IS-95 System Description

Code Division Multiple Access (CDMA), also known as IS-95 and J-STD-
008, is a spread spectrum technology platform that enables multiple users
to occupy the same radio channel, or frequency spectrum, at the same time.
CDMA has and is being utilized for microwave point-to-point communication
and satellite communication, as well as by the military.With CDMA,
each of the subscribers, or users, utilize their own unique code to differentiate
themselves from the other users. CDMA offers many unique features,
including the capability to thwart interference and improved immunity to
multipath affects due to its bandwidth. The IS-95 technology has been
championed by many system operators in the United State and Asia.
IS-95 has two distinct versions, IS-95A and IS-95B, besides the J-STD-
008. The J-STD-008 is compatible with both the IS-95A and B, with the
exception of the frequency band of operation. However, the difference
between IS-95A and IS-95B is that IS-95B enables ISDN-like data rates to
exist. Although this would seem to be an interim step between 2G and 3G,
for the purpose of this text the IS-95A and B are considered 2G only.

CDMA is based on the principal of direct sequence (DS) and is a wideband
spread spectrum technology. The CDMA channel utilized is reused in
every cell of the system and is differentiated by the pseudorandom number
(PN) code that it utilizes. Depending on whether the system will be
deployed in an existing AMPS or new PCS band system, the design concepts
are fundamentally the same, with the exception of frequency band
particulars that are directly applicable to the channel assignments in an
existing cellular band. Beyond the nuances, the design principals for CDMA
are the same for a cellular and PCS system.

The introduction of CDMA into an existing cellular network is not simple
due to the issue of immediate capacity reduction, but with a long-term
upside. Also, for PCS operators, a requirement specifies that they must
relocate existing microwave links to clear the spectrum for their use.
The degree of ease or difficulty for implementing CDMA into the PCS market
will be directly impacted by the ability to clear microwave spectrum.
The diagram shown in Figure 3-19 is a simplified version of the IS-95A/B
architecture.