Self-cancelling full-duplex RF communication system

• US 5,691,978 A
• Filed: 01/21/1997
• Issued: 11/25/1997
• Est. Priority Date: 04/07/1995
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Signal Science, Inc. (ITT, Inc.)
• Inventors: Kenworthy, Gary Robert
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US08/786,197
• Time in Patent Office: 308 Days
• Field of Search: 370/276, 370/277, 370/278, 370/279, 370/282, 370/286, 370/287, 370/288, 370/289, 370/290, 370/291, 379/219, 379/346, 379/350, 379/406, 379/410, 379/411, 375/230, 375/232, 455/67.3, 455/296, 455/307, 455/541
• US Class Current: 370/278
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 1/408 the transmitter oscillator frequency being identical to the receiver local oscillator frequency
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 1/56 with provision for simultaneous communication in two directions
• CPC Class Codes: H04B 7/002 Reducing depolarization effects

Abstract

A method is presented herein whereby both transceivers of a full-duplex RF communications system can use the same spectrum at the same time. Self-interference is cancelled using a combination of antenna placement, analog RF suppression, and digital adaptive filtering. The details of this self-cancelling technique are presented.

Claims

1. A full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, at least one of the first transceiver and the second transceiver comprising:

a modulator responsive to one of said first and second signals to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified signal of substantially said predetermined frequency;

a transmit antenna coupled to said amplified signal for radiating said amplified signal in a radiation pattern;

a receive antenna for picking up a radiated signal and producing in response thereto a picked-up signal, said receive antenna being positioned in at least a local minimum of said radiation pattern;

means responsive to said picked-up signal for selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and for producing an intermediate signal; and

a demodulator responsive to said intermediate signal for producing the other of said first and second signals.

2. A full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, at least one of the first transceiver and the second transceiver comprising:

a modulator responsive to one of said first and second signals to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified signal of substantially said predetermined frequency;

a power splitter responsive to said amplified signal for producing a transmit signal and a reference signal;

a transmit antenna coupled to said transmit signal for radiating said transmit signal in a radiation pattern;

a receive antenna for picking up a radiated signal and producing in response thereto a picked-up signal, said receive antenna being positioned in at least a local minimum of said radiation pattern;

an analog RF canceller responsive to said picked-up signal and said reference signal for cancelling from said picked-up signal energy attributable to said transmit signal to produce an at least partially self-cancelled signal;

means responsive to said at least partially self-cancelled signal for selectively receiving a portion of said at least partially self-cancelled signal of substantially said predetermined frequency and for producing an intermediate signal; and

a demodulator responsive to said intermediate signal for producing the other of said first and second signals.

3. A full-duplex radio communications transceiver comprising:

a modulator responsive to a first information signal to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified signal of a predetermined frequency;

a power splitter responsive to said amplified signal for producing a transmit signal and a reference signal;

a transmit antenna coupled to said transmit signal for radiating said transmit signal in a radiation pattern;

a receive antenna for picking up a radiated signal and producing in response thereto a picked-up signal, said receive antenna being positioned in at least a local minimum of said radiation pattern;

an analog RF canceller responsive to said picked-up signal and said reference signal for cancelling from said picked-up signal energy attributable to said transmit signal to produce a first self-cancelled signal;

means responsive to said first self-cancelled signal for selectively receiving a portion of said first self-cancelled signal of substantially said predetermined frequency and for producing an intermediate signal;

means responsive to said intermediate signal and said modulated signal for cancelling from said intermediate signal further energy attributable to said transmit signal to produce a second self-cancelled signal; and

a demodulator responsive to said second self-cancelled signal for producing a second information signal.

4. The apparatus of claim 3, wherein said modulator is a baseband modulator.

5. The apparatus of claim 4, wherein said means for producing an amplified signal comprises a upconverter/power amplifier.

6. The apparatus of claim 3, wherein said modulator is an RF modulator.

7. The apparatus of claim 6, wherein said means for producing an amplified signal comprises an power amplifier.

8. The apparatus of claim 6, wherein said means for cancelling comprises a downconverter and an adaptive filter.

9. A full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, at least one of the first transceiver and the second transceiver comprising:

a modulator responsive to one of said first and second signals to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified signal of substantially said predetermined frequency;

a power splitter responsive to said amplified signal for producing a transmit signal and a reference signal;

a directional coupler coupled to said transmit signal;

a transmit/receive antenna coupled to said directional coupler for radiating said transmit signal in a radiation pattern and for picking up a radiated signal and producing in response thereto a picked-up signal, said directional coupler producing a receive signal in response to said picked-up signal;

an analog RF canceller responsive to said receive signal and said reference signal for cancelling from said receive signal energy attributable to said transmit signal to produce an at least partially self-cancelled signal;

means responsive to said at least partially self-cancelled signal for selectively receiving a portion of said at least partially self-cancelled signal of substantially said predetermined frequency and for producing an intermediate signal; and

a demodulator responsive to said intermediate signal for producing the other of said first and second signals.

10. A full-duplex radio communications transceiver comprising:

a modulator responsive to a first information signal to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified signal of a predetermined frequency;

a power splitter responsive to said amplified signal for producing a transmit signal and a reference signal;

a directional coupler coupled to said transmit signal;

a transmit/receive antenna coupled to said directional coupler for radiating said transmit signal in a radiation pattern and for picking up a radiated signal and producing in response thereto a picked-up signal, said directional coupler producing a receive signal in response to said picked-up signal;

an analog RF canceller responsive to said receive signal and said reference signal for cancelling from said receive signal energy attributable to said transmit signal to produce a first self-cancelled signal;

means responsive to said first self-cancelled signal for selectively receiving a portion of said first self-cancelled signal of substantially said predetermined frequency and for producing an intermediate signal;

means responsive to said intermediate signal and said modulated signal for cancelling from said intermediate signal further energy attributable to said transmit signal to produce a second self-cancelled signal; and

a demodulator responsive to said second self-cancelled signal for producing a second information signal.

11. In a full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, a method of performing full-duplex communications over a single communications channel, comprising the steps of, at at least one of said first transceiver and said second transceiver:

positioning a receive antenna in at least a local minimum of a known radiation pattern;

during transmission;

modulating one of said first and second signals to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified signal of a predetermined frequency; and

radiating said amplified signal in said known radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and producing an intermediate signal; and

demodulating said intermediate signal to produce the other of said first and second signals.

12. In a full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, a method of performing full-duplex communications over a single communications channel, comprising the steps of, at at least one of said first transceiver and said second transceiver:

positioning a receive antenna in at least a local minimum of a known radiation pattern;

during transmission;

modulating one of said first and second signals to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified signal of a predetermined frequency;

splitting said amplified signal to produce a transmit signal and a reference signal; and

radiating said transmit signal in said known radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

inputting said picked-up signal and said reference signal to an RF canceller and using said RF canceller to cancel from said picked-up signal energy attributable to said transmit signal to produce an at least partially self-cancelled signal;

selectively receiving a portion of said at least partially self-cancelled signal of substantially said predetermined frequency and producing an intermediate signal; and

demodulating said intermediate signal to produce the other of said first and second signals.

13. In a radio communications transceiver having a receive antenna, an analog RF canceller, and an adaptive filter, a method of performing full-duplex communications over a single communications channel, comprising the steps of:

positioning said receive antenna in at least a local minimum of a known radiation pattern;

during transmission;

modulating a first information signal to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified signal of a predetermined frequency;

splitting said amplified signal to produce a transmit signal and a reference signal; and

radiating said transmit signal in said known radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

inputting said picked-up signal and said reference signal to said RF canceller and using said RF canceller to cancel from said picked-up signal energy attributable to said transmit signal to produce a first self-cancelled signal;

selectively receiving a portion of said first self-cancelled signal of substantially said predetermined frequency and producing an intermediate signal;

inputting said intermediate signal and said modulated signal into said adaptive filter and using said adaptive filter to cancel from said intermediate signal further energy attributable to said transmit signal to produce a second self-cancelled signal; and

demodulating said second self-cancelled signal to produce a second information signal.

14. In a full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, a method of performing full-duplex communications over a single communications channel, comprising the steps of, at at least one of said first transceiver and said second transceiver:

during transmission;

modulating one of said first and second signals to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified signal of a predetermined frequency;

splitting said amplified signal to produce a transmit signal and a reference signal;

distinguishing said transmit signal from a combined transmit/receive signal using a directional coupler; and

radiating said transmit signal in a radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

distinguishing said picked-up signal from said combined transmit/receive signal using said directional coupler;

inputting said picked-up signal and said reference signal to an RF canceller and using said RF canceller to cancel from said picked-up signal energy attributable to said transmit signal to produce an at least partially self-cancelled signal;

selectively receiving a portion of said at least partially self-cancelled signal of substantially said predetermined frequency and producing an intermediate signal; and

demodulating said intermediate signal to produce the other of said first and second signals.

15. In a radio communications transceiver having a transmit/receive antenna, a directional coupler, an analog RF canceller, and an adaptive filter, a method of performing full-duplex communications over a single communications channel, comprising the steps of:

during transmission;

modulating a first information signal to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified signal of a predetermined frequency;

splitting said amplified signal to produce a transmit signal and a reference signal;

distinguishing said transmit signal from a combined transmit/receive signal using said directional coupler; and

radiating said transmit signal in a radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

distinguishing said picked-up signal from said combined transmit/receive signal using said directional coupler;

inputting said picked-up signal and said reference signal to said RF canceller and using said RF canceller to cancel from said picked-up signal energy attributable to said transmit signal to produce a first self-cancelled signal;

selectively receiving a portion of said first self-cancelled signal of substantially said predetermined frequency;

inputting said intermediate signal and said modulated signal into said adaptive filter and using said adaptive filter to cancel from said intermediate signal further energy attributable to said transmit signal to produce a second self-cancelled signal; and

demodulating said second self-cancelled signal to produce a second information signal.

16. A full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, at least one of the first transceiver and the second transceiver comprising:

a modulator responsive to one of said first and second signals to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified transmit signal of a predetermined frequency;

antenna means for radiating said transmit signal in a radiation pattern and for picking up a radiated signal and producing in response thereto a picked-up signal;

means responsive to said picked-up signal for selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and for producing an intermediate signal;

means responsive to said intermediate signal and said modulated signal for cancelling from said intermediate signal further energy attributable to said transmit signal to produce a self-cancelled signal; and

a demodulator responsive to said self-cancelled signal for producing the other of said first and second signals.

17. A full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, at least one of the first transceiver and the second transceiver comprising:

a modulator responsive to one of said first and second signals to be transmitted for producing a modulated signal;

means responsive to said modulated signal for producing an amplified transmit signal of a predetermined frequency;

a transmit antenna coupled to said transmit signal for radiating said transmit signal in a radiation pattern;

a receive antenna for picking up a radiated signal and producing in response thereto a picked-up signal, said receive antenna being positioned in at least a local minimum of said radiation pattern;

means responsive to said picked-up signal for selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and for producing an intermediate signal;

means responsive to said intermediate signal and said modulated signal for cancelling from said intermediate signal energy attributable to said transmit signal to produce a self-cancelled signal; and

a demodulator responsive to said self-cancelled signal for producing the other of said first and second signals.

18. In a full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, a method of performing full-duplex communications over a single communications channel, comprising the steps of, at at least one of said first transceiver and said second transceiver:

during transmission;

modulating one of said first and second signals to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified transmit signal of a predetermined frequency; and

radiating said transmit signal;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and producing an intermediate signal;

inputting said intermediate signal and said modulated signal into an adaptive filter and using said adaptive filter to cancel from said intermediate signal energy attributable to said transmit signal to produce a self-cancelled signal; and

demodulating said self-cancelled signal to produce the other of said first and second signals.

19. In a full-duplex radio communications system comprising a first transceiver that transmits a first signal of a predetermined frequency and a second transceiver that transmits a second signal of substantially said predetermined frequency, the first signal being a desired signal of the second transceiver and the second signal being a desired signal of the first transceiver, wherein at a particular instant of time both the first signal and the second signal are being transmitted, a method of performing full-duplex communications over a single communications channel, comprising the steps of, at at least one of said first transceiver and said second transceiver:

positioning a receive antenna in at least a local minimum of a known radiation pattern;

during transmission;

modulating one of said first and second signals to be transmitted to produce a modulated signal;

processing said modulated signal to produce an amplified transmit signal of a predetermined frequency; and

radiating said transmit signal in said known radiation pattern;

during reception, concurrent with said transmission;

picking up a radiated signal and producing in response thereto a picked-up signal;

selectively receiving a portion of said picked-up signal of substantially said predetermined frequency and producing an intermediate signal;

inputting said intermediate signal and said modulated signal into an adaptive filter and using said adaptive filter to cancel from said intermediate signal energy attributable to said transmit signal to produce a self-cancelled signal; and

demodulating said self-cancelled signal to produce the other of said first and second signals.