玉米田环境中915MHz直接序列扩频系统性能仿真

在面向农业应用的无线传感器网络中，用于裸地和草地的直接序列扩频收发器能否适应农田环境，需要进一步的研究探索。该文用Simulink 仿真了915MHz直接序列扩频系统与农田环境下的无线信道，多径衰落模型根据 Saleh-Valenzuela模型修改而得，路径损耗模型是根据成熟期玉米地实地测量得到的数据分析拟合而得。仿真结果表明，小尺度多径衰落对系统性能的影响较大，直接序列扩频系统可以在一定程度上补偿多径衰落的影响，但在多径现象严重的玉米田环境中，补偿能力非常有限，仅在很短的传输范围内（＜80 m）系统性能良好，很难满足面向广域空间农田信息采集的无线传感器网络的要求。扩频技术虽然在无线传感器节点设计中被广泛应用，但在传输环境恶劣的农田环境中，并不是一个最优的解决方案。

Performance simulation of 915MHz direct sequence spread spectrum system in maize fields

In terms of wireless sensor networks (WSN) for agricultural applications, whether the transceiver using direct sequence spread spectrum (DSSS) technology can meet the requirements of cropland environments needs further investigation. Using Simulink, the 915MHz DSSS system with the wireless channel in cropland environments was simulated. The clustered Rayleigh model was adopted for multipath fading, which was modified from the Saleh-Valenzuela model, and large-scale path loss model was obtained from the field test data in the cropland with maize in mature growth stage. It is found that the small-scale multipath fading affects the system performance greatly, and the DSSS system could compensate the effect of multipath fading to a certain extent. However, in the cropland with severe multipath fading phenomena, the compensation capacity was limited, and the system performance was only good (bit error rate <5%) within short transmission range (<80 m). It was very hard to meet the requirements of wireless sensor networks for agricultural information acquisition in wide-area croplands. Although spread spectrum technology has been widely employed in the design of WSN nodes, it is not an optimal solution for the agricultural applications in croplands with worse transmission environments.