I have collected some VLC videos:
Harald Haas: Wireless data from every light bulb (TED Talk)
Monthly Archives: February 2013
VLC for location, positioning and navigation
Posted on July 27, 2011 by GordonPovey
Visible Light Communications has been considered as a communications technology but you will note from my blog post on 18th March that one of my top 10 VLC applications is Location Based Services. This is a topic close to my heart since I was the founder and chairman of mobile location technology company, Trisent, prior to it being sold. Having worked on radio location technology for a number of years I thought it useful to consider the location techniques used in wireless radio and see how well they apply to optical wireless location.
So here are the main radio location techniques and my assessment of how well they are likely to perform in the optical domain.
Cell ID
Cell ID systems broadcast a unique identifier (ID) for that cell. The location of the ID source is stored in a database. When a receiver sees a particular ID, the location for that ID can be read from the database.
Radio: This technique is widely used in cellular systems; however the accuracy can be quite poor – many kilometres in error because of the large cell sizes in many places.
Optical: The Cell ID is identified via VLC transmitting the ID and/or location of the emitter. Very good accuracy of 2-5m is possible due to the small size of the illumination cell.
Received Signal Strength
Received signal strength (RSS) is a measure of the signal power detected at the receiver. The power diminishes with distance from the transmitter and so the distance of the receiver from the transmitter can be calculated.
Radio: The radio signal propagation is dependent on the physical environment and varies dramatically from location to location. Constructive and destructive interference adds further errors to any static RSS measurements. Even by averaging dynamic RSS measurement very large errors occur and so RSS is rarely used in cellular radio location.
Optical: Being mainly line of sight, the RSS quite predictably attenuates according to a square law in free space. The received signal also does not suffer from constructive and destructive interference. So the optical RSS can be used as a relatively accurate distance measurement if the emitter power and beam pattern is known.
Time of Arrival
Trilateration is used by TOA to find point X
Time of arrival (TOA) is based on the trilateration. Signals from multiple – say 3 sources are sent at exactly the same known time. The time they are each received is used to calculate the distance they will have propagated in that time (they all travel at the speed of light). If a circle with a radius equal to that distance if plotted for each source, S1, S2 & S3 then the point at which all circles intersect, X, is the location of the receiver. This is 2D trilateration. 3D trilateration can be performed using spheres instead of circles to give both the location and height.
Radio: TOA with 3D trilateration is the method used for GPS. It leads to high accuracy results if the transmitters are accurately synchronised and the receiver has a good clock.
Optical: TOA is equally difficult to implement in the optical domain since the synchronisation and accuracy issues remain.
Time Difference of Arrival
Time difference of arrival or TDOA differs from TOA in one important respect, the receiver clock does not need to be as accurate since it is the time difference between the signals from different sources which is important and not the absolute time of arrival. Accurate synchronisation of the signal sources is still required. Techniques called multilateration are used to solve a series of simultaneous equations to calculate the receiver position.
Radio: TDOA has been used in cellular systems with limited success due to the difficulty and expense of synchronising the base stations.
Optical: It is easy to synchronise emitters if they are in close proximity to each other since that can share the same clock. This is often the case for LED lighting applications. Imagine an array of LEDs in a luminaire or clusters of LEDs in a cars tail lights, these can be physically connected and synchronised.
Angle of Arrival
Angle of arrival (AoA) is widely used for location finding using triangulation. If you take your bearing to one know position (e.g. Mountain A) and do the same for another, Mountain B. The projection of the measured bearing from each mountain will intersect at your location.
Radio: It is difficult to measure the angle of arrival of a radio signal. Antenna arrays can be used for this purpose but they are expensive to implement. Aircraft navigation used this principal in reverse. A VOR system transmits different identifiable signals at different angles so the receiver knows the bearing relative to the transmitter of the received signal.
Image sensors can be used to find angle of arrival.
Optical: It is relatively simple to detect the angle of arrival of an optical signal. If two light sources A and B come from different locations (so from a different angle), their positions will be projected onto different positions A’ and B’ of an imaging sensor. This enables the angle from the sensor to the source to be calculate and then triangulation can be applied to find the actual location.
Hybrid Systems
When I worked on mobile location technology at Trisent we adopted a hybrid approach in order to improve location accuracy and remove ambiguities. I believe the same approach would work well in the optical domain. In particular Cell-ID and RSS techniques are simple to apply but combined with angle-of-arrival if more than one cell (lamp) can be seen by a sensor array would lead to a highly accurate positioning system – more accurate than GPS and it would work indoors.
Smart Positioning!
Locating and positioning is a great application for VLC. High accuracy positioning indoors would be extremely useful, but you would need a device with an imaging sensor and some processing. But hey, don’t you already have a smart phone with a camera and a processor? Okay it would need to be adapted a little for a higher frame rate, but essentially you have all of the hardware there already.
VLC for accurate indoor positioning on your smart phone. You heard it here first!
Sorry, America: Your wireless airwaves are full [CNN]
By David Goldman @CNNMoneyTech
This is part one of a week-long series on the cell phone capacity crunch.
NEW YORK (CNNMoney) — The U.S. mobile phone industry is running out of the airwaves necessary to provide voice, text and Internet services to its customers.
The problem, known as the “spectrum crunch,” threatens to increase the number of dropped calls, slow down data speeds andraise customers’ prices. It will also whittle down the nation’s number of wireless carriers and create a deeper financial divide between those companies that have capacity and those that don’t.
Wireless spectrum — the invisible infrastructure over which all wireless transmissions travel — is a finite resource. When, exactly, we’ll hit the wall is the subject of intense debate, but almost everyone in the industry agrees that a crunch is coming.
The U.S. still has a slight spectrum surplus. But at the current growth rate, the surplus turns into a deficit as early as next year, according to the Federal Communications Commission’s estimates.
“Network traffic is increasing,” says an official at the FCC’s wireless bureau. “[Carriers] can manage it for the next couple years, but demand is inevitably going to exceed the available spectrum.”
How did we get here?
The number-one biggest driver is consumers’ insatiable thirst for e-mail, apps and particularly video on their mobile devices — anywhere, anytime. Global mobile data traffic is just about doubling every year, and will continue to do so through at least 2016, according to Cisco’s (CSCO,Fortune 500) Mobile Visual Networking Index, the industry’s most comprehensive annual study.
The iPhone, for instance, uses 24 times as much spectrum as an old-fashioned cell phone, and the iPad uses 122 times as much, according to the Federal FCC. AT&T says wireless data traffic on its network has grown 20,000% since the iPhone debuted in 2007.
Video and mobile are breaking the Internet
“We got into this principally because technology and demand exploded at a rate that nobody had anticipated,” says Rory Altman, director of technology consultancy Altman Vilandrie & Co.
Another catalyst is the way the U.S. government allocated spectrum. The bands that wireless companies hold were broken up into small chunks across various markets, which was helpful in increasing competition in the 1990s.
But the patchwork nature has proven problematic for new technologies likehigh-speed 4G broadband. Bigger swaths of uninterrupted spectrum provide the larger amounts of bandwidth needed for delivering faster speeds.
One more contributing factor is that TV broadcasters and government agencies like NASA and the Department of Defense hold some of the best spectrum — relatively low-frequency radio waves that can travel long distances and penetrate buildings.
There are also businesses such as Dish Network (DISH, Fortune 500) that have large spectrum allotments but aren’t currently using them. (Dish is exploring its options for either using or selling its spectrum. A group of cable companies with unused spectrum recently struck a $3.6 billion pact to sell their holdings to Verizon in a deal that’s facing heavy regulatory scrutiny.)
The spectrum crunch is not an inherently American problem, but its effects are magnified here, since the United States has an enormous population of connected users. This country serves more than twice as many customers per megahertz of spectrum as the next nearest spectrum-constrained nations, Japan and Mexico.
When spectrum runs short, service degrades sharply: calls get dropped and data speeds slow down.
That’s a nightmare scenario for the wireless carriers. To stave it off, they’re turning over rocks and searching the couch cushions for excess spectrum.
They have tried to limit customers’ data usage by putting caps in place,throttling speeds and raising prices. Carriers such as Verizon (VZ,Fortune 500), AT&T (T, Fortune 500), Sprint (S, Fortune 500), T-Mobile, MetroPCS (PCS) and Leap (LEAP) have been spending billions to make more efficient use of the spectrum they do hold and billions more to get their hands on new spectrum. And they have tried to merge with one another to consolidate resources.
The FCC has also been working to free up more spectrum for wireless operators. Congress reached a tentative deal last week, approving voluntary auctions that would let TV broadcasters’ spectrum licensesbe repurposed for wireless broadband use.
But freeing up more spectrum won’t be enough to solve the problem.
“There is no one solution that will address all the needs of the wireless industry,” says Dan Hays, a partner at PricewaterhouseCoopers who specializes in telecom issues.
The good news is that there are ways to buy time. Several innovative approaches are in the works, and there’s a decent amount of spectrum out there that could be turned over to the carriers’ possession.
The bad news is that none of the fixes are quick, and all are expensive. For the situation to improve, carriers — and, therefore, their customers — will have to pay more.
“For a while we won’t notice the quality of service changes, but over time as devices get better and use more data, we’ll start to take notice,” Altman says. “Consumers will notice it, and the burden will fall on the carriers to fix it.”
Coming Wednesday: Why the capacity crunch means there will soon be fewer wireless players. 
First Published: February 21, 2012: 5:16 AM ET
Visible Light Communication and Localization 