CF-End Frame Transmission for Hidden Node Resolution in Wireless LAN
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Solution Overview
Problem
In wireless LANs, the CSMA/CA method is ineffective when legacy stations cannot analyze HT format frames due to errors, leading to unfair medium access contention and hidden node problems, causing collisions and channel wastage.
Innovation Solution
A method and apparatus that deliver a CF-End frame with time information for medium access control, allowing all stations in a BSS to receive the same access information, ensuring fair contention and resolving hidden node issues by selectively broadcasting the CF-End frame based on BSSID matching and using SIFS timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HT format frames are transmitted at high data transfer rates, then data transmission efficiency is improved, but legacy stations cannot analyze the frames causing CSMA/CA mechanism to become ineffective
Solution Approach 1:
The patent segments the frame structure into two parts: a legacy format portion (L-SIG field) that legacy stations can analyze to determine medium access timing, and an HT format portion that provides high throughput data transmission. This segmentation allows legacy stations to participate in CSMA/CA contention based on information from the legacy portion while HT stations achieve high-speed transmission through the HT portion.
Solution Approach 2:
The patent applies different quality characteristics to different parts of the transmission: the L-SIG field uses legacy format characteristics that ensure compatibility and analyzability by all stations, while the HT format data portion uses advanced modulation and coding schemes optimized for high throughput. This local differentiation resolves the contradiction between legacy compatibility and high-speed transmission.
2Quantity of substance
If a transmitting station sends multiple PPDUs within a single TxOP, then data transmission volume is increased, but if an error occurs more time is required for retransmission causing longer NAV and channel wastage
Solution Approach 1:
The patent uses the L-SIG field in the legacy format portion to preliminarily inform all stations of the intended transmission duration and medium access timing before the actual high-speed HT format transmission begins. This preliminary action allows stations to set their NAV timers appropriately, preventing them from accessing the medium during the TxOP even if errors occur and retransmissions are needed, thus avoiding channel wastage.
3Adaptability or versatility
If legacy stations and HT stations coexist in the wireless LAN, then network compatibility is improved, but legacy stations cannot analyze HT format frames causing unfair medium access contention
Solution Approach 1:
The patent makes the L-SIG field serve multiple functions: it acts as a legacy format indicator that legacy stations can analyze to determine medium access timing, and simultaneously provides timing information that HT stations use for coordinated transmission. This multi-functionality ensures that both legacy and HT stations operate fairly under the same CSMA/CA rules while maintaining network compatibility.
Data Source
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AI summary
A method and apparatus of delivering a Contention Free-End, CF-End, frame for a device which communicates through a wireless local area network, LAN. Embodiments can comprise checking a Basic Service Set ID, BSSID, in a CF-End frame and transmitting the CF-End frame after a Short Inter Frame Spacing, SIFS, if the BSSID in the CF-End frame matches a BSSID of a Basic Service Set, BSS.