ELR PPDU Retransmission Using Chase Combining for WLAN Range
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Solution Overview
Problem
Existing wireless local area network (WLAN) technologies face challenges in achieving reliable long-range data transmission due to issues such as UL/DL Tx power imbalance and path losses, leading to increased retransmissions and longer durations, particularly with the introduction of enhanced long range (ELR) data rates in 802.11bn.
Innovation Solution
Implementing chase combining (HARQ-CC) for ELR PPDU retransmissions, where log-likelihood ratio (LLR) metrics from initial and retransmitted packets are combined to enhance signal-to-noise ratio (SNR), reducing the number and duration of retransmissions by retransmitting only failed codewords.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If ELR data rates are introduced to support long-range transmission, then transmission range is improved, but reliability deteriorates due to increased path losses and UL/DL power imbalance
Solution Approach 1:
The system performs preliminary actions by calculating and storing LLR metrics from the initial transmission before retransmission occurs. This allows the receiver to have soft information ready to be combined with retransmitted data, improving the likelihood of successful decoding in subsequent attempts without requiring additional real-time processing during the critical retransmission window.
Solution Approach 2:
The system implements feedback through block acknowledgment frames that inform the transmitter whether the initial transmission was successfully decoded. This feedback mechanism enables the transmitter to determine when retransmission is necessary and allows the receiver to know when to combine LLR metrics from multiple transmissions, creating a closed-loop system that adapts to channel conditions.
2Reliability
If traditional retransmission methods are used for ELR PPDU, then reliability is improved through retransmission, but transmission duration increases due to multiple retransmission attempts
Solution Approach 1:
The system changes the parameter of combining methodology by using LLR metric combination instead of simple packet retransmission. By combining soft information from multiple transmissions, the system achieves better decoding reliability with fewer retransmission attempts, thereby reducing overall transmission duration while maintaining or improving reliability.
Solution Approach 2:
The system creates copies of the transmitted data in the form of LLR metrics from the initial transmission and stores them for later combination with retransmitted data. This copying of soft information allows the receiver to leverage information from the first transmission even when decoding fails, reducing the need for multiple full retransmissions and shortening total transmission time.
3Reliability
If LLR metrics are stored and combined from initial and retransmitted packets, then decoding performance is improved, but device complexity increases
Solution Approach 1:
The receiver performs preliminary action by calculating and storing LLR metrics immediately after the initial transmission, before retransmission occurs. This advance preparation of soft information simplifies the retransmission processing, as the combining operation becomes a straightforward addition of pre-calculated metrics rather than requiring complex real-time processing during the retransmission window.
Solution Approach 2:
The system extracts and stores only the essential LLR metrics from the initial transmission, separating this soft information from the full packet data. This extraction of critical decoding information allows the system to combine only the necessary elements during retransmission, reducing memory requirements and processing complexity compared to storing and processing entire packets.
Data Source
AI summary
An apparatus configured to generate an initial transmission including a first enhanced long range (ELR) physical layer (PHY) protocol data unit (PPDU) comprising a first preamble and a first data frame (ELR PPDU), the first ELR PPDU encoded by forward error correction (FEC) encoding, mapped to orthogonal frequency division multiplexing (OFDM) symbols, and duplicated multiple times over multiple resource units (RU) within a channel bandwidth, detect a first block acknowledgment (BA) frame indicating at least part of the initial transmission was not properly decoded and generate a first retransmission including a second ELR PPDU comprising a second preamble and a second data frame corresponding to the first data frame, the second preamble indicating the first retransmission to indicate that a receiver decoding the first retransmission combines soft bits stored from the initial transmission with soft bits from the first retransmission during decoding.