WLAN Frame Bandwidth Detection via Cross-Correlation
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Solution Overview
Problem
In wireless local area networks (WLANs) compliant with IEEE 802.11 standards, particularly in versions 802.11n and 802.11ac, there is a challenge in assessing the bandwidth of incoming frames on the fly to ensure interoperability between devices operating at different channel widths, such as 20MHz, 40MHz, and 80MHz, without prior knowledge of the frame's bandwidth, which affects demodulation efficiency and backward compatibility with legacy standards.
Innovation Solution
A method that computes a cross-correlation of signals received on the primary and secondary channels to accurately determine the frame bandwidth during the reception of the preamble, reducing computational complexity and cost by eliminating the need for time lag and multiple correlation computations, allowing for real-time bandwidth assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-correlation is computed between primary and secondary channel signals to determine frame bandwidth, then measurement precision and speed are improved, but device complexity increases
Solution Approach 1:
The patent segments the bandwidth detection process by performing cross-correlation only on specific signal portions (preamble fields such as L-STF, L-LTF, or HT-STF) rather than entire frames, and only on primary and secondary channel pairs. This segmentation reduces the computational burden while maintaining detection accuracy for determining whether a frame occupies 20MHz or 40MHz bandwidth.
Solution Approach 2:
The patent applies preliminary action by performing bandwidth detection during the reception of preamble fields before the actual data payload is processed. The cross-correlation computation is executed on training sequences embedded in the preamble, allowing the receiver to determine frame bandwidth early in the reception process, which enables subsequent processing to be optimized based on the detected bandwidth.
2Speed
If cross-correlation computation is performed without time lag to enable real-time bandwidth assessment, then speed is improved, but measurement precision deteriorates
Solution Approach 1:
The patent performs bandwidth detection during the preamble reception phase, which occurs before the main data payload. By computing cross-correlation on preamble training sequences (L-STF, L-LTF, or HT-STF) without introducing additional time lags, the system achieves real-time bandwidth assessment while maintaining accuracy through the use of known training sequence properties.
Solution Approach 2:
The patent utilizes the inherent structure and repetition in training sequences (such as the repeated patterns in L-STF or the known structure of L-LTF and HT-STF) as reference copies for cross-correlation. These training sequences contain embedded patterns that serve as reliable references for detecting bandwidth without requiring time-lagged comparisons, thereby maintaining both speed and precision.
3Measurement precision
If multiple correlation computations are performed to accurately determine bandwidth, then measurement precision is improved, but device complexity and computational cost increase
Solution Approach 1:
The patent segments the correlation computation task by focusing on specific channel pairs (primary and secondary channels) and specific time portions (preamble fields) rather than computing correlations across all channels and entire frames. This selective segmentation reduces the number of required computations from potentially multiple full-frame correlations to a focused set of preamble-based correlations on relevant channel pairs.
Solution Approach 2:
The patent extracts and utilizes only the essential information needed for bandwidth detection from the received signal - specifically, the training sequences in the preamble fields. By taking out and processing only these critical portions rather than the entire frame, the system achieves accurate bandwidth determination with minimal correlation computations, eliminating the need for multiple redundant computations.
4Productivity
If bandwidth detection is performed during preamble reception to enable early identification, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent performs bandwidth detection during the preamble reception phase, which is the initial portion of frame reception. By completing the cross-correlation computation and bandwidth determination before processing the main data payload, the system enables early identification of frame bandwidth. This preliminary action allows subsequent processing stages to be optimized based on the detected bandwidth, improving overall frame processing efficiency.
Data Source
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AI summary
A method for determining the bandwidth of an incoming frame in a wireless local area network (WLAN) is disclosed. The method comprises the following steps, executed at least by a processor, upon reception of a first plurality and a second plurality of samples of the frame, the first plurality of samples being representative of a first signal of the frame received at a primary WLAN channel and the second plurality of samples being representative of a second signal of the frame received at a secondary WLAN channel: - computing at least a correlation of a sample among the first plurality of samples with a sample among the second plurality of samples; - if the correlation exceeds a threshold then setting a receiver mode to a first bandwidth otherwise setting a receiver mode to a second bandwidth. A device corresponding to said method and a system integrating said device are also provided.