Abstract: A radiocommunication system and method using a combination of a geostationary (GEO) and a plurality of medium earth orbit (MEO) satellites are disclosed. First, a GEO satellite is launched to provide initial system capacity. Next, MEO satellites are successively launched into positions where they can supplement the coverage of the GEO satellite during peak traffic hours. Finally, when a sufficient number of MEO satellites are in place, the GEO satellite can provide the supplementary capacity.

Abstract: A conductive strap configured to attach to a circuit board containing a component sensitive to electronmagnetic interference (EMI) and to slidably contact an enclosure having a conductive internal surface can reduce or eliminate EMI in an electronic device. The strap is positioned on the circuit board to shield the sensitive component from EMI. Slidable contact between the shielding strap and the enclosure internal surface renders the strap suitable for almost any enclosure configuration without any design modification.

Abstract: A device and method for receiving and reconstructing signals with improved perceived signal quality in a digital communications system is disclosed. The device and method utilize side information defining the quality or accuracy of recovered digital symbols representing an information signal and also utilizing past frame erasure information to determine whether to erase or use a frame to reconstruct the original information signal even though an error detection mechanism indicates that no error exists in the recovered digital symbols of the frame.

Abstract: A conductive strap configured to attach to a circuit board containing a component sensitive to electronmagnetic interference (EMI) and to slidably contact an enclosure having a conductive internal surface can reduce or eliminate EMI in an electronic device. The strap is positioned on the circuit board to shield the sensitive component from EMI. Slidable contact between the shielding strap and the enclosure internal surface renders the strap suitable for almost any enclosure configuration without any design modification.

Abstract: In a trunked communications network, a multiple site information distribution control "switch" (multisite switch) provides access to digitized audio and control signals from various audio sources to one or more audio destinations connected at various "nodes" in the multisite switch. A dedicated Network Interface Module (NIM) is provided in the multisite switch to facilitate interconnection and communication between multiple networks of similar multisite switch controlled architectures to create an "extended" mega-network. The NIM allows an entire remote network to appear as a just another multisite switch node in a local network and vice versa. A trunked communications network having a NIM can communicate through this "node" with other networks having a NIM, thus establishing inter-network communications in a manner that is essentially transparent to users in either network.

Abstract: A distributed trunked radio frequency (RF) switching network (multisite switch) distributes audio routing control information and digitized audio signals to communications interface modules (nodes) throughout the multisite switch, thus avoiding a centralized mixing matrix, increasing fault tolerance and providing low routing request latency time. Each audio source, (for example, RF repeater transmitter, dispatch console microphone) is preassigned an audio channel on a time division multiplexed (TDM) digitized "audio network" or bus within the switch. The audio sources continually provide digitized audio signals to all other nodes within the switch over the assigned TDM bus channels. Audio routing is performed at the audio destinations (for example, interface modules/nodes associated with RF repeater receivers, dispatch console speakers) by selectively "listening" to active TDM network channels.

Abstract: A digital radio communication system achieves low envelope variations in a transmitted signal by encoding digital information as phase angle differences in a transmitted radio signal and by constraining the maximum possible phase angle difference. This reduction in envelope variation relaxes the linearity requirements for a desired level of distortion suppression of a radio frequency (RF) amplifier means employed for transmitting the radio signal. In addition, lower envelope variations imply a higher average transmit power for a given maximum transmitted power, thereby extending range and battery life.

Abstract: A new digital radio includes codec, vocoder and encryption/decryption processing all on a single integrated circuit chip module. Great flexibility is provided in terms of different operating modes (e.g., encrypt/decrypt only, vocode only, or encrypt/decrypt and vocode). Radio control processor overhead is reduced substantially, because the radio control processor does not need to transfer data between codec, vocoder and encryption/decryption processes and/or components. An internal executive routine within the module handles all vocoder and encryption command and data processing. A special synchronization scheme is provided to synchronize the transceiver modem rate with the speech processing rate. The single-chip speech processing module is sufficiently flexible to allow users to define, write, load and use their own encryption/decryption routines without requiring a new masked ROM.

Abstract: In a digital data decoder such as a Viterbi algorithm decoder, digital data transmitted over a communications channel are estimated by a receiver using a variable decision depth technique to thereby improve bit error rate (BER) and channel estimation and to reduce decision delay. In the context of conventional trellis structures used for sequence estimation, the decoder assigns group flags to each state for each time interval being considered and stores those group flags along with corresponding accumulated path metrics associated with the states. More specifically, from a just decoded state, flags from different groups, e.g. each group representing a color, number, etc., are assigned to successor states connected by a survivor path to the just decoded state. Each offspring state of a parent state is assigned the parent's group flag. The decoder detects where in the trellis all of the survivor states have the same group flag.

Abstract: A radio communications system includes plural radios with each radio having a microprocessor, a modem, and corresponding automatic number identification (ANI) information as well as a predetermined pattern of tones or digital codes corresponding to a particular radio frequency channel stored in memory. For each transmission, the radio microprocessor encodes the corresponding radio identification data that provides the encoded radio identification data to the radio modem in parallel format. The radio modem converts the encoded identification data into a serial data stream at the same time that the microprocessor is generating the predetermined pattern of tones or digital codes. Thereafter, the generated pattern of tones or digital codes is combined with the serial data stream and simultaneously transmitted over the transmission radio frequency channel.

Abstract: A radio receiver for demodulating and equalizing digital information is disclosed. The receiver receives radio signals and processes the signals to produce data samples which are then stored. Reference values that model what the receiver should receive for various transmitted symbol sequence hypotheses are also stored. The receiver equalizes the received data using the stored reference values to produce symbol detection information, and updates the reference values based on the symbol detection information.

Abstract: An amplifying apparatus for linearly amplifying a desired signal using a pair of coupled non-linear amplifiers is disclosed. The amplifying apparatus comprises a limiter for separating amplitude variations from the desired signal and producing a constant amplitude signal bearing the phase of the desired signal and an amplitude related signal. In addition, a drive signal generater produces two drive signals each dependent on the constant amplitude signal and the amplitude related signal such that each drive signal depends on the phase of the desired signal and such that the sum of the squares of the amplitudes of the drive signals is constant. Finally, a coupler couples the two drive signals to produce two constant amplitude signals for driving the pair of non-linear power amplifiers and for coupling the outputs of the power amplifiers to produce two amplified output signals, one of which is the linearly amplified desired signal and the other of which is a waste energy signal.

Abstract: Demodulation of a CDMA downlink signal is performed by filtering correlations of the received signal with a known signature sequence. Unlike the conventional RAKE receiver, the filtering is not necessarily a FIR filter with coefficients equal to the conjugates of channel tap estimates. Instead, the present invention filters in such a way as to maximize the output signal-to-noise ratio, accounting for the fact that part of the noise comes from the same base station as the signal, so that it is colored by the same channel as the signal.

Abstract: A power amplifier circuit for efficiently generating an output signal into a load at more than one alternative power level has at least two amplifiers, each having optimum efficiency at different power output levels. The power amplifier circuit may be operated in several modes, including activating one amplifier during an entire cycle of an input signal to be amplified, or alternatively activating one amplifier based on a control signal that is independent of the amplified output signal. In either case, remaining amplifiers are deactivated. Coupling between the amplifiers prevents deactivated amplifiers from impeding the flow of power from the activated amplifier to the load. In another aspect of the invention, optimum efficiency at different power output levels is achieved by means of coupling each amplifier to a common power source and to the load via an impedance matching circuit, the impedance transformation being different for different amplifiers.

Abstract: A retractable key assembly comprising a key top and an externally extending pivot arm. The pivot arm allows arcuate movement of the key top about a pivot axis such that the key top can be used in an upper, active keying position or stored in a lower, inactive position. The use of a pivot arm enables a lower profile keyboard when the keyboard is in the retracted, inactive position. Displacement of the internal actuation assembly allows the keytop to actually rest on the keyboard base. A translatable base member is useful to raise or retract the key assembly. The disclosed key assembly provides an aesthetic appearance and improved keying accuracy, relative to conventional keyboard arrangements.

Abstract: A method for demodulating or decoding a digitally modulated data signal is disclosed wherein AGC parameters are retain and update or discard in parallel with deciding the data patterns most likely to have been transmitted. First, the received signals are converted from analog to digital to obtain numerical signal samples. The numerical signal samples are then compared with sample values expected for each of a number of possible symbol sequences using a scaling factor associated with each of the symbol sequences in order to determine a mismatch value for each sequence. The mismatch values are then logically self-consistent. Then, the lowest cumulative mismatch value is chosen from among all the foregoing sequences that can logically precede a new sequence to be accumulated with the mismatch value from the new sequence, wherein the selected mismatch identifies a best predecessor sequence.

Abstract: In half-duplex, trunked digitized voice communications between mobile transceivers, the present invention minimizes time delays occurring after one transceiver ends a transmission and before other transceiver communications may commence. A disconnect signal is transmitted from the currently transmitting transceiver during a time frame immediately following indication that a current communication has ended. Channel access time delays are minimized by permitting speech input to a transmitting transceiver immediately upon receipt of a working communications channel. The present invention has particular applicability in trunked TDMA radio communication systems.

Abstract: An amplifying apparatus for linearly amplifying a desired signal using a pair of coupled non-linear amplifiers is disclosed. The amplifying apparatus comprises a limiter for separating amplitude variations from the desired signal and producing a constant amplitude signal bearing the phase of the desired signal and an amplitude related signal. In addition, a drive signal generater produces two drive signals each dependent on the constant amplitude signal and the amplitude related signal such that each drive signal depends on the phase of the desired signal and such that the sum of the squares of the amplitudes of the drive signals is constant. Finally, a coupler couples the two drive signals to produce two constant amplitude signals for driving the pair of non-linear power amplifiers and for coupling the outputs of the power amplifiers to produce two amplified output signals, one of which is the linearly amplified desired signal and the other of which is a waste energy signal.

Abstract: A radio access method for facilitating communication between at least one first station and a plurality of second stations is disclosed. First, each signal intended for transmission is buffered at a first station. The signals are then divided into equal length segments. The signal segments intended for a particular one of the second stations is transmitted using a corresponding time slot in a regularly repeating time multiplex frame. The signal segments transmitted by the first station are received at at least one of the second stations and the signal segments are assembled from successive corresponding time slots to reconstruct said intended signal. A transmit frequency channel uniquely associated with the corresponding receive time slot is determined at the second station.

Abstract: A demodulator for demodulating a signal modulated with digital information symbols so as to extract the information symbols is disclosed. A receiver receives a signal over a communications channel and samplers and digitizers produce a sequence of numerical sample values representative of the received signal. Memories are provided each having a number of state memories each associated with a hypothesized symbol string. A controller selectively retrieves values from the memory means and controls the timing of operations thereupon. A metric computer computes candidate metrics using a hypothesis of a next of the information symbols to be demodulated made by the controller, one of the numerical sample values, path metric values, B-matrices, and U-vectors and the candidate metrics associated state number selected by the controller from the memory means.