By: Chris Downey, Product Manager
IEEE 802.15.4 is a standard developed by the IEEE to enable low power, mesh networks. It has seen tremendous use for SCADA, Wireless Sensor Networks, Industrial controls and other industries due to its ability to enable low-power sensing and controlling. 802.15.4 is also the physical layer and media access standard used by the Zigbee Alliance for the Zigbee network architecture. While the relatively low power consumption, generally around 20mA-30mA for RX and 20mA-40mA for TX for less than 10dBm, of most 802.15.4 transceivers has allowed for a number of unique applications, developers are undoubtedly running into issues due to 802.15.4’s physical layer.IEEE 802.15.4 specifies for a direct sequence spread spectrum system which effectively means the signal is spread over a 5Mhz bandwidth centered on a single frequency.For 2.4Ghz there are 16 of these channels available for 802.15.4, but since these are based on a fixed frequency they are susceptible to interference on at that frequency. Implementing algorithms to change frequencies based on interferers is problematic, especially for spatially diverse systems, where nodes are spread out and may experience different interferers at different frequencies at different times.
Non-FHSS networks are susceptible to a single interferer.
If you are developing with 802.15.4, you should probably ask why. Is it for the potential meshing, if so do you really need meshing or is your system fundamentally a point to multipoint star network? Do you need the mesh because you are transmitting at less than 10dBm? Why not increase your output power 10 fold and remove the headaches of trying to set up a routed network on memory constrained devices. Are you using 802.15.4 for the low power consumption? RAMP ISM modules from Laird have an average idle current of 10mA and sleep modes to produce even lower average current consumption. Do you think 802.15.4 is necessary for handling large networks of hundreds or thousands of nodes?RAMP modules such as the RM024, LT1110 or AC4490 can handle more than 16million devices in a network, without the additional latency or network congestion of having to route traffic through intermediaries.RAMP modules can do these things while also employing a frequency hopping spread spectrum technology to use the entire available bandwidth to provide interference immunity.
Check out all our RAMP ISM modules here: http://www.lairdtech.com/ramp