An approach is provided for supporting signal acquisition and frame synchronization in a digital broadcast system utilizing Low Density Parity Check (LDPC) codes. Hierarchical modulation is utilized to provide backward compatibility, whereby the lower layer signal is encoded using LDPC coding. A signal is received, whereby the signal is modulated according to the hierarchical modulation scheme including an upper layer and a lower layer. The signal includes a data pattern and a coded frame. The dependency of the received signal on the upper layer modulation is removed. The modulation removed signal is correlated with multiple predetermined data patterns to determine the data pattern of the signal. The code rate of the coded frame is derived based on the determined data pattern. The above arrangement is particularly suited to a digital satellite broadcast system.