Rate 2/3 coded nonuniform phase/frequency modulation

The authors propose the coded nonuniform FSK/PSK modulation technique to achieve further improvement of the performance over coded FSK/PSK system. They focus on a rate R=2/3 nonuniform coded 2-FSK/4-PSK modulations. The behavior of the free Euclidean distance is considered by varying the modulation index and three rotation angles which determine the nonuniform signal constellations. They also consider the effect of encoder structure and mapping method on the free Euclidean distance of nonuniform coded 2-FSK/4-PSK. The asymptotic performance gains due to coding and nonuniform constellation are evaluated in terms of the free Euclidean distance of the trellis. It is shown that at given modulation index the free Euclidean distance can be maximized by selecting the nonuniform signal constellations and the mapping method appropriately without increasing average or peak power or changing the bandwidth constraints imposed on the system.<>