TRANSMIT LEAKAGE CANCELLATION IN A WIDE BANDWIDTH DISTRIBUTED ANTENNA SYSTEM

• US 20120052892A1
• Filed: 08/22/2011
• Published: 03/01/2012
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Powerwave Technologies Incorporated
• Inventors: BRAITHWAITE, RICHARD NEIL
• Granted Patent: US 9,042,838 B2
• Time in Patent Office: Days
• US Class Current: 455/501
• CPC Class Codes: H04B 1/48 in circuits for connecting transmitter and receiver to a common transmission path, e.g. by energy of transmitter H04B1/46 takes precedence
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 2001/485 inhibiting unwanted transmission
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A system and methods for cancelling transmission leakage signals in a wide bandwidth Distributed Antenna System (“DAS”) having remote units is disclosed. An internal cancellation circuit within the remote unit is employed to reduce the transmitted leakage signals by generating a cancellation signal. This cancellation signal is added to the received signal to cancel the transmission leakage signal in the receiving signal path. A pilot signal generation circuit is employed to optimize the cancellation circuit operating parameters. The frequency of the pilot signal is swept over a range to determine the pilot frequency having the highest electromagnetic coupling. The amplitude and phase of the cancellation signal is then optimized to minimize the level of transmission leakage in the receiving transmission path.

Claims

1. A distributed antenna system (“

DAS”

) comprising a plurality of wireless remote units coupled to one or more base stations, wherein said wireless remote units comprise;

a first signal path for providing a transmission signal;

a transmitting antenna for outputting the transmission signal;

a receiving antenna for receiving a received signal;

a second signal path for providing the received signal; and

,

a cancellation circuit coupled to the first signal path and the second signal path, wherein the cancellation circuit includes a means for providing a cancellation signal to the second signal path for substantially cancelling a transmission leakage signal in the received signal.

2. A DAS comprising a plurality of wireless remote units coupled to one or more base stations as set out in claim 1, wherein the cancellation circuit comprises a delay circuit configured for matching a delay associated with the first signal path, the transmitting antenna, the receiving antenna, and the second signal path.

3. A DAS comprising a plurality of wireless remote units coupled to one or more base stations as set out in claim 2, wherein the means for providing a cancellation signal comprises a vector modulator configured for substantially cancelling a transmission leakage signal in the received signal by adjusting the amplitude and phase of the cancellation signal.

4. A DAS comprising a plurality of wireless remote units coupled to one or more base stations as set out in claim 3, wherein the cancellation circuit further comprises a bandpass filter having a bandwidth substantially less than the bandwidth of said DAS.

5. A DAS comprising a plurality of wireless remote units coupled to one or more base stations as set out in claim 1, wherein the cancellation bandwidth has a bandwidth in the range of approximately 60 Megahertz to approximately 200 Megahertz.

6. A distributed antenna system (“

DAS”

) including a plurality of wireless remote units, each comprising;

a first signal path for providing a transmission signal;

a transmitting antenna for outputting the transmission signal;

a receiving antenna for receiving a received signal;

a second signal path for providing the received signal;

a pilot signal generation circuit coupled to the first signal path and the second signal path, the pilot signal generation circuit comprising a first bandpass filter having a first bandwidth, wherein the pilot signal generation circuit is configured for generating a pilot signal in the first signal path;

a detector for detecting the pilot signal in the second signal path; and

,

a cancellation circuit coupled to the first signal path and the second signal path, wherein the cancellation circuit is controlled responsive to the detected pilot signal for providing a cancellation signal to the second signal path for substantially cancelling a transmission leakage signal in the received signal.

7. A DAS including a plurality of wireless remote units as set out in claim 6, each further comprising:

a first amplifier in the first signal path; and

a second amplifier in the second signal path;

wherein the pilot signal generation circuit is coupled to the input of the first amplifier and is coupled to the output of the second amplifier and the cancellation circuit is coupled to the output of the first amplifier and the input of the second amplifier.

8. A DAS including a plurality of wireless remote units as set out in claim 7, wherein the cancellation circuit further comprises:

a cancellation circuit bandpass filter coupled to the first signal path;

a delay circuit coupled to the bandpass filter;

a vector modulator coupled to the delay circuit, wherein the vector modulator is configured for substantially cancelling a transmission leakage signal in the received signal by adjusting the amplitude and phase of the cancellation signal; and

,

an additive coupler coupled to the output of the vector modulator and the second signal path.

9. A DAS including a plurality of wireless remote units as set out in claim 8, wherein the pilot signal generation circuit further comprises a controller configured for controlling the vector modulator based on the detected pilot signal in the second signal path.

10. A DAS including a plurality of wireless remote units as set out in claim 9, wherein the pilot signal generation circuit further comprises:

a limiter configured for limiting overall gain of the pilot signal generation circuit, the first amplifier, the cancellation circuit, and the second amplifier; and

,

a phase shifter configured for shifting the frequency of the pilot signal.

11. A DAS including a plurality of wireless remote units as set out in claim 10, wherein the pilot signal generation circuit further comprises an absorptive switch configured for disabling the pilot signal generation circuit.

12. A DAS including a plurality of wireless remote units as set out in claim 7, each further comprising:

a second pilot signal generation circuit configured for providing a second pilot signal in the first signal path, the second pilot signal generation circuit comprising a second bandpass filter having a second bandwidth differing from the first bandwidth of the first bandpass filter, wherein the second pilot signal generation circuit is coupled to the input of the first amplifier and is coupled to the output of the second amplifier;

a second detector for detecting the second pilot signal in the second signal path; and

,

a second cancellation circuit configured for providing a second cancellation signal to the second signal path;

wherein the second cancellation circuit is coupled to the output of the first amplifier and the input of the second amplifier.

13. A DAS including a plurality of wireless remote units as set out in claim 12, wherein:

the pilot signal generation circuit further comprises;

a limiter configured for limiting gain of the pilot signal generation circuit, the first amplifier, the cancellation circuit, and the second amplifier; and

,

a phase shifter configured for shifting the phase of the pilot signal;

the second pilot signal generation circuit further comprises;

a second limiter configured for limiting gain of the second pilot signal generation circuit, the first amplifier, the second cancellation circuit, and the second amplifier; and

,

a second phase shifter configured for shifting the phase of the second pilot signal.

14. A DAS including a plurality of wireless remote units as set out in claim 7, each further comprising:

a second cancellation circuit configured for providing a second cancellation signal to the second signal path;

wherein the second cancellation circuit is coupled to the output of the first amplifier and the input of the second amplifier;

wherein the pilot signal generation circuit is further configured for generating a second pilot signal in the first signal path.

15. A method for transmission leakage cancellation in a wireless remote unit in a distributed antenna system (“

DAS”

), the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna, comprising;

generating a pilot signal;

providing the pilot signal to a transmission antenna;

generating a cancellation signal;

receiving the received signal having a transmission leakage signal in a receiving antenna;

providing the received signal to a second signal path; and

,

cancelling the transmission leakage signal by adding the cancellation signal with the received signal.

16. A method for transmission leakage cancellation in a wireless remote unit in a DAS, the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna as set out in claim 15, further comprising:

filtering the pilot signal with a bandpass filter having a first bandwidth; and

,

filtering the cancellation signal with a second bandpass filter having the first bandwidth

17. A method for transmission leakage cancellation in a wireless remote unit in a DAS, the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna as set out in claim 15, wherein cancelling the transmission leakage signal comprises:

detecting a residual pilot signal after the cancellation signal has been added to the received signal; and

,

adjusting an amplitude and phase of the cancellation signal based on the detected residual pilot signal.

18. A method for transmission leakage cancellation in a wireless remote unit in a DAS, the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna as set out in claim 17, further comprising:

shifting the frequency of the pilot signal to find a pilot frequency with a highest RF coupling; and

,

adjusting the amplitude and phase of the cancellation signal to minimize the detected residual pilot signal.

19. A method for transmission leakage cancellation in a wireless remote unit in a DAS, the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna as set out in claim 18, wherein adjusting the amplitude and phase of the cancellation signal further comprises performing a two-dimensional descent-based search.

20. A method for transmission leakage cancellation in a wireless remote unit in a DAS, the remote unit having a first signal path coupled to a transmission antenna and a second signal path coupled to a receiving antenna as set out in claim 18, wherein adjusting the amplitude and phase of the cancellation signal further comprises determining the optimized amplitude and phase parameters.