生猪养殖环境RFID信号多径-莱斯信道干扰评估模型

    Multipath-Rician channel interference evaluation model of RFID signal in pig breeding environment

    • 摘要: 射频识别(radio frequency identification,RFID)技术在生猪个体识别应用中,易受复杂养殖环境中多径效应影响,表现为信号相位波动、包络起伏及读取性能下降。为提升生猪个体识别效率,该研究基于莱斯信道(Rician channel)理论,提出一种动态多径干扰评估模型。模型通过引入动态莱斯因子估计机制,实现直射径与散射径功率比,构建以动态莱斯因子和接收信号强度指示(received signal strength indicator,RSSI)方差为核心的综合干扰评分体系S(t),用于量化多径干扰强度。试验结果表明,S(t)能够有效区分不同养殖场景,静态非金属环境S值45.0~49.2,石壁与猪群活动场景约60.0~65.2,而金属结构与猪群叠加环境最高达79.2,反映环境复杂性对信号稳定性的影响。与对数距离、瑞利、静态莱斯及广义莱斯等模型对比,研究提出的动态莱斯模型在读取率、接收功率及干扰适应性方面表现更佳,能够更准确地表征动态养殖环境下的时变特性。为RFID系统在生猪养殖环境中的优化部署与抗干扰策略设计提供理论依据和数据支撑。

       

      Abstract: Radio frequency can be expected to apply to individual pig recognition in intensive breeding environments. However, it is highly susceptible to multipath interference, leading to degraded signal stability and reading accuracy. In this study, a quantitative framework was developed to characterize the time-varying channel disturbances in order to guide the system optimization. A dynamic interference model was established using Rician fading channels. The power ratio between the direct path and the scattered components was continuously estimated rather than assumed to be constant. A dynamic estimation was implemented for the so-called K-factor. The recursive optimization was carried out with sliding time windows. The statistical features were also coupled with the received signal strength indicator and phase fluctuations. The impacts of environmental factors were captured, such as the metallic structures and animal movement. An interference scoring function was then formulated to combine the instantaneous K-factor and the variance of received signal strength. A continuous quantitative index was obtained with the interference intensity from 0 to 100. Both controlled laboratory simulations and on-site pig farm experiments were conducted to validate the optimization. In the laboratory, a custom testbed was constructed with a high-precision spectrum analyzer, directive antennas, and resin pig models mounted on mobile platforms, in order to reproduce the dynamic occlusion and reflection. A series of measurements was achieved at 920 MHz. There were clear transitions from Rayleigh-like fading with the severe envelope fluctuation under strong scattering to near-Gaussian stability under strong direct paths, as the K-factor increased. There was a suitability of the channel representation. Field deployments in the commercial pig houses further confirmed that the different physical settings led to systematic differences. The interference score remained low (45.0 to 49.2) under noise or simple tag-reader interaction scenarios, indicating relatively stable communication. In contrast, the environments with stone walls produced scores 60.0. Dynamic individual pig movement raised values to 65.2, while the dense static groups reached 68.8. Metal railings caused the sharp degradation with the scores 76.0. The most severe condition occurred when the metallic structures coincided with pig groups. The scores were 79.2, indicating the substantial attenuation of the direct path and dominance of scattering. Correspondingly, the average read success rates varied from 98% in the background conditions to only 28% under metal railing interference. The received power levels ranged from approximately -58 decibels-milliwatt in the favorable conditions to -70 decibels-milliwatt in unfavorable cases. Comparative analysis against conventional modeling demonstrated the better performance of the dynamic framework. The log-distance path loss model was 75% read success with the average attenuation. The Rayleigh model reached 80%, but it was lacking in adaptability for the mixed propagation. The static Rician model was improved to 85%, but the temporal variability was less captured. Even the generalized Rician model was effective in the static industrial environments, with about 88% read success. It was computationally heavy and unsuitable for real-time agriculture. In contrast, the dynamic Rician approach was achieved in the 92% read rates. The higher received power was maintained for the best adaptability index of 0.91. Its robustness was also obtained under diverse farm conditions. As such, the time-varying direct-to-scattered power ratio was incorporated into the channel representation. The findings can also provide a realistic and flexible description of the multipath propagation in livestock houses. Great contributions can also be gained for the structural reflection, animal density, and movement. In conclusion, the dynamic interference evaluation model is obtained using Rician channel theory. A reliable quantitative tool can also be used to assess the signal stability and then diagnose the high-risk interference zones, in order to guide the antenna placement and system configuration. Both theoretical support and practical data can be deployed the robust RFID systems in pig breeding environments. Ultimately, the high accuracy of individual animal monitoring can greatly contribute to intelligent livestock.

       

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