  Concatenation is a method of building long codes out of shorter ones, it
attempts to meet the problem of decoding complexity by breaking the required
computation into manageable segments. Concatenated Continuous Phase Frequency
Shift Keying (CPFSK) facilitates powerful error correction. CPFSK also has the
advantage of being bandwidth efficient and compatible with nonlinear
amplifiers. Bandwidth efficient concatenated coded modulation schemes were
designed for communication over Additive White Gaussian noise (AWGN), and
Rayleigh fading channels. An analytical bounds on the performance of serial
concatenated convolutional codes (SCCC), and parallel concatenated
convolutionalcodes (PCCC), were derived as a base of comparison with the third
category known as hybrid concatenated trellis codes scheme (HCTC). An upper
bound to the average maximum-likelihood bit error probability of the three
schemes were obtained. Design rules for the parallel, outer, and inner codes
that maximize the interleaver's gain were discussed. Finally, a low complexity
iterative decoding algorithm that yields a better performance is proposed.
