Ericsson MINI-LINK E - Descrambling and FEC Decoding; Transmit Baseband Signal Processing

MINI-LINKEandEMicro
4.4.3 Transmit Baseband Signal Processing
The c omposite data stream from the Radio Frame Mul tiplexer is C-QPSK*
modulated, D/A converted and pulse shaped in a Nyqvist filter to optimize the
transm it spectrum.
*C-Q
PSK (Constant envelope offset – Quadrature Phase Shift Keying) is
an of
fset-QPSK phase modulated signal. It is optimized for high frequency
effi
ciency since it combines the properties of constant envelope with high
inte
rference discrimination.
4.4. 4 Radio Frame Demulti plexer and Forward Error Corre ction (FEC)
On the receiving side the received composite data stream is demultiplexed and
FEC corrected. The frame alignment function searches and locks the receiver
to the frame alignment bit patterns i n t he received data stream.
Descrambling and FEC decoding
FEC is accomplished using FEC parity bits in combination with a data quality
measurement from t he demodulator. The descrambler transforms the signal to
its original state enabling the demultiplexer to properly distribute the received
inform ation to its destinations.
Demultiplexing
Demultiplexing is perfor med according to the stored frame for m at. The
demultiplexer generates a frame fault alar m if frame synchronization is lost.
The number of errored bits in the traffic data stream is measured using parity
bits. These are used for BER detection and performance monitoring. Stuffing
control bits are processed for the traffic channels
Received Traffic Data
On the receiving side the following is performed to the traffic data:
• AIS insertion (at signal loss or BER ≤ 10
–3
)
• AIS detection
• Elastic buffering and clock recover y
4.4.5 Receive Baseband Signal Processing
The received 140 MHz signal is AGC amplified and filtered before conversion
to I/Q baseband signals. The baseband signals are pulse shaped in a Nyqvist
filter and A/D converted before being C-QPSK demodulated.
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AE/LZT 110 2012 R8C 2002- 03-04