1. A method of acoustic echo cancellation (AEC) and noise cancellation (NC) wherein a microphone signal resulting from an unobservable signal corrupted by both additive background noise and an acoustic echo is processed in an attempt to restore the unobservable signal, the acoustic echo being a speaker signal modified by an acoustic path, wherein an adaptive filter models the echo path in the frequency domain, and wherein a noise cancellation filter is implemented in the frequency domain, the method comprising:
receiving the microphone signal;
applying the adaptive filter to the speaker signal to produce an echo signal that models the acoustic echo;
applying the noise cancellation filter to the microphone signal to produce an NC-filtered microphone signal;
applying a copy of the noise cancellation filter to the echo signal to produce an NC-filtered echo signal;
subtracting the NC-filtered echo signal from the NC-filtered microphone signal to produce a first echoless signal that resembles the unobservable signal; and
adapting the adaptive filter based on the first echoless signal.
2. The method of claim 1 wherein processing takes place independently in a plurality of subbands.
3. The method of claim 1 wherein the adaptive filter utilizes a data reuse normalized least mean square adaptive filter algorithm.
4. The method of claim 1 further comprising:
subtracting the echo signal from the microphone signal to produce a second echoless signal; and
applying a second noise cancellation filter to the second echoless signal to produce an output signal that resembles the unobservable signal.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An exhaust system for a tiltrotor aircraft, the exhaust system comprising:
a fixed exhaust in gaseous communication with an engine;
a primary exhaust duct in gaseous communication with the fixed exhaust, the primary exhaust being rotatable relative to the fixed exhaust about a nozzle rotational axis; and
a nacelle configured as a housing for the engine, the nacelle being rotatable relative to a wing of the tiltrotor aircraft about a nacelle rotational axis;
wherein the nozzle rotational axis and the nacelle rotational axis are approximately parallel.
2. The exhaust system according to claim 1, further comprising:
wherein the nacelle is rotatably between an approximately vertical orientation configurable for a helicopter mode operation of the tiltrotor aircraft and an approximately horizontal orientation configurable for an airplane mode operation of the tiltrotor aircraft.
3. The exhaust system according to claim 2, wherein the primary exhaust duct is configured to selectively direct an exhaust flow in an aft direction while the nacelle is vertically oriented.
4. The exhaust system according to claim 2, wherein the primary exhaust duct is configured to selectively direct an exhaust flow in an upwardoutboard direction while the nacelle is vertically oriented.
5. The exhaust system according to claim 2, wherein the primary exhaust duct is configured to selectively direct an exhaust flow in an upwardoutboard direction while the nacelle is horizontally oriented.
6. The exhaust system according to claim 1, further comprising:
an outer exhaust duct located adjacent to the primary exhaust duct creating a gap therebetween.
7. The exhaust system according to claim 6, wherein the gap is configured for the flow of cooling air between the primary exhaust duct and the outer exhaust duct.
8. The exhaust system according to claim 7, wherein the cooling air is drawn from an inlet formed between a base portion of the outer exhaust duct and the primary exhaust duct.
9. The exhaust system according to claim 6, further comprising:
an actuator configured for imparting a rotational force to the primary exhaust duct.
10. The exhaust system according to claim 9, further comprising:
a drive belt operably associated with the actuator, the drive belt at least partially wrapped around the outer exhaust duct.
11. The exhaust system according to claim 1, further comprising:
a bellows seal in pressing contact with the fixed exhaust and the primary exhaust duct, the bellows seal being configured to prevent the leakage of exhaust gas while allowing a relative rotation between the fixed exhaust and the primary exhaust duct.
12. An exhaust system for a tiltrotor aircraft, the exhaust system comprising:
a nacelle configured for housing an engine, the nacelle being rotatable relative to a wing of the tiltrotor aircraft, wherein the nacelle is rotatably between an approximately vertical orientation configurable for a helicopter mode operation of the tiltrotor aircraft and an approximately horizontal orientation configurable for an airplane mode operation of the tiltrotor aircraft;
a fixed exhaust in gaseous communication with an engine;
a vector nozzle comprising:
a primary exhaust duct in gaseous communication with the fixed exhaust, the primary exhaust being rotatable relative to the fixed exhaust;
a control system configured to process an input to selectively command an actuator to rotate the vector nozzle.
13. The exhaust system according the claim 12, wherein the input is one of:
a pilot control input;
an operating condition input; and
an automatic control input.
14. The exhaust system according the claim 12, wherein the control system is configured to selectively position the vector nozzle in a helicopter hover ground heating reduction mode such that an exhaust flow is directed in an aftward direction while the nacelle is positioned approximately vertical.
15. The exhaust system according the claim 12, wherein the control system is configured to selectively position the vector nozzle in a helicopter hover infrared signature suppression mode such that an exhaust flow is directed in an upward direction while the nacelle is positioned approximately vertical.
16. The exhaust system according the claim 12, wherein the control system is configured to selectively position the vector nozzle in an airplane infrared signature suppression mode such that an exhaust flow is directed in an upward direction while the nacelle is positioned approximately horizontal.
17. The exhaust system according the claim 12, the vector nozzle further comprising:
an outer exhaust duct located adjacent to the primary exhaust duct creating a gap therebetween, the outer exhaust duct being configured to hide the primary exhaust duct from a line of site vision of an infrared signature detector.
18. The exhaust system according to claim 12, the vector nozzle further comprising:
an outer exhaust duct located adjacent to the primary exhaust duct creating a gap therebetween, the gap being configured to allow for a flow of cooling air between the primary exhaust duct and the outer exhaust duct.
19. A method of suppressing infrared signature of a tiltrotor aircraft having a nacelle, the method comprising:
orienting a rotatable vector nozzle to direct an exhaust gas in an upward direction;
maintaining an approximate orientation of the rotatable vector nozzle as the nacelle rotates between a vertical position and a horizontal position by rotating the rotatable vector nozzle relative to the nacelle.
20. The method according to claim 19, wherein the step of maintain the approximate orientation of the rotatable vector nozzle is achieved by rotating the vector nozzle in the opposite direction of the nacelle rotation direction.