正交匹配追踪和BIC准则的自适应双频段预失真模型优化算法

针对双频段预失真模型复杂度高以及当前的模型优化算法不具有自适应性的问题,提出一种自适应的模型优化算法.采用双频段广义记忆多项式作为预失真模型,通过正交匹配追踪算法对原始模型的基函数项进行排序,每次迭代时用所有已挑选的基函数项构成备选模型,推导了模型输出向量元素服从非独立同分布情况下的贝叶斯信息准则(Bayesian Information Criterion,BIC),并将BIC值最小的备选模型作为优化后模型,从而在原始模型稀疏度和拟合误差门限未知情况下,实现了模型的自适应优化.结果表明:优化后模型与原始模型相比,二者分别预失真后的信号在邻道功率比和归一化均方误差方面均非常接近,预失真效果良好,而模型的系数量减少了75%以上.国家自然科学基金项目(No.61401099);;福建省教育厅项目(No.JAT170087

Digital Signal Processing Techniques Applied to Radio over Fiber Systems

The dissertation aims to analyze different Radio over Fiber systems for the front-haul applications. Particularly, analog radio over fiber (A-RoF) are simplest and suffer from nonlinearities, therefore, mitigating such nonlinearities through digital predistortion are studied. In particular for the long haul A-RoF links, direct digital predistortion technique (DPDT) is proposed which can be applied to reduce the impairments of A-RoF systems due to the combined effects of frequency chirp of the laser source and chromatic dispersion of the optical channel. Then, indirect learning architecture (ILA) based structures namely memory polynomial (MP), generalized memory polynomial (GMP) and decomposed vector rotation (DVR) models are employed to perform adaptive digital predistortion with low complexities. Distributed feedback (DFB) laser and vertical capacity surface emitting lasers (VCSELs) in combination with single mode/multi-mode fibers have been linearized with different quadrature amplitude modulation (QAM) formats for single and multichannel cases. Finally, a feedback adaptive DPD compensation is proposed. Then, there is still a possibility to exploit the other realizations of RoF namely digital radio over fiber (D-RoF) system where signal is digitized and transmits the digitized bit streams via digital optical communication links. The proposed solution is robust and immune to nonlinearities up-to 70 km of link length. Lastly, in light of disadvantages coming from A-RoF and D-RoF, it is still possible to take only the advantages from both methods and implement a more recent form knows as Sigma Delta Radio over Fiber (S-DRoF) system. Second Order Sigma Delta Modulator and Multi-stAge-noise-SHaping (MASH) based Sigma Delta Modulator are proposed. The workbench has been evaluated for 20 MHz LTE signal with 256 QAM modulation. Finally, The 6x2 GSa/s sigma delta modulators are realized on FPGA to show a real time demonstration of S-DRoF system. The demonstration shows that S-DRoF is a competitive competitor for 5G sub-6GHz band applications

Digital predistortion of concurrent multiband communication systems

In this semi-tutorial paper, we derive the general form of a predistorter for a concurrent multiband system. Further, we derive complexity-reduced forms, and we compare the resulting algorithms with previously proposed algorithms in the literature