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Technical Manual
Airbridge BTS3612A CDMA Base Station
7.2 Abis Traffic Signal Flow
The Abis traffic is carried by the Fundamental Channel (FCH), the Supplemental
Channel (SCH) and the Dedicated Control Channel (DCCH). The FCH and DCCH
carry voice traffic and inband signal, while the SCH carries data traffic.
The Abis traffic signal flow is represented by the red continuous line in Figure 7-1. The
following introduces the signals in the forward and the reverse directions respectively.
I. Forward
1)
The ATM cells from the BSC are carried by E1/T1 links to the BCIM. The BCIM
processes the ATM cells through the IMA, and then under the control of BCKM
sends the signal to the BCPM through the Cell Bus.
2)
The BCPM completes channel processing. The baseband signals carrying the
Abis traffic (received over the FCH, SCH and DCCH) from the BCIM are coded,
interleaved, spread, modulated and multiplexed by the BCPM before being sent to
the BRDM over the electrical Gbit Ethernet interface.
3)
The BRDM allocates channel resources, and sends the baseband signals over the
optical Gbit Ethernet interface to the BTRM.
4)
The BTRM performs demultiplexing, up-conversion and wave filtering on the
received baseband signals, and sends them to the BHPA.
5)
The BHPA amplifies the signals and forwards them to the DDU, from where the
signals will be transmitted by the antenna.
II. Reverse
In the reverse direction the signals are handled in the reverse order.
1)
Through the main and diversity antennae, the DDU receives two CDMA signals
transmitted from the MS. After being divided and amplified by the RLDU, the
signals are sent to the BTRM.
2)
The BTRM performs wave filtering, down-conversion and multiplexing on the main
and diversity signals, and sends them to BRDM over the optical Gbit Ethernet.
3)
The BRDM allocates channel resources, and sends the baseband signals over the
electrical Gbit Ethernet interface to the BCPM.
4)
The BCPM completes channel processing. The baseband signals carrying the
Abis traffic (received over the FCH, SCH and DCCH) from the BRDM are
demultiplexed, demodulated, de-interleaved and decoded by the BCPM. Then
under the control of BCKM, the obtained signals are sent to the BCIM over the Cell
Bus in form of ATM cells.
5)
The ATM cells are processed by the BCIM through the IMA, and then sent to the
BSC over the E1/T1 link.
7-3
System Principle
Chapter 7 BTS Signal Flows
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