Multiplex communications – Communication over free space – Signaling for performing battery saving
Reexamination Certificate
1998-10-02
2002-12-24
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Signaling for performing battery saving
C455S522000
Reexamination Certificate
active
06498785
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to power control in cellular telecommunication systems and, more particularly, to a method and system for power control on a common channel that may be shared by a plurality of mobile stations operating in a cellular telecommunication system.
BACKGROUND OF THE INVENTION
Power control for mobile station transmissions is an important aspect of cellular telecommunication systems. One type of cellular technology in which power control is particularly important is code division multiple access (CDMA) technology. In a CDMA-type system multiple users, each using a channel identified by a uniquely assigned digital code, simultaneously communicate with the system while sharing the same wideband frequency spectrum. In a CDMA cellular system, the signals from multiple mobile stations are received at the same frequency simultaneously at a base station. Because of the nature of CDMA demodulation, it is necessary that the signal received at the base station from each mobile station be as close as possible to a single power level so that the signal from one mobile station does not overwhelm the signal from another mobile station (near-far problem).
In a CDMA cellular system a power control process may be used to control each mobile station's transmission power level so that the signal level received at the base station from each mobile station is as close as possible to a single predetermined level. Additionally, the power control process may also be used to assure that the received signal levels at the base station are of an adequate level, so that calls are not dropped. One example of a CDMA mobile station power control scheme is the power control used by systems specified in the
Telecommunications Industry Association/Electronic Industries Association (TIA/EIA) IS-95 standard. Another related CDMA mobile station power control scheme is the power control used by systems specified in the ANSI-008 standard, which is the personal communications system (PCS) 1900 MHz version of IS-95.
In IS-95, a mobile station first adjusts its transmission power level using an access channel assigned to a base station through which the mobile station is attempting to gain access to the system. To gain access, the mobile station follows an open loop power control process that involves transmitting access probe transmissions at a relatively low power level on the access channel and gradually increasing the level of subsequent access probe transmissions in access probe correction increments set by the system, until a response is obtained from the system and the mobile station gains access to the system. The access probe includes an access preamble and an access channel message capsule. The transmission power of each access probe transmission on the access channel is given by the equation:
Mean
output
power
(
dBm
)
=
-
mean
input
power
(
dBm
)
-
73
+
NOM_PWR
(
dBm
)
+
INIT_PWR
(
dBm
)
+
the
sum
of
all
access
probe
corrections
(
1
)
The values NOM_PWR and INIT_PWR are system parameters having values assigned by the system. The mean input power is the total received power at the mobile station antenna connector.
The ANSI-008 standard equation is similar but, because of the frequency difference, has a constant equal to 76 instead of 73 and also includes an additional value that is added to increase the range of NOM_PWR, the additional value being defined as 16*NOM_PWR_EXT, which is a system parameter. IS-95 could also be modfied to include a similar value.
Once the mobile station gains access to the system, it waits in an idle mode until a call is initiated from either the mobile station to the base station, or from the base station to the mobile station. A dedicated reverse traffic channel and a dedicated forward traffic channel are then assigned for the call. When transmitting on the IS-95 reverse traffic channel, the mobile station initializes at the power level at which access was obtained on the access channel using the open loop process defined by equation (1). Once the reverse traffic channel transmission power level is initialized and the call begins, the system and mobile station then also begin a closed loop power control process. The closed loop power control process allows the signal level received at the base station from each mobile station transmitting on a reverse traffic channel to be set as close as possible to a single predetermined level. In the closed loop power control process, the base station transmits closed loop power control corrections in the form of power control bits to the mobile station that are transmitted in a power control subchannel that is included in the forward traffic channel. A single power control bit is transmitted in the power control subchannel every 1.25 msec. A “one” bit transmitted in the power control subchannel indicates that the mobile station should increase its transmission power 1 dB, while a “zero” bit indicates that the mobile station should decrease its transmission power 1 dB. Each time a valid control bit is received at the mobile station in the power control subchannel, the mobile station adjusts its output power level up or down in an increment of 1 dB. The mobile station is capable of adjusting the transmission power within a range of ±24 dB around the level set by the open loop power control process on the access channel and, as the call is ongoing, the transmission power of the mobile station on the reverse traffic channel is adjusted so that a desired power level is reached and maintained. The mobile station also simultaneously continues the open loop power control process, this time using the forward traffic channel. In the open loop process the mean input power received on the forward traffic channel is the determining value. When involved in the call, the inputs that effect changes in the mobile station's transmission power are the mean input power as received from the base station on the forward traffic channel and the closed loop power corrections indicated by the power control bits received on the forward power control channel. During a call, the mobile station output power level on the reverse traffic channel is given by the equation:
Mean
output
power
(
dBm
)
=
-
mean
input
power
(
dBm
)
-
73
+
NOM_PWR
(
dBm
)
+
INIT_PWR
(
dBm
)
+
the
sum
of
all
access
probe
corrections
+
the
sum
of
all
closed
loop
power
control
corrections
(
2
)
As for equation (1), the ANSI-008 standard equation is similar but, because of the frequency difference, has a constant equal to 76 instead of 73 and also includes an additional value that is added to increase the range of NOM_PWR, the additional value defined as 16*NOM_PWR_EXT, which is a system parameter.
A third generation CDMA system is being developed to provide more sophisticated and better services (data, etc.) than provided by IS-95 and eventually to replace IS-95. In the proposed standard for third generation CDMA known as CDMA 2000 TTU-R RTT, it has been proposed that third generation systems have a common control channel that is not used in IS-95. The reverse common control channel (R-CCCH) has been proposed as a common random access channel to be shared by multiple mobile stations to allow transmissions to the system without explicit authorization by a base station. I
Derryberry Roy Thomas
Gray Steven D.
Rong Zhigang
Abelson Ron
Nguyen Chau
Nokia Mobile Phones Ltd
Rivers Brian T.
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