Preamble-data superposition random access in massive MIMO systems

In this letter, we propose a massive multiple input multiple output (MIMO) based preamble-data superposition random access (RA) (mPDSRA) scheme to improve the spectral efficiency scarcity of the conventional massive MIMO based grant-free RA (mGFRA). The key idea of the mPDSRA is to allow a group of RA users transmit preambles, while simultaneously, another group of RA users, whose channel information has already been obtained, transmit data. Thanks to asymptotic orthogonality of channel vectors in massive MIMO, simultaneous transmissions of preamble and data can be allowed and sequentially detected/decoded. Both theoretical analysis and simulation results reveal promising significant performance gains in terms of access success rate and achievable sum rate by the proposed mPDSRA over the conventional mGFRA schemes.