In cellular wireless networks, it is very important to deal with Mobile station (MS) handoff between cells so that they can maintain a continuous and QoS-guaranteed service. There are four basic types of handoff protocols; network-controlled handoff (NCHO), mobile-assisted handoff (MAHO), soft handoff (SHO), and mobile-controlled handoff (MCHO). From NCHO to MCHO, the control protocols tend to decentralize the decision making process, which help shorten handoff delays; however, the decentralization makes the measurement information available to make a handoff decision also decreased. Next, we briefly introduce these four types of handoff mechanisms. (more…)