Research On Blind Equalization Algorithm Based On Error Function

In underwater acoustic communication system, due to the need to frequently transmit training sequence, the conventional adaptive equalization technique severely reduces the efficiency of channel utilization. While blind equalization technology not only does not need to send training sequence, but also it well overcomes intersymbol interference brought by multi-path fading, therefore saves bandwidth and increases the transmission rate, applicable to underwater acoustic channel equalization. This paper takes the error function as an entry point, conducts in-depth study of dual-mode blind equalization algorithm, variable step-size blind equalization algorithm and decision feedback blind equalization algorithm based on error function. The underwater acoustic channel simulation experiments prove the superiority of the algorithm. The main contents are as follows:(1)Aiming at the characteristics of the statistics and instantaneous blind equalization algorithm, based on analysis of the dual-mode algorithm switching mode, a dual-mode hybrid blind equalization algorithm based on error function is proposed. Against the characteristics of Constant Modulus Algorithm (CMA) and Decision Directed (DD) algorithm, utilize error function cross-correlation of two algorithms, a new weighting factor selection method is proposed, dynamic control of dual-mode mixed weight ratio of the two algorithms, to more accurately control the switch timing. Even in case of erroneous judgment, it is possible to switch back to the appropriate weight ratio because of its dynamic characteristics. Thereafter, on this basis, by replacing the error function term, improve its capacity on the phase correction.(2)In order to further improve the convergence speed of the exponential variable step-size constant modulus algorithm, a variable step size constant modulus algorithm which based on the exponential multi-delay error function autocorrelation is proposed on the basis of the analysis of the error function autocorrelation, and by using the multi-delay error signal autocorrelation functions to control the steps. Compared with the non-delay and unit delay, the multi-delay error signal autocorrelation functions of the algorithm can provide simpler and more accurate information for training trajectory, so the algorithm converges faster, and the convergence process is smoother and more stable. After the normalization process to further improve the convergence rate.(3) Based on the analysis of same and different error function items of decision feedback blind equalization algorithm, respectively study the feedforward tap and feedback tap. Through control conditions, the update of the real part and imaginary part of feedforward taps are controlled separately, to ensure the fast and accuracy of update, the subsequent decision feedback part, as the supplement of the iteration process, to further ensure the stability of convergence process. Then again improve the feedforward and feedback parts respectively. For feedforward part, use the dual-mode to play different algorithm performance; for feedback part, use the soft-decision feedback as a supplement to ensure the performance of the convergence.