Comsat Corporation

Saraband Wireless, Inc

Hughes Electronics Corporation

Donald Stuart Arnstein

Paul Ebert

Todd R Czerner

Stanley Edward Kay

Bala Subramaniam

Jong Lee

John E Corrigan, Iii

Francois T Assal

Harry M Johnson

John I Upshur

James H Buzzelli

Moshe Lieberman

Multiple antenna wireless communication systems require accurate knowledge of the transfer function between all paths. This invention discloses a system wherein a test signal generator at a transmitter station and a facsimile generator at a receiver station go through an acquisition and tracking process which aligns the two signals, removing errors in the time base of generation, the frequency offset of generation and the time of arrival, so that a logical processor can compute the frequency transfer function of propagation pathways between the multiple input and multiple output antennas. In turn, these channel measurements are used in an adaptive, concurrently sent communication signal. The frequency transfer functions are conveyed back to the transmit end via a control channel permitting an adaptivity function at the transmit end to influence subsequent selection of communication parameters, among which are typically transmitted data rate, selection of modulation, selection of forward error correcting coding, and selection of frequency band for transmission. The same measurement is conveyed to an adaptivity function at the receive end for use in the communications receiver to select signal combining variables such as gain control, and equalization of amplitude and phase, versus frequency. An alternate embodiment invention of this type is described which is additionally useful for mobile multiple antenna communications channels. Another variation embodiment is described for pure propagation measurements only, absent conveyance of end-user information.

Channel estimation applique for multiple antenna wireless communications

A test signal generator at a transmitter station and a facsimile generator at a receiver station go through an acquisition and tracking process which aligns the two signals, removing errors in the time base of generation, the frequency offset of generation and the time of arrival, so that a logical processor can compute the frequency transfer function of the entire propagation path for use in an adaptive, concurrently sent communication signal. The frequency transfer function is conveyed back to the transmit end via a control channel permitting an adaptivity function at the transmit end to influence subsequent selection of communication parameters, among which are typically transmitted data rate, selection of modulation, selection of forward error correcting coding, and selection of frequency band for transmission. The same measurement is conveyed to an adaptivity function at the receive end for use in the communications receiver to select demodulator variables such as gain control, and equalization of amplitude and phase, versus frequency. The adaptivity function also permits interspersing of reverse-direction communications over the same frequency bands in a time-share mode between forward-direction and reverse-direction communication with the measurement signals having to be transmitted in only one direction. An alternate embodiment invention of this type is described which is additionally useful for mobile communications channels. Another variation embodiment is described for pure propagation measurements only, absent conveyance of end-user information.

Channel estimation applique for wireless communications

A test signal generator at a transmitter station and a facsimile generator at a receiver station go through an acquisition and tracking process which aligns the two signals so that a logical processor can compute the frequency transfer function of the entire propagation path for use in an adaptive, concurrently sent communication signal. The frequency transfer function is conveyed back to the transmit end via a control channel permitting an adaptivity function at the transmit end to influence subsequent selection of communication parameters, among which are typically transmitted data rate, selection of modulation, selection of forward error correcting coding, and selection of frequency band for transmission. The same measurement is conveyed to an adaptivity function at the receive end for use in the communications receiver to select demodulator variables such as gain control, and equalization of amplitude and phase, versus frequency. The adaptivity function also permits interspersing of reverse-direction communications over the same frequency bands in a time-share mode between forward-direction and reverse-direction communication with the measurement signals having to be transmitted in only one direction. An alternate embodiment invention of this type is described which is additionally useful for mobile communications channels. Another variation embodiment is described for pure propagation measurements only, absent conveyance of end-user information.

Vector network analyzer applique for adaptive communications in wireless networks

A radio, and related methods of radio communication, consisting of a multi-modulation modem, wherein the multi-modulation modem that modulates and demodulates signals using a plurality of modulations. The radio also comprises a frequency converter coupled to the multi-modulation modem for converting the signals to a radio frequency and a transceiver unit including an antenna coupled to the frequency converter for transmitting the signals over a radio communications link. The multi-modulation modem includes a modulator that includes a modulation selector unit that selects respective ones of the plurality of modulations to modulate the signals. The multi-modulation modem also includes a demodulator for demodulating the signals having been modulated using the plurality of modulations.

Multi-modulation radio communications

A swept frequency communication system includes a modulator that multiplies a frequency sweep signal with one or more underlying modulated communication signals to produce a swept frequency signal having a number of headerless tracks located directly adjacent one another in the swept frequency/time domain. A demodulator receives the swept frequency signal after that signal has been passed through a wireless channel, isolates a particular track of the received swept frequency signal to prevent a near/far problem, A/D converts the isolated track, resweeps the digitized isolated track, and then equalizes the isolated track using a blind channel equalizer to eliminate time-varying amplitude/phase impairments caused by transmission of that track through the wireless channel. The demodulator then removes the sweep signal from the equalized swept frequency track and decodes or demodulates the underlying modulated communication signal.

Swept frequency modulation and demodulation technique

A method and apparatus to enable high-quality digital transmissions to a satellite terminal operating in proximity to a radar source combines interleaving a sequence of channel symbols at a land station before transmission of an RF signal to a satellite, increasing the satellite's EIRP to compensate for the effects of the radar's duty factor on received signal power and code distance, detecting the radar pulses at a satellite terminal, blanking the received RF signal to prevent reception of the signal by the modem at the satellite terminal during the radar's ON time, having the modem recognize and eliminate the effect of the gap in the channel signals on its metric calculation, and de-interleaving the sequence of channel symbols. As a result, satellite terminals operating in proximity to radar sources can provide the same quality of service as if there were no radars operating.

Low noise front-end blanking and interleaving for satellite reception in

An enhanced nonlinear processor for RFI suppression uses a biased inverting limiter circuit. There are two parallel paths in the device; the first one is used to estimate the intensity of the RFI signal, the second one is used to process the signal. The first signal path employs an envelope detector and filter (to estimate RFI intensity) followed by a comparator circuit to avoid use of the processing if the RFI is too small; the second path has a biased inverting limiter whose characteristic is controlled by the output of the first path. When the estimate of the RFI intensity is close to being correct, the biased inverting limiter traps the large RFI signal, converting it into a higher order harmonic which is filtered out. The wanted signal is not trapped, but instead sees an 'effective' positive gain which allows it to pass through unaffected except for a gain factor. The net result is a reduction in the ratio of unwanted signal to wanted signal.

Voltage-variable biased inverting limiter for RFI suppression overview

An enhanced nonlinear signal processor for RFI suppression using either biased null zone amplifier or a biased inverting limiter. Two or more nonlinear interference processors are connected in cascade. As a result, a deliberate tracking error, selected to provide only a small amount of relative interference rejection, is introduced into each processor. The effect of each stage is cumulative until some limit to performance improvement, determined by the input/output characteristic of each stage, is reached. The benefits of this discovery are increased dynamic range capability (higher levels of interference-to-wanted signal ratio can be fully rejected), simplification of gain control, and increased flexibility in hardware implementation options resulting from reduced sensitivity to RFI tracking error.

RFI suppression by cascading nonlinear devices

Improved automatic gain control for an amplifier is obtained by controlling the size of a null zone in a drive signal for the amplifier. The size of the null zone is controlled by estimating strength of an interference signal, and dynamically varying the size of the null zone based on the estimated strength of the interference signal. As a result, the amplifier rarely saturates, regardless of signal strength. The invention is useful to reduce the harmful effects of jamming or interference.

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Fairfax Station, VA, United States of America

Donald Stuart Arnstein