Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
2000-12-13
2004-07-20
Ho, Duc (Department: 2665)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C370S329000, C370S327000, C370S436000, C455S234200, C331S023000
Reexamination Certificate
active
06765879
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to communications apparatus such as a mobile telephone set to perform mobile communications, a frequency control method for communications apparatus, and a recording medium on which a program to execute the frequency control method is recorded, and in particular, to communications apparatus, a frequency control method for communications apparatus, and a recording medium which allow frequency offset correction without degradation in the accuracy of the sending or sending/receiving reference frequency and demodulation characteristics, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator or reference oscillator.
FIG. 4
is a block diagram of related communications apparatus equipped with a frequency offset correction feature (hereinafter referred to as a first related art).
In
FIG. 4
, communications apparatus according to the first related art comprises antennas
401
and
411
, mixers
402
and
412
, local oscillators
403
and
413
, voltage-controlled oscillators
404
, an A/D converter
405
, D/A converters
406
and
415
, demodulating means
407
, receiving frequency offset estimating means
408
, modulating means
417
and a central processing unit (CPU)
421
.
According to communications apparatus of the first conventional related art, reception signals received via the antenna
401
are frequency-converted via the mixer
402
, and a frequency offset estimate FOS is determined via the receiving frequency offset estimating means
408
. Reference frequency control, so-called the AFC (Auto Frequency Control) is made by using the CPU
421
to feedback a control value based on the determined frequency offset estimate FOS to the voltage-controlled oscillator
404
via the D/A converter
406
.
While the demodulating means
407
demodulates intermediate-frequency signals frequency-converted by the mixer
402
and outputs upstream control data DTD and downstream control data DCD to the CPU
421
, the CPU
421
can control the sending reference frequency by using the downstream control data DCD from the demodulating means
407
, besides the AFC processing. In this case, a frequency offset control value is generated by the CPU
421
based on a sending reference frequency command on the downstream control data DCD, and fed back to the voltage-controlled oscillator
404
via the D/A converter
406
.
FIG. 5
is a block diagram of another conventional communications apparatus equipped with the frequency offset correction feature (hereinafter referred to as a second related art).
In
FIG. 5
, communications apparatus according to the second related art comprises antennas
401
and
411
, mixers
402
and
412
, local oscillators
403
and
413
, a reference oscillators
404
, an A/D converter
405
, D/A converters
406
and
515
, demodulating means
407
, receiving frequency offset estimating means
408
, modulating means
517
, sending frequency offset estimating means
518
and a central processing unit (CPU)
521
.
Also, according to communications apparatus of the second related art, receive signals received via the antenna
401
are frequency-converted via the mixer
402
, and a frequency offset estimate FOS is determined via the receiving frequency offset estimating means
408
. Reference frequency control, so-called the AFC (Auto Frequency Control) is made by using the CPU
521
to feed back a control value based on the determined frequency offset estimate FOS to the sending frequency offset control means
518
as a frequency offset control value FOC.
While the demodulating means
407
demodulates intermediate-frequency signals frequency-converted by the mixer
402
and outputs upstream control data DTD and downstream control data DCD to the CPU
521
, the CPU
521
can control the sending reference frequency by using the downstream control data DCD from the demodulating means
407
, besides the AFC processing. In this case, a frequency offset control value FOC is generated by the CPU
521
based on a sending reference frequency command on the downstream control data DCD and fed back to the sending frequency offset control means
518
.
According to the conventional communications apparatus equipped with the frequency offset correction feature of the first related art, however, it is a common practice that a VCTCXO (a VCO (voltage controlled oscillator) equipped with a temperature-compensated crystal oscillator (TCXO)) as a reference oscillator is used in terms of power consumption and apparatus cost. This causes degradation in the accuracy of the VCTCXO due to its nonlinearity, temperature characteristics and secular change. As mentioned earlier, According to communications apparatus which controls the sending reference frequency by using downstream control data DCD, it is necessary to feed back the sending reference frequency command to the voltage-controlled oscillator (VCTCXO)
404
. In this case, such apparatus cannot control the sending reference frequency with high accuracy due to nonlinearity, temperature characteristics and secular change of the VCTCXO, thus inviting degradation in the accuracy of the sending reference frequency.
Similarly, according to communication apparatus which controls, by using the downstream control data DCD, the sending reference frequency immediately after a new channel is assigned, such as via a handover, it is necessary to feed back the sending reference frequency command to the voltage-controlled oscillator (VCTCXO)
404
. In this case, such apparatus cannot control the sending reference frequency with high accuracy due to nonlinearity, temperature characteristics and secular change of the VCTCXO, thus inviting degradation in the accuracy of the sending reference frequency.
According to the conventional communications apparatus equipped with the frequency offset correction feature of the second related art, however, it is a common practice that a temperature-compensated crystal oscillator as a reference oscillator
404
is used in terms of power consumption and apparatus cost. This causes degradation in the accuracy of the TCXO due to its initial deviation, temperature characteristics and secular change. That is, a receiving frequency offset caused by initial deviation, temperature characteristics and secular change inherent to the TCXO invites degradation in the demodulation characteristics in the demodulating means
407
.
SUMMARY OF THE INVENTION
The invention, in view of the aforementioned circumstances and problems, aims at providing communications apparatus, a frequency control method for communications apparatus, and a recording medium which allow high-accuracy frequency offset correction without degradation in the accuracy of the sending or sending/receiving reference frequency and demodulation characteristics, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator (VCTCXO) or reference oscillator (TCXO).
To solve the aforementioned problems, communications apparatus according to the first aspect of the invention comprises receiving frequency offset estimating means for estimating a receiving frequency offset based on receive signals, a voltage-controlled oscillator for controlling a local oscillator frequency based on an estimate determined by the receiving frequency offset estimating means, demodulating means for demodulating the receive signals to obtain control data, and sending frequency offset control means for controlling a sending frequency offset based on control data obtained by the demodulating means, wherein a sending reference frequency is controlled by using the voltage-controlled oscillator and the sending frequency offset control means.
According to the second aspect of the invention, communications apparatus performing TDMA communications comprises receiving frequency offset estimating means for estimating a receiving frequency offset based on receive signals, a voltage-controlled osci
Miyashita Shinichiro
Yamamoto Naoyuki
Ho Duc
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
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