Abstract: A satellite communications system uses multiple ground stations and one or more satellites for communicating between mobile subscribers and a land-based communications network, such as the PSTN or the Internet. Multiple ground stations geographically dispersed minimize toll charges incurred routing calls from a mobile subscriber through the land network by reducing the need for long-distance calling. Further, because each ground station communicates with a given satellite using the same frequency spectrum, the subscriber capacity of the system increases and/or bandwidth requirements for the communications link between ground stations and satellites may be reduced. The present system uses ground-based beamforming techniques enabling each satellite to transmit signals in multiple transmission beams, each beam supporting one or more mobile subscribers. Each beam may reuse the same frequency spectrum, thereby increasing the number of subscribers supported by each satellite.

Abstract: A wireless communication network processes composite loop-back signals received at one or more network antennas from a plurality of mobile stations, each transmitting an individual, mobile-specific loop-back signal. Using its knowledge of the prior network-transmitted signal(s) from which the mobile stations derive their individual loop-back signals, and its knowledge of the mobile-specific loop-back signal modifications made by each of the mobile stations, the network derives mobile-specific downlink channel information based on processing the composite loop-back signals. That is, use of the mobile-specific loop-back signals enables the network to determine downlink channel estimates as between each participating network antenna and each participating mobile station to be used for transmit signal interference and/or power pre-compensation, for example.

Abstract: A method of determining an encryption key used by two or more parties for encrypted communications in a manner that prohibits any of the parties from forcing the final value of the encryption key. The encryption key is determined based on numbers exchanged by the parties using a key generation function, such as the Diffie-Hellman algorithm. To prevent any party from forcing the final value of the encryption key to a desired value, a first party divides its number into a plurality of parts, which are transmitted incrementally to the another. After transmitting a first part, the first party waits for receipt of at least a part of a second exchanged number from another party before the first party transmits the remaining parts of its exchanged number.

Abstract: The invention comprises using beamforming antenna to coherently transmit an information signal to a receiver using two or more directional beams. In one embodiment, the phase and timing of the information signals carried by each directional beams are adjusted such that the signals arrive synchronously at the mobile terminal. Time synchronization may be obtained by delaying signals transmitted on selected directional beams to compensate for different propagation delays, or by preconditioning and filtering the signals using a channel coefficient matrix.

Abstract: A quartz crystal oscillator comprises a balanced circuit with a quartz crystal resonator device connected in series resonance across a balanced, low-impedance node within a sustaining amplifier. A phase modulator such as a quadrature modulator is included in the feedback loop to allow programming of the loop phase shift thereby to alter the frequency point on the crystal resonance curve at which the circuit oscillates. The in-phase loop signal is hardlimited while the quadrature loop signal component is not hardlimited with the effect that the frequency control curve slope is more accurately defined. An active neutralization of the crystal's parasitic shunt capacitance is disclosed for obtaining a linear frequency control curve.

Abstract: A method for bilateral identity authentication over a communication channel provides a secure method for authenticating the identity of the communicating parties and establishing a secret key. Each party computes an authentication challenge based on an exchanged value used in a key generation procedure. The authentication challenge is encrypted to the other party's public key. After receiving an encrypted authentication channel from the other party, each party deciphers the authentication challenge and generates an authentication response based on the authentication challenge. The authentication response includes bits that the challenging party cannot predict in advance to prevent fraudulent use of the authentication response by the challenging party or some other third party. After receiving an authentication response from the other party, each party verifies that the expected authentication response was received.

Abstract: A method and system for performing cryptographic calculations on a bitstring using secret information. A cipher key is manipulated to obtain a modified cipher key. An indicator word is generated that corresponds to the modified cipher key and includes a plurality of indicator bits. A first product is computed with an insecure processor as a function of the bitstring and the modified cipher key. A second product is computed with a secure processor as a function of the bitstring and the indicator. A final product is then computed as a function of the first and second products.

Abstract: Quadrature modulators include a quadrature splitter and a pair of Gilbert Multiplier Cells coupled to the quadrature splitter, each of which is biased in Class-B. The quiescent current bias in the Gilbert Multiplier Cells may be substantially zero. Each of the Gilbert Multiplier Cells may include a pair of cross-coupled, emitter-coupled transistor pairs transistor pairs and a driver circuit that is coupled to at least one of the emitter-coupled transistor pairs and that is biased in Class-B. The driver circuit may include at least one current mirror circuit that is coupled to at least one of the emitter-coupled transistor pairs. The driver circuit also may include at least one current source that selectively applies current to at least one of the emitter-coupled transistor pairs, more specifically by selectively applying current to the at least one current mirror circuit.

Abstract: An improved satellite communications system allows for greater spectral efficiency by requiring just two frequencies for wireless communications between a first ground-based station and a second ground-based station via a satellite. Both the first station and the second station use the first frequency to transmit signals to the satellite; the satellite transponds the signals it receives on the first frequency to the second frequency and transmits the signals to the first and second stations on the second frequency. Use of two frequencies in such a manner results in some own-signal interference. The first station preferably stores its outgoing signals in memory and then subtracts out these stored signals to eliminate the its own-signal interference. The second station may likewise store and subtract out its transmissions, but this is not required.

Abstract: A receiver receives communication signals on an assigned frequency channel while monitoring the signals received on other frequency channels. A communication processor processes the received communication signals from the current base station while a wideband digitizer processes received filtered signals on the other frequency channels, which correspond to the neighboring base stations. The wideband digitizer generates numerical samples representing the filtered signals in response to a control signal generated by a control processor. The control processor then determines characteristic signals of the frequency channels.

Abstract: According to the exemplary embodiments, a voltage or current-controlled oscillator is controlled in frequency by the signal (i.e., voltage or current) from a microphone. The frequency modulated signal is applied to a direct digital discriminator that produces a digital representation of the instantaneous frequency at the desired speech sampling rate. The digital discriminator may be formed, for example, by applying the oscillator signal to a direct phase digitizing circuit along with a reference frequency and calculating a sequence of instantaneous phases of the oscillator relative to the reference frequency. The phase sequence is then applied to a digital phase locked loop (or otherwise numerically differentiated) to generate a sequence of binary words representative of instantaneous frequency and therefore representative of the speech waveform.

Abstract: A quartz crystal oscillator comprises a balanced circuit with a quartz crystal resonator device connected in series resonance across a balanced, low-impedance node within a sustaining amplifier. A phase modulator such as a quadrature modulator is included in the feedback loop to allow programming of the loop phase shift thereby to alter the frequency point on the crystal resonance curve at which the circuit oscillates. The in-phase loop signal is hardlimited while the quadrature loop signal component is not hardlimited with the effect that the frequency control curve slope is more accurately defined. An active neutralization of the crystal's parasitic shunt capacitance is disclosed for obtaining a linear frequency control curve.

Abstract: A transceiver for a code division multiple access communication system comprises a receiver to receive coded information signals and a transmitter to transmit coded information signals. A local oscillator provides a time and frequency reference for the receiver and the transmitter. A timing controller provides timing signals for the receiver and the transmitter. A signal processor decodes received signals to determine a common error associated with the timing controller. A timing correction circuit smoothly adjusts the timing of the coded information signals transmitted by the transmitter responsive to the timing error to reduce the timing error over a desired time interval.

Abstract: A system and method for sequence estimation decoding allows a receiver to decode a received signal modulated according to one of plurality of possible modulating methods. In a preferred approach, a sequence estimation decoder detects the modulating method that was applied to the received signal, and adjusts its decoding process accordingly. In this manner, the decoder adjusts its operations to the specific one of the plurality of possible modulating methods used by the transmitting system originating the received signal. In an exemplary application, signals are modulated using either Gaussian Minimum Shift Keying (GMSK) or Offset Quadrature Amplitude Modulation (Offset-QAM), and the decoder adjusts its operations to either one of these modulating methods based on its detection of the particular method used.

Abstract: A method and apparatus is described for transforming a key variable used for scrambling mobile data traffic between a terminal and a network in alternate ways based on a value transmitted to the terminal from the network. Transformation is accomplished by passing portions of the key variable through a series of S-boxes, which provide a mapping between inputs and outputs. The method and apparatus is explained also in the context of a satellite communications system, in which a terminal can be located in a different continent/country from the terminal's home location. Enciphered communication is enabled between the foreign satellite gateway and the roaming terminal after the foreign gateway communicates with the terminal's native gateway. The native gateway transmits one or more cipher variables in the communication. Moreover, the value determining which way to cipher the data traffic can be based on numerous factors, including aspects of the satellite communication system.

Abstract: Exemplary embodiments of the present invention describe terminal position location methods and systems. Relative powers of nearby spot beams which are generated by array antennas are determined. For example, powers from six neighboring spot beams relative to a center spot beam within which a mobile station is currently operating, can be measured relative to the power of the center spot beam. Using information from these measurements, the mobile stations position can be determined using, for example, an exponential model of the spot beam pattern.

Abstract: In CDMA systems, a message to be transmitted is redundantly coded for transmission using a combination of error-correction coding and a spread-spectrum access code. The coded message is modulated to a first radio frequency channel, or band, and also to at least one other frequency channel, which may be either an adjacent or a non-adjacent channel. Other messages for transmission are generated likewise and the signals for transmission on the first channel are summed using a set of weighting factors, with the weighted sum transmitted on the first channel. The same signals are summed for transmission on the at least one other frequency channel, but using weighting factors that have a progressive relative phase rotation compared to their Values on the first channel. The sequence of weighting factors used for one signal across the different frequency channels is preferably orthogonal to the sequence of weighting factors used for a different signal.

Abstract: Methods and systems for time synchronizing a receiver to a spread spectrum signal are described. Exemplary embodiments of the present invention provide for at least a two step process in which, at a first step, a number of candidate synchronization frequencies or timings are identified, followed by confirming one of the candidates as a correct synchronization state at a second or final step. According to the present invention, the confirmation step may be performed at the same time as the step of identifying further candidates by processing the same received signal samples in different ways.

Abstract: A method and system for the transmission, reception, and processing of 4-level and 8-level signaling symbols is provided. An inventive modulator is provided for modulating 4-level signaling symbols using an 8-level modulator. Further, this inventive modulator is able to produce 4-level modulation when modulating 4-level signaling symbols using an 8-level modulator, where the 4-level modulation represents the 4-level symbol sequence modulated. Further, a constrained/unconstrained demodulator is provided which is able to demodulate both 4-level signaling symbols and 8-level signaling symbols. The inventive demodulator accomplishes this by limiting the number of new symbol hypotheses and path histories to 4 when working with 4-level signaling symbols, and setting the number of new symbol hypotheses and path histories to 8 when working with 8-level signaling symbols.

Abstract: Methods and systems for amplitude-modulating a power amplifier based on sensed current and sensed voltage provided to the power amplifier are provided. The sensed current and sensed voltage may be summed to provided both current and voltage feedback to modulate the power supplied to the power amplifier. Alternatively, both the current feedback and the voltage feedback may be selectively utilized to modulate the power supplied to the power amplifier.