Suppressed-carrier amplitude modulation ($s(t)=m(t)\cos (2\pi f_{c}t)$)

In suppressed-carrier amplitude modulation, a message $m(t)$ multiplies a carrier without adding a large standalone carrier term. The double-sideband form is $s(t)=m(t)\cos (2\pi f_{c}t)$, with spectrum $[M(f-f_c)+M(f+f_c)]/2$. Multiplying by a phase-aligned local oscillator $2\cos (2\pi f_{c}t)$ and low-pass filtering recovers $m(t)$ under appropriate bandwidth separation. A phase error $\varphi$ instead scales the recovered message by $\cos \varphi$. Thus ordinary envelope detection is not generally enough; coherent carrier phase information matters. Suppressing the carrier changes power allocation without removing both sidebands.