Reducing scanning delay for WiFi-to-WhiteFi handovers

Today, providing ubiquitous wireless networks have become more important due to the widespread use of smartphones. To achieve Always Best Connectivity (ABC), mobile nodes should handover to a new point of attachment to maintain connection. IEEE 802.21 is a protocol used to unify the handover process independently of the network types involved. The newly deployed IEEE 802.11af, known as WhiteFi, is a new standard that introduced an amendment to the MAC/PHY layers of IEEE 802.11 to allow WiFi to operate on the TV White Space (TVWS) spectrum. TVWS is an unused licensed radio spectrum that provides superior propagation and building penetration compared to other spectrums. Thus, WhiteFi can be used to fill the gaps between WiFi networks created by the large coverage area. This work studies the handover delay from WiFi to WhiteFi. In the case of IEEE 802.11 networks, the scanning phase creates the majority of the total handover delay. However, in WhiteFi, the scanning time will increase due to the increasing number of TVWS channels compared to WiFi. Therefore, this work proposes a new approach to reducing the scanning time based on the IEEE 802.21 standard. The proposed solution consists of a scan-free approach where a Mobile Node (MN) keeps a record of free TVWS. This information will be updated every 48 hours by the querying Information Server (IS) used in the IEEE 802.21 standard. To further reduce the scanning time, a scan-active approach is proposed where the MN queries the IS to retrieve the current active channels from a Registered Location Secure Server (RLSS), which is a local database introduced in the IEEE 802.11af standard. The projected performance of these two schemes is evaluated using an analytical model, and compared against the scan-all initial scheme. The results show that the scan-active approach will reduce the scanning delay, irrespective of the network conditions, in the case of a limited number of active channels. The scan-free scheme is more stab- e, but with the probability of extra time spent to scan empty channels.