Low Power Wide Area Networks have emerged as a leading communications technology in the field of Internet of Things sensor and monitoring networks. In such networks, uplink traffic is characterized as a combination of periodic data reports and event-triggered alarm reports. When an many devices detect an event in a short timespan, a burst of concurrent transmissions can occur, leading to a surge of collisions, and thus severe data delivery performance degradation. In this paper, a hybrid random/scheduled access strategy is proposed for mitigating the impact of traffic-triggering events on network performance. Under periodic report traffic the LoRaWAN standard Class A protocol is in effect, but after an event a TDMA scheme is applied. Three implementations of this strategy are described. The first is a pair of novel MACs for LoRaWAN, allowing (a) synchronization of end devices with the network using the event detection as a crude synchronization point, and (b) the dynamic scheduling of groups of devices. The other two implementations build upon a single-hop and a two-hop previously proposed LoRaWAN-based wake-up architectures, respectively. The above approaches are validated and studied through extensive simulation. The results show improved packet delivery ratio over the Class A MAC. The effect is more prominent as the event propagation velocity increases. The proposed approach also surpasses LoRaWAN in energy per delivered bit for high event propagation velocities. Finally, the novel protocol has a lower hardware and deployment complexity than the wake up radio based alternatives, at the cost of higher energy consumption.
Local area networks often comprise nodes that run applications that belong to different traffic classes, with each class having different bandwidth requirements. Traditional Medium Access Control (MAC) protocols treat all nodes in the same manner. This may lead to a disproportionate allocation of bandwidth to the nodes and, consequently, to significant performance degradation. In this paper, a new MAC algorithm, is presented, that allocates different amounts of bandwidth to the nodes according to their traffic class. The bandwidth allocated to the nodes of each traffic class is proportional to the bandwidth requirements of the nodes of that class. The performance of the proposed Node Classification-based Bandwidth Allocation (NCBA) algorithm is studied via extensive simulation results, which indicate that it achieves a significant performance improvement compared to the well-known TDMA scheme. Overall, the new protocol achieves higher throughput, lower delay and exhibits a higher delay Fairness compared to TDMA for various network configurations, under asymmetric bursty traffic. 12 INDEX TERMS Traffic-based node classification, adaptive MAC, broadcast LAN, TDMA. above approach satisfactorily solves the problem of lack of 49 fairness in the bandwidth allocation process, as is the case 50 in traditional MAC protocols, owing to the equal treatment 51 of all nodes, despite their heterogeneity in terms of band-52 width requirement. Specifically, a new collision-free family 53 TDMA-based protocols, that partially base the decision of 54 time slot allocation, on an a priori classification of the nodes, 55 by their traffic profiles are introduced. Another contribu-56 tion of this study is the use of a metric equalization-based 57 optimization process, specifically the incorporation of delay 58 feedback into the bandwidth allocation process. The proposed 59 classification-based MAC uses traffic class information in 60 conjunction with queuing delay to adjust the allocated chan-61 nel resources to each class and node. The approach is demon-62 strated via extensive simulation results to outperform TDMA 63 under asymmetric bursty traffic conditions. 64 The rest of the paper is structured as follows: Section II 65 summarizes related work by presenting the proposed MAC 66 protocols, aimed at the efficient operation of broadcast net-67 works. Section III describes the system environment, defines 68 the categorization scheme of nodes in the broadcast network 69 and describes the type of traffic generated within the net-70 work. The proposed MAC protocol is presented in section IV.
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