1. Field of the Invention
This invention relates to techniques of modulating a carrier by changing its waveform without altering its frequency, phase or amplitude. In particular, this invention relates to a form of modulation called waveform modulation.
2. Description of the Prior Art
Modulation of a carrier signal with information contained in a modulation signal is well known in the art. Common techniques include pulse modulation, amplitude modulation, phase modulation, frequency modulation and quadrature amplitude modulation. Typically, in such forms of modulation, a sine wave is used as a carrier.
The selection of the modulation technique, of course, alters parameters of that carrier sine wave such as whether there is a sine wave (pulse modulation), the amplitude of the sine wave (amplitude modulation), the phase of the sine wave (phase modulation), the frequency of the sine wave (frequency modulation) and the amplitude of both a sine and a cosine wave carrier (quadrature amplitude modulation). Depending upon the selection of the modulation technique, the permitted bandwidth for the trasmitted signal and the expected signal to noise ratio in the communications channel, the maximum data transmission rate can be calculated.
Generally, as the sophistication of the modulation technique increases, the complexity of the circuitry required for the transmitter and the receiver increases. For example, in quadrature amplitude modulation, computers are frequently used for demodulation.
To maximize the data transmission rate, numerous techniques have been devised for transmitting two signals in the same bandwidth. For example, a common technique used in satellite communications is to have orthogonally polarized waves transmitted at the same frequency. However the polarization of such orthogonally polarized waves can be substantially degraded by precipitation. Other techniques include frequency interleaving such a used in the NTSC television standard.
Theoretically, for example, a phase shift keyed signal can imposed upon an amplitude modulated carrier to increase the transmission rate. However, the demodulation circuitry for such a transmitted signal is complex to avoid artifacts in the demodulated phase modulated data occurring in the demodulated amplitude signal.
Thus, it is a first goal of this patent to arrive at a new way of modulating a carrier signal with information without requiring complex circuitry for the transmitter or the receiver. It is a further object of the invention to modulate and demodulate the signal in a manner that allows for a maximum data rate. It is yet another object of the instant invention to have the modulated signal to be transparent to other types of signals.