UE-AIDED CHANNEL RECIPROCITY COMPENSATION FOR RADIO ACCESS IN MIMO WIRELESS COMMUNICATION SYSTEMS

• US 20180048492A1
• Filed: 08/10/2017
• Published: 02/15/2018
• Est. Priority Date: 08/11/2016
• Status: Active Grant

• Current Assignee: National Instruments Corporation (Emerson Electric Company)
• Original Assignee: National Instruments Corporation (Emerson Electric Company)
• Inventors: Kundargi, Nikhil U., Nieman, Karl F., Sung, Junmo
• Granted Patent: US 10,447,352 B2
• Time in Patent Office: Days
• CPC Class Codes: H04B 17/11 for calibration
• CPC Class Codes: H04B 17/14 of the whole transmission and reception path, e.g. self-test loop-back
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/0398 Restoration of channel reciprocity
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 5/001 the frequencies being arranged in component carriers
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/0051 of dedicated pilots, i.e. pilots destined for a single user or terminal
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/542 using measured or perceived quality
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A wireless cellular base station (BS) transmitter transmits a downlink calibration pilot symbol. A receiver receives from a user equipment (UE) an uplink calibration pilot symbol and an effective downlink channel estimate transmitted by the UE. The effective downlink channel estimate is computed by the UE using the downlink calibration pilot symbol received from the BS. Processing devices compute an effective uplink channel estimate using the uplink calibration pilot symbol received from the UE and compute channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the BS. The BS includes multiple antennas, and the BS computes the channel reciprocity calibration coefficients for each antenna. Alternatively, the uplink channel estimate received by the BS is an inverted version of the effective downlink channel estimate, which the processing devices use for channel reciprocity compensation.

Claims

1. A method, comprising:

transmitting, by a cellular base station, a downlink calibration pilot symbol;

computing, by a user equipment (UE), an effective downlink channel estimate using the downlink calibration pilot symbol received from the base station;

transmitting, by the UE, an uplink calibration pilot symbol;

computing, by the base station, an effective uplink channel estimate using the uplink calibration pilot symbol received from the UE;

transmitting, by the UE, the effective downlink channel estimate; and

computing, by the base station, channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the base station.

2. The method of claim 1, further comprising:

wherein the UE transmits the uplink calibration pilot symbol within a channel coherence time as the base station transmits the downlink calibration pilot symbol.

3. The method of claim 1, further comprising:

applying the calculated channel reciprocity calibration coefficients within receive and/or transmit path circuitry of the base station.

4. The method of claim 1, further comprising:

wherein the base station comprises a plurality of antennas; and

wherein said computing the channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the base station is performed for each antenna of the plurality of antennas of the base station.

5. The method of claim 4, further comprising:

wherein said transmitting the downlink calibration pilot symbols is performed in a frequency-multiplexed manner using a different frequency subcarrier per antenna of the plurality of antennas.

6. A wireless cellular base station, comprising:

a transmitter that transmits a downlink calibration pilot symbol;

a receiver that receives from a user equipment (UE);

an uplink calibration pilot symbol; and

an effective downlink channel estimate transmitted by the UE, the effective downlink channel estimate being computed by the UE using the downlink calibration pilot symbol received from the base station; and

one or more processing devices that compute;

an effective uplink channel estimate using the uplink calibration pilot symbol received from the UE; and

channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the base station.

7. The wireless cellular base station of claim 6, further comprising:

wherein the transmission of the downlink and uplink calibration pilot symbols are within a channel coherence time.

8. The wireless cellular base station of claim 6,

wherein the base station applies the calculated channel reciprocity calibration coefficients within receiver and/or transmitter.

9. The wireless cellular base station of claim 6, further comprising:

a plurality of antennas; and

wherein the one or more processing devices compute the channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the base station for each antenna of the plurality of antennas.

10. The wireless cellular base station of claim 9, further comprising:

wherein the transmitter transmits the downlink calibration pilot symbols in a frequency-multiplexed manner using a different frequency subcarrier per antenna of the plurality of antennas.

11. A method, comprising:

transmitting, by a cellular base station, a downlink calibration pilot symbol;

computing, by a user equipment (UE), an effective downlink channel estimate using the downlink calibration pilot symbol received from the base station;

transmitting, by the UE, an uplink calibration pilot symbol that is an inverted version of the effective downlink channel estimate; and

using, by the base station, the uplink calibration pilot symbol received from the UE for channel reciprocity compensation.

12. The method of claim 11, further comprising:

transmitting, by the UE, a quantized version of the effective downlink channel estimate; and

using, by the base station, the quantized version of the effective downlink channel estimate received from the UE for channel reciprocity compensation to normalize ill-conditioned values transmitted from the UE to the base station.

13. The method of claim 11, further comprising:

wherein the base station comprises a plurality of antennas; and

wherein said using the uplink calibration pilot symbol received from the UE for channel reciprocity compensation is performed for each antenna of the plurality of antennas of the base station.

14. The method of claim 13, further comprising:

wherein said transmitting the downlink calibration pilot symbols is performed in a frequency-multiplexed manner using a different frequency subcarrier per antenna of the plurality of antennas.

15. The method of claim 13, further comprising:

wherein for each subcarrier of the different frequency subcarriers;

the subcarrier of the uplink calibration pilot symbol is the inverted version of the effective downlink channel estimate at the subcarrier.

16. A wireless cellular base station, comprising:

a transmitter that transmits a downlink calibration pilot symbol;

a receiver that receives from a user equipment (UE);

an uplink calibration pilot symbol transmitted by the UE that is an inverted version of an effective downlink channel estimate, the inverted version of the effective downlink channel estimate being computed by the UE using the downlink calibration pilot symbol received from the base station; and

one or more processing devices that use the uplink calibration pilot symbol received from the UE for channel reciprocity compensation.

17. The wireless cellular base station of claim 16, further comprising:

the receiver also receives from the UE a quantized version of the effective downlink channel estimate; and

the one or more processing devices also use the quantized version of the effective downlink channel estimate received from the UE for channel reciprocity compensation to normalize ill-conditioned values transmitted from the UE to the base station.

18. The wireless cellular base station of claim 16, further comprising:

a plurality of antennas;

wherein for each antenna of the plurality of antennas;

the one or more processing devices use an uplink calibration pilot symbol received from the UE that is an inverted version of an effective downlink channel estimate for channel reciprocity compensation for the antenna.

19. The wireless cellular base station of claim 18, further comprising:

the transmitter transmits the downlink calibration pilot symbols in a frequency-multiplexed manner using a different frequency subcarrier per antenna of the plurality of antennas.

20. The wireless cellular base station of claim 18, further comprising:

wherein for each Jth subcarrier of the different frequency subcarriers;

the Jth subcarrier of the uplink calibration pilot symbol is the inverted version of the effective downlink channel estimate at the Jth subcarrier.