Research And Implementation Of NB-IoT System Random Access Process

Narrow Band Internet of Things(NB-IoT),as a new cellular technology,one of the key issues is to efficiently use limited spectrum resources to support large-scale IoT terminals.The random access is an important process for establishing uplink synchronization between user equipment(UE)and the network in the NB-IoT system.Based on the key research of Chongqing Science and Technology Commission project of "NB-IoT terminal SOC development and application",the thesis givessolutions to the key and difficult problems during the processes of transmission and reception of Narrow Band Physcial Random Access Channel(NPRACH),and carries out digital signal processing(DSP)implement.Simultaneously,based on the technologies of uplink Non-Othogonal Multiple Access(NOMA)and Successive Interference Cancellation(SIC),the author proposes a Narrow-Band Non-orthogonal Random Access(NB-NORA)mechanism.This thesis compares the systematic characteristics of LTE-A and NB-IoT,explains the structure of NPRACH and the design principle of preamble value,designs a preamble index detection scheme based on frequency hopping pattern comparison,and applies it to the preamble index detection of the receiver.This thesis proposes two time advanced(TA)detection algorithms based on time domain and frequency domain,and estimates the TA of the receiver.The results show that the false detection probability and missed detection probability of the preamble index are lower than 0.1% and 1% of the standard index under three coverage levels,and the probability of TA estimation error is 100% in the range of [-2.5-2.5us],which meets the standard requirement of more than 90%.For the proposed NB-NORA scheme,the main steps are as follows: 1)The terminal initiates Msg1 transmission,then the BS detects the NPRACH signals of different terminals carried on the same resource,and captures TA of each terminal;2)The BS packages NB-NORA Responses(NB-NORA-RARs),and the terminal obtains the TA approximation of according to the Narrow Band Positioning Reference Signal(NPRS)correlation peak to match the the closest value in the NB-NORA-RARs to obtain the corresponding Msg3 configuration parameters.3)the terminal sends Msg3 over the Narrow Band Physical Uplink Shared Channel(NPUSCH)according to the specified power in the response,and the base station decodes separately based on SIC;4)the competition is solved.In this thesis,the effects of power backoff step,number of repetition codes and signal-to-noise ratio on the throughput of the scheme are analyzed by modeling and simulation.The results show that under the same channel environment,the maximum throughput of Msg1 is about twice as much as that of traditional narrowband orthogonal random access scheme,and the number of access success of random access process is increased by about 75%.In the case of sudden congestion,NBNORA scheme can alleviate the conflict to a certain extent.The thesis implements the processes of transmission and reception of the NPRACH on the chip of TMS320C6670 with DSP.Additionally,the thesis describes the implementation process of each submodule based on the downsampling frequency domain correlation estimation algorithm and the preamble index detection.The implementation result of DSP satisfies the TA error value range and the preamble index detection accuracy specified by the standard,and the feasibility analysis of the whole scheme is also carried out from the aspects of memory and time.The results indicate that both memory and time can meet the requirements of both project and standard.