Phase-inversion symmetric method principle and application

The Phase-Inversion Symmetric Method (PISM) means two signals of the mutual reverse phase are sent from the information source, and are transmitted through two adjacent channels, then put two signals subtraction at the receiver, in order to get larger SNR. Theory and practice indicate that, PISM can improve the system's SNR effectively. Nowadays, PISM are used widely in FDMA, TDMA and CDMA systems.