Composite crest factor reduction

Abstract

Systems and methods are provided for providing a hybrid signal having a reduced crest factor. An analog exciter generates an analog signal having an associated phase. A digital exciter generates a digital signal that assumes one of a plurality of vector states at discrete sampling times associated with the hybrid signal. Each of the plurality of vector states has an associated phase. The digital signal and the analog signal are combined to provide the hybrid signal. The hybrid signal is compressed maximally when the digital signal assumes a vector state that is in phase with the analog signal.

1 . A method for providing a hybrid signal having a reduced crest factor comprising: 
 generating a digital signal that assumes one of a plurality of vector states at discrete sampling times, each of the plurality of vector states having an associated phase;    generating a frequency modulated analog signal having an associated phase;    combining the digital signal and the analog signal to provide the hybrid signal; and    compressing the hybrid signal maximally when the digital signal assumes a vector state that is in phase with the analog signal    
   
   
       2 . A method as set forth in  claim 1 , wherein compressing the hybrid signal includes selectively predistorting the digital signal.  
   
   
       3 . A method as set forth in  claim 2 , wherein selectively predistorting the digital signal includes reducing the amplitude of digital signal when it assumes a vector state that is in phase with the analog signal.  
   
   
       4 . A method as set forth in  claim 1 , wherein compressing the hybrid signal includes providing the hybrid signal to a limiting system that compresses amplitude peaks associated with the hybrid signal.  
   
   
       5 . A method as set forth in  claim 4 , the limiting system comprising a power amplifier.  
   
   
       6 . A method as set forth in  claim 5 , the limiting system further comprising a soft limiter.  
   
   
       7 . A method as set forth in  claim 1 , wherein the digital signal is modulated via quadrature phase shift keying.  
   
   
       8 . A method as set forth in  claim 1 , wherein the hybrid signal is compressed maximally when the digital signal is in-phase with the analog signal, compressed minimally when the digital signal is directly out of phase with the analog signal, and compressed at a variable level between a minimum and maximum level of compression.  
   
   
       9 . A system for producing a hybrid signal having a reduced crest factor, comprising: 
 an analog exciter that produces an analog signal having an associated phase;    a digital exciter that produces a digital signal that assumes one of a plurality of vector states at discrete sampling times associated with the hybrid signal, each of the plurality of vector states having an associated phase;    a signal combiner that combines the analog signal and the digital signal to produce the hybrid signal; and    a limiting system that significantly compresses the hybrid signal when the digital signal assumes a vector state that is in phase with the analog signal.    
   
   
       10 . The system of  claim 9 , wherein the limiting system compressed the hybrid signal maximally when the digital signal is in-phase with the analog signal, compresses the hybrid signal minimally when the digital signal is directly out of phase with the analog signal, and compresses the hybrid signal at a variable level between a minimum and maximum level of compression.  
   
   
       11 . A system set forth in  claim 9 , wherein the limiting system comprises a digital predistorter that selectively predistorts the digital signal.  
   
   
       12 . A system as set forth in  claim 10 , wherein the digital predistorter significantly reduces the amplitude of digital signal when it assumes a vector state that is in phase with the analog signal.  
   
   
       13 . A system as set forth in  claim 9 , the limiting system comprising a power amplifier.  
   
   
       14 . A system as set forth in  claim 13 , the limiting system further comprising a soft limiter.  
   
   
       15 . A system as set forth in  claim 14 , the soft limiter comprising a limiter and a band-pass filter.  
   
   
       16 . A system as set forth in  claim 14 , the soft limiter comprising a cascaded series of limiters and bandpass filters.  
   
   
       17 . A system as set forth in  claim 9 , wherein the digital signal is modulated via quadrature phase shift keying.  
   
   
       18 . A system as set forth in  claim 9 , the analog exciter comprising an FM analog exciter.