Channel calibration for a time division duplexed communication system
First Claim
1. A method of calibrating communication links in a wireless time division duplexed (TDD) communication system, comprising:
- obtaining a channel response estimate for a downlink channel from an access point to a user terminal;
obtaining a channel response estimate for an uplink channel from the user terminal to the access point; and
determining correction factors for the access point and correction factors for the user terminal based on the channel response estimates for the downlink and uplink channels, the correction factors for the access point and the correction factors for the user terminal being used to obtain a calibrated downlink channel response and a calibrated uplink channel response.
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Abstract
Techniques are described to calibrate the downlink and uplink channels to account for differences in the frequency responses of the transmit and receive chains at an access point and a user terminal. In one method, pilots are transmitted on the downlink and uplink channels and used to derive estimates of the downlink and uplink channel responses, respectively. Correction factors for the access point and correction factors for the user terminal are determined based on (e.g., by performing matrix-ratio computation or minimum mean square error (MMSE) computation on) the downlink and uplink channel response estimates. The correction factors for the access point and the correction factors for the user terminal are used to obtain a calibrated downlink channel and a calibrated uplink channel, which are transpose of one another. The calibration may be performed in real time based on over-the-air transmission.
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Citations
40 Claims
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1. A method of calibrating communication links in a wireless time division duplexed (TDD) communication system, comprising:
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obtaining a channel response estimate for a downlink channel from an access point to a user terminal;
obtaining a channel response estimate for an uplink channel from the user terminal to the access point; and
determining correction factors for the access point and correction factors for the user terminal based on the channel response estimates for the downlink and uplink channels, the correction factors for the access point and the correction factors for the user terminal being used to obtain a calibrated downlink channel response and a calibrated uplink channel response. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An apparatus in a wireless time division duplexed (TDD) communication system, comprising:
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means for obtaining a channel response estimate for a downlink channel from an access point to a user terminal;
means for obtaining a channel response estimate for an uplink channel from the user terminal to the access point; and
means for determining correction factors for the access point and correction factors for the user terminal based on the channel response estimates for the downlink and uplink channels, the correction factors for the access point and the correction factors for the user terminal being used to obtain a calibrated downlink channel response and a calibrated uplink channel response. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. A method of calibrating communication links in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:
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transmitting a pilot on a first communication link from a first station to a second station;
obtaining a channel response estimate for the first communication link derived based on the pilot transmitted on the first communication link;
receiving a pilot on a second communication link from the second station;
deriving a channel response estimate for the second communication link based on the pilot received on the second communication link; and
determining correction factors for the first station and correction factors for the second station based on the channel response estimates for the first and second communication links, the correction factors for the first station and the correction factors for the second station being used to obtain a calibrated channel response for the first communication link and a calibrated channel response for the second communication link. - View Dependent Claims (25, 26, 27)
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28. An apparatus in a wireless time division duplexed (TDD) communication system, comprising:
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a transmit spatial processor to transmit a first pilot on a first communication link from a first station to a second station;
a receive spatial processor to receive a second pilot on a second communication link from the second station, to derive a channel response estimate for the second communication link based on the received second pilot, and to receive a channel response estimate for the first communication link derived based on the transmitted first pilot; and
a controller to determine correction factors for the first station and correction factors for the second station based on the channel response estimates for the first and second communication links, the correction factors for the first station and the correction factors for the second station being used to obtain a calibrated channel response for the first communication link and a calibrated channel response for the second communication link. - View Dependent Claims (29, 30, 31, 32)
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33. A method of transmitting data in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:
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applying correction factors for a first station on a transmit side, or a receive side, or both the transmit and receive sides at the first station;
transmitting a pilot on a first communication link from the first station to a second station; and
receiving a data transmission sent on a second communication link from the second station to the first station, wherein the data transmission is spatially processed based on a channel response estimate for the first communication link derived from the pilot transmitted on the first communication link. - View Dependent Claims (34, 35, 36)
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37. An apparatus in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:
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means for applying correction factors for a first station on a transmit side, or a receive side, or both the transmit and receive sides at the first station;
means for transmitting a pilot on a first communication link from the first station to a second station; and
means for receiving a data transmission sent on a second communication link from the second station to the first station, wherein the data transmission is spatially processed based on a channel response estimate for the first communication link derived from the pilot transmitted on the first communication link.
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38. An apparatus in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:
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a transmit processor to transmit a pilot on a first communication link from a first station to a second station; and
a receive processor to receive a data transmission sent on a second communication link from the second station to the first station, wherein the data transmission is spatially processed based on a channel response estimate for the first communication link derived from the pilot transmitted on the first communication link, and wherein the transmit processor applies correction factors to the transmitted pilot, or the receive processor applies correction factors to the received data transmission, or both the transmit processor applies correction factors to the transmitted pilot and the receive processor applies correction factors to the received data transmission.
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39. A method of transmitting data in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:
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transmitting a pilot on a first communication link from a first station to a second station;
receiving a data transmission sent on a second communication link from the second station to the first station, wherein the second station applies correction factors on a transmit side, or a receive side, or both the transmit and receive sides at the second station, and wherein the data transmission is spatially processed based on a channel response estimate for the first communication link derived from the pilot transmitted on the first communication link; and
processing the received data transmission with a minimum mean square error (MMSE) receiver at the first station. - View Dependent Claims (40)
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Specification