# An Intelligent Parking Management System for Urban Areas
## 3 Description of the System
### System Architecture
#### 3.1.1 Sensor Nodes  
The sensor nodes send data packets that notify the entry or exit of a vehicle into or out of the monitored parking area. These packets include the identification number of the network and of the node to identify the parking area in question. Each sensor node interprets the messages received from the data centre. These packets contain the same fields as those sent by the node, but the identification fields of the network and node will correspond in this case to the terminal or terminals to which the message is directed, and the data field will contain the order sent by the data centre to the sensor nodes. For the hardware components of the nodes two circuit boards were used: a mainboard and a sensor board. The mainboard includes the components responsible for data processing and communication between nodes, while the sensor board is connected to the sensor. These two circuit boards, the batteries and a solar panel are housed in a box with IP67 protection measuring 82 mm \(\times\) 80 mm \(\times\) 85 mm. The batteries are lithium polymer 1900 mAh, with a nominal voltage of 3.7 V, and the solar panel has a power output of 0.4 W (5 V/80 mA). The main component of the mainboard is the CC2530 system-on-chip from Texas Instruments [26], a system that includes a microcontroller and a radio module in the integrated circuit. The microcontroller is the 16-bit Intel 8051 and has 8 KB of RAM and a programmable flash memory of 256 KB. The radio module is a transceiver that operates in the 2.4 GHz band and is compatible with the IEEE 802.15.4 protocol, with programmable output power of up to 4.5 dBm, allowing a maximum transmission speed of 250 Kbps. Another component that has been integrated into the mainboard is the CC2591 amplifier, also manufactured by Texas Instruments, which is compatible with the proposed radio system because it also operates in the 2.4 GHz band. This amplifier extends the range of communications by providing a power amplifier that increases output power and improves receiver sensitivity. One of the main characteristics of the mainboard is its small size (50 \(\times\) 70 mm). Wireless communication is established using the 6 LoWPAN standard that enables the use of IPv6 over the IEEE 802.15.4 standard. The main objective of using this standard is to be able to use IPv6 on a low-energy WSN, thereby enabling small devices, with limited processing power, to achieve broad connectivity (interoperability) and to maximise the battery life ([PERSON] [27]). The mainboard also has an RS-232 interface, JTAG, and a number of expansion connectors allowing communication with external devices. As shown in Figure 2, in addition to these devices, a 3 V DC/DC converter has been added to the mainboard to adapt the voltage supplied by the battery to that required by the integrated circuits. This is necessary because the nominal battery voltage is 3.7 V.  
Figure 2: Block diagram of the mainboard. As shown in Figure 3, the sensor board is composed of a series of interfaces and voltage converters to allow connection to a wide range of sensors. It has two DC/DC voltage converters, 12 V and 5 V, an SDI-12, and a 4-20 mA interface. This circuit board also features a battery charging system through an external solar panel, thus increasing the autonomy of the nodes. The photoelectric sensor used is a SHARP-GP2Y0D02 YK0F (Sharp Corporation, Osaka, Japan) [28], shown in Figure 4.  
This photoelectric sensor allows detection by the three types of standard sensing modes listed in Table 1.  
The chosen sensing mode is the diffuse mode, justified by its simple installation requirements, with no calibration needed, and its detection performance. During the experimental process, sensors were deployed in speed bumps. However, future deployments could be altered and make use of street furniture like bollards, street lights, or traffic lights. When those are not available, the most straightforward installation is to deploy sensors on the ground, avoiding the need for retro-reflective or through-beam sensors.