Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-06-14
2002-12-10
Nguyen, Lee (Department: 2683)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C455S522000, C455S437000, C455S116000
Reexamination Certificate
active
06493333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power control device and method for a mobile communication system, and more particularly, to a power control device and method of controlling a gain of pilot signals and a gain of traffic signals in a different manner, respectively.
2. Description of the Related Art
It is common to employ code division multiple access (CDMA) technology for a mobile communication system. The CDMA mobile communication system employs power control for forward link and reverse link. In the CDMA mobile communication system, a receiver of a mobile station receives pilot signals via a pilot channel, which is among the channels used for receiving frame signals transmitted from a transmitter of a base station, and measures the strength of the received pilot signals. The receiver generates a power control signal based on the strength of the pilot signals and sends the generated power control signal back to the transmitter. Concretely, the receiver compares the strength of the pilot channel signal with a reference value (or threshold) for the power control. If the strength of the pilot channel signal is lower than the reference value, the receiver sends a power-up signal; otherwise, the receiver sends a power-down signal back to the transmitter.
In the case where the channel surroundings are poor during communication with a base station (a first base station) at a first frequency having a specific frequency range, a mobile station searches for another base station (a second base station) with better channel surroundings that uses a second frequency having a different frequency. If the searching result indicates that the signal strength of the second base station is better than that of the first base station, the mobile station performs a hard handoff (an inter-frequency hard handoff) from the first base station to the second base station. The searching process, a preliminary step that the mobile station performs for a hard handoff, will be described in the following. The mobile station changes the first frequency as a communication frequency to the second frequency in order to search the second base station for a predetermined time period. Then the mobile station receives the pilot signals from the second base station at the second frequency before returning to the original first frequency. In some cases, transmission of the traffic signals in the mobile station may be discontinued to the presently connected first base station during an interval where the pilot signals are received from the second base station at the new second frequency.
As stated above, the traffic signals are punctured during an interval where the pilot signals are received at another frequency, resulting in a loss of energy. In order to compensate for the loss of energy, the transmitter increases power of the non-punctured frame signals. This is further detailed below.
Generally, the amplitude of a signal denotes a gain or power. The power is the square of a gain. Hereinafter, it will be given to you uniformly as a gain regarding the amplitude of the signal.
FIG. 1
illustrates a device for controlling gain during transmission of a punctured frame on a reverse link, in accordance with the related art, in which signals are composed of pilot signals and traffic signals. Referring to
FIG. 1
, a controller
100
controls the entire operation of a receiver. The controller
100
controls a pilot signal generator
110
, a traffic signal generator
120
, and a first signal controller
180
according to signalling information, e.g., data rate, puncturing start time and puncturing interval, etc., received from an upper layer. Under the control of the controller
100
, the pilot signal generator
110
generates pilot signals and outputs the generated pilot signals to a first gain controller
130
. Upon receipt of the pilot signals, the first gain controller
130
controls the gain of the pilot signals using a predetermined gain G
P
and outputs the gain controlled pilot signals to a signal combiner
150
. Similarly, the traffic signal generator
120
, under the control of the controller
100
, generates traffic signals and outputs the generated traffic signals to a second gain controller
140
. Upon receipt of the traffic signals, the second gain controller
140
controls the gain of the traffic signals using a predetermined gain G
T
and outputs the gain controlled traffic signals to the signal combiner
150
. A ratio of the pilot gain from the first gain controller
130
to the traffic gain from the second gain controller
140
is set to a predetermined value. The signal combiner
150
combines the traffic signals and the pilot signals received from the first and second gain controllers
130
and
140
, respectively.
Also, the controller
100
calculates a compensation gain for a puncturing interval based on information concerning the puncturing start time and puncturing interval received from the upper layer. After completion of the calculation, the controller
100
outputs the puncturing interval and the calculated compensation gain to the first signal controller
180
. Then, the first signal controller
180
outputs the received compensation gain to a multiplier
170
during the puncturing interval.
The multiplier
170
multiplies the combined signals of the pilot signals and the traffic signals as, outputted from the signal combiner
150
, by the compensation gain, and outputs the result to a second signal controller
160
. The second signal controller
160
receives the compensated pilot signals and traffic signals and adjusts power control according to the condition of the transmission channels. If a mobile station searches for another base station having a different frequency, puncturing occurs after signal controlling is performed by the second signal controller
160
. Thus, both the pilot signals and the traffic signals are punctured during the same time interval.
FIG. 2
illustrates gain distribution for a punctured frame. When a frame is not punctured, the non-punctured frame will be transmitted with a constant gain G
A
without a gain loss over the entire frame duration A. However, when the frame is punctured causing a gain loss G
A
at a punctured duration A
P
, the non-punctured durations B increase in gain by G
B
to compensate for the gain loss G
A
at the punctured duration Ap. In conclusion, the total gain for the punctured frame outputted from the multiplier
170
is G
Total
=G
A
+G
B
.
In the case where the punctured frame is transmitted in the above gain control method, the transmission gain for the non-punctured portion is increased consequently causing an increase in the transmission gain for the pilot signals, which results in the estimated gain of the pilot channel being higher than a reference value during most time intervals. Thus, the gain control signal is generated as a gain-down signal. This gain control method however cannot provide maintenance of a reception performance at the receiver, since the reception performance for decoding the punctured frame is maintained only with a continuous increase in the gain by that time interval for decoding the punctured traffic frame. To avoid such an impairment, the transmitter performs gain control ignoring the gain-down signal among the gain control signals fed back from the receiver, after having decreased during fading and having then recovered therefrom.
As described above, the transmitter ignores the gain-down signal among the gain control signals fed back from the receiver such that only the gain-up signal is activated with the gain-down signal inactivated after having recovered from a deep fading, resulting in a waste of gain.
Furthermore, another problem arises in that data transmission with high gain causes an increase in interference on the reverse link and reduces the capacity of the reverse link.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a device and method for controlling gain during the transmission of a punctur
Ahn Jae-Min
Kim Jae-Yoel
Kim Young-Ky
Dilworth & Barrese LLP
Nguyen Lee
Samsung Electronics Co,. Ltd.
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