Spectrally efficient digital fm modulation system

Claim 1

A method for generating an optimized electric pulse suitable for the transmission of information to a frequency modulated (FM) receiver for minimizing intersymbol interference, said method comprising the steps of: selecting a first pulse P o (t)=(sin πt)/πt which exhibits the property of low intersymbol interference; multiplying the first pulse P o (t) with a first predetermined window function K(t) to obtained a second pulse P 1 (t) minimizing the energy density outside the window; determining the spectrum P 1 (f) by taking the Fourier transform of the second pulse P 1 (t); determining a filter function FR(f) which is the reciprocal of the transfer function of the receiver post detection low pass filter; multiplying the spectrum P 1 (f) with the reciprocal filter function FR(f) to obtain a spectrum P 2 (f); determining a third pulse P 2 (t) by taking the inverse Fourier transform of the spectrum P 2 (f); and multiplying the third pulse P 2 (t) by a second predetermined window function W(t) to obtain the optimized electric pulse P 3 (t).

Claim 2

A method for generating an optimized electric pulse suitable for the transmission of information to a frequency modulated (FM) receiver for minimizing intersymbol interference, said method comprising the steps of: selecting a first pulse P o (t)=(sin πt)/πt which exhibits the property of low intersymbol interference; multiplying the first pulse P o (t) with a first predetermined window function K(t) to obtained a second pulse P 1 (t) minimizing the energy density outside the window; determining the spectrum P 1 (f) by taking the Fourier transform of the second pulse P 1 (t); determining a filter function FR(f) which is the reciprocal of the transfer function of the receiver post detection low pass filter; multiplying the spectrum P 1 (f) with the reciprocal filter function FR(f) to obtain a spectrum P 2 (f); determining a third pulse P 2 (t) by taking the inverse Fourier transform of the spectrum P 2 (f); and multiplying the third pulse P 2 (t) by a second predetermined window function W(t) to obtain the optimized electric pulse P 3 (t).

Claim 5

A method for transmitting digital information to a communication receiver employing a post detection low pass filter having predetermined filter transfer function, said method comprising the steps of: storing an optimized electric pulse which is derived from the processing of an electric pulse exhibiting minimum intersymbol interference characteristics with the reciprocal transfer function of the post detection low pass filter of the communication receiver, the optimized electric pulse when received and processed by the post detection low pass filter of the communication receiver providing a pulse shape exhibiting minimal intersymbol interference; recovering the stored, optimized electric pulse in response to the digital information to be transmitted, for generating a sequence of the optimized prototype pulses corresponding thereto; and transmitting the sequence or optimized electric pulses.

Claim 6

A method for transmitting digital information to a communication receiver employing a post detection low pass filter having predetermined filter transfer function, said method comprising the steps of: storing an optimized electric pulse which is derived from the processing of an electric pulse exhibiting minimum intersymbol interference characteristics with the reciprocal transfer function of the post detection low pass filter of the communication receiver, the optimized electric pulse when received and processed by the post detection low pass filter of the communication receiver providing a pulse shape exhibiting minimal intersymbol interference; recovering the stored, optimized electric pulse in response to the digital information to be transmitted, for generating a sequence of the optimized prototype pulses corresponding thereto; and transmitting the sequence or optimized electric pulses.