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Handover is a technique in a cellular network where to get the continuous connection between transmitter and moving receiver device, the network has to switch the connection to the new transmitter. It is manage by Mobile Switching Center (MSC), where when the mobile move, the MSC will transfer the connection belonging to the new station . The handover technique is actually to avoid the drop out connection for the mobile device. The implementation of mobile handover is widely use by several mobile communication provider like GSM band. The mobile communication provider give emphasis to optimize handover, since it is strongly related to drop calls, connection dropped and network overload . There are two types of handover which is Hard Handover and Soft Handover. The use of two types is depending on the condition of the mobile network. This term paper will discuss about the implementation of mobile handover and how it works.
Handover is a technique in cellular network that offer a switching connection among the appropriate base station when the device is moving. The role of Mobile Switching Center (MSC) is important to manage the switching connection. Due to the awareness of drop out connection when the device is moving from one cell to another, the mobile handover is proposed to improve the connectivity of the communication. The implementation of mobile handover is actually widely use by GSM band. Since the burst of wireless technology nowadays, the implementation of mobile handover also being used by the 2G and 3G communication.
The handover is related to the cellular network technology. The cellular network means the network coverage is divided into a group of cell within the every cell is supported with a single base station equip with antenna, controller and receiver. The connection switching is supported by MSC where the connection transfer is base on a certain criteria like a moving device, overload connection and connection lost.
2.0 Cellular Network Systems
Cellular network is a radio network that have been made up by a several number of radio cells. The cell is assign to a specific area depends on how long it covers a signal. Each cells is served by its own antenna and manage by a base station consist of transmitter, receiver and controller. Every cell is allocated with a specific band of frequencies. The specific frequencies cannot be same next to each cell to avoid the channel or frequencies congestion.
Figure 1: Cellular Network Systems
Figure 1 shows the Cellular Network Systems where it shows how the two receivers are connected to each other. The Base Station is representing for a single cell area. The switching connection is manage by Mobile Telecommunication Switching Office (MTSO) where it responsible to establish the connection between receiver and Base Station. MTSO also responsible for mobile unit initialization, mobile-originated call, paging, call accepted and ongoing call. The switching management for the MTSO will be discussing in detail within next chapter.
Figure 2: Network Cells
Figure 2 shows how network cells are divided. Every cell is representing by one base station. The single cell also can be break up into the micro cells where it is important for high density of connection.
The high number of micro cells will create high coverage of the network. The implementation of micro cells is proposed at high density of user like in a city area.
3.0 Mobile Handover
Handover or handoff is the term that use in a cellular communication system that refer to the switching of the network connection between a base stations to another.
The switching of base station is processed by the MTSO where the MTSO is responsible to manage all the switching connection. Handover occur when the mobile device is moving away from the area that covered by one cell and entering the area that covered by another cell. It also can be happen when the cell is overloaded.
Handover procedure consists of cell selections, handover decision and time synchronization to target base station . Cell selections in Mobile Station (MS) are an effective way to perform handover where the MS will scan the neighbor Base Station to get the best quality of coverage. Sometimes, the handover is not actually performed only in a moving devices but it also perform in a static mobile devices that searching for a good coverage.
3.1 Hard Handover
Hard Handover is one of the types of handover. Following hard handover procedure, the connection between the current base stations is terminated before the connection transferred to another base station.
Figure 3: Hard Handover Technique
Figure 3 shows the connection between mobile devices through hard handover procedure. The connection of the mobile device to the base station can be established in one connection only in a single period of time. Hard handover is important for connections that rely on bandwidth efficiency.
So, in a period of time, the mobile devices only connected to one base station only. Itï¿½s also known as break-before-make technique. By the way, the weakness of the hard handover is the delay that will occur when the process of switching the current base station to another is taking part.
Hard handover is widely used in Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) in cellular systems.
3.2 Soft Handover
Figure 4: Soft Handover Technique
Soft handover is another type of handover technique and it also known as make-before-break technique.
Figure 4 shows the connection between mobile devices through soft handover technique. The connection of the mobile device to the current base station remains constant while the network is trying to make a new connection between new base stations. When the connection with the new base station is already established, the connection with the current base station will be break.
This technique may involve more than 1 new base station for connection request. This is one of the advantages for soft handover while the mobile device can be connected to more than 1 base station. It can perform a sharing base station to provide a better signal and transmission.
Soft handover is important for Code Division Multiple Access (CDMA) where CDMA is relying on the soft handover advantages such as Power Control. Soft handover also provide Fade Margin Improvement and Higher Reverse Link Capacity.
3.3 Fast Handover Protocol
For the current technology, some of the network allows the Fast Handover protocol. By allowing the mobile device to use a fast Hand Over Protocol, the mobile device has an ability to learn new Router Information when still attached to current router. The advantages of this technique are it enables a fast movement detection, expedites new address configuration and facilitates the immediate transmission upon new link establishment.
The Fast Handover Protocol also allow the mobile device to receive packet sent to its previous IP address until the binding update to home agent and the correspondent is completed.
Figure 5: Fast Handover Protocol
Figure 5 shows how the Fast Handover Protocol operates. The mobile node request for packet before it moves to the next destination. The mobile node is learn for a new router information and ready for handover. The packet is sent before handover and queue in the Router 1. When the handover to the new router is established, the mobile devices announce for the attachment and the tunnel is created from Router 1 to Router 2 with a new IP address. After that, the packet is sent through the new Router by using the tunnel that created from Router 1 to Router 2.
Network handover is important for the mobile network communication. The application of mobile network handover will make the mobile network communication more efficient. The techniques that involve in the handover decision have the unique characteristic and depend on what type of the application that will be use.