Per-Frame LO Trimming for Wi-Fi 6 Uplink Frequency Alignment
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Solution Overview
Problem
The existing Wi-Fi™ 6 standards require stringent levels of timing synchronization, power control, and high signal quality for uplink multi-user transmission, but they do not provide practical methods for transmission devices to pre-correct for in-band and out-of-band distortions such as error vector magnitude (EVM), unused tone error (UTE), and carrier frequency offset (CFO).
Innovation Solution
Wireless devices are configured to perform local oscillator (LO) trimming based on a carrier frequency offset (CFO) estimation from a trigger frame, adjusting the LO frequency to match the AP/BS frequency within a threshold tolerance, combined with digital pre-correction for fine adjustments, to meet the stringent Wi-Fi™ 6 requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If transmission devices use standard Wi-Fi 6 methods for uplink multi-user transmission, then basic communication functionality is achieved, but stringent requirements for EVM, UTE, and CFO cannot be met due to lack of practical pre-correction methods
Solution Approach 1:
The patent applies preliminary action by performing local oscillator trimming and digital pre-correction before transmission to pre-compensate for carrier frequency offset and carrier leakage. The transmission device estimates CFO from the trigger frame, adjusts its LO frequency accordingly, and applies digital pre-correction to the data frame, enabling the device to meet stringent EVM, UTE, and CFO requirements without adding significant complexity to the overall system architecture.
2Reliability
If transmission devices perform LO trimming and digital pre-correction, then carrier leakage is reduced and signal quality is improved, but device complexity increases
Solution Approach 1:
The patent implements feedback by using the trigger frame received from the access point as a reference to estimate carrier frequency offset. This estimated CFO feedback is then used to adjust the local oscillator frequency and apply digital pre-correction, creating a closed-loop system that automatically compensates for frequency deviations and carrier leakage without requiring complex external calibration equipment or manual intervention.
3Measurement precision
If transmission devices estimate CFO from trigger frame and adjust LO frequency, then timing synchronization and frequency alignment are improved, but processing time and complexity increase
Solution Approach 1:
The patent performs LO trimming and digital pre-correction in advance during the SIFS period between the trigger frame and the data frame transmission. By completing the frequency estimation, LO adjustment, and pre-correction application before the actual data transmission begins, the system achieves precise frequency alignment without extending the overall transmission time or creating delays in the uplink multi-user communication flow.
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.