基于发射功率自适应的稻田无线传感器网络节点设计

Design of WSN node with adaptive transmitting power for rice field

针对水稻生长过程环境因素变化较大以及传感器节点的能量大部分被无线射频阶段所消耗,设计了发射功率自适应的无线传感器节点,建立了长时间、稳定、高可靠性的稻田无线传感器网络。试验测试了水稻的株高、叶面积与生长天数的关系以及对无线信道的影响,结果表明水稻株高和叶面积的增加会降低无线信号强度和通信成功率;通过增大发射功率可以提高通信质量克服由于水稻生长因数对无线信道的影响。在软件设计方面,传感器节点采用睡眠、苏醒工作机制来降低功耗。同时为了延长工作时间、提高通信质量,提出了根据水稻生长周期、通信距离、接收信号强度、平均丢包率等因素自动调整节点发射功率的能量自适应功耗调整机制。田间试验结果表明,水稻田节点发射功率越大,有效通信距离越远,且水稻的密度和高度等对通信有重要的影响;节点发射功率在5 dBm以下时,发射功率的改变对节点工作电流影响较小,节点工作电流均小于40 mA;采用该机制对发射功率进行调整,增大节点发射功率可使通信成功率有大幅的提升;降低节点发射功率仍然保持良好的通信效果。水稻分蘖和抽穗2个生长时期的田间试验结果表明,采用发射功率自适应策略,提高了通信质量,平均丢包率在5%以下,通信成功率大于97%,达到了预期设计目的。

The environmental factors during the rice growing process have wide changes and most of the energy consumption of the sensor node is used for transmitting data. Meantime, wireless sensor networks on the basis of reliable communication consuming the lowest energy, has been a hot research topic. In order to establish a long time, stable and highly reliable wireless sensor network, a node for working on the rice fields was designed. The basis experiments study the relationship between plant height, leaf area, and the growth days and the impact on the radio channel. The basis results showed that the relationship of the plant height of the rice and the growth days caused attenuation to exist according to a logarithmic model, and the regression coefficient R2 was in the range of 0.9604 and 0.9485. Plant height and leaf area increase reduced the radio signal strength and communication success rate. The experimental results also showed that increasing the transmitting power could improve communication quality because of the rice growth factor for adverse wireless channel impact. First, sensor nodes use sleeping waking up as a working mechanism to reduce power consumption. Second, to extend the working time and improve communication quality, the node uses under rice growth cycle, the communication distance, the received signal strength, the average packet loss rate and other factors, automatically adjusts the transmitting power of the energy adaptive mechanisms. The experiments demonstrated that the larger transmitting power had the effective communication distance farther and rice density and height had important impact on the wireless communication. Finally, the verification experiments results proved that if the transmitting power was less than 5 dBm, the transmitting power changes had little effect on the working current of the node. Meantime, the verification experiments showed the node operating current was less than 40 mA. Moreover, with increasing transmit power the communication success rate improved dramatically. The node reducing the transmitting power in the allowable range still resulted in a high communication success rate. With this power adaptive strategy, the wireless node working in rice tiller and heading time, the impact of transmitting power changing on the communication quality was finished. The results showed that the average packet loss rate was 5%or less, and that the received signal strength stayed within acceptable range. In short, the node designing achieved the desired purpose.