Single-User Beamforming Preamble Format for WLAN Hidden Node Resolution
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Solution Overview
Problem
In wireless local area networks (WLANs), especially those operating in sub-1 GHz frequencies, existing technologies face challenges in efficiently transmitting data units due to the 'hidden node' problem, where beamforming can cause interference and prevent devices orthogonal to the beamformed transmission from detecting or decoding data units, leading to communication conflicts.
Innovation Solution
The implementation of a longer preamble format for single-user beamformed (SU-BF) data units that includes both non-beamformed and beamformed portions, allowing devices other than the intended recipient to detect and decode the data unit, thereby reducing the hidden node problem. This format is similar to multi-user (MU) data unit preambles, with specific fields indicating whether the data unit is SU-BF or MU, and using symbol constellation rotation to differentiate between normal and low bandwidth modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If beamforming is used to improve data transmission efficiency and range, then communication range and throughput are improved, but devices orthogonal to the beamformed transmission cannot detect or decode data units, causing hidden node problems and communication conflicts
Solution Approach 1:
The data unit is segmented into two distinct parts: a non-beamformed preamble portion and a beamformed data portion. The preamble is transmitted without beamforming to ensure all devices can detect and decode it, while the data portion uses beamforming for efficient targeted transmission. This segmentation resolves the contradiction by allowing universal detection in one segment while maintaining directed high-speed transmission in another.
Solution Approach 2:
Different transmission qualities are applied to different parts of the data unit. The preamble uses omnidirectional non-beamformed transmission with uniform signal distribution for maximum detectability, while the data portion uses directional beamformed transmission with concentrated signal energy for high-speed targeted communication. This local quality differentiation allows each part to optimize for its specific function.
2Productivity
If a shorter preamble format is used to reduce transmission overhead, then transmission efficiency is improved, but devices cannot properly set automatic gain control levels and estimate channels
Solution Approach 1:
The patent uses a longer preamble format than the minimum required, incorporating additional training fields and signal structures that exceed basic detection needs. This excessive action in the preamble provides sufficient information for devices to accurately set automatic gain control levels and perform channel estimation, while the overall transmission remains efficient due to the compact beamformed data portion that follows.
Data Source
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AI summary
A method includes generating a preamble of a first data unit according to a first format. Generating the preamble of the first data unit according to the first format includes generating a first preamble portion of the first data unit and generating a second preamble portion of the first data unit. The first preamble portion of the first data unit includes information indicating to a receiving device that the first data unit is a single-user data unit, and the second preamble portion of the first data unit follows the first preamble portion of the first data unit. The method also includes applying a beamforming steering matrix to the second preamble portion of the first data unit but not to the first preamble portion of the first data unit.