Huawei Airbridge BTS3612A-1900 Technical Manual page 32

Technical Manual
Airbridge BTS3612A CDMA Base Station
On receiving the analog intermediate frequency signals via the radio interface, the
down-converter converts them into digital intermediate frequency signals via
analog-digital conversion. Then the digital intermediate frequency signals are
converted into baseband I/Q signals via digital down-conversion and baseband filtering.
As last, the I/Q signals are transmitted to the demultiplexer/multiplexer.
Demultiplexer/multiplexer
Under the control of the CPU, the demultiplexer/multiplexer de-multiplexes the forward
I/Q signals, and multiplexes the reverse I/Q signals. At the same time, it
multiplexes/de-multiplexes the operation & maintenance (O&M) signals of the OML.
Optical interface
The optical interface performs channel coding and decoding, and accomplishes
optical-electrical signal conversion and electrical-optical signal conversion. It is the
interface between the BIFU and the BRDM of the upper-level BTS, and the interface
between the BIFU and the MTRM (Micro-bts Transceiver Module) in the lower-level
SoftSite.
Clock
The clock generates all the clock signals needed by the BIFU, which include the clocks
for up/down conversion, analog-digital conversion (ADC), and digital-analog
conversion (DAC), as well as other working clocks. It also provides the reference clock
for the BRCM.
CPU
The CPU is in charge of the control of BTRM, which includes the initialization upon
power-on, alarm collecting and reporting, and processing operation & maintenance
related messages.
Power supply
With input voltage of +24V, the power supply sub-unit provides power supply to BIFU
and BRCU.
II. BRCM
The BRCM consists of transmitter, main/diversity receiver and local oscillator. It
up-converts, amplifies the intermediate frequency signals output by BIFM, and
performs spuriousness-suppression wave filtering. It also performs analog
down-conversion, amplification of BTS main/diversity receiving signal input from the
RLDU, and channel-selection wave filtering. The functions of each sub-unit are as
below.
Transmitter
When receiving the modulated analog intermediate frequency signals output by BIFM,
the transmitter converts them to specified RF band via two times of up-conversions.
Before and after the up-conversion, wave filtering, signal amplification and power
Chapter 3 Radio Frequency Subsystem
3-4
System Principle