Appendix B - understanding wireless basics - Johnson Controls - LIT-12013765 - Wireless field bus - SEC - UCB

Smart Equipment Control Wireless Installation Guide

Johnson Controls
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Installation Guide
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The following information provides a general understanding of Johnson Controls wireless solutions, how the technology works, things to watch out for to avoid issues, and ways to ensure the best performance.

Wireless spectrum basics

  • The Johnson Controls wireless solution is based on the 802.15.4 standard operating at 2.4 GHz frequency.
  • The 2.4 GHz spectrum is unlicensed and shared with Wi-Fi, streaming video, and Bluetooth.
    • Unlike a typical Wi-Fi network, the Johnson Controls ZFR wireless network does not connect a user to the Internet.
  • Just like in normal conversation between people in a crowd, the more people carrying on the conversation, it is harder and harder for two people to converse the farther they are from each other. This is the fundamental principle of signal to noise; signal being my conversation, noise being other conversation occurring in the crowd.

Building construction impacts

Within the 2.4 GHz spectrum, certain building characteristics can make wireless conversation more challenging.

  • Metal within the path of the conversation can impact the quality of both the strength and decoding of the signal. Follow the recommended guidelines for installing the radio devices with respect to metal.
  • Metal is used generically here, but typically refers to large duct runs, metal support structure, metal mesh in plaster walls, for example.
  • Other building materials such as concrete block or poured concrete wall can also create considerable loss to the signal strength.
  • Fire walls or doors between building sections.
  • Hurricane or tornado concrete construction.

Frequency band utilization

  • ZFR wireless uses channels between the main Wi-Fi channels.
Figure 1. IEE802.15.4 and IEE802.11 channels

  • Same frequency band as IEEE 802.11 (Wi-Fi), but different sized channels; ZFR system automatically selects non-overlapping, quiet channels such as 15, 20, or 25.
  • Field-selectable channels for customer requests and custom applications.

Understanding interference

  • Some sites may exhibit interference after the initial installation.
    • Not all Wi-Fi is managed within the building, for example, channels are rotated or varied so that the same channel does not exist directly above or below a specific PAN.
Figure 2. IEEE802.15.4 and IEEE802.11 channel bonding
  • IEEE 802.11 A and N enables channel bonding which creates a 40 MHz channel and can potentially step on the IEEE 802.15.4 reserved space and cause potential for more communication errors.
  • Knowledge of market based Wi-Fi tools, for example, WiSpy, might be required to properly consider a site as a wireless candidate.