"Machine LLRning": Learning to Softly Demodulate
This work addresses computational complexity in communication systems for engineers, but it is incremental as it applies existing machine learning methods to a known bottleneck.
The paper tackles the problem of soft demodulation in modern receivers by introducing LLRnet, a neural network-based demodulator that achieves LLR estimates close to optimal log maximum a-posteriori inference with an order of magnitude fewer operations than exact implementations, as demonstrated for QAM, 5G-NR, and DVB-S.2.
Soft demodulation, or demapping, of received symbols back into their conveyed soft bits, or bit log-likelihood ratios (LLRs), is at the very heart of any modern receiver. In this paper, a trainable universal neural network-based demodulator architecture, dubbed "LLRnet", is introduced. LLRnet facilitates an improved performance with significantly reduced overall computational complexity. For instance for the commonly used quadrature amplitude modulation (QAM), LLRnet demonstrates LLR estimates approaching the optimal log maximum a-posteriori inference with an order of magnitude less operations than that of the straightforward exact implementation. Link-level simulation examples for the application of LLRnet to 5G-NR and DVB-S.2 are provided. LLRnet is a (yet another) powerful example for the usefulness of applying machine learning to physical layer design.