# Reliability Improved Cooperative Communication over Wireless Sensor Networks
## 4 Main Design of RICC  
### Motivations of RICC  
The research motivations of this paper originate from the two reasons:  
**Observation 1**.: Generally, a large data transmission power can improve the link quality between nodes, which we validated in a network using a communication scheme named NCCC and found that a higher data transmission power could achieve a lower MFR; however, the energy consumption was increased [28]. Thus, there must be a tradeoff between the energy usage and reliability [26; 27]. According Equation (18), this situation is discussed by Figure 2. As the data transmission power increases from 0.015 to 0.1 (J/Hop/Message), the MFR reduces from 0.024 to 1.577\(\times\)10\({}^{-4}\), which means that an increase in the data transmission power by a factor of 6.66 can reduce the MFR by a factor of 155. Therefore, increasing the data transmission power can effectively reduce the MFR, but it consumes more energy.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Symbol** & **Meaning** & **Value** & **Symbol** & **Meaning** & **Value** \\ \hline \(N_{f}\) & the receiver noise figure & \(10\) dB & \(w\) & the carrier wavelength & 0.12 m \\ \hline \multirow{2}{*}{\(M_{l}\)} & the link margin compensating the hardware process variations & \multirow{2}{*}{40 dB} & \multirow{2}{*}{\(d_{0}\)} & the close-range reference distance between the receiver and transmitter & \multirow{2}{*}{1 m} \\ \hline \(U\) & communication constants & \(3.47\times 10^{8}\) & \(M\) & The number of splits of the network & \multirow{2}{*}{2} \\ \hline \(G_{\text{r}}G_{r}\) & the transmitter and receiver antenna gains, respectively & \multirow{2}{*}{7 dBi} & \multirow{2}{*}{\(l_{h}\)} & the size of the packet header & \multirow{2}{*}{44 bits} \\ \hline \(SNR_{0}\) & a threshold of Signal-to-Noise Ratio (SNR) & \multirow{2}{*}{0 dB} & \multirow{2}{*}{\(l_{d}\)} & the size of the data packet & \multirow{2}{*}{1200 bits} \\ \hline \(\lambda\) & the probability of generating data in a period & \multirow{2}{*}{0.1} & \multirow{2}{*}{\(l_{s}\)} & the size of the status message & \multirow{2}{*}{100 bits} \\ \hline \(d\) & the transmission distance & - & \multirow{2}{*}{\(N_{r}\)} & the PSD of the total effective noise at the receiver input & \multirow{2}{*}{-} \\ \hline \(E_{Amp}\) & the energy consumption of the power amplifier for transmitting one bit of data & - & \multirow{2}{*}{\(\eta\)} & the drain efficiency of the RF power amplifier & \multirow{2}{*}{-} \\ \hline \(h\) & the channel gain & - & \(\xi\) & the Peak-to-Average Ratio (PAR) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._  
Figure 2: Message Fail Delivering Ratio (MFR) versus energy used for delivering a packet per hop (J/Hop/Packet).  
Observation 2.In NCCC, which employs equal transmission power throughout the whole network [31], there is much remaining energy in the region far from the sink node (see Figure 3, which shows the experimental result in Section 6) due to the impact of the energy hole. We are inspired to adopt unequal transmission powers in different places in the network; more specifically, a higher transmission power is used in the area where much energy remains. Hence, the network can increase data collection reliability without reducing the network lifetime. Meanwhile, the energy utilization ratio is also improved.  
For those two reasons, the Reliability Improved Cooperative Communications (RICC) data collection scheme is proposed. The main idea are that: the reliability is guaranteed by each node in the routing path; however, since the nodes have unbalanced energy consumption, RICC uses the remaining energy to increase the data transmission power, and adopts the same data transmission power in the area near to the sink as in previous studies. Thus, the goal of enhancing the network reliability without decreasing the lifetime can be achieved.