Error Floor Analysis of Coded Slotted ALOHA over Packet Erasure Channels
  We present a framework for the analysis of the error floor of coded slotted ALOHA (CSA) for finite frame lengths over the packet erasure channel. The error floor is caused by stopping sets in the corresponding bipartite graph, whose enumeration is, in general, not a trivial problem. We therefore identify the most dominant stopping sets for the distributions of practical interest. The derived analytical expressions allow us to accurately predict the error floor at low to moderate channel loads and characterize the unequal error protection inherent in CSA. 
Mikhail Ivanov, Fredrik Brannstrom, Alexandre Graell i Amat, Petar   Popovski
cs.IT math.IT