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Design of a Coded Modulation for Deep Space Optical Communications

We show how to design a modulation and error correcting code (ECC) to achieve near-capacity performance on a deep space optical link. We begin by comparing the capacity of various modulations, given the power and bandwidth constraints of the channel and show that pulse position modulation (PPM) is near-optimal for a nominal mission scenario to Mars. We present a coded PPM solution comprised of the serial concatenation of a convolutional code, interleaver, accumulator, and PPM. This code is amenable to a high-speed, low-complexity hardware implementation and has performance with about 1 dB of capacity and several dB better than competing coded PPM designs.