Research On Coverage Enhancement Technology For Nb-IoT

Narrowband Internet of Things(NB-IoT),a large-scale low power wide area(LPWA)technique proposed by 3GPP,is mainly used by application scenarios for data acquisition and sensing,which is applied to fields of intelligent electric-meters,intelligent agriculture,intelligent logistics,etc.In order to provide wireless communication services,the cell base station of the NB-IoT system must be able to successfully establish a connection with the terminal.There are some challenges of establishing a connection between cell base stations and terminals: First,the cell has a wide coverage,a large number of scattered deployed terminals are greatly affected by the distribution of terrain and features;Second,the coexistence of heterogeneous terminals with different functions will form mutual interference;Third,the distribution of cell base stations and terminals is random,and traditional hexagonal cells are no longer suitable for network planning and performance analysis.This thesis analyzes and researches the coverage enhancement technique of NB-IoT,including random access process and signal enhancement processing of terminals.The former is based on random deployment of base stations and terminals to research the random access success rate and average access delay,which make a successful and reliable connection between base stations and terminals.The latter is based on the ability of stochastic resonance technology to convert noise energy into useful signals,which improves detection and identification capabilities of base stations and reduces the signal transmission power of terminals.(1)Performance analysis of coverage enhancement based on repetition and retransmission.Considering the detection probability and collision probability involved in the NB-IoT random access process,a preamble detection probability model based on random geometry and a conflict probability model based on multiband multichannel slot ALOHA are established.In the preamble detection probability model,the standard hexagon cell is expanded to meet the actual Tyson polygon cell.Based on the random geometry theory,the detection probability of the base station for the preamble and the detection probability after the preamble repetition are derived;In the collision probability model,the multiband and multichannel time slot ALOHA protocol is used to simulate the channel competition process of the terminal,and the competing success probability of terminal to channel is derived.Further,the preamble detection probability and channel competition success probability are integrated to derive the random access success rate of the NB-IoT terminal.In order to assess the impact of repetition and retransmission on system performance,the average access delay is derived,and the simulation is carried out in combination with the coverage category of NB-IoT.(2)Performance analysis of coverage enhancement based on stochastic resonance.Taking the maximum coupling loss as the performance index of NB-IoT coverage enhancement,a NB-IoT coverage enhancement mechanism based on stochastic resonance was proposed.Bistable stochastic resonance models is selected to analysis SNR performance,and the terrain factor is mapped to different Gaussian white noise intensities to simulate the differences in channel environments of different terminals.According to the Okumura-Hata wireless channel model,the corresponding simulation test environment is built to evaluate the detection capability of base station before and after introducing stochastic resonance,and the transmission power of the terminal before and after stochastic resonance is obtained by back modeling.