Wireless: Parking lot gets smart with ZigBee

With, according to various studies, average time spent cruising for a parking space in urban public parking areas varying from 3.5 to 12 minutes, and distance traveled ranging from a half mile to over a mile, Paris-based hi-tech startup Innovative Technologies SARL singled out this arena as a prime application area for automation.

By Control Engineering Staff September 27, 2007

With, according to various studies, average time spent cruising for a parking space in urban public parking areas varying from 3.5 to 12 minutes, and distance traveled ranging from a half mile to over a mile, Paris-based hi-tech startup Innovative Technologies SARL singled out this arena as a prime application area for automation.

Wireless technologies have always been an area of interest for the company. Already possessing expertise in RFID, the company recently broadened its portfolio with ZigBee standard for wireless sensor monitoring and control.

The automation process requires placing “smart” detection sensors next to the parking spaces throughout the parking lot. The sheer size of an average underground parking lot ruled out running wires to each sensor. Besides the apparent potential technical difficulties, the cost of wires easily runs up to a prohibitive level of over€200 per meter. Going wireless was an obvious solution.

The next challenge was to select the right wireless protocol. There are a considerable variety of standards-based and proprietary wireless solutions available. Standards offer clear benefits, such as interoperability and vendor independence. Among available wireless standards are Bluetooth, Wi-Fi, and ZigBee.

One of the critical requirements was a self-healing multi-hop mesh network, capable of rerouting a signal if line-of-sight is blocked. Another important factor was that the wireless devices must be battery operated. The company’s engineers concluded that only ZigBee, a low-power standard for mesh networks, based on IEEE802.15.4, could meet both criteria.

Searching online, Innovative Technologies found a number of vendors offering 802.15.4/ZigBee modules. Two module characteristics were of key importance: power consumption and size. The sensor device has to work autonomously for 4 years on one 9 V battery. Plus, the PCB board had very little “real estate” left for module integration.

Most of the leading ZigBee modules boast very low power consumption. However, the engineers chose ZigBit modules from MeshNetics because they feature a tiny footprint of just over three square centimeters.

The next step was to try out the ZigBit modules. Innovative Technologies ordered the ZigBee Evaluation Kit from MeshNetics to achieve this goal. Containing three ZigBit-based development boards with sensors, accessories and software, the kit provided sufficient tools to evaluate the module’s performance, ensuring that it lived up to expectations. After a successful test run, Innovative Technologies began prototyping their application.

ZigBit modules featuring dual chip antennas are integrated into boards connected with a range finder sensor and 9 V battery. ZigBit modules take full advantage of the new Atmel’s RF transceiver AT86RF230, which possesses -101dBm of Rx sensitivity and up to +3dBm of Tx power.

Most of the time, the devices remain in sleep mode, saving the batteries. The devices wake up every minute for a few milliseconds to take measurements, and then go back to sleep.

Vehicle Detection Modules are mounted on the ceiling right above the parking spaces, or on the walls. Inside every VDM unit is a ZigBit 802.15.4/ZigBee module, enabling it to communicate with other VDMs and form ZigBee network. Compact displays serve to communicate the useful information to a driver, such as a number of available parking spaces and the number of the closest free spot. Source: MeshNetics

A ZigBee network normally has three types of nodes: end devices, routers, and coordinators. The end devices, featuring sensors, collect the data, which they then transfer on to a coordinator. In case a coordinator is located too far for a direct link, the routers are used.

In Innovative Technologies’ project, the relative compactness of the parking lot and strong RF performance of the ZigBit modules eliminated the need to use routers. The sensor data from the end devices is transmitted within the network on to a coordinator. The coordinator serves a gateway, transferring data to a central server. This can be accomplished directly or via GPRS gateway serving as an intermediary. The data collection and flow processes are automated.

Innovative Technologies selected one client’s underground parking lot for a trial deployment. The parking lot automation system, called “E-Park,” includes three components:

Vehicle detection modules (VDMs) are mounted on the ceiling above the parking spaces, or on the walls. The trial setup was with one VDM monitoring two parking spaces, although the tests showed that a one VDM can efficiently monitor four parking spaces. Each VDM is powered by 9 V battery allowing for 4 years of autonomous operation. Inside every VDM unit is a ZigBit 802.15.4/ZigBee module, enabling it to communicate with other VDMs and form a ZigBee network.

Compact displays serve to communicate the useful information to a driver, such as a number of available parking spaces and the number of the closest free spot.

Data management software visualizes the graphic map of each parking level, so that an operator can see in real time the occupied and free spots. The software also displays the current number of free spots, the parking lot filling trend, and an average turnover rate for individual parking spaces and the entire parking lot.

The system generates alerts when the parking lot is almost full, when a “parking space hogger” is detected, when the temperature exceeds the set threshold, or when the unauthorized vehicle movement takes place. Besides being displayed on a PC screen, the alerts can be broadcast to PDAs and cellular phones as text messages. An operator can set up the system’s various parameters. The system logs all data and provides historical statistics, which can be accessed for further analysis. Remote operators can access the system via the Web.

At the parking lot’s entry, users are greeted by a large display clearly showing the number of available spaces on each level with a separate number indicating spaces for the disabled. After making sure that there are spaces available, users proceed to a toll booth where another display repeats that information and recommends the closest free spot. Upon reaching a parking level, a smaller display repeats the parking space number previously recommended, or suggests a new one, if it was already taken. As soon as the user parks the vehicle, the system shows that space as occupied. When a vehicle leaves, the system updates immediately, so that other drivers can use the space.

The ZigBee-based implementation reduced average cruising distance by 30% and time to find a free space and park by 25%. This led to increased vehicle turnover and a better occupancy rate, which noticeably added to the parking lot operator’s bottom line.

— Edited by C.G. Masi , senior editor from information provided by MeshNetics.