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Radio spectrum is the fundamental resource upon which all wireless communication depends. Unlike wired networks where you can simply add more cables, spectrum is finite and shared. The frequencies allocated to WiFi determine everything: maximum range, wall penetration, interference susceptibility, achievable data rates, and the number of simultaneous networks that can coexist.
WiFi operates in three unlicensed frequency bands: 2.4 GHz, 5 GHz, and most recently 6 GHz. Each band has distinct physical characteristics, regulatory constraints, and optimal use cases. Understanding these differences is not optional for serious network engineering—it's foundational knowledge that informs every deployment decision.
This page examines each frequency band in depth: the physics governing radio propagation at each frequency, the regulatory frameworks that shape channel availability, practical channel planning strategies, and the real-world tradeoffs that network engineers must navigate daily.
By the end of this page, you will: (1) Understand the physics of radio propagation at 2.4 GHz, 5 GHz, and 6 GHz, (2) Navigate regulatory channel allocations for different regions, (3) Design channel plans that minimize co-channel interference, and (4) Select the appropriate band for specific deployment scenarios.
Before examining specific bands, we must understand how radio waves behave. The frequency of a signal fundamentally affects how it propagates through space and interacts with materials.
Free Space Path Loss (FSPL):
Radio signals weaken as they travel, following the inverse square law. The free space path loss equation quantifies this:
FSPL (dB) = 20 × log₁₀(d) + 20 × log₁₀(f) + 20 × log₁₀(4π/c)
Simplified for practical use:
FSPL (dB) = 20 × log₁₀(d_km) + 20 × log₁₀(f_MHz) + 32.44
Key insight: Signal loss increases with both distance AND frequency. A 5 GHz signal experiences approximately 6 dB more loss than a 2.4 GHz signal at the same distance. In power terms, the 5 GHz signal is only 1/4 as strong.
| Frequency Band | Frequency (MHz) | FSPL at 10m | Relative Loss |
|---|---|---|---|
| 2.4 GHz | 2437 | 60.2 dB | Baseline |
| 5 GHz (UNII-1) | 5180 | 66.8 dB | +6.6 dB |
| 5 GHz (UNII-3) | 5745 | 68.6 dB | +8.4 dB |
| 6 GHz | 6525 | 70.0 dB | +9.8 dB |
Material Attenuation:
Real-world environments aren't free space. Signals must penetrate walls, floors, furniture, and human bodies. Material attenuation varies dramatically with frequency:
Typical Attenuation Values:
| Material | 2.4 GHz Loss | 5 GHz Loss | 6 GHz Loss |
|---|---|---|---|
| Interior drywall | 3-5 dB | 4-7 dB | 5-8 dB |
| Exterior brick | 8-10 dB | 12-15 dB | 15-20 dB |
| Concrete | 10-15 dB | 15-25 dB | 20-30 dB |
| Glass (standard) | 2-4 dB | 3-6 dB | 4-8 dB |
| Low-E glass | 20-30 dB | 25-35 dB | 30-40 dB |
| Water (human body) | 3-5 dB | 5-8 dB | 8-12 dB |
The practical impact: A 5 GHz signal crossing two interior walls might lose 15-20 dB, while a 2.4 GHz signal loses only 6-10 dB. This can mean the difference between a usable connection and no connection at all.
Low-emissivity (Low-E) glass, common in energy-efficient buildings, contains metallic coatings that devastate wireless signals. A single Low-E window can cause 20-40 dB attenuation—equivalent to several concrete walls. Always survey sites with Low-E glass before deployment, and expect to need additional APs or specialized coverage solutions.
Multipath Propagation:
In indoor environments, signals reflect off surfaces, creating multiple paths between transmitter and receiver. These reflected signals arrive at slightly different times (delay spread) and can constructively or destructively interfere.
Frequency Impact on Multipath:
Lower frequencies (2.4 GHz): Longer wavelengths (~12.5 cm) experience less severe multipath fading. The larger wavelength 'averages' over small-scale reflectors.
Higher frequencies (5/6 GHz): Shorter wavelengths (~5-6 cm) are more susceptible to multipath fading. Small environmental changes can cause significant signal variation.
OFDM mitigation: Modern WiFi uses OFDM with guard intervals to combat multipath, but the fundamental wavelength physics still favor lower frequencies for stable coverage.
Fresnel Zone Considerations:
Radio signals don't travel in a laser-like line but occupy an ellipsoidal region called the Fresnel zone. Obstructions within the first Fresnel zone (especially the inner 60%) cause significant signal degradation.
First Fresnel zone radius: r = 17.3 × √(d / f)
Where d = distance in km, f = frequency in GHz, r = radius in meters.
At higher frequencies, the Fresnel zone is narrower, making signals more sensitive to precise obstacle placement but less likely to be blocked by distant objects.
The 2.4 GHz ISM (Industrial, Scientific, Medical) band was WiFi's original home and remains important for legacy compatibility and maximum range. However, it has become severely congested.
2.4 GHz Band Specifications:
Channel Layout and Overlap:
2.4 GHz channels are spaced only 5 MHz apart, but each 802.11g/n 20 MHz channel occupies ~22 MHz of actual bandwidth. This creates the infamous overlap problem:
| Channel | Center Freq | Bandwidth Span |
|---|---|---|
| 1 | 2.412 GHz | 2.401 - 2.423 GHz |
| 2 | 2.417 GHz | 2.406 - 2.428 GHz |
| 3 | 2.422 GHz | 2.411 - 2.433 GHz |
| 4 | 2.427 GHz | 2.416 - 2.438 GHz |
| 5 | 2.432 GHz | 2.421 - 2.443 GHz |
| 6 | 2.437 GHz | 2.426 - 2.448 GHz |
| 7 | 2.442 GHz | 2.431 - 2.453 GHz |
| 8 | 2.447 GHz | 2.436 - 2.458 GHz |
| 9 | 2.452 GHz | 2.441 - 2.463 GHz |
| 10 | 2.457 GHz | 2.446 - 2.468 GHz |
| 11 | 2.462 GHz | 2.451 - 2.473 GHz |
| 12* | 2.467 GHz | 2.456 - 2.478 GHz |
| 13* | 2.472 GHz | 2.461 - 2.483 GHz |
| 14** | 2.484 GHz | 802.11b only, Japan |
*Channels 12-13: Available in Europe/Japan; restricted low-power in US **Channel 14: Japan only, 802.11b exclusive
In the Americas and most of Asia, use ONLY channels 1, 6, and 11 for 2.4 GHz deployments. These are the only three truly non-overlapping channels. Using channels like 3 or 9 creates adjacent channel interference with BOTH 1 and 6 (or 6 and 11), making performance worse for everyone. In Europe/Japan, channels 1, 5, 9, 13 provide a 4-channel plan, but 1, 6, 11 remains more common globally.
2.4 GHz Interference Sources:
The ISM band's unlicensed nature means WiFi shares spectrum with many devices:
Major 2.4 GHz Interferers:
Microwave Ovens: Generate broadband interference across the entire band, especially around 2.45 GHz. Can cause complete WiFi blackout within 10-20 feet during operation.
Bluetooth: Frequency-hopping across 2.402-2.480 GHz. Modern adaptive frequency hopping (AFH) avoids active WiFi channels, but older devices cause significant disruption.
Cordless Phones (DECT 6.0 excepted): Legacy 2.4 GHz cordless phones cause severe interference. DECT 6.0 phones use 1.9 GHz and don't interfere.
Wireless Video Transmitters: Baby monitors, security cameras with analog wireless video create wideband interference.
ZigBee/Thread (802.15.4): Smart home sensors use 16 channels (11-26) overlapping WiFi channels 1-14.
Other WiFi Networks: In multi-tenant buildings, dozens of competing networks create co-channel and adjacent-channel interference.
USB 3.0 Cables: Poorly shielded USB 3.0 cables emit RF interference in the 2.4 GHz range due to 5 Gbps signaling harmonics.
When to Use 2.4 GHz:
Despite its challenges, 2.4 GHz remains valuable for specific scenarios:
Appropriate Uses:
Avoid 2.4 GHz For:
While 802.11n allows 40 MHz channels at 2.4 GHz (theoretically doubling throughput), this is almost always counterproductive. A 40 MHz channel consumes 2 of the 3 non-overlapping channels, guaranteeing interference from neighboring networks in any multi-AP environment. Most enterprise vendors disable or heavily discourage 40 MHz at 2.4 GHz. Use 20 MHz channels exclusively at 2.4 GHz.
The 5 GHz band offers dramatically more spectrum than 2.4 GHz, enabling the high-capacity networks required for modern applications. However, this expanded spectrum comes with regulatory complexity—5 GHz is shared with radar systems, requiring sophisticated coexistence mechanisms.
5 GHz Band Overview:
UNII Bands: The 5 GHz Subbands
In the United States (and similarly in other regions), 5 GHz is divided into UNII (Unlicensed National Information Infrastructure) bands:
UNII-1 (5.150 - 5.250 GHz):
UNII-2A (5.250 - 5.350 GHz):
UNII-2C / UNII-2 Extended (5.470 - 5.725 GHz):
UNII-3 (5.725 - 5.850 GHz):
UNII-4 (5.850 - 5.925 GHz):
| UNII Band | Frequency Range | Channels | DFS Required | Max Power |
|---|---|---|---|---|
| UNII-1 | 5.150-5.250 GHz | 36, 40, 44, 48 | No | 1 W (30 dBm) |
| UNII-2A | 5.250-5.350 GHz | 52, 56, 60, 64 | Yes | 250 mW (24 dBm) |
| UNII-2C | 5.470-5.725 GHz | 100-144 (odd) | Yes | 1 W (30 dBm) |
| UNII-3 | 5.725-5.850 GHz | 149, 153, 157, 161, 165 | No | 1-4 W |
DFS (Dynamic Frequency Selection): Radar Coexistence
Channels in UNII-2A and UNII-2C are shared with radar systems—primarily weather radar and military radar. WiFi devices must detect radar and vacate the channel within 10 seconds.
DFS Operation:
Channel Availability Check (CAC): Before using a DFS channel, the AP must scan for radar for 60 seconds (10 minutes for weather radar channels in some regions). No transmissions during this period.
In-Service Monitoring (ISM): While operating, the AP continuously monitors for radar pulses.
Channel Evacuation: Upon detecting radar, the AP must:
DFS Implications:
For enterprise deployments: (1) Use UNII-1 and UNII-3 channels for mission-critical traffic, (2) Enable DFS channels to increase capacity but don't rely on them exclusively, (3) Configure automatic channel selection to include DFS channels as secondary options, (4) Monitor radar event logs—frequent false positives indicate interference sources to investigate.
80 MHz and 160 MHz Channel Planning:
802.11ac/ax support wide channels, but planning requires understanding which 20 MHz channels combine:
80 MHz Channel Groups:
| Primary 20 MHz | 80 MHz Channel | Component 20 MHz Channels |
|---|---|---|
| 36 | 42 | 36, 40, 44, 48 |
| 52 | 58 | 52, 56, 60, 64 (DFS) |
| 100 | 106 | 100, 104, 108, 112 (DFS) |
| 116 | 122 | 116, 120, 124, 128 (DFS) |
| 132 | 138 | 132, 136, 140, 144 (DFS) |
| 149 | 155 | 149, 153, 157, 161 |
160 MHz Availability:
True contiguous 160 MHz channels are limited:
80+80 MHz mode uses two non-contiguous 80 MHz channels, providing equivalent bandwidth without requiring contiguous spectrum.
5 GHz Deployment Guidelines:
Channel Assignment Strategy:
Non-DFS Priority: Assign UNII-1 (36-48) and UNII-3 (149-165) first for critical APs
DFS as Capacity Relief: Use DFS channels for additional APs after non-DFS is exhausted
80 MHz Allocation:
Power Reduction: In dense deployments, reduce transmit power to create smaller cells and increase channel reuse
Band Steering: Configure APs to prefer 5 GHz for capable clients, reducing 2.4 GHz congestion
The 6 GHz band, opened for unlicensed use in 2020-2021, represents the most significant expansion of WiFi spectrum in the technology's history. With up to 1,200 MHz of new spectrum (2.4 GHz and 5 GHz combined offer only ~500 MHz), 6 GHz enables use cases previously impossible with WiFi.
6 GHz Band Specifications:
6 GHz Channel Allocation:
The US divides 6 GHz into four sub-bands:
UNII-5 (5.925 - 6.425 GHz):
UNII-6 (6.425 - 6.525 GHz):
UNII-7 (6.525 - 6.875 GHz):
UNII-8 (6.875 - 7.125 GHz):
| Channel Width | Number of Channels | Non-Overlapping | Example Channels |
|---|---|---|---|
| 20 MHz | 59 | 59 | 1, 5, 9, 13, ... 233 |
| 40 MHz | 29 | 29 | 3, 11, 19, 27, ... |
| 80 MHz | 14 | 14 | 7, 23, 39, 55, ... |
| 160 MHz | 7 | 7 | 15, 47, 79, 111, 143, 175, 207 |
| 320 MHz (WiFi 7) | 3 | 3 | 31, 95, 159 |
AFC (Automated Frequency Coordination): Incumbent Protection
Unlike 5 GHz DFS (which relies on local radar detection), 6 GHz uses a database-driven approach for incumbent protection:
How AFC Works:
Registration: Standard Power (SP) devices register their location with an AFC database provider
Database Query: Device queries AFC database, providing GPS coordinates and device parameters
Channel/Power Response: AFC returns list of permitted channels and maximum power levels for that location
Periodic Updates: Device must re-query periodically (typically every 24 hours) to maintain authorization
AFC vs. DFS Comparison:
| Aspect | DFS (5 GHz) | AFC (6 GHz) |
|---|---|---|
| Protection Mechanism | Local radar detection | Database coordination |
| Channel Acquisition | 60-second scan | Database query (seconds) |
| False Positives | Common | Rare (location-based) |
| Outdoor Use | Automatic | Requires AFC registration |
| Implementation | Physical layer | Software/network service |
Operating Modes: LPI vs. SP
6 GHz defines two distinct operating modes with different power levels and deployment constraints:
Low Power Indoor (LPI):
Standard Power (SP):
Very Low Power (VLP):
6 GHz enables 'overlay' deployments: add 6 GHz-capable APs alongside existing 5 GHz infrastructure. All WiFi 6E clients get dedicated spectrum with no legacy interference, while older devices continue using 5 GHz. This staged approach maximizes investment protection while immediately benefiting from new spectrum.
6 GHz Propagation Realities:
Higher frequency brings shorter range and poorer penetration:
Coverage Planning Adjustments:
Ideal 6 GHz Use Cases:
WiFi regulations vary significantly by country and region. Equipment manufacturers must certify devices for each market, and network engineers must understand local constraints.
Major Regulatory Regions:
FCC (United States):
ETSI (Europe):
MIC (Japan):
China (MIIT):
| Region | UNII-1 | UNII-2A | UNII-2C | UNII-3 | Total 20 MHz Channels |
|---|---|---|---|---|---|
| United States | 36-48 | 52-64 (DFS) | 100-144 (DFS) | 149-165 | 25 |
| Europe (ETSI) | 36-48 | 52-64 (DFS) | 100-140 (DFS) | 149-161* | 19-21 |
| Japan | 36-48 | 52-64 (DFS) | 100-140 (DFS) | — | 19 |
| China | 36-48 | 52-64 | 149-165 | — | 13 |
| Australia | 36-48 | 52-64 (DFS) | 100-144 (DFS) | 149-165 | 25 |
Always configure the correct country/regulatory domain on WiFi equipment. Incorrect settings can: (1) Enable illegal channels/power levels, risking interference with licensed services, (2) Restrict available channels unnecessarily, reducing capacity, (3) Cause interoperability issues with clients expecting region-specific parameters. Enterprise controllers typically enforce country codes; standalone APs require manual or auto-configuration.
6 GHz Regional Status (as of 2024):
| Region | Allocated Spectrum | Status |
|---|---|---|
| United States | 5.925-7.125 GHz (1,200 MHz) | Fully available |
| Canada | 5.925-7.125 GHz (1,200 MHz) | Fully available |
| European Union | 5.925-6.425 GHz (500 MHz) | Available (LPI only initially) |
| United Kingdom | 5.925-6.425 GHz (500 MHz) | Available |
| Japan | Under study | Not yet allocated |
| South Korea | 5.925-7.125 GHz (1,200 MHz) | Partially available |
| Australia | 5.925-6.425 GHz (500 MHz) | Available (2023) |
| Brazil | 5.925-7.125 GHz (1,200 MHz) | Available |
The regulatory landscape continues evolving rapidly. Always verify current rules before deployment.
With three bands available, selecting the right one for each use case requires systematic analysis:
Decision Framework:
| Use Case | Primary Band | Rationale | Fallback |
|---|---|---|---|
| Legacy device support | 2.4 GHz | Only band supported by 802.11b/g devices | None |
| Maximum range, few APs | 2.4 GHz | Best wall penetration, largest coverage per AP | 5 GHz UNII-1 |
| Standard enterprise office | 5 GHz | Balance of capacity and coverage | 6 GHz overlay |
| High density (stadiums, conf rooms) | 6 GHz | Most channels, no legacy, OFDMA | 5 GHz 20 MHz |
| Low-latency applications (VR/gaming) | 6 GHz | Greenfield spectrum, minimal contention | 5 GHz non-DFS |
| IoT sensors (low bandwidth) | 2.4 GHz | Best range, simple radios | 5 GHz UNII-1 |
| Video streaming (4K/8K) | 5 GHz/6 GHz | Wide channels available | — |
| Outdoor campus | 5 GHz UNII-3 or 6 GHz SP | High power permitted | 5 GHz UNII-1 |
Band Steering Implementation:
Modern APs broadcast the same SSID on multiple bands and steer capable clients to the optimal band:
Steering Mechanisms:
Probe Response Suppression: Don't respond to 2.4 GHz probes from dual-band clients, forcing them to discover 5 GHz SSID.
802.11v BSS Transition: Suggest preferred band/AP to clients supporting this standard.
802.11k Neighbor Reports: Provide clients with information about better APs, including band preferences.
RSSI Thresholds: Only accept 2.4 GHz associations if 5 GHz signal is below a minimum level.
Band Steering Caveats:
You now understand the three WiFi frequency bands in depth: their physics, regulatory frameworks, channel planning strategies, and deployment considerations. The next page explores data rates—how different combinations of bandwidth, modulation, and spatial streams determine actual throughput.