A RELAYING METHOD FOR LoRa NETWORKS

Abstract

The proposed invention provides an adaptive, low-complexity relaying mechanism for LoRa devices (30). The positioning of the relay (20) is chosen to be geometrically effective so that it maintains a reliable connection with the gateway (10) and nearby end devices (30). Based on RSSI and SF and link budget calculations, the relay (20) can distinguish between devices (30) that can reach the gateway (10), cannot reach the gateway (10) without tuning existing transmission parameters and cannot communicate with the gateway (10) whatever the transmission parameters are. Thus, the relay (20) takes an action or not according to communication status of the end devices (30)..

Description

[0001] A RELAYING METHOD FOR LoRa NETWORKS

[0002] Technical Field

[0003] The present invention proposes a method that uses a smart repeater / relay for LoRa (Long Range) networks to extend range, adapt transmission parameters, and manage resources.

[0004] Background

[0005] In urban and suburban areas, the range of LoRa devices is between 5 and 15 km. In practice, however, it can be less than 250m [1] due to multiple factors, such as path loss. Conventional relays cannot be used to amplify the signals because LoRa devices operate in ISM frequencies that are subject to power limitations [2], In addition, when sensors awaken to transmit an uplink, they use the preset parameters, which frequently prevent the signal from reaching its intended destination. As a result, they progressively seek for the optimal parameters to transmit with. As a result, these sensors lose their allowed time on air (TOA), consume more power, increase packet loss, and cause signal collusion, resulting in a significant decrease in data rate as they use a greater symbol frequency (SF) to transmit data or ingest a packet portion during parameter tuning and retransmission.

[0006] Extending the range of LoRa systems is extensively discussed in [3]-[6]. Nonetheless, the majority of these studies violate the stringent constraints of power, available resources, and minimal complexity that are the pillars of wireless sensor networks (WSNs) [7], In addition, classical transmission parameter adjustments [8] deplete LoRa's resources, which degrades the overall system's performance.

[0007] To address the emphasized limitations of LoRa networks, a variety of commercial and academic solutions are available [9]-

[0019] . In [9], the authors propose partitioning multihop LoRa networks into clusters based on SF in order to accomplish fairness. Essentially, there are high SF and low SF cluster nodes. The gateway (GW) chooses the relay node using the naive Bayes algorithm, just as the relay node chooses the clusters. The study in

[0010] proposes a two-hop amplify and forward relaying LoRa network in a random node distance, with the gateway employing a joint SF and power allocation optimization algorithm to achieve the highest data rates. Based on concurrent transmissions

[0011] , a LoRaHop protocol that extends LoRaWAN by forming a mesh network that relays uplink and downlink packets without collision. Based on this flexible radio scheduling mechanism in the network, any node can transmit an uplink to the GW without causing a collision, using the LoRaHop protocol. The paper

[0012] proposes a scalable relay control scheme for LoRa-based LPWAN (Low-Power Wide Area Network). The authors used a genetic algorithm to solve the non-convex problem of employing the minimal SF and increasing the probability of coverage while adhering to the duty-cycle regulation constraint.

[0008] The article

[0013] provides a comprehensive mathematical model for a multi-hop network that modifies the Distance Ring Exponential Stations Generator. The authors employ intermediate GWs that are distributed in rings according to the Fibonacci distance propagation model. If the ED determines that its packet should transit through an intermediate GW, the intermediate GW will forward the packet directly to the primary GW without delay. An implicit overhearing node-based multi-hop communication (IOMC) scheme for LoRa networks

[0014] is presented, which exploits implicit relay nodes for performing the overhearing in order to promote relay operation while meeting duty cycle regulations. These overhearing nodes monitor the channels for ED transmissions and then forward them to the GW using multihop transmission; the ED is also expected to open a third reception window to receive the delayed ACK from the GW. The LoRa alliance proposed a system relaying mechanism

[0015] that employs a relay that is activated by a wake-on radio signal transmitted by the EDs. This relay is apparent in the network and modifies both uplink and downlink transmitted frames.

[0009] Concerning existing patents that address the aforementioned limitations, in a mesh network topology

[0016] is proposed in application numbered CN111970739A, with a relay node that calculates the optimal cost of each path between the relay and GW and transmits the payload along with the cost factors to the next node until it reaches the GW. The patent application numbered CN113613186A

[0017] describes a Lora central device for determining the number of relay devices based on the number of terminals, distance information, and relay channel capacity. The relay device transmits any uplink from the terminal to the control device, which is responsible for determining the relay device's downlink channel, subsequent transmission windows, and transmission parameters. In addition, as stated in application numbered CN115119216A, the terminal communicates with the GW via the LoRa relay device, and the LoRa relay device determines whether the terminal is relayed for the first time

[0018] . The LoRa relay device generates new window receiving and delay times and transmits them to the terminal. Finally, the relay

[0019] presented in the patent numbered KR102396399B1 comprises the following steps: allowing a node selected as a source node to directly transmit a packet to a GW without relaying or transmitting the packet to a relay device in a broadcasting phase after a change to a low SF, followed by the node that receives the source node's packet forwarding it to the GW in a relay phase. The decision as to whether a packet should proceed through the relaying phase is based on RSSI (Received Signal Strength Indicator), SNR (Signal to Noise Ration), and SNIR (Signal to Interference and Noise Ratio), with the duty cycle constraint taken into account.

[0010] Although deploying new GWs appears to be the most straightforward option, it conflicts with the low-cost requirement of WSNs. In addition, these GWs will be located within the coverage area of an existing gateway, so they will share the same limited and joint LoRa system resources (bandwidth and spreading factors). The relays discussed thus far blindly amplify LoRa signals, whereas some proposed amplifiers alter the modulation of the downlink sent by the GW, making the system more complex and adding more computational burden to low-end devices. In addition, some of the proposed relaying mechanisms use EDs as forwarding nodes, so these nodes utilize their allotted TOA in order to forward the packets of other nodes. In addition, these sensors require their RF chain to either be continuously active or to include reference signals to activate them. According to the LoRaWAN (Long Range Wide Area Network) specification [2], LoRa employs a star-of-stars topology to connect distributed sensors to the gateway; therefore, altering the topology will render deployed networks incompatible. In addition, mesh networks are proposed in which nodes (sensors) forward transmitted signals to the subsequent nodes until the signal reaches the GW, requiring the sensor's RF chain to be continuously active. Consequently, the sensor will consume all of its power, and because LoRa imposes restrictions on the duty cycle, which is 1 % of the time, the sensors will consume their allotted power while transmitting packets. The same comments that have been made about mesh topology can be applied to the proposed protocol and concurrent transmissions, which are non-compliant with the LoRa systems' standards and specifications

[0020] . Briefly, technical problems available in prior art are as follows:

[0011] • High PDR percentage, especially in urban areas and wireless unfriendly zones (WUZs). Mainly due multipath and failure to establish communication between the system’s two EDs.

[0012] • Reduced expected battery life (energy efficiency) in low-end devices as a result of the need to retransmit the unsuccessful transmission to the GW.

[0013] • A reduction in the coverage area owing to numerous factors. Primarily, path loss, obstacles, and WUZs.

[0014] • Low data rate as a result of retransmission, PDR, the conventional procedure for changing SF, and the requirement to use higher SF, resulting in a low data rate.

[0015] • Consuming TOA while adjusting transmission parameters.

[0016] • Collision between frames due to extended symbol duration and usage of similar SF.

[0017] Summary

[0018] The proposed smart relay provides an adaptive, low-complexity relaying mechanism for LoRa devices based on the calculation of SF, RSSI, and link budget (calculation of all gains and losses encountered by a signal as it travels from the transmitter to the receiver in a communication link). The positioning of the relay is chosen to be geometrically effective so that it maintains a reliable connection with the GW and nearby sensors. Specifically, the proposed design seeks to achieve the following objectives:

[0019] • Extend the communication range of LoRa systems by relaying devices that are inaccessible to the GW. In other words, extend the communication range for unreachable sensors, while locking them into low SF to increase their data rate, without exceeding power limitations of ISM bands.

[0020] • Adaptive and intelligent relaying mechanism depending on sensor state. The smart relay can allocate resources (primarily frequency channels) to prevent collisions in the event that multiple sensors use the same SF at the same time.

[0021] • Designate optimal transmission parameters adaptively to EDs that require parameter refining, bypassing the traditional incremental increase of SF.

[0022] • Save EDs resources that are both limited and bounded by specification. Specifically, TOA, power consumption, and number of retransmissions. Those resources are used for data transmission; thus, the data-rate will increase by using TOA, and power for actual data transmission. • The invisibility of the smart relay in the network, such that the functionality and protocols of both the GW and the sensors are unaffected.

[0023] • Compatibility with extant LoRaWAN regulations and specifications for network control repeaters, as described in release 18

[0021] .

[0024] • Support large scale connectivity of loT devices. Reduces packet drop ratio which is an already existing limitation in LoRa systems.

[0025] The proposed intelligent relay is compatible with deployed LoRa networks without requiring changes to the governing protocols, standards, or topology. Unlike existing repeaters, which indiscriminately amplify any signal they receive, the proposed relay differentiates between sensors / devices that require transmission parameter adjustments, those that require amplification, and those that can reach the GW. In addition, the proposed relay decreases the likelihood of packet collisions by assigning sensors to distinct channels.

[0026] In the proposed method, aforementioned limitations are surmounted by adaptively reacting to environmental change and basing decisions on that.

[0027] The smart relay is network invisible device, such that its existence will not be noticed at both ends: it will emulates itself as a GW to the sensors and as a sensor to the GW. The relay calculates RSSI and SF of the received frame efficiently and decides whether it can reach the GW or not. In the case the sensor’s signal can reach the GW, the relay will hold. In the case the ED cannot reach the GW whatever its transmission parameters are. The relay will forward the signal to the GW and sends a downlink to the sensor without instructing it to change its parameters.

[0028] In the case that the sensor cannot reach the GW, but can if it modifies its SF. The relay will dynamically designate new transmission parameters to the sensor and sends it along the downlink to the EDs. As opposed to allowing the sensor steadily increases its SF each time, thereby exhausting its limited resources (power, maximum number of retransmissions, and most importantly TOA). Then, the smart relay will transmit the initial signal to the GW, and the ED will transmit with the newly assigned parameters during the subsequent transmission window. In the case multiple EDs are assigned with the same SF within a period of time T (can be changed accordingly). The relay will schedule them in different channels to reduce probability of collision. Brief Description of the Figures

[0029] Figure 1 shows system model with the proposed smart relay distributed efficiently in the network.

[0030] Figure 2 shows flowchart of the relay functionality.

[0031] Figure 3 shows flowchart in case of adjustable sensor communication.

[0032] Figure 4 shows flowchart in case of non-reachable sensor communication.

[0033] Part References

[0034] 10. Gateway

[0035] 20. Relay

[0036] 30. End device

[0037] 31 . Reachable end device

[0038] 32. Adjustable end device

[0039] 33. Non-reachable end device

[0040] Detailed Description

[0041] In any existing LoRa network consisting of a gateway and sensors / end devices (EDs), the proposed relay (20) will suit without modification. No additional protocols or reference signals are required for full functionality of the relay (20). The only requirement is that the relay (20) knows the addresses and keys of the devices (30), although this is not a strict requirement because the majority of Eds (30) use ABP (Activation by Personalization) and the keys are assigned prior to initializing communications. These keys are primarily used by the relay (20) for sending downlinks. The fact that the vast majority of LoRa devices (30) are of type A that makes the compatibility of the proposed adaptive relaying mechanism more practical and realizable.

[0042] In order to establish a reliable communication link with the GW (10) and end devices (30) dispersed around it, and to reduce the number of relays (20) required, the relay (20) will be located geometrically effectively. This is based on geography and can be adjusted based on the preferences of the side using the relays (20). This relay (20) requires no changes to the network's topology, MAC layer, or signaling specifications, nor does it require registration on either end. In the context of network control repeaters, the relay (20) is network-invisible, emulating itself as a GW (10) to the sensors and as a sensor to the GW (10).

[0043] Using only the preamble to reduce latency and complication, the relay (20) then calculates the RSSI and SF of the received LoRa signal without decoding the received frames. On the basis of these parameters and link budget calculations, the smart relay (20) can differentiate between the following sensor types:

[0044] 1. Those that can directly reach the GW (10) with the current transmission parameters. In this case, the relay (20) does not respond and direct communication between the EDs (30) and the GW (10) is established.

[0045] 2. Sensors that cannot reach the GW (10) regardless of their transmission parameters, i.e. maximal coding rate, power, and SF. In this case, the relay (20) forwards their signal directly to the GW (10) and transmits a downlink to the Eds (30) while locking them to the current SF to increase their achievable data rate.

[0046] 3. EDs (30) that cannot reach the GW (10) with their current signal metrics but can reach the GW (10) by modifying their transmission parameters. For this type of sensors, the relay (20) assigns optimal transmission parameters adaptively based on the status of the ED (30) using a look-up table, so that the minimum required SF and transmission parameters are selected. The relay (20) then transmits a downlink containing the updated transmission parameters to the sensor. Using the LoRaWAN specifications' existing adaptive data-rate (ADR) medium access control (MAC) commands. The relay (20) then forwards the first transmitted frame to the GW (10) after a delay to ensure that the downlink transmitted by the GW (10) falls within the ED's (30) sleeping state.

[0047] In the event that the relay (20) assigns similar transmission parameters to multiple sensors within a predefined time period 'T,' the smart relay (20) schedules them on various frequency channels to reduce the likelihood of packet collisions, given that they share the same SF. Figure 2 depicts the complete mechanism of the proposed relay (20). The proposed method of using presented relay (20) is following:

[0048] • Place the relay (20) geometrically efficiently such that it maintains a reliable link with the GW (10) and can communicate with the sensors distributed in the network either outside or inside the coverage area of the GW (10).

[0049] • The smart relay (20) calculates the RSSI and SF of the received signals efficiently using the preamble only and without decoding the whole frame.

[0050] • Based on RSSI and SF and a link budget calculation, the relay (20) can distinguish between sensors which can reach the GW (10), those which cannot reach the GW (10) with the current transmission parameters but can reach it if they tune their transmission parameters. And the Eds (30) which cannot communicate with the GW (10) whatever their transmission parameters are.

[0051] • In the case of sensors which can reach the gateway, the relay (20) holds (i.e, does not react). For non-reachable end devices (33), the relay (20) forwards their uplinks to the GW (10) and sends a downlink to them without instructing them to change their transmission parameters in order to save higher SF and maximize their data-rate.

[0052] • For adjustable Eds (32), the relay (20) decides that they cannot reach the GW (10) with the current transmission parameters, thus based on a look-table it decides the optimal parameters to be used in the next transmission window and sends it along with the downlink. Then it forwards the first frame to the GW (10) after a delay such that the downlink from the GW (10) will fall in the sleeping window of the sensor.

[0053] • In case the relay (20) assigns the same SF to multiple sensors in a specific period of time (can be adjusted depending on environment), it schedules those Eds (30) to different channels to reduce probability of collisions.

[0054] References

[0055] [1] P. J. Radcliffe, K. G. Chavez, P. Beckett, J. Spangaro, and C. Jakob, “Usability of LoRaWAN Technology in a Central Business District,” in 2017 IEEE 85th Vehicular Technology Conference (VTC Spring), IEEE, Jun. 2017, pp. 1-5. doi: 10.1109 / VTCSpring.2O17.8108675.

[0056] [2] LoRa Alliance. 2020. TS001 -1.0.4 LoRaWAN® L2 1.0.4 Specification.

[0057] [3] Aslam, M. S., Khan, A., Atif, A., Hassan, S. A., Mahmood, A., Qureshi, H. K., & Gidlund, M. (2019). Exploring multi-hop LoRa for green smart cities. IEEE Network, 34(2), 225-231 .

[0058] [4] Ikhsan, M. G., Saputro, M. Y. A., Arji, D. A., Harwahyu, R., & Sari, R. F. (2018, November). Mobile LoRa gateway for smart livestock monitoring system. In 2018 IEEE International Conference on Internet of Things and Intelligence System (IOTAIS) (pp. 46-51 ). IEEE.

[0059] [5] Li, C., & Cao, Z. (2022). Lora networking techniques for large-scale and long-term iot: A down-to-top survey. ACM Computing Surveys (CSUR), 55(3), 1-36.

[0060] [6] Cuomo, F., Campo, M., Caponi, A., Bianchi, G., Rossini, G., & Pisani, P. (2017, October). EXPLoRa: Extending the performance of LoRa by suitable spreading factor allocations. In 2017 IEEE 13th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob) (pp. 1-8). IEEE.

[0061] [7] Kandris, D., Nakas, C., Vomvas, D., & Koulouras, G. (2020). Applications of wireless sensor networks: an up-to-date survey. Applied system innovation, 3(1 ), 14.

[0062] [8] Jouhari, M., Saeed, N., Alouini, M. S., & Amhoud, E. M. (2023). A survey on scalable LoRaWAN for massive loT : Recent advances, potentials, and challenges. IEEE Communications Surveys & Tutorials.

[0063] [9] Mugerwa, D., Nam, Y., Choi, H., Shin, Y., & Lee, E. (2022). SF-Partition-Based Clustering and Relaying Scheme for Resolving Near-Far Unfairness in loT Multihop LoRa Networks. Sensors, 22(23), 9332.

[0064]

[0010] Xu, W., Cai, G., Fang, Y., Mumtaz, S., & Chen, G. (2022). Performance analysis and resource allocation for a relaying LoRa system considering random nodal distances. IEEE Transactions on Communications, 70(3), 1638-1652.

[0065]

[0011] Tian, P., Boano, C. A., Ma, X., & Wei, J. (2023). LoRaHop: Multi-Hop Support for LoRaWAN Uplink and Downlink Messaging. IEEE Internet of Things Journal.

[0012] Lee, S., Lee, J., Park, H. S., & Choi, J. K. (2020). A novel fair and scalable relay control scheme for Internet of Things in LoRa-based low-power wide-area networks. IEEE Internet of Things Journal, 8(7), 5985-6001.

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[0013] Islam, M. R., Bokhtiar-AI-Zami, M., Paul, B., Palit, R., Gregoire, J. C., & Islam, S. (2023). Performance Evaluation of Multi-hop LoRaWAN. IEEE Access.

[0067]

[0014] Mugerwa, D., Nam, Y., Choi, H., Shin, Y., & Lee, E. (2023). Implicit Overhearing Node-Based Multi-Hop Communication Scheme in loT LoRa Networks. Sensors, 23(8), 3874.

[0068]

[0015] LoRa Alliance. "LoRaWAN® Relay Specification." TS011-1.0.0, LoRa Alliance, September 20, 2022.

[0069]

[0016] Yang Fengmin; Cai Jilong; Zhang Jian; Mo Jia; Wang Yaoting. (2020). China. Patent No. CN111970739A. China National Intellectual Property Administration.

[0070]

[0017] Lu Deliang; Ma Yongbo. (2021 ). China. Patent No. CN113613186A. China National Intellectual Property Administration.

[0071]

[0018] Dong Yinfeng; Xie Yuanzhi; Fan Yusen. (2022). CN115119216A. China National Intellectual Property Administration.

[0072]

[0019] Junkyun Choi; Lee Sanghyun; Hongshik Park. (2022). KR102396399B1 . Korean Intellectual Property Office (KIPO).

[0073]

[0020] LoRa Alliance, "LoRaWAN® Regional Parameters RP002-1.0.4."

[0074]

[0021] 3rd Generation Partnership Project (3GPP) (2018). 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Release 18; (Release 18). https: / / www.3gpp.org / release-16-17-18

Claims

CLAIMS1. A relaying method for LoRa networks, comprising steps of;• positioning a relay (20) at such a distance that the relay (20) can maintain a link with a gateway (10) and access end devices (30) distributed in a network either outside or inside coverage area of the gateway (10),• calculating strength indicator and spreading factor of received signals from the end devices (30) without decoding the whole network via the relay (20),• distinguishing between the end devices (30) that can reach the gateway (10), cannot reach the gateway (10) without tuning existing transmission parameters and cannot communicate with the gateway (10) whatever the transmission parameters are,• the relay (20) differentiates between following cases: o the end devices (30) that can reach the gateway (10) with the current transmission parameters, the relay (20) does not react and direct communication between the devices (30) and the gateway (10) is established, o the end devices (30) that cannot reach the gateway (10) with the current transmission parameters but can reach the gateway (10) by modifying the transmission parameters, the relay (20);■ assigns the transmission parameters adaptively based on the status of the device (30) using a look-up table, so that the required spreading factor and transmission parameters are selected,■ transmits a downlink containing the updated transmission parameters to the device (30) and■ forwards first transmitted frame to the gateway (10) after a delay to ensure that the downlink transmitted by the gateway (10) falls within the device’s (30) sleeping state, o the devices (30) that cannot reach the gateway (10) regardless of the transmission parameters, the relay (20) forwards their uplinks to the gateway (10) and sends a downlink to the devices (30) without instructing to change the transmission parameters.The relaying method according to claim 1 , wherein the relay (20) schedules the end devices (30) to different channels to reduce probability of collisions in case the relay (20) assigns the same spreading factor to multiple end devices (30) in a specific period of time.

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