Multiplex communications – Communication over free space – Portable address responsive receiver
Reexamination Certificate
1999-08-11
2004-04-27
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication over free space
Portable address responsive receiver
C370S342000, C375S130000, C455S127300, C330S133000
Reexamination Certificate
active
06728224
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a portable mobile terminal and a transmission unit, and more particularly to a portable mobile terminal and a transmission unit suitably applicable to communication systems in which a transmission power needs to be variable.
(2) Description of the Related Art
In mobile communication (multiplex radiocommunication) services including portable telephone services, there is a case that a base station needs the same receive power (reception strength) from mobile units (portable mobile terminals) irrespective of the distances from the mobile units. For instance, this requirement is imposed on a CDMA (Code-Division. Multiple Access) system in which a plurality of mobile units (subscribers) share the same frequency band in a manner that each of the mobile units performs a spread (diffusion) spectrum modulation of a transmission signal using a different code.
This is generally referred to as the “far and near (distance) problem”, and in the case of the CDMA system, a transmission signal (that is, an undesired wave) from another mobile unit produces an interference component to some base station (receiver). For instance, if a mobile unit generating an undesired wave exists in a range close to the base station, significant level interference may take place by that undesired wave; hence, there is a need to equalize the signal reception levels from the mobile units in the base station by controlling the transmission powers of the mobile units finely.
For this reason, the mobile unit needs to be designed such that its transmission power is variable in a range as wide as possible and is controllable in multistage (stepwise) fashion (for example, in units of 1 dB to several dB).
One configuration to realize such a function may be, for example, as shown in FIG.
11
. That is, as shown in
FIG. 11
, in a mobile unit, a transmission system (transmission unit)
1
′ is included which principally comprises an oscillator
3
, a modulator
4
, a variable gain type amplifier (variable gain circuit)
5
, a frequency converting section (up-converter)
5
C, a power amplifier
6
, a directional coupler
7
, a duplexer (an antenna sharing unit)
8
, a transmission/receive antenna
9
, a frequency converting section (down-converter)
10
A, a received signal strength indicator (RSSI) detector (a direct-current voltage converting section)
12
, a controller
13
′ containing a memory
14
′, a digital/analog (D/A) converter
15
and others. Incidentally reference numeral
2
designates a reception system made generally to share the transmission/receive antenna
9
with the transmission system
1
′ through the duplexer
8
.
In this configuration, the oscillator
3
is made to generate a carrier signal, while the modulator (modulating section)
4
is, for example, made to perform an orthogonal modulation (QPSK or the like: primary modulation) of a transmission signal (baseband signals I, Q) through the use of the carrier signal from the oscillator
3
, before conducting spread modulation (secondary modulation) thereof with a predetermined spread code. The variable gain (gain varying) circuit
5
is designed to be capable of changing the gain of a transmission signal undergoing the modulation in the modulator
4
, with its gain being controlled by the controller
13
′ in a state where the D/A converter
15
is interposed therebetween.
The up-converter
5
C is made such that a mixer
51
mixes a transmission signal [intermediate frequency (IF) signal], whose gain is changed in the gain variable circuit
5
, with a signal from an oscillator
52
to frequency-convert (up-convert) the transmission signal into a radio frequency (RF) signal.
The power amplifier
6
is for conducting a linear amplification of a transmission signal (RF signal) from this up-converter
5
C. After passing through the directional coupler
7
and the duplexer
8
, the transmission signal amplified is transmitted toward a base station (not shown).
The directional coupler
7
is for deriving a portion of the transmission signal (transmission power) amplified linearly in the power amplifier
6
, with the transmission signal, (RF signal) taken out being supplied to the down-converter
10
A. The down-converter
10
A is for frequency-converting (down-converting) the transmission signal (RF signal) taken out by the directional coupler
7
into a signal with an intermediate frequency (IF) in a manner that a mixer
10
mixes this transmission signal with a signal from an oscillator
11
, while the RSSI detector
12
is for converting the transmission signal, down-converted by the mixer
10
into a direct-current voltage (RSSI signal) of a value corresponding to its power [that is, the present transmission power in the transmission system
1
′ (the present RSSI in the base station)].
Thus, a portion composed of the directional coupler
7
, the mixer
10
, the oscillator
11
and the RSSI detector
12
functions as a transmission power detecting section
18
to detect (monitor) the transmission power of the transmission signal amplified by the power amplifier
6
.
Furthermore, the controller
13
′ is for producing a gain control signal to control the gain of the variable gain circuit
5
so that the aforesaid RSSI signal (the present transmission power of the transmission system
1
′) assumes a power value corresponding to a transmission power control signal from a base station (external) detected in the reception system
2
. For instance, referring to data representative of the mapping (corresponding relationship) of gain control signals (control voltage values) to RSSI signals and Transmission power control signals, stored in the built-in memory
14
′ in advance, the corresponding control voltage value is outputted, for example, in the form of digital data of n-bit (n depicts a natural number).
The D/A converter
15
is for converting the control voltage value (n-bit digital data) outputted from the controller
13
′ into analog data which in turn, comes in the variable gain circuit
5
.
That is, the controller
13
′ and the D/A converter
15
, together with the transmission power detecting section
18
(the directional coupler
7
, the mixer
10
, the oscillator
11
and the RSSI detector
12
), form a feedback control system
16
to implement the feedback-control of the present transmission power by adjusting the gain of the variable gain circuit
5
so that the present transmission power assumes a power value corresponding to a transmission power control signal from a base station.
In the transmission system
1
′ thus constructed, a carrier signal outputted from the oscillator
3
is fed to the modulator
4
where it is orthogonally modulated with the baseband signals I, Q and then spread-modulated. The output of this modulator
4
passes through the variable gain circuit
5
and the up-converter
5
C and reaches the power amplifier
6
to undergo the linear amplification, before being transmitted through the transmission/receive antenna
9
toward a base station.
Meanwhile, at this time, in the feedback control system
16
, the directional coupler
7
derives the present transmission power while the controller
13
′ controls the gain of the variable gain circuit
5
so that that transmission power comes to a power voltage corresponding to a transmission power control signal from a base station, detected in the reception system
2
.
However, in the case of such mobile unit (transmission system
1
′), in general the stable gain-variable range the variable gain circuit
5
can provide is approximately 30 dB to 40 dB. Accordingly, although operating well when the gain-variable range needed is relatively narrow (for example, the PDC system requires approximately 20 dB), the mobile unit handles poorly when the gain-variable range needed is extremely wide (particularly, the CDMA system requires approximately 70 dB). In addition, extreme difficulty is experienced to re
Kakizaki Shinji
Kawasaki Katsuhiko
Nakata Youji
Yonekura Kunitoshi
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Kizou Hassan
Swickhamer Christopher M.
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