837  Wi-Fi Frequency Bands and Channel Planning

Prerequisites: Wi-Fi Standards Evolution | Wireless Fundamentals

This enables: Wi-Fi Deployment Planning | Wi-Fi Security

837.1 Learning Objectives

By the end of this chapter, you should be able to:

• Compare the characteristics of 2.4 GHz, 5 GHz, and 6 GHz bands
• Identify non-overlapping channels and avoid interference
• Understand why only channels 1, 6, and 11 are recommended for 2.4 GHz
• Use channel planning strategies for multi-AP deployments
• Diagnose and resolve channel congestion issues
• Select the appropriate band for different IoT device types

837.2 Frequency Band Overview

Wi-Fi operates in three main frequency bands, each with distinct characteristics:

Band	Frequency Range	Channels	Penetration	Speed	Congestion	Best For
2.4 GHz	2400-2483.5 MHz	11-14*	Excellent	Lower	High	Sensors, range priority
5 GHz	5150-5850 MHz	23+	Moderate	Higher	Lower	Cameras, high bandwidth
6 GHz	5925-7125 MHz	59	Poor	Highest	Lowest	Industrial, dense deployments

*Channel availability varies by region (US: 11, EU: 13, Japan: 14)

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graph LR
    subgraph BAND24["2.4 GHz Band"]
        R24[Long Range<br/>Good Wall Penetration<br/>3 Non-Overlapping Channels<br/>More Interference]
    end

    subgraph BAND5["5 GHz Band"]
        R5[Medium Range<br/>Moderate Penetration<br/>23+ Channels<br/>Less Interference]
    end

    subgraph BAND6["6 GHz Band (Wi-Fi 6E)"]
        R6[Short Range<br/>Poor Penetration<br/>59 Channels<br/>No Legacy Interference]
    end

    style BAND24 fill:#16A085,stroke:#2C3E50,stroke-width:2px
    style BAND5 fill:#E67E22,stroke:#2C3E50,stroke-width:2px
    style BAND6 fill:#9B59B6,stroke:#2C3E50,stroke-width:2px

Figure 837.1: Wi-Fi frequency bands: 2.4 GHz, 5 GHz, and 6 GHz with key characteristics

837.3 2.4 GHz Band: The IoT Workhorse

837.3.1 Channel Layout and Overlap

The 2.4 GHz band has 14 channels (11 in US), but each channel is 22 MHz wide with only 5 MHz spacing between centers. This causes significant overlap:

Channel Layout (2.4 GHz):
          CH1   CH2   CH3   CH4   CH5   CH6   CH7   CH8   CH9  CH10  CH11
Freq:   2412  2417  2422  2427  2432  2437  2442  2447  2452  2457  2462 MHz

Each channel spans 22 MHz:
CH1:  |<-------- 22 MHz -------->|
      2401                      2423

CH6:               |<-------- 22 MHz -------->|
                   2426                      2448

Result: Channels 1-5 overlap with each other!
        Only 1, 6, 11 are truly non-overlapping.

ImportantThe 1-6-11 Rule

NEVER use channels 2, 3, 4, 5, 7, 8, 9, or 10 in the 2.4 GHz band!

These “in-between” channels overlap with BOTH neighboring non-overlapping channels, causing worse interference than using 1, 6, or 11.

Example of WRONG configuration: - AP1: Channel 3 (overlaps with channels 1-6) - AP2: Channel 8 (overlaps with channels 5-11) - Result: Both APs interfere with ALL three non-overlapping channels

CORRECT configuration: - AP1: Channel 1 - AP2: Channel 6 - AP3: Channel 11 - Result: No overlap, maximum efficiency

837.3.2 2.4 GHz Interference Sources

The 2.4 GHz band is crowded with non-Wi-Fi devices:

Device	Interference Type	Affected Channels
Microwave ovens	Broadband noise	All (worst on 7-11)
Bluetooth	Frequency hopping	All channels
Zigbee	Constant	Channels 11-13 (Zigbee 15-26)
Cordless phones	Varies	Often 1-3 or 6
Baby monitors	Continuous	Often 1 or 6
USB 3.0 ports	Broadband	1-3
Wireless cameras	Continuous	Varies

TipCoexistence Strategy

Wi-Fi + Zigbee in same building: - Use Wi-Fi channel 1 or 6 (lower frequency) - Use Zigbee channel 25 or 26 (upper frequency, above Wi-Fi 11) - Maintain physical separation where possible

Wi-Fi + Bluetooth: - Bluetooth uses adaptive frequency hopping to avoid Wi-Fi - Most modern devices handle this automatically - Enable Bluetooth coexistence in AP settings if available

837.4 5 GHz Band: The High-Bandwidth Option

837.4.1 Channel Structure

The 5 GHz band offers 23+ non-overlapping channels (varies by region), organized into UNII bands:

UNII Band	Frequency	Channels (20 MHz)	DFS Required?	Notes
UNII-1	5150-5250 MHz	36, 40, 44, 48	No	Best for IoT - no DFS
UNII-2A	5250-5350 MHz	52, 56, 60, 64	Yes	Radar detection required
UNII-2C	5470-5725 MHz	100-140	Yes	Weather radar overlap
UNII-3	5725-5850 MHz	149, 153, 157, 161, 165	No	Preferred for outdoor

WarningDFS (Dynamic Frequency Selection) Caution

Channels 52-64 and 100-140 require DFS to avoid radar interference.

What this means for IoT: - If radar is detected, AP must switch channels within 10 seconds - IoT devices must re-associate (1-5 seconds downtime) - Not suitable for latency-critical applications - Outdoor APs may frequently trigger DFS near airports

Recommendation for IoT: Use UNII-1 (36-48) or UNII-3 (149-165) to avoid DFS disruptions.

837.4.2 Channel Width Options (5 GHz)

Width	Throughput	Channels Available	Use Case
20 MHz	~100 Mbps	23+	Low-bandwidth IoT, maximum channels
40 MHz	~200 Mbps	11+	Balanced (common default)
80 MHz	~400 Mbps	5-6	Video streaming, cameras
160 MHz	~800 Mbps	2-3	Only for ultra-high bandwidth

IoT Recommendation: Use 40 MHz for most deployments. Reserve 80 MHz for video cameras only.

837.5 6 GHz Band (Wi-Fi 6E): The Clean Slate

The 6 GHz band (5925-7125 MHz) offers 1200 MHz of new spectrum with no legacy devices:

837.5.1 Advantages for IoT:

• No legacy interference: Only Wi-Fi 6E devices allowed
• 59 channels at 20 MHz (vs 11 at 2.4 GHz)
• 7 non-overlapping 160 MHz channels
• Lower latency: Less contention, no legacy protection

837.5.2 Disadvantages for IoT:

• Shorter range: Higher frequency = more path loss
• Poor wall penetration: Concrete/brick blocks signal
• New hardware required: Wi-Fi 6E chips (2021+)
• Limited device support: Most IoT devices still 2.4/5 GHz

837.5.3 When to Use 6 GHz for IoT:

• High-density industrial environments
• Enterprise deployments with new equipment
• Applications requiring ultra-low latency
• When 2.4/5 GHz is severely congested

837.6 Frequency Selection Decision Guide

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flowchart TD
    START[IoT Device Type?]

    START --> BATTERY{Battery Powered?}

    BATTERY -->|Yes| USE24A[Use 2.4 GHz<br/>Lower power draw<br/>Longer sleep cycles]

    BATTERY -->|No| BW{High Bandwidth<br/>Needed?}

    BW -->|Yes, >5 Mbps| VIDEO{Video/Audio<br/>Streaming?}
    BW -->|No, <1 Mbps| RANGE{Range<br/>Critical?}

    VIDEO -->|Yes| USE5A[Use 5 GHz<br/>More bandwidth<br/>Less interference]
    VIDEO -->|No| USE5B[Use 5 GHz<br/>40 MHz channels<br/>UNII-1 preferred]

    RANGE -->|Yes, through walls| USE24B[Use 2.4 GHz<br/>Channel 1, 6, or 11<br/>Better penetration]
    RANGE -->|No, same room| DENSE{Dense<br/>Deployment?}

    DENSE -->|>50 devices| USE6[Consider 6 GHz<br/>If Wi-Fi 6E available<br/>Otherwise 5 GHz]
    DENSE -->|<50 devices| USE24C[Use 2.4 GHz<br/>Simple, reliable]

    style START fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style USE24A fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style USE24B fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style USE24C fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style USE5A fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff
    style USE5B fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff
    style USE6 fill:#9B59B6,stroke:#2C3E50,stroke-width:2px,color:#fff

Figure 837.2: Decision tree for selecting the appropriate Wi-Fi frequency band for IoT devices

837.7 Interactive Channel Analyzer

Use this interactive tool to explore Wi-Fi channel congestion and find the best channel for your IoT deployment:

NoteWi-Fi Channel Analyzer Simulation

This simulation helps you understand channel congestion in the 2.4 GHz and 5 GHz bands.

mutable networks = []
mutable selectedBand = "Both"

spectrumWidth = 900
spectrumHeight = 280
channelWidth = viewof channelWidthSlider

// 2.4 GHz channels with center frequencies
channels24GHz = [
  {ch: 1, freq: 2412}, {ch: 2, freq: 2417}, {ch: 3, freq: 2422},
  {ch: 4, freq: 2427}, {ch: 5, freq: 2432}, {ch: 6, freq: 2437},
  {ch: 7, freq: 2442}, {ch: 8, freq: 2447}, {ch: 9, freq: 2452},
  {ch: 10, freq: 2457}, {ch: 11, freq: 2462}
]

// 5 GHz channels
channels5GHz = [
  {ch: 36, freq: 5180}, {ch: 40, freq: 5200}, {ch: 44, freq: 5220}, {ch: 48, freq: 5240},
  {ch: 52, freq: 5260}, {ch: 56, freq: 5280}, {ch: 60, freq: 5300}, {ch: 64, freq: 5320},
  {ch: 100, freq: 5500}, {ch: 104, freq: 5520}, {ch: 108, freq: 5540}, {ch: 112, freq: 5560},
  {ch: 116, freq: 5580}, {ch: 120, freq: 5600}, {ch: 124, freq: 5620}, {ch: 128, freq: 5640},
  {ch: 132, freq: 5660}, {ch: 136, freq: 5680}, {ch: 140, freq: 5700},
  {ch: 149, freq: 5745}, {ch: 153, freq: 5765}, {ch: 157, freq: 5785}, {ch: 161, freq: 5805}, {ch: 165, freq: 5825}
]

viewof channelWidthSlider = Inputs.range([20, 80], {value: 20, step: 20, label: "Channel Width (MHz)"})
viewof bandSelector = Inputs.radio(["2.4 GHz", "5 GHz", "Both"], {value: "Both", label: "Show Band"})

viewof addNetworkBtn = Inputs.button("Add Random Network")
viewof clearBtn = Inputs.button("Clear All Networks")

{
  if (addNetworkBtn > 0) {
    const networkNames = ["Home_WiFi", "Office_5G", "Guest_Net", "IoT_Hub", "Neighbor_AP", "Coffee_Shop", "Smart_Home", "Factory_IoT"];
    const is24 = Math.random() > 0.4;
    const channels = is24 ? [1, 6, 11] : [36, 40, 44, 48, 149, 153, 157, 161];
    const randomChannel = channels[Math.floor(Math.random() * channels.length)];
    const newNetwork = {
      name: networkNames[Math.floor(Math.random() * networkNames.length)] + "_" + Math.floor(Math.random() * 100),
      channel: randomChannel,
      band: is24 ? "2.4" : "5",
      width: channelWidth
    };
    mutable networks = [...networks, newNetwork];
  }
}

{
  if (clearBtn > 0) {
    mutable networks = [];
  }
}

congestion24 = {
  const counts = {};
  channels24GHz.forEach(c => counts[c.ch] = 0);
  networks.filter(n => n.band === "2.4").forEach(n => {
    counts[n.channel] = (counts[n.channel] || 0) + 1;
  });
  return counts;
}

congestion5 = {
  const counts = {};
  channels5GHz.forEach(c => counts[c.ch] = 0);
  networks.filter(n => n.band === "5").forEach(n => {
    counts[n.channel] = (counts[n.channel] || 0) + 1;
  });
  return counts;
}

// Find best channels
recommendedChannels = {
  const best24Ch = [1, 6, 11].reduce((best, ch) =>
    (congestion24[ch] || 0) < (congestion24[best] || 0) ? ch : best, 1);
  const best5Ch = [36, 40, 44, 48, 149, 153, 157, 161].reduce((best, ch) =>
    (congestion5[ch] || 0) < (congestion5[best] || 0) ? ch : best, 36);
  return {
    band24: {ch: best24Ch, congestion: congestion24[best24Ch] || 0},
    band5: {ch: best5Ch, congestion: congestion5[best5Ch] || 0}
  };
}

// 2.4 GHz Spectrum Display
html`<div style="margin-bottom: 20px; ${bandSelector === "5 GHz" ? "display: none;" : ""}">
  <h4 style="color: #2C3E50; margin-bottom: 10px;">2.4 GHz Band (2400-2483.5 MHz)</h4>
  <svg width="${spectrumWidth}" height="${spectrumHeight}" style="background: linear-gradient(180deg, #1a1a2e 0%, #16213e 100%); border-radius: 8px; border: 2px solid #16A085;">
    <!-- Channel markers and bars -->
    ${channels24GHz.map((ch, i) => {
      const x = 60 + i * 75;
      const congestionLevel = congestion24[ch.ch] || 0;
      const barHeight = Math.min(congestionLevel * 50 + 30, 200);
      const isNonOverlapping = [1, 6, 11].includes(ch.ch);
      const isRecommended = recommendedChannels.band24.ch === ch.ch;

      return `
        <g>
          <!-- Channel bar -->
          <rect x="${x - 30}" y="${spectrumHeight - 60 - barHeight}" width="60" height="${barHeight}"
                fill="${congestionLevel > 2 ? '#E74C3C' : congestionLevel > 0 ? '#E67E22' : '#16A085'}"
                opacity="0.8" rx="4"/>

          <!-- Channel number -->
          <text x="${x}" y="${spectrumHeight - 35}" fill="#fff" text-anchor="middle" font-weight="bold" font-size="14">
            ${ch.ch}
          </text>

          <!-- Frequency -->
          <text x="${x}" y="${spectrumHeight - 18}" fill="#888" text-anchor="middle" font-size="9">
            ${ch.freq}
          </text>

          <!-- Non-overlapping indicator -->
          ${isNonOverlapping ? `<circle cx="${x}" cy="30" r="10" fill="#16A085"/>
            <text x="${x}" y="35" fill="#fff" text-anchor="middle" font-size="12" font-weight="bold">OK</text>` : ''}

          <!-- Recommended badge -->
          ${isRecommended && congestionLevel === 0 ? `
            <rect x="${x - 25}" y="10" width="50" height="18" fill="#27AE60" rx="4"/>
            <text x="${x}" y="24" fill="#fff" text-anchor="middle" font-size="11" font-weight="bold">BEST</text>
          ` : ''}

          <!-- Network count -->
          ${congestionLevel > 0 ? `
            <circle cx="${x + 25}" cy="55" r="12" fill="#E67E22"/>
            <text x="${x + 25}" y="60" fill="#fff" text-anchor="middle" font-size="11" font-weight="bold">${congestionLevel}</text>
          ` : ''}
        </g>
      `;
    }).join('')}

    <!-- Legend -->
    <g transform="translate(20, ${spectrumHeight - 12})">
      <circle cx="0" cy="0" r="6" fill="#16A085"/>
      <text x="12" y="4" fill="#aaa" font-size="11">Clear</text>
      <circle cx="80" cy="0" r="6" fill="#E67E22"/>
      <text x="92" y="4" fill="#aaa" font-size="11">Moderate</text>
      <circle cx="180" cy="0" r="6" fill="#E74C3C"/>
      <text x="192" y="4" fill="#aaa" font-size="11">Congested</text>
    </g>
  </svg>
</div>`

// 5 GHz Spectrum Display
html`<div style="margin-bottom: 20px; ${bandSelector === "2.4 GHz" ? "display: none;" : ""}">
  <h4 style="color: #2C3E50; margin-bottom: 10px;">5 GHz Band - Selected Channels</h4>
  <svg width="${spectrumWidth}" height="${spectrumHeight}" style="background: linear-gradient(180deg, #1a1a2e 0%, #16213e 100%); border-radius: 8px; border: 2px solid #E67E22;">
    ${[36, 40, 44, 48, 149, 153, 157, 161, 165].map((chNum, i) => {
      const ch = channels5GHz.find(c => c.ch === chNum);
      const x = 50 + i * 95;
      const congestionLevel = congestion5[ch.ch] || 0;
      const barHeight = Math.min(congestionLevel * 50 + 30, 200);
      const isRecommended = recommendedChannels.band5.ch === ch.ch;

      return `
        <g>
          <!-- Channel bar -->
          <rect x="${x - 35}" y="${spectrumHeight - 60 - barHeight}" width="70" height="${barHeight}"
                fill="${congestionLevel > 2 ? '#E74C3C' : congestionLevel > 0 ? '#E67E22' : '#16A085'}"
                opacity="0.8" rx="4"/>

          <!-- Channel number -->
          <text x="${x}" y="${spectrumHeight - 35}" fill="#fff" text-anchor="middle" font-weight="bold" font-size="14">
            ${ch.ch}
          </text>

          <!-- Frequency -->
          <text x="${x}" y="${spectrumHeight - 18}" fill="#888" text-anchor="middle" font-size="9">
            ${ch.freq}
          </text>

          <!-- Recommended badge -->
          ${isRecommended && congestionLevel === 0 ? `
            <rect x="${x - 25}" y="15" width="50" height="18" fill="#27AE60" rx="4"/>
            <text x="${x}" y="29" fill="#fff" text-anchor="middle" font-size="11" font-weight="bold">BEST</text>
          ` : ''}

          <!-- Network count -->
          ${congestionLevel > 0 ? `
            <circle cx="${x + 30}" cy="55" r="12" fill="#E67E22"/>
            <text x="${x + 30}" y="60" fill="#fff" text-anchor="middle" font-size="11" font-weight="bold">${congestionLevel}</text>
          ` : ''}
        </g>
      `;
    }).join('')}

    <!-- 5 GHz advantage note -->
    <text x="${spectrumWidth/2}" y="50" fill="#16A085" text-anchor="middle" font-size="12" font-weight="bold">
      23+ non-overlapping channels available (vs only 3 in 2.4 GHz)
    </text>
  </svg>
</div>`

// Recommendations panel
html`<div style="display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 15px;">
  <div style="background: #f8f9fa; padding: 15px; border-radius: 8px; border-left: 4px solid #2C3E50;">
    <h4 style="color: #2C3E50; margin: 0 0 10px 0;">Active Networks (${networks.length})</h4>
    ${networks.length === 0 ?
      '<p style="color: #7F8C8D; font-style: italic;">Click "Add Random Network" to simulate nearby Wi-Fi networks</p>' :
      `<div style="max-height: 150px; overflow-y: auto;">
        ${networks.map(n => `
          <div style="display: flex; justify-content: space-between; padding: 6px; background: ${n.band === '2.4' ? '#e8f6f3' : '#fef5e7'}; margin: 4px 0; border-radius: 4px; font-size: 12px;">
            <span><strong>${n.name}</strong></span>
            <span>Ch ${n.channel} (${n.band} GHz)</span>
          </div>
        `).join('')}
      </div>`
    }
  </div>

  <div style="background: #f8f9fa; padding: 15px; border-radius: 8px; border-left: 4px solid #16A085;">
    <h4 style="color: #2C3E50; margin: 0 0 10px 0;">Recommendations</h4>
    <div style="font-size: 14px;">
      <p style="margin: 8px 0;"><strong>2.4 GHz Best:</strong>
        <span style="background: #16A085; color: white; padding: 3px 10px; border-radius: 4px; font-weight: bold;">
          Channel ${recommendedChannels.band24.ch}
        </span>
        ${recommendedChannels.band24.congestion > 0 ? ` (${recommendedChannels.band24.congestion} networks)` : ' (Clear!)'}
      </p>
      <p style="margin: 8px 0;"><strong>5 GHz Best:</strong>
        <span style="background: #E67E22; color: white; padding: 3px 10px; border-radius: 4px; font-weight: bold;">
          Channel ${recommendedChannels.band5.ch}
        </span>
        ${recommendedChannels.band5.congestion > 0 ? ` (${recommendedChannels.band5.congestion} networks)` : ' (Clear!)'}
      </p>
    </div>
  </div>
</div>`

// Key insights
html`<div style="background: #fff3cd; padding: 15px; border-radius: 8px; border-left: 4px solid #ffc107; margin-top: 15px;">
  <h4 style="color: #856404; margin: 0 0 10px 0;">Key Insights from This Simulation</h4>
  <ul style="margin: 0; padding-left: 20px; color: #856404;">
    <li><strong>2.4 GHz limitation:</strong> Only channels 1, 6, and 11 are non-overlapping. Other channels cause worse interference.</li>
    <li><strong>5 GHz advantage:</strong> 23+ non-overlapping channels significantly reduce congestion in dense environments.</li>
    <li><strong>Channel width trade-off:</strong> Wider channels = faster speeds but more overlap and interference susceptibility.</li>
    <li><strong>IoT recommendation:</strong> For most IoT sensors, use 2.4 GHz with 20 MHz channels. For cameras, prefer 5 GHz.</li>
  </ul>
</div>`

837.8 Channel Planning Strategies

837.8.1 Single AP Deployment

For homes and small offices with one access point:

2.4 GHz Strategy: 1. Use a Wi-Fi analyzer app to scan neighboring networks 2. Count networks on channels 1, 6, and 11 3. Select the least congested of the three 4. If all equally congested, choose channel 1 or 11 (edge channels)

5 GHz Strategy: 1. Use UNII-1 channels (36-48) for indoor IoT (no DFS) 2. Use UNII-3 channels (149-165) for outdoor or if 36-48 is busy 3. Avoid DFS channels (52-140) for latency-sensitive devices

837.8.2 Multi-AP Deployment

For offices or large homes with multiple access points:

Floor Plan Channel Assignment (2.4 GHz):

3-AP Layout (linear):
  [AP1: Ch 1] -------- [AP2: Ch 6] -------- [AP3: Ch 11]

4-AP Layout (square):
  [AP1: Ch 1]          [AP2: Ch 6]
       |                    |
  [AP3: Ch 11]         [AP4: Ch 1]

Multi-floor (checkerboard):
  Floor 2: [Ch 6]  [Ch 11]
  Floor 1: [Ch 1]  [Ch 6]

5 GHz Multi-AP (more flexibility):

Use different UNII bands for adjacent APs:
  [AP1: Ch 36] -------- [AP2: Ch 149]
       |                    |
  [AP3: Ch 44] -------- [AP4: Ch 153]

837.9 Knowledge Check

{
  const container = document.getElementById('kc-freq-1');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "An apartment complex installs a Zigbee smart home hub in each unit, plus Wi-Fi smart displays. Residents report that Zigbee devices are unreliable. A spectrum analyzer shows Wi-Fi channel 6 is heavily used by neighbors. What channel should Zigbee use to minimize interference?",
      options: [
        {text: "Zigbee channel 11 (2405 MHz) - lowest frequency available", correct: false, feedback: "Incorrect. Zigbee channel 11 (2405 MHz) overlaps with Wi-Fi channel 1 (2401-2423 MHz). If neighbors also use channel 1, interference would continue."},
        {text: "Zigbee channel 18 (2440 MHz) - midpoint between Wi-Fi channels", correct: false, feedback: "Incorrect. Zigbee channel 18 (2440 MHz) falls within Wi-Fi channel 6 (2426-2448 MHz), which you identified as heavily used. This would maximize interference, not minimize it."},
        {text: "Zigbee channel 25 or 26 (2475-2480 MHz) - above all Wi-Fi channels", correct: true, feedback: "Correct! Zigbee channels 25 (2475 MHz) and 26 (2480 MHz) are above Wi-Fi channel 11 (2451-2473 MHz), in spectrum that Wi-Fi doesn't use. This provides the cleanest coexistence."},
        {text: "Auto-select - Zigbee coordinators automatically avoid interference", correct: false, feedback: "Partially true but not reliable. While some Zigbee coordinators scan for interference at startup, they don't continuously adapt. Manual channel selection based on site survey is more reliable."}
      ],
      difficulty: "medium",
      topic: "wifi-zigbee-coexistence"
    }));
  }
}

{
  const container = document.getElementById('kc-freq-2');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "A smart home camera is 20 m from the access point and must penetrate 3 concrete walls. Which Wi-Fi band is most likely to provide a more stable link?",
      options: [
        {text: "5 GHz - higher throughput for video", correct: false, feedback: "Incorrect. While 5 GHz offers higher throughput, it attenuates significantly through concrete walls. At 20m through 3 concrete walls, 5 GHz signal would likely be too weak."},
        {text: "2.4 GHz - better penetration and lower attenuation", correct: true, feedback: "Correct! Lower frequencies attenuate less through obstacles. 2.4 GHz penetrates concrete walls better than 5 GHz. While throughput is lower, a stable connection is more important than speed."},
        {text: "6 GHz (Wi-Fi 6E) - always has best range", correct: false, feedback: "Incorrect. 6 GHz has the worst wall penetration of all Wi-Fi bands. It would require line-of-sight or very close AP placement."},
        {text: "Band choice does not affect penetration", correct: false, feedback: "Incorrect. Frequency directly affects signal attenuation through materials. Higher frequencies are absorbed more by walls, especially concrete and brick."}
      ],
      difficulty: "easy",
      topic: "frequency-selection"
    }));
  }
}

837.10 Worked Example: Channel Planning for Multi-Floor Building

Scenario: A 4-floor office building needs Wi-Fi channel planning. Site survey reveals neighboring networks causing interference.

Given: - Building: 4 floors, 800 sqm each - APs per floor: 2 (8 total) - Site survey (2.4 GHz): - Channel 1: 3 networks (-65 to -75 dBm) - Channel 6: 7 networks (-55 to -70 dBm) - HIGH - Channel 11: 1 network (-80 dBm) - LOW - Floor separation: 15 dB attenuation

Solution:

1. Avoid Channel 6 - Too congested with 7 competing networks
2. Use diagonal pattern for vertical separation:

Floor	West AP	East AP
4	Ch 11	Ch 1
3	Ch 1	Ch 11
2	Ch 11	Ch 1
1	Ch 1	Ch 11

Why this works: - Same-channel APs separated by 2 floors + horizontal offset - Combined isolation: 30+ dB (2 floors + distance) - No adjacent same-channel APs

Key Insight: In multi-floor buildings, use only channels 1 and 11, avoiding channel 6 entirely in urban environments where it’s typically most congested.

837.11 What’s Next

Continue to Wi-Fi Power Consumption to learn about optimizing Wi-Fi for battery-powered IoT devices, comparing power consumption across protocols, and implementing power-saving strategies.

NoteRelated Chapters

• Wi-Fi Overview - Introduction and basics
• Wi-Fi Standards Evolution - 802.11 generations
• Wi-Fi Power Consumption - Battery optimization
• Wi-Fi Deployment Planning - Capacity and case studies