A method is provided for enhancing a legacy satellite digital radio audio service (SDARS) by overlaying a hierarchically modulated data stream on a base layer (legacy) data stream and improving the synchronization of the received signal in which an overlay layer frame is synchronized to a base layer frame. The base layer frame includes additional data that is used to synchronize the receivers to demodulate and decode the overlay layer and the base layer. The additional data is modulated using a technique that aids the receiver in synchronizing the received signal that is different from the overlay layer.