Uplink Multi-User Transmission Cyclic Shift for Unintentional Beamforming
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Solution Overview
Problem
In Wireless Local Area Networks (WLANs), unintentional beamforming occurs during multi-user simultaneous transmissions, leading to poor signal quality and decoding failures at the Access Point (AP) despite high signal quality from individual stations, due to combined signals being out-of-phase or experiencing deep fading.
Innovation Solution
Implementing a method where each station applies a unique cyclic shift value to its frame's common part during uplink multi-user simultaneous transmissions, determined based on scheduling information, explicit indication, or randomness, to avoid unintentional beamforming by creating a frequency-selective channel condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple STAs simultaneously transmit the same information in the same transmission waveform to an AP, then the individual transmissions have high signal quality, but unintentional beamforming occurs at the AP causing poor signal quality and decoding failures
Solution Approach 1:
The patent applies cyclic shift values to the common part of uplink frames transmitted by multiple STAs. This parameter change in the time domain causes frequency-selective fading patterns, ensuring that combined signals from multiple STAs do not always experience deep fading at the same frequencies, thereby preventing unintentional beamforming and improving decoding reliability
Solution Approach 2:
The patent introduces dynamic cyclic shift values that can be determined based on scheduling information, explicit indication from the AP, or randomness. This dynamic adjustment ensures that the cyclic shift values change across different transmissions and STAs, creating varying frequency-selective channel conditions that prevent consistent constructive interference causing beamforming
2Productivity
If multiple STAs transmit simultaneously in the same frequency resources, then network capacity and throughput are improved, but unintentional beamforming causes signal degradation at the AP
Solution Approach 1:
By applying cyclic shift values to the common part of frames, the patent transforms the uniform transmission waveform into frequency-selective transmissions. This parameter change in the time domain creates different frequency responses for each STA, preventing the constructive interference that causes unintentional beamforming while allowing simultaneous transmissions to coexist
Solution Approach 2:
The patent converts the harmful effect of signal combining (unintentional beamforming) into a beneficial frequency-diversity effect. By using cyclic shifts, the patent ensures that signals from multiple STAs experience different fading patterns, transforming the potential harm of simultaneous transmission into a benefit where frequency diversity improves overall signal quality
Data Source
AI summary
The embodiments provide a method implemented by a first station (STA) for transmitting a frame to an Access Point (AP) as part of an uplink multi-user simultaneous transmission. The method avoids unintentional beamforming at the AP. The method includes receiving a first frame from the AP, where the first frame includes scheduling information for scheduling a simultaneous uplink transmission for the first STA and one or more other STAs, generating a second frame having a common part and a user-specific part, where the second frame is to be transmitted simultaneously with other frames according to the scheduling information, determining a cyclic shift value to be applied to the common part, where the cyclic shift value is determined to be different from one or more cyclic shift values to be applied by each of the other STAs, applying the cyclic shift value to the common part and transmitting the second frame to the AP.