Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-04-20
2002-04-02
Yao, Kwang B. (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C375S287000
Reexamination Certificate
active
06366570
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to signal processing techniques and more particularly to an apparatus and method of processing CDMA signals.
BACKGROUND OF THE INVENTION
The use of code division multiple access (CDMA) signals is a convenient technique of transmitting wireless signals. Many wireless systems process CDMA signals for the transmission of information. However, typical CDMA signal processing techniques suffer inefficient power in the desired band of frequencies for transmitted signals and unacceptable intersymbol interference. Therefore, it is desirable to increase frequency band power and reduce intersymbol interference.
SUMMARY OF THE INVENTION
From the foregoing, a need has arisen for processing CDMA signals to increase frequency band power. A need has also arisen for processing CDMA signals to reduce intersymbol interference.
An object of the invention is to provide an apparatus and method of processing CDMA signals that substantially eliminate or reduce disadvantages and problems associated with conventional CDMA processing techniques.
In accordance with one aspect of the invention, there is provided a method of processing CDMA signals, comprising the steps of:
performing a spreading function on CDMA signals from a plurality of channels;
combining the CDMA signals of the plurality of channels to create a summed signal;
removing a portion of the summed signal above and below a desired threshold range to create a clipped signal.
In accordance with another aspect of the invention, there is provided a method of processing CDMA signals, comprising the steps of:
performing a spreading function on CDMA signals from a plurality of channels;
combining the CDMA signals of the plurality of channels to create a summed signal;
converting the summed signal into two separate data channels for modulating a radio frequency carrier transmission signal, each of the two separate data channels carrying information in a half-width pulse configuration, wherein a first half of the pulse contains valid information and a second half of the pulse has a return to zero format.
In accordance with a further aspect of the invention, there is provided an apparatus for processing CDMA signals, comprising:
a summer circuit operable to combine CDMA signals from a plurality of channels, the summer circuit operable to generate a summed signal therefrom;
a clipping circuit operable to remove a portion of the summed signal above and below a desired threshold range, the clipping circuit operable to generate a clipped signal therefrom;
a digital to analog processing circuit operable to convert the clipped signal into a half width encoded format, the half width encoded format having information contained in a first half of a signal pulse and no information in a second half of the signal pulse, the digital to analog processing circuit operable to convert the clipped signal in the half width encoded format to an analog signal;
a filter operable to reduce inter-symbol interference in the analog signal.
According to an embodiment of the present invention, a method of processing CDMA signals includes performing a spreading function on CDMA signals from a plurality of channels. The CDMA signals from the plurality of channels are combined to create a summed signal. A portion of the summed signal above and below a desired threshold range is removed to create a clipped output signal.
The present invention provides various technical advantages over conventional CDMA processing techniques. For example, one technical advantage is to clip CDMA signals from multiple channels to improve handling of more frequently occurring values falling within the desired clipping region. Another technical advantage is to effectively filter clipped CDMA to reduce intersymbol interference. Yet another technical advantage is to encode clipped CDMA signals into a half width format for increased power in a desired band of frequencies. Other technical advantages are readily ascertainable to one skilled in the art from the following figures, description, and claims.
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Sedra et al.,Microelectronic Circuit,Sauders College Publishing, pp. 163, 164, ©1991.
Alcatel USA, Inc.
Baker & Botts L.L.P.
Yao Kwang B.
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