Forward Channel

The forward link for a CDMA2000 channel, whether for 1X or 3X implementation,
utilizes the structure shown in Figure 7-19.
Reviewing the channel structure, the base station transmits multiple
common channels as well as several dedicated channels to the subscribers
in their coverage area. Each CDMA2000 user is assigned a forward traffic
channel that consists of the following combinations. An important point to
note is that F-FCHs are used for voice, while F-SCHs are for data.
■ 1 Forward Fundamental Channel (F-FCH)
■ 0–7 Forward Supplemental Code Channels (F-SCHs) for both RC1
and RC2
■ 0–2 Forward Supplemental Code Channels (F-SCHs) for both RC3
and RC9
When the channel is associated with a 3XRTT implementation, the data
for the subscriber is mapped to each of the three different carriers, enabling
the high throughput. However, the Walsh codes are the same for each carrier,
meaning they share the same throughput, distributing the traffic load
evenly.
The CDMA2000 channel utilizes different modulation schemes depending
on the radio configuration that is employed. The description of the radio
configurations are shown later. However, the modulation scheme used for
RC1 and RC2 is Binary Phase Shift Keying (BPSK), while Quadrative
Phase Shift Keying (QPSK) is used for RC3-RC9. For RC3 through RC9, the
data is converted into a two-bit-wide parallel data stream that initially
would seem counterintuitive because it reduces the data rate for each
stream by a factor of two. Each data stream, however, is then spread by a
128 Walsh code to get the spreading rate up to 1.2288 Mbps, which effectively
doubles the processing gain, allowing for greater throughput at the
same effective power level.
The following are some forward channel descriptions:
■ Forward Supplemental Channel (F-SCH) Up to two F-SCHs can
be assigned to a single mobile for high-speed data ranging from 9.6K
to 153.6K in release 0 and 307.2 Kbps and 614.4 Kbps in release A. It
is important to note that each F-SCH assigned can be assigned at
different rates. The F  SCH must be assigned with a R-SCH when
only one F-SCH is assigned.
■ Forward Quick Paging Channel (F-QPCH) The quick paging
channel enables the mobile battery life extension by reducing the
amount of time the mobile spends parsing pages that are not meant
for it. The mobile monitors the F-QPCH and when the flag is set, the
mobile looks for the paging message. There are a total of three F-QPCH
channels per sector.
■ Forward Dedicated Control Channel (F-DCCH) This replaces
the dim and burst and the blank and burst. It is used for messaging
and control for data calls.
■ Forward Transmit Diversity Pilot Channel (F-TDPICH) This is
used to increase RF capacity.
■ Forward Common Control Channel (F-CCCH) This is used to
send paging, data messages, or signaling messages.
Table 7-6 helps to quantify the channel types and quantity of each for
CDMA2000, both 1X and 3X.