Providing low power and long range (LoRa) connectivity is the goal of most Internet of Things networks, e.g., LoRa, but keeping communication reliable is challenging. LoRa networks are vulnerable to the capture effect. Cell-edge nodes have a high chance of losing packets due to collisions, especially when high spreading factors (SFs) are used that increase time on air. Moreover, LoRa networks face the problem of scalability when they connect thousands of nodes that access the shared channels randomly. In this paper, we propose a new MAC layer-RS-LoRa-to improve reliability and scalability of LoRa wide-area networks (LoRaWANs). The key innovation is a two-step lightweight scheduling: 1) a gateway schedules nodes in a coarse-grained manner through dynamically specifying the allowed transmission powers and SFs on each channel and 2) based on the coarse-grained scheduling information, a node determines its own transmission power, SF, and when and on which channel to transmit. Through the proposed lightweight scheduling, nodes are divided into different groups, and within each group, nodes use similar transmission power to alleviate the capture effect. The nodes are also guided to select different SFs to increase the network reliability and scalability. We have implemented RS-LoRa in NS-3 and evaluated its performance through extensive simulations. Our results demonstrate the benefit of RS-LoRa over the legacy LoRaWAN, in terms of packet error ratio, throughput, and fairness. For instance, in a singlecell scenario with 1000 nodes, RS-LoRa can reduce the packet error ratio of the legacy LoRaWAN by nearly 20%.
In this work, we propose a new communication system for illuminated areas,
indoors and outdoors. Light sources in our environments -such as light bulbs or
even the sun- are our signal emitters, but we do not modulate data at the light
source. We instead propose that the environment itself modulates the ambient
light signals: if mobile elements 'wear' patterns consisting of distinctive
reflecting surfaces, single photodiode could decode the disturbed light signals
to read passive information. Achieving this vision requires a deep
understanding of a new type of communication channel. Many parameters can
affect the performance of passive communication based on visible light: the
size of reflective surfaces, the surrounding light intensity, the speed of
mobile objects, the field-of-view of the receiver, to name a few. In this
paper, we present our vision for a passive communication channel with visible
light, the design challenges and the evaluation of an outdoor application where
our receiver decodes information from a car moving at 18 km/h.Comment: 8 pages, 17 figures in ACM CoNEXT 2016 (Best Paper Runner-Up
The emerging wireless vehicular communication technology is intended to improve safety and comfort of transportation systems. Different types of traffic information could be delivered through vehicle-to-vehicle and vehicle-toinfrastructure communications. This paper proposes a Quality-of-Service (QoS) supported multi-channel MAC scheme for Vehicular Ad Hoc Networks (VANETs), which can adaptively tune the contention window for different services at each node, and dynamically adjust the intervals of the Control Channel (CCH) and the Service Channels (SCHs) working in multi-rate. Theoretical model is proposed to obtain the contention window and optimize the intervals based on traffic conditions. Analysis and simulation results show that the proposed MAC is able to help IEEE 1690.4 MAC support QoS services, while ensuring the high saturation throughput and the prioritized transmission of critical safety information.
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