CSI enhancement for multi-user superposed transmission using the second best feedback

In this paper we investigate and enhance the user-pairing probability in a system employing multi-user superposition transmission (MUST). In order to improve the multiuser pairing probability, we propose an additional feedback of the second best channel state information (CSI) consisting of channel quality indicator (CQI) and precoding matrix indicator (PMI). We analyze the pairing-probability and show that the additional feedback increases significantly the pairing possibilities at the scheduler. By system level simulations we confirm that the proposed enhanced feedback is improving significantly MUST performance in the context of MUST operation on the same-beam with Gray-mapped super-constellation. In addition, we suggest a simple link-to-system mapping for maximum likelihood (ML) MUST receiver, which can re-use legacy mutual-information-to-block-error-rate tables.