AM SSB demodulation

Tim Wescott wrote:

   ...

> He's got two baseband signals: inphase and quadrature.  It's the 
> mathematicians way of expressing a phasing-method SSB demodulator.  In 
> the real world you don't have r(t) = m(t) + j m(t) * h(t), you have the 
> inphase and quadrature channels from a dual-mixer system that were 
> separately demodulated.


That can't be the whole story. He to demodulate them. If they are what
you say, which is what he seems to say but which I doubt (what does
one-sided AROUND the origin mean?), then either the I or Q parts (or
their sum or difference!) will do. What do you make of the overall phase
term that he thinks is bothersome? He clearly has a receiver in mind.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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Jerry Avins wrote:

> Tim Wescott wrote:
> 
>   ...
> 
>> He's got two baseband signals: inphase and quadrature.  It's the 
>> mathematicians way of expressing a phasing-method SSB demodulator.  In 
>> the real world you don't have r(t) = m(t) + j m(t) * h(t), you have 
>> the inphase and quadrature channels from a dual-mixer system that were 
>> separately demodulated.
> 
> 
> 
> That can't be the whole story. He to demodulate them. If they are what
> you say, which is what he seems to say but which I doubt (what does
> one-sided AROUND the origin mean?), then either the I or Q parts (or
> their sum or difference!) will do. What do you make of the overall phase
> term that he thinks is bothersome? He clearly has a receiver in mind.
> 
> Jerry

You're right, that can't be the whole story.  I think one-sided AROUND 
the origin just means that it's a hard concept to describe gracefully. 
I grant other intelligent people infinite rights to sticking their feet 
in their mouths as long as they'll forgive me when I do it.  I'm 
deducing I and Q parts from his math; when you're playing around inside 
a DSP it's often easier to pretend that a pair of real numbers is one 
complex number -- it's what I'd do, even if I'd call them I and Q if I 
were implementing a radio in hardware.

I have no idea why he thinks the phase term is bothersome.

Vikram, why do you think the phase term is bothersome?  If you're 
demodulating speech the phase term doesn't matter.  If you're 
demodulating Hi-Fi you're (probably) wasting your time -- what gives?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Hello all,
 Let me start from basics.

Transmitter:
----------

m(t): message signal
mh(t): Hilbert transform of m(t)
fc: carrier frequency
s(t): transmit passband signal

s(t)=Re{[m(t)+j*mh(t)]*exp(j*2*pi*fc*t)}=m(t)cos(2*pi*fc*t)-mh(t)sin(2*pi*fc*t)

At receiver, the oscillator may have a frequency ambiguity and phase
ambiguity.

Receiver:
-------
received signal: s(t)
sh(t): Hilbert transform of
s(t)=m(t)sin(2*pi*fc*t)+mh(t)cos(2*pi*fc*t)
                                             
=[m(t)+j*mh(t)]*exp(2*pi*fc*t)
Recovered baseband signal=[s(t)+j*sh(t)]*exp(-2*pi*fc1*t-phi)
                                        
=[m(t)+j*mh(t)]*exp(2*pi*(fc-fc1)*t-phi)
where fc1 is the receiver mixer frequency and phi is a phase ambiguity


I figured out that adding a tone that is known to both TX and RX helps
remove the phase/freqency
offset ambiguity.

I hope this mail makes it clear that my system model representing the
equivalent baseband model is accurate.

Thanks
Vikram









"Matt Timmermans" <mt0000@sympatico.nospam-remove.ca> wrote in message news:<Kgbfc.13037$vF3.1239825@news20.bellglobal.com>...
> Hi Vikram,
> 
> > I am trying to demodulate an AM SSB (single side band) baseband
> > signal. Are there any standard techniques/papers for AM SSB baseband
> > demodulation in the presence of arbitrary phase/frequency offsets?
> 
> Since that sort of offset can be simulated by the signal, you'll need to
> correct the offset before the signal can be recovered.  The easiest way to
> do that is with accurate oscillators.  If you really can't do that, then
> you'll need to add some information to the transmission that will let the
> receiver sync to the correct carrier frequency.