Subscribe / Unsubscribe Enewsletters | Login | Register

Pencil Banner

Understanding the difference between Wi-Fi signal strength and Wi-Fi speed

Michael Lok, Managing Director, Southeast Asia, Ruckus Wireless | Aug. 31, 2015
The relationship between Wi-Fi signal strength and the speed at which data can be transferred over that signal is something that is essential to understand when it comes to Wi-Fi performance.

Michael Lok, Ruckus
Photo: Michael Lok

This vendor-written piece has been edited by Executive Networks Media to eliminate product promotion, but readers should note it will likely favour the submitter's approach.

The relationship between Wi-Fi signal strength and the speed at which data can be transferred over that signal is something that is essential to understand when it comes to Wi-Fi performance.

One question we constantly get is this: "When I connect my computer to a wireless network, does a stronger signal always imply faster webpage loading and downloads?"

The answer, like all answers to Wi-Fi questions, can be difficult to•get a grip on. So here's a good, fairly simple explanation that should help clarify things.

All other factors (of which there are many) being equal, stronger signal strength is correlated with higher data transfer speeds, with a couple exceptions and assuming an optimal physical layer data rate selection algorithm. The diagram below shows a typical relationship for any modern wireless system with adaptive modulation:

Ruckus_Wi-Fi signal
Chart: Wi-Fi signal strength vs. throughput

The data transfer speed increases up to a point as signal strength increases since higher signal strengths enable the use of higher PHY (PHYsical layer data) rates, also known as MCS (Modulation and Coding Scheme) in modern Wi-Fi. A simple way of putting it is to think of different MCS as being somewhat like different gears on a motorcycle or car.

Once there is sufficient signal strength to operate reliably in the maximum supported MCS rate, additional signal strength does not produce additional throughput gains. In fact at some point, usually a few centimetres away from the Wi-Fi access point (AP), you can eventually run into a signal strength so high that the receiver's front-end is unable to process it, at which point throughput will drop precipitously.

All of the details, especially the scale, of this graph are highly dependent on the capabilities of the transmitting radio, the receiving radio and the environment. Variability in the environment and in the radios themselves makes real-world wireless throughput a random variable that can only be assessed accurately via statistical methods.

The physical layer data rate selection algorithm is critical to achieving the monotonically increasing relationship shown here up to saturation. There have been many examples of poor rate control algorithms loose in the wild, in both popular AP's and common client devices, that do not actually achieve this monotonic performance, especially when subject to unexpected environmental inputs or certain radio degradations.

So, what to do? Get smart
Finding the right balance between optimum performance and reliability with adaptive data rate algorithms is what separates the great Wi-Fi systems from those that are good enough.

 

1  2  Next Page 

Sign up for CIO Asia eNewsletters.