the fingers
31
to
3
n
are RAKE-synthesized.
The fingers
31
to
3
n
also have a function of detecting frequency errors &Dgr;f
1
to &Dgr;fn of the passes assigned to themselves, in the results of the despreading, and is constituted as shown in FIG.
2
.
The baseband signal from the receiving unit
103
is input to a multiplier
310
. The multiplier
310
multiplies the baseband signal by a scramble code generated by a CPICH scramble code generator
320
. The CPICH scramble code generator
320
has generated the scramble code at a timing based on the pass synchronization information assigned by the searcher
10
.
The result of multiplication of the multiplier
310
is integrated during a period equivalent to 1 symbol by an integrator
330
. The result of the integration is output to a 1-symbol delay unit
340
and a multiplier
360
.
The 1-symbol delay unit
340
delays the result of integration of the integrator
330
for a period equivalent to 1 symbol and outputs it to a complex conjugate unit
350
.
The complex conjugate unit
350
inverts a code of a complex component in the result of integration which is input from the 1-symbol delay unit
340
and outputs the result of the inversion to the multiplier
360
.
The multiplier
360
obtains an amount of phase rotation in successive symbols, i.e. frequency errors (&Dgr;f
1
to &Dgr;fn), as shown in
FIG. 3
by multiplying the outputs of the integrator
330
and complex conjugate unit
350
, which are shaped in a complex number.
The frequency errors &Dgr;f
1
to &Dgr;fn obtained by the respective fingers
31
to
3
n
in the above-mentioned manner are added in an adder (&Sgr;)
4
. The result of the addition is averaged by a low-pass filter (LPF)
5
and output to a tan
−1
circuit
6
as the frequency error &Dgr;f.
The tan
−1
circuit
6
obtains an arc tangent component of the frequency error &Dgr;f. The arc tangent component is integrated by an integrator
7
and output to a VCO control conversion table
8
.
The VCO control conversion table
8
stores voltage values corresponding to various values that are input from the integrator
7
and outputs the information of voltage values corresponding to the output values of the integrator
7
. The voltage value information that is output from the VCO control conversion table
8
is converted to a voltage signal corresponding to the information by a D/A converter (D/A)
9
.
The voltage signal obtained in this manner is used as a control signal of a voltage control oscillator inside a synthesizer
104
. Thus the oscillation frequency of the voltage control oscillator is controlled so that the output (frequency error &Dgr;f) of the low-pass filter
5
can be zero.
Incidentally, recently, transmission diversity has been conducted at the base station. The base station comprises two transmission antennas ANT
1
and ANT
2
for transmission to the mobile radio terminal apparatus, and the transmission diversity allows the phase between the signals transmitted from the antennas to be controlled at the base station so that the signals can be in a proper condition in the mobile radio terminal apparatus.
Symbols of patterns shown in
FIG. 4
(hereinafter “AFC control symbols”) are transmitted in a 15-frame cycle from the transmission antennas ANT
1
and ANT
2
, for the automatic frequency control (AFC) in the mobile radio terminal apparatus. The symbol patterns of
FIG. 4
are examples according to 3GPP (3rd Generation Partnership Project).
FIG. 5
shows parts of the patterns of the AFC control symbols. In the pattern of the symbols transmitted from the transmission antenna ANT
1
, all the symbols are “A” (A=1+j). In the pattern of the symbols from the transmission antenna ANT
2
, “A”, “A”, “−A” and “−A” are repeated. “−A” indicates −1−j.
If the transmission from the transmission antennas ANT
1
and ANT
2
to the mobile radio terminal apparatus is conducted at the same channel, a 0-th symbol as shown in
FIG. 5
is “A” at both the transmission antennas ANT
1
and ANT
2
and thus becomes as shown in FIG.
6
.
The first symbol in
FIG. 5
is “A” at the transmission antenna ANT
1
and “−A” at the transmission antenna ANT
2
. Therefore, the transmitted signal becomes a signal whose signal amplitude is almost zero as shown in FIG.
6
.
For this reason, even if the conventional circuit as shown in
FIG. 2
obtains the phase differences between symbols &Dgr;&thgr;
01
, &Dgr;&thgr;
12
, &Dgr;&thgr;
23
, &Dgr;&thgr;
34
, &Dgr;&thgr;
45
, . . . , in accordance with the signals transmitted from the base station which conducts the transmission diversity in order to obtain the frequency error &Dgr;f from the phase differences, the circuit cannot detect the frequency error &Dgr;f or normally execute the frequency-locking operation under the condition as shown in
FIG. 6
or the condition that, particularly, the frequency error &Dgr;f is great as seen when the power supply is turned on.
That is, if the communication partner executes the transmission diversity, the conventional automatic frequency control circuit cannot detect the frequency errors under the condition that, particularly, frequency error &Dgr;f is great as seen when the power supply is turned on and, therefore, cannot normally execute the frequency-locking operation.
BRIEF SUMMARY OF THE INVENTION
The present invention aims to provide a mobile radio terminal and automatic frequency control circuit capable of executing a normal frequency-locking operation regardless of whether or not the communication partner executes the transmission diversity.
To achieve this object, there is provided a mobile radio terminal and automatic frequency control circuit comprising: symbol pattern storing means for storing patterns of symbols transmitted to allow a communication terminal to execute transmission diversity; synchronous information detecting means for detecting synchronous information of slots and frames of the signal received from the communication terminal, in the baseband signal; despreading means for despreading the baseband signal; integrating means for integrating a result of the despreading of the despreading means; integration controlling means for controlling the integrating means, to allow the integrating means to integrate the result of despreading of the despreading means corresponding to two successive predetermined periods in which combinations of the symbols are the same, in each of the predetermined periods, in accordance with the synchronous information detected by the synchronous information detecting means and the symbol patterns stored in the sy
Asanuma Yutaka
Saito Naritoshi
Ghebretinsae Temesghen
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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