A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> 4) RECEIVE WINDOWS <s> Today the LoRaWAN is among the most widely adopted Low Power Wide Area Network (LPWAN) technologies. In contrast to the other alternatives, LoRaWAN enables deploying both continent-wide public networks, and private networks composing one or several gateways. In this paper, we empirically investigate how does the presence of the downlink traffic affects the performance of uplink for LoRaWAN operating in 868 MHz EU bands. Our results show that in real-life the downlink transmissions can compromise performance of uplink and must be accounted for when planning a network. Also we demonstrate the effects that the selection of secondary frequency channels and data rates have on the performance of a LoRaWAN network. The reported results reveal new dependences and provide the ground truth reference for the future analytical works. For these reasons, the paper can be of interest to both practitioners, planning and deploying LoRaWAN networks, and the researchers performing analytical work on LoRaWAN. <s> BIB001 </s> A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> 4) RECEIVE WINDOWS <s> LoRaWAN is gaining momentum in the arena of IoT connectivity technologies thanks to the low cost, ease of deployment, and support for adaptable transmission rates and bidirectional communications. The research community has then been working to develop suitable analytical models that can be instrumental in the study of this technology. In this work we propose a mathematical model that makes it possible to accurately estimate the packet success probability of a LoRaWannetwork in presence of bi-directional traffic, i.e., both uplink (UL) and downlink (DL) transmissions, and that accounts for the most critical features of the LoRa chipset and the LoRaWanstandard. The proposed model, furthermore, makes it possible to study the effect of different parameters configurations, thus offering a valid tool to investigate possible improvements to the system configuration. The proposed model is first validated by comparison with some accurate simulation results and, then, its potential is exemplified by analyzing the system settings that yield the best network performance. <s> BIB002 </s> A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> 4) RECEIVE WINDOWS <s> Low-power wide-area networks are continuously gaining momentum as enablers of massive machine-type communication, thanks to long-range wireless technologies operating either on unlicensed spectrum like, e.g., Long-Range (LoRa) and Sigfox, or on licensed spectrum, as Narrowband-IoT. For the former category of technologies, stringent requirements in terms of channel utilization and radiated power must be fulfilled, thus algorithms and protocols for enhanced radio-resource management need to be investigated. In this paper, we propose a disruptive approach for LoRa systems, exploiting a novel operational mode at the gateways side called time-power multiplexing, which fully exploits the degrees of freedom of the unlicensed bands regulations. The simulation results show that the proposed solution boosts the number of users that a LoRa network can support with respect to the default operational mode. <s> BIB003 </s> A Survey on the Viability of Confirmed Traffic in a LoRaWAN <s> 4) RECEIVE WINDOWS <s> LoRaWAN is an emerging low-power wide-area network (LPWAN) technology, which is gaining momentum thanks to its flexibility and ease of deployment. Conversely to other LPWAN solutions, LoRaWAN indeed permits the configuration of several network parameters that affect different network performance indexes, such as energy efficiency, fairness, and capacity, in principle making it possible to adapt the network behavior to the specific requirements of the application scenario. Unfortunately, the complex and sometimes elusive interactions among the different network components make it rather difficult to predict the actual effect of a certain parameters setting, so that flexibility can turn into a stumbling block if not deeply understood. In this article, we shed light on such complex interactions for a single-gateway (GW) system by analyzing the effect of some built-in features and configurations, including the GW’s limitations in terms of duty cycle and the number of parallel reception paths, the number of allowed retransmissions for confirmed traffic, and the preconfigured data rate used in downlink transmissions. The simulation-based analysis reveals various tradeoffs and highlights some inefficiencies in the design of the LoRaWAN standard. Furthermore, we show how significant performance gains can be obtained by wisely setting the system parameters, possibly in combination with some novel network management policies (e.g., enabling selective prioritization of downlink transmissions at the GW). <s> BIB004
Gateways are required to respond in either of the two receive windows and have to consider the DC restrictions as well as potential interference problems of each window. The first window uses by default the same channel as the original uplink. The use of this window will cause interference with uplink messages from nodes in the network BIB003 . Most works examining confirmed traffic make use of mathematical models or simulation tools, an empirical approach was however followed in BIB001 . A gateway and several nodes were placed in an anechoic chamber with the duty cycle restrictions for the nodes selectively disabled. This allowed a single device to emulate 88 to 700 nodes (depending on the SF used). Their experiments found that downlink traffic caused a significant increase in uplink traffic's PER. This is due to the uplink-downlink interference when receive window one is used. Additionally, it was found that the gateway tended to respond using receive window two for high SF traffic and used window one for low SF traffic. This was attributed to the duty cycle limitations that a gateway must adhere to. The time-on-air of high SF ACKs will cause a gateway to quickly exhaust window one, and will thus force the use of window two which has a more relaxed DC requirement. The second window is on a dedicated downlink only channel, which would be used only by gateways. A network will contain significantly fewer gateways than nodes, making this window a better choice from an interference perspective. However, the DC restrictions applied to each window's channels and the SF used for the response also have to be considered. The use of the second channel tend to occur with higher SFs, the default is SF12, resulting in longer on-air time for transmissions BIB001 . This will also increase the interference one gateway's transmissions have on another and thus the lowest possible SF should rather be used BIB002 . The impact of swapping the sub-bands used by each window was investigated in BIB004 .In a mixed traffic network swapping the sub-bands showing a marginal improvement in confirmed packet success ratio, implying that the uplink-downlink interference normally experienced in window one had minimal impact. A potential solution to eliminate uplink-downlink interference is to disable the use of receive window one and to only rely on window two. This idea is explored in BIB003 , which is discussed in more detail in Section .