Terminology » Other Wireless » Wi-SUN Protocol Stack: RF Driver, PHY, and MAC Layers

Wi-SUN Protocol Stack: RF Driver, PHY, and MAC Layers

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This page provides an overview of the Wi-SUN protocol stack layers, explaining the functions of each layer, including the RF driver, PHY layer, and MAC layer.

What is Wi-SUN?

Wi-SUN stands for Wireless Smart Ubiquitous Network Field Area Network. Unlike star-based networks like WiFi or LTE, Wi-SUN utilizes a mesh topology.

Wi-SUN FAN (Field Area Network) is designed to support a larger number of end nodes and cover greater distances compared to technologies like Zigbee and Thread. The Wi-SUN Alliance, a consortium of global corporations and organizations from various countries including the United States, Canada, Australia, China, Europe, Japan, Brazil, Korea, and India, governs the technology.

Members of the Wi-SUN Alliance can be promoters, contributors, observers, or adopters of the technology. With approximately 240 members across 40 countries, these leaders oversee the certification, interoperability, and standardization of Wi-SUN compliant devices.

Wi-SUN supports a wide range of applications in sectors such as smart utilities, smart cities, smart homes, M2M (Machine-to-Machine), and the Internet of Things (IoT). Key use cases for Wi-SUN FAN include:

  • AMI Metering (Advanced Metering Infrastructure)
  • EV Charging
  • Smart Transport
  • SCADA (Supervisory Control and Data Acquisition)
  • Parking Management
  • Distributed Generation
  • Environmental Sensors
  • Traffic Management
  • Smart Lighting
  • Direct Load Control

Wi-SUN operates in the sub-1 GHz and 2.4 GHz frequency bands. Depending on the modulation techniques used, it supports various symbol rates, including 50, 100, 150, 200, and 300 Ksymbols/sec. It offers a long range of approximately 4 km point-to-point with a 1W output from a non-directional antenna and boasts a very low latency of about 0.02 seconds.

Wi-SUN Protocol Stack Layers

Wi-SUN Protocol Stack

Figure-1 : Wi-SUN Protocol Stack

The figure above illustrates the Wi-SUN protocol stack layers. The physical layer specifications are defined in IEEE 802.15.4g, while the MAC layer specifications are defined in the IEEE 802.15.4e standard. Wi-SUN FAN 1.0 devices are typically line-powered and utilize FSK modulation, whereas FAN 1.1 devices are battery-powered and use OFDM modulation.

Let’s delve into the functions of each protocol layer in Wi-SUN technology:

RF Layer

The RF layer is responsible for modulating physical layer data onto the RF carrier for transmission and demodulating the RF signal during reception. It operates on specific radio frequencies allocated for Wi-SUN in different countries. Some frequency bands are 470-510MHz, 779-787MHz and 920.5-924.5MHz in China, 863-870MHz and 870-876MHz in Europe, or 920-928MHz in USA, Canada and Japan, 2.45 GHz worldwide.

PHY Layer

The Physical layer provides services to the MAC layer above and interfaces with the RF driver below. It modulates the MAC layer information using FSK or OFDM modulation, depending on the FAN profile.

The PHY layer supports various data rates. The specifications for the PHY layer are outlined in IEEE 802.15.4g (i.e., IEEE 802.15.4-2015). Wi-SUN FSK supports data rates up to 300 kbps. Error correction is supported in the Wi-SUN FSK version. OFDM PHY offers higher spectrum efficiency. Wi-SUN OFDM supports data rates up to 2.4 Mbps.

The MAC layer is defined in IEEE 802.15.4e and IE extensions.

It handles various functions, including frequency hopping, discovery/join processes, protocol dispatch (IEEE 802.15.9), and frame exchange patterns. Wi-SUN FAN defines seven frame formats for different services.

It also defines its own IEs (Information Elements) to support certain operations. These IEs come in two types: Wi-SUN header IEs and Wi-SUN payload IEs. The MAC frames include:

  • Advertisement Frame
  • Advertisement Solicit Frame
  • Configuration Frame
  • Configuration Solicit Frame
  • Acknowledgment Frame
  • Application Data Frame (from the upper layer)
  • EAPOL (Extensible Authentication Protocol over LAN) Frame

Network Layer

This layer encompasses:

  • 6LoWPAN adaptation and header compression
  • DHCPv6 for IP address management
  • Routing using RPL (Routing Protocol for Low-Power and Lossy Networks)
  • ICMPv6 (Internet Control Message Protocol version 6)
  • Unicast/multicast forwarding

Transport Layer

The UDP protocol is used at this layer. TCP is an optional protocol for implementation.

Application Layer

Different protocols are used at the application layer, depending on the specific application requirements, such as:

  • MQTT (Message Queuing Telemetry Transport)
  • CoAP (Constrained Application Protocol)
  • HTTP (Hypertext Transfer Protocol)
  • SCADA
  • DLMS (Device Language Message Specification)

Security Layer

Wi-SUN supports various security mechanisms, including:

  • 802.1X/EAP-TLS/PKI Authentication
  • 802.11i Key management
  • Optional ETSI-TS-102-887-2 Node 2 Node Key management

Wi-SUN Network Architecture

References

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