In NarrowBand Internet of Things (NB-IoT) systems, the Internet of Things (IoT) terminals should decode Downlink Control Information (DCI) quickly to receive resource allocation and scheduling information of the data channel correctly. Therefore, a low complexity Narrowband Physical Downlink Control Channel (NPDCCH) blind detection algorithm using correlation detection was proposed for NPDCCH with search space size being greater than or equal to 32. By employing two correlation judgments on the data in a possible minimum repetition transmission unit of NPDCCH, the invalid data in searching space was removed to reduce the computation complexity. Then, the repetition periods with the valid data were combined and decoded to improve the blind detection performance. Finally, theoretical and simulation analysis of two correlation thresholds used in correlation detection were carried out. Results show that compared with conventional exhaustive blind detection algorithm, the decoding complexity of the proposed algorithm is reduced by at least 75% and the detection performance gain is increased by 2.5 dB to 3.5 dB. The proposed algorithm is more beneficial for engineering practice.

Narrow Band Internet of Things (NB-IoT) technology is developing rapidly. Compared with the original wireless communication, the spectrum bandwidth of NB-IoT is only 180 kHz. Therefore, how to use resources or spectrum more efficiently (ie. resource allocation and scheduling) becomes a key issue for NB-IoT technology. In order to solve this problem, the related factors of NB-IoT uplink resource scheduling were analyzed, including resource allocation, power control and uplink transmission gap, and different options for comparison to select the optimal scheme were provided. In addition, modulation and coding scheme and the selection of the number of repeated transmissions were also analyzed in detail. A greedy-stable selection modulation and coding strategy based on different coverage levels and power headroom report were proposed, with which modulation and coding level was initially selected. A compensation factor was introduced to select the number of retransmissions and the update of the modulation and coding level. Finally, the proposed scheme was simulated. The simulation results show that the proposed scheme can save more than 56% of the activity time and 46% of the resource consumption compared with the direct transmission method.