Efficient link quality estimation in DS spread systems

The author describes an algorithm for generating a link quality estimate (LQE) for direct-sequence (DS) phase-shift-keyed (PSK) signals that simultaneously possess good estimator properties, low-computational requirements, and a form easily incorporated into a digital receiver architecture. The algorithm exploits the nonlinear magnitude operations, available in the noncoherent and data automatic gain control (AGC) hardware. Taking the ratio of the mean value of two signals obtainable from the AGC circuitry produces a monotonically increasing function of signal-to-noise ratio (SNR) usable as a measure of link quality. Inverting this function provides an estimate of SNR. Extensive Monte Carlo simulation results are presented to quantify the LQE and SNR estimator's performance. The results show that under reasonable conditions both estimators have an asymptotic unbiased behavior with error variance monotonically decreasing with sample size, suggesting consistency. The performance of the SNR estimator is shown to be superior to that of an alternative SNR estimator previously reported, while possessing reduced complexity.<
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