Hi,
I understand that simplified equalization is one of the good reasons
for going with OFDM. But, how do they manage it ?
That is,
The OFDM may be viewed as using many slowly-modulated narrowband
signals rather than one rapidly-modulated wideband signal.
So, The Differential modulation such as DPSK / DQPSK if applied to
each sub-carrier, equalization can be completely omitted. ( Reason -
These schemes are insensitive to slowly changing amplitude and phase
distortion )
But, it produces more erroneous demodulations. :(:(

So, how do they overcome this erroneous demodulation scenarios in
WiMAX ? What is the demodulation technique
normally used in overcoming erroneous demodulations w.r.t
DPSK ?

Thx in advans,
Karthik Balaguru

On Jan 6, 8:30 pm, karthikbalaguru <karthikbalagur...@gmail.com>
wrote:
> Hi,
> I understand that simplified equalization is one of the good reasons
> for going with OFDM. But, how do they manage it ?
> That is,
> The OFDM may be viewed as using many slowly-modulated narrowband
> signals rather than one rapidly-modulated wideband signal.
> So, The Differential modulation such as DPSK / DQPSK if applied to
> each sub-carrier, equalization can be completely omitted. ( Reason -
> These schemes are insensitive to slowly changing amplitude and phase
> distortion )
> But, it produces more erroneous demodulations. :(:(
>
> So, how do they overcome this erroneous demodulation scenarios in
> WiMAX ? What is the demodulation technique
> normally used in overcoming erroneous demodulations w.r.t
> DPSK ?

By not using DPSK!  Instead, QAM is used, along with interleaving and
error-correction coding.


--
Oli

On Jan 7, 1:30 am, karthikbalaguru <karthikbalagur...@gmail.com>
wrote:
> Hi,
> I understand that simplified equalization is one of the good reasons
> for going with OFDM. But, how do they manage it ?

assuming no inter symbol interference, the transmit symbol X gets
multplied by channel H to
produce Y (and N is the noise)
Y = HX + N
so, dividing Y by H gives an estimate of X, aka single tap equalizer.

> That is,
> The OFDM may be viewed as using many slowly-modulated narrowband
> signals rather than one rapidly-modulated wideband signal.
> So, The Differential modulation such as DPSK / DQPSK if applied to
> each sub-carrier, equalization can be completely omitted. ( Reason -
> These schemes are insensitive to slowly changing amplitude and phase
> distortion )

hmm... I do not follow your train of thoughts. Phase okay, but how do
you extent to amplitude?

> But, it produces more erroneous demodulations. :(:(

:)

>
> So, how do they overcome this erroneous demodulation scenarios in
> WiMAX ? What is the demodulation technique
> normally used in overcoming erroneous demodulations w.r.t
> DPSK ?

Nice write up on DBPSK
http://tinyurl.com/2l9ukh

~
Krishna
http://www.dsplog.com