Abstract A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver. The receiver separates the analog FM signal from the digital signal and thereafter demodulates the digital data-carrying waveforms and outputs a stream of digital data. It has been determined to be resistant to multipath degradation.
A signal receiver for receiving through a medium a radio frequency signal including a digital signal, said digital signal being robust to multipath degradation and intersymbol interference, said receiver comprising: means for receiving said radio frequency signal wherein said digital signal is composed of a modulated set of spectrally shaped and substantially orthogonal modulated waveforms defined by multivalued numerical sequences of substantially equal length having good autocorrelation properties; and demodulation means for determining and outputting digital data from said digital signal represented as said spectrally shaped and substantially orthogonal waveforms.
Claim 2
Dependent Claim
90 words
A signal receiver for receiving through a medium a radio frequency signal including a digital signal, said digital signal being robust to multipath degradation and intersymbol interference, said receiver comprising: means for receiving said radio frequency signal wherein said digital signal is composed of a modulated set of spectrally shaped and substantially orthogonal modulated waveforms defined by multivalued numerical sequences of substantially equal length having good autocorrelation properties; and demodulation means for determining and outputting digital data from said digital signal represented as said spectrally shaped and substantially orthogonal waveforms.
Claim 3
Dependent Claim
88 words
The signal receiver of claim 1, further comprising frequency tracking means for following frequency variations of a wideband reference signal transmitted along with said digital signal, said frequency tracking means comprising: means for establishing a center of gravity of said reference signal; means for measuring the rate of precession of the center of gravity, and, based on the measured rate of precession of the reference signal center of gravity, means for issuing adjustment instructions to an oscillator for adjusting frequency of a baud clock determined by said oscillator.
Claim 4
Dependent Claim
112 words
The receiver of claim 1, said radio frequency signal comprising a composite FM/wideband digital signal, said composite signal being a linear combination of an FM signal and a wideband digital signal, said wideband digital signal being constrained to occupy a first spectrum portion and a second spectrum portion about a center frequency of said FM signal, said receiver further comprising: tracking means for following a reference signal transmitted along with said composite FM/wideband digital signal; means for adjusting a baud clock in said receiver based on frequency of said wideband reference signal; and means for separating said composite FM/wideband digital signal into a conventional FM channel and a wideband digital signal channel.