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428 From GSM to LTE-Advanced Pro and 5G

Table 6.7 Achievable 802.11ac datarates in practice.

Date rate Network setup

700 Mbit/s 3 × 3 MIMO, high‐end access point and PCI express WLAN card in a PC with
three external antennas, same room, very close range
300–380 Mbit/s 3 × 3 MIMO, standard access point and PCI express WLAN card in a PC with
three external antennas, close range
200 Mbit/s 2 × 2 MIMO, USB WLAN stick with two antennas, close range
160–190 Mbit/s 3 × 3 MIMO, high‐end access point and PCI express WLAN card in a PC with
three external antennas, 20 m distance between client and access point with
walls in between
100 Mbit/s 2 × 2 MIMO, USB WLAN stick with two antennas, 20 m distance between
client and access point with walls in between

reception as normal acknowledgement frames directly follow the transmission of a data
packet. This is not possible for multi‐user frames as only one acknowledgment frame
can be sent at a time. Therefore, the acknowledgment frames have to be separated in
time. This is achieved with the deferred block acknowledgement mechanism that is
already known from 802.11n. This method was initially introduced to allow the
acknowledgement of a transfer of several blocks after a certain time has elapsed to give
the device some time to check if all transmissions were received successfully. In multi‐
user beamforming, only a single multi‐user frame is sent so the delayed block ACK
mechanism is used for a different purpose, that is, to separate responses from different
devices in the time domain.
All enhancements taken together increase the theoretical peak datarate to 6.93 Gbit/s.
This would require a combination of a 160 MHz channel, eight MIMO streams, 256‐
QAM modulation and a short guard interval between packets. In practice, this is obviously
difficult to realize. At the time of publication, 802.11ac APs support up to three MIMO
streams over an 80 MHz channel, which results in a theoretical top speed of 1.3 Gbit/s.
In practice, achievable speeds on the IP layer are far lower. Table 6.7 gives an overview
of the typical speeds that can be reached in practice, as reported in [13]. Although
achievable datarates are significantly higher when compared to those of 802.11n, they
are currently nowhere near the theoretical maximum values.
It should be noted at this point that not all 802.11ac APs and client devices support
the complete 5 GHz range. Some models support only the lowest 80 MHz part of the
channel (channel numbers 36–48) as they do not support dynamic frequency selection
(DFS). DFS is required in some countries, however, to automatically detect other users
in the band (e.g. weather radar) and to automatically change to a different part of the
channel.

6.6.6 IEEE 802.11ad – Gigabit Wireless at 60 GHz

While WLAN product innovation continues in the 5 GHz frequency range with future
enhancements beyond 802.11ac, there is little additional bandwidth available to go
beyond the 160 MHz of aggregated spectrum for a single network. Another frequency