Noncoherent Aggregation for Over-the-Air Federated Learning

A novel technique known as resource-element energy difference (REED) facilitates noncoherent aggregation in over-the-air federated learning (OTA-FL), eliminating the necessity for real-time channel state information (CSI) and coherent phase alignment. By assigning positive and negative components of real-valued updates to transmit energies across two orthogonal resource elements with independent phase dithers, the server can derive the signed aggregate based on their energy difference. REED only requires slow-timescale calibration of average channel powers, maintains an unbiased approach for the intended signed sum, and provides an exact closed-form variance under Rayleigh fading. This method is integrated into the full-participation FedAvg framework.