Alternative Communications : Survey and Idea Lee, Gunhee

Contents Fiber Optical comm. Free-Space Optical comm. (FSO) –Visible light comm. –Laser comm. Near-Field Induction comm. (NFI) or Magnetic Field Area Network (MFAN)

Fiber Optical Comm. In fiber optic comm., the carrier wave is visible light ( at ) Due to very high frequency, modulating the electric field is very difficult Nearly all optical comm. systems use intensity modulation On-off keying (OOK), which only uses two states for encoding, is used

Idea Can we use a frequency (in this case, the color of light) to increase the efficiency of encoding?

Color-code Intensity Keying Similar to QAM scheme, but uses colors instead of phase. Constellation diagram would be intensity vs. color in polar coordinates RGB color diodes (LEDs or lasers) can represent 8 colors – black, red, green, blue, yellow, cyan, magenta, white – by combination. Modern Bayer-masked CCDs can easily distinguish the color, hence reducing the complexity of the system

Example Constellation Blue Red Black Cyan Magenta Yellow White Green

Color Multiplexing There is a patent on Color Multiplexing in fiber optic transmission(Quick, 1980) It is very different from my idea, however. CIK uses multiple source of colored diodes, but CM uses a prism to disperse white light into spectrums Also, my idea uses Bayer-masked CCDs to distinguish colors, but their method uses photoelectric detectors.

Another Issue Optical fiber is unarguably better than UTP cable in terms of interference and throughput However, optical fiber is made of glass, which is fragile and stiff Glass fiber is also expensive, so there are two alternatives –Find another material (It’s not my area) –Eliminate the cable

Free-Space Optical Comm. Compared to conventional wireless comm., –Minimum interference –High speed –Security There are two main implementations –Visible light comm. (non-directional) –Laser comm. (directional)

Visible Light Comm. Lighting + Communication (multi-purpose) Started by Nakagawa Lab., Keio University, Japan (2003). (will be in IEEE ) Only uses visible light that is not injurious to vision 10 kbit/s using ordinary fluorescent lamps 500 Mbit/s using LEDs

Laser Comm. High speed, directional This is an experimental implementation 8-beam laser link, 1 Gbit/s at 2 km.

Networking Viewpoint Both laser comm. and visible light comm. are not complete technologies They can make a link, not a network A novel idea to establish networks is not found yet Networking using directional comm. Idea : almost no interference and collisions in these comms, so ways to exploit these can be useful

Near-Field Induction Core technology of NFI is patented by a company, FreeLinc FreeLinc made some products Wireless energy transfer I found two critical problems of this technology which should be solved, however

n-Body Problem R T1 T2 ? ? If there are more than three coils, a transmitter cannot properly generate current because of collision

Chain Reaction Problem R1TR2 Even if Tx range of T doesn’t reach R2, R2 get unnecessary current from R1. Also there is a possibility of further propagation.

Conclusion Using NFI or MFAN as an alternative method for wireless network seems hard Also, it suffers from heavy decaying compared to far-field radiation

References H. Willebrand, B. S. Ghuman, Free space optics : enabling optical connectivity in today’s networks, 2005 A. Mahdy, J. S. Deogun, Wireless optical communication : a survey, 2004 A. Attarian, A survey of terrestrial and free space based optical communications systems, 2007 W. H. Quick, Means for sensing and color multiplexing optical data over a compact fiber optic transmission system, 1980