  Recently, there has been significant interest in the integration and
co-existence of Third Generation Partnership Project (3GPP) Long Term Evolution
(LTE) with other Radio Access Technologies, like IEEE 802.11 Wireless Local
Area Networks (WLANs). Although, the inter-working of IEEE 802.11 WLANs with
3GPP LTE has indicated enhanced network performance in the context of capacity
and load balancing, the WLAN discovery scheme implemented in most of the
commercially available smartphones is very inefficient and results in high
battery drainage. In this paper, we have proposed an energy efficient WLAN
discovery scheme for 3GPP LTE and IEEE 802.11 WLAN inter-working scenario. User
Equipment (UE), in the proposed scheme, uses 3GPP network assistance along with
the results of past channel scans, to optimally select the next channels to
scan. Further, we have also developed an algorithm to accurately estimate the
UE's mobility state, using 3GPP network signal strength patterns. We have
implemented various discovery schemes in Android framework, to evaluate the
performance of our proposed scheme against other solutions in the literature.
Since, Android does not support selective scanning mode, we have implemented
modules in Android to enable selective scanning. Further, we have also used
simulation studies and justified the results using power consumption modeling.
The results from the field experiments and simulations have shown high power
savings using the proposed scanning scheme without any discovery performance
deterioration.
