WiFi 5 (802.11ac)
- WiFi 5 represents the fifth generation of WiFi standards, formally known as 802.11ac (ratified in 2013)
- Operates exclusively in the 5 GHz band to avoid congestion from 2.4 GHz devices (microwaves, Bluetooth, older WiFi)
- Delivers theoretical maximum speeds up to 6.93 Gbps through advanced modulation and MIMO techniques
- Backward compatible with previous 802.11 standards but only when operating in dual-band mode
Key Technical Features
- 256-QAM modulation increases data density compared to 64-QAM in WiFi 4 (802.11n)
- Multi-User MIMO (MU-MIMO) allows simultaneous transmission to up to 4 clients (downlink only)
- Channel bonding supports 20, 40, 80, and 160 MHz channel widths for increased throughput
- Beamforming focuses RF energy toward specific clients for improved signal quality and range
- Uses up to 8 spatial streams (8x8 MIMO) though most consumer devices support 2x2 or 4x4
Channel and Frequency Details
| Channel Width | Available Channels | Typical Use Case |
|---|---|---|
| 20 MHz | 25 non-overlapping | High-density environments |
| 40 MHz | 12 non-overlapping | Balanced performance/capacity |
| 80 MHz | 6 non-overlapping | High-performance applications |
| 160 MHz | 2-3 non-overlapping | Maximum throughput (limited availability) |
- DFS (Dynamic Frequency Selection) required for some 5 GHz channels to avoid radar interference
- Channels 36-48 and 149-165 are generally DFS-free in most regions
- Automatic channel selection becomes critical due to limited non-overlapping channels at wider bandwidths
Performance Characteristics
- Real-world speeds typically 30-50% of theoretical maximum due to overhead and environmental factors
- Range is shorter than 2.4 GHz but provides cleaner spectrum with less interference
- Power consumption optimized through features like Target Wake Time (TWT) precursor technologies
- Performance degrades significantly with distance due to 5 GHz propagation characteristics
Implementation Considerations
- Wave 1 (early 2013): Up to 80 MHz channels, 3x3 MIMO, 1.3 Gbps max
- Wave 2 (2015): Added 160 MHz channels, MU-MIMO, 4x4 MIMO, 3.47 Gbps max
- Enterprise deployments often use 80 MHz channels as optimal balance of speed and capacity
- Client device capabilities vary significantly (check client specs before planning deployment)
Vocabulary
256-QAM: Quadrature Amplitude Modulation using 256 constellation points, allowing 8 bits per symbol transmission
MU-MIMO: Multi-User Multiple Input Multiple Output - technology allowing simultaneous data streams to multiple clients
Beamforming: RF technique that focuses wireless signal energy toward specific client locations
DFS: Dynamic Frequency Selection - regulatory requirement to detect and avoid radar systems on certain 5 GHz channels
Spatial Streams: Independent data paths transmitted simultaneously using multiple antennas
Notes
- Plan for 80 MHz channels in enterprise - provides good balance of performance and capacity without excessive channel reuse issues
- Client compatibility varies significantly - older 802.11ac Wave 1 devices may not support all features
- 5 GHz-only operation means you need dual-band infrastructure to support legacy 2.4 GHz devices
- DFS channel availability varies by region and can cause temporary service interruptions during radar detection
- MU-MIMO only works on downlink in WiFi 5 (uplink MU-MIMO introduced in WiFi 6)
- Consider heat and power requirements - 802.11ac access points typically require more power than previous generations
- Real-world performance testing essential - theoretical speeds rarely achieved in production environments