User Manual
iSiteC BTS3601C CDMA Base Station
System Description
Chapter 3 System Function
3-9
VIII. Power control
Coordinating with the MS and BSC, BTS provides various power control mechanisms
(as detailed in Section 3.4.1 Power Control).
3.3 Baseband Processing
Baseband processing performs physical layer functions on Um interface, and
processes baseband data of all full-duplex channels in CDMA system.
In the forward direction (transmitting direction), baseband processing fulfills channel
coding, rate adaptation, interleaving, spreading spectrum and modulation. In the
reverse direction (receiving direction), it fulfills multi-path signaling demodulation,
de-interleaving, channel decoding and information bit extraction.
For different Radio Configuration (RC), baseband processing is different. But basically
it can be summarized into the following procedures:
I. Forward channel baseband processing
In CDMA forward channel, the baseband processing of one traffic channel includes
channel coding, rate adaptation, block interleaving, long code scrambling, power
control bit insertion, Walsh code spreading spectrum, signal modulation and
baseband filtering, as shown in Figure 3-5.
Channel
coding
Rate
adaptation
Block
interleave
Long code
scrambling
Walsh code
spreading
spectrum
QPSK
modulation
Baseband
filtering
Channel
coding
Rate
adaptation
Block
interleave
Long code
scrambling
Walsh code
spreading
spectrum
QPSK
modulation
Baseband
filtering
Figure 3-5
Baseband processing in forward channel
l
Channel coding
CDMA system uses Convolutional code and Turbo code for channel coding. Its
function is error correction. Convolutional code is used for ordinary speech service
and Turbo code for high-speed data service.
l
Rate adaptation
Since the system supports frames of different rates. The frame rates after channel
coding are different. Rates should be adapted to ensure that the rate of frames meets
the requirement before entering the interleaver. In CDMA system, rate adaptation is
realized by symbol repetition and code puncturing.
l
Block interleaving
The purpose of interleaving is to resist fast fade in the radio channel environment.
l
Long code scrambling
