Improving Downlink Scalability in LoRaWAN

Abstract

Although LoRaWAN offers many advantages, one of its main limitation is the insufficient downlink capacity in large-scale scenarios. This makes reliable communication impractical as, in LoRaWAN, reliability is achieved through the acknowledgement of confirmed messages. The contribution of this paper is to provide a comprehensive description of the problems associated with the presence of downlink traffic and to propose solutions to enable the use of acknowledgments for low to medium downlink load. The proposed mechanisms build on a more adequate and flexible choice of the gateway for each downlink transmission by the network server. Thus, they are entirely compatible with existing LoRaWAN technologies and deployments. Our simulation results show that the proposed solutions enable the successful realization of a higher percentage of LoRaWAN confirmed messages. Thus, the common practice of strongly discouraging the use of confirmed messages could be reconsidered to allow applications that require reliable communication.

On Spatial Diversity for LoRaWAN: Experimental Evaluation of Performance of a Dual-Gateway Network With and Without Downlink

“…The possible reasons after such a strong effect of the downlink traffic on the performance of uplink reception for a GW are two-fold. First, if the GW's transceiver is half-duplex (i.e., does not support transmission and reception at the same time), this is easy to expect the receiver to get disconnected from the antenna by a switch, when the GW's transmitter is on, as this is discussed, e.g., in [17]. Obviously, this will prevent the GW from receiving anything in the uplink.…”

High Reliability in LoRaWAN

“…Assuming a Rayleigh channel for LoRa, then the SNR follows an exponential distribution with cumulative distribution function, F (x) = 1 − e −x (and its inverse F −1 (x) = −log(1 − x)). We can compute F −1 (0.9 1/60 ) ≈ 6.3 ≈ 10 8 10 , which means that there is 90% chances for the last 60 packets' maximal SNR to be less than 8 dB over the mean SNR. Notice that the NS estimates the link quality by taking the maximal SNR over the last 20 received packets without taking into account retransmissions or losses.…”

“…Many limitations of LoRaWAN in terms of scalability and effective throughput are inherent to its ALOHA access [4], [5]. Moreover, LoRaWAN reliable uplink traffic handling is very limited by its downlink traffic capacity [5], [9], even though improvements are possible [10].…”

“…end while end if 30: end while a typical LoRaWAN network deployed in the Grenoble urban area 9 , and it is publicly available 10 .…”

A Survey on the Viability of Confirmed Traffic in a LoRaWAN

“…Downlink traffic in a LoRaWAN can be in the form of transmitting an ACK for a confirmed uplink message, sending MAC commands, application layer downlink data or a combination of all of these [41]. Accurate network models are key when determining the impact of downlink traffic on network performance, and modelling should include the PHY and MAC layers.…”