Wireless Sensor Networks and Duty-Cycle Scheduling

Wireless sensor networks has a wide range of applications like environmental monitoring, target tracking, battlefield surveillance. It consists of large number of distributed nodes that organize themselves into multihop wireless sensor network. A typical wireless sensor node consists of three main components: (i) a sensing subsystem including one or more sensors (with associated analog-to-digital converters) for data acquisition; (ii) a processing subsystem including a microcontroller and memory for local data processing; (iii) a radio subsystem for wireless data communication. Typically, these nodes coordinate to perform a common task [1].

The medium access control (MAC) layer has been proposed in wireless sensor networks mainly to reduce energy consumption of sensor nodes. Medium access control (MAC) is an important technique that enables the successful operation of the network. One fundamental task of the MAC protocol is to avoid collisions from interfering nodes [1]. The major sources of the energy waste are collision, overhearing and control packet overhead. The Collision defined as when a transmitted packet is corrupted, it has to be discarded, and follow on re-transmission increase the energy consumption. Collision increases the latency as well. The Overhearing defined as a node picks up packets that are destined to other nodes. The Control packet overhead defined as RTS and CTS request consume energy too. The major source of energy consumption is idle listening. If nothing is sensed, nodes are in the idle mode for most of the time. Idle listening consumes approximately same power as in transmitting and receiving mode [8].

The problems occur by idle listening can be solved by the efficient technique called duty cycle. Dut...

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...-MAC each sensor node is synchronized so that each sender can transmit a packet to an intended receiver during their synchronized listening period. These protocols can provide low energy consumption.

In static duty-cycle scheduling all the sensor nodes wakes up with a static duty-cycle ( ). Dynamic duty-cycle scheduling (DS) used to solve the problems occurred in SS. The DSR scheme allows sensor nodes to calculate their duty-cycle according to the current amount of residual energy. In energy harvesting WSNs, the residual energy of nodes can increase over time depending on their harvesting opportunity. Each sensor nodes estimates the prospective increase in residual energy with time so that it can reduce duty-cycle more aggressively (DSP). In DEES when a node needs to transmit a packet only the neighboring nodes gets synchronized until node complete its transmission.