General Instrument Corporation

M/a-com Linkabit, Inc.

M/a-com Government Systems, Inc.

Cable/home Communication Corp.

Corning Incorporated

Woo H Paik

Edward A Krause

Vincent C Liu

Paul Shen

Scott A Lery

Jerrold A Heller

Allen Wu

Gordon Kent Walker

James N Esserman

Chris Heegard

Vincent Hok Liu

John M Fox

Vinay Sathe

Paul Moroney

Henry Derovanessian

Adam S Tom

David Grubb

Stephen C Pollmann

David E Charlton

William Fong

Jim Essserman

John E McCormick

Ashok K Goerge

David Iii Grubb

The effects of noise in a video processing system are reduced, resulting in improved image quality. A digital video signal containing a luminance component in Y color space is processed by increasing the amplitude of the luminance data in accordance with a nonlinear transfer function. As a result, low-amplitude components of the luminance signal are reduced. Subsequent quantization errors in transform coefficients produced by a spatial compression routine in a video encoder are consequently reduced. Inverse operations are performed at a video decoder to recover the original luminance data. The invention reduces quantization noise which is manifested particularly as dust-like variations in luminance intensity in an otherwise darkened region of a video image. A decoder apparatus is also presented.

Reduction of noise visibility in a digital video system

An apparatus and method for adaptively compressing blocks of video image data provide a local coding level for use in compressing successive blocks of video image data. Each block is preliminarily compressed using a global coding level. The preliminarily compressed data is processed to provide a measure of the randomness of an image area represented by the block of video image data. A local coding level is generated based on the randomness measure. The video image data is then compressed using the local coding level to provide compressed data for transmission. One or more intermediate compression stages can be provided, each generating an intermediate coding level, to better refine the randomness measure for use in generating the local coding level.

Adaptive coding level control for video compression systems

Digital video signals are adaptively compressed for communication to a receiver. Superblocks, each containing a plurality of blocks of digital video data, are compressed using PCM, DPCM with a general motion vector for the entire superblock, and DPCM with a specific motion vector for each block contained within a superblock. The result of each compression mode is compared after accounting for overhead data, to determine which results in the least amount of data for each block. These blocks are assembled into a superblock, and compared together with necessary overhead and motion vector data to the same superblock processed using all PCM as well as the superblock processed using all DPCM. The comparison determines which compression mode produces the least amount of data for the superblock. The most compact superblock is selected for transmission. The transmitted superblocks are decoded by a decoder that recovers the necessary motion vectors and overhead information which identifies the type of compression used to provide the superblock.

Adaptive compression of digital video data using different modes such as

A quadrature amplitude modulation (QAM) communication system is provided in which data can be communicated in any one of a plurality of QAM modes, such as 16-QAM, 32-QAM, and 64-QAM. A receiver detects the particular QAM mode transmitted on a trial and error basis, by attempting to decode the received data using different QAM modes until a synchronization condition is detected. The synchronization condition can require that a plurality of different synchronization tests be met. In a specific embodiment, a first synchronization test is met when a renormalization rate of a trellis decoder is below a threshold value. A second synchronization test is met when a first synchronization word is detected in the received data. A third and final synchronization test is met when a second synchronization word is detected in the received data. In order to reduce the cost of the receiver, most of the QAM mode dependent components are implemented using look-up tables stored in PROMs.

Mode selective quadrature amplitude modulation communication system

A method and apparatus for communicating high definition television signals is provided. Video signals are divided into blocks of PCM data. The PCM data is processed using motion estimation and compensation to provide DPCM data. For each block, one of PCM and DPCM data is selected for transmission based on a predetermined criteria. The selected data is compressed using the discrete cosine transform to provide blocks of transform coefficients. The coefficients are quantized to improve their coding efficiency and variable length coded. The variable length coded coefficients are coded using a concatenated coding scheme with a Reed-Solomon outer code and trellis inner code to provide coded signals for transmission. The coded signals are transmitted using QAM.

Method and apparatus for communicating digital information such as

A multiple serial access memory which includes a dynamic random access memory array is disclosed. The array is randomly addressed to input blocks of data. Address signals are provided to the array to output rows of data. A plurality of serial output ports are coupled to the output of the array for selectively latching different rows of data output from the array. The serial output ports are clocked to output the latched data therefrom. In an illustrated embodiment, each of the serial output ports contains a shift register having a length equal to the width of the memory array. The shift register is responsive to a first timing signal for latching a row of data from the array. A second timing signal actuates the shift register to shift a row of latched data. The serial access selector coupled to the shift register outputs a selected portion of the shifted data from the serial output port. The serial access memory has particular application as the frame store for a motion compensated interframe image coding/decoding system.

Multiple serial access memory for use in feedback systems such as motion

A method and apparatus are provided for adaptively equalizing data signals in a communications receiver. An unequalized data signal is demodulated. The demodulated data signal is filtered in an adaptive equalizer that initially updates adaptive filter coefficients using error signals derived from a first algorithm. A carrier lock signal is generated when a phase error of a filtered signal output from the adaptive equalizer reaches a threshold value. The adaptive filter coefficients are updated using error signals derived from a second algorithm instead of the first algorithm in response to the carrier lock signal. The first algorithm is a self-recovering equalization algorithm such as the Constant Modulus Algorithm. The second algorithm can be a decision directed algorithm. Carrier phase is recovered without the use of a phase rotator or phase de-rotator, by locating the adaptive equalizer inside of the carrier recovery loop. The invention is particularly adapted for use in the recovery of multilevel amplitude modulated data, such as QAM data.

Carrier phase recovery for an adaptive equalizer

A two stage accumulator is provided for updating coefficients. The accumulator is particularly useful in an adaptive equalizer. A first stage of the accumulator receives an error word and outputs sign and carry bits resulting from the addition of the error word and an N-bit LSB portion of a larger M-bit coefficient. A second stage is responsive to the sign and carry bits for updating the (M-N) MSB's of the M-bit coefficient. New error words are cyclically provided to the first stage during successive coefficient update cycles. The first stage can be implemented using an N-bit twos complement adder. The second stage can be implemented using an up/down counter. A leakage function is provided by causing the up/down counter to periodically skip over increment and decrement cycles.

Two stage accumulator for use in updating coefficients

Convergence of a complex adaptive equalizer used in digital communications is substantially improved by updating all coefficients of the equalizer during each filter clock cycle. Complex signal data is passed through a plurality of successive delay stages to provide N sets of delayed complex signal data. The product of each set and a complex error signal is obtained. Each product is concurrently updated with previous product data for the set to provide N sets of updated complex coefficients for selective input to equalizer filters. In an illustrated embodiment, the updated coefficients are truncated and their gain is adjusted prior to input to the filters. The updated coefficients can be multiplexed to provide a clocked stream of coefficient sets for input to the equalizer filters. A VLSI implementation of the equalizer is also disclosed.

Method and apparatus for updating coefficients in a complex adaptive

A macroblock packet format is provided for use in a digital HDTV system wherein successive video frames are divided into a plurality of macroblocks. The macroblocks comprise a plurality of superblocks, each containing a plurality of luminance and chrominance video data blocks. A DLEN field is provided in the macroblock packet format to identify the length of the macroblock packet. The packets also include variable length encoded portions of video data. The macroblock packets are transmitted in a data multiplex that also includes a next macroblock position (NMP) word. A receiver compares the DLEN information with the NMP word to verify synchronization, and reacquires the signal if synchronization has been lost.

Digital HDTV data packet format and receiver therefor

An interleaver processes information in a pseudorandom order to provide pseudorandom interleaved data for communication to a deinterleaver. The pseudorandom interleaved data is processed at the deinterleaver in a pseudorandom order corresponding to that used at the interleaver means, to recover the original information. The pseudorandom processing at the deinterleaver is synchronized with the pseudorandom processing at the interleaver on a trial and error basis. In one embodiment, full synchronization occurs when a Viterbi decoder receiving data from the deinterleaver has a renormalization rate within a designated threshold and when enough synchronization words are detected in data output from the deinterleaver to meet a predetermined criterion. In another embodiment, a timer is used to initiate a new starting address for the pseudorandom processing at the deinterleaver during successive time intervals. Synchronization is achieved when a start address is found that results in the detection of enough synchronization words in data output from the deinterleaver to meet a predetermined synchronization criterion.

Method and apparatus for communicating interleaved data

Coded modulation schemes based on codes for QPSK modulation are directly incorporated into QAM based modulation systems, forming trellis coded QAM for communicating information. Concatenated coding with QPSK based trellis coding and symbol error correcting coding is used. In an encoder, an N-bit QAM constellation pattern is divided into four subsets, each including N/4 symbol points of the constellation pattern. A two-bit QPSK codeword is assigned to each of the four subsets. A symbol to be transmitted is first encoded using an outer error correcting encoding algorithm. Part of the symbol is then encoded with an inner code that comprises a rate 1/2 trellis encoding algorithm to provide a QPSK codeword, which is mapped with the remaining bits of the symbol to provide a modulation function. The remaining bits correlate the symbol with one of the symbol points included in the subset defined by the QPSK codeword. A receiver is provided to recover information from the modulation function.

Method and apparatus for communicating digital data using trellis coded

Apparatus is provided for decoding variable length code words to recover transform coefficients, such as DCT transform coefficients provided by a high definition television encoder. A first category of the code words has a length of no more than n bits. A second category has a length of greater than n bits. A feedback ROM is used to decode the code words. Code words from the first category are processed by directly addressing a lookup table in the ROM. Code words from the second category are processed using multiple passes through the ROM, wherein a portion of the data output during a prior pass is fed back to address the memory during a subsequent pass.

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Encinitas, CA, United States of America

Woo H Paik