802.11ac Wi-Fi: Advantages and Disadvantages

This page explores the pros and cons of the 802.11ac Wi-Fi standard.

What is 802.11ac?

Introduction:

802.11ac is a Wi-Fi standard that evolved from IEEE 802.11n. It was designed to provide faster data rates (in the Gigabit per second range) for wireless devices, primarily for WLAN applications. Unlike earlier 802.11 standards which were built for single-user operation, 802.11ac introduced the concept of multi-user MIMO. Beamforming technology was also included to improve coverage by focusing the signal towards specific areas.

Here’s a summary of key 802.11ac features:

• Frequency Bands: 5 GHz
• Channel Bandwidths: 20 MHz, 40 MHz, 80+80 MHz, 160 MHz
• FFT sizes: 64, 128, 256, 512
• Subcarrier spacing: 312.5 KHz
• OFDM symbol duration: 3.2µs + 0.8/0.4 µs CP
• Modulation scheme (highest): 256 QAM
• Data rates: 433 Mbits/sec (with 80 MHz and 1 Spatial Stream(SS)), 6.933 Gbits/sec (with 160MHz, 8 SS)

For more detailed information, refer to the 802.11ac tutorial.

Benefits (Advantages) of 802.11ac

Here are the benefits of using 802.11ac Wi-Fi:

• Gigabit Speeds: Offers speeds up to three times faster than 802.11n.
• Improved Coverage: Provides whole-home coverage with fewer dead spots.
• Wider Channel Bandwidths: Utilizes wider channel bandwidths (80 MHz and 160 MHz).
• Advanced Modulation: Employs complex modulation schemes up to 256-QAM, resulting in a 33% increase in data rates.
• Multiple Spatial Streams: Uses multiple spatial streams, delivering an N-fold increase in efficiency.
• Multi-User MIMO (MU-MIMO): Supports Multi-User MIMO, enabling simultaneous downlink transmission to single-stream clients, which improves overall network capacity.

Drawbacks (Disadvantages) of 802.11ac

Despite its advantages, 802.11ac also has some drawbacks:

• No 2.4 GHz Support: Does not support the 2.4 GHz frequency band.
• Limited Symbol Duration Support: Only supports symbol durations with shorter lengths.
• No 1024-QAM: Higher modulation schemes, such as 1024-QAM, are not supported.
• Contention-Based Uplink: Uplink access is contention-based, which can lead to collisions, backoffs, and a reduction in effective throughput when many devices are connected.
• Limited Uplink MU-MIMO: MU-MIMO is not supported in the uplink. In 802.11ac Wave 2, MU-MIMO is only used in the downlink with 4 simultaneous streams.