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Study Of Vertical Handover Between Wifi Wimax Computer Science Essay

Abstract: Many advanced data services are used in wireless technology, which are further boosted by growth in advanced market segments. Providing end-to-end communication in heterogeneous internetworking environments is a challenge. Handover delay is one of the problematic issues that users are face in the heterogeneous networks. However, in the case of both WiMAX and WiFi technologies located at the same base station (BS); the vertical handover (VHO) delay will be less compared with two conventional WiMAX/WiFi heterogonous networks with two different wireless Internet service providers (WISP). In this paper, In order to reduce the delay in protocol conversion, a new proposed design for WiWi (WiMAX and WiFi) adaptation layer is studied. The realization of the internetworking between these two standards is discussed and evaluated. This paper focuses on concepts of WI-MAX technology, which employs microwave for the transfer of data wirelessly and focuses on heterogeneous seamless handover between WiFi and WiMAX.

Key words: WiFi, WiMAX, Convergence, Heterogeneous

Network, Seamless Handover


Data service refers to a telecommunications service that transmits high-speed data rather than voice. Internet access is the most common data service, which may be provided by the telephone and cable companies as well as cellular carriers. Text messaging is a cellular data service. The wireless industry is evolving from a web of independent networks into a single integrated network with multiple standards. Wireless technology describes telecommunications in which electromagnetic waves, carry the signal over part or the entire communication path without cables. Wireless broadband refers to fixed wireless connectivity that can be utilized by enterprises, businesses, households and telecommuters who travel from one fixed location to another fixed location. Wireless broadband is an extension of the point-to-point, wireless-LAN bridging concept to deliver high-speed and high capacity pipe that can be used for voice, multi-media and Internet access services. Though there are many technologies available for providing broadband wireless access to the Internet such as Blue tooth, WiFi and WiMAX, but here the main focus is on WiMAX and WiFi/WiMAX seamless handover.

II. WiFi

WiFi stands for wireless fidelity and generally refer to any type of 802.11 networks, whether 802.11b, 802.11a, 802.11g. WiFi is a wireless technology that uses radio frequency to transmit data through the air. WLAN access point or hub or transmitter sends out a wireless signal that allows Wireless devices to access within a circle of roughly 100 meters. Zone around the transmitter is known as hot spot. Computers connected to WiFi receivers near a hot spot can connect to Internet at high speeds without cable. WiFi refers to three types of wireless protocols that can work with each other: IEEE 802.11b ("Wireless B"), IEEE 802.11a ("Wireless A"), and the newer IEEE 802.11g ("Wireless G"). They can connect computers very fastly: 11 Mbps for Wireless B, 54Mbps for Wireless A, and 54 Mbps for Wireless G, which are described in subsequent sections.


* It is the longest, well-supported, stable, and cost effective standard, runs in the 2.4 GHz range that makes it prone to interference from other devices (microwave ovens, cordless phones, etc) and also has security disadvantages

* Limits to the number of access points to three.

* It has 11 channels, with 3 non-overlapping, and supports rates from 1 to 11 Mbps.


* It is an extension of 802.11b, with the same disadvantages (Security and interference)

* It has a shorter range than 802.11b.

* It is backwards compatible with 802.11b so it allows a

* It runs at 54 Mbps.

802. 11a

* It is completely different from 11b and 11g.

* It is flexible because multiple channels can be combined for faster throughput and more access points can be collocated.

* It runs in the 5 GHz range, so having less interference from other devices.

* It has 12 channels, 8 non-overlapping, and supports rates from 6 to 54 Mbps.

A. WiFi building block

Block diagram shows mapping of the IEEE 802.11 requirements into a functional WiFi building block. The WiFi building blocks are:

a) Antenna b) Access Point (AP)

c) Router d) Internet access

Fig. 1. Wi-Fi Block Diagram


WiMAX (Worldwide Interoperability for Microwave Access) is a telecommunications protocol that provides fixed and fully mobile Internet access. The current WiMAX revision provides up to 100 Mbit/s with the IEEE 802.16m update expected to offer up to 1 Gbit/s fixed speeds. The name "WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to promote conformity and interoperability of the standard. The forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL".

Fig. 2: WiMAX delivers 72 Mbps over 30 miles point to point and 4 miles NLOS.

WiMAX technology often misinterpreted by the people by the names of mobile WiMAX, 802.16d, fixed WiMAX and 802.16e. Actually 802.16-2004 or 802.16d is developed by the third party as a standard and it is also referred to called as Fixed WiMAX because this standard is lacking behind just because of the non-mobility feature that’s why it’s often called as Fixed WiMAX. During the maturity period of WiMAX technology some of the amendments were made to the above mentioned 802.16d and they referred this amending standard as 802.16e. 802.16e introduced mobility and some other features amongst other standards and is also known as Mobile WiMAX. WiMAX provide speed of 72 Mbps over 30 miles point to point network and 4 miles point to multipoint non line of sight network. Figure2 illustrates these exciting capabilities.

A. WiMax architecture 

The WiMAX Forum has proposed an architecture that defines how a WiMAX network can be connected with an IP based core network, which is typically chosen by operators that serve as Internet Service Providers (ISP); Nevertheless the WiMAX BS provide seamless integration capabilities with other types of architectures as with packet switched Mobile Networks.

Fig. 3: WiMAX architecture

The WiMAX forum proposal defines a number of components, plus some of the interconnections (or reference points) between these, labeled R1 to R5:

SS/MS: the Subscriber Station/Mobile Station

ASN: the Access Service Network

BS: Base station, part of the ASN

ASN-GW: the ASN Gateway, part of the ASN

CSN: the Connectivity Service Network

HA: Home Agent, part of the CSN

AAA: Authentication, Authorization and Accounting Server, part of the CSN

NAP: a Network Access Provider

NSP: a Network Service Provider.

It is important to note that the functional architecture can be designed into various hardware configurations rather than fixed configurations. For example, the architecture is flexible enough to allow remote/mobile stations of varying scale and functionality and Base Stations of varying size - e.g. femto, pico, and mini BS as well as macros.


Table.1 Wireless Technology Comparison

WiFi (a)

WiFi (b)

WiFi (g)







Frequency (GHz)




2 - 66

Speed (Mbps)












Low Cost


Speed, Range




Cost, Range



Handovers are an important part of a network technology. When moving between different BSs, the connection also has to move. Seamlessness in this report is defined as follows: the current session, QoS must be maintained during and after handover. In other words, a seamless handover is a handover that is seamless to the user. Obviously this also depends on the kind of service the user is requiring. With real-time applications like videoconferencing or streaming media, the user will probably notice a decrease of them connection. On the other hand, while browsing a website or transferring a file, the user does not have to notice anything of the handover process. The latency and packet loss are the two crucial factors for seamless handover. These two factors have to be as small as possible to make the handover seamless. Before discussing several handover issues, the next part will go into detail about handovers in general first. There can be several reasons why and when a handover should be initiated:

• MS current position and velocity

High velocity can result in different handover decisions.

• Link quality

Another BS can deliver a higher quality link (e.g. higher speed, stronger signal, better QoS).

• Load at a BS

When a BS in a subnet is currently overloaded; the network can decide to relocate some MSs.

• Conserving battery power

In order to save battery power, a MS can choose to switch to a closer station to be more energy efficient.


Together, WiMAX and WiFi are ideal partners for service providers to deliver convenient, affordable mobile broadband Internet services in more places. Both are open IEEE wireless standards built from the ground up for Internet Protocol (IP) - based applications and services. IEEE 802.11 has accelerated the network deployment for providing high transmission rate in limited geographical coverage, while IEEE 802.16 offers more flexibility in while maintaining the technology's data rate and transmission range. The limited coverage range of WiFi makes it difficult to meet the future ubiquitous networks need while IEEE 802.16 can provide high speed Internet access in wide area. A natural trend is the combination of IEEE 802.16 and IEEE 802.11 to create a complete wireless solution for delivering high speed Internet access to businesses, homes and hotspots.

Fig. 4. The interaction of WiWi protocol Stack with the WiMAX BS and WiFi device.

However, both techniques have their own sets of advantages and disadvantages. On the one hand, WiFi may offer a high data rate (up to 500Mb/s is envisaged), but it is power limited due to the use of unlicensed band and are therefore much more confined in coverage, while on the other hand, even though WiMAX is data rate limited (up to 70Mb/s fixed), it can provide extensive coverage much like the cellular systems. Because of that it is instructive to employ both technologies in the laptop/mobile for ubiquitous connection with high data rates. In this report we introduce a new combination of WiMAX and WiFi (called WiWi). The WiWi module comprised of WiMAX and WiFi OSI located at the mobile WiMAX will work as a relay nodes (a.k.a mobile relay node).

Figure 4 shows the protocol stack of the proposed WiWi module. The scope of WiWi module is to increase the laptop range when the user moves out of the WiFi coverage by joining WiMAX network using WiWi module installed in the WiMAX mobile, see Figure 5. The scope of this paper is to discuses the handover decision for the WiFi device to either join WiFi or WiMAX network.


From Figure 5 we can see that there are two possible scenarios; (a) the Laptop within WiWi and WiFi networks coverage and (b) the Laptop out of WiFi network coverage. Scenario (b) is straightforward in which the laptop will see only one network connection, that provided by WiWi module.

Fig. 5 .WiMAX and WiFi coverage in indoor and outdoor (a) the laptop in the WiFi coverage (b) laptop is out of WiFi coverage.

Directly the device will start network entry process to join WiMAX network using WiWi module installed at the WiMAX mobile. There are two modes for WiWi operation: open access mode, which the user opens the access for everybody to access his WiMAX mobile (WiWi module), while in the close mode the user allows only his WiFi device to access his WiMAX mobile to get the Internet access.

On the other hand, in scenario Figure 5 (a) there are two networks available WiMAX (using WiWi module) and WiFi network, the device should select only one of them to access the Internet based on the received signal strength indicator (RSSI) message received from the AP/BS. In this scenario using the conventional handover for network selection based on RSSI message is problematic. This is because WiFi device will sense two WiFi signals coming from WiWi Module and WiFi access point (AP).


Figure 6 shows the handover decision based on RSSI and throughput. The total throughput for WiWi network is calculated based on WiMAX throughput and the effect of vertical handover within the WiWi module. This is done as follows:

Fig. 6. Network selection scheme in the WiFi to WiMAX handoff scenario

where is the degradation of throughput due to multihop relay . is the WiMAX capacity and n is the number of hops (i.e. in WiWi, n=2). is the total throughput loss due to protocol converter and interference between WiFi and WiMAX.

Fig. 7. Signaling process in the WiFi to WiMAX handover scenario

Figure 7 shows the flow of the messages for connecting WiFi devices the WiWi network. Here we assume the WiWi in the closed mode so that there are no other nodes sharing the channel with the WiFi device. The throughput depends on the WiMAX channel bandwidth (i.e. 1.25-20MHz) and total number of tones (256 for fixed and 1024 for mobile) and channel quality.


This paper focused on one of the intelligent data services Bluetooth, WiFi and WiMax and also issues of wireless air technologies; seamless handover. As wireless technologies are emerging, the need for constant connectivity is growing. This can not be done without the possibility to roam between different networks and different air technologies. The process which facilitates this is called a handover. Seamless handover is the kind of handover the user does not notice, and thus the preferred one. Unfortunately, it is not always that easy to support seamless handover. There is a period of time in which a user can not receive or send any data because it has to switch between access points or even change its IP-address. This period of time is called handover latency and is one of the most crucial factors in the success of a handover protocol. Furthermore, there are more issues to consider when reviewing handover solutions: packet loss, complexity and inefficient use of resources can cause serious problems. As the most promising new wireless access technology, the research first focused on WiMAX. In this paper a new vertical handover algorithm for WiWi network is studied. The vertical handover is performed at the logical adaptation layer above the MAC layer.

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