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LoRa modulation has gained considerable attention in wireless Internet of Things applications, from sensor networks to smart systems, due to its long-range and low-power capabilities, and it is currently one of the major technologies used in low-power wide-area networks. However, like many wireless technologies, LoRa-based networks remain vulnerable to jamming attacks, which can lead to denial-of-service. This paper proposes a technique to mitigate jamming attacks by estimating and canceling the jamming signal in scenarios where a gateway is jammed by a nearby adversary. Additionally, the benefits of a centralized radio access network architecture are explored for networks with multiple gateways and jammers, enabling post-cancellation demodulation at a central unit to enhance the legitimate signal against residual jamming signals. The simulation results show that this approach achieves an overall frame success rate (FSR) of more than 90% in areas covered by multiple gateways, with the centralized processing providing up to 1.5× gain over the standard distributed anti-jamming approach at low signal-to-noise ratio (SNR). Increasing the code rate from 4/5 to 4/7 further improves the FSR, up to 3× at low SNR and 1.5× at high SNR, at the cost of an increase in frame air-time. Finally, jammers located within 20 m of a gateway significantly degrade the achieved FSR, keeping it below 55% even with a code rate of 4/7 and the centralized processing, suggesting that gateway placement should prioritize restricted-access locations.