Link Layer Multicast in Low Power Wide Area Networks
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Solution Overview
Problem
Low power wide area networks (LPWAN) face challenges in deploying network layer operations like multicasting due to link constraints that limit power consumption and require single-hop communications, precluding the use of link layer mesh topologies or network layer routing, which hinders reliable data transmission in large-scale deployments of very constrained network devices.
Innovation Solution
The implementation of a method that establishes reliable link-layer multicast by using wired gateways to manage listening intervals and collision avoidance parameters, allowing constrained wireless network devices to switch between low-power optimized and listening modes, and selectively transmit multicast data packets based on randomly selected wait intervals and redundancy constants, ensuring reliable data delivery without the need for mesh or network topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If link layer mesh topology or network layer routing is used to enable multicast, then multicast reliability is improved, but power consumption increases and device complexity increases
Solution Approach 1:
The patent extracts the multicast routing function from the constrained wireless devices and concentrates it in the wired gateways. The gateway executes the multicast routing protocol and manages the multicast group, while constrained devices simply send and receive multicast packets without routing responsibilities. This extraction eliminates the need for complex routing logic in power-constrained devices while maintaining multicast reliability.
Solution Approach 2:
The wired gateway acts as an intermediary between the network layer and the link layer in constrained devices. It handles the complex multicast routing, group management, and packet forwarding, allowing constrained devices to operate in simple low-power mode while still benefiting from reliable multicast through the gateway's mediation.
2Reliability
If wired gateways continuously transmit multicast packets, then multicast delivery reliability is improved, but collision probability increases
Solution Approach 1:
The patent implements periodic transmission of multicast packets by wired gateways at scheduled intervals rather than continuous transmission. The gateway transmits multicast packets at specific time periods, allowing the wireless medium to clear between transmissions and reducing collision probability while maintaining reliable periodic delivery to constrained devices.
Solution Approach 2:
The wired gateway performs preliminary actions by pre-scheduling multicast packet transmissions and managing transmission timing before actual packet delivery. It prepares the multicast data structures, determines optimal transmission times, and coordinates with multiple constrained devices to minimize collisions while ensuring reliable delivery.
Data Source
AI summary
A management device for a low power wide area network can: generate and send, to each constrained wireless network device via a wired gateway, a link layer multicast listener command specifying a listening interval and causing each constrained wireless network device to change from a low-power optimized mode to a listening mode until reception of a multicast data packet within the listening interval; generate collision avoidance parameters including a minimum waiting interval, a maximum waiting interval relative to the listening interval, and a redundancy constant; and instruct the wired gateways to selectively transmit the multicast data packet based on the collision avoidance parameters, wherein each wired gateway responds by waiting a randomly-selected wait interval between the minimum and maximum waiting intervals, and selectively transmitting the multicast data packet only if a received number of the multicast data packet by the corresponding wired gateway is less than the redundancy constant.