  Low Power Wide Area (LPWA) networks are attracting a lot of attention
primarily because of their ability to offer affordable connectivity to the
low-power devices distributed over very large geographical areas. In realizing
the vision of the Internet of Things (IoT), LPWA technologies complement and
sometimes supersede the conventional cellular and short range wireless
technologies in performance for various emerging smart city and
machine-to-machine (M2M) applications. This review paper presents the design
goals and the techniques, which different LPWA technologies exploit to offer
wide-area coverage to low-power devices at the expense of low data rates. We
survey several emerging LPWA technologies and the standardization activities
carried out by different standards development organizations (e.g., IEEE, IETF,
3GPP, ETSI) as well as the industrial consortia built around individual LPWA
technologies (e.g., LORa Alliance,WEIGHTLESS-SIG, and DASH7 Alliance). We
further note that LPWA technologies adopt similar approaches, thus sharing
similar limitations and challenges. This paper expands on these research
challenges and identifies potential directions to address them. While the
proprietary LPWA technologies are already hitting the market with large
nationwide roll-outs, this paper encourages an active engagement of the
research community in solving problems that will shape the connectivity of tens
of billions of devices in the next decade.
