# Service-Aware Clustering: An Energy-Efficient Model for the Internet-of-Things
## 2 The Energy-Efficient Internet-of-Things Model
### Radio Model and Energy Budget Computation  
Every node in the hybrid IoT network contains a radio communication subsystem that consists of transmitter/receiver electronics, antennae and an amplifier. To determine the energy dissipated by these components, this paper follows the radio energy model discussed in [17] described in Figure 2. In this model, the energy associated with the transfer of \(k\) bits of data between a transmitter and a receiver node separated by a distance \(d\) meters is given by Equation (1).  
\[E =E_{Tx}+E_{Rx}\] \[E_{Tx} =E_{elce}*k+E_{amp}*k \tag{1}\] \[E_{Rx} =E_{elce}*k\]  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Node Type** & **Service Delivery** & **Energy Consumption Profile** & **Potential Routing Role** \\ \hline CSN & Sensing & 1 & CH, CS \\ STN & Sensing + tagging & 2 & RS \\ HSN & Sensing + reading & 3 & CS, RM \\ BSN & aggregation + analysis + forwarding & 4 & BS \\ \hline
**Routing Role** & **Network Service** & **Energy Consumption Level** & **Potential Node** \\ \hline RS & Identification & 1 & STN \\ CS & Sensing & 2 & CSN, HSN \\ RM & Reading & 3 & HSN \\ CH & aggregation + forwarding & 4 & CSN, HSN \\ BS & aggregation, analysis + processing & 5 & BSN \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mapping nodes’ service delivery into routing roles. CSN, conventional sensor node; STN, sensor tag node; BSN, base station node; RS, reader slave; CS, cluster slave; RM, reader master; CH, cluster head.  
Figure 2: The radio energy model.  
where \(E_{Tx}\) is the energy spent by a node for transmitting and \(E_{Rx}\) is the energy spent by a node for receiving. \(E_{elec}\) is the energy needed to run the electronics of the transmitter/receiver, and \(E_{amp}\) is the energy required to amplify the transmitted signal. The value of \(E_{amp}\) depends on the transmission distance.  
Given a threshold transmission distance \(d_{0}\), the free space propagation model using parameter \(\xi_{FS}\)[11] is employed when \(d<d_{0}\) and the two-ray ground reflection model using parameter \(\xi_{TR}\) when \(d\geq d_{0}\). Using these two models, the energy required to amplify a signal is given by [10].  
\[E_{amp} = \left\{\begin{array}{ccc}\xi_{FS}*d^{2}&if&d<d_{0}\\ \xi_{TR}*d^{4}&if&d\geq d_{0}\end{array}\right. \tag{2}\]  
where \(d_{0}=\sqrt{\frac{\xi_{FS}}{\xi_{TR}}}\) and the parameters \(\xi_{FS}\) and \(\xi_{TR}\) were set to \(\xi_{FS}=10\) pJ/bit/m\({}^{2}\) and \(\xi_{TR}=0.0013\) pJ/bit/m\({}^{4}\) following [10].  
The role that each node performs in the network has a significant impact on the total energy dissipation. Therefore, in order to assign roles fairly, a good understanding of the energy consumption of the different types of nodes is required. This is provided by a radio energy model that describes the energy consumption of each of the hardware components involved in radio communication. Furthermore, a cluster energy budget calculation that considers the energy associated with the different roles played by the system is required. The total energy dissipated by each node is the sum of the energy dissipated for its functions and its role in the network.  
* A CSN sensor node acting as CM spends energy on sensing and transmitting data to its cluster head.
* A CSN sensor node acting as CH dissipates energy for receiving, processing and transmitting data from its cluster members, as well as relaying data from other cluster heads.
* An HSN sensor node acting as CM spends energy for sensing and transmitting data to its cluster head, in addition to interrogating sensor tags and relaying data from other HSNs.
* An HSN acting as CH also spends energy for receiving, processing and transmitting data from its cluster members, as well as on interrogating sensor tags and relaying data from other HSNs.