# A Survey on Adaptive Data Rate Optimization in LoRaWAN: Recent Solutions and Major Challenges
## 3 Review of Adaptive Data Rate Algorithms
### Throughput
Further study on how this approach can be used to aggregate transmission settings from different gateways in a single updating packet in a LoRa system with multiple gateways is open for research. Channel attenuation and data collision are classified as reasons for packet loss in [42]. The authors formulated an ADR selection scheme with enhanced loss differentiation which selects a reasonable data rate that maximizes throughput. The solution comprises three parts: prediction of channel attenuation, data collision probability and a data rate controller. They establish a channel attenuation model which they use to determine packet loss probability by channel attenuation. They then find the probability of data collision due to interference. A simulation model is established to investigate the correlation between the number of end nodes and the packet loss ratio (PLR) in the LoRa network using one gateway. They use MATLAB simulation to analyse and validate the performance of the technique. The proposed scheme showed reduced packet loss and improved DER compared to the standard ADR scheme and EXPLoRa. In this approach the authors only considered a situation where the nodes report periodically. Future work could look at event-driven applications as a consideration. A concept of network slicing was introduced in [43]. The LoRaWAN network is partitioned into several virtual networks, termed network slices, to efficiently assign network resources to support specific QoS requirements for every slice. Within the IoT, every end node demands specific QoS requirements regarding delay and reliability determined by the type of IoT application being run. The authors use various network slicing strategies with different SF distributions to evaluate the network performance and optimise SF allocation for each slice. They propose an adaptive dynamic inter-slicing algorithm wherein the BW is reserved on each LoRaWAN gateway using Maximum Likelihood Estimation (MLE). They then improve that algorithm by considering each gateway individually, reserving its BW after utilising MLE on the end nodes within its range (intra-slicingalgorithm). They compared the two adaptive dynamic slicing propositions to a standard fixed slicing strategy in which the gateway's BW is reserved uniformly among all the slices. Their results indicated an improvement in the optimisation of ADR due to an efficient coordination of resources. The strength of this approach is the provision of isolation of end nodes and its ability to maximize the efficiency of resource allocation in each LoRaWAN slice. The drawback is that energy consumption in the adaptive dynamic network slicing algorithm is increased compared to the static and dynamic configuration. The authors extended this work in [44] by taking into consideration some smart city applications representative of different QoS classifications and used a slice-based SF and TP configuration optimization. They proposed a new slicing optimization method called TOPG that is formulated on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Geometric Mean Method (GMM). Their suggested scheme sets the LoRa SF and TP parameters efficiently to improve the performance of every slice in terms of QoS, reliability and energy utilization. The results showed that TOPG outperforms static and dynamic configuration strategies, highlighting its effectiveness in the provision dynamic slice-based configurations and improving the performance of LoRa slices with regard to reliability and the percentage of end nodes that fulfilled their throughput and delay requirements. The joint SF assignment and transmit power allocation algorithm has been investigated in [45]. They consider both co-SF and inter-SF interferences for the improvement of throughput fairness. In theory, there is a dramatic decrease in performance levels when orthogonality conditions are not met under the same SF conditions and communication channel.