The Accuracy of Signal-to-Noise Ratio Estimation on a Fully Functional QPSK Transceiver

Using received signal constellation to estimate the signal-to-noise ratio is an easy and popular method, however, its accuracy of the estimation is a common pitfall. Instead of studying only on AWGN channel in previous works, SNR estimation for a fully functional QPSK transceiver is evaluated in this paper. We design a frame format consisted of a framing pattern and a maximum length sequence payload to verify SNR estimation problem of QPSK signal. The framing pattern is used to estimate the SNR, and meanwhile the payload is used to calculate BER. A complete QPSK transceiver is simulated in Simulink and also implemented in the Zynq SDR software defined radio. The results show that the estimated SNR using received signal constellation is usually underestimated and its offset is not consistent with theoretical BER curve. The proposed method is more consistent and easier to compensate for the theoretical value.