Spread Spectrum Archives

A basic chirp with real and imaginary signals

October 3, 2022 Wireless/SDR

Understanding LoRa PHY (Long-Range Physical Layer)

LoRa PHY (Long-Range Physical Layer) is a very exciting communication technique based on Chirp Spread Spectrum (CSS) modulation mixed with Frequency Shift Keying (FSK). It is a proprietary physical layer methodology patented by Semtech. On the other hand, LoRaWAN is a Low Power Wide Area Network (LPWAN) protocol that is built on top of LoRa PHY. Some of the benefits of LoRa are resistance to multipath fading and Doppler effect, robustness against narrowband interference and jamming, low RF power consumption owing to the constant envelope signal, computationally simple from signal processing perspective, long-range transmission and reception, and inherent ranging capability

December 29, 2020 Miscellaneous / Wireless/SDR

CDMA or OFDM

Reading about interference cancellation techniques today, I recalled an interesting article by Sridhar Vembu titled Two Philosophies in CDMA: A Stroll Down Memory Lane. Vembu is the founder and CEO of Zoho Corporation, a venture which has turned him into a billionaire. He spent time both in academia (at Princeton) and in industry (at Qualcomm) working with the likes of Sergio Verdu in one camp and Andrew Viterbi in the other. Here are some excerpts from his article which is not available online anymore at the time of this writing. I have now worked a little over 10 years in