I and Q component

Discussion in 'Radio and Communications' started by tomshong, Apr 16, 2012.

  1. tomshong

    tomshong Thread Starter Member

    Joined:
    Oct 6, 2011
    Messages:
    30
    Location:
    Orange County, CA, USA
    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?
  2. dig1

    dig1 Member

    Joined:
    Jul 31, 2008
    Messages:
    18
    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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