Huawei BTS3 Series Hardware Description Manual page 109

M900/M1800 BTS3X Series Base Transceiver Station
Hardware Description Manual
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Issue 01 (2006-11-18)
When the signals received from one path is in poor quality due to complicated radio
transmission condition, there are different signal qualities if the other path receives
signals from other paths.
The BTS receives signals from two channels, that is, main set and diversity. It is possible
to provide 3 dB to 5 dB of diversity gain to improve communication quality after
demodulation with combining algorithm.
Each channel of receiving path is made up of a primary down-conversion circuit. The
receiving signals are sent to frequency mixer to generate an intermediate-frequency (IF)
signal. The IF signals are amplified to a certain level to be sent to the base band part for
digital demodulation.
TDP
The TDP includes the transmitting excitation unit, frequency synthesizer and loop test
unit.
Transmitting excitation unit
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The transmitting process is in direct modulation mode. The transmitting excitation
unit modulates the I and Q signals sent from TBPU into the RF signals needed for
transmitting with the quadrature modulator. The modulated signals provide PAU with
a certain power level.
Transmitting excitation unit also provides the dynamic and static power control for
BTS. The static power control is defined during network planning to decide the
maximum transmitting power of BTS. Dynamic power control is implemented during
the process of communication. The static power levels are Level 0 to 9, and the
decrease step is 2 dBm. The levels of dynamic power control are Level 0 to 15, and
the decrease step is 2 dBm.
To lower the noise level in radio environment, and improve network capacity and
QoS, it is necessary to lower the transmitting power of BTS as much as possible
without harming the QoS, so that each TCH is at the lowest dynamic power level, and
the transmitting power of idle channels is closed. Transmitting excitation unit also
supports PA over-power alarm signal. An alarm will be generated when the output
power of PA exceeds the set level by 3 dB.
Frequency synthesizer
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The frequency synthesizer is crucial to the entire transceiver. It generates various
local oscillations of transceiving up and down-conversion, such as transmitting
oscillation, receiving oscillation and loop test local oscillation. Both transmitting
local oscillation and receiving local oscillation have two loops for FH loop switching.
Loop test unit
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Loop test unit is designed for TRX loop test. It attenuates part of the signals coupled
at the output terminal of PAU to the receiving band, and then sends them to the
receiver after coupling. Its major function is to test the operation of TRX transmitting
channel and receiving channel.
PAU
The PAU amplifies the radio signal. The maximum output power of the PAU is 47.8dBm.
The PAU also provides the feedback sampling signals controlled by transmitting APC
and the following alarm signals:
Over temperature alarm: When the temperature of PA is over 85 ÿC, the PAU reports
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the over temperature alarm via base band unit, and automatically closes the PAU.
Standing wave alarm: When the output standing wave exceeds 3.5, the PAU reports
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this alarm to base band unit.
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