wireless ad hoc

8/2/2019 Wireless Ad Hoc

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1. INTRODUCTION

Parking meters deployed on strategic streets and places by municipalities to collect money in

exchange for the right to park for a limited time. They allow municipalities to implement

their traffic and mobility management policies as well as to maintain security and equitable

access to parking. Indeed, the use of conventional parking meters involve a lot of human

resources to regularly monitor these devices in place and hand down fines for violators of

parking rules.

The present paper suggests using new wireless communication technologies to make

monitoring parking meters cost-effective and more efficient in the sense that no infraction

may occur without sanction.

An intelligent wireless based system may replace conventional methods of monitoring by

deploying low power sensors to detect parked vehicles and by wirelessly networking the

parking meters in a power-aware way.

The detection sensor proactively informs the system, the embedded on the parking meter, of

the presence of a vehicle. Parking time starts to be decremented if valid coins are inserted.

The state of each parking meter is transmitted through an ad hoc wireless network to the

central station which monitors all smart parking meters.

The paper presents the design and implementation of both the Ad Hoc wireless network and

its node which is the smart parking meter. The system emerge new technology namelyZigBee which utilizes IEEE 802.15.4 standard as radio layer (media access control (MAC)

and physical layer) [1-4] also it enables monitoring which provides municipalities with

valuable information to update their strategies and policies. The expected immediate result is

the reduction of parking violations and/or the increase of revenues through more fines.

Our research contribution mainly concerns the study of limitations of the wireless Ad Hoc

network in various conditions (snow and hard weather condition) which may significantly

affect the node range and the bit rate.

2. RELATED WORK

Today, there are several automated or manually systems and methods to detect parking

infractions. The first method requires physical presence in place yielding the deployment of

huge human resources (control agents) working sometimes in non comfortable weather


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conditions. Control agents are only able to cover a limited number of vehicles especially at

rush hours.

Automatic detection emerged last years with embedded parking solutions. The cost inherent

to these solutions and the covered area are still serious issues. More efficient and cost-

effective solutions are required [5-7].

Systems deploying cameras to capture digital images of vehicles need a high bit rate

technology to deliver these images in real time like Wi-Fi [8]. In fact, covering a large area

with such a technology makes the system very expensive due to the high cost of Wi-Fi and to

high energy consumption [9-10]. Moreover, the system will still dependent on other

infrastructural considerations, and external failures may generate system breakdown.

In this context we propose to develop a hardware and software solution that is based on

innovative technologies and less expensive. The system is the first of its kind using the

ZigBee technology to detect infraction and to monitor the elapsed time on the parking

meters. It outperforms other technologies like Wi-Fi [10] in terms of low cost and it enables

covering large areas without need of another network infrastructure.

The system is feeded locally by using a 12V battery which makes the system mobile and

feedable by solar panels.

3. METHOD

The paper illustrates the real-time monitoring advantage of the parking traffic, whileintegrating the less expensive wireless communication technology namely ZigBee compared

to other technologies like Bluetooth and Wi-Fi [10].

Our contribution consists in designing and implementation of a wireless Ad Hoc network

based on a smart parking meter enabling the management and monitoring of parking places

in large regions with minimum human and material resource deployment. The work also

includes the manufacture of the smart parking meters.

The study consists of two parts: the first concerns the architecture of the wireless ad hoc

network whereas the second deal with the task of implementing a network node.

3.1 Network node design and implementation

3.1.1 Hardware contribution

The system has a variety of integrated hardware elements. Indeed, the node includes liquid

crystal display (LCD) showing the allocated time that is decremented just after inserting the


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coins. It also includes a sensor detecting the presence of vehicles if any. This sensor uses

infrared light (we can other types such as ultrasound) and it can also calculate the distance

from the parking meter to the parked vehicle (Fig. 1).

Figure 1. Parked vehicle detection.

The microcontroller, which is the smart part of the system, handles the capture and the

processing of data because it allows us receiving the signal and storing data from the sensor

on the one hand and sending data through the serial port to the network wireless module (Fig.

2) on the other hand. Thereafter the data is circulated in the network, according to the used

architecture and the protocols adopted by the modules. These protocols and architecture willbe explained later.

Figure 2. Node architecture.

3.1.2 Software challenge

Concerning the smart parking meter, the software part handles both the microcontroller and the

wireless communication module. The microcontroller is connected to the infrared sensor and coin


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acceptor output. The flow diagram is shown in Figure 4. When a vehicle is sensed, the system starts

the processing mode, then it checks if a coin is already entered. The microcontroller is always

listening to the sensor and coin acceptor output and never goes to the sleep mode: If a coin is entered

a thread displays and decrement the time allocated. If allocated time is over and no more money

entered in the coin acceptor, a warning will be sent instantly to the control station via the ZigBee

module and a security officer will be dispatched. If the driver parks the vehicle and does not put

coins, after a certain time-out delay a warning will be sent to the control station and a security officer

will be dispatched also. Concerning the wireless communication module, it also has two inputs,

which are the data reaching the microcontroller via the serial pins or the neighboring node via the

antenna. These data will be treated and sent to the next node or the destination.

When the module is turned on, it will go to the idle mode with the default configuration and does not

send data until it is received from the microcontroller or the neighboring node. The flow diagram is

shown in Figure 3.

Figure 3. Flow diagram of the wireless communication module


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Figure 4. Flow diagram of the Microcontroller.

3.2 Ad Hoc network

For the data transmission via wireless network, we opted for ZigBee technology for our

application which require low data rates and low power consumption. This choice took into

account cost, speed and coverage [11]. In fact the low cost allows the ZigBee to be widely


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deployed in wireless control and monitoring applications. The low power-usage allows

longer life with smaller batteries. The Ad Hoc networking provides high reliability and larger

range [11].

The ZigBee communication protocol includes two sub stack and one application layer which

define the software part of the module developed by the customer. The first stack, defined by

the IEEE 802.15.4 standard characterizes the hardware, includes the Physical and Media

Access Control layers. The second stack, developed by the ZigBee Alliance and included in

the network layer, supports the routing topology and the security option adopted by the

customer in a frame called API [11] (Fig. 5).

Table 1 presents the reasons for choosing this technology. First, the battery life extends over

about three years. Second, the number of nodes within a single network can reach 64 000.

Third, the transmission range of the ZigBee module can reach the 1600 meter with high gain

antenna. All the advantages make this technology the most suited for such application.

Table 1: ZigBee Applications [1, 11].

3.2.1 Network Formation

The networks include three different device types, namely coordinator, router, and end

device node [11] (Fig. 6). The network is formed when a coordinator node located in the

control station is turned on. All parking meter nodes are defined as routers and end devices

that may join our network. They inherit the coordinators node identification. Each network


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is defined by a single coordinator node. Each group of smart parking meters must be

connected to at least one node configured as a router to enable data routing to the

coordinator. The neighbor routers node must respect the range limit to successfully perform

data delivery.

3.2.2 Network Routing

The network supports mesh routing, allowing data to traverse multiple parking meter nodes

in order to reach the destination located in the control station. This allows the network nodes

to be spread out over a large region.

Data can be sent as either unicast or broadcast transmissions so the application has two types

of transmission. The first one concerns the case where a single source (control station) sends

requests to several parking meter nodes in order to change one or more network parameters.

For this kind of transmission we can use the process called route discovery which is based on

the AODV (Ad-hoc On-demand Distance Vector routing) protocol. The second type is that

the parking meter automatically sends data to a single destination (station control) informing

it about an infraction. In this case, we can use the Many-To-One routing protocol [11].

Figure 6. Parking meter based on ZigBee Network Topology.

The main advantage of the two routing protocols is that routes between parking meters, who

wants to send data, and control station are established on demand and is not known in


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advance [12]. Moreover, the capacity of the network is so big that the latter may contain

thousands of nodes.

Figure 7. Ad-hoc On-demand Distance Vector routing.

The AODV protocol allows route request (RREQ) message broadcasting when a node needs

to discover a route to a destination. Once destination is reached, the destination route is made

available by unicasting a route replay, referred to as RREP, back to the source route (Fig. 7).

During Network operation, intermediate nodes update their routing tables. If a node does not

work anymore an error message will be send to the source and the route discovery process

will started again [8].

Figure 8. Many-To-One Routing

The Many-To-One protocol is another routing protocol supported by the wireless module and

an improved version of the AODV protocol.

The idea is to send Many-To-One broadcast message (MTORR) in the reverse way by the

coordinator (control station) in order to establish route on all devices (Fig. 8) after each node

know in advance the route to the coordinator and data will be send [9].


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The XBee modules support both transparent and API (Application Programming Interface)

communication mode. When operating in transparent mode, the modules act as a line

replacement and all data received is queued up for RF transmission. API mode is an

alternative to transparent mode in the sense that all data entering and leaving the module is

contained in Packets [11]. We use the API mode because is recommended when receiving

RF data from multiple nodes, and we need to know which node sent which data. API allow

us supporting multiple ZigBee end devices and routers [11], which is the case for our

application since knowing the source address allows us to locate the parking meter. All the

node addresses and their locations are stored in a database.

4. RESULTS

We tested the performance of our implemented system equipments. We started by measuring

the range of the infrared sensor, it turned out that it can reach three meters as shown in Figure

9 which is far enough to detect the parked vehicle.

The sensor developed by Sharp Company, is characterized by its long range and low power

consumption. The environmental temperature and the operating duration do not depend on

the distance of detection since it the measurement is based on the triangulation method [13].

The field of vision considered by the smart parking meter is between 50 centimeters and 2.5

meters. Thus it does not include both the pedestrian and vehicles in the street. To eliminate

the consideration of an undesirable object in the parking area, we set a time limit in themicrocontroller. The sensor delivers a voltage inversely proportional to the distance. It will

be later converted and processed by the microcontroller.

Figure 9. Sensor range.


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We tested also the performance of the wireless communication module used. It is an XBee-

PRO ZB series 2 RF Modules with integrated chip antenna. The modules operate within the

ISM 2.4 GHz frequency band [11].

Figure 10. Module delivery rate.

The tests have been made in an urban area, exactly in a street behind the University of

Moncton (NB, Canada) during a snowy day.

The test revealed that the range limit for the XBee Pro series 2 modules is about 110 meter

for both the packet delivery and the sensitivity (Figures 10, 11).

Figure 11. Unicast API data transmission to the coordinator.


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The format of the packet sent, also called API frame is fixed by the manufacturer and has

several standard fields. The manufacturer has developed several types of packets. We give an

example used to send unicast data (Fig. 12) from parking meter to the Coordinator located in

the control station.

Figure 12. Unicast API data transmission to the coordinator.

This format of API frame is the most used in the application. In fact, if an infraction occurred

the concerned parking meter will send data to the control station in this format including

data, length and checksum fields.

5. DISCUSSION

We succeeded to implement the smart parking meter and the Ad Hoc network with mesh

routing. The API packet delivery was successfully completed and the infraction detection

resulted in an automatic way.

We conclude that the level of reflectivity and attenuation in the wireless transmission is

related to the snow density and weather condition. The system could operate with good

deliverance rates in severe conditions which allows for better results under ordinary

conditions.

It outperforms the conventional parking meter in the following aspects:

ided.

Also it outperforms existing automatic system in terms of:

the other wireless transmission technology.

We faced some difficulties and limitations:


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the range system.

ime of batteries is always a limitation for the use of the system. The

implementation of solar energy will be the subject of a future work.


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References

[1] ZigBee Alliance, ZigBee Specifications, version 1.0, April 2005.

[2] IEEE 802.15.4-2006. IEEE standard for information technology Telecommunications and

information exchange between system Local and metropolitan area networks specific

requirements, Part 15.4: Wireless MAC and physical layer (PHY) specifications for low-rat

wireless personal area networks (LR-WPANs). 2006

[3] IEEE 802.11 WG. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer

(PHY) Specification Standard, IEEE. Aug. 1999.

wireless ad hoc

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