>
> It appears {I(t),Q(t)} is baseband signal. I guess w is the carrier
> frequency at RF level.
>
> From your Eqs,
> I(t)= A(t)cos(phi(t))
> Q(t)= -A(t)sin(phi(t))
>
> So A(t)=sqroot(I(t)^2+ Q(t)^2)
> phi(t)=arg(-Q(t)/I(t))
>
> From your Eqn. I expect "bw of rf signal/baseband signal" only
> depends on
> phi(t)- wonder why you suspect "good estimate"! Secondly "bw of
> cos(phi(t))" hardly makes any sense!
>
> Regards,
> Santosh
>
> >
Well, bandwidth at passband is not supposed to depend on carrier frequency
value.
In cos(wt + phi(t)) , you set carrier freq to zero and you get
cos(phi(t)).
Reply by santosh nath●September 18, 20032003-09-18
kbc32@yahoo.com (kbc) wrote in message news:<a382521e.0309170414.10b3c684@posting.google.com>...
> Hi,
>
> The bandwidth in quadrature modulation is typically
> assumed to be max(B1,B2) where
> B1 = bandwidth of I(t)
> B2 = bw of Q(t)
>
> rf signal = I(t) cos wt + Q(t) sin wt = A(t) cos(wt + phi(t) )
> w = carrier frequency
>
> It seems to me that for a given amount of phase change
> happening during a given time, constraining the envelope
> to remain constant increases the bandwidth. If yes , why ?
>
> ( Notice that in GMSK-GSM, the maximum phase variation allowed
> during a symbol is pi/2 which happens if 3 consecutive bits
> are identical. But in QPSK with same symbol rate, even
> pi phase change is possible per symbol duration. ) I assume
> that for same symbol rate, GMSK and QPSK are going to take
> approximately the same bandwidth. I dont have the data in
> front of me .
>
> Quadrature modulation will result in phase/frequency modulation
> of the carrier. This should result in consuming more bandwidth
> than that of I(t) or Q(t). Why this does not happen ?
>
> Does bw of cos(phi(t)) give a good estimate of bw of rf signal ?
It appears {I(t),Q(t)} is baseband signal. I guess w is the carrier
frequency at RF level.
From your Eqs,
I(t)= A(t)cos(phi(t))
Q(t)= -A(t)sin(phi(t))
So A(t)=sqroot(I(t)^2+ Q(t)^2)
phi(t)=arg(-Q(t)/I(t))
From your Eqn. I expect "bw of rf signal/baseband signal" only
depends on
phi(t)- wonder why you suspect "good estimate"! Secondly "bw of
cos(phi(t))" hardly makes any sense!
Regards,
Santosh
>
> thanks
> shankar
Reply by kbc●September 17, 20032003-09-17
Hi,
The bandwidth in quadrature modulation is typically
assumed to be max(B1,B2) where
B1 = bandwidth of I(t)
B2 = bw of Q(t)
rf signal = I(t) cos wt + Q(t) sin wt = A(t) cos(wt + phi(t) )
w = carrier frequency
It seems to me that for a given amount of phase change
happening during a given time, constraining the envelope
to remain constant increases the bandwidth. If yes , why ?
( Notice that in GMSK-GSM, the maximum phase variation allowed
during a symbol is pi/2 which happens if 3 consecutive bits
are identical. But in QPSK with same symbol rate, even
pi phase change is possible per symbol duration. ) I assume
that for same symbol rate, GMSK and QPSK are going to take
approximately the same bandwidth. I dont have the data in
front of me .
Quadrature modulation will result in phase/frequency modulation
of the carrier. This should result in consuming more bandwidth
than that of I(t) or Q(t). Why this does not happen ?
Does bw of cos(phi(t)) give a good estimate of bw of rf signal ?
thanks
shankar