The Basic Purpose Of Handover Predictions Computer Science Essay

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In this project I will define handover perditions. I will explain basic purpose of handover predictions. I will briefly describe handover predictions in heterogeneous networks. I will discuss how handover can maintain the seamless transmission in wireless networks. I will also discuss the main problems with handover in heterogeneous networks.

In wireless network every mobile node or mobile device is connected to its Base Station (BS) or Access Point. Every base station is has its own coverage area or range called Cell. When mobile node or mobile device moves from one base station to another the signal strength of its original base station becomes weak. So when mobile node enters to another base station its control is transferred to new base station. This process is called handover.

The mobile wireless networks should be able to provide a full mobility (mobile node can move easily) to users with a good Quality of Service (QoS). Quality of Service is part of mobility of users. When mobile node moves the base station to which it is connected has to be updated. During the movement of mobile node the Mobile Station (MS) scans its neighbor's base stations and monitors communication parameters for example Signal Strength (SS) or packet delays of all available base stations. When some of signal parameters of the base station to which the Mobile Station is connected drops below the certain level the Mobile Station performs a handover. So Mobile Station break all connections from previous base station and establish a new connection to the new base station called target base station. During this process the QoS may decrease but it should be least.

Handover prediction or prediction of handover is a process in which target base station is predicted. Handover prediction helps to know target base station in advance. So it enables to perform a fast handover and it minimizes the interference. [3]

Introduction to heterogeneous network:

A heterogeneous network is a network that consist different operating systems and protocols to connect mobile nodes or computer with other mobile nodes or devices. The heterogeneous network has a range of different access networks so user or subscriber can access the internet. Heterogeneous network is a collection of various wireless techniques including WLAN, GSM, UMTS, satellite networks and BLUETOOTH etc. In third generation (3G) the WLAN provides a low mobility and low communication cost over a geographically small area and with higher data rates to mobile nodes. UMTS cellular networks provide a wide coverage area with a low bandwidth and high communication cost to Mobile node with high mobility. So integration of these networks has formed a heterogeneous network that provides service at any where or any time mobility connectivity and the main benefit is very low cost to those Mobile nodes who want a high speed wireless access. [4]

Available at: http://www.comp.nus.edu.sg/~chenbinb/heterogeneous/index.htm

Handover predictions for heterogeneous networks

wireless technologies for example 2G, 3G, WLAN, WMAN etc has been developed in combination with the evolution of Mobile Terminals (MTs) with multiple network interfaces and the IP-based applications has allowed the user to have access to IP services anywhere at anytime from any network. Fourth generation (4G) a heterogeneous wireless network has brought up a great change in wireless communication. Heterogeneous networks offer a better quality of services, high speed and low cost as compared to 2G and 3G. In heterogeneous networks handover management has a vital role in order to perform a successful handover.

Handover Management in heterogeneous networks:

In handover management different functions are performed such as metrics, mobility scenarios, algorithms and procedures. Mobility scenarios are generally divided as horizontal and vertical handover. In homogeneous networks, horizontal handovers are take place when serving base station can not fulfill user's requirement or signal strength becomes weak. Handover management is a vital component of wireless communication because it maintains the connection active during the moving movement of mobile node or device.

Handover management Process:

Handover management process has three phases.

Information gathering:

It is used to collect all the information which is required for handover and can initiate it. It is also called handover initiation phase or system discovery.

Handover decision:

It determines when and how to perform the handover by selecting the most suitable access network and it gives instructions to the execution phase. It is also known as network or system selection.

Handover execution:

It connects the mobile node with new base station and forward data to the previous base station.

The handover Procedure:

The handover procedure can be categorized into many types. Some common types are given below.

Hard handover:

The handover is hard when the mobile node is connected to only one base station at a time.

Soft handover:

The handover is soft when the mobile node is connected to two or more base station for a while.

For seamless communication the handover has to be seamless. In fast handover the handover latency should be minimum. In smooth handover there should be a minimum packet loss.

Handover decision mechanism:

The handover decision is based on some kind of mathematical calculations and information about when and where to perform a handover.

Network Controlled Handover (NCHO)

The handover which is controlled by network is called Network Controlled.

Client Controlled Hanover (CCHO).

The handover which is controlled by client or user is called Client Controlled.

Handover decision criteria:

Handover criteria are the qualities that are considered to give and indication of whether or not a handover is needed.

Network related:

Coverage

Bandwidth

Latency

Link quality (Received Signal Strength)

Carrier to Interferences Ratio (CIR).

Signal to Interferences Ratio (SIR).

Bit Error Rate (BER).

Monetary cost and security level.

Terminal related:

Velocity

Battery power

Location information.

User related:

User profile

Performance

Service related:

Service capabilities

Quality of service

Handover management solution:

For handover management there is a one most popular solution is Mobile IP. It is an IP layer mobility management protocol. This protocol manages the redirecting packets sent by a Correspondent Node (CN) to the Mobile node to its recent location. Its introduce mobility agents such Home Agent and Foreign Agent. The Mobile IP works as follows:

Agent discovery: Mobile node detects whether it has moved to a new network by sending or receiving messages from or to mobility agents.

Registration: Mobile node gets a new temporary address that is called Care of Address when it enters a new access network. Mobile node registers this new CoA with its Home Agent. Home Agent sets up a new tunnel up to the end point of the new CoA and removes the tunnel to the old CoA.

Routing and tunneling: When the new tunnel is set up the Home Agent tunnels packets destined to the Mobile node using the Mobile node's new CoA.

Vertical handover decision strategies:

There are so many strategies that are used in vertical handover some of them given below.

Decision function based strategies.

Fuzzy logic and neural networks based strategies.

Multiple attribute decision strategies.

User centric strategies.

Context aware strategies. [5]

Vertical handover in heterogeneous networks:

Heterogeneous wireless networks are the combination of different technologies for example 2G, 3G, UMTS, Satellite networks and WiFI etc. In heterogeneous networks handover could be horizontal within same network but most of time it would be vertical because heterogeneous network is a collection of several different networks.

Vertical handover can be categorized as network controlled and client controlled.

Before heterogeneous networks, network controlled handover was normally used so Base station maintains up to date context information for the mobile node. It also decide where and when should perform a handover.

Network controlled handover is not very sufficient in heterogeneous networks because in heterogeneous networks mobile node is connected with many base stations and with also different service providers.

Client controlled handover could be more efficient in heterogeneous network environment. In client controlled the mobile node can manage the handover decisions. In client controlled Mobile node is directly connected with network so mobile node will decide where and when a vertical handover should perform.

In heterogeneous networks it is very important to analyze and select best network channel to establish a connection. It is very helpful to minimize packet loss and latency due to handover mechanisms.

For example and mobile node is aware that it may loose WLAN coverage in next minute it will avoid download a video stream. So it will choose the best next available network. In other example a user may pick up the coverage of a WLAN for a while when he walks near a hotspot but mobile node would not perform a handover if it is aware it would loose connection in next few minutes. [6]

Problems and challenges with handover in heterogeneous networks:

In a heterogeneous network handover decision is a very important phase. In handover decision decides whether it should perform a handover or not? And it also decides which could be the most suitable target network. Horizontal handover takes place within the same network when Signal Strength of the serving Base Station (BS) goes down below a certain threshold value and vertical handover takes place between different networks.

In heterogeneous network environment, users can move between different networks. They will get advantage from different network characteristics such coverage, bandwidth, latency, power consumption and cost etc. The handover process is more complex in heterogeneous networks. So there are more challenging problems in handover decision and resolving it. It also affects handover performance. In vertical handover decision the decision criteria is different than horizontal handover.

To select most suitable access network.

To avoid unnecessary handovers.

Correct handover predictions.

To provide best Quality of Service.

Must satisfy network and user requirements by deciding over which access network to connect when many access networks are available for a specific service.

Issues:

Combining decision criteria.

Handover delays

Packets loss

Seamless data transmission

User satisfaction problem

A context aware problem

Incorrect handover predictions.

Interruption

Slow speed [5]

Conclusion:

In this project I have described the handover. I have analyzed the basic handover operation. I defined heterogeneous networks and handover in heterogeneous networks. Handover is a process that switches the control from one base station to another during the movement of mobile node. There are several possible reasons that cause a handover for example signal strength of serving base station and user's requirements. In heterogeneous networks there are also two types of handovers, horizontal and vertical. But in heterogeneous networks most of handovers are vertical because heterogeneous network is a combination of different networks. Vertical handovers are complicated in heterogeneous networks because it is difficult to determine the most suitable target network among several access networks.

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