Express Retransmission of Time Sensitive Frames in Wireless Mesh Networks

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Solution Overview

Problem

Wireless mesh networks experience significant latency issues due to multi-hop delays, which are exacerbated by hidden nodes and contention-based access protocols, making it difficult to meet the Quality of Service (QoS) requirements for real-time applications like VoIP and multimedia, especially in environments where single-hop latency constraints are not met.

Innovation Solution

Implementing express forwarding and retransmission mechanisms, where Time Sensitive Quality of Service (TSQ) frames are prioritized by designating them for immediate retransmission without waiting for a predetermined backoff period, and using a special flag to mark these frames for priority access, along with adjusting the Duration field to ensure rapid channel access for forwarding nodes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional contention-based access protocols are used in wireless mesh networks, then channel access is distributed and fair, but latency increases due to multi-hop delays and collisions

Engineering Contradiction:

ImproveQoS complianceVSAvoidend-to-end delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The source node performs preliminary channel reservation before actual data transmission by sending RTS/CTS frames. This preliminary action secures the channel in advance, allowing subsequent data frames to be transmitted without contention delays, thus reducing end-to-end latency while maintaining fair channel access through the reservation mechanism

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

RTS (Request to Send) and CTS (Clear to Send) frames act as intermediary control frames that mediate between the source node and the channel. These intermediary frames establish a reservation that protects subsequent data transmissions from collisions, thereby reducing latency without compromising the distributed fair access nature of the protocol

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If frame-by-frame reservation is used to extend channel access, then transmission flexibility is improved, but collision probability increases with each extended reservation

Engineering Contradiction:

Improvetransmission flexibilityVSAvoidcollision probability

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The Duration field in the initial RTS/CTS exchange performs a preliminary action by reserving the channel for the entire anticipated transmission sequence in advance. This preliminary long-term reservation eliminates the need for repeated frame-by-frame extensions, thereby maintaining transmission flexibility while significantly reducing collision probability by securing the channel upfront

Inventive Principle:

Principle #10Preliminary action

3Object-affected harmful factors

If backoff period is waited before retransmission to avoid collisions, then collision avoidance is improved, but latency increases for time-sensitive frames

Engineering Contradiction:

Improvecollision avoidanceVSAvoidretransmission delay

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The channel reservation performed preliminarily through RTS/CTS exchange creates a protected time window before actual data transmission. When retransmission is needed within this reserved window, the channel is already secured, allowing immediate retransmission without backoff delay while maintaining collision avoidance. This preliminary reservation acts as a safety buffer that eliminates the need for reactive backoff waiting

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The channel reservation maintains continuous access rights for the source node throughout the transmission sequence, including during retransmissions. This continuity of useful action ensures that when a frame needs retransmission, the source node can immediately retransmit without breaking the continuous channel access, thereby eliminating backoff delays while preventing collisions through the ongoing reservation

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentUS8301955B2Method and apparatus performing express retransmission of frames

Publication Date: 2012.10.30 SIGNAL POINT NETWORKS LLC

AI summary

A method, apparatus and computer program product for the express forwarding are presented. A node attempts to transmit a frame designated as a Time Sensitive Quality of Service (TSQ) frame to be express forwarded from a first node to a second node of a plurality of nodes. A collision is detected involving the TSQ frame while attempting to transmit the TSQ frame. A retransmission of the TSQ frame is attempted without waiting a predetermined back off period.