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Sensors 2010, 10
Definition 1: Fault-tolerant priority p. p indicates the level of reliability requirements of a sensor. It
can be dynamically adjusted at runtime.
Definition 2: Fault-tolerant priority set. Each sensor has a fault-tolerant priority set. Based on the
fault-related information, the control node dynamically selects an appropriate priority for the sensor
from its priority set.
Definition 3: Fault-tolerant priority queue Q. The Q is a priority queue managing the fault-tolerant
priorities of all the sensors in the system. The sensors in Q are sorted by priority in descending order.
Figure 1. BSN application scenario.
Internet
Hospital
Biosensor
Control node
Base station
Patient
Table 1. Variables and Notations.
Length of each interval divided in VMAC
Maximum of packets handled within each interval
Effective data payload size in bytes
Minimum response time for handling a packet request
Maximum response time for handling a packet request
A sensor with a specific function
The time for MAC to send a packet for sensor S
i
Packet number should be sent within T
i
×D
i
for sensor S
i
Actual wait time of the control node in a polling process
Number of packets received by the control node
Data payload of data packet size in bytes
Data payload of polling packet size in bytes
Priority tuner for fault-tolerant priority p of sensor S
i
Adjustment factor of priority p for sensor S
i
The time that S
i
wants to maintain p at time t