Standard CDMA Cell Site Configurations

Several general types of cell sites are currently usable at this time. The configuration
is slightly different for both cellular and PCS due to colocation
issues with the legacy systems. However, both cellular and PCS have the
commonality of either being a omni or three-sector cell site; it is just the
amount of antennas per sector that drive the difference.

It is important to note that the radio equipment for both cellular and
PCS is fundamentally the same also. The difference between the two is that
for PCS the frequency for transmitting and receiving is up-banded; that is,
an additional mix is taking place. Typically, each cell or sector will require
a separate transmit antenna per CMDA carrier per sector and two receive
antennas. The reason for the separate transmit antennas per sector lies in
the forward transmit power for the cell in that combing the channels either
through use of a cavity or hybrid results in about a 3-dB loss.

The generic configurations that follow are meant for PCS and cellular
CDMA-only cells and only a single sector, or omni site, is represented. The
first configuration involves a PCS system deploying CDMA only in Figure
3-20.

Figure 3-20 depicts several situations that do occur for PCS operators.
The first configuration is one that involves only a single carrier when three
antennas can be installed on a per-sector or cell site basis. The second configuration
is where, due to a multitude of reasons, only two antennas can be
installed, thereby requiring the use of a duplexer. The third situation
assumes that three antennas are used and shows how multiple carriers can
be supported by three antennas.

Regarding cellular systems, initially the common use of the antennas at
a cell site that had legacy 1G technology was promoted. However, after
implementation, it was found that this might not have been the best
choice. The reason for the error was the AMPS system and the CDMA system
have different design requirements, and having the common antenna
system restricts the flexibility of either system for optimization and expansion
purposes.

Therefore, where possible, the use of a separate set of antennas for
CDMA and AMPS systems is preferred. However, as the reader would surmise,
the leasing, loading, roof space, and, of course, local ordinances may
preclude this method of deployment.

Figure 3-21 illustrates a common situation when integrating 2G systems
into a 1G environment. The first diagram shown represents the typical situation
where only three antennas are available for use in a given sector,
necessitating the use of duplexers. However, as discussed briefly, the sharing
of antennas can lead to optimization problems because both systems have different design criteria. The second diagram shown in Figure 3-21
illustrates a configuration where the AMPS and CDMA systems share the
same cell site location, but the systems utilize different antenna systems.