After the encoder has been overfit to a certain input block, the original decoder may still be used at inference stage because during overfitting the original decoder was used and its weights were not modified. This enables optimizing the encoder during data transmission without a need to send updated weights of the decoder to the receiver. 

## Second embodiment: decoder overfittinq 

Overfitting the decoder means that the neural decoder network is further optimized on the current block so that the decoding or reconstruction of the encoded block is improved. Fig. 5 illustrates an example of decoder overfitting. The transmitter 510 overfits the decoder 512 by using the original block as ground-truth, in order to obtain the overfitted decoder 514. The overfitted decoder 514 will be evaluated and compared to other decoders which are available at receiver’s520 side, in order to decide if it is worth using such overfitted decoder 514 with respect to the bitrate increase of sending the needed additional information. This evaluation is done for the current block and N subsequent blocks. If it is worth, in order to enable the receiver 520 to perform the overfitting, the transmitter 510 computes the block residual and sends it to the receiver 520. The receiver 520 uses the block residual to recover the high quality block and uses it as ground-truth for performing the overfitting. It is realized that the overfitting is done at the receiver (decoder) device based on the residual, instead of just receiving the overfitted version of the neural network from the transmitter. This avoids sending the updated decoder weights to receiver 520 and reduces the overhead to the block residuals. 

Training a neural network may involve using ground-truth data in order to compute the loss or error value, which is then differentiated with respect to the network’s weights, and the obtained gradients are used for updating the weights’value. The ground-truth for training a decoder is the desired reconstructed blocks, which usually are the original blocks which are input to the encoder. However, the original blocks are available only at transmitter’sside. Therefore, two possible alternatives are possible: 

a) The transmitter sends the block residual to the receiver, i.e., the difference between the original block and the decoded block. This way, the receiver can recover the original block and use it as ground-truth for performing the overfitting. The additional signaling associated with this option may include informing the receiver that the transmitted data is the block 

