OPTCOMNET: Optimized Neural Networks for Low-Complexity Channel Estimation

The use of machine learning methods to tackle challenging physical layer signal processing tasks has attracted significant attention. In this work, we focus on the use of neural networks (NNs) to perform pilot-assisted channel estimation in an OFDM system in order to avoid the challenging task of estimating the channel covariance matrix. In particular, we perform a systematic design-space exploration of NN configurations, quantization, and pruning in order to improve feedforward NN architectures that are typically used in the literature for the channel estimation task. We show that choosing an appropriate NN architecture is crucial to reduce the complexity of NN-assisted channel estimation methods. Moreover, we demonstrate that, similarly to other applications and domains, careful quantization and pruning can lead to significant complexity reduction with a negligible performance degradation. Finally, we show that using a solution with multiple distinct NNs trained for different signal-to-noise ratios interestingly leads to lower overall computational complexity and storage requirements, while achieving a better performance with respect to using a single NN trained for the entire SNR range.