Why wireless usually doesn’t work – and what we will do about it.
First of all, never forget that marketers sell us wireless statistics, in a one-up game of showmanship. Advertising theoretical wireless speeds to the end consumer is a little misleading – most of us are not standing within a few feet of the wireless router in a Farday cage that is blocking all neighboring electro-magnetic fields. That scenario also assumes we have a client with a wireless radio that is also able to transmit at those speeds. Only certain very high end devices have the latest and greatest wireless cards, with the rest of us just dreaming of these “advertised” speeds.
In a perfect scenario, sitting about 10 feet from a wireless router with no obstructions, a single high quality device will generally transmit and receive at one-third two two-thirds of the PHY rate for the channel it is connected to, multiplied by the number of MIMO streams it can transmit on. For a real world example, an iPhone 7 has a 2×2 MIMO 802.11AC wireless chip. With the chip maker advertising a rate of 876Mbps PHY rate at 80Mhz channel width, the maximum speeds for this phone will fall between 300Mbps and 450 Mbps in a testing scenario.
But this is further complicated – wireless data rates are dependent upon the number of clients connected. If you are the only one connected – you get the whole pie. But with proliferation of smart devices, the number of devices to any AP at one time can rapidly slice that pie up into smaller pieces.
The other thing to be aware of with wireless is interference. Interference is similar to polite conversations in a room. The wireless point that is hearing a conversation from a neighbor will wait for their turn to broadcast. You then have competing access points taking turns, and thus slowing down their transfer rates.
Spectrum is also another complicator – wireless originally broadcasted within the 2.4GHz spectrum, with 11 channels. Unfortunately, because of the width and the “bleed over” of these channels, we really only have 3 useable channels in the 2.4GHz spectrum (1,6,11). This causes a lot of interference, and destroys transmission rates. Fortunately, most devices and access points are now capable of utilizing the 5GHz spectrum. This has much better channel control, and the ability to limit the channel widths and “bleed over”. The 5GHz spectrum allows us to have up to nine channels in the standard frequencies, and an additional sixteen channels in the expanded DFS spectrum.
The common method normally seen in deployments is to centralize access points to cover areas, and to broadcast enough power to cover these areas, in both spectrums. This is not efficient – there is interference between channels, interference caused by structures, and devices may not have the power to transmit back. All of this degrades performance and the user experience.
The better method is to eliminate the usage of the 2.4GHz spectrum as much as possible, and have a higher density of devices only using the 5GHz spectrum, and beaming at lower power levels. The only need for the 2.4GHz spectrum is to allow older devices to connect to the wireless.
The other item to take in consideration is the channel width. Narrowing down the channel widths does decrease bandwidth rates, but also decreases interference. Remember that interference from a neighbor on the same channel forces the access points to take turns, dramatically decreasing performance. Wireless design and performance must address interference, through limited power output and narrower channel width.