# US 2005/0152487 A1 · Adaptive channel equalization technique and method for wideband passive digital receivers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2005/0152487 A1 - Document ID: US20050152487A1 - Status: Published application - Kind: A1 - Application number: 10/880,441 - Filed: 2004-06-29 - Published: 2005-07-14 - Earliest claimed: 2004-01-14 - Assignees: L-3 Communications Integrated Systems L.P. - Inventors: Timothy Reichard - Web page: https://patentgrep.com/patent/US20050152487A1 ## CPC - H04L 25/03133: {with a non-recursive structure (H04L25/03127 takes precedence)} - H04L 2025/03477: {not time-recursive} - H04L 2025/03617: {Time recursive algorithms (H04L2025/03643 takes precedence)} - H04L 2025/03757: {only on the request of a user} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract An adaptive channel equalization technique and method for wideband passive receivers is disclosed that reduces and tends to minimize distortions caused by circuitry within passive digital receivers. This equalization architecture provides an adaptive equalization solution for a wideband passive channel that receives unknown signals from the RF environment both temporally and spectrally. A wideband chirp signal or calibration signal is periodically injected to capture the spectral response of the receiver channel as it varies from the distortions induced over time and temperature for synthesis of equalization filter coefficients. Thus, the channel equalization is performed independent of receiver signal source and is employed to minimize digital receiver signal measurement distortions across the passband by providing an equalization filter whose magnitude and phase response compensates for the channel distortions of the passive data collection system. ## Claims ### Claim 1 A wideband passive receiver system having channel equalization, comprising: a wideband passive receiver coupled to receive an RF input signal spectrum or to receive a calibration input signal, the receiver being configured to output digital signals representing the RF input signal spectrum or the calibration input signal; an equalizing filter coupled to receive the digital signals from the receiver, the filter having a filter response controlled by filter control signals and being configured to output filtered digital signals; a calibration signal generator configured to generate a wideband calibration signal to provide the calibration input signal for the receiver and configured to generate a desired output signal; and equalizer control circuitry coupled to receive the filtered digital signals as feedback and coupled to receive the desired output signal from the calibration signal generator, the equalizer control circuitry being configured to generate the filter control signals, and the filter control signals being configured to correct distortions caused by operational variations in transfer function characteristics of the receiver system. ### Claim 2 (depends on 1) The wideband passive receiver system of claim 1, wherein the distortions comprise distortions inherent to analog circuitry within the receiver system that may cause variations in the transfer function characteristics due to internal or external operational conditions. ### Claim 3 (depends on 2) The wideband passive receiver system of claim 2, wherein the analog circuitry has a non-linear transfer characteristics that may vary in time during operation. ### Claim 4 (depends on 1) The wideband passive receiver system of claim 1, wherein the calibration input signal comprises a plurality of wideband calibration signals generated periodically to provide calibration dwells for the receiver system. ### Claim 5 (depends on 1) The wideband passive receiver system of claim 1, wherein the equalizer control circuitry comprises an adder configured to subtract the feedback signal from the desired output signal to produce an error correction signal and equalizer algorithm control circuitry configured to receive the error correction signal from the adder. ### Claim 6 (depends on 1) The wideband passive receiver system of claim 1, further comprising a rate converter coupled to the output of the receiver and configured to provide an input to the equalizing filter. ### Claim 7 (depends on 1) The wideband passive receiver system of claim 1, further comprising signal processing circuitry coupled to receive the output of the equalizing filter. ### Claim 8 (depends on 7) The wideband passive receiver system of claim 7, wherein the signal processing circuitry is configured to perform electronic intelligence signal processing or configured to perform specific emitter identification signal processing. ### Claim 9 (depends on 1) The wideband passive receiver system of claim 1, wherein the receiver comprises an RF signal detector, an anti-aliasing filter and an analog-to-digital converter. ### Claim 10 (depends on 1) The wideband passive receiver system of claim 1, wherein the equalizing filter comprises a FIR filter having coefficients set by the equalizer control circuitry. ### Claim 11 (depends on 1) The wideband passive receiver system of claim 1, wherein the equalizer control circuitry comprises circuitry configured to model circuitry within the receiver and wherein the model circuitry processes the desired output signal. ### Claim 12 A channel equalizer system for a wideband passive receiver, comprising: an equalizing filter coupled to receive digital signals from a receiver, the filter having a filter response controlled by filter control signals and being configured to output filtered digital signals; a calibration signal generator configured to generate a wideband calibration signal to provide as a calibration input signal to the receiver and configured to generate a desired output signal; and equalizer control circuitry coupled to receive filtered digital signals as feedback and coupled to receive the desired output signal from the calibration signal generator, the equalizer control circuitry being configured to generate the filter control signals, and the filter control signals being configured to correct distortions caused by operational variations in transfer function characteristics of the receiver system. ### Claim 13 (depends on 12) The channel equalizer system of claim 12, wherein the distortions comprise distortions inherent to analog circuitry within the receiver system that may cause variations in the transfer function characteristics due to internal or external operational conditions. ### Claim 14 (depends on 13) The channel equalizer system of claim 13, wherein the analog circuitry has a non-linear transfer characteristics that may vary in time during operation. ### Claim 15 (depends on 12) The channel equalizer system of claim 12, wherein the equalizer control circuitry comprises an adder configured to subtract the feedback signal from the desired output signal to produce an error correction signal and equalizer algorithm control circuitry configured to receive the error correction signal from the adder. ### Claim 16 (depends on 12) The channel equalizer system of claim 12, wherein the equalizing filter comprises a FIR filter having coefficients set by the equalizer control circuitry. ### Claim 17 (depends on 12) The channel equalizer system of claim 12, wherein the digital signals received by the equalizing filter are complex digital signals. ### Claim 18 (depends on 12) The channel equalizer system of claim 12, wherein the digital signals received by the equalizing filter are real digital signals. ### Claim 19 (depends on 12) The channel equalizer system of claim 12, wherein the equalizer control circuitry comprises a block least means square (BLMS) architecture. ### Claim 20 (depends on 12) The channel equalizer system of claim 12, wherein the equalizer control circuitry comprises circuitry configured to model circuitry within the receiver and wherein the model circuitry processes the desired output signal. ### Claim 21 A method for equalizing a channel within a wideband passive receiver system, comprising: receiving an RF input signal spectrum or an injected calibration input signal and processing the input signal to produce digital output signals; filtering the digital signals to produced equalized digital output signals, the filtering being controlled by filter control signals; generating a wideband calibration signal to provide the injected calibration input signal and generating a desired output signal; and processing the equalized digital output signals as feedback and the desired output signal to generate the filter control signals, and the filter control signals being configured to correct distortions caused by operational variations in transfer function characteristics of the receiver system. ### Claim 22 (depends on 21) The method of claim 21, wherein the distortions comprise distortions inherent to analog circuitry within the receiver system that may cause variations in the transfer function characteristics due to internal or external operational conditions. ### Claim 23 (depends on 22) The method of claim 22, wherein the analog circuitry has a non-linear transfer characteristics that may vary in time during operation. ### Claim 24 (depends on 21) The method of claim 21, wherein generating step comprises generating a plurality of wideband calibration signals to provide periodic calibration dwells for the receiver system. ### Claim 25 (depends on 21) The method of claim 21, wherein the processing step comprises subtracting the feedback signal from the desired output signal to produce an error correction signal and utilizing the error correction signal to generate the filter control signals. ### Claim 26 (depends on 21) The method of claim 21, further comprising performing additional signal processing on the equalized digital output signals. ### Claim 27 (depends on 26) The method of claim 26, wherein the additional signal processing circuitry comprises electronic intelligence signal processing or specific emitter identification signal processing. ### Claim 28 (depends on 21) The method of claim 21, wherein filtering step comprises utilizing a FIR filter having coefficients determined by the filter control signals. ### Claim 29 (depends on 21) The method of claim 21, wherein the processing step comprises utilizing circuitry that models circuitry within the receiver system to processes the desired output signal.