Method and apparatus for eliminating intermodulation interference in cellular telephone systems

• US 6,584,081 B1
• Filed: 08/19/1999
• Issued: 06/24/2003
• Est. Priority Date: 02/06/1996
• Status: Expired due to Term

• Current Assignee: Cellco Partnership, Inc. (Verizon Communications Inc.)
• Original Assignee: Cellco Partnership, Inc. (Verizon Communications Inc.)
• Inventors: Lee, William Chien-Yeh, Farrill, F. Craig
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US09/377,443
• Time in Patent Office: 1,405 Days
• Field of Search: 370/315, 370/328, 370/317, 370/320, 455/446, 455/63, 455/426
• US Class Current: 370/315
• CPC Class Codes: H04B 1/71 the interference being narrowband interference
• CPC Class Codes: H04W 16/32 Hierarchical cell structures

Abstract

The invention describes method and apparatus for reducing intermodulation interference caused by reception of undesired signals in wireless receivers. The apparatus comprises an antenna for receiving the desired signal, a low noise amplifier for amplifying this signal, an adjustable attenuator, and a transmitting antenna to transmit the amplified signal to the wireless receiver. By increasing the strength of the desired signal, the present invention eliminates intermodulation distortion caused by the undesirable signals. The invention also describes an apparatus further comprising an adjustable filter for limiting the spectral content of the transmitted amplified signal, and an apparatus for selecting the characteristics of the adjustable filter in accordance with the measured characteristics of the desired and undesired signals.

Claims

1. An apparatus for reducing intermodulation interference from an external signal transmitted from an external transmitter, comprising:

a first antenna for receiving signals comprising duplex communications having a forward channel signal transmitted over a forward channel from a base transceiver and a reverse channel signal transmitted over a reverse channel by a wireless transceiver;

a signal generator, coupled to the first antenna, comprising a filter for passing the forward channel signal and for rejecting reverse channel signal, and an amplifier, coupled to the filter, for amplifying the filtered signal;

a second antenna, coupled to the amplifier, for transmitting the amplified and filtered signal to the wireless transceiver to reduce intermodulation interference in the wireless transceiver from the external signal; and

wherein the second antenna is disposed proximate to the external transmitter.

2. The apparatus of claim 1, further comprising an attenuator, coupled between the amplifier and the second antenna, for reducing the amplitude of the amplified filtered signal.

3. The apparatus of claim 2, wherein the attenuator is an adjustable attenuator.

4. The apparatus of claim 3, wherein the adjustable attenuator is adjusted according to a distance from the external transmitter to the second antenna.

5. The apparatus of claim 1, wherein the filter is adjustable to shape the spectral content of the received signals.

6. The apparatus of claim 5, wherein the adjustable filter is a notch filter tuned to reject the external signal.

7. The apparatus of claim 5, further comprising an adjustable attenuator coupled between the amplifier and the second antenna and wherein the apparatus further comprises a signal processor coupled to the receiving antenna, the adjustable attenuator, and the adjustable filter, the signal processor for providing a control signal to the adjustable filter and the adjustable attenuator based on a characteristic of the external signal.

8. The apparatus of claim 7, wherein the external signal characteristicis selected from a group comprising external signal power and external signal spectral content.

9. The apparatus of claim 7, further comprising an adaptive nuller responsive to a command signal from the base transceiver, the adaptive nuller coupled between the first antenna and the filter, the adaptive nuller for modifying the received signals according to the control signal from the signal processor.

10. The apparatus of claim 7, further comprising a trigger coupled to the amplifier, the trigger providing a trigger signal in response to a command signal from the signal processor.

11. The apparatus of claim 10 wherein the signal processor provides a command signal to the trigger when a forward channel signal is detected.

25. The system in claim 2, wherein the wireless receiver is a cellular telephone receiver.

33. The apparatus of claim 5, wherein the filter is adjusted according to a characteristic of the external signal.

34. The apparatus of claim 10, wherein the signal processor provides the command signal to the trigger when the external signal is detected.

12. A method of reducing intermodulation interference from an external signal received from an external transmitter, comprising the steps of:

receiving signals comprising communications from the base transceiver, the duplex communications comprising a forward channel signal transmitted over a forward channel by a base transceiver and a reverse channel signal transmitted over a reverse channel by a wireless receiver;

filtering the received signals to pass the forward channel signal and to reject the reverse channel signal;

amplifying the filtered signal; and

transmitting the filtered and amplified signal to the wireless transceiver from an antenna disposed proximate to the external transmitter to reduce intermodulation interference in the wireless transceiver from the external signal.

13. The method of claim 12, further comprising the step of attenuating the filtered and amplified signals.

14. The method of claim 13, further comprising the step of determining a distance from the external transmitter to the antenna used to transmit the filtered and amplified received signals, and attenuating the filtered and amplified received signals according to the distance from the external transmitter to the antenna.

15. The method of claim 12, further comprising the steps of:

measuring the power of the external signal; and

attenuating the filtered and amplified signal according to the measured power of the external signal.

16. The method of claim 12, further comprising the steps of:

measuring the spectral content of the external signal; and

filtering the received signals according to the measured spectral content of the external signal.

17. The method of claim 12, wherein the step of processing the received signal to pass the forward channel signals and to reject the reverse channel signals comprises the step of filtering the received signals to pass only the forward channel signals.

18. The method of claim 12, wherein the amplifying step is performed only when a forward channel signal is present.

19. The method of claim 12 wherein the amplifying step is performed only when an external signal is detected.

20. A system for reducing intermodulation interference in a wireless receiver during reception of a first signal, comprising:

a first antenna for receiving a first signal from a first source and an interfering second signal from a second source having a location relative to the first source defining an interference region;

a filter for passing the first signal and for rejecting the second signal, coupled to the first antenna;

an amplifier, coupled to the filter, for amplifying the filtered signal; and

a second antenna, coupled to the amplifier, and located within the interference region, for transmitting the amplified and filtered first signal to the wireless receiver to reduce interference in the wireless receiver caused by the second signal.

21. The system in claim 20, wherein the filter is a notch filter tuned to substantially reject the second signal.

22. The system in claim 20, wherein the second signal is stronger than the first signal.

23. The system in claim 20, wherein the first source is a first cellular telephone transmitter for transmitting a desired signal.

24. The system in claim 20, wherein the second source is a second cellular telephone transmitter for transmitting an undesired signal.

26. An apparatus for reducing intermodulation interference in a wireless receiver during reception of a first signal transmitted by a first source in the presence of a second signal transmitted by a second source, wherein a relationship between the first source and the second source describe an interference region, comprising:

a first antenna;

a filter for passing the first signal and rejecting the second signal, the filter coupled to the first antenna;

an amplifier, coupled to the filter, for amplifying the filtered signal; and

a second antenna, coupled to the amplifier, and disposed within the intermodulation interference region, for transmitting the amplified and filtered signal to the wireless receiver to reduce interference in the wireless receiver from the second signal.

27. The apparatus in claim 26, wherein the filter is a notch filter tuned to reject the second signal.

28. The apparatus in claim 26, wherein the second signal is stronger than the first signal.

29. The apparatus in claim 26, wherein the first source is a cellular telephone transmitter for transmitting a desired signal.

30. The apparatus in claim 26, wherein the second source is a cellular telephone transmitter for transmitting an undesired signal.

31. The apparatus in claim 26, wherein the wireless receiver is a cellular telephone receiver.

32. A method for reducing interference in a wireless receiver during reception of a first signal transmitted by a first source in a first location in the presence of a second signal transmitted by a second source in a second location, wherein a relationship between the first source and the second source defines an interference region, comprising the steps of:

receiving the first signal and the second signal;

filtering the received first signal and the received second signal, to substantially pass the first signal and substantially reject the second signal;

amplifying the filtered signal; and

transmitting the filtered and amplified signal from within the interference region.