Uplink NOMA Random Access Systems With Space–Time Line Code

This work proposes a random access system with uplink non-orthogonal multiple access (NOMA), where users transmit their packets by using the space-time line code (STLC) to fully exploit the spatial diversity without channel state information at the receiver. More specifically, users with a single antenna estimate channel gain from the base station (BS) with two antennas, encode the information using the STLC, and then transmit it using transmit power control so that the received power of their packets at the BS can be one of the predetermined values. The BS decodes the received packets via STLC decoding and the successive interference cancellation technique. Owing to spatial diversity, we show that the proposed scheme improves energy efficiency in comparison to the conventional system with a single antenna BS.