Pulse or digital communications – Transmitters
Reexamination Certificate
1998-03-30
2001-10-02
Pham, Chi (Department: 2631)
Pulse or digital communications
Transmitters
Reexamination Certificate
active
06298094
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for power control in a transmitter.
BACKGROUND OF THE INVENTION
Wireless telecommunications systems sometimes are divided into a series of cell areas covering a service area. Each cell area has a transmitting base station using an operating frequency set comprising a plurality of radio channels to communicate with mobile subscribers. Each channel represents an information signal at a particular frequency carrier or band.
In many instances it is advantageous to combine these channels for transmission purposes. The channels can all be combined by a broadband signal combiner into a multichannel signal at low power levels and then amplified by a single linear amplifier (or its equivalent, a plurality of linear amplifiers in parallel, each amplifying a reduced power version of the same multi-channel signal) to raise the multi-channel signal to an appropriate transmit power level.
Peak to average ratio compression is a technique of improving average power levels from a transmitter with limited peak power capability. Traditionally, this has been accomplished with adaptive gain control and clipping. These techniques create frequency domain splatter and increase the noise floor of the transmitted signal. In addition, such techniques are not very useful for amplitude modulated signals, which require a high degree of linearity. Thus, a need exists for a method and apparatus for power control in a transmitter that can maintain linear transmitter operation while increasing the average power output of the transmitter.
SUMMARY OF THE INVENTION
An aspect of the present invention is a method for power control in a transmitter. The method comprises the steps of receiving an input signal comprising symbols for transmission, and determining an output signal for a symbol period from a predetermined range of symbols of the input signal in combination with a modulating phasor vector and a matrix of filter coefficients. The method further comprises the steps of comparing samples of the output signal with a predetermined amplitude limit; and, in response to a sample of the output signal exceeding the predetermined amplitude limit, the step of adjusting the symbols of the predetermined range of symbols that are not pilot symbols by a first adjustment factor, thereby creating a new input signal. The method further comprises, in response to the sample of the output signal exceeding the predetermined amplitude limit, the steps of computing a new output signal from the new input signal in combination with the modulating phasor vector and the matrix of filter coefficients; and generating a power-controlled modulated radio signal from the new output signal.
Another aspect of the present invention is a transmitter with improved average power. The transmitter comprises a processor for receiving an input signal comprising symbols for transmission. The processor is programmed to determine an output signal for a symbol period from a predetermined range of symbols of the input signal in combination with a modulating phasor vector and a matrix of filter coefficients, and to compare samples of the output signal with a predetermined amplitude limit. In response to a sample of the output signal exceeding the predetermined amplitude limit, the processor is further programmed to adjust the symbols of the predetermined range of symbols that are not pilot symbols by a first adjustment factor, thereby creating a new input signal; and to compute a new output signal from the new input signal in combination with the modulating phasor vector and the matrix of filter coefficients. The transmitter also includes an exciter coupled to the processor for generating a power-controlled modulated radio signal from the new output signal.
REFERENCES:
patent: 5343499 (1994-08-01), Jasper et al.
patent: 5371481 (1994-12-01), Tiittanen et al.
patent: 5381449 (1995-01-01), Jasper et al.
patent: 5606285 (1997-02-01), Wang et al.
patent: 5694431 (1997-12-01), McCoy
patent: 5870436 (1999-02-01), Kolanek et al.
Dehner Leo George
McCoy James Wesley
Breeden R. Louis
Burd Kevin M
Motorola Inc.
Pham Chi
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