Research And Realization Of Narrowband Physical Downlink Channel In NB-IoT System

Narrowband Internet of Things(NB-IoT)is a low-power wide-area network(LPWAN)technology that uses license spectrum.Because of the low deployment cost and the widely range of IoT business,NB-IoT is favored by the internet of things industry.In order to ensure normal communication of the transceiver,the physical layer needs to correctly transmit and receive data on the downlink channel,which include the narrowband physical downlink control channel(NPDCCH)carrying the control information and the narrowband physical downlink shared channel(NPDSCH)carrying the downlink data such as the system information and paging.According to the demand of the major projects “Development and Application of NB-IoT Internet of Things Terminal SOC” in laboratory.This thesis mainly study the NPDCCH and NPDSCH in the NB-IoT system.The main works and innovations are as follows:1.In order to improve the performance of decoding downlink data for NB-IoT terminal under the unknown channel environment,this thesis proposes a maximum ratio combining(MRC)algorithm based on the offset distance weighting.The Euclidean distance between the frequency domain data and the estimated modulation symbol is used as the weighting coefficient of the MRC algorithm.The results of simulation show that the proposed algorithm improves 2~2.5dB bit error rate(BER)gain,and is closer to the MRC algorithm under ideal conditions compared with the single-branch decoding scheme.In terms of computational complexity,the number of algorithm executions is high,but the overall complexity is still in the linear order which is within the acceptable range.2.When the time domain range of the NPDCCH search space is greater than 16,the computational complexity of the NB-IoT terminal using the exhaustive search algorithm to detect downlink control information(DCI)is large.Therefore,a low complexity blind decoding algorithm based on the correlation detection is proposed.This algorithm mainly uses the correlation between the repeated data transmitted in the NPDCCH repetition period to eliminate invalid data in the search space,and narrows the blind detection range of the terminal.In addition,the combining algorithm for valid data can improve detection performance.The simulation results show that the proposed blind detection algorithm can reduce at least 75% for the computational complexity,and does not affect the detection performance under reasonable configuration of two relevant thresholds compared with the exhaustive search algorithm.3.Combined with the proposed detection algorithm,the NPDCCH and NPDSCH transceiver signal processing are implemented by Digital Signal Processor(DSP).In addition,the DSP implementation performance and resource consumption of the receiver combining module and the NPDCCH blind detection module are analyzed.It verify the feasibility of the proposed algorithm and has the practical value in project realization.