Please contact Baofeng Zhou (bzhou at cse.unl.edu) for any questions.
Indoor Testbed Design
Overview
To conduct wireless underground channel experiments in the outdoor and field environment is a challenging task due to soil’s physical phenomena and unpredictable climatic conditions. Being the most dominant factor that affects the performance of wireless underground communication, the soil moisture level is dependent on the precipitation and irrigation events in outdoor settings. The lack of availability of a wide range of soil moisture levels over a short period of time prohibits productive and efficient wireless research. These challenges of conducting experiments underscore the need for developing an indoor testbed for scalable and controllable underground channel characterization.
In this project, an indoor testbed is developed for efficient wireless underground communication research. The testbed is located in greenhouse settings and provides soil moisture control, easy replacement of soil type, effortless installation and replacement of related equipment, and protection of equipment from extreme weather in the outdoor environment.
Testbed Design
Testbed: front view
Testbed: antenna deployment
Design
The indoor testbed is a 100 "x36 "x48 " wooden box assembled with wooden planks and contains 90 ft^3 of packed soil. A drainage system is installed in the bottom, and sides of the box are covered with waterproof tarp to stop water seepage from sides. Before installation of antennas and sensors, 3" layer of gravel is laid in the bottom of the box for free drainage of water and then the soil is placed in the box. Soil is packed after every 30 cm by using a tamper tool to achieve the bulk density to mimic real-world field conditions. Currently, sandy soil is used in the testbed.
Soil Moisture Sensing
To monitor the soil moisture level, 8 Watermark sensors are installed on each side of the box at 10 cm, 20 cm, 30 cm, and 40 cm depths. These sensors are connected to two Watermark dataloggers. This process is repeated for antenna installation at each depth. Three sets of four dipole antennas are installed at the depths of 10 cm, 20 cm, 30 cm, and 40 cm. These sets are 50 cm apart from each other.
Underground Antenna Characteristics
To evaluate the antenna performance in soil, a variety of antennas are installed in the testbed, including:
- 433 MHz band dipole antenna
- 915 MHz band dipole antenna
- CPN Lab's patented underground antenna
- GSM band quad-band antenna
The antennas are installed at 10 cm, 20 cm, 30 cm, and 40 cm depths. Antenna and wireless channel characteristics are therefore evaluated by using Vector Network Analyzer.
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