WLAN Frame Mode Detection Using Segmented Signal Fields
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Solution Overview
Problem
In wireless local area networks (WLANs), there is a need to determine the transmission mode of frames, especially with the coexistence of new and previous version devices, as existing methods may lead to misinterpretation of frame formats, affecting compatibility and operation.
Innovation Solution
A method involving the generation and transmission of frames with specific training fields and signal fields, including a mode field and check bits, modulated using BPSK and QBPSK, to accurately determine the transmission mode, ensuring compatibility with previous versions like IEEE standards 802.11a, 802.11g, and 802.11ac, and new versions like 802.11ax.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a new version WLAN device transmits frames using legacy modulation schemes (BPSK for L-SIG), then backward compatibility with previous version devices is maintained, but transmission mode detection accuracy deteriorates because legacy devices cannot distinguish between legacy mode and new mode frames
Solution Approach 1:
The signal field is divided into multiple symbols with different modulation schemes. The first symbol uses BPSK modulation for legacy compatibility, while the second symbol uses QBPSK modulation for new mode indication. This segmentation allows different parts of the same frame to serve different functions: legacy devices read the first symbol, while new devices read both symbols to determine transmission mode.
Solution Approach 2:
A mode field is introduced as an intermediary element between the legacy L-SIG and the data field. This mode field contains mode information that is modulated using QBPSK in the second symbol, serving as a mediator that legacy devices ignore while new devices use to determine transmission mode, thus resolving the detection accuracy issue without breaking compatibility.
2Measurement precision
If QBPSK modulation is used in the first symbol to indicate new mode, then transmission mode detection accuracy is improved, but compatibility with legacy devices deteriorates because they cannot interpret QBPSK modulated signals
Solution Approach 1:
The signal field is segmented into at least two symbols with different modulation schemes. The first symbol uses BPSK (compatible with legacy devices), while the second symbol uses QBPSK (for new mode indication). This segmentation ensures that legacy devices can successfully decode the first symbol without interference, while new devices can interpret the QBPSK modulated second symbol for accurate mode detection.
Solution Approach 2:
Different parts of the signal field have different modulation qualities tailored to their specific functions. The first symbol uses BPSK modulation optimized for legacy device compatibility, while the second symbol uses QBPSK modulation optimized for new mode indication. This local differentiation of modulation quality allows simultaneous support for both legacy and new devices without mutual interference.
3Measurement precision
If the frame structure is extended with additional signal fields for mode indication, then transmission mode detection accuracy is improved, but frame complexity increases
Solution Approach 1:
The additional signal field is segmented into multiple symbols with different modulation schemes, allowing compact encoding of mode information. By using QBPSK modulation in the second symbol, multiple bits of mode information can be conveyed efficiently without requiring a proportional increase in the number of symbols, thus limiting the increase in frame complexity while maintaining detection accuracy.
Data Source
AI summary
In a WLAN, a device generates a short training field and a long training field following the short training field. The device generates a first signal field following the long training field, and the first signal field includes a mode field for indicating a transmission mode of a frame to be transmitted and a check bit for protecting at least the mode field. The device transmits the frame including the short training field, the long training field, and the first signal field.