卫星高速宽带数传系统的变步长LMS均衡算法研究

A Modified Variable Step LMS Adaptive Filtering Algorithm for Satellite High-Speed Broadband Digital Transmission System

对码间干扰实现快速有效的均衡是卫星高速宽带数字传输的关键之一,针对S型函数(Sigmoid函数和双曲正切函数)变步长LMS均衡算法在误差e(n)接近零处μ(n)变化大的缺陷及算法复杂度高的问题,提出了一种改进的变步长LMS自适应均衡算法。算法通过简化步长更新式的复杂度,增加误差信息量,优化改进的S型函数结构,建立了新的步长因子μ(n)与误差函数e(n)非线性关系,使算法误差接近零处步长因子变化平滑缓慢,消除不相关噪声序列的影响,且算法复杂度比其它同类改进算法小。仿真结果表明新算法性能优于其它改进算法。文中给出了卫星高速宽带数字传输系统的仿真模型,将新算法应用到系统模型的自适应均衡器中,系统误码性能得到较大改善。

Equalizing inter-symbol interference（ISI） quickly and effectively is one of keys for satellite high-speed broadband digital transmission.A kind of S-type function（Sigmoid function and hyperbolic tangent function） variable step LMS algorithms is discussed in this paper.These algorithms have flaws that μ（n） changes a lot when error e（n） is close to zero and high complexity.Therefore,an improved variable step LMS adaptive equalization algorithm is proposed.Through simplifying the complexity of step formula update,increasing the amount of error information,optimizing the structure of modified S-type functions and building new nonlinear relations between step factor μ（n） and error function e（n）,the step of new algorithm changes not only smoothly and slowly when error e（n） is close to zero,but also eliminates the impact of uncorrelated noise sequences.The complexity of the new algorithm is smaller than other similar modified algorithms.Simulation results show that the performance of new algorithm is superior to other modified algorithms.The satellite high-speed broadband digital transmission system simulation model is also given in this paper.When the new algorithm is applied to the adaptive equalizer of system model,the system bit error rate（BER） performance is improved greatly.