improvements to a layered modulation implementation are disclosed . the present invention discloses two implementations of lm , using single and multiple transponders per signal frequency , respectively . layered hierarchical 8psk is a special case of lm . by re - encoding the high - priority portion of an h - 8psk signal , lm can improve carrier - to - noise ratio of a h - 8psk signal . lm can be computer - simulated and a two - layered signal can be sequentially demodulated with a predicted cnr performance . an lm signal can be simulated 10 using live signals for off - line processing . in addition , a signal processing apparatus can process in real time lm signals emulated from live satellite signals .