Showing papers on "Encoder published in 1991"

An adaptive coding scheme for time-varying channels

Abstract: An adaptive coding scheme for digital communication over time-varying channels is presented. The scheme is based on a finite-state Markov channel model. Emphasis is on the adaptation of the error protection to the actual channel state. The throughput gains that are achieved by the adaptive scheme relative to the conventional nonadaptive coding methods are demonstrated by several examples. Of special interest is the use of punctured convolutional codes with maximum-likelihood Viterbi algorithm to enable adaptive encoding and decoding without modifying the basic structure of the encoder and the decoder. >

Motion-compensated video coding with adaptive perceptual quantization

Abstract: The authors address the problem of adapting the Motion Picture Experts Group (MPEG) quantizer for scenes of different complexity (at bit rates around 1 Mb/s), such that the perceptual quality of the reconstructed video is optimized. Adaptive quantisation techniques conforming to the MPEG syntax can significantly improve the performance of the encoder. The authors concentrate on a one-pass causal scheme to limit the complexity of the encoder. The system employs prestored models for perceptual quality and a bit rate that have been experimentally derived. A framework is provided for determining these models as well as adapting them to locally varying scene characteristics. The variance of an 8*8 (luminance) block is basic to the techniques developed. Following standard practice, it is defined as the average of the square of the deviations of the pixels in the block from the mean pixel value. >

System for the secure storage and transmission of data

Abstract: A system for the secure storage and transmission on data utilizes a visual algorithm to encode sensitive data in a secure manner on a data carrier. A camera (2) digitizes the image of a subject (4). The camera output is received at the encoder (6), where it is fed into a scrambler (8) and a transmitter (10). The transmitter sends the scrambled data to the recorder (12). The image data are scrambled on color at a time, with the scrambling instructions being encoded in the pixels themselves. A character assigned to each color is used for additional verification of the authorization of the user during decoding.

Compression of video signals

Abstract: A digital video signal is compressed by spatial sub-band filtering to form data sets constituting respective sub-bands of the two-dimensional spatial frequency domain. The data sets for a field or frame are stored. A first sequencer controls writing, in accordance with a desired sequence, of the stored data to a quantizer in which they are quantized in accordance with respective values, those values being such that the amount of quantization of at least a data set constituting a sub-band to which dc luminance information of the signal is at least predominantly confined is less than the average of the amounts of quantization of the remaining data sets. The quantized data sets are then encoded in an entropy encoder which has a first coding portion for coding quantized data representative of dc luminance information and a second coding portion for coding quantized data representative of ac luminance information. A second sequencer, which may be the same sequencer as the first sequencer, controls operation of the quantizer so that each datum (sample) written thereto is appropriately quantized, and controls operation of the entropy encoder so that each quantized sample is directed to the appropriate one of the first and second coding portions.

Layered DCT video coder for packet switched ATM networks

Abstract: A digital video encoder encodes a video frame into a differential video frame for transmission over a packet switched network. The video encoder includes an inter-frame encoder, an intra-frame encoder, and an encoding selector for selecting between the inter-frame and intra-frame encoder depending on the relative motion between the video frame being encoded and the previous video frame. A composite frame combiner provides a composite intra/inter-frame encoded difference frame having one set of pixels encoded by the inter-frame encoder, and another set of pixels encoded by the intra-frame encoder. The set of intra-frame encoded pixels includes at least one square or rectangular pixel block, a vertical strip of pixel blocks, and a horizontal strip of pixel blocks. Difference frames are encoded into separable data sets representing video information within a particular range of image resolution. A discrete cosine transform (DCT) is used to transform the difference pixels into corresponding DCT coefficients which are separable, by resolution, into the data sets providing coefficient layers. A packetizer formats the data sets into asynchronous transfer mode (ATM) packets for transmission over network.

Trellis-coded vector quantization

Abstract: Trellis-coded quantization is generalized to allow a vector reproduction alphabet. Three encoding structures are described, several encoder design rules are presented, and two design algorithms are developed. It is shown that for a stationary ergodic vector source, if the optimized trellis-coded vector quantization reproduction process is jointly stationary and ergodic with the source, then the quantization noise is zero-mean and of a variance equal to the difference between the source variance and the variance of the reproduction sequence. Several examples illustrate the encoder design procedure and performance. >

Hdtv encoder with forward estimation and constant rate motion vectors

Abstract: A motion compensated encoder where motion vectors are selected based on the prediction error generated in localized areas of the encoded image and based on an available bit budget. The motion vectors are created by dividing the image into blocks of two sizes and by considering the best mix of large and small size blocks, and their associated motion vectors, that minimize the overall prediction error, within the constraints of the bit budget. For convenience, the image division is arranged so that a given number of small sized blocks forms one large sized block (e.g. 16:1). Also, the block sizes are arranged so that employing only large sized blocks does not exceed the given bit budget, while employing only the small sized blocks does exceed the given bit budget.

SEU hardened memory cells for a CCSDS Reed-Solomon encoder

Abstract: A design technique to harden CMOS memory circuits against single event upset (SEU) in the space environment is reported. The design technique provides a recovery mechanism which is independent of the shape of the upsetting event. A RAM cell and flip-flop design are presented to demonstrate the method. The flip-flop was used in the control circuitry for a Reed-Solomon encoder designed for the Space Station and Explorer platforms. >

Low bit rate speech coding system and compression

Abstract: A speech coder apparatus operates to compress speech signals to a low bit rate. The apparatus includes a continuous speech recognizer (CSR) which has a memory for storing templates. Input speech is processed by the CSR where information in the speech is compared against the templates to provide an output digital signal indicative of recognized words, which signal is transmitted along a first path. There is further included a front end processor which is also responsive to the input speech signal for providing output digitized speech samples during a given frame interval. A side information encoder circuit responds to the output from the front end processor to provide at the output of the encoder a parameter signal indicative of the value of the pitch and word duration for each word as recognized by the CSR unit. The output of the encoder is transmitted as a second signal. There is a receiver which includes a synthesizer responsive to the first and second transmitted signals for providing an output synthesized signal for each recognized word where the pitch, duration and amplitude of the synthesized signal is changed according to the parameter signal to preserve the quality of the synthesized speech.

Two and three wire utility data communications system

Abstract: A two wire/three wire utility data communications system for remotely reading utility meter registers. In the two wire version, a hand-held reading unit is inductively coupled over two wires via a port located remotely from a meter register. Alternatively, a meter interface unit (MIU) may be connected directly to the register via three wires. Each register includes one or more wheel position encoders. An AC interrogation signal is applied by the reading unit to encoder circuitry at the meter which powers the circuitry and causes the position of each encoder wheel to be read. In the two wire mode, register display information (e.g. the current meter reading) is transmitted back to the reading unit by varying the load (impedance) presented by the register side of the circuit. This causes a corresponding variation of the amount of current drawn from the reading unit. The current-modulated signal is decoded by the reading unit and converted into a register reading. The system can also operate in a three wire mode and read older fourteen wire encoded registers. Other features include remote programmability of register characteristics, the ability to interrogate multiple registers which share a common data bus, verification of encoder wheel positions before accepting a reading, real-time flow rate/leak detection, pulse output, and the capability of reading compound meters (i.e. meters having two registers to separately measure high/low flow rates).

Digital wavelength division multiplex optical transducer having an improved decoder

Abstract: A fiber optic optical transducer or encoder is described. The outputs of two detectors receiving signals from an optical multiplexer/demultiplexer arrangement are compared to determine whether a given code bit is "on" or "off". When the bit is "on" the power received by the second detector will, for example, be greater than the power received by a first detector. When the bit is "off" the reverse is true. A simple power level comparison thus determines the logic state of each given code bit.

Head position control system for fixed drive including position encoder, temperature sensor and embedded fine servo information

Abstract: A micro-Winchester disk drive subsystem includes a data block sequencer, cache memory and interface for a host computing machine. The drive includes a base and a plurality of non-removable directly rotated disks forming data storage surfaces. A balanced rotary head transducer actuator is mounted to the base for a plurality of data transducer heads among a multiplicity of concentric data tracks formed on each data storage surface of each of the disks. The track following servo system includes a position encoder coupled between the actuator structure and the base, prerecorded data track centerline information at a radially outermost region and at a radially innermost region of each data surface, and a temperature sensor for sensing temperature of the base at the vicinity of the position encoder. An actuator driver circuit is connected to supply electrical driving current to the actuator structure; and, a single, time divided multi-tasked digital including an analog to digital converter is connected to receive the position information from the position encoder, centerline information from the disk surfaces read by the data transducer and temperature sensed by the temperature sensor during a calibration operation in one phase of its operational cycle, the other phase being devoted to supervision data block handling functions of disk drive data block sequencer cache memory and interface. During track following operations, centerline information is derived from information obtained in the calibrate operation. The temperature sensor is periodically checked and recalibration is carried out when drive temperature changes.

Error bounds for trellis-coded MPSK on a fading mobile satellite channel

Abstract: Analytical performance bounds are presented for trellis-coded MPSK, transmitted over a satellite-based land mobile channel. Upper bounds are evaluated using the well-known transfer function bounding technique, and lower bounds are achieved through knowledge of exact pairwise error probabilities. In order to analyze practical trellis-codes (four or more states), the uniform properties displayed by a certain class of trellis-codes are exploited, enabling the encoder transfer function to be obtained from a modified state transition diagram, having no more states than the encoder itself. Monte Carlo simulation results are presented in confirmation of all performance bounds and indicate a general weakness in the transfer function upper bounds. A new asymptotically tight upper bound is derived based on a simple modification to the standard transfer function bound, and results are presented for the four- and eight-state trellis-codes in Rician and Rayleigh fading. >

Video compression algorithm with adaptive bit allocation and quantization

Abstract: The emerging ISO MPEG video compression standard is a hybrid algorithm which employs motion compensation, spatial discrete cosine transforms, quantization, and Huffman coding. The MPEG standard specifies the syntax of the compressed data stream and the method of decoding, but leaves considerable latitude in the design of the encoder. Although the algorithm is geared toward fixed-bit-rate storage media, the rules for bit rate control allow a good deal of variation in the number of bits allocated to each picture. In addition, the allocation of bits within a picture is subject to no rules whatsoever. One would like to design an encoder that optimizes visual quality of the decoded video sequence subject to these bit rate restrictions. However, this is difficult due to the elusive nature of a quantitative distortion measure for images and motion sequences that correlates well with human perception. This paper describes an MPEG encoder designed to produce good quality coded sequences for a wide range of video source characteristics and over a range of bit rates. The novel parts of the algorithm include a temporal bit allocation strategy, spatially adaptive quantization, and a bit rate control scheme.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Encoder system using linear array sensor for high resolution

Abstract: An encoder system and method wherein an encoder element driven by a motor has a series of segments arranged along a path with adjacent segments having different properties meeting at an edge or transition, two adjacent segments of different properties comprising a cycle and the encoder element having a number of cycles equally spaced along the path and defining a relatively coarse pitch relationship. A coupling medium, preferably optical, images the encoder segments onto a number of individual sensor elements of an array, such as a charge-coupled device sensor, wherein the sensor elements are spaced at a relatively fine pitch along the array. As the encoder element is moved by the motor, images of the edges or transitions are applied to the array sensor elements After a sampling interval, signals from the array are digitized and shifted into a microprocessor which compares the present locations of the applied edges to the previous locations stored in the memory thereof and which calculates the present position and velocity output signals which can be used to control operation of the motor in a closed loop feedback control system. The encoder system achieves high resolution with a relatively coarse pitch and thus low cost encoder element. In addition, both position and velocity signals are derived from operation of the single encoder element.

An adaptive data compression system

Abstract: An adaptive data compression system comprises an encoder (2) which responds to input characters by producing output codewords according to a stored encoding map or table of characters and codewords, and adapting means (4, 5) which adapts the encoding map or table in accordance with the input characters so as to increase the compression ratio between the input characters and output codewords, characterised in that optimisation means (5) monitors the performance of the system and accordingly varies adaptation of the encoding map or table by the adapting means (4) so as to optimise performance of the system. Performance of the system is preferably monitored in terms of the computational loading of the processor and the compression ratio it achieves. A decoder (7) subsequently decodes the codewords by reference to a corresponding decoding map or table which is adapted (9, 10) in accordance with the output data from the decoder and in accordance with variations in the adaptation process in the encoder.

Multi-mode data stream generator

Abstract: Improved apparatus and method for encoding and decoding information is disclosed herein. The invention uses the same marker segment information to engage an encoder or a decoder. The technique eliminates many of the complexities associated with building parameter lists, and generating various types of marker segments in a form compatible with both the decode and encode processing.

Real-time analytic pseudocolor encoder system

Abstract: Continuous analytic transform functions implemented optically in U.S. Pat. No. 4,623,245 are instead implemented electronically and in real-time. An improved scheme is disclosed where the range of amplitudes of the monochromatic signal input is divided into n sections and constant, linear or sinusoidal transform functions are utilized in each section for transforming the monochromatic video input to three pseudocolor video signals. Even complex transform functions can be implemented by simple transform functions in each of the sections to reduce the overall complexity of the implementing circuit. The television camera, a pseudocolor encoder and a liquid crystal television monitor are placed within the same housing to form a portable hand-held unit. The weight and size of the unit can be reduced as a result of the simple electronic implementation of the encoder.

System including packet structure and devices for transmitting and processing output information from a signal encoder

Abstract: A system for structuring information outputted at a variable bit rate from a video signal encoder and for organizing the information into information units or packets. The information packets are compatible for transmission and processing by packet transmission networks such as asynchronous transfer mode (ATM), capable of sending transmission data streams at variable speed. In a preferred embodiment, the system uses an encoder that comprises video units. Each video unit contains information classified into three distinct classes. Each video unit is associated with a video packet comprising a header and a body. Each of the three distinct classes of information associated with a video unit uses a different technique for tho providing protection of that information against transmission errors and/or information packet loss.

Sunset: a hardware-oriented algorithm for lossless compression of gray-scale images

Abstract: Sunset is a lossless gray scale compression algorithm designed for a simple hardware implementation based on the prediction error context approach for predictive gray-scale compression. Sunset uses adaptive binary arithmetic coding with neighboring prediction error buckets as compact conditioning contexts for directly encoding the prediction error. A prototype card was built to send or receive either compressed or uncompressed images across the IBM PC/AT bus. A special interface was designed to load the memory buffer of a high resolution color display. The result is a component of a workstation prototype for radiologists and the physician who referred the patient. The Sunset approach handles gray scale images where the bits-per-pel precision is simply an input parameter to the algorithm; the compression algorithm itself is relatively insensitive to this parameter. For hardware simplicity, the error bucket (bin) identifier is determined by a leading-one detector (or priority encoder) circuit on the prediction error so the number of prediction error values per bucket is a power of two. The next less significant bits of the prediction error become the ''extra-bits'' which, when encoded, make the algorithm lossless. The number of extra-bits in a final (catch-all) bucket depends on the bits-per-pel parameter of the uncompressed image.

Bounds On The Number Of States In Encoder Graphs For Input-constrained Channels

Abstract: The authors obtain general lower bounds on the number of states in any encoder for a given constrained system and rate. Lower bounds on the number of states are exhibited in a fixed-rate finite-state encoder that maps unconstrained n-ary sequences into a given set of constrained sequences, defined by a finite labeled graph G. In particular, one simple lower bound is given by min/sub x/max/sub v/x/sub v/ where x=(x/sub v/) ranges over certain (nonnegative integer) approximate eigenvectors of the adjacency matrix for G. In some sense, the bounds are close to what can be realized by the state splitting algorithm and in some cases, they are shown to be tight. In particular, these bounds are used to show that the smallest (in number of states) known encoders for the

A hybrid ARQ scheme with adaptive forward error correction for satellite communications

Abstract: A hybrid automatic-repeat-request system combined with adaptive forward error correction (ARQ/AFEC) which adaptively alters the error-correcting capability according to channel state using a nonsystematic Reed-Solomon code is presented. lt is shown that the system can alter the error-correcting capability by varying the number of information symbols fed to the decoder only, and not change the hardware of the encoder. Performance evaluations indicate that the ARQ/AFEC system has much higher frame efficiency than ARQ without AFEC for low-bit error rate and has high frame efficiency in a wide range of bit error rates. >

Digital beam-forming technique using temporary noise injection

Abstract: An efficient digital beam-forming network (100) utilizing a relatively few small-scale A/D converters is disclosed herein The inventive beam-forming network (100) is disposed to generate an output beam B in response to a set of N input signals The set of input signals is provided by an antenna array (110) having N elements, upon which is incident an electromagnetic wavefront of a first carrier frequency The present invention includes an orthogonal encoder circuit (170) for generating a set of N orthogonal voltage waveforms A set of biphase modulators (162-168) modulates the phase of each of the input signals in response to one of the orthogonal voltage waveforms, thereby generating a set of N phase modulated input signals The N phase modulated input signals are combined within an adder (180) to form a composite input signal The inventive network (100) further includes a downconverting mixer (184) for generating an IF input signal in response to the composite input signal The IF input signal is then separated into baseband in-phase and quadrature-phase components by an I/Q split network 192 A pair of A/D converters (198, 200) then sample the in-phase and quadrature-phase components of the input signal A decoder (202), coupled to the orthogonal encoder circuit (170), provides decoded digital in-phase signals and decoded digital quadrature phase signals in response to the digital in-phase and quadrature-phase signals The present invention further includes a digital beam-former (130) for generating the output beam B by utilizing the decoded in-phase and quadrature-phase signals

Reed-Solomon VLSI codec for advanced television

Abstract: A VLSI implementation of a Reed-Solomon codec circuit is reported. The 1.6- mu m double metal CMOS chip is 8.2 mm by 8.4 mm, contains 200000 transistors, operates at a sustained data rate of 80 Mbits/s and executes up to 1000 MOPS while consuming less than 500 mW of power. The 10-MHz sustained byte rate for the data is independent of the error pattern. The circuit has complete decoder and encoder functions and uses a single data/system clock. Block lengths of 255 bytes as well as shortened codes are supported with no external buffering. Erasure corrections as well as random error corrections are supported with selectable correction of up to ten symbol errors. Corrected data is output at a fixed latency. These features make this Reed-Solomon processor suitable for use in advanced television systems. >

Image signal coding/decoding system using adaptive quantization

Abstract: An image signal coding/decoding system comprises an encoder for encoding an image signal by using the adaptive quantization, and a decoder for decoding the coded image signal by using the adaptive inverse-quantization The encoder comprises an activity detection element for detecting, every blocks obtained by dividing an image signal every a specific time length, activities indicating degree of changes in the signal in the respective blocks; a quantization class determination element for determining class values of a plurality of quantization classes set in correspondence with respective stages of the adaptive quantization from the detected activities; and for outputting the determined class values as class information to the decoder, a filter element for filtering not only the class values but also class values at the peripheral blocks; and a quantization step width determination element for determining, every blocks, widths of quantization steps corresponding to a value obtained by multiplying these class values by fixed coefficients on the basis of class values subjected to filtering The decoder comprises a decode element for decoding coded data transmitted from the encoder by using the variable-length codes, and an inverse-quantization element for inverse-quantizing the variable-length decoded signal of the basis of class information transmitted from the quantization class determination element

Laser optical disk position encoder with active heads

Abstract: An angular position encoder that minimizes the effects of eccentricity and other misalignments between the disk and the read stations by employing heads with beam steering optics that actively track the disk in directions along the disk radius and normal to its surface is discussed. The device adapts features prevalent in optical disk technology to the application of angular position sensing.

Variable pitch position encoder

Abstract: The invention provides an optical encoder for use with various density code wheels. The encoder provides a geometric offset for a photodetector that is fully illuminated. A circuit offset is provided for a photodetector that is not illuminated. The encoder comprises a light source; a principal photodetector; a pair of secondary photodetectors on opposite edges, respectively, of the principal photodetector; and a code wheel having plural alternating windows and spokes which respectively transmit or block light from the light source. The code wheel is mounted between the light source and the photodetector. The principal photodetector has a unit width and a first length. The secondary photodetectors each have a half-unit width and a second length; the second length is less than the first length. The encoder also includes a circuit biased for producing one logic level when all photodetectors are illuminated and producing the opposite logic level when only the secondary photodetectors are illuminated or when no photodetectors are illuminated.

Model-based halftoning

Abstract: New model-based approaches to digital halftoning are proposed. They are intended primarily for laser printers, which generate 'distortions' such as 'dot overlap'. Conventional methods, such as clustered-dot ordered dither, resist distortions at the expense of spatial and gray-scale resolution. Our methods rely on printer models that predict distortions and, rather than merely resisting them, they exploit them to increase, rather than decrease, gray-scale and spatial resolution. We propose a general framework for printer models, and find a specific model of laser printers. As an example of model-based halftoning we propose a modification of error diffusion, which is often considered the best halftoning method of CRT displays with no significant distortions. The new version exploits the printer model to extend the benefits of error diffusion to printers. Experiments show that it provides high quality reproductions with reasonable complexity. The quality of printed images obtained using the new technique on a 300 dots/inch printer is comparable to the quality of images obtained with traditional techniques (e.g. 'Classical' screening) on a 400 dots/inch printer. Model-based halftoning can be especially useful in transmission of high quality documents using high fidelity gray-scale image encoders. As we show in a companion paper, is such cases halftoning is performed at the receiver, just before printing. Apart form coding efficiency, this approach permits the halftoner to be tuned to the individual printer, whose characteristics may vary considerably from those of other printers, for example, write-black vs. write-white laser printers.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Prediction of bit rate sequences of encoded video signals (for ISDN)

Abstract: A new approach for video traffic characterization (VTC) is proposed. In this approach, it is assumed that every video sequence is characterized by a set of fundamental indexes or parameters and that the bit rate process can be generated by a parametric model of the corresponding indices. Among the implications of this approach are: the encoding process is no longer necessary to simulate the bit rate process for a particular video sequence: a video sequence needs to be processed only once to obtain its fundamental parameters: and, in general, the computation of the index processes requires much less processing than the actual encoding. If parametric models are identified for all encoding algorithms of interest, then the problem of developing models for various combinations of encoders and classes of video sequences reduces to the problem of developing a single model for the index processes of various classes of video sequences. >

Audio signal subband encoder

Abstract: There is provided an audio signal subband encoder which attains improved quality of sound by controlling allocation of the number of quantization bits to subband signals on the basis of an evaluation function combining the noise-to-mask ratio criterion with noise-to-signal ratio criterion in order to lessen the influence of the application error of the auditory masking rule such as the aliasing distortion of subband filters.