Abstract—A novel narrowband and low-power wide area network (LPWAN) technology named Narrowband Internet of Things (NB-IoT) based on Long Term Evolution (LTE) has been standardized by 3rd Generation Partnership Project (3GPP) in Release-13 to provide massive connectivity for Internet of Things (IoT). In NB-IoT systems, repeating same signal over additional period of time has been taken as a key technique to enhance radio coverage up to 20 dB compared to the legacy General Packet Radio Service (GPRS). NB-IoT system modeling and optimization of system performance is still challenging particularly coverage improvement in the case of practical applications. In this paper, we develop a repetitiondominated system model and evaluate the link-level coverage performance of NB-IoT uplink systems. Coverage performance based on signal repetition is also depended on the channel estimation accuracy. Besides, narrowband demodulation reference signal (NDMRS) assisted channel estimation and frequency-domain equalization are exploited on the receiver side. Link-level extensive simulations are performed to validate the uplink coverage performance for both single-tone and multitone transmissions. The results show that our proposed system model with repetition-dominated approach guarantees the transmission reliability in worse channel conditions of NB-IoT uplink systems as well as enhance the radio coverage.