Pulse or digital communications – Receivers – Automatic gain control
Reexamination Certificate
1999-07-14
2003-09-30
Liu, Shuwang (Department: 2734)
Pulse or digital communications
Receivers
Automatic gain control
C375S146000, C375S227000, C375S340000, C370S342000, C455S522000
Reexamination Certificate
active
06628732
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system, in particular, to a received power calculating method of a receiver of a radio portion of a mobile communication system, the receiver calculating a received power and controlling a down-link transmission power of a base station.
2. Description of the Related Art
In the CDMA (Code Division Multiple Access) system, when a base station spreads a spectrum of a transmission signal with a plurality of predetermined codes and communicates with mobile stations using the spread signal, the same frequency band can be assigned to a plurality of subscribers or channels. Thus, frequencies can be effectively used. In the CDMA system, when a receiver receives a spread spectrum signal from the base station, unless the receiver de-spreads the spread spectrum signal with the same code at the same timing, the receiver cannot extract the original transmission signal. Thus, the bit error rate of the received signal deteriorates.
In the CDMA system, a high power transmission signal transmitted from a transmitter disposed in a near location interferes with a weak transmission signal transmitted from a transmitter disposed in a far location. Such a problem is referred to as location problem.
To alleviate such a problem, it is necessary to accurately and widely control a transmission power.
Generally, a transmission power control signal can be generated with the average received power. When a mobile station controls the transmission power of a base station, if the received power calculated by the mobile station is lower than a predetermined threshold value defined in the system, the received power becomes information that causes the transmission power to increase. The information is transmitted from the mobile station to the base station. Thus, the information causes the base station to increase the transmission power by, for example,
dB.
On the other hand, when the received power calculated by the mobile station is higher than the predetermined threshold value defined in the system, the received power becomes information that causes the base station to decrease the transmission power. The information is transmitted from the mobile station to the base station. Thus, the information causes the base station to decrease the transmission power by
dB.
After the transmission power is controlled, the average received power converges on the threshold value in a predetermined time period.
A receiver of a conventional mobile station has a gain changing means and a variable gain amplifying means. The gain changing means and the variable gain amplifying means are disposed upstream of a frequency converting means that converts a radio frequency signal into an intermediate frequency signal. The gain changing means selects a radio frequency amplifying means or an attenuating means so as to prevent the frequency converting means from operating in the saturation region. The variable gain amplifying means controls the gain so that an input power to an analog-digital converting means (A/D converting means) that converts an analog signal of the received signal into a digital signal becomes constant. When the received power at an antenna is relatively high, the gain of the gain changing means is changed so as to prevent the frequency converting means from operate in the saturation region. When the gain of the gain changing means is changed, a control amount corresponding to a gain variation amount of the gain changing means is placed in a gain control signal of the variable gain amplifying means so as to keep the input power of the A/D converting means constant.
To control the transmission power of the base station, the received power is converted into a digital signal by the A/D converting means. The average received power in a predetermined time period is calculated. Corresponding to the calculated result, the transmission power of the base station is controlled.
FIG. 1
is a block diagram showing the structure of a conventional mobile station. Referring to
FIG. 1
, the mobile station has an antenna
101
, an duplexer means
102
, a first radio frequency amplifying means
103
, a first band pass filter means
104
, a gain changing means
105
, a second band pass filter means
108
, a first local signal oscillating means
110
, a frequency converting means
109
, a channel filter means
111
, a variable gain means
112
, a second local signal oscillating means
113
, an quadrature demodulating means
114
, low pass filter means
115
and
116
, analog/digital (A/D) converting means
117
and
118
, a digital signal processing means
120
, a radio portion controlling means
119
′, a transmitting means
122
, and a controlling means
121
′. The duplexer means
102
separates a transmission signal from a received signal. The gain changing means
105
has an attenuating means
106
and a second radio frequency amplifying means
107
. The frequency converting means
109
converts a radio frequency signal into an intermediate frequency signal with a first local oscillation signal of the first local signal oscillating means
110
. The channel filter means
111
separates a desired channel from the received signal. The quadrature demodulating means
114
converts the intermediate frequency signal into a base band signal with a second local oscillation signal oscillated by the second local signal oscillating means
113
and a signal phase-shifted by a 90° phase shifter, quadrature demodulates the base band signal, and outputs an I channel signal and a Q channel signal. The low pass filter means
115
and
116
pass only base band signals that have been quadrature demodulated.
The digital signal processing means
120
receives the I channel signal and the Q channel signal, performs a de-spreading process, an error-correcting process, and so forth for the I channel signal and the Q channel signal, and supplies the de-spread signals to the radio portion controlling means
119
′. The radio portion controlling means
119
′ receives the I channel signal and the Q channel signal, outputs signals that control the gain changing means
105
and the variable gain means
112
, and outputs a transmission signal.
FIG. 2
is a block diagram showing the structure of the radio portion controlling means
119
′. Referring to
FIG. 2
, the radio portion controlling means
119
′ has a received power calculating means
401
, a gain changing means controlling means
402
, a transmission power controlling means
403
, and a transmission signal generating means
404
. The received power calculating means
401
calculates the average power of the I and Q channel signals received from the A/D converting means
117
and
118
in a predetermined time period, controls the variable gain means
112
so that the powers of the signals supplied to the A/D converting means
117
and
118
become constant. Further, the received power calculating means
401
supplies the calculated results to the transmission power controlling means
403
, the gain changing means controlling means
402
, and the controlling means
121
. The gain changing means controlling means
402
compares a threshold value of the received power at the antenna means
102
with the average power calculated from the received power calculating means
401
and generates a gain selection control signal of the gain changing means
105
so as to prevent the frequency converting means
109
from operating in the saturation region. The transmission power controlling means
403
calculates the power of the received channel with the average received power value received from the received power calculating means
401
and the de-spread received signal received from the digital signal processing means
120
. When the power of the received channel is lower than a predetermined threshold value, the transmission power controlling means
403
generates a control signal that causes the base station to increase the transmission power. In contrast, when the
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