Performance Analysis of LoRa Waveform for Joint Communications and Radar System

In this paper, a joint communications and radar (JCAR) system is considered, where the transmitter is capable of delivering information to a receiver as well as sensing targets with a mono-static radar platform. A new JCAR waveform is developed, which uses alternating up-chirp and down-chirp versions of the long range (LoRa) modulated signals. Closed-form expressions for the ambiguity function (AF) of the proposed waveform are derived for different number of symbols and it is demonstrated that the derived analytical expressions align well with the simulation results. The results also show that the peak side lobe ratio (PSLR) in the zero-Doppler cut of the AF decreases and the Doppler resolution improves with increase in the number of symbols. As such, when compared to the standard chip, the proposed waveform significantly reduces the PSLR while yielding similar range and Doppler resolutions. This sensing performance is achieved with a much higher data rate than that of the standard chirp. Our scheme also achieves a low symbol error rate (SER) in the medium signal-to-noise-ratio (SNR) regime, thereby indicating a good communications performance. Moreover, the aforementioned characteristics of the AF are achieved without altering the original data rate of the LoRa system. These aspects render the proposed LoRa-based waveform a potential candidate for next generation JCAR systems.