Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1996-08-30
1999-07-20
Negash, Kinfe-Michael
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359172, 359184, 359186, 359189, 375239, 34082572, H04B 1000, H04B 1004
Patent
active
059263016
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a method and apparatus for optical communication based on pulse-position-modulation (PPM).
BACKGROUND OF THE INVENTION
With the rapidly increasing number of workstations and personal computers (e.g. desktop or handheld ones) in all areas of business, administration, fabrication etc., there is also an increasing demand for flexible and simple interconnection of these systems. There is a similar need as far as the hook-up and interconnection of peripheral devices, such as keyboards, computer mice, printers, plotters, scanners, displays etc., is concerned. The use of electrical wire networks and cables becomes a problem in particular with increasing density of systems and peripheral devices and in the many cases where the location of systems, or the configuration of subsystems, must be changed frequently. It is therefore desirable to use wireless communication systems for interconnecting such devices and systems to eliminate the requirement of electrical cable networks.
In particular the use of infrared signals for exchanging information between systems and remote devices received increased interest during recent years. The advantage of such wireless infrared communications systems is the elimination of most of the conventional wiring. With respect to radio frequency (RF) wireless transmission, optical infrared (IR) wireless transmission has the advantages that no communication regulations apply and no PTT or FCC license is required. Additionally, no disturbance by electro-magnetic interference and no interference from other RF channels can occur, and the radiation is confined to a room so that better data security is guaranteed than with RF systems. There is thus no interference with similar systems operating next door and a higher degree of data security is afforded than radio-frequency transmission can offer. In contrast to radio-frequency antennae, the dimensions of light emitting diodes (LED) and photodiodes are usually smaller, which is of particular interest when designing portable computers.
Given an optical channel where the optical transmitter power, the ambient light conditions, and the photodiode area are all fixed quantities, power efficiency becomes the main criterion in choosing a modulation scheme in order to maximize the distance over which reliable transmission can be maintained. Judged by the power efficiency and ignoring bandwidth efficiency, L-slot pulse-position-modulation (L-PPM) would be the preferred modulation scheme for optical communication. Being a baseband modulation scheme, L-PPM is not suited for those applications where multiple collocated optical networks are required, since only a single L-PPM system can operate in a given location without coordination between collocated networks. As already mentioned, there is an increasing demand for optical wireless local area networks (WLANs) and peer-to-peer networks which can coexist independently within the same location. PPM is not suited for these kind of collocated networks.
There is no approach known which satisfies the requirements for high power efficiency and reliability under adverse conditions as well as the demand for collocated independent disturbance- and interference-free optical networks. While L-PPM might be the preferred method with respect to power efficiency, it cannot provide for
In addition, optical PPM communications systems suffer from interference caused by fluorescent light sources at frequencies up to 500 kHz.
Frequency Shift Keying (FSK), on the other hand, is a carrier (bandpass) modulation scheme which is well suited for multiple channel operation but is poor in terms of power efficiency when compared to L-PPM. IR communications systems with bandwidths of up to 30 MHz can be achieved with todays component technology and further advances in terms of available bandwidth are expected in the future. Present baseband PPM systems do not fully exploit this available frequency spectrum.
It is another disadvantage of known optical communication systems that they are
REFERENCES:
patent: 4151407 (1979-04-01), McBride et al.
patent: 4584720 (1986-04-01), Garrett
patent: 4648133 (1987-03-01), Vilnrotter
patent: 5113278 (1992-05-01), Degura et al.
Patent Abstracts of Japan, vol. 15, No. 46 (E-1029) 1991 & JP,A,02 279 035 (Mitsui Mining & Smelting).
Patent Abstracts of Japan, vol. 2, No. 104 (E-053) 1978 & JP,A,53 070 709 (Fujitsu).
Patent Abstracts of Japan, vol. 15, No. 29 (E-1026) 1991 & JP,A,02 272 928 (Mitsui Mining & Smelting).
Flynn John D.
International Business Machines - Corporation
Negash Kinfe-Michael
LandOfFree
Method and apparatus for optical wireless communication does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for optical wireless communication, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for optical wireless communication will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1327177