  We consider the problem of fair coexistence between LTE and Wi-Fi systems in
the unlicensed 5 GHz U-NII bands. We focus on the misbehavior opportunities due
to the heterogeneity in channel access mechanism and the lack of a common
control plane. We define selfish misbehavior strategies for the LTE that yield
an unfair share of the spectrum resources. Such strategies are based on
manipulating the operational parameters of the LTE-LAA standard, namely the
backoff mechanism, the traffic class parameters, the clear channel access (CCA)
threshold, and others. Prior methods for detecting misbehavior in homogeneous
settings are not applicable in a spectrum sharing scenario because the devices
of one system cannot decode the transmissions of another. We develop implicit
sensing techniques that can accurately estimate the operational parameters of
LTE transmissions under various topological scenarios and {\em without
decoding.} These techniques apply correlation-based signal detection to infer
the required information. Our techniques are validated through experiments on a
USRP testbed. We further apply a statistical inference framework for
determining deviations of the LTE behavior from the coexistence etiquette. By
characterizing the detection and false alarm probabilities, we show that our
framework yields high detection accuracy at a very low false alarm rate.
Although our methods focus on detecting misbehavior of the LTE system, they can
be generalized to other coexistence scenarios.
