When dealing everyday with baseband complex signals, I often forget those are not real (yes).
I write this post in order to commit strongly to not forgetting those lines.
Constant envelope baseband signal - complex
sb(t)=ejθ(t)=cosθ(t)+jsinθ(t)=i+jq
Send it - real
su(t)=2ℜ[ejθ(t)ejωt]=2ℜ[(i+jq)(cosωt+jsinωt)]=2(icosωt−qsinωt)
Get it back - complex
sd(t)sd(t)=su(t)cosωt−jsu(t)sinωt=2(icos2ωt+jsin2ωt−qsinωtcosωt−jisinωtcosωt)=2(2i+j2q+2cos(2ωt)−j2cos(2ωt)−qsinωtcosωt−jisinωtcosωt)... Apply Low Pass Filter=sb(t)