Handover mechanism is extremely important in cellular network because of the cellular architecture employed to maximize spectrum utilization. Handover is the procedure that transfers an ongoing call from one cell( ageographical area covered by a BTS/cell phone tower) to another as the user’s moves through the coverage area of cellular system.
A cellular network is made up of numbers of cells (or radio cells). Each cell is allocated a band of frequencies and served by base station consisting of
transmitter, receiver and control unit. Adjacent cells are assigned different frequencies to avoid interference or cross talk . As more customers use the cellular network with single base station traffic may be build up so there are not enough frequency bands assigned to a cell to handle its calls. An approach can be used to
cope with this situation to use the same radio frequency can be reused in different area for a completely different transmission. The degree of reuse determined by how apart cells must be reuse the same frequency is depending upon the actual implementation of the radio link. The reuse of frequencies in different cells is a form of space division multiple access and it requires that location of each mobile agent to be known this is provided through a service known location management or
mobility management. The obstruction in cellular network involves the problem when a mobile user travels from one cell to another during a call. As adjacent cell do not use the same radio channels, a call must be transferred from one radio channel to another when a user crosses the line between the adjacent cells.
The process of handover takes place that transfer an ongoing call from one cell to another cell as the user moves through the coverage area of a cellular network. In handover process cellular network automatically transfer a call from one radio channel to another radio channel while maintaining quality of services (QoS) of a call.
Handover mechanism is extremely important in mobile network because of the cellular architecture employed to maximize spectrum utilization. The number of cell
boundaries increases because smaller cells are deployed in order to meet the demand of increased capacity. Each handover require network resources to route the call to next base station. If handover does not occur at right time the QoS may be drop below an adequate level and connection will be dropped. There are
several different reasons needed to be known to determine whether a handover is required. The signal strength of the base station, along signal strengths of the surrounding stations. In addition the availability of the channels also needed to be known.The mobile monitors the strength of the base stations, but only
the cellular network knows the status of channel availability and the network make the decision about the handover.In addition when a user moves into new cell, bandwidth is reserved in the new neighboring cell and the reserved bandwidth in the cell which are no longer used to the new cell is released.
However from the operation point of view there are several weaknesses in CAC scheme. First it seems difficult for CAC scheme to handle the user’s request where the capacity is not enough to deal with all the requirements. In the situation the calls blocking and dropping probability increases which affects QoS of the wireless cellular network. But if the user has predefined priority then the CAC can distribute capacity according to each user so that the requirements of each with
higher priority will be fulfilled prior to any other user.
Besides, in GSM due to hard hand off the calls are dropped whereas in CDMA soft handoff is present.
One way to improve the cellular network performance is to use efficient handover prioritization schemes when user is switching between the cells.
