LGC-340/345W
8
LGIC
LG Information & Communications, Ltd.
2.6 Frequency Re-Use(Segmentation) and Sectorization
Unlike the existing analog cellular system, the CDMA system can reuse the same frequency at the adjacent cell
and accordingly, there is no need to prepare a separate frequency plan. Total interference generated on mobile
station signals received from the cell site is the sum of interference generated from other mobile stations in the
same cell site and interference generated from the mobile station of adjacent cell site. That is, each mobile station
signal generates interference in relation to the signals of all the other mobile signals.
Total interference from all the adjacent cell sites is the ratio of interference from all the cell sites versus total
interference from other mobile stations in the same cell site (about 65%). In the case of directional cell site, one
cell normally uses a 120
¡ Æ
sector antenna in order to divide the sector into three. In this case, each antenna is
used only for 1/3 of mobile stations in the cell site and accordingly, interference is reduced by 1/3 on the average
and the capacity that can be supported by the entire system is increased by three times.
2.7 Soft Capacity
The subscriber capacity of CDMA system is flexible depending on the relation between the number of users and
service classes. For example, the system operator can increase the number of channels available for use during
the busy hour despite the drop in call quality. This type of function requires 40% of normal call channels in the
standby mode during the handoff support, in an effort to avoid call disconnection resulting from the lack of
channels.
In addition, in the CDMA system, services and service charges are classified further into different classes so that
more transmit power can be allocated to high class service users for easier call set-up; they can also be given
higher priority of using hand-off function than the general users.
