Performance measures for coupled digital phase-locked loops for the separation of co-channel signals

Coupled digital phase-locked loops (CDPLLs), derived from extended Kalman filter theory, have been shown to suppress adjacent and cochannel interferers. The ability of these CDPLLs to separate cochannel signals is addressed. State observability criteria are defined and examined for nonlinear state observations which model phase modulation. These metrics can then be used to address signal separation and tracking behavior of CDPLLs