Peak-to-Average - looking only for the numbers

[RiffMaster]

qpsk par

I am looking only for the numbers and not for explanation to the following questions:

1. What is the peak-to-average of a Sine Wave signal?
2. What is the peak-to-average of FSK signal?
3. What is the peak-to-average of a GMSK signal?
4. What is the peak-to-average of QPSK signal?
5. What is the peak-to-average of OQPSK (Offset-QPSK) signal?
6. What is the peak-to-average of 16QAM signal

thanks

 

[RiffMaster]

Re: Peak-to-Average

I'm still looking for these values...at least for some of them.
thanks

 

[kspalla]

Peak-to-Average

1. What is the peak-to-average of a Sine Wave signal?
Answer is infinity.

 

[biff44]

Re: Peak-to-Average

Good answer! But I think he neglected to add the word "power" to his questions. Sine and FSK should have a ratio of 1. The others, depends on how it is filtered, etc.

 

[Communications_Engineer]

Peak-to-Average

I'd actually want to know about why PAPR is a problem

 

[biff44]

Re: Peak-to-Average

If you have a complex modulation scheme, like 64 QAM, the information is contained in small changes in amplitude or phase of the signal. If you use a transmit amplifier that has 10 degrees of phase shift when it is transmitting 1 watt, but 20 degrees of phase shift when it is transmitting 2 watts, then you have a built-in phase error depending on how compressed the amplifier is instantaneously. That results in bad bit decisions.

You might, in that case have to either
1) go to a modulation scheme with a more constant amplitude envelope, or
2) get a better transmit amplifier.


Rich
www.MaguffinMicrowave.com

 

[RiffMaster]

Re: Peak-to-Average

Thanks but you see, the net and a lot of technical books are full of explanations, but most of them are in contradiction.
For example I found here some of the answers:

https://en.wikipedia.org/wiki/Crest_factor

1. Sine wave PAR is 3.01dB
2. - ?
3. - ?
4. QPSK PAR is maximum 4dB
5. I found in a CDMA IS-95 uplink specification that OQPSK PAR is ~1dB lower than QPSK (resulting OQPSK PAR= ~3dB)
6. From the above site you can see that 64QAM is 7.7dB. In other place is mentioned that 16QAM is 3dB lower than 64QAM, so 16QAM PAR will be 4.7dB !?

Still confused with FSK and GMSK. Maybe 3dB is the answer, the same as sine wave. Hopefully!

 

[kspalla]

Peak-to-Average

I agree with Biff that for a sine wave without modulation peak power is same as average power.
The same is valid for FSK and GMSK as they are constant envelop.
So their PAPR is 1.