Cancellation system for frequency reuse in microwave communications
View Patent ↗Substantial improvements in frequency reuse in microwave communications systems is achieved by canceling co-channel interference and transmitter leakage. Interferometric beam-narrowing reduces beamwidth without reducing preak magnitude of the beam pattern. Frequency-dependent beam-shaping compensates for frequency-dependent distortions of the beam pattern thereby improving bandwidth. A spatial demultiplexing technique utilizes spatial gain distributions of received signals to separate signals, even from co-located transmit sources, and uses microwave lensing to enhance received spatial gain distributions. Predetermined cross-polarization interference is used to separate differently polarized receive signals. A reference branch provides a cancellation signal to a receiver to cancel transmitter leakage signals. An error signal controls an impedance-compensation circuit that is responsive to changes in antenna impedance but not to receive signals. A dc bias magnetic field applied to a magnetic permeable material adjusts non-linear distortion in a cancellation circuit for canceling distortion in a transmitter leakage signal. Discreet impedance elements approximate a circuit having distributed impedance.
1. A method of providing frequency rate in a communication system, the method including:
receiving a plurality of transmission signals with a plurality of receiver elements wherein said plurality of transmission signals are transmitter by a transmitter having a plurality of transmitting elements, the receiver elements capable of providing a plurality of received signals having known ratios of co-channel interference,
providing the received signals with algebraically unique ratios of co-channel interference, and
separating at least one desired signal from the received signals.
2. The method of claim 1 wherein the step of providing the received signals with algebraically unique ratios of co-channel interference includes shaping at least one spatial gain distribution of at least one of the transmitted signals.
3. The method of claim 1 wherein the step of providing the received signals with algebraically unique ratios of co-channel interference includes shaping at least one spatial gain distribution of at least one of the received signals.
4. The method of claim 1 wherein the step of providing the received signals with algebraically unique ratios of co-channel interference includes at least one of a set of methods including aperture synthesis, beam steering, lensing, and interferometric combining.
5. The method of claim 1 wherein the step of providing the received signals with algebraically unique ratios of co-channel interference is performed in response to a feedback signal from at least one receiver.
6. The method of claim 1 wherein the receiver elements are spatially separated array elements.
7. The method of claim 1 wherein the receiver elements include more than two polarization elements and the co-channel interference includes cross polarization.
8. The method of claim 1 wherein the step of providing the received signals with algebraically unique ratios of co-channel interference includes an optimization process wherein the optimization process controls the step of providing the received signals with algebraically unique ratios of co-channel interference.
9. The method of claim 8 wherein the ratios of co-channel interference result from spatial gain distributions of the received signals.
10. The method of claim 9 wherein the spatial gain distribution includes at least one minima in a predetermined spatial region.
11. The method of claim 9 wherein the spatial gain distribution includes at least one spatial region having at least one predetermined ratio of signal levels.
12. The method of claim 9 wherein the spatial gain distribution is controlled by directionality of the receivers.
13. The method of claim 9 wherein the spatial gain distribution is created by an overlap of at least two transmitted signals.
14. The method of claim 1 wherein the ratios of co-channel interference provide weights to a cancellation step that is included in the step of providing separation of the transmitted signals from the received signals.
15. The method of claim 14 wherein the weights have complex values.
16. The method of claim 14 wherein at least one of the weight includes a delay element.
17. The method of claim 14 wherein the weights are frequency-dependent weights, the transmission signals have diverse frequency characteristics.
18. The method of claim 14 wherein the weights are frequency-dependent weights and the transmission signals have a plurality of signal frequencies.
19. A method of bandwidth-efficient communications that achieves frequency reuse, the method including:
transmitting a plurality of transmission signals from a transmitter having a plurality of transmitting element wherein the plurality of transmission signals have at least one common frequency channel,
receiving the plurality of transmitted signals with a plurality of receiver elements for providing a plurality of received signals, the received signals having known ratios of co-channel interference,
providing the received signals with algebraically unique ratios of co-channel interference, and
separating at least one desired signal from the received signals.
20. A method of array processing that enables simultaneous frequency use of a plurality of transmitted signals from a transmitter having a plurality of transmitter elements, the method including steps of:
determining a plurality of ratios of co-channel interference occurring between the transmitted signals received at each of a plurality of receivers,
receiving the transmitting signals at the receivers, the receivers capable of being responsive to the received transmitted signals for providing a plurality of received signals, the received signals having known ratios of co-channel interference,
providing the received signal with algebraically unique ratios of co-channel interference, and
separating the transmitted signals from the received signals.
21. A method of bandwidth-efficient communications that achieves frequency reuse, the method including steps of:
providing transmission by a transmitter having a plurality of transmitter elements of a plurality of transmission signals having at least one common frequency channel,
providing determination of a plurality of ratios of co-channel interference occurring between the transmitted signals received by a plurality of receivers,
receiving the transmitted signals, with the receivers, the receivers capable of being responsive to the received transmitted signals for providing a plurality of received signals having known ratios of co-channel interference,
providing the received signals with algebraically unique ratios of co-channel interference, and
providing separation of the transmitted signals from the received signals.