Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Reexamination Certificate
1998-04-29
2001-09-11
Chin, Stephen (Department: 2734)
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
C375S295000, C375S297000, C455S115200, C455S126000
Reexamination Certificate
active
06286994
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention is directed to control of transmit signal power using digital representations of expected output power.
II. Description of the Related Art
In signal transmission systems it is important to maintain expected power levels in transmit signals. For example, in code division multiple access (CDMA) cellular systems, performance is dependent on accurate control of radiated power from both subscriber units and base stations. The precise level of radiated power for the forward link serves to balance the forward and reverse link boundaries of a sector or cell. This, in turn helps to reduce the size of hand-off regions, increase overall system capacity and improve subscriber performance in the hand-off region. In addition, industry standards require that the total transmitted power remain within +2 dB and −4 dB of the nominal power rating.
In order to maintain the forward transmit power at a desired level it is necessary to implement a mechanism that compensates for unintentional gain fluctuations observed in various components of the transmit chain. Unintentional variations can be caused by drifting operating points resulting from aging, changes in the ambient temperature, air pressure and humidity levels. Other contributing factors such as saturation of amplifiers and changes in the traffic load (i.e., desired power level) can be included. Calibration procedures do not generally ensure precise levels of output power over time. A signal-based control system that compares an expected output level to the actual output level is desired.
In addition to unintentional power fluctuations, many types of signal transmission systems intentionally vary or fluctuate output power. For example, in CDMA systems, output power levels are intentionally varied based upon such factors as, for example, the number of active mobile units, the amount of traffic to each mobile unit, and the location of mobile units. Moreover, each channel in a CDMA system can have an independent expected power level. In many of the channels, such as in forward traffic channels, expected output power levels can vary from frame to frame. Thus, one of the difficulties that is encountered in such systems is distinguishing between intentional fluctuations and unintentional fluctuations.
What is needed is a system, method and computer program product for compensating for unintentional power fluctuations.
SUMMARY OF THE INVENTION
The present invention is a novel and improved system, method and computer program product that controls the overall gain of a transmit chain such that the actual transmitted power matches a calculated desired transmit power. The present invention is referred to herein as a transmit power tracking loop (TPTL).
The TPTL receives digital power data from a digital signal processing portion of a transmitter and actual output data from a transmitting portion of the transmitter. The digital power data is sampled and filtered to generate an expected average output power level. The actual output data is sampled and filtered to generate an actual average output power level. A comparator periodically compares the expected output power level to the actual output power level. Preferably, the comparator first removes a correction value from the actual output power level that was added to the transmit signal to correct for unintentional power fluctuations. The resultant ratio is sent to a correction module which generates a correction value therefrom. The correction value is converted to a suitable quantity and used to adjust correction values.
In one embodiment, the TPTL is implemented in a code division multiple access (CDMA) cellular telephone system that includes a digital signal processor which includes multiple digital channels. Digital power data from the digital channels is sampled, filtered and added together to generate the expected output power level. The digital power data can include, for example, a forward traffic gain value (G
t
), a power control gain value (G
s
) and a traffic data rate value (r
t
) that are associated with the respective channel.
In one embodiment of a CDMA application, the digital power data is sampled and filtered every frame, the actual power data is sampled and filtered every other frame and the comparator compares the expected output power level with the actual power level once every fifty frames. In this embodiment, the filter that filters the actual power has a time constant that is twice the time constant of the filter that filters the expected power data such that the averaging time windows are identical.
The present invention distinguishes between unintentional power fluctuations that vary slowly over time and intentional power fluctuations that vary dynamically. The present invention accurately corrects for slowly changing unintentional power fluctuations that can be due to, for example, temperature changes and component aging. The present invention is a signal-based system and thus is not dependent on calibration conditions for accuracy.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
REFERENCES:
patent: 5303268 (1994-04-01), Tsutsumi et al.
patent: 5715526 (1998-02-01), Weaver, Jr. et al.
patent: 5809420 (1998-09-01), Ichiyanagi et al.
patent: 5842114 (1998-11-01), Ozluturk
patent: 5930242 (1999-07-01), Mimura
patent: 6009119 (1999-12-01), Jovanovich et al.
Aydin Levent
Boesel Robert W.
Weaver, Jr. Lindsay A.
Chin Stephen
Edwards Christopher O.
Ha Dac V.
Hom Raymond B.
Qualcomm Incorporated
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