At the heart of smart grid and smart city solutions is the ability to remotely control and manage multiple applications, whether for energy use (smart meters), traffic monitoring, or public lighting. LED-based street lighting is an obvious starting point for many smart city initiatives around the world, with networking (wired and wireless) being the enabling technology, enabling monitoring and control.
Further benefits are envisaged as networked street lighting is integrated, along with other smart city applications such as smart meters and traffic monitoring, into a coherent smart city grid infrastructure.
This article will review the major trends in the networking protocols that street lighting OEMs are using, namely Power Line Communications (PLC) and IP6LoWPAN, claimed to be the network most commonly associated with ‘Internet of Things’ applications.
It will consider the devices required to build these wired and wireless networks. Typical components for PLC include Cypress Semiconductor’s CY8CPLC modem chips and development kit, and the TMDSIACLEDCOMKIT development kit from Texas Instruments. For 6LoWPAN, Atmel’s ATmega 256RFR2 transceivers and evaluation board come under scrutiny, together with the CC-6LoWPAN-DK868 development kit from TI, and the deRFusb range of radio transceiver modules and development kit from Dresden Elektronik, based on Atmel’s ATmega devices.
Cities’ smart start
Smart public lighting is proving to be a compelling starting point for most smart city initiatives around the world. The motivation is not simply the energy savings gained by replacing traditional luminaires with low-power LEDs, but the further benefits enabled through connectivity and control. Networked street lighting delivers additional energy savings, reduced maintenance costs, and improved safety and security. Integration with other smart city and smart grid projects yields yet greater potential.
Figure 1: The ability to control the light levels of connected LED streetlights is the key to reducing over-lighting, therefore saving more energy, and enhancing safety and security.
Switching to LED street lighting can generate energy savings of 50 to 70%, according to networking giant Cisco, based on data from monitored trials in 12 cities worldwide. When coupled with smart, adaptive controls and an interoperable infrastructure, savings can increase to 80%. A White Paper: ‘The time is right for connected public lighting smart cities’,1 written in conjunction with LED partner Philips, explains that smart lighting enhances safety by improving driving conditions, and boosts security by discouraging crime. It can help revitalize urban spaces and establish a vibrant, distinctive city image to attract business and tourism.
“The LED lighting revolution is gaining traction,” the paper’s author states. By 2020, it is estimated that 80% of all new street lighting installations will be LED-based. Certainly, independent market reports concur with this expectation.
Marketsandmarkets2 claims that street lighting accounts for 40% of a city’s power consumption. With such a huge scope for lighting control systems, it is not surprising that the smart-lighting market is growing at a phenomenal rate, the company claims. Developments in LED, sensor, and wireless technologies are cited as the main drivers. The greatest opportunity area in this market is noted as the prospect of integration with other important systems such as traffic signals, smart energy meters, pollution sensors, parking lot lights, and traffic sensors, as part of a broader smart city initiative.
Pike Research,3 part of Navigant, has stated that dramatically falling costs of LED lamps for street lighting are driving up sales, boosted through recognition of the benefits attainable via control and integration. Unit shipments of LED lamps for streetlights are increasing rapidly year on year. By 2015, LEDs will become the second leading type of lamp for street lights, behind high pressure sodium, and by 2020, the study concludes, LED lamps for street lights will generate more than $2 billion in annual revenues. The report remarks that smart street lighting can provide a backbone for other smart city applications.
The big picture
Despite falling LED prices and the well-documented energy-saving benefits, switching to LED street lighting represents a huge investment, requiring some years before returns may be realized. LED lamp unit costs are still higher than conventional lamp technologies, and despite the knowledge of longer lifetimes, the cost and disruption of installation can create a significant barrier. For many, however, and certainly for municipalities already following the ‘smart city’ route, it is the additional benefits that accrue with a controllable, integrated public lighting infrastructure that make the case for change so convincing.
Automatic reporting of lamp-failure locations obviate the need for mobile patrols and reduce maintenance costs. Dimmer control can be used to save energy in quiet residential areas overnight. Lighting can be enhanced in problem areas when necessary. Centralized control of zoned public lighting can be linked to emergency services control centers so that flashing or brighter lights can direct emergency vehicles to the scene. Integration with smart-energy metering and billing systems provides accurate monitoring of energy usage and consequently provides a marker for reduced consumption and cost savings.
As part of a smart city initiative, lighting poles are ideal for hosting traffic monitoring devices, wireless networks, and environmental and weather sensors. Street lighting can be programmed to switch-on in low daylight levels caused by rain or fog, or to be dimmed under the reflected light from snow cover. Motion sensors can be used to switch on lamps or raise dimmed lighting levels.
The underlying technologies behind most of these ‘bigger picture’ benefits are adaptive controls and, closely linked to the implementation of control technology, networking.
Adaptive controls for LED streetlights are regarded as the emerging mechanism to deliver 80% energy savings over traditional installations, rather than the 50% expected simply by switching to LEDs. The ability to eliminate over-lighting is the key to enhanced energy savings, and thereby the factor that can significantly reduce the time of return on investment, and encourage more municipalities to make the change.
However, discussions continue about certain safety and security aspects of adaptive controls. For example, there is controversy in some areas about turning off residential street lights for a few hours a night to save energy. Some householders fear a rise in crime rates as a result. Dimming, rather than switching off the lamps, and movement sensors to re-illumine the lights are touted as partial solutions. Smarter controls that project the direction of travel in order to brighten subsequent lights on approach are envisaged.
With ‘tunable’ features such as programmable control and dimming, the need for lighting networks and control/management platforms increases. However, there is a wide range of open and proprietary network protocol standards in use. The major OEMs installing citywide systems are tending to standardize on either wired Power Line Communications (PLC), which is finding favor in a range of smart grid applications, or 6LoWPAN, claimed to be the wireless network most commonly associated with ‘Internet of Things’ applications. Both have advantages and disadvantages.
The question, as usual, is what standard(s) will prevail? Lighting giants Osram, GE, and Philips have all declared support for open standards, which theoretically will allow interoperability. At present, the major lighting companies are involved in disparate city projects supporting both PLC and 6LoWPAN. Ultimately, as smart city initiatives expand, the most likely scenario will be the adoption of multiple open standards, and interoperability will be the watchword. Indeed, some lighting/networking partnerships are already working with PLC at the luminaire level and 6LoWPAN to communicate with the centralized smart city control centers. This makes some sense, given that 6LoWPAN is an IP protocol that can facilitate the integration of both wired and wireless networks.
Cabling reuse
Power Line Communication (PLC), as the name suggests, enables data to be sent over existing power cables. Narrowband PLC, operating at frequencies in the 3 to 500 kHz range, provides data rates up to several hundred kpbs, with a range up to several kilometers. It has already been selected for use in a number of smart grid applications including smart meters, microinverters for solar panels, home automation, and lighting control.
Power lines are inherently noisy, and so a robust PLC architecture is required to ensure data reliability. A flexible programmable platform allows for optimized design to suit differing applications’ communications schemes and protocol standards, and supports evolving standards. In terms of hardware, some chip-based PLC solutions implement only the physical layer, while others integrate all seven layers, and may be based on a digital signal processor, microcontroller, or dedicated system-on-chip device.
System on chip solutions
Cypress Semiconductor offers the CYC8PLCXX range of system-on-chip solutions. The CY8CPLC20 includes MAC and PHY, combining the FSK modem and network protocol with the Cypress PSoC core. See Figure 2 below. The device provides a complete, fully-programmable PLC with optimized filters and amplifiers to work with high- and low-voltage power lines. The network protocol layer supports bidirectional communication with acknowledgement-based signaling, error detection, and data packet retransmission capability.
Figure 2: Block diagram of the CY8CPLC20 from Cypress Semiconductor SoC for full PLC implementation.
A simpler fixed-function version, the CY8CPLC10, includes the MAC, PHY, and network protocol stack. However, without the dedicated core the device requires an external microcontroller to control the communication.
A number of evaluation kits are available to help designers develop PLC-based lighting-control applications. The CY3274 uses the CY8CPLC20 device to transmit data up to 2400 bps over high-voltage (110 V-240 VAC) power lines. This kit is compliant with FCC (North America) and CENELEC (Europe) standards. An Application Note4 is also available, explaining the PLC control and programmability features of the devices in the CYC8C range, including a dedicated part for LED lighting applications.
Pioneer in PLC
Texas Instruments has long been a pioneer in developing OFDM modulation techniques for PLC communications networks. Designed to increase data throughput rates and reliability in inherently noisy environments such as electric grids, TI’s PLC solution comprises an optimized TMS320FPLC83 Piccolo MCU and a fully-integrated AFE031 analog front-end. See Figure 3 below.
Figure 3: Block diagram of TI’s PLC modem.
Complemented by a comprehensive development platform, plcSUITE, providing programmable modulation and protocol within a software framework, the solution supports FSK, SFSK, and OFDM (PRIME, G3 compliant) in the CENELEC frequency band.
The MCU combines programmable host processor, 12-bit analog-to-digital converter, and DSP, allowing it to execute all of the PLC algorithms from the low-level physical layer through the networking layer. The AFE is responsible for creating the transmit signal given by the MCU through the serial peripheral interface (SPI), providing transmit and receive filtering, and it subsequently operates as a power amplifier to push the signal on the power line. The dedicated AFE features active band-pass filter, programmable gain amplifier, and digital-to-analog converter to process the received signal, and a direct digital interface to the PLC processor with up to 20 V peak-to-peak output at 1.5 A.
A good starting point for intelligent digital control in lighting and lighting communications is the TMDSPIACLEDCOMKIT C2000-based LED lighting and power line developer’s kit. It features the C2000 Piccolo MCU for digital control of the power supply, lighting, and communications. The development board features up to 250 W output supporting six LED strings and optional intelligent communications. The integrated power supply is full AC-mains connected with Piccolo MCU control of an efficient, isolated, resonant LLC DC/DC power topology.
Users are guided from simple open-loop design through full closed-loop control. Communications software examples are likewise featured, detailing common lighting-communication protocol software implementations. The kit is supplied with a user-friendly graphical user interface with sliders, buttons, and text boxes to demonstrate PLC and LED control. A more advanced GUI and extended application options are available for further experimentation at the software level. An Application Report for PLC with AC LED lighting can be downloaded.5
The kit is used in conjunction with the TMDSPLCKITv3, which provides the PLC modems for peer-to-peer communication with the LED lighting kit. The TMDSPLCMODA-P3X add-on kit provides the analog front-end module and Piccolo control card to enable PLC with the LED lighting kit.
Wireless compatibility
Compatible with IEEE802.15.4 wireless protocols, 6LoWPAN is strictly defined as a header compression mechanism that allows IPv6 packages to be routed in low-power wireless networks. IEEE802.15.4 is the standard that underlies ZigBee, variations of which are widely used in smart home and building automation systems. Being an Internet protocol (IP) means that 6LoWPAN devices can be addressed from anywhere using a standard computer or other connected device. Key advantages of using 6LoWPAN are Internet interoperability and smaller code and packet sizes compared to other protocols and stacks.
Figure 4: A typical 6LoWPAN setup showing how the protocol can be integrated into a ‘smart city’ initiative, with multiple wireless sensor network clusters.
Atmel offers a microcontroller-based IEEE802.15.4-compliant single-chip 2.4 GHz RF transceiver, designed for 6LoWPAN control applications. The 16 MHz ATmega256RFR2 with 256 kbytes Flash memory, features a link budget of 103.5 dBm, yet consumes just 12.5 mA in receive mode and 14.5 mA when transmitting.
Development kits are available for evaluation and prototyping. The basic ATmega256RFR2XPRO includes transceiver, digital I/O, user LEDs, and embedded debugger. Supported by the Atmel Studio development platform, the Xplained Pro kit explains how to integrate the device into wireless networked LED control applications. For more complex systems, the ATmegaRFR2XSTK adds extension prototyping and OLED add-on boards.
Atmel now licenses the popular Sensinode 6LoWPAN stack and router solutions NanoStack2.0 and NanoRouter3.0 (recently acquired by ARM), available as part of Atmel Studio 6 and beyond.
Sensinode solutions are described as ideal for large-scale street lighting projects, integrating real-time light monitoring and control, alarms, and light group management.
Coincidentally, Texas Instruments is also a Sensinode licensee, with NanoStack2.0 running on its CC-LoWPAN-DK-868 development kit for sub-1 GHz 6LoWPAN systems. The kit contains two 6LoWPAN network nodes based on the CC430F5137 microcontroller-based wireless transceiver, two nodes based on the CC1180 network processor and the MSP430F5438A microcontroller, and an IPv6-to-6LoWPAN gateway. Figure 5 below shows how the devices are configured with the Sensinode solution.
Figure 5: Functional block diagram of the CC1180 network processor as deployed in a 6LoWPAN IP network node.
The development kit demonstrates an example of a typical sensor network with simple network-analyzer software running on the nodes. The nodes are automatically given a unique IPv6 address and can be pinged from a PC using standard tools. This kit is for applications in the 868 MHz frequency band and can quickly be reconfigured for operation in the 915 MHz ISM band.
European wireless network specialist, systems integrator, and Osram partner Dresden Elektronik offers lighting control and RF solutions. It has developed a range of development boards for 6LoWPAN applications, providing node, gateway, and radio modules, plus drivers, software, and documentation. The deRF development kit contains radio modules based on Atmel and ARM cores, the deRFgateway board, two deRFnodes, and a USB radio stick analyzer to create an easy start-up evaluation of a 6LoWPAN sensor network. Additional sensors and network nodes are available to allow developers to extend their trials.
Summary
This article provides some insight into how both wired (PLC) and wireless (6LoWPAN) network protocols are enabling the integration of connected, controllable LED-based public lighting systems into a multi-application smart city infrastructure. Reference to specific devices and development kits provide a graphic illustration of circuit solutions available.
References:
- Cisco White Paper: The time is right for connected public lighting within smart cities
- Markets and markets: Smart Lighting Market (2013-2018)
- Pike Research
- Cypress Semiconductor Application Note: LED lighting control using Power Line Communication
- Texas Instruments Application Note
