Design And Implementation Of NB-IoT Downlink Broadcast Channel Codec

Narrow Band Internet of Things(Narrow Band Internet of Things,NB-Io T),as the main communication method of the Internet of Things,has been determined by the three major domestic communication operators as the preferred solution for the communication of Internet of Things.NB-Io T has the advantages of strong coverage,low power consumption,low cost and large connection,and is easier to deploy on existing cellular networks to achieve the goal of "Internet of Everything".When arranging the location of the NB-Io T base station,a kind of miniaturized NB-Io T portable network test analyzer is usually used to help determing the best location of the base stations to deal with the problem of redundant or missing signal coverage caused by the poor location of the base stations.However,in actual testing,it has been found that the performance of the encoding and decoding module of the existing NB-Io T portable network test analyzer was not ideal,and there could be improved further.At present,the NB-Io T portable network test analyzer mainly uses Viterbi decoding algorithm and ML decoding algorithm.The bit error rate of the ML decoding algorithm is the lowest,but the computational complexity of the algorithm is high,and the decoding takes a long time,which is difficult to meet the realtime requirements of NB-Io T.While the computational complexity of the Viterbi decoding algorithm is Relatively low,but the bit error rate performance of the algorithm is relatively poor.Therefore,the study of a channel decoding algorithm that has good computational complexity and decoding performance and is suitable for hardware implementation is of great significance for the promotion and application of NB-Io T.Therefore,this thesis focuses on the research on the codec module of the NB-Io T portable network test analyzer,carring out research on algorithm design and hardware and software implementation to reduce computational complexity and improve decoding performance.Strive to improve the existing NB-Io T portable network test analyzer,such as high bit error rate,high delay,weak anti-interference ability,etc,to provide technical support for the NB-Io T portable network tester with high-performance codec modules.The main work and innovations of this thesis are as follows:(1)Aiming at the problem that the decoding effect of the encoding and decoding module of the current NB-Io T portable network test analyzer is not ideal,an improved Viterbi decoding algorithm based on forward and backward combinations is innovatively proposed.The decoding order is changed on the basis of the algorithm.If the branch metric value at k/2 is less than one-half of k,the effect of reverse decoding is better than forward decoding,and reverse decoding will be adopted.Conversely,the effect of forward decodingis better than reverse decoding,and traditional Viterbi forward decoding will be used.Through Matlab simulation experiments,it is found that the proposed Viterbi decoding algorithm can gain in AWGN and Rayleigh multipath fading channel environments by 1d B more than the unimproved Viterbi decoding algorithm,which can reduce the current Viterbi translation.The bit error rate of the coding algorithm and the decoding time can also be greatly reduced.In addition,When the performance of the improved Viterbi decoding algorithm is close to the maximum likelihood algorithm,its decoding performance is lower than that of the maximum likelihood algorithm.It is very suitable for the hardware implementation of encoding and decoding modules,so the proposed Viterbi algorithm is a performance-impaired decoding algorithm,suitable for the decoding function of the NBIo T downlink broadcast channel codec module.(2)A software implementation module based on Matlab is designed to test the decoding performance of the improved Vitabi decoding algorithm.The software implementation interface designed in this paper can simulate the simulation curve of the codec module in different SNR environments.By calculating decoding time and the bit error rate,the module can test the performance of the improved algorithm.After 3000 times of decoding simulation results comparison and time complexity and bit error rate analysis,it is proved that the improved Viterbi decoding algorithm can still maintain a good decoding performance curve in a complex environment and can solve the weak antiinterference ability of the NB-Io T portable network test analyzer.(3)Based on Universal Software Radio Peripheral(USRP),a hardware verification environment for the improved algorithm mentioned in this thesis is built.In this hardware verification environment,the PC side generates an NB-Io T signal,the USRP at the transmitting end encodes and sends the original signal,and then the USRP at the interference end adds different strengths of additive white Gaussian noise to simulate a complex noise environment.The USRP at the receiving end receives and frequencyconverts the signal after superimposed interference,recovers the baseband signal,demodulates and decodes it,and finally evaluates the decoding performance at the PC monitoring end.According to the experimental results,in the hardware environment based on software radio peripherals,the improved algorithm has similar bit error rate and time complexity to the software experimental environment,which further proves that the improved algorithm in the article has excellent decoding performance.