SYSTEM AND METHOD FOR PROVIDING EXTERNAL RECEIVER GAIN COMPENSATION WHEN USING AN ANTENNA WITH A PRE-AMPLIFIER

• US 20100315978A1
• Filed: 06/10/2009
• Published: 12/16/2010
• Est. Priority Date: 06/10/2009
• Status: Active Grant

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: Clear Wireless LLC (Deutsche Telekom AG)
• Inventors: Satapathy, Durga P., Rausch, Walter
• Granted Patent: US 8,811,925 B2
• Time in Patent Office: Days
• US Class Current: 370/294
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 21/08 the units being spaced along or adjacent to a rectilinear path waveguide fed H01Q21/0037
• CPC Class Codes: H01Q 23/00 Antennas with active circuits or circuit elements integrated within them or attached to them
• CPC Class Codes: H03G 3/02 Manually-operated control H03G3/001 and H03G3/002 take precedence
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H04L 27/08 Amplitude regulation arrangements
• CPC Class Codes: H04L 5/1469 using time-sharing

Abstract

In various embodiments, a system and method for improving a noise figure (NF) of a time division duplex (TDD) communications system includes a pre-amplified antenna unit having a plurality of antennas and associated low-noise amplifiers (LNA). Each of the associated LNA'"'"'s is arranged to receive signals from a phase-matched pair of antennas selected from the plurality of antennas. For each of the phase-matched antenna pairs, a variable negative gain circuit may be coupled to a TDD signal output of the associated LNA such that a remote radio head (RRH) may be suitably coupled to an output of the variable gain circuit. The variable gain circuit is configured to provide a negative gain to the TDD signal appropriate to ensure that a dynamic range of the RRH is not reduced from a desired dynamic range due to excess gain provided by the LNA. A method of retrofitting a conventional pre-amplified antenna unit includes inserting a variable negative gain circuit so that the modified pre-amplified antenna may be used with any vendor'"'"'s RRH.

Claims

1. A communications system configured to improve a noise figure (NF) of a time division duplex (TDD) communications system, the system comprising:

a pre-amplified antenna unit comprising a first plurality of antennas and first associated low-noise amplifiers (LNA) contained therein, each of said first associated LNA'"'"'s being arranged to receive a signal from a first phase-matched pair of antennas selected from the plurality of antennas; and

a variable gain circuit coupled to a TDD output signal of at least one of the first associated LNA'"'"'s,

wherein the variable gain circuit is configured to provide a selected negative gain to the TDD output signal.

2. The system of claim 1, wherein the selected negative gain ensures that an output TDD signal from the variable gain circuit is suitable for application to a remote radio head (RRH) input such that a dynamic range of the RRH input is not reduced below a desired dynamic range.

3. The system of claim 2, further comprising a remote radio head (RRH) arranged in the system so as to receive the output TDD signal from the variable gain circuit.

4. The system of claim 1, wherein the variable gain circuit is arranged to receive a combined TDD input signal obtained from a plurality of LNA'"'"'s each coupled to a different first phase-matched pair of antennas selected from the first plurality of antennas.

5. The system of claim 1, wherein the first plurality of antennas comprises 10 antennas each having a same first phase relationship associated therewith.

6. The system of claim 1, further comprising a second plurality of antennas and second associated low-noise amplifiers (LNA) contained therein, each of said second associated LNA'"'"'s being arranged to receive a signal from a second phase-matched pair of antennas selected from the second plurality of antennas, wherein the second phase-matched pair of antennas has a different phase relationship than the first phase-matched pair of antennas.

7. The system of claim 1, wherein said variable gain circuit comprises:

a first circulator having a first port coupled to the at least one of the first associated LNA'"'"'s, a second port coupled to a receive signal path, and a third port coupled to a transmit signal path;

an adjustable negative gain amplifier coupled to the second port and configured to receive the TDD signal output of the at least one of the first associated LNA'"'"'s at an input thereof;

a second circulator having a first port coupled to an output of the adjustable negative gain amplifier on the receive signal path, a second port coupled to an output terminal configured to provide an output to the RRH, and a third port coupled to the third port of the first circulator to form the transmit signal path,

wherein the adjustable negative gain amplifier is configured to be adjusted to reduce a power level of the TDD signal output of the at least one of the first associated LNA'"'"'s to a lower power level so as to avoid overdriving an input of the RRH.

8. The system of claim 2, wherein the variable gain circuit is adapted to operate in a wireless wide area network (WAN) data communications system.

9. The system of claim 3, wherein the WAN data communications system operates in a Gigahertz frequency band.

10. The system of claim 7, wherein the pre-amplified antenna unit is a bi-directional antenna unit,

wherein, in a transmit mode, the second port of the second circulator receives a transmit TDD signal that is supplied to the third port of the first circulator on the transmit path,

wherein the transmit TDD signal is output from the first port of the first circulator and coupled to the plurality of antenna pairs after bypassing the associated LNA'"'"'s.

11. The system of claim 1, wherein the TDD communications system comprises a wireless wide area network (WAN) data communications system.

12. The system of claim 1, wherein the plurality of first phase-matched antenna pairs comprise five antenna pairs.

13. The system of claim 1, wherein the pre-amplified antenna unit comprises a bi-directional antenna unit suitable for both transmitting and receiving TDD signals.

14. The system of claim 1, further comprising a bypass control signal configured to bypass the first associated LNA'"'"'s when the TDD communications system is in a transmit mode.

15. The system of claim 1, wherein said variable gain circuit is arranged and enclosed within the pre-amplified antenna unit.

16. A variable gain circuit configured to receive a time division duplex (TDD) communication signal from a pre-amplified antenna unit at a first power level and to output the communication signal to an external remote radio head (RRH) at a second power level different than the first power level, the circuit comprising:

an input terminal configured to receive a pre-amplified TDD communication signal from a low-noise amplifier (LNA) in the pre-amplified antenna unit;

a first circulator having a first port coupled to the input terminal, a second port coupled to a receive signal path, and a third port coupled to a transmit signal path;

a variable negative gain amplifier coupled to the second port and configured to receive the pre-amplified TDD communication signal at an input thereof;

a second circulator having a first port coupled to an output of the variable negative gain amplifier on the receive signal path, a second port coupled to an output terminal configured to provide an output to the external RRH, and a third port coupled to the third port of the first circulator to form the transmit signal path,

wherein the variable negative gain amplifier is configured to be adjusted to reduce the first power level to the second power level so as to avoid overdriving the external RRH and undesirably reducing a dynamic range associated therewith.

17. The variable gain circuit of claim 16, wherein the transmit signal path bypasses an amplifying unit the variable negative gain amplifier.

18. The variable gain circuit of claim 16, wherein the variable negative gain amplifier comprises a manual gain adjustment.

19. The variable gain circuit of claim 16, wherein the variable negative gain amplifier comprises a gain adjustment responsive to a gain adjustment command signal.

20. The variable gain circuit of claim 19, wherein the gain adjustment command signal is in compliance with AISG 2.0 remote antenna control standards.

22. The variable gain circuit of claim 16, wherein an absolute value of the negative gain of the variable negative gain amplifier is at least 2 dB less than a fixed gain value of the LNA in the pre-amplified antenna unit.

23. The variable negative gain amplifier of claim 16, wherein a negative gain associated therewith is adjustable between 0 and −

12 dB.

24. The variable negative gain amplifier of claim 16, wherein a negative gain associated therewith is adjustable as a function of a fixed gain value of the LNA in the pre-amplified antenna unit.

25. A method of improving a noise figure (NF) of a time-division duplex (TDD) communications system comprising a pre-amplified antenna arrangement, a variable gain element, and a remote radio head (RRH) operatively coupled together, the method comprising:

measuring a TDD signal power output by the pre-amplified antenna arrangement to an input of the RRH;

determining whether the RRH input is being overdriven by the TDD signal power;

if said RRH input is being overdriven, increasing a negative gain provided by the variable gain element so as to reduce a TDD signal power level provided to the RRH input; and

if said RRH input is not being overdriven, maintaining a current negative gain setting of the variable gain element so as to at least temporarily set the TDD signal power level provided to the RRH input at predetermined power level,

wherein the predetermined power level is established to maintain a full dynamic range of the RRH by avoiding overdriving the RRH input.

26. The method of claim 25, further comprising inserting a test signal to represent the TDD signal output by the pre-amplified antenna arrangement.

27. The method of claim 25, further comprising reevaluating the current negative gain setting of the variable gain element to determine whether the RRH input is being overdriven.

28. The method of claim 27, wherein said reevaluating is conducted on a periodic basis.

29. A method of retrofitting a pre-amplified antenna unit configured to operate in a time-division duplex TDD communications system comprising a remote radio head (RRH), the method comprising:

opening the pre-amplified antenna unit;

opening one or more electrical connections between a low-noise amplifier (LNA) in the pre-amplified antenna unit and an output configured to connect to the RRH;

operatively coupling a variable gain circuit between the LNA and the output,

wherein the variable gain circuit is configured to provide a negative gain to a TDD communications signal output from the LNA so as to reduce a power level of the TDD communications signal passed therethrough,

wherein the reduced power level TDD signal is provided as an input to the RRH, and

wherein the negative gain is selected to avoid overdriving the input to the RRH and to preserve a desired dynamic range of the RRH.

30. The method of claim 29, further comprising closing the pre-amplified antenna unit and securing the variable gain circuit external to the pre-amplified antenna unit.

31. The method of claim 29, further comprising securing the variable gain circuit completely within the pre-amplified antenna unit and closing the pre-amplified antenna unit.