LoRa Beyond ALOHA: An Investigation of Alternative Random Access Protocols

Beltramelli, Luca; Mahmood, Aamir; Österberg, Patrik; Gidlund, Mikael

doi:10.1109/tii.2020.2977046

Cited by 98 publications

(65 citation statements)

References 23 publications

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“…We rely on a time-slotted medium access control (MAC) approach to enable efficient bulk data transmissions in LoRa-based networks. In the literature, similar MAC approaches have been considered as they typically offer higher reliability than that of Pure Aloha [ 19 ]. In [ 20 , 21 , 22 ], various time-slotted MAC strategies are used to mitigate the collisions in dense LoRa/LoRaWAN networks and, thus, improve their scalability.…”

Section: Related Researchmentioning

confidence: 99%

Optimal Data Collection Time in LoRa Networks—A Time-Slotted Approach

Zorbas

Caillouet

Abdelfadeel

et al. 2021

Sensors

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LoRa is a low-power and long range radio communication technology designed for low-power Internet of Things devices. These devices are often deployed in remote areas where the end-to-end connectivity provided through one or more gateways may be limited. In this paper, we examine the case where the gateway is not available at all times. As a consequence, the sensing data need to be buffered locally and transmitted as soon as a gateway becomes available. However, due to the Aloha-style transmission policy of current LoRa-based standards, such as the LoRaWAN, delivering a large number of packets in a short period of time by a large number of nodes becomes impossible. To avoid bursts of collisions and expedite data collection, we propose a time-slotted transmission scheduling mechanism. We formulate the data scheduling optimisation problem, taking into account LoRa characteristics, and compare its performance to low complexity heuristics. Moreover, we conduct a set of simulations to show the benefits of synchronous communications on the data collection time and the network performance. The results show that the data collection can reliably be achieved at least 10 times faster compared to an Aloha-based approach for networks with 100 or more nodes. We also develop a proof-of-concept to assess the overhead cost of communicating the schedule to the nodes and we present experimental results.

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Section: Related Researchmentioning

confidence: 99%

Optimal Data Collection Time in LoRa Networks—A Time-Slotted Approach

Zorbas

Caillouet

Abdelfadeel

et al. 2021

Sensors

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“…Despite the advantages of allocating resources, the random access approach has been considered due to its simplicity. In [ 14 , 15 ], the performance of LoRaWAN enabling carrier-sense multiple access (CSMA), end devices listen to the channel before attempting transmissions, is evaluated. They show the performance of LoRaWAN with CSMA improves than that of the ALOHA-based network through mathematical modeling and network simulation.…”

Section: Literature Reviewmentioning

confidence: 99%

DG-LoRa: Deterministic Group Acknowledgment Transmissions in LoRa Networks for Industrial IoT Applications

Lee

Yoon

et al. 2021

Sensors

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In this paper, we propose a novel MAC protocol, called DG-LoRa, for improving scalability in low power wide area networks. DG-LoRa is backward compatible with legacy LoRaWAN and adds new features, such as group acknowledgment transmissions in the time-synchronized frame structure that supports determinism on channel access. In DG-LoRa, the number of responses to data frames that are transmitted from end devices is maximized by allocating the spreading factor and timeslot in the frame structure. We evaluate the performance of DG-LoRa using the Monte-Carlo simulation and then compare it with the performance of legacy LoRaWAN in terms of data drop rate and the number of retransmissions. Our numerical results show that DG-LoRa supports approximately five times more connections to the LoRa network satisfying a 5% data drop rate. Also, it is observed that DG-LoRa enables low overhead by reducing the number of data frame retransmissions.

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“…where M , the number of timeslot in a contention period, is given by (5). As a matter of fact, it is feasible to assume that M 1, since in real scenarios T g + ToA T SYNC , being T g < γ × T SYNC .…”

Section: Co-design Of the Synchronization And Communication Parametersmentioning

confidence: 99%

Synchronous LoRa Communication by Exploiting Large-Area Out-of-Band Synchronization

Beltramelli

Mahmood

Ferrari

et al. 2021

IEEE Internet Things J.

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Many new narrowband low-power wide-area networks (LPWANs) (e.g., LoRaWAN, Sigfox) have opted to use pure ALOHA-like access for its reduced control overhead and asynchronous transmissions. Although asynchronous access reduces the energy consumption of IoT devices, the network performance suffers from high intra-network interference in dense deployments. Contrarily, adopting synchronous access can improve throughput and fairness, however, it requires time synchronization. Unfortunately, maintaining synchronization over the narrowband LPWANs wastes channel time and transmission opportunities. In this paper, we propose the use of out-ofband time-dissemination to relatively synchronize the LoRa devices and thereby facilitate resource-efficient slotted uplink communication. In this respect, we conceptualize and analyze a co-designed synchronization and random access communication mechanism that can effectively exploit technologies providing limited time accuracy, such as FM radio data system (FM-RDS). While considering the LoRa-specific parameters, we derive the throughput of the proposed mechanism, compare it to a generic synchronous random access using in-band synchronization, and design the communication parameters under time uncertainty. We scrutinize the transmission time uncertainty of a device by introducing a clock error model that accounts for the errors in the synchronization source, local clock, propagation delay, and transceiver's transmission time uncertainty. We characterize the time uncertainty of FM-RDS with hardware measurements and perform simulations to evaluate the proposed solution. The results, presented in terms of success probability, throughput, and fairness for a single-cell scenario, suggest that FM-RDS, despite its poor absolute synchronization, can be used effectively to realize time-slotted communication in LoRa with performance similar to that of more accurate time-dissemination technologies.

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LoRa Beyond ALOHA: An Investigation of Alternative Random Access Protocols

Cited by 98 publications

References 23 publications

Optimal Data Collection Time in LoRa Networks—A Time-Slotted Approach

Optimal Data Collection Time in LoRa Networks—A Time-Slotted Approach

DG-LoRa: Deterministic Group Acknowledgment Transmissions in LoRa Networks for Industrial IoT Applications

Synchronous LoRa Communication by Exploiting Large-Area Out-of-Band Synchronization

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