Functions
The GRFU performs modulation and demodulation of baseband signals and RF signals,
processes data, and combines or divides signals.
The GRFU has the following functions:
l
Implements the direct frequency conversion technique in the transmit channel, modulates
the baseband signals to GSM RF signals; then sends the signals to the antenna for
transmission through the duplex filter after filtering, amplifying, and combining the RF
signals (the combining can be performed as required)
l
Receives RF signals from the antenna and performs down-conversion, amplification,
analog-to-digital conversion, digital down-conversion, matched filtering, and Automatic
Gain Control (AGC), and then transmits the signals to the BBU for further processing
l
Provides power control and Voltage Standing Wave Ratio (VSWR) detection
l
Provides reverse power detection
l
Provides frequency synthesis and loopback test
l
Generates the CPRI clock, recovers the CPRI clock of lost synchronization, and detects
alarms
The GRFU consists of the high-speed interface unit, signal processing unit, power amplifier,
and duplexer.
shows the logical structure of the GRFU.
Figure 4-32
Logical structure of the GRFU
The High-speed interface unit has the following functions:
l
Transmits the signals received from the BBU to the signal processing unit
l
Transmits the signals received from the signal processing unit to the BBU
The signal processing unit consists of two UL RX channels and one DL TX channel.
l
The UL RX channel has the following functions:
–
Performs down-conversion of the RF signals to IF signals
–
Amplifies the IF signals and performs IQ demodulation
–
Performs analog-to-digital conversion through the ADC
4 BTS3900 Components
BTS3900
Hardware Description
4-40
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Issue 04 (2011-02-15)