Chirp spread spectrum

Channel (broadcasting)

Orthogonality

Link level

Computer network

Mathematics

Wireless

Gene

Spread spectrum

Network packet

Throughput

Chemistry

Capture effect

Direct-sequence spread spectrum

Geometry

Interference (communication)

Computer science

Code division multiple access

Biochemistry

Robustness (evolution)

Telecommunications

IEEE Communications Letters

In this letter, we focus on the evaluation of link-level performance of LoRa technology, in the usual network scenario with a central gateway and high-density deployment of end-devices. LoRa technology achieves wide coverage areas, low power consumption and robustness to interference thanks to a chirp spread-spectrum modulation, in which chirps modulated with different spreading factors (SFs) are quasi-orthogonal. We focus on the performance analysis of a single receiver in presence of collisions. First, we analyze LoRa modulation numerically and show that collisions between packets modulated with different SFs can indeed cause packet loss if the interference power received is strong enough. Second, we validate such findings in experiments based on commercial devices and software-defined radios. Contradicting the common belief that SFs can be considered orthogonal, our results demonstrate that inter-SF collisions are indeed an issue in LoRa networks and, thus, allocating higher SFs to users far from the gateway might not necessarily improve their link capacity, in case of congested networks.

Impact of LoRa Imperfect Orthogonality: Analysis of Link-Level Performance