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SIGNAL CHAIN BASICS (Part 30): Protocol selection over IEEE 802.15.4 silicon

(Editor's note : there are closely related articles, plus a complete list of previous installments of this popular, long-running series, at the end of this article.)

In Signal Chain Basics #24 , we covered basic networking using the IEEE 802.15.4 PHY/MAC Protocol. We started simple, identifying the fundamentals of the IEEE 802.15.4 PHY and MAC layers. Now I would like to build on this foundation taking some time to discuss some of the options a system architect has when moving forward with an 802.15.4-based networking solution.

First things first : If your project requires something such as ZigBee® or Smart Energy compliance due to mandates by the utility company or RF4CE interoperability with one or more of the major lines of LCD TVs, you should not be contemplating networking protocols, as the need to adhere to a specific standard there has been solidified. Instead, focus your time and effort on vendor selection and hardware alternatives, taking into careful consideration the maturity of the software you will be provided, any hidden costs with the silicon provider, and what tools and system level support you expect to receive once development is under way.

However, if you are not encumbered by partnerships, compatibility requirements, or non-technical micro-managerial bosses who dictate design decisions, then there are definitely options available based on system attributes, required or desired functionality and performance requirements.

If your system has two devices in the network, then please-please-please: keep things simple. There's nothing more frustrating than trying to help architect the network startup sequence of a customer's ZigBee mesh network, only to find out that in fact there's only two devices in the system, communicating 10 ft apart at most, pre-configured to work together out of the box. Whether peer-to-peer only, one-to-many, or multi-hop, communication must be supported.

Most silicon vendors offer a range of network protocol options ranging from basic proprietary software that simply configures the radio and has a basic communication interface, through more complex, ad-hoc, potentially multi-hop proprietary or standard protocols such as ZigBee or 6LoWPAN. I suggest under even this simple case, you consider your requirements from the simplest case, where devices are pre-programmed as a fixed network with fixed addressing and pre-configured pairing, to the more dynamic case where devices don't have a prior knowledge of one another.

Or if your devices must dynamically establish a unique network identifier, pairing (often with security restrictions) must take place. So-called “out-of-the-box” protocols, whether proprietary (such as TI's SimpliciTI protocol) or standard (ZigBee or RF4CE), have established methods for accomplishing these tasks. You must carefully consider whether the protocol fits your system requirements.

Beyond matching your system/product requirements with an appropriate networking protocol, it is crucial to look at your own resources and design capabilities before getting in over your head. For those product experts who don't have the RF-layout and software-networking experience to build a solution from the ground up, I recommend seeking out one of several module providers.

These modules can provide a drop-in FCC or otherwise certified pre-programmed solution where a simple API is provided over UART, SPI, or other interface, to allow you to set up specific parameters (such as Network ID, channel, application port identifier), connect to a network, search for and pair to another device, and send/receive basic application data. Working with a module can be protocol limited and more expensive on a per-device basis, but for smaller product runs (less than 50k) we find that the cost of a module more than makes up for the NRE cost of RF-layout, design, assembly and test, as well as software development and testing.

Whether you build up a custom solution from scratch, or cut-and-paste from a pre-existing solution, I wish you the best of luck in your development efforts and hope this brief article was able to shed some light on some of the points to consider before jumping in.

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About the Author
Brian M. Blum is a ZigBee Product Marketing Engineer with Texas Instruments, where he is responsible for 802.15.4 and ZigBee Low Power RF product line. He received his Master's of Computer Science w/ focus on Wireless Sensor Networking from University of Virginia. In his spare time he enjoys rock climbing, volleyball, yoga and nature.

Previous installments of this series:

  • SIGNAL CHAIN BASICS (Part 29): Digital interfaces – Single-ended versus differential interfaces, click here
  • SIGNAL CHAIN BASICS (Part 28): Building (Electrical) Bridges, click here
  • SIGNAL CHAIN BASICS (Part 27): Control EMI resulting from board-level clock distribution, click here
  • SIGNAL CHAIN BASICS (Part 26): How to close timing on High-Speed ADCs, click here
  • SIGNAL CHAIN BASICS (Part 25): Designing the audio-signal chain for non-audio experts, Part 1, click here
  • SIGNAL CHAIN BASICS (Part 24): Basic networking using the IEEE 802.15.4 PHY/MAC protocol, click here
  • SIGNAL CHAIN BASICS (Part 23): EIA-485: Receiver equalization boosts networking performance, click here
  • SIGNAL CHAIN BASICS (Part 22): Phantom microphone power–the ghost in the machine, click here
  • SIGNAL CHAIN BASICS (Part 21): Understand and configure analog and digital grounds, click here
  • SIGNAL CHAIN BASICS (Part 20): Understand the basics of op amps and speed, click here
  • SIGNAL CHAIN BASICS (Part 19): Exploring and understanding linear voltage regulators, click here
  • SIGNAL CHAIN BASICS (Part 18): The op amp as integrator, click here
  • SIGNAL CHAIN BASICS (Part 17): Hysteresis–Understanding more about the analog voltage comparator, click here
  • SIGNAL CHAIN BASICS (Part 16): Understanding the analog voltage comparator, click here
  • SIGNAL CHAIN BASICS (Part 15): Analog/digital converter–dynamic parameters, click here
  • SIGNAL CHAIN BASICS (Part 14): Analog/digital converter–static parameters, click here
  • SIGNAL CHAIN BASICS (Part 13): Putting the Bode plot to use, click here
  • SIGNAL CHAIN BASICS (Part 12): The Bode plot, an essential ac-parameter display tool, click here
  • SIGNAL CHAIN BASICS (Part 11): Introducing voltage- and power-conditioning circuits, click here
  • SIGNAL CHAIN BASICS (Part 10): Exploring the Delta-Sigma Converter, click here
  • SIGNAL CHAIN BASICS (Part 9): SAR Converter Operation Explored, click here
  • SIGNAL CHAIN BASICS (Part 8): Flash- and Pipeline-Converter Operation Explored, click here
  • SIGNAL CHAIN BASICS (Part 7): Op Amp Performance Specification–Bias Current, click here
  • SIGNAL CHAIN BASICS (Part 6): Op Amp Input Voltage Offset, click here
  • SIGNAL CHAIN BASICS (Part 5): Introduction to the Instrumentation Amplifier, click here
  • SIGNAL CHAIN BASICS (Part 4): Introduction to analog/digital converter (ADC) types, click here
  • SIGNAL CHAIN BASICS (Part 3): Analog and the digital world, click here
  • SIGNAL CHAIN BASICS (Part 2): Op Amp–Basic operations, click here
  • SIGNAL CHAIN BASICS: Operational Amplifier–The Basic Building Block, click here

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