MINI-LINKEandEMicro
Composite Rates
The following composite bit rates are used:
• 4.5195 Mbit/s for 2x2 Mbit/s
• 8.9316 Mbit/s for 4x2/8 Mbit/s
• 17.6071 Mbit/s for 2x8 Mbit/s
• 37.5369 Mbit/s for 34+2 Mbit/s
3.8.2.4 Modulator
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
transmit spectrum .
The modulator consists of a phase locked Voltage Controlled Oscillator (VCO)
operating at 350 MHz. For test purposes an IF loop signal of 140 MHz is
generated by mixing with a 490 MHz signal.
* C-QPSK (Constant envelope offset - Quadrature Phase Shift Keying) is an
offset-QPSK phase modulated signal. It is optimized for high frequency
efficiency since it combines the properties of constant envelope with high
interference discr imination.
3.8.2.5 Radio Frame Demultiplexer and Forward Error Correction (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 alarm 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. S tuffing control
bits are processed for the traffic and service channels.
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AE/LZT 110 2012 R8C 2002- 03-04
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