In the 5 GHz band, certain channels like 144 are not universally supported across all devices, especially older
802.11n clients. If the AP is operating on channel 144, and the client's regulatory domain or hardware does not support this channel, the SSID will not be visible to the client.
The CWDP-305 Official Study and Reference Guide notes:
"Client devices may not support all channels in the 5 GHz band, depending on their regulatory domain and hardware capabilities. Channel 144, for example, is not supported by all 802.11n clients." Reference: CWDP-305 Official Study and Reference Guide, Chapter on Post-Design ValidationandTroubleshooting

Elevator shafts and similar structures can create RF "dead zones" due to their highly attenuating materials like metal. In such cases, simply increasing power or gain typically does not solve the issue due to shadowing. The recommended approach is to move APs or install additional APs on the obstructed side.
From CWDP-305:
"Obstructions such as elevator shafts may require re-positioning or the addition of APs to ensure proper coverage. These obstructions can block RF propagation regardless of transmit power or antenna gain."
- Reference: CWDP-305 Official Study Guide, Post-Design ValidationandTroubleshooting Chapter

Co-Channel Interference (CCI) occurs when multiple APs on the same channel are heard in the same area, even at relatively low signal levels. CCI is not eliminated simply because signals are below #75 dBm. In fact, CCI is a concern even when APs are heard at levels as low as #85 dBm or lower.
From CWDP-305:
"CCI can be problematic even when the signal from neighboring APs is heard at levels between #85 dBm to
#93 dBm. Effective channel planning requires minimizing overlap of same-channel signals at or above these thresholds."
- Reference: CWDP-305 Official Study Guide, Post-Design ValidationandTroubleshooting Chapter

In the 2.4 GHz band, 40 MHz channels are formed by bonding two adjacent 20 MHz channels. The primary channel is the one the client uses to initiate communication, and the secondary channel is either above (+1) or below (-1) the primary.
For channel 4 as primary with a +1 secondary offset:
Primary channel: 4 (2.427 GHz)
Secondary channel: 5 (2.432 GHz)
This configuration stays within the allowed channels 1-11.
Reference: CWDP-305 Official Study and Reference Guide, Chapter on ProtocolandSpectrum Analysis

The introduction of a new requirement, such as supporting RFID location tracking, after the site survey has commenced constitutes scope creep.Scope creep refers to the uncontrolled expansion of project scope without corresponding adjustments to time, cost, and resources.Implementing location tracking requires specific design considerations, including AP placement and calibration, which should be planned from the project's outset.Introducing such requirements mid-project can lead to design inefficiencies and increased costs.
Reference: CWDP-305 Official Study and Reference Guide, Chapter on Wireless Design Process