利用无约束函数的QAM信号自适应盲均衡方法

本文针对正交幅度调制(QAM)信号的盲均衡与载波相位恢复问题，首先在对现有的基于功率最大化盲均衡算法分析的基础上，依据向量范数间的关系，给出了一种QAM信号盲均衡与载波相位恢复的无约束代价函数；然后对代价函数的收敛性和解的唯一性进行严格论证，证明代价函数在取得最优解时能够同时实现盲均衡与载波相位恢复；之后将其转化为采用随机梯度法实现的自适应算法。相对CMA、MMA等其他自适应算法，新算法可获得更好的性能，通过对高阶QAM信号的均衡仿真，进一步验证了算法的有效性。 

Adaptive method for blind equalization of QAM signals utilizing unconstrained function

Aiming at the problem of blind equalization and carrier-phase recovery of Quadrature Amplitude Modulation (QAM) signal. Based on the analysis of blind equalization algorithms that optimize the equalizer output energy, a new unconstrained cost function for blind equalization and carrier-phase recovery of QAM using the relationships of vector norm is proposed in this paper. Then, the convergence and the uniqueness of solution of the cost function are discussed, and we show that a perfect equalization solution and carrier-phase recovery can be achieved at the optimum of the objective function. By reformulating the unconstrained cost function, an adaptive algorithm that can be optimized via stochastic gradient descent method is obtained. The new proposed algorithm can provide better performance in comparison to some existing adaptive methods, such as CMA and MMA, moreover, the validity of the new proposed algorithm is verified through computer simulations of blind equalization and carrier-phase recovery of higher-order QAM signals.