On 10/18/07, Johnathan Corgan <[EMAIL PROTECTED]> wrote:
> One approach then would be to ensure this never happens, i.e., add a
> small epsilon to each input stream, and make epsilon small enough to not
> sufficiently impact the results for "typical" input values. Normalizing
> the conjugate product will then give you the cosine as the real value,
> as you mentioned. Or, you could just divide the abs value into the real
> value of the product, and avoid the extra calculation of the normed
> imaginary part which you are going to throw away.
Thanks for the replies guys. The above is the approach I went with.
It seems to work well, and gave a further BER improvement to my GMSK demod
experiments.
For those interested, here is how I'm using it in the context of GMSK demod:
self.kc = gr.kludge_copy(gr.sizeof_gr_complex)
self.delay = gr.delay(gr.sizeof_gr_complex,
2*self._samples_per_symbol) #2T delay
self.conj = gr.conjugate_cc()
self.mult = gr.multiply_cc()
self.c2mag = gr.complex_to_mag()
self.safety_add = gr.add_const_ff(0.0000001)
self.c2f = gr.complex_to_float()
self.rescaler = gr.divide_ff()
self.sub = gr.add_const_ff(-self._decision_threshold)
samp_per_sec = samples_per_symbol * sym_per_sec
pre_cr_filt_bw = sym_per_sec*pre_cr_filt_bt
pre_cr_filt_taps = gr.firdes.low_pass(1.0, samp_per_sec,
pre_cr_filt_bw, pre_cr_filt_tr*samp_per_sec, gr.firdes.WIN_HAMMING)
self.pre_cr_filt = gr.fir_filter_fff(1, pre_cr_filt_taps)
# the clock recovery block tracks the symbol clock and resamples as
needed.
# the output of the block is a stream of soft symbols (float)
self.clock_recovery = gr.clock_recovery_mm_ff(self._omega,
self._gain_omega,
self._mu,
self._gain_mu,
self._omega_relative_limit)
# slice the floats at 0, outputting 1 bit (the LSB of the output
byte) per sample
self.slicer = gr.binary_slicer_fb()
[...]
# Connect & Initialize base class
self.connect(self, self.kc, self.delay, self.conj, (self.mult, 0))
self.connect(self.kc, (self.mult, 1))
self.connect(self.mult, self.c2f, (self.rescaler, 0))
self.connect(self.mult, self.c2mag, self.safety_add, (self.rescaler,
1))
self.connect(self.rescaler, self.pre_cr_filt, self.sub,
self.clock_recovery, self.slicer, self)
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