User's Manual

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Chapter 3 System Structure
LTE eNB System Description v2.0 31
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Figure 14. RRH Configuration (RFD01P-13A)
In downlink path, RRH performs O/E conversion for the baseband signals, which
is received from CDU via the optic CPRI. The converted O/E signals are
converted again into analog signals by the DAC.
The frequency of those analog signals is converted upward through the modulator
and those signals are amplified into high-power RF signals through the power
amplifier.
The amplified signals are transmitted to antenna through the filter part.
In uplink path, RF signals received through the filter of RRH are low-noise
amplified in the Low Noise Amplifier (LNA) and their frequency is then down-
converted through the demodulator. These down-converted frequency signals are
converted to baseband signals through the ADC. The signals converted into
baseband are changed to E/O through CPRI and transmitted to CDU.
The control signals of the RRH are transmitted through the control path in the
CPRI.
To save energy, RRH provides the function to turn ON or OFF the power amplifier
output through to the software command set according to traffic changes.
When adjusting the maximum output after the initial system installation, RRH
adjusts the voltage applied to the main transistor through the software command
set in high/low mode to optimize efficiency of the system.
RET
The eNB can support RET function through connection to antenna and RRH,
which satisfies the AISG 2.2 interface.
To provide RET function, eNB transmits/receives the control messages to/from
LSM through the RET controller within LCC4 and CPRI path of CPRI FPGA.
By using this path, LSM can carry out RET function that controls the antenna
tilting angle remotely. In addition, for RET operation, RRH provides power to
every connected antenna.