Frequency & time offset problem at low SNR region

Dear all,

I’ve been trying to implement a system that operates over a wide range
of
signal-to-noise-ratio (SNR) (e.g. -5dB ~ 30dB).

For the first step, I tried to measure bit-error-rate (BER) of QPSK at
various SNRs.
I used a pn sequence to implement channel compensation and accurately
measure instantaneous SNR.

At high SNR region (>10dB), everything is fine. Good SNR and good BER.

However, at low SNR region (<10dB), mpsk_receiver(Costas & MM) fails to
fix
the freq and time offset.
Therefore, nothing can be done in low SNR region.

Is there any way to measure SNR and BER at low SNR region?

(FYI, I’m using USRP1 and WBX with Ubuntu 10.04)

  • Minsuk Kang

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