802.11b channel planning: In the 2.4 GHz band, how many non-overlapping 20 MHz channels are available for 802.11b/g in most regulatory domains (e.g., channels 1, 6, and 11 in the U.S.)?

Introduction / Context:
Channel reuse in the 2.4 GHz band is constrained by the 5 MHz channel center spacing and the 20–22 MHz occupied bandwidth of 802.11b/g channels. Effective frequency planning minimizes adjacent-channel interference by choosing non-overlapping channels.

Given Data / Assumptions:

• Standard 2.4 GHz band allocation with 11 channels in the U.S. (13 in many other regions).
• Channel width 20–22 MHz; center-to-center spacing 5 MHz.
• Goal is non-overlapping operation for co-channel reuse.

Concept / Approach:

Because adjacent channels overlap significantly, only certain channel separations avoid interference. In practice, channels 1, 6, and 11 (U.S.) are spaced far enough apart to provide three non-overlapping 20–22 MHz channels. Other domains may use 1, 5, 9, 13, but the non-overlapping count is still effectively three in most planning guides.

Step-by-Step Solution:

Verification / Alternative check:

Spectrum analysis in a lab confirms that channels 1, 6, and 11 show minimal spectral overlap. Vendor design guides universally recommend this triad for 2.4 GHz deployments.

Why Other Options Are Wrong:

12 and 23 correspond to 5 GHz counts (depending on DFS availability), not 2.4 GHz.

40 is unrelated to any standard 20 MHz non-overlapping count in Wi-Fi.

Common Pitfalls:

Attempting to use channels like 3, 8, and 11 expecting non-overlap; mixing regulatory domains and assuming additional channels increase the non-overlapping count beyond three for 20 MHz in 2.4 GHz.

Final Answer:

3