Which modulation scheme is the best

Hi,
I am trying to design a modem so can anyone tell me which is the best modulation scheme for wired communicatiion.

I am confused between qpsk,gmsk and bpsk which is the best.
On what factor u determine the best.

Hi dspbegin,

it depend on channel limitation and complixity of implimentation.
but about chennel constrant this cases can be noted:

Interference limitation (sp. multiuser) => CPM (e.g. GMSK)
power limitation (sp. in fading channel)=> QPSK
Bandwidth limitation (sp. cable channel and MW links) => QAM

regards

Mod/Demod schemes can also be decided based on the following criterions as there should be a balance in the whole channel design. Considering a practical channel (6Mhz BW and ~15db noise), if u use QAM and a complex FEC algorithm ur channel will bang up against the Shannon's limit theorem, but if ur using PSK ur BER will comparatively increase but receiver complexity increases too!(PLL design, phase recovery etc.),..when BER/SER is desired low at any cost in the channel irrespective of BW, GMSK should work providin ur following Mase's law and ur multlipexing is in accordance with frame rate.

Added after 9 minutes:

Here's a configuration file for general voice/data/fax modem contructs. Specifies all the necessary terms required along with the user values for optimisation.

GMSK is best for power efficincy
and pi/4-DQPSK - for spectral efficiency

QPSK is bettter than BPSK in terms of spectral efficiency