Radio Network

The radio network for a CDMA2000 system has several enhancements over
existing IS-95/J-STD-008 wireless systems. These enhancements involve
better power control, diversity transmitting, modulation-scheme changes,
new vocoders, uplink pilot channels, expansion of the existing Walsh codes,
and channel-bandwidth changes. The CDMA2000 radio system, following
the IS-2000 specification, is designed to provide an existing cdmaOne operator
with a phased entrance into the 3G arena.
The CDMA2000 radio network for phase 1 implementation, also called
CDMA2000 1xRTT, is the same as that defined for IS-95/J-STD-008 systems
where the channel bandwidth is 1.25 MHz. However, a bandwidth
change takes place with the introduction of CDMA2000 phase 2, which is referred to as CMDA2000-3xRTT where multiple carriers are now used. A
brief and simplified channel bandwidth diagram is shown in Figure 7-18,
which illustrates the radio carrier differences between a CDMA IS-95,
1xRTT, and a 3xRTT system.
CMDA2000 introduces several new channel types for the radio access
scheme. The new channel types are implemented in both the 1xRTT and
3xRTT schemes and are introduced to support high-speed data as well as
enhanced paging functions. To accomplish the higher data rates,
CDMA2000 uses a combination of expanded Walsh codes along with modulation
and vocoder changes.
As depicted in Figure 7-18, a wireless operator can migrate to
CDMA2000 from either the IS-95A or IS-95B platforms using the same
amount of existing spectrum when transitioning to a 1xRTT format. The
two common migration paths for implementing CDMA2000 are relative to
operators utilizing CDMAOne (Is-95A/B) platforms:
■ cdmaOne (IS-95A)—CDMA2000 (phase 1)—CDMA2000 (phase 2)
■ cdmaOne (IS-95A)—cdmaOne (IS-95B)—CDMA2000 (phase 1)—
CDMA2000 (phase 2)
The CDMA2000 radio access scheme has several enhancements over the
existing IS-95 systems and they are as follows: ■ Forward link:
■ Fast power control
■ Quadrature Phase Shift (QPS) keying modulation, rather than dual
Binary Phase Shift (BPS) keying
■ Reverse link:
■ Pilot signal, to enable coherent demodulation for the reverse link
■ Hybrid Phase Shift (HPS) keying spreading in the reverse link
Table 7-3 shows the various relationships between the IS-95 and
CDMA2000 radio channels.