Reverse Channel

The reverse link or channel for CDMA2000 has many similar properties as
the forward link and therefore differs significantly from that used in IS-95.
One of the major differences or rather enhancements to CDMA2000 over
IS-95 is the inclusion of a pilot on the reverse link. The structure of the
reverse channel for CDMA2000 is shown in Figure 7-20.
Elaborating on the reverse channel, the subscriber, or mobile, is allowed
to transmit more than one code channel to accommodate the high data
rates. The minimum configuration consists of a Reverse Pilot (R-Pilot) channel
to enable the base station to perform synchronous detection and a
Reverse Fundamental Channel (R-FCH) for voice. The inclusion of additional
channels, such as the Reverse Supplemental Channels (R-SCHs) and
the Reverse Dedicated Control Channel (R-DCCH) can be used to send data
or signaling information. The association between the radio configuration
and the spreading rates is best shown in Table 7-9. It is important to note
that the reverse channel for 3X is different than 1X in that it is a direct
spread but can be overlaid over a 1X implementation. Depending on the
subscribers operating in that sector, the appropriate SR and RC are then
selected.
The following are some of the Reverse Link channel descriptions:
■ Reverse Supplemental Channel (R-SCH) When data rates are
greater than 9.6K, a R-SCH is required and also a R-FCH is also assigned for power control. A total of one or two R-SCHs can be
assigned per mobile.
■ Reverse Pilot Channel (R-PICH) The R-PICH provides pilot and
power control information. The R-PICH enables the mobile to transmit
at a lower power level and allows the mobile to inform the base station
of the forward power levels being received, enabling the base station to
reduce power.
■ Reverse Dedicated Control Channel R-DCCH This replaces the
dim and burst and the blank and burst. It is used for messaging and
control for data calls.
■ Reverse Enhanced Access Channel (R-EACH) This is meant to
minimize the collisions and therefore reduce the access channel’s
power.
■ Reverse Common Control Channel (R-CCCH) Used by mobiles
to send their data information after they have been granted access.
Table 7-7 helps to quantify the reverse channel types and the quantity of
each for CDMA2000, both 1X and 3X.