Multiple sub-channel modulation and demodulation with arbitrarily defined channel spacing and sampling rates

Abstract

A modulator, and demodulator, apparatus and method for use in a multiple sub-channel communication system is taught. A commutator is employed for fractionally sampling, or distributing, signals from, or to, a multiple channel polyphase filter. The filter is coupled with a discrete Fourier transform, or its inverse, such that the relationship between the base-band sampling rate of a plurality of sub-channel signals, the frequency spacing of the sub-channel signals, and the sampling rate of a composite signal can be related by any rational number, thereby freeing designers to optimize system design respecting channel spacing, bandwidth, and signaling rates. The advantages of the present invention are realized by adjusting the interpolation and decimation rates of the filter, and by adjusting the resolution and decimation rates of the transform.

1. A modulator for receiving a plurality of sub-channel signals that are sampled at a base-band sampling frequency and separated by a frequency spacing, and, for generating a composite signal, combining the plurality of sub-channel signals, that is sampled at a composite sampling frequency, comprising:
 an inverse discrete Fourier transform coupled to receive and transform the plurality of sub-channel signals into a plurality of time domain signals;  
 a multiple channel polyphase filter coupled to receive said plurality of time domain signals and output a plurality of filter signals, and  
 a commutator operable to fractionally sample said plurality of filter signals at a rate defined by the ratio of said frequency spacing and a greatest common divisor between said composite sampling rate  frequency and said frequency spacing.  
 
     
     
       2. The modulator in  claim 1 , and wherein said commutator fractional sampling ratio is the  equal to a decimation rate of the inverse discrete Fourier transform. 
     
     
       3. The modulator in  claim 1 , further comprising a wireless modulator operable to mix the composite signal with a wireless carrier for wireless transmission. 
     
     
       4. The modulator in  claim 1 , and wherein said transform, said filter, and said commutator are implemented with executable software on a processing means. 
     
     
       5. The modulator in  claim 4 , and wherein said processing means is a digital signal processor. 
     
     
       6. A modulator for receiving a plurality of sub-channel signals that are sampled at a base-band sampling frequency and separated by a frequency spacing, and, for generating a composite signal, combining the plurality of sub-channel signals, that is sampled at a composite sampling frequency, comprising:
 an inverse discrete Fourier transform coupled to receive and transform the plurality of sub-channel signals into a plurality of time domain signals, said inverse discrete Fourier transform resolution  transform having a resolution defined by the ratio of said composite sampling frequency and the greatest common divisor between said composite sampling frequency and said frequency spacing, and, said inverse discrete Fourier transform having a transform decimation rate defined by the ratio of said frequency spacing and a greatest common denominator between said composite sampling frequency and said frequency spacing;  
 a multiple channel polyphase filter coupled to receive said plurality of time domain signals and output a plurality of filter signals, said filter having an interpolation rate defined by a least common multiple between said base-band sampling frequency and said composite sample frequency divided by said base-band sampling frequency, said multiple channel polyphase filter having a filter decimation rate defined as said filter interpolation rate times said base-band sample frequency and divided by said composite sampling frequency, and  
 a commutator operable to fractionally sample said plurality of filter signals at a rate defined by the ratio of said frequency spacing and a greatest common divisor between said composite sampling rate  frequency and said frequency spacing.  
 
     
     
       7. The modulator in  claim 6 , and wherein said commutator sampling rate is said decimation rate. 
     
     
       8. The modulator in  claim 6 , further comprising a wireless modulator operable to mix the composite signal with a wireless carrier for wireless transmission. 
     
     
       9. The modulator in  claim 6 , and wherein said transform, said filter, and said commutator are implemented with executable software on a processing means. 
     
     
       10. The modulator in  claim 9 , and wherein said processing means is a digital signal processor. 
     
     
       11. A method of modulating a plurality of sub-channel signals that are sampled at a base-band sampling frequency and separated by a frequency spacing, onto a composite signal that is sampled at a composite sampling frequency, comprisingthe steps of :
 converting the plurality of sub-channel signals into a plurality of time domain signals by performing an inverse Fourier transform that has a resolution defined by the ratio of the composite sampling frequency and a greatest common divisor between the composite sampling frequency and the frequency spacing, and, a decimation rate defined by the ratio of the frequency spacing and a greatest common divisor between the composite sampling frequency and the frequency spacing;  
 filtering said plurality of time domain signals using a multiple channel polyphase filter to produce a plurality of filter signals, the multiple channel polyphase filter having an interpolation rate defined by a least common multiple between the base-band sampling frequency and the composite sample frequency divided by the base-band sampling frequency, the filter decimation rate defined as the filter interpolation rate times the base-band sample frequency and divided by the composite sampling frequency, and  
 fractionally sampling said plurality of filter signals at a rate defined by the ratio of the frequency spacing and a greatest common divisor between the composite sampling rate  frequency and the frequency spacing.  
 
     
     
       12. A system comprising:
   a modulator to receive a first plurality of sub - channel signals that are sampled at a first base - band sampling frequency and separated by a first frequency spacing, and to generate a first composite signal, combining the first plurality of sub - channel signals, that is sampled at a first composite sampling frequency, comprising:      an inverse discrete Fourier transform coupled to receive and transform the first plurality of sub - channel signals into a plurality of time domain signals;        a first multiple channel polyphase filter coupled to receive said plurality of time domain signals and output a plurality of first filter signals, and        a first commutator operable to fractionally sample said plurality of first filter signals at a rate defined by the ratio of said first frequency spacing and a greatest common divisor between said first composite sampling frequency and said first frequency spacing; and        a demodulator to receive a second composite signal that is a combination of a second plurality of sub - channel signals and that is sampled at a second composite sampling frequency, and to discriminate the second plurality of sub - channel signals each at a second base - band sampling frequency and separated by a second frequency spacing, comprising:      a second commutator operable to fractionally distribute said second composite signal to a plurality of filter input signals at a rate defined by the ratio of said second frequency spacing and a greatest common denominator between said second composite sampling frequency and said second frequency spacing;        a second multiple channel polyphase filter having a plurality of filter inputs coupled to receive said plurality of filter input signals, said filter to output a plurality of second filter signals; and        a discrete Fourier transform coupled to receive and transform said plurality of second filter signals and to output the second plurality of sub - channel signals.         
     
     
       13. The system of  claim 12 , wherein said demodulator comprises a wireless demodulator operable to receive a wireless carrier signal and discriminate the second composite signal therefrom for wireless reception. 
     
     
       14. The system of  claim 12 , wherein said second commutator, said second multiple channel polyphase filter, and said discrete Fourier transform are implemented with executable software on a processing means. 
     
     
       15. The system of  claim 14 , wherein said processing means comprises a digital signal processor. 
     
     
       16. A method of modulating a plurality of sub- channel signals that are sampled at a base - band sampling frequency and separated by a frequency spacing, and generating a composite signal, combining the plurality of sub - channel signals, that is sampled at a composite sampling frequency, the method comprising:      converting the plurality of sub - channel signals into a plurality of time - domain signals using an inverse discrete Fourier transform;        filtering the plurality of time - domain signals using a multiple channel polyphase filter, to thereby output a plurality of filter signals; and        fractionally sampling said plurality of filter signals at a rate defined by the ratio of said frequency spacing and a greatest common divisor between said composite sampling frequency and said frequency spacing.     
     
     
       17. The method of  claim 16 , wherein said commutator fractional sampling ratio is equal to a decimation rate used in said converting. 
     
     
       18. The method of  claim 16 , further comprising:
   mixing the composite signal with a wireless carrier for wireless transmission.     
     
     
       19. A non- transitory processor - readable medium containing instructions that, when executed by a processor, cause the processor to implement a method of modulating a plurality of sub - channel signals that are sampled at a base - band sampling frequency and separated by a frequency spacing, and generating a composite signal, combining the plurality of sub - channel signals, that is sampled at a composite sampling frequency, the method comprising:      converting the plurality of sub - channel signals into a plurality of time - domain signals using an inverse discrete Fourier transform;        filtering the plurality of time - domain signals using a multiple channel polyphase filter, to thereby output a plurality of filter signals; and        fractionally sampling said plurality of filter signals at a rate defined by the ratio of said frequency spacing and a greatest common divisor between said composite sampling frequency and said frequency spacing.     
     
     
       20. The medium of  claim 19 , wherein said commutator fractional sampling ratio is equal to a decimation rate used in said converting. 
     
     
       21. The medium of  claim 19 , wherein the operations further comprise:
   mixing the composite signal with a wireless carrier for wireless transmission.     
     
     
       22. A method of modulating a first plurality of sub- channel signals that are sampled at a first base - band sampling frequency and separated by a first frequency spacing, and to generate a first composite signal, combining the first plurality of sub - channel signals, that is sampled at a first composite sampling frequency and of demodulating a second composite signal that is a combination of a second plurality of sub - channel signals and that is sampled at a second composite sampling frequency, and to discriminate the second plurality of sub - channel signals each at a second base - band sampling frequency and separated by a second frequency spacing, the method comprising:      transforming the first plurality of sub - channel signals by using an inverse discrete Fourier transform, to obtain a plurality of time domain signals;        filtering the plurality of time domain signals using a first multiple channel polyphase filter, to output a plurality of first filter signals;        fractionally sampling said plurality of first filter signals at a rate defined by the ratio of said first frequency spacing and a greatest common divisor between said first composite sampling frequency and said first frequency spacing;        fractionally distributing said second composite signal to a plurality of filter input signals at a rate defined by the ratio of said second frequency spacing and a greatest common denominator between said second composite sampling frequency and said second frequency spacing;        filtering the plurality of filter input signals using a second multiple channel polyphase filter to output a plurality of second filter signals; and        transforming said plurality of second filter signals using a discrete Fourier transform, to output the second plurality of sub - channel signals.     
     
     
       23. The method of  claim 22 , further comprising:
   receiving a wireless carrier signal;        and discriminating the second composite signal therefrom for wireless reception.     
     
     
       24. A non- transitory processor - readable medium containing instructions that, when executed by a processor, cause the processor to implement a method of modulating a first plurality of sub - channel signals that are sampled at a first base - band sampling frequency and separated by a first frequency spacing, and to generate a first composite signal, combining the first plurality of sub - channel signals, that is sampled at a first composite sampling frequency and of demodulating a second composite signal that is a combination of a second plurality of sub - channel signals and that is sampled at a second composite sampling frequency, and to discriminate the second plurality of sub - channel signals each at a second base - band sampling frequency and separated by a second frequency spacing, the method comprising:      transforming the first plurality of sub - channel signals by using an inverse discrete Fourier transform, to obtain a plurality of time domain signals;        filtering the plurality of time domain signals using a first multiple channel polyphase filter, to output a plurality of first filter signals;        fractionally sampling said plurality of first filter signals at a rate defined by the ratio of said first frequency spacing and a greatest common divisor between said first composite sampling frequency and said first frequency spacing;        fractionally distributing said second composite signal to a plurality of filter input signals at a rate defined by the ratio of said second frequency spacing and a greatest common denominator between said second composite sampling frequency and said second frequency spacing;        filtering the plurality of filter input signals using a second multiple channel polyphase filter to output a plurality of second filter signals; and        transforming said plurality of second filter signals using a discrete Fourier transform, to output the second plurality of sub - channel signals.     
     
     
       25. The medium of  claim 24 , wherein the operations further comprise:
   receiving a wireless carrier signal;        and discriminating the second composite signal therefrom for wireless reception.