Interleaved Chirp Spreading LoRa-Based Modulation

LoRa has established itself as one of the leading technologies within evolving low power wide area networks. In the patented LoRa modulation, a linearly increasing basis chirp signal spans the LoRa bandwidth. Cyclic shifts of this basis chirp signal create a multidimensional space for the orthogonal signaling of nonbinary LoRa symbols. The number of bits per LoRa symbol as well as the symbol rate depend on an applied spreading factor (SF) that could vary between 7 and 12. In this paper, interleaved chirp spreading LoRa (ICS-LoRa) is proposed as a physical layer-inspired approach to enhance data rates of the capacity-limited LoRa networks. In ICS-LoRa, interleaved versions of the nominal LoRa chirp signals constitute a new multidimensional space with the purpose of adding one extra bit within each transmitted ICS-LoRa symbol. The proposed interleaving pattern of ICS-LoRa maintains the same communication robustness of nominal LoRa. The ICS interleaving pattern is also designed to simplify implementation where both ICS-LoRa modulation and demodulation can share the same ICS-interleaver block. An accurate approximation for BER performance of the proposed ICS-LoRa is derived in order to evaluate the underlying reception sensitivities. It is shown that the 14% capacity gain of ICS-LoRa with an SF of 7 is associated with a sensitivity loss at the scale of only 0.8 dB. On the other hand, ICS-LoRa achieves more than 8% in capacity gain with virtually no impact on sensitivity performance when using an SF of 12 that governs the maximum coverage range.