A multi-step channel prediction method based on pseudo-3D convolutional neural network with attention mechanism
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摘要: 现有大规模MIMO信道预测多以广义平稳假设为前提,且多采用单步预测。面对非平稳场景,单步结果极易失效,频繁迭代亦显著抬高导频开销。为此,本文构建一套融合伪三维卷积与注意力模块的时频联合多步预测框架。方案以伪三维卷积替代3D卷积实现CSI在时域与频域的高效特征提取,并叠加通道与空间的混合注意力(CBAM),增强网络对全局依赖的表征能力,从而提升预测精度。基于实测信道的实验验证显示,该方法在多步预测任务上具有明显优势。与此同时,结合迁移学习思路,完成了由单天线到多天线场景的平滑扩展。
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关键词:
- 大规模MIMO /
- 多步CSI预测 /
- 伪三维卷积(P3D) /
- 混合注意力(CBAM) /
- 时频联合特征
Abstract:Objective With the rapid increase in the number of connections and data traffic in the fifth generation mobile networks, massive MIMO has become the key to improving network performance. The spectral efficiency and energy efficiency of massive MIMO transmission performance depend on accurate channel state information (CSI). However, the non-stationary characteristics of the wireless channel, the delay of terminal processing and the application of ultra-high frequency band aggravate the outdated problem of CSI, which needs to be compensated by channel prediction. Most of the mainstream prediction schemes are based on generalized stationary channels, and most of them are single-step channel prediction methods. In non-stationary environments, the CSI obtained by single-step prediction is highly likely to be outdated, and frequent single-step prediction will greatly increase the pilot overhead of the system. In order to cope with these challenges, this study proposes a multi-step channel prediction method based on pseudo-three-dimensional convolutional neural network and attention mechanism, which can learn the time-frequency characteristics of CSI at the same time. By using the high correlation in frequency domain, the influence of low correlation in time domain on multi-step prediction can be alleviated, and the performance of prediction can be improved. Methods In this paper, the uplink model of massive MIMO system is constructed ( Fig. 1 ). The channel state information is obtained by channel estimation through IFFT at the transmitter and FFT at the receiver. Through the actual channel measurement, the channel state information data set with dimension of time domain-frequency domain is obtained, and the autocorrelation analysis of time dimension and frequency dimension is carried out. Based on pseudo three-dimensional convolution and mixed attention mechanism CBAM, a multi-step channel prediction network structure (P3D-CNN-CBAM) (Fig. 13 ) is designed. The P3D-CNN structure is used to replace the traditional 3D-CNN structure. The three-dimensional convolution operation is decomposed into two-dimensional convolution operation in the frequency domain and one-dimensional convolution operation in the time domain, which greatly reduces the computational complexity. The mixed attention mechanism CBAM is introduced to extract the global information in the frequency domain and the channel domain, which further improves the channel prediction accuracy.Results and Discussions Based on the measured channel state information data set, this paper uses the channel prediction method based on AR model, the channel prediction method based on fully connected long short-term memory (FC-LSTM) and the channel prediction method based on P3D-CNN-CBAM to compare the prediction performance under different prediction steps. The simulation results show that the average NMSE of the proposed channel prediction method based on P3D-CNN-CBAM is smaller than that of the other two methods ( Fig. 17 ). As the prediction step increases from 1 to 10, the prediction error rises sharply because the AR model and FC-LSTM only use the correlation in the time domain. When the prediction step size is 10, the average NMSE of the prediction method based on AR model and FC-LSTM reaches0.5868 and0.7648 , respectively. The average NMSE of the prediction method based on P3D-CNN-CBAM is only0.3078 , maintaining good prediction ability. This paper also compares and confirms the improvement of P3D-CNN network prediction performance brought by the hybrid attention mechanism CBAM (Fig. 18 ). Finally, using the method of transfer learning, the proposed method is transformed from a single day to a single day.Conclusions Based on the measured channel state information data set, this paper adopts the information based on AR model. Aiming at the CSI outdated problem of single-step prediction method in massive MIMO channel prediction, this paper proposes a multi-step channel prediction method based on pseudo-three-dimensional convolutional neural network and attention mechanism. By using pseudo-three-dimensional convolution instead of three-dimensional convolution, the information of CSI time-frequency domain is extracted, and a hybrid attention mechanism (CBAM) is introduced to improve the learning ability of channel prediction network for global information. The experimental results based on the measured channel data show that: (1) The proposed method has great advantages over the prediction methods based on AR model and FC-LSTM; (2) Based on the idea of transfer learning, the multi-step channel prediction is extended from single antenna to multi-antenna. -
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