General Instrument Corporation

Scott A Lery

Woo H Paik

Chris Heegard

John M Fox

Edward A Krause

Adam S Tom

Jerrold A Heller

Allen Wu

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 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

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

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.

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Leucadia, CA, United States of America

Scott A Lery