802.11ac: Next 5th Generation

 What is 802.11ac?

• IEEE 802.11ac is the new draft standard for Gigabit WiFi.
• 802.11ac promises data rates of up to 1.73Gbps between an access point and a wireless client.
• The terminology used by the 802.11ac Working Group - "Very High Throughput (VHT) for lower 6GHz band" - essentially means "data rates higher than those of 802.11n" .. "working in the 5GHz band".
• The IEEE Task Group for 802.11ac (IEEE 802.11 TGac) published its first draft of 802.11ac on 20 January 2011 - the Initial Technical Specification Draft 0.1. The 802.11ac standard will support data rates of around 1Gbps by using advanced features over and above 802.11n, including:
• 256-QAM modulation, with advanced coding schemes
•  80MHz and 160MHz channels in the 5GHz band
• MU-MIMO - Multiple User MIMO
• Up to 8 spatial streams (using Space Division Multiple Access - SDMA - where streams are not separated by frequency, but are resolved spatially).

        It is important to note that 802.11ac will NOT work in the 2.4GHz band, since there is insufficient spectrum there for the 80MHz and 160MHz channel widths that 802.11ac will use.

What data rates will 802.11ac deliver?

802.11ac will be the first standard to introduce Multi-User MIMO - MU-MIMO. 802.11ac with MU-MIMO will allow simultaneous MIMO transmissions to different users - but using a single channel.

So, theoretically, an 8-antenna access point working with four two-antenna client stations - all sharing a 160MHz channel, could burst data at 1.73 Gbps to each station. That is - a burst rate of 6.93 Gbps!

Moreover, you must in no way expect to achieve these 802.11ac data rates - which are actually maximum instantaneous transmit speeds - as real-world 802.11ac throughputs.

Why? - Because of the usual 802.11 overheads: frame headers, Preambles, Inter-Frame Spaces (quiet periods), Control Frames .. lower-bit-rate clients contending for the same channel; co-channel interference (mutual interference) - especially in WiFi networks that are not expertly designed .. .. and much more.

802.11ac speed enhancements and MU-MIMO are nonetheless key technologies for high-capacity WiFi wireless networks. For example, 802.11ac operating at 1Gbps should allow simultaneous streaming of three lightly-compressed HDTV channels.

In LEVER's view however, the users who stand to benefit the most will be Enterprise Wi-Fi networks with medium-to-high user densities. This includes Universities, Colleges, Schools - in fact many situations where existing user applications currently only work well over switched/wired 100/1000 Mbps Ethernet networks.

What is IEEE 802.11ad?

Meanwhile, there's the IEEE 802.11ad standard - for Very High Throughput in 60GHz spectrum (milli-metre wavelengths). 802.11ad will operate at instantaneous burst speeds of up to 7Gbps. The IEEE 802.11ad Working Group have also now aligned with the Wireless Gigabit Alliance (WiGig). The resulting 60GHz wireless technogies will offer even higher data rates than 802.11ac, but only at relatively short distances - and where walls, ceilings and other obstructions don't appear in the path. 802.11ad and WiGig will therefore be more suitable for cable-replacement applications.

The primary benefit of operating at 60GHz is that there are hundreds of megahertz of spectrum available.