In non-cooperative communication, symbol rate estimation is an important basis for blind estimation and blind demodulation of digital signals. The traditional symbol rate estimation methods, such as the cyclic correlation method and the envelope spectrum method, show a dramatic decline of performance in low SNR. To solve this problem, a method based on wavelet transform is studied, and the optimal range of its best wavelet function and flex factor is deduced. Theoretical analysis and simulation experiments show that the proposed algorithm has many advantages, such as low data demand, high estimation accuracy, and so on. It has good robustness and universality in low SNR environment.
The error vector magnitude (EVM) is extensively applied as a metric for digital transmitter signal quality compliance in modern communication systems. In cooperative communication, signal carrier frequency and symbol rate are predicted, and the reference signal can be recovered from demodulated symbols directly. However in non-cooperative communications, the signal carrier frequency and symbol rate are estimated. Since the demodulation and EVM are very sensitive to symbol rate, we focus on the EVM of non-cooperative communication in this paper. In our proposal, a novel wavelet-based EVM recovery of reference signal is presented. This method can recover reference signal accurately to achieve the true EVM, if the estimation error of symbol rate has been bounded within a small range. The experimental results depict the validity of our algorithm.
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