oor environments. Smart LED lighting Clock Encoded data Wireless (on/off) thermostat Printer HD video streaming Laptop Internet access (water me) Figure 12.15 A visible light communications system [27] Broadband Telecommunications Technologies and Management On the negative side, the high frequency of operation makes it very susceptible to channel conditions: physical objects can block the light and interrupt any communications. Networking can also be an impediment: while lighting in new homes can be wired using power-on- Ethernet, retro-fitting homes can be costly and impractical. Internet over power lines has been suggested as a solution but the transmission rate over these power lines is much slower com- pared with 802.11 wireless LANs. High VLC transmission rates of several gigabits per second have been demonstrated by researchers in a number of laboratories, and many applications have been proposed. Foremost among these is the research work carried out in Harald Haas' laboratory at Edinburgh University (e.g. precise location, gigabit/s local area networking, robotics, etc.).A good over- view of technologies and applications may be found in [28]. Example 12.4 An interesting application of VLC technology is in diving and snorkelling communications [29]. Electromagnetic waves do not propagate well in salty water, and sonar systems have very low capacity. In contrast VLC systems can support high transmission rates. They can also facilitate a natural way of communications between divers since they can be seen by divers. Marine Com Ryukyu, a company based in Okinawa, Japan, manufactures and markets i- MAJUN, an underwater VLC device. According to the company's website, i-MAJUN can support underwater voice communications of up to a distance of 30 m [30]. Ubiquitous wireless connectivity may be accomplished in a number of ways. Broadband wireless standards may be adopted to provide machine-to-machine connectivity over a range of distances. In practice connectivity is provided through a number of different standards 