Wireless Symbol Preemption for Low-Latency Priority Transmission
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Solution Overview
Problem
Wireless industrial communication systems lack mechanisms to preempt the transmission of low-priority packets in favor of higher-priority packets, leading to significant latency degradation when lower-priority packets are long compared to higher-priority packets.
Innovation Solution
Implement fragmentation of physical layer PDUs into symbols, allowing immediate start of higher-priority PDU transmission after the completion of the current symbol, and use a dedicated tag to indicate preemption to the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the transmission of a low-priority packet is allowed to complete before transmitting a higher-priority packet, then the transmission order is maintained and protocol simplicity is preserved, but the latency for high-priority packets increases significantly
Solution Approach 1:
The patent segments the transmission process into individual symbol units rather than treating entire PDUs as atomic units. This allows the system to transmit symbols one by one and insert preemption indicators between symbols, enabling fine-grained control over transmission priority without requiring complex protocol changes. The segmentation of transmission at the symbol level resolves the contradiction by allowing low-priority packet transmission to be interrupted after just one symbol rather than requiring complete PDU transmission.
Solution Approach 2:
The patent introduces a preemption indicator as an intermediary element that mediates between low-priority and high-priority packet transmissions. This indicator, inserted between symbols of the low-priority packet, signals the receiver to pause decoding and prepares it for the incoming high-priority packet. The intermediary preemption indicator enables priority-based preemption without requiring fundamental protocol restructuring, thus reducing latency while maintaining acceptable protocol complexity.
2Loss of time
If the entire PDU must be transmitted before switching to a higher-priority packet, then transmission integrity is maintained, but the waiting time for high-priority packets becomes unacceptably long
Solution Approach 1:
The patent segments the PDU transmission into individual symbol units, allowing the transmission to be divided and interrupted at symbol boundaries. This segmentation enables the system to transmit only one symbol of a low-priority packet before preempting for a high-priority packet, dramatically reducing waiting time while maintaining transmission integrity through the use of preemption indicators that guide the receiver through the fragmented transmission sequence.
Solution Approach 2:
The patent implements a feedback mechanism where the preemption indicator provides real-time information to the receiver about the transmission state. When the receiver detects a preemption indicator, it knows to pause decoding and prepare for a high-priority packet interruption. This feedback loop maintains transmission integrity by ensuring the receiver can correctly interpret fragmented transmissions and reconstruct the original data sequences despite the preemption interruptions.
3Speed
If a preemption mechanism is implemented at the packet level, then high-priority packets can interrupt low-priority packets, but the interruption can only occur at PDU boundaries causing significant delay
Solution Approach 1:
The patent segments the transmission granularity from the PDU level down to the symbol level. By allowing preemption to occur after individual symbol transmission rather than at PDU boundaries, the system achieves much faster response speed for priority switching. The symbol-level segmentation reduces the minimum preemption interval from potentially hundreds of microseconds (PDU level) to just the duration of one symbol, eliminating significant delays while maintaining implementation feasibility.
Data Source
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AI summary
There is provided mechanisms for preparing transmission of physical layer protocol data units (PDUs). A method is performed by a packet transmitter (120). The method comprises detecting (S102) a need to transmit a second stream (220) of symbols having higher priority than a first stream (210, 210a, 210b) of symbols currently being transmitted from the packet transmitter (120) to a packet receiver (130). The method comprises inserting (S104) a dedicated tag (240) after the recent-most transmitted symbol of the first stream (210, 210a, 210b) of symbols, the dedicated tag (240) indicative of the packet the first stream (210, 210a, 210b) of symbols being subjected to pre-emption. The method comprises inserting symbols of the second stream (220) of symbols following the dedicated tag (240) for transmission of the second stream (220) of symbols to the packet receiver (130).