802.11az NDP Frame Length Calculation for Accurate Ranging
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Solution Overview
Problem
Existing wireless communication technologies face challenges in accurately determining the position of wireless communication devices within buildings or tunnels due to the lack of a defined frame format for null data packet frames, leading to inefficiencies in channel sounding measurements and increased overhead costs.
Innovation Solution
A system and method for computing and encoding the UL-Length and L-SIG Length subfield values in trigger frames and response physical layer protocol data units using lookup tables or equations based on NHE-LTF and NLTF-REP values, ensuring accurate positioning in multipath environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a trigger frame is used to solicit uplink transmissions for channel sounding, then positioning capability is improved, but frame format definition is missing causing implementation failure
Solution Approach 1:
The patent defines the frame format for trigger-based NDP frames in advance, before actual channel sounding operations are performed. This preliminary definition of the frame structure, including the UL-Length field and L-SIG Length subfield, enables initiators to properly format and send trigger frames, and responders to correctly interpret and respond to these frames for accurate positioning measurements.
2Measurement precision
If NDP frames are used for channel sounding measurements, then positioning accuracy is improved, but processing overhead and timing costs increase
Solution Approach 1:
The patent optimizes the frame format parameters for NDP frames, specifically defining the UL-Length field and L-SIG Length subfield to accurately reflect the actual transmission duration. This parameter optimization enables precise time-of-flight measurements while minimizing unnecessary overhead, achieving a balance between positioning accuracy and processing efficiency.
Solution Approach 2:
The patent uses the existing 802.11 frame structure as a template, copying and adapting proven fields (L-SIG, HE-SIG, HE-LTF) into the trigger-based NDP frame format. This approach leverages familiar structures to reduce processing complexity while maintaining the enhanced positioning capabilities needed for accurate distance measurement.
3Adaptability or versatility
If UL-Length and L-SIG Length values are not aligned, then flexibility is maintained, but positioning accuracy deteriorates
Solution Approach 1:
The patent establishes a feedback mechanism where the UL-Length field in the trigger frame directly determines the L-SIG Length value in the response NDP frame. This feedback loop ensures that the length parameters are consistently aligned between transmit and receive operations, enabling accurate time-of-flight measurements while maintaining the flexibility to support various channel sounding scenarios.
Data Source
AI summary
In an 802.11az wireless system, a first station device transmits an NDP PPDU data unit in accordance with a range measurement packet exchange by constructing the NDP PPDU data unit to include an uplink (UL) length field element or a legacy signal length (LLEN) field element derived from a specified number of symbols (NHE-LTF) and number of repetitions (NLTF-REP) for the NDP PPDU data unit, and then sending the NDP PPDU data unit to a second STA device, where the values of the UL-length and LLEN field elements are computed as UL-Length=LLEN=10+y+6*Σi=1NUM_USERS((NLTF-REP(i)+1)*NHE-LTF(i)), where y=0 for NTB I2R/R2I NDP and TB R2I NDP PPDUs, and where y=3 for TB-I2R NDP PPDUs.