Motorola Corporation

Eric F Ziolko

Michael W Bright

Alan L Wilson

David L Weiss

Gary W Grube

Robert J Novorita

Michelle M Bray

Harry A Hennen

Michael D Kotzin

Bradley Michael Hiben

Mark Conrad Cudak

Steven C Jasper

Larry C Puhl

Scott James Pappas

Ezzat A Dabbish

Tim A Williams

Kenneth J Zdunek

Paul M Bocci

Daniel P Brown

John Paul Byrns

Michael J McClaughry

A method and apparatus for reducing echo feedback in a wireless communication system () is accomplished when a receiving communication unit () senses a feedback signal, or echo, via an ancillary communication path. The receiving communication unit is a targeted recipient of an original audio signal generated by a transmitting communication unit (), where the original audio signal () is conveyed to the receiving communication unit. Upon detecting the feedback signal and determining that it exceeds a feedback threshold, the receiving communication unit attenuates an audible output of the original signal to reduce echo to the transmitting communication unit. In addition, the receiving communication unit, and/or the transmitting communication unit include echo canceller to further minimize the echo within the digital communication system.

Method and apparatus for reducing echo feedback in a communication system

A method and apparatus for reducing echo feedback in a wireless communication system ( ) is accomplished when a receiving communication unit ( ) senses a feedback signal, or echo, via an ancillary communication path. The receiving communication unit is a targeted recipient of an original audio signal generated by a transmitting communication unit ( ), where the original audio signal ( ) is conveyed to the receiving communication unit. Upon detecting the feedback signal and determining that it exceeds a feedback threshold, the receiving communication unit attenuates an audible output of the original signal to reduce echo to the transmitting communication unit. In addition, the receiving communication unit, and/or the transmitting communication unit include echo canceller to further minimize the echo within the digital communication system.

An apparatus and method for indicating sources of high error conditions, including out-of-range and interference conditions, to a user of a digital voice communication system. When the vocoder ( ) of a communication unit ( ) silences due to high error conditions, a source of the high error conditions (e.g., out-of-range or interference) is determined based on the signal strength, and a source indicator ( ) is generated to inform the user of the source of the high error conditions. In one embodiment, where a repeater ( ) is used, sources of high error conditions are detected both inbound to and outbound from the repeater. In an event of high error conditions on the inbound signal path ( ), the repeater puts out a distinctive erasure ( ) identifying the source. The communication unit ( ) detects the erasure and generates a source indicator associated with the erasure. In the event of high error conditions on the outbound signal path, the communication unit determines the source based on the signal strength and generates an appropriate source indicator. By using distinctive source indicators ( ), the communication unit thereby informs the user of error conditions on the inbound or outbound path from the repeater.

Differentiation of error conditions in digital voice communication systems

Group communications between subscribers (20, 22) affiliated with a terrestrial communication system (12, 14) and subscribers (46, 48) affiliated with a satellite communication system (10) is begun when a subscriber has initiated a group communication request. The request is provided, via a controller (i.e., a terrestrial system controller or satellite system controller depending on which communication system the requesting subscriber is affiliated with), to a systems interface (36). Upon receiving the request, the systems interface determines whether subscribers that are identified to participate in the group communication are located in the terrestrial system and/or the satellite system. If the group of subscribers have members in both communication systems, the systems interface establishes satellite communication links for each subscriber affiliated with the satellite communication system and establishes a terrestrial communication link for subscribers affiliated with a terrestrial communication system. Once the communication links are established, the systems interface arbitrates transmissions of the group of subscribers. The arbitration of transmissions insures that each subscriber in the group of subscribers receives the transmission.

Method and apparatus for establishing group communications between

An apparatus for and method of correcting errors in a received signal comprised of a rate-one orthogonal convolutional code generated by an LFSR involved feeding (403) a received signal into a multiple-stage shift register (201). Estimates of one of the stages of the shift register are performed by estimators (203, 205, 207, 209, 211, 213, and 215) and are based on the outputs of several of the other stages of the shift register (201). These estimates are combined on a bit-by-bit basis to provide a corrected received signal, which is used as the output of the shift register (201).

Method and apparatus for correcting errors using multiple estimates

A transceiver compatible with both wide channel constant envelope 4 level FSK FM modulation and narrow channel .pi./4 differential QPSK linear modulation allows compatible interaction between modified constant envelope and non-constant envelope transmitters. All Nyquist filtering occurs in the transmitters, and none in the receiver.

Multi-modulation scheme compatible radio

A cryptographic apparatus for encrypting and decrypting digital words includes a mechanism that permits a cipher algorithm to be electronically stored after the manufacture of the apparatus. The storing mechanism includes at least one electrically erasable, programmable gate array containing a portion of the cipher algorithm and at least one random access memory device coupled to the array for storing digital data generated by the algorithm. A mechanism which is coupled to the gate array and memory device controls the execution of the algorithm for each digital word thereby decrypting encrypted digital words and encrypting non-encrypted digital words.

Cryptographic method and apparatus with electronically redefinable

Disclosed is a method and apparatus for time companding a digital voice signal wherein, single bits are periodically removed from the digital voice signal, which is then compressed thereby forming a contiguous area of removed bits. A synchronization signal is inserted into this area and the combined signal is transmitted. At the receiver, the synchronization signal is extracted and is used to synchronize the receiver. The digital voice signal is then expanded and the removed bits are predicted and replaced.

Method and apparatus for time companding a digital voice signal

Disclosed is a synchronous secure communication system wherein an information signal is encrypted in an encryption means. The encrypted signal is compressed to allow the insertion of a synchronization signal, and the combined signals are transmitted. At the receiver, the synchronization signal is extracted and used to synchronize the receiver to the incoming data stream thereby improving receiver sensitivity and range.

Secure communication system

A trunked communications system that accommodates encrypted secure communications. The system uses both non-encrypted message detectors and encrypted message detectors to assure that the trunked central control unit receives the signals it must receive in order to properly allocate and maintain channel assignments.

Secure trunked communications system

A synchronization detector is disclosed wherein a portion of the received data stream is parallel loaded into a sequence generating means. The sequence generating means provides a local synchronization sequence that is compared to the transmitted synchronization signal, and an error count is tallied. If the number of errors occurring in a predetermined 'window' is below a predetermined threshold, a synchronization detect signal is asserted. However, if the errors in a predetermined window exceed the threshold, the sequence generating means is reloaded with another portion of the received data stream and the process is repeated until the synchronization detect signal is asserted.

Method and apparatus to detect and recover a pseudo-random sequence

A detector locates a shift register sequence within a digital data stream by correlating the data stream with a sequence generated locally from a portion of the data stream. Error correction circuitry estimates errors that may have corrupted the sequence during transmission across a noisy channel and corrects them to the extent possible. The data stream and local sequence are correlated during an interval that is shifted either ahead or behind the portion of the error-corrected data stream used to initialize the local sequence generator, thereby avoiding the region during which short-term correlation between the data stream and local sequence would otherwise cause false indications of detection when only noise or random data is being received.

Linear feedback sequence detection with error correction

Disclosed is an error corrector for a linear feedback shift register sequence employing an open loop linear feedback shift register (LFSR) having selected bits 'tapped' and combined to form a feedback signal. The taps implement an orthogonal convolutional code that is inherently redundant, therefore, the transmission of parity bits is not required. The feedback signal is combined with the received synchronization signal to form an error estimate that is temporarily stored in a syndrome register. By majority voting a selected outputs of the syndrome register a reliable determination of a received error can be made. Once an error determination is made, a correction signal is generated to correct the bit in error thereby providing a high probability of initiating and maintaining synchronization.

Error corrector for a linear feedback shift register sequence

CVSD modulation is detected by applying a digital signal containing CVSD information to a digital filter that is in the CVSD loop that includes a syllabic filter and a rule circuit. The digital filter includes voltage-operated switches that switch one of two voltages to a resistor network and thereby combine multiplication and digital filtering. The output of the digital filter is the output of the circuit.

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Schaumburg, IL, United States of America

Eric F Ziolko