Per-Frame LO Trimming for Wi-Fi 6 Uplink Frequency Alignment
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Solution Overview
Problem
Current wireless devices face challenges in meeting the stringent Wi-Fi™ 6 requirements for uplink multi-user transmission, particularly in terms of in-band and out-band distortions such as error vector magnitude (EVM), unused tone error (UTE), and carrier frequency offset (CFO), as the existing standards do not provide practical methods for pre-correction.
Innovation Solution
The implementation of per-frame-based local oscillator (LO) trimming in wireless devices, which involves determining the carrier frequency offset (CFO) from a trigger frame and adjusting the LO frequency to match the access point's frequency within a threshold tolerance, thereby enhancing carrier frequency alignment and reducing distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If per-frame local oscillator trimming is implemented, then carrier frequency alignment is improved and carrier leakage is reduced, but device complexity increases due to additional LO adjustment mechanisms
Solution Approach 1:
The patent applies preliminary action by performing local oscillator trimming in advance of each uplink transmission frame. The AP determines CFO from the trigger frame, calculates the required LO trim amount, and communicates this to the station before the actual data transmission. This allows the LO to be pre-adjusted to the correct frequency, ensuring accurate carrier alignment and reducing carrier leakage at the start of transmission.
Solution Approach 2:
The patent implements feedback by using the trigger frame to convey CFO information from the AP to the station. The AP measures the carrier frequency offset and feeds this information back to the station through the trigger frame, enabling the station to adjust its LO accordingly. This closed-loop feedback mechanism ensures continuous frequency synchronization between AP and stations.
2Manufacturing precision
If larger LO frequency adjustments are made, then distortion correction capability is improved, but timing synchronization requirements become more stringent
Solution Approach 1:
The patent applies preliminary action by completing all LO trimming calculations and adjustments during the SIFS period between the trigger frame and the uplink data transmission. This ensures that frequency corrections are finalized before transmission begins, allowing larger adjustment ranges without compromising timing synchronization. The SIFS period provides a guaranteed time window for these preliminary actions.
3Measurement precision
If per-frame LO trimming is performed continuously, then carrier frequency offset is reduced, but power consumption increases due to frequent adjustments
Solution Approach 1:
The patent applies periodic action by performing LO trimming on a per-frame basis rather than continuously. The trimming operation is triggered periodically with each uplink transmission opportunity, synchronized with the trigger-based transmission framework. This periodic approach maintains frequency accuracy while allowing the LO to remain stable between adjustments, reducing overall power consumption compared to continuous trimming.
Data Source
AI summary
A wireless device includes a radio having a front end and a first local oscillator (LO) and control logic coupled to the radio. The control logic determines, from a received trigger frame, 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. The control logic triggers, 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. The radio can then transmit, to the access point, a protocol data unit frame using the trimmed first LO, the protocol data unit frame being associated with the multi-user transmission mode.