Radio Link Monitoring (RLM) is one of the important procedures in LTE. It is used to keep track of the radio link condition so that appropriate steps can be taken if Radio Link Failure (RLF) is declared. The figure below (taken from T-doc R2-133859) captures the RLM process:
From the same T-doc:
PCell radio link monitoring is to determine whether the PCell radio link should be considered as failed (i.e. radio link is worse than Qout for time period determined by N310). If so, UE performs two actions; 1) stopping autonomous uplink transmission by releasing SPS, CQI, SRS, SR and 2) starting cell selection procedure to find a cell providing acceptable radio link.