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1.2 Radio configuration
Radio configuration (RC) defines the physical channel configuration
based upon a specific channel data rate. Each RC specifies a set of data
rates based on either 9.6 or 14.4 kbps. These are the two existing data rates
supported for cdmaOne. Each RC also specifies the spreading rate (either
SR1 or SR3) and the physical coding. Currently there are nine radio
configurations defined in the cdma2000 system for the forward link and
six for the reverse link. Examples are:
• RC1 is the backwards compatible mode of cdmaOne for 9600-bps
voice traffic. It includes 9.6, 4.8, 2.4, and 1.2 kbps data rates and
operates at SR1. It does not use any of the new cdma2000 coding
improvements.
• RC3 is a cdma2000-specific configuration based on 9.6 kbps that
also supports 4.8, 2.7, and 1.5 kbps for voice, while supporting data
at 19.2, 38.4, 76.8, and 153.6 kbps and operates at SR1.
Each base transceiver station (BTS) or MS must be capable of transmitting
using different RCs at the same SR. Refer to [2] for detailed information on
the different RCs.
1.3 Forward link air interface
The forward link air interface for a cdma2000 SR1 channel is very similar
to that of cdmaOne. In order to preserve compatibility, cdma2000 uses the
same structure as cdmaOne for the forward pilot (F-Pilot), forward sync
(F-Sync), and forward paging (F-Paging) channels.
In cdma2000, each user is assigned a forward traffic (F-Traffic) channel,
which consists of
• zero to one forward fundamental channel (F-FCH)
• zero to seven forward supplemental code channels (F-SCCHs)
for RC1 and RC2
• zero to two forward supplemental channels (F-SCHs) for RC3 to RC9
• zero to one forward dedicated control channels (F-DCCHs)
The F-FCHs are used for voice and the F-FCCHs and F-SCHs are used for
data. The BTS may also send zero or one F-DCCHs. An F-DCCH is associated
with traffic channels (either FCH, SCH, or SCCH) and may carry signaling
data and power control data.
One of the main differences between cdmaOne and cdma2000 is that the
latter uses true quadrature phase shift keying (QPSK) modulation (as
opposed to dual-BPSK) for all traffic channels from RC3 to RC9. As an
example, Figure 2 shows the forward link structure for an RC4 F-FCH. The
coding is identical to cdmaOne up through the long code scrambling of the
voice data. The F-FCH is optionally punctured with the reverse link power
control data bits. The data is then converted from a serial bit stream into a
two-bit wide parallel data stream to produce true QPSK modulation. This
reduces the data rate of each stream by a factor of two. Each branch is
spread with a 128 Walsh code to generate a spreading rate of 1.2288 Mcps.
In this case, the processing gain is doubled for each channel relative to
cdmaOne. Each channel is transmitted at one-half the power used before,
but there are now two of them for no apparent gain. The actual processing
gain for each channel depends on its data rate and RC.
The outputs of the I and Q Walsh spreaders are then complex multiplied
against the same I and Q channel short codes used in cdmaOne. Complex
scrambling is used in the forward link instead of regular scrambling
because it is a more robust scheme against interference.
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