Schlumberger Technology Corporation

Pacific Communications

Viadux, Inc.

Pacific Communications Sciences, Inc.

Chanchai Poonpol

Michael Andrew Montgomery

Jimmy Everett Neeley

David Lewis Lyon

Seton Paul Kasmir

George M Peponides

Naom Chaplik

Shahin Hedayat

Chun-Meng Su

Mark T Robinson

Michael L Lubin

Surendra Babu Mandava

Kathryn A Kubasak

Gregory A Hein

Donald W Burtis

A hybrid circuit models a plurality of attributes of a communication system including a subscriber line coupled to a line interface circuit. The plurality of attributes includes subscriber line impedance, and impedance of a coupling transformer. The attributes are based on other factors, such as whether or not bridge taps exist at or near the line interface circuit on the subscriber line. The plurality of attributes are modeled by a specific arrangement of resistive and capacitive elements to substantially duplicate the collective transformative effects of the attributes on a transmission signal being sent out on the subscriber line. The transmission signal is transformed and provided to an output, where it is subtracted from a composite signal representing a combination of the actual transformed transmission signal and a receive signal. The subtraction yields an isolated receive signal, which is later processed to recover the full receive signal.

Method and circuit for echo-cancellation in two-way communications

A portable radio telephone handset includes the capability of operating as a data transfer terminal as well as an analog cellular telephone subscriber station. Two modes of operation are available in the handset, an analog cellular communication mode and a Cellular Digital Packet Data (CDPD) mode. A paging function for incoming analog cellular communication is carried out on a CDPD channel. The handset distinguishes between paging signals identifying CDPD mode communications and paging signals identifying analog cellular communications. The handset automatically preempts CDPD communications in favor of analog cellular communications such as those carried out in an AMPS configuration.

Portable communications and data terminal having multiple modes of operation

A method and apparatus for transmitting and receiving acquired digital data over bandpass channels (i.e. channels having a limited range of frequencies) at high data transmission rates. Combined amplitude and phase modulation (quadrature amplitude modulation) is applied to the digital data and the sampled digital waveform converted to an analog waveform for passage over the bandpass channel. The sample rate is chosen as an integer multiple of the symbol rate and carrier frequency to significantly reduce processing overhead. Reception of the acquired data is similar to transmission and involves an analogous amplitude and phase demodulation. The quadrature amplitude modulation technique of the present invention is applied to an oil well-logging application to transmit the data acquired from the downhole logging instruments over the logging cable (bandpass channel) at high transmission rates.

Method and apparatus for transmitting and receiving digital data over a bandpass channel

Method and apparatus for transmitting and receiving digital data over a

For every TDMA block the receiver operation starts with a forward processing procedure and operates on received samples in a first-in first-served order. A sync word detector 32a (see FIG. 4 ) ensures the correct TDMA frame timing and starts the equalizer training. Detected data is stacked in a decision buffer 46. An adaptive equalizer 34a outputs a decision error signal that is used to generate a latch-type loss-of-lock flag. Without loss-of-lock, the receiver works through to the last data symbol and the frame processing is finished. Forward processing is halted and the receiver switches to a backward processing branch if the receiver loses lock midway through the data block. The backward processing branch processes received samples from the input buffer 30 in reverse order. The sync word detector 32b detects the reverse trailing sync word (SYNC #2) and recovers the TDMA symbol timing. The receiver then trains the equalizer and starts data processing in a reverse mode. The detected data is then stacked in the decision buffer 46, starting from Nth symbol. The reverse loss-of-lock detector works the same as the forward loss-of-lock detector, however the control logic is modified such that backward processing works until either detected data overwrites a portion of the forward-processed data, or a loss-of-lock is declared. In the former case, the frame processing is finished. In the latter case, the midpoint between the two loss-of-lock points is calculated and, if needed, both processes are enabled toward the midpoint.

Method and apparatus for reducing multipath distortion

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San Diego, CA, United States of America

Chanchai Poonpol