ZChirp: Speeding Up LPWANs by Combining the Chirp with Binary Sequences

Low Power Wide Area Networks (LPWAN), such as LoRa, support long range wireless connections for a vast number of low power IoT devices. One of the main challenges in LPWANs is to provide high network capacity. In this paper, a novel modulation technique, referred to as ZChirp, is proposed. ZChirp augments the chirp modulation in LoRa by multiplying the chirp with a binary sequence called the Z sequence, which serves dual purposes. First, chirps multiplied with different Z sequences have very low cross-correlations, which enables simultaneous transmissions of multiple nodes and increases the network capacity. Second, additional data can be modulated by using different Z sequences for different data values, which proves to be an effective option to increase the data rate. Experiments and simulations show that ZChirp does not increase bandwidth usage nor reduce the communication range comparing to the original LoRa. Experiments in the POWDER platform demonstrate that the ZChirp gateway successfully decoded packets from multiple nodes transmitted simultaneously at random times. Simulations further show that the capacity gain of ZChirp over the state-of-the-art solution that also modifies the LoRa modulation is 2.0×.