Hi guys,
I am trying to analyze the functionality of each of the blocks in the dbpsk
mod/demod when I noticed the following behavior.
The high level modulator flow control is as | Symbols |-> | RRC filter |
-> |amplifier | -> channel
and that for the demodulator is channel -> | Pre-scaler| ->
|agc| -> |RRC | -> |clock recovery| -> |slicer|
My understanding is that the real part of the output of the clock recovery
must be close to that of the symbols or some scaled version of it(+a, -a in
case of bpsk).
However, my observations (in the link below) show that the output of the
clock recovery depends a lot on the bit pattern, i.e., for the bit pattern
1010 the peaks of the 1s and the 0s are way smaller than those of the bit
pattern 1111110000.
http://nms.csail.mit.edu/~gshyam/data/clock.pdf
Since we are using a RRC I would doubt it is due to ISI . and since the
radios are close to each other and there is a direct LOS I donot think this
is due to multi-path (or is it?). Is this behavior due to some component on
RFX 2400/USRP or something else?
thanks
Shyam
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