Abstract: Systems and methods of determining ionosphere delay for a GNSS system are provided. In one embodiment, a GNSS system includes an antenna configured to receive GNSS signals from one or more GNSS satellites. The system further includes a signal processing circuit coupled to the antenna and configured to down convert the GNSS signals from RF to IF. The system further includes a processing device coupled to a memory, the memory including a database of a plurality of weights and an activation function for a neural network, the neural network trained to output an approximation of an output of a NeQuick model. The processing device configured to: apply the plurality of weights and the activation function for the neural network to a plurality of inputs generated from the GNSS signals; and estimate an indication of ionosphere delay based on an output of the neural network.