A handoff refers to the process of transferring an active call or data session from one cell in a cellular network to another or from one channel in a cell to another. A well-implemented handoff is important for delivering uninterrupted service to a caller or data session user.
Cellular networks are composed of cells, each of which is capable of
providing telecommunications services to subscribers roaming within them. Each
cell can only serve up to a certain area and number of subscribers. Thus, when
any of these two limits is reached, a handoff ensues.
For instance, if a subscriber moves out of the coverage area of a particular cell while entering another, a handoff takes place between the two cells. The cell that served the call prior to the handoff is relieved of its duties, which are then transferred to the second cell. A handoff may also be triggered when the number of subscribers using a particular cell has already reached the cell’s maximum limit (capacity).
Such a handoff is possible because the reach of the cell sites serving these cells can sometimes overlap. Thus, if a subscriber is within an overlapping area, the network may opt to transfer one subscriber’s call to the cell involved in the overlap.
Sometimes a handoff can take place even if no limit is breached. For example, suppose that a subscriber initially inside the jurisdiction of a large cell (served by an umbrella-type cell site) enters the jurisdiction of a smaller cell (one served by a micro cell). The subscriber can be handed off to the smaller cell in order to free up capacity on the larger one.
Handoffs may be classified into two types:
- Soft Handoff: Entails two connections to the cell phone from two different base stations. This ensures that no break ensues during the handoff. Naturally, it is more costly than a hard handoff.
- Hard Handoff: Characterized by an actual break in the connection while switching from one cell or base station to another. The switch takes place so quickly that it can hardly be noticed by the user. Because only one channel is needed to serve a system designed for hard handoffs, it is the more affordable option. It is also sufficient for services that can allow slight delays, such as mobile broadband Internet.
Also Read: Difference Between GSM And CDMA
A handover is a process in telecommunications and mobile
communications in which a connected cellular call or a data session is
transferred from one cell site (base station) to another without disconnecting
the session. Cellular services are based on mobility and handover, allowing the
user to be moved from one cell site range to another or to be switched to the
nearest cell site for better performance.
Handovers are a core element in planning and deploying cellular networks. It allows users to create data sessions or connect phone calls on the move. This process keeps the calls and data sessions connected even if a user moves from one cell site to another.
There are two types of handovers:
- Soft Handover: A substantial handover where the connection to the new channel is made before the connection from the source channel is disconnected. It is performed through the parallel use of source and destination channels over a period of time. Soft handovers allow parallel connection between three or more channels to provide better service. This type of handover is very effective in poor coverage areas.
- Hard Handover: An instantaneous handover in which the existing connection is terminated and the connection to the destination channel is made. It is also known as a break-before-make handover. The process is so instantaneous that the user does not hear any noticeable interruption.