Compressed Preamble OFDM Symbols for WLAN Compatibility
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Solution Overview
Problem
Wireless local area networks (WLANs) face challenges in efficiently transmitting data across devices with different communication protocols, particularly in maintaining throughput and compatibility between legacy and high-efficiency communication standards like IEEE 802.11ac and 802.11ax, due to differences in tone spacing and guard intervals.
Innovation Solution
The method involves generating PHY data units with long and short OFDM symbols, where short OFDM symbols are used for training fields with reduced tone spacing, and long OFDM symbols for data portions, allowing for flexible tone spacing and guard intervals to improve communication range and throughput, while ensuring compatibility across different protocols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If short OFDM symbols with reduced tone spacing are used for training fields, then compatibility and detection accuracy are improved, but transmission throughput and communication range are limited
Solution Approach 1:
The patent segments the PHY data unit into distinct portions: a preamble portion using short OFDM symbols with reduced tone spacing for accurate detection, and a data portion using long OFDM symbols with normal tone spacing for high-speed data transmission. This segmentation allows each portion to be optimized independently for its specific function.
Solution Approach 2:
Different tone spacing configurations are applied locally to different portions of the transmission. The preamble portion uses reduced tone spacing (1/2 or 1/4 of normal) to improve detection accuracy in challenging channel conditions, while the data portion uses normal tone spacing to maintain high throughput for actual data transmission.
2Productivity
If long OFDM symbols with normal tone spacing are used for data transmission, then throughput is improved, but compatibility with legacy devices and detection reliability are reduced
Solution Approach 1:
The patent introduces a compatibility layer in the form of a preamble using short OFDM symbols that conforms to legacy IEEE 802.11 standards. This preamble acts as an intermediary that legacy devices can recognize and process, while newer devices can utilize the full capabilities including the data portion with long OFDM symbols for high-speed transmission.
Solution Approach 2:
The system dynamically adapts to different device types by using a unified transmission structure where the preamble portion ensures legacy compatibility and the data portion enables high-speed transmission for supporting devices. Receivers can selectively process the appropriate portions based on their capabilities.
3Length of stationary object
If reduced tone spacing is used in training fields, then communication range and signal detection are improved, but transmission efficiency and data rate are reduced
Solution Approach 1:
The transmission is segmented into a preamble portion using reduced tone spacing for extended communication range and reliable detection, and a data portion using normal tone spacing for efficient high-rate data transmission. This allows the system to achieve both long range and high speed in different portions of the same transmission.
Solution Approach 2:
The patent changes the tone spacing parameter selectively: using 1/2 or 1/4 normal tone spacing in the preamble portion to extend communication range and improve detection reliability, then switching to normal tone spacing in the data portion to maximize data transmission rate for devices that support it.
Data Source
AI summary
A physical layer (PHY) preamble of a PHY data unit is generated, including generating one or more short orthogonal frequency division multiplexing (OFDM) symbols for one or more long training fields of the PHY preamble. Each of the one or more short OFDM symbols corresponds to a frequency domain sequence having a number of tones. Every N-th tone is modulated and tones between modulated tones are zero tones, where N is a positive integer greater than one. A time duration of each short OFDM symbol is 1/N of a time duration of a full inverse discrete Fourier transform (IDFT) of the frequency domain sequence. A data portion of the PHY data unit is generated, including generating one or more long OFDM symbols. A time duration of each long OFDM symbol is greater than a time duration of each of the one or more short OFDM symbols.