Challenges and Implementation on Cross Layer Design for Wireless Sensor Networks

Abstract

Cross-layer design (CLD) has emerged as an important area in wireless sensor networks (WSNs). Cross-layer enables interaction between different non- adjacent layers and, thereby, exchanging information between layers, which, indeed is not possible in traditional architectures. CLD is used for enhancing the performance of the existing architectures by utilizing the flexible prospects of the protocol layers to improve system performance and to satisfy QoS demands of the applications. The CLD leads to increase in network efficiency and optimized network throughput. In this paper, the various cross-layer design methodologies for WSNs have been reviewed, which have basically been designed to enhance the network performance in WSN. At the end, the paper proposes a CLD based on ongoing research.

Appendix: Calculation of Optimum Hop Distance

Consider that a node sends L bits of information when a event occurs and retransmits the information when there is an error. Suppose that, n is the maximum number of retransmissions, then the resultant number of bits transferred is given by [62],

$$\begin{aligned} L_{res}= L* \sum _{j=1}^{n+1}\left( j*PER^{j-1}*(1-PER)\right) + (n+1)*PER^{n+1} \end{aligned}$$

(1)

where PER is the Packet Error Rate and if BER is the Bit Error Rate, PER is given by

$$\begin{aligned} PER= 1-(1-BER)^L \end{aligned}$$

(2)

The circuit has three modes of operation. The on state is used for the transmission and receiving of information. The nodes are in sleep state when there is no data to send or receive. Transient state is the state between on state and sleep state. The total energy consumed in transmitting and receiving $L_{res}$ bits of information to a hop, ignoring the power consumed in sleep state, is given by [63]

$$\begin{aligned} E_{hop}=\left( (1+\alpha )P_{t}+ P_{ct}+P_{cr}\right) T_{on}+P_{tr} T_{tr} \end{aligned}$$

(3)

where $P_{tr}$ is the power consumed in transient state $T_{tr}$. The $P_{on}$, power consumed in on ($T_{on}$) state, consists of the power consumed by transmitted signal ($P_{t}$), the transmitting circuit ($P_{ct}$), the receiving circuit ($P_{cr}$), and power consumed by power amplifier ($P_{pa}$). $\alpha = \frac{\zeta }{\eta }-1$ with $\zeta$ peak-to-average power ratio (PAR) of the signal and $\eta$ is the drain efficiency of the power amplifier. Assuming an N-th-power path-loss model at distance d (meters), the transmission power is expressed as [53]

$$\begin{aligned} P_{t}=P_{r} G_{1} M_{l} d^{N} \end{aligned}$$

(4)

In which $M_{l}$= link margin compensating the hardware process variations and noise and $G_{1}$ = the gain factor at d = 1 m, Now, if the sink node is k hop away the source node, the total energy per bits is given by

$$\begin{aligned} E_{tot} =\sum _{i=1}^{k} \left( \left( (1+\alpha )P_{r} G_{1} M_{l} d^N_{i}+ P_{ct}+P_{cr}\right) T_{on}+P_{tr} T_{tr}\right) /L_{res} \end{aligned}$$

(5)

And, the received power strength is given in term of SNR (Signal to Noise Ratio) as [64]

$$\begin{aligned} P_{r}=\psi (N_{o} N_{f})/T_{s} \end{aligned}$$

(6)

where $\psi$=Received SNR, $N_0/2$= Power spectral density of the noise per dimension, $N_f$=receiver noise, $T_s$=symbol period

Applying Jension Inequality, the inter layer distance, $d_{0}= d/k$ and differentiating it w. r. t. k and equating to 0, we get

$$\begin{aligned} d_{0}=\root N \of {\frac{\left( (P_{ct}+P_{cr})+P_{tr}\frac{T_{tr}}{T_{on}}\right) \eta T_{s}}{\zeta \psi N_{o} N_{f} G_{1} M_{l}(N-1)}} \end{aligned}$$

(7)

For M-ary Phase-shift Keying Modulation (MPSK) For MPSK, we use $\eta = 0.35$ which is typical value of class A power amplifier. Also, PAR $\zeta$ for MPSK is unity. Also, $m = L_{res} T_s/T_{on}$ where the number of bits per symbol is defined as $m= log_{2} M$ Considering B is the bandwidth in Hz of the signal, $T_s\approx 1/B$

$$\begin{aligned} d_{0}\approx \root N \of {\frac{0.35\left( (P_{ct}+P_{cr})+P_{tr}T_{tr}B\frac{log_{2}M}{L_{res}}\right) }{\psi N_{o} N_{f} G_{1} M_{l}B(N-1)}} \end{aligned}$$

(8)

M-ary Quadrature amplitude modulation (MQAM) For MQAM, $\eta =0.35$, PAR= $\zeta = \frac{3(\sqrt{M}-1)}{\sqrt{M}+1}$, $m=\frac{L_{res}T_{s}}{T_{on}}$ and $T_{s}\approx \frac{1}{B}$

$$\begin{aligned} d_{0}\approx \root N \of {\frac{0.117\left( (P_{ct}+P_{cr})+P_{tr}T_{tr}B\frac{log_{2}M}{L_{res}}\right) (\sqrt{M}+1)}{\psi N_{o} N_{f} G_{1} M_{l}B(N-1)(\sqrt{M}-1)}} \end{aligned}$$

(9)

Multiple frequency-shift keying Modulation (MFSK) For MFSK we use $\eta =0.75$ which is typical value of class B or higher power amplifier. Also, PAR $\eta$ for MFSK is unity and $T_{s}=\frac{M}{2B}$. Also $\frac{2log_{2}M}{M}\cong \frac{L_{res}}{BT_{on}}$

$$\begin{aligned} d_{0}\approx \root N \of {\frac{0.375\left( (P_{ct}+P_{cr})+2P_{tr}T_{tr}B\frac{log_{2}M}{ML_{res}}\right) (M)}{\psi N_{o} N_{f} G_{1} M_{l}B(N-1)}} \end{aligned}$$

(10)