Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-12-12
2004-02-17
Nguyen, Lee (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S272000, C455S575100, C348S014020, C348S552000
Reexamination Certificate
active
06694151
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to digital cameras that incorporate digital wireless RF communication systems operating in a microwave band such as the 2.4 to 2.5 GHz ISM (Industrial Scientific and Medical) Band. Such communication is useful, for example, for sending digital imaging data at high data rates; e.g. rates equal and greater than 10 Mega bits per second (Mbps).
BACKGROUND OF THE INVENTION
With the advent of digital photography and file compression techniques like JPEG for still images and MPEG2 for video, the wireless transmission of digital files, for example between a 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 very desirable because both digital images and streaming video represent a large amount of data (often greater than 1 MByte in size) and short transmission times are needed.
Short transmission times are needed in order to send and receive these large files quickly allowing the user freedom to do other things. At data rate speeds greater than 10 Mbps, these large files can be sent in a second or two. Short transmission times would also reduce battery power consumption for portable devices like a digital camera.
An additional desirable feature is being able to communicate at distances greater than 300 feet and also to communicate through walls. These features would enable digital cameras to communicate with utilization devices like photofinishing or multimedia equipment when the equipment is located inside a retail store, and the camera is being operated for example, inside an automobile from the parking lot of the store. Another useful feature would be for the wireless communication to be unlicensed and worldwide so that the digital camera could be taken on vacation and used in any country in the world without air time costs.
One way to send files from digital cameras without wires is through the use of radio waves. A use of radio waves to perform image communication is described in U.S. Pat. No. 5,806,005 issued Sep. 8, 1998 to Hull et al. entitled
Wireless ImageTransfer From A Digital Still Video Camera to a Networked Computer
. This patent demonstrates a potential solution of moving digital images using a cellular telephone transmitter. Unfortunately this technique has very slow data rates (i.e. 9.6 Kbps) due to the use of the cellular telephone and a large and cumbersome antenna. The cellular phone is physically too large to be incorporated into the body of the digital camera and results in a expensive system to both purchase and operate. The user of the system would not only need to purchase both the digital camera, connecting wire, and cellular phone but also pay by the minute for the air time (talk time) for using the cell phone. Worldwide use would be restricted and battery consumption would be high due to the slow 9.6 Kbps transmission rate.
One of the most important factors in determining the usefulness of the wireless system in a digital camera is in selecting the frequency band of operation. The frequency band also by way of its associated wavelength, determines size of the antenna needed. The higher the frequency of operation, the smaller the antenna needed since the wavelength of the signal is shorter. Because cameras are handheld portable devices, the overall small size of a camera is an important selling feature. Smaller invisible imbedded antennas are very desirable for appearance reasons in a digital camera. There are several radio frequency bands that could be used for such type of transmissions. One of the most attractive communication bands for such a digital communication system is the 2.4 to 2.5 GHz ISM Band since it is a microwave band with a quarter wavelength of about 1.2 inches, and that the band is unlicensed and the only band available internationally to date.
There are however, several major problems that exist with the use of this band for the wireless communication of digital images. One problem is the distortion of the antenna pattern due to human body effects. The user's hands and the closeness of the user's body to the digital camera alter the transmit and receive pattern of the antenna while holding the camera. Many types of antennas used in portable devices for operation in microwave bands are available in the marketplace today. They are typically retractable single stub monopoles, patch, F or L shaped antennas. Some recently developed antennas made of ceramic material are not much larger than the head of a pencil. While such antennas generally work well in wireless phones for instance, they all have antenna patterns with omnidirectional characteristics that do not work well when placed in a digital camera and held with both hands close to the torso of the body.
One important requirement in the wireless communication from a digital camera is the capability of the user to be able to view the Graphic User Interface (GUI) of the camera during operation. This means that the camera must transmit while being held by ones hands and while ones fingers operate the controls. In order for the transmission of the signal to be as efficient as possible, the antenna pattern should be designed in such a way as to avoid emitting energy at the human body.
Another problem with the use of the microwave band is the effect known as multipath fading on the propagation of the microwave signal. The effect of multipath fading on radio waves is a well known problem. The term multipath fading is used to describe the variations in signal strength that occur at a receiver during the time a signal is being sent. Fading occurs when a signal sent by a transmitter is reflected or blocked by a conductive medium such as a metal surface like a building, or the ground of the earth. The effects of multipath fading differ based on the physical characteristics of conductive obstructions versus the carrier frequency of the radio communication system, and the type of modulation technique employed. In general, the effects of multipath fading are greater at higher frequencies because the phenomenon of diffraction is slowed. One problem with using microwave bands is that the effect of multipath fading is also increased due to signal reflections and absorption by small objects and also by the human body.
To reduce or avoid the effect of multipath fading, communication equipment has traditionally used methods like diversity. Diversity refers to a level of redundancy or duplication in order to achieve an improvement in performance under multipath fading conditions. Space or antenna diversity refers to the use of two or more antennas. Frequency diversity refers to the changing of carrier frequencies in order to avoid the multipath fading.
Antenna diversity is well know and taught in several patents. In U.S. Pat. No. 4,696,058 issued Sep. 22, 1987 to Tachita et al. entitled
Diversity Receiver
, a diversity receiver uses more than one antenna and a means to switch to the one antenna with the greatest signal strength. In International Patent No. WO 95/30290 published Nov. 9, 1995, entitled Method for Transmitting Messages in Multipath Propagation Using Space and Time Diversity by Sandler et al., the patent teaches a solution using two transmit antennas with appropriate separation greater than ½ wavelength to create sufficient spatial diversity to assure that the propagated signal can be received without experiencing a destructive fade. The problem with antenna diversity is that there is often not enough room for the two properly spaced antennas to fit within the body of a consumer digital camera.
Other techniques for reducing the effects of multipath fading are spread spectrum modulation techniques like frequency hopping and direct sequence. But these two techniques add considerable size, weight and cost to RF systems also making them too difficult to incorporate into a consumer digital camera.
Accordingly, there is a need for an antenna apparatus for digital cameras that incorporates
Close Thomas H.
Eastman Kodak Company
Nguyen Lee
LandOfFree
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