Control host
6.2 Simulation Results
Different structures of buildings should be taken into consideration in measurements.
However, this is difficult to achieve by real experiments. Furthermore, large-scale experiments are infeasible. Below, we present our simulation results to test our algorithm under more complex scenarios. Unslotted CSMA/CA protocol following
(a)
roof gateway go upstairs go downstairs 1F
Figure 6.4: Some guidance results in 4-store buildings.
the IEEE 802.15.4 [14] is used in the simulation. The PHY rate of 250 kbps is assumed. The values altemg, lemg, and δ are the same as above experiments except that D is set to 2.
We consider a 4-store building and each floor is a 7x7 grid network. Fig. 6.4(a) shows a case where some emergencies occur near the center of the second floor and how sensors on the second floor guide people to avoid hazardous regions. Fig. 6.4(b) simulates a building with no roof stair and only one stairs. Emergency events are detected nearby the stair on fourth floor. Since the stair sensor on fourth floor realizes that there is no rooftop, it guides people to downstairs. Fig. 6.4(c) shows a case where some emergencies occur near the stair sensor on the third floor. Sensors on the forth floor will guide people to the ground floor instead of to the roof. Note that the stair sensor on the center of the third floor will direct people to upstairs.
This is reasonable because people currently in the staircase between the third and the forth floor should be guided to upstairs. Fig. 6.4(d) is a case with only one stairs and has one roof top. As there are emergencies nearby the floor gateway on the second floor, the stair sensor on the fourth floor will adjust its weight until its weight becomes larger than the virtual sensor. As a result, the sensors on the fourth floor will direct people to the roof top and then sensors on the third floor will also guide people to upstairs. Fig. 6.4(e) is a case with roof stairs. As there are emergencies nearby the two stair sensors on the third floor, stair sensors on fourth floor will adjust their weights until their altitudes become larger than the virtual sensor. After this adjustment, these stair sensors will direct people to roof stairs since there is no safer path to the ground. Since the floor gateways on the third floor are all in the hazardous regions, they will direct people to upstairs through the middle stair gateway. Fig. 6.4(f) is a case that an exit senses an emergency occurred. All the upstairs sensors will direct people downstairs through the floor gateways that are not in hazardous regions.
In Fig. 6.5, we simulate our algorithm in 4-store buildings of various kinds of shapes. Fig. 6.5(a)-(d) are similar cases but are for different shapes of buildings.
These results indicate that our guidance protocol is suitable for various kinds of building architectures. Fig. 6.5(e) shows a case where some emergencies occur nearby a floor gateway on the third floor. Since the left-hand side floor gateways on the third and the fourth floors are all in hazardous regions, the sensor on these two floors will direct people downstairs through the other floor gateways. The sensors on the first and second floors are in the dangerous regions, so they will guide people to exits using the shortest paths. Fig. 6.5(f) is a case similar with Fig. 6.4(f), where
roof gateway go upstairs go downstairs
Figure 6.5: Some guidance results in 4-store buildings of various shapes of architec-ture.
(a) (b)
Figure 6.6: Comparison of escaping paths, convergence times, and message over-heads against [18].
there is an emergency on one of the exits. We should pay attention to the floor gateway in the dangerous region on the first floor. Since sensors around this stair gateway are all in the dangerous region, this stair gateway can only guide people to upstairs.
In Fig. 6.4 and Fig. 6.5, the convergence time and packet counts are obtained assuming two cases: no packet loss and a 10% packet loss rate. The loss of EMG packets may lead to unstable guidance results, which will be connected by our pe-riodical reporting scheme. Sensors will broadcast EMG packets every 0.5 seconds when emergencies occur. The convergence time, as well as packet count, is measured by the time the last sensor updating its guidance direction.
In Fig. 6.6, we compare our escaping paths, convergence times, and message overheads against those obtained by [18]. In the comparison, we only simulate the case of no packet loss. In Fig. 6.6(a), sensors near the left corner exit on the ground floor detect an emergency. The scheme in [18] will pull some sensors on the second and the third floors to go downstairs, which is more dangerous. This is
because the scheme in [18] does not implement the concept of dangerous regions.
On the contrary, ours will lead people away from such dangerous regions. Fig. 6.6(b) illustrates another case where sensors nearby the stairs on the second floor detect an emergency. Again, because shorter paths are preferred, the algorithm in [18] will guide some people to pass the hazardous region. Fig. 6.6(c) shows a case where all floor gateways are not in dangerous regions, therefore sensors on the ground and third floors will guide people using the shortest path to the floor gateway.
Nevertheless, on the second floor, the algorithm in [18] will still guide some people to across the hazardous region. Besides providing safer escape paths, our scheme also outperforms [18] in packet counts and convergence time.