  Indoor localization has recently witnessed an increase in interest, due to
the potential wide range of services it can provide by leveraging Internet of
Things (IoT), and ubiquitous connectivity. Different techniques, wireless
technologies and mechanisms have been proposed in the literature to provide
indoor localization services in order to improve the services provided to the
users. However, there is a lack of an up-to-date survey paper that incorporates
some of the recently proposed accurate and reliable localization systems. In
this paper, we aim to provide a detailed survey of different indoor
localization techniques such as Angle of Arrival (AoA), Time of Flight (ToF),
Return Time of Flight (RTOF), Received Signal Strength (RSS); based on
technologies such as WiFi, Radio Frequency Identification Device (RFID), Ultra
Wideband (UWB), Bluetooth and systems that have been proposed in the
literature. The paper primarily discusses localization and positioning of human
users and their devices. We highlight the strengths of the existing systems
proposed in the literature. In contrast with the existing surveys, we also
evaluate different systems from the perspective of energy efficiency,
availability, cost, reception range, latency, scalability and tracking
accuracy. Rather than comparing the technologies or techniques, we compare the
localization systems and summarize their working principle. We also discuss
remaining challenges to accurate indoor localization.
