LED lamps and bulbs can emit visible light communication (VLC) signals as long as they are modulated at a frequency of kHz. At the same time, they can provide positioning functions like GPS. Although the technology is still in the early stage of development, there are still some technical bottlenecks to be overcome, but with the rapid development of the LED lighting market, the prospects are limitless.
The luminaire can broadcast the positioning signal by adjusting the brightness of the output light. This communication concept has been proposed for a long time, such as the application of optical fiber; but until recently, the industry has begun to effectively adjust the general lighting and the bulb. High power light. The technology that led to this change is the high-power white light-emitting diode (LED), which quickly replaced the fluorescent lamp as the first choice for future lighting technology because of its relatively high energy efficiency, lower cost, and environmental impact. Also relatively small.
The premise that LED lights should perform well-positioned functions is that visible light communication (VLC) signals must be properly designed to ensure that the main lighting functions are not affected. Key design considerations include impact on human vision, ability to support larger dimming ranges, power savings, and compatibility with existing hardware.
Lumicast messaging mechanism has dual functions
To this end, Qualcomm proposed a visible light positioning technology called Lumicast, which will provide a corresponding solution to the above problems. Unlike small-sized fluorescent tubes, LEDs are semiconductor components, so the output light can be adjusted at a relatively higher frequency. Signal modulation at a frequency of the kHz level not only ensures that the VLC signal does not produce visible light flicker, but also delivers information at the data rate required for positioning.
Lumicast allows the VLC signal to not affect the power saving of the luminaire through simple binary modulation. This modulation mechanism uses a boost converter that is itself a dimmable LED driver circuit integrated component. It saves signal resources, is compatible with existing driver circuits, and can coexist with various standard dimming methods.
Lumicast's communication mechanism was designed with these limitations in mind. With these conditions, LED luminaires can simultaneously satisfy the main functions of providing power-saving lighting and the role of positioning center.
VLC positioning has a unique advantage
The VLC signal transmitted by each luminaire has a unique identification tag that can be used to distinguish it from other luminaires in the venue. When the system is enabled, a position map of all the luminaires and their identification tags will be established. The location will be stored in the remote server. When the location is to be determined, the mobile device must first download the location map, whenever it is to be found through the VLC signal. When you come out of a particular fixture, you have to refer to this location map. The identification tag, if not stored inside the drive component, is provided by an external system, such as from a Bluetooth wireless network. The luminaire can be switched to transmit a new identification tag at regular intervals to prevent unauthorized use of this location function. By establishing this "rolling ID" mechanism, companies can prevent unauthorized third-party mobile applications from providing location services in their homes.
In Lumicast's communication mechanism, the key operating component of the mobile phone is a CMOS image sensor. After setting, it can extract a VLC signal change from a series of film pictures of a specific lamp, and receive the VLC. After the signal is demodulated and decoded by the smart phone, it produces a unique luminaire identification tag (Figure 1). In addition, as long as the image sensor is within the reach of the image sensor, it is important to simultaneously extract a plurality of VLC signals from the captured video images of the plurality of lamps, because the mobile phone or the mobile device can pass through multiple A separate location information source confirms the location and corrects it (Figure 2).
Figure 1 Schematic diagram of lamp identification label generation
Figure 2 LED light positioning correction process
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