On Tue, 18 Jun 2013 05:46:25 -0500, manishp wrote:
> Sirs,
>
> For some of the cellular communications standards, multiple modulations
> schemes are adopted (16QAM, 64QAM etc.). I have feq questions on this,
>
> - are these modulation used for modulation of carrier signals or this
> is baseband related modulation
If you can tell me how to get a quadrature signal out of a baseband
channel, I will tell you that 16QAM is used in baseband.
Otherwise you need a carrier.
> -- assuming this is for carrier modulation, how does the receiver know
> what modulation has been done used while transmission
Presumably there's a protocol that dictates how the receiver will know.
Find the applicable standard, and read.
> -- if 16QAM, 64QAM is not for carrier modulation, what modulation is
> used for the carriers
Once again, this information is in the applicable standard.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply by Eric Jacobsen●June 18, 20132013-06-18
On Tue, 18 Jun 2013 05:46:25 -0500, "manishp" <58525@dsprelated>
wrote:
>Sirs,
>
>For some of the cellular communications standards, multiple modulations
>schemes are adopted (16QAM, 64QAM etc.). I have feq questions on this,
>
>- are these modulation used for modulation of carrier signals or this is
>baseband related modulation
I'm not sure what you mean by this. QAM is a "suppressed carrier"
modulation, like PSK. The signal can be generated at baseband and
then just translated up to the IF/RF frequency with a mixer.
>-- assuming this is for carrier modulation, how does the receiver know what
>modulation has been done used while transmission
It either has to know ahead of time or there has to be signalling in a
framing structure (or otherwise available) to tell the demodulator
what is being transmitted. Cellular systems usually have a control
channel, either a separate channel or a sub-channel within a
transmitted stream, that tells the configuration for the receiver.
Many systems have multiple modulation schemes, with some being
adaptive to automatically adjust to channel conditions. Signalling
tells the receiver what to expect. e.g., in 802.11 there is a header
that is always transmitted in BPSK that tells how the next part of the
transmission is modulated and coded.
>-- if 16QAM, 64QAM is not for carrier modulation, what modulation is used
>for the carriers
I think you have some misconceptions about "carriers" and modulation.
Often the "carrier" is just the center frequency of the signal (like
it is for QAM).
>Thanks, manish
>
>_____________________________
>Posted through www.DSPRelated.com
Sirs,
For some of the cellular communications standards, multiple modulations
schemes are adopted (16QAM, 64QAM etc.). I have feq questions on this,
- are these modulation used for modulation of carrier signals or this is
baseband related modulation
-- assuming this is for carrier modulation, how does the receiver know what
modulation has been done used while transmission
-- if 16QAM, 64QAM is not for carrier modulation, what modulation is used
for the carriers
Thanks, manish
_____________________________
Posted through www.DSPRelated.com