bhargava
03-25-2008, 07:40 PM
hi all...
I've implemented a GMSK modem in MATLAB and also obtained the PSD of th
modulated GMSK signal...
In doing so I'm being haunted by an inconsistency...
we know that MSK and GMSK signal power spectral density theoretically hav
a main lobe width of 1.5*Rb (where Rb is the bit rate)hence theoreticall
bandwidth of GMSK and MSK signal is considered as 1.5*Rb.(here the PS
will be nearly 40 dB down compared to the value at F=Fc)
but GSM 5.04 standard specifies bitrate Rb=270.833kbps and
bandwidth/channel=200KHz now this is not as given in theory according
theoritical calculations the band width ie., 1.5*Rb will be 406.2495KH
now this means the power level at the cut off band width inGSM ha
attenuation way less than 40 dB...
now here where am I going wrong here???
and if this reasoning is true why/how does GSM specify a BW much less tha
theoretical band width??
Regards...
Bhargava
I've implemented a GMSK modem in MATLAB and also obtained the PSD of th
modulated GMSK signal...
In doing so I'm being haunted by an inconsistency...
we know that MSK and GMSK signal power spectral density theoretically hav
a main lobe width of 1.5*Rb (where Rb is the bit rate)hence theoreticall
bandwidth of GMSK and MSK signal is considered as 1.5*Rb.(here the PS
will be nearly 40 dB down compared to the value at F=Fc)
but GSM 5.04 standard specifies bitrate Rb=270.833kbps and
bandwidth/channel=200KHz now this is not as given in theory according
theoritical calculations the band width ie., 1.5*Rb will be 406.2495KH
now this means the power level at the cut off band width inGSM ha
attenuation way less than 40 dB...
now here where am I going wrong here???
and if this reasoning is true why/how does GSM specify a BW much less tha
theoretical band width??
Regards...
Bhargava