Multi‐Level Block Coded Modulations with Unequal Error Protection for the Rayleigh Fading Channel

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Abstract
Block coded 8‐DPSK modulations are presented for the time selective Rayleigh fading channel. These coded modulations are based on multi‐level code constructions and utilize short binary block codes of length 2 to 8 (binary symbols) as building blocks to construct 8‐DPSK codes of length 2 to 8 symbols, respectively. All the constructed block coded modulations have a built in time diversity of at least 2 to combat Rayleigh fading. Unequal error protection (UEP) is obtained by providing higher time diversity for the important data. Further UEP can be obtained by using a non‐uniform signal constellation that provides higher product distance (through increased component Euclidean distance) for the more important data. Low transmission delay is obtained by matching the code rate and interleaver to the channel conditions (Doppler spread). Block coded 8‐DPSK schemes with rate 1.5‐2.25 information bits per symbol and code length 2 to 8 symbols have been designed and simulated for various values of Doppler spread. Gains of more than 15 dB can be obtained at a bit error rate of 10−3for a fraction of the data that is deemed to be most important. By using different binary codes in the multilevel scheme and by using different nonuniform signal constellations, the unequal error probability profile and the data rates can be controlled in a flexible manner.

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