Adaptive Power-Control Based Energy-Efficient Routing in Wireless Sensor Networks

Abstract

Efficient utilization of energy is a hot topic of research in the field of wireless sensor networks. Limited battery resource at a sensor node coupled with the hostile multi-path fading propagation environment makes the task of the network to provide reliable data services with an enhanced lifetime, challenging. In order to achieve this goal, a number of efforts have been made by the researchers; one such key strategy is an energy-aware routing embedded with transmission power control mechanism. In this strategy, every sensor node in a network transmits at a lowest possible power level to maintain on one hand reliable wireless links with other neighboring nodes and saves the energy on the other. In this paper, we propose a novel routing technique embedded with transmission power control for wireless sensor networks while considering a realistic radio fading environment. The proposed strategy considers channel fading in the propagation environment and mitigate it through transmission power control mechanism. The main aim of the proposed protocol, APCEER, is to reduce the communication interference among sensor nodes, establish energy-efficient routes from source to sink and thus, to save energy of each and every sensor node in the network. This results in an overall increase of network lifetime, transmission throughput, energy saving and reduce communication interference and collision. Simulation and experimental results show that the proposed scheme outperforms the existing energy-aware routing strategies that are not equipped with a power control mechanism. The proposed protocol thus utilizes in urban applications of wireless sensor networks that need ultra efficient utilization of energy by power-constrained nodes operating in severe fading conditions.

Appendix

Appendix A explains the procedure for calculating current drawn and energy consumed by the radio in transmission, reception and listening modes.

1.1 Energy Consumption by LEDs

LEDs (if equipped) on a sensor node also use power from the pool of battery. Sun SPOT is the sensor node used by the authors to evaluate the proposed protocol for its onward comparison with existing energy-aware routing strategies. The currents drawn by a single LED mounted on a Sun SPOT shown in the Table 8 are based on the information provided in [36].

Table 8 Sun SPOT specification for LEDs

The LEDs used in the experiments are in half-brightness mode. There are two types of LEDs used on a Sun SPOT node, i.e. $Power LED$ and $Activity LED$. Power LED has a continuously-glowing green element; while activity LED glows only when a node transmits or receives. In transmission mode, this LED glows in green; while turns red when the radio is in reception mode. Thus, energy consumption in mJoules used by LEDs in transmission and reception modes are calculated as follows. Here, $\mathbf v$ denotes the voltage that is $3.7\,\text {V}$.

$$\begin{aligned} i_{{{\text {LED}}}}^{{{\text {Rx}}}}= &\, {} i_{{{\text {Green}}}}^{{{\text {Pow}}}} + i_{{{\text {Red}}}}^{{{\text {Act}}}} \nonumber \\ \nonumber= & \,{} 2.5{{\text {mA}}}+4.5{{\text {mA}}} \nonumber \\= & \,{} 7{{\text {mA}}} \end{aligned}$$

(13)

where,$i_{{{\text {LED}}}}^{{{\text {Rx}}}}$ is the current drawn by the LED when a node is in receiving mode, $i_{{{\text {Green}}}}^{{{\text {Pow}}}}$ is the current drawn by the power LED having only green element with half-brightness and $i_{{{\text {Red}}}}^{{{\text {Act}}}}$ is the current drawn by the activity LED having only red element with half-brightness.

Multiply Eq. 13 by $t_{\text {Packet}}$ (from Table 4) and $v$ to get energy consumption in mJoules.

$$\begin{aligned} E_{{{\text {LED}}}}^{{{\text {Rx}}}}= & \,{} i_{{{\text {LED}}}}^{{{\text {Rx}}}}\times v \times t_{{{\text {Packet}}}}\nonumber \\= & \,{} 7{{\text {mA}}}\times 3.7\text {V}\times 0.039{{\text {Sec.}}}\nonumber \\= & \,{} 1.01\text {mJoules} \end{aligned}$$

(14)

where, $E_{LED}^{Rx}$ is the energy consumed by LEDs when a node is in receiving mode.

Now, current drawn by LEDs when a node is in transmitting mode can be calculated as

$$\begin{aligned} i_{{{\text {LED}}}}^{{{\text {Tx}}}}= & \,{} i_{{{\text {Green}}}}^{{{\text {Pow}}}} + i_{{{\text {Green}}}}^{{{\text {Act}}}} \nonumber \\= &\, {} 2.5{{\text {mA}}}+2.5{{\text {mA}}} \nonumber \\= &\, {} 5{{\text {mA}}} \end{aligned}$$

(15)

where, $i_{{{\text {LED}}}}^{{{\text {Tx}}}}$ is the current drawn by the LED when a node is in transmitting mode, $i_{{{\text {Green}}}}^{{{\text {Pow}}}}$ is the current drawn by the power LED having only green element with half-brightness and $i_{{{\text {Green}}}}^{{{\text {Act}}}}$ is the current drawn by the activity LED having only red element with half-brightness.

Multiply the Eq. 15 by $t_{{{\text {Packet}}}}$ (from Table 4) and $v$ to get energy consumption in mJoules

$$\begin{aligned} E_{{{\text {LED}}}}^{{{\text {Tx}}}}= &\, {} i_{LED}^{Tx}\text {mA}\times v \times t_{\text {Packet}} \nonumber \\= & \,{} 5\text {mA}\times 3.7\text {V}\times 0.039\text {Sec.}\nonumber \\= & \,{} 0.7215\text {mJoules} \end{aligned}$$

(16)

where, $E_{{{\text {LED}}}}^{{{\text {Tx}}}}$ is the energy consumed by LEDs when a node is in transmitting mode.

1.2 Energy Consumption by Receiver

When a node receives a packet, it uses both power and activity LEDs. The processor board state is awake, actively calculating and the radio is in receiving mode. The net energy consumed in mJoules by the node is calculated as follows

$$\begin{aligned} E_{{{\text {Rx}}}}= & \,{} i_{{{\text {Rx}}}}\times v \times t_{{{\text {Packet}}}}+E_{{{\text {LED}}}}^{{{\text {Rx}}}}\nonumber \\= &\, {} 99.7\text {mA}\times 3.7\text {V}\times 0.039\text {Sec.}+1.01{{\text {mJoules}}}\nonumber \\= & \,{} 15.39671\text {mJoules} \end{aligned}$$

(17)

where, $E_{{{\text {Rx}}}}$ is the total energy consumed, $i_{{\text {Rx}}}$ (from Table 5) is the total current drawn by a node in receiving mode with a processor having state awake and actively calculating and $E_{{{\text {LED}}}}^{{{\text {Rx}}}}$ (from “Energy Consumption by LEDs” section of “Appendix”) is the energy consumed by LEDs when the node is in receiving mode.

1.3 Energy Consumption by Transmitter

When a node transmits a packet, it also uses both power and activity LEDs. The processor board state is awake, actively calculating and the radio is in transmitting mode using $k{\text{th}}$ transmission power level. The net energy consumed in mJoules by the node is calculated as follows

$$\begin{aligned} E_{Tx}= & \,{} i_{{\text {TX}}}^\text {k}\times v \times t_{\text {Packet}}+E_{LED}^{Tx}\nonumber \\= & \,{} i_{{\text {TX}}}^\text {k}\times 3.7\text {V}\times 0.039\text {Sec.}+0.7215\text {mJoules}\nonumber \\= & \,{} (0.1443i_{{\text {TX}}}^\text {k}+0.7215)\text {mJoules} \end{aligned}$$

(18)

where, $E_{{{\text {Tx}}}}$ is the total energy consumed and $i_{{{\text {Tx}}}}^\text {k}$ is the total current drawn by a node in transmitting mode with transmission power level $\text {k}$. The possible value of $i_\text {TX}^\text {k}$ are listed in Table 6 and depends upon the transmission power level used. $E_{\text {LED}}^{\text {Rx}}$ is discussed in “Energy Consumption by LEDs” section of “Appendix”.

1.4 Energy Consumption by Listener

When a node neither transmits nor receives, it is in listening mode where the node is in shallow sleep and only the power LED is ON. The total energy consumed in listening mode is given by the following equation.

$$\begin{aligned} E_{Lx}= & \,{} (i+i_{Green}^{Pow})\times v \times t_{\text {Packet}}\nonumber \\= & \,{} (43.7\text {mA}+2.5\text {mA})\times 3.7\text {V}\times 0.039\text {Sec.}\nonumber \\= & \,{} 6.67\text {mJoules} \end{aligned}$$

(19)

where, $E_{\text {Lx}}$ is the energy consumed in listening, i is the current drawn by a node in shallow sleep mode with radio on. $i_{\text {Green}}^{\text {Pow}}$ is discussed in “Energy Consumption by LEDs” section of “Appendix”.