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

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