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Old 04-16-2012, 08:37 PM
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tomshong tomshong is offline
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Default I and Q component

Hi experts,

I started playing with a system level simulator called CppSim by following thru their tutorial on a GMSK transceiver. Here's the link to the tutorial.

http://www.cppsim.com/Tutorials/gmsk_tutorial.pdf

Since this is a free software there's really no support from them. I am only in the first section of this tutorial, and i noticed something on their setup that I would like to get the experts opinion on this.

On Page 5 of the tutorial it shows the setup depicting a GMSK transmitter transmit a single channel to a GMSK receiver. I assumed the gain = 1/5 between the two block represents a 3dB loss over the air.

On page 8 and 9 it shows the wave form of the I and Q components of the transmitter, and the I and Q components come out of the receiver.

Here are my questions:

1) How is it is that they only use the I component of the transmitter to transmit to the receiver? Why is the Q component ignored?

2) At the receiver output, the Q component appear to be the inverting equivalent of the transmit Q component. But, how does the receiver know how the Q waveform is if only the I component is transmitted?
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Old 04-27-2012, 05:13 AM
dig1 dig1 is offline
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i didn't look at the link you gave but i bet they are using what is called a SSB transmission. there is a great paper entitled "Complex Signal processing is not so complex" which describes the method step by step. I wish i had stumbled upon that paper like 5 years ago. anyway, please read that... the method is usually called if i remember correctly a weaver SSB transmission method...
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