Antenna Configurations

The site configurations for the CDMA2000 sites can and do take advantage
of many of the IS-95 lessons learned through the deployment phases. Taking
a simplistic view of CDMA2000 antenna requirements, a total of two
receive antennas (or paths) are needed per sector, as was the case with IS-95
systems. The diagram shown in Figure 13-1 illustrates the requirement for
a single CDMA2000-1X Tx channel and that of a single 3X channel.
Figure 13-1 addresses two issues with 1XRTT deployments: to utilize
or not to utilize transmit diversity. Figure 13-1 illustrates for a
CDMA2000-1X carrier, a single TX antenna is needed; however, Figure
13-1 shows that two antennas are needed for STD TX diversity. The transmit
diversity scheme has technical advantages that can be exploited by
the system operator, however, at the cost of deploying or using a second
antenna for TX diversity. Now this is normally not an issue with a CDMA
carrier because there are usually two antennas or a cross pole used, and
the duplexers provide the dual path. Where the rub comes is when a second
carrier is deployed, and unless the link budget shows the splitting
loss that can be accommodated, more antennas will need to be added to
the system or sector.
TX diversity can also be deployed with a single antenna used for transmit
following the Orthoginal Transmit Diversity (OTD) method.