  Contention-based grant-free transmission is very promising for future massive
machine-type communication (mMTC). In contention-based transmission, the random
pilot collision is a challenging problem. To solve this problem, multiple
pilots scheme is used to reduce the pilot collision probabliltiy. However, the
existing work on multiple pilots relies on the low correlation of spatial
channels, limiting its applicability. In this paper, an independent multi-pilot
scheme is proposed, which utilizes the diversity of multiple pilots and is not
limited by the spatial correlation. The receiver employs interference
cancellation for both data symbols and multiple pilots to ensure the
performance. The simulation results also show that the proposed independent
multi-pilot scheme can significantly improve the BLER performance and increase
the number of simultaneous access users.
