An Encoder-Decoder Network for Beamforming over Sparse Large-Scale MIMO Channels

Abstract-- We develop an end-to-end deep learning framework for downlink beamforming in large-scale sparse multiple-input multiple-output (MIMO) channels. The core is a deep encoder-decoder network (EDN) architecture with three modules: (i) an encoder neural network (NN), deployed at each user end, that compresses estimated downlink channels into low-dimensional latent vectors. The latent vector from each user is compressed and then fed back to the BS. The training of EDN leverages two key strategies: (a) semi-amortized learning, where the beamformer decoder NN contains an analytical gradient ascent during both training and inference stages, and (b) knowledge distillation, where the loss function consists of a supervised term and an unsupervised term, and starting from supervised training with MMSE beamformers, over the epochs, the model training gradually shifts toward unsupervised using the sum-rate objective. The proposed EDN beamforming framework is extended to both far-field and near-field hybrid beamforming scenarios.