The TOP 5 Checklist to Successfully Deploy 802.15.4 Wireless

Dave Craven has once again bestowed upon us some valuable insight into wireless design. Follow his TOP 5 Checklist if you still want to have hair left on your head at the end of your install.


Range in Geography

This is by far the most important metric that affects any wireless application. Most manufacturers rely on a range metric based upon Line of Sight (LOS). Unfortunately, it is the only absolute value that can be used as a solid benchmark. With no obstacles in between two Radios, no rain, no snow, no foliage, no walls, no buildings; the transmission distances of their products can be accurate and repeatable. Trouble is your site, from a practical sense, would need to be located in outer space to use this metric.

 

Frequency Spectrum of the Product

The lower the frequency the better the penetrating capability through walls and floors. 400 to 900 MHz devices have larger wavelengths. Downside is the data able to be transmitted is usually less. Higher Frequencies such as 2.4 – 5.8 GHz have less penetration capability through materials but have much higher data transmission rates.

 

Transmit and Receive Sensitivities

These sensitivities are ratings of the various chipset manufacturers coupled with antenna design by the device manufacturer.

Transmit Sensitivity is a measure of overall power of the device while transmitting, measured in Dbm. Various products on the market range from 1 to 30 Dbm nominally. This value can also be expressed in Milli-Watts. The higher the power, generally the greater the distance.

Receive Sensitivity is measured in Dbm as well, but unlike pure power it is more a reflection of the quality of the overall assembly. Receive Sensitivity for most products available on the market is usually between -85 and -105 Dbm.

Under the IEEE 802.15.4 Standard by which most products we are talking about here must conform to; there is a complicated formula for certification that governs how many devices and at what power levels and data transmission rates the overall architecture is allowed to support. If for instance, you have very high Transmit Sensitivity ratings, the likelihood is that the product will have relatively small numbers of devices allowed to be on a given Network.

 

Existing Wireless Devices and Environment

The next topic for consideration is the existing wireless applications in use at the facility you are intending to populate. No need to get wordy here, 802.11 Wi-Fi networks are everywhere, plus a host of other technologies, operating in different RF Spectrums. This is not so much a problem in stand-alone facilities like Big Box / Small Box retail stores, C-Stores and the like, but it is a major consideration in facilities like Hospitals and Multi-Tenant Office Buildings.

WiFi Tools by METAGeekIn general you need to understand how saturated a particular environment is with other systems. One of the best tools I have found for doing this is an application program that you can load on a laptop called inSSIDer HOME. It is a free application which you can download. The main thing that this accomplishes is understanding where not to physically locate your various devices.

802.15.4 RF Devices are generally far less powerful than 802.11 network devices such as access points. Locating the PAN Coordinator or an FFD within 15 Ft of an 802.11 access point can cause a phenomenon known as Antenna Desensitisation of the 802.15.4 device. Another device to avoid proximity to is an Indoor Cell Repeater, you need 25 Ft of separation here from any 802.15.4 devices.

 

Materials Used in the Building or Structure

Almost everyone understands interior and exterior walls affect the horizontal coverage of wireless and because there is a lot to be said about it… There will be a separate article written specifically on just this point. Stay Tuned!

 

 

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