Networking Wireless

5Ghz

The evolution of the spectrum and various applications in Wifi standards

5GHz WiFi

  • 5GHz band operates from 5.150 GHz to 5.825 GHz providing significantly more spectrum than 2.4GHz (83.5 MHz vs 300+ MHz of usable spectrum)
  • Higher frequency means shorter wavelengths - results in less penetration through walls/obstacles but higher data rates due to more available channels
  • UNII bands (Unlicensed National Information Infrastructure) divide 5GHz spectrum into specific segments with different power restrictions and indoor/outdoor usage rules

Channel Allocation and Standards

  • 5GHz provides up to 25 non-overlapping 20MHz channels (compared to only 3 in 2.4GHz)
  • Channel bonding allows 40MHz, 80MHz, and 160MHz channels for higher throughput at cost of fewer available channels
  • DFS (Dynamic Frequency Selection) required on many 5GHz channels to avoid interference with radar systems - causes brief disconnections during radar detection
UNII Band Frequency Range Channels Power Limit Restrictions
UNII-1 5.150-5.250 GHz 36,40,44,48 200mW Indoor only
UNII-2A 5.250-5.350 GHz 52,56,60,64 200mW DFS required
UNII-2C 5.470-5.725 GHz 100-144 1W DFS required
UNII-3 5.725-5.825 GHz 149,153,157,161,165 1W No DFS

WiFi Standards Supporting 5GHz

Standard Max Speed Channel Width Key Features
802.11a 54 Mbps 20 MHz First 5GHz standard, OFDM
802.11n 600 Mbps 20/40 MHz MIMO, dual-band capable
802.11ac 6.93 Gbps 20/40/80/160 MHz 5GHz only, MU-MIMO
802.11ax (WiFi 6) 9.6 Gbps 20/40/80/160 MHz OFDMA, improved efficiency

Practical Deployment Considerations

  • Range vs Speed tradeoff - 5GHz provides higher speeds but approximately 50% less range than 2.4GHz due to higher path loss
  • Dual-band deployment recommended - use 5GHz for high-bandwidth devices near access points, 2.4GHz for IoT devices and extended coverage
  • Band steering techniques encourage capable clients to prefer 5GHz while maintaining 2.4GHz fallback
  • Channel planning easier due to abundant non-overlapping channels - typically use channels 36, 44, 149, 157, 165 for minimal interference

Vocabulary

  • UNII: Unlicensed National Information Infrastructure - regulatory framework dividing 5GHz spectrum into bands with specific rules
  • DFS: Dynamic Frequency Selection - mechanism to detect and avoid radar interference on shared spectrum
  • Channel Bonding: Combining adjacent channels to increase bandwidth (40MHz uses 2 channels, 80MHz uses 4 channels)
  • MU-MIMO: Multi-User Multiple Input Multiple Output - allows simultaneous transmission to multiple clients
  • OFDMA: Orthogonal Frequency Division Multiple Access - divides channels into smaller resource units for efficient multi-user access

Notes

  • UNII-3 band (channels 149-165) most reliable for enterprise deployment since no DFS required and higher power limits allowed
  • DFS channels (52-144) provide more spectrum but may cause connectivity issues during radar detection events (can last 60+ seconds)
  • 80MHz and 160MHz channels significantly reduce channel reuse - in dense environments, stick to 20MHz or 40MHz channels
  • 5GHz penetration issues often require additional access points compared to 2.4GHz-only deployments
  • Client device capabilities vary significantly - older devices may only support 802.11a speeds even on modern infrastructure
  • Regulatory differences by country - always verify local channel availability and power limits before deployment
  • Consider automatic channel selection on controllers to adapt to changing interference patterns, especially on DFS channels