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In general footings, mobility is the ability that an component or a individual has of traveling easy. In footings of computing machines or cellular webs the device is non attached by a wire to the nucleus platform. This device needs to be on the same coverage country. If this device, for case a nomadic phone goes beyond its coverage zone and it drops the connexion, this system has limitation in mobility.
Organizations are to a great extent puting in new engineerings such as mobility equipments, Internet and incorporate communications systems, among others, in order to supply better client service.
One of the challenges of mobility is to supply uninterrupted communications irrespective of the current location over the same entree nexus. For illustration: Wi-Fi. Communications mobility supreme purpose is keeping communications every clip the entree nexus alterations.
These mobility solutions have been in changeless development through the old ages, get downing with the first coevals 1G launched in 1980 ‘s. 1G was voice oriented and it was characterised by all the systems were parallels, the deficiency of security and roaming. The 2nd coevals 2G was released 10 old ages subsequently. The systems were digital and engineerings such as CDMA and TDMA emerged. This engineering was besides voice oriented ; nevertheless, they offered informations limited at approximately 10 kbps. 2.5 and 3rd coevalss were designed to fulfill characteristics beyond merely voice. This engineering was designed peculiarly for informations connexion. In add-on real-time picture conferencing, nomadic cyberspace and better informations transmittal rate evolved with these engineerings. GPRS, WCDMA, GSM, WirelessLAN, etc. However, in recent old ages convergence has become the new construct in communications. Convergence is the ability to incorporate all the systems or engineerings under one common protocol. Some people believe that converged solutions or 4G webs are the integrating within engineerings, 2G, 3G and WIMAX [ 1 ] that can seamlessly incorporate all bing and freshly developed radio communications systems instead than develop a new unvarying criterion to replace all the bing engineerings [ 2 ] .
The purpose of 4G webs is the combine user installations such as: IMS, applications, multimedia using seamless rolling across different sorts of wireless webs keeping the benefits of the existent coevals, planetary coverage and a better bandwidth than the provided by the existent radio service suppliers.
In wireless communicating webs, users can alter their location from one cell to another while they are still connected to the chief station, this construct is called handover. This is besides one of the most critical procedures during the whole communicating pattern. It is cardinal to maintain path of all the nodes current location and possible finish in order to present the informations right and apportioning a suited channel in the new cell. Previous coevalss started to unite radio and nomadic engineerings using IP engineerings, although the manner how these systems perform the interchange will be different. When nomadic nodes change the location to another web, diverse jobs can be faced e.g. informations loss, out of synchrony and latency jobs.
A bad handover leads the expiration of the session, where the terminal user assumes it as a quality of service issue and overall a service unconformity.
There are four types of handover or mobility [ 3 ] : 1st Within an organisation and a web. 2nd Handover between organisations but on the same webs. 3rd Migration within organisations but within the same web. 4th Migrations betweens organisations and webs, for case from WLAN to GSM service.
In order to accomplish seamless mobility, the nomadic node demands to migrate between two different organisations that are owned and operate autonomously. The web may utilize a different protocol stack, specially on the lower bed and each web has it ain alone reference for the nomadic device. [ 3 ]
During the last old ages the handover across webs takes topographic point more normally, terminal users are willing to keep their connexions and applications up at any clip, despite of the mobility entree they are utilizing, for case walking or drive.
The nomadic webs are increasing while the cellular size is diminishing with the purpose of suiting more nodes in a predesigned country. Because of that the handover mechanism in the 4G webs is of import to ease a successful communications.
One of the chief points in 4 coevals webs is the fast and seamless handovers, as a consequence of this is one of the best ways to provide uninterrupted voice and informations communications with the less service break. Mobile IP mechanism can be utilized speed uping it with the methods ( fast and hierarquical Mobile IP )
For the simpleness of this undertaking merely CDMA2000, UMTS, WLAN and Mobile IP will be illustrated.
The typical handover procedure is established on wireless frequence RF standards “ signal degree and quality ” [ 3 ] , although, the RSS ( Radio Signal Strength ) is different for each architecture, foregrounding that 4G webs is defined as an agreement of different engineerings, which can interact together, follow that the RSS is non an appropriated mechanism to put to death an equal handover in 4G and guaranty a non intermittence in the communications.
In add-on, for analysis of heterogenous webs: voice, informations and existent clip applications the handover latency and frequence of mobility-related signal demand to be reduced with the purpose of provide a better quality of service.
In 4G systems, the major concern is that handover mechanism is more hard to cover with, due to it concerns about horizontal handover, perpendicular handover and addition of figure of cells in the same country.
The aim of this paper is to analyse the existent handover mechanisms and the chance that they can be used in the new communications coevals.
Background and Related Work
Actually there are many nomadic webs in the market ; all of them have been designed by different organisations, for different intents, even though they agreed different criterions and bandwidth. In add-on, users do non necessitate a leased line to convey. Messages can be segmented in little packages prior to the transmittal ; this process helps with the resources optimization, nevertheless, due to the channel an the clip sharing it can generates quality of service issues.
The figure 1 illustrates one of the most celebrated diagrams in Mobile. [ 1 ] It is possible to detect the broad scope of mobility webs engineerings. Harmonizing to the writer Wiley, there is ever a tradeoff between the scope, spot rate and mobility.
The figure 1 shows the bulk criterions of nomadic engineering. With our proposal the aim is analyse if exist a mechanism that allow them handover with out hazard the connectivity and the quality of service. [ 1 ]
The Universal Mobile Telecommunications Service UMTS is one of the radio engineerings mentioned in the figure 1. This engineering is portion of 3G webs. UMTS is 3G broadband, packet-based transmittal of text, digitalized voice, picture and multimedia services to mobile computing machines and nomadic phones, irrespective of their connexion in the universe. It offers a information rate of up to 2Mbps. [ 3 ]
Harmonizing to Othman, one time the UMTS web is to the full implemented and available, users will be connected to the cyberspace as they are in motion without interrupting the connexion.
The handover procedure makes certain that the connexion between the nomadic device and the base station is maintained once it moves from one cell to another. When the nomadic device passes the cell boundaries it needs to trade the connexion over a new base station with the intent of maintain the communicating if the handover procedure is non realised. In add-on to the enrollment to establish station, the channel allotment process is besides considered.
In wireless webs systems there are two types of handovers: horizontal handover besides known as intra handover. This is defined as the handover between the base station under the control of the same maestro exchanging control ( MSC ) of the same web engineering. [ 3 ] When the Handover is completed between different web engineerings for case UMTS and WLAN webs, this type of handover is called as inter handover or perpendicular handover.
A wireless local country web ( WLAN ) is a web architecture where the nomadic node can pass on with the base station or other nomadic nodes through wireless links. WLAN is flexible and can be installed anyplace. The execution cost is low. It can be configured for little or big concern. WLAN besides provides Internet entree at public topographic points for case, fast nutrient eating houses, airdromes.
Wireless LAN gives to the terminal users the possibility to travel around of the covered country and still connected to the web.
The best know criterion of WLAN is the 802.11 household which has been defined by the Institute of Electrical and Electronic Engineers ( IEEE ) . WLAN uses bearer sense multiple entree with hit turning away CSMA/CA.
WLAN has become so popular that most of the devices “ laptops and 3G nomadic phones ” are pre-equipped with the necessary to work in wireless engineerings environments.
In order to entree or alteration between two different webs, a nomadic station is set up wit different interfaces, for case: one for the Wireless LAN webs and the 2nd 1 for UMTS webs. One of the major issues is the non compatibility between wireless interfaces. The usage of two interfaces is besides for leting parallel connexion. When the nomadic station is located within the radio local web country the information is passed through the radio web instead than the UMTS, in malice of this, the voice connexion is linked by the UMTS. In instance of failure of one of these interfaces the handover mechanism will non be executed.
Mobile IP was ab initio designed to work in WLAN, Mobile IP supports users altering between webs by executing Accounting, Authentication ( AAA ) and Authorization services. [ Perkins 2000 ] . This service, Mobile IP and AAA is the nucleus of the mobility architecture for voice over IP and other 1000s of nomadic Stationss. AAA is the key for users to be authenticated in the system and it is the of import system for the charge when the communicating base on balls through cyberspace. [ 3 ]
Othman ( 2007 ) emphasises the explosive growing of radio webs has resulted in several independent and independent webs. End users will happen several webs even if they do non alter the location. He says that to supply seamless mobility this fluctuation should be handled for the terminal user device. The user environment demands to be homogenous, if there is a fluctuation in the background, the communicating for the user needs to be ever clear.
A nomadic station with multiple nexus interfaces should be able to travel uniformly between different webs without upseting the communications regardless is voice, informations or applications. The nomadic station demands to be able to car modulate the quality of service. It is besides possible to province and agreed with Othman that in order to supply seamless mobility the nomadic station demands to back up adaptability. In heterogenous nomadic webs is it possible to happen different bandwidth, latency, mistake rectification and entree methods. The figure 2 illustrates seamless mobility across different radio engineerings.
The figure 2 displays the coveted seamless rolling in nomadic webs. [ 1 ]
The handover mechanism is required to be managed accurately. End users are non willing to accept a bad quality of service sing they are paying for a service and sometimes their productiveness is besides affected.
Code Division Multiple Access CDMA is a communicating mechanism where many users can portion the spectrum or channel, directing the information out in different clocking utilising different sequence codifications. A CDMA user that is actively connected to the web, the existent cell place is defined as active cell.
CDMA2000 is another engineering of the 3G webs. CDMA2000 offers twice the voice capacity of the standard CDMA and informations rates up to 144 Kilobits per second. The chief feature of CDMA20000 is that the mobility direction is based on Mobil IP protocol. It grants an easy integrating with the Internet mobility and the IP universe.
WiMax is the new coevals in nomadic informations. Its coverage reaches up to 50 Kms and provides information rates up to 280 Megabits per base station. [ 1 ] WiMax utilises Orthogonal Frequency Division Multiplexing Access ( OFDM ) which splits the spectrum in up to 100s of configured extraneous bearers. Each of these bearers has different wireless extension. WiMax has been developed by the computing machine and french friess industry and it can be to the full implemented with the existing IP engineerings. Geoff Haigh describes WiMax as “ WLAN on steroids ”
In 4 Generation webs the challenge for keeping the connexion additions in perpendicular handovers.
A really of import point in 4G webs is the fast and seamless handovers, as a consequence this is one of the best ways to provide uninterrupted voice and informations communications with the less service break.
Harmonizing to [ C, Makaya ] , the handover procedure in 4G webs is composed of three stages: web find, handover determination and handover executing.
The nomadic node should so feel the possible new web and analyse if this is better than the current one before to gain the handover. [ 4 ] [ C, Makaya ] besides refers to the trigger of the handover as the signal strength degree and resources available in the base station, for illustration bandwidth, although, the RSS ( Radio Signal Strength ) is different for each architecture 4G. In most of the mobility webs technologies the hallmark operation is the most clip devouring due to the fact the web waiter may be connected to the web through many hops in the anchor webs. Authentication may take seconds to finish. [ 5 ]
Integrating 802.11 WLAN and UMTS
There are two possible scenarios for the deployment of WLANs in public countries. [ 6 ] The fist option makes mention to a hot topographic point that is deployed as a standalone web that is non connected to the UMTS webs. The 2nd option is using rolling where the WLAN is employed for high velocity transmittal informations and it works in combination with the UMTS [ 3 ] The webs are configured as the internal cells are the WLAN and the UMTS are the external cells.
With the integrating of two different engineerings the quality of service ( QoS ) is impacted. The QoS in UMTS webs correspond of 4 degrees. Best attempt, synergistic, voice and informations, while the QoS in 802.11 merely support best attempt. [ 6 ]
A decision subdivision is non required. Although a decision may reexamine the chief points of the paper, do non retroflex the abstract as the decision. A decision might lucubrate on the importance of the work or propose applications and extensions.
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