The rapid growth of Internet of Things (IoT) in recent years has led to large-scale and wide-area applications, resulting in the emergence of the wide-area Internet of Things. Low-power wide-area networks (LPWANs) such as LoRaWAN form a crucial part of wide-area IoT, to support long-term applications across a vast geographical area. The diversity of applications and the large number of end devices in LPWANs define specific requirements for these networks such as low energy consumption, high reliability, long lifespan, low cost, and scalability. However, the continuous expansion of network size makes these more challenging. One method to address this challenge is the optimal placement of gateways within the network and the optimal allocation of parameters to end devices. This method aims to reduce network costs by using fewer gateways. However, considering the limited capacity of each gateway, excessive reduction in their number will decrease network reliability. Therefore, it is necessary to handle this trade-off by appropriately setting the parameters of end-devices (spreading factor and transmission power) to achieve the optimal number of gateways and deploy them in suitable locations. This research addresses the problem of placing the minimum required number of gateways in the network environment, considering the limited capacity of gateways and also the number of end-devices, while simultaneously optimizing the parameter values of end-devices to improve energy consumption, reliability, and network costs. Given that the problem is NP-Hard, it is reformulated as a problem of finding the minimum energy consumption state of end-devices, which is defined as an approximate solution to the problem. Then, by modeling various aspects of the network, it will be demonstrated that the reformulated problem provides a good approximation of the solution for the main problem. Subsequently, a method comprising three greedy algorithms will be presented to solve the problem of finding the minimum energy consumption state of end-devices. Finally, the effectiveness of the proposed method is eva‎luated through simulation, demonstrating that the minimum energy consumption state of end-devices serves as a near-optimal solution to the original problem. Based on the obtained results, in the proposed method, energy consumption for packet transmission in end-devices, the number of gateways, and network costs are reduced by more than 50% in various cases. Additionally, in some cases, the packet delivery ratio has improved, and in the remaining cases, its decrement has been negligible.

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عارف كريمي افشار , مجيد نبي