Smart Phone and Next Generation Mobile Computing

Supporting Wireless Technologies 135

to a new base station until connection to the current mobile sta-

tion is released. Generally, only when the signal strength of the new

base station is sufficiently stronger than that of the current one plus a

threshold does the mobile station proceed to connect to the new base

station. The reason for utilizing signal strength for hard handoff is

frequency reuse among neighbor cells. As a mobile station moves

toward a neighboring cell, the signal strength from the new one

tends to increase gradually. Unfortunately, such spatial frequency

reuse does not exist in CDMA at all. In CDMA, a different handoff

approach is used, namely soft handoff. Because all cells essentially use

the same frequency band, it is not possible ...