Over the air coupling for digital pre-distortion calibration

1. A multiple input multiple output (MIMO) transceiver configured for digital pre-distortion (DPD) calibration, the MIMO transceiver comprising:

a first communication chain that includes both a first receive chain and a first transmit chain, the first transmit chain configured to wirelessly transmit a calibration signal at a first frequency, the first transmit chain comprising a pre-distorter circuit configured to accept pre-distortion parameters to pre-distort data signals prior to transmission and a power amplifier (PA) configured to amplify the data signals of the first transmit chain prior to transmission;

a second communication chain that includes both a second receive chain and a second transmit chain, the second receive chain configured to wirelessly receive the calibration signal at the first frequency, the second receive chain comprising:

a converter circuit configured to convert the calibration signal to a baseband frequency; and

a buffer configured to buffer the calibration signal at the baseband frequency; and

a DPD circuit configured to calibrate the pre-distortion parameters based on the buffered calibration signal to compensate for non-linearity in amplification provided by the PA of the first transmit chain,

wherein the first communication chain is configured to be in a transmit mode to transmit the calibration signal while the second communication chain is configured to simultaneously be in a receive mode to receive the calibration signal.

2. The MIMO transceiver of claim 1 further comprising a clear to send circuit configured to transmit a CTS-to-Self signal to other MIMO transceivers within an operational environment of the MIMO transceiver, the CTS-to-Self signal reserving a duration of time for the MIMO transceiver to perform DPD calibration using the first communication chain and the second communication chain.

3. The MIMO transceiver of claim 1 , wherein the calibration signal comprises a first calibration signal, the converter circuit comprises a first converter circuit, the pre-distorter circuit comprises a first pre-distorter circuit, the PA comprises a first PA, the pre-distortion parameters comprise first pre-distortion parameters, and the buffer comprises a first buffer, and responsive to calibration of the first pre-distortion parameters, the first transmit chain is further configured to stop wirelessly transmitting the first calibration signal and the second transmit chain is configured to start wirelessly transmitting a second calibration signal at the first frequency, and:

the second transmit chain comprises:

a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals prior to transmission; and

a second PA configured to amplify the data signals of the second transmit chain prior to transmission; and

the first receive chain is configured to wirelessly receive the second calibration signal at the first frequency, the first receive chain comprises:

a second converter circuit configured to convert the second calibration signal to the baseband frequency; and

a second buffer configured to buffer the second calibration signal at the baseband frequency, the DPD circuit further configured to calibrate the second pre-distortion parameters based on the buffered second calibration signal to compensate for non-linearity in amplification provided by the second PA of the second transmit chain.

4. The MIMO transceiver of claim 1 , wherein the calibration signal comprises a first calibration signal, the pre-distorter circuit comprises a first pre-distorter circuit, the PA comprises a first PA, and the MIMO transceiver further comprises a third communication chain configured to wirelessly transmit a second calibration signal at the first frequency, the third communication chain comprising a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals prior to transmission and a second PA configured to amplify the data signals of the third communication chain prior to transmission, and the second receive chain is further configured to receive a combined calibration signal that includes the first calibration signal and the second calibration signal at the first frequency, and the DPD circuit is further configured to:

isolate the first calibration signal and the second calibration signal from the combined calibration signal; and

calibrate the second pre-distortion parameters based on the second calibration signal to compensate for non-linearity in amplification provided by the second PA of the third transmit chain.

5. The MIMO transceiver of claim 1 , wherein the calibration signal comprises a first calibration signal, the MIMO transceiver further comprises a third communication chain configured to wirelessly transmit a second calibration signal at the first frequency, and responsive to calibration of the pre-distortion parameters:

the first transmit chain is configured to stop wirelessly transmitting the first calibration signal; and

the third communication chain is configured to start wirelessly transmitting the second calibration signal.

6. The MIMO transceiver of claim 5 , the pre-distorter circuit comprises a first pre-distorter circuit, the PA comprises a first PA, the pre-distortion parameters comprise first pre-distortion parameters, and the third communication chain comprises a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals prior to transmission and a second PA configured to amplify the data signals of the third communication chain prior to transmission, wherein:

the second receive chain is further configured to wirelessly receive the second calibration signal at the first frequency;

the converter circuit is further configured to convert the second calibration signal to the baseband frequency;

the buffer is further configured to buffer the second calibration signal at the baseband frequency; and

the DPD circuit is further configured to calibrate the second pre-distortion parameters based on the buffered second calibration signal to compensate for non-linearity in amplification provided by the second PA of the third communication chain.

7. The MIMO transceiver of claim 1 , wherein the buffer is a first buffer, and the converter circuit is a first converter circuit, the first communication chain comprising:

a second buffer configured to buffer data signals to be transmitted by the first communication chain at the baseband frequency; and

a second converter circuit configured to convert the data signals to be transmitted by the first communication chain to the first frequency, the pre-distorter circuit configured to pre-distort the data signals at the first frequency based on the pre-distortion parameters, the first communication chain is configured to wirelessly transmit the data signals at the first frequency.

8. The MIMO transceiver of claim 1 , wherein the pre-distorter circuit uses the pre-distortion parameters to compensate for the non-linearity in amplification provided by the PA of the first transmit chain by pre-distorting data signals transmitted by the first transmit chain equal to an additive inverse of the non-linearity in amplification provided by the PA of the first transmit chain.

9. The MIMO transceiver of claim 1 , wherein the second receive chain further comprises an analog to digital converter configured to convert the calibration signal at the baseband frequency to a digital calibration signal.

10. The MIMO transceiver of claim 1 , wherein the second receive chain is configured as a linear receive chain to avoid distortion of the calibration signal in the second receive chain.

11. The MIMO transceiver of claim 1 , wherein the second transmit chain is configured to wirelessly transmit data signals at the first frequency.

12. The MIMO transceiver of claim 1 , wherein the first transmit chain further comprises a digital to analog converter configured to convert the calibration signal at the baseband frequency to an analog calibration signal.

13. The MIMO transceiver of claim 1 , wherein the first communication chain and the second communication chain share a DPD calibration chain that includes the DPD circuit.

14. A method to operate a multiple input multiple output (MIMO) transceiver configured for digital pre-distortion (DPD) calibration, the method comprising:

wirelessly transmitting a calibration signal at a first frequency from a first communication chain of the MIMO transceiver, the first communication chain including both a first receive chain and a first transmit chain, the first transmit chain comprising a pre-distorter circuit configured to accept pre-distortion parameters to pre-distort data signals prior to transmission and a power amplifier (PA) configured to amplify the data signals of the first transmit chain prior to transmission;

wirelessly receiving the calibration signal at the first frequency at a second communication chain of the MIMO transceiver, the second communication chain including both a second receive chain and a second transmit chain;

converting, by the second receive chain, the calibration signal to a baseband frequency;

buffering, by the second receive chain, the calibration signal at the baseband frequency; and

calibrating the pre-distortion parameters based on the buffered calibration signal to compensate for non-linearity in amplification provided by the PA of the first transmit chain.

15. The method of claim 14 further comprising transmitting a CTS-to-Self signal to other MIMO transceivers within an operational environment of the MIMO transceiver, the CTS-to-Self signal reserving a duration of time for the MIMO transceiver to perform DPD calibration using the first communication chain and the second communication chain.

16. The method of claim 14 , wherein the calibration signal comprises a first calibration signal, the pre-distorter circuit comprises a first pre-distorter circuit, the PA comprises a first PA, the pre-distortion parameters comprise first pre-distortion parameters, and responsive to calibration of the first pre-distortion parameters, the method further comprises:

stopping wireless transmission of the first calibration signal from the first communication chain of the MIMO transceiver;

starting wireless transmission of a second calibration signal at the first frequency from the second transmit chain of the second communication chain of the MIMO transceiver, the second transmit chain comprising a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals prior to transmission and a second PA configured to amplify the data signals of the second transmit chain prior to transmission;

wirelessly receiving the second calibration signal at the first frequency at the first communication chain of the MIMO transceiver;

converting, by the first receive chain, the second calibration signal to the baseband frequency;

buffering, by the first receive chain, the second calibration signal at the baseband frequency; and

calibrating the second pre-distortion parameters based on the buffered second calibration signal to compensate for non-linearity in amplification provided by the second PA of the second transmit chain.

17. The method of claim 14 , wherein the calibration signal comprises a first calibration signal, the pre-distortion parameters comprise first pre-distortion parameters, the pre-distorter circuit comprises a first pre-distorter circuit, and the PA comprises a first PA, the method further comprising:

wirelessly transmitting a second calibration signal at the first frequency from a third communication chain of the MIMO transceiver, the third communication chain comprising a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals prior to transmission and a second PA configured to amplify the data signals of the third communication chain prior to transmission;

receiving a combined calibration signal that includes the first calibration signal and the second calibration signal at the first frequency at the second communication chain of the MIMO transceiver;

isolating the first calibration signal and the second calibration signal from the combined calibration signal; and

calibrating the second pre-distortion parameters based on the second calibration signal to compensate for non-linearity in amplification provided by the second PA of the third communication chain.

18. The method of claim 14 further comprising:

buffering, by the first communication chain, data signals to be transmitted by the first communication chain at the baseband frequency;

converting, by the first communication chain, the data signals to be transmitted by the first communication chain to the first frequency;

pre-distorting the data signals to be transmitted by the first communication chain at the first frequency based on the pre-distortion parameters; and

wirelessly transmitting the data signals at the first frequency from the first communication chain of the MIMO transceiver.

19. The method of claim 14 , wherein the calibration signal comprises a first calibration signal and responsive to calibration of the pre-distortion parameters, the method further comprises:

stopping wireless transmission of the first calibration signal from the first communication chain of the MIMO transceiver; and

starting wireless transmission of a second calibration signal from a third communication chain of the MIMO transceiver.

20. The method of claim 19 , wherein the pre-distortion parameters comprise first pre-distortion parameters, the PA comprises a first PA, the pre-distorter circuit comprises a first pre-distorter circuit, and the third communication chain comprises a second pre-distorter circuit configured to accept second pre-distortion parameters to pre-distort data signals of the third communication chain prior to transmission and a second PA configured to amplify the data signals of the third communication chain prior to transmission, the method further comprising:

wirelessly receiving the second calibration signal at the first frequency at the second communication chain of the MIMO transceiver;

converting, by the second receive chain, the second calibration signal to the baseband frequency;

buffering, by the second receive chain, the second calibration signal at the baseband frequency; and

calibrating the second pre-distortion parameters based on the buffered second calibration signal to compensate for non-linearity in amplification provided by the second PA of the third communication chain.

21. The method of claim 14 further comprising converting the calibration signal at the baseband frequency to a digital calibration signal.