A variable-length coding method to improve the performance of downlink NOMA. Depending on the channel conditions and the amount of data waiting to be transmitted the UEs served by the NN, the NN groups UEs (e.g., pairs two UEs) with appropriate channel qualities and adapts the transmission powers in different sub-codewords as well as the codeword length such that the UEs minimum quality-of-service requirements are satisfied. This makes it possible to improve the UEs/network achievable rates and the NN energy efficiency.