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In the LoRaWAN protocol, the confirmed message is used for the reliable transmission service. Once a server received a confirmed message from an end device, it responds with an acknowledgement message to make sure that the uplink message was successfully delivered. For doing this, the protocol reserves two receive windows that follows uplink message transmission in the specified intervals. However, when GW responds with an acknowledgement message in one of the receive windows, it fails to receive messages from other end devices since it operates in half-duplex mode. This can cause high data loss as the number of confirmed messages increases. In this paper, we study how the increase of confirmed messages and message traffic affects packet delivery ratio. The simulation results shown that up to 24% number of uplink messages is lost or collided when 1000 end devices transmit data with 0.1% duty cycle and the confirmed message ratio is 0.2.

LoRa technology draws attention for its use in industrial monitoring and control systems in which each end device or task is required to send data periodically to a (cloud) server. Despite its provision of a stable link, it suffers from data loss by signal suppression and interference. A real-time LoRa protocol is proposed that uses a slot scheduling to remove collision and device or node grouping based on signal attenuation to deal with signal suppression. Based on the definition of a frame-slot structure, a logical slot indexing algorithm is devised to tag a logical index to each slot. The logical indices enable the easy allocation of slots to nodes such that if each node sends data in the allocated slots, it can satisfy time constraint. To handle external interference caused by other networks, the protocol uses a multiple listen-before-talk (mLBT) mechanism that allows channel detection multiple times within one slot. Our protocol is compared analytically and experimentally with other ones to show its superior throughput and reliability against signal suppression and interference.

The greedy routing that reduces the Euclidean distance to destination continuously to the possible maximum in every forwarding is suitable for vehicular ad hoc networks with high node mobility due to operation simplicity and low overhead. However, the selection of a next forwarding node based on the forward progress distance alone suffers from varying link conditions by high node mobility and communication obstructions. Thus, a compound node selection function is developed to include link quality factor. In this function, the accuracy of the forward progress distance largely depends on the node location error that comes from either GPS measurement error or the elapse of time after measurement. Location prediction is conducted by the Kalman filter and link quality is assessed using the successfully transmitted Hello messages. The compound function is evaluated against variations of fading and shadowing effects and the injected GPS error and is applied to a greedy routing protocol to prove its superiority.

To cope with the internal and external interference induced by other ambient signals, physical obstacles and the dynamic change of topology in wireless sensor networks, we propose an efficient and reliable MAC protocol combining TDMA and CSMA with channel hopping. The principle operation of the proposed protocol relies on the Big Slot Scheduling Algorithm that uses the tree routing and the notion of a sharable slot. A sharable slot of an appropriate size is allocated to each tree level and shared by all the nodes at the same level for data transmission. To adapt the dynamic change of topology, a node performs a slot scheduling in a distributed manner depending on its level. Data transmission is performed progressively, starting with the highest tree level. To mitigate external interference, the proposed protocol uses a blind channel hopping mechanism in which in channel switching, each node simply follows the selected channel sequence based on its ID every data transmission period. A sender follows the channel hopping sequence of a receiver or its parent for data transmission. We implemented the proposed protocol in Contiki OS and evaluated it in a 25-node testbed under various interference sources.