Pulse or digital communications – Receivers – Automatic gain control
Reexamination Certificate
1997-09-15
2001-03-20
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Automatic gain control
C455S232100, C455S234100, C455S234200
Reexamination Certificate
active
06205189
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C §119 from an application entitled Digital Automatic Gain Control Method And Device For Use In Communication Terminal Of Mobile Radio Communication System earlier filed in the Korean Industrial Property Office on Sep. 13, 1996, and there duly assigned Serial No. 96-39867 by that Office.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a band spread radio communication system, and more particularly to an automatic gain control method and device for use in a communication terminal of a mobile radio communication system employing a time-division duplex (TDD) transmission.
2. Description of the Related Art
In a conventional mobile radio communication system employing a time-division duplex (TDD) transmission, a mobile station automatically controls a gain of a transmitter/receiver in a communication terminal, in order to prevent a deterioration of the system performances due to a mutual interference with another mobile station. The time-division duplex transmission refers to a bidirectional transmission for periodically (e.g.,
1
msec) switching a channel to a transmission mode and a reception mode. A mobile station controls a gain of a transmission power amplifier disposed in a transmitter based on a mobile station transmission power control command included in a received frame from a base station, in order to maintain an appropriate transmission power during a transmission mode. Further, the mobile station appropriately controls a gain of a reception amplifier in order to compensate for an attenuation of a reception power according to a distance from the base station, during a reception mode.
Conventionally, the gains of the transmission power amplifier and the reception amplifier are controlled by an analog automatic gain control method in which the gain is controlled according to an intensity of a received signal. Such a prior art method is well disclosed in U.S. Pat. No. 5,257,283, issued on Oct. 26, 1993, by Klein S. Gilhousen, el al., entitled Spread Spectrilm Transismitter Power Control Method And System.
Referring to
FIG. 1
, which is described in the U.S. Pat. No. 5,257,283 patent, there is illustrated a block diagram of an analog automatic gain control system for use in a mobile radio communication system. As illustrated, a signal received from an antenna is transferred to an intermediate frequency amplifier (IF AMP)
6
via a down-converter
2
and a band pass filter (BPF)
4
. An output of intermediate frequency amplifier
6
is applied to a base band processor
10
via an analog-to-digital (A/D) converter
8
, and also applied to an automatic gain control (AGC) detector
12
. Automatic gain control detector
12
has a double function. First, in the reception mode, automatic gain control detector
12
generates a control voltage for controlling a gain of intermediate frequency amplifier
6
to maintain a constant level of the received signal. Second, in the transmission mode, an output of automatic gain control detector
12
is compared with a reference power level value generated from a control processor
18
, in order to control a transmission power based on a value set by a transmission signal from the base station. A comparator
14
compares the output of the automatic gain control detector
12
with the reference power level value received from control processor
18
via a digital-to-analog (D/A) converter
20
. An output of comparator
14
is applied to a nonlinear filter
16
which has a nonlinear output characteristic with respect to a variation of the output of comparator
14
. The output characteristic of nonlinear filter
16
sets an increasing rate of the transmission power control voltage to a value lower than a decreasing rate thereof, in order to prevent the deterioration of the system performances due to a rapid increase of the transmission power. In the meantime, an intermediate frequency amplifier
24
controls a signal generated from a transmission modulator (not shown) based on a control signal generated from control processor
18
via a digital-to-analog converter
22
, in the transmission mode of the mobile station. Digital-to-analog converter
22
generates the control signal for controlling a gain of intermediate frequency amplifier
24
. An output signal from intermediate frequency amplifier
24
is applied to an intermediate frequency amplifier
26
. Since a gain of intermediate frequency amplifier
26
is controlled by an output of nonlinear filter
16
, a transmission is signal output of intermediate frequency amplifier
26
is automatically controlled.
It is noted from the foregoing description that the prior art analog automatic gain control system includes the automatic gain control detector
12
for detecting an intensity of the received signal. However, it is difficult to form automatic gain control detector
12
at a broad variation range of a reception power level. Further, there is needed an additional means for converting an output level of automatic gain control detector
12
into a proper control voltage range for controlling the gain of intermediate frequency amplifier
6
. Moreover, the prior art analog automatic gain control system needs comparator
14
for comparing the control signal output from control processor
18
with the output value of automatic gain control detector
12
in order to control the transmission power during the transmission and reception modes. However, as being composed of analog elements, comparator
14
is sensitive to noise so that a response time may be limitative. Therefore, it is not easy to accurately control the output of comparator
14
. Besides, the prior art analog automatic gain control system needs digital-to-analog converter
20
for converting the digital signal output from control processor
18
into the analog value to supply the analog value to comparator
14
. However, a low conversion speed of digital-to-analog converter
20
becomes a main cause that delays the response time of the automatic gain control system. In particular, in case that the signal that the mobile station has received is a burst signal, it is difficult to control the gain in order to maintain a constant received signal level through one data frame interval. Further, it is not easy to realize nonlinear filter
16
in the light of its features. In order for nonlinear filter
16
to control the gain of intermediate frequency amplifier
26
, there is needed an additional circuit, i.e., a level converter for converting an output level of nonlinear filter
16
within a gain variable control voltage range of intermediate frequency amplifier
26
. However, although the level converter is additionally used, it is still not easy to constitute nonlinear filter
16
in the light of its nonlinear output characteristic. It should be noted that all the problems mentioned above are mainly caused because the prior art system employs the analog automatic gain control method.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a digital automatic gain control method and device for controlling a gain of a communication terminal of a mobile radio communication system.
It is another object of the present invention to provide a method for easily realizing a digital automatic gain control device for controlling a transmission/reception gain of a communication terminal of a mobile communication system.
It is still another object of the present invention to provide a digital automatic gain control method and device capable of performing an automatic gain control based on an accurate timing control.
According to an aspect of the present invention, a digital automatic gain control device for use in a transmitting/receiving terminal of a mobile radio communication system includes, a transmission power amplifier disposed in a transmitter and a reception amplifier disposed in a receiver, gains of the transmission amplifier and reception ampl
Bushnell , Esq. Robert E.
Chin Stephen
Ha Dae V.
Samsung Electronics Co,. Ltd.
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