Abstract: An electromagnetic transmission carrying a bauded signal, such as a transmission from an orbiting satellite, is processed for Doppler shift analysis. The electromagnetic transmission is captured and a non-linear operation is performed to expose a cyclostationary feature of the captured transmission that defines a rate-line having a rate-line frequency that is related to the bauded signal and to the motion of the transmitter relative to the receiver. The rate-line frequency is tracked in time to generate data indicative of Doppler shift associated with the satellite. The data are then supplied to a tracking receiver.

Abstract: An electromagnetic transmission carrying a bauded signal, such as a transmission from an orbiting satellite, is processed for Doppler shift analysis. The electromagnetic transmission is captured and a non-linear operation is performed to expose a cyclostationary feature of the captured transmission that defines a rate-line having a rate-line frequency that is related to the bauded signal and to the motion of the transmitter relative to the receiver. The rate-line frequency is tracked in time to generate data indicative of Doppler shift associated with the satellite. The data are then supplied to a tracking receiver.

Abstract: The receiver captures an electromagnetic transmission carrying a bauded signal, such as a transmission from an orbiting satellite, and processes it for Doppler shift analysis. The electromagnetic transmission is captured and a non-linear operation is performed to expose a cyclostationary feature of the captured transmission that will define a rate-line. This rate-line will exist at a frequency that is related to the bauded signal and Doppler shift relative to the motion of the transmitter to the receiver. The rate-line frequency is tracked in time to generate data indicative of a Doppler shift associated with the satellite and processed by an estimator fed by satellite propagator to supply positioning, navigation and timing services at the receiver output.

Abstract: A signal processing system according to various aspects of the present invention includes an excursion signal generator, a scaling system and a filter system. The excursion signal generator identifies a peak portion of a signal that exceeds a threshold and generates a corresponding excursion signal. The scaling system applies a real scale factor to contiguous sets of excursion samples in order to optimize peak-reduction performance. The filter system filters the excursion signal to remove unwanted frequency components from the excursion signal. The filtered excursion signal may then be subtracted from a delayed version of the original signal to reduce the peak. The signal processing system may also control power consumption by adjusting the threshold. The signal processing system may additionally adjust the scale of the excursion signal and/or individual channel signals, such as to meet constraints on channel noise and output spectrum, or to optimize peak reduction.

Abstract: An RF transmitter (10) is configured to transmit either wideband multichannel modulations or narrowband multichannel modulations in a variety of licensed frequency bands (70) using a single set of hardware. For narrowband modulations, a digital IF upconversion stage is performed so that, after upconversion to RF, image signals 74 are sufficiently displaced from the licensed frequency band (70) so as to be filtered off. For wideband modulations, no IF modulation stage occurs, and a direct upconversion takes place from baseband to RF. LO leakage is cancelled using a negative feedback loop that combines a digital DC signal with a communication signal (26, 52) prior to a direct or final analog upconversion stage (62).

Abstract: A transceiver (10) includes an RF transmitter (12) and an RF receiver (14) coupled together through a duplexer (30). An RF transmit signal (20) passes through the duplexer (30) from the transmitter (12) toward an antenna (18), and an RF receive signal (44) passes through the duplexer (30) from the antenna (18) toward the receiver (14). The duplexer (30) may leak significant portions (56, 58) of the transmit signal (20) into the receive signal (44), and the duplexer (30) may significantly distort the transmit signal (20). Such distortion is compensated in the transmitter (12) through the use of a linear predistorter (68) that is adjusted in response to an RF feedback signal obtained from the antenna-side of the duplexer (30) . Transmit signal leakage is compensated in the receiver (14) by producing a processed-cancellation signal (106) that, when combined with the receive signal (44) cancels the transmit signal portions (56, 58) leaked into the receive signal (44).

Abstract: A digital communication transmitter serves as a signal path (10) which uses an adaptive equalizer (18) in a predistortion role. The adaptive equalizer (18) pre-distorts a complex digital communication signal (12) that need not exhibit any distortion. Subsequent analog distortion-introducing segments (24, 30, 36, 42) then distort a predistorted signal (22) output from the adaptive equalizer (18). An error signal (46) is formed from a reference signal (52) and a return signal (54). The equalizer (18) implements an adaptation algorithm that adjusts filter (68) coefficients to minimize correlation between one of the reference and return signals (52, 54) and the error signal (46). The equalizer (18) generates four sets of coefficients for four different filters. Consequently, the equalizer (18) exhibits four degrees of freedom in introducing predistortion into a complex signal to counter the distortion subsequently introduced in the signal path (10) by the distortion-introducing segments (24, 30, 36, 42).

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Linear distortion is first compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Linear distortion is first compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200, 1800) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Distortion introduced by an analog-to-digital converter (304) may be compensated using a variety of adaptive techniques. Linear distortion is compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112).

Abstract: A digital communication transmitter serves as a signal path (10) which uses an adaptive equalizer (18) in a predistortion role. The adaptive equalizer (18) pre-distorts a complex digital communication signal (12) that need not exhibit any distortion. Subsequent analog distortion-introducing segments (24, 30, 36, 42) then distort a predistorted signal (22) output from the adaptive equalizer (18). An error signal (46) is formed from a reference signal (52) and a return signal (54). The equalizer (18) implements an adaptation algorithm that adjusts filter (68) coefficients to minimize correlation between one of the reference and return signals (52, 54) and the error signal (46). The equalizer (18) generates four sets of coefficients for four different filters. Consequently, the equalizer (18) exhibits four degrees of freedom in introducing predistortion into a complex signal to counter the distortion subsequently introduced in the signal path (10) by the distortion-introducing segments (24, 30, 36, 42).

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Linear distortion is first compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200, 1800, 2800) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Distortion introduced by an analog-to-digital converter (304) may be compensated using a variety of adaptive techniques. Linear distortion is compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112).