Electrical computers and digital data processing systems: input/ – Input/output data processing – Peripheral adapting
Reexamination Certificate
1999-03-29
2002-05-28
Lee, Thomas (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Peripheral adapting
C710S068000, C348S574000, C360S040000, C360S041000
Reexamination Certificate
active
06397276
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a system and method for data communication and storage. More particularly, the present invention relates to both lossless and lossy compression techniques to concentrate relevant signal information for data communication and storage.
There are a variety of techniques for the compression of data which may be stored digitally or by analog techniques. This data represents audio, visual or other information for which there are numerous and different constraints to their compression.
Computer data files are, with few exceptions, stored digitally. The inherent advantages of digital communication and storage techniques are primarily due to the fact that information which is transmitted and stored in a binary form is much less susceptible to corruption due to noise or distortion than conventional analog systems. In addition, the conversion of analog signals to a digital form enables the user to employ noise reduction techniques and advanced signal processing algorithms which cannot typically be conducted on conventional analog signals. Moreover, digital communication and storage can also provide exact reproduction of the system output signals.
This is important because computer files must retain all of their information during storage or transmission, as an error of even one bit can totally corrupt the file. Corruption of a computer file can result in either failure of the entire computer system, or in the case of corruption of a non-operating file, such as a word processing file, inability to recreate the exact copy of the original file. Accordingly, the storage or transmission of computer data files or the like require highly reliable systems which maintain file integrity. Moreover, any compression of a computer file must be lossless, meaning not result in the loss of any data and provide exact reproduction of the uncompressed data.
Unfortunately, digital transmission and storage techniques disadvantageously require much wider frequency bandwidth. This is particularly true with respect to video information and modern multimedia systems which require the processing and storage of high volumes of data. Moreover, the transmission of video must often be accomplished in real time wherein the video information is transmitted at the same rate or faster than video playback.
To illustrate the complexity of the problem, each channel of the Common Interface Format (CIF) resolution standard for video systems requires 352 pixels per line and 288 lines per frame. In addition, CIF requires 2 chrominace channels with half resolution of 176 pixels per line, 146 lines per frame and 8 bits per pixel. With full motion video requiring approximately 30 frames per second transmission rate, video transmission requires approximately 36 Mbit per second. By means of an example, using a 56.6 k bits per second modem, it would take almost 11 minutes to transmit 1 second of video data over a telephone line. As a separate example, a CD-ROM having a capacity of 650 megabytes can only store approximately 18 seconds of uncompressed (CIF) video data.
Present systems do not provide adequate transmission rate of video signals over available communication channels. Presently, the most popular and inexpensive means for transmission of digital data is through the public telephone network. Unfortunately, the public telephone network was designed to transmit analog signals in a voice frequency range which is significantly lower than the frequency range required for most present day communication systems including digital data, voice and video communication.
To transmit digital information over the public telephone network, one typically uses a modem. Digital information is converted to an analog form. The modem filters the digital signal by shifting the signal and frequency to form a band limited signal. The modem then modulates that signal within the bandwidth of the communications channel which is typically between 300 Hz and 3500 Hz. Present modems employ quadrature modulation to increase the transmission rate of the digital information. Unfortunately, quadrature modulation has only increased present modem speed to approximately 56,600 bits per second. Accordingly, for practical digital transmission or storage, it is necessary to reduce the amounts of data to be transmitted or stored by either eliminating redundant information or by reducing the quality of the information.
As opposed to lossless compression techniques, data that is ultimately observed by the human senses can often be compressed with the loss of some information without any discernable alteration, as the human senses have limited capabilities in perception. Accordingly, audio and visual information is often compressed by lossy methods, for which there is a loss of information, since it is only necessary to recreate (decompress) a signal to the degree required for a subjective quality level rather then to perfectly recreate the signal.
For example, U.S. Pat. No. 5,819,215 issued to Dobson, U.S. Pat. No. 5,812,915 issued to Zhang and U.S. Pat. No. 5,845,243 issued to Smart each disclose lossy compression methods. U.S. Pat. Nos. 5,819,215 and 5,845,243 teach a wavelet based compression method having an adaptive bit rate control. An analog signal is digitally sampled at a desired rate and samples are transformed into the wavelet domain to form wavelet coefficients. The data is then compressed by reducing the total number of coefficients to be saved.
U.S. Pat. No. 5,812,195 teaches compressing video by using a prediction video signal to predict image blocks of a video image. An error measurement is obtained from comparing the predicted image to the actual image.
U.S. Pat. No. 5,426,665 issued to Cleverley et al. discloses a compression technique for spread spectrum communication systems. For spread spectrum communication systems or radar pulse compression systems, data is mixed with a pseudo random code with the frequency alternated during radio transmission. In a receiver, the process is reversed with the received signal down converted and then decoded to extract the data.
U.S. Pat. No. 5,184,229 issued to Saito et al. discloses a data compression system utilizing Huffman coded data.
Meanwhile, U.S. Pat. No. 5,818,870 issued to Yaguchi discloses transmitting an analog signal through a digital communication device. The amplitude to the signal is modulated to provide analog information, while the frequency is maintained at the normal rate of the digital communication device.
U.S. Pat. No. 5,661,718 issued to Bremer et al. discloses the simultaneous transmission of analog and digital communications. A sampled analog signal can be quantisized and represented in digital form. The analog signal which is then converted to digital form is then converted to amplitude quantisized pulse amplitude modulated format, such as conventional PCM.
Unfortunately, in such prior art compression techniques, the data transmission rates are still too slow for many practical applications. In addition, amplitude modulation of a transmitted signal often suffers from signal-to-noise ratio (S/N) problems. Moreover, it would be advantageous to provide a compression system and apparatus which did not result in the loss of any information during storage or transmission.
SUMMARY OF THE PRESENT INVENTION
Briefly, in accordance with the invention, I provide an improved apparatus and method for compressing digital data by converting the digital data to an analog signal. Generally, it is thought that information, stored in digital or in analog format, can be more quickly or more efficiently transmitted by digital processing than by known analog methods. Contrary to past teachings, I have discovered that digital information can be more quickly or efficiently transmitted if first translated into an analog format.
Digital data is comprised of “bits” in the form of “ones” and “zeros”. For example, applying traditional digital techniques, a signal transmitted at 3000 Hz provides the opportunity to transmit 3000 individual bits in o
Lee Thomas
Perveen Rehana
Skjerven Morrill LLP
LandOfFree
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