A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> B. GROUPING TRAFFIC AND ACK AGGREGATION <s> LoRaWAN is a flagship Low-Power Wide Area Network (LPWAN) technology that has highly attracted much attention from the community in recent years. Many LoRaWAN end-devices, such as sensors or actuators, are expected not to be powered by the electricity grid; therefore, it is crucial to investigate the energy consumption of LoRaWAN. However, published works have only focused on this topic to a limited extent. In this paper, we present analytical models that allow the characterization of LoRaWAN end-device current consumption, lifetime and energy cost of data delivery. The models, which have been derived based on measurements on a currently prevalent LoRaWAN hardware platform, allow us to quantify the impact of relevant physical and Medium Access Control (MAC) layer LoRaWAN parameters and mechanisms, as well as Bit Error Rate (BER) and collisions, on energy performance. Among others, evaluation results show that an appropriately configured LoRaWAN end-device platform powered by a battery of 2400 mAh can achieve a 1-year lifetime while sending one message every 5 min, and an asymptotic theoretical lifetime of 6 years for infrequent communication. <s> BIB001 </s> A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> B. GROUPING TRAFFIC AND ACK AGGREGATION <s> Recently, the development of the Internet of Things (IoT) applications has become more active with the emergence of low-power wide-area network (LPWAN), which has the advantages of low-power and long communication distance. Among the various LPWAN technologies, long-range wide-area network (LoRaWAN, or LoRa) is considered as the most mature technology. However, since LoRa performs uplink-oriented communication to increase energy efficiency, there is a restriction on the downlink function from the network server to the end devices. In this paper, we propose cooperative downlink listening to solve the fundamental problem of LoRa. In particular, the proposed scheme can be extended to various communication models such as groupcasting and geocasting by combining with the data-centric model. Experiments also show that the proposed technology not only significantly reduces network traffic compared to the LoRa standard, but also guarantees maximum energy efficiency of the LoRa. <s> BIB002 </s> A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> B. GROUPING TRAFFIC AND ACK AGGREGATION <s> LoRaWAN promises to provide wide-area network access to low-cost devices that can operate for up to ten years on a single 1000-mAh battery. This makes LoRaWAN particularly suited for the data collection applications (e.g., monitoring applications), where device lifetime is a key performance metric. However, when supporting a large number of devices, LoRaWAN suffers from a scalability issue due to the high collision probability of its Aloha-based MAC layer. The performance worsens further when using acknowledged transmissions due to the duty-cycle restriction at the gateway. For this, we propose FREE , a fine-grained scheduling scheme for reliable and energy-efficient data collection in LoRaWAN. FREE takes advantage of applications that do not have hard delay requirements on data delivery by supporting the synchronized bulk data transmission. This means data are buffered for transmission in scheduled time slots instead of transmitted straight away. FREE allocates spreading factors, transmission powers, frequency channels, time slots, and schedules slots in frames for LoRaWAN end-devices. As a result, FREE overcomes the scalability problem of LoRaWAN by eliminating collisions and grouping acknowledgments. We evaluate the performance of FREE versus different legacy LoRaWAN configurations. The numerical results show that FREE scales well and achieves almost 100% data delivery and the device lifetime is estimated over ten years independent of traffic type and network size. In comparison to poor scalability, low data delivery and device lifetime of fewer than two years for acknowledged data traffic in the standard LoRaWAN configurations. <s> BIB003
Should the confirmation that data is received be important but latency not be grouping several measurements and transmitting them as 1 large payload will have several benefits. Doing so not only has a power consumption benefit BIB003 , BIB001 but also reduces the number of ACKs sent when compared to sending the data as several smaller packets. The simulations conducted in BIB003 , showed how their scheme's approach of sending fewer but larger packets helped reduce the total number of sent packets significantly (an order of magnitude) which helps reduce the number of collisions. Acknowledging several devices using one packet can be a method to reduce the number of transmissions required by gateways. This would, however, increase the time-on-air of the transmissions and potentially increase the number of packets a gateway did not receive as it now transmitting for longer periods. This approach would differ from the existing design as the protocol currently aims to minimise the time-onair of downlink transmissions through steps such as excluding a CRC for the PHYPayload. Should a packet containing a grouped ACK become corrupted it would no longer impact only one node, but rather all of the nodes who were expecting an ACK in this message. How often this would occur, and the impact of the resulting retransmissions, as well as the impact of the increasing time-on-air, is something that needs to be examined further. This is a growing area of LoRaWAN research, with some suggested methods already proposed. An adaptation of the LoRaWAN protocol to enable broadcasts via a cooperative downlink listening algorithm was proposed in BIB002 . This method can also be used to broadcasts ACKs to several devices at once thereby reducing the gateway's transmission times. This approach also introduces different methods of reducing traffic volume in a network via groupcasting (requesting data from only certain devices) and geocasting (request that only devices in a certain area transmit). Experiments showed that this method does lead to slightly higher energy consumption in networks where devices don't transmit often, e.g. 1 packet per hour, but the consumption soon matches LoRaWAN when the transmission frequency increases.