Wireless Performance Explained

Let’s talk about wireless performance.

At what wireless frequencies (bands) does wifi work on?

On two bands:

  • 2.4Ghz band (older standard)
  • 5Ghz band (newer standard)

Which band is more important (2.4Ghz or 5Ghz)?

  • 802.11ac wifi systems (and soon 802.11ax) advertise that it operates on two wireless frequency bands, 2.4Ghz and 5Ghz
  • 2.4Ghz band (of wireless frequencies) is an older and slower standard
  • Once 802.11ac (wifi5) got released, it started operating on 5Ghz band (of wireless frequencies)
  • The advantage of 5Ghz band is faster speeds (and less wireless interference from neighbour wifi systems)
  • Most cellphones/tablets/laptops produced after mid-2013 have a 802.11ac chip that uses 5Ghz band
  • So when you’re considering which wifi system to get, look at 5Ghz band speed

So if 2.4Ghz is less important, does it mean we don’t need it?

  • Some devices in your network are legacy (meaning produced at the time when 2.4Ghz band was the only standard), so they require 2.4Ghz band
  • Internet of Things (IoT) device are very low-power, and require low power wifi (2.4Ghz band)

What is a spatial stream?

Each radio can send a specific number of independent data streams, called spatial streams, at the same time, which can increase overall throughput.

How many “Spatial Streams” does your device support?

Quick Answer:

  • Apple iPhone 6S (released Sep 2015) and later models has 2 spatial streams.
  • Most Android phones since 2015 have 2 spatial streams.
  • Most laptops support 2 spatial streams. Some laptops, like Macbook Pro, have 3 spatial streams.

Long Answer:

  • You can look at packet capture between your device and the wifi system.
  • You can find your model’s spatial streams on mikealbano.com

Let’s talk about 802.11ac (wifi 5) Theoretical Speed

Let’s take a look at the maximum theoretical 802.11ac speed on 5Ghz band (using 80Mhz channel, 256-QAM, 400 ns GI):

  • 4 spatial streams x 433.3 mbps/stream = 1733.2 mbps
  • This is the speed that wifi systems advertise. This is the maximum theoretical speed from the wifi system to your device(s).

Let’s talk about 802.11ac (wifi 5) Actual Speed

Theoretical vs Actual:

  • Companies usually advertise the layer 1 (physical layer) speed.
  • Due to the overhead in the 802.11 protocol, layer 2 (data link layer) adds processing overhead which results in lower throughput than at the layer 1.
  • Actual speed (throughput) is about 70% of Advertised/Theoretical speed. cisco.com (PDF)

Realistically, a user with a modern cellphone/laptop (with a 802.11ac wifi chip) will receive:

  • # of spatial streams * receiving data rate (receiving on 5Ghz band using 80Mhz channel, 256-QAM, 400 ns GI) * throughput loss due to 802.11 protocol = actual throughput in mbps received on your device
  • 2 streams * 433.3 mbps/stream * 70% = 606.62 mbps

Will you see these speeds on your device?

  • If you’re standing next to the wifi system, then, possibly.
  • The farther you move away from the wifi system, the less signal strength and corresponding throughput your device will receive.

Let’s talk about 802.11ax (wifi 6) Actual Speed

Theoretical vs Actual:

  • Companies usually advertise the layer 1 (physical layer) speed.
  • Due to the overhead in the 802.11 protocol, layer 2 (data link layer) adds processing overhead which results in lower throughput than at the layer 1.
  • Actual speed (throughput) is about 70% of Advertised/Theoretical speed. cisco.com (PDF)

Realistically, a user with a modern cellphone/laptop (with a 802.11ax wifi chip) will receive:

  • # of spatial streams * receiving data rate (receiving on 5Ghz band using 80Mhz channel, 1024-QAM, 800 ns GI) * throughput loss due to 802.11 protocol = actual throughput in mbps received on your device
  • 2 streams * 600 mbps/stream * 70% = 840 mbps (aka 38% improvement over 802.11ac with the same number of spatial streams)

Note:

  • The assumption here is that clients will stay with 2 Spatial Streams, when vendors release 802.11ax chips. We know that a requirement of the 802.11ax spec says devices should theoretically support up to 4 Spatial Streams. If vendors ship client devices that can receive 4 Spatial Streams, you can expect a 2X in performance throughput, compared to 802.11ac.

Will you see these speeds on your device?

  • If you’re standing next to the wifi system, then, possibly.
  • The farther you move away from the wifi system, the less signal strength and corresponding throughput your device will receive.