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
DPSK's relation with OFDM and Demodulation
Started by ●January 6, 2008
Reply by ●January 6, 20082008-01-06
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
Reply by ●January 7, 20082008-01-07
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