User Manual
Airbridge cBTS3612 CDMA Base Station
System Description
2 Hardware Architecture
2-26
1) BTS Intermediate Frequency Unit (BIFU)
BIFU consists of up-c onverter, down-converter, multiplexer/demultiplexer, optical
interface, clock, CPU, and power supply sub-unit. It is in charge of the conversion
between the analog intermediate frequency signals and the digital baseband signals,
and the control of the MTRB. The functions of each sub-unit are as below:
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Up-converter
The up-converter accomplishes the wave filtering, digital up-conversion and
digital-analog conversion of the signals in the transmit path.
On receiving the baseband I/Q signals that have been de-multiplexed, it performs
digital up-conversion after baseband filtering. Then the digital intermediate
frequency signals are converted into analog intermediate frequency signals after
digital-analog conversion and wave filtering. At last, the analog intermediate
frequency signals are sent to the transmitter in BRCU via radio frequency (RF)
interface. BRCU.
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Down-converter
The down-converter accomplishes the analog-digital conversion, digital
down-conversion and baseband filtering of the signals in the receive path.
On receiving the analog intermediate frequency signals via the radio interface, it
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.
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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.
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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.
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Clock
The clock generates all the clocks needed by the BIFU, which include the clocks for
up/down conversion, analog -digital conversion (ADC), and digital-analog conversion
(DAC), and other working clocks. At the same time, it also provides the reference
clock for the BRCU.
