What is the spacing between ZigBee channels when operating in the 2.4 GHz frequency band?

ZigBee is based on the IEEE 802.15.4 standard, which defines the physical (PHY) and MAC layers. For operation in the 2.4 GHz ISM band, the standard specifies 16 channels, numbered 11 through 26. The center frequency for the first channel (11) is 2405 MHz. Each subsequent channel's center frequency is separated by 5 MHz. For example, channel 12 is at 2410 MHz, channel 13 is at 2415 MHz, and so on, up to channel 26 at 2480 MHz. This consistent 5 MHz separation between adjacent channel center frequencies is the channel spacing.

A. 25 MHz is incorrect. This spacing is not used by the IEEE 802.15.4 standard for any of its frequency bands.

B. 2 MHz is the approximate channel bandwidth (the width of the signal itself) for ZigBee in the 2.4 GHz band, not the spacing between channel centers.

D. 1 MHz is incorrect. This spacing is too narrow for the 2 MHz channel bandwidth and is not defined by the IEEE 802.15.4 standard.

1. CWNP. (2021). CWISA-102 Certified Wireless IoT Solutions Administrator Official Study Guide. Chapter 4: The Internet of Things, Section: "IEEE 802.15.4," p. 118. The guide states, "In the 2.4 GHz band, there are 16 channels (11–26) with 5 MHz spacing between channel center frequencies."

2. IEEE Standard for Low-Rate Wireless Networks. (2020). IEEE Std 802.15.4-2020. Section 11.2.3 "Channel numbering and center frequencies," p. 183. The standard provides the formula for calculating the center frequency in the 2.4 GHz band: FC = 2405 + 5(k − 11) MHz, for k = 11, 12, ..., 26, which mathematically defines the 5 MHz spacing.

3. Stallings, W. (2016). Foundations of Modern Networking: SDN, NFV, QoE, IoT, and Cloud. Pearson Education, Inc. Chapter 11: The Internet of Things, Section 11.3 "IoT Networking," p. 354. The text describes the IEEE 802.15.4 channel structure, noting, "In the 2.4-GHz band, there are 16 channels, with 5 MHz between center frequencies."