Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
2000-11-22
2004-08-17
Trinh, Sonny (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S063100, C455S067130
Reexamination Certificate
active
06778815
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-333375, filed Nov. 24, 1999; and No. 11-371763, filed Dec. 27, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a mobile radio terminal apparatus in the Code Division Multiple Access (CDMA) scheme for use in a mobile radio communication system such as a mobile telephone system or a portable telephone system.
Recently, a mobile radio communication system employing the CDMA scheme has been noticed. This system employs the spread spectrum communication scheme as the communication scheme thereof.
A conventional mobile radio terminal apparatus in the mobile communication system will be explained with reference to FIG.
1
. The receiving system relating to the invention will be mainly explained here.
A transmitting device
12
modulates the transmission data of the speech communication, data communication and the like in the digital modulation scheme such as the PSK modulation and spreads the modulated data to a broad-band baseband signal by using a spread code.
The transmitting device
12
up-converts the baseband signal to a radio-frequency signal, inputs the signal to a first antenna
10
via a duplexer
11
, and irradiates the signal into the space from the first antenna
10
to transmit the signal to a base station (not shown).
On the other hand, the radio signal transmitted from the base station is received by the first antenna
10
and input to a receiving device
13
via the duplexer
11
. The receiving device
13
is composed of a radio circuit
14
, an intermediate frequency circuit
15
and a RAKE receiver
16
.
First, in the radio circuit
14
, the radio signal received from the duplexer
11
is input to an attenuator
14
a
, which attenuates the signal at a preset amount.
The signal passing through the attenuator
14
a
is amplified up to a predetermined level by an amplifier
14
b
, mixed with a signal generated by a frequency synthesizer
14
d
in a mixer
14
c
and then down-converted to an intermediate frequency.
The signal down-converted to the intermediate frequency is input to the intermediate frequency circuit
15
and amplified up to a predetermined level by an amplifier
15
a
. A desired band, of the result of the amplification, passes through a band-pass filter (BPF)
15
b
and is input to a mixer
15
c.
In the mixer
15
c
, the signal which has passed through the band-pass filter
15
b
and a signal generated by a frequency synthesizer
15
d
are mixed and converted to a baseband signal. The baseband signal converted to a digital signal by an A/D converter (A/D)
15
e
and input to the RAKE receiver
16
.
The RAKE receiver
16
is composed of a searcher
16
a
, fingers
16
b
,
16
c
and
16
d
, and a symbol combiner
16
e
. The digital signal is input to the searcher
16
a
and also to the fingers
16
b
,
16
c
and
16
d.
The searcher
16
a
despreads the digital signal at various timings by using the same spread code as that used for the spreading on the transmitting side, in order to execute the detection of signals arriving in a plurality of paths from the base station to its own terminal, or what is called multi-pass detection.
The searcher
16
a
obtains Ec/Io (Io: spectral density of overall electric power in the receiving range, Ec: pilot energy stored during a PN chip period) of a plurality of paths and a delayed time difference (delay profile) of these paths from the result of the despreading. On the basis of these, the searcher
16
a
obtains a receiving timing (despread timing) of a path suitable for the reception and assigns it to each of the fingers
16
b
,
16
c
and
16
d.
The fingers
16
b
,
16
c
and
16
d
despread the digital signal by using the same spread code as that used in the spreading on the transmitting side, at the despreading timings assigned by the searcher
16
a.
The symbol combiner
16
e
symbolically combines the multi-pass components respectively despread by fingers
16
b
,
16
c
and
16
d
by considering the despreading timings assigned to the respective fingers
16
b
,
16
c
and
16
d.
The signal symbolically combined in the symbol combiner
16
e
is subjected to the demodulation corresponding to the digital modulation of the transmitting side in a signal processing section
17
of the rear stage and thereby the receiving data is reproduced.
In this mobile radio terminal apparatus, a control section (not shown) executes the control operation for the handoff, in accordance with the value of Ec/Io of the pilot signal obtained in the searcher
16
a.
When the intermittent reception is executed in a reception standby state under this control, if the value of Ec/Io satisfies conditions that (1) the value is smaller than a predetermined value, (2) the value is more deteriorated than a predetermined value as compared with the previous receiving time, (3) a difference between the value and Ec/Io of a neighboring base station becomes within a predetermined value, and the like, Ec/Io of the pilot signal from the other base station is measured to execute the hand off. If Ec/Io of the pilot signal of the other base station becomes greater than the predetermined value, the signal is handed off to the other base station.
If Ec/Io of the pilot signal of the currently connected base station becomes smaller than the predetermined value and if Ec/Io of the pilot signal of the neighboring base station becomes greater than the predetermined value while the mobile radio terminal apparatus executes the communication, the mobile radio terminal apparatus executes the hand off while having communication with a plurality of base stations including the base station satisfying the determined conditions.
The above-described CDMA scheme have advantages that (1) the scheme is superior in the secrecy of communication as the spread spectrum technique is employed, (2) the scheme has high resistance to fading as the Rake receiving scheme is employed, (3) the scheme is capable of stable handoff including no instantaneous interruption of communication or what is called soft handoff, and the like.
In the conventional mobile radio terminal apparatus in the CDMA scheme, however, the multi-pass resolution of the searcher
16
a
is determined in accordance with the reciprocal of the chip rate, i.e. one PN chip period. Therefore, if the extension of the multi-pass delay time is smaller than the resolution, the multi-pass components cannot be separated respectively at the fingers
16
b
,
16
c
and
16
d
or symbolically synthesized.
That is, extension of the delay time of the multipass (direct wave, first reflected wave and second reflected wave) received by the fingers
16
b
,
16
c
and
16
d
is small, and the Rake reception cannot be executed if the multipass is not delayed by more than the reciprocal of the chip rate.
Thus the reflected wave which is more delayed than the direct wave cannot be reproduced in accordance with the delay time difference in the multipass. Therefore, there is a problem that the resistance to fading is deteriorated and stable communication quality cannot be maintained. This problem arises more remarkably in a low-speed motion such as walking or a stationary condition than in a high-speed motion.
In addition, if the multipass fading occurs under the condition that the Rake reception cannot be executed as the multipass delay time is small, so as to detect a predetermined number of frame errors in the pilot signal from the current base station even temporarily, it is estimated that the system is lost and the process starts from the system capture.
The reception is executed at a location where the receiving energy is accidentally deteriorated due to the influence of the fading as shown in FIG.
2
.
As described above, if it is estimated that the system is lost and the process starts again from the system capture, the communication will be interrupted during the communication time. At the standby t
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Trinh Sonny
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