## 4 LoRaWAN Issues and Recent Solutions
### Pure Data Extraction  
Improvement of the data extraction rate (DER) aims to enhance the network throughput. In [41], the authors modeled the uplink nodes' activity using a mathematical model based on collected experimental data by implementing DER as a new metric for measuring LoRa network performance. The transmitted messages in a LoRa network should be received at the backend system. In other words, each transmitted message must be received by at least one LoRa gateway. Thus, the authors defined the DER metric as the ratio of received to transmitted messages in a defined interval. The obtained ratio of the DER is a function of the node or gateway locations, number, and activity. LoRa exhibits the capture effect since it is a form of frequency modulation. The capture effect happens when two signals with different strengths reach the receiver. If the difference in the signals' strengths is too small, the receiver will not be able to decode any of the received signals. Thus, the study suggests adding more gateways to enhance the LoRa throughput. SF allocation was the focus of [42] to enhance the capacity of the LoRa network. An optimization for SF allocation in relation to the LoRa network's capacity was defined by maximizing the packet success probability (PSP) to increase the connectivity of the end devices. During the SF allocation assignment process, the suggested method took both inter- and intra-SF interference into consideration. When the signal of interest has a signal-to-interference ratio (SIR) greater than a predetermined threshold, the capture effect is used to combine the two types of considered interference into the signal of interest. The propositional scheme controls the SF distribution based on the assigned distances obtained from the problem optimization instead of conventional allocation, which is based on coverage distances according to the sensitivities of the LoRa's physical layer. The authors used stochastic geometry for calculation of the PSP average and assigned SFs to the end devices according to the received power and SIR of the end devices. Although the proposed approach is complex, the global optimization solver can overcome this issue. Another approach to maximize the LoRa network capacity based on SF network clustering was developed in [43]. A tree-based SF clustering algorithm allocates end devices to many subnetworks. Several transmission parameters of LoRa are considered to form multi-mesh subnets with different SFs that are rooted at the gateway for enabling simultaneous transmissions. The proposed approach balances the traffic load among the end devices using an SF capacity estimation based on the node number, data rates, and number of hops, thus avoiding bottlenecks of the subnets. The higher SF values increase the delay due to the greater air time required to transmit the packets. The authors claimed that their approach improved the network performance compared with the conventional SF allocation of the LoRaWAN network with a single hop. Nevertheless, the analysis ignored the positive impact of the offloading method since the time response was not fairly distributed among all the cluster heads. Moreover, the transmitted overhead raises the energy consumption at the relay nodes. Further investigation is required for faster prediction of the efficiency and connectivity of the SF based on higher speed data rates. The ADR can be utilized to enhance the DER and maximize network throughput. The authors of [44] proposed extension modules for ns-3 by implementing the ADR in the LoRaWAN library to allow the simulation of a real LoRaWAN scenario. The introduced improvement optimized the data rate of the end nodes, and thus the conducted simulations achieved a minimal convergence time for the LoRa nodes. Therefore, an enhancement in the PDR was attained in a dynamic LoRa network. The authors claimed that their proposed ADR outperformed the standard algorithm in the considered scenarios, while their algorithm can be integrated easily to replace the existing ADR LoRaWAN network.