Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-07-26
2002-07-09
Hunter, Daniel (Department: 2749)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S442000
Reexamination Certificate
active
06418322
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 arising from an application entitled, METHOD FOR FORWARD POWER CONTROL IN CELLULAR SYSTEM, earlier filed in the Korean Industrial Property Office on Jul. 30, 1998, and there duly assigned Ser. No. 1998-30790.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cellular radio communication system, and more particularly, to a method for controlling the transmission power of a forward link to improve a call drop rate caused by a deterioration in the forward link in a code division multiple access (CDMA) system.
2. Description of the Related Art
In a cellular radio telecommunication system, the whole coverage area is divided into areas of a plurality of base stations (BSs) and a plurality of cells. The base stations are controlled by a mobile switching center MSC for allowing many subscribers to maintain a call while they are moving between the cells.
FIG. 1
illustrates a configuration of a conventional cellular radio communication system. It includes base stations (BSs) (
200
,
300
and
400
) for providing a mobile communication services to a mobile station (MS) (
100
), and a mobile switching center (MSC) (
500
) for connecting the (BSs) (
200
,
300
and
400
) to a public switched telephone network PSTN
600
.
In the cellular system as illustrated in the
FIG. 1
, a forward link is directed from a base station to a mobile station, and a reverse link is directed from a mobile station to a base station. In a radio communication, a transmission power is controlled in order to suppress the transmission power. The power control is used to adjust the transmit power of the base station for each traffic channel. When the mobile station is affected by the signals traveling through propagation paths or other multi-path characteristic interference, the transmission power control is performed such that the received power levels of signals transmitted from the mobile stations and received by the base station, or the SIR (Signal-to-interference power ratio) associated with the received power levels are kept constant at the base station. By means of this forward power control, there is provided a saving of power consumption and a reduction of interference to other radio channels.
It will be appreciated by those skilled in the relevant art based on the detailed description provided herein that in a typical forward power control known in the art include a mobile station unit for measuring the quality of a communication signal received by the mobile station from a base station and a unit for producing a base station transmission power control data/forward power control signal, and the base station include a unit for measuring a receiving the forward power control signal, a unit for calculating a power level command based on the received forward power control signal, and a unit for producing a mobile station transmission power control data specifying a mobile station transmission power in accordance with the received.
Typically, a base station and a mobile station transmit a voice signal or a control signal in the frame unit of 20 ms. Each frame has error check bits known as cyclic redundancy checks (CRC). The mobile station checks for the error check bits in a forward frame received from the base station and determines whether the forward frame contains an error or not. At a data rate of 8 kbps, the mobile station periodically or when the number of non-proper frames received from the base station falls under a predetermined threshold value transmits a power measurement report message (PMRM) as a forward power control signal. The PMRM contains information about the quality of a forward link, i.e. the total number of properly received or non-properly received forward frames that the mobile station received from the base station. Using the PMRM, the base station adjusts its digital gain in the parameter to increase or decrease the transmit power at a predetermined level, which is indispensable in the CDMA scheme, as a reduction of an amount of interference with other radio channels can directly lead to an increase of a subscriber capacity. This procedure is referred as a Forward Power Control.
FIG. 2
illustrates a graph representing the forward power control as known in the prior art. As shown in the
FIG. 2
, a base station establishes a call with a mobile station and transmits a transmission power to the mobile station with a digital gain indicated as a nominal gain. Then, the base station starts to gradually decrease the transmission power. In other words, the base station gradually decreases the digital gain to reduce the transmission power at a decrement, referred as a “slow down delta” in
FIG. 2
, starting from the peak of the nominal gain for every “slow down time.”
If a power measurement report message (PMRM) is not received from the mobile station during the first slow down time, the process of gradually decreasing the digital gain is repeated for a predetermined number of times, three times as shown in
FIG. 2
, the base station starts to rapidly decrease the digital gain to reduce the transmission power at another decrement, referred to as a “fast down delta” in
FIG. 2
, for “fast down time,” repeatedly.
However, if the decreased digital gain is equal to a predetermined minimum gain, referred to as “floor one way” in
FIG. 2.
, in either the slow down procedure or the fast down procedure, the base station ceases to further decrease the digital gain and maintains the digital gain at a predetermined minimum gain.
Meanwhile, the mobile station checks continually for the forward frames received from the base station and determines whether the forward frames have an error or not. Then, the mobile station informs the base station of the number of the forward frames and the number of forward bad frames via a power measurement report message (PMRM) periodically, or whenever the number of forward bad frames reaches at a predetermined threshold of bad frames (PWR
13
REPT_THRESH).
If the PMRM is received by the base station via a reverse link during the slow down procedure or the fast down procedure, the base station calculates a frame error rate (FER) of the forward link, using the number of all forward frames and the number of bad forward frames as indicated in the PMRM.
If the calculated forward frame error rate exceeds the predetermined threshold of forward frame error rate (FER_THRESHOLD), the base station increases the digital gain of the base station to increase the transmission power by an increment, represented as “big up delta” at P
10
in FIG.
2
. Similarly, if the calculated forward frame error rate does not exceeds the FER_THRESHOLD, the base station increases the digital gain of transmission power by an increment, represented as “small up delta” at P
20
in FIG.
2
.
Accordingly, after the digital gain is increased either by the “big up delta” or the “small up delta,” the base station decreases the digital gain according to the same slow down procedures and the fast down procedures described early. Whenever the power measurement report message is received from a mobile station, the base station adjusts the digital gain to increase or decrease the transmission power according to the newly received PMRM to carry out the forward power control.
Despite of performing such a forward power control, the quality of forward link is always susceptible to interference causing the mobile station to receive the forward frames having errors therein. As shown in
FIG. 3
, if 12 bad frames were received continuously for the duration of 240 ms (P
1
) after a call is established with a base station, the mobile station then stops outputting transmission power and enters into OFF mode.
If two good frames were not received within 5 seconds continuously, the mobile station releases the established call at P
2
as shown in FIG.
3
. However, if the mobile station in the OFF mode (between P
1
~P
2
) receives two good forward f
Kim Gun Yeob
Wee Pyeong Hwan
Hunter Daniel
Klauber & Jackson
Tran Pablo N
LandOfFree
Method for forward power control in cellular system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for forward power control in cellular system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for forward power control in cellular system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2896585