Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-03-18
2001-02-06
Tsang, Fan (Department: 2746)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000
Reexamination Certificate
active
06185431
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of wireless telecommunications, and more specifically, to the field of mobile station closed loop power control under weak signal conditions in wireless telecommunications systems, such as code division multiple access (CDMA) wireless telephone systems.
One of the primary standard specifications relevant to the present invention is TIA/EIA/IS-95-A “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System.” This CDMA industry standard specification is considered understood by those reasonably skilled in the art of the present invention. The invention disclosed herein is applicable to other variants of CDMA technology, other than TIA/EIA/IS-95-A.
In CDMA wireless telephone systems (including cellular systems, personal communications systems, satellite communications systems, etc.) power control is crucial to the functionality of the communications system. The available number of simultaneous connections is a function of the transmitted power of the mobile and base stations in the CDMA system. If the mobile and base stations are transmitting at power levels higher than necessary, the overall noise level in the system in increased due to interference between the transmitted signals, thus reducing system capacity. If the mobile and base stations are transmitting power levels lower than necessary, the performance of the CDMA system will be sub-par. Also, since the distance, therefore the received power, between the different mobile stations and the base station will be different, each mobile station and base station pair will be transmitting at a different power level. This implies that transmitted power control has to be performed on an individual basis.
There are two different types of power control, open loop power control and closed loop power control. Open loop power control in a mobile station is a gradual system which dictates that output power should increase as the strength of received signals from a base station decreases, and output power should decrease as received signal strengths increase. As specified in the TIA/EIA/IS-95-A standard, the closed loop power control is performed with the assistance of the base station. The base station measures the signal to noise ratio (SNR) of the signals received from a mobile station and makes a comparison of the measured SNR with a predetermined threshold. Depending on the result of the comparison, the base station will notify the mobile station via power control commands injected into the forward traffic channel to either increase or decrease its transmitted power.
In conditions with low received signal strength, i.e., when the mobile station is far from the base station or there is some large physical body blocking the reception of the transmitted signal, the simple injection of power control commands into the forward traffic channel is not a reliable method of transmitting control information to the mobile station because the injected power control commands are not encoded as is all other data in the CDMA system. In fact, in low received signal strength situations, the mobile station's version of the received power control command may be erroneous and may not represent the true intent of the base station. This can result in the mobile station erratically changing its power output due to unreliable power control data.
There is, therefore, a need in the industry for a system for addressing these and other related and unrelated problems.
SUMMARY OF INVENTION
The present invention is a system in a wireless CDMA telephone system for increasing the stability of the transmitted output power under weak signal conditions which includes the addition of an additional variable, power control threshold (PWR_CNTL_THRESH
s
), to the CDMA system. The PWR_CNTL_THRESH
s
variable is added to control messages in the CDMA telephone system. The PWR_CNTL_THRESH
s
indicates the signal level below which the power control command should be considered unreliable. This variable can be communicated to the mobile station from the base station via several different control messages which it regularly sends to the mobile station. In the first preferred embodiment of the present invention, two bits will be used to represent values for PWR_CNTL_THRESH
s
, giving the system a total of four different threshold values.
According to the first preferred embodiment of the present invention, after the mobile station becomes synchronized with the base station or alternatively, after the mobile station powers up, the mobile station sets the PWR_CNTL_THRESH
s
variable to value 0. This disables any effects of the PWR_CNTL_THRESH
s
variable. Through communication with the mobile station, if the base station senses that the mobile station is behaving erratically, by noticing a high variance in the transmitted output power from the mobile station according to one implementations the base station will send to the mobile station a control message with the PWR_CNTL_THRESH
s
set to a particular value in an attempt to make the operation of the mobile station more reliable, i.e., to reduce the variance of the output power. If after the setting of a particular threshold using the PWR_CNTL_THRESH
s
parameter, the variance of the output power does not decrease, the base station may decide to increase the threshold by sending additional messages with PWR_CNTL_THRESH
s
set at larger values.
According to the second preferred embodiment of the present invention, the mobile station will initialize with a pre-determined non-zero value for PWR_CNTL_THRESH
s
that will remain until the mobile station output power becomes erratic.
According to the third preferred embodiment of the present invention, the mobile station has a specific value for PWR_CNTL_THRESH
s
hard coded into its circuitry and will always use this hard coded value.
It is therefore an object of the present invention to improve the reliability of the closed loop power control system.
Another object of the present system is to better handle the different operating conditions between each base station and mobile station pair by providing a more robust power control system.
Yet another object of the present system is to increase the overall system capacity of the CDMA system by having each mobile station transmitting at the optimum power level.
Yet another object of this invention is to make the mobile station more immune to the effects of power control commands from multiple base stations when the mobile station is at the edge of multiple base station coverage ranges.
Other objects, features, and advantages of the present invention will become apparent upon reading and understanding the present specifications, when taken in conjunction with accompanying drawings.
REFERENCES:
patent: 4261054 (1981-04-01), Scharla-Nielsen
patent: 4510460 (1985-04-01), Tamura
patent: 4602218 (1986-07-01), Vilmur et al.
patent: 4636741 (1987-01-01), Mitzlaff
patent: 4811421 (1989-03-01), Havel et al.
patent: 4870698 (1989-09-01), Katsuyama et al.
patent: 5036532 (1991-07-01), Metroka et al.
patent: 5056109 (1991-10-01), Gilhousen et al.
patent: 5093840 (1992-03-01), Schilling
patent: 5107225 (1992-04-01), Wheatley, III et al.
patent: 5107487 (1992-04-01), Vilmur et al.
patent: 5129098 (1992-07-01), McGirr et al.
patent: 5144258 (1992-09-01), Nakanishi et al.
patent: 5241690 (1993-08-01), Larsson et al.
patent: 5257283 (1993-10-01), Gilhousen et al.
patent: 5265119 (1993-11-01), Gilhousen et al.
patent: 5267262 (1993-11-01), Wheatley, III
patent: 5278992 (1994-01-01), Su et al.
patent: 5283536 (1994-02-01), Wheatley, III et al.
patent: 5299226 (1994-03-01), Schilling
patent: 5345598 (1994-09-01), Dent
patent: 5383219 (1995-01-01), Wheatley, III et al.
patent: 5442322 (1995-08-01), Kornfeld et al.
patent: 5452473 (1995-09-01), Weiland et al.
patent: 5461639 (1995-10-01), Wheatley, III et al.
patent: 5467055 (1995-11-01), Wray et al.
patent: 5485486 (1996-01-01), Gilhousen et al.
patent: 5528593 (1996-06-01), En
Li Kaiping
Ong Chung-yen
Oki Telecom, Inc.
Perez-Gutierrez Rafael
Thomas Kayden Horstemeyer & Risley LLP
Tsang Fan
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