Generalized concatenation of encoded CPFSK modulation

Using the principles of generalized concatenation we introduce a new design for coded M-ary CPFSK systems with modulation index h = 1/M. This techniqu e is based on a set partitioning method of inner CPFSK into nested subsyste ms with increasing free Euclidean distance which are combined with several outer convolutional codes having different error-correcting capabilities. I n other words, we construct multilevel codes on the basis of inner modulati on with memory, namely CPFSK. The new generalized concatenated construction s were simulated in an additive white Gaussian noise channel. The multistep decoding algoritm is described where for soft output decoding the well-kno wn symbol-by-symbol maximum a posteriori probability (MAP) algorithm is app lied to the inner CPFSK. A comparison of the generalized concatenated codes with the best known trellis-coded CPFSK schemes is also presented.