  We propose a pilot-data transmission overlay scheme for multipair massive
multiple-input multiple-output (MIMO) relaying systems employing either half-
or full-duplex (HD or FD) communications at the relay station (RS). In the
proposed scheme, pilots are transmitted in partial overlap with data to
decrease the channel estimation overhead. The RS can detect the source data
with minimal destination pilot interference by exploiting the asymptotic
orthogonality of massive MIMO channels. Then pilot-data interference can be
effectively suppressed with assistance of the detected source data in the
destination channel estimation. Due to the transmission overlay, the effective
data period is extended, hence improving system throughput. Both theoretical
and simulation results confirm that the proposed pilot-data overlay scheme
outperforms the conventional separate pilot-data design in the limited
coherence time interval scenario. Moreover, asymptotic analyses at high and low
SNR regions demonstrate the superiority of the proposed scheme regardless of
the coherence interval length. Because of simultaneous transmission, the proper
allocation of source data transmission and relay data forwarding power can
further improve the system performance. Hence a power allocation problem is
formulated and a successive convex approximation approach is proposed to solve
the non-convex optimization problem with the FD pilot-data transmission
overlay.
