Bhaskar,
Ravi might not know what is EVM - error vector magnitude. Does EVM
exists for GMSK?
I guess we normally measure phase error(RMS(0 to 10 degree) and peak(0
to 40 degree)) for GMSK modulation type and
EVM (RMS(0-20%) and peak(0-40%) for 8PSK modulation. Please correct me
if I am wrong.
Santosh
Reply by Bhaskar Thiagarajan●January 31, 20062006-01-31
"ravi" <rkant_nitw@rediffmail.com> wrote in message
news:1138745295.249752.68540@f14g2000cwb.googlegroups.com...
> i want to identify the presence og GMSK modulation in the incoming
> signal at the receiver side. and can u clarify what is meant by. '
> relative to what ?PSK ?QAM?Voice?'
What do you know about your input signal? Do you know that it can only
contain GMSK and some other type of modulation or can it contain pretty much
anything and you only want to see if GMSK is present? In the latter case,
you pretty much have to demodulate it assuming that it is a GMSK signal (if
it is GMSK, is it part of the GSM standard or a custom GMSK modulated
signal?). After demodulation, you can use metrics based on the demodulation
to see if you got GMSK or not (say EVM). If your input signal has a lot of
noise, your detection algorithm will need to take that into account as well.
Cheers
Bhaskar
Reply by ravi●January 31, 20062006-01-31
i want to identify the presence og GMSK modulation in the incoming
signal at the receiver side. and can u clarify what is meant by. '
relative to what ?PSK ?QAM?Voice?'
regards,
ravi
Reply by ravi●January 31, 20062006-01-31
i want to identify the presence og GMSK modulation in the incoming
signal at the receiver side. and can u clarify what is meant by. '
relative to what ?PSK ?QAM?Voice?'
Reply by Tim Wescott●January 31, 20062006-01-31
Bhaskar Thiagarajan wrote:
> "Tim Wescott" <tim@seemywebsite.com> wrote in message
> news:4b2dnXXsMMyCVELenZ2dnUVZ_tqdnZ2d@web-ster.com...
>
>>Bhaskar Thiagarajan wrote:
>>
>>
>>>"Tim Wescott" <tim@seemywebsite.com> wrote in message
>>>news:LOmdnb-GFvGROkLenZ2dnUVZ_tqdnZ2d@web-ster.com...
>>>
>>>
>>>>Nilnod wrote:
>>>>
>>>>
>>>>
>>>>>I guess Ravi is interested with received signal which was GMSK
>>>>>modulated at transmission side - a typical mobile communication like
>>>>>GSM or EDGE scenario.
>>>>>
>>>>>The is related to something called "blind demodulation" where we do not
>>>>>know in advance what received signal is coming - GMSK/8PSK etc.
>>>>>
>>>>>I can not give detailed algorithm here. For example, a GSM burst
>>>>>training sequence is known a prior. Someone can exploit correlation
>>>>>property and calculate engery. If the engegy achieved through GMSK
>>>>>correlation is high enough compared to that of others (say 8PSK) then
>>>>>modulation type is GMSK.
>>>>>Cheers
>>>>>Santosh
>>>>>
>>>>
>>>>In the GSM case it's moot -- GSM includes a frequency correction burst
>>>>which is around 68kHz above the carrier for GMSK and below the carrier
>>>>for 8PSK. That's pretty distinctive. Unless he just couldn't wait
>>>>around for the FB he could easily tell.
>>>
>>>
>>>I'm fairly sure a FB uses GMSK strictly. So you'd only get the 68kHz
>
> offset
>
>>>above the carrier. 8PSK is not used in FBs (frequency correction
>
> bursts).
>
>>See page 19 of GSM 05.02 version 8.4.1 Release 1999, section 5.2.4 at
>>the bottom where it says "NOTE:". I could be mistaken about the meaning
>>of the "COMPACT" format -- if it means 8PSK then my statement is correct.
>
>
> No - COMPACT doesn't mean 8PSK.
> Usually, if something uses 8PSK, the bit definitions will be shown in groups
> of 3 (to show 3 bits per symbol). See the previous section 5.2.3 for an
> example in the Normal burst definition.
> COMPACT is just a slightly different access method with minor differences in
> frame structure, etc - not sure of the exact details but it doesn't seem
> like it is widely used.
>
Reply by Bhaskar Thiagarajan●January 31, 20062006-01-31
"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:4b2dnXXsMMyCVELenZ2dnUVZ_tqdnZ2d@web-ster.com...
> Bhaskar Thiagarajan wrote:
>
> > "Tim Wescott" <tim@seemywebsite.com> wrote in message
> > news:LOmdnb-GFvGROkLenZ2dnUVZ_tqdnZ2d@web-ster.com...
> >
> >>Nilnod wrote:
> >>
> >>
> >>>I guess Ravi is interested with received signal which was GMSK
> >>>modulated at transmission side - a typical mobile communication like
> >>>GSM or EDGE scenario.
> >>>
> >>>The is related to something called "blind demodulation" where we do not
> >>>know in advance what received signal is coming - GMSK/8PSK etc.
> >>>
> >>>I can not give detailed algorithm here. For example, a GSM burst
> >>>training sequence is known a prior. Someone can exploit correlation
> >>>property and calculate engery. If the engegy achieved through GMSK
> >>>correlation is high enough compared to that of others (say 8PSK) then
> >>>modulation type is GMSK.
> >>>Cheers
> >>>Santosh
> >>>
> >>
> >>In the GSM case it's moot -- GSM includes a frequency correction burst
> >>which is around 68kHz above the carrier for GMSK and below the carrier
> >>for 8PSK. That's pretty distinctive. Unless he just couldn't wait
> >>around for the FB he could easily tell.
> >
> >
> > I'm fairly sure a FB uses GMSK strictly. So you'd only get the 68kHz
offset
> > above the carrier. 8PSK is not used in FBs (frequency correction
bursts).
>
> See page 19 of GSM 05.02 version 8.4.1 Release 1999, section 5.2.4 at
> the bottom where it says "NOTE:". I could be mistaken about the meaning
> of the "COMPACT" format -- if it means 8PSK then my statement is correct.
No - COMPACT doesn't mean 8PSK.
Usually, if something uses 8PSK, the bit definitions will be shown in groups
of 3 (to show 3 bits per symbol). See the previous section 5.2.3 for an
example in the Normal burst definition.
COMPACT is just a slightly different access method with minor differences in
frame structure, etc - not sure of the exact details but it doesn't seem
like it is widely used.
> > You could try to see the phase transitions in the signal. 90 degree
phase
> > changes will be GMSK and smaller changes would be 8PSK. But I'm not sure
if
> > the OP wants to distinguish GMSK and 8PSK or just find GMSK amongst
*any*
> > time of incoming demodulations. In the latter case, I'd say, try to
> > demodulate assuming it is GMSK...and if it is GSM, you can try to see if
you
> > have a TSC in your bursts. If you get a match, then you have GMSK.
> >
> Yea, if he just wants to distinguish GMSK from anything else then I
> think that's what he's got to do.
>
> It gets hard if it has an arbitrary baud rate, or lots of noise, though.
>
> --
>
> Tim Wescott
> Wescott Design Services
> http://www.wescottdesign.com
Reply by Tim Wescott●January 31, 20062006-01-31
Bhaskar Thiagarajan wrote:
> "Tim Wescott" <tim@seemywebsite.com> wrote in message
> news:LOmdnb-GFvGROkLenZ2dnUVZ_tqdnZ2d@web-ster.com...
>
>>Nilnod wrote:
>>
>>
>>>I guess Ravi is interested with received signal which was GMSK
>>>modulated at transmission side - a typical mobile communication like
>>>GSM or EDGE scenario.
>>>
>>>The is related to something called "blind demodulation" where we do not
>>>know in advance what received signal is coming - GMSK/8PSK etc.
>>>
>>>I can not give detailed algorithm here. For example, a GSM burst
>>>training sequence is known a prior. Someone can exploit correlation
>>>property and calculate engery. If the engegy achieved through GMSK
>>>correlation is high enough compared to that of others (say 8PSK) then
>>>modulation type is GMSK.
>>>Cheers
>>>Santosh
>>>
>>
>>In the GSM case it's moot -- GSM includes a frequency correction burst
>>which is around 68kHz above the carrier for GMSK and below the carrier
>>for 8PSK. That's pretty distinctive. Unless he just couldn't wait
>>around for the FB he could easily tell.
>
>
> I'm fairly sure a FB uses GMSK strictly. So you'd only get the 68kHz offset
> above the carrier. 8PSK is not used in FBs (frequency correction bursts).
See page 19 of GSM 05.02 version 8.4.1 Release 1999, section 5.2.4 at
the bottom where it says "NOTE:". I could be mistaken about the meaning
of the "COMPACT" format -- if it means 8PSK then my statement is correct.
>
> You could try to see the phase transitions in the signal. 90 degree phase
> changes will be GMSK and smaller changes would be 8PSK. But I'm not sure if
> the OP wants to distinguish GMSK and 8PSK or just find GMSK amongst *any*
> time of incoming demodulations. In the latter case, I'd say, try to
> demodulate assuming it is GMSK...and if it is GSM, you can try to see if you
> have a TSC in your bursts. If you get a match, then you have GMSK.
>
Yea, if he just wants to distinguish GMSK from anything else then I
think that's what he's got to do.
It gets hard if it has an arbitrary baud rate, or lots of noise, though.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Bhaskar Thiagarajan●January 31, 20062006-01-31
"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:LOmdnb-GFvGROkLenZ2dnUVZ_tqdnZ2d@web-ster.com...
> Nilnod wrote:
>
> > I guess Ravi is interested with received signal which was GMSK
> > modulated at transmission side - a typical mobile communication like
> > GSM or EDGE scenario.
> >
> > The is related to something called "blind demodulation" where we do not
> > know in advance what received signal is coming - GMSK/8PSK etc.
> >
> > I can not give detailed algorithm here. For example, a GSM burst
> > training sequence is known a prior. Someone can exploit correlation
> > property and calculate engery. If the engegy achieved through GMSK
> > correlation is high enough compared to that of others (say 8PSK) then
> > modulation type is GMSK.
> > Cheers
> > Santosh
> >
> In the GSM case it's moot -- GSM includes a frequency correction burst
> which is around 68kHz above the carrier for GMSK and below the carrier
> for 8PSK. That's pretty distinctive. Unless he just couldn't wait
> around for the FB he could easily tell.
I'm fairly sure a FB uses GMSK strictly. So you'd only get the 68kHz offset
above the carrier. 8PSK is not used in FBs (frequency correction bursts).
You could try to see the phase transitions in the signal. 90 degree phase
changes will be GMSK and smaller changes would be 8PSK. But I'm not sure if
the OP wants to distinguish GMSK and 8PSK or just find GMSK amongst *any*
time of incoming demodulations. In the latter case, I'd say, try to
demodulate assuming it is GMSK...and if it is GSM, you can try to see if you
have a TSC in your bursts. If you get a match, then you have GMSK.
Cheers
Bhaskar
> I guess Ravi is interested with received signal which was GMSK
> modulated at transmission side - a typical mobile communication like
> GSM or EDGE scenario.
>
> The is related to something called "blind demodulation" where we do not
> know in advance what received signal is coming - GMSK/8PSK etc.
>
> I can not give detailed algorithm here. For example, a GSM burst
> training sequence is known a prior. Someone can exploit correlation
> property and calculate engery. If the engegy achieved through GMSK
> correlation is high enough compared to that of others (say 8PSK) then
> modulation type is GMSK.
> Cheers
> Santosh
>
In the GSM case it's moot -- GSM includes a frequency correction burst
which is around 68kHz above the carrier for GMSK and below the carrier
for 8PSK. That's pretty distinctive. Unless he just couldn't wait
around for the FB he could easily tell.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Nilnod●January 31, 20062006-01-31
I guess Ravi is interested with received signal which was GMSK
modulated at transmission side - a typical mobile communication like
GSM or EDGE scenario.
The is related to something called "blind demodulation" where we do not
know in advance what received signal is coming - GMSK/8PSK etc.
I can not give detailed algorithm here. For example, a GSM burst
training sequence is known a prior. Someone can exploit correlation
property and calculate engery. If the engegy achieved through GMSK
correlation is high enough compared to that of others (say 8PSK) then
modulation type is GMSK.
Cheers
Santosh