Amplitude-Weighted Quadrature Phase Shift Keying Using SAW Technology

Surface acoustic wave (SAW) convolvers are capable of performing programmable matched filtering with the desirable properties of large processing gain, good dynamic range, broad bandwidth, small size and weight, and low power requirements. Equally powerful are the SAW-based modulators, which produce the desired pseudo-random code sequence for secure transmission in a spread-spectrum system. The SAW filter provides precise reproducible pulse shaping of the coded waveform with the same advantages of the convolver. It is very important as spectrum space becomes more crowded to optimize the spectral efficiency of transmitted information. Quadrature phase (QPSK) and minimum phase shift keying (MSK) are the two most popular quadrature modulation schemes. A new modulation technique that is composed of several amplitude-weighted QPSK signals (AWQPSK) and exhibits better bandwidth efficiency than QPSK or MSK is introduced. System analysis and performance parameters are presented for evaluation. A SAW modulator implementation is discussed and proposed.