Abstract: A method and apparatus for reducing group delay and/or amplitude errors applied to a transmission signal by one or more transmission filters is described herein. The present invention characterizes the errors introduced by one or more transmission filters relative to a desired frequency response, e.g., the group delay and/or amplitude errors relative to a flat group delay and flat amplitude, respectively. Based on the errors, the present invention pre-compensates the digital frequency domain samples used to generate the transmission signal. In so doing, the present invention reduces the errors in the filtered transmission signal without placing limits on the design of the transmission filters.

Abstract: The present invention uses newly received signal samples to update previously determined scatterer parameters, and therefore, reduces the processing effort required for characterizing scattering objects in a wireless channel. Broadly, the present invention determines a first set of scatterer parameters based on signal samples derived from signals received during one or more previous time intervals, and determines an updated set of scatterer parameters for a subsequent time interval based on the first set of scatterer parameters and the new signal samples. In one exemplary embodiment, the receiver uses a continuous sequential update process, e.g., a per-symbol-period inverse Prony process, to update the scatterer parameters. In another exemplar embodiment, the receiver uses an integrated Doppler approach to update the scatterer parameters.

Abstract: Where two or more multi-valued digital data symbols are modulated so that they overlap after passing through a channel, forming a combined signal, a receiver receives the combined signal and forms detection statistics to attempt to recover the symbols. Where forming detection statistics does not completely separate the symbols, each statistic comprises a different mix of the symbols. A receiver determines the symbols which, when mixed in the same way, reproduce or explain the statistics most closely. For example, the receiver hypothesizes all but one of the symbols and subtracts the effect of the hypothesized symbols from the mixed statistics. The remainders are combined and quantized to the nearest value of the remaining symbol. For each hypothesis, the remaining symbol is determined. A metric is then computed for each symbol hypothesis including the so-determined remaining symbol, and the symbol set producing the best metric is chosen as the decoded symbols.

Abstract: Circuits and methods are disclosed for compensating for received signal distortion caused by non-linearities in wideband receivers. An exemplary receiver includes a distortion waveform generator configured to approximate non-linear response characteristics of a downconverter circuit used to downconvert the received radio frequency signal. The resulting estimated distortion waveform is filtered, using filter(s) substantially similar to those used for filtering an intermediate frequency signal that includes the desired signal and non-linear distortion products caused by strong interfering signals. The filtered estimated distortion waveform and intermediate frequency signal are sampled, to obtain a sampled distortion signal and a sampled signal of interest. The sampled distortion signal and the sampled signal of interest are divided into a plurality of frequency channels.

Abstract: A multiple antenna system is described herein that mitigates the negative effects of mutually coupled antennas on the connected transmitters and/or receivers. The antenna system comprises a directional coupler and two or more antennas. The directional coupler comprises multiple communication ports that each connect to corresponding antenna ports. The connection ports each connect to a different transmitter, receiver, or transceiver. A transmission line connects each antenna port to an antenna. The lengths of the transmission lines and the coupling factor of the directional coupler are selected to decouple the communication ports of the directional coupler. More particularly, the coupling factor and the transmission line lengths are selected so that antenna crosstalk signals caused by mutual coupling between the antennas and the coupled signals produced by the directional coupler have the same magnitude but opposite phase at the communication ports of the directional coupler.

Abstract: Circuits and methods are disclosed for compensating for received signal distortion caused by non-linearities in the receiver circuitry. An exemplary receiver circuit includes a distortion waveform generator configured to approximate one or more non-linear response characteristics of a downconverter circuit used to downconvert the received radio frequency signal. The estimated distortion waveform thus produced is filtered, using a filter or filters substantially similar to those used for filtering an intermediate frequency signal that includes the desired signal and non-linear distortion products caused by strong interfering signals. The filtered estimated distortion waveform and the intermediate frequency are sampled, to obtain a sampled distortion signal and a sampled signal of interest. The sampled distortion signal is scaled, and subtracted from the sampled signal of interest to obtain reduced-interference signal samples.

Abstract: A method and apparatus described herein uses a mobility server to supplement the mobility management operations of a conventional mobile switching circuit (MSC). The mobility server receives mobility messages from a wireless terminal, and updates a location register associated with the MSC responsive to the received mobility messages. According to one exemplary embodiment, the mobility server has a pre-determined network address, such as a phone number, IP address, etc. The wireless terminal sends the mobility messages as user-plane messages to the pre-determined network address over a traffic data channel. In one exemplary embodiment, the mobility messages indicate the imminent loss of usable base station signals at an identified wireless terminal. For this embodiment, the mobility server may identify a satellite beam associated with the wireless terminal's location based on the received mobility messages, and update the location register accordingly.

Abstract: Circuits and methods are disclosed for reducing interference from transmitter leakage in a radio transceiver. An exemplary method for reducing interference from transmitter leakage in a radio transceiver comprises downconverting, filtering, and sampling a radio frequency signal comprising a desired signal and a transmitter leakage signal to obtain a sampled signal of interest. The method further comprises generating a sampled distortion signal estimate that estimates one or more distortion products of the transmitter leakage signal, such as a squared amplitude obtained from a square-law device or corresponding digital function. Further, the method comprises dividing the sampled distortion signal estimate and the sampled signal of interest into a plurality of frequency channels.

Abstract: The present invention uses newly received signal samples to update previously determined scatterer parameters, and therefore, reduces the processing effort required for characterizing scattering objects in a wireless channel. Broadly, the present invention determines a first set of scatterer parameters based on signal samples derived from signals received during one or more previous time intervals, and determines an updated set of scatterer parameters for a subsequent time interval based on the first set of scatterer parameters and the new signal samples. In one exemplary embodiment, the receiver uses a continuous sequential update process, e.g., a per-symbol-period inverse Prony process, to update the scatterer parameters. In another exemplar embodiment, the receiver uses an integrated Doppler approach to update the scatterer parameters.

Abstract: The method described herein characterizes scattering objects in a wireless channel. Broadly, the present invention determines non-equally spaced path delays and Doppler parameters for a plurality of scattering objects in a wireless channel. More particularly, a frequency-to-time transform applied to a plurality of OFDM pilot samples received over a plurality of OFDM symbol periods generates a set of non-equally spaced path delays and a set of associated complex delay coefficients. Further, a time-to-frequency transform applied to the complex delay coefficients determined for one path delay over multiple OFDM symbol periods generates a set of Doppler parameters comprising a plurality of non-equally spaced Doppler frequencies and their corresponding scattering coefficients for that path delay.

Abstract: Methods, software and apparatuses for decoding received delayed path signals are described. A receiver receives a signal via different paths with relative delay, e.g., on the same frequency channel. The signal is sampled at at least one sample per symbol. A channel estimator determines channel coefficients associated with the channel over which the signals were transmitted. A processor selects samples that include a dependence on a particular symbol being decoded and computes an error metric for each possible value of the particular symbol, for combinations of hypothesized future symbol values on which the selected samples depend, and for single values of previous symbols on which the selected samples depend. Error metrics calculated for each symbol are stored in memory. A soft symbol is generated based on said signal samples from the sampler, the channel coefficients and estimates of symbols computed.

Abstract: A multiple antenna system is described herein that mitigates the negative effects of mutually coupled antennas on the connected transmitters and/or receivers. The antenna system comprises a directional coupler and two or more antennas. The directional coupler comprises multiple communication ports that each connect to corresponding antenna ports. The connection ports each connect to a different transmitter, receiver, or transceiver. A transmission line connects each antenna port to an antenna. The lengths of the transmission lines and the coupling factor of the directional coupler are selected to decouple the communication ports of the directional coupler. More particularly, the coupling factor and the transmission line lengths are selected so that antenna crosstalk signals caused by mutual coupling between the antennas and the coupled signals produced by the directional coupler have the same magnitude but opposite phase at the communication ports of the directional coupler.

Abstract: An antenna arrangement, method, and cellular communications system for transmitting and receiving signals between a base station tower, ground-based mobile subscribers, and an aircraft. The antenna arrangement includes a vertically oriented array of antenna elements, and a feedline arrangement that feeds the antenna elements with progressively phase-retarded signals, thereby generating an elevated antenna beam directed upward toward the aircraft and away from the ground-based mobile subscribers. In one embodiment, the antenna arrangement also generates a horizontal antenna beam for communicating with the ground-based subscribers. The horizontal beam and the elevated beam are sufficiently separated in elevation to prevent mutual interference when using the same frequency spectrum.

Abstract: A method and apparatus for reducing group delay and/or amplitude errors applied to a transmission signal by one or more transmission filters is described herein. The present invention characterizes the errors introduced by one or more transmission filters relative to a desired frequency response, e.g., the group delay and/or amplitude errors relative to a flat group delay and flat amplitude, respectively. Based on the errors, the present invention pre-compensates the digital frequency domain samples used to generate the transmission signal. In so doing, the present invention reduces the errors in the filtered transmission signal without placing limits on the design of the transmission filters.

Abstract: An improved channel estimation technique is provided herein that determines accurate scatterer parameters for the scattering objects in the wireless channel, and extrapolates the scatterer parameters in both time and frequency to characterize the scattering objects for a different time and a different frequency. In one embodiment, a wireless device determines scatterer parameters that characterizes the scattering objects of a reception channel, and extrapolates the scatterer parameters in both time and frequency to predict the scatterer parameters for a future time and frequency, e.g., a future transmission time and frequency.

Abstract: A method and apparatus for configuring a variable filter in an OFDM transmitter based on the number of subcarrier frequencies selected for the input data block is described herein. An exemplary OFDM transmitter comprises a control unit, OFDM modulator, and variable filter. The control unit selects the number of subcarriers for the input data block, and configures one or more filter properties for the variable filter based on the selected number of subcarriers. The modulator, which has a size greater than the selected number of subcarriers, pads an input data block generated for the selected number of subcarriers to generate an expanded data block having a size equal to the size of the modulator, and modulates the expanded data block to generate an OFDM signal. The filter, as configured by the control unit, filters the OFDM signal.

Abstract: A rheometer uses a removable integrated environmental control cartridge that includes at least one environmental control unit, at least one supply port operative to interact with the supply port for a chassis of the rheometer. It also includes at least one mechanical alignment interface that is operative to interact with the mechanical alignment interface of the chassis to align both the mobile part with respect to the fixed part and the chassis supply port with respect to the environmental control cartridge part. In another general aspect, a rheometer can use an environmental control cartridge interface operative to report an identity of the integrated environmental control cartridge to an environmental control cartridge identification interface of its chassis.

Abstract: Circuits and methods are disclosed for reducing interference from transmitter leakage in a radio transceiver. An exemplary method for reducing interference from transmitter leakage in a radio transceiver comprises downconverting, filtering, and sampling a radio frequency signal comprising a desired signal and a transmitter leakage signal to obtain a sampled signal of interest. The method further comprises generating a sampled distortion signal estimate that estimates one or more distortion products of the transmitter leakage signal, such as a squared amplitude obtained from a square-law device or corresponding digital function. Further, the method comprises dividing the sampled distortion signal estimate and the sampled signal of interest into a plurality of frequency channels.

Abstract: Circuits and methods are disclosed for compensating for received signal distortion caused by non-linearities in wideband receivers. An exemplary receiver includes a distortion waveform generator configured to approximate non-linear response characteristics of a downconverter circuit used to downconvert the received radio frequency signal. The resulting estimated distortion waveform is filtered, using filter(s) substantially similar to those used for filtering an intermediate frequency signal that includes the desired signal and non-linear distortion products caused by strong interfering signals. The filtered estimated distortion waveform and intermediate frequency signal are sampled, to obtain a sampled distortion signal and a sampled signal of interest. The sampled distortion signal and the sampled signal of interest are divided into a plurality of frequency channels.

Abstract: A method and ALU for implementing logarithmic arithmetic in a multi-stage pipeline is described herein. According to one embodiment, a master function is decomposed into two or more sub-functions. Memory associated with the pipeline stores a look-up table for each stage of the pipeline, where each table represents function values generated based on the corresponding sub-function, and where the look-up table associated with one stage differs from the look-up table(s) associated with at least one other stage. Each stage computes a stage output based on the stage input and the corresponding look-up table. By combining the stage outputs, the multi-stage pipeline outputs the logarithmic arithmetic output.