The Research On NB-IoT Data Repeating Transmission Mechanisms And Optimization Strategies

As one of the key supporting technologies in 5G,NB-Io T holds the characteristics of wide coverage,large connection,low power consumption and low cost.Because it works in the licensed spectrum,NB-IoT has lower construction cost and higher security than unlicensed spectrum technologies such as LoRa and SigFox,etc.Coverage enhancement is a major technical advantage of NB-IoT.The design objective of NB-Io T is to achieve coverage enhancement of 20 dB compared to GPRS and LTE,reaching 164 dB.Repeating transmission of data and control signals has been considered as a promising approach for enhancing coverage.However,too larger repetition number can cause problems such as low data transmission rate,spectrum efficiency,too much system resources consuming and higher cost.Therefore,the selection of the repetition number must be carefully considered.First,we introduce the traditional coverage situation of NB-IoT,and analyze the problem of selecting the repetition number.We find that the coverage granularity is too coarse so to bring the obstacle for data transmission rate.We hence propose a repetition number selection algorithm for static scenarios where the user is stationary or moving in a small range.The algorithm selects a finer division on the coverage enhancement level,selects the minimum repetition number,and adjusts the repetition times according to the data priority.The experimental results show that it could significantly reduce the average repetition number required to transmit data and increase the average revenue of the dataSecond,we analyze the link adaptation techniques and correlation models in NBIoT,and conclude that in the link adaptation of NB-IoT,we should consider both the choices of MCS level and the repetition number at the same time.We then propose a new NB-IoT link adaptation method based on multi-dimensional parameter adjustment for the dynamic scenes with low speed moving scenario.The scheme first adjusts the repetition number according to the link state to adapt to rapid situations changes,and then dynamically adjusts the MCS and the repetition number according to the HARQ feedback to solve the problem that the channel quality changes slowly.The performance of the proposed scheme is verified by simulation experiments.Experimental results show that our method can improve data transmission rate and improve system performance.