Wireless per-frame-based local oscillator trimming for uplink multi-user transmission

1. A wireless device comprising:

a radio comprising a front end and a first local oscillator (LO); and

control logic coupled to the radio, the control logic to:

determine, from a received trigger frame directed at a plurality of wireless devices, a carrier frequency offset (CFO) between a first carrier frequency of the first LO and a second carrier frequency of a second LO of an access point operating in a multi-user transmission mode; and

trigger, based on the CFO, an LO trim of the first LO to adjust the first carrier frequency to match, within a threshold tolerance, the second carrier frequency; and

wherein the radio is to transmit, to the access point, a protocol data unit frame using the trimmed first LO, the protocol data unit frame to facilitate the access point to, within the multi-user transmission mode, synchronize concurrent reception of multiple uplink transmissions from the plurality of wireless devices.

2. The wireless device of claim 1 , wherein the control logic is implemented in at least one of a microcontroller or hardware, and wherein the control logic is to continuously trigger the LO trim of the first LO on a per-frame basis in response to detecting changes to the CFO during transmission of multiple protocol data unit frames to one or more access points.

3. The wireless device of claim 1 , wherein the control logic is further to:

calculate an LO trim value based on the CFO after trigger frame reception and content validation at a medium access control level;

store a default phase-locked loop (PLL) frequency for the first LO; and

trigger the LO trim of the first LO in sufficient time that the first LO settles before an end of a short interface space (SIFS) time period.

4. The wireless device of claim 1 , wherein the radio further comprises a radio frequency (RF) phase-locked loop (PLL) that includes the first LO, and wherein the control logic is further to:

calculate an updated RF PLL frequency based on the CFO;

trigger the RF PLL to operate at the updated RF PLL frequency in response to the LO trim; and

after transmission of the protocol data unit frame, cause the RF PLL to operate at a default RF PLL frequency.

5. The wireless device of claim 1 , wherein the radio further comprises a radio frequency (RF) phase-locked loop (PLL) that includes the first LO, and wherein the control logic is further to:

determine whether the CFO is greater than a threshold value;

in response to the CFO not being greater than the threshold value, employ digital pre-correction to the protocol data unit frame; and

in response to the CFO being greater than the threshold value:

calculate an updated RF PLL frequency based on the CFO; and

trigger the RF PLL to operate at the updated RF PLL frequency in response to the LO trim.

6. The wireless device of claim 1 , wherein the control logic is further to:

determine that the LO trim is insufficient to satisfy a target residual frequency offset value when transmitting to the access point;

calculate a digital pre-correction offset required to satisfy the target residual frequency offset value; and

cause digital up-conversion, using the digital pre-correction offset, of a waveform driving digital processing of the protocol data unit frame.

7. The wireless device of claim 1 , wherein the control logic is configured to adjust the first carrier frequency of the first LO to within a few hertz of a target frequency associated with the second carrier frequency.

8. A wireless device comprising:

a radio comprising:

a radio frequency phase-locked loop (RF PLL);

an analog-to-digital converter (ADC) coupled to a demodulator that is driven by the RF PLL;

a digital-to-analog converter (DAC) coupled to a modulator that is driven by the RF PLL; and

an analog front end PLL to generate a clock to drive the ADC and the DAC; and

trim logic coupled to the RF PLL and the analog front end PLL, the trim logic to:

determine, from a received trigger frame, a carrier frequency offset (CFO) between a first carrier frequency of the RF PLL and a second carrier frequency of a local oscillator (LO) of an access point operating in a multi-user transmission mode;

trigger, based on the CFO, a first trim of the RF PLL to adjust the first carrier frequency to match, within a threshold tolerance, the second carrier frequency; and

trigger, based on the CFO, a second trim of the analog front end PLL to support meeting the threshold tolerance; and

wherein the radio is to transmit, to the access point, a protocol data unit frame using the trimmed RF PLL.

9. The wireless device of claim 8 , further comprising:

receive (Rx) processing hardware coupled to the ADC and the trim logic; and

transmit (Tx) processing hardware coupled to the DAC.

10. The wireless device of claim 8 , wherein the trim logic is to continuously trigger the first trim of the RF PLL and the second trim of the analog front end PLL in response to detecting changes to the carrier frequency offset during transmission of multiple protocol data unit frames to the access point.

11. The wireless device of claim 8 , wherein the trim logic is further to:

calculate an LO trim value based on the CFO after trigger frame reception and content validation at a medium access control level;

store a default phase-locked loop (PLL) frequency for the RF PLL; and

trigger the first trim of the RF PLL in sufficient time that the RF PLL settles before an end of a short interface space (SIFS) time period.

12. The wireless device of claim 8 , wherein the trim logic is further to:

calculate an updated RF PLL frequency based on the CFO;

trigger the RF PLL to operate at the updated RF PLL frequency in response to the first trim of the RF PLL; and

after transmission of the protocol data unit frame, cause the RF PLL to operate at a default RF PLL frequency.

13. The wireless device of claim 8 , wherein the trim logic is further to:

determine whether the CFO is greater than a threshold value;

in response to the CFO not being greater than the threshold value, employ digital pre-correction to generation of the protocol data unit frame; and

in response to the CFO being greater than the threshold value:

calculate an updated RF PLL frequency based on the carrier frequency offset; and

trigger the RF PLL to operate at the updated RF PLL frequency in response to the first trim of the RF PLL.

14. The wireless device of claim 8 , wherein the trim logic is further to:

determine that the first trim and the second trim are insufficient to satisfy a target residual frequency offset value when transmitting to the access point;

calculate a digital pre-correction offset required to satisfy the target residual frequency offset value; and

cause digital up-conversion, using the digital pre-correction offset, of a waveform driving digital processing of the protocol data unit frame.

15. A method comprising:

detecting, by control logic coupled to a radio having a first local oscillator (LO), that a preamble of a trigger frame received from an access point has been processed, the access point operating in a multi-user transmission mode and the trigger frame being directed at a plurality of wireless devices;

estimating, based on information derived from the trigger frame after preamble processing, a carrier frequency offset (CFO) between a first carrier frequency of the first LO and a second carrier frequency of a second LO of the access point;

determining a LO trim value based on the CFO; and

causing an adjustment, by the control logic, using the LO trim value, to the first carrier frequency of the first LO in advance of the radio transmitting, to the access point, an uplink protocol data unit frame configured to facilitate the access point to, within the multi-user transmission mode, synchronize concurrent reception of multiple uplink transmissions from the plurality of wireless devices.

16. The method of claim 15 , further comprising continuously adjusting the LO trim value of the first LO on a per-frame basis in response to detecting changes to the CFO during transmission of multiple uplink protocol data unit frames to one or more access points.

17. The method of claim 15 , wherein determining the LO trim value comprises estimating a shift in the first carrier frequency required so that the first carrier frequency matches the second carrier frequency within a threshold tolerance.

18. The method of claim 15 , further comprising, before causing the adjustment:

determining that a frame sequence check as passed;

receiving a trigger frame from the access point; and

performing content validation of the trigger frame.

19. The method of claim 15 , further comprising:

storing, before causing the adjustment, a default phase-locked loop (PLL) frequency for the first LO; and

triggering an LO trim of the first LO in sufficient time that the first LO settles before an end of a short interface space (SIFS) time period.

20. The method of claim 15 , further comprising:

after causing the adjustment, causing the radio to transmit, to the access point, the uplink protocol data unit frame; and

after transmission of the uplink protocol data unit frame, restoring a default phase-locked loop (PLL) frequency to the first LO.