  This paper deals with the reliability of random access (RA) protocols for
massive wireless smart grid communication (m-SGC). We propose and analyze an
improved grant-free RA (GF-RA) protocol for critical SG applications under
strict QoS m-SGC requirements. At first, we discuss the main features of the SG
neighborhood area network (NAN) architecture. We explore the main features of
low-rate machine-type wireless networks, and also we describe a technology
characterization of wireless neighborhood area networks (WNAN) in medium-range
coverage applications. We propose a new-improved irregular repetition slotted
ALOHA, combing Raptor codes and irregular ALOHA, namely RapIRSA random access
protocol, to better respond to critical high-reliability QoS requirements under
a 5G network perspective. Then, we compare and comprehensively analyze the
proposed RapIRSA protocol with two existing RA protocols, the IRSA protocol,
and the classical Slotted Aloha. Finally, We summarize the potential challenges
in implementing the proposed RA protocol for SG critical applications
considering many smart sensors (SS).
