CDS has applied an innovative approach
to data recovery in our demodulator. Our
digital demodulator operates on a stream
of complex (I/Q) data. When used with
our digital beamforming antenna, this
data stream is an accurate reflection of
the transmitted information translated
to baseband frequencies.
Bit Synchronization
We use band limited differentiation to
enhance the data transitions and feed a
phase-locked loop which is used to
provide the bit synchronization
information. The bit synchronizer
produces a clock for the user, while
also providing the correct data framing
for the subsequent data recovery
process.
Data recovery using multiple
symbols
Once the data has been framed by the bit
synchronizer, we consider a symbol on
either side of the (current) symbol
being demodulated. We estimate the shape
of the phase trajectory around the
current symbol through a 4DOF
curvefitting process. This process
yields a vector of coefficients that is
translated into an element of a ternary
alphabet. The ternary alphabet serves
well to demodulate PCM/FM as well as PSK
modulations. The ternary alphabet
decision is then fed into a state table
to produce the current decision after
considering the previous decisions.
Input and output formatting
The data formatting feature allows the
user to receive and re-format data using
the following formats
NRZ
-L,M,S
Bi-Phase
-L,M,S
PN
-5,6,7,9,11,15,20,23
Tight filtering
Digital filters at the first stage of
the demodulator are tailored to the
modulation scheme being decoded and
serve well to reject noise and enhance
performance.
10 channels
Our Demodulator provides up to 10
channels of 20 Mbps data simultaneously
on a single 6U VME card.
Performance
We can demonstrate demodulation
performance similar to any multi-symbol
demodulator on the market
