| As a low-cost and efficient transmission technology for transmitting high-frequency wireless signal,radio over fiber has attracted the attention of the industry and many researchers in 5G communication.Digital radio over fiber technology adds a digital-to-analog module to the base station,which increases the processing ability of the base station.In D-RoF system,RF bandpass analog signal is converted to digital signal modulation for transmission over fiber optic transmission system.The advantage of D-RoF technology is that it reduces the signal-to-noise ratio requirement of the fiber link.Meanwhile,the performance of the digital fiber link is relatively stable.The nonlinear and dispersion effects are small and easy to compensate.Hence,it is suitable for long-distance high-performance transmission,which arouses the attention of the industry.However,in the D-RoF system,after analog-to-digital conversion and quantization coding,the original data amount increases sharply with the quantization digits increasing,resulting in high transmission cost and low transmission efficiency in actual scenes.In order to improve the data transmission efficiency,the main work of this thesis is as follows:Aiming at the quantization coding and decoding inverse quantization process of D-RoF system,a fast statistical estimation with vector quantization(FSE-VQ)method is proposed.And the simulation verification and complexity analysis are also carried out in the D-RoF system.FSE-VQ algorithm firstly uses the companding transformation to transform the data of Gaussian distribution into uniformly distributed data.Secondly,reasonable grouping method is used in the algorithm to eliminate the data correlation between continuous signals in the process of vector construction.Finally,the algorithm combines vector quantization technology to improve data compression efficiency and system performance.The performance of the FSE-VQ algorithm is evaluated from the perspective of the error vector magnitude(EVM)and time complexity.In the D-RoF system with raw data rates of 2Gbit/s,the EVM of FSE and Lloyd algorithm with 8-bit quantized bits are 1.32% and 1.33% respectively.The same EVM performance is obtained in the FSE-VQ method with the only 6-bit quantized bits,thus reducing the amount of data by 25%.In addition,the EVM performance of FSE-VQ algorithm is almost the same as the multi-dimensional quantization algorithm based on k-means clustering under the same quantization digits.However,the advantage of the FSE-VQ algorithm is that it does not require multiple iterations to update the codebook,thus greatly reducing the computational complexity,which is beneficial to its application in real-time transmission scenarios. |
