CDMA2000-1X

The following is a brief design example that is relevant for a new
CDMA2000-1X system being deployed as a green field situation.The design
example focuses on the issues that are more relevant to the internal network
and does not factor into the mix any possible networking and coordination
issues with adjacent systems.

Because this is a new CDMA2000 system, the concerns of legacy equipment
are not relevant and it will be assumed that only CDMA2000 capable
handsets are used by the system. However in real life, the issue of roaming
mobiles into the system that are legacy, IS-95, will need to be factored into
the design.
For this design, both CDMA2000-1x and CDMA2000-1xDO channel
types will be available for deployment.
The initial design calls for coverage of a selected area within the network.
The first step in this case is to determine the desired traffic load for
both circuit switched as well as packet data. Utilizing the traffic loading
numbers presented earlier Tables 13-26 and 13-27 show the expected traffic
load from a total of 50,000 potential users of the wireless system that sales
and marketing expect will use the system. Because the actual throughput
is undefined due to the lack of actual traffic data from the network, the
design will encompass all the possible traffic loads.

Naturally, if packet data services of only 70 Kbps will be offered, then
some of the services included in the example can be eliminated.
Table 13-27 shows the expected load on the overall system in Erlangs
and Mbps. The reason for Erlangs is relative for circuit switched data
whereas that for packet is in Mbps. In previous comments, if only an estimate
from marketing is available regarding packet data usage given in a
percentage of voice usage, then the estimation should be done using an
Erlang-C model.

Table 13-28 is a summary of the calculations derived for the system traffic
load. However some additional information is contained in the table and
that is the relative geographic areas associated with each type of traffic. For
the purposes of this example, the areas will be considered to be contained
adjacent to each other for simplifying the example. However in real life, the
areas will be intertwined.

The next step is to determine the number of sites required to support the
expected load. An assumption needs to be made at this time and that is all
the CDMA2000-1x sites will be sector sites, three sectors per cell. In addition
it is assumed that for this design, a total of 8.2 Erlangs per sector can
be supported for circuit switch per sector, which is derived from a 2 percent
GoS using Erlang B with 14 trunk members. The packet throughput is
based on 2.35 trunk members at 76.8 Kbps. Both the packet and circuit
switch traffic-handling capacities are very conservative and are driven by
the link budget and process gain used
Cell voice Erlangs
8.2 Erlangs/sector  2.64 (sector gain)

21.648 Erlangs per cell
Packet throughput
2.35  76.8 Kbps/sector  2.64

453.15 Kbps per cell
NCircuit Switched
Estimated traffic/cell capacity
21.648/680 .15

32 cells total for the system
Packet data
(Estimated traffic/overbooking)/cell capacity

(72.15 Mbps/[10])/453.15 Kbps
16 total for the system
The next step is to determine the radius for the site(s) involved with each
area. In this example, the same pathloss will be used because it is assumed
the same morphology is used for all three areas.
From the link budget PL max
140 dB.
Therefore radius (r)
140
132  38log(r).

41.89 1vehicular PL max
1502

15.18 1pedestrian PL max
1452
Area of cells
8.279 1building2
R
1.623

132  38log 1r2
PL
132  38log 1r

Obviously from the example, the system is coverage, limited and not
capacity-limited. However, in briefly looking at the traffic data, the treatment
of one section of the system, building, needs a higher throughput than
the vehicular areas, which is obvious. Therefore the deployment recommendation
is to have two carriers deployed F1 being 1x while F2 is
1xEV-DO or 1xEV-DV which is assigned for data transport only.
Figure 13-3 represents possible channel deployment schemes that apply
to a PCS system operating with 15 MHz of duplexed spectrum. The inclusion
of 1x, DO, and DV channels is listed but is really left up to the traffic
mix as well as true availability for the technology. A 3X deployment is also
included from which to see that the later channels being deployed are positioned
correctly with the channel bit map.

Now the next issue is what do you do with this wonderful information.
Well you need to lay out a rough system topology from where you can begin
to determine if it is valid to centralize or decentralize the BSCs or have
intermediate nodes in the network. Typically for a system having 1100 sq
km in size, it would be expected to have several MSCs or concentration
nodes to reduce the leased-line costs and improve on interconnection transport
fees.

It is recommended that the core of the network consisting of the building
environment utilize two CDMA-2000 carriers while the pedestrian and
vehicular zones use only one carrier. A hard handoff of course will need to
take place between the F2 and F1 zone. However, it is recommended that in
a situation like this that the BTS F1 carriers process primarily voice traffic
while the F2 is more a data only situation. As mentioned earlier, this configuration
can be done via software and user-definable parameters.
The various pipe sizes were estimated for the initial concept. From Figure
13-5 it, would be advantageous to collocate BSC 1 with the MSC provided
the MSC is located near a tandem. The other BSCs, however, due to
their initial traffic load, should be considered to be remotely located provided
the operational and support issues can be met. In addition, the BSCs
will have on average 15 sites connected to them for the design example with
the exception of the core where a total of 12 BTS are associated with the
BSC.

The facilities between the BTS and BSC are assumed to be unstructured
TDM because this is a more readily-available circuit type. The connectivity to
the off-net data networks assumes a 80/20 mix of public verse private networks.
The assumption used is that 100 percent of the packet traffic is off-net.
Looking at the BTSs, two different configurations are proposed to help
facilitate different areas of the network. The first shown in Figure 13-6 is for the core area of the network and involves using STD for the transmit
diversity scheme because two carriers are initially needed. One could also
install more antennas if feasible.

Figure 13-7 shows a configuration recommended for the rest of the network
that involves using OTD transmit diversity.
The PN offset assignment scheme that is presented in the earlier part of
the chapter should be used for the system design following an N
19 reuse
pattern for the PN offsets.
Obviously there are more issues that are involved when designing a
CDMA2000 system, but the preceding material should help in the construction
of the thought process to achieve the desired goal of supporting
the customer requirements for service delivery and transport. 550