Handoff is a process where a mobile radio operating on a particular channel is reassigned to a new channel. This can be a new frequency channel, new code channel, or a new logical channel. The process is often used to allow subscribers to travel throughout the large radio system coverage area by switching the calls (handoff) from cell-to-cell (and different channels) with better coverage for that particular area when poor quality conversation is detected.

Handoff may also occur when a mobile device requests a service that can only be provided by a radio channel that has different service capabilities. This might mean assignment from an IS-95 CDMA voice channel to an EVDO high-speed data only channel.

There are two primary types of handoff in the EVDO system; a frequency transfer (called a hard handoff) and a simultaneous code channel transfer (called a soft handoff). A hard handoff is a communication channel handoff (or handover) that occurs when a connection with the initial server (e.g. cellular base station) is disconnected before the connection with the next communications access point is completed. A soft handoff is a process that maintains a communication connection with an initial transmitter site (e.g. base station) while simultaneously communicating with one or more additional transmitter sites (base stations) during the handover process.

While it is only possible for an access terminal (the mobile device) to receive data from one access point (the base station) at a time, the access terminal can quickly switch from communicating with one...