Telecommunications – Transmitter and receiver at separate stations – Distortion – noise – or other interference prevention,...
Reexamination Certificate
2000-02-17
2001-07-03
Maung, Nay (Department: 2744)
Telecommunications
Transmitter and receiver at separate stations
Distortion, noise, or other interference prevention,...
C455S067150, C455S067700, C455S466000
Reexamination Certificate
active
06256478
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a digital wireless wideband RF communication system operating in periodic noise environments. Such a system is useful, for example, for communicating digital data at high data rates; e.g. rates greater than 1 Mega bits per second (Mbps).
BACKGROUND OF THE INVENTION
With the advent of digital photography, the wireless transmission of digital images, for example between a portable transmitting device like a digital camera and a receiving device such as a personal computer or other image appliance such as a printer, has become a desirable feature. High data rate transmissions are desirable because digital images represent a large amount of data and short transmission times are needed. Short transmission times result in shorter wait times while an image is being transferred from a camera to a receiver and in reduced battery power consumption.
Although there are several useful communication bands available for such a digital communication system, the 2.4 to 2.5 GHz ISM Band is particularly attractive because the band is unlicensed and available internationally. However, a major problem exists with the use of this band for wireless communication. The band is allocated for microwave ovens and other devices, which as described below, generate a great deal of periodic noise in the band. Other communication bands like the 5.75 GHz band can also have periodic noise generators present. For the purpose of describing the present invention, references will only be made to periodic microwave noise as is present in the 2.4 to 2.5 GHz ISM band. It will be understood that the same principles can be used in the presence of any other kind of periodic noise in any communication band.
Radio frequency (RF) transmissions in the 2.4 to 2.5 GHz ISM Band have historically had to deal with the presence of man-made noise from microwave ovens that predominately operate in the center of this band at 2.45 GHz. The noise emanates from the oven by leakage through the enclosure of the oven. The leakage noise is periodic and has a radiated output power approximately 20 dB greater in strength than that allowed by the FCC for operation of Part
15
non spread spectrum radios. With over 200 million microwave ovens in use throughout the world, they are by far the greatest and most significant source of noise in this band. In addition microwave lighting and illumination systems are soon to be in use in the same band creating additional noise interference. Some examples of locations where it would be desirable to transmit images in the presence of periodic microwave noise are in the home (particularly in the kitchen), or in a supermarket or department store where a photo kiosk may be located near a microwave oven or lighting system.
One possible way to communicate in the presence of microwave noise is to use a spread spectrum communication technique. One type of spread spectrum technique spreads the signal over a band which is much larger than the bandwidth of the signal so that the narrow band noise from the noise source has a reduced effect on the demodulated signal to noise ratio. This technique however is relatively expensive to implement, significantly limits the data throughput (e.g. by a factor of 8 or more) and does not work well if the receiver is located very close to the noise source. Another way to communicate in the presence of microwave noise is described in U.S. Pat. No.
5
,
574
,
979
, issued Nov. 12, 1996 to West, entitled “Periodic Interference Avoidance in a Wireless Radio Frequency Communication System”. This patent demonstrates a potential solution by avoiding microwave oven periodic noise by sensing the periodicity of the AC power line main in which the oven is connected to. Unfortunately this technique does not work for periodic noise sources other than microwave ovens or in cases where multiple microwave noise sources on different phases exist. This technique also does not work in cases where the RF communication equipment is battery powered and no connection to an AC power main can be made, nor can the AC main E field radiation be received by the RF communication equipment. Furthermore this approach does not address the problem where one of the wireless communication stations can sense the noise, but the other wireless communication station cannot; when both stations are subjected to noise having different characteristics; or when three or more stations are trying to communicate and one or more are in a noise environment.
There is a need therefore for an improved means of digital communication in environments with periodic noise.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide for an improved means of efficient digital communication in the presence of periodic noise.
This object is achieved in a wireless communication system operating in the presence of the periodic noise such as from a microwave oven, the communication system, comprising: the wireless communication system including at least two wireless communication stations with transceiver in microwave communication with each other, each such station including: i) means for detecting periodic microwave signals for producing a signal indicating the duration of a periodic microwave signal's quiescent period; ii) means for controlling the transmitter to send an data packet which includes data and the duration of quiescent periods in the periodic microwave signal; and iii) means for adjusting the amount of data sent in an data packet as a function of the duration of the quiescent period.
The present invention provides a means to detect the presence of periodic microwave energy and controls the communications of data during quiescent periods of the periodic energy signal. In a digital radio system, the data is formatted into data packets. Data packets are transmitted until the quiescent period ends. This invention uses the knowledge of the quiescent period's starting time and duration to dynamically change the length of a data packet. In this way, all of the available quiescent time is used to transport data and the data throughput is maximized.
The advantages of the present invention is the ability to use information about the quiescent period to maximize data communications throughput by changing the size of the data payload in the data packet and making it fit into the allowed time period.
REFERENCES:
patent: 5574979 (1996-11-01), West
patent: 5768687 (1998-06-01), Marzoug
patent: 5802060 (1998-09-01), Fischbach et al.
patent: 5828293 (1998-10-01), Rickard
patent: 6006071 (1999-12-01), Roberts et al.
patent: 6009332 (1999-12-01), Haartsen
patent: 6072784 (2000-06-01), Agrawal et al.
Allen James D.
Carlson Grant B.
Heberling Allen D.
Close Thomas H.
Eastman Kodak Company
Maung Nay
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