基于Wi-Fi无线感知技术的奶牛爬跨行为识别

    Recognition of crawling behavior of dairy cows using Wi-Fi wireless sensing technology

    • 摘要: 奶牛发情和爬跨行为之间存在着密切的联系,及时发现奶牛的爬跨行为是检测奶牛发情、提高养殖收益需要考虑的重要问题。为了在自然环境下可靠地检测奶牛的爬跨行为,同时避免引起应激反应,研究并提出基于Wi-Fi信号的奶牛爬跨行为检测与识别方法。首先,应用部署在日常生活环境中通用的Wi-Fi设备捕获奶牛的运动状态数据;其次,通过载波聚集、移动加权平均滤波对数据进行预处理;第三,基于局部离群因子LOF算法,实现信号跳变检测并以此为基础获取包含奶牛动作的信道状态信息(Channel State Information, CSI)序列片段;第四,设计并提取CSI序列片段的特征,构建了包含3类奶牛动作,共计8 127个样本的数据集;最后,基于长短时记忆网络(Long Short Term Memory, LSTM)构建奶牛行为识别模型。通过使用数据集中2 497个样本作为测试集检验提出的网络模型,检验结果表明,系统能够可靠地捕获包含奶牛动作的CSI序列片段,并以较高的准确率识别奶牛的爬跨行为。模型在测试集上对3类样本的总体分类准确率为96.67%,其Kappa系数为0.943 1,获得了较高的性能。研究结果将基于Wi-Fi信号的无线感知技术引入农业信息化领域,扩展了动物行为监控的技术手段,为无线传感技术在农业智能化方面的应用提供参考。

       

      Abstract: In the dairy farming industry, there is a close relationship between estrus and the crawling behavior of dairy cows. Timely detection of the crawling behavior of dairy cows is an important issue to be considered to detect the estrus of cows and improve breeding income. Due to the traditional wearable sensing method is easy to cause animals' stress response and generally detrimental to their welfare, it is necessary to find a new way. In 802.11 a/g/n standards, channel response can be partially extracted from off-the-shelf Orthogonal Frequency Division Multiplexing (OFDM) receivers in the format of the Channel State Information (CSI), which reveals a set of channel measurements depicting the environment changes. To reliably detect and effectively recognize the crawling behavior of dairy cows and avoid stress response in a natural farming environment, a method based on the CSI of Wi-Fi signals was proposed in this study. Firstly, in the breeding shed of about 150 m2, a wireless router was used as the signal transmitter, and a computer equipped with Intel 5300 wireless Network Interface Card (NIC) was used as the signal receiver to set up a Multiple Input and Multiple Output (MIMO) wireless communication system, which could be used to obtain dairy cows' motion state data in the format of the CSI. Secondly, the obtained CSI series data was preprocessed step by step (i) the CSI values of 30 subcarriers in each radio beam were aggregated into one by using the algorithm of carrier aggregation so that the module of signal jump detection could be run; (ii) the environmental noise caused by factors such as temperature and shed layout were filtered by using the algorithm of moving weighted average filtering; (iii) based on the algorithm of local outlier factor, a signal jump detection module was designed to find out the beginning and end time of the dairy cows' motion in each CSI sequence fragment. Thirdly, the characteristics of CSI sequences were designed and extracted to construct a dataset containing 8 127 samples of three types of cows' movements. Finally, given the advantages and recent success of recurrent neural networks in the domains of time series, a multi-classification recognition model was build based on the Long Short Term Memory (LSTM) network. The LSTM network is constructed with an 8-layer architecture and was trained by 5 630 samples in the dataset. Through repeated training model and modification of network parameters, a set of optimized network parameters was finally obtained. To evaluate the model, the indices of classification accuracy and Kappa coefficient were defined. Meanwhile, the remaining 2 497 samples in the dataset were fed into the model to verify its performance. The test result showed that (i) the proposed method reliably captured the CSI series signal fragments containing dairy cows' movements; (ii) the validity and accuracy of the model were closely related to the model structure and the quality of the dataset. Generally, the higher the number of layers in the network and the higher the quality of the dataset, the better performance of the model can be achieved; (iii) when the LSTM network adopts an 8-layer structure and trained under specific parameters setting, the Kappa coefficient of the trained model on the test set was 0.934 1, and the classification accuracy was 96.67%. Based on the channel state information of the Wi-Fi signal and combined with the machine learning method, a high-performance behavior recognition model can be constructed in specific application fields. The key to the problem lies in the construction of the dataset and the careful tuning of the model. This study introduced wireless sensing technology based on the Wi-Fi signal into the field of agricultural informatization, the results could expand the technical means of animal behavior monitoring and provide a reference for the application of wireless sensing technology in intelligent agriculture.

       

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