Low-power wide-area networks (LPWANs), which achieve low-power consumption, enabling long-term battery operation and long-range communication capabilities, have emerged as a new standard for realizing massive wireless sensor networks (WSNs). LPWANs are becoming increasingly popular due to low introduction costs, which stem from features, such as using unlicensed bands and low-cost nodes. LPWANs are particularly useful for Internet of Things (IoT) applications that periodically collect information about specific observation targets. However, LPWAN generally adopts a simple medium access control (MAC), which significantly degrades communication quality due to packet collisions when the traffic load increases. Thus, MAC design is critical for realizing large-scale LPWANs. Carrier sense multiple access (CSMA) can autonomously avoid packet collisions. However, its performance is drastically deteriorated due to the hidden node problem in large-scale LPWANs. This article proposes an autonomous distributed MAC strategy that can suppress the hidden node problem by utilizing traffic periodicity. The proposed method is designed carefully considering LPWAN-specific constraints, such as duty cycle limitations in unlicensed bands, low clock accuracy of nodes, and limited downlink communication opportunities. From numerical results, the proposed method improves the packet delivery rate (PDR) performance by up to approximately by 29%, 9%, and 8% compared to ALOHA, CSMA-x, and the state-of-the-art LoRa MAC, respectively.

Low Power Wide Area Networks (LPWANs), including Long-Range Wide Area Network (LoRaWAN), that enable long-distance communication with low-power consumption have been attracting attention along with the development of the Internet-of-Things (IoT). Carrier Sensing (CS) is mandated before packet transmission in some regions and countries. However, the hidden node problem becomes more serious as the communication area becomes larger. Packet-Level Index Modulation (PLIM) assigns indexes to the frequency channel and time slot of packet transmission to increase throughput. This paper proposes a PLIM-based method to enable the GateWay (GW) to obtain the sensing relationships among nodes without explicit signaling. The obtained information can be used for node clustering and resource allocation to alleviate the hidden terminal problem. Computer simulation results show that the proposed method improves Packet Delivery Rate (PDR) by up to 13% compared to the conventional method using PLIM. And can achieve a similar PDR performance as the situation where the inter-node distance is ideally known.

Low-power wide area networks (LPWANs), such as long-range wide area networks, are increasingly adopted as a communication standard for wireless sensor networks. LPWAN has been adopted for systems that periodically collect data from sensors, such as in environmental monitoring. However, continuous packet collisions may occur in periodic traffic systems owing to the adoption of a simple random-access scheme in LPWAN. In addition, the use of low-cost nodes results in clock drift, rendering the synchronization of nodes in the system challenging. Thus, this study proposes a wireless resource allocation scheme to avoid continuous packet collisions under the adverse effect of such clock drift. In the proposed scheme, the gateway determines the transmission offset and frequency channel for each node utilizing the periodic traffic feature and clock drift. Based on computer simulation results, the proposed scheme can improve the packet delivery rate by over 20% compared with benchmark methods.

With the fast growth of Internet-of-things (IoT) and machine-to-machine (M2M) communications technology, low- power wide area networks (LPWAN) such as long-range wide area network (LoRaWAN) are attracting attention. One of the main applications of LPWAN is information collected from a large number of sensor nodes, where network traffic is generally dominated by periodic uplink (UL) traffic. In LPWAN, each sensor node transmits packets at arbitrary timing, which causes packet collisions and degrades the system communication quality. Especially in the case of periodic UL, continuous packet collisions may occur. Therefore, this paper proposes a centralized radio resource allocation scheme that avoids packet collisions of periodic traffic in LPWANs, taking into account the characteristics of the periodical traffic. The computer simulation results show that the proposed scheme can improve the average packet delivery ratio (PDR) by 18% and the age-of-information (AoI) performance compared to the ALOHA protocol.

Low-power wide-area network (LPWAN), which includes the long-range wide-area network (LoRaWAN) protocol, is an enabling technology that satisfy low power consumption and long-range communication. In many applications of LPWAN, an end node (EN) transmits data at regular intervals. Based on this, we had previously proposed the concept of packet-level index modulation (PLIM) to increase the number of information bits transmitted by one data packet. In PLIM, the generation interval between two consecutive packets is split into multiple time slots. Each EN transmits its packet in a specific combination of time slot and frequency channel, which represents the index, to convey additional information bits. To retrieve additional information, the gateway (GW) detects the time slot in which the data packet is being transmitted. Therefore, accurate synchronization between EN and GW is essential. However, clock drift occurs due to the inexpensive real-time clock oscillator on each EN, which results in timing misalignment between each node and the GW. This article proposes a simple clock drift estimation and compensation method for the PLIM. An experimental measurement is performed to model the clock drift. The numerical results obtained using the clock drift model show that it can accurately detect the time slot index under the influence of clock drift. Furthermore, PLIM is implemented on a commercial LoRaWAN node and GW to demonstrate its practicability.