“Street Lamps as a Platform”
Communications of the ACM, June 2020, Vol. 63 No. 6, Pages 75-83
Review Articles
By Max Mühlhäuser, Christian Meurisch, Michael Stein, Jörg Daubert, Julius Von Willich, Jan Riemann, Lin Wang
Street lamps with their unique characteristics can actually enable an economic large-scale deployment of cloudlets, making the breakthrough of practicable edge computing at long last.
Street lamps constitute the densest electrically operated public infrastructure in urban areas. Their changeover to energy-friendly LED light quickly amortizes and is increasingly leveraged for smart city projects, where LED street lamps double, for example, as wireless networking or sensor infrastructure. We make the case for a new paradigm called SLaaP—street lamps as a platform. SLaaP denotes a considerably more dramatic changeover, turning urban light poles into a versatile computational infrastructure. SLaaP is proposed as an open, enabling platform, fostering innovative citywide services for the full range of stakeholders and end users—seamlessly extending from everyday use to emergency response. In this article, we first describe the role and potential of street lamps and introduce one novel base service as a running example. We then discuss citywide infrastructure design and operation, followed by addressing the major layers of a SLaaP infrastructure: hardware, distributed software platform, base services, value-added services and applications for users and ‘things.’ Finally, we discuss the crucial roles and participation of major stakeholders: citizens, city, government, and economy.
Recent years have seen the emergence of smart street lamps, with very different meanings of ‘smart’—sometimes related to the original purpose as with usage-dependent lighting, but mostly as add-on capabilities like urban sensing, monitoring, digital signage, WiFi access, or e-vehicle charging. Research about their use in settings for edge computing or car-to-infrastructure communication (for example, traffic control, hazard warnings, or autonomous driving) hints at their great potential as computing resources. The future holds even more use cases: for example, after a first wave of 5G mobile network rollouts from 2020 onward, a second wave shall apply mm-wave frequencies for which densely deployed light poles can be appropriate ‘cell towers.’
Street lamps: A (potential) true infrastructure. Given the huge potential of street lamps evident already today and given the broad spectrum of use cases, a city’s street lamps may obviously constitute a veritable infrastructure. However, cities today do not consider street lamps—beyond the lighting function—as an infrastructure in the strict sense. Like road, water, energy, or telecommunication, infrastructures constitute a sovereign duty: provision and appropriate public access must be regulated, design and operation must balance stakeholder interests, careful planning has to take into account present and future use cases and demands, maintenance, threat protection, and more. Well-considered outsourcing or privatization may be aligned with these public interests.
The LED dividend: A unique opportunity. The widespread lack of such considerations in cities is even more dramatic since a once-in-history opportunity opens up with the changeover to energy efficient LED lighting, expected to save large cities millions in terms of energy cost, as we will discuss, called ‘LED dividend’ in the following. Given their notoriously tight budgets, cities urgently need to dedicate these savings if they want to ‘own’ and control an infrastructure, which, once built, can foster innovation and assure royalties and new business as sources of city and citizen prosperity.
Computing platform and extensible hardware: The indispensable core. It is common knowledge that in the current era of digitization, computers are at the core of most innovation and added value. Large consortia and initiatives like OpenFog and MEC (mobile edge computing) arose around the conviction that ‘the cloud’ will, at least in part, move closer to the user and to the applications. Reasons include the increasing need for real-time (short delay, reliably connected) computing and resource-demanding AI algorithms that overstrain mobile devices’ batteries or compute power but are too bandwidth-demanding to be offloaded to a distant cloud. Many services and applications discussed in the article, such as our running example, support these arguments.
It seems obvious that computing and storage resources should be the core of a true smart street lamp infrastructure, at least in part directly integrated with the lamp posts. A second absolutely crucial characteristic of such a true infrastructure is obviously the versatility and extensibility of lamp posts. They must be prepared for exchange and extension with respect to electricity, mounting space (partly with line-of-sight to the urban scene), weather/vandalism protection, and ease of (dis-)mounting, among others. These characteristics are not automatically a primary interest of street lamp customers and providers as they cannot be easily matched with aesthetics and competitive pricing.
Our call stands in stark contrast to reality, namely mostly project-based extension of street lamps. Such projects follow opportunities, perceived pressing needs, or selective flagship efforts. Moreover, the LED dividend is often spent in a short-sighted manner. Most city councils ignore reasons to become edge-computing providers; just as many cities took too long to realize the need to become WiFi providers, they may ‘wake up’ too late here, this time losing a historic opportunity to be in the driver’s seat of a novel true infrastructure and its potentials (for innovation, citizen wealth, or city income) as well as its risks (to privacy, dependability, and so on). This may also erect a classical innovation barrier where application providers wait for infrastructures (and hence, a customer base) and infrastructure providers wait for application demands.
To summarize these arguments, we proposed a citywide true infrastructure based on augmented street lamps as a platform (termed SLaaP) that can bootstrap smart cities and enrich them with novel services, ensure stakeholder tradeoffs (such as data analytics and novel services versus privacy risks) and extend seamlessly to sovereign interests such as emergency preparedness and response, safety, and security. Figure 1 presents an overview of this new infrastructure and the remaining structure of this article. Authorities must define and assume their sovereign role and ensure the dedication of the LED dividend to this historic duty. Versatile extensible hardware and integrated compute infrastructure and base services must form the base of this effort.
Unique characteristics and opportunity. Street lamps are a basic and important facility of cities, illuminating roads and sidewalks in order to increase the safety of road users and pedestrians’ sense of security. This leads to three characteristics that make them highly attractive from an ICT perspective and for smart city concepts.
- Electrically operated. In most cities, street lamps are connected to subterranean power grids, which are usually separated from the main power grid. Most of them are still only powered from dusk till dawn since the lamps lack operable switches (power-on means light-on). Later, we will discuss the resulting considerations for power supply, but the existing power lines definitely predestine street lamps as a digital infrastructure, augmented with computing, networking, and Internet-of-Things (IoT) components.
- Densely deployed. Due to their dense deployment along roads and sidewalks, street lamps are already ubiquitous in our everyday urban life. In view of the use as digital infrastructure, this dense deployment makes them accessible anywhere in the city and provides high scalability due to tens and hundreds of thousands of instances per city.
- Publicly owned. Public ownership is ideal for assuring a true infrastructure as explained (compared to sovereign duties like assuring no access or use-case discrimination, or emergency operation). When regulations are established and enforced, privatization is possible, but the inverse, that is, turning private goods into a veritable infrastructure is socially unacceptable. This notion rules out the consideration of electrically operated and densely deployed devices under private ownership like wireless routers, which could, in principle, be qualified as ICT infrastructure (yet hardly in the IoT respect that is relevant for cities).
These three characteristics qualify street lamps as the scalable vehicle for a novel urban digital infrastructure—SLaaP. As discussed, such an infrastructure has extensible lamp post hardware and a general-purpose computing platform (a distributed edge cloud) as its basic constituents (as illustrated in Figure 2). However, the success of this infrastructure comes from enablements and services, such that the selection of provided hardware add-ons and base services as well as a proper bootstrapping of them will be crucial—and hence the key aspects of this article.
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Sidebar: Numerical Example Illustrating the Feasibility of a Resilient Infrastructure
Energy harvesting. Theoretically, a solar cell generates about 100mW/cm2 during the daytime, which is however highly influenced by many factors (for example, time of day, or seasonal weather). Assuming a realistic conversion efficiency rate of 10%-20% on the Earth’s surface and a typical LED lamp head of 75 x 40 cm=0.3m2, on which a solar panel can be mounted ‘invisibly,’ we get an average energy harvesting level of 100mW/cm2 * 0.3m2 * 0.1-0.2 = 30W–60W. Often used but ‘visible’ solar panels have an area of 1m2 ($100) and would generate about the triple: 100W–200W.
Energy consumption. Despite new LED technology, the lightning still consumes 15W–100W depending on the model and luminance. A proposed lightweight upgrade required for our 4D-service example, consisting of Raspberry PI3 (≤ 5W) and Intel RealSense depth camera (2W–3W), would consume less than 10W in total. A more powerful yet compact upgrade, consisting of Udoo Ultra/Bolt (≤ 12W/25W) and Velodyne Puck Lite (8W), would require around 20W–33W.
About the Authors:
Max Mühlhäuser is a full professor at TU Darmstadt, Germany. He served as co-first author of this article.
Christian Meurisch is a research assistant at TU Darmstadt, Germany. He served as co-first author of this article.
Michael Stein is a postdoctoral researcher at TU Darmstadt, Germany.
Jörg Daubert is a postdoctoral researcher at TU Darmstadt, Germany.
Julius Von Willich is a research assistant at TU Darmstadt, Germany.
Jan Riemann is a postdoctoral researcher at TU Darmstadt, Germany.
Lin Wang is a postdoctoral researcher at TU Darmstadt, Germany.
