Cancellation of spurious intermodulation products produced in nonlinear channels by frequency hopped signals and spurious signals
A method and apparatus for intermodulation product (IMP) cancellation. In one embodiment, the method comprises: acquiring copies of source signals that create IMPs in a passband of interest; creating copies of the IMPs for use as IMP cancellation signals by either multiplying the source signals together as a series of digital samples such that the multiplied signals create a near real and continuous time copy of the IMPs or creating a sum of the source signals in near real and continuous time and convolving the sum of the source signals with a mathematical model to effectively multiply the signals together to create a copy of the IMPs; adjusting one or both of phase and amplitude of the copies; and using the copies to cancel the IMPs inband of the passband of interest.
1. An apparatus comprising:
an input to acquire a full passband of a transmitter;
a processing path to convolve the full passband of the transmitter with a nonlinear model of the transmitter passband to create one or more composite intermodulation product (IMP) signals; and
a cancellation unit operable to use the one or more composite IMP signals to cancel IMPs in the transmitter passband and out of band interference caused by a non-linear channel of the transmitter.
2. The apparatus of claim 1 , wherein the composite IMP signal is a broadband IMP signal created by multiplying the transmitter passband signal by itself two or more times.
3. The apparatus of claim 1 , wherein the processing path is performed at one location and control and calibration signals for the one or more composite IMP signals are passed to a receive signal of interest processing path.
4. The apparatus of claim 1 , wherein the processing path is operable to perform frequency shifting one or more of the composite IMP signals to produce simulated intermodulation products, adjusted to compensate for phase, frequency and amplitude differences between the IMPS and the one or more composite IMP signals used for cancellation by the cancellation unit.
5. An apparatus comprising:
an input to acquire copies of source signals;
a first processing path to create intermodulation product (IMP) cancellation signals in response to the source signals, including compensating for differences between the IMP cancellation signals and IMPs in a band of a signal of interest by applying frequency, amplitude and phase adjustments for variances in frequency, amplitude and phase; and
a cancellation unit operable to use the IMP cancellation signals to cancel IMPs in the signal of interest.
6. The apparatus of claim 5 wherein the first processing path is operable to determine the frequency, amplitude and phase adjustments by cross correlating one or more of the IMP cancellation signals with the signal of interest and adjusts the frequency, amplitude and phase to reduce the cross correlation between an IMP in the band of the signal of interest and the IMP cancellation signals.
7. A method comprising:
processing a source signal that covers a full passband of a signal of interest, wherein the source signal is the signal of interest or has a same passband as the signal of interest;
multiplying a passband in the signal of interest by itself three times to create intermodulation cancellation signal (ICS) for cancellation of the 3 rd order intermodulation signals centered in the passband of the signal of interest including the out of band interference; and
convolving the signal of interest with a mathematical model of the nonlinearity to create an ICS signal.
8. A method comprising:
creating an estimate of all the 3 rd order intermodulation products (IMPs) by cubing a full passband of a signal of interest to create all of the potential 3 rd order IMPs including the IMP caused by the signal of interest, wherein the full passband includes all source signals that can create IMPS in the passband of the signal of interest;
filtering an estimate of all of the higher order IMPs to pass only those IMPs components that fall within the passband of the signal of interest to create an IMP cancellation signal (ICS);
canceling the IMPs in-band of the signal of interest using the filtered estimate; and
adjusting the ICS in phase and amplitude to improve the cancellation process.
9. A method comprising:
create an estimate of all the intermodulation products (IMPs) by convolving a full passband of a receiver with a mathematical model of the nonlinearity (a power series expansion) to create all of the potential IMPS including the IMP caused by a signal of interest, wherein the full passband includes all source signals that can create intermodulation products (IMP) in the passband of the signal of interest;
filtering the estimate of all of the IMPS to pass only those IMPS components that fall within the passband of the signal of interest and create an IMP cancellation signal (ICS);
cancelling the IMPs in-band of the signal of interest using the filtered estimate (ICS) as part of a cancellation process; and
adjusting the ICS in phase and amplitude to improve the cancellation process.