Improving Co-Channel Interference Robustness In Direct Detection Receivers Using A Surface Acoustic Wave (SAW) Correlator

Using direct-detection architecture in Radio Frequency (RF) receivers allows for ultra-low power dissipation and is often used in Wake-Up receivers. Unfortunately direct-detection receivers suffer from high sensitivity to co-channel interference which reduces the communication performance and reliability. In this paper, it is shown that co-channel interference robustness of direct-detection receivers is improved by using Binary Phase Shift Keying (BPSK) Barker code modulated Surface Acoustic Wave (SAW) correlator as a prior stage to the RF envelope detector. Replacing the band select filter with SAW correlator does not result in higher receiver hardware cost. In our receiver, the SAW correlator functions as a passive signal processor, providing gain for a BPSK Barker code modulated signal, while suppressing in-band interferers. This improves the co-channel interference robustness of the direct-detection receiver while preserving its advantage of power efficiency. The concept is verified by means of a direct-detection receiver with discrete components on an RF PCB including an SAW Barker Code correlator at a center frequency of 2.44 GHz fabricated on Lithium Niobate substrate. Measurements with WiFi signals demonstrate that the interference robustness is improved by more than 10 dB compared to a conventional direct-detection receiver.