Enhancing passive UHF RFID backscatter energy using chirp spread spectrum signals and channel shortening

Performance of passive ultrahigh frequency radio-frequency identification (UHF RFID) systems depends on the energy level of the backscattered signal from the RF tag to the RFID reader. In the indoor environment, the transmitted signals are corrupted by the multi-path channels fading that reduce the energy of the backscatter signal and modify the waveform of the continuous wave (CW) that result a short read range. Chirp spread spectrum (CSS) signals and channel shortening (CS) techniques are used separately to combat the effect of the multi-path channel fading in different contexts. In this paper, we propose two methods that use jointly CSS and CS in the multiple-input single-output (MISO) passive UHF RFID system that employs multiple antennas at the reader and one antenna at the tag First method increases significantly the received energy on the tag. The harvest energy ensures the backscatter communication from tag to reader. Second method offers a good trade-off between maintaining of high received energy and preserving the main characteristics of the waveform of the CSS, on the tag. This method is required to ensure a secured communication between reader and tag.