Design of multilevel coded M-ary CPFSK systems with modulation index 1/2

In this paper, based on multilevel coding and multistage decoding techniques, multilevel schemes for M-ary continuous phase frequency shift keying (CPFSK) with modulation index 1/2 are introduced. At each level of the multilevel system classical or punctured convolutional codes and at the last level, where the phase continuity is satisfied, fast frequency shift keying (FFSK) codes are used. The new systems with M=4, 8 and 16 are compared with corresponding previously designed schemes and uncoded cases. It is shown that the proposed systems have coding gain and decoding complexity advantages.