## 5 Experiment and Performance
### Laboratory Experiments  
A test was performed in a laboratory corridor which is about 90 m long, 2 m wide and 2.5 m high. The corridor simulates the underground coal mine laneway, while the rooms and the stairs along the corridor simulate the mining areas and the mined-out areas. As the landform of the laboratory is similar to the landform of an underground coal mine [23], tests were first carried out in the laboratory to examine the performance of the proposed WSN technologies and WSN management schemes. When the transmission power of the WSN nodes was 0 dbm, the communication distance was about 32 m [24,25]. A WSN was established with one sink node, six routing nodes and 20 sensor nodes, and the network depth was four. The routing nodes were placed along the corridor in two symmetrical lines with an interval of 15 m, as depicted in Figure 2, and their transmission powers were all set to 0 dbm. The sensor nodes were scattered around the routing nodes randomly. There were two types: (I) one equipped with a MC112 gas sensor, a LM35 temperature sensor and a HM1 humidity sensor, which numbered 16; (II) the other equipped with a random number generator, with threshold value of 0 XC0 and number of four, that means it overruns if the value is greater than 0 XC0. The sink node is connected with a PC via a RS232 interface. The PC simulated the GMDC, it could display environmental parameters and information about the network state received from the WSN on a tool called serial debug terminal, and it could also publish commands to the WSN via the tool. The laboratory environment is shown in Figure 4. The working period was set to 5 min, and the working state of the network was recorded continuously for 3 h.  
Through a tool called Packet Sniffer running on the PC, some data frames were captured during communication. Figure 5 shows part of data frames about the routing node 0X0001 communicating with its three children sensor nodes 0X0D4E, 0X0D4F and 0X0D50, where, the sensor nodes 0X0D4E, 0X0D4F belonged to type (I), while the sensor node 0X0D50 belonged to type (II). By analysis of the data frames, information such as frame type, source address, destination address and application layer data could be parsed easily. Figure 4: Testing in the laboratory environment. Figure 5: Data frames during communication between a routing node and its three children sensor nodes. (**a**) Sensor node 0X0D4E sending normal parameters of gas, temperature and humidity to 0X0001; (**b**) Sensor node 0X0D4F sending normal parameters of gas, temperature and humidity to 0X0001; (**c**) Sensor node 0X0D50 sending normal parameters of random number to 0X0001; (**d**) Router 0X0001 gathering parameters from (a–c); (**e**) 0 XE0 is larger than 0 XC0, so 0X0D50 sends it to the sink node directly with Limit of 1 As can be known from Figure 5, the WSN ran well both in periodic inspection mode and in interrupt service mode. The sensor nodes could correctly collect environmental parameters according to the command and aggregate them, and they could also report the overrun parameter to the sink node instantly. The routing nodes could correctly aggregate the parameters received from different types of sensor nodes. As plotted in this figure, we can see that the sink node received parameters from most of sensor nodes every 5 min, meaning the periodic inspection function is stable; Meanwhile, it received some parameters from a few sensor nodes, their Limit field was 0X01 by parsing these frames, that is, they were overrun parameters, so the interrupt service function is stable. We note that the sink node did not receive  
Figure 6: _Cont._  
parameters from all sensor nodes in some periods. Nevertheless, the number was relatively small so that we have reason to consider that the WSN works stably. Finally, the performance on the management scheme was tested.