Aerospace and Electronic Systems Magazine April 2018 - 20

Fully Optical Spacecraft Communications

Figure 5.

High-level block diagram of the VLC downlink transmitter.

compression algorithm. This allows us to maximize the channel
bandwidth. Communications systems generally require mathematically tractable models [8]. However, in the interest of lowering
costs of development and deployment in production environments,
it is more economically feasible to eschew traditional multiplestage communication systems in the favor of a single, end-to-end,
deep learning system optimized for the specific hardware and
channels, lowering development time and cost.
Because certain types of deep learning systems (specifically,
recurrent neural networks) are known to be Turing complete [9]
and universal function approximators [10], we are able to combine the various parts of classical communication architecture into
a single block and have the neural network model it in its entirety.

The cost of deep learning systems has been falling rapidly, and as
efficiency of graphical processing unit (GPU) systems improves, it
is possible to embed such a system into a CubeSat. There are research efforts to create specialized application-specific integrated
circuits optimized for neural network systems, including Google's
tensor processing units. In future iterations, it should be possible to
integrate such chips into CubeSats instead of off-the-shelf GPUs
designed for embedded systems (in this case, the Raspberry Pi onboard GPU) that will be flown on Calypso, allowing higher-power
efficiency and better optimization.
The autoencoder system (Figure 8) will be implemented with
a one-hot input vector of the maximum size that the Calypso's embedded Raspberry Pi module is capable of efficiently running in

Figure 7.
Figure 6.

Prototype VLC transmitter with amplifier and bias tee.

20

Early transmitter test showing a FM (frequency modulation) sweep. A
direct current-biased quadrature phase-shift keying link was demonstrated using the same hardware.

IEEE A&E SYSTEMS MAGAZINE

APRIL 2018



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