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NB-IoT is an emerging cellular technology that provides better coverage for applications with large connectivity,low power,low throughput,low device cost and high latency tolerance.Compared with Long Term Evolution(LTE)system,the Narrow-band Physical Random Access Channel(NPRACH)of NB-IoT system has been modified a lot.Therefore,the structure design of NPRACH in NB-IoT system is analyzed in detail by comparison with LTE system.And a 2-D FFT-based NPRACH receiver detection algorithm is proposed. Through MATLAB simulation analysis,the results show that under different coverage levels,the algorithm detects NPRACH Preamble missed detection probability of less than 0.05% Misdetection Probability(MDP),Alarm Probability(FAP)less than 0.1%, which meets the standard requirements of 1% MDP and 0.1% FAP indicator,and the probability of Time-of-arrival(ToA) Error in the range of -2.5～2.5 μs is higher than 95%.

As an important process of UE initial access and uplink synchronization, the random access procedure is simplified and modified on the basis of LTE system in NB-IoT. Through the random access procedure in LTE system, a random access procedure based on competitive mode which is currently supported by NB-IoT is deeply analyzed and a conformance test platform based on TTCN-3 is built to verify the consistency of the random access procedure with the standard.