“Every hop in a network is a decision, every decision is a tradeoff, and every tradeoff defines the intelligence of the system. True engineering excellence is not in eliminating complexity, but in mastering it.” – MJ Martin
Introduction
A Wi-SUN mesh network, aligned with Advanced Metering Infrastructure 2.0, represents a distributed, self-healing communications fabric engineered for utility-grade resilience. Each smart meter, router, or field device participates in packet forwarding, creating a multi-hop network capable of adapting dynamically to environmental and operational variability. This model is particularly effective in Canadian utility deployments where mixed urban density, rural expanses, and climatic extremes demand a communications layer that is both robust and flexible.
What Is a Routed Network
A routed network is a communications architecture in which data packets are transmitted from a source to a destination through a sequence of intermediate nodes. Each node makes forwarding decisions based on routing intelligence derived from network topology and link conditions. In Wi-SUN, routing is typically implemented using IPv6 over low-power wireless personal area networks, with protocols such as RPL forming a Directed Acyclic Graph. This structure allows nodes to continuously evaluate and select optimal upstream paths toward a root node, ensuring resiliency in the presence of interference, node failure, or changing radio conditions.
The Concept of Path Cost
Path cost represents the relative efficiency and reliability of a route through the network. Rather than relying solely on physical distance, Wi-SUN defines cost as a composite metric that captures the operational quality of each link along a path. Lower cost routes are preferred because they offer higher probability of successful delivery with minimal retransmissions and latency. This abstraction allows the network to optimize performance in real time rather than relying on static topology assumptions.
Metrics Used to Calculate Path Cost
Path cost is derived from multiple weighted parameters that collectively describe link performance. Expected Transmission Count is a primary metric, estimating how many attempts are required to successfully deliver a packet. Signal quality indicators such as Received Signal Strength Indicator and Signal to Noise Ratio provide insight into link stability. Additional factors include packet error rate, channel congestion, latency, and, in some configurations, node energy constraints. These inputs are synthesized into a rank value that determines how each node positions itself within the routing hierarchy.
Modulation Techniques in Wi-SUN Networks
Wi-SUN networks operate primarily in sub-gigahertz frequency bands and leverage modulation techniques defined by the IEEE 802.15.4g standard. The most commonly deployed modulation scheme is Orthogonal Frequency Division Multiplexing. This approach divides the available spectrum into multiple orthogonal subcarriers, allowing data to be transmitted in parallel streams. The result is improved spectral efficiency and enhanced resilience to multipath fading and interference, both of which are common in urban and industrial utility environments.
In addition to Orthogonal Frequency Division Multiplexing, Wi-SUN supports Frequency Shift Keying and, in some configurations, Offset Quadrature Phase Shift Keying. Frequency Shift Keying is valued for its robustness and simplicity, making it suitable for long-range, lower data rate applications where link reliability is paramount. Offset Quadrature Phase Shift Keying provides higher data throughput but requires stronger signal conditions and more precise synchronization.
The choice of modulation directly influences network performance characteristics, including data rate, range, and latency. Lower order modulation schemes such as binary or quadrature Frequency Shift Keying offer extended range and better penetration through obstacles, which is advantageous in rural or heavily obstructed Canadian environments. Higher order schemes within Orthogonal Frequency Division Multiplexing enable greater throughput but are typically used in shorter range, higher density deployments. Wi-SUN networks dynamically balance these tradeoffs through configuration profiles and adaptive data rate mechanisms.
Latency Per Hop
Latency per hop in a Wi-SUN mesh network is determined by transmission time, channel access delays, and potential retransmissions. Under typical operating conditions, per-hop latency ranges from approximately 10 to 50 milliseconds. Network congestion or degraded link quality can increase this value due to additional backoff intervals and retransmission attempts governed by carrier sense multiple access protocols.
Maximum Distance of a Hop
The maximum distance of a single hop depends on frequency band, transmit power, antenna configuration, and environmental conditions. In sub-gigahertz Wi-SUN deployments, a typical hop distance ranges from 300 to 800 metres in urban settings and can exceed one kilometre in rural or line-of-sight scenarios. Network design generally prioritizes link quality over maximum distance to ensure consistent performance and minimize retransmissions.
Practical Hop Count in Smart Meter Networks
For standard AMI 2.0 applications such as meter reading and interval data collection, practical hop counts typically fall between 5 and 10 hops. Beyond this range, cumulative latency and increased transmission overhead begin to impact network efficiency. Optimal designs aim to maintain average hop counts closer to 4 to 6 to preserve predictable communication performance.
Impact of Adding Smart Grid Applications
The integration of smart grid applications introduces stricter requirements for latency and reliability. Functions such as distribution automation and voltage control demand faster and more deterministic communication. As a result, practical hop counts are generally reduced to 3 to 5 hops for these use cases. Utilities often implement traffic prioritization and network segmentation to ensure that critical grid operations are insulated from routine AMI traffic.
Worst Case Latency in Distribution Network Fabric
Worst case latency is a function of hop count and per-hop delay under constrained conditions. Assuming an upper bound of 50 milliseconds per hop, a 10 hop AMI path may experience latency approaching 500 milliseconds. In a smart grid context with a reduced 5 hop path, worst case latency is approximately 250 milliseconds. These values are acceptable for many supervisory and control applications but are not sufficient for protection schemes requiring near real-time response.
Summary
Wi-SUN mesh networks provide a sophisticated routing framework that balances reliability, scalability, and performance. By leveraging composite path cost metrics and adaptive routing, these networks maintain operational integrity across diverse environments. The selection of modulation techniques further refines performance by aligning data rate and range with deployment conditions. Effective network design requires careful consideration of hop count, link quality, and application requirements to ensure that both AMI and smart grid functions operate within acceptable performance thresholds.
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees – in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 80 next generation MOOC (Massive Open Online Courses) [aka Micro Learning] continuous education programs in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.