|Planet Fox > Microwaves
> List of Real World 802.11 Bandwidths
It always kind of bothered me that tech companies list
the bandwidth of wireless devices way the hell higher than what they're
really capable of.. It's like storage devices where they list a
gigabyte as 1,000,000,000 bytes instead of 1,073,741,824 bytes which is a real gigabyte.
Sorry, got off track there. Anyway, I decided to test out different
levels of wifi network and see what the actual data rate is. This isn't
definitively accurate, like the RFC 2544 test used to qualiy carrier
ethernet would be, but it gives you
a good idea of how it will handle real internet traffic in a best case
the test setup, I used two Mikrotik Routerboard RB911G-5HPac
802.11a/n/ac radios with their output power lowered to 1dBm (1mW),
connected directly to each other with a short length of Andrew Heliax
low-loss, low delay coaxial cable and a 40dB microwave attenuator. I
tried connecting them through a section of WR159 flexible waveguide,
but it didn't lower the RSL or change any of the test results.
radios reported a -40dBm received signal level (RSL), which is
equivalent to an "Excellent" signal level on a Windows PC, but not so
high that it would overwhelm the receiver and degrade performance,
which starts to happen at signal levels over -20dBm. The radios reported a
noise floor of -107dBm for a signal to noise ratio (SNR) of 67dB.
to the published documentation, 802.11n and 802.11ac only report their
maximum bandwidth of 300 Mb/S and 866.6 Mb/S respectively with two
channels. Ideally, these channels would be connected to separate
antennas oriented orthogonally (crossed) to one another on both the
receive and transmit sides. The only situation where this is likely to
happen in the real world is in a fixed point-to-point link with dual
polarized antennas. In the context of an access point this is much less
likely to happen, since the antennas on the AP are usually oriented
vertically and the orientation of the antenna(s) on the client device
can change depending on how it's being held. So, I started off by
measuring single channel bandwidth.
Results, Single Channel
(Simultaneous TX + RX)
As you can see, the actual bandwidth is much lower than what's claimed.
Where did the excess bandwidth go? The payload for this test was
randomly generated TCP packets. If I had used UDP packets, the results
would have been much higher; for example, I got 337 Mb/S of receive
only bandwidth on 802.11ac/80 MHz using randomly generated UDP packets.
The reason I used TCP packets is because most internet traffic runs
over TCP, including web, file transfer, and email. UDP packets are
mostly used where a real-time response is more important than message
integrity, such as live video, VoIP, and the like.