Abstract: A decoding system discriminates between different types of communications traffic signals. Each type of traffic signal is encoded using a different error correction code. Plural, parallel decoders each decode a received traffic signal using a different decoding technique. Each decoding technique operates in accordance with one of the error correction codes. A quantitative measurement of the reliability of a decoded result is generated by each decoder. A comparison processor accumulates the quantitative measurements made by each decoder and compares the accumulated values. That decoder having the most reliable, accumulated value is selected to decode the current traffic signals. The remaining decoders are deactivated to conserve processing time.

Abstract: In a phase digitizer for converting phase information of an analog signal into a digital representation, a phase accumulator stores incremental phase angle values of a reference signal. A trigger circuit which is responsive to an input signal and a sample signal generates a strobe signal which causes the incremental phase angle value stored in the phase accumulator to be transferred to a holding latch. The value of the holding latch is then transferred to an output latch which provides a digital representation of the phase angle of the input signal.

Abstract: Subtractive CDMA demodulation optimally decodes a coded information signal embedded in many other overlapping signals making up a received, composite signal. A radio receiver correlates a unique code corresponding to the desired signal to be decoded with the composite signal. Moreover, after each information signal is successfully decoded, it is recoded and removed from the composite signal. Subtractive CDMA demodulation is enhanced by decoding the composite signal in the order of strongest to weakest signal strength. The individual information signals are spread using block error correction codes which are correlated with the composite signal using Fast Walsh transforms. Correlated signals identified as the largest transform component are removed from the composite signal and the remaining composite signal is reformulated using an inverted Fast Walsh transform.

Abstract: An electronic comparator for selecting and outputting the larger of first and second electrical, binary-coded input values presented bit-serially, most-significant-bit first, has first and second input terminals; a logical exclusive-OR gate; a first resettable flip-flop; a second flip-flop; and a device for selecting one of the input values as an output of the comparator. In a second embodiment, the electronic comparator has first and second input terminals; a logical exclusive-OR gate; a first flip-flop synchronized with a train of bitclock pulses; a second resettable flip-flop; a third flip-flop; and a device for selecting one of the input values as an output of the comparator. Devices for generating traceback signals indicating which input values were selected and a signal indicating that the maximum value has been identified are also disclosed.

Abstract: In a radio communication system such as a cellular telephone system having battery powered mobile stations which receive radio frequency signals, an amplifier in the receiver of the mobile station is operated in a plurality of different modes in order to reduce power consumption. The modes of the amplifier depend upon the strength of the incoming signal and whether the transmitter is transmitting. The receiver is also periodically disconnected from the battery in order to further reduce power consumption.

Abstract: In a cellular telephone of the type capable of operating in both analog and digital modes, a power amplifier is provided which can operate efficiently in both the analog and digital modes of operation. The power amplifier includes a non-linear power amplifier stage and a linear power amplifier stage which are controlled by a switching means. During the analog mode of operation, the switching means causes the non-linear amplifier stage to amplify the RF signals. During the digital mode of operation, the non-linear amplifier amplifies the RF signal when there is a requirement for a relatively low power output. During the digital mode when there is a requirement for a relatively high level output, the switching means causes the non-linear power stage and the linear power stage to amplify the RF signals.

Abstract: Substractive CDMA demodulation optimally decodes a coded information signal embedded in may other overlapping signals making up a received, composite signal. A radio receiver correlates a unique code corresponding to the desired signal to be decoded with the composite signal. Moreover, after each information signal is successfully decoded, it is recoded and removed from the composite signal. As a result, subsequent correlations are performed with greater accuracy. Substractive CDMA demodulation is enhanced by decoding the composite signal in the order of strongest to weakest signal strength. Interference caused by the presence of the strongest information signal and the composite signal during the decoding of weaker signals is removed. The individual information signals are assigned a unique block error correction code with is correlated with the composite signal using Fast Walsh transforms. Correlated signals are recoded using inverted Fast Walsh transforms and removed from the composite signal.

Abstract: A system for generating a pseudo-random bit sequence which may be used in enciphering digital data prior to transmission or storage of the data. The bit sequence is generated by expanding a plurality of secret key bits in a manner suitable for implementation with a conventional microprocessor arithmetic logic unit (ALU). The system of the present invention may be used, for example, to secure voice or data communications between a base station and a mobile station in a digital cellular communications system.

Abstract: A radio transceiver comprising a housing including a front cover, a plurality of interchangeable control panels adapted for selective alternative attachment to the front cover, and a plurality of interchangeable keypads adapted for selective alternative attachment to the front cover in underlying relationship with a respective one of the control panels, wherein each control panel is configured for use with a similarly configured one of the keypads. Each of the control panels comprises a relatively thin planar member having front and rear faces and defined by upper, lower and a pair of side edges, and includes a projection or locking bar extending along and away from the upper edge, and fastening means located adjacent the lower edge. A standardized electronic circuit board is provided within the unit, some or all of the switches included on the circuit being accessible, depending on the particular keypad and control panel employed.

Abstract: A system for adjusting the frequency of transmissions between a base station and a mobile station. The mobile station detects the frequency of the signal received from the base station, determines whether the signal was received from the current base station and adjusts the output signal of a local crystal-controlled reference oscillator in accordance with the difference between the frequency of the output signal and the frequency of the received signal.

Abstract: A system for the authentication of mobile stations and base stations in a cellular communications network. The system includes an algorithm which generates not only a key dependent response to a random challenge, but also a temporary conversation key or call variable which may be used to encipher traffic in the network. To protect against clones in the network, the algorithm uses a rolling key which contains historical information. A bilateral authentication procedure may be used to update the rolling key and to generate a new conversation key.

Abstract: A system for the synchronization of encryption and decryption in a duplex cellular radio system in which an encrypted call may be switched from one cell to another. At the instant of handoff, a rapid first resynchronization means temporarily seizes the voice channel in one direction only and transmits synchronization information in such one direction. The first resynchronization means ceases to transmit the synchronization information and releases such one direction of the voice channel as soon as an indicator of successful resynchronization is detected in the other direction. Transmission of speech traffic in such one direction is then resumed after such detection of successful resynchronization.

Abstract: In a phase locked loop having a variable divider, a dual modulus counter is used to provide the variable divider with selection signals. The variable divider is capable of providing an overall division ratio in increments of one over a contiguous range of values. The dual modulus counter includes a counter, a comparator and logic gates which generate selection signals that allow the variable divider to divide an input signal by at least division ratios R1 and R2. A phase locked loop utilizing the dual modulus counter is particularly well suited for use in a digital frequency synthesizer.

Abstract: A system for the synchronization of encryption devices in a digital cellular communications system. Each of the encryption devices includes a multi-bit counter and generates a pseudo-random keystream which is combined with the data to be encrypted. The keystream is a function of the multi-bit counter value which is periodically incremented in response to a series of clock pulses. To allow proper decryption of the encrypted data, the system of the present invention provides continuous or very frequent updates of the transmitter counter value which may be used to reset the receiver counter and to resynchronize the system without the necessity of reinitialization and repetition of the intervening clock pulses.