Hi, I have a few questions regarding receiving Direct Sequence Spread Spectrum signals using USRP and gnuradio. I am transmitting a signal that is spread using gold codes at 2.4GHz. The USRPs that I have show a frequency offset of about 8kHz. In order to receive the signal so as to be able to de-spread and demodulate them I must implement a signal acquisition and tracking scheme. Can someone suggest me ideas to do this. I came across a few things that gave me an idea of accomplishing this.
"Fundamentals of Global Positioning System Receivers - A software approach" was once suggested to me on this list. The acquisition scheme suggested in this book is FFT based and the tracking scheme consists of Early-Late-Prompt Correlation scheme for code tracking and Costas loop for carrier tracking. 1. Is there any such acquisition scheme already present in Gnuradio? I looked at usrp_spectrum_sense and I have an idea of what to do. I want a system that should work in real time with simultaneous transmissions from different Tx. 2. If I know the offset then by tuning my usrp to a frequency such that the offset is negated will I be able to skip the acquisition part? 3. What other things should I be looking into or taking care of in order to implement a DSSS system. I have just started working on my "Communication Systems" knowledge so please bear with me. Thanks, Ali
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