BER performance with non-costant group delay filter

Hi, I'm trying to set up a Matlab simulation in order to see the effect of real analog base band filter on my receiver. If I use a FIR filter, I generally remove some samples equal to the filter group delay before sending the received vector to the demodulator. If I model a real filter, the group delay is not constant over frequency ( it can vary over the channel bandwidth too) and moreover it is not an integer number. How should I trim the filter output? Thanks Alberto

On Sep 3, 8:02=A0am, "alberto.fuggetta" <alberto.fuggetta@n_o_s_p_a_m.gmail.com> wrote: > Hi, > > I'm trying to set up a Matlab simulation in order to see the effect of re= al > analog base band filter on my receiver. > If I use a FIR filter, I generally remove some samples equal to the filte= r > group delay before sending the received vector to the demodulator. > > If I model a real filter, the group delay is not constant over frequency = ( > it can vary over the channel bandwidth too) and moreover it is not an > integer number. > > How should I trim the filter output? > Thanks > > Alberto You can trim off the transient response of the filter in the same way, but you will be left with distortion at all time instants for the following reason. The frequencies in your signal do not experience identical delay through the filter. If you signal contains little or no power at the frequencies where your filter has a large group delay variation, the distortion could be minimal. An equalizer can be used to compensate for the distortion, or you can change the filter design. John John

alberto.fuggetta wrote: > Hi, > > I'm trying to set up a Matlab simulation in order to see the effect of real > analog base band filter on my receiver. > If I use a FIR filter, I generally remove some samples equal to the filter > group delay before sending the received vector to the demodulator. > > If I model a real filter, the group delay is not constant over frequency ( > it can vary over the channel bandwidth too) and moreover it is not an > integer number. > > How should I trim the filter output? > Thanks If you only want to see what happens with the signal in the dispersive channel, there is no necessity to overcomplicate the problem with equalizers and synchronizers. Just oversample the signal so to adjust the delay to necessary precision. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com

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7/25/2012 3:08:01 AM