Internet of Things (IoT) has become the new trend of industrialized technology. LoRa technology and LoRaWAN network architecture have a big portion in the market deployment of LPWAN IoT with applications across industries such as agriculture, smart cities, manufacturing and transportation. In this paper, we conducted a simulation of LoRa technology using NS3 simulator in smart city scenario. Our simulations using NS3 is carried out to observe the characteristic of LoRA's transmission behavior and the radius coverage for understanding the performance limitation. The simulations show that higher Spreading Factor allows a higher packet success rate and time on air packet. Increasing the radius of gateway to the end device will reduce the packet success rate transmission. The best packet success rate value at the radius 6500 meters is 0.932 with the amount of End Node are 850.