CDMA2000-1X to 3X

Migrating from a 1X to a 3X CDMA2000 system is being advertised to be
relatively transparent from a radio aspect, provided you have three contiguous
1X channels or you have cleared the spectrum for the new 3X channel. But in reality, the introduction of a 3X platform will not be transparent
due to the variety of operating issues like the real traffic mix.
The fundamental concept behind the migration from 1X to 3X is that the
3X platform comprises of three individual 1X carriers enabling a three fold,
with trunking efficiency, in throughput as well as improvements in the
modulation scheme and processing gains. The 3X carrier is expected to be
overlaid on top of the existing 1X carriers as shown in Figure 13-15.
The various channel schemes that are planned for 3X involve the PCS
plans that are shown in Figure 13-16 for a 5-MHz license holder. It is interesting
to note that overlaying a 3X platform onto a 1X system needs to be
thought out well in advance in order to minimize the impact on traffic loading
and carrying. The reason for the traffic concern is that a single 3X
mobile will impact all three carriers on a downlink even for a single voice
call due to how the Walsh codes are used.
The channel plans shown in Figures 13-17 and 13-18 represent two different
alternatives out of the many that are possible. In Figure 13-17, the
use of 1X and 3X carriers and their migration paths is shown from a pure
1X environment. It is important to note that the 1X carriers are left for the
purpose of supporting circuit switched traffic.
The scenario that Figure 13-18 implies is the possible bifurcation of a 15-
MHz PCS license for the purpose of deploying CDMA2000 1X and 3X plus
WCDMA.
One can see many possible alternative configurations and options with
Figures 13-17 and 13-18. However a very interesting and complex issue
arises when focusing on the AMPS band and determining how CDMA2000-
3X will be integrated into it. The issue is more complex than just adding a
single carrier because a large portion of the spectrum needs to be cleared in
order to support the channels introduction. Now the channel associated with
3X may already be operational with CDMA2000-1X carriers, making the
transition more efficient. However, if the channels are still in use by 1G systems,
then the pain of capacity shifting and migration will need to take place.
Figures 13-19 and 13-20 are examples of how a 3X channel can be
deployed into a cellular system. Both figures are slightly different in that
Figure 13-19 has two legacy CDMA channels while Figure 13-20 only has
one legacy channel. It is assumed that when 3X is introduced to the system
that all IS-95 platforms have been retired or moved to voice only areas of
the network.
What follows next is an example of traffic calculations associated with
the introduction of the 3X platform into the system. For this design, it is
assumed that there are no green field applications and that this is a pure
integration of an existing CDMA2000-1X system.

The expansion of the existing system will only take place with
CDMA2000-3X-capable handsets. Obviously the mix of handset-compatible
units can and will differ depending on the price and delivery factors that
have to meet the marketing and sales objectives of the system.
Establishing a simple design for a CDMA2000-3X system calls for a total
of 10,000 new subscribers and their relative traffic contributions are shown
in the accompanying Tables 13-37, 13-38, 13-39, and 13-40.
Unlike the other designs, the packet data usage is split between the 1X
and 3X platforms. Depending on the design objectives defined, the existing
packet data users can be rolled up into the new 3X platform. Alternatively,
the new packet data users can be allocated to the 3X platform only, and the
legacy systems remain in place until the subscribers are migrated over a
multi-year process.
If the spectrum is available, then it is recommended to jointly deploy the
1X and 3X platforms. The reason behind this scheme lies in the Walsh code
usage because the same Walsh codes are used for all carriers that comprise
a 3X radio per sector. Additionally, the 3X platform should be used for
packet data only while the legacy systems support voice, circuit switched,
until the time that the packet voice is implemented and the legacy subscriber
units have been successfully migrated to the new platform.
In examining the traffic defined for the system as a total, which includes
existing and new usage, a few issues arise that need to be thought about.
With the 1:1 overlay of the 3X system, results in treating new and existing
packet data, along with circuit switched data, are being combined.
However, if you were to separate the platforms from a system integration
aspect, then 1X could be allocated for circuit switched traffic while 3X is allocated all the packet traffic. Because the radio system is backward compatible,
1X capable mobiles can interact with 3X carriers so the 3X can be
used for data only applications.
Another thought comes about for the system layout and that is that the
system as it is defined in this example is not capacity-of-coverage driven
but rather capability-driven, which is fundamentally different than past
designs.
Using the existing sites from the design example done previously for
integrating a 1X system into an existing platform, the following underlying
numbers will be used to base the 1:1 overlay on shown in Table 13-41.
Taking things just a little further, the basic configuration of the 1X system
is shown in Figure 13-21.
The basic configuration shows that parts of the system, in the core region
defined as being BSC1, have both 1x and DO channels deployed whereas
the rest of the system only has a 1x channel deployed.With the introduction
of a 3X platform and the decision to do a 1:1, overlay for the system is shown
in Figure 13-22 with the channels associated with the 3X carriers having
the legacy 2.5G or 1X configurations for legacy mobiles. The requirement
for additional spectrum over the existing 1X system deployment is rather
an obvious issue.
Looking at Table 13-42, the issue deployment of 3X into a system is
shown in Figure 13-22 but only for the core of the system to facilitate the
illustration only.
The next obvious question that needs to be quickly discussed is the issue
of what platforms need to be altered in order to support the new 3X system.

The change required for migrating from a 1X to a 3X platform is expected
to require physical changes to
■ BTS radios
■ Channel elements
The rest of the PDSN network, as well as the BSC connectivity with the
PDSN and circuit-switched networks, should remain the same. The difference
would arise if VoIP is deployed but this would impact the BSCs primarily
and require the introduction of a VoIP gateway and supporting functions
that were covered in detail in Chapter 8, “Voice Over IP Technology.”
Therefore the configuration for the previous example, due to the low traffic
loading, is the same as shown in Figure 13-5 because the 1X to 3X migration
in this example is a capability-driven migration—not capacity-driven. 582