Abstract: Multipath delay estimation of a direct sequence spread spectrum (DS-SS) signal transmitted in a multipath fading channel is accomplished by measuring the envelope of the signal to determine a new delay estimate. Delay estimates are also obtained in ray strength order, by subtracting out the influence of the stronger rays on the weaker ones. This subtraction approach can be performed iteratively, allowing further refinement of the delay estimates. Delay estimates can also be determined by minimizing the mean square error (MSE) between a measured correlation function and a modeled correlation function. The minimum mean square error (MMSE) approach can performed iteratively, to further refine the delay estimates. Maximum likelihood (ML) delay estimates can also be obtained by exploiting side information regarding the transmit and receive pulse shapes.

Abstract: A universal four-contact plug and jack assembly permits interconnection of microphone and stereo audio signals between an audio peripheral incorporating the four-contact plug and an audio device that includes the four-contact jack. Dimensionally, the interconnecting segments of the four-contact plug are, in terms of overall length, consistent with standard three-contact audio plugs which allows the four-contact plug to be plugged into a three-contact jack intended for use with conventional three-contact audio plugs. Similarly, the four-contact jack has three of its contacts positioned as a conventional three-contact jack but with a fourth contact position to interconnect with the additional contact of four-contact plugs. With this configuration, an audio device including the four-contact plug is compatible with audio peripherals including stereo headsets, monaural headsets with microphones, and others.

Abstract: A radio communication system includes a base station having a directional antenna for generating a plurality of beams. A first set of the beams is used to receive signals which are decoded at the base station. A second set of the beams is used for interrogating a cell to identify beams which should be added to the first set of beams (for example, in response to mobile terminals entering the cell). In one embodiment, the second set of beams comprises a plurality of searcher beams produced by a fixed-beam phased array antenna. In a second embodiment, the second set of beams comprises a single searcher beam which is scanned through the cell by an adaptive phased array antenna. The radio communication system can be used to communicate with indoor mobile terminals through a plurality of radio heads, and also can be used to communicate with orbiting satellites.

Abstract: Mobile terminal having virus resistant security module architecture. An embedded security module can control the presentation of information on a display by controlling access to display memory. In some embodiments, the security module is also provided with an interface to enable it to handle user input function as well. In this way, the presentation of transaction information and receipt of user input can be substantially isolated from the main, control microprocessor of the terminal for enhanced security, especially protection against resident viruses. In addition, the security module can copy display data into the authentication and/or authorization message that is returned by the terminal to the base station. The return of the display data provides an extra, secure confirmation of the transaction.

Abstract: A radio communication system includes a base station having a directional antenna for generating a plurality of beams. A first set of the beams is used to receive signals which are decoded at the base station. A second set of the beams is used for interrogating a cell to identify beams which should be added to the first set of beams (for example, in response to mobile terminals entering the cell). In one embodiment, the second set of beams comprises a plurality of searcher beams produced by a fixed-beam phased array antenna. In a second embodiment, the second set of beams comprises a single searcher beam which is scanned through the cell by an adaptive phased array antenna. The radio communication system can be used to communicate with indoor mobile terminals through a plurality of radio heads, and also can be used to communicate with orbiting satellites.

Abstract: A detector selector and method are provided for selecting among detectors, where a less complex detector detects known symbols in a received signal, and a bit error rate for the known symbols is used to determine whether the less complex detection method is sufficient. If the less complex detector is not sufficient, a more complex detector is used to detect the signal. Additionally, assured symbols are used as known symbols to increase the accuracy for the determination of whether the less complex detector is sufficient.

Abstract: A receiving apparatus Doppler spread estimator includes a receiver receiving signals over a transmission channel that varies over time due to fading and converting the signals to digital samples for processing. A stationarizer operatively associated with the receiver stationarizes the digital samples. An estimator is operatively associated with the stationarizer for estimating spectral density of the stationarized digital samples. The correlator is operatively coupled to the estimator for correlating the spectral density estimates with functions corresponding to hypotheses of plural Doppler spread values to select one of the Doppler spread values as an estimate of actual Doppler spread.

Abstract: A method for improving the performance of a random access communications system in a variable radio environment is disclosed, whereby at least one valid set of burst signatures is used for transmission by one or more mobile stations. Each set includes at least one signature with a different signature-length than the signatures in other sets. The different signature-lengths can be optimized for the operational environments involved (e.g., longer signatures for slower-moving mobile stations, and shorter signatures for high-speed mobile stations). Alternatively, at least one differentially-encoded signature is used for random access transmissions, in order to reduce the radio channel's sensitivity to large doppler spreads and frequency errors.

Abstract: A radiotelephone includes a base unit mounted within the vehicle having a wide area transceiver for communicating with a station outside the vehicle, a control unit disposed in the vehicle remotely from the base unit, and a local area network for establishing a communication link between the base unit and the control unit. The local area network is adapted to transmit control and data signals between the base unit and the control unit. The control unit includes a keypad for entering commands and data that are transmitted to the base unit via the local area network, and a display for displaying information to the user. The control unit may also include a speaker and microphone. Alternatively, the speaker and microphone may be contained in a remote audio unit that is linked to the base unit via the local area network. The control unit may, for example, be incorporated into the steering wheel of a vehicle while the base unit is concealed in the trunk or under the seat of the vehicle.

Abstract: A diversity scheme for allowing a transmitter/receiver, such as a mobile unit in a mobile telecommunications system, to exchange communication signals with more than one control station, such as a base station or satellite. According to an exemplary embodiment of the diversity scheme, the mobile unit scans for the control channel of a second satellite during idle time slots while communicating with a first satellite during active time slots. Once the mobile unit detects a control channel from a second satellite, the mobile unit stores synchronization information and establishes a communication link with the second satellite if shadowing or other severe fading causes signal quality over a communication link established with a first satellite to fall below a threshold level. The diversity scheme also allows the mobile unit to communicate simultaneously with two satellites, using alternate TDMA frames.

Abstract: A system and method for permitting variable information rates and improved error performance using orthogonal or near-orthogonal codes is disclosed. This is achieved by simultaneously transmitting two or more Walsh code words from a given orthogonal code set and/or by transmitting multiple shorter orthogonal codewords sequentially such that their combined length equals the original codeword. It should be emphasized that the present invention can be used with any orthogonal or near-orthogonal code set.

Abstract: A method and system for transmitting short data messages in a control station-based TDMA radiocommunication system. Selected TDMA frames are assigned as message frames, and one or more data slots from each message frame are assigned to transmitter/receivers. Data messages can be encoded and transmitted multiple times, at an increased power level, from a control station to a transmitter/receiver over the appropriate data slots in each message frame. The selected TDMA frames are preferably slow associated control channel frames. Also, short alphanumeric messages can be transmitted over the broadcast control channel of a digital radiocommunication link, or another communication channel consisting of one or more slots from successive frames in a TDMA communication link. An increase in transmission power is used in combination with repetition to increase effective signal margin without complications in the mobile unit design, significant delay, or co-channel interference.

Abstract: A method and apparatus for communicating auxiliary information between a cellular telephone network and a GPS receiver positioned within a mobile station and identifying the location of the mobile station. A dedicated channel between the mobile station and the network is assigned by the network and uplink timing between the mobile station and the network is adjusted. The network requests auxiliary information and also requests the GPS receiver to perform a GPS code shift search at a common reference time. Upon receiving the auxiliary information, the network transmits the auxiliary information to the GPS receiver which then performs the GPS code shift search. The GPS receiver incorporates a bank of correlators and accumulators to perform multiple parallel searches for various Doppler frequency shifts resulting from a moving GPS receiver. The mobile station subsequently transmits the location information to the cellular telephone network.

Abstract: An apparatus for joint synchronization of digital communication signals from multiple receive channels comprises a control unit, a metric computer, and a decimator. The control unit generates test sampling phase vectors for use in decimating the signals. The output of the decimator is used by the metric computer to form a metric predictive of the performance of a demodulator. The metric is used by the control unit to select an optimal sampling phase vector. In one embodiment, the metric computer calculates the signal to impairment plus noise ratio (SINR) at the output of the demodulator based on the decimated signals. In one embodiment, a data correlation estimator generates a data correlation estimate for use in calculating output SINR. In another embodiment, the apparatus includes a select unit and a metric computer. The select unit may include a control unit and a decimator. The metric computer also includes at least one decimator.

Abstract: Combined equalization and decoding of codewords in a coded modulation symbol sequence that has been received from a channel is accomplished in a number of ways. In an intersymbol interference (ISI) cancellation technique, channel impulse response (CIR) estimates corresponding to each received symbol of the coded modulation symbol sequence are determined. Codeword k of the received symbol sequence is then decoded using a maximum likelihood decoding trellis with a path metric that depends upon the CIR estimates and that includes at least one term representing intersymbol interference resulting from symbols of previously decoded codewords. The decoding step is repeated until all of the codewords of the received coded modulation symbol sequence have been decoded.

Abstract: A communication system and method for transmitting relatively short data messages in the communication system. A dedicated frequency is sequentially switched into each of a plurality of satellite beams or traffic channels to transmit data messages at an increased power level to provide an increased signal margin. The increased power level of the dedicated frequency can be combined with coding and bit and message repetition to further increase the signal margin.

Abstract: An apparatus and method for selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal, wherein a gain imbalance exists between the antennas.

Abstract: Diversity and inter-frequency mobile-assisted handoff (MAHO) are achieved under continuous reception cellular access methods by using strategic timing and switching optimizations. Strategic timing is achieved by avoiding the non-reception of power control bits. For example, the mobile terminal can make measurements for diversity in the last eight bits of a sub-frame of an IS-95 downlink transmission. Switching is optimized, for example, by storing rake taps for a first antenna prior to switching to a second antenna so that the rake tap positions can be restored upon returning to the first antenna. With these and other disclosed measurement techniques, the benefits of diversity and inter-frequency MAHO can be achieved in continuous reception cellular systems.

Abstract: A source sequence of symbols is communicated over a communications medium by encoding the source sequence according to respective first and second error correction codes to produce respective first and second encoded sequences of symbols. The first and second encoded sequences are processed to produce a communications signal, which is then communicated over the communications medium. The communicated communications signal is processed to produce first and second received sequences of symbols corresponding to the first and second encoded sequences, respectively. The first and second received sequences are selectively recursively decoded according to the associated error correction codes augmented by previous estimates of a symbol of the source sequence to repeatedly produce revised estimates of the symbol until an estimate satisfying a predetermined reliability criteria is obtained.

Abstract: A multi-signal cancelling demodulator in which signals of interest are demodulated using information obtained during demodulation of adjacent signals. By utilizing detected information in an across-channel fashion, exemplary cancelling demodulators provide superior adjacent channel interference rejection. The cancelling demodulation is conducted in either serial or parallel fashion. In exemplary parallel demodulation embodiments, two channels are demodulated simultaneously in iterative fashion. Detected information obtained at each step in the iterative process is used as a priori information for demodulation in a following step. In exemplary serial demodulation embodiments, the stronger of two received signals is demodulated, and the resulting detected information is used as a priori information for demodulation of the weaker of the two received signals.