**3. System requirements**

340 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

workstations and applications.

computer software, among others. Therefore, the photocell relay mechanism can be attached to an Information Technology structure, through device and sensor networks, supervision

The stage of development of public lighting projects in Brazil is restricted to rationing energy and improving lighting efficiency, by replacing sodium or mercury lamps by LED lamps, installing photovoltaic panels for sustainable lighting, powered by solar energy, and,

LED lamps offer better color reproduction; they do not emit ultraviolet and infrared rays, they propagate less heat, and they attract fewer insects. They also show good efficiency and longer life, estimated at approximately 50,000 hours of operation. Sodium vapor lamps, most commonly used today, last up to 32,000 hours; mercury vapor lamps may last 12,000

The Companhia Energética de Minas Gerais (Cemig), an electric energy utility company in the State of Minas Gerais, Brazil, together with the municipal government of Belo Horizonte, began testing LED lamps. Some luminaires have been already installed on poles near San Francisco Church (CEMIG, 2009). Cemig provides annual reports and sustainability reports

In addition, driven by the investments for the World Cup 2014, Cemig's project "Minas Solar 2014" seeks to install photovoltaic panels to power public lighting, aiming to improve public

Cemig signed a cooperation agreement with the U.S. government, through the U.S. Trade and Development Agency (USTDA), to fund their smart grid project. The U.S. agency will provide US\$ 710,000 for the Brazilian company, to be applied on the study that analyzes the feasibility of implementing smart grids, which has been developed by the company together

CPFL Energia, an electric energy utility company in Brazil, together with the Development Foundation from the University of Campinas (FUNCAMP), the Foundation for Research and Advisory Service to the Industry from the Federal University of Itajubá (UNIFEI), HYTRON Hydrogen technology, FUSION, and the AQUA GENESIS Institute for Studies and Projects on Energy, Hydrogen and Environment, is currently investing in a project of a solar photovoltaic and/or wind hybrid system to generate electricity, which can operate connected to the distribution network or isolated, and the goal is to evaluate the integration of distributed generation at low voltage, with and without energy storage. Considering the increasing use of local alternative sources of energy generation, low power systems, renewable energy sources, and technological availability that allow immediate applications, utilization of solar photovoltaic and wind energy, with and without energy storage, stands

A project that involves communication, however not between sensors (PORTAL DE INOVAÇÃO CPFL, 2011b), called "failure diagnostic system for public lighting points", is being developed by CPFL in partnership with companies MATRIX and PLAYMUSIC. The

finally, luminaires to reduce lighting focus dispersion (CPFL CAMPINAS, 2011).

hours, and metal halide lamps, commonly used in facades of buildings, 10,000 hours.

that can be accesses at the company's website (CEMIG, 2011).

out above other options (PORTAL INOVAÇÃO CPFL, 2011a).

infrastructure and soccer stadiums (CHIARETTI, 2011).

with Light (SMART ENERGY ONLINE, 2011).

The recent document proposed by IETF (RFC 5548, 2009), which describes requirements for routing on urban networks, also affirms that these networks must attend convergent traffic, where one node (usually a gateway or sink) receives messages from several low frequency meters (a maximum of one measurement per hour, and a minimum of one measurement per day). The number of nodes must be in the order of 102 to 107, distributed in areas varying from hundreds of meters to one square kilometer, considering that nodes are commissioned in groups, and the battery shelf life is usually in the order of 10 to 15 years. The frequency band must be ISM (Industrial, Scientific and Medical), and the nodes will probably have from 5 to 10 immediate neighbors to communicate. The routing protocol must enable the network to be autonomous and organize itself, requiring a minimum energetic cost for maintenance functions. The protocol must also ensure that any diagnostic or failure information from the nodes is communicated without interfering on the network operational mode, respecting the time limits.

The project of a Wireless Sensor Network depends on the application where the network will be used, and it should be based on functional and non-functional requirements. Functional requirements for this type of project are:


• Automatic programmed actions: for example, the city lights should be turned on at 7 PM;

Street Lighting System Based on Wireless Sensor Networks 343

To understand the non-functional requirements, the list below briefly describes parameters

• Scalability: when proposing an approach to sensor networks, it is important to consider that the project should apply to small (up to 25 nodes), medium (25 to 103 nodes), or

• Fault tolerance: depending on the physical conditions, it may be necessary to adopt sensor nodes with special characteristics. In addition, due to difficult accessibility in some environments, it may be unmanageable to replace damaged nodes or batteries. Therefore, it is necessary to provide sensor nodes with adaptive capacities to deal with unstable environments. In the type of application described in this work, nodes must support high temperatures and heavy rain. Considering the failures related to sensor nodes, the routing algorithm proposed in this work must be fault-tolerant because the

• Delivery Guarantee: regarding the unstable wireless communication nature, because of external interference and/or electronic noise, it is necessary to create a point-to-point acknowledgment mechanism, which is a consensus among researches in the wireless network area. End-to-end confirmation messages are implemented in higher layers,

• Lifetime: sensor nodes depend on batteries, which require the use of efficient protocols in energetic terms. However, for this project, most sensor nodes are powered by energy cables that are already used in current street lighting structures. Avoiding the use of batteries is an ecological issue, because devices' maintenance involves a considerable amount of trash. Batteries would be used only in areas where there is no energy cable structure, such as rural areas. Therefore, the lifetime estimation should be medium to high, but it should not be prioritized in detriment of other requirements, especially not

• Latency: this parameter reflects the time interval the network has to inform the observer about a specific phenomenon. Some applications can be sensible to latency, therefore it is necessary to respond in a short time interval (equal or less than one second), for example, in control process supervision. On the other hand, other applications do not depend on a quick response time (for example, monitoring bridge stabilization). In relation to street lighting application, the acceptable latency should be on a time

Routing protocols are used in two types of package traffic in Wireless Sensor Networks: the first type directs packages from the sink node to the network nodes (i); the second type directs packages from the network nodes to the sink node (ii). Different terminologies may be used for these two traffic types: Tian and Georganas [1] and She et. al [2] use the terms *downstream traffic* for (i) and *upstream traffic* for (ii); Watteyne et al. [3] use the terms *divergent traffic* for (i) and *convergent traffic* for (ii); in other works, such as [4], authors name (i) as *gradient-descendent traffic* and (ii) as *gradient-descent traffic*, if routing is based on gradient.

This works uses the terms *divergent traffic* for (i) and *convergent traffic* for (ii).

relevant to the application, in order of importance (KHALIFA et al., 2011):

messages must find a reliable path to reach the destination;

large networks (102 to 107 nodes);

preferably in the transport layer (TCP);

to compromise the delivery rate;

interval in the order of tens of seconds.


To meet the functional requirements, a control and monitoring application is required to report system information to the user (Figure 2). This application is able to monitor operating conditions, for example, notifying the user about the end of life of a lamp if it exceeds a particular limit of hours, and graphically displaying city maps on a supervision screen, with the lighting points in operation. Figure 2 shows an example of status of lighting points, which are represented in different colors: lighting points in yellow indicate lit points; lighting points in blue indicate unlit points; lighting points in red indicate the boundaries of a specific region in which the application must act. Regarding control, the application sends commands to activate or deactivate lighting points as pre-programmed or when there is a request from the system operator.

As non-functional requirements, portability and robustness are considered essential factors in the application project. For more information, section 4 covers the details about the application project.

**Figure 2.** Control and Monitoring Tool Display

To understand the non-functional requirements, the list below briefly describes parameters relevant to the application, in order of importance (KHALIFA et al., 2011):

342 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

should be able to select a region through a remote tool to actuate;

companies) should be applied to simplify and streamline the process.

PM;

occurs;

request from the system operator.

**Figure 2.** Control and Monitoring Tool Display

application project.

• Automatic programmed actions: for example, the city lights should be turned on at 7

• Actuate the nodes through a remote tool: besides the automatic actions, the operator

• Diagnostic and alarms: trigger an event when a network, hardware or lamp failure

• Automation of information storage: mechanisms automating the storage process of related street lighting information (geodesic coordinates supplied for electrical

To meet the functional requirements, a control and monitoring application is required to report system information to the user (Figure 2). This application is able to monitor operating conditions, for example, notifying the user about the end of life of a lamp if it exceeds a particular limit of hours, and graphically displaying city maps on a supervision screen, with the lighting points in operation. Figure 2 shows an example of status of lighting points, which are represented in different colors: lighting points in yellow indicate lit points; lighting points in blue indicate unlit points; lighting points in red indicate the boundaries of a specific region in which the application must act. Regarding control, the application sends commands to activate or deactivate lighting points as pre-programmed or when there is a

As non-functional requirements, portability and robustness are considered essential factors in the application project. For more information, section 4 covers the details about the


Routing protocols are used in two types of package traffic in Wireless Sensor Networks: the first type directs packages from the sink node to the network nodes (i); the second type directs packages from the network nodes to the sink node (ii). Different terminologies may be used for these two traffic types: Tian and Georganas [1] and She et. al [2] use the terms *downstream traffic* for (i) and *upstream traffic* for (ii); Watteyne et al. [3] use the terms *divergent traffic* for (i) and *convergent traffic* for (ii); in other works, such as [4], authors name (i) as *gradient-descendent traffic* and (ii) as *gradient-descent traffic*, if routing is based on gradient. This works uses the terms *divergent traffic* for (i) and *convergent traffic* for (ii).

Figure 3 represents the two types of package traffic, differing by the communication flow in relation to the sink node.

Street Lighting System Based on Wireless Sensor Networks 345

**4. Control and monitoring application** 

communicate via a wireless network.

cover an urban center.

network.

The proposed architecture is based on the cell model. The cell should provide access to supervision and control of a number of sensor nodes for the management applications. By definition, the sensor node is the device coupled to the lighting point, which is able to

A cell is composed by a compartment, an industrial computer, a GPS antenna, a communication controller, and sensor nodes. Numerous cells can be formed to completely

The industrial computer is installed inside the compartment and it is connected to a communication controller, communicating via a serial protocol, while the communication

The GPS (Global Positioning System) antenna is considered the only time basis among several cells, and then alarms that occurred in different cells can be ordered. Management applications (Configuration/Topology, remote operation server and monitoring) are installed on the Operation computer and they communicate to the cells via Ethernet

Remote access is done through an Internet browser from the remote operation application computer to the remote operation server. The Google Maps library (GOOGLE MAPS

Figure 5 shows the system architecture and illustrates cell 01, which is responsible for grouping some sensors, and also shows the capability of adding new cells until all lighting

controller communicates to the sensor nodes via wireless network.

FAMILY, 2011) is used to plot the lighting points on the maps (Figure 4).

**Figure 4.** Screen obtained with Google Maps library

points from the city are mapped.

**Figure 3.** Typical WSN simplified architecture

In order to control and monitor public lighting systems, which is the goal of this work, the following message types based on RFC 5548 are needed, according to the mentioned requirements, subdivided in convergent and divergent traffic.

Convergent traffic:


Divergent traffic:

