[Paper Review] D2D-aided LoRaWAN LR-FHSS in Direct-to-Satellite IoT Networks

Alireza Maleki, Ha H. Nguyen+2 more|arXiv (Cornell University)|Dec 8, 2022

IoT Networks and Protocols4 citations

TL;DR

This paper proposes a D2D-aided LR-FHSS scheme for LoRaWAN in direct-to-satellite IoT networks to enhance network capacity under realistic shadowed-Rice fading conditions. By integrating network coding and D2D relaying, the scheme achieves a 249.9% and 150.1% increase in capacity at 10⁻² outage probability for DR6 and DR5, respectively, with only one to two additional transmissions per device per timeslot.

ABSTRACT

In this paper, we present a device-to-device (D2D) transmission scheme for aiding long-range frequency hopping spread spectrum (LR-FHSS) LoRaWAN protocol with application in direct-to-satellite IoT networks. We consider a practical ground-to-satellite fading model, i.e. shadowed-Rice channel, and derive the outage performance of the LR-FHSS network. With the help of network coding, D2D-aided LR-FHSS transmission scheme is proposed to improve the network capacity for which a closed-form outage probability expression is also derived. The obtained analytical expressions for both LR-FHSS and D2D-aided LR-FHSS outage probabilities are validated by computer simulations for different parts of the analysis capturing the effects of noise, fading, unslotted ALOHA-based time scheduling, the receiver's capture effect, IoT device distributions, and distance from node to satellite. The total outage probability for the D2D-aided LR-FHSS shows a considerable increase of 249.9% and 150.1% in network capacity at a typical outage of 10^-2 for DR6 and DR5, respectively, when compared to LR-FHSS. This is obtained at the cost of minimum of one and maximum of two additional transmissions per each IoT end device imposed by the D2D scheme in each time-slot.

Motivation & Objective

• Address the limited network capacity of conventional LoRaWAN in dense, direct-to-satellite IoT deployments due to duty cycle constraints and ALOHA-based MAC.
• Overcome the limitations of prior LR-FHSS studies that assume ideal channels by modeling realistic shadowed-Rice fading and noise effects.
• Enhance network reliability and capacity in low-Earth orbit (LEO) satellite-based IoT networks using device-to-device (D2D) cooperation with network coding.
• Derive closed-form expressions for outage probability in both standard LR-FHSS and D2D-aided LR-FHSS to enable theoretical performance evaluation.

Proposed method

• Propose a D2D-aided LR-FHSS transmission scheme where nearby IoT devices relay signals to improve reception diversity and reliability in satellite uplink links.
• Integrate network coding at the D2D relay nodes to combine multiple packets and reduce redundant transmissions while maintaining data integrity.
• Model the ground-to-satellite link using a shadowed-Rice fading channel to reflect realistic path loss and multipath fading effects.
• Derive the outage probability for LR-FHSS using a Laplace transform-based approach on the signal-to-interference-plus-noise ratio (SINR), incorporating the capture effect and unslotted ALOHA scheduling.
• Use the generalized gamma distribution to model the aggregate interference and derive the cumulative distribution function (CDF) of the interference power via infinite series and confluent hypergeometric functions.
• Formulate the packet capture probability using the inverse Laplace transform and the Kummer’s function (1F1), enabling closed-form analysis of the outage performance.

Experimental results

Research questions

• RQ1 How does the outage performance of LR-FHSS in direct-to-satellite LoRaWAN degrade under realistic shadowed-Rice fading and noise conditions compared to ideal assumptions?
• RQ2 To what extent can D2D cooperation with network coding improve the network capacity of LR-FHSS in satellite-based IoT networks?
• RQ3 What is the analytical impact of the receiver’s capture effect and unslotted ALOHA medium access on the outage probability in D2D-aided LR-FHSS systems?
• RQ4 Can a closed-form expression for the outage probability be derived for D2D-aided LR-FHSS under practical fading and interference models?

Key findings

• The D2D-aided LR-FHSS scheme achieves a 249.9% increase in network capacity at a 10⁻² outage probability for data rate DR6 compared to standard LR-FHSS.
• For DR5, the network capacity improves by 150.1% under the same outage threshold, demonstrating significant performance gains across data rates.
• The derived closed-form outage probability expressions for both LR-FHSS and D2D-aided LR-FHSS are validated through simulations, confirming accuracy across noise, fading, distance, and device distribution effects.
• The performance gain is achieved with only one to two additional transmissions per IoT device per timeslot, indicating low overhead for D2D cooperation.
• The inclusion of the capture effect and realistic interference modeling significantly improves the accuracy of the outage analysis compared to prior works that ignored noise or fading.
• The use of generalized gamma distribution and confluent hypergeometric functions (1F1) enables tractable yet precise analytical modeling of interference and outage in the D2D-aided system.