## 3 Hardware and System  
### Hardware Architecture  
In this section, we present the hardware architecture of our designed sensor node. Basically, a node includes three main components: sensor, processor and radio frequency (RF) transceiver. The sensor is a device that produces data measurements in order to monitor the physical environment. Sensed data could be temperature, pressure, humidity, voltage, etc. The sensor gives an analog signal based on the observed phenomenon converted to digital information by the AD converters and sent to the processor for further processing. In our system, we opt for the \"Aosong DHT22\" temperature-humidity sensor. The processor is generally integrated with the microcontroller. It performs tasks, processes data and coordinates the functionality of all components connected to the sensor board. In our system, we used the \"Atmel Sam3x8e ARM Cortex-M3\" micro-processor embedded on an \"Arduino Due\" microcontroller [24]. A similar system using the Xbee mote, also based on Arduino, has been presented in [25] for a railway control case. Another advantage of working with the Arduino microcontroller is that it gives an easy programming interface for all layers, while many other commercial nodes are fixed for the physical and MAC layers. The radio frequency (RF) transceiver connects the sensor node to the network. Generally, the RF module operates in three different modes: transmit, receive and sleep. The transmit mode consumes more energy. The energy consumed during the other modes may vary according to the used medium access algorithm. In our system, we used the \"Microship MRF24J40 MA\" ZigBee transceiver [9] for routers and end-devices and the \"Microship MRF24J40 MD\" for the coordinator due to it high transmission range. Tables 1 and 2 present comparisons between the characteristics of some sensor nodes, including our designed sensor node, based respectively on the CPU, memory and data rate in Table 1 and power consumption, range and sensitivity in Table 2.  
This comparison shows that our hardware gives an alternative solution concerning the transmission range-energy consumption problem, by reducing considerably the energy consumption while maintaining a high transmission range compared with the other sensor nodes. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Name of** & **Micro** & **RF** & **Flash** & **Program** & **Frequency** & **Data Rate** \\
**Sensor Node** & **Controller** & **Module** & **Memory** & **Memory** & **Range** & **(kbps)** \\ \hline Texas Instruments & ARM Cortex-M3 & SmartRF05 EB & 512 K & 8 K RAM & 868–870 MHz & 250 \\ \hline Microchip & PIC24 & MRF24J40 & 128 K & 4 K RAM & 2.405–2.48 GHz & 250 \\ \hline TelosB & Atmega128 & TI CC2420 & 48 K & 10 K RAM & 2.4 GHz & 250 \\ \hline Memsic & ATmega128L & TI Chipcon CC2420 & 128 K & 4 K RAM & 2.4 GHz & 250 \\ \hline Tiny Node & TI MSP430 & Smart RF 125 MTD & 512 K & 8 K RAM & 2.4–2.4835 GHz & 152.3 \\ \hline Lotus & NXPLPC1758 & RF231 & 512 K & 64 K SRAM & 2.4 GHz & 250 \\ \hline Sun SPOT & ARM 920T & TI CC2420 & 512 K & 128 K + 4 K + 4 K & 2.4 GHz & 250 \\ \hline Our Designed Node &
\begin{tabular}{c} Atmel \\ SAM3 XSE ARM \\ \end{tabular} & MRF24J40 & 512 K & 64 K RAM & 2.4 GHz & 250 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sensor Nodes’ Comparison 1: hardware specifications. The circuit design of the node (excluding the Arduino board) is modeled in Figure 2, and a prototype of it is shown in Figure 3.  
We also note that, besides the three main components cited above, the sensor node includes other hardware components: one eight-bit, so the node provides a MAC address to nodes before the logical address assignment, and two capacitors. The circuit board, including all electronic components, is finally connected to the Arduino microcontroller.