Asynchronous orthogonal differential modulation for MAC systems

We propose a differential encoding scheme and several differential decoding schemes for asynchronous multiuser MIMO systems based on orthogonal space-time block codes (OSTBCs) where neither the transmitters nor the receiver has knowledge of the channel. We derive novel low complexity differential decoders by performing interference cancelation in time and employing different decoding methods. The decoding complexity of these schemes grows linearly with the number of users. The proposed schemes achieve full diversity and work for any square OSTBC, any number of users, and any number of receive antennas. Simulation results show that our differential schemes provide good performance. To the best of our knowledge, the proposed differential detection schemes are the first differential schemes for asynchronous multi-user systems.