  Wireless Local Area Network (WLAN) has become a promising choice for indoor
positioning as the only existing and established infrastructure, to localize
the mobile and stationary users indoors. However, since WLAN has been initially
designed for wireless networking and not positioning, the localization task
based on WLAN signals has several challenges. Amongst the WLAN positioning
methods, WLAN fingerprinting localization has recently achieved great attention
due to its promising results. WLAN fingerprinting faces several challenges and
hence, in this paper, our goal is to overview these challenges and the
state-of-the-art solutions. This paper consists of three main parts: 1)
Conventional localization schemes; 2) State-of-the-art approaches; 3) Practical
deployment challenges. Since all the proposed methods in WLAN literature have
been conducted and tested in different settings, the reported results are not
equally comparable. So, we compare some of the main localization schemes in a
single real environment and assess their localization accuracy, positioning
error statistics, and complexity. Our results depict illustrative evaluation of
WLAN localization systems and guide to future improvement opportunities.
