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Odd Order of Hilbert Transform Question?

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xie.qiang

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Hi All,

I have a baseband signal 0Hz~48KHz, and sampling rate is Fs = 1.536MHz, I need to mix this base signal to IF, which is about 384KHz, but when doing mix, I do not want the Double-Side-Band (DSB) signal but Single-Band-Signal (SSB), so I will considering design a Hilbert transform to mix my base band signal to IF. Since there are two types of Hilbert FIR, even order with integer group delay and odd order with non-integer group delay,
even order Hilbert have non-flatness at high frequency band, but odd order have.
So, what I am trying is using the flatness of Hilbert response of high frequency band, and I am doing the following step:
Step(1): mix my base baseband signal to high-frequency, near Fs/2 by a carry frequency of Fs/2, then all my baseband signal become to high-frequency signal.
Step(2): Applying the odder order Hilbert FIR to my signal, then I get delay path xd and Hilbert path output xh with a difference of 0.5 non-integer delay, which is:
|---Delay---xd(n)---->
x(n)---|
|---HT-FIR--xh(n)---->

Step(3): (also become my big problem!!!!!!!!).
Interpolate the xd(n) and xh(n) to xd2(n) and xh2(n), one path shift one more sample unit.
After doing this, I can get my Hilbert transform for the x(n), but at this time, the spectrum shifts, and introduce one more un-desirable spectrum, and it is very hard to filter (because of the double side spectrum is so close, equal to zero!!!)..

What I am asking now is there any way that I do not use a x2 interpolation to get the non integer delay, then I can escape those problems? Or Is there any ways to translate a baseband signal to bandpass signal as well as convert the bandpass signal to SSB rather than DSB???
 

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