Learning Objectives

• Apply basic wireless site survey and AP placement principles
• Calculate AP coverage requirements based on client density and application needs
• Understand channel planning for 2.4 GHz, 5 GHz, and 6 GHz bands

The Foundation of Wireless Design

A well-designed Wi-Fi network starts with the physical environment. Every wall, ceiling, and furniture layout affects RF propagation. The goal of wireless design is to provide adequate coverage, sufficient capacity, and seamless roaming across the entire service area — without over-engineering or creating interference.

The five key variables in any wireless design:

1. Coverage area — The physical space that must be served
2. Client density — How many devices will connect per AP
3. Application requirements — Bandwidth and latency needs per device
4. Environmental factors — Building materials, obstructions, interference sources
5. Channel availability — Which frequencies can be used without co-channel interference

AP Placement Basics

AP placement is the single most impactful decision in wireless design. The rule is simple: APs belong on the ceiling, not on walls. Ceiling-mounted APs with omnidirectional antennas create a circular coverage pattern downward, minimizing obstructions.

A basic AP placement process:

1. Obtain or create a floor plan with accurate measurements and material annotations
2. Mark all structural elements (concrete columns, elevator shafts, stairwells) — these block RF
3. Place APs to ensure at least -67 dBm RSSI across the coverage area for high-density (classroom, office) or -70 dBm for general coverage
4. Overlap cell edges by 15–20% to support seamless roaming
5. Place channels so that adjacent APs never use the same or overlapping channels

Channel Planning

Channel planning prevents co-channel interference (CCI) — the biggest killer of Wi-Fi performance. CCI occurs when two APs on the same channel can hear each other's transmissions. In CSMA/CA, they must take turns, halving throughput for both.

2.4 GHz (Only 3 non-overlapping channels)

The 2.4 GHz band has channels 1–11 (US) or 1–13 (EU). Each channel is 20 MHz wide, and only channels 1, 6, and 11 are non-overlapping. In a multi-AP deployment, the classic plan is a 1/6/11 reuse pattern, but with only 3 channels, every fourth AP reuses a channel. This severely limits density.

5 GHz (23 non-overlapping channels)

The 5 GHz band has vastly more spectrum: 23 non-overlapping 20 MHz channels (depending on regulatory domain and DFS availability). With 40 MHz channels, you get 11 channels. With 80 MHz, you get 5. This flexibility makes 5 GHz the preferred band for high-density design.

6 GHz (59 non-overlapping channels for Wi-Fi 6E/7)

Wi-Fi 6E opened the 6 GHz band (5925–7125 MHz), providing up to 59 additional 20 MHz channels, 29 at 40 MHz, 14 at 80 MHz, or 7 at 160 MHz. This is a transformative amount of clean spectrum — no legacy devices, no DFS requirements, and no coexistence overhead.

Site Plan Visualization

The diagram below shows an example floor plan with AP placements optimized for coverage, channel reuse, and roaming overlap.

Capacity Planning

Coverage is not enough — you must plan for capacity. A single AP in a 20 MHz channel at 2.4 GHz can realistically deliver about 30–50 Mbps of TCP throughput in ideal conditions. If you need to serve 100 clients each using video conferencing (5 Mbps per client), you need 500 Mbps of capacity — requiring multiple APs and channels.

A practical capacity planning formula:

Required APs = (Total clients × Average throughput per client) / (Realistic AP throughput)

For example: 200 clients, each needing 2 Mbps, with APs delivering 40 Mbps each: 200 × 2 / 40 = 10 APs. The coverage-based estimate from our earlier example (6 APs) would fall short, so capacity drives the final count.

Key Takeaways

• Ceiling-mount APs for best coverage; avoid wall-mounting unless necessary
• Overlap cell edges by 15–20% for seamless roaming
• 2.4 GHz has only 3 non-overlapping channels — use 5 GHz or 6 GHz for density
• -67 dBm RSSI is the target for high-density design; -70 dBm for general coverage
• Always calculate both coverage and capacity; capacity often drives the final AP count
• Wi-Fi 6E's 6 GHz band provides transformative spectrum for high-density deployments