Zigbee Frequency Bands

Zigbee is a low-power, low data rate wireless connectivity technology that is used to create short range wireless personal area networks (WPAN). It is a wireless communication protocol that is intended to simplify the network architecture and make it less expensive compared to other WLAN technologies like Bluetooth and Wi-Fi. 

Zigbee is based on the IEEE 802.15.4 specification or standard set by the Institute of Electrical and Electronics Engineers (IEEE) that defines the amount of transmit power to be sent out from Zigbee radios, frequency range, bandwidth, data rate and other parameters. This standard defines operation of Zigbee radios in the unlicensed Industrial, Scientific, and Medical (ISM) bands that are from 2.4 to 2.4835 GHz, 902 to 928 MHz, and 868 to 868.6 MHz.

The table given below shows various frequency bands used by Zigbee along with the corresponding data rates, modulation techniques, and others.

ZigBee Frequency Bands

Zigbee uses 16 channels (from 11 to 26) in the 2.4 GHz throughout the world, 13 channels in the 915 MHz band in North America, and a single channel in the 868 MHz band in Europe. Some devices also use the 784 MHz band in China for Zigbee.

Like Wi-Fi, Zigbee technology also uses a number of channels in these frequency bands to transmit and receive data from Zigbee-enabled devices in applications such as home automation, medical device data collection, wireless light switches, energy and traffic monitoring, and other consumer electronic devices that requires relatively low-power and data rate. The channels Zigbee uses are divided across different countries with each country using different set of channels for various purposes. In general, the common frequency band of Zigbee is 2.4 GHz.

Across these channels, every Zigbee device utilizes a bandwidth of up to 2 MHz while any two different channels are separated by a guard band of 5 MHz to prevent interference due to other Zigbee devices. The data rate that can be achieved in the 2.4 GHz band is 250 Kbps per channel, 40 Kbps per channel in the 915 MHz band, and 20 Kbps per channel in the 868 MHz band. However, the actual throughput that can be delivered is inevitably less than the specified values, owing to various factors such as packet overhead, processing delays, and channel latency. Zigbee radios generally deliver an output power of 1-100 mW across these frequency bands.

It is also worth pointing out that since Wi-Fi and Zigbee utilize the 2.4 GHz band, it is possible that Zigbee radios may face interference due to Wi-Fi devices, thereby degrading the signal quality of Zigbee network. However, channel numbers 1, 6, or 11 are generally occupied by Wi-Fi networks which imply that many Zigbee channels are interference-free. Specifically, channels 15, 20, 25 and 26 of Zigbee are always free and do not interfere due to Wi-Fi regardless of which Wi-Fi channel is utilized at any time. Therefore, when Zigbee radios face interference issues, they can be switched to these channels in order to maintain a stable network performance, data rate, and minimize latency. The Figure shown below illustrates the various frequency bands used by both Zigbee and Wi-Fi.

Zigbee and Wi-Fi frequencies (occupied) in the 2.4 GHz Band

Another protocol called Thread is also used for Mesh Networking. Click here to learn more about the Thread Protocol.