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 (M-FAN)

Fiber Optical Comm.

• In fiber optic comm., the carrier wave is visi-ble light ( at )

• Due to very high frequency, modulating the electric field is very difficult

• Nearly all optical comm. systems use inten-sity modulation

• On-off keying (OOK), which only uses two states for encoding, is used

142 10f Hz 1.5 m

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 in-stead of phase. Constellation diagram would be intensity vs. color in polar coordinates

• RGB color diodes (LEDs or lasers) can repre-sent 8 colors – black, red, green, blue, yel-low, cyan, magenta, white – by combination.

• Modern Bayer-masked CCDs can easily dis-tinguish the color, hence reducing the com-plexity 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 dis-tinguish colors, but their method uses photo-electric detectors.

Another Issue

• Optical fiber is unarguably better than UTP cable in terms of interference and through-put

• 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-pur-pose)

• Started by Nakagawa Lab., Keio Univer-sity, Japan (2003). (will be in IEEE 802.15)

• Only uses visible light that is not injuri-ous 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 colli-sions 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 tech-nology 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

R1T R2

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

6

1E

d

2

1E

d

References

• H. Willebrand, B. S. Ghuman, Free space optics : en-abling optical connectivity in today’s networks, 2005

• A. Mahdy, J. S. Deogun, Wireless optical communica-tion : 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