Prediction of time reversal channel with neural network optimized by empirical knowledge based genetic algorithm

Abstract

Because of the strong non-linear fitting capability, the artificial neural network (ANN) can be used to establish the mapping relationship between the terminal position and the received signal for obtaining the channel characteristics at different locations. The accuracy of an ANN model is, in general, determined by the number of the training sets used in constructing the model. The more the training sets, the better the accuracy is. However, getting a large number of training sets by deterministic model is expensive. Therefore, under the same number of training sets, improving the accuracy of the model is crucial to develop an effective time reversal (TR) modeling method based on ANN. In this paper, a new TR channel modeling method based on the back propagation neural network is proposed. Genetic algorithm (GA) with excellent global search capability is used to optimize the weight and threshold of the ANN to avoid the possibility of the ANN falling into local minimum. According to the basic principle of time reversal, the peak characteristics are obtained by the fitting method. In order to improve the accuracy of the model, the peak value characteristics are integrated into the GA as empirical knowledge to change the fitness function. Meanwhile, the principal component analysis technology is utilized to process data, which reduces the data dimension and the training time of ANN while data characteristics are ensured. Once the terminal antenna positions are input to the proposed model, the accurate TR received signals can be quickly obtained. Finally, the deconvolution operation of the received signal is performed by the clean algorithm to obtain the channel characteristics. A simple indoor TR scenario is used as an example to demonstrate the effectiveness of the proposed method. The results show that the three channel characteristics obtained by the model, i.e., channel impulse response peak value, 15 dB multipath number, and average delay, have high accuracy. Furthermore, the proposed model has more excellent performance than the other two ANN models under the condition of the same number of training samples. Based on the basic principle of TR technology, the electromagnetic waves have better focusing effect in more complex environments. Therefore, the proposed method is also applicable to more complicated environments than the simple indoor scenario.