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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 1
Deciding Handover Points based on Context Aware
Load Balancing in a WiFi-WiMAX Heterogeneous
Abhijit Sarma, Member, IEEE, Sandip Chakraborty, Member, IEEE, Sukumar Nandi, Senior Member, IEEE
Abstract—Heterogeneous network (HetNet) is an important concept for next generation wireless Internet architecture and
Internet of Things (IoT), where several wireless technologies can coexist, and the users should have the flexibility to select the connectivity based on the environmental condition and application demands. IEEE 802.11 (or WiFi) and IEEE 802.16 (or WiMAX) are the two primary building block technologies for HetNets because of their sustainability, cost-effectiveness, well-deployed architectures and ability to support high data rate wireless communications. The existing literature has well studied the interoperability between these two technologies, and seamless handover schemes are designed to support WiFiWiMAX integration in a HetNet environment. However, effective utilization of these two technologies from the end users’ pointof-view is another important research area. The question is: when a user should migrate between these two technologies in a
HetNet environment? This paper proposes a handover decision mechanism in a WiFi-WiMAX integrated HetNet environment, that supports the ‘Quality of Service’ (QoS) and ‘Quality of Experience’ (QoE) requirements of the end users. The effectiveness of the proposed scheme is analyzed using simulation results.
Keywords-Vertical handover; WiFi; WiMAX; QoS; Load balancing
WiFi-WiMAX integration is an important and challenging research topic for next generation wireless Internet architecture and IoT designs that attract significant attentions among the researchers –. The recent developments in WiFi-WiMAX integration technologies drive the developers to launch commercially available products, such as Intel WiMAX/WiFi
Link 5350 and Intel WiMAX/WiFi Link 5150 . However,
WiFi provides wireless connectivity within short communication range, but with minimal infrastructure support, whereas
WiMAX requires specific infrastructure deployments through it can be used for long distance point-to-point communications.
One of the important design aspect for WiFi-WiMAX integration is: when should a user perform handover from the
WiFi interface to the WiMAX interface and vice versa? A
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However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to email@example.com.
Abhijit Sarma is with the Department of Computer Science at Gauhati
University, Guwahati 781014, India. E-mail: abhijit firstname.lastname@example.org
Sandip Chakraborty is with the Department of Computer Science and
Engineering at Indian Institute of Technology Kharagpur, India 721302. Email: email@example.com
Sukumar Nandi is with the Department of Computer Science and Engineering at Indian Institute of Technology Guwahati, India 781039. E-mail: firstname.lastname@example.org lot of researches has been already carried out to answer how to handover between WiFi and WiMAX –, however most of these works remain silent on when to perform the handover. IEEE 802.21 or media independent handover (MIH) framework  standardizes the vertical handover (handover between two different technologies) procedure, although it discusses about ‘how to perform the handover’, rather than ‘when to perform the handover’. In a typical WiFi-WiMAX
HetNet environment, the WiMAX connectivity symbolizes an umbrella like coverage under which the WiFi access points (APs) or basic service sets (BSSs) formulate small WiFi connectivity areas. Because of its long communication ranges, it can be safely assumed that in such a HetNet environment, users have always access to the WiMAX connectivity, however access to WiFi is only available at few areas, typically known as ‘HotSpots’. Users prefer WiFi over WiMAX because of its low-cost availability1, and less power consumption2, and
WiMAX is typically used to provide connectivity to the endusers when Wi-Fi network is not available or performs poorly.
A user migrates from WiFi to WiMAX either because there is no WiFi connectivity, or the WiFi fails to provide desired
Mobility is not the only issue that triggers handover between two technologies in a HetNet environment. A quintessential problem of WiFi hotspots is unbalanced traffic load distribution among the APs or BSSs . The traffic load at WiFi access points are highly dynamic and varies with time of the day and geographic locations . This causes overload in some APs where as other APs in the network remains underutilized. QoE of users connected through the overloaded
APs deteriorates  as the traffic load increases in the
APs. Real time applications have strict bounds on network parameters such as end-to-end delay, jitter and packet loss rate.
Violation of these bounds may cause disruptions in application performance. Users running voice over IP applications on their terminal may experience echo, noise or empty gaps in the communications if end-to-end delay exceeds 150 ms or packet loss exceeds 2%.
This paper considers a scenario where users migrate from 1Typically, WiMAX uses licensed bandwidth, whereas WiFi operates over unlicensed 2.4GHz channel. Therefore cost per bit is less in WiFi, compared to WiMAX. 2WiFi interface and AP consumes significantly less power compared to