Motorola Corporation

David L Weiss

Eric F Ziolko

Michael W Bright

Scott James Pappas

Alan L Wilson

Michelle M Bray

Tim A Williams

Kevin M Cutts

Robert J Locascio

Richard H Coe

Harry A Hennen

Daniel J McQuade

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

In a receiver (100), an encrypted communication (104) is decrypted using a decryptor (101) and a key (107) to produce a decrypted communication (105). A comparator (103) compares decrypted symbol patterns in the decrypted communication against a set of predetermined symbol patterns (108). When the decrypted symbol patterns are distributed non-uniformly relative to the set of predetermined symbol patterns, the receiver is identified as a target of the encrypted communication.

Method and apparatus for detecting correctly decrypted communications

A key management system for encryption keys removes the effect of secure communications loss during a rekey period in a secure communications system. Use of key indexes to partition encryption keys into usable subgroups such that during a rekey period, continuous secure communications are maintained throughout the entire secure communications system.

Key management in encryption systems

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

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.

Receiver for CVSD modulation with integral filtering

A digital voice privacy electronic communication system and method provides protection for an information signal. Either a clear voice signal or a scrambled digitized version of the voice signal is selected for transmission. At the receive end of the system a determination that a clear voice signal or a scrambled signal has been sent is made. This information is used to automatically switch the clear audio signal if present to an output circuit or to switch to the output circuit either a regenerated version of the scrambled signal or an unscrambled version of the information signal. The switching is done automatically so that a user does not have to manually select the proper receiver mode in response to reception of a signal, that is, whether the received signal was a clear voice signal or a scrambled signal. At the transmitter the information signal to be scrambled is analog-to-digital converted and the digital signal is then put into a scrambled form. The scrambled signal may be then processed through base stations, repeaters, satellite receivers, etc., while still in the digitally scrambled form, thereby providing a high degree of protection for such a signal. A receiver may regenerate, or reshape, the scrambled digital signals or the signal may be unscrambled in the receiver depending upon whether the receiver is part of, for example, a repeater system or is a terminal destination for the signal. The digital privacy system of this invention may also be utilized in signal voting systems, either analog or digital, while still maintaining, if necessary, the secure format of the scrambled information.

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Roselle, IL, United States of America

David L Weiss