Search

Despite that the LoRa technology has its salient features such as long transmission range and low power consumption, it suffers from data collision and signal suppression. The signal suppression problem not only degrades reliability in data transmission, but also tends to incur the unfairness such that a receiver demodulates only the strongest one of multiple received signals. To tackle this problem, the proposed approach tries to avoid the situation that multiple nodes send data simultaneously. It allows every node to transmit data only at the boundary of transmission slots and uses both random delay slots and the listen-before-talk (LBT) mechanism for collision avoidance. It is proven by experiments that the proposed approach, named ST/CA, achieves high reliability and fairness against the variation of traffic loads compared with LoRaWAN.

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.