Saikat Guha, Mark M. Wilde
In the low-energy high-energy-efficiency regime of classical optical
communications---relevant to deep-space channels for instance---there is a big
gap between the reliable communication rates achievable via conventional
optical receivers and the ultimate (Holevo) capacity. Achieving the Holevo
capacity would require not only optimal codes but also receivers that make
collective measurements on long (modulated) codeword waveforms, and it is not
possible to implement these collective measurements via symbol-by-symbol
detection along with postprocessing in the electronics/software domain. In this
paper, we apply our recent results on the classical-quantum polar code---the
first near-explicit, linear, symmetric-Holevo-rate achieving code---to the
lossy optical channel, and we show that it almost closes the entire gap to the
Holevo capacity in the low photon number regime. An optical realization of the
successive-cancellation joint-detection receiver remains an open question.
View original:
http://arxiv.org/abs/1202.0533
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