Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-12-31
2004-06-01
Zimmerman, Brian (Department: 2635)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S332000, C370S252000, C455S522000, C455S442000
Reexamination Certificate
active
06744754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to the control of forward link power in a CDMA mobile communication system.
2. Description of the Prior Art
In a mobile communication system using a code division multiple access (CDMA), such as a cellular mobile communication system or a personal communication service system, a plurality of mobile stations transmits and receives frames via a base station or a cell-site. The communication path used by a base station to transmit data frames to a user is called a forward link. Conversely, the reverse link refers to the communication path used by a user to transmit data frames back to a base station.
Each of the frames is composed of symbols indicating a digitized voice and related data. These frames may fade during transmission through a multipath because reflections in the transmission environment as the mobile stations move. The frames may also fade by an interference of one specific mobile station with another mobile stations due to a high transmission power.
Also, if a certain mobile station is extremely low in power, the associated base station cannot recover the data of a frame transmitted from the mobile station, resulting in a loss of data. Thus, the base station has to control the frame transmission power of the mobile station to adequately recover the data of the transmitted frame while minimizing the fading of the transmitted frames.
For frame transmission power control, the base station is adapted to measure the transmission power of the frame transmitted from the mobile station and send a power control command to the mobile station according to the measured result. The power control command instructs the mobile station to adjust the transmission power through separate channels.
This power control command is composed of a transmission power increment bit or a transmission power decrement bit for maintenance of an average reception power.
FIG. 1
is a block diagram showing a portion of a conventional apparatus for controlling a reverse link power in a CDMA mobile communication system. A spread-band CDMA signal transmitted from a mobile station (not shown) is received at a receiving antenna
20
of a base station, generally through a reverse link CDMA channel. A radio frequency (RF) receiver
21
performs a frequency down process with respect to the received CDMA signal.
An analog/digital (A/D) converter
22
converts the CDMA signal frequency down-processed by the RF receiver
21
into a digital signal, and a PN correlator
23
performs a correlation process with respect to the digitized CDMA signal from the A/D converter
22
on the basis of a PN code provided from a PN code generator (not shown). The PN correlator
23
supplies an output signal to a decoder
24
which performs a decoding operation and to a power estimator
25
which estimates the average reception power of the mobile station transmitting the CDMA signal.
The decoder
24
decodes the output signal from the PN correlator
23
into a code symbol of the received CDMA signal and also supplies code error metrics indicating the quality of the received CDMA signal to an outer loop power controller
26
. In response to the code error metrics from the decoder
24
, the outer loop power controller
26
detects a sufficient power of the mobile station to transmit data and supplies a power control reference value for the control of reverse link power to a comparator
27
.
The comparator
27
compares the average reception power of the mobile station estimated by the power estimator
25
with the power control reference value from the outer loop power controller
26
and supplies a deviation of the average reception power from the power control reference value to a power control bit generator
28
. The power control bit generator
28
generates a reception power increment bit or a reception power decrement bit according to the deviation supplied from the comparator
27
and provides the generated reception power increment bit or reception power decrement bit to a transmitter
29
.
The transmitter
29
transmits the reception power increment bit or reception power decrement bit from the power control bit generator
28
together with the frequency up-processed user data to the mobile station through a transmitting antenna
30
while placing them on a traffic channel among the CDMA channels of a forward link.
The CDMA channels in the forward link are generally a pilot channel, a synchronous channel, a paging channel and a traffic channel for forward connection and communication from the base station to the mobile station. The CDMA signals through these CDMA channels are orthogonally processed based upon Walsh function codes and processed as orthogonal pairs of a pseudo noise (PN) sequence based upon a fixed chip rate such that the signals can be code-symbolized.
Generally, a CDMA signal may be transmitted at various rates of 9.6 kbps (full rate), 4.8 kbps (half rate), 2.4 kbps (quarter rate) and 1.2 kbps (eighth rate). The CDMA signal is also encoded in the mobile station. Typically, the CDMA signal is encoded into a frame at an interval of 20 msec. An error correcting code is used in the encoding process to automatically correct an error of the digital data.
Referring back to
FIG. 1
, the power control through the power estimator
25
, the comparator
27
and the power control bit generator
28
forms a closed loop power control. In the closed loop power control, the base station measures a transmission rate-based reception power of a signal received from the mobile station, compares the measured reception power with a predetermined power control reference value and sends an appropriate power control command as a result of the measurement together with user data to the mobile station. Thus, the mobile station adjusts the transmission power in response to the sent power control command and transmit a signal at the adjusted transmission power.
In the closed loop power control, the power control reference value is determined differently for each mobile stations depending on various parameters such as the moving speeds of the mobile station, the surroundings of the mobile stations, etc. Particularly, the outer loop power controller
26
in the base station adjusts the power control reference value appropriately according to a frame error rate of the received data. Such power control is called an outer loop power control.
As discussed above, the conventional power control of the CDMA mobile communication system is mainly a reverse link control. Particularly, the mobile station aids the base station in the control of the power on the forward channel by transmitting a power control message to the base station on the reverse link. The mobile station estimates the reception power and informs the base station via the power control message.
The base station may accordingly adjust the transmission power, i.e. the reception power at the mobile station, to each mobile station. Through the power control message, the base station may minimize the necessary transmission power to each individual mobile station for maintaining a link of a specified quality. By minimizing each transmission power, the total interference generated is also minimized, thereby improving the capacity of the system.
In the conventional CDMA mobile communication system, the mobile station evaluates its error performance and sends a power control message for each frame. Thus, the base station adjusts the transmission power output every frame or 50 Hz. The power output to each mobile station is updated on a frame by frame basis through a feedback mechanism from the mobile station to the base station. The feedback mechanism allows the mobile station to inform the base station on whether the frames are received correctly or incorrectly by including such information in every frame of data transmitted to the base station.
However, the conventional power control for the CDMA mobile communication system fundamentally limits the
Fleshner & Kim LLP
LG Information & Communications Ltd.
Zimmerman Brian
LandOfFree
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