Padding Symbol in WLAN PPDU for ACK Timing
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Solution Overview
Problem
In the 802.11ax wireless LAN system, the increased FFT size for OFDM modulation improves throughput but prolongs symbol duration, potentially leading to missed ACK frames due to unchanged SIFS times, especially in scenarios with many access points and stations where resource utilization efficiency is critical.
Innovation Solution
A method where a STA adds a padding symbol to the signal, allowing sufficient processing time by determining the capabilities of receiving STAs and signaling this information, thereby ensuring timely ACK frame transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the FFT size is increased to improve throughput in 802.11ax system, then the data transmission rate is improved, but the symbol duration is prolonged causing ACK frames to be missed
Solution Approach 1:
The transmitting STA determines the receiving STA's capability to process extended SIFS time before actual data transmission. This preliminary capability assessment allows the system to pre-configure appropriate SIFS time values, ensuring that receiving STAs are ready to process ACK frames within the extended time window before the actual transmission occurs.
Solution Approach 2:
The patent implements dynamic SIFS time adjustment based on FFT size. When FFT size is increased (e.g., 4x), the SIFS time is automatically extended proportionally. This dynamic adaptation allows the system to maintain reliable ACK frame reception while benefiting from higher throughput, as the SIFS time is no longer fixed but adjusts according to the actual transmission parameters.
2Reliability
If the SIFS time is extended to accommodate longer symbol duration, then ACK frames can be transmitted successfully, but the network latency is increased
Solution Approach 1:
The patent changes the SIFS time parameter dynamically based on the FFT size being used. Instead of using a fixed SIFS time, the system adjusts this critical timing parameter to match the actual symbol duration requirements. This allows the minimum necessary SIFS time to be used for each transmission scenario, avoiding unnecessary latency extensions while ensuring reliable ACK transmission.
Solution Approach 2:
The capability exchange mechanism performs preliminary determination of appropriate SIFS time values before actual data transmission. By establishing the timing parameters in advance through capability negotiation, the system avoids trial-and-error adjustments during operation, thereby minimizing overall network latency while ensuring ACK frames are transmitted successfully.
3Reliability
If capability exchange messages are added to signal SIFS time requirements, then proper timing coordination is achieved, but the protocol complexity is increased
Solution Approach 1:
The capability exchange mechanism serves multiple functions simultaneously: it not only signals SIFS time requirements but also establishes other transmission parameters, confirms compatibility between transmitting and receiving STAs, and enables dynamic adaptation to different FFT sizes. This multi-functionality reduces the need for separate dedicated signaling messages, thereby limiting the increase in protocol complexity.
Solution Approach 2:
The patent modifies existing capability exchange message parameters to include SIFS time indication information, rather than creating entirely new complex signaling protocols. By reusing and extending existing message structures with additional parameter fields, the implementation achieves proper timing coordination while minimizing the increase in protocol complexity.
Data Source
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Figure 3(a)~3(d)
AI summary
Disclosed herein is a method for sending, by a station (STA) device, data in a wireless LAN (WLAN) system. A method for sending, by a station (STA), data includes generating a physical protocol data unit (PPDU) including a physical preamble and a data field, determining whether or not to add a padding symbol to the PPDU, generating the padding symbol and adding the generated padding symbol to the PPDU if it is determined that the padding symbol is generated, and sending the PPDU.