Downlink Overloaded Multiple Access Based on Constellation Fxpansion

A new overloaded multiple access scheme for the downlink of wireless systems is presented. It performs simultaneous transmission of multiple data streams intended for users experiencing similar signal-to-noise ratios (SNR). The proposed scheme performs stream multiplexing by mapping the coded bits of each stream onto the labels of an expanded constellation according to a time-varying pattern designed for providing the same level of protection against errors to all streams. Using this scheme, multiple data streams can be concurrently transmitted on the same time-frequency resource blocks of OFDMA systems, thus achieving a higher aggregate spectral efficiency and tighter delay constraints.