Handoff techniques in cellular communication

Handoff techniques are required when a mobile unit moves from one cell to another. Every cell has an allocated set of frequency band for its functioning.  The mobile unit uses the channels available in a cell base system and then establishes a connection to a free channel.  Poor signal strength at mobile unit and base station is a serious issue of concern. If the signal strength is below a threshold level, receiver call may get disrupted. This situation can be avoided by providing a free channel in the new cell.  This changeover must be carried out with utmost perfection and without causing any interruption to the progress of the call. This changeover process is called handoff. In this process, the tuned frequency of the transreceiver in the mobile station is changed when it crosses the boundary of a cell. This frequency change affects the free channel of the new cell to which the mobile unit has moved in. Three important issues to be tackled during handoff management are handoff detection, channel assignment and link transfer.  The important parameters to be measured before fixing handoff technique are quality indicator, word error indicator and received signal strength indicator. The three types of handoff techniques are mobile controlled handoff, network controlled handoff and mobile assisted handoff.