VLC: A success story or a failure? – A personal assessment

Through the previous posts Visible Light Communications were dealt from different points of view. The necessity for alternatives in order to complement RF wireless communications and expand their capabilities was stressed; potential applications that are currently using the RF spectrum or completely new applications were presented, the pros and cons of the technology were marked. Then after a short and simplified technology description we moved into standardization issues in order to define and understand the necessity for standards and how they affect our everyday life. Lastly some more specific topics like the history of standardization in VLC and the commercialization and market perspectives where dealt.

As it was underlined VLC is a new, promising technology with a main orientation of complementing RF communications. Some drawbacks are there but many advantages as well. Finally, what is going to be the fate of this technology? Is it going to be established as a new, advanced and accessible to everyone technology or is it going to stay in the laboratories as a part of research history? And if it succeeds, when is this decisive bounce in the market going to take place? What will be the critical factors for these? Personally I believe that VLC will penetrate the market. Sooner or later, that will depend on the research community and its advances and industry’s initiative, decisiveness and willingness for exposure to risks. In the future, visible light communications will complement and even replace RF communications in some occasions that is practically feasible.

Starting exactly from what is technically and practically feasible VLC is considered as a rather young technology. Despite this, it is quite competitive with certainly more mature RF technologies in terms of data rates for instance and much space for improvements exists while regarding other properties is much more superior, as for example power consumption. In my opinion in the near future more improvements will come and VLC will have an edge over the existing wireless communication technologies so there will be good incentives for consumers to adopt them. On the other hand some fundamental limitations such as range will always constrain their use only for certain applications.

Moving to our ever increasing needs, a new complementary technology is a “must”. Data traffic is doubling every year thus soon RF communications will be unable to accommodate them. VLC is the most convincing candidate until now. Solutions like using other unlicensed bands such as the one at 60GHz are investigated but VLC is actually a more long term solution with many advantages compared to RF. VLC is a quite simple technology. Not much hardware in needed and not too much power for operating. Moreover nowadays a big focus is given on energy consumption. LEDs are a big step forward and given that they can be a very efficient and cheap data source for VLC, we can almost consider that the infrastructure is there and waits to be exploited. This is a significant point as negligible resources, money and time, should be spend on building new infrastructures and installing them for enabling VLC use. This also yields that even for domestic use VLC should be very affordable when the equipment becomes commercially available.

Commercialization seems to be one of the main problems for now. Lighting and mobile devices industries have to find a point of intersection in order to initiate and give a boost to the massive use of VLC. I strongly believe they will, as both of them will profit from such cooperation. It is a win – win situation. The most probable scenario is to introduce some low data rate applications that can be supported by already existing devices in order to achieve an acceptance and then start equipping their mobile devices with VLC technology thus forcing the penetration to the market. For other applications like vehicle to vehicle communication things seem to be more difficult and complicated. I have my doubts how this could work out and if indeed will yield any significant advantages over RF communications. Data rates needed are low and as road safety for these applications is the main concern, RF communications seem adequate while VLC would suffer from inherent limitations like very high attenuation due to fog, rain etc. that could cause link failures thus safety issues. Furthermore the incentives for manufacturers or consumers don’t seem so strong in order to force VLC spread in this market sector, at least for the moment.

Another important factor will be the integration/hybridization of some applications. For example Li – Fi is not destined to replace Wi – Fi but if they coexist and interact an optimum point can be reached as the advantages of both technologies can be combined and exploited. Or GPS (Global Positioning System) can be extended for indoor use thus increasing its range but also its accuracy. This integration is assigned to standardization organizations which must ensure the compatibility between different technologies thus helping new ones to enter the market.

Some small steps have already been done. IEEE 802.15.7 standard is available and it offers satisfying specifications and some commercial products are available (for example Fraunhofer HHI offers commercially available plug and play solutions). Research and standardization communities along with industry will define if VLC will become a widespread everyday used technology or not. VLC have all the qualifications to become that but will they?

VLC: Market and Commercialization

As an emerging technology, VLC have received great attention from the academic, research and standardization communities and industry after experiencing a decisive push due to the LED technology evolution. Nevertheless, VLC have not succeeded in gaining market’s acceptance yet therefore not making the great step for large - scale commercialization and market penetration. The major decisive factors that will allow VLC to achieve these, are the development of robust and efficient applications, the implementation of incremental commercialization strategies, how standardization activities will move forward in order to offer attractive features and functionalities and if hybrid technologies will be adequately and effectively supported in order to offer benefits to the users. If everything works out well, VLC will increasingly complement RF communications in the near future.

LED Market

Due to its dramatic improvement LED technology has started conquering the market. LED’s are used for numerous applications and are deployed in many electronic devices such as TV, mobile phones, computer monitors, cameras, advertising boards and the vast market of illumination. LED illumination is penetrating both commercial and residential sectors and according to [1] it is expected that it will dominate the general illumination market by 2020 and will be very prominent in commercial lighting due to the market’s sensitivity in cost benefits offered by LED.

Industry Diversity

VLC offer illumination and “piggyback” wireless data transmission at the same time. The other side of the coin though is that in order to cover the needs of such coexistence two different industries have to cooperate. Of course this happens successfully in many cases but in many others it results in long delays for the commercialization of the technology or ends up in complete failure. In this case lighting and mobile devices original equipment manufacturers must proceed to certain necessary modifications in their products with the corresponding side effects.

On the one hand lighting original equipment manufacturers must make certain modifications in their illumination products and the mobile devices manufacturers need to add high – speed photodiode receivers in their devices. Both sides have very good reasons for making VLC a commercially available technology. LED manufacturers are facing a double – edged sword as the lifetime of LED’s has risen above 50,000 hours. In the near future consumers will be driven in replacing their old illumination equipment thus increasing the revenue of LED manufacturers but in the long run this will result in “socket saturation”. By enabling VLC technology lighting industry will give extra motives to consumers for buying their VLC products and by differentiating them they could mitigate the market saturation and have extra revenues. Mobile devices original manufacturers can also benefit from incorporating VLC equipment to their devices by adding a competitive edge and also justifying reasonably higher sale prices.

There are two plausible scenarios for introducing VLC to the market. The first, that can also be considered more realistic, regards the category of applications that do not require extra hardware in the mobile devices. In practice all the mobile devices (or at least the vast majority of them) that are available in the market today are equipped with at least one camera. Cameras are essentially a 2-D array of LEDs which can be used for low data rate light signals detection. Such a strategy could have a positive reflection on the market thus result in larger acceptance and faster adoption of VLC technology. Of course the limited power of mobile terminals should be taken into count and mitigate that by using smart algorithms for example. In the other case mobile device manufacturers could unilaterally introduce VLC to the market through their products and applications like device – to – device pairing, file transfer, wireless docking etc. For this kind of applications new hardware must be added in mobile devices for achieving higher data rates. In such a case lighting manufacturers will immediately be driven to turn towards VLC and offer compatible products.

Indoor Positioning

Retail stores and enterprise markets are two of the markets in which LED lighting is vastly spread. These markets see their revenues decrease due to unfound products in their stores and moreover recognize potential revenue increase due to targeted product advertising (up to 70% of the sales are made at the aisle level) [2]. By adopting VLC technology and indoor positioning applications they can increase their revenues. Manufacturers can also immediately profit from this high demand, as low data rates allow to the already existing equipment in mobile devices the reception of such signals. It is expected that by 2018 the indoor positioning in the retail sector will reach $5 billion.

In March of 2013 a major supermarket in Korea orginized an event called Sale Navigation so their customers could experience a navigation in the supermarket and help them to find discounted products. For this event, LED downlight luminaires, VLC receivers on the shopping carts and smart phones were used as shown in the above figure [8].

Vehicle to Vehicle (V2V) Communication

Up to date a big effort is put into vehicle to vehicle (V2V) communications mainly for safety reasons. VLC can be the enabling technology for these applications. One of the obstacles in which the implementation stops at is the lack of motivation for new users to buy cars that are equipped with this technology. A minimum percentage of 10% penetration in the market is required in order for it to be functional [3]. Even if every car sold from now on bears such equipment it will take up to 2 years to reach the adequate penetration thus consumers are left with extra costs and no benefits. Two possible scenarios can help in overcoming this barrier. Either complexity of the systems is minimized resulting in cost minimization also, either a way in which the applications become functional immediately is found.

References and Sources

[1] Lighting the Way: Perspectives on the Global Lighting Market, 2nd ed., McKinsey & Company, 2012, http://www.mckinsey.com

[2] P. Connolly and D. Bonte, “Indoor Location in Retail: Where Is the Money?,” ABI Research Report, Mar. 2013, http://www.abiresearch.com/research/product/1013925-indoor-location-in-retail-where-is-themon

[3] M. Ergen, “Critical Penetration for Vehicular Networks”, IEEE Communications. Letters, vol. 14, no. 5, 2010, pp. 414–16

[4] S. Hranilovic, L. Lampe, S. Hosur, “Visible light communications: The Road to Standardization and Commercialization”, IEEE Communications Magazine, December 2013

[5] A. Jovicic, J. Li, T. Richardson, “Visible light communication: Opportunities, Challenges and the Path to Market”, IEEE Communication Magazine, December 2013

[6] L. Grobe, A. Paraskevopoulos, J. Hilt, D. Schulz, C. Kottke, V. Jungickel, K. D. Langer, “High – Speed Visible Light Communication Systems”, IEEE Communication Magazine, December 2013

[7] S. H. Yu, O. Shih, H. M. Tsai, N. Wisitpongphan, R. D. Roberts, “Smart Automotive Lighting for Vehicle Safety”, IEEE Communication Magazine, December 2013

[8] S. K. Lim, K. G. Ruling, I. Kim, I. S. Jang, “Entertainment Lighting Control Network Standardization to Support VLC Services”, IEEE Communications Magazine, December 2013

IEEE Standard 802.15.7: Short – Range Wireless Optical Communication Using Visible Light – A Brief Overview

As an IEEE standard, 802.15.7 is a voluntary and open standard. It has been created in order to fulfill the increasing societal needs for communication that today's standards will soon not be adequately to serve. It also has direct influence on the market by creating for instance new applications and thus the necessary hardware or by broadening and upgrading already existing ones like LED market which should make available LEDs for wireless data transmission. As VLC are located in a free, unlicensed band they suffer minimum political interventions unlike mobile communications for example which are operating in licensed bands (800 or 900MHz, 1.9GHz, etc) and they are subject to political decisions regarding that part of the spectrum. On the other hand precautions are taken for health hazards by restricting the maximum power emission. The 802.15.7 standard has been technically kept as simple as possible and also based on a structure which allows that while some other widely used and mature standards such as IEEE Std 802.15.4 – 2006, ITU – T I.432.1, ANSI/INCITS 373 are fundamental for its application.

Furthermore, some critical points that hold for all IEEE standards and IEEE itself are presented below as were taken from an IEEE standard and give some more insights to the nature of the standards:

• IEEE develops its standards through a consensus development process, approved by ANSI which brings together volunteers representing varied viewpoints and interests to achieve the final product

• Volunteers are not necessarily members of the Institute and serve without compensation

• Use of an IEEE standard is wholly voluntary

• The existence of an IEEE standard does not imply that there are no other ways to produce, test, measure, purchase, market or provide other goods and services to the scope of the IEEE standard

• The viewpoint expressed at the time a standard is approved and issued is subject to change brought about through developments in the state of the art and comments received from users of the standard

• Every IEEE standard is subjected to review at least every five years for revision or reaffirmation, or every ten years for stabilization

These points reveal exactly that IEEE is open to everyone and acceptable to new ideas for developing new standards. Its products (standards) are available for everyone and it is up to every individual to use them and in what way or not adopt them at all.

The 802.15.7 (2011) standard is the first IEEE standard that involves wireless optical communication technology using visible light. It defines both physical layer (PHY) and media access control layer (MAC). The architecture is based on defining several layers and sub – layers to simplify the standard and offer services and logical links from lower layers to higher ones. It takes into consideration many factors thus adding characteristics and functionalities like diming and visibility support, color function and color – stabilization support. The standard is designed for supporting multimedia data transfer and other services. The scope of the standard as it is stated in the document itself is as follows: 

“This standard defines a PHY and MAC layer for short-range optical wireless communications using visible light in optically transparent media. The visible light spectrum extends from 380 nm to 780 nm in wavelength. The standard is capable of delivering data rates sufficient to support audio and video multimedia services and also considers mobility of the visible link, compatibility with visible-light infrastructures, impairments due to noise and interference from sources like ambient light and a MAC layer that accommodates visible links. The standard adheres to applicable eye safety regulations.”

The 802.15.2 standard describes how visible light can be used for wireless personal networks (WPAN) while offering the illumination functionality at the same time. In a WPAN each device is given a short 16 – bit address or an extended 64 – bit address. Light emitting diodes (LED) and laser diodes (LD) can be used as light sources and find applications in several places like lighting, signboards, streetlights, vehicles, traffic signals.

In the standard three different topologies are defined. In figure 1 the peer – to – peer, star and broadcast are depicted. Moreover three classes of devices are defined, namely infrastructure, mobile and vehicle which are shown in the table of figure 2 along with some of their properties.

In a peer – to – peer topology two devices are communicating and one of the two handles the communication administration thus becoming the coordinator. In a star topology all devices have a bidirectional communication with the coordinator. The third topology is broadcast in which users only receive data from a transmitter. In the framework of these topologies three types of data transfer transactions are used. The first comprises the data sent from a device to the coordinator, the second the data send from the coordinator to the device and the third the data transferred between the devices in a peer – to – peer connection. In the latter all three types of data exist but in a star topology only the first two. 

Figure 1

Figure 2

 

The three classes of devices (fig.2) are infrastructure, mobile and vehicle. According to their physical properties and capabilities - limitations like physical mobility, power supply and of course their applications, their specifications such as range and data rates are defined. For instance infrastructure has “unlimited” power supply while vehicle moderate and mobile terminals very limited. These yield higher power light sources for infrastructures and vehicles and furthermore potentially higher range. Regarding mobility, only the infrastructure type has no physical mobility. Based in their applications vehicle devices need low data rates for exchanging information about traffic for example while mobile and infrastructure devices can reach much higher rates for exchanging multimedia like high definition videos, online gaming etc.

The physical layer of communication in the 802.7.15 standard supports three types. PHY I finds outdoor use for low data rates in the order of tens to hundreds kb/s (up to 266.6kb/s) and uses OOK (ON – OFF keying) and VPPM (variable pulse position modulation). On the other hand PHY II is intended for indoor use and delivers data rates of tens of Mb/s (up to 96Mb/s). PHY III achieves the same high data rates as PHY II but instead of OOK and VPPM it deploys CSK (color shift keying) as it is destined for applications with multiple sources and detectors. In figure 3 the spectrum usage is shown. PHY I uses lower frequencies (longer wavelengths) while PHY II and III use higher ones (shorter wavelengths). They in fact use the same part of the spectrum. Furthermore PHY II and III accommodate higher data rates thus are in need of broader slice of the spectrum.

Figure 3

As already mentioned there are two types of devices that present mobility (mobiles and vehicles). In order to support this mobility there are some provisions in the standard. Two types of mobility are defined, the physical and the logical, and are depicted in figure 4. The physical mobility occurs when a mobile device is physically moving and the logical one when the terminal happens to be in the light beam of two different light sources and a hand – over must take place. In this case, after the hand – over has occures the mobile even though physically remains in the same place it appears to be in a different place from the source perspective.  

Figure 4

Lastly in this post the security of the personal network will be dealt. VLC are inherently safer than RF wireless networks as they do not penetrate walls and are more directive. In principle if an unwanted receiver interferes can be easily recognized. Nevertheless, security algorithms are still implemented for data confidentiality, authentication and replay protection. The limited resources though, such as computing power, available storage and power drain, impose limitations in the level of security as a high – quality random number generator is not always the case for example.